JP6996182B2 - Image forming device, control method of image forming device, and program - Google Patents

Description

The present invention relates to an image forming apparatus, a control method for the image forming apparatus, and a program. More specifically, the present invention relates to heating control of a heater in an image forming apparatus having a fixing device.

Conventionally, in an electrophotographic image forming apparatus including a process unit for forming a toner image and a fixing device for thermally fixing the toner image transferred to the sheet to the sheet, electric power is supplied to the heater of the fixing device. Heating control is performed to bring the surface temperature of the rotating body of the fixing device closer to the set temperature by switching between the state and the non-energized state in which electric power is not supplied.

For example, Patent Document 1 discloses the heating control of the fixing device. Patent Document 1 describes an image forming apparatus that performs PID control as heating control of a fixing device, and a proportional gain is set so that the faster the transport speed, the higher the duty ratio, which is the ratio of the energized state within a predetermined cycle. The configuration to be enlarged is disclosed.

Japanese Unexamined Patent Publication No. 2016-21259

The surface temperature of the rotating body of the fixing device fluctuates by repeating paper passing and non-paper passing at the fixing nip portion. Therefore, as disclosed in Patent Document 1, even when the proportional gain is changed based on the transport speed, it is possible to suppress the so-called temperature ripple, which is the fluctuation of the surface temperature of the rotating body during continuous printing. Insufficient. When the differential control is performed as the heating control of the fixing device, the followability to the temperature change is enhanced by increasing the differential gain, and as a result, the temperature ripple can be reduced. However, if the followability to a temperature change is high, the change in the duty ratio becomes sensitive and flicker is likely to occur.

The present invention has been made to solve the problems of the above-mentioned conventional techniques. That is, the problem is to provide an image forming apparatus provided with a fixing device, which provides a technique for balancing the reduction of temperature ripple during continuous printing and the suppression of flicker.

The image forming apparatus made for the purpose of solving this problem is a second rotation forming a fixing nip portion between a heater, a first rotating body heated by the heater, and the first rotating body. A body, a temperature sensor that outputs a different signal depending on the surface temperature of the first rotating body, and a control unit are provided, and the control unit is based on the signal of the temperature sensor. The detection process for detecting the surface temperature of the first rotating body, the first value based on the difference between the set temperature of the first rotating body and the surface temperature of the first rotating body, and the first rotating body per unit time. A control value determination process for determining a control value using a second value based on the amount of change in surface temperature and the paper-to-paper time during continuous transfer of sheets, and the control value determined by the control value determination process. The power determination process for determining the amount of power to be supplied to the heater is executed using the above, and the absolute value of the second value is the first time when the change amount is a predetermined value and the paper-to-paper time is the first time. In the case of, the change amount is the predetermined value, and the paper-to-paper time is larger than that of the second time, which is shorter than the first time.

The image forming apparatus disclosed in the present specification detects the surface temperature of the first rotating body based on the signal of the temperature sensor. Further, the first value based on the difference between the set temperature of the first rotating body and the surface temperature of the first rotating body, the amount of change in the surface temperature of the first rotating body per unit time, and the continuous transfer of the sheet. The amount of power supplied to the heater is determined by using the second value based on the paper-to-paper time and the control value determined by using. Then, if the amount of change is the same predetermined value, the image forming apparatus increases the absolute value of the second value when the paper-to-paper time is long as compared with the case where the paper-to-paper time is short.

That is, the image forming apparatus disclosed in the present specification uses a second value having a larger absolute value when the paper-to-paper time is long than when the paper-to-paper time is short. The second value is a component of the control values based on the amount of change in the surface temperature of the first rotating body per unit time, that is, a component of differential control. The larger the absolute value of the second value, the more the temperature change. Followability is improved. When the paper-to-paper time is long, the temperature ripple tends to be larger than when the paper-to-paper time is short. When the paper-to-paper time is long, the image forming apparatus increases the absolute value of the second value to improve the followability to the temperature change, so that the temperature ripple can be suppressed. On the other hand, when the paper-to-paper time is short, the temperature ripple is unlikely to increase. Therefore, the image forming apparatus suppresses flicker by lowering the followability to a change in temperature when the paper-to-paper time is short and when the paper-to-paper time is long. As a result, it is possible to achieve a balance between reducing the temperature ripple during continuous printing and suppressing flicker.

A control method for realizing the functions of the above-mentioned apparatus, a computer program, and a computer-readable storage medium for storing the computer program are also new and useful.

According to the present invention, an image forming apparatus including a fixing device is realized, and a technique for achieving a balance between reduction of temperature ripple during continuous printing and suppression of flicker is realized.

It is sectional drawing which shows the schematic structure of the printer which concerns on embodiment. It is a block diagram which shows the electric structure of a printer. It is explanatory drawing which shows the example of the duty control of a heater. It is explanatory drawing which shows the example of the correspondence table which shows the relationship between a control value and a duty ratio. It is explanatory drawing which shows the example of the change of the detection temperature in the case of double-sided printing. It is explanatory drawing which shows the example of the change of the detection temperature in the case of single-sided printing. It is a flowchart which shows the procedure of a temperature control process. It is a flowchart which shows the procedure of the initial setting process. It is explanatory drawing which shows the example of the mode table which shows the relationship between the transport mode and the differential gain. It is a flowchart which shows the procedure of a duty change process. It is explanatory drawing which shows the example of the change of the detection temperature at the time of performing double-sided printing by changing a set temperature. It is explanatory drawing which shows the example of the change of the detection temperature when the control of this embodiment is performed by double-sided printing. It is explanatory drawing which shows the example of the relationship between the paper-to-paper time, the amount of temperature change, and the differential component value.

Hereinafter, embodiments in which the image forming apparatus according to the present invention is embodied will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a printer having an electrophotographic image forming function.

As shown in FIG. 1, the printer 100 of the present embodiment forms a toner image with a paper feed tray 11 for accommodating a sheet S before printing, a paper output tray 12 for accommodating a printed sheet S, and a sheet S. A process unit 5 for transferring the toner image and a fixing unit 8 for fixing the toner image to the sheet S are provided. The paper feed tray 11 is an example of a storage unit.

