JP2011002511A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing abnormal temperature rise of a fixing roller when a print gap becomes wide during printing operation.SOLUTION: In the image forming apparatus, when the print gap calculated in a step S4 (Fig.5) exceeds a reference threshold, a CPU 43 of an engine part 41 sets a temperature control period T70 in which a fixing heater 12e is controlled so that temperature of a heating roller 12a may be target temperature ST2 lower than target temperature ST1 by a heater controller 54. Thus, the life of the heating roller 12a is prevented from being shortened by preventing a situation that the temperature of the heating roller 12a exceeds upper limit temperature Tmax to cause overshoot in a long non-contact period P23 caused by the wide print gap exceeding the reference threshold.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus that can prevent an abnormal temperature rise of a fixing roller.

  Since the last sheet of a plurality of sheets to be printed in one print job of the image forming apparatus passes through the fixing roller, the sheet acting as a heat absorber to the fixing roller is not in contact with the fixing roller. Abnormal temperature rise may occur.

  Therefore, in the image forming apparatus disclosed in Patent Document 1, the last one sheet or the last several sheets among a plurality of sheets to be printed in one print job is fixed at the time of fixing when the fixing roller passes through the fixing roller. By turning off the heater, the amount of overshooting of the temperature of the fixing roller after the last sheet has passed the fixing roller is reduced to prevent abnormal temperature rise of the fixing roller.

  By the way, there is a case where the paper interval is widened in the middle of one print job due to the influence of paper feed retry or image data processing time. Also in this case, since the time during which the sheet serving as the heat absorber does not contact the fixing roller becomes longer, there is a possibility that the amount of heat that the sheet absorbs heat from the fixing roller decreases and the fixing roller abnormally rises in temperature.

  However, the image forming apparatus disclosed in Patent Document 1 cannot prevent an abnormal temperature increase of the fixing roller when the sheet interval is widened in the middle of one print job.

JP 2003-76189 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of preventing an abnormal temperature increase of a fixing roller when a sheet interval is widened during a printing operation.

In order to solve the above problems, an image forming apparatus of the present invention includes a fixing roller for fixing a toner image transferred onto a sheet,
A fixing heater for heating the fixing roller;
A temperature sensor for detecting the temperature of the fixing roller;
A temperature controller for controlling the output of the fixing heater so that the temperature of the fixing roller becomes a target temperature based on the temperature detected by the temperature sensor;
A paper interval calculation unit that calculates the paper interval in the paper conveyance path based on information defining the paper interval in the paper conveyance path;
When paper interval information representing the paper interval calculated by the paper interval calculation unit is input and the paper interval by the paper interval information exceeds a preset threshold value, the paper interval information is based on the paper interval information. The fixing heater by the temperature control unit so that the temperature of the fixing roller does not exceed a preset upper limit temperature during a non-contact period in which the sheet is not in contact with the fixing roller due to a sheet interval larger than a threshold value. And a heater control content changing unit for changing the control content to reduce the output of the fixing heater.

  According to this invention, the heater control content changing unit is configured to control the temperature control unit based on the sheet interval information when the sheet interval calculated by the sheet interval calculation unit exceeds a preset threshold value. The temperature of the fixing roller is reduced during a non-contact period in which the sheet is not in contact with the fixing roller due to a sheet interval larger than the threshold value by changing the control content of the fixing heater by Does not exceed a preset upper temperature limit. Therefore, according to the present invention, it is possible to prevent the fixing roller from exceeding the upper limit temperature and raising the temperature abnormally when the sheet interval becomes wide during the printing operation.

In the image forming apparatus according to the embodiment, the heater control content changing unit is
The control content of the fixing heater by the temperature control unit is changed by lowering the target temperature by the temperature control unit.

  According to this embodiment, the heater control content changing unit lowers the target temperature by the temperature control unit so that the fixing roller is heated abnormally when the sheet interval becomes wide during the printing operation. Can be prevented.

In the image forming apparatus according to the embodiment, the heater control content changing unit is
By forcibly turning off the fixing heater for a certain period of time, the control content of the fixing heater by the temperature control unit is changed.

  According to this embodiment, the heater control content changing unit changes the control content of the fixing heater by the temperature control unit to forcibly turn off the fixing heater for a certain period of time. Thereby, it is possible to prevent the temperature of the fixing roller from rising abnormally when the sheet interval becomes wide during the printing operation.

