JP2019174545A - Fixing device and image forming apparatus - Google Patents

Abstract

To stabilize a surface temperature of a heating member to prevent fixing failure.SOLUTION: A fixing device 13 comprises: a fixing roller 20 that heats a toner image formed on a sheet; a pressure roller 21 that is pressed against the fixing roller 20 and applies pressure to the sheet passing through between the fixing roller 20 and the pressure roller; and a heat source 22 that heats the fixing roller 20. The heat source 22 includes a main heater 31 that is provided at the center in a width direction orthogonal to a conveyance direction of the sheet, and sub heaters 32 that are provided at the ends in the width direction of the sheet. A control unit 15 of the fixing device 13 performs feedback control of the power of the main heater 31 and sub heaters 32 on the basis of a result of detection of the surface temperature of the fixing roller 20, and increases a second duty ratio of the power supplied to the sub heaters 32 by a predetermined correction amount during a period from when the leading end of the sheet reaches the fixing roller 20 and a predetermined standby period elapses until when the rear end of the sheet passes through the fixing roller 20.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet, and an image forming apparatus including the fixing device.

  The image forming apparatus includes a fixing device that fixes a toner image formed on a sheet. The fixing device includes a heating member that heats the toner image and a pressure member that pressurizes the toner image against the paper. The fixing device detects the surface temperature of the heating member and feedback-controls the heating of the heating member so that the surface temperature becomes the target temperature. The heat source for heating the heating member includes, for example, a plurality of heating bodies.

  For example, in the image forming apparatus disclosed in Patent Document 1, a fixing roller that fixes a toner image on a sheet, a first heater that generates heat at one end in the axial direction of the fixing roller, and a heat generation at the other end. Has a second heater larger than one end. Then, the temperature gradient value in the axial direction of the fixing roller generated by turning on the first heater, turning on the second heater, and turning off both the first heater and the second heater is obtained, and the heater that reduces the temperature gradient value is obtained. Turn on with priority.

JP 2017-111253 A

  In the fixing device, when the sheet contacts the heating member when passing through the heating member, the heat of the heating member is taken away by the sheet, so that the surface temperature of the heating member decreases. When the surface temperature of the heating member decreases, the toner image cannot be sufficiently heated and fixing failure occurs. Therefore, the heat source is set so that the surface temperature of the heating member becomes the target temperature while the paper passes through the heating member. The heating of the heating member is controlled. For example, some conventional fixing devices perform feedback control based on the detection result of the surface temperature of the heating member so as to increase the surface temperature of the heating member when the surface temperature of the heating member decreases.

  However, image forming apparatuses tend to increase the linear speed (conveyance speed) of paper conveyance as performance increases. For this reason, in the fixing device, if the feedback control of the heating member is performed on the paper conveyed at high speed, it cannot react immediately to the decrease in the surface temperature, and the fixing process is performed around the target temperature on the front end side of the paper On the other hand, on the rear end side of the paper, there is a risk that fixing will occur due to the fixing process being performed with the surface temperature lowered.

  In contrast, when the sensitivity of feedback control is set well, for example, when a change in the surface temperature in a short time interval is detected, the duty ratio of the power supplied to the heat source is controlled, so that the duty is quickly reduced when the surface temperature decreases. The surface temperature can be increased by increasing the ratio. However, in this case, even when the surface temperature rises, the duty ratio is immediately lowered to lower the surface temperature.

  Alternatively, by setting the target temperature higher, the surface temperature can be increased over the entire period during which the paper passes through the heating member, regardless of the contact between the paper and the heating member. However, in this case, since the leading edge of the sheet comes into contact with the heating member before the surface temperature of the heating member is lowered, the toner image on the leading edge side of the sheet is excessively heated, which may cause a fixing failure.

  In view of the above circumstances, an object of the present invention is to stabilize the surface temperature of a heating member and suppress fixing failure.

