JP2020129048A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can efficiently execute preliminary drive of a developing device to remove a toner dropped onto a developing roller.SOLUTION: An image forming apparatus comprises an image carrier, a developing device, and a control unit. The image carrier has an electrostatic latent image formed thereon. The developing device develops the electrostatic latent image formed on the image carrier, and has a developer container that accommodates a developer containing toner, a developing roller that is arranged in the developer container and supplies the toner in the developer accommodated in the developer container to the image carrier, and a bulk variation detection sensor that detects the bulk variation of the developer accommodated in the developer container. The control unit controls the drive of the developing device. When the bulk variation detection sensor detects that an impact is applied to the developing device during a power-off state or a power-saving mode, the control unit executes preliminary drive of the developing device during a power-on state or at the return from the power-saving mode.SELECTED DRAWING: Figure 5

Description

The present invention relates to an electrophotographic image forming apparatus including a developing device that supplies a developer to an image carrier.

An electrophotographic image forming apparatus irradiates the peripheral surface of an image carrier (photosensitive drum) with light based on image information read from a document image or image information transmitted from an external device such as a computer. Form an electrostatic latent image. Toner is supplied from the developing device to the electrostatic latent image to form a toner image, and then the toner image is transferred to a sheet. The sheet after the transfer process is subjected to a toner image fixing process and then discharged to the outside.

With the recent increase in the speed of image forming processing in an image forming apparatus, it is inevitable that a stirring and conveying member that stirs and conveys the developer in the developing device rotates at high speed. As a result, the toner floating in the developing device adheres and accumulates on the inner wall surface of the developing device. If the accumulated toner agglomerates and adheres to the developing roller, the agglomerated toner may be output to an image, so-called toner loss, and an image defect may occur.

In particular, in a developing method using a two-component developer containing a magnetic carrier and a toner and using a magnetic roller carrying the developer and a developing roller carrying only the toner, in a portion where the developing roller and the magnetic roller face each other, Only the toner flies from the magnetic roller to the developing roller, and the toner not used for development flies from the developing roller to the magnetic roller. Therefore, the toner is likely to float near the portion where the developing roller and the magnetic roller face each other.

In order to solve the above-mentioned inconvenience, for example, in Patent Document 1, a time acquisition unit that acquires a leaving time of the developing roller from a previous stop, a humidity detecting unit that detects the environmental humidity inside the machine, and a rotation of the developing roller. A drive control unit that independently controls the rotation of the conveying screw that stirs the developer is provided.The drive control unit is based on the history of the left time and the detected environmental humidity of the developing roller from the previous stop. An image forming apparatus is disclosed in which the driving of the developing roller and the conveying screw at the start of the next image forming operation is controlled, and the conveying screw is rotated after the developer on the developing roller is collected by the image forming apparatus.

Further, in Patent Document 2, in a developing device having a toner recovery mode in which scattered toner adhered in the developing device due to toner scattering is dropped by vibration by a vibration generating means, the toner concentration detected by a toner concentration detection sensor is predetermined. When the value exceeds the value, an image forming apparatus is disclosed in which the driving time of the vibration generating means is shortened.

JP, 2011-59153, A JP, 2017-72628, A

By the way, when a large impact is applied by the opening/closing of the side cover of the image forming apparatus or the movement for changing the layout, the toner agglomerates adhering to the upper portion of the inner surface of the developing device and the like drop onto the developing roller. This toner agglomerate may fly from the developing roller and adhere to the photoconductor drum at the time of the next image formation, and the toner may fall off and be output to the image.

In the method of Patent Document 1, when the environmental humidity and the standing time satisfy certain conditions, the image forming apparatus is always driven at the start of the next image forming operation regardless of the presence or absence of impact, so that the toner aggregates are generated by the impact. If the developing roller is not driven even though the toner has fallen onto the developing roller, there is a problem that toner is dropped. On the other hand, when the developing roller is driven even if the toner aggregates have not dropped onto the developing roller due to the impact, the waiting time before starting the image forming operation becomes long and the developer is deteriorated. was there.