The process unit 5 forms a toner image by an electrophotographic method, and transfers the toner image to the sheet S. As shown in FIG. 1, the process unit 5 includes a photoconductor 51, a charging unit 52, an exposure unit 53, a developing unit 54, a transfer unit 55, and a cleaner 56. The photoconductor 51 is rotated clockwise in FIG. 1, and the charging unit 52, the exposure unit 53, the developing unit 54, the transfer unit 55, and the cleaner 56 are arranged around the photoconductor 51 in the rotation direction of the photoconductor 51. They are arranged in this order.

The charging unit 52 is, for example, a scorotron charging device, and charges the surface of the photoconductor 51 substantially uniformly. The exposure unit 53 is, for example, a laser exposure device, which irradiates the photoconductor 51 with a laser beam to partially expose the photoconductor 51 to form an electrostatic latent image based on image data on the photoconductor 51. The developing unit 54 accommodates toner and develops it by supplying toner to the electrostatic latent image on the photoconductor 51 to form a toner image on the photoconductor 51. The transfer unit 55 electrically attracts the toner image on the photoconductor 51 and transfers it to the sheet S. The cleaner 56 is, for example, a sponge roller, and removes toner and the like remaining on the photoconductor 51 even after transfer from the photoconductor 51.

As shown in FIG. 1, the fixing portion 8 includes heating members 81 and pressure rollers 82 arranged on both sides of the sheet transport path 13. Both the heating member 81 and the pressurizing roller are rotatably provided rotating bodies. Then, the heating member 81 and the pressure roller 82 are pressed against each other, and a fixing nip portion is formed between the heating member 81 and the pressure roller 82. The heating member 81 is an example of the first rotating body, and the pressure roller 82 is an example of the second rotating body. The fixing section 8 heat-fixes the toner image to the sheet S by transporting the sheet S on which the toner image is transferred by the process section 5 while heating it at the fixing nip section.

The heating member 81 is provided with a heater 810 inside, and is heated by the heater 810. As a result, the surface of the heating member 81 rises in temperature, and the heat is applied to the sheet S passing through the fixing nip portion. As the heating member 81, for example, a roller member or an endless belt member can be applied. Further, as the heater 810, for example, a halogen heater, a ceramic heater, and an IH heater (induction heating member) can be applied. The heater 810 may be arranged inside the heating member 81 to heat the heating member 81 as a whole from the inside, or may be arranged outside the heating member 81 to heat the surface of the heating member 81 as long as the surface of the heating member 81 can be heated. The surface of the member 81 may be directly heated.

The pressure roller 82 is a rubber roller having heat resistance, and is, for example, a metal shaft center coated with an elastic layer made of silicone rubber or the like and a mold release layer having mold releasability. The pressure roller 82 is pressed toward the heating member 81 by a pressing member (not shown). Further, the pressure roller 82 is rotationally driven counterclockwise in FIG. 1 when the sheet is conveyed, and the heating member 81 is driven clockwise in FIG. 1 in accordance with the rotation of the pressure roller 82. To. The heating member 81 may be on the drive side. Further, as the second rotating body, an endless belt member can also be applied.

Further, as shown in FIG. 1, the printer 100 includes a temperature sensor 811 for detecting the surface temperature of the heating member 81. The temperature sensor 811 outputs, for example, different signals depending on the surface temperature of the heating member 81 at the central position in the axial direction of the heating member 81. The detection position of the temperature sensor 811 is arranged within the range of the region through which the sheet passes regardless of the size of the sheet S. The temperature sensor 811 may be a contact type that contacts the heating member 81 or a non-contact type that does not contact the heating member 81. The printer 100 may further include another temperature sensor.

Further, as shown in FIG. 1, the printer 100 is formed with a sheet transport path 13 which is a path of the sheet S from the paper feed tray 11 to the output tray 12. The printer 100 is provided with various transport members for transporting the sheet S along the sheet transport path 13. The printer 100 includes, for example, a pickup roller 21, a resist roller 22, and a paper ejection roller 23 as transport members for transporting the sheet S. Further, the fixing unit 8 and the photoconductor 51 of the process unit 5 also have a function of transporting the sheet S. The sheet transport path 13 is an example of a transport path, and the pickup roller 21 is an example of a carry-in section.

The pickup roller 21 is rotationally driven at a predetermined timing, pulls out one sheet S from the paper feed tray 11, and carries one sheet into the sheet transport path 13. The resist roller 22 conveys the sheet S pulled out by the pickup roller 21 toward the process unit 5 in time with the toner image forming operation of the process unit 5. The paper ejection roller 23 ejects the printed sheet S to the paper ejection tray 12.

Further, as shown in FIG. 1, the sheet transport path 13 includes a print path 13a and a reverse path 13b. The print path 13a is a path from the paper feed tray 11 to the paper output tray 12 via the process unit 5 and the fixing unit 8 in this order. The inversion path 13b is a path that branches from the print path 13a on the downstream side of the fixing section 8 and joins the print path 13a on the upstream side of the process section 5. The reversal path 13b is a path for reversing the sheet S that has passed through the fixing section 8 and guiding the sheet S to the process section 5 again without passing through the process section 5 and the fixing section 8.

The printer 100 of this embodiment is a device capable of double-sided printing, and when double-sided printing is performed, the sheet S drawn out from the paper feed tray 11 is first conveyed by the printing path 13a, and then the process unit 5 and the fixing unit 8 An image is formed on one surface of the sheet S. When the sheet S on which the image is formed on one surface passes through the branch point between the print path 13a and the inversion path 13b, the printer 100 reverses the transport direction of the sheet S and advances the sheet S to the inversion path 13b. Further, the printer 100 advances the sheet S from the confluence of the print path 13a and the inversion path 13b to the print path 13a, and passes the process section 5 and the fixing section 8 again, whereby the other surface of the sheet S is reached. Form an image. The printer 100 ejects the sheet S having an image formed on both sides to the output tray 12.

Further, the printer 100 includes a sheet sensor 71 for detecting the passage of the sheet S on the sheet transport path 13. The sheet sensor 71 is arranged at a position downstream of the confluence of the printing path 13a and the reversing path 13b and upstream of the process unit 5 in the transport direction of the sheet S. The seat sensor 71 outputs different signals depending on the presence or absence of the seat S at the detection location. The printer 100 may be provided with a plurality of sheet sensors 71 on the sheet transport path 13.

Subsequently, the electrical configuration of the printer 100 will be described. As shown in FIG. 2, the printer 100 of this embodiment includes a controller 30 including a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. Further, the printer 100 includes a process unit 5, a sheet sensor 71, a fixing unit 8, a network interface (network IF) 37, and an operation panel 40, which are electrically connected to the controller 30. ..

