JP6972712B2 - Image forming device and control method - Google Patents

Description

The technique disclosed in the present invention is a technique related to processing at the time of abnormal discharge of a corona charger that charges a photoconductor by corona discharge.

Conventionally, for example, there is an image forming apparatus for charging a photoconductor with a corona charger having a charging wire and a grid (for example, Patent Document 1 and the like). The corona charger, for example, applies a wire voltage to the charging wire to generate a corona discharge between the charging wire and the photoconductor, and uniformly positively charges the surface of the photoconductor. In this type of corona charger, abnormal discharge may occur due to adhesion of toner, paper dust, or the like to the charging wire. The abnormal discharge referred to here is, for example, a spark discharge or an arc discharge, unlike a corona discharge.

For example, when toner or paper dust adheres to the charged wire, the resistance value of the charged wire increases. As the resistance value of the charged wire increases, the image forming apparatus further increases the wire voltage in the control operation of the wire voltage. As a result, abnormalities in the output of the corona charger, such as excessive increase in wire voltage and abnormal discharge, occur. Therefore, it is necessary to perform error processing for an abnormality in the output of the corona charger, such as notifying the user of the cleaning of the charging wire.

In the image forming apparatus described in Patent Document 1, the wire voltage supplied from the charge voltage generation circuit to the charge wire is changed by controlling the PWM control signal supplied to the charge voltage generation circuit that generates the wire voltage. .. When the PWM control signal in the current control operation is smaller than the PWM control signal at the time of the previous abnormal discharge, the image forming apparatus determines that the charged wire to which the toner is attached has been cleaned. Further, the image forming apparatus displays on the display unit that the charging wire is to be cleaned when the PWM control signal in the current control operation is larger than the PWM control signal at the time of the previous abnormal discharge.

Japanese Unexamined Patent Publication No. 2009-053422

Here, for example, when a conductive foreign substance adheres to the charging wire, the insulation distance at a specific portion between the charging wire and the grid may be temporarily shortened. By shortening the insulation distance between the charged wire at a specific location and the grid, the resistance value of the charged wire does not increase as much as when toner etc. adheres and accumulates, and even though the PWM control signal does not increase, abnormal discharge occurs. May occur.

On the other hand, in the above-mentioned image forming apparatus, the presence or absence of cleaning of the charged wire is determined based on the reduction of the PWM control signal before and after cleaning the charged wire, and the display of the display unit is changed. Therefore, when the above-mentioned foreign matter adheres, there is a possibility that there is no difference between the PWM control signal before cleaning and the PWM control signal after cleaning. The image forming apparatus may continue to determine that the charged wire has not been cleaned, and may not be able to complete error processing such as a display prompting the cleaning of the charged wire.

The present application has been proposed in view of the above problems, and an object of the present application is to provide an image forming apparatus and a control method capable of appropriately ending error processing started with an abnormal discharge.

The image forming apparatus made to solve the above problems includes a photoconductor, a corona charger that charges the photoconductor by corona discharge, and a charge output circuit that outputs a charging voltage that is a voltage applied to the corona charger. , A detection circuit that outputs a detection signal related to the charging voltage, and a control device that has an input port connected to the detection circuit and inputs a detection signal from the detection circuit to the input port, and the control device is an input port. Based on the detection signal input to, the value related to the charging voltage is detected, and based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected, and the abnormal discharge is detected. , Whether the first detection value, which is the value related to the charging voltage detected before the abnormal discharge is detected, is equal to or less than the first threshold value in response to the error processing that is a countermeasure against the abnormal discharge and the detection of the abnormal discharge. The second detection value, which is a value related to the charging voltage detected after the abnormal discharge is detected, is equal to or less than the second threshold value according to the determination of whether or not the first detection value is not equal to or less than the first threshold value. Depending on whether or not it is determined and it is determined that the second detection value is equal to or less than the second threshold, the error processing is terminated and the first detection value is determined to be equal to or less than the first threshold. , End error processing.

According to this, the control device determines that the first detection value detected before detecting the abnormal discharge is not equal to or less than the first threshold value, that is, the abnormal discharge occurs due to the adhesion of toner or the like. According to the determination that the detected value has increased, it is determined whether or not the second detected value when the charged output circuit is operated again after the abnormal discharge is detected is equal to or less than the second threshold value. The control device can determine whether or not the charged wire has been cleaned by determining whether the discharge is abnormal due to toner adhesion or the like and determining whether or not the second detection value is equal to or less than the second threshold value.

On the other hand, the control device determines that the first detection value is not increased due to an abnormal discharge caused by a conductive foreign substance or the like in response to the determination that the first detection value is equal to or less than the first threshold value. Accordingly, the error processing for abnormal discharge (display prompting to clean the charged wire, etc.) is terminated. In this case, the control device does not compare the second detected value with the second threshold value, that is, determines whether or not the charged wire is cleaned, and ends the error processing. Therefore, even if the error processing is started due to the occurrence of an abnormal discharge caused by a foreign substance or the like, the error processing can be appropriately terminated.

It should be noted that the present invention can be realized not only in the form of an image forming apparatus but also in the form of a control method of the image forming apparatus, for example.

It is sectional drawing which shows the schematic structure of the color laser printer which concerns on embodiment. It is a schematic circuit diagram concerning the high voltage power supply device of a printer. It is a circuit diagram of a charge voltage generation circuit. It is a circuit diagram which shows the connection relation of the ASIC, the abnormal discharge detection circuit, and the charge voltage output circuit which concerns on embodiment. It is a flowchart which shows the content of a charge operation. It is a flowchart which shows the content of a charge operation.

Hereinafter, embodiments of the present application will be described with reference to the drawings. The laser printer 1 according to the embodiment of the image forming apparatus according to the present application shown in FIG. 1 is a color laser printer that forms a color image on paper P or the like by an electrophotographic method, and is a so-called tandem laser using four color toners. It is a printer. In the following description, as shown in FIG. 1, the right side of the paper surface in the figure is defined as the front side of the laser printer 1, and the left side of the paper surface is defined as the rear surface side. Hereinafter, the laser printer 1 is simply referred to as a printer 1. Further, the front side of the paper surface in FIG. 1 is defined as the left side when viewed from the front side of the printer 1, and the back side of the paper surface is defined as the right side. Further, the upper side of the paper surface in FIG. 1 is defined as the upper side of the printer 1, and the lower side of the paper surface is defined as the lower side.

As shown in FIG. 1, the printer 1 has a substantially box-shaped device main body 2, and a paper feeding unit 10, an image forming unit 20, and the like are housed inside the device main body 2. On the upper surface of the apparatus main body 2, a discharge tray 5 for storing the paper P on which the image is formed is provided in a laminated state. The apparatus main body 2 has a housing 3 that opens upward, and a cover 7 that is rotatably connected to the housing 3 via a hinge portion 4 so as to close the opening of the housing 3. An open / close detection sensor 8 for detecting the open / closed state of the cover 7 is attached to the inner wall of the housing 3. The ASIC 61 (see FIG. 2) of the printer 1 described later can detect the open / closed state of the cover 7 based on the open / close signal Sg (see FIG. 2) of the open / close detection sensor 8. The open / close detection sensor 8 outputs, for example, a high-level open / close signal Sg (an example of the first signal) to the ASIC 61 when the cover 7 is open. Further, the open / close detection sensor 8 outputs a low-level open / close signal Sg (an example of a second signal) to the ASIC 61, for example, when the cover 7 is closed. Thereby, the ASIC 61 can determine the open / closed state of the cover 7 by determining the signal level of the open / close signal Sg.

Further, a display unit 6 is provided on the upper portion on the rear side of the cover 7. The display unit 6 is, for example, a touch panel, and includes a liquid crystal panel, a light source such as an LED that irradiates light from the back side of the liquid crystal panel, a contact sensing film attached to the surface of the liquid crystal panel, and the like. The ASIC 61 of the printer 1 (see FIG. 2) displays various information about the printer 1 on the display unit 6. The ASIC 61 of the present embodiment displays on the display unit 6 that the grid 43 is to be cleaned in the charging operation shown in FIGS. 5 and 6 to be described later.

Further, the device main body 2 is provided with an exhaust fan 9. The exhaust fan 9 is provided, for example, on the rear side of the apparatus main body 2. The exhaust fan 9 rotates based on the control of the ASIC 61 (see FIG. 2) of the printer 1 described later, and exhausts the air inside the apparatus main body 2 to the outside of the apparatus main body 2. A motor 67 (see FIG. 2) capable of transmitting a driving force to the exhaust fan 9 is provided in the apparatus main body 2. By outputting the drive signal DS to the motor 67, the ASIC 61 can control the start of the drive of the motor 67, the stop of the drive, the rotation direction, the rotation speed, and the like.

The paper feed unit 10 has a paper feed tray 11 in which the paper P is housed and various rollers, and drives the various rollers to feed the paper P to the image forming unit 20. Further, the paper feed tray 11 is configured to be detachable from the lower part of the apparatus main body 2.

The image forming unit 20 has a transport unit 21, four process cartridges 30C, 30M, 30Y, 30K, an exposure unit 35, and a fixing unit 50. The transfer unit 21 is provided between the paper feed section 10 and the process cartridge 30C and the like in the vertical direction, and has a transfer belt 23 and four transfer rollers 25 and the like. The transport belt 23 is an endless belt formed by forming an annular belt, and is wound around a drive roller 27 located below the rear end side of the image forming portion 20 and a driven roller 29 located below the front end side. The upper surface of the transport belt 23 extends substantially horizontally directly under the process cartridge 30C and the like, and comes into contact with the back surface of the paper P supplied from the paper feed unit 10. The drive roller 27 rotates the transport belt 23 in a predetermined direction. Further, the transport belt 23 is negatively charged by applying a transfer voltage to each transfer roller 25, and while the paper P is attracted to the upper surface by electrostatic force, the sucked paper P is discharged along the transport path R. Transport toward 5. A transfer output circuit 65 (see FIG. 2) for applying a transfer voltage to the transfer roller 25 is provided in the apparatus main body 2. The ASIC 61 (see FIG. 2) of the printer 1 controls the transfer output circuit 65 to adjust the transfer voltage applied to the transfer roller 25.

Each of the process cartridges 30C, 30M, 30Y, and 30K corresponds to four colors of cyan (C), magenta (M), yellow (Y), and black (K). Each of the process cartridges 30C and the like contains toner of the corresponding color (C, M, Y, K). Further, the four process cartridges 30C and the like are provided in the order of process cartridges 30K, 30Y, 30M, 30C from the front to the rear of the printer 1.

The process cartridge 30C has a drum-shaped photoconductor 31, a corona charger 41, a toner cartridge 33, a cleaning roller 26, and the like. Although the other process cartridges 30M, 30Y, and 30K have different toner colors, the other configurations are the same as those of the process cartridge 30C. Therefore, in the following description, the process cartridge 30C will be described as a representative, and the description of the other process cartridges 30M, 30Y, and 30K will be omitted as appropriate.

The photoconductor 31 is located above the transfer roller 25, and sandwiches the transport belt 23 between the photoconductor 31 and the transfer roller 25 in the vertical direction. The corona charger 41 is, for example, a scorotron type corona charger in which the charging wire 42 and the grid 43 are housed in the shield case 45. The charging wire 42 is made of a metal, for example, gold-plated tungsten or a simple substance of tungsten. The shield case 45 is formed in a substantially square cylinder shape that is long in the left-right direction. An opening is formed in the portion of the shield case 45 facing the photoconductor 31. The grid 43 is configured by stretching a conductive wire rod in a mesh shape at the opening of the shield case 45. Further, the charging wire 42 is stretched along the left-right direction in the shield case 45, and is arranged at an upper position on the rear side with respect to the photoconductor 31 at a distance. Therefore, the grid 43 is arranged between the photoconductor 31 and the charging wire 42.

The corona charger 41 uniformly positively charges the surface of the photoconductor 31 when forming an image. Specifically, when a voltage is applied to the charging wire 42 and the grid 43, an electric field is formed between the charging wire 42 and the photoconductor 31, and a corona discharge is generated. When an electric field is formed between the charging wire 42 and the grid 43, a voltage different from that of the charging wire 42 is applied to the grid 43, whereby the strength of the electric field is controlled and the charge amount of the photoconductor 31 is increased. Be controlled.