  The fixing device according to the present invention includes a heating member that heats a toner image formed on a sheet, a pressure member that pressurizes the sheet that is pressed against the heating member and passes between the heating member, A heat source for heating the heating member, wherein the heat source is provided at the center in the width direction perpendicular to the paper transport direction, and the second heating body is provided at the end in the width direction. And the feedback of the electric power for heating the first heating body and the second heating body based on the detection result of the surface temperature of the heating member, while the leading edge of the paper reaches the heating member The duty ratio of the power supplied to the second heating body is increased by a predetermined correction amount after the predetermined standby period has elapsed until the trailing edge of the sheet passes through the heating member. Characterized by

  The fixing device described above sets at least one of the standby period and the correction amount based on at least one of the linear speed and type of the paper.

  The fixing device described above sets at least one of the standby period and the correction amount based on at least one of the surface temperature and the environmental temperature of the heating member.

  The image forming apparatus of the present invention includes the above-described fixing device.

  According to the present invention, it is possible to stabilize the surface temperature of the heating member and suppress fixing failure.

1 is a cross-sectional view illustrating a printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. 1 is a side view showing a fixing device according to an embodiment of the present invention. 6 is a graph illustrating an example of a driving current of a heat source in the fixing device according to the embodiment of the present invention. 1 is a block diagram illustrating an electrical configuration of a fixing device according to an embodiment of the present invention. 6 is a flowchart showing an operation of fixing processing in the fixing device according to the embodiment of the present invention. In the fixing device according to an embodiment of the present invention, it is a schematic diagram showing a state where the leading edge of the paper has reached the fixing roller. FIG. 4 is a schematic diagram illustrating a state in which a sheet is passing through a fixing roller in the fixing device according to the embodiment of the present disclosure. In the fixing device according to an embodiment of the present invention, it is a schematic diagram showing a state where the trailing edge of the paper has passed the fixing roller. 6 is a graph illustrating an example of ideal heating control of a fixing roller in a fixing device. 6 is a graph illustrating an example of heating control of a fixing roller in a fixing device according to an embodiment of the present invention.

  First, the overall configuration of a printer 1 (image forming apparatus) according to an embodiment of the present invention will be described with reference to FIG. Hereinafter, for convenience of explanation, the front side of the sheet in FIG. Arrows L, R, U, Lo, Fr, and Rr appropriately attached to the drawings indicate the left side, right side, upper side, lower side, front side, and rear side of the printer 1, respectively.

  The printer 1 includes a substantially box-shaped printer main body 2, a paper feed cassette 3 for storing paper is provided in the lower part of the printer main body 2, and a paper discharge tray 4 is provided in the upper part of the printer main body 2. In FIG. 1, one paper feed cassette 3 is shown, but the printer 1 can be of different sizes (for example, A4 size, A3 size, etc.) or different types (plain paper, cardboard, thin paper, postcard, envelope, etc.). A plurality of paper feed cassettes 3 may be provided so as to accommodate paper.

  An exposure device 5 composed of a laser scanning unit (LSU) is disposed below the paper discharge tray 4 in the upper part of the printer main body 2. An image forming unit 6 is provided below the exposure device 5 in the printer main body 2. The image forming unit 6 is rotatably provided with a photosensitive drum 7 as an image carrier. Around the photosensitive drum 7, a charging device, a developing device connected to a toner container, a transfer roller, A cleaning device is arranged along the rotation direction of the photosensitive drum 7.

  In addition, a paper conveyance path 10 is provided inside the printer main body 2. A paper feeding unit 11 is provided in the vicinity of the paper feeding cassette 3 at the upstream end of the conveyance path 10, and a transfer unit 12 including a photosensitive drum 7 and a transfer roller is provided in the middle part of the conveyance path 10. A fixing device 13 is provided in the downstream portion of the transport path 10, and a paper discharge unit 14 is provided in the vicinity of the paper discharge tray 4 at the downstream end of the transport path 10. In addition, a control device 15 that controls the fixing device 13 is provided inside the printer body 2.

  Next, an image forming operation of the printer 1 will be described. The printer 1 starts an image forming operation when image data is input from an external computer or the like and an instruction to start printing is given. At this time, the size and type of paper to be printed are specified. In the image forming operation, first, the surface of the photosensitive drum 7 is charged by the charging device of the image forming unit 6, and then exposure corresponding to image data is performed on the photosensitive drum 7 by the laser light from the exposure device 5. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 7. Next, the developing device of the image forming unit 6 develops the electrostatic latent image into a toner image using toner.