The ROM 32 stores firmware, which is a control program for controlling the printer 100, various settings, initial values, and the like. The RAM 33 is used as a work area for reading various control programs or as a storage area for temporarily storing data such as image data. The NVRAM 34 is used as a storage area for storing various set values and the like.

The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 according to the control program read from the ROM 32 and the signals sent from various sensors. The CPU 31 is an example of a control unit. Further, the controller 30 may be a control unit. The controller 30 in FIG. 2 is a general term for hardware used for controlling the printer 100, such as the CPU 31, and does not necessarily represent a single hardware that actually exists in the printer 100.

The network IF 37 is hardware for communicating with a device connected via a network. The printer 100 receives a print job from, for example, an external device via the network IF37. The communication method by the network IF37 may be wireless or wired. Further, the printer 100 may have a means of communication with an external device such as a USB interface in addition to the network IF37.

The operation panel 40 is hardware that displays a notification to the user and accepts an instruction input by the user. The operation panel 40 includes, for example, a liquid crystal display and a group of buttons including a start key, a stop key, a numeric keypad, and the like. The printer 100 can also accept print jobs via the operation panel 40.

Subsequently, the temperature control of the fixing unit 8 in the printer 100 of the present embodiment will be described. The printer 100 of this embodiment controls the heater 810 so that the detected temperature approaches the set temperature. The detected temperature is the surface temperature of the heating member 81 acquired based on the output signal of the temperature sensor 811. The set temperature is a target value of the detected temperature. Specifically, the printer 100 controls the amount of electric power supplied to the heater 810 based on the output signal of the temperature sensor 811 and the set temperature.

The printer 100 of this embodiment performs feedback control by, for example, PD control as temperature control. That is, the printer 100 has a proportional control based on a proportional component obtained by multiplying the difference between the set temperature and the detected temperature by a proportional gain, and a derivative control based on the differential component obtained by multiplying the temperature change amount by the differential gain. , Are used together to control the temperature. The amount of change in temperature is a quantity representing a change in the detected temperature per unit time.

Specifically, the printer 100 switches the amount of electric power supplied to the heater 810 based on the control value Y obtained by the following equation (1).
Y = (Set temperature-Detected temperature) x Kp-Temperature change amount x Kd ... (1)
In the above equation (1), Kp is a proportional gain and Kd is a differential gain. In this embodiment, the proportional gain Kp is a positive fixed value and the differential gain Kd is a positive variable value. Further, "(set temperature-detection temperature) x Kp" is a proportional component value, and "temperature change amount x Kd" is a differential component value. The proportional component value is an example of the first value, and the differential component value is an example of the second value.

The printer 100 of this embodiment performs duty control for switching the duty ratio D of the electric power supplied to the heater 810 based on the acquired control value Y. For example, as shown in FIG. 3, the printer 100 generates a zero-cross signal synchronized with the zero-cross timing of the AC voltage supplied from the commercial power source, and controls the AC voltage in half-wavelength units based on the zero-cross signal. By controlling the wave number, the heater 810 is switched on and off in the energized state.

FIG. 3 shows an example of a heater-on period when the duty ratio is 60%. In this figure, an example is shown in which the heater 810 is supplied with power for a period of three and a half wavelengths in one cycle, that is, a period of 60% of one cycle, where the five half wavelength period of the AC voltage is one cycle. .. The period for energizing the heater 810 may be a period of three and a half wavelengths in one cycle, and is not limited to a continuous period as shown in FIG. 3, and any combination of half wavelengths may be used.

As shown in FIG. 3, in the printer 100 of this embodiment, the duty ratio D of the heater 810 is set to 0% by setting the 5 half wavelength period to 1 cycle and the heater on period to be any of 0 half wavelength to 5 half wavelength. , 20%, 40%, 60%, 80%, 100%. The duty ratio option is not limited to the above example, and the one cycle period is not limited to the five-half wavelength period. By changing the one-cycle period, the printer 100 can further select a duty ratio other than the above.

Then, the printer 100 increases the duty ratio D of the electric power supplied to the heater 810 as the control value Y calculated by the above-mentioned equation (1) becomes larger. For example, as shown in FIG. 4, the printer 100 stores the correspondence table 815 showing the correspondence relationship between the control value Y and the duty ratio D in the ROM 32 or the NVRAM 34. The printer 100 acquires the control value Y based on the detected temperature, and determines the duty ratio D corresponding to the acquired control value Y with reference to the correspondence table 815. Then, the printer 100 switches the duty ratio D of the electric power supplied to the heater 810 to the determined duty ratio D in the next cycle.

In the printer 100 of this embodiment, the heater 810 is provided inside the heating member 81, and it takes some time from the start of energization of the heater 810 until the detection temperature starts to rise. Further, for example, even if the energization of the heater 810 is stopped because the detected temperature becomes equal to or higher than the set temperature, the detected temperature does not always start to decrease immediately. Further, since the duty control is performed as described above, there is a delay of up to one cycle from the change of the detection temperature to the change of the power supply to the heater 810. That is, in the feedback control, a control delay occurs. This delay in control is one of the causes of temperature ripple.

When the sheet S passes through the fixing nip portion, the sheet S takes heat from the fixing nip portion, so that the surface temperature of the heating member 81 tends to drop during fixing. On the other hand, the pressure roller 82 is heated to the same level as the heating member 81, and the amount of heat taken from the heating member 81 is small during the period of the inter-paper time T in which the sheet S does not exist in the fixing nip portion. The surface temperature of the heating member 81 tends to rise.

The "paper-to-paper time" is defined as the subsequent sheet S from the time when the rear end of the preceding sheet S passes through a predetermined position in the sheet transfer path 13 in the transfer direction of the sheet S during the continuous transfer of the sheet S. It means the time until the tip of the paper passes through the same place. Note that continuous transport is in progress when the printer 100 is transporting at least two sheets S in a predetermined paper-to-paper time T. The paper-to-paper time T is, in particular, the time from when the preceding sheet S passes through the fixing nip portion to when the succeeding sheet S enters the fixing nip portion. The paper-to-paper time T is, for example, 0.1 seconds to 10 seconds.

