JP7187254B2 - image forming device - Google Patents

Description

The present invention relates to image forming apparatuses such as copiers and printers.

2. Description of the Related Art Image forming apparatuses such as electrophotographic copiers and printers are equipped with a fixing device. In a film heating type fixing device, a fixing film that rotates along a film guide, a heater that is arranged in the fixing film and heats the fixing film, and a pressure roller that has a heat-resistant elastic layer formed on a metal core of aluminum or iron. and

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

When the large-size recording material passes through the fixing nip after the small-size recording material has passed through the fixing nip, the non-passing area heated when the small-size recording material passed through the fixing nip is replaced with the large-size recording material. The recording material passes through. At this time, the temperature rises excessively, and 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, a cooling operation is performed so as to flatten the temperature of the heater in the longitudinal direction after the image forming operation is finished. As an example of the cooling operation, after the image forming operation is completed, the heater is turned off and the pressure roller and the fixing film are rotated.

In Japanese Patent Application Laid-Open No. 2002-100001, after the pressure roller and the fixing film are post-rotated after image formation, 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. This prevents accumulation of toner stains on the surface of the pressure roller, thereby preventing the recording material from winding around the pressure roller and staining of the recording material.

In Japanese Patent Application Laid-Open No. 2002-200003, the heater is stopped from being energized when the pressure roller and the fixing film are rotated afterward. At this time, the fixing thermistor detects how much the temperature of the heater drops in an arbitrary time after power supply to the heater is turned off. Then, the temperature control time or the temperature control temperature 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 poor cleaning of the surface of the pressure roller 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 perpendicular to the conveying 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, after the recording material passes through the fixing nip portion, the heater is turned off and post-rotation is performed in order to cool the recording material until the temperature distribution in the longitudinal direction of the heater becomes flat. Then, the temperatures of the fixing film and the pressure roller are lowered as a whole.

As in Patent Documents 1 and 2, after the post-rotation for cooling the fixing nip portion is completed, as shown in FIG. is energized and heated. Then, only the fixing film 15 within 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, expansion unevenness occurs in the circumferential direction of the fixing film 15 due to portions that thermally expand and portions that do not thermally expand in the circumferential direction of the fixing film 15 .

In addition, in the case of a configuration using heaters having different heat generation amounts in the longitudinal direction, when the pressure roller 21 is stopped and the heater 19 is again energized for heating, a temperature difference occurs in the longitudinal direction. Expansion unevenness occurs in the longitudinal direction of the fixing film 15 due to portions that thermally expand in the direction and portions that do not thermally expand.

Thermal stress is applied to the fixing film 15 due to uneven expansion in the circumferential direction and the longitudinal direction of the fixing film 15 , causing local distortion in the fixing film 15 . In this state, as shown in FIG. 20(b), when the image forming operation is started and the pressure roller 21 is driven, the distorted fixing film 15, which cannot locally maintain its circular shape, is pushed out of the pressure roller. 21 is pulled in the rotational direction (clockwise direction in FIG. 20(b)). When the pressure roller 21 is driven to rotate, a tensile stress is applied to the locally distorted fixing film 15 in the direction of rotation of the pressure roller 21 . As a result, the fixing film 15 is permanently deformed (plastically deformed) to form a concave portion 15a, and the life of the fixing device 27 is shortened.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which prevents a fixing device from being shortened due to permanent deformation of a heating rotator.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
a 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 rotator; and a control means for increasing the temperature of the heating rotator outside the fixing nip portion by rotating the heating rotator while heating it.

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

1 is a cross-sectional explanatory view showing the configuration of an image forming apparatus according to the present invention; FIG. FIG. 2 is a cross-sectional explanatory view showing the configuration of a fixing device; FIG. 5 is a plan explanatory view showing the positional relationship between the thermistor in the longitudinal direction of the heater and the widthwise end of the recording material; 2 is a block diagram showing the configuration of a control system of the image forming apparatus; FIG. FIG. 10 is a diagram showing heaters and a driving state of a pressure roller during an image forming operation; FIG. 10 is a diagram showing the relationship between the generation of dents permanently deformed in the fixing film and the temperature; FIG. 10 is a cross-sectional view of occurrence of dents in the fixing film; FIG. 4 is a temperature distribution diagram when heating elements with different heat generation amounts generate heat; Transition of conventional fixing film temperature during heating after image formation It is a temperature transition of the fixing film of the first embodiment in heating after image formation. 5 is a flow chart showing the operation of a conventional image forming apparatus; 4 is a flow chart showing the operation of the image forming apparatus of the first embodiment; FIG. 10 is a diagram for explaining the effect of the fixing film of the first embodiment on the depression. It is a temperature transition of the fixing film in the first example in the heating after the end of image formation in a state where the temperature of the edge portion is raised. It is a temperature transition of the fixing film in the second example in the heating after the end of the image formation in the state where the temperature of the end portion is raised. 9 is a flow chart showing the operation of the image forming apparatus of the second embodiment; FIG. 10 is a diagram for explaining the effect of the fixing film of the second embodiment on the dent in the state where the temperature of the edge portion is increased;

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

[First embodiment]
A configuration of a first embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 to 13. FIG.