The exposure unit 35 is provided at the uppermost part of the inside of the apparatus main body 2, and forms an electrostatic latent image based on image data on the surface of each charged photoconductor 31. The toner cartridge 33 supplies toner to the surface of the photoconductor 31 by supporting the contained toner (an example of a developer) on the surface of the developing roller 47. A development output circuit 66 (see FIG. 2) for applying a development voltage to the development roller 47 is provided in the apparatus main body 2. The ASIC 61 (see FIG. 2) of the printer 1 controls the development output circuit 66 and adjusts the development voltage applied to the development roller 47. The developing roller 47 rotates while being supplied with the developing voltage, so that the toner in the toner cartridge 33 is triboelectrically charged by the friction accompanying the rotation and is supplied onto the photoconductor 31. The photoconductor 31 forms a toner image (an example of a developer image) by supplying toner to an electrostatic latent image formed on the surface. The transport unit 21 transfers the paper P toward the fixing portion 50, and transfers the developed toner image on the surface of the photoconductor 31 to the paper P by applying a transfer voltage to the transfer roller 25.

Further, the cleaning roller 26 is provided close to the rear side of the photoconductor 31. The cleaning roller 26 recovers the toner supported on the surface of the photoconductor 31 by applying a cleaning voltage.

The fixing portion 50 is provided on the downstream side of the transport path R as compared with the transport unit 21. The fixing portion 50 has a heating roller 51 and a pressure roller 52. The heating roller 51 is arranged on the image forming surface side of the paper P, rotates in synchronization with the transport belt 23 and the like, and transports the paper P while heating the toner transferred to the paper P. The pressurizing roller 52 sandwiches the paper P with the heating roller 51 and rotates drivenly while pressing the paper P toward the heating roller 51. As a result, the fixing unit 50 transports the paper P along the transport path R while heating and melting the toner transferred to the paper P and fixing it to the paper P.

Next, with reference to FIG. 2, the electrical configuration of the printer 1 according to the present application will be described. FIG. 2 shows a schematic block diagram of a high-voltage power supply device 60 mounted on a circuit board (not shown) built in the printer 1 and a connection configuration related to the high-voltage power supply device 60. In the following description, when distinguishing each component for each color, the code of each part is subscripted with Y (yellow), M (magenta), C (cyan), K (black), or "1". A subscript such as "~ 4" is added (for example, grid voltage GRID1 to GRID4), and the subscript is omitted (for example, expressed as grid voltage GRID) when no distinction is made.

The high-voltage power supply device 60 has an ASIC (IC for a specific application) 61, a high-voltage power supply circuit 62 connected to the ASIC 61, a ROM 63, and a RAM 64. The ASIC 61 (an example of a control device) controls the entire printer 1 in addition to controlling the high-voltage power supply circuit 62. The ROM 63 is a storage medium for storing various operation programs and the like executed by the ASIC 61. The ROM 63 of the present embodiment stores a program PG for executing the charging operation shown in FIGS. 5 and 6, which will be described later. The RAM 64 stores temporary data in various processes, image data used in print processes, and the like.

The high-voltage power supply circuit 62 has a grid voltage adjustment circuit 81 including a plurality of charge voltage generation circuits 70 and a grid current detection circuit 82 corresponding to each color. Four charge voltage generation circuits 70 (charge voltage generation circuits 70K, 70Y, 70M, 70C) are provided corresponding to each color. Each of the charge voltage generation circuits 70K to 70C is connected to each of the ports PT1 to PT4 of the ASIC 61 in this order. Each of the charge voltage generation circuits 70K to 70C is supplied with PWM (Pulse Width Modulation) signals Sp1 to Sp4 from the ASIC 61 via the ports PT1 to PT4. Further, each of the charge voltage generation circuits 70K to 70C is connected to a corona charger 41 (41K to 41C) that charges the photoconductor 31 of each color. Each of the four charge voltage generation circuits 70 applies wire voltages CHG1 to CHG4 to each corona charger 41. Each of the charge voltage generation circuits 70 controls the voltage value of the wire voltage CHG1 to CHG4 according to the duty ratio of the PWM signals Sp1 to Sp4. For example, as the duty ratio of the PWM signal Sp1 is increased, the voltage value of the wire voltage CHG1 gradually increases. The detailed configuration of the charging voltage generation circuit 70 will be described later.

Further, the grid voltage adjusting circuits 81K to 81C and the grid current detecting circuits 82K to 82C are provided corresponding to the respective corona chargers 41K to 41C. The grid voltages GRID1 to GRID4 applied to the grid 43 are adjusted by the grid voltage adjusting circuits 81K to 81C. The wire voltage CHG is, for example, about 5.5 kV to 7 kV. The grid voltage GRID is, for example, about 700V.

Each of the grid voltage adjustment circuits 81 has a voltage detection circuit 83 and an operational amplifier OP1. Since the circuit configurations of the grid voltage adjustment circuits 81K to 81C are the same, the grid voltage adjustment circuit 81K corresponding to the K (black) color will be described in the following description, and the other grid voltage adjustment circuits 81Y to 81Y will be described. The description of 81C will be omitted as appropriate. The voltage detection circuit 83K has two voltage dividing resistors R7 and R8 connected in series. A shunt current Id1 of a grid current Ig1 flowing through the grid 43K flows through the voltage dividing resistors R7 and R8. The voltage detection circuit 83K outputs the detection voltage Vgr1 corresponding to the grid voltage GRID1 applied to the grid 43K from the connection point of the two voltage dividing resistors R7 and R8. The voltage detection circuit 83K supplies the detection voltage Vgr1 as the voltage divider detection signal Sid1 to the ports A / D2 of the ASIC 61. The capacitor C3 is connected in parallel with the voltage dividing resistor R8 to form an RC filter.

Further, the port PWM2 of the ASIC 61 is connected to the operational amplifier OP1 via the output resistor R9. The output resistor R9 is grounded to the ground via the capacitor C4. The ASIC 61 supplies the PWM signal Spp1 from the port PWM2, and supplies the PWM signal Spp1 to the operational amplifier OP1 via the output resistor R9. Therefore, the ASIC 61 is configured so that the reference voltage and the like of the operational amplifier OP1 can be changed.

A smoothing circuit including a voltage dividing resistor R4 and a capacitor C2 is connected to the output terminal of the operational amplifier OP1. The connection point on the grid 43K side of the voltage dividing resistor R4 (opposite to the output terminal of the operational amplifier OP1) is grounded to the ground via the capacitor C2. Further, a base of a transistor Q1 for converting the grid voltage GRID1 to a constant voltage is connected to a connection point on the grid 43K side of the voltage dividing resistor R4. Further, the transistor Q1 is connected to the voltage control line Ln1 connected to the connection point between the voltage dividing resistor R7 and the grid 43K. The transistor Q1 is, for example, an NPN transistor, and the collector is connected to the connection point (voltage control line Ln1) on the grid 43K side, and the emitter is connected to the grid current detection circuit 82K (resistor R3). The transistor Q1 is not limited to the bipolar transistor, and may be, for example, an FET (field effect transistor).

The base current of the transistor Q1 is controlled by the output of the operational amplifier OP1. The collector resistance of the transistor Q1 is changed depending on the magnitude of the base current, and the transistor Q1 functions as a variable resistance. The collector resistance here is a resistance value obtained by dividing the collector-emitter voltage by the collector current. For example, increasing the base current lowers the resistance value, and conversely decreasing the base current increases the resistance value. As a result, the collector-emitter voltage is changed.

The ASIC 61 performs feedback control based on the detection voltage Vgr1 detected by the voltage detection circuit 83K. The ASIC 61 changes the PWM signal Spp1 to change the base current of the transistor Q1 and changes the grid voltage GRID1. Therefore, the ASIC 61 can change the voltage value of the grid voltage GRID1 to a predetermined target voltage value by changing the duty ratio of the PWM signal Spp1. A capacitor C1 for charging the grid voltage GRID is provided between the voltage control line Ln1 and the grid 43K.

Further, a grid current detection circuit 82K for detecting the line current Ir1 corresponding to the grid current Ig1 flowing through the grid 43K is connected to the voltage control line Ln1. The resistor R3 of the grid current detection circuit 82K is connected between the emitter of the transistor Q1 and the ground. The grid current detection circuit 82K supplies the terminal voltage on the positive side of the resistor R3 as the line voltage detection signal Sir1 to the ports A / D3 of the ASIC 61.

The ASIC 61 controls the voltage value of the wire voltage CHG1 supplied from the charging voltage generation circuit 70 based on the current value of the grid current Ig1 (line voltage detection signal Sir1). Similarly, the ASIC 61 controls the voltage values of the wire voltages CHG2 to CHG4 of the charging voltage generation circuits 70Y, 70M, 70C based on the grid currents Ig2 to Ig4 (line voltage detection signals Sir2 to Sir4) of other colors.

The ASIC 61 calculates the line current Ir1 (grid current Ig1) from, for example, the resistance value of the resistor R3 and the voltage value of the line voltage detection signal Sir1. The ASIC 61 controls the charging voltage generation circuit 70K based on the calculated current value of the grid current Ig1, and makes the current value of the grid current Ig1 match the desired target current value. The ASIC 61 changes the duty ratio of the PWM signal Sp1 output from the port PT1 so that the current value of the grid current Ig1 matches the desired target current value.

(Structure of charge voltage generation circuit 70)
Next, the circuit configuration of the charge voltage generation circuit 70 will be described. The four charge voltage generation circuits 70K to 70C of the present embodiment have the same circuit configuration, although the circuit constants (resistance value, capacitance value, transformer turns ratio, etc.) and output capacity may differ. There is. Therefore, in the following description, the charging voltage generation circuit 70K mainly corresponding to the black (K) will be described, and detailed description of the other charging voltage generation circuits 70Y, 70M, 70C will be omitted.

As shown in FIG. 3, the charge voltage generation circuit 70K includes a charge voltage output circuit 71K, an abnormal discharge detection circuit 72K, and a charge voltage detection circuit 78. The charging voltage output circuit 71K (an example of the charging output circuit) has a transformer drive circuit 73 and a booster circuit 74. The charging voltage output circuit 71K generates a wire voltage CHG1 to be applied to the charging wire 42K of the corona charger 41K (see FIG. 2).

The transformer drive circuit 73 inputs the PWM signal Sp1 from the port PT1 of the ASIC 61 and smoothes the PWM signal Sp1. The transformer drive circuit 73 supplies the smoothed PWM signal Sp1 to a drive transistor (not shown), and drives the drive transistor to oscillate the primary winding 75a of the transformer 75 of the booster circuit 74. Supply current. The booster circuit 74 includes a transformer 75, a rectifier diode 76, and a smoothing capacitor 77. A DC power supply (24V) is connected to the primary winding 75a of the transformer 75. The transformer 75 changes the voltage value of the output voltage (wire voltage CHG1) output from the secondary winding 75b according to the duty ratio of the oscillation current supplied from the transformer drive circuit 73. For example, as the duty ratio of the PWM signal Sp1 increases, the transformer 75 generates a wire voltage CHG1 having a large voltage value. A rectifier diode 76 and a smoothing capacitor 77 are connected to the secondary winding 75b.

As a result, the voltage generated in the primary winding 75a of the transformer 75 is boosted via the secondary winding 75b, rectified and smoothed by the rectifying diode 76 and the smoothing capacitor 77, and generated as the wire voltage CHG1. .. The wire voltage CHG1 is applied from the booster circuit 74 to the charging wire 42K of the corona charger 41K via the high-voltage side output end T1 of the booster circuit 74 and the power line L1. By applying the wire voltage CHG1 to the charged wire 42K, a corona discharge is generated between the charged wire 42K and the photoconductor 31K. Along with this corona discharge, a grid voltage GRID1 is generated in the grid 43K.

The abnormal discharge detection circuit 72K is provided between the low voltage side output end T2 of the booster circuit 74 and the ground. The low voltage side output end T2 is connected to the low voltage side of the secondary winding 75b of the transformer 75. The abnormal discharge detection circuit 72K detects the presence or absence of abnormal discharge based on the abnormal discharge current that momentarily flows through the grid 43K and the ground due to the abnormal discharge generated by the corona charger 41K. The abnormal discharge is, for example, a spark discharge or an arc discharge caused by contamination of the charged wire with toner or paper dust, unlike the corona discharge.