For example, when the printer 100 of the present embodiment executes a print job for printing on a plurality of sheets S, the sheets S are continuously fed at predetermined intervals and continuously conveyed. During the continuation of continuous transport, the printer 100 continuously passes a plurality of sheets S to the fixing unit 8 at intervals of a predetermined paper-to-paper time T. Further, even when straddling different print jobs, the paper spacing between the last sheet of the preceding print job and the first sheet of the succeeding print job is equal to the paper spacing T of the preceding print job, and the sheets are continuous. Transport may continue.

In double-sided printing, after printing on one side, the printer 100 conveys the sheet S to the process unit 5 via the inversion path 13b. Therefore, it takes a predetermined time to convey the inversion path 13b between printing on one surface and printing on the other surface of the same sheet S. That is, in double-sided printing, the paper-to-paper time T is longer than in single-sided printing.

FIG. 5 shows an example of the change in the detected temperature Q when double-sided printing is continuously performed, together with the duty ratio D of the heater 810 and the paper passing timing. Note that FIG. 5 and other similar figures described later (FIGS. 6, 11, 11 and 12) show a state after several tens of seconds have elapsed from the start of continuous printing. In FIG. 5 and the like, the paper passing timing is shown by a alternate long and short dash line at the lower part of the figure. The period in which the paper passing timing is on is the period in which the sheet S has passed through the fixing portion 8. The length of the period during which the paper passing timing is off is the paper-to-paper time T. Further, in FIG. 5 and the like, the duty ratio D is shown by a solid line in the middle part of the figure.

In the case of double-sided printing, as shown in FIG. 5, the paper-to-paper time T is the paper-to-paper time Ta, which is the period during which the sheet S is conveyed by the inversion path 13b, and after printing on both sides of one sheet S, There is a paper-to-paper time Tb, which is a period until printing on one side of the next sheet S. The paper-to-paper time Ta is longer than the paper-to-paper time Tb. Then, for example, as shown in FIG. 5, when the detected temperature Q is lower than the set temperature P at the initial stage of the long inter-paper time Ta, the heating continues even after the inter-paper time Ta is entered, and the detected temperature Q is set. The temperature P may be significantly exceeded and the temperature may rise. When this happens, as shown by the broken line in FIG. 5, the detected temperature Q changes significantly and the temperature ripple becomes large.

On the other hand, even if the temperature is controlled using the same differential gain Kd as in the example of FIG. 5, in the case of single-sided printing, the temperature ripple is small as shown in FIG. The paper-to-paper time Tc in single-sided printing is about the same as the paper-to-paper time Tb in double-sided printing, and is shorter than the paper-to-paper time Ta. When the paper-to-paper time T is short, even if the surface temperature of the heating member 81 rises after the preceding sheet S has passed through the fixing nip portion, the succeeding sheet S reaches the fixing nip portion in a short time. Since heat is taken away by the subsequent sheet S, it is unlikely that the detection temperature Q will rise too much.

The printer 100 of this embodiment is controlled so that the longer the paper-to-paper time T is, the larger the absolute value of the differential component value of the control value Y when the temperature change amount is the same during continuous printing. do. Specifically, in the printer 100 of the present embodiment, when the paper-to-paper time T is long, the differential gain Kd used for calculating the control value Y is larger than when the paper-to-paper time T is short. The differential component value of the control value Y is the product of the amount of temperature change and the differential gain Kd. When the amount of temperature change is the same, the larger the differential gain Kd, the larger the absolute value of the differential component value. It becomes.

In the feedback control by PD control, the differential component value of the control value Y is a component representing the followability to the change of the detected temperature, and the larger the differential gain Kd, the higher the sensitivity to the temperature change. That is, the printer 100 of the present embodiment performs temperature control in which the paper-to-paper time T is long and the followability to the change in the detection temperature is higher than that in the case where the paper-to-paper time T is short. If the control has high followability to changes in the detected temperature, it is highly possible that the temperature ripple can be reduced.

If the differential gain Kd is increased in order to reduce the temperature ripple, the followability to the temperature change is improved and flicker is likely to occur. Since the printer 100 of this embodiment increases the differential gain Kd when the paper-to-paper time T is long and does not increase the differential gain Kd when the paper-to-paper time T is short, the differential gain is uniformly generated regardless of the paper-to-paper time. The generation of flicker can be suppressed as compared with the case where Kd is increased.

Subsequently, the procedure of the temperature control process for realizing the temperature control of the fixing portion 8 described above will be described with reference to the flowchart of FIG. 7. The temperature control process is executed by the CPU 31 when a print instruction for printing two or more sheets in succession is received.

In the temperature control process, the CPU 31 first executes an initial setting process for temperature control before starting printing (S101). The procedure of the initial setting process will be described with reference to the flowchart of FIG.

In the initial setting process, the CPU 31 acquires a transport mode for transporting the sheet S based on the print settings specified in the print instruction (S201). As shown in FIG. 9, the printer 100 of this embodiment has four types of transport modes, for example, in continuous printing, which are a standard single-sided mode, a small size single-sided mode, an intermittent single-sided mode, and a standard double-sided mode. It has a mode. The mode table 816 shown in FIG. 9 shows the correspondence between the transport mode and the differential gain Kd.

The standard single-sided mode is a transfer mode for continuously executing single-sided printing on a sheet S of plain paper having a standard size such as A4, and the inter-paper time T0 in the standard single-sided mode is that of other transfer modes. Short compared to the paper-to-paper time.

The small size single-sided mode is a transport mode in which a sheet smaller than the standard size sheet S is carried in at the same timing as the standard single-sided mode. That is, in the small size single-sided mode, the carry-in start interval in which the pickup roller 21 carries the sheet S into the sheet transport path 13 is equal to the carry-in start interval in the standard single-sided mode. The carry-in start interval is a time interval from the start of the carry-in of the Nth sheet S to the start of the carry-in of the N + 1th sheet S by the pickup roller 21. In the small size single-sided mode, the type of the sheet S housed in the paper feed tray 11 is a type having a shorter length in the transport direction than the sheet S in the standard single-sided mode.

That is, in the small size single-sided mode, the carry-in start interval of the sheet S is the same as in the standard single-sided mode, and the length of the sheet S is short, so that the paper spacing is longer than in the standard single-sided mode. That is, the paper spacing time T1 in the small size single-sided mode is longer than the paper spacing T0 in the standard single-sided mode. In this case, the small size sheet S is an example of the second type of sheet, and the standard size sheet S is an example of the first type of sheet. The paper-to-paper time T1 is an example of the first time, and the paper-to-paper time T0 is an example of the second time. The carry-in start interval in the small size single-sided mode is the same as the carry-in start interval in the standard single-sided mode, and both are examples of the first time interval.

