JP2010002605A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of detecting abnormality of a non-contact type temperature sensor without increasing a cost. <P>SOLUTION: The fixing device secures a nip 107 by bringing a roller 102 into press-contact with a heated roller 101, and thermally fixes an image on paper by making the paper pass through the nip. The non-contact type temperature detection sensor 105 is arranged on the roller 102 side relative to a conveyance path 37 on a more downstream side in a paper conveying direction than the nip, and the non-contact type temperature detection sensor 106 is arranged on the roller 101 side relative to the conveyance path on a more downstream side in the paper conveying direction than the nip. Temperature of a first surface (front surface) of the paper just after passing through the nip is detected by the sensor 106, and temperature of a second surface (back surface) is detected by the sensor 105. The difference value ΔV of output voltage between both sensors is calculated. When the value is not within a predetermined range previously set as a range expressing a threshold for deciding normality of the sensor, the abnormality of the sensor is detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device that thermally fixes an unfixed image on a sheet and an image forming apparatus including the same, and more particularly to a temperature control technique of the fixing device.

An image forming apparatus such as a copying machine includes a fixing device for fixing an unfixed image on a sheet by heating and pressing. The fixing device includes, for example, a fixing roller, a pressure roller pressed against the fixing roller, a first heater that heats the fixing roller, and a second heater that heats the pressure roller.
In such a fixing device using heat fixing, the temperature of the fixing roller and the pressure roller is detected by a temperature detecting element, and the surface temperature of the fixing roller and the pressure roller is controlled to a temperature suitable for fixing based on the detection result. Is done.

Conventionally, as a temperature detection element, a contact type thermistor that detects the temperature by contacting the surface of the fixing roller has been used in many cases. A temperature sensor, for example, an infrared temperature sensor such as a thermopile is used.
Patent Document 1 discloses an example using an infrared temperature sensor for detecting the surface temperature of the fixing roller and another infrared temperature sensor for detecting the surface temperature of the pressure roller. An infrared temperature sensor is usually formed so that a thermopile arranged on a stem is covered with a case, and infrared rays emitted from a detection target are received by the thermopile through an incident window provided in the case. The electric signal corresponding to the amount of received light is output.

In the case of a configuration that receives infrared rays through the entrance window, if toner particles or paper dust floating in the device adheres to the entrance window of the case and the entrance window becomes dirty, the stain is blocked by the dirt and the accurate The temperature cannot be detected.
As a configuration for detecting that such an accurate temperature cannot be detected, Patent Document 2 discloses an environmental temperature sensor for detecting the temperature of the installation environment, in addition to the infrared temperature sensor, as the heat of the fixing device. The structure which arrange | positions in the location which is not influenced by this, and detects that the temperature detection by an infrared temperature sensor is abnormal from the difference of the output signal of an infrared temperature sensor and an environmental temperature sensor is disclosed.
JP 2000-259035 A JP 2007-41306 A

In the configuration of the above-mentioned Patent Document 2, it may be possible to detect an abnormality of the infrared temperature sensor, but it is necessary to separately arrange a temperature sensor not related to fixing, which is disadvantageous in terms of cost. Further, since the difference between the output signals of the infrared temperature sensor and the environmental temperature sensor is used, there is a problem that the abnormality cannot be detected until the environmental temperature becomes constant.
The present invention has been made in view of the above-described problems, and provides a fixing device capable of detecting an abnormality of a non-contact type temperature sensor without increasing the cost, and an image forming apparatus including the same. It is an object.

  In order to achieve the above object, a fixing device according to the present invention heats at least one of the first and second rotating bodies and press-contacts the peripheral surface of the first rotating body and the peripheral surface of the second rotating body. A fixing device that secures a fixing nip between the two, passes the sheet through the fixing nip, and thermally fixes an unfixed image on the sheet, and is downstream of the fixing nip in the sheet conveying direction. And a first temperature sensor disposed on the second rotating body side with respect to the sheet conveying path and detecting the surface temperature of the first rotating body in a non-contact manner, and the fixing nip in the sheet conveying direction. A second temperature sensor disposed downstream of the sheet conveying path and closer to the first rotating body and detecting a surface temperature of the second rotating body in a non-contact manner; Use the detection results of the 1st and 2nd temperature sensors Temperature control means for controlling the temperatures of the first and second rotating bodies, and the first temperature when the sheet after passing through the fixing nip passes through the detection region of the first temperature sensor. The temperature detection result of the first surface of the sheet facing the first temperature sensor by the sensor and the second temperature sensor when the sheet passes through the detection region of the second temperature sensor And detecting means for detecting an output abnormality of the temperature sensor based on the temperature detection result of the second surface of the sheet on the side facing the second temperature sensor.

Further, the detection means is configured such that a difference value between a temperature detection value of the first surface of the sheet by the first temperature sensor and a temperature detection value of the second surface of the sheet by the second temperature sensor is a difference. The output abnormality is detected when the value does not fall within a preset range as a normal range of values.
Furthermore, the detection means changes the size of the range according to the type of the sheet.

Here, the range is characterized in that the upper limit value and the lower limit value of the sheet having the second thickness that is thinner than the first thickness are smaller than the sheet having the first thickness. .
The sheet has a single-side mode in which an unfixed image is formed only on one side, an unfixed image is formed on one side, and the formed non-fixed image is thermally fixed, and then separated on the other side. The sheet is sent from an image forming apparatus that can be switched between a double-side mode for forming an unfixed image, and the detection means detects whether the sheet to be fixed is (a) the unfixed image in the single-side mode. In the case of the formed sheet and in the case of the sheet on which the unfixed image is formed on the other surface in the duplex mode, or (b) the unfixed image is formed on the one surface in the duplex mode The size of the range is changed between a sheet and a sheet on which an unfixed image is formed on the other surface in the duplex mode.

  Furthermore, a first heater for heating the first rotating body and a second heater for heating the second rotating body are provided, and the temperature control means is detected by the first temperature sensor. In addition, the temperature of the first surface of the sheet is compared with a preset first target temperature, and the power supply to the second heater is controlled based on the comparison result, and the second temperature sensor The detected temperature of the second surface of the sheet is compared with a preset second target temperature, and power supply to the first heater is controlled based on the comparison result.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an unfixed image on a sheet and thermally fixes the formed unfixed image by a fixing unit, and includes the above-described fixing device as the fixing unit. It is characterized by that.