FIG. 1 is a cross-sectional explanatory view showing the configuration of an 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, which is a charging means that rotates in contact with the surface of the photosensitive drum 3, which is a rotating image carrier, is charged. A charging bias is applied from the bias power supply 1 . As a result, the surface of the photosensitive drum 3 is charged to a predetermined constant potential. An exposure device 4 serving as an exposure means exposes the uniformly charged points on the surface of the photosensitive drum 3 for forming an image with light corresponding to image information, thereby lowering the surface potential of the photosensitive drum 3 to a predetermined potential. The toner 17 (developer) stored in the developing container of the developing device 5 serving as developing means is uniformly carried on the surface of the developing sleeve 6 serving as the developer carrier. Using the effect of the electric field formed by the difference between the potential on the surface of the photosensitive drum 3 that has lowered the toner 17 by exposure and the potential applied to the developing sleeve 6, the pre-charged developing sleeve 6 is removed. The toner 17 on the surface is caused to fly and adhere to the surface of the photosensitive drum 3 .

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

The recording material 16 onto which the toner image has been transferred at the transfer nip portion N is nipped between the photosensitive drum 3 and the transfer roller 8 and conveyed along the inlet guide 11 . Then, it is conveyed to a fixing nip portion 22 formed by a fixing unit 20 of a fixing device 27 serving as fixing means and a pressure roller 21 serving as a pressure rotating member. The toner image is thermally melted and thermally transferred to the recording material 16 by being heated and pressurized in the process of being pinched and conveyed by the pressure roller 21 and the outer peripheral surface of the fixing film 15 serving as a heating rotating body provided in the fixing unit 20 . be. After that, it is discharged out of the machine by discharge means (not shown).

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

The heater 19 consists of a heating element 25 printed with heating paste on an electrically insulating ceramic substrate 29 shown in FIG. configured with A power-controlled alternating current is supplied to the heating element 25 from a power source (not shown) to generate heat.

The film thickness of the base layer of the fixing film 15 (heating rotator) is 100 μm or less. The base layer material of the fixing film 15 (heating rotator) is made of metal. The fixing film 15 of the present embodiment is made of stainless steel (SUS) with 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 a heater 19 (heating means). The fixing film 15 efficiently transfers 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 . As a result, the rotation of the fixing film 15 is assisted 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 pressure to the film guide 13 in the longitudinal direction.

Thermistors 18 a and 18 b provided on the back side of the substrate 29 detect temperature changes of the heater 19 . The target temperature of the heater 19 is determined based on the detection results detected by the thermistors 18a and 18b. A CPU (Central Processing Unit) serving as control means controls the heater driving section 30 to control the 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 has an elastic layer 32 made of conductive silicon rubber having a volumetric efficiency of about 1×10 ⁵ Ω·cm on the outer periphery of a core metal 26 made of aluminum having an outer diameter of 12 mm. A surface layer 33 covering an insulating tube having a thickness of about 60 μm is provided on the outer periphery of the elastic layer 32 . The pressure roller 21 has an outer diameter of 20 mm.

The pressure roller 21 is pressed against the heater 19 at a predetermined pressure (fixing nip pressure) with the fixing film 15 interposed therebetween by an urging 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 of 5 mm to 8 mm in the recording material conveying direction (horizontal direction in FIG. 2).

The pressure roller 21 is rotationally driven by a motor 34 as driving means. The fixing film 15 rotates following the pressure roller 21 due to contact resistance with the surface of the pressure roller 21 or 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 in a state of 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 conveyed while being nipped between the outer peripheral surface of the fixing film 15 and the surface of the pressure roller 21 . It is heated and pressed by the heat and the pressure of the fixing nip to be fixed.

