JP2019204053A - Fixing device and image forming apparatus - Google Patents

Abstract

To prevent the occurrence of toner offset and a fixing failure, while preventing an increase in the number of components of a fixing device.SOLUTION: A fixing device 8 according to the present invention comprises: a fixing member 11 that fixes a toner image to a recording medium, the fixing member 11 including a center part and first and second ends provided on both outsides of the center part in the axial direction of the fixing member 11; a main heater 13 that heats the center part; a sub heater 14 that heats the first and second ends; a main detection unit 15 that detects the temperature of the center part; a sub detection unit 16 that detects the temperature of the first end; and a control unit 21 that calculates an estimated temperature of the second end on the basis of the temperature ratio between the center part and first end.SELECTED DRAWING: Figure 4

Description

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

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus includes a fixing device that fixes a toner image on a recording medium such as paper. The fixing device includes, for example, a fixing member that fixes a toner image on a recording medium, a main heater that heats the central portion of the fixing member, a sub-heater that heats both ends of the fixing member, and a temperature at the central portion of the fixing member. And a sub-detecting unit that detects the temperature of one end of the fixing member (see Patent Document 1).

JP 2005-55527 A

  In the fixing device as described above, since there is a variation in the calorific value distribution of the sub heater, there is also a variation in the temperature distribution of the fixing member heated by the sub heater. The temperature at one end of the fixing member can be confirmed based on the detection result of the sub detection unit, but the temperature at the other end of the fixing member cannot be confirmed only by the detection result of the sub detection unit. Therefore, there is a possibility that the temperature of the other end of the fixing member exceeds the target temperature range and toner offset occurs, or the temperature of the other end of the fixing member falls below the target temperature range and fixing failure occurs.

  Note that if a sub-detecting unit that detects the temperature of the other end of the fixing member is newly installed, it is possible to suppress the occurrence of toner offset and fixing failure as described above. However, when such a configuration is adopted, the number of parts of the fixing device increases, which may increase the manufacturing cost of the fixing device.

  Therefore, an object of the present invention is to suppress the occurrence of toner offset and fixing failure while suppressing an increase in the number of parts of the fixing device.

  The fixing device according to the present invention is a fixing member for fixing a toner image on a recording medium, and includes a central portion and first and second end portions provided on both outer sides of the central portion in the axial direction of the fixing member. , A main heater for heating the central portion, a sub-heater for heating the first and second ends, a main detection portion for detecting the temperature of the central portion, and the first end A sub-detecting unit that detects the temperature of the part, and a control unit that calculates an estimated temperature of the second end part based on a temperature increase ratio of the central part and the first end part.

  The controller estimates a temperature difference between the first end and the second end based on a temperature increase ratio between the central portion and the first end, and based on the estimated temperature difference, You may calculate the estimated temperature of a 2nd edge part.

  The control unit may calculate an estimated temperature of the second end portion based on a temperature increase ratio between the central portion and the first end portion when starting up from a cold state.

  The control unit may control the sub-heater based on the temperature of the first end and the estimated temperature of the second end.

  The fixing device further includes a storage unit that stores a target temperature range of the first and second end portions, and the control unit is configured to include a temperature of the first end portion and an estimated temperature of the second end portion. The sub-heater may be controlled so that the one outside the target temperature range is included in the target temperature range.

  The fixing device further includes a storage unit that stores target temperatures of the first and second end portions, and the control unit includes the temperature of the first end portion and the estimated temperature of the second end portion. The sub-heater may be controlled so that the one that is far from the target temperature approaches the target temperature.

  An image forming apparatus according to the present invention includes the fixing device.

  According to the present invention, it is possible to suppress the occurrence of toner offset and fixing failure while suppressing an increase in the number of parts of the fixing device.