In the case of normal operation, when the wire voltage CHG1 is applied to the corona charger 41K from the high voltage side of the secondary winding 75b of the transformer 75, the grid current Ig1 (see FIG. 2) flowing through the grid 43K becomes, for example, a grid. It flows to the ground via the current detection circuit 82K (see FIG. 2). When an abnormal discharge occurs in the corona charger 41K, a part of the abnormal discharge current flows from, for example, the grid current detection circuit 82K to the abnormal discharge detection circuit 72K via the ground, and from the low voltage side output end T2. It returns to the low voltage side of the secondary winding 75b of the transformer 75. When the abnormal discharge current returned via such a ground becomes equal to or higher than a predetermined current value, the abnormal discharge detection circuit 72K outputs an abnormal discharge detection signal Sv1 indicating the occurrence of abnormal discharge.

The abnormal discharge detection circuit 72K includes, for example, a Zener diode 91, a detection resistor 92, a capacitor 93, a transistor Tr1, resistors 94 and 95, and a capacitor 96. The positive terminal of the detection resistor 92 and the capacitor 93 is connected to the low voltage side output end T2 of the booster circuit 74. The negative terminal of the detection resistor 92 and the capacitor 93 is grounded to the ground. The detection resistor 92 and the capacitor 93 smooth the abnormal discharge current returning via the ground. The positive terminal of the detection resistor 92 and the capacitor 93 is connected to the anode of the Zener diode 91.

The transistor Tr1 is, for example, a PNP transistor, and the emitter is connected to the DC power supply Vcc1. The voltage of the DC power supply Vcc1 is, for example, 5.0V. The cathode of the Zener diode 91 is connected to the base of the transistor Tr1 via a resistor 94. Further, the resistor 95 is connected between the emitter of the transistor Tr1 and the terminal on the base side of the resistor 94. Similarly, the capacitor 96 is connected between the emitter of the transistor Tr1 and the terminal on the base side of the resistor 94. The circuit configuration of the abnormal discharge detection circuit 72K of this embodiment is an example and can be changed as appropriate. For example, the abnormal discharge detection circuit 72K does not have to include the capacitor 96. Further, the transistor Tr1 is not limited to the bipolar transistor, and may be, for example, an FET (field effect transistor).

For example, when a spark discharge occurs between the charging wire 42K and the grid 43K, the abnormal discharge current flowing through the grid 43K fluctuates greatly intermittently. A part of the abnormal discharge current flows through the ground to the detection resistor 92, and the voltage of the terminal on the positive side of the detection resistor 92 drops. When the voltage of the terminal on the positive side of the detection resistor 92 drops to the Zener voltage (yield voltage) of the Zener diode 91, a base current suddenly flows through the base of the transistor Tr1. Then, when an abnormal discharge current (spark discharge) of a predetermined current value or more is generated, the transistor Tr1 is turned on. When the transistor Tr1 is turned on, a current flows between the emitter and collector of the transistor Tr1, and the collector outputs an abnormal discharge detection signal Sv1 according to the voltage value of the DC power supply Vcc1.

FIG. 4 shows the connection relationship between the abnormal discharge detection circuit 72 and the ASIC 61. In FIG. 4, the charge voltage output circuit 71C corresponding to cyan is not shown in order to avoid complication of the drawing. As shown in FIG. 4, each of the four abnormal discharge detection circuits 72 is connected to a common signal line SL, which is a common signal line. The collector of the transistor Tr1 in each abnormal discharge detection circuit 72 is connected to the port A / D1 of the ASIC 61 via the common signal line SL. Therefore, although the charging voltage generation circuit 70 is provided corresponding to each color, the signal paths of the abnormal discharge detection signals Sv1 to SV4 output from the charging voltage generation circuit 70 (abnormal discharge detection circuit 72) are standardized. There is.

The ASIC 61 of the present embodiment has four ports A / D1 connected to the abnormal discharge detection circuit 72, and the abnormal discharge detection signals Sv1 to Sv4 are input to the ports A / D1 from each of the abnormal discharge detection circuits 72. It is composed. Each of the abnormal discharge detection circuits 72 is connected to different charging voltage output circuits 71K to 71C.

A detection resistor 101 for detecting the abnormal discharge detection signal Sv is connected between the common signal line SL and the ASIC 61. A resistor 103 and a capacitor 104 are connected to the terminal on the ASIC61 side of the detection resistor 101. One end of the resistor 103 and the capacitor 104 is connected to the detection resistor 101 (port A / D1 of the ASIC 61), and the other end is grounded to the ground. The resistor 103 and the capacitor 104 smooth the abnormal discharge detection signal Sv detected by the detection resistor 101.

In the normal state, the transistor Tr1 is turned off. The abnormal discharge detection signal Sv is not output from the collector of the transistor Tr1. Further, when an abnormal discharge occurs, the transistor Tr1 is turned on. The abnormal discharge detection signal Sv is input from the transistor Tr1 to the ASIC61. The ASIC 61 can detect the presence or absence of an abnormal discharge based on the abnormal discharge detection signal Sv input from the ports A / D1. For example, when the ASIC 61 detects an abnormal discharge, it notifies the user to that effect and performs processing such as prompting the user to clean the charging wire 42.

Here, the on / off characteristic of the transistor Tr1 of the abnormal discharge detection circuit 72, that is, the characteristic (sensitivity) of outputting the abnormal discharge detection signal Sv with respect to the magnitude of the abnormal discharge (abnormal discharge current) is the abnormal discharge detection circuit. It can be changed by changing the circuit constants of 72 and the like. For example, the Zener diode 91 is changed to one having a different Zener voltage (yield voltage). The resistors 94 and 95 and the capacitor 96 are changed to those having different resistance values and capacitance values. Alternatively, the transistor Tr1 may be changed to one having different IV characteristics.

For example, in the abnormal discharge detection circuit 72, in which the connection path between the detection resistor 92 and the corona charger 41 via the ground is long and the abnormal discharge current from the corona charger 41 to the detection resistor 92 is greatly attenuated, another abnormality is obtained. It becomes necessary to increase the sensitivity as compared with the discharge detection circuit 72. If you want to increase the sensitivity, for example, reduce the absolute value of the Zener voltage (decay voltage) of the Zener diode 91 to make it easier to turn on the transistor Tr1 (so that it turns on with an abnormal discharge current of a smaller current value) and abnormal discharge. Increase the sensitivity of the detection circuit 72. Conversely, if you want to lower the sensitivity, for example, increase the absolute value of the Zener voltage of the Zener diode 91, make it difficult to turn on the transistor Tr1 (so that it turns on with an abnormal discharge current with a larger current value), and detect abnormal discharge. Decrease the sensitivity of the circuit 72. By adjusting the sensitivity of each abnormal discharge detection circuit 72 in this way, it is possible to average the sensitivity of the abnormal discharge and improve the detection accuracy. If the sensitivity of the abnormal discharge detection circuit 72 having high sensitivity is lowered and adjusted, the overall sensitivity is lowered. Therefore, it is preferable to adjust the sensitivity by increasing the sensitivity of the abnormal discharge detection circuit 72 having a low sensitivity.

On the other hand, the four abnormal discharge detection circuits 72 of the present embodiment have the same circuit configuration. The abnormal discharge detection circuit 72 has the same circuit configuration, but the sensitivity can be adjusted by changing the circuit constants and the like. Therefore, it is possible to individually change the sensitivity of each abnormal discharge detection circuit 72 while reducing the manufacturing cost.

Further, the charge voltage detection circuit 78 shown in FIG. 3 is for detecting the wire voltage CHG1, is connected to the power line L1, and has a voltage dividing resistor and the like. The charge voltage detection circuit 78 is connected to the port PT5 of the ASIC 61, and outputs the wire voltage detection signal Vs1 corresponding to the magnitude of the wire voltage CHG1 to the ASIC 61. Similarly, the charge voltage detection circuit 78 provided in each charge voltage generation circuit 70 outputs each of the wire voltage detection signals Vs2, Vs3, and Vs4 to the ports PT6, PT7, and PT8 of the ASIC61. As a result, the ASIC 61 can detect the wire voltages CHG1 to CHG4 of each charging voltage output circuit 71.

(Charging operation)
Next, the charging operation of the printer 1 of the present embodiment will be described with reference to FIGS. 5 and 6. For example, when the ASIC 61 receives a print instruction and starts the charging voltage generation circuit 70 or the like, the ASIC 61 starts the processing of the charging operation shown in FIGS. 5 and 6. Alternatively, for example, when the power of the printer 1 is turned on and the warm-up operation is performed, the ASIC 61 starts the processing of the charge operation shown in FIGS. 5 and 6. The ASIC 61 reads the program PG from the ROM 63 and executes it to execute the charging operation processing shown in FIGS. 5 and 6.

First, in S11 shown in FIG. 5, for example, in order to start the operation of the four charge voltage generation circuits 70 and the grid voltage adjustment circuit 81 in response to the acceptance of the print instruction, the ASIC 61 of the PWM signal Sp and the PWM signal Spp. Start supplying. The ASIC 61 changes the duty ratio of the PWM signals Sp1 to Sp4 based on the current values of the grid currents Ig1 to Ig4 to control the charging voltage generation circuits 70K to 70C. By controlling the charging voltage generation circuit 70, the ASIC 61 starts control to match the current value of the grid current Ig with a desired target current value (S11). Further, the ASIC 61 changes the duty ratio of the PWM signal Spp and controls the grid voltage adjusting circuit 81 to start control to match the voltage value of the grid voltage GRID with a desired target voltage value (S11).

For example, when the ASIC 61 receives a print instruction and starts the charge operation shown in FIGS. 5 and 6, when the grid current Ig and the grid voltage GRID reach a desired target value, the ASIC 61 executes the received print instruction. Further, for example, when the charge operation shown in FIGS. 5 and 6 is started in association with the warm-up operation, the ASIC 61 ends the warm-up operation when the grid current Ig and the grid voltage GRID reach a desired target value.

Each of the wire voltages CHG1 to CHG4 increases with each increase of the grid currents Ig1 to Ig4. The ASIC 61 stores the voltage values of the increasing wire voltages CHG1 to CHG4 at predetermined time intervals (S13). The ASIC 61 detects the wire voltages CHG1 to CHG4 based on the wire voltage detection signal Vs of the charge voltage detection circuit 78 (see FIG. 3). The ASIC 61 stores the detected wire voltage CHG voltage value in, for example, a RAM 64. The ASIC 61 may calculate the wire voltage CHG based on, for example, the voltage dividing detection signal Sid (grid voltage GRID). In this case, the printer 1 does not have to include the charge voltage detection circuit 78.

When the wire voltage CHG of each charging voltage generation circuit 70 is stored (S13), the ASIC 61 determines whether or not an abnormal discharge has occurred (S15). The ASIC 61 determines whether or not an abnormal discharge has occurred based on the abnormal discharge detection signals Sv1 to Sv4 output from each abnormal discharge detection circuit 72 (S15). The ASIC 61 repeatedly executes the process of S13 according to the determination that no abnormal discharge has occurred (S15: NO). The ASIC 61 repeatedly executes the process of S13 every 100 ms, for example, and stores the detected wire voltage CHG voltage value. Further, when the printing operation or the warm-up operation is terminated, for example, the ASIC 61 stops the charging voltage generation circuit 70 and the grid voltage adjusting circuit 81 while the S13 is repeatedly executed, and is shown in FIGS. 5 and 6. End the charging operation.

On the other hand, the ASIC 61 starts an error process (S17), which is a process for dealing with the abnormal discharge, in response to the determination that the abnormal discharge has occurred (S15: YES). In the error processing of S17, for example, if printing is being executed, the ASIC 61 cancels the printing being executed. The ASIC 61 executes, for example, a stop of the charge voltage generation circuit 70, a stop of transport of the paper P, or both as a process of stopping printing. Further, in the error processing, the ASIC 61 displays, for example, on the display unit 6 (see FIG. 1) that the toner adhering to the charging wire 42 is to be cleaned. Here, when the DC power supplies Vcc1 (see FIG. 3) of the four abnormal discharge detection circuits 72 are set to different voltage levels and the voltage values of the abnormal discharge detection signals Sv1 to Sv4 are set to different values, the ASIC 61 is an abnormal discharge detection signal. Based on the voltage value of Sv, the corona charger 41 (printing color) in which the abnormal discharge has occurred can be specified. In this case, the ASIC 61 may indicate on the display unit 6 which color of the charging wire 42 should be cleaned. The ASIC 61 may display only the fact that an abnormal discharge has occurred on the display unit 6. This makes it possible to urge the user who sees the display of the display unit 6 to clean the charging wire 42. Further, the ASIC 61 only cancels printing, and does not have to display anything on the display unit 6. Alternatively, the ASIC 61 may execute only the display of the display unit 6 without stopping the printing.