  In the image forming apparatus according to the embodiment, the heater control content changing unit may be controlled by the temperature control unit when the interval between sheets calculated by the sheet interval calculation unit exceeds a preset threshold value. The control content of the fixing heater is changed, and the changed control content is executed for a preset setting period. After the setting period has elapsed, the control content of the fixing heater by the temperature controller is Return to the control content before the change.

  According to this embodiment, the heater control content changing unit changes the control content of the fixing heater by the temperature control unit for a preset time period, and the sheet interval becomes wide during the printing operation. In addition, the temperature of the fixing roller can be prevented from rising abnormally. Further, after the set period has elapsed, the control content of the fixing heater by the temperature control unit is returned to the control content before the change, and normal temperature control for the fixing roller is continued.

In the image forming apparatus according to the embodiment, the heater control content changing unit is
Material information representing the material of the paper is input, and the temperature control is performed so that the temperature of the fixing roller does not exceed a preset upper limit temperature during the non-contact period based on the material information and the paper interval information. The content of control of the fixing heater by the unit is changed.

  According to this embodiment, the heater control content changing unit changes the control content of the fixing heater by the temperature control unit based on not only the paper interval but also the material of the paper, and the non-contact period. In addition, the temperature of the fixing roller does not exceed a preset upper limit temperature. Therefore, it is possible to more reliably prevent the fixing roller from abnormally rising in temperature when the sheet interval becomes wide during the printing operation.

  According to the image forming apparatus of the present invention, the heater control content changing unit is configured to control the temperature control unit based on the sheet interval information when the sheet interval calculated by the sheet interval calculation unit exceeds a preset threshold value. The temperature of the fixing roller does not exceed a preset upper limit temperature in a non-contact period in which the sheet is not in contact with the fixing roller due to a sheet interval larger than the threshold value by changing the control content of the fixing heater by Like that. Therefore, according to the present invention, it is possible to prevent the fixing roller from exceeding the upper limit temperature and raising the temperature abnormally when the sheet interval becomes wide during the printing operation.

It is the schematic which shows the center cross section of embodiment of the image forming apparatus of this invention. It is a block diagram which shows the engine part 41 and the controller part 42 of the said embodiment. 2 is a block diagram showing a controller unit 42, an engine unit 41, and a fixing unit 51 for thermally fixing a toner image on a sheet according to the embodiment. FIG. It is a timing chart which shows the temperature control content of the heating roller by the comparative example with respect to the said embodiment. It is a timing chart which shows the temperature control content of the heating roller by the said embodiment. It is a flowchart explaining operation | movement of the said embodiment.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 is a schematic view showing a central section of a full-color image forming apparatus 1 as an embodiment of the image forming apparatus of the present invention. First, the configuration of the image forming unit provided in this embodiment will be described. The image forming unit includes a cartridge (yellow) 28a, a cartridge (magenta) 28b, a cartridge (cyan) 28c, and a cartridge (black) 28d. In the cartridges 28a, 28b, 28c, and 28d, there are charging portions 5a, 5b, 5c, and 5d for charging the photoreceptors 3a, 3b, 3c, and 3d, and image patterns for the photoreceptors 3a, 3b, 3c, and 3d, respectively. An exposure section 6 for exposing the toner and developing sections 4a, 4b, 4c, and 4d for developing the toner are incorporated.

  The image forming section is formed on the intermediate transfer belt 2 that forms an image by superimposing four color toner images formed on the photoreceptors 3a, 3b, 3c, and 3d. A secondary transfer roller 11 for transferring the toner image onto a sheet as a recording medium. Further, the image forming unit includes an intermediate transfer belt cleaner 7 that separates the transfer residual toner from the intermediate transfer belt 2 and a waste toner box 15 that stores the separated transfer residual toner.

