Fixing device and image forming apparatus

Abstract

To provide a fixing device that can quickly detect a rotation failure of a fixing rotating body with a simple configuration.SOLUTION: A fixing device comprises: a first failure state detection unit that, during warm-up, detects if a fixing rotating body is in a rotation failure state based on information on an increase in surface temperature of the fixing rotating body; and a control unit that, when the fixing rotating body is detected to be in the rotation failure state, controls a heat source and a motor to execute stop operations to stop heating of the fixing rotating body and rotation of a pressure rotating body.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a fixing device and an image forming apparatus, and more particularly to a fixing device and an image forming apparatus that include, for example, a fixing rotor and a pressure rotor, and thermally fixes a toner image formed on a recording medium. [Background technology]

[0002] An example of a conventional fixing device is disclosed in Patent Document 1. The fixing device in Patent Document 1 includes a fixing belt (fixing rotator), a pressure roller (pressure rotator), a fixed member that is in pressure contact with the pressure roller via the fixing belt to form a nip, a pipe-shaped metal member that is fixed to face the inner circumferential surface of the fixing belt and heats the fixing belt, a first temperature detection means that detects the surface temperature of the fixing belt on the upstream side of the nip, and a second temperature detection means that detects the surface temperature of the pressure rotator on the downstream side of the nip. When the temperature difference between the temperatures detected by the two temperature detection means, which are detected at the same time, exceeds a predetermined threshold, heating by the heating means is stopped. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-186001 A Summary of the Invention [Problem to be solved by the invention]

[0004] The technique of Patent Document 1 requires a temperature sensor for detecting the temperature of the pressure rotating body in addition to a temperature sensor for detecting the temperature of the fixing rotating body, which increases costs.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Therefore, a primary object of the present invention is to provide a novel fixing device and image forming apparatus.

[0006] Another object of the present invention is to provide a fixing device and an image forming apparatus capable of detecting as quickly as possible a state in which the fixing rotator is in a rotational failure state with a simple configuration. [Means for solving the problem]

[0007] A first aspect of the present invention is a fixing device for thermally fixing a toner image formed on a recording medium, the fixing device comprising: a fixing rotor; a heat source for heating the fixing rotor; a pressure rotor that comes into contact with an outer circumferential surface of the fixing rotor to form a nip portion between the fixing rotor and the heat source and drives the fixing rotor to rotate; and a motor that drives the pressure rotor to rotate. a contact pressure changing mechanism capable of changing the contact pressure of the pressing rotor with respect to the fixing rotor; The fixing device includes a temperature detection unit that detects a surface temperature of the fixing rotator, a first defective state detection unit that detects whether the fixing rotator is in a rotation failure state based on information on a temperature rise of the surface temperature of the fixing rotator detected by the temperature detection unit during a warm-up period in which the fixing rotator is heated to a target temperature while rotating, and a control unit that controls a heat source and a motor to execute a stop operation for stopping the heating of the fixing rotator and the rotation of the pressure rotator when the first defective state detection unit detects that the fixing rotator is in a rotation failure state. After executing the stop operation, the control unit executes a retry operation to resume heating of the fixing rotator and rotation of the pressure rotator, and when the first fault condition detection unit detects that the fixing rotator is in a faulty rotation state after the stop operation and the retry operation are executed a predetermined number of times, the control unit executes an error notification and stops the startup of the fixing device, and further, after executing the stop operation and before executing the retry operation, the control unit controls the contact pressure change mechanism and the motor to execute a low contact pressure rotation operation in which the contact pressure of the pressure rotator against the fixing rotator is set to a low contact pressure and the pressure rotator is rotated for a predetermined time. This is a fixing device.

[0008] According to the first aspect of the present invention, since it is determined whether the fixing rotor is in a rotation failure state based on information on the temperature rise of the surface temperature of the fixing rotor, it is possible to quickly detect the fixing rotor in a rotation failure state with a simple configuration, and therefore it is possible to appropriately prevent damage to the fixing rotor due to an abnormal temperature rise.

[0011] No. 2 The invention is 1 The present invention is directed to the above-mentioned invention, and includes a second defective state detection unit that detects whether the fixing rotor is in a state of poor rotation based on information on a temperature drop in the surface temperature of the fixing rotor detected by the temperature detection unit when a low contact pressure rotation operation is performed, and when the second defective state detection unit detects that the fixing rotor is in a state of poor rotation, the control unit controls the heat source and the motor to execute a heating and rotation operation in which the pressure rotor is rotated for a predetermined time while heating the fixing rotor.

[0012] The third invention is the first invention. or second The present invention is directed to the above-mentioned invention, and includes a threshold memory unit that stores a plurality of rising speed thresholds set according to the value of the supply voltage to the fixing device, and a supply voltage detection unit that detects the supply voltage to the fixing device, and a first fault state detection unit that detects that the fixing rotor is in a faulty rotation state when the temperature rising speed detected by the temperature detection unit is equal to or higher than the rising speed threshold selected based on the supply voltage detected by the supply voltage detection unit.

[0013] No. 4 The inventions are the first to the second 3 The present invention is according to any one of the above, and further includes an integrated number storage unit that stores an integrated number of times that the first defective state detection unit has detected that the fixing rotator is in a rotation defective state, and a display unit that can display the integrated number.

[0014] No. 5 The inventions are the first to the second 4 The present invention relates to an image forming apparatus including a fixing device according to any one of the above aspects. Effect of the Invention

[0015] According to this invention, since it is determined whether the fixing rotor is in a rotation failure state based on information on the surface temperature of the fixing rotor, it is possible to quickly detect the fixing rotor in a rotation failure state with a simple configuration, and therefore it is possible to appropriately prevent damage caused by, for example, an abnormal temperature rise of the fixing rotor.

[0016] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing a fixing device. [Diagram 3] FIG. 2 is a plan view showing a pressure roller provided in the fixing device. [Figure 4] FIG. 2 is a perspective view showing a pressure unit included in the fixing device. [Diagram 5] FIG. 2 is a schematic front view showing a pressurizing unit. [Figure 6] FIG. 4 is a front view showing a separation and engagement cam provided in the pressure unit. [Figure 7] FIG. 2 is a block diagram showing an example of an electrical configuration of the image forming apparatus. [Figure 8] FIG. 8 is a diagram illustrating an example of a memory map of a RAM illustrated in FIG. 7. [Figure 9] 8 is a flowchart showing an example of a warm-up process executed by the CPU shown in FIG. 7. FIG. [Figure 10] FIG. 11 is a flowchart showing an example of a warm-up process executed by a CPU of an image forming apparatus according to a second embodiment of the present invention. [Figure 11] FIG. 11 is a flowchart showing an example of a warm-up process executed by a CPU of an image forming apparatus according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [First Example] 1, an image forming apparatus 10 according to a first embodiment of the present invention is an apparatus for forming a multi-color or monochrome image on paper by electrophotography. As will be described in detail later, the image forming apparatus 10 includes a fixing device 46 that thermally fixes a toner image formed on paper (recording medium).