Next, the ASIC 61 executes a process of reading the value of the wire voltage CHG stored before the abnormal discharge detected in S15 from the RAM 64 (S19). For example, among the wire voltage CHGs stored every 100 ms in S13, the ASIC 61 reads the data of the wire voltage CHG closest to the time when the abnormal discharge is detected in S15 from the RAM 64. The data of this wire voltage CHG is, for example, the data recorded within 100 ms before the occurrence of the abnormal discharge.

Next, the ASIC 61 determines whether or not the voltage value of the wire voltage CHG read in S19 is equal to or less than the first threshold value TH1 (S21). Here, when an abnormal discharge occurs due to the adhesion of toner to the charged wire 42, the wire voltage CHG before the occurrence of the abnormal discharge increases due to the decrease in the resistance value of the charged wire 42. On the other hand, when the insulation distance between the charging wire 42 and the grid 43 is temporarily shortened and an abnormal discharge occurs, such as when a conductive foreign substance adheres to the charging wire 42, the resistance value of the charging wire 42 It is highly possible that the wire voltage CHG before the occurrence of the abnormal discharge does not increase as compared with the time when the toner adheres. Therefore, in S21, the ASIC 61 determines whether or not the wire voltage CHG has increased before the abnormal discharge by using the first threshold value TH1. Therefore, the first threshold value TH1 used in S21 is a value capable of discriminating between the wire voltage CHG increased before the abnormal discharge due to toner adhesion and the wire voltage CHG before the abnormal discharge due to foreign matter or the like. For the first threshold TH1, for example, an intermediate value between the voltage value (high voltage) of the wire voltage CHG before abnormal discharge due to toner adhesion and the voltage value of the wire voltage CHG before abnormal discharge due to foreign matter or the like is used. Can be done. Thereby, the ASIC 61 can determine whether or not the abnormal discharge has occurred due to the adhesion of the toner.

In S21, the ASIC 61 determines whether or not the cover 7 has been opened / closed according to the voltage value of the wire voltage CHG being equal to or less than the first threshold value TH1 (S21: YES) (S23). The ASIC 61 determines whether the cover 7 is open or closed based on the open / close signal Sg of the open / close detection sensor 8. When the cover 7 is opened once and then closed, it is highly possible that the user has opened the cover 7 such as cleaning the charging wire 42 according to the contents displayed on the display unit 6 by the error processing of S17. By cleaning the user, not only the toner adhering to the charging wire 42 but also the conductive foreign matter and the like are removed.

Further, when the voltage value of the wire voltage CHG is equal to or less than the first threshold value TH1 in S21 (S21: YES), the temporary abnormal discharge caused by the adhesion of conductive foreign matter or the like is not the abnormal discharge caused by the adhesion of toner. Is more likely to be. In this case, even if the charged wire 42 is cleaned, the reduction of the wire voltage CHG during normal operation (during constant current control) after cleaning is small as compared with the wire voltage CHG at the time of abnormal discharge. Therefore, in the ASIC 61 of the present embodiment, when the voltage value of the wire voltage CHG is equal to or less than the first threshold value TH1 (S21: YES), the charged wire based on the reduction of the wire voltage CHG of S27 to S43 shown in FIG. The process of determining the cleaning of 42 is not performed. As a result, the wire voltage CHG is not reduced, and the occurrence of a situation in which error processing is continued and cannot be completed is suppressed.

If the cover 7 is not opened, or if it is opened but not closed (S23: NO), it is considered that the charging wire 42 has not been cleaned or is in the middle of cleaning. Therefore, the ASIC 61 repeatedly executes the process of S23 until it is detected that the cover 7 is closed after the cover 7 is opened (S23: NO).

Further, depending on whether the cover 7 is opened and then closed (S23: YES), the ASIC 61 ends the error processing started in S17 (S25). For example, when the ASIC 61 stops the printing being executed in S17, the ASIC 61 restarts the printing stopped in S25. Further, for example, when the display unit 6 (see FIG. 1) indicates that the toner adhering to the charging wire 42 is to be cleaned in S17, the ASIC 61 performs a process of erasing the display in S25. After executing S25, the ASIC 61 ends the processes shown in FIGS. 5 and 6.

(Cleaning judgment of charged wire 42 by reducing wire voltage CHG)
On the other hand, in the above-mentioned S21, the ASIC 61 starts the processing after S27 shown in FIG. 6 according to the voltage value of the wire voltage CHG being larger than the first threshold value TH1 (S21: NO). In this case, the possibility of abnormal discharge due to the adhesion of toner increases. Therefore, the ASIC 61 determines whether or not the charged wire 42 has been cleaned by the user by reducing the wire voltage CHG.

In S27, the ASIC 61 determines the determination reference voltage Vt for determining the wire voltage CHG (presence or absence of cleaning). The ASIC 61 determines, for example, the voltage value of the wire voltage CHG at the time of the occurrence of the abnormal discharge this time as the determination reference voltage Vt (second threshold value, determination reference value). Alternatively, the ASIC 61 may calculate the determination reference voltage Vt by multiplying the voltage value of the wire voltage CHG at the time of the occurrence of the abnormal discharge this time by a predetermined coefficient. Further, the corresponding data indicating the correspondence relationship between the wire voltage CHG and the determination reference voltage Vt at the time of the occurrence of the abnormal discharge may be stored in advance in the ROM 63. Then, the ASIC 61 may read the corresponding data from the ROM 63 and search for and determine the determination reference voltage Vt from the corresponding data using the wire voltage CHG at the time of abnormal discharge. The above-mentioned predetermined coefficient and corresponding data can be set in advance based on the correlation between the wire voltage CHG at the time of abnormal discharge due to toner adhesion and the wire voltage CHG after cleaning the toner. Further, the ASIC 61 is not limited to the wire voltage CHG at the time of abnormal discharge, and may determine the determination reference voltage Vt based on the voltage value of the wire voltage CHG before or after the abnormal discharge.

Further, for example, the ASIC 61 raises the sensitivity for detecting an abnormal discharge in the abnormal discharge detection circuit 72, and gradually lowers the wire voltage CHG from the voltage value of the wire voltage CHG at the time of the occurrence of the abnormal discharge this time, resulting in an abnormality. The wire voltage CHG from which discharge is no longer detected may be determined as the determination reference voltage Vt. In this case, the voltage value of the determination reference voltage Vt becomes smaller than the voltage value of the wire voltage CHG at the time of the occurrence of the abnormal discharge this time by the amount of increasing the sensitivity. In other words, the determination reference voltage Vt can be set according to the increase in sensitivity. In this case, the abnormal discharge detection circuit 72 may include a circuit element for adjusting the sensitivity, for example, an operational amplifier that amplifies the abnormal discharge detection signal Sv, or a comparator for comparison. Then, the ASIC 61 may be configured to be able to control the amplification factor of the operational amplifier and the reference value voltage of the comparator.

Further, in S27, the ASIC 61 sets the counter value CT to "1". This counter value CT is a value for confirming the number of times the constant current control after S31 described later is executed. The ASIC 61 stores the set counter value CT in, for example, the RAM 64.

Next, the ASIC 61 determines whether or not the charging wire 42 has been cleaned based on whether or not the cover 7 has been opened and closed, as in S23 of FIG. 5 (S29). If the cover 7 is not opened, or if it is opened but not closed (S29: NO), the ASIC 61 repeatedly executes the process of S29. During this period, it is considered that the cleaning of the charging wire 42 is not completed.

On the other hand, in response to the cover 7 being opened and then closed (S29: YES), the ASIC 61 starts the constant current control on a trial basis with the target voltage value of the grid voltage GRID lowered (S31). .. This is whether or not the wire voltage CHG when the grid current Ig is increased to the target current value It by constant current control in S35 described later is equal to or less than the determination reference voltage Vt, that is, the target current value It is reached. This is because it is determined whether or not the charged wire 42 is cleaned by determining whether or not the wire voltage CHG at the time of abnormal discharge is lower than that at the time of abnormal discharge.

If the ASIC 61 can identify the corona charger 41 in which the abnormal discharge has occurred, the constant current control may be executed only by the corona charger 41 in which the abnormal discharge has occurred. As a result, it is possible to improve the efficiency of the confirmation work and reduce the power consumption in the confirmation work by executing the constant current control and confirming only the corona charger 41 in which the abnormal discharge has occurred.

The ASIC 61 controls the charging voltage generation circuit 70 based on the grid current Ig, and starts constant current control to match the grid current Ig with the target current value It (S31). At this time, by lowering the target voltage value (second target value) of the grid voltage GRID, the increase of the grid voltage GRID by the grid voltage adjusting circuit 81 is suppressed. For example, if the charging wire 42 is not cleaned only by opening and closing the cover 7, the abnormal discharge may reoccur as the wire voltage CHG increases due to the constant current control started in S31. Therefore, the ASIC 61 of the present embodiment lowers the target voltage value of the grid voltage GRID when executing the constant current control to suppress the recurrence of abnormal discharge. For example, the ASIC 61 detects the grid voltage GRID based on the voltage divider detection signal Sid, and controls the grid voltage adjustment circuit 81 so that the value of the grid voltage GRID matches the target voltage value (second target value) (. Second constant voltage control). The ASIC 61 performs this constant voltage control (second constant voltage control) during the constant current control starting in S31. For example, the ASIC 61 sets a voltage value smaller than the target voltage value in the constant voltage control (second constant voltage control) performed at the time of warming up before the occurrence of abnormal discharge to the constant voltage control (constant current control of S31). ). This makes it possible to suppress the recurrence of abnormal discharge. In the constant current control, the ASIC 61 preferably rotates the photoconductor 31 in order to reduce the load applied to the photoconductor 31. Further, the method of suppressing the occurrence of abnormal discharge while increasing the wire voltage CHG is not limited to the method of reducing the target voltage value of the grid voltage GRID. For example, the ASIC 61 may lower the target current value It (an example of the first target value) of the grid current Ig in the constant current control. In this case, the determination reference voltage Vt may be lowered in accordance with the reduction of the grid current Ig.

Further, the ASIC 61 controls the development output circuit 66 (see FIG. 2) in S31, and lowers the development voltage applied to the development roller 47 as compared with the development voltage before detecting the abnormal discharge. For example, if the amount of charge charged to positively charge the photoconductor 31 decreases due to the decrease in the grid voltage GRID, the toner may move from the developing roller 47 to the photoconductor 31 even though it is not exposed. Therefore, by lowering the developing voltage of the developing roller 47, it is possible to suppress the adhesion of toner to the photoconductor 31 having a reduced amount of charge. The decrease in the developing voltage referred to here includes a state in which the developing voltage is stopped and the voltage value of the developing voltage is set to zero. Further, the printer 1 may include a mechanism for moving the photoconductor 31 and the developing roller 47 in the front-rear direction. Then, in order to suppress the movement of toner from the developing roller 47 to the photoconductor 31, the distance between the developing roller 47 and the photoconductor 31 may be temporarily separated.

Further, the ASIC 61 may control the transfer voltage of the transfer roller 25 and the cleaning voltage of the cleaning roller 26 in S31 in order to suppress a decrease in the charge amount of the photoconductor 31. For example, the ASIC 61 controls the transfer output circuit 65 so that the polarity of the transfer voltage output from the transfer output circuit 65 (see FIG. 2) has the same polarity (positive electrode property) with respect to the polarity of the toner (developer). do. The ASIC 61 may apply a positive transfer voltage to the transfer roller 25 and positively charge the photoconductor 31 by the transfer roller 25 to suppress a decrease in the amount of charge. Alternatively, the ASIC 61 may apply a positive cleaning voltage to the cleaning roller 26 to positively charge the photoconductor 31 by the cleaning roller 26 to suppress a decrease in the amount of charge. As a result, it is possible to suppress a decrease in the charge amount of the photoconductor 31 and suppress the adhesion of toner to the photoconductor 31. The ASIC 61 may control only one of the transfer roller 25 and the cleaning roller 26 in order to suppress a decrease in the charge amount of the photoconductor 31.