  Thus, by using the first temperature sensor for detecting the surface temperature of the first rotating body and the second temperature sensor for detecting the surface temperature of the second rotating body, both of these sensors are used. Since the temperature of the first surface and the second surface of the sheet immediately after passing through the fixing nip is detected and the sensor abnormality is detected from the detection result, another sensor not related to the fixing control is arranged for detecting the sensor abnormality. Therefore, it is possible to detect a sensor abnormality without increasing the cost.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described by taking a digital copying machine (hereinafter simply referred to as “copying machine”) as an example.
<Embodiment 1>
(1) Configuration of Copying Machine FIG. 1 is a diagram showing the overall configuration of the copying machine 1.

As shown in FIG. 1, the copying machine 1 is roughly divided into a scanner unit 2 and a printer unit 3. The copying machine 1 scans the surface of an original and prints (prints) on one sheet, and both sides of the original ( A double-sided copy job can be executed in which the front side and the back side are sequentially read and printed on the first side (front side) and the second side (back side) of one sheet.
The scanner unit 2 is a known unit that conveys a set original to a reading position and reads an image by a CCD image sensor (not shown) to obtain an image signal. The image signal is sent to the control unit 4. It is done. In the case of a double-sided copy job, both sides of the document are sequentially read, and front and back image signals are sent to the control unit 4 respectively. The control unit 4 performs necessary processing on the received electrical signal to generate image data, and converts this into a drive signal for driving a laser diode (not shown) of the printer head 10.

The printer unit 3 includes a printer head 10, an image processing unit 20, a paper feeding unit 30, a fixing unit 40, and a duplex conveying unit 50.
The printer head 10 drives a laser diode based on a drive signal output from the control unit 4 to emit laser light L, and performs exposure scanning on the photosensitive drum 21 that is rotationally driven.
The image processing unit 20 includes a photosensitive drum 21, a charging charger 23, a developing unit 24, a transfer charger 25, a separation charger 26, a cleaner 22 and the like arranged around the photosensitive drum 21.

The paper feed unit 30 is configured to feed a sheet as an example of a recording sheet, a paper feed cassette 31, a feed roller 32 that feeds the paper from the paper feed cassette 31 toward the transport path 37, and transports the fed paper. A pair of conveying rollers 33, 34, and 35, and a timing roller pair 36 for taking a timing for feeding the sheet to the photosensitive drum 21.
The photosensitive drum 21 is uniformly charged by the charging charger 23 after the residual toner on the surface is removed by the cleaner 22 before exposure by the printer head 10, and the laser beam is thus uniformly charged. When exposed to L, an electrostatic latent image is formed on the surface of the photosensitive drum 21.

  This electrostatic latent image is developed with toner by the developing device 24, thereby forming a toner image on the surface of the photosensitive drum 21. In synchronization with the toner image forming operation, the sheet is conveyed to the transfer position below the photosensitive drum 21 by the timing roller pair 36 and is formed on the surface of the photosensitive drum 21 by the electrostatic force of the transfer charger 25 at the transfer position. The transferred toner image is transferred onto the paper.

The sheet on which the toner image is transferred is separated from the photosensitive drum 21 by the electrostatic force generated by the separation charger 26. The sheet separated from the photosensitive drum 21 is conveyed to the fixing unit 40 by the conveying belt 28, where it is heated and pressurized, and the toner particles on the surface are fused and fixed on the surface of the sheet. 38 is discharged to a discharge tray 39.
In the case of duplex copying, the conveyance path is switched by a switching claw (not shown) or the like immediately after the leading edge of the sheet on which the image is formed passes through the fixing unit 40 and is guided to the duplex conveyance path 51. . The paper guided to the double-sided conveyance path 51 is once conveyed to the retreat path 55 by the conveyance roller pairs 52 to 54, and after being retracted to the retraction path 55, it is switched back by the reverse rotation of the conveyance roller pairs 53 and 54 and re-supplied. Guided to paper path 56. Then, it is returned again to the conveyance path 37 by the conveyance roller pairs 57 to 59 and conveyed to the transfer position via the timing roller pair 36.

  In synchronization with this transport operation, charging, exposure, development, and the like for image formation are performed on the back side of the paper in the image processing unit 20, and the toner image on the photosensitive drum 21 is transferred to the back side of the paper at the transfer position. Transcribed. The sheet on which the toner image has been transferred on the back surface is fixed by heating and pressurization at the fixing unit 40 and then discharged onto the discharge tray 39 via the discharge roller pair 38.

(2) Configuration of Fixing Unit 40 FIG. 2 is a cross-sectional view showing the configuration of the fixing unit 40, and FIG. 2A shows a state immediately before the paper reaches the fixing unit 40. FIG. b) shows a state in which the sheet passes through the fixing unit 40.
As shown in both figures, the fixing unit 40 includes a cylindrical fixing roller 101, a cylindrical pressure roller 102 that is pressed by the fixing roller 101 and secures a fixing nip 107 between the fixing roller 101, and fixing. A main heater 103 inserted in the roller 101, a sub heater 104 inserted in the pressure roller 102, non-contact type infrared temperature detection sensors 105, 106, etc. The fused toner image is heated and melted and pressed to be fixed.

The pressure roller 102 is rotationally driven in the direction of the arrow in the figure by a rotational driving force from a drive motor (not shown), whereby the fixing roller 101 is driven to rotate.
The main heater 103 and the sub heater 104 are made of a halogen lamp heater or the like, and the main heater 103 has a larger amount of heat generation than the sub heater 104.
An infrared temperature detection sensor 105 (hereinafter abbreviated as “sensor 105”) is disposed on the downstream side of the fixing nip 107 in the paper conveyance direction and on the pressure roller 102 side of the conveyance path 37. An infrared temperature detection sensor 106 (hereinafter abbreviated as “sensor 106”) is disposed on the downstream side of the fixing nip 107 in the sheet conveyance direction and on the fixing roller 101 side of the conveyance path 37.