[0019] First, a basic configuration of the image forming apparatus 10 will be briefly described. In this specification, the front-rear direction (depth direction) of the image forming apparatus 10 and its components is defined with the surface facing the user's standing position, that is, the surface on which the operation unit 106 (see FIG. 7) is provided, as the front (front). The left-right direction (horizontal direction) of the image forming apparatus 10 and its components is defined with reference to the state in which the image forming apparatus 10 is viewed from the user.

[0020] 1, in this first embodiment, the image forming apparatus 10 is a multifunction peripheral (MFP) having a copy function, a printer function, a scanner function, a facsimile function, etc. The image forming apparatus 10 includes an apparatus main body 12 equipped with an image forming unit 30, etc., and an image reading device 14 disposed above the apparatus main body 12.

[0021] The image reading device 14 includes a document placement platform 16 formed of a transparent material. A document pressing cover 18 is attached above the document placement platform 16 via a hinge or the like so as to be freely opened and closed. This document pressing cover 18 is provided with an ADF (automatic document feeder) 24 that automatically feeds documents placed on a document placement tray 20 one by one to an image reading position 22. In addition, on the front side of the document placement platform 16, an operation unit 106 is provided that accepts input operations such as printing instructions by a user. This operation unit 106 is appropriately provided with a display such as a touch panel display, various operation buttons, and the like.

[0022] The image reading device 14 also includes an image reading unit 26 that includes a light source, multiple mirrors, an imaging lens, a line sensor, and the like. The image reading unit 26 exposes the surface of the document to the light source, and guides the light reflected from the document surface to the imaging lens via multiple mirrors. The imaging lens then forms an image of the reflected light on the light receiving element of the line sensor. The line sensor detects the luminance and chromaticity of the reflected light that forms an image on the light receiving element, and generates image data based on the image of the document surface. The line sensor may be a CCD (Charge Coupled Device) or a CIS (Contact Image Sensor), and the like.

[0023] The device main body 12 incorporates a control unit 28 including a CPU 100, a RAM 102, and a HDD 104 (see FIG. 7), and an image forming unit 30. The control unit 28 (specifically, the CPU 100) transmits control signals to each part of the image forming device 10 including the fixing device 46 in response to an input operation by a user to an operation unit 106, and causes the image forming device 10 to perform various operations.

[0024] The image forming section 30 includes an exposure unit 32, a developing device 34, a photoconductor drum 36, a cleaner unit 38, a charger 40, an intermediate transfer belt unit 42, a secondary transfer roller 44, and a fixing device 46, and forms an image on paper conveyed from a paper feed tray 48 or a manual paper feed tray 50, and discharges the paper on which the image has been formed onto a paper discharge tray 52. ​​As image data for forming an image on the paper, image data read by the image reading section 26 or image data transmitted from an external computer, etc., are used.

[0025] The image data handled by the image forming apparatus 10 corresponds to color images of four colors: black (K), cyan (C), magenta (M), and yellow (Y). For this reason, four of each of the developing device 34, the photoconductor drum 36, the cleaner unit 38, and the charger 40 are provided so as to form four types of latent images corresponding to each color, and these constitute four image stations.

[0026] The photoconductor drum 36 is an image carrier in which a photosensitive layer is formed on the surface of a cylindrical base body having electrical conductivity, and the charger 40 is a member that charges the surface of the photoconductor drum 36 to a predetermined potential. The exposure unit 32 is configured as a laser scanning unit (LSU) equipped with a laser emission section and a reflecting mirror, and exposes the charged surface of the photoconductor drum 36 to light, thereby forming an electrostatic latent image on the surface of the photoconductor drum 36 according to image data. The developer 34 visualizes the electrostatic latent image formed on the surface of the photoconductor drum 36 with four-color (YMCK) toners. The cleaner unit 38 removes toner remaining on the surface of the photoconductor drum 36 after development and image transfer.

[0027] The intermediate transfer belt unit 42 includes an intermediate transfer belt 54, a driving roller 56, a driven roller 58, and four intermediate transfer rollers 60, and is disposed above the photosensitive drum 36. The intermediate transfer belt 54 is a flexible endless belt that is stretched by a plurality of rollers, such as the driving roller 56 and the driven roller 58, and is disposed so that its surface (outer circumferential surface) abuts against the surface of the photosensitive drum 36. The intermediate transfer belt 54 rotates (moves in a circular motion) in a predetermined direction in accordance with the rotational drive of the driving roller 56. The intermediate transfer rollers 60 are disposed at positions facing the photosensitive drums 36 with the intermediate transfer belt 54 in between. During image formation, the intermediate transfer rollers 60 are used to transfer the toner images of each color formed on each photosensitive drum 36 to the intermediate transfer belt 54 in a superimposed manner, thereby forming a multi-color toner image on the intermediate transfer belt 54.

[0028] The secondary transfer roller 44 is disposed so as to face the drive roller 56 across the intermediate transfer belt 54. When a sheet of paper passes through a secondary transfer nip between the secondary transfer roller 44 and the intermediate transfer belt 54, the toner image formed on the intermediate transfer belt 54 is transferred to the sheet of paper.

[0029] The fixing device 46 includes a fixing belt 62, a pressure roller 64, etc., and is disposed above the secondary transfer roller 44 (downstream in the paper conveying direction). A fixing pad 76, a heat source 82, etc. (see FIG. 2) are provided within the fixing belt 62, and the fixing belt 62 is heated by the heat source 82 to a predetermined fixing temperature (for example, 170° C.). The pressure roller 64 is provided so as to press the fixing belt 62 between itself and the fixing pad 76. When the paper passes through a fixing nip portion N (see FIG. 2) between the pressure roller 64 and the fixing belt 62, the toner image transferred to the paper is melted, mixed, and pressed against the paper, and the toner image is thermally fixed to the paper. The specific configuration of the fixing device 46 will be described later.