  The image forming unit includes a toner bottle (yellow) 25a, a toner bottle (magenta) 25b, a toner bottle (cyan) 25c, and a toner bottle (black) 25d. The toner bottles 25a, 25b, 25c, and 25d operate the stirring blades 26a, 26b, 26c, and 26d so that the toner (yellow), toner (magenta), and toner (cyan) are added to the cartridges 28a, 28b, 28c, and 28d. , Supply toner (black). The stirring blades 26a, 26b, 26c, and 26d are driven by toner replenishing motors 23 and 24, respectively. The toner replenishing motor 23 is for yellow and magenta. When the toner replenishment motor 23 rotates forward and reverse, the toner (yellow) is transferred from the toner bottles 25a and 25b to the developing portions 4a and 4b of the cartridge 28a and cartridge 28b by the action of the one-way clutch. , Toner (magenta) can be replenished. The toner replenishment motor 24 is for cyan and black. When the toner replenishment motor 24 rotates in the forward and reverse directions, toner (cyan), toner is transferred from the toner bottles 25c and 25d to the developing portions 4c and 4d of the cartridge 28d by the action of the one-way clutch. Toner (black) can be replenished. The toner density in the developing units 4a to 4d of the cartridges 28a to 28d can be detected by a toner density sensor (not shown) using a magnetic sensor. Further, the detected toner density is corrected by the environment or the like, and the toner replenishment amount is calculated according to the toner consumption calculated by the corrected toner density, printing rate, and the like.

  Next, the configuration of a paper transport unit as a recording medium will be described. The transport unit includes a standard cassette paper feed roller 8 that feeds paper from the recording medium storage unit 16 and a timing roller 10 that temporarily stops the fed paper. In addition, the transport unit includes the secondary transfer roller 11 and a fixing roller unit 12 that fixes the toner image transferred onto the sheet. The fixing roller unit 12 includes a heating roller 12a and a pressure roller 12b that form a fixing roller. A fixing heater 12e for heating the heating roller 12a is attached to the heating roller 12a. The fixing roller section 12 has a fixing temperature detection thermistor 12c as a temperature sensor for detecting the temperature of the heating roller 12a.

  The conveyance unit discharges the fixed sheet or conveys it to the double-sided conveyance path 33, and double-sided conveyance rollers 14a and 14b for conveying the sheet to the timing roller 10 via the double-sided conveyance path 29. Have The double-sided conveyance rollers 14 a and 14 b are driven by a double-sided conveyance motor 22.

  In FIG. 1, 9 is a multi-manual paper feed roller, 17 is a color PC motor, 18 is a main motor for driving the paper feed rollers 8, 9, paper discharge roller 13, etc., and 19 is for driving the fixing roller section 12. It is a fixing motor. In FIG. 1, 20 is a color developing motor, and 21 is a developing motor. In FIG. 1, reference numeral 27 denotes a fixing loop sensor that determines whether or not a loop (slack) formed on the sheet by the secondary transfer roller 11 and the fixing roller 12 has reached a preset value. In FIG. 1, reference numeral 32 denotes a paper material detection sensor.

  Next, FIG. 2 shows an engine unit 41 and a controller unit 42 of the image forming apparatus of this embodiment. The engine unit 41 includes a CPU 43 that controls the image forming apparatus. The CPU 43 controls various loads 44 such as a print head including the exposure unit 6, a motor for paper conveyance, and a fixing heater 12e. The engine unit 41 includes a nonvolatile memory 45 as a storage medium connected to the CPU 43. The nonvolatile memory 45 is composed of, for example, an EEPROM. The nonvolatile memory 45 can store initial setting data and the like. Further, the nonvolatile memory 45 can store measurement data by various sensors (the fixing temperature detection thermistor 12c, the paper material detection sensor 32, etc.) via the CPU 43.

  Further, a CSIC (Customer Specific IC) is attached to the consumables (for example, the cartridges 28 a to 28 d), and the CSIC has a nonvolatile memory 46. The nonvolatile memory 46 can store information on the consumables. A controller unit 42 is connected to the engine unit 41, and the engine unit 41 exchanges necessary information for printing such as a print instruction from the user via the controller unit 42. The controller unit 42 includes a nonvolatile memory 47, and control information, adjustment information, and the like are stored in the nonvolatile memory 47.

  The controller unit 42 is connected to a PC (personal computer) or the like via a network, and can obtain information from the network. A print instruction or the like is issued from the PC or the like via the network. In addition, since the controller unit 42 is connected to a network, printer information can be acquired from the PC, and electronic mail can be exchanged via the network.

  Next, FIG. 3 shows the controller unit 42, the engine unit 41, and the fixing unit 51 for thermally fixing the toner image to the sheet. The fixing unit 51 includes a fixing motor 19 that drives the fixing roller unit 12, a fixing heater 12 e, a fixing temperature detection thermistor 12 c as a temperature sensor, and a fixing unit position sensor 50. The fixing unit position sensor 50 detects the paper and sends a detection signal to the CPU 43. The CPU 43 drives the fixing motor 19 and the fixing heater 12e to perform the sheet passing and heat fixing operations.