As shown in FIG. 2A, the sensor 105 detects the surface temperature of the fixing roller 101 in a non-contact manner when no sheet is present in the detection area 110 between the sensor 105 and the fixing roller 101, and FIG. When a sheet is present as shown in FIG. 5, the temperature of the back surface of the sheet (the first surface facing the sensor 105) is detected without contact.
On the other hand, as shown in FIG. 2A, the sensor 106 detects the surface temperature of the pressure roller 102 in a non-contact manner when there is no sheet in the detection area 110 between the sensor 106 and the pressure roller 102. When a sheet is present as shown in 2 (b), the temperature of the surface of the sheet (the second surface facing the sensor 106) is detected without contact. As described above, the two sensors 105 and 106 are arranged so that the light receiving surfaces face each other in a crossing positional relationship. The voltage (output voltage) of the detection signal from the sensors 105 and 106 has an output characteristic that increases when the temperature of the detection target (roller surface / paper) increases and decreases when the temperature of the detection target decreases. Detection signals from the sensors 105 and 106 are sent to the control unit 60 (FIG. 1).

(3) Configuration of Control Unit 60 FIG. 3 is a block diagram showing the configuration of the control unit 60.
As shown in the figure, the control unit 60 includes a CPU 61, a ROM 62, a RAM 63, a fixing temperature adjustment control unit 64, an EEPROM 65, and the like.
The ROM 62 stores a program for executing a job such as a copy job. The RAM 63 is a work area for the CPU 61.

The CPU 61 reads a necessary program from the ROM 62, controls the operations of the scanner unit 2 and the printer unit 3 in a unified manner with timing, and based on image data read by the scanner unit 2, Smoothly execute a copy job for forming an image on top.
The fixing temperature control unit 64 controls power supply to the main heater 103 and the sub heater 104 based on the output voltages of the sensors 105 and 106. This control differs depending on whether the surface temperature of the fixing roller 101 and the pressure roller 102 is detected as a detection target and when the front and back surfaces of the paper are detected. This control will be specifically described below with reference to FIG.

(4) Details of Heater Control FIG. 4 is a diagram showing the transition of changes in the output voltages (when normal) of the sensors 105 and 106 during heater control during warm-up, standby, and printing.
Here, during the warm-up in the figure, power supply from the power-on to the main heater 103 and the sub-heater 104 is started when the power is turned on, and the fixing roller 101 and the pressure roller 102 are heated and the surface temperature is increased. Until the target temperature T1 or T2 (temperature suitable for fixing) is reached.

The standby state is a period in which the surface temperatures of the fixing roller 101 and the pressure roller 102 are maintained at the target temperatures T1 and T2 and waiting for a print instruction. This figure conceptually shows the state of the output change, and the portion where the temperature is a straight line actually varies somewhat.
As shown in the figure, when the warm-up is started by turning on the power (time point A), the output voltages of the sensors 105 and 106 increase as the fixing roller 101 and the pressure roller 102 rise in temperature. At this time, the sensor 105 detects the surface temperature of the fixing roller 101, and the sensor 106 detects the surface temperature of the pressure roller 102.

When the output voltages of the sensors 105 and 106 become V1 and V2 (time point B), the warm-up is finished assuming that the surface temperatures of the fixing roller 101 and the pressure roller 102 have reached the target temperatures T1 and T2. The voltages V1 and V2 indicate voltage values that would be output if the sensors 105 and 106 were normal when the roller surface temperature was T1 and T2 (here, T1> T2).
In the figure, the surface temperature of the fixing roller 101 and the pressure roller 102 is an example in which the target temperatures T1 and T2 are reached at the same time. However, one of them may be delayed, in which case it is delayed. When the temperature reaches the target temperature, the warm-up is finished.

During standby (time points B to C), the power supply amounts to the main heater 103 and the sub heater 104 are individually controlled so that the output voltages of the sensors 105 and 106 are maintained at V1 and V2.
When printing is started (time point C) and the leading edge in the paper conveyance direction after image formation passes through the fixing nip 107 and reaches the detection area 110 (time point D), the detection target of the sensors 105 and 106 is the paper from the roller surface. Changes to. That is, the sensor 105 detects the temperature of the back surface of the paper, and the sensor 106 detects the temperature of the front surface of the paper. Since the surface temperature of the fixing roller 101 is higher than that of the pressure roller 102, the temperature of the sheet immediately after passing through the fixing nip 107 is higher than that of the back surface.

  During the sheet detection, the power supply amounts to the main heater 103 and the sub heater 104 are individually controlled so that the output voltages of the sensors 105 and 106 become V3 and V4. Here, V3 and V4 are T3 and T4 (here, T3>) the temperatures of the front and back surfaces of the paper (target temperature of the paper) when an appropriate amount of heat is applied to the paper in the fixing nip 107, respectively. When T4), the voltage value that will be output if the sensors 105 and 106 are in a normal state is shown. As described above, the temperature of the front and rear surfaces of the sheet immediately after passing through the fixing nip 107 is detected, and the heater control is performed by feeding back the detected temperature for the following reason.

  In other words, the sheet temperature immediately after passing through the fixing nip 107 can be said to indicate the amount of heat supplied to the sheet at the fixing nip 107. If the sheet temperature is detected, has the heat necessary for fixing been supplied to the sheet? By controlling the amount of heat generated by the main heater 103 and the sub heater 104 based on the determination result, the surface temperature of the fixing roller 101 and the pressure roller 102 is maintained at a temperature more suitable for fixing, and the fixing property is improved. This is because improvement can be achieved. For example, when different types of paper are selectively used, fixing performance can be improved by determining a target temperature for each of the papers and performing control so that the target temperature is maintained.

  Note that the detection of the sheet is performed, for example, by detecting a time point (time point D) at which the temperature of the detection target is drastically decreased from the start of printing. A timer or the like can also be used. For example, a time required for the leading end of the sheet to pass through the fixing nip 107 from a specific position (not shown) on the conveyance path 37 is obtained in advance, and a timer is started after the leading end of the sheet passes the specific position, and the count value It may be possible to take a method of detecting that the time has been reached. The voltage values V <b> 1 to V <b> 4 are obtained in advance from experiments as a reference voltage corresponding to the target temperature, and the data is stored in the EEPROM 65.

