JP2019053164A - Image formation apparatus, method of controlling image formation apparatus, and program - Google Patents

Abstract

To provide a technique for balancing reduction of a temperature ripple in continuous printing and suppression of a flicker for an image formation apparatus comprising a fixing device.SOLUTION: A printer 100 comprises a heating member 81 and a pressure roller 82 which form a fixation nip part, and detects a surface temperature of the heating member 81 based upon a signal of a temperature sensor 811. The printer 100 determines a control value Y using a proportional component value based upon a difference between a set temperature and a detected temperature of the heating member 81, and a differential component value based upon a temperature variation quantity Yd and an inter-sheet time T in successive conveyance of sheets. Further, the printer 100 determines electric energy to be supplied to a heater 810 using the control value Y. The absolute value of the differential component value is larger when the temperature variation quantity Yd has a specific value and the inter-sheet time T is a first time than when the temperature variation quantity Yd has the same specific value and the inter-sheet time T is a second time shorter than the first time.SELECTED DRAWING: Figure 9

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 heater heating control in an image forming apparatus having a fixing device.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus that includes a process unit that forms a toner image and a fixing device that thermally fixes the toner image transferred to the sheet to the sheet, energization that supplies power to the heater of the fixing device The heating control is performed so that the surface temperature of the rotating body of the fixing device approaches the set temperature by switching between the state and the non-energized state in which power is not supplied.

  As a document disclosing the heating control of the fixing device, there is, for example, Patent Document 1. Patent Document 1 discloses an image forming apparatus that performs PID control as heating control of a fixing device, and a proportional gain is set so that a duty ratio, which is a ratio of an energized state within a predetermined period, increases as a conveyance speed increases. A configuration for increasing the size is disclosed.

JP 2016-212259 A

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

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide an image forming apparatus including a fixing device, which provides a technique for balancing the reduction in temperature ripple during continuous printing and the suppression of flicker.

  An image forming apparatus for solving this problem includes a second rotation that forms 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 according to a surface temperature of the first rotating body, and a control unit, the control unit based on a signal from the temperature sensor. Detection processing for detecting a surface temperature of the first rotating body, a first value based on a difference between a set temperature of the first rotating body and a surface temperature of the first rotating body, and the first rotating body per unit time A control value determining process for determining a control value using a second value based on a change amount of the surface temperature and a sheet interval time during continuous conveyance of the sheet; and the control value determined in the control value determining process A power determination process for determining the amount of power supplied to the heater, and When the amount of change is a predetermined value and the time between sheets is the first time, the amount of change is the predetermined value and the time between sheets is the absolute value of the second value. Compared with the case of the second time shorter than the first time, it is characterized by being larger.

  The image forming apparatus disclosed in the present specification detects the surface temperature of the first rotating body based on a signal from the temperature sensor. Furthermore, 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 conveyance of the sheet The amount of power to be supplied to the heater is determined using the control value determined using the second value based on the sheet interval time. Then, if the change amount is the same predetermined value, the image forming apparatus increases the absolute value of the second value when the time between sheets is long than when it is short.

  That is, the image forming apparatus disclosed in the present specification uses the second value having a larger absolute value when the paper interval time is long than when the paper interval time is short. The second value is a component 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, among the control values. The larger the absolute value of the second value, the more the temperature value changes. Followability increases. When the paper interval time is long, the temperature ripple is likely to be larger than when the paper interval time is short. When the time between sheets is long, the image forming apparatus increases the absolute value of the second value and improves the followability to the temperature change, so that the temperature ripple can be suppressed. On the other hand, when the time between sheets is short, the temperature ripple is difficult to increase. For this reason, the image forming apparatus suppresses flicker by lowering the followability to a change in temperature when the paper interval time is short compared to when the paper interval time is long. As a result, it is possible to achieve a balance between reduction in temperature ripple during continuous printing and suppression of flicker.

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

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

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. FIG. 2 is a block diagram illustrating an electrical configuration 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 corresponding | compatible 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 detected temperature in the case of duplex printing. It is explanatory drawing which shows the example of the change of the detected 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 an initial setting process. It is explanatory drawing which shows the example of the mode table which shows the relationship between conveyance mode and a 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 detected temperature when changing preset temperature and performing double-sided printing. It is explanatory drawing which shows the example of the change of detected temperature at the time of performing control of this form by double-sided printing. It is explanatory drawing which shows the example of the relationship between paper interval, temperature variation, and a differential component value.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Embodiments of an image forming apparatus according to the invention will be described below 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 according to this embodiment includes a paper feed tray 11 that stores a sheet S before printing, a paper discharge tray 12 that stores a printed sheet S, and a sheet S that forms a toner image. And a process section 5 for transferring the toner image and a fixing section 8 for fixing the toner image to the sheet S. The paper feed tray 11 is an example of a storage unit.