FIG. 3 is an explanatory plan view showing the positional relationship between the thermistor in the longitudinal direction of the heater and the end portion in the width direction perpendicular to the conveying direction of the recording material. In this embodiment, the recording material 16 is conveyed in the longitudinal direction of the fixing nip portion 22 with the center as the reference. As shown in FIG. 3, on the substrate 29 of the heater 19, a heat generating element 25 (a) having the same heat generation amount at the ends compared to the center (C) in the width direction and from the end D compared to the center (C) in the width direction. Two heat generating elements 25(b) with a large heat generation amount on the outside are provided on both sides in the width direction with a width direction center (C) perpendicular to the conveying direction of the recording material 16 as a reference, each having a length of 110 mm. A thermistor 18a is arranged at the center (C) in the width direction to control the temperature of the heating elements 25(a) and 25(b). The thermistor 18 a 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. As shown in FIG. The thermistor 18 b detects the temperature of a non-passing area where the recording material 16 does not pass through the fixing nip portion 22 . The temperature of the heater 19 is detected by these thermistors 18a and 18b, and the temperature of the fixing device 27 is controlled.

FIG. 4 is a block diagram showing the configuration of the control system of the image forming apparatus 28. As shown in FIG. The control unit 36 shown in FIG. 4 has a CPU 31 that executes processing according to a control program. Further, it has a ROM (Read Only Memory) 37 in which programs executed by the CPU 31 and data are stored. Furthermore, 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 performs time management. The CPU 31 also controls the heater driving section 30 based on the detection results of thermistors 18a and 18b, which are temperature detecting means provided on the back side of the substrate 29 made of ceramic, to control the electric power to the heater 19. FIG. Thereby, the CPU 31 serving as a control means keeps the heater 19 at the target temperature. The CPU 31 rotates the pressure roller 21 by driving the motor 34 via the motor driver 35 . Although not shown, in the case where the heater 19 has a plurality of heating elements, providing a plurality of heater driving units 30 makes it possible to individually control the power of each heating element.

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 a print job, the CPU 31 drives (turns ON) the motor 34 via the motor driver 35 shown in FIG. is driven (ON). Then, image forming preparations are performed until the heater 19 reaches a temperature of about 200° C., which is necessary for fixing. When the heater 19 reaches a predetermined temperature (approximately 200° C.), feeding means (not shown) starts feeding the recording material 16 , 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 . to transcribe. The recording material 16 bearing 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 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, a post-rotation operation for cooling the fixing nip portion 22 is performed. 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 in the fixing nip portion 22 is increased to approximately 180° C., which is the temperature at which the toner 17 adhering to the surface of the pressure roller 21 melts. Then, the temperature in the fixing nip portion 22 is maintained at about 180° C. for a predetermined time. After that, the driving of the heater 19 is turned off at time t3.

After a predetermined time has passed since the heater 19 was turned off at time t3, the temperature drops to about 60° C., which is the temperature at which the toner 17 adhering to the outer peripheral surface of the fixing film 15 adheres to the outer peripheral surface of the fixing film 15. . In this state, the motor 34 is driven at time t4 to rotate the pressure roller 21 by the width of the fixing nip portion 22 in the recording agent conveying direction. As a result, the toner 17 adhering 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 in the fixing film outside the fixing nip portion, and the generation of dents that cause permanent deformation in the fixing film. is shown. As shown in FIG. 6, when the heater 19 is heated when the pressure roller 21 is stopped, 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.degree. Then, the motor 34 is driven to rotate the pressure roller 21 and the fixing film 15 is driven to rotate. As a result, the fixing film 15 was permanently deformed to form a recessed portion. On the other hand, when 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 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 recessed portion that caused permanent deformation.

Further, although not shown, it has been confirmed that local distortion occurs in the fixing film 15 in the fixing nip portion 22 when a temperature difference is generated in the fixing film 15 in the longitudinal direction of the fixing nip portion 22 . In view of the above, in order to prevent permanent deformation of the fixing film 15 from occurring, it is necessary to control the temperature difference of the fixing film to 100° C. or less.

FIG. 7 is a cross-sectional view of occurrence of dents in the fixing film. When temperature unevenness is caused in the circumferential direction and the longitudinal direction of the fixing film 15, stress is generated due to the uneven expansion of the fixing film 15, and as shown in FIG. 7A, the fixing film 15 is locally distorted. . When the image forming operation is started in this state and the pressure roller 21 is driven, as shown in FIG. It is pulled in the direction of rotation by being driven by

As a result, the locally distorted fixing film 15 is subjected to tensile stress in the direction of rotation due to the rotational driving of the pressure roller 21, and as shown in FIG. It is thought that Further, from this experiment, it has been found that even if the fixing film 15 is distorted, the depression 15a that permanently deforms does not occur unless the pressure roller 21 is rotationally driven in that state. As a result, in order to prevent the fixing film 15 from forming the dented portion 15a which permanently deforms, when the heater 19 is heated while the pressure roller 21 is stopped, the temperature unevenness in the circumferential direction and the longitudinal direction of the fixing film 15 is reduced. It is sufficient if the fixing film 15 is not locally distorted.