Further, the method of Patent Document 2 aims to maintain the collection performance of the toner accumulated on the toner receiving member and suppress the image defect due to the toner drop even when the toner concentration in the developer is changed. The toner aggregates dropped on the developing roller were not efficiently collected.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an image forming apparatus capable of efficiently performing pre-driving of a developing device for removing toner that has fallen onto a developing roller.

To achieve the above object, the first configuration of the present invention is an image forming apparatus including an image carrier, a developing device, and a controller. An electrostatic latent image is formed on the image carrier. The developing device includes a developing container that stores a developer containing toner, a developing roller that is disposed in the developing container and that supplies the toner in the developer that is stored in the developing container to the image carrier, and a developing container. And a bulk fluctuation detection sensor that detects a bulk fluctuation of the contained developer, and develops the electrostatic latent image formed on the image carrier. The control unit controls driving of the developing device. The control unit determines the difference |A1-A2 between the detection value A1 of the bulk fluctuation detection sensor immediately before the power is turned off or the power saving mode is started and the detection value A2 of the bulk fluctuation detection sensor when the power is turned on or when returning from the power saving mode. When | is equal to or more than a predetermined value, it is determined that the developing device is impacted during the power-off or the power saving mode, and the pre-driving of the developing device is executed when the power is turned on or the power saving mode is restored.

According to the first configuration of the present invention, the developing device is preliminarily driven only when it is determined that a shock is applied to the developing device. Therefore, the preliminary driving of the developing device is suppressed to a necessary minimum, and the developing device is dropped onto the developing roller. It is possible to effectively suppress the occurrence of toner drop when the toner aggregates are output as an image.

Schematic configuration diagram of a color printer 100 according to an embodiment of the present invention. Perspective view of the developing device 3a installed in the color printer 100 Side sectional view of the developing device 3a Block diagram showing an example of a control path used in the color printer 100 6 is a flowchart showing an example of preliminary drive control of the developing devices 3a to 3d when the color printer 100 is powered on or returned from sleep mode. FIG. 3 is a side cross-sectional view of the developing device 3a, showing a state during an image forming operation. FIG. 3 is a side cross-sectional view of the developing device 3a, showing a state when the power is off or when a sleep mode is started. FIG. 3 is a side cross-sectional view of the developing device 3a, showing a state in which an impact is applied while the power is off or in the sleep mode. FIG. 9 is a side sectional view of the developing device 3a, showing a state in which the developing device 3a is preliminarily driven from the state of FIG.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention, and shows a tandem type color printer here. Inside the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side (the right side in FIG. 1) in the transport direction. These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are formed by the steps of charging, exposing, developing, and transferring, respectively. And a black image are sequentially formed.

Photosensitive drums 1a, 1b, 1c and 1d carrying a visible image (toner image) of each color are disposed in these image forming portions Pa to Pd, respectively, and further rotated clockwise in FIG. The intermediate transfer belt 8 is provided adjacent to each of the image forming portions Pa to Pd.

When image data is input from a host device such as a personal computer, first, the chargers 2a to 2d uniformly charge the surfaces of the photoconductor drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and forms an electrostatic latent image according to the image data on each of the photoconductor drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer (hereinafter, simply referred to as a developer) containing toners of cyan, magenta, yellow and black in the toner containers 4a to 4d. The toner in the developer is supplied onto the photoconductor drums 1a to 1d by 3a to 3d and electrostatically adheres thereto. As a result, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photoconductor drums 1a to 1d by a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and cyan, magenta, yellow and The black toner image is primarily transferred onto the intermediate transfer belt 8. Toners and the like remaining on the surfaces of the photoconductor drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

The transfer paper P to which the toner image is transferred is accommodated in a paper cassette 16 arranged in the lower part of the image forming apparatus 100, and the transfer paper P is a predetermined one via a paper feed roller 12a and a registration roller pair 12b. At a timing, the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 and the intermediate transfer belt 8 are conveyed to the nip portion (secondary transfer nip portion). The transfer paper P to which the toner image is secondarily transferred is conveyed to the fixing unit 13.

The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a to fix the toner image on the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P on which the full-color image has been formed is discharged to the discharge tray 17 as it is (or after being distributed to the reverse conveyance path 18 by the branching unit 14 and images are formed on both surfaces) by the discharge roller pair 15.