  The process unit 5 forms a toner image by electrophotography and transfers the toner image to the sheet S. As shown in FIG. 1, the process unit 5 includes a photoreceptor 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 charger, and charges the surface of the photoreceptor 51 almost uniformly. The exposure unit 53 is, for example, a laser exposure unit, which partially exposes the photoconductor 51 by irradiating a laser beam, and forms an electrostatic latent image on the photoconductor 51 based on image data. The developing unit 54 stores toner, develops the toner by supplying the toner to the electrostatic latent image on the photoconductor 51, and forms a toner image on the photoconductor 51. The transfer unit 55 electrically draws the toner image on the photoreceptor 51 and transfers it to the sheet S. The cleaner 56 is, for example, a sponge roller, and removes toner or the like remaining on the photoconductor 51 after transfer from the photoconductor 51.

  As shown in FIG. 1, the fixing unit 8 includes a heating member 81 and a pressure roller 82 disposed on both sides of the sheet conveyance path 13. Both the heating member 81 and the pressure roller are rotating bodies provided rotatably. The heating member 81 and the pressure roller 82 are in pressure contact with 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 a first rotating body, and the pressure roller 82 is an example of a second rotating body. The fixing unit 8 heat-fixes the toner image on the sheet S by conveying the sheet S on which the toner image is transferred by the process unit 5 while heating the sheet S at the fixing nip portion.

  The heating member 81 includes a heater 810 inside, and is heated by the heater 810. As a result, the surface of the heating member 81 is heated, 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, or an IH heater (induction heating member) can be applied. The heater 810 only needs to be able to raise the temperature of the surface of the heating member 81. The heater 810 may be disposed inside the heating member 81 to heat the heating member 81 entirely from the inside, or may be disposed outside the heating member 81 for heating. The surface of the member 81 may be directly heated.

  The pressure roller 82 is a heat-resistant rubber roller. For example, a metal shaft is coated with an elastic layer made of silicone rubber or the like and a release layer having releasability. The pressure roller 82 is pressed toward the heating member 81 by a pressing member (not shown). Further, the pressure roller 82 is driven to rotate counterclockwise in FIG. 1 when the sheet is conveyed, and the heating member 81 is rotated clockwise in FIG. 1 following the rotation of the pressure roller 82. The The heating member 81 may be on the driving side. An endless belt member can also be applied as the second rotating body.

  The printer 100 also includes a temperature sensor 811 for detecting the surface temperature of the heating member 81 as shown in FIG. For example, the temperature sensor 811 outputs different signals according to 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. Note that the printer 100 may further include another temperature sensor.

  Further, as shown in FIG. 1, the printer 100 is provided with a sheet conveyance path 13 that is a path of the sheet S from the paper feed tray 11 to the paper discharge tray 12. The printer 100 includes various conveyance members for conveying the sheet S along the sheet conveyance path 13. The printer 100 includes, for example, a pickup roller 21, a registration roller 22, and a paper discharge roller 23 as conveying members that convey the sheet S. The fixing unit 8 and the photosensitive member 51 of the process unit 5 also have a function of conveying the sheet S. The sheet conveyance path 13 is an example of a conveyance path, and the pickup roller 21 is an example of a carry-in unit.

  The pickup roller 21 is rotationally driven at a predetermined timing, pulls out one sheet S from the sheet feeding tray 11 and carries it one by one into the sheet conveyance path 13. The registration roller 22 conveys the sheet S pulled out by the pickup roller 21 toward the process unit 5 in synchronization with the toner image forming operation of the process unit 5. The paper discharge roller 23 discharges the printed sheet S to the paper discharge tray 12.

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

  The printer 100 according to the present embodiment is an apparatus capable of duplex printing. When performing duplex printing, the sheet S pulled out from the paper feed tray 11 is first transported through the printing path 13a, and the process unit 5 and the fixing unit 8 An image is formed on one side of the sheet S. When the sheet S on which an image is formed passes through the branch point between the printing path 13a and the reversing path 13b, the printer 100 reverses the conveyance direction of the sheet S and advances the sheet S to the reversing path 13b. Further, the printer 100 advances the sheet S from the joining point of the printing path 13a and the reversing path 13b to the printing path 13a, and passes through the process unit 5 and the fixing unit 8 again, so that the other side of the sheet S is obtained. An image is formed on. The printer 100 discharges the sheet S on which images are formed on both sides to the discharge tray 12.

  In addition, the printer 100 includes a sheet sensor 71 for detecting the passage of the sheet S on the sheet conveyance path 13. The sheet sensor 71 is disposed downstream of the junction of the printing path 13 a and the reversing path 13 b and upstream of the process unit 5 in the conveyance direction of the sheet S. The sheet sensor 71 outputs different signals depending on the presence or absence of the sheet S at the detection location. Note that the printer 100 may include a plurality of sheet sensors 71 on the sheet conveyance path 13.