  When the print job determination unit 52 of the CPU 43 determines that the controller unit 42 has received a print instruction representing a print job from the user, the engine unit 41 starts a printing operation. The sheet passing control unit 53 of the CPU 43 controls image formation by the image forming unit and paper supply and conveyance by the conveying unit to print a desired image on the sheet.

  The heater controller 54 of the CPU 43 serves as a temperature controller, receives a temperature detection signal indicating the temperature of the heating roller 12a from the fixing temperature detection thermistor 12c, and based on this temperature detection signal, the temperature of the heating roller 12a. The output of the fixing heater 12e is controlled so that becomes the set target temperature. Further, the CPU 43 performs various controls in order to control the fixing operation by the fixing unit 51 by adjusting the temperature of the heating roller 12a during standby or printing.

  Next, referring to FIGS. 4A and 4B in order, the temperature control content of the heating roller (fixing roller) 12a in the comparative example with respect to the present embodiment and the temperature control content of the heating roller 12a according to the present embodiment will be compared. To do. FIG. 4A represents a temperature control timing chart according to the comparative example, and FIG. 4B represents a temperature control timing chart according to the present embodiment. 4A and 4B, the horizontal axis represents time, and the vertical axis represents the temperature of the heating roller 12a. 4A and 4B, P11 to P13 represent contact periods in which the sheet is in contact with the heating roller 12a, and P22 and P23 represent non-contact periods in which the sheet is not in contact with the heating roller 12a. 4A shows a temporal temperature transition characteristic T101 of the heating roller 12a in the comparative example, and FIG. 4B shows a temporal temperature transition characteristic T1 of the heating roller 12a in the present embodiment.

  The engine unit 41 receives a print instruction representing a print job from the controller unit 42 for each series of jobs or for each sheet, and sequentially performs printing based on the information of the print job. Usually, the interval between prints is controlled to be a fixed time according to the specifications of the apparatus. Therefore, in continuous printing on the same sheet, printing is usually performed sequentially at the same sheet interval.

  However, image development by the controller unit 42, automatic adjustment for stabilizing the image, cleaning operation in the apparatus, color / monochrome switching, toner supply, post-processing apparatus processing time, paper feed retry (retry), etc. For this reason, the paper interval is not always constant.

  For this reason, when the paper interval becomes wider than the normal paper interval due to the time required for image development by the controller unit 42 during continuous printing, as shown in FIGS. 4A and 4B, the normal non-contact period P22 is reached. A longer non-contact period P23 occurs. During the long non-contact period P23, the heating roller 12a is not deprived of heat by the paper.

  Here, in the comparative example, as shown in FIG. 4A, the target temperature ST1 of the heating roller 12a is always constant. That is, during the printing operation, the heater control unit 54 controls the fixing heater 12e to control the temperature of the heating roller 12a toward the target temperature ST1. In this case, as shown in the temperature transition characteristic T101 of FIG. 4A, the heating roller 12a is not absorbed by the paper in the normal non-contact period P22 with the normal paper interval, and the temperature of the heating roller 12a rises above the target temperature. Sometimes. However, before the temperature of the heating roller 12a exceeds the preset upper limit temperature Tmax, the next sheet reaches the heating roller 12a and takes heat from the heating roller 12a, and the temperature of the heating roller 12a decreases. Therefore, the temperature of the heating roller 12a does not exceed the upper limit temperature Tmax due to the normal non-contact period P22. However, when the non-contact period P23 that is longer than the normal non-contact period P22 occurs, it takes a long time for the next sheet to come into contact with the heating roller 12a and take heat away. An overshoot V101 that not only exceeds but also exceeds the upper limit temperature Tmax occurs. If the temperature of the heating roller 12a exceeds the upper limit temperature Tmax due to the overshoot V101, it adversely affects the components of the heating roller 12a as a fixing roller, leading to a short life of the heating roller 12a.

