Image forming device

Abstract

To prevent accumulation of attachments in a sensor.SOLUTION: An image forming apparatus has: a rotating member that extends in a width direction, is rotatably provided, and conveys a medium; a drive unit that rotates the rotating member in a normal direction for conveying the medium and in a reverse direction opposite to the normal direction during image formation; a sensor that is in contact with a surface of the rotating member; and a position changing unit that changes the relative positions of the rotating member and the sensor in the width direction. The image forming apparatus performs a first operation. In the first operation, the drive unit rotates the rotating member in the reverse direction, and the position changing unit changes the relative positions of the rotating member and the sensor in the width direction from first relative positions in which the distance between one end in the width direction of the rotating member and the sensor becomes a first distance to second relative positions in which the distance between one end of the rotating member and the sensor becomes a second distance.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus that forms an image on a medium. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known an image forming apparatus that forms an image on a medium, and that is provided with a contact type sensor that comes into contact with a rotating member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-15920 A (see paragraph 0042) Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of a contact-type sensor that comes into contact with a rotating member, deposits may accumulate at the contact portion between the rotating member and the sensor, which may reduce detection accuracy and affect image quality.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to suppress the accumulation of deposits on a sensor. [Means for solving the problem]

[0006] The image forming apparatus of the present disclosure includes a rotating member that is rotatably disposed to extend in the width direction and transports a medium, a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction, a sensor that contacts the surface of the rotating member, and a position change unit that changes the relative position of the rotating member and the sensor in the width direction. 、 has. The position changing unit includes a rotating member moving mechanism that moves the rotating member in the width direction. The image forming apparatus executes a first operation. In the first operation, the driving unit rotates the rotating member in the reverse direction, and Rotating member moving mechanism but By moving the rotating member in the axial directionThe relative position between the rotating member and the sensor in the width direction is changed from a first relative position in which the distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position in which the distance between the one end of the rotating member and the sensor is a second distance. The image forming apparatus of the present disclosure also includes a rotating member that extends in the width direction and is rotatably provided to transport a medium, a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction, and a sensor that contacts the surface of the rotating member. and a position changing unit that changes the relative position between the rotating member and the sensor in the width direction. The position changing unit has a first helical gear to which rotation of the drive unit is transmitted, and a second helical gear that is connected to the rotating member, meshes with the first helical gear, and transmits the rotation of the first helical gear to the rotating member. The image forming apparatus executes a first operation. In the first operation, the drive unit rotates the rotating member in the reverse direction, and moves the rotating member in the width direction by the rotation of the drive unit, thereby changing the relative position between the rotating member and the sensor in the width direction from a first relative position where the distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position where the distance between one end of the rotating member and the sensor is a second distance. The image forming apparatus of the present disclosure also includes a rotating member extending in the width direction and rotatably provided to transport a medium, a driving unit for rotating the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction, a sensor that contacts the surface of the rotating member, a position changing unit that changes the relative position between the rotating member and the sensor in the width direction, a fixing member that contacts the rotating member to form a nip, and a separation mechanism that brings the rotating member and the fixing member into contact with each other and separates them from each other. The image forming apparatus performs a first operation after separating the rotating member and the fixing member from each other by the separation mechanism. In the first operation, the driving unit rotates the rotating member in the reverse direction, and the position changing unit changes the relative position between the rotating member and the sensor in the width direction from a first relative position where a distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position where a distance between one end of the rotating member and the sensor is a second distance.