[0030] In the device main body 12, a first paper transport path L1 is formed for sending paper from the paper feed tray 48 or the manual paper feed tray 50 to the paper output tray 52 via the registration rollers 68, the secondary transfer roller 44 and the fixing device 46. In addition, when performing double-sided printing on the paper, a second paper transport path L2 is formed for returning the paper after single-sided printing is completed and the paper has passed through the fixing device 46 to the first paper transport path L1 upstream in the paper transport direction of the secondary transfer roller 44. In the first paper transport path L1 and the second paper transport path L2, a plurality of transport rollers 66 for providing auxiliary propulsion force to the paper are appropriately provided.

[0031] 2 to 6, the mechanical configuration of the fixing device 46 will be described. The fixing device 46 includes a fixing belt 62, which is an example of a fixing rotor, and a pressure roller 64, which is an example of a pressure rotor, and fixes a toner image onto the paper by passing the paper through a fixing nip N formed between them.

[0032] 2, the fixing device 46 includes a heater unit 70 having a fixing belt 62 and the like, and a pressure unit 72 having a pressure roller 64 and the like. The members of the heater unit 70 and the pressure unit 72 are integrally held in a predetermined arrangement by a fixing frame (not shown).

[0033] The heater unit 70 includes a fixing belt 62 that is formed in a substantially cylindrical shape and extends in the front-rear direction (width direction of the paper). The fixing belt 62 is, for example, a belt-shaped base material formed of a synthetic resin such as polyimide or a metal such as nickel, on the surface of which a release layer is provided. The fixing belt 62 is provided so as to be rotatable about its axis, and has an inner diameter of, for example, 30 mm. Inside the fixing belt 62, a fixing pad 76, a support member 78, a reflector 80, a heat source 82, and the like are provided.

[0034] The fixing pad 76 is a fixed member fixedly provided so as to be in sliding contact with the inner peripheral surface of the fixing belt 62, and is formed in a long plate shape extending along the axial direction of the fixing belt 62. The fixing pad 76 has a sliding sheet 76a on its outer peripheral surface (at least the surface that comes into sliding contact with the fixing belt 62), and sliding oil is applied to this sliding sheet 76a to reduce frictional force with the fixing belt 62. The length of the fixing pad 76 is the same as the axial length (width) of the fixing belt 62.

[0035] The support member 78 is a member that supports the fixing pad 76 while pressing it against the inner circumferential surface of the fixing belt 62, and both ends of the support member 78 are fixed to the fixing frame. In this first embodiment, the support member 78 is formed in a substantially L-shaped cross section, and has a long plate-like fixed portion 78a to which the fixing pad 76 is fixed, and a long plate-like standing portion 78b standing from the width direction end of the fixed portion 78a. In addition, a thin plate-like reflecting plate 80 is attached to the support member 78 so as to cover the surface on the heat source 82 side.

[0036] The heat source 82 is a member for heating the fixing belt 62, and is provided so as to extend along the axial direction of the fixing belt 62. A lamp heater such as a halogen lamp is used as the heat source 82. In this first embodiment, the heat source 82 includes a first lamp heater 82a for heating the axial center portion of the fixing belt 62, and a second lamp heater 82b for heating both axial end portions of the fixing belt 62. The first lamp heater 82a and the second lamp heater 82b are used differently depending on the paper width.

[0037] The pressure unit 72 includes a pressure roller 64 disposed at a position facing the fixing pad 76 with the fixing belt 62 sandwiched therebetween. The pressure roller 64 is provided so as to extend parallel to the axial direction of the fixing belt 62, and forms a fixing nip portion N between the pressure roller 64 and the fixing pad 76 by pressing the fixing belt 62 against the fixing belt 62.

[0038] 3, the pressure roller 64 includes a cylindrical roller portion 84. The roller portion 84 includes a cylindrical core material made of a metal such as aluminum, an elastic layer made of an elastic material such as silicone rubber and covering the surface of the core material, and a release layer made of a material with a low friction coefficient such as a fluorine-based resin and covering the surface of the elastic layer. The axial length of the roller portion 84 is the same as the axial length of the fixing belt 62.

[0039] In addition, in this first embodiment, both ends of the roller portion 84 are provided with thin grip portions 86 made of a material with high friction resistance (i.e., good gripping power) such as silicone rubber. The grip portions 86 are positioned on the outer side in the width direction (outside the paper width) of the paper passing through the fixing nip portion N, and have a thickness (protruding height from the release layer) of, for example, 200 μm. By providing such grip portions 86 on the roller portion 84, the rotational force of the pressure roller 64 can be appropriately transmitted to the fixing belt 62 even when the pressure roller 64 is in a low contact pressure state as in a second embodiment described later.

[0040] A first motor 90 (see FIG. 7) is connected to one end (rear end) of the roller shaft 88 of the pressure roller 64 via a gear or gear train (not shown). The pressure roller 64 is driven to rotate by receiving a driving force from the first motor 90, and as the pressure roller 64 is driven to rotate, the fixing belt 62 is driven to rotate in the direction opposite to the rotation direction of the pressure roller 64. That is, the pressure roller 64 comes into contact with the outer circumferential surface of the fixing belt 62 to form a fixing nip portion N between the pressure roller 64 and the fixing belt 62, and transmits a rotational driving force to the fixing belt 62 via the fixing nip portion N, thereby rotating the fixing belt 62.

[0041] 2, the fixing device 46 includes a temperature sensor 94 such as a thermopile that detects the surface temperature of the fixing belt 62. The temperature sensor 94 includes, for example, a first temperature sensor that detects the surface temperature of the axial center portion of the fixing belt 62, and a second temperature sensor that detects the surface temperature of the axial end portion of the fixing belt 62. The type of the temperature sensor 94 is not particularly limited, but in order to more appropriately perform the rotation failure detection process of the fixing belt 62 described below, it is preferable to use a thermopile that is capable of high-speed response.

[0042] Further, a peeling plate 96 for preventing the paper from wrapping around the fixing belt 62 is provided on the downstream side of the fixing nip portion N in the paper transport direction.

[0043] Furthermore, the fixing device 46 includes a contact pressure change mechanism 110 (separation mechanism) capable of changing the contact pressure of the pressure roller 64 against the fixing belt 62. In this first embodiment, the contact pressure change mechanism 110 is provided in the pressure unit 72, and the contact pressure (pressing force) of the pressure roller 64 against the fixing belt 62 is changed by moving the pressure roller 64 in the contact / separation direction relative to the fixing belt 62. The contact pressure change mechanism 110 is also capable of completely separating the pressure roller 64 from the fixing belt 62. An example of the contact pressure change mechanism 110 will be described below with reference to FIGS. 4 to 6. However, the specific configuration of the contact pressure change mechanism 110 is not limited thereto.

