JP2020067476A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that prevents the occurrence of permanent deformation in a heating rotating body.SOLUTION: A fixing device comprises: a fixing film 15 that is heated by a heater 19; a pressure roller 21 that forms a fixing nip part 22 with the fixing film 15; and a CPU 31 (control means) that energizes first and second heating elements in a state where rotation drive is performed after the end of an image forming operation, stops the rotation drive after the timing to reduce the heating and lighting ratio of the second heating element compared with that of the first heating element, and stops the energization to the first and second heating elements.SELECTED DRAWING: Figure 12

Description

  The present invention relates to an image forming apparatus such as a copying machine and a printer.

  An image forming apparatus such as an electrophotographic copying machine or a printer includes a fixing device. In a film heating type fixing device, a fixing film rotating along a film guide, a heater arranged in the fixing film to heat the fixing film, and a pressure roller having a heat resistant elastic layer formed on a core metal of aluminum or iron. It has and.

  In such a fixing device, a fixing film is pressed against a pressure roller by a spring or the like, and a recording material carrying unfixed toner is passed through a fixing nip portion formed by the pressure to heat and press. As a result, the unfixed toner is fixed on the recording material. The length in the longitudinal direction of the heating element provided in the heater is set longer than the maximum size of the recording material used. When the recording material passes through the fixing nip portion, the temperature of the non-passage area where the recording material does not pass rises.

  When a large-sized recording material passes through the fixing nip portion after the small-sized recording material passes through the fixing nip portion, the non-passage area heated up when the small-sized recording material passes through the fixing nip portion The recording material passes through. At this time, the temperature rises excessively and a high temperature offset occurs in which the toner on the recording material adheres to the outer peripheral surface of the fixing film.

  In order to prevent such a high temperature offset, the cooling operation is performed after the image forming operation is finished so that the temperature of the heater is flat in the longitudinal direction. As an example of the cooling operation, after the image forming operation is finished, the heater is turned off and the pressure roller and the fixing film are rotated to perform the post-rotation.

  In Patent Document 1, after the image formation is completed, the pressure roller and the fixing film are post-rotated, and then the temperature of the heater is controlled to heat the fixing nip portion to a temperature equal to or higher than the softening point of the toner. As a result, accumulation of toner stains on the surface of the pressure roller is prevented, and winding of the recording material on the pressure roller and contamination of the recording material are prevented.

  In Patent Document 2, energization to the heater is stopped when the pressure roller and the fixing film are rotated backward. At this time, the fixing thermistor detects how much the temperature of the heater decreases at an arbitrary time after the power supply to the heater is turned off. Then, the temperature control time or temperature control for temperature control after stopping the pressure roller and the fixing film is changed according to the temperature detected by the fixing thermistor. This prevents abnormal temperature rise of the pressure roller due to post-heating, and prevents defective cleaning of the pressure roller surface due to insufficient cooling of the toner in the fixing nip portion.

JP-A-11-344894 JP 2001-228744 A

  When a recording material whose length in the direction orthogonal to the transport direction is shorter than the length of the heating element of the heater in the longitudinal direction passes through the fixing nip portion, temperature unevenness occurs in the longitudinal direction of the fixing nip portion. Therefore, in order to cool the recording material until the temperature distribution in the longitudinal direction of the heater becomes flat after the recording material passes through the fixing nip portion, the heater is turned off and post-rotation is performed. Then, the temperatures of the fixing film and the pressure roller are lowered as a whole.

  After the post-rotation for cooling the fixing nip portion is finished as in Patent Documents 1 and 2, as shown in FIG. 20A, the heater 19 is again driven in a state where the driving of the pressure roller 21 is stopped. Energize to heat. Then, only the fixing film 15 in the fixing nip portion 22 formed by the fixing film 15 and the pressure roller 21 thermally expands, and the fixing film 15 outside the fixing nip portion 22 does not thermally expand. Therefore, unevenness in expansion occurs in the circumferential direction of the fixing film 15 due to the portion that thermally expands in the circumferential direction of the fixing film 15 and the portion that does not thermally expand.

  Further, in the case of using a heater having a different amount of heat generation in the longitudinal direction, when the pressure roller 21 is stopped and the heater 19 is energized and heated again, a temperature difference occurs in the longitudinal direction. Unevenness occurs in the longitudinal direction of the fixing film 15 due to the portion that thermally expands in the direction and the portion that does not thermally expand.

  Due to uneven expansion in the circumferential direction and the longitudinal direction of the fixing film 15, thermal stress is applied to the fixing film 15 and local distortion is generated in the fixing film 15. In this state, as shown in FIG. 20B, when the image forming operation is started and the pressure roller 21 is driven, the distorted fixing film 15 that cannot locally maintain the circular shape is deformed by the pressure roller. 21 is pulled in the rotation direction (clockwise direction in FIG. 20B). By the rotational driving of the pressure roller 21, a stress that pulls in the rotational direction of the pressure roller 21 is applied to the locally distorted fixing film 15. As a result, the fixing film 15 has a recess 15a that is permanently deformed (plastically deformed), and the fixing device 27 has a short life.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus which prevents permanent deformation of a heating rotator and shortens the service life of a fixing device.

In order to achieve the above object, the image forming apparatus according to the present invention,
Heating means, a heating rotator heated by the heating means, a pressure rotator forming a fixing nip portion between the heating rotator, and the heating means during post-rotation performed after the image forming operation is completed. Control means for rotating the heating rotator while heating to raise the temperature of the heating rotator outside the fixing nip portion.

  According to the image forming apparatus of the present invention, it is possible to prevent permanent deformation of the heating rotator and shorten the life of the fixing device.