The fixing temperature adjustment control unit 64 detects an abnormality in the output signals of the sensors 105 and 106 in addition to the heater control. This abnormality detection method will be specifically described below with reference to FIGS.
(5) Sensor Abnormality Detection FIG. 5 is a diagram illustrating an example of a change in sensor output voltage when the sensor 106 is abnormal (the sensor 105 is normal). The abnormality of the sensor 106 in the figure is that toner particles or paper powder floating in the apparatus accumulates in an infrared incident window (not shown) of the sensor 106 and a part of incident infrared rays is shielded. In addition, this is an example in the case where the phenomenon that the output voltage becomes lower at the same temperature as compared with the normal time occurs.

  As shown in the figure, during standby (time points B to C), the heater is controlled so that the output voltage of the sensor 106 becomes V2, but the sensor 106 is in an abnormal state as described above, and the output voltage is Since the pressure becomes lower, the surface temperature of the pressure roller 102 is maintained at T2u higher than the normal temperature T2. Since the sensor 105 is normal, the surface temperature of the fixing roller 101 is maintained at T1 as in the normal state.

  When the object to be detected is changed from the roller to the sheet by the start of printing (time point D), the sensor 105 detects the temperature of the back side of the sheet, but the temperature of the back side of the sheet becomes T4u higher than the normal temperature T4. Should be. This is because the surface temperature of the pressure roller 102 is T2u higher than normal, and the back surface of the sheet is in contact with the surface of the pressure roller 102 of the high temperature T2u, and the pressure roller 102 increases more than normal. This is because the heat is applied. Since the sensor 105 is normal, it can accurately detect the temperature of the back surface of the paper having a high T4u, and the output voltage at this time should be V4u higher than the voltage V4 at normal time.

On the other hand, the sensor 106 detects the temperature of the surface of the paper. The temperature of the surface of the paper should be the same as the normal temperature T3. However, since the output voltage of the sensor 106 is lower, the output voltage of the sensor 106 becomes V3d, which is lower than the normal time.
Since the output voltage of the sensor 105 is increased and the output voltage of the sensor 106 is decreased as compared with the normal time, the difference value ΔVβ between the output voltages of the sensors 105 and 106 is the difference value ΔVα between the V3 and V4 at the normal time (FIG. 4). Smaller than.

The output voltage of the sensor 106 and the difference value ΔV have a relationship that the difference value ΔVβ decreases as the dirt on the incident window of the sensor 106 becomes more severe and the output voltage comes out lower. From such a relationship, if a lower limit value that can be regarded as normal is determined in advance and it is determined that the magnitude of the difference value ΔV is below the lower limit value, an abnormality of the sensor 106 can be detected.
In the above description, the heater control is performed so that the output voltages of the sensors 105 and 106 become V3 and V4 during the paper detection at the normal time. The power supply to the heater 103 and the sub heater 104 is stopped.

FIG. 5 illustrates an example in which the sensor 106 becomes abnormal, but FIG. 6 illustrates an example in which the sensor 105 becomes abnormal. FIG. 6 is also an example of the case where the output voltage becomes lower at the same temperature because the entrance window of the sensor 105 becomes dirty as in FIG.
As shown in FIG. 6, during standby (time points B to C), the heater control is performed so that the output voltage of the sensor 105 becomes V1, but since the output voltage of the sensor 105 becomes lower as described above, fixing is performed. The surface temperature of the roller 101 is maintained at T1u higher than the normal temperature T1. Since the sensor 106 is normal, the surface temperature of the pressure roller 102 is maintained at T2 as in the normal state.

When the object to be detected is changed from a roller to a sheet by starting printing (time point D), the sensor 105 detects the temperature of the back side of the sheet. The temperature on the back side of the paper should be the same as the normal temperature T4, but the output voltage of the sensor 105 is lower, so the output voltage of the sensor 105 is V4d, which is lower than the normal time.
On the other hand, the sensor 106 detects the temperature of the surface of the paper. At this time, the temperature of the paper surface should be T3u higher than the normal temperature T3. This is because the surface temperature of the fixing roller 101 is T1u higher than normal, and the surface of the sheet is in contact with the surface of the fixing roller 101 having the high temperature T1u, so that more heat is generated from the fixing roller 101 than normal. It is because it is granted. Since the sensor 106 is normal, it is possible to accurately detect the temperature of the paper surface that has reached the high temperature T3u, and the output voltage at this time is V3u, which is higher than the normal voltage V3.

Since the output voltage of the sensor 105 decreases and the output voltage of the sensor 106 increases compared to the normal time, the difference value ΔVβ of the output voltages of the sensors 105 and 106 becomes larger than the difference value ΔVα in the normal time.
Here, the output voltage of the sensor 105 and the difference value ΔV are opposite to the relationship between the sensor 106 and the difference value ΔV. The reverse relationship is that when the sensor 106 is abnormal (lower), the surface temperature of the pressure roller 102 rises higher than normal and the difference from the surface temperature of the fixing roller 101 becomes smaller. This is because, when the sensor 105 is abnormal (lower), the surface temperature of the fixing roller 101 is higher than normal and the difference from the surface temperature of the pressure roller 102 is increased. Therefore, when the sensor 105 is abnormal, the difference value ΔVβ increases as the output voltage of the sensor 105 becomes lower.

From such a relationship, if an upper limit value that can be regarded as normal is determined in advance and it is determined that the magnitude of the difference value ΔV exceeds the upper limit value, an abnormality of the sensor 105 can be detected.
5 and 6 show examples in which the output voltage is lowered. FIGS. 7 and 8 show examples in which the output voltage is increased. Here, for example, a case where an abnormality occurs in a thermopile arranged in the sensor is assumed to be higher.