After starting the constant current control of the grid current Ig in S31, the ASIC 61 can, for example, increase the grid current Ig to the target current value It to stabilize the grid current Ig, the wire voltage CHG, the grid voltage GRID, and the like. End constant current control. On the other hand, the ASIC 61 increases the wire voltage CHG so as not to further increase the wire voltage CHG if the voltage value of the wire voltage CHG increases above the determination reference voltage Vt during the constant current control of the grid current Ig. The constant voltage control to be equal to or less than the determination reference voltage Vt is executed (S33). When the wire voltage CHG increases as compared with the determination reference voltage Vt, abnormal discharge may occur again. Therefore, the constant current control is switched to the constant voltage control, the wire voltage CHG is suppressed from increasing to the determination reference voltage Vt or more, and the recurrence of the abnormal discharge is suppressed. In this case, there is a high possibility that the toner adhering to the charging wire 42 has not been cleaned or the cleaning is insufficient.

Further, if the voltage value (detection signal) of the wire voltage CHG temporarily increases due to noise or the like, there is a possibility that it is erroneously determined that the voltage value (detection signal) has increased from the determination reference voltage Vt by exceeding once. Therefore, the ASIC 61 of the present embodiment maintains constant voltage control for a while even after the wire voltage CHG increases from the determination reference voltage Vt, and determines that the wire voltage CHG surely increases to about or more than the determination reference voltage Vt. do. As a result, although the toner can be cleaned and constant current control can be performed at the judgment reference voltage Vt or less, the wire voltage CHG temporarily increases due to noise or the like, and the wire voltage CHG is erroneously increased from the judgment reference voltage Vt. Judgment can be suppressed.

The ASIC 61 may shift to constant voltage control when the wire voltage CHG increases from the determination reference voltage Vt to a predetermined value or more, or when the wire voltage CHG exceeds the determination reference voltage Vt a predetermined number of times. Further, the ASIC 61 may be configured to stop the constant current control by determining that the constant current control cannot be performed once the wire voltage CHG exceeds the determination reference voltage Vt (S35: NO described later). In this case, the ASIC 61 does not have to perform switching between constant current control and constant voltage control.

Next, the ASIC 61 determines whether or not the grid current Ig could be stabilized at the target current value It while the wire voltage CHG was maintained at the determination reference voltage Vt or less in the constant current control started in S31. (S35). When the grid current Ig can be controlled to a constant current below the determination reference voltage Vt (S35: YES), it is highly possible that the charging wire 42 has been cleaned by the user because the wire voltage CHG is lower than that at the time of abnormal discharge. .. Therefore, the ASIC 61 finishes the cleaning confirmation work.

The ASIC 61 deletes the data used in the constant current control started in S31 according to the fact that the grid current Ig can be controlled to a constant current at a determination reference voltage Vt or less (S35: YES) (S37). For example, when the data used for calculating the judgment reference voltage Vt, the data used for calculating the judgment reference voltage Vt, the voltage value of the wire voltage CHG during constant current control, etc. are stored in the RAM 64, the process of deleting those data is executed. do. In addition, a process of restoring the target voltage value of the grid voltage GRID and the development voltage, which have been temporarily lowered, is executed. When the ASIC 61 executes S37, it ends the error processing started in S17 of FIG. 5 (S25 of FIG. 5), and ends the processing shown in FIGS. 5 and 6.

On the other hand, the ASIC 61 determines whether or not the counter value CT is equal to or greater than the threshold CTt in S35 according to the fact that the grid current Ig could not be controlled to a constant current at the determination reference voltage Vt or less (S35: NO) (S35: NO). S39). That is, the ASIC 61 determines whether or not the constant current control is performed the number of times of the predetermined threshold CTt. In this case, the wire voltage CHG does not fall below the determination reference voltage Vt due to the constant current control, and the determination process (S29 to S35) as to whether or not the toner has been cleaned is repeated, and the error process (S17 in FIG. 5) is performed. This is to prevent the occurrence of situations that cannot be canceled forever. The threshold CTt is, for example, "3" times. In this case, if the wire voltage CHG does not become equal to or less than the determination reference voltage Vt even if the constant current control is performed only twice, the ASIC 61 ends the process shown in FIG. 6 through the process of S41 described later.

The ASIC 61 rotates the exhaust fan 9 at full speed for a predetermined time (for example, 120 seconds) according to the counter value CT equal to or higher than the threshold value CTt (S39: YES), and discharges the air inside the apparatus main body 2. .. This is, for example, the work of cleaning the toner or the work performed after cleaning the toner, and there is a possibility that the user maintains the inside of the apparatus main body 2 by spraying or the like containing flammable gas. In this case, if the cover 7 is closed immediately after maintenance, flammable gas may stay in the apparatus main body 2. The accumulated flammable gas may cause a malfunction (abnormal discharge or the like) in the printer 1. Therefore, the ASIC 61 outputs a drive signal DS (see FIG. 2) for a predetermined time before returning to the normal operating state by ending the processing of FIGS. 5 and 6 when the counter value CT becomes equal to or higher than the threshold value CTt, and the motor 67. Is controlled to rotate the exhaust fan 9 at full speed, and the air in the apparatus main body 2 is discharged. The ASIC 61 does not have to rotate the exhaust fan 9 at full speed. Further, the ASIC 61 may rotate the exhaust fan 9 longer or shorter than 120 seconds. Alternatively, the ASIC 61 may take in outside air to ventilate the inside of the apparatus main body 2, and may notify the user that the cover 7 is opened or closed.

When the rotation operation of the exhaust fan 9 is completed (S41), the ASIC 61 deletes the data used in the constant current control started in S31 (S37). The ASIC 61 ends the error processing started in S17 of FIG. 5 (S25 of FIG. 5), and ends the processing shown in FIGS. 5 and 6.

On the other hand, the ASIC 61 again notifies the user that the toner adhering to the charging wire 42 is to be cleaned according to the fact that the counter value CT is smaller than the threshold value CTt (S39: NO) (S43). For example, when the ASIC 61 erases the display indicating that the toner displayed on the display unit 6 in S17 of FIG. 5 is to be cleaned, the ASIC 61 redisplays the toner (S43). Further, the ASIC 61 may display, for example, on the display unit 6 that the charging wire 42 is not sufficiently cleaned. Further, the ASIC 61 increases the value of the counter value CT by one in S43. Then, after executing S43, the ASIC 61 re-executes the process from S29 described above. In this way, the ASIC 61 determines whether or not the charging wire 42 is cleaned based on the reduction of the wire voltage CHG.

Incidentally, the printer 1 is an example of an image forming apparatus. The open / close detection sensor 8 is an example of the sensor. The exhaust fan 9 is an example of a fan. The ASIC 61 is an example of a control device. The charge voltage output circuit 71 is an example of a charge output circuit and a wire output circuit. The abnormal discharge detection circuit 72 is an example of a detection circuit. The charge voltage detection circuit 78 is an example of a wire voltage detection circuit. The grid voltage adjustment circuit 81 is an example of a grid output circuit. The voltage detection circuit 83 is an example of a grid voltage detection circuit. The wire voltage CHG is an example of the charging voltage. The abnormal discharge detection signal Sv and the partial pressure detection signal Sid are examples of detection signals. Ports A / D1, A / D2, A / D4, A / D6, A / D8, PT5 to PT8 are examples of input ports. The determination reference voltage Vt is an example of the second threshold value. The open / close signal Sg is an example of a detection signal.

According to the above-described embodiment, the following effects are obtained.
(1) The printer 1 (image forming apparatus) of the embodiment includes a photoconductor 31, a corona charger 41 that charges the photoconductor 31 by corona discharge, and a wire voltage CHG (voltage applied to the corona charger 41). A charging voltage output circuit 71 (charging output circuit) that outputs a charging voltage) and a detection circuit that outputs a detection signal (abnormal discharge detection signal Sv, wire voltage detection signal Vs, voltage division detection signal Sid) related to the wire voltage CHG (charged voltage). It has an abnormal discharge detection circuit 72, a charge voltage detection circuit 78, a voltage detection circuit 83) and input ports (ports A / D1, PT5-PT8, A / D2, etc.) connected to the detection circuit, and inputs from the detection circuit. It includes an ASIC 61 (control device) that inputs a detection signal to the port. The ASIC 61 detects a value related to the charging voltage (wire voltage CHG) based on the detection signal (wire voltage detection signal Vs) input to the input port, and uses the detection signal (abnormal discharge detection signal Sv) input to the input port. Based on this, the abnormal discharge generated in the corona charger 41 was detected, and in response to the detection of the abnormal discharge, error processing was performed to deal with the abnormal discharge (S17 in FIG. 5), and the abnormal discharge was detected. Accordingly, it is determined whether or not the first detection value (wire voltage CHG), which is a value related to the charging voltage detected before detecting the abnormal discharge, is equal to or less than the first threshold value TH1 (S21), and the first detection value. The second detection value (wire voltage CHG), which is a value related to the charging voltage detected after the abnormal discharge is detected, is the second threshold (determination) according to the determination that is not equal to or less than the first threshold TH1 (S21: NO). It is determined whether or not the voltage is equal to or less than the reference voltage Vt (S35), and the error processing is performed according to the determination that the second detection value is equal to or less than the second threshold voltage (determination reference voltage Vt) (S35: YES). It is terminated (S25), and the error processing is terminated according to the determination that the first detection value is equal to or less than the first threshold TH1 (S21: YES) (S25).

According to this, the ASIC61 (control device) determines that the first detection value (wire voltage CHG) detected before detecting the abnormal discharge is not equal to or less than the first threshold TH1 (S21: NO). That is, in response to the determination that an abnormal discharge has occurred due to adhesion of toner or the like and the wire voltage CHG (first detection value) has increased, the charged voltage output circuit 71 (charged output circuit) is restarted after the abnormal discharge is detected. It is determined whether or not the second detection value at the time of operation or the like is equal to or less than the second threshold value (determination reference voltage Vt) (S35). The ASIC 61 can determine whether or not the charging wire 42 has been cleaned by determining whether or not the second detection value is equal to or less than the second threshold value by determining that the discharge is abnormal due to toner adhesion or the like.

On the other hand, in the ASIC 61, in response to the determination that the first detection value is equal to or less than the first threshold value TH1 (S21: YES), that is, an abnormal discharge occurs due to a conductive foreign substance or the like, and the first detection value increases. The error processing (display prompting the cleaning of the charging wire 42, etc.) for the abnormal discharge is terminated according to the determination that the non-existence is not performed (S25). In this case, the ASIC 61 does not execute the comparison between the second detection value and the second threshold value, that is, S35 or the like for determining whether or not the charging wire 42 is cleaned, and ends the error processing. Therefore, even if the error processing is started due to the occurrence of an abnormal discharge caused by a foreign substance or the like, the error processing can be appropriately terminated.

(2) Further, the detection circuit includes a charge voltage detection circuit 78 (voltage detection circuit) that outputs a wire voltage detection signal Vs (detection signal) according to the magnitude of the wire voltage CHG (charge voltage). The ASIC 61 (control device) detects the value of the wire voltage CHG based on the wire voltage detection signal Vs input from the charge voltage detection circuit 78 to the port PT5 or the like (input port).

According to this, the printer 1 has, as a detection circuit, a charge voltage detection circuit 78 that outputs a wire voltage detection signal Vs (detection signal) corresponding to the magnitude of the wire voltage CHG (charge voltage). The ASIC 61 detects the voltage value of the wire voltage CHG based on the wire voltage detection signals Vs1 to Vs4 input from the charge voltage detection circuit 78 to the ports PT5, PT6, PT7, and PT8. Then, when an abnormal discharge occurs, the ASIC 61 can compare the voltage value of the wire voltage CHG with the first threshold value TH1 and the determination reference voltage Vt (second threshold value), and can appropriately end the error processing.

(3) Further, the detection circuit includes an abnormal discharge detection circuit 72 that outputs an abnormal discharge detection signal Sv (detection signal) corresponding to the occurrence of abnormal discharge. The ASIC 61 (control device) detects an abnormal discharge based on the abnormal discharge detection signal Sv (detection signal) input from the abnormal discharge detection circuit 72 to the port A / D1 (input port).

According to this, the printer 1 (image forming apparatus) has an abnormal discharge detection circuit 72 for detecting an abnormal discharge as a detection circuit. Then, the ASIC 61 can detect the abnormal discharge based on the abnormal discharge detection signals Sv1 to Sv4 input to the ports A / D1 from the abnormal discharge detection circuit 72.

(4) Further, the corona charger 41 has a charging wire 42 and a grid 43 provided between the charging wire 42 and the photoconductor 31. The charging output circuit includes a charging voltage output circuit 71 (wire output circuit) that outputs a wire voltage CHG, which is a voltage applied to the charging wire 42. The voltage detection circuit includes a charge voltage detection circuit 78 (wire voltage detection circuit) that outputs a wire voltage detection signal Vs (detection signal) according to the magnitude of the wire voltage CHG. The ASIC 61 (control device) detects the value of the wire voltage CHG based on the wire voltage detection signal Vs (detection signal) input from the charge voltage detection circuit 78 to the port PT5 or the like (input port).