FIG. 2 is an external perspective view of the developing device 3a installed in the color printer 100, and FIG. 3 is a side sectional view of the developing device 3a. Note that FIG. 3 shows the developing device 3a as viewed from the back side of FIG. 1, and the arrangement of each member in the developing device 3a is the opposite of that in FIG. Further, in the following description, the developing device 3a arranged in the image forming portion Pa of FIG. 1 is illustrated, but the configurations of the developing devices 3b to 3d arranged in the image forming portions Pb to Pd are basically the same. Therefore, the description is omitted.

As shown in FIGS. 2 and 3, the developing device 3a includes a developing container (casing) 20 in which a two-component developer including toner and magnetic carrier is stored. The developing container 20 is agitated and conveyed by a partition wall 20a. It is divided into a chamber 21 and a supply and transport chamber 22. In the stirring/transporting chamber 21 and the feeding/transporting chamber 22, a stirring/transporting screw 25a for feeding the toner (positively charged toner) supplied from the toner container 4a (see FIG. 1) with the carrier to stir and charge the toner, and the feeding/transporting The screws 25b are rotatably arranged.

The developer is conveyed in the axial direction (direction perpendicular to the paper surface of FIG. 2) while being agitated by the agitating/conveying screw 25a and the supplying/conveying screw 25b, and passes through a developer (not shown) formed at both ends of the partition wall 20a. It circulates between the agitating transfer chamber 21 and the supply transfer chamber 22 via a path. That is, a circulation path for the developer is formed in the developer container 20 by the agitating transfer chamber 21, the supply transfer chamber 22, and the developer passage.

The developing container 20 extends obliquely to the upper right in FIG. 3, a toner supply roller 30 is disposed above the supply and conveyance screw 25b in the developing container 20, and a developing roller is located obliquely above the toner supply roller 30. 31 are arranged facing each other. The developing roller 31 faces the photosensitive drum 1a (see FIG. 1) on the opening side (right side in FIG. 3) of the developing container 20. The toner supply roller 30 and the developing roller 31 rotate counterclockwise in FIG. 3 about the rotation axis.

A toner concentration sensor 37 is arranged on the inner surface of the stirring/transporting chamber 21 so as to face the stirring/transporting screw 25 a. In this embodiment, as the toner concentration sensor 37, a magnetic permeability sensor that detects the magnetic permeability of the developer in the developing container 20 and outputs a voltage value corresponding to the detection result is used. The sensor output value changes according to the toner concentration, and the higher the toner concentration, the higher the ratio of the toner to the magnetic carrier, and the higher the ratio of the toner that does not pass magnetism, the lower the output value. On the other hand, the lower the toner concentration, the lower the ratio of the toner to the carrier, and the higher the ratio of the magnetically permeable carrier, resulting in a higher output value.

The toner supply roller 30 is a magnetic roller that includes a non-magnetic rotating sleeve that rotates counterclockwise in FIG. 3 and a fixed magnet body that has a plurality of magnetic poles contained in the rotating sleeve.

The developing roller 31 includes a cylindrical developing sleeve that rotates counterclockwise in FIG. 3 and a developing roller side magnetic pole fixed in the developing sleeve. The toner supply roller 30 and the developing roller 31 are opposed to each other at a facing position (opposing position) with a predetermined gap. The magnetic pole on the developing roller side has a polarity different from that of the magnetic pole (main pole) facing the fixed magnet body.

Further, a brush cutting blade (regulating blade) 33 is attached to the developing container 20 along the longitudinal direction of the toner supply roller 30 (direction perpendicular to the paper surface of FIG. 3). The bristle cutting blade 33 is fastened and fixed to a blade support stay 35 mounted on the developing container 20 by a blade fixing screw 36, and in the rotation direction of the toner supply roller 30 (counterclockwise direction in FIG. 3), the developing roller 31. Is located upstream of the position where the toner supply roller 30 and the toner supply roller 30 face each other. A slight gap is formed between the tip of the spike cutting blade 33 and the outer peripheral surface of the toner supply roller 30.