The intermittent single-sided mode is a transport mode in which the standard-sized sheet S is fed at a longer interval than the standard single-sided mode. In the intermittent single-sided mode, the carry-in time interval in which the pickup roller 21 carries the seat S into the seat transport path 13 is longer than in the standard single-sided mode. In the intermittent single-sided mode, the sheet S has the same size as the standard single-sided mode, and the carry-in time interval is long. Therefore, the paper spacing time is longer than that in the standard single-sided mode. That is, the paper spacing time T2 in the intermittent single-sided mode is longer than the paper spacing T0 in the standard single-sided mode. In this case, the intermittent single-sided mode is an example of the first mode, and the standard single-sided mode is an example of the second mode. The paper-to-paper time T2 is an example of the first time, and the paper-to-paper time T0 is an example of the second time. The carry-in start interval in the intermittent single-sided mode is an example of the first time interval, and the carry-in start interval in the standard single-sided mode is an example of the second time interval.

In the printer 100 of this embodiment, as shown in FIG. 9, the inter-paper time T2 in the intermittent single-sided mode is longer than the inter-paper time T1 in the small-sized single-sided mode. For example, when the printer 100 determines that the temperature of the axial end portion of the fixing portion 8 is overheated, the printer 100 is in the intermittent single-sided mode in order to provide a time for the temperature of the fixing portion 8 to be leveled in the axial direction. The sheet S of the sheet S is transported.

The standard double-sided mode is a mode for performing double-sided printing on a standard-sized sheet S. As described above, in the case of double-sided printing, it takes time for inversion and transfer between the fixing operation on one side and the fixing operation on the other side. Therefore, the paper spacing time T3 in the standard double-sided mode is longer than the paper spacing time in the other modes. In this case, the inter-paper time T3 is an example of the first time, and the inter-paper time T0 or T1 or T2 is an example of the second time.

That is, in the present embodiment, the paper spacing in each transport mode is the paper spacing in the standard single-sided mode T0 <paper spacing in the small size single-sided mode T1 <paper spacing in the intermittent single-sided mode T2 <paper spacing in the standard double-sided mode. It is T3. The transport mode is determined by the print settings included in the received print instruction.

Then, the CPU 31 determines the differential gain Kd corresponding to the acquired transfer mode (S202). As shown in FIG. 9, the printer 100 associates each transfer mode with the differential gain Kd in the mode table 816 and stores them in, for example, the ROM 32 or the NVRAM 34. That is, the CPU 31 determines the initial value of the differential gain Kd used for calculating the control value Y as the value read from the mode table 816.

Thereby, the printer 100 can acquire the transfer mode based on, for example, the type of the sheet, the presence / absence of double-sided printing, and the like, and can determine the differential gain Kd corresponding to the transfer mode. As will be described later, the printer 100 can also actually measure the inter-paper time T based on the output signal of the sheet sensor 71. However, by estimating the paper-to-paper time T based on the transport mode, the calculation load can be reduced as compared with the case where the paper-to-paper time T is actually measured. Further, when the inter-paper time T is actually measured, the inter-paper time T can be determined only after the transfer of at least the second sheet S is started, but if the inter-paper time T is estimated based on the transfer mode, the inter-paper time T can be estimated. The differential gain Kd can be determined before the first sheet S is conveyed.

Further, the CPU 31 acquires the detected temperature based on the output signal of the temperature sensor 811 (S203). Further, the CPU 31 determines the set temperature of the temperature control (S204). Further, the CPU 31 determines the initial value of the duty ratio by using the detected temperature acquired in S203 and the set temperature determined in S204, and starts the temperature control (S205). Then, when the detected temperature reaches a temperature suitable for fixing, the CPU 31 controls a transport member such as the pickup roller 21 to start transporting the sheet S (S206), and ends the initial setting process.

Returning to the temperature control process, the CPU 31 determines whether or not it is the temperature detection timing (S111). The CPU 31 periodically acquires the detected temperature based on the output signal of the temperature sensor 811 at a predetermined timing. That is, when it is determined that the temperature detection timing is reached (S111: YES), the CPU 31 detects the temperature based on the output signal of the temperature sensor 811 (S112), and stores the detected temperature in the RAM 33. S112 is an example of the detection process. If it is determined that it is not the temperature detection timing (S111: NO), the CPU 31 skips S112.

Further, the CPU 31 determines whether or not it is the timing for changing the duty ratio (S121). As described above, since the duty ratio is set for each cycle, the CPU 31 changes the duty ratio after one cycle is completed and before the next cycle is started. Then, when it is determined that it is the duty ratio change timing (S121: YES), the CPU 31 executes the duty change process (S122).

Next, the procedure of the duty change process will be described with reference to the flowchart of FIG. In the duty change process, the CPU 31 calculates the temperature change amount Yd (S301). The CPU 31 uses the latest detected temperature C and the detected temperature Cd detected before a predetermined change time X to obtain the temperature change amount Yd by the following equation (2).
Yd = (C-Cd) / X ... (2)
In order to suppress the measurement error of the detection temperature and the influence of noise, the change time X is preferably set to be, for example, 10 times or more longer than the interval of the temperature detection timing.

Then, the CPU 31 calculates the control value Y by the above-mentioned equation (1) using the latest detected temperature, the temperature change amount Yd obtained in S301, and the determined differential gain Kd (S302). ). That is, the CPU 31 obtains the differential component value by multiplying the temperature change amount Yd and the differential gain Kd, and the result of subtracting the differential component value from the proportional component value is used as the control value Y. S302 is an example of the control value determination process.

Further, the CPU 31 determines the duty ratio D corresponding to the calculated control value Y with reference to the above-mentioned correspondence table 815 (see FIG. 4) (S303). S303 is an example of the power determination process. Further, at the end of the cycle period, the CPU 31 changes the duty ratio D of the electric power supplied to the heater 810 to the duty ratio D determined in S303 (S304), and ends the duty change process.

When returning to the temperature control process and determining that it is not the timing for changing the duty ratio D (S121: NO), the CPU 31 skips S122. Next, the CPU 31 determines whether or not the output signal of the seat sensor 71 has changed from the signal indicating the presence or absence of the seat to the signal indicating the absence of the seat (S131). Then, when it is determined that the output signal of the seat sensor 71 has changed from the signal indicating the presence of the seat to the signal indicating the absence of the seat (S131: YES), the CPU 31 starts measuring the time (S132). When it is determined that the output signal of the seat sensor 71 has not changed from the signal indicating the presence of the seat to the signal indicating the absence of the seat (S131: NO), the CPU 31 skips S132.