[0044] As shown in FIG. 4 and FIG. 5, the contact pressure change mechanism 110 includes a pair of pressure levers 112 provided at both ends of the pressure unit 72 and extending in a direction perpendicular to the axial direction of the pressure roller 64. Each of the pressure levers 112 rotatably supports the roller shaft 88 of the pressure roller 64 at its center via a bearing 114. Each of the pressure levers 112 has an engagement hole 118 at one end (lower end) thereof that engages with a rotation support shaft 116 provided in the fixing frame. The rotation support shaft 116 is provided so as to extend parallel to the axial direction of the fixing belt 62, and the pressure lever 112 is rotatable in a direction (left and right direction) in which it moves toward and away from the fixing belt 62 with the rotation support shaft 116 as a fulcrum. The pressure roller 64 is displaced in a direction in which it moves toward and away from the fixing belt 62 in conjunction with the rotation of the pressure lever 112. Furthermore, each of the pressure levers 112 has, at the other end (upper end), a locking portion 120 that locks one end of a tension coil spring (not shown), which is an example of a biasing member. The other end of the tension coil spring is locked to the fixing frame, and a predetermined biasing force acts on the pressure lever 112 (and thus on the pressure roller 64) in the direction in which the pressure roller 64 presses against the fixing belt 62 (to the left).

[0045] The contact pressure change mechanism 110 also includes a cam shaft 122 extending parallel to the axial direction of the fixing belt 62. Both ends of the cam shaft 122 are rotatably supported by the fixing frame. Also, at both ends of the cam shaft 122, a contact cam 124 is provided adjacent to the pressure lever 112, and the pressure lever 112 is provided with a contact portion 126 for contacting the contact cam 124. Furthermore, a second motor 128 (see FIG. 7) is connected to one end (rear end) of the cam shaft 122 via a gear or gear train (not shown). The cam shaft 122 receives a driving force from the second motor 128 and is driven to rotate in the forward and reverse directions around its axis, and the contact cam 124 rotates together with the cam shaft 122.

[0046] 6, the separation and engagement cam 124 is shaped so that the distance from the axial center of the cam shaft 122 gradually increases from Ls to Le in region R1. Therefore, the separation and engagement cam 124 receives a rotational driving force from the second motor 128 and rotates in the forward and reverse directions at a rotation position where the contact position with the contact portion 126 is in region R1, thereby turning the pressure lever 112 and changing the contact pressure (pressing force) of the pressure roller 64 against the fixing belt 62. Note that in a state where the separation and engagement cam 124 contacts the contact portion 126 at position E where the distance from the axial center of the cam shaft 122 is the farthest (state in FIG. 5), the pressure roller 64 is separated from the fixing belt 62.

[0047] In the fixing device 46, during image formation, the fixing belt 62 maintains a predetermined fixing temperature, and the pressure roller 64 contacts the fixing belt 62 with a predetermined contact pressure (pressing force), so that the paper passes through the fixing nip N, and the toner image is fixed on the paper. Therefore, when the temperature of the fixing belt 62 is low (for example, 40° C. or less) at the time of start-up, a warm-up operation is performed to increase the temperature to a predetermined fixing temperature (target temperature) while rotating the fixing belt 62 before forming an image on the paper. At this time, when the temperature of the fixing belt 62 is low, the viscosity of the sliding oil of the fixing pad 76 becomes high, and a high frictional force is generated between the fixing belt 62 and the fixing pad 76. For this reason, the fixing belt 62 may slip against the pressure roller 64, or a large load may be applied to the first motor 90 that drives the pressure roller 64, causing the first motor 90 to lock, resulting in poor rotation of the fixing belt 62. If the fixing belt 62 becomes heated in a state where the belt is not rotating properly, a portion of the fixing belt 62 will heat up suddenly and abnormally, causing the fixing belt 62 to become distorted, peeled off, or otherwise damaged.

[0048] For this reason, in the prior art, a control has been proposed to stop heating the fixing belt 62 when the temperature of the fixing belt 62 reaches a specified temperature (high temperature warning temperature). However, since the heat source 82 heats the fixing belt 62 from the inside, while the temperature sensor 94 detects the surface (outer surface) temperature of the fixing belt 62, a time lag (detection delay) corresponding to the thickness of the fixing belt 62 occurs, and the temperature of the inside of the fixing belt 62 may exceed the specified temperature. On the other hand, if a separate temperature sensor is provided to detect the temperature of the pressure roller 64, as in the technology of the above-mentioned Patent Document 1, the cost increases. Therefore, a technology is required to detect the fixing belt 62 in a rotation failure state as quickly as possible with a simple configuration. In addition, a technology is also required to appropriately restore (restart) the fixing belt 62 from the rotation failure state.

[0049] Therefore, in this first embodiment, during warm-up in which the temperature of the fixing belt 62 is raised to a target temperature while rotating, the rate of rise in the surface temperature of the fixing belt 62 (one example of information on temperature rise) is referenced to quickly detect whether the fixing belt 62 is in a rotational failure state. This is based on the knowledge found by the inventors and confirmed by verification experiments that, while the fixing belt 62 is rotating, the temperature of the fixing belt 62 rises as heat is absorbed by the pressure roller 64, whereas, when the fixing belt 62 is stopped, there is less transfer of heat from the fixing belt 62 to the pressure roller 64, so that the rate of temperature rise is faster when the fixing belt 62 is stopped than when it is rotating.

[0050] Furthermore, in this first embodiment, if a rotation failure of the fixing belt 62 is detected during warm-up, a stop operation is performed to stop the heating of the fixing belt 62 and the rotation of the pressure roller 64. After the stop operation, a retry operation is performed to resume the heating of the fixing belt 62 and the rotation of the pressure roller 64. When the fixing belt 62 returns to a normal rotation state by the retry operation, a normal job such as a print job is executed. On the other hand, if the detection of the rotation failure continues, an error notification is executed and the start-up of the fixing device 46 is stopped.