FIG. 7 is an example when the sensor 106 is abnormal, and FIG. 8 is an example when the sensor 105 is abnormal.
In FIG. 7, since the sensor 105 is normal, during standby (time points B to C), the surface temperature of the fixing roller 101 is maintained at T1 as in the normal state. On the other hand, since the output voltage of the sensor 106 is increased, the surface temperature of the pressure roller 102 is maintained at T2d, which is lower than the normal temperature T2.

  During paper detection (after time D), the sensor 105 detects the temperature of the back side of the paper. At this time, the temperature of the back side of the sheet should be T4d lower than the normal temperature T4. This is because the surface temperature of the pressure roller 102 is T2d which is lower than normal. Since the sensor 105 is normal, it can accurately detect the temperature of the back side of the paper at the low temperature T4d, and the output voltage at this time is V4d lower than the voltage V4 at normal time.

On the other hand, the sensor 106 detects the temperature of the paper surface. The temperature of the paper surface should be the same as the normal temperature T3. However, since the output voltage of the sensor 106 is higher, the output voltage of the sensor 106 becomes V3u, which is higher than the normal time.
Since the output voltage of the sensor 105 is lower and the output voltage of the sensor 106 is higher than in the normal state, the difference value ΔVβ is larger than the difference value ΔVα in the normal state.

From this, if an upper limit value that can be regarded as normal is determined in advance and it is determined that the magnitude of the difference value ΔV exceeds the upper limit value, an abnormality of the sensor 106 can be detected.
In FIG. 8, since the output voltage of the sensor 105 becomes higher, the surface temperature of the fixing roller 101 is maintained at T1d lower than the normal temperature T1 during standby (time points B to C).
Since the sensor 106 is normal, the surface temperature of the pressure roller 102 is maintained at T2 as in the normal state.

During paper detection (after time D), the sensor 105 detects the temperature of the back side of the paper. At this time, the temperature of the back side of the sheet should be the same as the temperature T4 at the normal time, but the output voltage of the sensor 105 becomes higher, so the output voltage of the sensor 105 becomes V4u higher than the normal time.
On the other hand, the sensor 106 detects the temperature of the paper surface. The temperature of the paper surface at this time should be T3d lower than the normal temperature T3. This is because the surface temperature of the fixing roller 101 is T1d, which is lower than normal. Since the sensor 106 is normal, it is possible to accurately detect the temperature of the paper surface at the low temperature T3d, and the output voltage at this time is V3d lower than the normal voltage V3.

Since the output voltage of the sensor 105 increases and the output voltage of the sensor 106 decreases compared with the normal time, the difference value ΔVβ is smaller than the normal difference value ΔVα.
Therefore, if a lower limit value that can be regarded as normal is determined in advance and it is determined that the magnitude of the difference value ΔV is lower than the lower limit value, an abnormality of the sensor 105 can be detected.
As described above, the range of the difference value ΔV in which the sensor can be regarded as normal from the temperature detection value that would be output if both the sensors were normal so as to satisfy all the detection conditions in the four patterns in FIGS. (Upper limit and lower limit) are obtained in advance from experiments and the like, and if the difference value ΔV is within the range, it can be determined that the sensor is normal, and if it is not, the sensor is determined to be abnormal.

(6) Flowchart of Heater Control and Sensor Abnormality Detection FIG. 9 is a flowchart showing the contents of heater control processing by the fixing temperature adjustment control unit 64. This process is executed every time it is called at a predetermined interval, for example, several milliseconds in a main routine (not shown) during standby and printing.
As shown in the figure, the detection signals of the sensors 105 and 106 are received (step S1).

  It is determined whether or not the value of the output voltage of the sensor 105 is smaller than a predetermined value V1 (step S2). If it is determined that the value of the output voltage is smaller than the predetermined value V1 (“YES” in step S2), the main heater 103 is turned on (step S3), and the process proceeds to step S5. On the other hand, if it is determined that the output voltage value of the sensor 105 is equal to or greater than the predetermined value V1 (“NO” in step S2), the main heater 103 is turned off (step S4), and the process proceeds to step S5.

  In step S5, it is determined whether or not the value of the output voltage of the sensor 106 is smaller than a predetermined value V2. If it is determined that the value of the output voltage is smaller than the predetermined value V2 (“YES” in step S5), the sub heater 104 is turned on (step S6), and the process returns to the main routine. On the other hand, when it is determined that the value of the output voltage of the sensor 106 is equal to or greater than the predetermined value V2 (“NO” in step S5), the sub heater 104 is turned off (step S7), and the process returns to the main routine. The processes in steps S1 to S7 are repeated at a predetermined interval.

As a result, when no sensor abnormality has occurred, the surface temperatures of the fixing roller 101 and the pressure roller 102 change up and down within a range of about several degrees Celsius, for example about 5 degrees Celsius, centering on the target temperatures T1 and T2. However, it will be changed. When the sensor is abnormal, for example, when the output value is low, the roller surface temperature is maintained higher than the target temperature.
In the above description, the case where the object to be detected is on the roller surface such as in standby is described. However, when the object to be detected is changed to a sheet immediately after passing through the fixing nip 107, the predetermined values V1 and V2 are set to the predetermined value V3 together with the change. , V4 is executed after resetting.

FIG. 10 is a flowchart showing the processing contents of sensor abnormality detection. This process is executed every time a call is made at a predetermined interval, for example, several milliseconds in a main routine (not shown) during printing.
As shown in the figure, it is determined whether or not a sheet immediately after passing through the fixing nip 107 is detected (step S11). This determination of paper detection is made by detecting that the sensor output voltage has dropped significantly during printing as described above (after time D in FIG. 4).

If it is determined that the sheet has not been detected (“NO” in step S11), the process returns to the main routine. On the other hand, if it is determined that the sheet is detected (“YES” in step S11), the detection signals of the sensors 105 and 106 are received (step S12).
Then, a difference value ΔV between the output voltages of the two sensors is calculated (step S13).
It is determined whether or not ΔV is within a certain range (step S14). Here, the fixed range is an appropriate range of the difference value ΔV obtained from the temperature detection value that would be output if both sensors are normal, that is, the upper limit to the lower limit of the difference value ΔV when the sensor is considered normal. This is a range determined in advance as the voltage range. The data is stored in the EEPROM 65, for example.