FIG. 3 is an explanatory cross-sectional view showing the configuration of the image forming apparatus according to the present invention. FIG. 3 is a cross-sectional explanatory diagram showing a configuration of a fixing device. FIG. 4 is a plan view illustrating the positional relationship between the thermistor in the longitudinal direction of the heater and the widthwise end of the recording material. FIG. 3 is a block diagram showing a configuration of a control system of the image forming apparatus. FIG. 6 is a diagram showing a driving state of a heater and a pressure roller during an image forming operation. It is a figure which shows the generation | occurrence | production of the hollow part which carries out permanent deformation in a fixing film, and temperature. FIG. 5 is a sectional view of a fixing film in which a recess is generated. It is a temperature distribution chart at the time of making the heat generating body from which a calorific value differs differs. Changes in the temperature of the conventional fixing film due to heating after image formation 7 is a temperature transition of the fixing film of the first embodiment in heating after the image formation is finished. 9 is a flowchart showing an operation of the image forming apparatus of the conventional example. 3 is a flowchart showing the operation of the image forming apparatus of the first embodiment. It is a figure explaining the effect with respect to the dent of the fixing film of 1st Example. The temperature transition of the fixing film in the first example in the heating after the image formation is completed in the state where the temperature is increased at the edges is shown. The temperature transition of the fixing film in the second embodiment in the heating after the image formation is completed in the state where the temperature is increased at the edges is shown. 9 is a flowchart showing the operation of the image forming apparatus of the second embodiment. It is a figure explaining the effect with respect to the depression | indentation of the fixing film of 2nd Example in the state which edge temperature raised.

  An embodiment of an image forming apparatus according to the present invention will be specifically described with reference to the drawings. Note that the numerical values and configuration conditions shown in each of the following embodiments are reference numerical values and reference configurations, and do not limit the present invention.

[First Embodiment]
The configuration of the first embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS.

  FIG. 1 is a cross-sectional explanatory view showing the configuration of the image forming apparatus according to the present invention. In the image forming apparatus 28 shown in FIG. 1, the flow of image formation is as follows. First, the charging roller 2 serving as a charging unit that contacts the surface of the photosensitive drum 3 serving as the rotating image carrier in FIG. A charging bias is applied from the bias power source 1. As a result, the surface of the photosensitive drum 3 is charged to a predetermined constant potential. Light corresponding to image information is exposed to a point on the surface of the photosensitive drum 3 that is uniformly charged to form an image by the exposure device 4 serving as an exposing unit to reduce the surface potential of the photosensitive drum 3 to a predetermined potential. The toner 17 (developer) contained in the developing container of the developing device 5 serving as the developing means is uniformly carried on the surface of the developing sleeve 6 serving as the developer carrier. Utilizing the action of the electric field formed by the difference between the potential on the surface of the photosensitive drum 3 which is lowered by the exposure of the toner 17 and the potential applied to the developing sleeve 6, the pre-charged developing sleeve 6 is charged. The toner 17 on the surface is made to fly and adhere to the surface of the photosensitive drum 3.

  On the other hand, the recording material 16 such as paper fed by the feeding means (not shown) is formed along the pre-transfer guide 7 by the transfer nip portion N formed by the surface of the photosensitive drum 3 and the transfer roller 8 serving as the transfer means. Be transported to. By applying a transfer bias to the transfer roller 8 from the transfer bias power source 12 shown in FIG. 2, the toner 17 attached to the surface of the photosensitive drum 3 is transferred to the recording material 16. The toner 17 remaining on the surface of the photosensitive drum 3 after the transfer is scraped off by the cleaning blade 9 serving as a cleaning unit and collected in the collecting container 10.

  The recording material 16 on which the toner image has been transferred at the transfer nip portion N is nipped by the photosensitive drum 3 and the transfer roller 8 and conveyed along the entrance guide 11. Then, the sheet is conveyed to a fixing nip portion 22 formed by a fixing unit 20 of a fixing device 27 that serves as a fixing unit and a pressure roller 21 that serves as a pressure rotator. In the process of being nipped and conveyed by the outer peripheral surface of the fixing film 15 serving as a heating rotator provided in the fixing unit 20 and the pressure roller 21, the toner image is heated and pressed, and the toner image is melted by heat and transferred to the recording material 16. It Then, it is discharged to the outside of the machine by a discharging means (not shown).

  Next, the configuration of the fixing device will be described with reference to FIG. FIG. 2 is a cross-sectional explanatory diagram showing the configuration of the fixing device 27. The fixing device 27 shown in FIG. 2 includes the fixing unit 20 and a pressure roller 21 serving as a pressure unit. The fixing unit 20 includes a heater 19 serving as a heating unit, a fixing film 15, a film guide 13, a stay 14, and thermistors 18a and 18b including temperature detecting elements.

  The heater 19 includes a heating element 25 in which a heating paste is printed on a ceramic substrate 29 having electrical insulation as shown in FIG. 3, and a glass coating layer for protecting the heating element 25 and ensuring insulation. Configured to have. An alternating current whose power is controlled is supplied from a power source (not shown) to the heating element 25 to generate heat.

  The base film thickness of the fixing film 15 (the heating rotator) is 100 μm or less. Further, the base layer material of the fixing film 15 (heated rotating body) is made of metal. The fixing film 15 of this embodiment is made of stainless steel (SUS) having a thickness of about 70 μm, and has a cylindrical shape with an outer diameter of 32 mm. The fixing film 15 (heating rotator) is heated by the heater 19 (heating means). The fixing film 15 efficiently transfers the heat from the heater 19 to the toner 17 on the recording material 16.

  The film guide 13 is provided with a plurality of arc-shaped ribs that slide on the inner peripheral surface of the fixing film 15 along the longitudinal direction of the film guide 13. This assists the rotation of the fixing film 15 while suppressing the sliding resistance with the inner peripheral surface of the fixing film 15. The stay 14 is made of a steel plate and uniformly applies a pressing force in the longitudinal direction of the film guide 13.

  The thermistors 18 a and 18 b provided on the back side of the substrate 29 detect a temperature change of the heater 19. The target temperature of the heater 19 is determined based on the detection result detected by the thermistors 18a and 18b. A CPU (Central Processing Unit) serving as a control unit controls the heater driving unit 30 to control the electric power of the alternating current supplied to the heater 19. This keeps the temperature of the heater 19 at the target temperature (printing temperature).

The pressure roller 21 covers an outer circumference of a core metal 26 made of aluminum having an outer diameter of 12 mm and an elastic layer 32 made of conductive silicone rubber having a volume low efficiency of about 1 × 10 ⁵ Ω · cm. On the outer circumference of the elastic layer 32, a surface layer 33 covering an insulating tube of about 60 μm is provided. The outer diameter of the pressure roller 21 is 20 mm.