1 is a schematic diagram illustrating an outline of an image forming apparatus according to an embodiment of the present disclosure. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. It is III-III sectional drawing of FIG. 1 is a block diagram illustrating a control system for a fixing device according to an embodiment of the present invention. 6 is a graph showing a calorific value distribution of a sub-heater in a fixing device according to an embodiment of the present invention. 6 is a graph showing a temperature distribution of a heat roller in a fixing device according to an embodiment of the present invention. 6 is a graph showing the relationship between the elapsed time and the temperature of the heat roller when starting up from a cold state in the fixing device according to the embodiment of the present invention. In the fixing device according to an embodiment of the present invention, a graph showing the relationship between the temperature rise ratio between the central portion and the first end portion and the temperature difference between the first end portion and the second end portion when starting up from the cold state. is there.

  First, the overall configuration of the image forming apparatus 1 will be described.

  Hereinafter, for the sake of convenience of explanation, the left side in FIG. 1 is the front side of the image forming apparatus 1. Arrows Fr, Rr, L, R, U, and Lo appropriately attached to the drawings indicate the front side, rear side, left side, right side, upper side, and lower side of the image forming apparatus 1, respectively.

  Referring to FIG. 1, an image forming apparatus 1 is, for example, a printer. The image forming apparatus 1 includes a box-shaped apparatus main body 2. A paper feed cassette 3 that stores paper S (an example of a recording medium) is housed in the lower part of the apparatus main body 2. A paper discharge tray 4 is provided on the upper surface of the apparatus main body 2. An exposure unit 5 is accommodated below the paper discharge tray 4 at the upper part of the apparatus main body 2.

  A conveyance path CP for the paper S is provided inside the apparatus main body 2. A paper feed unit 6 is provided at the upstream end of the transport path CP. An image forming unit 7 is provided in the middle portion of the conveyance path CP. A fixing device 8 is provided downstream of the conveyance path CP.

  Next, the operation of the image forming apparatus 1 having such a configuration will be described.

  First, an electrostatic latent image is formed in the image forming unit 7 by laser light from the exposure unit 5 (see the two-dot chain line in FIG. 1). Next, the electrostatic latent image is developed in the image forming unit 7 to form a toner image. Thereby, the image forming operation is completed.

  On the other hand, the sheet S taken out from the sheet feeding cassette 3 by the sheet feeding unit 6 is conveyed to the image forming unit 7 in synchronization with the above-described image forming operation, and the toner image is transferred to the sheet S in the image forming unit 7. Is transcribed. The sheet S to which the toner image is transferred enters the fixing device 8, and the toner image is fixed to the sheet S in the fixing device 8. The paper S on which the toner image is fixed is discharged to the paper discharge tray 4.

  Next, the fixing device 8 will be further described.

  An arrow Z attached to FIG. 2 indicates the conveyance direction of the sheet S in the fixing device 8. 3 indicates the inner side in the left-right direction of the fixing device 8 (side approaching the center of the fixing device 8 in the left-right direction), and the arrow O attached in FIG. (The side away from the center of the fixing device 8 in the horizontal direction) is shown.

  2 and 3, the fixing device 8 includes a heat roller 11 (an example of a fixing member), a press roller 12 disposed below the heat roller 11, and a main housed in the heat roller 11. The heater 13 and the sub heater 14 are provided, and the main detection part 15 and the sub detection part 16 which are arrange | positioned ahead of the heat roller 11 are provided.

  The heat roller 11 of the fixing device 8 has a cylindrical shape that is long in the left-right direction. The heat roller 11 rotates around an axis X extending along the left-right direction. That is, in this embodiment, the left-right direction is the axial direction of the heat roller 11. The heat roller 11 includes, for example, a cored bar and a release layer that covers the cored bar.

  The heat roller 11 includes a central portion CP and first and second end portions EP1 and EP2 provided on both outer sides of the central portion CP in the left-right direction. The central portion CP is provided within the sheet passing width W of the heat roller 11 (the width in the left-right direction of the portion through which the sheet S passes). The left and right inner portions of the first and second end portions EP1 and EP2 are provided within the sheet passing width W of the heat roller 11, and the left and right outer portions of the first and second end portions EP1 and EP2 are the heat roller. 11 is provided outside the sheet passing width W.

  The press roller 12 of the fixing device 8 has a cylindrical shape that is long in the left-right direction. The press roller 12 rotates around an axis Y extending along the left-right direction. That is, in this embodiment, the left-right direction is the axial direction of the press roller 12. The press roller 12 includes, for example, a cored bar, an elastic layer provided around the cored bar, and a release layer that covers the elastic layer.