A DC voltage (hereinafter referred to as Vslv(DC)) and an AC voltage (hereinafter referred to as Vslv(AC)) are applied to the developing roller 31. A DC voltage (hereinafter, referred to as Vmag(DC)) and an AC voltage (hereinafter, referred to as Vmag(AC)) are applied to the toner supply roller 30. These DC voltage and AC voltage are applied from the developing bias power source 53 to the developing roller 31 and the toner supply roller 30 via the bias control circuit 55 (see FIG. 4 for both).

As described above, the toner in the developer is charged by being circulated in the stirring and carrying chamber 21 and the feeding and carrying chamber 22 in the developing container 20 while the developer is being stirred by the stirring and carrying screw 25a and the feeding and carrying screw 25b. The developer in the supply/conveyance chamber 22 is conveyed to the toner supply roller 30 by the supply/conveyance screw 25b. Then, a magnetic brush (not shown) is formed on the toner supply roller 30. After the layer thickness of the magnetic brush on the toner supply roller 30 is regulated by the bristle cutting blade 33, the magnetic brush is conveyed to the area where the toner supply roller 30 and the developing roller 31 face each other by the rotation of the toner supply roller 30. Then, a toner thin layer is formed on the developing roller 31 by the potential difference ΔV between Vmag (DC) applied to the toner supply roller 30 and Vslv (DC) applied to the developing roller 31, and the magnetic field.

The thickness of the toner layer on the developing roller 31 varies depending on the resistance of the developer, the difference in rotation speed between the toner supply roller 30 and the developing roller 31, and the like, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 31 becomes thicker, and when ΔV is decreased, the toner layer becomes thinner. Generally, a suitable range of ΔV during development is about 100V to 350V.

The thin toner layer formed on the developing roller 31 by contact with the magnetic brush on the toner supply roller 30 is conveyed to the area where the photosensitive drum 1 a and the developing roller 31 face each other by the rotation of the developing roller 31. Since Vslv(DC) and Vslv(AC) are applied to the developing roller 31, toner flies from the developing roller 31 to the photosensitive drum 1a due to the potential difference between the developing roller 31 and the photosensitive drum 1a, and Electrostatic latent image of is developed.

The toner remaining without being used for the development is conveyed again to the portion where the developing roller 31 and the toner supply roller 30 face each other, and is collected by the magnetic brush on the toner supply roller 30. Then, the magnetic brush is peeled off from the toner supply roller 30 at the same pole portion of the fixed magnet body, and then drops into the supply conveyance chamber 22.

After that, based on the detection result of the toner concentration sensor 37, a predetermined amount of toner is replenished from the toner container 4a into the developing container 20 through a toner replenishing port (not shown), and circulates in the supply transport chamber 22 and the stirring transport chamber 21. In the meantime, it becomes a two-component developer uniformly charged with an appropriate toner density. This developer is again supplied onto the toner supply roller 30 by the supply/conveying screw 25b to form a magnetic brush, and is conveyed to the bristle cutting blade 33.

FIG. 4 is a block diagram showing an example of a control path used in the color printer 100. In addition, since various controls of each part of the color printer 100 are performed when using the color printer 100, the control path of the entire color printer 100 becomes complicated. Therefore, here, of the control path, a portion necessary for implementing the present invention will be mainly described.

The bias control circuit 55 is connected to the charging bias power source 52, the developing bias power source 53, and the transfer bias power source 54, and operates each of these power sources according to the output signal from the control unit 90. By the control signal from the control circuit 55, the charging bias power source 52 is applied to the charging rollers in the charging devices 2a to 2d, the developing bias power source 53 is applied to the toner supply roller 30 and the developing roller 31 in the developing devices 3a to 3d, and the transfer bias power source. Reference numeral 54 applies a predetermined bias to each of the primary transfer rollers 6a to 6d and the secondary transfer roller 9.

The image input unit 60 is a receiving unit that receives image data transmitted to the color printer 100 from a personal computer or the like. The image signal input from the image input unit 60 is converted into a digital signal and then sent to the temporary storage unit 94.

The operation unit 70 is provided with a liquid crystal display unit 71 and LEDs 72 for indicating various states, and indicates the state of the color printer 100, and displays the image forming status and the number of print copies. Various settings of the color printer 100 are made from the printer driver of the personal computer.

The in-machine temperature/humidity sensor 80 detects the temperature and humidity inside the color printer 100, particularly the temperature and humidity around the developing devices 3a to 3d, and is arranged near the image forming units Pa to Pd.