  Next, the electrical configuration of the printer 100 will be described. As shown in FIG. 2, the printer 100 according to this embodiment includes a controller 30 including a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. The printer 100 also 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 from which various control programs are read, 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 setting values.

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

  The network IF 37 is hardware for communicating with devices connected via the network. For example, the printer 100 receives a print job from an external device via the network IF 37. The communication method using the network IF 37 may be wireless or wired. In addition to the network IF 37, the printer 100 may include a communication unit with an external device such as a USB interface.

  The operation panel 40 is hardware responsible for displaying a notification to the user and receiving an instruction input by the user. The operation panel 40 includes, for example, a liquid crystal display and a button group including a start key, a stop key, a numeric keypad, and the like. The printer 100 can also accept a print job via the operation panel 40.

  Next, temperature control of the fixing unit 8 in the printer 100 of this embodiment will be described. The printer 100 of the present 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 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 PD control, for example, as temperature control. That is, the printer 100 performs proportional control based on a proportional component obtained by multiplying a difference between a set temperature and a detected temperature by a proportional gain, and differential control based on a differential component obtained by multiplying a temperature change amount by a differential gain. The temperature is controlled by using together. The temperature change amount is an amount representing a change per unit time of the detected temperature.

Specifically, the printer 100 switches the amount of power supplied to the heater 810 based on the control value Y obtained by the following equation (1).
Y = (set temperature−detected temperature) × Kp−temperature change × 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−detected temperature) × Kp” is a proportional component value, and “temperature change amount × Kd” is a differential component value. The proportional component value is an example of a first value, and the differential component value is an example of a second value.

  The printer 100 according to the present embodiment performs duty control for switching the duty ratio D of the power supplied to the heater 810 based on the acquired control value Y. For example, as illustrated 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 units of half wavelengths based on the zero-cross signal. With the wave number control, the heater 810 is turned on and off.

  FIG. 3 shows an example of the heater-on period when the duty ratio is 60%. This figure shows an example in which power is supplied to the heater 810 during a period corresponding to three half wavelengths in one cycle, that is, a period of 60% in 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 three-half wavelength period in one cycle, and is not limited to the continuous period as shown in FIG.

  As shown in FIG. 3, the printer 100 according to the present embodiment sets the duty ratio D of the heater 810 to 0% by setting the 5 half wavelength period to one cycle and the heater on period to any one of 0 half wavelength to 5 half wavelengths. , 20%, 40%, 60%, 80%, 100%. Note that the choice of the duty ratio is not limited to the above example, and one cycle period is not limited to the 5 half wavelength period. If the one cycle period is changed, the printer 100 can further select a duty ratio other than the above.

  The printer 100 increases the duty ratio D of the power supplied to the heater 810 as the control value Y calculated by the above-described equation (1) is larger. For example, as illustrated in FIG. 4, the printer 100 stores a correspondence table 815 indicating the correspondence 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 refers to the correspondence table 815 to determine the duty ratio D corresponding to the acquired control value Y. Then, the printer 100 switches the duty ratio D of the power supplied to the heater 810 in the next cycle to the determined duty ratio D.

  In the printer 100 of this embodiment, the heater 810 is provided inside the heating member 81, and it takes some time until the detected temperature starts to rise after the heater 810 is energized. Also, for example, even if the energization of the heater 810 is stopped because the detected temperature is 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 one cycle at the maximum from the change of the detected temperature to the change of the power supplied to the heater 810. That is, in feedback control, a control delay occurs. This control delay 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 decrease during fixing. On the other hand, the temperature of the pressure roller 82 is raised to the same level as that of the heating member 81, and the amount of heat taken away from the heating member 81 is small during the paper interval time T when the sheet S does not exist in the fixing nip portion. The surface temperature of the heating member 81 is likely to rise.

  The “inter-sheet time” is the subsequent sheet S from the time when the trailing end of the preceding sheet S passes a predetermined position in the sheet conveying path 13 in the conveyance direction of the sheet S while continuous conveyance of the sheet S is continued. It means the time until the tip of passes through the same part. The continuous conveyance is a state in which the printer 100 is conveying at least two sheets S in a predetermined interval T. The inter-paper time T is the time from when the preceding sheet S passes through the fixing nip portion until the subsequent sheet S enters the fixing nip portion. The paper interval time T is, for example, 0.1 seconds to 10 seconds.

  For example, when executing a print job for printing on a plurality of sheets S, the printer 100 according to the present embodiment continuously feeds the sheets S at a predetermined interval and performs continuous conveyance. The printer 100 continuously feeds a plurality of sheets S to the fixing unit 8 at intervals of a predetermined paper interval T during continuous conveyance. Even when different print jobs are straddled, the inter-sheet time between the last sheet of the preceding print job and the first sheet of the subsequent print job is equal to the inter-sheet time T of the preceding print job, and the continuous sheet The conveyance may be continued.