[0051] Specifically, during warm-up, the surface temperature of the fixing belt 62 is detected by the temperature sensor 94 at predetermined time intervals, and the rate of rise X (°C / s) of the surface temperature of the fixing belt 62 is detected based on the detection result. Here, the rate of rise X refers to the amount of temperature rise (temperature rise gradient) per predetermined time, and is expressed as X=(U n -U n-1 ) / T, where T is the time (seconds) and is set to, for example, 0.1 seconds. n is the current detected temperature (℃), and U n-1 is the detected temperature (°C) T seconds before the present. When the detected rising speed X is equal to or greater than a preset threshold Y (rising speed threshold, for example, 50°C / s), it is determined that the fixing belt 62 is in a rotational improper state (slip has occurred). In this case, in order to reduce erroneous detection, it is preferable to detect the rising speed X multiple times, and determine that the fixing belt 62 is in a rotational improper state when the rising speed X is equal to or greater than the threshold Y a predetermined number of times K (for example, 3 to 5 times) or more in succession.

[0052] In the first embodiment, the temperature sensor 94 includes a first temperature sensor that detects the surface temperature of the axial center of the fixing belt 62 and a second temperature sensor that detects the surface temperature of the axial end of the fixing belt 62, so that the determination of the poor rotation state based on the rising speed X may be performed individually by both the first temperature sensor and the second temperature sensor. In this case, the threshold value Y may be set to a different value for the first temperature sensor and the second temperature sensor. Then, when the rising speed X of either the first temperature sensor or the second temperature sensor becomes equal to or greater than the threshold value Y, it may be determined that the fixing belt 62 is in a poor rotation state. However, when the rising speed X of both the first temperature sensor and the second temperature sensor becomes equal to or greater than the threshold value Y, it may be determined that the fixing belt 62 is in a poor rotation state. Also, the determination of the poor rotation state based on the rising speed X may be performed using only either the first temperature sensor or the second temperature sensor.

[0053] Then, when it is determined that the fixing belt 62 is in a rotation failure state based on the rising speed X, the heating of the fixing belt 62 is immediately stopped, and a stopping operation is performed to stop the rotation of the pressure roller 64. This makes it possible to appropriately prevent damage to the fixing belt 62 due to an abnormal rise in temperature.

[0054] After the heating and rotation of the fixing belt 62 is stopped, a retry operation is performed to resume heating of the fixing belt 62 and rotation of the pressure roller 64. When the fixing belt 62 returns to a normal rotation state by the retry operation, that is, when the rotation failure state is no longer detected, a normal job such as a print job is executed. On the other hand, when the fixing belt 62 is detected to be in a rotation failure state even after the stop operation and the retry operation are continuously executed a predetermined number M (for example, three times), it is determined that an abnormality (restart is difficult) is detected, and an error notification such as a maintenance display and a machine trouble display is executed, and the start of the fixing device 46 is stopped. This error notification includes displaying a trouble code on the display of the operation unit 106, turning on a warning lamp, and contacting a predetermined service through a communication line. In addition, when an abnormality occurs, operations involving printing on paper such as copying and printing using the fixing device 46 may be made inoperable, while operations such as scanning and faxing that do not use the fixing device 46 may be made operable. A specific method of controlling the fixing device 46 during warm-up will be described later using a flow chart.

[0055] Fig. 7 is a block diagram showing an example of the electrical configuration of the image forming apparatus 10. As shown in Fig. 7, the image forming apparatus 10 includes a CPU 100, to which a RAM 102, a HDD 104, an operation unit 106, an image reading device 14, an image forming unit 30, and the like are connected via a bus.

[0056] The CPU 100 performs overall control of the image forming apparatus 10 including the fixing device 46 according to a program stored in the HDD 104. The CPU 100 also executes the warm-up process of the first embodiment and functions as a temperature detection unit and a first defective state detection unit. The RAM 102 is used as a working area and a buffer area for the CPU 100. The HDD 104 appropriately stores a control program and necessary data for the CPU 100 to control the operation of each part of the image forming apparatus 10. However, instead of or together with the HDD, other non-volatile memories such as SSDs, flash memories, and EEPROMs may be used.

[0057] The operation unit 106 includes a display with a touch panel, operation buttons, and the like. The display is a general-purpose monitor such as an LCD, and is connected to the CPU 100 via a display control circuit (not shown). The display control circuit includes a GPU, a VRAM, and the like. Under the instruction of the CPU 100, the GPU uses image generation data stored in the RAM 102 to generate display image data in the VRAM for displaying various screens on the display, and outputs the generated display image data to the display. The touch panel detects a touch operation within the effective touch range, and outputs touch coordinate data indicating the position of the touch operation to the CPU 100. The operation buttons are hardware keys, and include various keys or buttons such as a home button, a power saving key, and a power button.

[0058] The image reading device 14 and the image forming section 30 are as described above, and the image forming section 30 includes the fixing device 46 and the like. The fixing device 46 also includes the heat source 82, the temperature sensor 94, the first motor 90, the second motor 128, and the like.

[0059] As described above, the heat source 82 is a heater for heating the fixing belt 62 from the inner surface side, and includes the first lamp heater 82a and the second lamp heater 82b. The temperature sensor 94 is a sensor for detecting the surface temperature of the fixing belt 62, and includes the first temperature sensor and the second temperature sensor. The temperature sensor 94 outputs the detection result (a signal according to the surface temperature of the fixing belt 62) to the CPU 100 based on an instruction from the CPU 100. The CPU 100 controls the heat source 82 based on the detection result by the temperature sensor 94 so that the surface temperature of the fixing belt 62 becomes a desired fixing temperature. In addition, in this first embodiment, the CPU 100 calculates the rising speed X of the surface temperature of the fixing belt 62 based on the detection result by the temperature sensor 94 during warm-up, and judges whether the fixing belt 62 is in a rotation failure state.

[0060] The first motor 90 is a motor for driving and rotating the pressure roller 64, and rotates the motor shaft so that the pressure roller 64 rotates at a desired rotation speed based on a control signal from the CPU 100. The second motor 128 is a motor for driving and rotating the cam shaft 122, and rotates the motor shaft so that the separation and engagement cam 124 is at a desired rotation position based on a control signal from the CPU 100. That is, the CPU 100 controls the rotation position (angle) of the motor shaft of the second motor 128, thereby controlling the rotation position of the separation and engagement cam 124 and controlling the contact pressure between the fixing belt 62 and the pressure roller 64.

[0061] Fig. 8 is a diagram showing an example of a memory map 200 of the RAM 102. As shown in Fig. 8, the RAM 102 includes a program storage area 202 and a data storage area 204. The program storage area 202 of the RAM 102 stores an operation detection program 202a, an image forming program 202b, a rotation failure detection program 202c, a restart program 202d, and the like.