In addition, the operation unit 70 includes a start button for instructing the user to start image formation, a stop/clear button used for stopping image formation, and various settings for the color printer 100 in default states. A reset button and the like to be used are provided.

The control unit 90 includes a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 that is a read-only storage unit, a RAM (Random Access Memory) 93 that is a readable/writable storage unit, and a temporary storage unit. A plurality of (here, two) units that transmit a control signal to each device in the temporary storage unit 94, the counter 95, and the color printer 100 that store image data and receive an input signal from the operation unit 50. At least an I/F (interface) 96 is provided. The control unit 90 can be arranged at any place inside the main body of the color printer 100.

The ROM 92 stores a control program for the color printer 100, data required for control, and other data that are not changed during use of the color printer 100. The RAM 93 stores necessary data generated during control of the color printer 100, data temporarily needed for control of the color printer 100, and the like. Further, the RAM 93 (or ROM 92) also stores sensor output values (threshold values) when the developing devices 3a to 3d are preliminarily driven based on the detection result of the toner concentration sensor 37 as described later. The temporary storage unit 94 temporarily stores the image signal input from the image input unit 60 and converted into a digital signal. The counter 95 cumulatively counts the number of printed sheets.

Further, the control unit 90 transmits a control signal from the CPU 91 to the respective parts and apparatuses of the color printer 100 through the I/F 96. In addition, a signal indicating the state and an input signal from each part and device are transmitted to the CPU 91 through the I/F 96. As the respective units and devices controlled by the control unit 90, for example, the image forming units Pa to Pd, the exposure device 5, the intermediate transfer belt 8, the secondary transfer roller 9, the fixing unit 13, the bias control circuit 55, and the image input unit 60. , The operation unit 70, and the like.

As described above, when a large impact is applied to the color printer 100 during non-image formation, the toner aggregate attached to the upper portion of the inner wall surface of the developing container 20 falls on the developing roller 31. The toner agglomerates that have fallen onto the developing roller 31 move to the photoconductor drums 1a to 1d and are output as an image, so that toner is dropped. Here, if the developing devices 3a to 3d are always preliminarily driven before the next image formation in order to prevent the toner from falling off, the developing devices 3a to 3d are unnecessarily driven even if the toner aggregates have not dropped. Will end up. Therefore, the waiting time until the image forming operation is started becomes long and the developer is deteriorated.

Therefore, in the color printer 100 of the present embodiment, when the color printer 100 is powered on or returned from the sleep mode (power saving mode), is the developing device 3a to 3d impacted while the power is off or in the sleep mode? It is determined whether or not the developing devices 3a to 3d are preliminarily driven only when an impact is applied.

FIG. 5 is a flowchart showing an example of preliminary drive control of the developing devices 3a to 3d when the color printer 100 is powered on or returned from the sleep mode. An execution procedure of pre-driving of the developing devices 3a to 3d will be described with reference to FIGS. 1 to 4 and FIGS. 6 to 9 described later.

The control unit 90 first determines whether power-off is input from the operation unit 70, or whether a sleep mode transition command has been input when a predetermined time has elapsed from the previous image forming operation (step S1). ). When the power off or the shift to the sleep mode is input (Yes in step S1), the control unit 90 acquires the detection value A1 of the toner concentration sensor 37 (step S2). After acquiring the detection value A1, the control unit 90 shifts the color printer 100 to the power-off state or the sleep mode (step S3).

FIG. 6 is a side sectional view of the developing device 3a during the image forming operation. During the image forming operation, the stirring/conveying screw 25a and the supplying/conveying screw 25b rotate in a fixed direction (clockwise direction in FIG. 6). Further, the toner concentration sensor 37 is located downstream of the moving direction (from right to left in FIG. 6) of the portion of the stirring and conveying screw 25a facing the bottom surface 21a of the stirring and conveying chamber 21 (the lower half of FIG. 6), that is, the stirring and conveying. It is arranged on the inner wall surface of the chamber 21 on the side (left side in FIG. 6) where the developer is lifted by the rotation of the stirring and conveying screw 25a (clockwise direction in FIG. 6).