  On the other hand, of the sheets stored in the sheet feeding cassette 3, a sheet of a specified size and type is taken out by the sheet feeding unit 11 and conveyed on the conveying path 10. The sheet on the conveyance path 10 is conveyed to the transfer unit 12 at a predetermined timing, and the toner image on the photosensitive drum 7 is transferred to the sheet by the transfer unit 12. The sheet on which the toner image has been transferred is conveyed to the fixing device 13 and the toner image is fixed on the sheet by the fixing device 13. The paper on which the toner image is fixed is discharged from the paper discharge unit 14 to the paper discharge tray 4.

  Next, the configuration of the fixing device 13 will be described with reference to FIGS. As shown in FIG. 2, the fixing device 13 includes a fixing roller 20 (heating member), a pressure roller 21 (pressure member), a heat source 22, a heater drive circuit 23, a first temperature sensor 24, A two-temperature sensor 25, a first sheet sensor 26, a second sheet sensor 27, and an environmental temperature sensor 28 are provided.

  The fixing roller 20 and the pressure roller 21 are respectively arranged on the upper side and the lower side of the substantially box-shaped fixing frame (not shown) with the conveyance path 10 interposed therebetween, and are arranged so as to face and contact each other. The The fixing frame is attached to the printer main body 2 so that the transport path 10 penetrates the fixing frame in the paper transport direction (left-right direction). A pressure region N is formed between the fixing roller 20 and the pressure roller 21 in the transport path 10.

  Note that the pressure region N is a region where the fixing roller 20 and the pressure roller 21 are in contact with each other, and the upstream side in the transport direction in which the pressure on the paper by the fixing roller 20 and the pressure roller 21 is 0 Pa. The region from the position to the downstream position in the conveyance direction where the pressure becomes 0 Pa again is shown through the position in the conveyance direction where the pressure is maximum.

  The fixing roller 20 is configured by a cylindrical roller that is long in the width direction (front-rear direction) of the sheet orthogonal to (crossing) the transport direction. The fixing roller 20 is composed of, for example, a cylindrical metal core material and an elastic layer made of resin such as silicon rubber provided around the core material, and the elastic layer is covered with a release layer of fluororesin. The The fixing roller 20 is rotatably attached to the fixing frame with the front-rear direction as the rotation axis direction, and rotates following the rotation of the pressure roller 21. The fixing roller 20 is heated by the heat source 22 and contacts the paper on which the toner image is formed to heat the toner image. In this embodiment, an example in which the heating member is configured by the fixing roller 20 will be described, but the heating member may be configured by a belt.

  The pressure roller 21 is formed in a substantially cylindrical shape that is long in the width direction. The pressure roller 21 is composed of, for example, a cylindrical metal core material and an elastic layer made of resin such as silicon rubber provided around the core material, and the elastic layer is covered with a release layer of a fluororesin. Is done. The pressure roller 21 is rotatably attached to the fixing frame with the front-rear direction as the rotation axis direction. For example, a driving gear (not shown) is attached to the rear end of the pressure roller 21, and the pressure roller 21 is connected to a driving source 29 (see FIG. 5) such as a motor via the driving gear. It is rotated by the rotational driving force transmitted from. The pressure roller 21 is pressurized toward the fixing roller 20, and pressurizes the paper passing through the pressure region N together with the fixing roller 20.

  The heat source 22 has a long shape in the width direction, is attached to the inside of the fixing roller 20, and heats the fixing roller 20 from the inside. Alternatively, the heat source 22 may be provided outside the fixing roller 20 and configured to heat the fixing roller 20 from the outside. Heating of the heat source 22 is controlled by the control device 15 by feedback control described later.