[0062] The operation detection program 202a is a program for detecting an operation on each part of the image forming apparatus 10 including the operation unit 106. The image forming program 202b is a program for controlling components such as the photoconductor drum 36 to print a multi-color or monochrome image on paper. The rotation failure detection program 202c is a program for calculating the rising speed X of the surface temperature of the fixing belt 62 based on the detection result by the temperature sensor 94, and for determining whether the fixing belt 62 is in a rotation failure state based on this rising speed X. The restart program 202d is a program for controlling the heat source 82, the first motor 90, etc., to execute a retry operation for restarting the heating of the fixing belt 62 and the rotation of the pressure roller 64 after stopping the heating and rotation of the fixing belt 62. The restart program 202d includes a program for executing an error notification and stopping the start of the fixing device 46 when the abnormality is not resolved even after executing the retry operation.

[0063] Although not shown, the program storage area 202 also stores other programs for causing the CPU 100 to execute various functions as appropriate.

[0064] Furthermore, the data storage area 204 of the RAM 102 stores a set value table 204a, temperature data 204b, cam position data 204c, and the like.

[0065] The setting value table 204a is a table that stores data such as setting values ​​used to perform warm-up operations in the fixing device 46, such as the target temperature of the fixing belt 62, the target rotation speed of the pressure roller 64, and the target contact pressure of the pressure roller 64, as well as the detection time T (detection interval) of the temperature sensor 94 used to detect a poor rotation state of the fixing belt 62, a threshold value Y, and predetermined numbers of times K and M.

[0066] The temperature data 204b is a value measured by the temperature sensor 94, that is, data on the surface temperature of the fixing belt 62. The temperature data 204b also includes a rise speed X (temperature rise gradient) calculated from the measurement value of the temperature sensor 94.

[0067] The cam position data 204c is data for identifying the cam position of the separation and engagement cam 124, and includes data indicating that the separation and engagement cam 124 is located at, for example, a target position, a low contact pressure position (pressure release position), and a separation position. Here, the target position is a cam position where the contact pressure of the pressure roller 64 becomes a predetermined contact pressure (target contact pressure) according to the paper type. The low contact pressure position is a cam position where the contact pressure of the pressure roller 64 becomes a pressure release state (a low contact pressure that does not cause the fixing belt 62 to slip). The separation position is a cam position where the pressure roller 64 becomes separated from the fixing belt 62.

[0068] Although not shown, the data storage area 204 is provided with a timer (counter) or register required for executing the control program, and stores other data required for executing the control program.

[0069] The above-described operation of fixing device 46 (image forming apparatus 10) is realized by CPU 100 executing a control program read into RAM 102. Hereinafter, an example of a warm-up process (rotation failure detection process and restart process) in fixing device 46 will be described with reference to the flow diagram shown in FIG.

[0070] 9, when the warm-up process is started, the CPU 100 starts rotating the pressure roller 64 in step S1. Here, a control signal is sent to the first motor 90 to rotate the pressure roller 64 at a predetermined rotation speed (target rotation speed). The fixing belt 62 rotates in accordance with the rotation of the pressure roller 64. In the next step S3, heating of the fixing belt 62 is started. That is, a control signal is sent to the heat source 82 to cause the heat source 82 to generate heat. The temperature of the fixing belt 62 increases as the heat source 82 generates heat.

[0071] In the next step S5, it is determined whether or not slippage has occurred, that is, whether or not the fixing belt 62 is in a rotation failure state. Here, the rising speed X is calculated multiple times from the detection result by the temperature sensor 94, and when the rising speed X is equal to or greater than the threshold value Y K times in succession, it is determined that the fixing belt 62 is in a rotation failure state. If "NO" in step S5, that is, if the fixing belt 62 is not in a rotation failure state, proceed to step S7. In step S7, it is determined whether or not the surface temperature of the fixing belt 62 has reached the target temperature. If "NO" in step S7, wait until the fixing belt 62 reaches the target temperature, and if "YES" in step S7, proceed to step S9. In step S9, a normal job such as copying and printing is performed, and then this process ends.

[0072] On the other hand, if step S5 is "YES", that is, if the fixing belt 62 is in a rotation failure state, the number of times that the rotation failure state has been detected is incremented, and the process proceeds to step S11. In step S11, a control signal is sent to the heat source 82 to stop heating the fixing belt 62. In the following step S13, a control signal is sent to the first motor 90 to stop the rotation of the pressure roller 64.

[0073] In the next step S15, it is determined whether the number of times that slippage has occurred is equal to or greater than a predetermined number M, that is, whether the number of times that the fixing belt 62 has been detected as being in a rotational improper state has reached M. If the answer is "NO" in step S15, that is, if the number of times that slippage has occurred is less than the predetermined number M, the process returns to step S1. In other words, a retry operation is performed. On the other hand, if the answer is "YES" in step S15, that is, if the number of times that slippage has occurred is equal to or greater than the predetermined number M, the process proceeds to step S17.

[0074] In step S17, the abnormality is notified. For example, a control signal is sent to the operation unit 106, and a trouble code indicating that a machine trouble has occurred is displayed on the display of the operation unit 106. In the following step S19, the start-up of the fixing device 46 is stopped, and then this process is terminated.

[0075] As described above, according to the first embodiment, whether the fixing belt 62 is in a rotation failure state is determined based on the rate of increase in the surface temperature of the fixing belt 62, so that it is possible to quickly detect that the fixing belt 62 is in a rotation failure state with a simple configuration without providing a separate temperature sensor for detecting the surface temperature of the pressure roller 64 or a separate encoder or the like for detecting the rotation of the fixing belt 62. Therefore, damage to the fixing belt 62 due to an abnormal temperature increase can be appropriately prevented.

[0076] [Second Example] Next, an image forming apparatus 10 according to a second embodiment of the present invention will be described with reference to Fig. 10. This second embodiment differs from the first embodiment in that a low contact pressure rotation operation is performed before a retry operation is performed. Since the other parts are similar, the same reference numbers are used for parts common to the first embodiment, and duplicated descriptions are omitted or simplified.