With this configuration, the developer in the agitating/conveying chamber 21 is lifted by the rotation of the agitating/conveying screw 25a on the side where the toner concentration sensor 37 is arranged (the left side in FIG. 6). As a result, the interface of the developer (indicated by a broken line) has an upward slope toward the side where the toner concentration sensor 37 is arranged. Therefore, during the image forming operation, the developer is always in contact with the detection surface of the toner concentration sensor 37, and the toner concentration sensor 37 can detect the concentration.

FIG. 7 is a side sectional view of the developing device 3a when the power is off or when the sleep mode is started. When the driving of the developing device 3a is stopped from the state of FIG. 6, the side where the developer is lifted by the rotation of the stirring and conveying screw 25a, that is, the side where the toner concentration sensor 37 is arranged (see FIG. 6). Stop when the developer is biased to the left). The detection value of the toner density sensor 37 at this time is acquired as A1.

Further, a part of the toner scattered at the facing portion of the toner supply roller 30 and the developing roller 31 during the image forming operation adheres to the upper portion of the inner surface of the developing container 20 to form a toner aggregate G.

Returning to FIG. 4, the control unit 90 determines whether a power-on is input from the operation unit 70 or a return command from the sleep mode is input by a print operation input from a host device such as a personal computer. Is determined (step S4). When the power-on or the return from the sleep mode is input (Yes in step S4), the control unit 90 sets the color printer 100 to the power-on state or returns from the sleep mode (step S5). Next, the control unit 90 acquires the detection value A2 of the toner detection sensor 37 (step S6).

FIG. 8 is a side cross-sectional view of the developing device 3a showing a state where a shock is applied while the power is off or in the sleep mode. When a shock is applied to the developing device 3 a, the toner aggregate G attached to the upper portion of the inner surface of the developing container 20 drops and accumulates on the developing roller 31. Further, the developer in the agitating/conveying chamber 21 and the supplying/conveying chamber 22 is leveled by the impact and sinks, so that the interface of the developer (indicated by a broken line) moves below the detection surface of the toner concentration sensor 37. The detection value of the toner density sensor 37 at this time is acquired as A2.

Next, the control unit 90 determines whether or not the absolute value |A1-A2| of the difference between the acquired detection values A1 and A2 is greater than or equal to the predetermined value X (step S7). If |A1−A2|≧X (Yes in step S7), it is estimated that the shock is applied during the power-off or the sleep mode as shown in FIG. 8, and thus the developing devices 3a to 3d. Pre-driving is performed (step S8). After that, the color printer 100 is set to the standby state (step S9), and the pre-driving control is ended.

FIG. 9 is a side cross-sectional view of the developing device 3a showing a state of being preliminarily driven from the state of FIG. To pre-drive the developing devices 3a to 3d, turn on the main motor 45 (see FIG. 4) or turn on a clutch (not shown) provided between the main motor 45 and the developing devices 3a to 3d. Thus, the toner supply roller 30 and the developing roller 31 are rotated in the same direction (counterclockwise direction in FIG. 9) as during image formation. The execution time of the pre-driving is appropriately about 30 seconds in order to surely remove the toner aggregates G accumulated on the developing roller 31.

As shown in FIG. 9, the toner aggregate G that has dropped onto the developing roller 31 is transferred from the developing roller 31 to the toner supplying roller 30, and then the toner supplying roller 30 is formed at the same pole portion of the fixed magnet body in the toner supplying roller 30. And is collected in the supply and transport chamber 22.

Since Vmag (DC) and Vslv (DC) are not applied to the toner supply roller 30 and the developing roller 31 during the preliminary driving of the developing devices 3a to 3d, the potential difference between the developing roller 31 and the photosensitive drum 1a is It becomes 0. Therefore, due to the rotation of the developing roller 31, even if the toner adheres to the surface of the developing roller 31 and passes through the portion facing the photoconductor drums 1a to 1d, the toner is moved to the photoconductor drums 1a to 1d side. That's not it.

Further, when pre-driving the developing devices 3a to 3d, Vmag (DC) having a polarity opposite to that of the toner may be applied to the toner supply roller 30 without applying Vslv (DC) to the developing roller 31. By doing so, a potential difference in the direction in which the toner moves from the developing roller 31 to the toner supplying roller 30 is generated, so that the phenomenon that the toner aggregate G attached to the toner supplying roller 30 moves to the developing roller 31 again is effective. Can be suppressed.