FIG. 8 is a temperature distribution diagram when heating elements having different calorific values generate heat. FIG. 8(a) shows a heating element 25(a) whose end portions have the same amount of heat generation as compared to the center portion in the width direction of the heater shown in FIG. It is a longitudinal temperature distribution diagram when b) is heated at a ratio of 1:1. For example, when the temperature of the center of the paper is controlled at 170° C., the heating element 25 (a), which has the same amount of heat generation at the edges of the paper as compared to the center of the paper, generates heat at 170° C. flatly. It can be seen that the heating element 25(b) having a large heat generation amount generates heat at the central portion at 170°C, while the temperature at the end portion rises to 206°C. For this reason, if the heating elements 25(a) and 25(b) are heated at the same lighting ratio, the end portions of the heating elements rise by about 36° C. compared to the center.

FIG. 8(b) shows a heating element 25(a) whose ends have the same amount of heat generation as compared to the central portion in the width direction of the heater shown in FIG. It is a longitudinal temperature distribution diagram when b) is heated at a ratio of 1:0.8. For example, when the center of the paper is temperature-controlled at 170°C, the heating element 25(a), which has the same amount of heat generation at the ends as compared to the center in the width direction, generates heat at 170°C flatly. It can be seen that the heating element 25(b), which generates a large amount of heat at the ends, generates heat at 135°C in the central portion, while the temperature rises to 171°C at the ends. By independently controlling the lighting ratios of the heating element 25(a) and the heating element 25(b) in this manner, the end temperature can be suppressed.

FIG. 9 shows transition of fixing film temperature in a conventional example in heating after completion of image formation. It shows the temperature change of the fixing film 15 when the heater 19 is heated again after the post-rotation is performed for cooling after the completion of the image formation. Graph A shows the temperature of the fixing film 15 at the edge in the fixing nip portion 22 when the heater shown in FIG. 3 is used. Graph B shows the temperature of the fixing film 15 at the central portion within the fixing nip portion 22 . Graph C shows the temperature of the fixing film outside the fixing nip portion 22 immediately inside (the center in the width direction) of the end D portion when the heater shown in FIG. 3 is used. A post-rotation is performed for cooling until the temperature distribution in the longitudinal direction becomes substantially flat. After image formation, the heater 19 is turned off in order to cool the fixing nip portion 22 so that the temperature distribution in the longitudinal direction becomes flat. Rotation is performed after rotation. Then, the temperature of the fixing film 15 inside the fixing nip portion 22 indicated by graph B in FIG. decreases uniformly.

At time t2, the heater 19 is energized again for heating. In this case, as shown in FIG. 9, the temperature of the fixing film 15 in the fixing nip portion 22 is changed while the pressure roller 21 is rotated by turning on the motor 34 without driving the motor 34 . It is controlled to reach a predetermined temperature.

This reduces the temperature difference of the fixing film 15 between the inside and outside of 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 (turned off) at time t11. As a result, the temperature of the fixing film 15 in the fixing nip portion 22 shown by 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 graph C decreases. For this reason, the temperature of the fixing film 15 in the circumferential direction, for example, is suppressed by a temperature difference of about 75° C. between the inside of the fixing nip portion 22 in graph B and the outside of the fixing nip portion 22 in graph C. A temperature difference of about 113.degree.

Therefore, only the fixing film 15 within 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, thermal stress is applied to the fixing film 15 due to uneven expansion in the longitudinal direction of the fixing film 15 between the thermally expanding portion and the non-thermally expanding portion of the film inside and outside the nip in the longitudinal direction of the fixing film 15 . 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 that cannot locally maintain its circular shape is pulled in the rotational direction following the pressure roller 21 . The locally distorted fixing film 15 is driven by the pressure roller 21 and subjected to tensile stress in the direction of rotation to generate a recessed portion 15a in which the fixing film 15 is permanently deformed.

FIG. 10 shows the temperature transition of the fixing film of the first embodiment during heating after the completion of image formation. Graph A, graph B, and graph C in FIG. 10 show the temperature transition described above. After the image forming operation is finished, post-rotation is performed to cool the fixing nip portion 22 until the temperature distribution in the longitudinal direction becomes substantially flat. After image formation, the heater 19 is turned off in order to cool the fixing nip portion 22 so that the temperature distribution in the longitudinal direction becomes flat. Rotation is performed after rotation. Then, the temperature of the fixing film 15 inside the fixing nip portion 22 indicated by graph B in FIG. decreases uniformly.