  As shown in FIG. 3, the heat source 22 includes a main heater 31 (first heating body) provided in the center in the width direction and two sub-heaters 32 (second heaters) provided on both ends of the main heater 31 in the width direction. Heating body). The main heater 31 and the sub heater 32 may be constituted by, for example, a halogen heater or a ceramic heater, or may be constituted by an IH unit. Note that each of the main heater 31 and each sub-heater 32 may be composed of one heater, but may be composed of two or more heaters.

  For example, when the sheet is passed with respect to the center in the width direction of the fixing roller 20, the main heater 31 is arranged in a central heating area corresponding to the sheet width of a relatively small size (for example, A4 vertical size) and is a sub heater. No. 32 is arranged in the end heating area corresponding to both ends of the center heating area within the range of the relatively large size (for example, A3 vertical size) paper width. The main heater 31 and the sub heater 32 are connected to the power source 33 via the heater driving circuit 23, and are lit by the power supplied from the power source 33 to generate heat. In the width direction, the central heating region and end heating of the fixing roller 20 are heated. Each area is heated.

  The heater drive circuit 23 is connected between the main heater 31 and the sub heater 32 and the power source 33, and is also connected to the control device 15. The heater drive circuit 23 is controlled by the control device 15 to control the power supplied from the power source 33 to the main heater 31 and the sub heater 32. Specifically, in the heater drive circuit 23, the lighting device duty ratio of the main heater 31 and the sub heater 32 in a predetermined cycle is set by the control device 15. The heater drive circuit 23 controls power supply so that the main heater 31 and the sub heater 32 are lit at a set duty ratio. In the heating state from when the main heater 31 or the sub heater 32 starts heating to when it stops, the amount of heat of the main heater 31 and the sub heater 32 depends on the lighting frequency in a predetermined cycle.

  For example, as shown in FIG. 4, the heater drive circuit 23 outputs a drive current having a predetermined frequency (for example, 50 Hz) based on the set duty ratio. This drive current has a pulse with a predetermined pulse width (for example, 20 msec) for a predetermined number of times (for example, 20 times) during a predetermined period (for example, 400 msec), and a duty ratio with respect to the predetermined period. The ratio of the period during which the pulse is turned on. For example, when the duty ratio is set to 5% for a drive current having 20 pulses during a 400 msec period, one pulse (indicated by hatching in FIG. 4) is set to ON. In FIG. 4, the pulse at the first position in one cycle is set to ON, but the position at which the pulse is turned on is not limited to the first position.

  While the drive current pulse is on, the main heater 31 and the sub heater 32 are turned on by energizing the power source 33, and while the drive current pulse is off, the main heater 31 and the sub heater 32 are not energized with the power source 33. Turns off. Different first duty ratio and second duty ratio are set for the main heater 31 and the sub heater 32, respectively, and the heater drive circuit 23 generates different drive currents for the main heater 31 and the sub heater 32, respectively. In other words, the first duty ratio and the second duty ratio are duty ratios of power supplied to the main heater 31 and the sub heater 32, respectively. When the first duty ratio and the second duty ratio are made to correspond to the drive current, the timing for turning on the pulse is adjusted so that the main heater 31 and the sub heater 32 do not turn on at the same time and flicker does not occur.

  Note that the heating of the heat source 22 is feedback-controlled by feedback control of the first duty ratio for lighting the main heater 31 and the second duty ratio for lighting the sub-heater 32 by the control device 15. In this feedback control, the second duty ratio is further adjusted according to various fixing conditions (for example, the linear speed (conveying speed) of the paper, the type of the paper, the surface temperature of the fixing roller 20, the environmental temperature, etc.). . The feedback control will be described later.

  The first temperature sensor 24 is configured by a temperature sensor such as a thermistor, and is provided in a non-contact manner with respect to the fixing roller 20 outside the fixing roller 20. The first temperature sensor 24 is disposed opposite to the surface of the fixing roller 20 at a position corresponding to the central heating area at the center in the width direction (for example, a position corresponding to the paper passing area). Detect the center surface temperature.

  The second temperature sensor 25 includes a temperature sensor such as a thermistor and is provided outside the fixing roller 20 and in contact with the surface of the fixing roller 20. The second temperature sensor 25 is disposed opposite to the surface of the fixing roller 20 at a position corresponding to the end heating area (for example, a position corresponding to the non-sheet passing area) at least on one end side in the width direction. The surface temperature at one end in the width direction of 20 is detected.