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

  FIG. 5 shows an example of a 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 sheet passing timing. Note that FIG. 5 and other similar drawings (FIGS. 6, 11, and 12) to be described later show a state after several tens of seconds have elapsed since the start of continuous printing. In FIG. 5 and the like, the sheet passing timing is indicated by a one-dot chain line at the bottom of the drawing. The period during which the sheet passing timing is ON is a period during which the sheet S passes through the fixing unit 8. The length of the period in which the sheet passing timing is off is the sheet interval time T. Further, in FIG. 5 and the like, the duty ratio D is indicated by a solid line in the middle portion in the figure.

  In the case of double-sided printing, as shown in FIG. 5, after printing on both sides of one sheet S, the sheet interval time T, which is a period during which the sheet S is conveyed by the reversing path 13b, as the sheet interval time T. There is a sheet interval time Tb which is a period until printing on one side of the next sheet S. The paper interval time Ta is longer than the paper interval time Tb. For example, as shown in FIG. 5, when the detected temperature Q is lower than the set temperature P at the beginning of the long paper interval time Ta, the heating continues even after the paper interval time Ta is entered, and the detected temperature Q is set. The temperature P may be greatly exceeded. In this case, as shown by a broken line in FIG. 5, the detected temperature Q changes greatly, and the temperature ripple increases.

  On the other hand, even if the temperature control is performed 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 inter-paper time Tc in single-sided printing is comparable to the inter-paper time Tb in double-sided printing, and is shorter than the inter-paper time Ta. When the sheet interval time T is short, even if the surface temperature of the heating member 81 rises after the preceding sheet S passes through the fixing nip portion, the subsequent sheet S reaches the fixing nip portion in a short time. Since the heat is taken away by the succeeding sheet S, there is little possibility that the detected temperature Q is excessively increased.

  The printer 100 according to the present embodiment is controlled so that the absolute value of the differential component value of the control value Y when the temperature change amount is the same value becomes longer as the inter-paper time T is longer during continuous printing. To do. Specifically, the printer 100 according to the present embodiment increases the differential gain Kd used for calculating the control value Y when the paper interval time T is long compared to when the paper interval time T is short. The differential component value of the control value Y is a product of the temperature change amount and the differential gain Kd. When the temperature change amount is the same value, the absolute value of the differential component value increases as the differential gain Kd increases. It becomes.

  In the feedback control by PD control, the differential component value of the control value Y is a component that represents the followability with respect to the change in the detected temperature. The greater the differential gain Kd, the higher the sensitivity to the temperature change. That is, the printer 100 according to this embodiment performs temperature control with higher followability with respect to changes in the detected temperature when the paper interval time T is long than when the paper interval time T is short. If the control has high followability to the change in the detected temperature, there is a high possibility that the temperature ripple can be reduced.

  Note that if the differential gain Kd is increased in order to reduce the temperature ripple, the followability to the temperature change is enhanced and flicker is likely to occur. The printer 100 of this embodiment increases the differential gain Kd when the paper interval time T is long, and does not increase the differential gain Kd when the paper interval time T is short. The occurrence of flicker can be suppressed as compared with the case where Kd is increased.

  Next, the temperature control processing procedure for realizing the temperature control of the fixing unit 8 will be described with reference to the flowchart of FIG. The temperature control process is executed by the CPU 31 when a print instruction for continuously printing two or more sheets is received.

  In the temperature control process, the CPU 31 first executes an initial setting process for performing 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 setting specified in the print instruction (S201). For example, the printer 100 according to the present embodiment has four types of conveyance modes such as a regular single-sided mode, a small-size single-sided mode, an intermittent single-sided mode, and a regular double-sided mode, as shown in FIG. Has a mode. A mode table 816 shown in FIG. 9 shows a correspondence relationship between the conveyance mode and the differential gain Kd.

  The regular single-sided mode is a conveyance mode for continuously executing single-sided printing on a regular paper sheet S having a regular size such as A4. The sheet interval time T0 in the regular single-sided mode is the same as that in the other conveyance modes. Short compared to the time between papers.

  The small size single-sided mode is a conveyance mode in which a sheet having a size 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-side mode, the carry-in start interval at which the pickup roller 21 carries the sheet S into the sheet conveyance path 13 is equal to the carry-in start interval in the standard single-side mode. The carry-in start interval is a time interval from when the pickup roller 21 starts to carry in the Nth sheet S to when the N + 1th sheet S starts to be carried in. In the small size single-sided mode, the type of the sheet S stored 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 sheet S carry-in start interval is the same as in the standard single-sided mode, and the time between sheets is longer than that in the standard single-sided mode because the sheet S is short. That is, the paper interval time T1 in the small size single-sided mode is longer than the paper interval time T0 in the standard single-sided mode. In this case, the small size sheet S is an example of the second type sheet, and the standard size sheet S is an example of the first type sheet. The inter-paper time T1 is an example of a first time, and the inter-paper time T0 is an example of a 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 regular single-sided mode, and both are examples of the first time interval.