  On the other hand, in this embodiment, as shown in FIG. 4B, when the paper reaches the heating roller 12a in the contact period P12 (t0), the paper indicates that a non-contact period P23 longer than normal occurs. The interval information DP is obtained in advance by the controller unit 42 and the engine unit 41. Then, the heater control unit 54 switches the target temperature TS1 to the sub target temperature ST2 lower than the target temperature TS1 before reaching the long non-contact period P23. As a result, the heater control unit 54 causes the temperature of the heating roller 12a to reach the sub target temperature ST2 in a period T70 from time t71 before the non-contact period P23 to a certain time t72 in the non-contact period P23. The fixing heater 12e is controlled. Therefore, in this period T70, compared with the period before and after this period T70, the amount of heat applied from the fixing heater 12e to the heating roller 12a is reduced, and the overshoot exceeding the target temperature TS1 in the non-contact period P23 is more than the overshoot V101. The overshoot V1 is reduced. Therefore, the temperature T1 of the heating roller 12a is suppressed to be lower than the upper limit temperature Tmax.

  The heater control unit 54 may perform control to forcibly turn off the fixing heater 12e during the period T70. Further, when a print instruction representing a series of print jobs is received from the controller unit 42 by the engine unit 41, paper interval information DP indicating that a non-contact period P23 longer than normal occurs in the controller unit 42 or the engine unit 41. You can also get Further, when the engine unit 41 receives a print request for the next sheet from the controller unit 42, the sheet interval information DP indicating that a non-contact period P23 longer than normal occurs in the controller unit 42 or the engine unit 41 is obtained. You can also

  Next, the operation of this embodiment will be described with reference to the flowchart of FIG.

  First, in step S1, the CPU 43 of the engine unit 41 determines whether or not the controller unit 42 has received a print instruction, waits until the print instruction is received, and proceeds to step S2 when determining that the print instruction has been received. In step S2, a preparatory operation before starting printing, that is, warming up of the cleaning and fixing control in the apparatus, is performed during printing, and an instruction to start the printing process is issued. Details of this print processing are omitted here.

  Next, the process proceeds to step S3, where it is determined whether or not there is a sheet to be printed next. If there is no sheet to be printed next, the process proceeds to step S9. A print end instruction is issued to perform the end process. On the other hand, if there is a sheet to be printed next, the process proceeds to step S4 to calculate the sheet interval. The sheet interval is calculated based on the time required for outputting image development information and image data from the controller unit 42 as described above, and the thickness, weight, sheet size, and the like of the sheet to be printed. This step S4 forms a sheet interval calculation unit.

  Next, the process proceeds to step S5, where it is determined whether or not the calculated sheet interval exceeds a preset reference threshold value. If it is determined that the calculated sheet interval exceeds the reference threshold value, the process proceeds to step S6. If it is determined that the threshold value is not exceeded, the process returns to step S3. The reference threshold value for the sheet interval is determined by the heat capacity of the heating roller (fixing roller) 12a. The heat storage capacity of the heating roller 12a varies greatly depending on the specifications of the device (high speed machine, low speed machine).

  In step S6, a timer for setting the timing for changing the control content of the fixing heater 12e by the heater control unit 54 is set. The timer value set in this timer can be set to a value that can print a plurality of sheets printed in a series of print jobs without any problem and can reduce overshoot so that the temperature of the heating roller 12a does not exceed the upper limit temperature Tmax. To do. The value that makes it possible to reduce the overshoot is taken from the paper by the heating roller 12a contacting the paper based on the paper interval calculated in step S4 and the paper material obtained from the paper material detection sensor 32. It can be calculated from design data obtained for the amount of heat. As described above, when the target temperature ST1 of the heating roller 12a is changed to the sub target temperature ST2 at the timing t71, the sub target temperature ST2 is calculated and set in step S6. Further, a temperature control period T70 in which temperature control is performed using the sub target temperature ST2 is also calculated in step S5. The sub target temperature ST2 is also calculated based on the sheet interval and the sheet material calculated in step S4. Steps S5 and S6 form a heater control content changing unit.

  Next, the process proceeds to step S7, where it is determined whether or not the timer has been counted up. If it is determined that the timer has been counted up, the process proceeds to step S8, and if it is determined that the timer has not been counted up, the count-up is continued. In step S8, the heater controller 54 of the CPU 43 controls the fixing heater 12e so that the temperature of the heating roller 12a becomes the sub target temperature ST2 calculated in step S5. The temperature control based on the sub target temperature ST2 is executed only during the temperature control period T70 calculated in step S5. After the temperature control period T70 ends, the temperature control returns to the normal target temperature ST1.