At time t2, the heater 19 is energized again for heating. In this case, as shown in FIG. 10, the temperature of the fixing film 15 in the fixing nip portion 22 is changed while the pressure roller 21 is being rotated with the motor 34 not being driven in a stopped state, and the motor 34 being turned ON. It is controlled 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 ends than at the center in the width direction of the heater 19, is adjusted so that the amount of heat generation at the ends is the same as that at the center in the width direction. The output is reduced to 80% of the output of the heating element 25(a). For this reason, the temperature of the fixing film 15 is suppressed, for example, by a temperature difference of about 75° C. between the inside of the fixing nip portion 22 of graph B and the outside of the fixing nip portion 22 of graph C in the circumferential direction, and the fixing temperature of 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 in graph C is suppressed to about 75°C.

Therefore, it is possible to prevent uneven expansion of the film inside and outside the nip in the circumferential direction and the longitudinal direction of the fixing film 15, and it is possible to prevent the fixing film 15 from being locally distorted due to thermal stress being applied to 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. It is possible to prevent the end of life.

FIG. 11 is a flow chart showing the operation of the image forming apparatus 28 of the conventional example. In step S1, when a print job is started, in step S2, the CPU 31 turns on the heater 19 to control the temperature at 200.degree. Furthermore, 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, where the CPU 31 turns off the heater 19 and continues to drive the motor 34 for two seconds to perform a post-rotation operation. Next, in step S6, the CPU 31 determines whether or not two seconds have passed since the post-rotation was started. In the step S6, the driving of the motor 34 is kept ON until 2 seconds have passed. Then, after two seconds have passed in step S6, the target temperature is set to 190° C. in step 7, and the end high heater that generates more heat at the end than the center in the width direction and the heat generation at the end compared to the center in the width direction are used. The output of flat heaters with the same amount is turned on at the same ratio to heat. The CPU 31 checks the detected temperature of the thermistor 18a (main thermistor) arranged in the center of the heating element 25 in FIG. 3 in the longitudinal direction. In step S8, the CPU 31 determines whether or not the temperature detected by the thermistor 18a is 190° C. or higher. In step S8, when the temperature detected by the thermistor 18a is 190° C. or higher, the CPU 31 proceeds to step S9 and turns off the driving of the motor .

After that, the CPU 31 advances to step S10, turns on the heater 19, and starts the timer 39 while controlling the temperature at 190°C. Next, in step S11, the CPU 31 determines whether four seconds have passed since the timer 39 was turned on. In step S11, the CPU 31 continues to drive the heater 19 until four seconds have passed since the timer 39 was turned on. In step S11, when four seconds have elapsed since the timer 39 was turned on, the process proceeds to step S12, where the CPU 31 turns off the driving of the heater 19. FIG. After that, the process proceeds to step S13 to end the print job.

FIG. 12 is a flow chart showing the operation of the image forming apparatus of the first embodiment. In step S21, when a print job is started, in step S22, the CPU 31 turns on the heater 19 to control the temperature at 200.degree. Furthermore, 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 finished, the process proceeds to step S25, where the CPU 31 turns off the heater 19 and continues to drive the motor 34 for two seconds to perform a post-rotation operation. Next, in step S26, the CPU 31 determines whether or not two seconds have passed since the post-rotation was started. At the step S26, the driving of the motor 34 is kept ON until 2 seconds have passed. After two seconds have elapsed in step S26, the target temperature is set to 190° C. in step S27, and the end high heater, which generates more heat at the ends than the center in the width direction, and the heat generation at the ends compared to the center in the width direction. The output of flat heaters with the same amount is turned on at the same ratio to heat. The CPU 31 checks the detected temperature of the thermistor 18a (main thermistor) arranged in the center of the heating element 25 in FIG. 3 in the longitudinal direction. In step S28, the CPU 31 determines whether the temperature detected by the thermistor 18a is 190° C. or higher. In step S28, if the temperature detected by the thermistor 18a is 190° C. or higher, in step S29, the output of the edge high heater that generates more heat at the edges than at the center in the width direction is increased. The heating value of the part is set to 80% or less of the output of the same flat heater, and the temperature is controlled at 190°C.

Simultaneously with step S29, the CPU 31 turns off the driving of the motor 34 in step S30. At step 31 , the CPU 31 starts the timer 39 . Next, in step S32, the CPU 31 determines whether four seconds have passed since the timer 39 was turned on. In step S32, the CPU 31 continues to drive the heater 19 until four seconds have passed since the timer 39 was turned on. In step S32, when four seconds have elapsed since the timer 39 was turned on, the process proceeds to step S33, where the CPU 31 turns off the driving of the heater 19. FIG. After that, the process proceeds to step S34 to end the print job.