[0077] In the second embodiment, after the rotation failure state of the fixing belt 62 is detected and a stop operation is performed, a low contact pressure rotation operation is performed in which the pressure roller 64 rotates for a predetermined time B (for example, 1.0 second) with the contact pressure of the pressure roller 64 against the fixing belt 62 set to a low contact pressure (a low contact pressure at which the fixing belt 62 does not slip). In this way, by reducing the load of the pressure roller 64 against the fixing belt 62, the friction between the fixing belt 62 and the fixing pad 76 is reduced, and deformation of the fixing belt 62 at the fixing nip N is also suppressed. As a result, the fixing belt 62 becomes easy to rotate, so that the fixing belt 62 is rotated for the predetermined time B in this state to make the fixing belt 62 and the fixing pad 76 familiar with the sliding oil, and the fixing belt 62 is less likely to become in a rotation failure state during a retry operation.

[0078] An example of the warm-up process in the fixing device 46 of the second embodiment will be described below with reference to the flow chart shown in Fig. 10. However, since the processes in steps S21 to S39 are similar to the processes in steps S1 to S19 in the first embodiment, the description thereof will be omitted.

[0079] 10, if the result in step S35 is "NO," that is, if the fixing belt 62 is not in a rotation failure state, the CPU 100 proceeds to step S41. In step S41, the fixing pressure of the pressure roller 64 is released. That is, a control signal is sent to the second motor 128 of the contact pressure change mechanism 110 to set the cam position of the contact / separation cam 124 to the low contact pressure position, and the contact pressure of the pressure roller 64 against the fixing belt 62 is set to the low contact pressure.

[0080] In the next step S43, a control signal is sent to the first motor 90 to rotate the pressure roller 64 for a predetermined time B and then stop it. In the following step S45, the fixing pressure is returned to the original state. That is, a control signal is sent to the second motor 128 to set the cam position of the separation and engagement cam 124 to the target position, and the contact pressure of the pressure roller 64 against the fixing belt 62 is returned to a predetermined contact pressure according to the paper type. When step S45 is completed, the process returns to step S21.

[0081] According to the second embodiment, as in the first embodiment, it is possible to quickly detect that the fixing belt 62 is in a rotation failure state with a simple configuration. In addition, since the low contact pressure rotation operation is performed before the retry operation is performed, it is possible to appropriately prevent the fixing belt 62 from becoming in a rotation failure state during the retry operation. Therefore, it is possible to appropriately restart the fixing device 46 (and thus the image forming apparatus 10).

[0082] [Third Example] Next, an image forming apparatus 10 according to a third embodiment of the present invention will be described with reference to Fig. 11. This third embodiment differs from the second embodiment in that when it is detected that the fixing belt 62 is in a poor rotation state during the low contact pressure rotation operation, a heating rotation operation is performed. Since the other parts are similar, the same reference numbers are used for parts common to the first and second embodiments, and duplicated descriptions are omitted or simplified.

[0083] In this third embodiment, the CPU 100, during the above-mentioned low contact pressure rotation operation, refers to the rate of drop in the surface temperature of the fixing belt 62 (one example of temperature drop information) to quickly detect whether the fixing belt 62 is in a rotation failure state. That is, the CPU 100 also functions as a second failure state detection unit. This is based on the knowledge found by the inventors and confirmed by a verification experiment that, contrary to when the fixing belt 62 is heated, when the fixing belt 62 is not heated, the temperature drop rate is slower when the fixing belt 62 is stopped than when it is rotating.

[0084] Specifically, during low contact pressure rotation operation, the surface temperature of the fixing belt 62 is detected by the temperature sensor 94 at predetermined time intervals, and the drop rate P (°C / s) of the surface temperature of the fixing belt 62 is detected based on the detection result. Here, the drop rate P refers to the amount of temperature drop (temperature drop gradient) per predetermined time, and is expressed as P=(U n-1 -U n ) / T, where T is the time (seconds) and is set to, for example, 0.1 seconds. n is the current detected temperature (℃), and U n-1 is the detected temperature (°C) T seconds before the present. When the calculated drop speed P is equal to or lower than a preset threshold Q (drop speed threshold, for example, 10°C / s), it is determined that the fixing belt 62 is in a rotational improper state (slip has occurred). In this case, in order to reduce erroneous detection, it is preferable to detect the drop speed P multiple times, and determine that the fixing belt 62 is in a rotational improper state when the drop speed P is equal to or lower than the threshold Q a predetermined number of times L (for example, 3 to 5 times) or more. As in the above-mentioned embodiment, the determination of the rotational improper state based on the drop speed P may be performed individually by both the first temperature sensor and the second temperature sensor.

[0085] Then, when it is detected that the fixing belt 62 is in a rotation failure state during the low contact pressure rotation operation, a heating rotation operation is performed in which the pressure roller 64 is rotated for a predetermined time C (for example, 3 seconds) while heating the fixing belt 62 while keeping the contact pressure of the pressure roller 64 at a low contact pressure. The fixing belt 62 becomes easier to rotate when in a low contact pressure state (pressure release state), but if rotation failure occurs even in this state, it is considered that the adhesion of the sliding oil and the deformation of the fixing belt 62 are severe. Therefore, when it is detected that the fixing belt 62 is in a rotation failure state during the low contact pressure rotation operation, the heating rotation operation is performed to alleviate the adhesion of the sliding oil and the deformation of the fixing belt 62. When performing this heating rotation operation, it is preferable to reduce the output of the heat source 82 to a state (for example, 50% output) lower than the output during normal times (when temperature is adjusted) and to heat the fixing belt 62 to a low heating state. The amount of heat may be reduced by a known method. For example, in the case of phase control, the phase angle may be made smaller, and in the case of wave number control, the wave number may be thinned out to reduce the power supplied to the heat source 82.

[0086] An example of the warm-up process in the fixing device 46 of the third embodiment will be described below with reference to the flow chart shown in Fig. 11. However, since the processes in steps S51 to S73 and S79 are similar to the processes in steps S21 to S45 in the first embodiment, the description thereof will be omitted.

[0087] As shown in Fig. 11, following the process of step S73, the process of step S75 is executed. In step S75, it is determined whether or not slippage occurs when the pressure roller 64 is rotated in step S73, that is, whether or not the fixing belt 62 is in a rotation failure state. Here, the descent speed P is calculated multiple times from the detection result by the temperature sensor 94 when the pressure roller 64 is rotated, and when the descent speed P is equal to or less than the threshold value Q L consecutive times, it is determined that the fixing belt 62 is in a rotation failure state. If "NO" in step S75, that is, if the fixing belt 62 is not in a rotation failure state, the process proceeds directly to step S79.