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

  In the printer 100 of this embodiment, as shown in FIG. 9, the paper interval time T2 in the intermittent single-sided mode is longer than the paper interval time T1 in the small size single-sided mode. For example, when the printer 100 determines that the temperature of the end portion in the axial direction of the fixing unit 8 is excessively high, in order to provide time for the temperature of the fixing unit 8 to be equalized in the axial direction, the printer 100 is in the intermittent single-sided mode. The sheet S is conveyed.

  The regular duplex mode is a mode in which duplex printing is performed on a regular size sheet S. As described above, when performing duplex printing, it takes time for reversal and conveyance between the fixing operation on one side and the fixing operation on the other side. Therefore, the paper interval time T3 in the regular duplex mode is longer than the paper interval time in the other modes. In this case, the inter-paper time T3 is an example of a first time, and the inter-paper time T0, T1, or T2 is an example of a second time.

  That is, in this embodiment, the sheet interval time in each conveyance mode is the interval time T0 in the regular single-sided mode <interval interval time T1 in the small size single-sided mode <interval interval T2 in the intermittent single-sided mode <interval interval in the regular duplex mode T3. The transport mode is determined by the print setting included in the received print instruction.

  Then, the CPU 31 determines a differential gain Kd corresponding to the acquired transport mode (S202). As illustrated in FIG. 9, the printer 100 stores each conveyance mode and the differential gain Kd in association with each other in the mode table 816, for example, in 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 a value read from the mode table 816.

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

  Further, the CPU 31 acquires the detected temperature based on the output signal of the temperature sensor 811 (S203). Further, the CPU 31 determines a set temperature for temperature control (S204). Further, the CPU 31 determines the initial value of the duty ratio using the detected temperature acquired in S203 and the set temperature determined in S204, and starts temperature control (S205). Then, when the detected temperature reaches a temperature suitable for fixing, the CPU 31 controls the conveying member such as the pickup roller 21 to start conveying 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 a temperature detection timing (S111). The CPU 31 acquires the detected temperature based on the output signal of the temperature sensor 811 periodically at a predetermined timing. That is, when it is determined that it is the temperature detection timing (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 a detection process. When determining 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 duty ratio change timing (S121). As described above, since the duty ratio is set for each cycle, the CPU 31 changes the duty ratio after the end of one cycle and before the start of the next cycle. If it is determined that it is the duty ratio change timing (S121: YES), the CPU 31 executes a duty change process (S122).

Next, the procedure of duty change processing will be described with reference to the flowchart of FIG. In the duty change process, the CPU 31 calculates a temperature change amount Yd (S301). CPU31 calculates | requires temperature variation amount Yd by the following formula | equation (2) using the latest detected temperature C and the detected temperature Cd detected only the predetermined change time X before.
Yd = (C−Cd) / X (2)
In order to suppress the measurement error of detection temperature and the influence of noise, it is preferable that the change time X is, for example, 10 times longer than the temperature detection timing interval.

  Then, the CPU 31 calculates the control value Y by the above-described 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 multiplication of the temperature change amount Yd and the differential gain Kd, and sets the control value Y as a result of subtracting the differential component value from the proportional component value. S302 is an example of a 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-described correspondence table 815 (see FIG. 4) (S303). S303 is an example of a power determination process. Further, at the end of the cycle period, the CPU 31 changes the duty ratio D of the power supplied to the heater 810 to the duty ratio D determined in S303 (S304), and ends the duty change process.

  Returning to the temperature control process, if it is determined 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 sheet sensor 71 has changed from a signal indicating the presence of the sheet to a signal indicating the absence of the sheet (S131). If it is determined that the output signal of the sheet sensor 71 has changed from a signal indicating the presence of a sheet to a signal indicating the absence of a sheet (S131: YES), the CPU 31 starts measuring time (S132). When the CPU 31 determines that the output signal of the sheet sensor 71 has not changed from the signal indicating the presence of the sheet to the signal indicating the absence of the sheet (S131: NO), the CPU 31 skips S132.

  Then, the CPU 31 determines whether or not the output signal of the sheet sensor 71 has changed from a signal indicating the absence of a sheet to a signal indicating the presence of a sheet (S141). If it is determined that the output signal of the sheet sensor 71 has changed from a signal indicating the absence of the sheet to a signal indicating the presence of the sheet (S141: YES), the CPU 31 elapsed time after starting the measurement in S132. Based on the above, the actually measured paper interval time T is acquired (S142). Thus, in the printer 100, the trailing edge of the Nth sheet during continuous conveyance of the sheet passes through a predetermined position (detection position of the sheet sensor 71), and then the leading edge of the (N + 1) th sheet passes through the same predetermined position. It is possible to obtain the measured paper interval time T, which is the time until the time.