  The pressure roller 21 is pressed against the heater 19 with a predetermined pressure (fixing nip pressure) with the fixing film 15 sandwiched by a biasing means such as a spring (not shown). The outer peripheral surface of the fixing film 15 and the surface of the pressure roller 21 form a fixing nip portion 22 having a length of 5 mm to 8 mm in the recording material conveying direction (left and right direction in FIG. 2).

  The pressure roller 21 is rotationally driven by a motor 34 that serves as a driving unit. The fixing film 15 is rotated by the pressure roller 21 due to the contact resistance with the surface of the pressure roller 21 or the contact resistance with the recording material 16 interposed in the fixing nip portion 22. As a result, the recording material 16 conveyed to the fixing nip portion 22 is conveyed while being in close contact with the outer peripheral surface of the fixing film 15.

  The recording material 16 is conveyed to the fixing nip portion 22, and is nipped and conveyed by the outer peripheral surface of the fixing film 15 and the surface of the pressure roller 21, whereby the unfixed toner image carried on the recording material 16 is transferred to the heater 19. And the fixing nip pressure is applied to heat and pressurize the fixing process.

  FIG. 3 is an explanatory plan view showing a positional relationship between the thermistor in the longitudinal direction of the heater and an end portion in the width direction orthogonal to the recording material conveyance direction. In this embodiment, the recording material 16 is conveyed with the longitudinal direction of the fixing nip portion 22 as the center reference. As shown in FIG. 3, on the substrate 29 of the heater 19, a heating element 25 (a) having the same amount of heat generation at the end portion as compared with the widthwise central portion (C) and an end portion D as compared with the widthwise central portion (C). The heating element 25 (b) having a large amount of heat generation on the outside is provided with two 110 mm lengths on both sides in the width direction with respect to the center (C) in the width direction orthogonal to the conveyance direction of the recording material 16. A thermistor 18a is arranged at the center (C) in the width direction in order to control the temperatures of the heating elements 25 (a) and 25 (b). The thermistor 18a detects the temperature of the passage area where the recording material 16 passes through the fixing nip portion 22. On the other hand, the thermistor 18b is arranged at the longitudinal end of the heating element 25. The thermistor 18b detects the temperature of the non-passage area where the recording material 16 does not pass through the fixing nip portion 22. The thermistors 18a and 18b detect the temperature of the heater 19 to control the temperature of the fixing device 27.

  FIG. 4 is a block diagram showing the configuration of the control system of the image forming apparatus 28. The control unit 36 illustrated in FIG. 4 includes a CPU 31 that executes processing according to a control program. Further, it has a ROM (Read Only Memory) 37 in which programs and data executed by the CPU 31 are stored. Further, it has a RAM (Random Access Memory) 38 which is a memory area used as a work area or the like. The CPU 31 has a timer 39 and manages time. Further, the CPU 31 controls the heater driving unit 30 based on the detection results of the thermistors 18a and 18b, which are temperature detecting means provided on the back side of the ceramic substrate 29, to control the electric power to the heater 19. As a result, the CPU 31, which is the control means, maintains the heater 19 at the target temperature. The CPU 31 drives the motor 34 via the motor driver 35 to rotationally drive the pressure roller 21. Although not shown, when there are a plurality of heating elements of the heater 19, it is possible to individually control the electric power control of each heating element by providing a plurality of heater driving units 30.

  FIG. 5 is a diagram showing driving states of the heater and the pressure roller during the image forming operation. As shown in FIG. 5, when the image forming apparatus 28 receives the print job, the CPU 31 drives (ON) the motor 34 via the motor driver 35 shown in FIG. 4, and controls the heater driving unit 30 to control the heater 19. Is driven (ON). Then, the image forming preparation is performed until the temperature of the heater 19 reaches about 200 ° C. which is a temperature required for fixing. When the heater 19 reaches a predetermined temperature (about 200 ° C.), the feeding of the recording material 16 is started by the feeding means (not shown), and the toner image formed on the surface of the photosensitive drum 3 is transferred onto the recording material 16 by the transfer roller 8. Transcribe. The recording material 16 carrying the unfixed toner image passes through the fixing nip portion 22 and the toner image is fixed on the recording material 16. After the image forming operation is completed, the driving of the heater 19 is turned off and the motor 34 is driven at time t1 in order to flatten the temperature distribution in the longitudinal direction of the fixing nip portion 22. As a result, the post-rotation operation for cooling the fixing nip portion 22 is executed. When the temperature in the longitudinal direction of the fixing nip portion 22 becomes flat, the driving of the motor 34 is stopped at time t2 and the heater 19 is driven again. As a result, the temperature inside the fixing nip portion 22 is heated to about 180 ° C., which is the temperature at which the toner 17 adhering to the surface of the pressure roller 21 melts. Then, the temperature inside the fixing nip portion 22 is maintained at about 180 ° C. for a predetermined time. After that, the drive of the heater 19 is turned off at time t3.

  After a lapse of a predetermined time from turning off the heater 19 at time t3, the temperature of the toner 17 adhering to the outer peripheral surface of the fixing film 15 decreases to about 60 ° C., which is the temperature at which the toner 17 adheres to the outer peripheral surface of the fixing film 15. . In this state, at time t4, the motor 34 is driven to rotate the pressure roller 21 by the width of the fixing nip portion 22 in the recording material conveyance direction. As a result, the toner 17 attached to the surface of the pressure roller 21 is moved to the outer peripheral surface side of the fixing film 15 to clean the surface of the pressure roller 21. This utilizes the difference between the heat capacity of the pressure roller 21 and the heat capacity of the fixing film 15.

  FIG. 6 shows the relationship between the temperature of the fixing film in the fixing nip portion when the heater is heated when the pressure roller is stopped, the temperature difference of the fixing film outside the fixing nip portion, and the occurrence of the concave portion that permanently deforms in the fixing film. Is shown. As shown in FIG. 6, when the heater 19 is heated when the pressure roller 21 is stopped and the difference between the temperature of the fixing film 15 inside the fixing nip portion 22 and the temperature of the fixing film 15 outside the fixing nip portion 22 is 113 ° C. The motor 34 is driven to rotate the pressure roller 21 and the fixing film 15 is driven to rotate. As a result, a concave portion was formed in which the fixing film 15 was permanently deformed. On the other hand, when the difference between the temperature of the fixing film 15 inside the fixing nip 22 and the temperature of the fixing film 15 outside the fixing nip 22 is 100 ° C., the motor 34 is driven to rotate the pressure roller 21. The fixing film 15 is driven to rotate. As a result, the fixing film 15 did not have a dent portion that is permanently deformed.