[0007] The image forming apparatus of the present disclosure also includes a rotating member that extends in the width direction and is rotatably provided to transport a medium, a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction, and a sensor that contacts the surface of the rotating member. By moving the rotating member in the width direction, a position changing unit that changes the relative position between the rotating member and the sensor in the width direction; 、 The image forming unit performs a first operation and a second operation. In the first operation, the position changing unit By moving the rotating member in the width direction In the second operation, the drive unit rotates the rotating member in the reverse direction while maintaining the second relative position. Effect of the Invention

[0008] According to the present disclosure, by rotating the rotating member in the reverse direction and changing the relative position in the width direction between the rotating member and the sensor, any deposits that have accumulated on the sensor can be dispersed, thereby suppressing degradation of image quality. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a basic configuration of an image forming apparatus according to a first embodiment. [Diagram 2] 1 is a cross-sectional view showing a fixing device according to a first embodiment. [Diagram 3] FIG. 2 is a perspective view showing the fixing belt and its inner components according to the first embodiment. [Figure 4] FIG. 2 is a front view showing the pressure roller according to the first embodiment. [Diagram 5] FIG. 2 is a perspective view showing the fixing device according to the first embodiment. [Figure 6] FIG. 2 is a rear view showing the fixing device according to the first embodiment. [Figure 7] 2 is a side view showing the periphery of a bearing of the fixing device according to the first embodiment. FIG. [Figure 8] FIG. 2 is a perspective view showing a mounting structure of a bearing of the fixing device according to the first embodiment. [Figure 9] FIG. 2 is a perspective view showing a bearing of the fixing device according to the first embodiment. [Figure 10] 3 is a cross-sectional view showing a mounting structure of a bearing of the fixing device according to the first embodiment. FIG. [Figure 11] 4A and 4B are diagrams illustrating the operation of the fixing device according to the first embodiment. [Figure 12] FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the first embodiment. [Figure 13] 4 is a timing chart showing a printing operation of the image forming apparatus according to the first embodiment. [Figure 14] 5 is a timing chart showing a cleaning operation of the image forming apparatus according to the first embodiment. [Figure 15] 5 is a timing chart showing a cleaning operation of the image forming apparatus according to the first embodiment. [Figure 16] 4A and 4B are schematic diagrams for explaining the operation of the first embodiment. [Figure 17] 4A and 4B are schematic diagrams for explaining the operation of the first embodiment. [Figure 18] 5 is a flowchart showing a cleaning operation of the image forming apparatus according to the first embodiment. [Figure 19] 1A is a perspective view and FIG. 1B is a front view showing a fixing device of a comparative example. [Figure 20] FIG. 11 is a cross-sectional view showing a fixing device of an image forming apparatus according to a second embodiment. [Figure 21]FIG. 11 is a block diagram showing a control system of an image forming apparatus according to a second embodiment. [Figure 22] 10 is a timing chart showing a cleaning operation of an image forming apparatus according to a second embodiment. [Diagram 23] 13A and 13B are diagrams illustrating a fixing device of an image forming apparatus according to a first modified example. [Figure 24] 13A and 13B are diagrams illustrating a fixing device of an image forming apparatus according to a second modified example. [Diagram 25] 13A and 13B are diagrams illustrating a fixing device of an image forming apparatus according to a third modified example. [Figure 26] 13A and 13B are diagrams illustrating a fixing device of an image forming apparatus according to a fourth modified example. [Figure 27] 13A to 13C are diagrams illustrating the operation of a fixing device of an image forming apparatus according to a fourth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] First embodiment. <Configuration of Image Forming Apparatus> First, an image forming apparatus 1 in the first embodiment will be described. Fig. 1 is a diagram showing the configuration of the image forming apparatus 1 in the first embodiment. The image forming apparatus 1 is a printer that forms a color image by using electrophotography.

[0011] The image forming apparatus 1 includes a medium supply section 80 that supplies a medium P such as printing paper, image forming units 60K, 60Y, 60M, and 60C that form toner images, a transfer unit 70 that transfers the toner image to the medium P, a fixing device 10 that fixes the toner image to the medium P, a medium discharge section 90 that discharges the medium P, and a housing 1A that houses these.

[0012] The medium supply section 80 has a paper feed tray 81 as a medium storage section that stores medium P in a stacked state, a feed roller 82 that sends the medium P stacked in the paper feed tray 81 to a conveying path, and a pair of conveying rollers 83 that convey the medium P along the conveying path.