  The press roller 12 is in contact with the heat roller 11 at a predetermined pressure, and a fixing nip N is formed at a contact portion between the heat roller 11 and the press roller 12. That is, in the present embodiment, a “hot roller method” is used in which the fixing nip N is formed by the pair of rollers 11 and 12.

  The main heater 13 of the fixing device 8 has a shape that is long in the left-right direction. The main heater 13 is composed of, for example, a halogen heater. The main heater 13 includes a glass tube 13a and a heat generating portion 13b accommodated in the glass tube 13a. The heat generating part 13b is constituted by a filament, for example. The position in the left-right direction of the heat generating portion 13 b overlaps with the position in the left-right direction of the central portion CP of the heat roller 11. That is, the heat distribution of the main heater 13 is concentrated on the central portion CP of the heat roller 11. The heat generating portion 13 b is disposed within the paper passing width W of the heat roller 11.

  The sub-heater 14 of the fixing device 8 has a shape that is long in the left-right direction. The sub heater 14 is composed of, for example, a halogen heater. The sub-heater 14 includes a glass tube 14a and a pair of left and right heat generating portions 14b accommodated in the glass tube 14a. Each exothermic part 14b is comprised by the filament, for example. The position of each heat generating part 14b in the left-right direction overlaps with the position in the left-right direction of the first and second ends EP1, EP2 of the heat roller 11, respectively. That is, in the sub heater 14, heat distribution is concentrated on the first and second end portions EP1 and EP2 of the heat roller 11. Each heat generating part 14 b is disposed within the sheet passing width W of the heat roller 11.

  The main detection unit 15 of the fixing device 8 is configured by, for example, a thermistor. The main detection unit 15 is opposed to the central portion CP of the heat roller 11 with an interval, and detects the temperature of the central portion CP of the heat roller 11. The main detection unit 15 is disposed within the sheet passing width W of the heat roller 11.

  The sub detection unit 16 of the fixing device 8 is configured by, for example, a thermistor. The sub detection unit 16 is in contact with the first end EP1 of the heat roller 11, and detects the temperature of the first end EP1 of the heat roller 11. The sub detection unit 16 is disposed outside the paper passing width W of the heat roller 11. The sub detection unit 16 is disposed on the right side (outside in the left-right direction) of the heat generation unit 14 b on the right side of the sub heater 14.

  Next, a control system for the fixing device 8 will be described.

  Referring to FIG. 4, the fixing device 8 includes a control unit 21. The control unit 21 is configured by a CPU (Central Processing Unit), for example.

  The control unit 21 is connected to the storage unit 22. The storage unit 22 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 22 stores a target temperature TX of the heat roller 11. The storage unit 22 stores a target temperature range TA (temperature range from the lower limit temperature TL to the upper limit temperature TH) of the heat roller 11.

  The control unit 21 is connected to the drive source 23. The drive source 23 is configured by a motor, for example. The drive source 23 is connected to the heat roller 11 via a gear train (not shown). The drive source 23 rotates the heat roller 11 based on a signal from the control unit 21.

  The control unit 21 is connected to the main heater 13. The main heater 13 heats the central portion CP of the heat roller 11 by causing the heat generating portion 13 b to generate heat based on a signal from the control portion 21.

  The control unit 21 is connected to the sub heater 14. The sub-heater 14 heats the first and second end portions EP1 and EP2 of the heat roller 11 by causing each heat generating portion 14b to generate heat based on a signal from the control portion 21.

  The control unit 21 is connected to the main detection unit 15. The main detection unit 15 detects the temperature of the central portion CP of the heat roller 11 and transmits the detection result to the control unit 21.

  The control unit 21 is connected to the sub detection unit 16. The sub detection unit 16 detects the temperature of the first end portion EP <b> 1 of the heat roller 11 and transmits the detection result to the control unit 21.

  Next, the operation of the fixing device 8 will be described.