Then, the CPU 31 determines whether or not the output signal of the seat sensor 71 has changed from the signal indicating the absence of the seat to the signal indicating the presence or absence of the seat (S141). Then, when it is determined that the output signal of the seat sensor 71 has changed from the signal indicating the absence of the seat to the signal indicating the presence or absence of the seat (S141: YES), the CPU 31 has elapsed time after starting the measurement in S132. Based on the above, the actually measured paper-to-paper time T is acquired (S142). As a result, in the printer 100, after the rear end of the Nth sheet during continuous transfer of sheets passes through a predetermined position (detection position of the sheet sensor 71), the tip of the N + 1th sheet passes through the same predetermined position. It is possible to obtain the actual measured value of the inter-paper time T, which is the time until.

In the case of double-sided printing, the paper spacing between printing on the first side of the same sheet S and printing on the second side, and printing on the second side of the preceding sheet S and the first side of the subsequent sheet The paper-to-paper time between printing on is different. When the CPU 31 has a plurality of types of paper-to-paper time actually measured in continuous printing, the longest paper-to-paper-to-paper time among them is set as the paper-to-paper time T. By doing so, the temperature ripple can be suppressed more reliably.

The CPU 31 determines the differential gain Kd based on the acquired measured inter-paper time T (S143). The CPU 31 determines the differential gain Kd by, for example, multiplying the inter-paper time T by a predetermined coefficient. That is, in this embodiment, the differential gain Kd and the inter-paper time T are generally in a linear function relationship. After starting the transfer of the second sheet S, the CPU 31 can actually measure the inter-paper time T based on the output signal of the sheet sensor 71. By setting the measured value as the inter-paper time T, a more appropriate differential gain Kd can be determined. The relationship between the differential gain Kd and the inter-paper time T is not limited to the relationship of the linear function, and may be, for example, a quadratic function.

When it is determined that the output signal of the seat sensor 71 has not changed from the signal indicating the absence of the seat to the signal indicating the presence or absence of the seat (S141: NO), the CPU 31 skips S142 and S143. Then, the CPU 31 determines whether or not printing has been completed (S151). When it is determined that printing has not been completed (S1511: NO), the CPU 31 returns to S111 and repeatedly executes each determination.

When it is determined that printing is completed (S151: YES), the CPU 31 stops supplying power to the heater 810 (S152), and ends the temperature control process. If the printer 100 further receives the next printing instruction before the end of printing, the printer 100 does not have to stop the supply of electric power to the heater 810.

The set temperature is not a fixed value, but may be, for example, a temperature that changes in a predetermined pattern based on the detection temperature or the transport mode. As an example of the change pattern of the set temperature, for example, the temperature is set to a low temperature in the paper-to-paper time T for double-sided printing, or when the detection temperature before the start of printing is low, the temperature is temporarily set to be higher than the temperature suitable for fixing. , Etc. are examples. For example, if the detection temperature is higher than the temperature suitable for fixing and the temperature is lower than the temperature suitable for fixing, such as when printing for the first time after the power is turned on or when time has passed since the previous printing, the initial stage from the start of control It is preferable to control the duty ratio D to be large by setting the set temperature to a high temperature and shorten the time until the start of printing.

Further, in the case of continuous double-sided printing, the set temperature P may be changed, for example, as shown in FIG. Specifically, control may be performed to significantly reduce the set temperature P in the initial period j of the non-passing period, which is the period in which the sheet S does not pass through the fixing nip. The non-paper period is an example of the first period. On the other hand, in the printer 100, the set temperature P is set to a temperature suitable for fixing during the paper passing period, which is the period during which the sheet S passes through the fixing nip. The paper passing period is an example of the second period.

The length of the non-passing period is the inter-paper time Ta. The length of the period j is shorter than the paper-to-paper time Ta. If the set temperature P is lowered in the period j, the proportional component value is sharply lowered, so that the duty ratio D is sharply reduced, and it is possible to prevent the detected temperature Q from rising too much during the non-passing period. Therefore, the temperature ripple is smaller in the example of FIG. 11 than in the example of FIG. 5 in which the set temperature P is constant.

When this set temperature P is applied to the printer 100 of the present embodiment, for example, as shown in FIG. 12, it is possible to further suppress an increase in the detected temperature Q during the non-passing period, so that the control has a smaller temperature ripple. The period j may be at least a part of the non-paper-delivery period. However, it is preferable that the period j is set to the initial stage of the non-passing period because the effect of lowering the temperature ripple is larger than that of other periods. Further, the control for changing the set temperature is not limited to double-sided printing, and may be applied to other types of print jobs. However, it is particularly effective for a print job having a long paper-to-paper time T such as double-sided printing.

In the temperature control process described above, the differential component value is calculated using the actually measured paper-to-paper time T. That is, the differential gain Kd is determined by multiplying the paper-to-paper time T by a predetermined coefficient (S143), and the differential component value of the equation (1) is obtained from the multiplication of the temperature change amount Yd and the differential gain Kd (S143). The duty change process was set to S302). However, the acquisition direction of the differential component value is not limited to the method by calculation such as multiplication.

As described above, the duty ratio D is determined by selecting from a limited number of values, and it is not necessary to strictly obtain the control value Y and the differential component value. As shown in FIG. 13, the printer 100 stores, for example, a differential component value table 817 showing the relationship between the temperature change amount Yd, the inter-paper time T, and the corresponding differential component value in the ROM 32 or NVRAM 34, and the differential component value table 817 is stored in the ROM 32 or NVRAM 34. The differential component value may be determined from the component value table 817. The numerical values of the differential component values in the differential component value table 817 are examples for showing the magnitude relationship, and the numerical values themselves have no special meaning.

As shown in FIG. 13, for example, when Yd = 3, the differential component value is -1 if the paper-to-paper time T = T0, and the differential component value is T3 if the paper-to-paper time T is larger than T0. -4. That is, the absolute value of the differential component value when the temperature change amount Yd is the same predetermined value and the paper-to-paper time is long is larger than the absolute value of the differential component value when the paper-to-paper time is short. As described above, if the differential component value table 817 is used, the CPU 31 does not need to calculate the differential component value.