13A and 13B are diagrams for explaining the effect of the fixing film of the first embodiment on the depression. FIG. After the image forming operation is completed, the motor 34 continues to be driven even after the post-rotation operation, and the heater 19 is turned on again to control the temperature at 190°C. In the control of the conventional example shown in FIG. 11, the outputs of the edge high heaters, which generate more heat at the ends than at the center in the width direction, and the flat heaters, which generate the same amount of heat at the ends than at the center in the width direction, are lit at the same ratio. Even if the target temperature for stopping the motor is 190° C., if the two heating elements are heated at the same rate, the temperature at the upper end of the heater structure rises. Therefore, while the temperature of the fixing film 15 inside the central fixing nip portion 22 reaches 190.degree. Even so, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed to approximately 75° C. (=190° C.−approximately 115° C.). However, since the temperature of the fixing film 15 in the fixing nip portion 22 at the end during the stop rises to 228° C., the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115° C. The temperature difference between the inside and outside of the portion 22 increases to approximately 113° C. (=approximately 228° C.-approximately 115° C.). As a result, the fixing film 15 is distorted in the longitudinal direction, and in this state, when the next print job is received and the pressure roller 21 is started to rotate, the fixing film 15 is permanently deformed to form a recessed portion 15a. , the life of the fixing device is short.

On the other hand, in the first embodiment, when the image forming operation is finished, the motor 34 continues to be driven even after the post-rotation operation, and the heater 19 is turned on again to control the temperature at 190° C. The output of the end high heater, which generates a large amount of heat at the edge, and the flat heater, which generates the same amount of heat at the edge compared to the center in the width direction, are turned on at the same ratio, and when the target temperature for stopping the motor of 190 ° C is reached, the motor 34 is turned off, and at the same time, the output of the high end heater, which generates more heat at the ends than the center in the width direction, is set to 80% or less of the output of the flat heater, which generates the same amount of heat at the ends as compared to the center in the width direction. The temperature is controlled at 190°C. Therefore, while the temperature of the fixing film 15 inside the central fixing nip portion 22 reaches 190.degree. Even so, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed to approximately 75° C. (=190° C.−approximately 115° C.). In addition, the temperature of the fixing film 15 in the fixing nip portion 22 at the end portion during the stop is also compared to the output of the edge high heater with a large amount of heat generation at the end portion and the output of the flat heater with the same amount of heat generation at the end portion in the width direction center. By suppressing the output with respect to the output of , and suppressing the temperature of the end portion to 190° C., even if the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115° C., the temperature difference between inside and outside the fixing nip portion 22 is , 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 of the pressure roller 21 is started, the fixing film 15 is permanently deformed in the circumferential direction and the longitudinal direction. Therefore, it is possible to 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 in the state where 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. 14 to 18. FIG. It should be noted that components configured in the same manner as in the first embodiment are denoted by the same reference numerals, or even if the reference numerals are different, the same member names are given, and the description thereof is omitted.

FIG. 14 shows the change in the temperature of the fixing film in the first embodiment in the heating after the end of the image formation with the end temperature raised.

Graph A, graph B, and graph C in FIG. 14 show the temperature transition described above. The temperature of the fixing film 15 inside the fixing nip portion 22 shown by graph B in FIG. decreases accordingly. Graph A indicates that the temperature of the end portions exceeds about 160° C. even after the end of the post-rotation due to the temperature rise of the end portions due to the image formation.

At time t2, the heater 19 is energized again for heating. In this case, as shown in FIG. 7, the motor 34 is not driven in a stopped state, but is controlled so that the temperature of the fixing film 15 in the fixing nip portion 22 reaches a predetermined temperature while the motor 34 continues to be 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 ends than at the center in the width direction of the heater 19, is adjusted so that the amount of heat generation at the ends is the same as that at the center in the width direction. The output is reduced to 80% of the output of the heating element 25(a). When the end portions are heated, the amount of heat generated at the end portions is greater than that at the center portion in the width direction. does not go down. Therefore, the temperature of the fixing film 15 has a temperature difference of about 125.degree. Therefore, only the fixing film 15 within 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, thermal stress is applied to the fixing film 15 due to uneven expansion in the longitudinal direction of the fixing film 15 between the thermally expanding portion and the non-thermally expanding portion of the film inside and outside the nip in the longitudinal direction of the fixing film 15 . 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 that cannot locally maintain its circular shape is pulled in the rotational direction following the pressure roller 21 . The locally distorted fixing film 15 is driven by the pressure roller 21 and subjected to tensile stress in the direction of rotation to generate a recessed portion 15a in which the fixing film 15 is permanently deformed.