  During operation of the fixing device 8, the drive source 23 rotates the heat roller 11 based on a signal from the control unit 21 (see arrow A in FIG. 2). When the heat roller 11 rotates in this way, the press roller 12 that contacts the heat roller 11 is driven to rotate in the opposite direction to the heat roller 11 (see arrow B in FIG. 2).

  Further, during operation of the fixing device 8, the main heater 13 heats the central portion CP of the heat roller 11 based on a signal from the control unit 21, and the sub-heater 14 includes first and second end portions of the heat roller 11. EP1 and EP2 are heated.

  When the sheet S enters the fixing nip N in such a state, the sheet S and the toner image T are heated and pressed by the heat roller 11 and the press roller 12, and the toner image T is fixed to the sheet S.

  Note that the first and second end portions EP1 and EP2 of the heat roller 11 are easier to escape from the heat than the central portion CP of the heat roller 11, and the heating rate is slow. Therefore, in the present embodiment, the heat distribution of the first and second end portions EP1 and EP2 of the heat roller 11 is made larger than the heat distribution of the central portion CP of the heat roller 11, so The heat generation amount of the two end portions EP1 and EP2 is set larger than the heat generation amount of the central portion CP of the heat roller 11.

  Next, an example of temperature control of the heat roller 11 will be described.

  Regarding the temperature control of the central portion CP of the heat roller 11, the control unit 21 detects the temperature of the central portion CP of the heat roller 11 detected by the main detection unit 15 (hereinafter, “detected temperature of the central portion CP of the heat roller 11”). The main heater 13 is controlled so as to approach the target temperature TX. For example, when the paper S passes through the fixing nip N, the heat of the central portion CP of the heat roller 11 is taken away by the paper S, so that the detected temperature of the central portion CP of the heat roller 11 is lower than the target temperature TX. In this case, the control unit 21 increases the lighting duty of the main heater 13 so that the detected temperature of the central portion CP of the heat roller 11 increases to the target temperature TX.

  On the other hand, regarding the temperature control of the first end portion EP1 of the heat roller 11, the control unit 21 detects the temperature of the first end portion EP1 of the heat roller 11 detected by the sub detection unit 16 (hereinafter referred to as “the first temperature of the heat roller 11”). The sub-heater 14 is controlled such that the “detected temperature of the one end EP1”) approaches the target temperature TX. Alternatively, the control unit 21 controls the sub heater 14 so that the detected temperature of the first end portion EP1 of the heat roller 11 is included in the target temperature range TA (temperature range from the lower limit temperature TL to the upper limit temperature TH). For example, when the detected temperature of the first end portion EP1 of the heat roller 11 is lower than the lower limit temperature TL, the control unit 21 increases the lighting duty of the sub heater 14. On the other hand, when the detected temperature of the first end portion EP1 of the heat roller 11 is higher than the upper limit temperature TH, the control unit 21 decreases the lighting duty of the sub heater 14.

  Next, the calorific value distribution of the sub heater 14 and the temperature distribution of the heat roller 11 will be described.

  As described above, each heat generating portion 14 b of the sub-heater 14 is disposed within the sheet passing width W of the heat roller 11, whereas the sub-detecting unit 16 is disposed outside the sheet passing width W of the heat roller 11. . In this relation, as shown in FIG. 5, the amount of heat generated by the sub-heater 14 varies greatly at the detection position of the sub-detection unit 16.

  By the way, since there is variation for each individual sub-heater 14 in the left-right position of each heat generating part 14b of the sub-heater 14, the distribution of heat generated by the sub-heater 14 also varies for each individual sub-heater 14. Existing. Therefore, the temperature distribution of the heat roller 11 heated by the sub heater 14 also varies.