  Further, although not shown, it has been confirmed that when a temperature difference is generated in the fixing film 15 in the longitudinal direction of the fixing nip portion 22, the fixing film 15 in the fixing nip portion 22 is locally distorted. From the above, it is necessary to control the temperature difference of the fixing film to be 100 ° C. or lower in order to prevent the fixing film 15 from being permanently deformed.

  FIG. 7 is a sectional view showing the occurrence of a dent in the fixing film. When temperature unevenness is generated in the circumferential direction or the longitudinal direction of the fixing film 15, stress is generated due to the uneven expansion of the fixing film 15, causing local distortion in the fixing film 15 as shown in FIG. 7A. . When the image forming operation is started in this state and the pressure roller 21 is driven, as shown in FIG. 7B, the distorted fixing film 15 which cannot locally maintain the circular shape is removed from the pressure roller 21. It is driven and pulled in the direction of rotation.

  For this reason, a stress that pulls in the rotational direction is applied to the locally distorted fixing film 15 by the rotational driving of the pressure roller 21, and as shown in FIG. 7B, a concave portion 15a in which the fixing film 15 is permanently deformed is generated. It is thought that. Further, it is known from this experiment that even if the fixing film 15 is distorted, the depression 15a that is permanently deformed does not occur unless the pressure roller 21 is rotationally driven in that state. From this result, in order to prevent the occurrence of the concave portion 15a in which the fixing film 15 is permanently deformed, the temperature unevenness in the circumferential direction and the longitudinal direction of the fixing film 15 when the heater 19 is heated when the pressure roller 21 is stopped is reduced, It suffices if the fixing film 15 is not locally distorted.

  FIG. 8 is a temperature distribution diagram in the case where heating elements having different heating values are heated. FIG. 8A shows a heating element 25 (a) which has the same amount of heat generation at the end portion as the widthwise central portion of the heater shown in FIG. It is a longitudinal temperature distribution figure at the time of making b) generate heat by 1: 1. For example, when the temperature of the central portion of the paper is controlled at 170 ° C., the heating element 25 (a), which has the same amount of heat generation at the end portion as that at the central portion of the paper, generates flat heat at 170 ° C. It can be seen that the heating element 25 (b), which has a large calorific value, generates heat at 170 ° C. at the central portion, while the temperature rises to 206 ° C. at the end portion. Therefore, when the heating element 25 (a) and the heating element 25 (b) are made to generate heat at the same lighting ratio, the end portion of the heating element rises by about 36 ° C. compared to the center.

  FIG. 8B shows a heating element 25 (a) having the same amount of heat generation at the end portion as the widthwise central portion of the heater shown in FIG. 3 and a heating element 25 (having a larger heat generation amount at the end portion than the widthwise central portion. It is a longitudinal temperature distribution figure at the time of making b) heat-generate at 1: 0.8. For example, when the temperature of the central portion of the paper is controlled at 170 ° C., the heating element 25 (a), which has the same amount of heat generation at the end portion as that at the central portion in the width direction, generates flat heat at 170 ° C. It can be seen that the heating element 25 (b), which has a large amount of heat generated at the ends, generates heat at 135 ° C. at the center, while the temperature rises to 171 ° C. at the ends. In this way, by independently controlling the lighting ratios of the heating element 25 (a) and the heating element 25 (b), the end temperature can be suppressed.

FIG. 9 shows the transition of the temperature of the fixing film of the conventional example in the heating after the image formation is completed. The temperature transition of the fixing film 15 when the heater 19 is heated again after the post-rotation is performed for cooling after the image formation is finished is shown. Graph A shows the temperature of the fixing film 15 at the end of the fixing nip portion 22 when the heater shown in FIG. 3 is used. Graph B shows the temperature of the fixing film 15 in the central portion of the fixing nip portion 22. Graph C shows the temperature of the fixing film outside the fixing nip portion 22 immediately inside (the center side in the width direction) of the end portion D when the heater shown in FIG. 3 is used. Post-rotation is performed in order to cool until the temperature distribution in the longitudinal direction becomes substantially flat. After the image formation is completed, the heater 19 is turned off to cool the fixing nip 22 until the temperature distribution in the longitudinal direction becomes flat, and the motor 34 is driven to rotate the pressure roller 21 to follow the fixing film 15. After rotation, rotation is performed. Then, the temperature of the fixing film 15 inside the fixing nip portion 22 shown by the graph B in FIG. 9 and the temperature of the fixing film 15 outside the fixing nip portion 22 shown by the graph C are substantially the same temperature of the entire fixing film 15. Will decrease uniformly.

  At time t2, the heater 19 is again energized to heat. In that case, as shown in FIG. 9, the temperature of the fixing film 15 in the fixing nip portion 22 is controlled in a state where the driving of the motor 34 is not stopped but the driving of the motor 34 is turned on and the pressure roller 21 is rotated. The temperature is controlled so as to reach a predetermined temperature.

  This reduces the temperature difference of the fixing film 15 inside and outside the fixing nip portion 22 when the heater 19 is reheated. After the temperature of the fixing film 15 reaches a predetermined temperature, the driving of the motor 34 is stopped (OFF) at time t11. As a result, the temperature of the fixing film 15 in the fixing nip portion 22 shown by the graphs A and B in FIG. 9 is maintained at a predetermined temperature. The temperature of the fixing film 15 outside the fixing nip portion 22 shown by the graph C decreases. Therefore, the temperature of the fixing film 15 can be suppressed by a temperature difference of about 75 ° C. between the inside of the fixing nip portion 22 of the graph B and the outside of the fixing nip portion 22 of the graph C in the circumferential direction, while the temperature of the fixing film 15 in the longitudinal direction is reduced to the graph A. There is a temperature difference of about 113 ° C. between the inside of the fixing nip portion 22 and the outside of the fixing nip portion 22 of Graph C.