  Thus, according to this embodiment, the CPU 43 of the engine unit 41 targets the heating roller 12a by the heater control unit 54 when the paper interval calculated in step S4 (FIG. 5) exceeds the reference threshold value. A temperature control period T70 for controlling the fixing heater 12e is set so that the target temperature ST2 is lower than the temperature ST1. As a result, the temperature of the heating roller 12a can be prevented from overshooting exceeding the upper limit temperature Tmax in the long non-contact period P23 with a wide paper interval exceeding the reference threshold value, and the short life of the heating roller 12a can be prevented. it can.

  In the description of the flowchart, the target temperature ST1 of the heating roller 12a by the heater control unit 54 is lowered to the sub target temperature ST2 in the temperature control period T70, but the fixing heater 12e is forcibly set in the temperature control period T70. It may be turned off. Further, the temperature of the heating roller 12a in the non-contact period P23 may not exceed the upper limit temperature Tmax by forcibly intermittently operating the fixing heater 12e during the temperature control period T70.

DESCRIPTION OF SYMBOLS 1 Full color image forming apparatus 2 Intermediate transfer belt 3a-3d Photoconductor 4a-4d Developing part 5a-5d Charging part 6 Exposure part 7 Intermediate transfer belt cleaner 8 Standard cassette paper feed roller 10 Timing roller 11 Secondary transfer roller 12 Fixing roller part 12a Heating roller 12b Pressure roller 12c Fixing temperature detection thermistor 12e Fixing heater 13 Paper discharge roller 14a, 14b Double-sided conveyance roller 16 Recording medium storage unit 17 Color PC motor 19 Fixing motor 20 Color development motor 21 Development motor 22 Double-sided conveyance motor 23, 24 toner supply motor 25a to 25d toner bottle 26a to 26d stirring blade 27 fixing loop sensor 28a to 28d cartridge 29 double-sided conveyance path 32 paper material detection sensor 41 engine unit 42 controller unit 43 CPU
44 Various loads 45, 46, 47 Nonvolatile memory 50 Fixing portion position sensor 51 Fixing portion 52 Print job determining portion 53 Paper passing control portion 54 Heater controlling portion ST1 Target temperature ST2 Sub target temperature Tmax Upper limit temperature P11 to P13 Contact period P22, P23 Non-contact period

Claims (5)

A fixing roller for fixing the toner image transferred on the paper;
A fixing heater for heating the fixing roller;
A temperature sensor for detecting the temperature of the fixing roller;
A temperature controller for controlling the output of the fixing heater so that the temperature of the fixing roller becomes a target temperature based on the temperature detected by the temperature sensor;
A paper interval calculation unit that calculates the paper interval in the paper conveyance path based on information defining the paper interval in the paper conveyance path;
When paper interval information representing the paper interval calculated by the paper interval calculation unit is input and the paper interval by the paper interval information exceeds a preset threshold, the paper interval information is based on the paper interval information. The fixing heater by the temperature control unit so that the temperature of the fixing roller does not exceed a preset upper limit temperature during a non-contact period in which the sheet is not in contact with the fixing roller due to a sheet interval larger than a threshold value. An image forming apparatus, comprising: a heater control content changing unit that changes the control content of the fixing heater to reduce the output of the fixing heater. The image forming apparatus according to claim 1.
The heater control content changing unit
An image forming apparatus, wherein the control content of the fixing heater by the temperature control unit is changed by lowering the target temperature by the temperature control unit. The image forming apparatus according to claim 1.
The heater control content changing unit
An image forming apparatus characterized in that the content of control of the fixing heater by the temperature control unit is changed by forcibly turning off the fixing heater for a certain period of time. The image forming apparatus according to any one of claims 1 to 3,
The heater control content changing unit
When the interval between sheets calculated by the sheet interval calculation unit exceeds a preset threshold value, the control content of the fixing heater by the temperature control unit is changed, and the changed control content is preset. An image forming apparatus, wherein the control content of the fixing heater is returned to the control content before the change by the temperature control unit after the set time period has elapsed. The image forming apparatus according to any one of claims 1 to 4, wherein:
The heater control content changing unit
Material information representing the material of the paper is input, and the temperature control is performed so that the temperature of the fixing roller does not exceed a preset upper limit temperature during the non-contact period based on the material information and the paper interval information. An image forming apparatus, wherein the control content of the fixing heater by the unit is changed.

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