If it is determined that ΔV is within a certain range (“YES” in step S14), it is determined that the sensor is not abnormal (normal), and the process returns to the main routine.
On the other hand, if it is determined that ΔV is not within the certain range (“NO” in step S14), a sensor abnormality is detected (“NO” in step S15), and the process returns to the main routine. When an abnormality is detected, the user is warned by displaying a message to that effect on a display unit of an operation panel (not shown). However, the present invention is not limited to this. For example, a job that is being executed may be canceled while giving the warning. Alternatively, only job cancellation may be performed.

  As described above, in this embodiment, the sensor 105 for detecting the surface temperature of the fixing roller 101 and the sensor 106 for detecting the surface temperature of the pressure roller 102 are provided. Heater detection and abnormality detection processing are performed based on the detection result of this and the temperature detection result of the front and back surfaces of the sheet immediately after passing through the fixing nip 107. It is not necessary to arrange a sensor, and sensor abnormality can be detected while reducing the cost.

In the above description, an example in which the magnitude relationship between the roller surface temperatures T1 and T2 and the front and back surface temperatures T3 and T4 of the sheet satisfies T1>T2>T3> T4 has been described, but depending on the apparatus configuration, for example, FIG. As shown, there are cases where T1>T3>T2> T4.
In this case, for example, as shown in FIG. 11 (b), if the sensor 106 is abnormal (when the output voltage is low) (corresponding to FIG. 5), the voltage difference ΔVβ is the normal value in FIG. 11 (a). It becomes smaller than ΔVα. Therefore, by determining a lower limit threshold value in the normal state in advance, a sensor abnormality can be detected when the voltage difference becomes smaller than that value. In addition to this condition, by considering the other three conditions, that is, when the sensor 105 becomes abnormal (corresponding to FIG. 6) and when the output value becomes high (corresponding to FIG. 7 and FIG. 8). As described above, a certain range of the voltage difference that can be regarded as normal for the sensor is determined, and if the detected voltage difference does not fall within the certain range, the sensor abnormality may be detected.

<Embodiment 2>
In the first embodiment, the range of the voltage difference indicating the sensor normal range is constant. However, in the second embodiment, the range is changed according to the type of paper, and this is different from the first embodiment. ing. Hereinafter, in order to avoid duplication of description, the description of the same contents as those of Embodiment 1 is omitted, and the same components are denoted by the same reference numerals.

FIG. 12 is a flowchart showing a part of the processing content of the sensor abnormality detection according to the present embodiment. The sensor abnormality detection process according to the present embodiment is a process in which steps S21 to S31 shown in the figure are executed instead of steps S14 and S15 of the sensor abnormality detection process in the first embodiment.
As shown in the figure, it is determined whether or not the used paper is an OHP (overhead projector) sheet (step S21). As a method of determining which type of paper is used, for example, a method of accepting input of a paper type from an operation panel (not shown) by a user can be used. As another method, for example, a method of discriminating the type from the difference in light transmittance of the conveyed paper may be used. Specifically, a transmissive optical sensor is disposed on the transport path 37, the surface of the transported paper is irradiated with light to receive the light transmitted through the paper, and the received light amount M is equal to or greater than the first threshold value. OHP sheet, thin paper if first threshold> M ≧ second threshold, plain paper if second threshold> M ≧ third threshold, thick paper if third threshold> M ≧ fourth threshold It is a method to discriminate.

  Here, if it is determined that it is OHP (“YES” in step S21), whether the difference value ΔV between the output voltages of both sensors is within the range of 0.5 [V] or more and less than 0.8 [V]. It is determined whether or not (step S22). This range is obtained in advance from experiments or the like as a voltage range of the difference value ΔV that can be regarded as a normal sensor when using OHP, and the data is stored in the EEPROM 65 or the like. The same applies to the voltage range of the difference value ΔV for other types of paper described later.

Here, the upper limit value and the lower limit value of the voltage range differ depending on the type of paper. For example, 0.4 [V] or more and less than 0.6 [V] (step S25) for plain paper, 0.2 [V] or more and less than 0.5 [V] (step S31) for thin paper. . The reason why the voltage range of the difference value ΔV is changed in accordance with the type of paper is as follows.
That is, the sheet surface is heated by the fixing roller 101 when it passes through the fixing nip 107, and the sheet back surface is heated by the pressure roller 102. Since the roller surface temperature is higher in the fixing roller 101 than in the pressure roller 102 as described above, the heat on the surface side with the higher temperature is conducted to the back surface side through the inside of the sheet, and is slightly on the back surface of the sheet. A phenomenon that raises the temperature occurs. The amount of heat conduction from the front side to the back side of the paper differs depending on the paper thickness and material. For example, the thinner the paper, the smaller the thicker.

This means that even if the roller surface temperature is the same, the temperature difference between the front and back surfaces of the paper changes slightly depending on the paper type. The temperature difference between the front surface and the back surface of the paper appears as a voltage difference ΔV between the output voltages of the sensors 105 and 106. If the temperature difference changes, the difference value ΔV also changes. Will also change.
The fact that thin paper has more heat conduction than thick paper means that the temperature difference between the front and back surfaces of thin paper is smaller than that of thick paper, and the difference value ΔV is also small. The difference value ΔV is smaller because the value in the normal sensor range should be smaller for thin paper than for thick paper.

In the present embodiment, when different types of paper are used by setting the voltage range values to be smaller in order of OHP sheet, thick paper, plain paper, and thin paper, and setting a part of the range to overlap. However, the sensor abnormality can be detected with higher accuracy.
If it is determined in step S22 that ΔV is within the above range (“YES” in step S22), it returns to the main routine assuming that the sensor is normal.

On the other hand, if it is determined that it is not within the above range (“NO” in step S22), a sensor abnormality is detected (step S23), and the process returns to the main routine.
If it is determined that the paper to be used is plain paper (“NO” in step S21, “YES” in S24), the difference value ΔV is within the range of 0.4 [V] or more and less than 0.6 [V]. It is determined whether or not there is (step S25). If it is determined that ΔV is within the above range (“YES” in step S25), the process returns to the main routine. If it is determined that ΔV is not included (“NO” in step S25), a sensor abnormality is detected ( Step S26), the process returns to the main routine.