[0013] Image forming units 60K, 60Y, 60M, and 60C are arranged in this order along the transport path of medium P. Image forming units 60K, 60Y, 60M, and 60C form toner images using black, yellow, magenta, and cyan toners (developers), respectively. Image forming units 60K, 60Y, 60M, and 60C have a common configuration except for the toner, and therefore will be described as "image forming unit 60."

[0014] The image forming unit (image forming section) 60 has a photosensitive drum 61 as an image carrier, a charging roller 62 as a charging member, a developing roller 64 as a developer carrier, a supply roller 65 as a supply member, a regulating blade 66 as a layer regulating member, and a cleaning member 67. An exposure head 63 is provided so as to face the surface of the photosensitive drum 61.

[0015] The photoconductor drum 61 is a drum-shaped member having a photosensitive layer (charge generating layer and charge transport layer) on the surface of a conductive substrate, and rotates clockwise in the figure by the rotation of a main motor described later.

[0016] The charging roller 62 is a roller disposed so as to come into contact with the surface of the photosensitive drum 61, and rotates following the rotation of the photosensitive drum 61. A charging voltage is applied to the charging roller 62, and the charging roller 62 uniformly charges the surface of the photosensitive drum 61.

[0017] The exposure head 63 has a light emitting element such as an LED (light emitting diode) and a lens array. The exposure head 63 irradiates light onto the uniformly charged surface of the photoconductor drum 61 to form an electrostatic latent image.

[0018] The developing roller 64 is a roller disposed so as to contact the photosensitive drum 61, and rotates by the rotation transmitted from the photosensitive drum 61. The developing roller 64 carries toner on its surface, and develops the latent image formed on the surface of the photosensitive drum 61.

[0019] The supply roller 65 is disposed so as to contact or face the developing roller 64, and rotates by the rotation transmitted from the photosensitive drum 61. The supply roller 65 carries toner on its surface and supplies it to the developing roller 64.

[0020] The regulating blade 66 is a metallic blade disposed so as to come into contact with the developing roller 64. The regulating blade 66 is pressed against the surface of the developing roller 64 to regulate the thickness of the toner layer on the surface of the developing roller 64.

[0021] The cleaning member 67 is a roller or blade made of an elastic material, and scrapes off the toner remaining on the surface of the photosensitive drum 61 .

[0022] Further, each image forming unit 60 is provided with a detachable toner cartridge 68 as a developer supplying section that supplies toner to the developing roller 64 and the supply roller 65 .

[0023] The transfer unit 70 has four transfer rollers 71 arranged to face each of the photosensitive drums 61 of the image forming units 60K, 60Y, 60M, and 60C, and an endless transfer belt 72 passing between each of the photosensitive drums 61 and the transfer rollers 71. The transfer belt 72 is stretched around a belt drive roller 73 and a tension roller 74.

[0024] A transfer voltage is applied to the transfer roller 71 to transfer the toner image formed on the photosensitive drum 61 to the medium P. The transfer belt 72 attracts and holds the medium P by electrostatic force and transports it. The belt drive roller 73 drives the endless transfer belt 72. The tension roller 74 applies tension to the transfer belt 72.

[0025] The fixing device 10 is disposed downstream of the image forming unit 60 along the transport path of the medium P. The fixing device 10 has a fixing belt 11 and a pressure roller 18, and applies heat and pressure to the toner image on the medium P to fix it to the medium P. The configuration of the fixing device 10 will be described later.

[0026] The medium discharge section 90 is disposed downstream of the fixing device 10 along the transport path of the medium P. The medium discharge section 90 has a pair of discharge rollers 91, 92 that discharge the medium P on which the toner image has been fixed to the outside of the device. The upper cover 1B of the image forming apparatus 1 is provided with a stacker section 93 for placing the discharged medium P.