According to this, the ASIC 61 (control device) compares the voltage value of the wire voltage CHG detected by the charge voltage detection circuit 78 (wire voltage detection circuit) with the first threshold value TH1 before detecting the abnormal discharge. Therefore, it can be determined whether the detected abnormal discharge is an abnormal discharge caused by adhesion of toner or the like, or an abnormal discharge caused by a conductive foreign substance or the like.

(5) Further, the detection circuit includes a grid current detection circuit 82 that outputs a line voltage detection signal Sir (detection signal) according to the magnitude of the grid current Ig, which is the current flowing through the grid 43. The ASIC61 (control device) is based on the line voltage detection signals Sir1 to Sir4 (detection signals) input from the grid current detection circuit 82 to the input ports (ports A / D3, A / D5, A / D7, A / D9). , The value of the grid current Ig is detected, and the value of the grid current Ig is set to the target current value It (S21: NO) according to the determination that the wire voltage CHG (first detected value) is not equal to or less than the first threshold TH1 (S21: NO). Constant current control for controlling the charging voltage output circuit 71 (wire output circuit) so as to match the first target value) is executed (S31). The ASIC 61 determines whether or not the second detection value, which is the value of the wire voltage CHG detected when the constant current control is executed, is equal to or less than the determination reference voltage Vt (second threshold value) (S35).

According to this, the printer 1 has, as a detection circuit, a grid current detection circuit 82 that outputs a line voltage detection signal Sir (detection signal) corresponding to the magnitude of the grid current Ig flowing through the grid 43. The ASIC 61 was detected by the line voltage detection signal Sir of the grid current detection circuit 82 in response to the determination that the wire voltage CHG (first detection value) before abnormal discharge was not equal to or less than the first threshold TH1 (S21: NO). Constant current control is performed to control the wire voltage CHG (charging voltage) based on the grid current Ig. Then, when the ASIC 61 can execute constant current control in a state where the voltage value (second detection value) of the wire voltage CHG is set to the determination reference voltage Vt (second threshold value) or less (S35: YES), the charging wire 42 is cleaned. It can be determined that the error processing has been performed, and the error processing can be appropriately terminated.

(6) Further, in the ASIC61 (control device), the value of the wire voltage CHG exceeds the determination reference voltage Vt (second threshold value) in response to the value of the wire voltage CHG exceeding the determination reference voltage Vt (second threshold value) in the constant current control. The first constant voltage control that controls the charging voltage output circuit 71 (wire output circuit) is executed (S33) so that the value of the wire voltage CHG is set to be equal to or less than the determination reference voltage Vt while executing the first constant voltage control. It is determined whether or not it can be maintained (S35).

For example, when the detection value (voltage value of the wire voltage CHG) of the detection circuit temporarily increases due to noise or the like, the wire voltage CHG exceeds the judgment reference voltage Vt (second threshold value) only once and increases from the second threshold value. There is a possibility that it is erroneously determined (S35: NO). Therefore, the ASIC 61 maintains constant voltage control (first constant voltage control) for a while even after the wire voltage CHG increases from the determination reference voltage Vt, and the wire voltage CHG surely increases to about or higher than the determination reference voltage Vt. Judge that. As a result, although the toner can be cleaned and the constant current can be controlled at the determination reference voltage Vt or less, it is possible to suppress erroneous determination that the wire voltage CHG has increased from the determination reference voltage Vt due to noise or the like.

(7) Further, the ASIC61 (control device) determines that the wire voltage CHG (first detection value) is not equal to or less than the first threshold value TH1, and the target current value It (first) when executing constant current control. The target value) is set lower than the first target value set in the constant current control before detecting the abnormal discharge (S31).

For example, when the constant current control is executed without cleaning the charged wire 42 after the abnormal discharge is detected, the abnormal discharge may reoccur as the wire voltage CHG increases due to the constant current control. Therefore, when the constant current control is executed, the ASIC 61 reduces the target current value It (first target value) of the grid current Ig compared to before the abnormal discharge and suppresses the increase in the wire voltage CHG, thereby causing the recurrence of the abnormality. Can be suppressed.

(8) Further, the charging output circuit includes a grid voltage adjusting circuit 81 (grid output circuit) that outputs a grid voltage GRID, which is a voltage applied to the grid 43. The detection circuit includes a voltage detection circuit 83 (grid voltage detection circuit) that outputs a voltage divider detection signal Sid (detection signal) according to the magnitude of the grid voltage GRID. The ASIC61 (control device) has a grid voltage GRID based on the voltage divider detection signals Sid1 to Sid4 input from the voltage detection circuit 83 to the input ports (ports A / D2, A / D4, A / D6, A / D8). Executes constant voltage control (second constant voltage control) that detects the value and controls the grid voltage adjustment circuit 81 (grid output circuit) so that the value of the grid voltage GRID matches the target voltage value (second target value). do. The ASIC 61 detects an abnormal discharge as a target voltage value (second target value) when executing constant current control in response to the determination that the wire voltage CHG (first detection value) is not equal to or less than the first threshold TH1. Set lower than the target voltage value (second target value) set in the previous constant voltage control (second constant voltage control).

According to this, the printer 1 has a grid voltage adjusting circuit 81 (grid output circuit) that outputs a grid voltage GRID applied to the grid 43. The voltage detection circuit 83 (grid voltage detection circuit) outputs a voltage divider detection signal Sid (detection signal) according to the magnitude of the grid voltage GRID to the ports A / D2 and the like of the ASIC61 (control device). The ASIC 61 detects the grid voltage GRID based on the voltage divider detection signal Sid, and controls the grid voltage adjustment circuit 81 so that the value of the grid voltage GRID matches the target voltage value (second target value) (second). Constant voltage control). The ASIC 61 performs this second constant voltage control during the constant current control starting in S31. Then, the ASIC 61 sets the target voltage value (second target value) of the second constant voltage control when the constant current control is executed in S31 in the constant voltage control (second constant voltage control) before detecting the abnormal discharge. Set lower than the set target voltage value (second target value). As a result, when the constant current control is executed, the target voltage value (second target value) of the grid voltage GRID is reduced as compared with that before the abnormal discharge, and the increase of the wire voltage CHG is suppressed, thereby suppressing the recurrence of the abnormality. be able to.

(9) Further, the printer 1 has a developing roller 47 (developer) that develops an electrostatic latent image formed on the photoconductor 31, and a developing output circuit that outputs a developing voltage that is a voltage applied to the developing roller 47. 66 and. The ASIC 61 (control device) is output from the developing output circuit 66 according to setting the target value of at least one of the target current value It (first target value) and the target voltage value (second target value) to be low. The development output circuit 66 is controlled so that the development voltage is smaller than the development voltage output from the development output circuit 66 before the abnormal discharge is detected.

For example, if the amount of charge that positively charges the photoconductor 31 decreases due to the decrease in the grid voltage GRID, the toner may move from the developing roller 47 (developer) to the photoconductor 31 even though it is not exposed. Therefore, the ASIC 61 can suppress the adhesion of toner to the photoconductor 31 having a reduced amount of charge by controlling the development output circuit 66 and reducing the development voltage applied to the development roller 47.

(10) Further, the printer 1 has a developing roller 47 (developer) that supplies toner (developer) to the electrostatic latent image formed on the photoconductor 31 to develop the image, and a toner image developed by the developing roller 47. It includes a transfer roller 25 (transfer device) that transfers (developer image) to paper P (sheet), and a transfer output circuit 65 that outputs a transfer voltage that is a voltage applied to the transfer roller 25. The ASIC 61 (control device) is output from the transfer output circuit 65 in response to setting the target value of at least one of the target current value It (first target value) and the target voltage value (second target value) low. The transfer output circuit 65 is controlled so that the polarity of the transfer voltage is the same as the polarity of the toner (developer).

According to this, the ASIC 61 (control device) controls the transfer output circuit 65 and changes the polarity of the transfer voltage applied to the transfer roller 25 (transfer device). The polarity of the transfer voltage is the same as the polarity of the toner (developer) (for example, positive polarity). As a result, it is possible to suppress a decrease in the charge amount (positive charge amount) of the photoconductor 31 and suppress adhesion of the toner (developer) to the photoconductor 31 having a reduced charge amount.

(11) Further, the ASIC 61 (control device) sets the wire voltage CHG (value related to the charging voltage) detected when the abnormal discharge is detected as the determination reference voltage Vt (second threshold value).

According to this, the ASIC 61 sets a value (wire voltage CHG) related to the charging voltage when an abnormal discharge is detected as a second threshold value for determining whether or not the charging wire 42 has been cleaned (determination reference voltage Vt). ). For example, when the wire voltage CHG at the time of the previous abnormal discharge is used as the second threshold value, there is a possibility that the presence or absence of cleaning of the charged wire 42 cannot be accurately determined from the difference between the previous wire voltage CHG and the current wire voltage CHG. Specifically, for example, when the environment (room temperature and humidity) at the time of the previous abnormal discharge and the current environment are significantly different, the preconditions for comparing the wire voltage CHG do not match due to the difference in the environment. Changes (reduction, etc.) in the wire voltage CHG due to cleaning of the charged wire 42 may not appear as a difference in the voltage values of the wire voltage CHG. Further, for example, the same applies when the printer 1 is not used for a long period of time and the wire voltage CHG at the time of the previous abnormal discharge is old data. As a result, it may not be possible to accurately determine whether or not the charged wire 42 is cleaned from the difference in the wire voltage CHG. Therefore, the ASIC 61 accurately determines whether or not the charged wire 42 is cleaned by using a value (determination reference voltage Vt) based on the wire voltage CHG when the abnormal discharge this time is detected as the second threshold value. Is possible.

(12) Further, the ASIC 61 (control device) executes a control for printing an image on the paper P (sheet), and performs a process of canceling the printing process being executed as an error process (S17).

According to this, the ASIC 61 can suppress the occurrence of a problem that the image with deteriorated image quality is printed on the paper P by stopping the printing due to the occurrence of the abnormal discharge.

(13) Further, the printer 1 includes a display unit 6. The corona charger 41 has a charging wire 42 for charging the photoconductor 31. As an error process, the ASIC 61 (control device) performs a process of displaying on the display unit 6 that the charging wire 42 is to be cleaned.

According to this, the ASIC 61 urges the user to clean the charging wire 42 as the abnormal discharge occurs. This makes it possible to suppress the recurrence of abnormal discharge.

(14) Further, the printer 1 has a housing 3 in which the corona charger 41 is arranged, a cover 7 that can be opened and closed with respect to the housing 3, and an opening / closing signal Sg (detection) according to the opening / closing state of the cover 7. It includes an open / close detection sensor 8 (sensor) that outputs a signal). In the ASIC61 (control device), the open / close signal Sg input from the open / close detection sensor 8 indicates that the cover 7 is closed from the first signal (for example, the high-level open / close signal Sg) indicating that the cover 7 is open. It is determined whether or not the two signals (for example, the low level open / close signal Sg) have changed (S23, S29). The ASIC 61 determines that the wire voltage CHG (first detection value) is not equal to or less than the first threshold value TH1 (S21: NO), and determines that the wire voltage CHG has changed from the first signal to the second signal (S29: YES). , It is determined whether or not the wire voltage CHG (second detection value) detected after detecting the abnormal discharge is equal to or less than the determination reference voltage Vt (second threshold value) (S35). Further, the ASIC 61 determines that the wire voltage CHG (first detection value) is equal to or less than the first threshold value TH1 (S21: YES), and determines that the wire voltage CHG has changed from the first signal to the second signal (S23). : YES), the error processing is terminated (S25).

According to this, the ASIC 61 determines whether the wire voltage CHG (second detection value) and the determination reference voltage Vt (second threshold value) are determined (determination of cleaning of the charging wire 42) according to the opening / closing operation of the cover 7. Executes the end of error processing. When the cover 7 is opened and closed, it is highly possible that the charging wire 42 and the like have been cleaned by the user. Therefore, after cleaning the charging wire 42 and confirming that the toner and foreign matter have been removed, the above-mentioned process can be started.