FIG. 15 shows the temperature change of the fixing film in the second example in the heating after the end of the image formation in the state where the edge temperature is raised. Graph A, graph B, and graph C in FIG. 15 show the temperature transition described above. The temperature of the fixing film 15 inside the fixing nip portion 22 indicated by graph B in FIG. decreases accordingly. Graph A indicates that the temperature of the end portions exceeds about 160° C. even after the end of the post-rotation due to the temperature rise of the end portions due to the image formation.

At time t2, the heater 19 is energized again for heating. In this 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 continuing to drive the motor 34 . Before the target temperature is reached, the output of the heating element 25(b) whose end portion has a larger amount of heat generation than that of the center portion in the width direction of the heater 19 is changed to ) 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, for example, by a temperature difference of about 75° C. between the inside of the fixing nip portion 22 in the graph B and the outside of the fixing nip portion 22 in the graph C in the circumferential direction. The temperature difference between the inside of the fixing nip portion 22 and the outside of the fixing nip portion 22 in graph C is suppressed to about 75°C.

Therefore, it is possible to prevent uneven expansion of the film inside and outside the nip in the circumferential direction and the longitudinal direction of the fixing film 15, and it is possible to prevent the fixing film 15 from being locally distorted due to thermal stress being applied to 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. It is possible to prevent the end of life.

FIG. 16 is a flow chart showing the operation of the image forming apparatus 28 of the second embodiment. In this 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 fixing nip portion from the detection results of the thermistors 18a and 18b that detect the temperature of the heater 19. The temperature of the fixing film 15 in 22 is predicted and controlled.

In step S41 of FIG. 16, when the print job is started, in step S42, the CPU 31 turns on the heater 19 to control the temperature at 200.degree. Furthermore, 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, where the CPU 31 turns off the heater 19 and continues to drive the motor 34 for two seconds to perform a post-rotation operation. Next, in step S46, the CPU 31 determines whether two seconds have passed since the post-rotation was started. At the step S46, the driving of the motor 34 is kept ON until 2 seconds have passed. After two seconds have elapsed in step S46, it is determined in step S47 whether or not the detected temperature of the sub-thermistor is 160° C. or lower. In step S47, the CPU 31 checks the detected temperature of the thermistor 18b (sub-thermistor) arranged at the longitudinal end of the heating element 25 in FIG. is set to 190° C., and the output of the high end heater, which generates more heat at the end than the center in the width direction, and the flat heater, which generates the same amount of heat at the end as compared to the center in the width direction, is turned on at the same ratio for heating. . Since subsequent steps S49 to S52 are the same as those in the first embodiment, description thereof is omitted.
In step S47, the CPU 31 checks the detected temperature of the thermistor 18b (sub-thermistor) arranged at the longitudinal end of the heating element 25 in FIG. The temperature is set to 190 ° C., and the output of the end high heater, which has more heat generation at the end than the center in the width direction, and the flat heater, which has the same heat generation at the end as compared to the center in the width direction, is turned on at the same ratio for heating. do. In step S54, the CPU 31 checks the detected temperature of the thermistor 18b (sub-thermistor) arranged at the longitudinal end of the heating element 25 in FIG. Temperature control is performed at 190°C by reducing the output of the high end heater, which generates more heat at the ends than at the center in the width direction, to 40% or less of the output of the flat heater, which generates the same amount of heat at the ends than at the center in the width direction. do. The CPU 31 checks the detected temperature of the thermistor 18a (main thermistor) arranged in the center of the heating element 25 in FIG. 3 in the longitudinal direction.
In step S56, the CPU 31 determines whether or not the temperature detected by the thermistor 18a is 190° C. or higher. When the temperature detected by the thermistor 18a reaches 190° C. in step S56, the CPU 31 proceeds to step S57 and turns the motor 34 off. Next, in step S58, the CPU 31 starts the timer 39. FIG. Next, in step S59, the CPU 31 determines whether four seconds have passed since the timer 39 was turned on. In step S59, the CPU 31 continues to drive the heater 19 until four seconds have passed since the timer 39 was turned on. In step S59, when 4 seconds have passed since the timer 39 was turned on, the process proceeds to step S60, and the CPU 31 turns off the driving of the heater 19. FIG. After that, the process proceeds to step S61 to end the print job.

17A and 17B are diagrams for explaining the effect of the fixing film of the second embodiment on the dent in the edge temperature rising state.