  If it is determined that the paper to be used is thick (“NO” in step S24, “YES” in S27), the difference value ΔV falls within the range of 0.4 [V] or more and less than 0.7 [V]. It is determined whether or not (step S28). If it is determined that ΔV is within the above range (“YES” in step S28), the process returns to the main routine, and if it is determined that it is not (“NO” in step S28), a sensor abnormality is detected ( Step S29), the process returns to the main routine.

  If it is determined that there is no OHP, plain paper, or thick paper (“NO” in step S27), it is determined that the paper to be used is thin paper (step S30), and the difference value ΔV is 0.2 [V] or more, 0 It is determined whether it is within the range of less than 5 [V] (step S31). If it is determined that ΔV is within the above range (“YES” in step S31), the process returns to the main routine, and if it is determined that it is not (“NO” in step S31), a sensor abnormality is detected ( Step S32) and return to the main routine.

  As described above, in the present embodiment, the value and width of the voltage range for determining sensor abnormality are changed according to the type of paper used, so that sensor abnormality can be detected with higher accuracy. It becomes like this. Needless to say, the voltage value is an example, and an appropriate value is set according to the device configuration. Also, the type of paper is not limited to the above, and other types of paper may be used. A range of difference values indicating a normal sensor range is set according to the paper.

<Embodiment 3>
In the second embodiment, the range of the difference value indicating the sensor normal range is changed according to the type of paper. However, in the third embodiment, the difference value is changed according to the single-sided and double-sided copy jobs. Is different from the above embodiment.
FIG. 13 is a flowchart showing a part of the processing content of the sensor abnormality detection according to the present embodiment. The sensor abnormality detection process is a process in which steps S41 to S46 shown in the figure are executed instead of steps S14 and S15 of the sensor abnormality detection process of the first embodiment.

As shown in the figure, whether the detected paper is a paper by a single-sided copy job or a paper that has been printed on the front surface by a double-sided copy job (paper that has not yet been printed on the back surface). Is determined (step S41).
If it is determined that the sheet is printed on the front side by single-sided or double-sided copying (“YES” in step S41), the difference value ΔV between the output voltages of both sensors is 0.4 [V] or more and 0.5 [V]. It is determined whether it is within the range below (step S42). This range is obtained in advance from an experiment or the like as a range in which the sensor can be regarded as normal with respect to a sheet printed by simplex copying and a sheet printed on the surface of duplex copying, and the data is stored in the EEPROM 65 or the like.

If it is determined that ΔV is within the above range (“YES” in step S42), it returns to the main routine assuming that the sensor is normal. On the other hand, if it is determined that it is not present ("NO" in step S42), a sensor abnormality is detected (step S43), and the process returns to the main routine.
If it is determined that the sheet is not a single-sided copy nor a sheet printed on the front side by double-sided copying ("NO" in step S41), the sheet printed on the back side by double-sided copying (paper that has been printed on the front side) (Step S44), it is determined whether or not the difference value ΔV between the output voltages of the two sensors is within a range of 0.3 [V] or more and less than 0.4 [V] (Step S44). S45). This range is obtained in advance from an experiment or the like as a range in which the sensor is normal with respect to a sheet printed on the back side by duplex copying, and the data is stored in the EEPROM 65 or the like. This voltage range is smaller by 0.1 [V] than the voltage range (0.4 V or more and less than 0.5 V) for the single-sided copy and the double-sided copy printed on the surface. The range is shifted. This is due to the following reason.

That is, the paper on which the back side is printed by double-sided copying can be said to be a paper that has not passed so much time after passing through the fixing nip 107 and thermally fixed at the time of printing on the front side immediately before. The temperature is higher than that of the paper on which the single-sided copy or the double-sided copy is printed.
Since the second heat fixing is performed in a state where the temperature is high, the temperature difference between the front and back surfaces of the sheet immediately after passing through the fixing nip 107 is smaller than that in the first time when the paper temperature is low. Will be. This can be said to be the same as in the case of using the above thin paper.

Therefore, the voltage range for the sheet immediately after the second fixing by duplex copying is set to be slightly smaller than the voltage range for the sheet by the first fixing.
If it is determined that ΔV is within the above range (“YES” in step S45), the process returns to the main routine. On the other hand, if it is determined that it is not present (“NO” in step S45), a sensor abnormality is detected (step S46), and the process returns to the main routine.

As described above, according to the present embodiment, the value of the voltage range for determining the sensor abnormality is changed according to the copy mode (according to the level of the detected paper temperature). Can be performed with higher accuracy. Note that the above voltage values are examples, as in the second embodiment.
The present invention is not limited to the image forming apparatus, and may be a method for detecting a sensor abnormality. Furthermore, the method may be a program executed by a computer. The program according to the present invention includes, for example, a magnetic disk such as a magnetic tape and a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and a flash memory recording medium. It can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of the recording medium, wired and wireless various networks including the Internet in the form of programs, In some cases, the data is transmitted and supplied via broadcasting, telecommunication lines, satellite communications, or the like.

<Modification>
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.
(1) In the above embodiment, an example in which an infrared temperature sensor using a thermopile is used as a non-contact type temperature sensor has been described. However, the present invention is not limited to this, and an NC sensor, for example, may be used.

  (2) In the above embodiment, the configuration example using the main heater 103 and the sub heater 104 has been described. However, it is sufficient if the fixing roller 101 and the pressure roller 102 can be heated to a temperature suitable for fixing. For example, one heater is used. It is also possible to adopt a configuration in which is provided on one roller side. In this case, for example, the one heater is controlled based on the detection results of the surface temperatures of the fixing roller 101 and the pressure roller 102.