  As shown in FIG. 6, when a sub-heater 14 having a calorific value distribution as designed (hereinafter referred to as “first sub-heater 14”) is used, detection of the first end EP1 of the heat roller 11 is detected. The temperature and the temperature of the second end portion EP2 of the heat roller 11 are both included in the target temperature range TA. On the other hand, when the sub-heater 14 (hereinafter referred to as “second sub-heater 14”) having a calorific value distribution that is maximally shifted to one side in the left-right direction with respect to the design value is used, The detected temperature of the first end EP1 is included in the target temperature range TA, but the temperature of the second end EP2 of the heat roller 11 is higher than the upper limit temperature TH and is not included in the target temperature range TA. In addition, when the sub heater 14 having a calorific value distribution that is maximally shifted to the other side in the left-right direction with respect to the design value is used (hereinafter referred to as “third sub heater 14”), the first end of the heat roller 11 is used. The detected temperature of the part EP1 is higher than the upper limit temperature TH and is not included in the target temperature range TA, but the temperature of the second end EP2 of the heat roller 11 is included in the target temperature range TA.

  As described above, there are also variations in the temperatures of the first and second end portions EP1 and EP2 of the heat roller 11 in accordance with variations in the calorific value distribution of the sub-heater 14. The temperature of the first end EP1 of the heat roller 11 can be confirmed based on the detection result of the sub detection unit 16, but the temperature of the second end EP2 of the heat roller 11 is the detection result of the sub detection unit 16. It cannot be confirmed by itself. Therefore, toner offset occurs when the temperature of the second end portion EP2 of the heat roller 11 exceeds the target temperature range TA, or fixing failure occurs because the temperature of the second end portion EP2 of the heat roller 11 falls below the target temperature range TA. May occur. Therefore, in the present embodiment, the occurrence of toner offset and fixing failure is suppressed as follows.

  As shown in FIG. 7, when the main heater 13 and the sub heater 14 are operated at a lighting duty of 100% when starting from a cold state (a state where the heat roller 11 is not heated at all), The temperature of the central portion CP and the first end portion EP1 increases. There is no variation in the heating rate of the central portion CP of the heat roller 11 regardless of which of the first to third sub-heaters 14 is used. On the other hand, the temperature increase rate of the first end portion EP1 of the heat roller 11 varies depending on which of the first to third sub heaters 14 is used.

  FIG. 8 shows the temperature rise ratio P (hereinafter simply referred to as “temperature rise ratio P”) between the central portion CP and the first end portion EP1 of the heat roller 11 and the first temperature of the heat roller 11 when starting up from the cold state. The relationship between the temperature difference D (hereinafter simply referred to as “temperature difference D”) between the end portion EP1 and the second end portion EP2 is shown. The temperature increase ratio P is calculated by dividing the temperature increase rate of the central portion CP of the heat roller 11 by the temperature increase rate of the first end portion EP1 of the heat roller 11. The temperature difference D is calculated by subtracting the temperature of the second end portion EP2 from the temperature of the first end portion EP1. The relationship between the temperature increase ratio P and the temperature difference D as shown in FIG. 8 is measured before the start of use of the fixing device 8 and is stored in the storage unit 22.

  As shown in FIG. 8, the temperature increase ratio P varies depending on which of the first to third sub-heaters 14 is used. For example, when the second sub-heater 14 is used, the temperature increase rate P of the first end portion EP1 is the slowest, so that the temperature increase ratio P is the largest. On the other hand, when the third sub-heater 14 is used, the temperature increase rate P of the first end portion EP1 is the fastest, so the temperature increase ratio P is the smallest.

  Further, the temperature difference D decreases as the temperature increase ratio P increases. That is, the temperature difference D is inversely proportional to the temperature increase ratio P. For example, when the third sub-heater 14 is used, the temperature increase ratio P is the smallest, so the temperature difference D is the largest. On the other hand, when the second sub-heater 14 is used, the temperature increase ratio P is the largest, so the temperature difference D is the smallest.

  At the time of start-up from the cold state, the control unit 21 calculates the temperature increase rate of the central part CP of the heat roller 11 based on the detected temperature of the central part CP of the heat roller 11 and the first end of the heat roller 11. Based on the detected temperature of the part EP1, the temperature increase rate of the first end part EP1 of the heat roller 11 is calculated. At that time, the detected temperatures of the central portion CP and the first end portion EP1 of the heat roller 11 are detected, for example, at time t1 in FIG. 7 (time immediately before the temperature rise of the central portion CP of the heat roller 11 is stopped). The Next, the control unit 21 calculates the temperature increase ratio P by dividing the temperature increase rate of the central portion CP of the heat roller 11 by the temperature increase rate of the first end portion EP1 of the heat roller 11.