  Therefore, only the fixing film 15 in the fixing nip portion 22 formed by the fixing film 15 and the pressure roller 21 thermally expands, and the fixing film 15 outside the fixing nip portion 22 does not thermally expand. For this reason, unevenness in expansion occurs in the longitudinal direction of the fixing film 15 between a portion of the fixing film 15 inside and outside the nip in the longitudinal direction that thermally expands, and a portion that does not expand thermally. The film 15 is locally distorted.

  When the image forming operation is started in this state and the pressure roller 21 is driven, the distorted fixing film 15 which cannot locally maintain the circular shape is pulled by the pressure roller 21 in the rotational direction. A stress that pulls in the rotational direction is applied to the locally distorted fixing film 15 by being driven by the pressure roller 21, so that the concave portion 15a in which the fixing film 15 is permanently deformed is generated.

  FIG. 10 is a temperature transition of the fixing film of the first embodiment in heating after the image formation is finished. Graph A, graph B, and graph C in FIG. 10 show the temperature transitions described above. After completion of the image forming operation, post-rotation is performed to cool the fixing nip portion 22 until the temperature distribution in the longitudinal direction becomes substantially flat. After the image formation is completed, in order to cool the fixing nip portion 22 until the temperature distribution in the longitudinal direction becomes flat, the heater 19 is turned off, the motor 34 is driven to rotate the pressure roller 21, and the fixing film 15 is driven. After rotation, rotation is performed. Then, the temperature of the fixing film 15 inside the fixing nip portion 22 shown by the graph B in FIG. 10 and the temperature of the fixing film 15 outside the fixing nip portion 22 shown by the graph C are substantially the same temperature of the entire fixing film 15. Will decrease uniformly.

  At time t2, the heater 19 is again energized to heat. In that case, as shown in FIG. 10, the temperature of the fixing film 15 in the fixing nip portion 22 is kept in a state where the driving of the motor 34 is not stopped but the driving of the motor 34 is turned on and the pressure roller 21 is rotated. The temperature is controlled so as to reach a predetermined temperature. After reaching the target temperature, the motor drive is stopped, and at the same time, the output of the heating element 25 (b), which has a larger amount of heat generation at the end portion than the widthwise center portion of the heater 19, has the same amount of heat generation at the end portion as compared to the widthwise center portion. The output of the heating element 25 (a) is reduced to 80%. Therefore, the temperature of the fixing film 15 is suppressed by, for example, a temperature difference of about 75 ° C. between the inside of the fixing nip portion 22 of the graph B and the outside of the fixing nip portion 22 of the graph C in the circumferential direction, and the fixing direction of the graph A in the longitudinal direction. The temperature difference between the inside of the nip portion 22 and the outside of the fixing nip portion 22 of graph C is suppressed to about 75 ° C.

Therefore, expansion unevenness can be prevented from occurring in the film inside and outside the nip of the fixing film 15 in the circumferential direction and the longitudinal direction, and thermal stress is applied to the fixing film 15 to prevent local distortion in the fixing film 15. .
Therefore, even if the image forming operation is started and the pressure roller 21 is driven, the fixing film 15 maintains its shape, so that the fixing film 15 does not have a recessed portion that permanently deforms, and the fixing device has a short length. It is possible to prevent it from reaching the end of its life.

  FIG. 11 is a flowchart showing the operation of the conventional image forming apparatus 28. When the print job is started in step S1, the CPU 31 turns on the heater 19 and controls the temperature at 200 ° C. in step S2. Further, the CPU 31 turns on the drive of the motor 34 to rotate the pressure roller 21 at a peripheral speed of 300 mm / sec. Then, in step S3, the image forming operation is started.

  Next, in step S4, after the image forming operation is completed, the process proceeds to step S5, and the CPU 31 turns off the drive of the heater 19 and carries out the post-rotation operation of continuing the drive of the motor 34 for 2 seconds. Next, in step S6, the CPU 31 determines whether or not 2 seconds have elapsed from the start of the post rotation. In step S6, the drive of the motor 34 is kept ON until 2 seconds have passed. Then, after 2 seconds have passed in step S6, the target temperature is set to 190 ° C. in step 7, and the end high heater that generates a large amount of heat at the end with respect to the widthwise center and the heat generated at the end compared to the widthwise center. The output of the flat heater with the same amount is turned on at the same ratio to heat. The CPU 31 confirms the detected temperature of the thermistor 18a (main thermistor) arranged at the center of the heating element 25 in the longitudinal direction of FIG. In step S8, the CPU 31 determines whether the temperature detected by the thermistor 18a is 190 ° C. or higher. In step S8, if the temperature detected by the thermistor 18a is 190 ° C. or higher, the process proceeds to step S9, and the CPU 31 turns off the drive of the motor 34.

  After that, proceeding to step S10, the CPU 31 turns on the heater 19 and controls the temperature at 190 ° C., while the CPU 31 starts the timer 39. Next, in step S11, the CPU 31 determines whether or not 4 seconds have elapsed since the timer 39 was turned on. In step S11, the CPU 31 continues to drive the heater 19 until 4 seconds have passed since the timer 39 was turned on. When 4 seconds have passed since the timer 39 was turned on in step S11, the process proceeds to step S12, and the CPU 31 turns off the drive of the heater 19. Then, the process proceeds to step S13 to end the print job.

  FIG. 12 is a flowchart showing the operation of the image forming apparatus of the first embodiment. When the print job is started in step S21, the CPU 31 turns on the heater 19 and controls the temperature at 200 ° C. in step S22. Further, the CPU 31 turns on the drive of the motor 34 to rotate the pressure roller 21 at a peripheral speed of 300 mm / sec. Then, in step S23, the image forming operation is started.