  The first paper sensor 26 is a sensor that detects the arrival of the leading edge of the paper transported along the transport path 10 to the fixing roller 20 (arrival to the pressurizing region N). Provided near the paper entrance of the frame. The first paper sensor 26 is configured to detect a paper physically or optically, for example. Based on the detection result of the first sheet sensor 26, the time point when the leading edge of the sheet reaches the fixing roller 20, that is, the fixing start point is measured. Alternatively, the first paper sensor 26 is provided along the transport path 10 at a position upstream of the fixing device 13 in the transport direction, and a paper detection position (distance to the fixing roller 20) by the first paper sensor 26, the paper Based on the detection time and the linear velocity of the paper, the time when the leading edge of the paper reaches the fixing roller 20 may be measured in advance before the arrival.

  The second paper sensor 27 is a sensor that detects the passage of the trailing edge of the paper transported through the transport path 10 from the fixing roller 20 (passing from the pressure region N). Provided near the paper exit of the fixing frame. For example, the second paper sensor 27 is configured to detect a paper physically or optically. Based on the detection result of the second paper sensor 27, the passing time from the fixing roller 20 at the trailing edge of the paper, that is, the fixing end time is measured. Alternatively, the second paper sensor 27 is not provided, and based on the time when the leading edge of the paper reaches the fixing roller 20, the length of the pressure area N and the linear velocity of the paper, The passing time point may be measured in advance before passing.

  The environmental temperature sensor 28 is attached to the outside of the fixing frame, and detects the temperature outside the fixing device 13 as the environmental temperature of the fixing device 13. Alternatively, when the printer 1 includes an internal temperature sensor that detects the temperature outside the fixing device 13 inside the printer body 2, the fixing device 13 does not provide the environmental temperature sensor 28, and the detection result of the internal temperature sensor is the environment. It may be applied as a temperature.

  Next, the electrical configuration of the control device 15 that controls the fixing device 13 will be described with reference to FIG. The control device 15 is composed of a CPU or the like, and is connected to a storage device 16 such as a ROM or a RAM. In addition, as the control device 15 and the storage device 16, a main control device and a main storage device that collectively control each unit of the printer 1 may be applied.

  The control device 15 controls each unit connected to the control device 15 based on a control program and control data stored in the storage device 16. For example, the control device 15 is connected to the heat source 22, the heater drive circuit 23, the first temperature sensor 24, the second temperature sensor 25, the first paper sensor 26, the drive source 29, the power source 33, and the like. The control device 15 controls the fixing process of the fixing device 13 and particularly controls the heating of the heat source 22.

  The storage device 16 stores an adjustment table used for adjusting the second duty ratio of the sub heater 32. For example, the adjustment of the second duty ratio is started after a predetermined standby period elapses after the leading edge of the sheet reaches the fixing roller 20, and standby periods corresponding to various fixing conditions are stored in the adjustment table. The Further, the second duty ratio is adjusted to increase from a value set by feedback control, and correction amounts corresponding to various fixing conditions are stored in the adjustment table.

  For example, the standby period stored in the adjustment table is set to be shorter as the fixing condition is such that the heat of the fixing roller 20 is easily removed, for example, the linear speed of the paper is higher. Note that the standby period is set shorter than the sheet passing time in the fixing roller 20. Further, the correction amount stored in the adjustment table is, as the fixing condition, the heat of the fixing roller 20 is easily deprived, for example, the faster the linear speed of the paper is, and the lower the surface temperature of the fixing roller 20 is, Many are set. Further, the lower the environmental temperature as the fixing condition, the larger the correction amount is set. For example, when the environmental temperature is lower than a predetermined threshold, a predetermined constant is added to the correction amount.

  Next, the fixing processing operation of the fixing device 13 will be described with reference to FIG. First, when an image forming operation is started in the printer 1, the control device 15 of the fixing device 13 operates the driving source 29 to rotate the pressure roller 21 and the fixing roller 20 before the sheet is conveyed to the fixing device 13. Is started (step S1). At this time, the control device 15 controls the rotational driving force of the drive source 29 so that the sheet is conveyed at a preset linear speed (conveyance speed).