  In the case of double-sided printing, the inter-sheet time between printing on the first side of the same sheet S and printing on the second side, printing on the second side of the preceding sheet S, and the first side of the subsequent sheet. The inter-paper time between printing on the paper is a different time. When there are a plurality of types of actually measured paper intervals in continuous printing, the CPU 31 sets the longest paper interval time as the paper interval time T. By doing in this way, a temperature ripple can be suppressed more reliably.

  The CPU 31 determines the differential gain Kd based on the acquired actual paper interval time T (S143). For example, the CPU 31 multiplies the inter-paper time T by a predetermined coefficient to determine the differential gain Kd. That is, in this embodiment, the differential gain Kd and the paper interval time T are generally in a linear function relationship. If the conveyance of the second sheet S is started, 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 paper interval time T, a more appropriate differential gain Kd can be determined. The relationship between the differential gain Kd and the paper interval time T is not limited to a linear function, and may be a quadratic function, for example.

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

  When it is determined that the printing is finished (S151: YES), the CPU 31 stops the supply of power to the heater 810 (S152), and finishes the temperature control process. Note that the printer 100 does not have to stop supplying power to the heater 810 when the next print instruction is received before the end of printing.

  Note that the set temperature is not a fixed value, and may be a temperature that changes in a predetermined pattern based on, for example, the detected temperature or the conveyance mode. As an example of the change pattern of the set temperature, for example, the temperature is lowered at the paper interval time T for double-sided printing, or the temperature is temporarily higher than the temperature suitable for fixing when the detected temperature before printing is low. , Etc. For example, if the detected temperature is lower than the temperature suitable for fixing, such as when printing for the first time after turning on the power or when time has passed since the previous printing, It is preferable that the temperature is set to a high temperature and the duty ratio D is increased to shorten the time until the start of printing.

  Moreover, when performing double-sided printing continuously, for example, as shown in FIG. 11, the set temperature P may be changed. Specifically, control may be performed to greatly reduce the set temperature P in the initial period j of the non-sheet passing period, which is a period during which the sheet S does not pass through the fixing nip. The non-paper passing period is an example of a first period. On the other hand, the printer 100 sets the set temperature P to a temperature suitable for fixing during a sheet passing period, which is a period during which the sheet S passes through the fixing nip. The paper passing period is an example of a second period.

  The length of the non-paper passing period is the paper interval time Ta. The length of the period j is shorter than the paper interval time Ta. If the set temperature P is lowered in the period j, the proportional component value decreases rapidly, so the duty ratio D decreases rapidly, and it is possible to suppress the detected temperature Q from rising excessively during the non-sheet passing period. Therefore, the temperature ripple is smaller in the example of FIG. 11 than in the example of FIG. 5 where the set temperature P is constant.

  When this set temperature P is applied to the printer 100 of this embodiment, for example, as shown in FIG. 12, an increase in the detected temperature Q during the non-sheet passing period can be further suppressed, so that control with smaller temperature ripple is performed. The period j may be at least a part of the non-paper passing period. However, it is preferable to set the period j at the beginning of the non-sheet passing period because the effect of reducing the temperature ripple is greater than in the other periods. Further, the control for changing the set temperature is not limited to duplex printing, and may be applied to other types of print jobs. However, this is particularly effective for a print job having a long paper interval T, such as duplex printing.

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

  As described above, the duty ratio D is selected and determined from limited types of values, and the control value Y and the differential component value do not need to be determined strictly. For example, as shown in FIG. 13, the printer 100 stores in the ROM 32 or the NVRAM 34 a differential component value table 817 indicating the relationship between the temperature change amount Yd, the paper interval T, and the corresponding differential component value. The differential component value may be determined from the component value table 817. In addition, the numerical value of the differential component value in the differential component value table 817 is an example for showing the magnitude relationship, and the numerical value itself has no special meaning.

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

  As described above in detail, the printer 100 according to the present embodiment acquires the detected temperature based on the output signal of the temperature sensor 811 and supplies 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 paper interval time T is longer. That is, as long as the temperature change amount Yd is the same, the longer the inter-paper time T is, the larger the absolute value of the differential component value is, thereby improving the followability to the temperature change. As a result, when the temperature ripple is likely to increase when the paper interval time T is long, the absolute value of the differential component value is increased to increase the sensitivity to the temperature change, thereby suppressing the temperature ripple. If the temperature ripple is difficult to increase, such as when the time is short, the absolute value of the differential component value can be reduced to reduce the sensitivity to temperature changes and to suppress flicker. . As a result, compared with the case where the differential component value is uniformly determined according to the temperature change amount, a balance between reduction of temperature ripple during continuous printing and suppression of flicker is achieved.