  Next, in step S24, after the image forming operation is completed, the process proceeds to step S25, and the CPU 31 turns off the drive of the heater 19 and executes the post-rotation operation of continuing the drive of the motor 34 for 2 seconds. Next, in step S26, the CPU 31 determines whether or not 2 seconds have elapsed from the start of the post rotation. In step S26, the drive of the motor 34 is kept ON until 2 seconds have passed. Then, after 2 seconds have passed in step S26, the target temperature is set to 190 ° C. in step 27, and the end high heater that generates a large amount of heat at the end with respect to the widthwise center and the heat generated at the end compared to the widthwise center. The output of the flat heater with the same amount is turned on at the same ratio to heat. The CPU 31 confirms the detected temperature of the thermistor 18a (main thermistor) arranged at the center of the heating element 25 in the longitudinal direction of FIG. In step S28, the CPU 31 determines whether the temperature detected by the thermistor 18a is 190 ° C. or higher. In step S28, when the temperature detected by the thermistor 18a is 190 ° C. or higher, in step 29, the output of the end high heater, which generates a large amount of heat at the end with respect to the widthwise central portion, is higher than that at the widthwise central portion. Temperature control is performed at 190 ° C. by setting the output of a flat heater with the same heat generation amount to 80% or less.

  Simultaneously with step S29, the CPU 31 turns off the drive of the motor 34 in step 30. In step 31, the CPU 31 starts the timer 39. Next, in step S32, the CPU 31 determines whether or not 4 seconds have elapsed since the timer 39 was turned on. In step S32, the CPU 31 continues to drive the heater 19 until 4 seconds have passed since the timer 39 was turned on. When 4 seconds have passed since the timer 39 was turned on in step S32, the process proceeds to step S33, and the CPU 31 turns off the drive of the heater 19. After that, the process proceeds to step S34 to end the print job.

  FIG. 13 is a diagram for explaining the effect of the fixing film of the first embodiment on the depression. Even after the image forming operation is completed and the post-rotation operation is performed, the motor 34 is continuously driven, the heater 19 is turned on again, and the temperature control is performed at 190 ° C. In the control of the conventional example shown in FIG. 11, the output of the end heater having a large amount of heat generation at the end with respect to the widthwise center and the output of the flat heater having the same amount of heat generation at the end as compared to the widthwise center are turned on at the same ratio. Then, even if the target temperature of the motor drive stop of 190 ° C. is reached, if the two heating elements are heated at the same ratio, the temperature of the upper end of the heater rises. Therefore, the temperature of the fixing film 15 in the central fixing nip portion 22 during the stoppage reaches 190 ° C., but the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115 ° C. However, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed by about 75 ° C. (= 190 ° C.-about 115 ° C.). However, since the temperature of the fixing film 15 inside the fixing nip portion 22 at the end during the stop time rises to 228 ° C., the temperature of the fixing film 15 outside the fixing nip portion 22 decreases to about 115 ° C. The temperature difference between the inside and outside of the portion 22 increases to about 113 ° C. (= about 228 ° C.-about 115 ° C.). Therefore, the fixing film 15 is distorted in the longitudinal direction, and in this state, when the next print job is received and the rotation driving of the pressure roller 21 is started, the fixing film 15 has a recessed portion 15a that is permanently deformed. The fixing device had a short life.

  On the other hand, in the first embodiment, when the image forming operation is completed and the motor 34 is continuously driven even after the post-rotation operation and the heater 19 is turned on again to control the temperature at 190 ° C., the end portion with respect to the center portion in the width direction is formed. Output from the high end heater that has a large amount of heat generation at the end and the flat heater that has the same amount of heat generation at the end as compared to the center in the width direction are turned on at the same ratio, and when the target temperature for stopping the motor drive reaches 190 ° C, the motor When the drive of 34 is turned off, the output of the end high heater, which has a large amount of heat generation at the end with respect to the widthwise center, is set to 80% or less of the output of the flat heater, which has the same amount of heat generation at the end as compared with the widthwise center. Temperature control at 190 ° C. Therefore, the temperature of the fixing film 15 in the central fixing nip portion 22 during the stoppage reaches 190 ° C., but the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115 ° C. However, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed to about 75 ° C. (= 190 ° C.-about 115 ° C.). Further, the temperature of the fixing film 15 in the fixing nip portion 22 at the end when stopped is also large in the amount of heat generated at the end. The output of the end high heater is the same as that at the center in the width direction. The output of the fixing film 15 is suppressed to 190 ° C. and the temperature of the fixing film 15 outside the fixing nip portion 22 is reduced to about 115 ° C., so that the temperature difference between the inside and outside of the fixing nip portion 22 does not change. , About 75 ° C. (= about 190 ° C.-about 115 ° C.). Therefore, since the fixing film 15 is not distorted, even if the next print job is received and the rotation driving of the pressure roller 21 is started, the fixing film 15 is permanently deformed in the circumferential direction and the longitudinal direction. It is possible to obtain the effect that it is possible to prevent the occurrence of shortage and prevent the fixing device from having a short life.

[Second Embodiment]
Next, in the second embodiment, the fixing film is controlled so as not to be locally distorted even when the end portion is heated.

  The configuration of the second embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. The same components as those of the first embodiment are designated by the same reference numerals or the same reference numerals are given even if the reference numerals are different, and the description thereof will be omitted.

  FIG. 14 is a temperature transition of the fixing film in the first embodiment in the heating after the image formation is completed in the state where the temperature is increased at the edges.

  Graphs A, B, and C in FIG. 14 show the temperature transitions described above. The temperature of the fixing film 15 inside the fixing nip portion 22 shown by the graph B in FIG. 14 and the temperature of the fixing film 15 outside the fixing nip portion 22 shown by the graph C are substantially the same, and the temperature of the entire fixing film 15 is equal. Like. In the graph A, since the temperature of the end portion is increased due to image formation, the temperature of the end portion exceeds about 160 ° C. even after the end of the post-rotation.