(15) Further, the printer 1 transmits the driving force to the housing 3 in which the corona charger 41 is arranged, the exhaust fan 9 (fan) that exhausts the air inside the housing 3, and the exhaust fan 9. It comprises a possible motor 67. The ASIC61 (control device) outputs a drive signal DS to the motor 67 in response to the determination that the wire voltage CHG (second detection value) is not equal to or less than the determination reference voltage Vt (second threshold value) (S35: NO). (S41), after the drive signal DS is output for a predetermined time, the error processing is terminated (S25).

For example, in the work of cleaning the toner or the work performed after cleaning the toner, the user may maintain the inside of the housing 3 by spraying or the like containing flammable gas. In this case, flammable gas may stay in the housing 3 immediately after maintenance. The accumulated flammable gas may cause a malfunction (abnormal discharge, etc.). Therefore, prior to terminating the error processing, the ASIC 61 outputs a drive signal DS to the motor 67 for a predetermined time, rotates the exhaust fan 9 (fan), and discharges the air in the housing 3. As a result, it is possible to suppress the occurrence of defects caused by the flammable gas and appropriately end the error processing.

Needless to say, the present application is not limited to the above embodiment, and various improvements and changes can be made without departing from the spirit of the present invention.
For example, in the above embodiment, the method for detecting abnormal discharge is not limited to the method using the abnormal discharge detection circuit 72. For example, when an abnormal discharge occurs, the wire voltage CHG suddenly increases or decreases. Therefore, the ASIC 61 may be configured to detect an abnormal discharge based on a sudden increase or decrease in the wire voltage CHG detected by the charge voltage detection circuit 78. In this case, the high-voltage power supply device 60 does not have to include the abnormal discharge detection circuit 72. Further, also in this case, when the abnormal discharge occurs due to a conductive foreign substance or the like, the wire voltage CHG before the abnormal discharge does not increase as compared with the wire voltage CHG before the abnormal discharge due to the adhesion of toner. Therefore, even when an abnormal discharge is detected based on a sudden increase or decrease in the wire voltage CHG, whether it is an abnormal discharge due to adhesion of toner or an abnormal discharge due to a foreign substance or the like based on the voltage value of the wire voltage CHG before the abnormal discharge. It is extremely effective to determine and change the processing content thereafter.

Further, in S21, the ASIC 61 compares the wire voltage CHG before the occurrence of the abnormal discharge with the first threshold value TH1 and determines whether the abnormal discharge is due to toner adhesion or an abnormal discharge due to a conductive foreign substance. Not limited to. The ASIC 61 compares, for example, the grid current Ig, the grid voltage GRID, the PWM signal Sp, the PWM signal Sp, etc. before the occurrence of the abnormal discharge with a predetermined threshold value (corresponding to the first threshold value TH1), and before the abnormal discharge. From the change in the grid current Ig and the like, it may be determined whether the abnormal discharge is due to the adhesion of toner or the abnormal discharge due to the conductive foreign matter.
Further, the ASIC 61 determines whether or not the wire voltage CHG when the grid current Ig is increased to the target current value It in the constant current control started in S31 is equal to or less than the determination reference voltage Vt, that is, the target current value It. By determining whether or not the wire voltage CHG has decreased, it was determined whether or not the charged wire 42 was cleaned. However, the ASIC 61 is not limited to the constant current control of the grid current Ig, and may determine whether or not the charging wire 42 is cleaned by the constant voltage control of the wire voltage CHG. For example, the ASIC 61 may determine whether or not the charging wire 42 is cleaned by determining whether or not the grid current Ig when the wire voltage CHG is controlled to a constant voltage at a constant voltage value is reduced. In this case, in order to suppress the recurrence of the abnormal discharge, the target voltage value of the wire voltage CHG when the constant voltage control is performed may be set to a value smaller than the target voltage value set before the abnormal discharge.

Further, the ASIC 61 lowered the target voltage value of the grid voltage GRID in the constant current control in S31, but it does not have to be lowered. That is, the ASIC 61 may carry out constant current control under the same conditions as before the occurrence of abnormal discharge.
Further, in S27, the ASIC 61 determines the determination reference voltage Vt (second threshold value) using the wire voltage CHG at the time of occurrence of abnormal discharge, but the present invention is not limited to this. For example, the ASIC 61 may determine the determination reference voltage Vt using the wire voltage CHG at the time of the previous abnormal discharge.
Further, the ASIC 61 may be configured not to perform the determination accompanying the opening / closing operation of the cover 7. In this case, the printer 1 does not have to include the open / close detection sensor 8.
Further, the ASIC 61 does not have to drive the exhaust fan 9 in S41. In this case, the printer 1 does not have to include the exhaust fan 9.
Further, the sheet of the present application is not limited to the paper P, and may be an OHP sheet.

Further, in the above embodiment, an example in which one corona charger 41 is associated with one photoconductor 31 has been described as an example, but the present invention is not limited to this. The present application has a configuration in which a plurality of corona chargers 41 correspond to one photoconductor 31, for example, a printer (image) in which toner images of each color are superimposed on one photoconductor 31 and then collectively transferred to paper P. It can also be applied to a forming device). In this case, the number of photoconductors 31 may be one.
Further, the printer 1 may be a monochrome printer including only the photoconductor 31K corresponding to black.
Further, the printer 1 may be configured to include only one corona charger 41.

Further, in the above embodiment, the drum-shaped photoconductor 31 is exemplified as the photoconductor, but the photoconductor is not limited to this, and for example, a belt-shaped photoconductor may be used.
Further, as the corona charger of the present application, a scorotron type corona charger 41 provided with a grid 43 is adopted, but the present invention is not limited to this. As the corona charger of the present application, a corona-type corona charger not provided with the grid 43 may be used.
Further, in the above embodiment, the ASIC 61 is used as the control device, but the control device in the present application is not limited to the case where it is configured by dedicated hardware such as the ASIC 61, and is configured by, for example, software that operates on the CPU. May be good. Further, the control device may be an ASIC equipped with a CPU.
Further, in the above embodiment, the electrophotographic laser printer 1 is adopted as the image forming apparatus of the present application, but the present invention is not limited to this. The image forming apparatus of the present application may be a multifunction device, a facsimile machine, a copying machine, or the like.

The technical ideas derived from the contents of the above embodiments are described below as additional notes.
(B) Photoreceptor and
A corona charger that charges the photoconductor by corona discharge,
A charging output circuit that outputs a charging voltage, which is the voltage applied to the corona charger,
A detection circuit that outputs a detection signal related to the charging voltage,
It has an input port connected to the detection circuit, and includes a control device for inputting the detection signal from the detection circuit to the input port.
The control device is
Based on the detection signal input to the input port, the value related to the charging voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the error processing, the determination reference value is determined based on the value related to the charging voltage when the abnormal discharge is detected.
After detecting the abnormal discharge, it is determined whether or not the value related to the charging voltage detected is equal to or less than the determination reference value.
An image forming apparatus that terminates the error processing according to the value related to the charging voltage detected after detecting the abnormal discharge being equal to or less than the determination reference value.

According to this, in the ASIC 61 (control device), the wire voltage CHG (value related to the charging voltage) when the charging voltage output circuit 71 (charging output circuit) is restarted after detecting the abnormal discharge is the determination reference voltage. It can be determined whether or not the charging wire 42 has been cleaned by determining whether or not it is Vt (determination reference value) or less. As the determination reference voltage Vt, the ASIC 61 uses a value based on the wire voltage CHG when an abnormal discharge is detected. For example, when the wire voltage CHG at the time of the previous abnormal discharge is used as the determination reference voltage Vt, there is a possibility that the presence or absence of cleaning of the charged wire 42 cannot be accurately determined from the difference between the previous wire voltage CHG and the current wire voltage CHG. Therefore, the ASIC 61 can accurately determine whether or not the charging wire 42 is cleaned by using a value based on the wire voltage CHG at the time of detecting before the abnormal discharge this time as the determination reference voltage Vt. ..

1 Laser printer (image forming device), 3 housing, 7 cover, 8 open / close detection sensor (sensor), 9 exhaust fan (fan), 20 image forming part, 25 transfer roller, 31 photoconductor, 41 corona charger, 42 Charging wire, 43 grid, 47 developing roller, 61 ASIC (control device), 65 transfer output circuit, 66 developing output circuit, 67 motor, 71 charging voltage output circuit (charging output circuit, wire output circuit), 72 abnormal discharge detection circuit (Detection circuit), 78 Charged voltage detection circuit (detection circuit, voltage detection circuit, wire voltage detection circuit), 81 grid voltage adjustment circuit (grid output circuit), 82 grid current detection circuit, 83 voltage detection circuit (detection circuit, grid) Voltage detection circuit), CHG wire voltage (charged voltage), Sv abnormal discharge detection signal (detection signal), Sid voltage division detection signal (detection signal), A / D1, A / D2, A / D4, A / D6, A / D8 port (input port), TH1 first threshold, Vt judgment reference voltage (second threshold), Ig grid current, GRID grid voltage, DS drive signal, Sg open / close signal (detection signal).

Claims (16)