As described in detail above, the printer 100 of the present embodiment acquires the detected temperature based on the output signal of the temperature sensor 811 and supplies the electric power to the heater 810 by PD control using the detected temperature and the set temperature. Control the amount. Then, the printer 100 sets the differential gain Kd for obtaining the differential component value to a larger value as the inter-paper time T is longer. That is, if the amount of temperature change Yd is the same, the longer the paper-to-paper time T, the larger the absolute value of the differential component value, thereby improving the followability to the temperature change. As a result, when the temperature ripple tends to be large, such as when the paper-to-paper time T is long, the absolute value of the differential component value is increased to increase the sensitivity to temperature changes and suppress the temperature ripple, so that the paper-to-paper time T is suppressed. When the temperature ripple is difficult to increase, such as when the temperature is short, it is possible to control according to the situation, such as reducing the absolute value of the differential component value to reduce the sensitivity to temperature changes and suppressing flicker. .. As a result, a balance between reduction of temperature ripple during continuous printing and suppression of flicker can be achieved as compared with the case where the differential component value is uniformly determined according to the amount of temperature change.

Further, in the printer 100 of this embodiment, the control value Y may be calculated by the above-mentioned equation (1) (reprinted below), and the amount of electric power supplied to the heater 810 may be controlled by using the control value Y.
Y = (Set temperature-Detected temperature) x Kp-Temperature change amount x Kd ... (1)
If the differential gain Kd in the equation (1) is set to a larger value as the inter-paper time T is longer, the absolute value of the differential component value becomes larger as the inter-paper time T is longer if the amount of temperature change is the same. ..

Further, the printer 100 of this embodiment is provided with a small size single-sided mode as the sheet S transport mode, and when the small size single-sided mode is selected, the differential gain Kd is higher than when the standard single-sided mode is selected. It may be increased. The paper spacing time T1 in the small size single-sided mode is longer than the paper spacing T0 in the standard single-sided mode. By estimating the paper-to-paper time according to the type of sheet, the calculation load can be reduced as compared with the case where the paper-to-paper time is calculated every time.

Further, the printer 100 of the present embodiment includes an intermittent single-sided mode as the transport mode of the sheet S, and when the intermittent single-sided mode is selected, the differential gain Kd is made larger than when the standard single-sided mode is selected. May be. The paper spacing time T2 in the intermittent single-sided mode is longer than the paper spacing T0 in the standard single-sided mode. By estimating the paper-to-paper time according to the operation mode, the calculation load can be reduced as compared with the case where the paper-to-paper time is calculated every time.

Further, the printer 100 of the present embodiment includes a standard double-sided mode as the sheet S transport mode, and when the standard double-sided mode is selected, the differential gain Kd is made larger than when the standard single-sided mode is selected. May be. The paper spacing time T3 in the standard double-sided mode is longer than the paper spacing T0 in the standard single-sided mode. By estimating the paper-to-paper time by double-sided printing, the calculation load can be reduced as compared with the case where the paper-to-paper time is calculated every time.

Further, the printer 100 of this embodiment may actually measure the paper-to-paper time based on the output signal of the sheet sensor 71. That is, in the printer 100, the output signal of the sheet sensor 71 changes from the time when the output signal of the sheet sensor 71 changes from the signal indicating the presence or absence of the sheet S to the signal indicating the absence of the sheet S during continuous transfer of the sheets. It may be the time from the time when the signal indicating the absence of the sheet S to the signal indicating the presence of the sheet S changes. If the measured value is the paper-to-paper time, a more appropriate control value can be determined.

Further, in the printer 100 of the present embodiment, for example, in double-sided printing, the set temperature P in the initial period j of the non-passing period may be reduced. By reducing the set temperature at least part of the non-passing period, the temperature ripple can be further reduced.

Further, in the printer 100 of the present embodiment, the duty ratio D of the electric power supplied to the heater 810 may be switched to a larger value as the control value Y is larger, based on the control value Y calculated by the above-mentioned equation (1). good. By switching the duty ratio D, the amount of electric power supplied to the heater 810 can be appropriately switched.

It should be noted that the present embodiment is merely an example and does not limit the present invention in any way. Therefore, as a matter of course, the present invention can be improved and modified in various ways within the range not deviating from the gist thereof. For example, the present invention is not limited to a printer, and can be applied to any device having an image forming function by an electrophotographic method, such as a multifunction device, a copying machine, and a fax machine. Further, it can be applied not only to a monochrome printer but also to a color printer.

Further, in the embodiment, an example in which the pressure roller 82 is the drive side is shown as the fixing portion 8, but the heating member 81 side may be the drive side. Further, the printer 100 is not limited to the printer 100 capable of double-sided printing, and may be a device dedicated to single-sided printing. In that case, the transport mode does not include the standard double-sided mode. That is, the transport mode is not limited to the four types shown in the mode table 816 in the embodiment. It is sufficient that there are two or more types of transport modes having different paper-to-paper times. Further, the small size single-sided mode may be further subdivided according to the size of the sheet S.

Further, the control of the amount of electric power supplied to the heater 810 is not limited to the wave number control described in the embodiment. For example, phase control, which is control based on the phase of the voltage waveform of the AC power supply, may be performed, or wave number control and phase control may be combined.

Further, in the embodiment, PD control is performed as the temperature control of the heater 810, but PID control may be performed by further adding an integral component. Further, although the proportional gain Kp is assumed to be a fixed value, it may be a variable value.

Further, for example, although the initial value of the paper-to-paper time T is determined based on the transport mode, it may be a fixed value. That is, the initial value of the differential gain Kd may be a fixed value regardless of the transport mode, and the differential gain Kd may be changed based on the measured value of the inter-paper time T after the transport is started. In this case, the determination of the transport mode and the mode table 816 are unnecessary. However, by determining the initial value based on the transport mode, appropriate control can be obtained from the initial stage.

Further, for example, it is not necessary to actually measure the paper-to-paper time T. That is, the differential gain Kd determined based on the transport mode may be used until the end of printing. In this case, the temperature control processes S131, S132, S141, S142, and S143 are unnecessary. However, more precise control is possible by performing control based on the measured value.

Further, in the case of double-sided printing, the set temperature is lowered for at least a part of the paper-to-paper time, but it is not necessary to lower the set temperature. However, it is preferable to lower the set temperature because the temperature ripple can be further reduced. Further, the period for lowering the set temperature is a predetermined period from the start of the inter-paper time T to before the end of the inter-paper time T, but the period is not limited to this.