  At time t2, the heater 19 is again energized to heat. In that case, as shown in FIG. 7, the motor 34 is not driven in a stopped state, and the temperature of the fixing film 15 in the fixing nip portion 22 is controlled to reach a predetermined temperature while the motor 34 is continuously driven. . After reaching the target temperature, the motor drive is stopped, and at the same time, the output of the heating element 25 (b), which has a larger amount of heat generation at the end portion than the widthwise center portion of the heater 19, has the same amount of heat generation at the end portion as compared to the widthwise center portion. The output of the heating element 25 (a) is reduced to 80%. When the end portion is heated, the output of the heating element 25 (b), which has a larger amount of heat generation at the end portion than the widthwise central portion, is throttled at the same time when the motor drive is stopped and the drive is stopped. Does not go down. Therefore, the temperature of the fixing film 15 has a temperature difference of about 125 ° C. between the inside of the fixing nip portion 22 of graph A and the outside of the fixing nip portion 22 of graph C in the longitudinal direction, for example. Therefore, only the fixing film 15 in the fixing nip portion 22 formed by the fixing film 15 and the pressure roller 21 thermally expands, and the fixing film 15 outside the fixing nip portion 22 does not thermally expand. For this reason, unevenness in expansion occurs in the longitudinal direction of the fixing film 15 between a portion of the fixing film 15 inside and outside the nip in the longitudinal direction that thermally expands, and a portion that does not expand thermally. The film 15 is locally distorted.

  When the image forming operation is started in this state and the pressure roller 21 is driven, the distorted fixing film 15 which cannot locally maintain the circular shape is pulled by the pressure roller 21 in the rotational direction. A stress that pulls in the rotational direction is applied to the locally distorted fixing film 15 by being driven by the pressure roller 21, so that the concave portion 15a in which the fixing film 15 is permanently deformed is generated.

  FIG. 15 is a temperature transition of the fixing film in the second embodiment in the heating after the image formation is completed in the state where the temperature is increased at the edges. Graph A, graph B, and graph C in FIG. 15 show the temperature transitions described above. The temperature of the fixing film 15 inside the fixing nip portion 22 shown by the graph B in FIG. 15 and the temperature of the fixing film 15 outside the fixing nip portion 22 shown by the graph C are substantially the same, and the temperature of the entire fixing film 15 is equal. Like. In the graph A, since the temperature of the end portion is increased due to image formation, the temperature of the end portion exceeds about 160 ° C. even after the end of the post-rotation.

  At time t2, the heater 19 is again energized to heat. In that case, the temperature of the fixing film 15 in the fixing nip portion 22 is controlled to reach a predetermined temperature while the pressure roller 21 is rotated by continuously driving the motor 34. Before the target temperature is reached, the output of the heating element 25 (b), which has a larger amount of heat generation at the end portion than the widthwise central portion of the heater 19, outputs the same amount of heat as the heating element 25 (a) at the end portion compared to the widthwise central portion. ) Output to 40% of the output. After that, the motor drive is stopped when the target temperature is reached. As a result, the temperature of the fixing film 15 is suppressed by a temperature difference of about 75 ° C. between the inside of the fixing nip portion 22 of the graph B and the outside of the fixing nip portion 22 of the graph C, for example, in the circumferential direction, and the temperature in the longitudinal direction is as shown in the graph A. The temperature difference between the inside of the fixing nip portion 22 and the outside of the fixing nip portion 22 of graph C is suppressed to about 75 ° C.

  Therefore, expansion unevenness can be prevented from occurring in the film inside and outside the nip of the fixing film 15 in the circumferential direction and the longitudinal direction, and thermal stress is applied to the fixing film 15 to prevent local distortion in the fixing film 15. . Therefore, even if the image forming operation is started and the pressure roller 21 is driven, the fixing film 15 maintains its shape, so that the fixing film 15 does not have a recessed portion that permanently deforms, and the fixing device has a short length. It is possible to prevent it from reaching the end of its life.

  FIG. 16 is a flowchart showing the operation of the image forming apparatus 28 of the second embodiment. In the present embodiment, since the temperature of the fixing film 15 in the fixing nip portion 22 is substantially the same as the temperature of the heater 19, the CPU 31 detects the temperature of the heater 19 from the detection results of the thermistors 18a and 18b. The temperature of the fixing film 15 in 22 is predicted and controlled.

  When the print job is started in step S41 of FIG. 16, the CPU 31 turns on the heater 19 and controls the temperature at 200 ° C. in step S42. Further, the CPU 31 turns on the drive of the motor 34 to rotate the pressure roller 21 at a peripheral speed of 300 mm / sec. Then, in step S43, the image forming operation is started.

Next, in step S44, after the image forming operation is completed, the process proceeds to step S45, in which the CPU 31 turns off the drive of the heater 19 and carries out the post-rotation operation of continuing the drive of the motor 34 for 2 seconds. Next, in step S46, the CPU 31 determines whether or not 2 seconds have elapsed from the start of the post rotation. In step S46, the drive of the motor 34 is kept ON until 2 seconds have passed. Then, after 2 seconds have elapsed in step S46, it is determined in step S47 whether the detected temperature of the sub thermistor is 160 ° C. or lower. In step S47, the CPU 31 confirms the detected temperature of the thermistor 18b (sub-thermistor) arranged at the longitudinal end of the heating element 25 in FIG. 3, and if the detected temperature is 160 ° C. or less, the target temperature is determined in step S48. Is set to 190 ° C., and the output of the end high heater, which has a large amount of heat generation at the end with respect to the widthwise center, and the flat heater, which has the same amount of heat generation at the end as compared to the widthwise center, are lit and heated at the same ratio. . Subsequent steps S49 to S52 are the same as those in the first embodiment, and therefore description thereof will be omitted.
In step S47, the CPU 31 confirms the detected temperature of the thermistor 18b (sub-thermistor) arranged at the longitudinal end of the heating element 25 in FIG. 3, and if the detected temperature is higher than 160 ° C., the target in step S53. The temperature is set to 190 ° C and the amount of heat generated at the end is much higher than that of the center of the width direction. To do. In step S54, the CPU 31 confirms the detected temperature of the thermistor 18b (sub-thermistor) arranged at the end of the heating element 25 in FIG. 3 in the longitudinal direction, and when 190 ° C. is detected, the process proceeds to step S55, and the CPU 31 There is a lot of heat generation at the end compared to the widthwise center. The output of the end high heater is 40% or less of the output of the flat heater that has the same heat generation at the end as compared to the widthwise center, and temperature control is performed at 190 ° C. To do. The CPU 31 confirms the detected temperature of the thermistor 18a (main thermistor) arranged at the center of the heating element 25 in the longitudinal direction of FIG.
In step S56, the CPU 31 determines whether the temperature detected by the thermistor 18a is 190 ° C. or higher. In step S56, when the temperature detected by the thermistor 18a reaches 190 ° C., the process proceeds to step S57, and the CPU 31 turns off the drive of the motor 34. Next, in step S58, the CPU 31 starts the timer 39. Next, in step S59, the CPU 31 determines whether or not 4 seconds have elapsed since the timer 39 was turned on. In step S59, the CPU 31 continues to drive the heater 19 until 4 seconds have passed since the timer 39 was turned on. When 4 seconds have passed since the timer 39 was turned on in step S59, the process proceeds to step S60, and the CPU 31 turns off the drive of the heater 19. After that, the process advances to step S61 to end the print job.