(3) In the above embodiment, the configuration example using the fixing roller 101 and the pressure roller 102 as the first and second rotating bodies has been described. However, the present invention is not limited to this, and for example, the first rotating body is fixed. The belt and the second rotating body may be configured as a pressure belt, one may be configured as a roller, and the other as a belt.
(4) In the above embodiment, the sensor abnormality is detected if the difference value ΔV of the output voltage when the paper temperature is detected by the two sensors 105 and 106 is not within the predetermined range. However, the present invention is not limited to this. For example, a normal voltage range may be determined in advance as a voltage value at the time of paper detection for each sensor, and a sensor abnormality may be detected when the voltage value is out of this range.

  (5) In the above embodiment, an example in which the image forming apparatus according to the present invention is applied to a monochrome copying machine capable of duplex copying has been described, but the present invention is not limited thereto. Regardless of single-sided copy, double-sided copy, color or monochrome image formation, at least one of the first and second rotating bodies is heated, and the peripheral surfaces of the first and second rotating bodies are pressed to contact the fixing nip. Any image forming apparatus provided with a fixing device that secures and allows a sheet to pass through the fixing nip to thermally fix an unfixed image on the sheet can be applied to, for example, a printer, a FAX, an MFP (Multiple Function Peripheral), and the like. In the above description, the sensors 105 and 106 are disposed at substantially symmetric positions via the conveyance path, but are not limited to being symmetric. Further, the sheet detection area by the sensor 105 and the sheet detection area by the sensor 106 are substantially the same position on the conveyance path. However, depending on the arrangement position of both sensors, the detection areas may be shifted from each other on the conveyance path. There is also.

  The contents of the above embodiment and the above modification may be combined.

  The present invention can be widely applied to a fixing device that thermally fixes an unfixed image on a sheet.

1 is a diagram illustrating an overall configuration of a copier according to a first embodiment. FIG. 3 is a cross-sectional view illustrating a configuration of a fixing unit provided in the copying machine. FIG. 2 is a block diagram illustrating a configuration of a control unit provided in a copying machine. It is a figure which shows the mode of the transition of the change of the output voltage from two non-contact-type infrared temperature sensors in warm-up, standby, and heater control during printing. It is a figure which shows the example of transition of the sensor output voltage in case one sensor is abnormal (the other sensor is normal). It is a figure which shows the example of transition of the sensor output voltage when the other sensor becomes abnormal. It is a figure which shows the example of another transition of the sensor output voltage when one sensor becomes abnormal. It is a figure which shows the example of another transition of the sensor output voltage when the other sensor becomes abnormal. It is a flowchart which shows the example of the processing content of the heater control by a control part. It is a flowchart which shows the processing content of a sensor abnormality detection. It is a figure which shows the example of transition of another sensor output voltage in case one sensor is abnormal and the other sensor is normal. 10 is a flowchart showing a part of processing contents of sensor abnormality detection according to the second embodiment. 10 is a flowchart showing a part of processing contents of sensor abnormality detection according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copy machine 37 Conveyance path 40 Fixing part 60 Control part 61 CPU
64 Fixing temperature control unit 101 Fixing roller 102 Pressure roller 103 Main heater 104 Sub heater 105, 106 Non-contact infrared temperature sensor 107 Fixing nip 110 Detection area

Claims (7)

At least one of the first and second rotating bodies is heated and the peripheral surface of the first rotating body and the peripheral surface of the second rotating body are pressed against each other to secure a fixing nip therebetween. A fixing device that passes a sheet and thermally fixes an unfixed image on the sheet,
A first sheet that is disposed downstream of the fixing nip in the sheet conveying direction and closer to the second rotating body than the sheet conveying path, and detects a surface temperature of the first rotating body in a non-contact manner. Temperature sensor,
A second sheet that is disposed downstream of the fixing nip in the sheet conveying direction and closer to the first rotating body than the sheet conveying path, and detects a surface temperature of the second rotating body in a non-contact manner. Temperature sensor,
Temperature control means for controlling the temperatures of the first and second rotating bodies using detection results of the first and second temperature sensors;
When the sheet after passing through the fixing nip passes through the detection region of the first temperature sensor, the first temperature sensor has a first surface on the side facing the first temperature sensor. The temperature detection result and the temperature of the second surface of the sheet facing the second temperature sensor by the second temperature sensor when the sheet passes through the detection region of the second temperature sensor Detection means for detecting an output abnormality of the temperature sensor based on a detection result;
A fixing device comprising: The detection means includes
The difference value between the temperature detection value of the first surface of the sheet by the first temperature sensor and the temperature detection value of the second surface of the sheet by the second temperature sensor is set in advance as a normal range of the difference value. The fixing device according to claim 1, wherein the output abnormality is detected when the output is not within a set range. The detection means includes
The fixing device according to claim 2, wherein the size of the range is changed according to a type of the sheet. The range is
4. The fixing according to claim 3, wherein the upper limit value and the lower limit value of the sheet having the second thickness that is thinner than the first thickness are smaller than those of the sheet having the first thickness. apparatus. The sheet is
Single-sided mode that forms an unfixed image only on one side, and an unfixed image is formed on one side, and after the formed unfixed image is heat-fixed, another unfixed image is formed on the other side. A sheet sent from an image forming apparatus that can be executed by switching between the duplex mode and
The detection means includes
The sheet to be fixed is (a) a sheet on which an unfixed image is formed in the single-side mode and a sheet on which an unfixed image is formed on the other side in the double-side mode, or (b) The size of the range between the case of a sheet on which the unfixed image is formed on the one surface in the duplex mode and the case of the sheet on which the unfixed image is formed on the other surface in the duplex mode. The fixing device according to claim 2, wherein the fixing device is changed. A first heater for heating the first rotating body;
A second heater for heating the second rotating body;
The temperature control means includes
The temperature of the first surface of the sheet detected by the first temperature sensor is compared with a preset first target temperature, and power supply to the second heater is controlled based on the comparison result. With
The temperature of the second surface of the sheet detected by the second temperature sensor is compared with a preset second target temperature, and power supply to the first heater is controlled based on the comparison result. The fixing device according to claim 1, wherein An image forming apparatus for forming an unfixed image on a sheet and thermally fixing the formed unfixed image by a fixing unit,
An image forming apparatus comprising the fixing device according to claim 1 as the fixing unit.

Images