[0027] Additionally, sensors M1 to M4 that detect the position of medium P are disposed along the transport path of medium P. Paper feed sensor M1 is disposed upstream of transport roller pair 83, and write sensor M2 is disposed downstream of transport roller pair 83. Fixing IN sensor M3 is disposed upstream of fixing device 10, and fixing OUT sensor M4 is disposed downstream of fixing device 10. Transport control of medium P or light emission timing of exposure head 63 is performed based on output signals from these sensors M1 to M4.

[0028] 1, the axial direction of the photoconductor drum 61 is defined as the X direction. The X direction is also the width direction of the fixing belt 11 and the axial direction of each roller in the image forming apparatus 1. The transport direction (the direction of movement of the medium P) when the medium P passes through the fixing device 10 is defined as the Y direction. The direction perpendicular to the X direction and the Y direction is defined as the Z direction.

[0029] For the Y direction, the transport direction of the medium P when it passes through the fixing device 10 is the +Y direction, and the opposite direction is the -Y direction. For the X direction, the right hand direction when facing the +Y direction is the +X direction, and the left hand direction is the -X direction. For the Z direction, the upward direction in FIG. 1 is the +Z direction, and the downward direction is the -Z direction.

[0030] <Configuration of the fixing device> Next, a description will be given of the components of the fixing device 10. Fig. 2 is a cross-sectional view showing the fixing device 10. The fixing device 10 has a fixing belt 11, which is an endless belt, as a fixing member, a heater 15 arranged on the inner peripheral side of the fixing belt 11, and a pressure roller 18 arranged on the outer peripheral side of the fixing belt 11 as a rotating member (or pressure member).

[0031] 3 is a perspective view showing fixing belt 11 and components arranged on its inner peripheral side. As described above, the width direction of fixing belt 11 is the X direction. The outer diameter of fixing belt 11 is, for example, 18 mm. The circumferential length of fixing belt 11 is, for example, about 57 mm.

[0032] The fixing belt 11 has a base layer and a release layer covering the surface of the base layer. An elastic layer may be provided between the base layer and the release layer. The base layer is made of a metal such as nickel or stainless steel (SUS), or a resin such as polyimide (PI). The release layer is made of a resin such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) or polytetrafluoroethylene (PTFE). The elastic layer is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber.

[0033] On the inner peripheral side of the fixing belt 11, a stay 12, a heater support member 13, a heater sensor 14, and a heater 15 are arranged.

[0034] The stay 12 is a member that is long in the X direction and has a substantially U-shaped cross section in a plane perpendicular to the X direction. More specifically, the stay 12 has two side plate portions 12b facing each other in the Y direction and a top plate portion 12a that connects the upper ends of the side plate portions 12b. The stay 12 is formed, for example, from sheet metal, and supports the heater support member 13, the heater sensor 14, and the heater 15. Both ends of the stay 12 in the X direction are fixed to a movable frame 23, which will be described later.

[0035] The heater support member 13 is fixed to the lower side (-Z direction) of the stay 12. The heater support member 13 is configured to have two side plate portions 13b fixed to the inner sides of the two side plate portions 12b of the stay 12, and a bottom plate portion 13a connecting the lower ends of the side plate portions 13b. The heater support member 13 is formed of a resin such as PEEK (polyether ether ketone).

[0036] The heater 15 is a planar heater that heats the fixing belt 11. The heater 15 has a base layer having insulation and strength, a heat generation layer made of an electric heating wire, an insulating layer covering both sides of the heat generation layer, and a conductive layer electrically connecting the heat generation layer. The heater 15 generates heat when a current is supplied to the heat generation layer. The top surface of the heater 15 is attached to the bottom plate portion 13a of the heater support member 13.

[0037] The heater sensor 14 is supported by a heater support member 13. The heater sensor 14 also contacts the upper surface of the heater 15 through an opening formed in the heater support member 13. The heater sensor 14 detects the temperature of the heater 15 and outputs a detection signal. The output signal of the heater sensor 14 is sent to a heater control unit 113 (FIG. 12) described later, and the temperature of the heater 15 is controlled based on this signal.