  Next, the control unit 21 refers to the relationship between the temperature increase ratio P and the temperature difference D stored in the storage unit 22 (see FIG. 8), and estimates the temperature difference D based on the temperature increase ratio P. Next, the control unit 21 calculates the estimated temperature of the second end EP2 of the heat roller 11 by subtracting the temperature difference D from the detected temperature of the first end EP1 of the heat roller 11.

  The control unit 21 controls the sub heater 14 based on the detected temperature of the first end EP1 of the heat roller 11 and the estimated temperature of the second end EP2 of the heat roller 11. Specifically, the control unit 21 determines the target temperature that is out of the target temperature range TA among the detected temperature of the first end EP1 of the heat roller 11 and the estimated temperature of the second end EP2 of the heat roller 11. The sub heater 14 is controlled to be included in the range TA. For example, in the control unit 21, the detected temperature of the first end EP1 of the heat roller 11 is included in the target temperature range TA, and the estimated temperature of the second end EP2 of the heat roller 11 is lower than the lower limit temperature TL. In this case, the estimated temperature of the second end portion EP2 of the heat roller 11 is increased by increasing the lighting duty of the sub heater 14.

  As described above, in the present embodiment, the control unit 21 calculates the estimated temperature of the second end portion EP2 of the heat roller 11 based on the temperature increase ratio P. Therefore, it becomes possible to control the sub-heater 14 while confirming the temperature of the second end portion EP2 of the heat roller 11 based on the estimated temperature of the second end portion EP2 of the heat roller 11. Therefore, toner offset occurs when the temperature of the second end portion EP2 of the heat roller 11 exceeds the target temperature range TA, or fixing failure occurs because the temperature of the second end portion EP2 of the heat roller 11 falls below the target temperature range TA. It can suppress generating.

  Further, since the temperature of the second end portion EP2 of the heat roller 11 can be confirmed based on the estimated temperature of the second end portion EP2 of the heat roller 11, the temperature of the second end portion EP2 of the heat roller 11 is detected. There is no need to newly install the sub detection unit 16. Therefore, an increase in the number of parts of the fixing device 8 can be suppressed, and the manufacturing cost of the fixing device 8 can be suppressed.

  Further, the control unit 21 calculates the temperature increase ratio P by dividing the temperature increase rate of the central portion CP of the heat roller 11 by the temperature increase rate of the first end portion EP1 of the heat roller 11. For this reason, it is possible to suppress variation in the temperature increase ratio P due to factors other than variations in the heat generation amount distribution of the sub-heater 14 (for example, variations in input power and environmental changes), and variations in the heat generation amount distribution of the sub-heater 14. It becomes easy to confirm.

  When the sub heater 14 is controlled in a state where the temperature of the second end portion EP2 of the heat roller 11 cannot be confirmed at all, the temperature of the second end portion EP2 of the heat roller 11 exceeds the upper limit temperature TH or the lower limit temperature TL. Therefore, it is necessary to control the sub-heater 14 by narrowing the target temperature range TA from the temperature range from the lower limit temperature TL to the upper limit temperature TH so that the temperature does not fall below. Therefore, it may be difficult to ensure a margin of the target temperature range TA necessary for appropriately controlling the sub heater 14.

  On the other hand, in this embodiment, since the sub heater 14 can be controlled while confirming the temperature of the second end portion EP2 of the heat roller 11, there is no need to narrow the target temperature range TA. Therefore, a sufficient margin of the target temperature range TA necessary for appropriately controlling the sub heater 14 can be secured.

  Further, the control unit 21 estimates the temperature difference D based on the temperature increase ratio P, and calculates the estimated temperature of the second end portion EP2 of the heat roller 11 based on the estimated temperature difference D. Therefore, the estimated temperature of the second end portion EP2 of the heat roller 11 can be accurately calculated.

  Moreover, the control part 21 is calculating the estimated temperature of 2nd end part EP2 of the heat roller 11 based on the temperature rising ratio P at the time of starting from a cold machine state. Therefore, the estimated temperature of the second end portion EP2 of the heat roller 11 can be accurately calculated.