  The control device 15 operates the heater drive circuit 23 to start heating the main heater 31 and the sub heater 32 of the heat source 22 (step S2). At this time, the control device 15 monitors the surface temperature of the fixing roller 20 with the first temperature sensor 24 and the second temperature sensor 25, and the first duty of the main heater 31 is set so that the surface temperature becomes a predetermined target temperature. The heater driving circuit 23 is controlled by setting the ratio and the second duty ratio of the sub heater 32.

  The feedback control (step S3) of the first duty ratio will be described. For example, the control device 15 performs feedback control of the first duty ratio by the following PID control using the first detected temperature that is the detection result of the first temperature sensor 24.

First, the control unit 15, a deviation _{E n} of the first detection temperature _{T n} of the current with respect to the target temperature T, is calculated by a formula _E n = _{T-T n,} the first detection temperature of the last with respect to the target temperature T _{T n- 1} of the deviation _{E n-1,} is calculated by a formula _{E n-1 = T-T} n-1.

Further, the control device 15 uses the current deviation E _n , the previous deviation E _n−1 , and the previous deviation E _n−2 to change the current first duty ratio change difference ΔMV _n [%] into the equation ΔMV. _n = Kp × (E _n −E _n−1 ) + K i × E _n + Kd × {(E _n −E _n−1 ) − (E _n−1 −E _n−2 )} Here, for example, the coefficient Kp is 2.0, the coefficient Ki is 0.05, and the coefficient Kd is 0.1. Note that the change difference ΔMV _n is calculated to the first decimal place, and that value is also used in the next calculation.

Then, the control device 15 uses the current first duty ratio I _n [%] as the current first duty ratio change difference ΔMV _n and the previous first duty ratio I _n−1 [%]. Calculated by the formula I _n = I _n-1 + ΔMV _n . However, when setting the first duty ratio to the heater drive circuit 23 as the lighting pattern of the main heater 31, the control device 15 rounds off less than 5% from the calculation result (for example, 4.5% is set to 0%, 26. 8% is set as 25%, and 98.7% is set as 95%).

  The second duty ratio feedback control (step S4) will be described. For example, the control device 15 performs feedback control of the second duty ratio using the second detected temperature that is the detection result of the second temperature sensor 25 as follows.

  First, the control device 15 determines the relationship between the second duty ratio corresponding to various combinations of the temperature difference between the target temperature and the second detected temperature (target temperature−second detected temperature) and the first duty ratio of the main heater 31. A second duty ratio table is stored in the storage device 16 in advance. In the second duty ratio table, the second duty ratio is set so that the sum of the second duty ratio and the first duty ratio does not exceed 100%. Thereby, the drive current of the main heater 31 and the sub heater 32 can be generated so that the pulses are not turned on at the same time, and flicker caused by simultaneous lighting of the main heater 31 and the sub heater 32 is suppressed.

  Then, the control device 15 calculates the current temperature difference between the target temperature and the current second detected temperature, and this time corresponding to the combination of the current temperature difference and the current first duty ratio calculated as described above. Are read from the second duty ratio table.

  The control device 15 performs the feedback control of the heating of the fixing roller 20 as described above while the sheet passes through the fixing roller 20 in the fixing process.

  The controller 15 uses the first paper sensor 26 to detect whether or not the leading edge of the paper has reached the fixing roller 20 (step S5). For example, the control device 15 uses the first paper sensor 26 to measure the time when the leading edge of the paper reaches the fixing roller 20 and monitors whether or not the current time has reached the arrival time. When the current time reaches the arrival point, the arrival of the leading edge of the sheet to the fixing roller 20 is detected (step S5: YES).