The effect of the condition when the image forming operation is finished and the edge temperature reaches 165° C. after the post-rotation operation is shown. In the control of the first embodiment shown in FIG. 12, the output of the high edge heater whose heat value is larger at the edge than the center in the width direction and the flat heater whose heat value is the same at the edge as compared to the center in the width direction is stopped. Therefore, when the main thermistor reaches the target temperature of 190° C. for stopping the motor drive, the temperature rises due to the temperature rise at the ends. Therefore, while the temperature of the fixing film 15 inside the central fixing nip portion 22 reaches 190.degree. Even so, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed to approximately 75° C. (=190° C.−approximately 115° C.). However, since the temperature of the fixing film 15 inside the fixing nip portion 22 at the end during the stop rises to 240° C., the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115° C. The temperature difference between the inside and outside of the portion 22 increases to approximately 125° C. (=approximately 240° C.-approximately 115° C.). As a result, the fixing film 15 is distorted in the longitudinal direction, and in this state, when the next print job is received and the pressure roller 21 is started to rotate, the fixing film 15 is permanently deformed to form a recessed portion 15a. , the life of the fixing device may be shortened.
On the other hand, in the second embodiment, when the image forming operation is finished and the motor 34 is continued to be driven even after the post-rotation operation, and the heater 19 is turned on again to control the temperature at 190° C., the edge of the center portion in the width direction is heated. When the sub-thermistor, which turns on the output of the flat heater with the same calorific value at the ends at the same ratio as compared with the high calorific value at the end and the center in the width direction, detects 190°C, the center in the width direction The output of the high edge heater, which generates a large amount of heat at the edge, is controlled to be 40% or less of the output of the flat heater, which generates the same amount of heat at the edge, compared with the center in the width direction. When the temperature of the main thermistor reaches 190° C., the target temperature for stopping the motor, the motor 34 is turned off. Therefore, while the temperature of the fixing film 15 inside the central fixing nip portion 22 reaches 190.degree. Even so, the temperature difference between the inside and outside of the fixing nip portion 22 can be suppressed to approximately 75° C. (=190° C.−approximately 115° C.). In addition, the temperature of the fixing film 15 in the fixing nip portion 22 at the ends during the stop is also compared to the output of the edge high heater, which has a large amount of heat generation at the ends, and the output of the flat heater, which has the same amount of heat generation at the ends, as compared with the center portion in the width direction. By suppressing the output against the output of , and suppressing the temperature of the end portion to 190° C., even if the temperature of the fixing film 15 outside the fixing nip portion 22 drops to about 115° C., the temperature difference between inside and outside the fixing nip portion 22 is , 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 of the pressure roller 21 is started, the fixing film 15 is permanently deformed in the circumferential direction and the longitudinal direction. Therefore, it is possible to 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 more heat at the ends than at the center in the width direction, not by the temperature but by the time.

Further, although not shown in the figure, it is possible to change the temperature, the timing of time, or the output itself for changing the output of the edge high heater, which generates more heat at the edge than the center in the width direction, according to the fixing temperature at the end of the post-rotation. Good effect is obtained.

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

Claims (5)

a first heating element ;
a second heating element having a larger amount of heat in both end regions than the first heating element in the paper width direction ;
Control means for independently energizing and controlling the first heating element and the second heating element ;
heating means for heating by at least the first heating element and the second heating element ;
a heating rotating body heated by the heating means ;
a temperature detection member that detects the temperature of the heating rotor;
a pressure rotator forming a fixing nip portion with the heating rotator;
The pressure rotating body is rotationally driven,
After the image forming operation is completed, the first heating element and the second heating element are deenergized, and then the first heating element and the second heating element are energized to control the temperature of the heating means. The control means for
After the image forming operation is completed, the control means energizes the first heating element and the second heating element while the pressure rotating body is driven to rotate, and sets the temperature detected by the temperature detection member as a target. When the temperature reaches the temperature, the heating lighting ratio of the second heating element decreases and the pressurizing rotator stops rotating, and the pressurizing rotator stops rotating and drives the first heating element. and a fixing device, wherein the power supply to the second heating element is stopped. After the image forming operation is completed , the pressure rotating body is driven to rotate , and the first heating element and the second heating element are energized at the same ratio until the heating lighting ratio of the second heating element is lowered. 2. The fixing device according to claim 1, wherein: 3. The fixing device according to claim 1 , wherein the timing for lowering the heating lighting ratio of the second heating element is varied according to the temperature of the fixing device after the image forming operation is completed. . 4. The fixing device according to claim 1, wherein the thickness of the base layer of the heating rotator is 100 [mu] m or less. 5. The fixing device according to claim 1 , wherein the base layer material of the heating rotator is made of metal.

Images