On the other hand, if |A1-A2|<X in step S7 (No in step S7), it is estimated that no impact was applied during the power-off or the sleep mode. Therefore, the pre-driving of the developing devices 3a to 3d is performed. The color printer 100 is set to the standby state without performing (step S9), and the pre-driving control is ended.

According to the above configuration, since the developing devices 3a to 3d are preliminarily driven only when it is determined that the impact is applied to the developing devices 3a to 3d, the preliminarily driving of the developing devices 3a to 3d is suppressed to a necessary minimum while developing. It is possible to effectively suppress the occurrence of toner drop when an image is output from the toner aggregate G that has dropped onto the roller 31.

Further, based on the difference between the detection value A1 of the toner concentration sensor 37 at the time of power-off or the transition to the sleep mode and the detection value A2 of the toner concentration sensor 37 at the time of the power-on or the return from the sleep mode, Therefore, it is possible to accurately determine the presence or absence of a shock without separately providing a dedicated sensor for detecting the shock in order to determine whether or not there is a volume fluctuation, that is, whether or not the shock is applied to the developing devices 3a to 3d. can do. Further, since the impact applied when the power source of the color printer 100 is turned off can be detected, the monitoring load of the color printer 100 can be reduced.

Further, the amount of floating toner generated in the developing devices 3a to 3d changes depending on the usage environment of the color printer 100. For example, when the temperature and humidity inside the machine are high, the fluidity of the toner decreases, so that the toner attached to the inner surface of the developing container 20 easily aggregates. On the contrary, when the temperature and humidity inside the machine are low, the fluidity of the toner is improved, so that the toner attached to the inner surface of the developing container 20 is less likely to aggregate.

Therefore, it is estimated that the impact value is detected by the detection values A1 and A2 of the toner concentration sensor 37 during the power-off or the sleep mode, and at the time of the power-on or the return from the sleep mode, the in-machine temperature/humidity sensor 80 (see FIG. 4). The preliminary drive may be executed only when the temperature/humidity detected by the above) is equal to or higher than a predetermined value.

The amount of floating toner generated in the developing devices 3a to 3d changes depending on the amount of toner consumed in the developing devices 3a to 3d. For example, when the printing rate of the formed image is high, the amount of toner consumed in the developing devices 3a to 3d is large, so that the amount of toner attached to the inner surface of the developing container 20 is also large. On the contrary, when the printing rate of the formed image is low, the amount of toner consumed in the developing devices 3a to 3d is small, so that the amount of toner attached to the inner surface of the developing container 20 is also small.

Therefore, it is inferred that the impact is applied during the power-off or the sleep mode by the detection values A1 and A2 of the toner concentration sensor 37, and the integrated printing rate for a predetermined number of sheets goes back from the time when the power is turned off or the sleep mode is entered. The pre-driving may be executed only when it is equal to or more than the predetermined value. Specifically, the control unit 90 calculates the print ratio for each image based on the image data in the temporary storage unit 94, and further calculates the integrated print ratio by integrating the print ratio for a predetermined number of sheets. Then, when the integrated print ratio is equal to or more than the predetermined value and |A1-A2|≧X, the pre-driving is executed.

According to the above control, only when the impact is applied during the power-off or the sleep mode, and when the printing is continued in the high temperature and high humidity environment or the high printing rate, the aggregation of the toner is likely to occur. Pre-driving is executed. Therefore, the toner aggregate G attached on the developing roller 31 can be reliably collected, and the pre-driving can be performed to the minimum necessary.

Others The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the present invention is not limited to the developing devices 3a to 3d including the toner supply roller 30 and the developing roller 31 as shown in FIGS. 2 and 3, but a two-component developer including toner and carrier. It can be applied to various developing devices using.