  As shown in FIG. 7A, when the leading edge of the paper reaches the fixing roller 20 (step S5: YES), the control device 15 fixes the current fixing device 13 in order to adjust the second duty ratio of the sub heater 32. A condition is acquired (step S6). For example, the control device 15 acquires a preset linear velocity, acquires a sheet type based on the print setting, acquires a surface temperature of the fixing roller 20 based on a detection result of the second temperature sensor 25, The environmental temperature is acquired based on the detection result of the environmental temperature sensor 28. Then, the control device 15 reads the standby period and the correction amount corresponding to the acquired fixing condition from the adjustment table of the storage device 16.

  The control device 15 determines whether or not a standby period has elapsed since the leading edge of the sheet reached the fixing roller 20 (step S7). For example, the control device 15 adds a waiting period to the time when the leading edge of the paper reaches the fixing roller 20, calculates the adjustment start time for starting the adjustment of the second duty ratio, and sets the current time as the adjustment start time. Monitor whether it has been reached. Then, when the current time reaches the adjustment start time, the control device 15 detects the elapse of the standby period (step S7: YES), and sets the correction amount to the second duty ratio of the sub heater 32 calculated by the feedback control. The adjustment duty ratio is calculated by addition, and set in the heater drive circuit 23 (step S8). As shown in FIG. 7B, the adjustment of the second duty ratio is continued during the adjustment period in which the sheet is passing the fixing roller 20 after the standby period has elapsed.

  The control device 15 uses the second paper sensor 27 to detect whether or not the paper passes from the fixing roller 20 at the rear end of the paper (step S9). For example, the control device 15 uses the second paper sensor 27 or the first paper sensor 26 to measure the passing time from the fixing roller 20 at the trailing edge of the paper, and determines whether or not the current time has reached the passing time. Monitor. Then, when the current time reaches the passage time point, the control device 15 detects the passage of the rear end of the sheet from the fixing roller 20 (step S9: YES), as shown in FIG. The adjustment of the 2 duty ratio is finished (step S10).

  According to the present embodiment, as described above, the fixing device 13 of the printer 1 (image forming apparatus) has a fixing roller 20 (heating member) that heats the toner image formed on the paper and the fixing roller 20. A pressure roller 21 (pressure member) that pressurizes the paper that is pressurized and passes between the fixing roller 20 and a heat source 22 that heats the fixing roller 20 are provided. The heat source 22 includes a main heater 31 (first heating body) provided in the center in the width direction orthogonal to the sheet conveyance direction, a sub-heater 32 (second heating body) provided at an end in the sheet width direction, Is provided. The control device 15 of the fixing device 13 feedback-controls the power for heating the main heater 31 and the sub heater 32 based on the detection result of the surface temperature of the fixing roller 20, while the leading edge of the paper reaches the fixing roller 20. After the predetermined waiting period elapses, the second duty ratio of the power supplied to the sub heater 32 is increased by a predetermined correction amount until the trailing edge of the sheet passes through the fixing roller 20.

  Incidentally, in the fixing device 13, as shown in FIG. 8, the surface temperature detection result of the fixing roller 20 by the first temperature sensor 24 and the second temperature sensor 25 regardless of the passage (contact) of the paper in the fixing roller 20 ( Ideally, the detected temperature is stable near the target temperature. However, in the conventional fixing device 13, when the sheet passes (contacts) with the fixing roller 20, the fixing roller 20 is taken away by the sheet, and the surface temperature of the fixing roller 20 is lowered as indicated by a dashed line in FIG. 9. Sometimes. At this time, if the surface temperature is equal to or higher than a predetermined lower limit temperature, the fixing process can be performed without causing a fixing failure (fixing is OK). However, if the surface temperature is lower than the lower limit temperature, a fixing failure occurs (fixing is NG). )

  Note that the rate of contribution of feedback control of heating of the heat source 22 is low, such as when the linear speed of the paper is slow, when the paper is of a type that is difficult to remove heat, when the surface temperature is set high, or when the environmental temperature is high. When is high, the surface temperature can be maintained near the target temperature by feedback control based on the detected temperature. However, the contribution rate of the feedback control of the heating of the heat source 22, such as when the linear speed of the paper is high, when the paper is a type that easily takes heat, when the surface temperature is set low, when the environmental temperature is low, etc. When the temperature is low, the feedback control based on the detected temperature is delayed and not in time, and the possibility that the surface temperature falls below the lower limit temperature increases.