[0088] On the other hand, if "YES" in step S75, that is, if the fixing belt 62 is in a rotation failure state, proceed to step S77. In step S77, a control signal is sent to the heat source 82 and the first motor 90 to rotate the pressure roller 64 while heating the fixing belt 62 for a predetermined time C. When the process of step S77 ends, proceed to step S79.

[0089] According to the third embodiment, as in the first embodiment, it is possible to quickly detect that the fixing belt 62 is in a rotation failure state with a simple configuration. Also, since the heating and rotating operation is executed when it is detected that the fixing belt 62 is in a rotation failure state during the low contact pressure rotation operation, it is possible to more appropriately prevent the fixing belt 62 from becoming in a rotation failure state during the retry operation. Therefore, the fixing device 46 can be more appropriately restarted.

[0090] In the above-described embodiments, a single preset value is used as the threshold value Y (rising speed threshold value) for determining whether the fixing belt 62 is in a rotation failure state. However, the threshold value Y can be changed according to the supply voltage to the fixing device 46 (i.e., the image forming device 10). The threshold value Y may be changed in proportion to the change in the supply voltage, or the threshold value Y may be corrected according to the characteristics of the heat source 82, to set the threshold value Y appropriate for the supply voltage at that time. For example, if the threshold value Y is set to 50° C. / s when the supply voltage is 100 V, the threshold value Y may be changed to 45° C. / s when the detected supply voltage is 95 V, or to 55° C. / s when the detected supply voltage is 105 V. Specifically, as another embodiment, the image forming device 10 is provided with a threshold value storage unit that stores a plurality of threshold values ​​Y set according to the value of the supply voltage to the fixing device 46, and a supply voltage detection unit that detects the supply voltage to the fixing device 46. Then, the CPU 100 functioning as the first defective state detection unit selects a threshold value Y from among a plurality of threshold values ​​Y stored in the threshold value storage unit based on the supply voltage detected by the supply voltage detection unit, and detects that the fixing belt 62 is in a defective rotation state when the rising speed X is equal to or greater than the selected threshold value Y.

[0091] As another embodiment, the cumulative number of times that the fixing belt 62 has been detected to be in a rotation failure state (the total number from the start of use (replacement) of the fixing belt 62 to the present) can be stored in a storage unit (cumulative number storage unit) such as the HDD 104 together with the number of sheets of paper passed, and the cumulative number can be displayed on a display unit such as a display of the operation unit 106. For example, the stored cumulative number can be used as a prescribed value for prescribing the life (lifespan or replacement time) of the fixing belt 62. Conventionally, the life of the fixing belt 62 is prescribing based on the number of sheets of paper passed (for example, set to 300,000 sheets), but in addition to this or instead, if the life of the fixing belt 62 is prescribing based on the cumulative number of detections of rotation failure (for example, set to 1,000 times), replacement of the fixing belt 62 can be more appropriately promoted in a usage situation where belt slippage occurs frequently.

[0092] In each of the above-described embodiments, the image forming apparatus 10 is exemplified as a multifunction machine combining a copier, a facsimile, a printer, etc., but the image forming apparatus 10 may be any one of a copier, a facsimile, a printer, etc., or a multifunction machine combining at least two of these.

[0093] Furthermore, the specific numerical values ​​and materials given above are merely examples and can be changed as appropriate according to the needs of the product specifications, etc. [Explanation of symbols]

[0094] 10...Image forming device 30...Image forming section 46... Fixing device 62 ... Fixing belt (fixing rotor) 64 ... Pressure roller (pressure rotating body) 82…Heat source 90 ... First motor (motor for pressure roller) 92 ... Current sensor 94 ...Temperature sensor 100...CPU 110 ... Contact pressure change mechanism 124 ... Disengagement cam 128 ... Second motor (motor for engagement / disengagement cam)

Claims

1. A fixing device for thermally fixing a toner image formed on a recording medium, comprising: Fixing rotor, A heat source for heating the fixing rotor; a pressure rotating body that comes into contact with an outer circumferential surface of the fixing rotating body to form a nip portion between the pressure rotating body and the fixing rotating body, and that rotates the fixing rotating body in a driven manner; A motor that rotates the pressurizing rotor; a contact pressure changing mechanism capable of changing the contact pressure of the pressing rotor with respect to the fixing rotor; a temperature detection unit for detecting a surface temperature of the fixing rotor; a first defective state detection unit that detects whether the fixing rotator is in a rotation defective state based on information on a temperature rise of the surface temperature of the fixing rotator detected by the temperature detection unit during a warm-up period in which the fixing rotator is rotated and heated to a target temperature; and a control unit that controls the heat source and the motor to execute a stop operation for stopping heating of the fixing rotor and rotation of the pressure rotor when the first malfunction detection unit detects that the fixing rotor is in a malfunction state, After executing the stopping operation, the control unit executes a retry operation of restarting heating of the fixing rotator and rotation of the pressure rotator, and when the first malfunction detection unit detects that the fixing rotator is in a malfunction state after the stopping operation and the retry operation are executed a predetermined number of times, the control unit executes an error notification and stops activation of the fixing device, The control unit, after performing the stop operation and before performing the retry operation, controls the contact pressure change mechanism and the motor to perform a low contact pressure rotation operation in which the contact pressure of the pressure applying rotor against the fixing rotor is set to a low contact pressure and the pressure applying rotor is rotated for a predetermined time in this state.

2. a second defective state detection unit that detects whether the fixing rotor is in a defective rotation state based on information on a temperature drop in the surface temperature of the fixing rotor detected by the temperature detection unit when the low contact pressure rotation operation is performed, 2. The fixing device according to claim 1, wherein when the second defective state detection unit detects that the fixing rotor is in a rotational defective state, the control unit controls the heat source and the motor to perform a heating and rotation operation in which the fixing rotor is heated while rotating the pressure rotor for a predetermined period of time.

3. a threshold storage unit that stores a plurality of increase speed thresholds that are set according to values ​​of a voltage supplied to the fixing device; a supply voltage detection unit that detects a supply voltage to the fixing device, 3. The fixing device according to claim 1, wherein the first fault condition detection unit detects that the fixing rotor is in a rotational fault condition when the rate of rise of the temperature detected by the temperature detection unit is equal to or greater than the rate of rise threshold selected based on the supply voltage detected by the supply voltage detection unit.

4. an integrated number storage unit that stores an integrated number of times that the first defective state detection unit has detected that the fixing rotator is in a rotation defective state; and The fixing device according to claim 1 , further comprising a display unit capable of displaying the integrated number.

5. An image forming apparatus comprising the fixing device according to claim 1 .

Images