Further, the process disclosed in the embodiment may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the process disclosed in the embodiment can be realized in various aspects such as a recording medium or a method in which a program for executing the process is recorded.

5 Process part 8 Fixing part 11 Paper feed tray 13 Sheet transport path 21 Pickup roller 31 CPU
71 Sheet sensor 81 Heating member 810 Heater 811 Temperature sensor 82 Pressurizing roller 100 Printer

Claims (8)

With a heater
The first rotating body heated by the heater and
A second rotating body forming a fixing nip portion with the first rotating body,
A temperature sensor that outputs a different signal depending on the surface temperature of the first rotating body, and
Control unit and
Equipped with
The control unit
A detection process for detecting the surface temperature of the first rotating body based on the signal of the temperature sensor, and
The first value based on the difference between the set temperature of the first rotating body and the surface temperature of the first rotating body, the amount of change in the surface temperature of the first rotating body per unit time, and the continuous transfer of the sheet. The control value determination process for determining the control value using the second value based on the time between papers, and the control value determination process satisfying the following equations (1) to (3) .
(1) The control value = the first value-the second value
(2) The first value = (the set temperature of the first rotating body-the surface temperature of the first rotating body) x proportional gain
(3) The second value = the amount of change x the differential gain,
A power determination process for determining the amount of electric power supplied to the heater by determining a duty ratio, which is a ratio of energized states within a predetermined cycle, using the control value determined in the control value determination process.
And run
The value of the differential gain is larger when the paper-to-paper time is the first time, as compared with the case where the paper-to-paper time is shorter than the first time.
The duty ratio determined by the power determination process is larger as the control value determined by the control value determination process is larger.
An image forming apparatus characterized in that. In the image forming apparatus according to claim 1 ,
A storage unit for accommodating seats and
Sheet transport path and
A carry-in section for carrying the sheets housed in the storage section into the transport path one by one, and a carry-in section.
Equipped with
When the type of the sheet accommodated in the accommodating unit is the first type or the second type having a shorter length in the conveying direction than the first type, the control unit continuously conveys the sheet. The carry-in start interval by the carry-in unit at the time is set to the first time interval, and the carry-in start interval is set.
When the type of the sheet is the second type of sheet, the inter-paper time is the first time.
When the type of the sheet is the first type of sheet, the inter-paper time is the second time.
An image forming apparatus characterized in that. In the image forming apparatus according to claim 1 ,
A storage unit for accommodating seats and
Sheet transport path and
A carry-in section for carrying the sheets housed in the storage section into the transport path one by one, and a carry-in section.
Equipped with
The control unit operates the carry-in unit with the carry-in start interval by the carry-in unit as the first time interval during continuous transport of sheets, and the carry-in start interval is shorter than the first time interval. It is possible to execute the second mode in which the carry-in unit is operated as the second time interval.
When the carry-in unit is operating in the first mode, the paper-to-paper time is the first time.
When the carry-in unit is operating in the second mode, the paper-to-paper time is the second time.
An image forming apparatus characterized in that. In the image forming apparatus according to claim 1 ,
In the case of double-sided printing, the paper-to-paper time is the first time.
In the case of single-sided printing, the paper-to-paper time is the second time.
An image forming apparatus characterized in that. In the image forming apparatus according to claim 1 ,
Sheet transport path and
A seat sensor that outputs different signals depending on the presence or absence of a seat at a predetermined position on the transport path, and
Equipped with
The time from the timing when the sheet sensor detects the presence or absence of the sheet to the timing when the sheet sensor detects the presence or absence of the sheet is the inter-paper time.
An image forming apparatus characterized in that. The image forming apparatus according to any one of claims 1 to 5 .
The control unit
For at least part of the first period during which the sheet has not passed through the anchoring nip.
The set temperature of the first rotating body is reduced as compared with the second period during which the sheet passes through the fixing nip portion.
An image forming apparatus characterized in that. With a heater
The first rotating body heated by the heater and
A second rotating body forming a fixing nip portion with the first rotating body,
A temperature sensor that outputs a different signal depending on the surface temperature of the first rotating body, and
It is a control method of an image forming apparatus provided with
A detection step of detecting the surface temperature of the first rotating body based on the signal of the temperature sensor, and
The first value based on the difference between the set temperature of the first rotating body and the surface temperature of the first rotating body, the amount of change in the surface temperature of the first rotating body per unit time, and the continuous transfer of the sheet. A control value determination step for determining a control value using a second value based on the time between papers, and the control value determination step satisfying the following equations (1) to (3) .
(1) The control value = the first value-the second value
(2) The first value = (the set temperature of the first rotating body-the surface temperature of the first rotating body) x proportional gain
(3) The second value = the amount of change x the differential gain,
A power determination step for determining the amount of electric power to be supplied to the heater by determining a duty ratio, which is a ratio of energized states within a predetermined cycle, using the control value determined in the control value determination step.
Including
The value of the differential gain is larger when the paper-to-paper time is the first time, as compared with the case where the paper-to-paper time is shorter than the first time.
The duty ratio determined in the power determination step is larger as the control value determined in the control value determination step is larger.
A control method for an image forming apparatus. With a heater
The first rotating body heated by the heater and
A second rotating body forming a fixing nip portion with the first rotating body,
A temperature sensor that outputs a different signal depending on the surface temperature of the first rotating body, and
An image forming apparatus equipped with
A detection process for detecting the surface temperature of the first rotating body based on the signal of the temperature sensor, and
The first value based on the difference between the set temperature of the first rotating body and the surface temperature of the first rotating body, the amount of change in the surface temperature of the first rotating body per unit time, and the continuous transfer of the sheet. The control value determination process for determining the control value using the second value based on the time between papers, and the control value determination process satisfying the following equations (1) to (3) .
(1) The control value = the first value-the second value
(2) The first value = (the set temperature of the first rotating body-the surface temperature of the first rotating body) x proportional gain
(3) The second value = the amount of change x the differential gain,
A power determination process for determining the amount of electric power supplied to the heater by determining a duty ratio, which is a ratio of energized states within a predetermined cycle, using the control value determined in the control value determination process.
To execute ,
The value of the differential gain is larger when the paper-to-paper time is the first time, as compared with the case where the paper-to-paper time is shorter than the first time .
The duty ratio determined by the power determination process is larger as the control value determined by the control value determination process is larger.
A program characterized by that.

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