Photoreceptor and
A corona charger that charges the photoconductor by corona discharge,
A charging output circuit that outputs a charging voltage, which is the voltage applied to the corona charger,
A detection circuit that outputs a detection signal related to the charging voltage,
It has an input port connected to the detection circuit, and includes a control device for inputting the detection signal from the detection circuit to the input port.
The corona charger
It has a charging wire and a grid provided between the charging wire and the photoconductor.
The control device is
Based on the detection signal input to the input port, the value related to the charging voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the detection of the abnormal discharge, it is determined whether or not the first detection value, which is the wire voltage of the charged wire detected before the abnormal discharge is detected, is equal to or less than the first threshold value.
In response to the determination that the first detection value is not equal to or less than the first threshold value, it is determined whether or not the second detection value, which is the wire voltage detected after the abnormal discharge is detected, is equal to or less than the second threshold value. death,
Depending on the determination that the second detection value is equal to or less than the second threshold value, the error processing is terminated.
Depending on the determination that the first detection value is equal to or less than the first threshold value, the error processing is terminated .
The detection circuit is
It has a voltage detection circuit that outputs the detection signal according to the magnitude of the charging voltage.
The control device is
The value of the charging voltage is detected based on the detection signal input from the voltage detection circuit to the input port.
The charge output circuit is
It has a wire output circuit that outputs a wire voltage that is a voltage applied to the charged wire.
The voltage detection circuit is
It has a wire voltage detection circuit that outputs the detection signal according to the magnitude of the wire voltage.
The control device is
The value of the wire voltage is detected based on the detection signal input to the input port from the wire voltage detection circuit.
The detection circuit is
It has a grid current detection circuit that outputs the detection signal according to the magnitude of the grid current, which is the current flowing through the grid.
The control device is
The value of the grid current is detected based on the detection signal input from the grid current detection circuit to the input port.
In response to the determination that the first detection value is not equal to or less than the first threshold value, constant current control for controlling the wire output circuit so as to match the value of the grid current with the first target value is executed.
It is determined whether or not the second detected value, which is the value of the wire voltage detected when the constant current control is executed, is equal to or less than the second threshold value.
In the constant current control, a first constant voltage control that controls the wire output circuit so that the value of the wire voltage becomes equal to or less than the second threshold value in response to the value of the wire voltage exceeding the second threshold value. And execute
An image forming apparatus for determining whether or not the value of the wire voltage can be maintained below the second threshold value while executing the first constant voltage control. Photoreceptor and
A corona charger that charges the photoconductor by corona discharge,
A charging output circuit that outputs a charging voltage, which is the voltage applied to the corona charger,
A detection circuit that outputs a detection signal related to the charging voltage,
It has an input port connected to the detection circuit, and includes a control device for inputting the detection signal from the detection circuit to the input port.
The corona charger
It has a charging wire and a grid provided between the charging wire and the photoconductor.
The control device is
Based on the detection signal input to the input port, the value related to the charging voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the detection of the abnormal discharge, it is determined whether or not the first detection value, which is the wire voltage of the charged wire detected before the abnormal discharge is detected, is equal to or less than the first threshold value.
In response to the determination that the first detection value is not equal to or less than the first threshold value, it is determined whether or not the second detection value, which is the wire voltage detected after the abnormal discharge is detected, is equal to or less than the second threshold value. death,
Depending on the determination that the second detection value is equal to or less than the second threshold value, the error processing is terminated.
Depending on the determination that the first detection value is equal to or less than the first threshold value, the error processing is terminated.
The detection circuit is
It has a voltage detection circuit that outputs the detection signal according to the magnitude of the charging voltage.
The control device is
The value of the charging voltage is detected based on the detection signal input from the voltage detection circuit to the input port.
The charge output circuit is
It has a wire output circuit that outputs a wire voltage that is a voltage applied to the charged wire.
The voltage detection circuit is
It has a wire voltage detection circuit that outputs the detection signal according to the magnitude of the wire voltage.
The control device is
The value of the wire voltage is detected based on the detection signal input to the input port from the wire voltage detection circuit.
The detection circuit is
It has a grid current detection circuit that outputs the detection signal according to the magnitude of the grid current, which is the current flowing through the grid.
The control device is
The value of the grid current is detected based on the detection signal input from the grid current detection circuit to the input port.
In response to the determination that the first detection value is not equal to or less than the first threshold value, constant current control for controlling the wire output circuit so as to match the value of the grid current with the first target value is executed.
It is determined whether or not the second detected value, which is the value of the wire voltage detected when the constant current control is executed, is equal to or less than the second threshold value.
The charge output circuit is
It has a grid output circuit that outputs a grid voltage that is a voltage applied to the grid.
The detection circuit is
It has a grid voltage detection circuit that outputs the detection signal according to the magnitude of the grid voltage.
The control device is
The value of the grid voltage is detected based on the detection signal input from the grid voltage detection circuit to the input port.
A second constant voltage control that controls the grid output circuit so that the value of the grid voltage matches the second target value is executed.
The second target value when the constant current control is executed in response to the determination that the first detection value is not equal to or less than the first threshold value is set in the second constant voltage control before the abnormal discharge is detected. Set it lower than the set second target value,
A developer that develops an electrostatic latent image formed on the photoconductor, and
Further, a developing output circuit for outputting a developing voltage, which is a voltage applied to the developing device, is provided.
The control device is
Corresponding to setting the target value of at least one of the first target value and the second target value to be low, the development voltage output from the development output circuit is the development output before the abnormal discharge is detected. An image forming apparatus that controls the development output circuit so as to be smaller than the development voltage output from the circuit. Photoreceptor and
A corona charger that charges the photoconductor by corona discharge,
A charging output circuit that outputs a charging voltage, which is the voltage applied to the corona charger,
A detection circuit that outputs a detection signal related to the charging voltage,
It has an input port connected to the detection circuit, and includes a control device for inputting the detection signal from the detection circuit to the input port.
The corona charger
It has a charging wire and a grid provided between the charging wire and the photoconductor.
The control device is
Based on the detection signal input to the input port, the value related to the charging voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the detection of the abnormal discharge, it is determined whether or not the first detection value, which is the wire voltage of the charged wire detected before the abnormal discharge is detected, is equal to or less than the first threshold value.
In response to the determination that the first detection value is not equal to or less than the first threshold value, it is determined whether or not the second detection value, which is the wire voltage detected after the abnormal discharge is detected, is equal to or less than the second threshold value. death,
Depending on the determination that the second detection value is equal to or less than the second threshold value, the error processing is terminated.
Depending on the determination that the first detection value is equal to or less than the first threshold value, the error processing is terminated.
The detection circuit is
It has a voltage detection circuit that outputs the detection signal according to the magnitude of the charging voltage.
The control device is
The value of the charging voltage is detected based on the detection signal input from the voltage detection circuit to the input port.
The charge output circuit is
It has a wire output circuit that outputs a wire voltage that is a voltage applied to the charged wire.
The voltage detection circuit is
It has a wire voltage detection circuit that outputs the detection signal according to the magnitude of the wire voltage.
The control device is
The value of the wire voltage is detected based on the detection signal input to the input port from the wire voltage detection circuit.
The detection circuit is
It has a grid current detection circuit that outputs the detection signal according to the magnitude of the grid current, which is the current flowing through the grid.
The control device is
The value of the grid current is detected based on the detection signal input from the grid current detection circuit to the input port.
In response to the determination that the first detection value is not equal to or less than the first threshold value, constant current control for controlling the wire output circuit so as to match the value of the grid current with the first target value is executed.
It is determined whether or not the second detected value, which is the value of the wire voltage detected when the constant current control is executed, is equal to or less than the second threshold value.
The charge output circuit is
It has a grid output circuit that outputs a grid voltage that is a voltage applied to the grid.
The detection circuit is
It has a grid voltage detection circuit that outputs the detection signal according to the magnitude of the grid voltage.
The control device is
The value of the grid voltage is detected based on the detection signal input from the grid voltage detection circuit to the input port.
A second constant voltage control that controls the grid output circuit so that the value of the grid voltage matches the second target value is executed.
The second target value when the constant current control is executed in response to the determination that the first detection value is not equal to or less than the first threshold value is set in the second constant voltage control before the abnormal discharge is detected. Set it lower than the set second target value,
A developer that supplies a developer to the electrostatic latent image formed on the photoconductor and develops it.
A transfer device that transfers the developer image developed by the developer onto a sheet, and
A transfer output circuit that outputs a transfer voltage, which is a voltage applied to the transfer device, is further provided.
The control device is
The polarity of the transfer voltage output from the transfer output circuit is the same as the polarity of the developer according to the setting of at least one of the first target value and the second target value to be lower. An image forming apparatus that controls the transfer output circuit so as to be. Photoreceptor and
A corona charger that charges the photoconductor by corona discharge,
A charging output circuit that outputs a charging voltage, which is the voltage applied to the corona charger,
A detection circuit that outputs a detection signal related to the charging voltage,
It has an input port connected to the detection circuit, and includes a control device for inputting the detection signal from the detection circuit to the input port.
The corona charger
It has a charging wire and a grid provided between the charging wire and the photoconductor.
The control device is
Based on the detection signal input to the input port, the value related to the charging voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the detection of the abnormal discharge, it is determined whether or not the first detection value, which is the wire voltage of the charged wire detected before the abnormal discharge is detected, is equal to or less than the first threshold value.
In response to the determination that the first detection value is not equal to or less than the first threshold value, it is determined whether or not the second detection value, which is the wire voltage detected after the abnormal discharge is detected, is equal to or less than the second threshold value. death,
Depending on the determination that the second detection value is equal to or less than the second threshold value, the error processing is terminated.
Depending on the determination that the first detection value is equal to or less than the first threshold value, the error processing is terminated.
With the housing in which the corona charger is arranged inside,
A fan that exhausts the air inside the housing,
Further equipped with a motor capable of transmitting driving force to the fan,
The control device is
A drive signal is output to the motor in response to the determination that the second detection value is not equal to or less than the second threshold value.
An image forming apparatus that terminates the error processing after outputting the drive signal for a predetermined time. Photoreceptor and
A corona charger having a charging wire and a grid provided between the charging wire and the photoconductor, and charging the photoconductor by corona discharge.
A charging output circuit that outputs a charging voltage, which is the voltage applied to the corona charger,
A detection circuit that outputs a detection signal related to the charging voltage,
A control device having an input port connected to the detection circuit and inputting the detection signal from the detection circuit to the input port.
The housing in which the corona charger is arranged and
A cover that can be opened and closed with respect to the housing,
It is equipped with an open / close detection sensor that outputs an open / close signal according to the open / closed state of the cover.
The control device is
The wire voltage applied to the charged wire is detected based on the detection signal input to the input port, and the wire voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the detection of the abnormal discharge, it is determined whether or not the first detection value, which is the wire voltage detected before the abnormal discharge is detected, is equal to or less than the first threshold value.
When it is determined that the first detection value is not equal to or less than the first threshold value, it is determined whether or not the second detection value, which is the wire voltage detected after the abnormal discharge is detected, is equal to or less than the second threshold value. , The error processing is terminated according to the determination that the second detection value is equal to or less than the second threshold value.
When it is determined that the first detection value is equal to or less than the first threshold value, it is determined that the open / close signal input from the open / close detection sensor has changed from the open state of the cover to the closed state of the cover. An image forming apparatus that terminates the error processing in response to the above. When it was determined that the first detection value was not equal to or less than the first threshold value, it was determined that the open / close signal input from the open / close detection sensor changed from the open state of the cover to the closed state of the cover. The image forming apparatus according to claim 5, wherein it is determined whether or not the second detection value detected after detecting the abnormal discharge is equal to or less than the second threshold value. The charged output circuit has a wire output circuit that outputs the wire voltage applied to the charged wire.
The detection circuit has an abnormal discharge detection circuit that is connected to the wire output circuit and outputs the detection signal in response to the occurrence of the abnormal discharge.
The image forming apparatus according to claim 5 or 6, wherein the control device detects the abnormal discharge based on the detection signal input from the abnormal discharge detection circuit to the input port. The charged output circuit has a wire output circuit that outputs the wire voltage applied to the charged wire.
The detection circuit has a wire voltage detection circuit that is connected to the wire output circuit and outputs the detection signal according to the magnitude of the wire voltage.
The image forming apparatus according to any one of claims 5 to 7, wherein the control device detects the wire voltage based on the detection signal input from the wire voltage detection circuit to the input port. The charged output circuit has a wire output circuit that outputs the wire voltage applied to the charged wire.
The detection circuit includes a grid current detection circuit that outputs the detection signal according to the magnitude of the grid current, which is the current flowing through the grid.
The control device is
The grid current is detected based on the detection signal input from the grid current detection circuit to the input port.
When it is determined that the first detection value is not equal to or less than the first threshold value, constant current control for controlling the wire output circuit so as to match the grid current with the first target value is executed.
The image according to any one of claims 5 to 8, wherein it is determined whether or not the second detection value, which is the wire voltage detected when the constant current control is executed, is equal to or less than the second threshold value. Forming device. The control device is
In the constant current control, the constant voltage control for controlling the wire output circuit is executed so that the wire voltage becomes equal to or less than the second threshold value in response to the wire voltage exceeding the second threshold value.
The image forming apparatus according to claim 9, wherein it is determined whether or not the wire voltage can be maintained below the second threshold value while executing the first constant voltage control. When the control device determines that the first detection value is not equal to or less than the first threshold value, the first target value when executing the constant current control is set to the constant current control before detecting the abnormal discharge. The image forming apparatus according to claim 9 or 10, which is set lower than the first target value set in 1. The charged output circuit has a grid output circuit that outputs a grid voltage which is a voltage applied to the grid.
The detection circuit has a grid voltage detection circuit that outputs the detection signal according to the magnitude of the grid voltage.
The control device is
The grid voltage is detected based on the detection signal input from the grid voltage detection circuit to the input port.
A second constant voltage control that controls the grid output circuit so that the grid voltage matches the second target value is executed.
When it is determined that the first detection value is not equal to or less than the first threshold value, the second target value for executing the constant current control is set in the second constant voltage control before detecting the abnormal discharge. The image forming apparatus according to any one of claims 9 to 11, which is set lower than the second target value. The image forming apparatus according to any one of claims 5 to 12, wherein the control device sets the wire voltage detected when the abnormal discharge is detected as the second threshold value. The image forming apparatus according to any one of claims 5 to 13, wherein the control device executes control for printing an image on a sheet, and performs a process of stopping the running printing process as the error process. Equipped with a display
The image forming apparatus according to any one of claims 5 to 14, wherein the control device performs a process of displaying on the display unit that the charging wire is to be cleaned as the error process. A photoconductor, a corona charger having a charging wire and charging the photoconductor by corona discharge, a charging output circuit that outputs a charging voltage that is a voltage applied to the corona charging device, and detection related to the charging voltage. A casing having a detection circuit that outputs a signal, an input port connected to the detection circuit, a control device that inputs the detection signal from the detection circuit to the input port, and a corona charger internally arranged. A method of controlling an image forming apparatus including a body and a cover that can be opened and closed with respect to the housing.
The wire voltage applied to the charged wire is detected based on the detection signal input to the input port, and the wire voltage is detected.
Based on the detection signal input to the input port, the abnormal discharge generated in the corona charger is detected.
In response to the detection of the abnormal discharge, error processing is performed to deal with the abnormal discharge.
In response to the detection of the abnormal discharge, it is determined whether or not the first detection value, which is the wire voltage detected before the abnormal discharge is detected, is equal to or less than the first threshold value.
Wherein when the first detection value is determined to not more than the first threshold value, determines whether the second detection value the a wire voltage detected after detecting the abnormal discharge is less than the second threshold value Then, in response to the determination that the second detection value is equal to or less than the second threshold value, the error processing is terminated.
A control method in which, when it is determined that the first detection value is equal to or less than the first threshold value , the error processing is terminated according to the change from the open state to the closed state of the cover.

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