In the above embodiment, the toner concentration sensor 37 is arranged on the inner wall surface of the stirring/transporting chamber 21 on the side where the developer is lifted by the rotation of the stirring/transporting screw 25a (the left side in FIG. 6). The toner concentration sensor 37 may be arranged on the inner wall surface on the side (right side in FIG. 6). In this case, the interface of the developer is lowered immediately before the power is turned off or the mode is changed to the sleep mode, and the developer is evenly raised when an impact is applied. Therefore, the relationship between the detection values A1 and A2 of the toner concentration sensor 37 is set. A1<A2, but by comparing |A1-A2|, it is possible to determine the presence or absence of a shock during power-off or in the sleep mode as in the above embodiment. However, in order to reliably detect the toner concentration during image formation, it is preferable to dispose the toner concentration sensor 37 on the side where the developer is lifted by the rotation of the stirring and conveying screw 25a.

Further, in the above embodiment, the developing devices 3a to 3d using the two-component developer containing the toner and the carrier have been described, but the present invention can be applied to the developing device using the one-component developer containing only the toner. .. In a developing device using a one-component developer, instead of a magnetic permeability sensor, a piezoelectric sensor that detects the amount of developer (developer bulk) in the developer container is placed near the interface of the developer, so that one component due to impact is generated. Since the bulk fluctuation of the developer can be detected, the pre-driving control according to the presence/absence of impact can be performed even in the developing device using the one-component developer.

Further, although the tandem color printer 100 has been described as an example in the above embodiment, the present invention can be applied to, for example, monochrome and color copying machines, digital multi-function peripherals, monochrome printers, facsimiles, and the like. is there.

INDUSTRIAL APPLICABILITY The present invention is applicable to an image forming apparatus equipped with a developing device. By utilizing the present invention, it is possible to provide an image forming apparatus capable of efficiently removing the toner that has dropped onto the developing roller from the inner wall surface of the developing container due to an impact.

Pa to Pd Image forming unit 1a to 1d Photoreceptor drum (image bearing member)
3a to 3d Developing device 4a to 4d Toner container 20 Developing container 20a Partition wall 30 Toner supply roller 31 Developing roller 33 Ear cutting blade 37 Toner concentration sensor (bulk fluctuation detection sensor)
80 In-machine temperature and humidity sensor (temperature and humidity detection device)
90 control unit 100 color printer (image forming apparatus)

Claims (6)

An image carrier on which an electrostatic latent image is formed,
A developing container for containing a developer containing toner,
A developing roller disposed in the developing container, for supplying the toner in the developer contained in the developing container to the image carrier,
A bulk fluctuation detection sensor for detecting a bulk fluctuation of the developer contained in the developing container;
And a developing device for developing the electrostatic latent image formed on the image carrier,
A control unit for controlling the drive of the developing device,
In an image forming apparatus equipped with
The control unit sets the detection value A1 of the bulk fluctuation detection sensor immediately before power-off or the start of the power saving mode and the detection value A2 of the bulk fluctuation detection sensor at power-on or at the time of returning from the power saving mode. If the difference |A1-A2| An image forming apparatus characterized by executing pre-driving of the apparatus. A temperature and humidity detecting device for detecting the temperature and humidity inside the image forming apparatus;
The control unit executes preliminary drive of the developing device only when the temperature and humidity detected by the temperature/humidity detection device when the power is turned on or when returning from the power saving mode are equal to or higher than predetermined values. The image forming apparatus according to claim 1. The control unit calculates the cumulative print ratio for a predetermined number of sheets, retroactively from the time when the power is turned off or when the power saving mode is entered, and the preliminary drive of the developing device is performed only when the calculated cumulative print ratio is equal to or more than a predetermined value. The image forming apparatus according to claim 1, wherein the image forming apparatus according to claim 1 or 2, is executed. The developing device includes a stirring and conveying member that stirs and conveys the developer in the developing container in a rotation axis direction,
4. The bulk variation detection sensor is arranged on the inner wall surface of the developing container on the side where the developer is lifted by the rotation of the stirring and conveying member, according to any one of claims 1 to 3. Image forming apparatus. The developer is a two-component developer containing the toner and a magnetic carrier,
The image forming apparatus according to claim 1, wherein the bulk fluctuation detection sensor is a magnetic permeability sensor that detects the magnetic permeability of the developer. The developing device includes a toner supply roller that is disposed to face the developing roller, supports the developer contained in the developing container, and supplies only the toner in the developer to the developing roller. The image forming apparatus according to claim 5, which is characterized in that.

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