  FIG. 17 is a diagram for explaining the effect of the fixing film of the second embodiment on the depressions in the edge temperature rising state.

The effect of the case where the temperature of the end portion becomes 165 ° C. after the post-rotation operation after the image forming operation is finished is shown. In the control of the first embodiment shown in FIG. 12, the output of the end high heater in which the amount of heat generated at the end is larger than that in the widthwise center and the output of the flat heater in which the amount of heat generated at the end is the same as that in the widthwise center are stopped. Since the main thermistor reaches the target temperature of 190 ° C. for stopping the driving of the motor, the temperature rises due to the effect of the temperature rise at the end. Therefore, the temperature of the fixing film 15 in the central fixing nip portion 22 during the stoppage reaches 190 ° C., but the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115 ° C. However, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed by about 75 ° C. (= 190 ° C.-about 115 ° C.). However, since the temperature of the fixing film 15 inside the fixing nip portion 22 at the end portion at the time of stop increases to 240 ° C., the temperature of the fixing film 15 outside the fixing nip portion 22 decreases to about 115 ° C. The temperature difference between the inside and outside of the portion 22 increases to about 125 ° C. (= about 240 ° C.-about 115 ° C.). Therefore, the fixing film 15 is distorted in the longitudinal direction, and in this state, when the next print job is received and the rotation driving of the pressure roller 21 is started, the fixing film 15 has a recessed portion 15a that is permanently deformed. However, the fixing device may have a short life.
On the other hand, in the second embodiment, when the image forming operation is completed and the motor 34 is continuously driven even after the post-rotation operation, and the heater 19 is turned on again to control the temperature at 190 ° C., the end portion with respect to the center portion in the width direction is formed. The amount of heat generated by the part is higher than that of the end high heater and the center of the width direction. The output of the end high heater, which generates a large amount of heat at the end, is controlled to be 40% or less of the output of the flat heater, which has the same amount of heat generated at the end, as compared to the center in the width direction. Then, when the main thermistor reaches the target temperature of 190 ° C. for stopping the motor drive, the drive of the motor 34 is turned off. Therefore, the temperature of the fixing film 15 in the central fixing nip portion 22 during the stoppage reaches 190 ° C., but the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115 ° C. However, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed to about 75 ° C. (= 190 ° C.-about 115 ° C.). Further, the temperature of the fixing film 15 in the fixing nip portion 22 at the end when stopped is also large in the amount of heat generated at the end. The output of the end high heater is the same as that at the center in the width direction. The output of the fixing film 15 is suppressed to 190 ° C. and the temperature of the fixing film 15 outside the fixing nip portion 22 is reduced to about 115 ° C., so that the temperature difference between the inside and outside of the fixing nip portion 22 does not change. , About 75 ° C. (= about 190 ° C.-about 115 ° C.). Therefore, since the fixing film 15 is not distorted, even if the next print job is received and the rotation driving of the pressure roller 21 is started, the fixing film 15 is permanently deformed in the circumferential direction and the longitudinal direction. It is possible to obtain the effect that it is possible to prevent the occurrence of shortage and prevent the fixing device from having a short life.

  Although not shown, the same effect can be obtained by controlling the timing of changing the output of the end high heater, which generates a large amount of heat at the end with respect to the center in the width direction, not by temperature but by time.

  Further, although not shown in the drawing, the temperature at which the output of the end high heater, which generates a large amount of heat at the end with respect to the widthwise center, is changed according to the fixing temperature at the end of the post-rotation, or by changing the timing of time or the output itself, Good effect can be obtained.

15 fixing film (heating rotary body), 19 heater (heating means),
21 pressure roller (pressure rotating body), 22 fixing nip portion,
31 CPU (control means; detection means)

Claims (8)

  A heating means having a heating element and a temperature detection member for detecting the temperature of the heating element, and a second heating element having a first heating element and a longitudinal portion having a larger calorific value than the first heating element; First, a control means for independently energizing and controlling the heating element and the second heating element, a heating rotator heated by the heating means, and a press forming a fixing nip portion between the heating rotator. A fixing device that includes a rotating body and controls the temperature of the heating means by energizing the heating element after the end of the image forming operation, and the first and second heat generating members in a state of being rotationally driven after the end of the image forming operation. After the timing of energizing the body and lowering the heat generation lighting ratio of the second heating element than that of the first heating element, stop the rotation drive and stop the rotation drive in the previous period, and then to the first and second heating elements in the previous period. Fixing device having control means for stopping energization of .   The fixing device according to claim 1, wherein the first and second heating elements are energized at the same ratio until the heat generation lighting ratio of the second heating element is reduced in a state of being rotationally driven after completion of the image forming operation. .   3. The fixing device according to claim 1, wherein the longitudinal portion of the second heating element, which has a larger amount of heat generation than the first heating element, is arranged at both ends of the longitudinal direction.   4. The timing for lowering the heat generation lighting ratio of the second heating element rather than that of the first heating element is varied according to the temperature of the fixing device after the image forming operation is completed. The fixing device described in 1.   5. The fixing according to claim 1, wherein a heat generation lighting ratio of the second heating element is changed from that of the first heating element according to the temperature of the fixing device after the image forming operation is completed. apparatus.   6. The fixing device according to claim 1, wherein the timing of lowering the heat generation lighting ratio of the second heating element than that of the first heating element is controlled based on temperature or time.   The fixing device according to any one of claims 1 to 6, wherein the base layer thickness of the heating rotator is 100 µm or less.   The fixing device according to claim 1, wherein the base layer material of the heating rotator is made of metal.