Further, in the printer 100 of the present embodiment, the control value Y may be calculated by the above-described equation (1) (the following reprint), and the amount of power supplied to the heater 810 may be controlled using the control value Y.
Y = (set temperature−detected temperature) × Kp−temperature change × Kd (1)
If the differential gain Kd in the equation (1) is set to a larger value as the paper interval time T is longer, the absolute value of the differential component value is increased as the paper interval time T is longer if the temperature variation is the same. .

  Furthermore, the printer 100 according to the present embodiment includes a small-size single-sided mode as the sheet S conveyance mode. When the small-size single-sided mode is selected, the differential gain Kd is greater than when the standard single-sided mode is selected. You may make it bigger. The inter-paper time T1 in the small size single-sided mode is longer than the inter-paper time T0 in the standard single-sided mode. By estimating the sheet interval time according to the sheet type, the calculation load can be reduced as compared with the case where the sheet interval time is calculated every time.

  Furthermore, the printer 100 of this embodiment includes an intermittent single-sided mode as the sheet S conveyance mode, and when the intermittent single-sided mode is selected, the differential gain Kd is made larger than when the regular single-sided mode is selected. It is good. The paper interval time T2 in the intermittent single-sided mode is longer than the paper interval time T0 in the regular single-sided mode. By estimating the paper interval time according to the operation mode, the calculation load can be reduced as compared with the case where the paper interval time is calculated every time.

  Furthermore, the printer 100 according to the present embodiment includes a regular double-side mode as the sheet S conveyance mode. When the regular double-side mode is selected, the differential gain Kd is increased as compared with the case where the regular single-side mode is selected. It is good. The sheet interval time T3 in the regular double-sided mode is longer than the sheet interval time T0 in the regular single-sided mode. By estimating the sheet interval time by duplex printing, the calculation load can be reduced as compared with the case of calculating the sheet interval time each time.

  Further, the printer 100 according to the present embodiment may actually measure the time between sheets based on the output signal of the sheet sensor 71. That is, the printer 100 determines that the sheet interval time during the continuous conveyance of the sheet changes from the time when the output signal of the sheet sensor 71 changes from the signal indicating the presence of the sheet S to the signal indicating the absence of the sheet S. The time from when the signal indicating the absence of the sheet S changes to the signal indicating the presence may be used. A more appropriate control value can be determined if the measured value is the sheet interval time.

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

  Furthermore, the printer 100 according to the present embodiment can switch the duty ratio D of the power supplied to the heater 810 to a larger value as the control value Y is larger, based on the control value Y calculated by the above-described equation (1). Good. By switching the duty ratio D, the amount of power supplied to the heater 810 is appropriately switched.

  In addition, this Embodiment is only a mere illustration and does not limit this invention at all. Therefore, the present invention can be variously improved and modified without departing from the scope of the invention. For example, the present invention is not limited to a printer, and can be applied to any apparatus having an image forming function using an electrophotographic method, such as a multifunction machine, a copier, and a FAX apparatus. Further, the present invention can be applied not only to a monochrome printer but also to a color printer.

  In the embodiment, the pressure roller 82 is on the driving side as the fixing unit 8, but the heating member 81 side may be on the driving side. In addition, the printer 100 is not limited to the printer 100 capable of duplex printing, and may be an apparatus dedicated to single-sided printing. In that case, the regular duplex mode is not included in the transport mode. That is, the transport modes are 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 conveyance modes having different sheet-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 power supplied to the heater 810 is not limited to the wave number control described in the embodiment. For example, phase control that 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.

  In the embodiment, the PD control is performed as the temperature control of the heater 810. However, the PID control may further include an integral component. Further, although the proportional gain Kp is a fixed value, it may be a variable value.

  For example, the initial value of the inter-paper time T is determined based on the transport mode, but may be a fixed value. That is, the initial value of the differential gain Kd may be a fixed value that does not depend on the transport mode, and the differential gain Kd may be changed based on the measured value of the inter-sheet 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 performed from the beginning.

  For example, the actual measurement of the paper interval time T may not be performed. That is, the differential gain Kd determined based on the conveyance mode may be used until the end of printing. In this case, S131, S132, S141, S142, and S143 of the temperature control process are unnecessary. However, more precise control is possible by performing control based on actual measurement values.

  In the case of double-sided printing, the set temperature is lowered in at least a part of the time between sheets, but it is not necessary to lower it. However, it is preferable that the temperature ripple can be further reduced by lowering the set temperature. Further, the period during which the set temperature is lowered is a predetermined period from the start of the inter-paper time T to the end of the inter-paper time T, but is not limited thereto.

  The processing disclosed in the embodiments 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 modes such as a recording medium or a method in which a program for executing the process is recorded.