  On the other hand, in the fixing device 13 of the present embodiment, the sub-heater 32 that heats the fixing roller 20 even if the surface temperature of the fixing roller 20 rapidly decreases and the feedback control of the heating of the fixing roller 20 is delayed. The second duty ratio is increased. Therefore, as shown by a solid line in FIG. 9, the fixing roller 20 can be sufficiently heated to obtain a surface temperature close to the target temperature, regardless of the delay of the feedback control. Therefore, since the surface temperature of the fixing roller 20 is stabilized, the fixing process is not performed in a state where the surface temperature is lowered, and fixing failure can be suppressed and image failure can be suppressed. Further, since the feedback control is maintained without adjusting the first duty ratio of the main heater 31, the behavior of the surface temperature of the fixing roller 20 can be stabilized.

  Since the time when the leading edge of the paper reaches the fixing roller 20 is determined, the time when the surface of the fixing roller 20 suddenly decreases due to the contact of the paper with the fixing roller 20, and the surface temperature decreases. Can react immediately. Further, since the passage of the trailing edge of the sheet from the fixing roller 20 is determined, it is possible to grasp the period during which the surface temperature of the fixing roller 20 decreases.

  Further, the control device 15 sets at least one of the standby period and the correction amount based on at least one of the linear velocity and type of the paper. As a result, the second duty ratio of the sub-heater 32 starts to increase appropriately in response to the time when the surface temperature of the fixing roller 20 decreases, regardless of the linear speed and type of the paper, and the surface of the fixing roller 20 The second duty ratio of the sub-heater 32 can be increased appropriately corresponding to the temperature decreasing tendency.

  Further, the control device 15 sets at least one of the standby period and the correction amount based on at least one of the surface temperature of the fixing roller 20 and the environmental temperature. As a result, regardless of the surface temperature of the fixing roller 20 or the environmental temperature, the second duty ratio of the sub-heater 32 starts to increase appropriately in response to the time when the surface temperature of the fixing roller 20 decreases. The second duty ratio of the sub-heater 32 can be increased appropriately corresponding to the tendency of the 20 surface temperature to decrease.

  In the present embodiment, the case where the configuration of the present invention is applied to the monochrome printer 1 has been described. However, in another different embodiment, the present invention is applied to other image forming apparatuses such as a color printer, a copier, a facsimile machine, and a multifunction machine. It is also possible to apply this configuration.

1 Printer (image forming device)
2 Printer Main Body 6 Image Forming Unit 10 Conveyance Path 13 Fixing Device 15 Control Device 16 Storage Device 20 Fixing Roller (Heating Member)
21 Pressure roller (pressure member)
DESCRIPTION OF SYMBOLS 22 Heat source 23 Heater drive circuit 24 1st temperature sensor 25 2nd temperature sensor 26 1st paper sensor 27 2nd paper sensor 28 Environmental temperature sensor 29 Drive source 31 Main heater (1st heating body)
32 Sub-heater (second heating element)
33 Power supply

Claims (4)

A heating member for heating the toner image formed on the paper;
A pressing member that pressurizes the paper that is pressurized against the heating member and passes between the heating member;
A heat source for heating the heating member,
The heat source includes a first heating body provided at the center in the width direction orthogonal to the conveyance direction of the paper, and a second heating body provided at an end portion in the width direction,
Based on the detection result of the surface temperature of the heating member, the leading edge of the paper reaches the heating member and performs a predetermined standby while feedback-controlling the power for heating the first heating body and the second heating body. The fixing is characterized in that the duty ratio of the power supplied to the second heating body is increased by a predetermined correction amount after the period elapses until the trailing edge of the sheet passes through the heating member. apparatus.   The fixing device according to claim 1, wherein at least one of the standby period and the correction amount is set based on at least one of a linear velocity and a type of the paper.   The fixing device according to claim 1, wherein at least one of the standby period and the correction amount is set based on at least one of a surface temperature and an environmental temperature of the heating member.   An image forming apparatus comprising the fixing device according to claim 1.

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