  Further, the control unit 21 controls the sub-heater 14 based on the detected temperature of the first end EP1 of the heat roller 11 and the estimated temperature of the second end EP2 of the heat roller 11. Therefore, it is possible to reliably suppress the occurrence of toner offset and fixing failure at both the first and second end portions EP1 and EP2 of the heat roller 11.

  Moreover, the control part 21 makes the direction which remove | deviated from the target temperature range TA among the detection temperature of 1st end part EP1 of the heat roller 11, and the estimated temperature of 2nd end part EP2 of the heat roller 11 into the target temperature range TA. The sub-heater 14 is controlled to include. Therefore, it is possible to more reliably suppress the occurrence of toner offset and fixing failure at both the first and second end portions EP1 and EP2 of the heat roller 11.

  Further, the image forming apparatus 1 includes the fixing device 8 described above. Therefore, it is possible to provide the image forming apparatus 1 including the fixing device 8 that can suppress the occurrence of toner offset and fixing failure.

  In the present embodiment, the control unit 21 determines the one that is out of the target temperature range TA among the detected temperature of the first end EP1 of the heat roller 11 and the estimated temperature of the second end EP2 of the heat roller 11 as the target temperature. The sub heater 14 is controlled so as to be included in the range TA. On the other hand, in another different embodiment, the control unit 21 is away from the target temperature TX among the detected temperature of the first end EP1 of the heat roller 11 and the estimated temperature of the second end EP2 of the heat roller 11. The sub-heater 14 may be controlled so that the temperature approaches the target temperature TX. By executing such control, it becomes easier to bring the temperatures of the first and second end portions EP1 and EP2 of the heat roller 11 closer to the target temperature TX.

  In the present embodiment, the heat roller 11 having no flexibility is used as the fixing member. On the other hand, in another different embodiment, a flexible heat belt may be used as the fixing member.

  In the present embodiment, the image forming apparatus 1 is a printer. On the other hand, in another different embodiment, the image forming apparatus 1 may be a copier, a facsimile machine, a multi-function machine (an image forming apparatus having a print function, a copy function, a fax function, etc.).

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 8 Fixing apparatus 11 Heat roller (an example of a fixing member)
CP (heat roller) center part EP1 (heat roller) first end part EP2 (heat roller) second end part 13 main heater 14 sub heater 15 main detection part 16 sub detection part 21 control part 22 storage part S paper (Example of recording medium)
T Toner image

Claims (7)

A fixing member for fixing a toner image on a recording medium, the fixing member including a central portion and first and second ends provided on both outer sides of the central portion in the axial direction of the fixing member;
A main heater for heating the central portion;
A sub-heater for heating the first and second ends;
A main detector for detecting the temperature of the central portion;
A sub-detecting unit for detecting the temperature of the first end;
And a controller that calculates an estimated temperature of the second end portion based on a temperature increase ratio between the central portion and the first end portion.   The controller estimates a temperature difference between the first end and the second end based on a temperature increase ratio between the central portion and the first end, and based on the estimated temperature difference, The fixing device according to claim 1, wherein an estimated temperature of the second end portion is calculated.   The said control part calculates the estimated temperature of the said 2nd end part based on the temperature increase ratio of the said center part and the said 1st end part at the time of starting from a cold machine state, or Claim 1 or 2 characterized by the above-mentioned. 3. The fixing device according to 2.   The fixing unit according to claim 1, wherein the control unit controls the sub-heater based on a temperature of the first end and an estimated temperature of the second end. apparatus. A storage unit for storing the target temperature range of the first and second ends;
The control unit controls the sub-heater so that the target temperature range includes a temperature out of the target temperature range among the temperature of the first end portion and the estimated temperature of the second end portion. The fixing device according to claim 4. A storage unit for storing target temperatures of the first and second ends;
The control unit controls the sub-heater so that a temperature of the first end portion and an estimated temperature of the second end portion that is far from the target temperature approaches the target temperature. The fixing device according to claim 4.   An image forming apparatus comprising the fixing device according to claim 1.

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