5 Process Unit 8 Fixing Unit 11 Paper Tray 13 Sheet Transport Path 21 Pickup Roller 31 CPU
71 Sheet sensor 81 Heating member 810 Heater 811 Temperature sensor 82 Pressure roller 100 Printer

Claims (10)

A heater,
A first rotating body heated by the heater;
A second rotating body that forms a fixing nip with the first rotating body;
A temperature sensor that outputs different signals according to the surface temperature of the first rotating body;
A control unit;
With
The controller is
A detection process for detecting a surface temperature of the first rotating body based on a signal from the temperature sensor;
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 conveyance of the sheet A control value determining process for determining a control value using a second value based on the time between papers;
Using the control value determined in the control value determination process, a power determination process for determining the amount of power supplied to the heater;
Run
The absolute value of the second value is such that when the change amount is a predetermined value and the inter-sheet time is the first time, the change amount is the predetermined value and the inter-paper time is the first time. Larger than in the case of the second time shorter than,
An image forming apparatus. The image forming apparatus according to claim 1,
The controller is
In the control value determination process, the following expressions (1) to (3) are satisfied:
(1) The control value = the first value−the second value (2) The first value = (set temperature of the first rotating body−surface temperature of the first rotating body) × proportional gain (3 ) The second value = the amount of change × the differential gain The value of the differential gain is larger when the paper interval time is the first time than when the paper interval time is the second time. ,
An image forming apparatus. The image forming apparatus according to claim 1 or 2,
An accommodating portion for accommodating the sheet;
A sheet conveyance path;
A carry-in unit for carrying the sheets stored in the storage unit one by one into the conveyance path;
With
When the type of the sheet stored in the storage unit is the first type or the second type whose length in the transport direction is shorter than the first type, the control unit continuously conveys the sheet. The loading start interval by the loading unit at the time is set to the first time interval,
When the sheet type is the second type sheet, the inter-paper time is the first time,
When the sheet type is the first type sheet, the inter-paper time is the second time.
An image forming apparatus. The image forming apparatus according to claim 1 or 2,
An accommodating portion for accommodating the sheet;
A sheet conveyance path;
A carry-in unit for carrying the sheets stored in the storage unit one by one into the conveyance path;
With
The control unit is configured to operate the carry-in unit with a carry-in start interval by the carry-in unit during continuous conveyance of sheets as a first time interval, and the carry-in start interval is shorter than the first time interval. A second mode in which the carry-in unit is operated as a second time interval, and
When the carry-in unit is operating in the first mode, the inter-paper time is the first time,
When the carry-in unit is operating in the second mode, the inter-paper time is the second time.
An image forming apparatus. The image forming apparatus according to claim 1 or 2,
In the case of duplex printing, the inter-paper time is the first time,
In the case of single-sided printing, the inter-paper time is the second time.
An image forming apparatus. The image forming apparatus according to claim 1 or 2,
A sheet conveyance path;
A sheet sensor that outputs different signals depending on the presence or absence of a sheet at a predetermined position in the conveyance path;
With
The time from the timing at which the sheet sensor detects presence / absence of a sheet to the timing at which presence / absence of a sheet is detected is the time between sheets.
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 6,
The controller is
In at least part of the first period during which the sheet does not pass through the fixing nip portion, the set temperature of the first rotating body is compared with the second period during which the sheet passes through the fixing nip portion. And make it smaller,
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 7,
The controller is
In the power determination process,
Using the control value determined in the control value determination process, a duty ratio that is a ratio of energized states within a predetermined period is determined, and the duty ratio to be further determined is determined in the control value determination process The larger the control value is, the larger
An image forming apparatus. A heater,
A first rotating body heated by the heater;
A second rotating body that forms a fixing nip with the first rotating body;
A temperature sensor that outputs different signals according to the surface temperature of the first rotating body;
An image forming apparatus control method comprising:
A detection step of detecting a surface temperature of the first rotating body based on a signal of the temperature sensor;
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 conveyance of the sheet A control value determination step for determining a control value using a second value based on a time between sheets, wherein the absolute value of the second value is a predetermined value when the amount of change is a predetermined value When the time is the first time, the control value determining step is larger than the case where the change amount is the predetermined value and the inter-paper time is a second time shorter than the first time. ,
Using the control value determined in the control value determining step, determining the amount of power to be supplied to the heater; and
A control method for an image forming apparatus. A heater,
A first rotating body heated by the heater;
A second rotating body that forms a fixing nip with the first rotating body;
A temperature sensor that outputs different signals according to the surface temperature of the first rotating body;
An image forming apparatus comprising:
A detection process for detecting a surface temperature of the first rotating body based on a signal from the temperature sensor;
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 conveyance of the sheet A control value determination process for determining a control value using a second value based on a time interval between sheets, wherein the absolute value of the second value is a predetermined value when the change amount is a predetermined value. When the time is the first time, the control value determination process is larger than the case where the amount of change is the predetermined value and the time between sheets is a second time shorter than the first time. ,
Using the control value determined in the control value determination process, a power determination process for determining the amount of power supplied to the heater;
A program characterized by having executed.

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