[0038] The fixing belt 11 is supported at both ends in the X direction (i.e., the width direction) by a pair of belt guides 17. The belt guide 17 has a cylindrical portion 17a that supports the fixing belt 11 from the inner peripheral side, and an annular portion 17b that abuts against the width direction end surface of the fixing belt 11. The belt guide 17 is attached to a movable frame 23, which will be described later.

[0039] 2, the pressure roller 18 is disposed below the fixing belt 11. The axial direction of the pressure roller 18 is the X direction. The outer diameter of the pressure roller 18 is, for example, 25 mm. The circumferential length of the pressure roller 18 is, for example, about 79 mm.

[0040] The pressure roller 18 has a core metal 18a, an elastic layer 18b formed on the surface of the core metal 18a, and a release layer 18c covering the surface of the elastic layer 18b. The core metal 18a is made of metal. The elastic layer 18b is made of a resin such as foamed silicone rubber or silicone rubber. The release layer 18c is made of a resin such as PFA or PTFE.

[0041] The pressure roller 18 is pressed against the fixing belt 11 by the biasing force of a biasing member 24 described later, and the elastic layer 18b is crushed to form a fixing nip. The pressure roller 18 is rotated by the rotation transmitted from a fixing motor 43 described later.

[0042] Fig. 4 is a front view showing the pressure roller 18. As shown in Fig. 4, a shaft portion 18e extending in the X direction is formed on both axial ends of the pressure roller 18. Each shaft portion 18e of the pressure roller 18 is rotatably supported by a bearing 25 described later.

[0043] A large diameter portion 18d having a larger diameter than the shaft portion 18e is formed at the base of each shaft portion 18e of the pressure roller 18. The shaft portion 18e and the large diameter portion 18d are part of the core metal 18a (FIG. 2). The large diameter portion 18d has a stopper surface 18f, which is an end surface perpendicular to the X direction.

[0044] The pressure roller 18 moves a predetermined amount (e.g., 6 mm) in the X direction as described below. The stopper surface 18f functions as a stopper when the pressure roller 18 moves in the +X direction and the -X direction. A fixing gear 41 is attached to the tip end (indicated by the symbol H) of one shaft portion 18e of the pressure roller 18.

[0045] A portion of the pressure roller 18 including the elastic layer 18b (FIG. 2) and the release layer 18c in the axial direction is referred to as a roller portion. The roller portion of the pressure roller 18 forms a fixing nip with the fixing belt 11.

[0046] 5 and 6 are a perspective view and a front view showing the fixing device 10. As shown in Fig. 5 and Fig. 6, the fixing device 10 has a pair of side frames 21 as frames facing each other in the X direction, and a bottom frame 20 connecting the lower ends of the side frames 21.

[0047] The fixing belt 11, the stay 12, the heater support member 13, the heater sensor 14, the heater 15, and the pressure roller 18 are disposed between a pair of side frames 21. The pressure roller 18 is rotatably supported by the pair of side frames 21.

[0048] A pair of movable frames 23 are provided inside the pair of side frames 21 in the X direction. Each movable frame 23 is made of sheet metal and is rotatably supported by a support shaft 22 in the X direction provided on each side frame 21. The support shaft 22 is disposed upstream of the fixing nip between the fixing belt 11 and the pressure roller 18, i.e., in the -Y direction. Each movable frame 23 has a support shaft bearing portion 23a (FIG. 2) that engages with the support shaft 22.

[0049] An end portion in the X direction of the stay 12 (FIG. 3) is fixed to each movable frame 23. In addition, a belt guide 17 that supports the fixing belt 11 is attached to each movable frame 23. As a result, the pair of movable frames 23 support the fixing belt 11 via the pair of belt guides 17, and also support the stay 12 and each of the components supported thereby (the heater support member 13, the heater sensor 14, and the heater 15).

[0050] As shown in Fig. 5, the fixing device 10 has a biasing member 24 that biases the movable frame 23. The biasing member 24 is, for example, a coil spring. One end of the biasing member 24 is fixed to an engagement piece 23b formed on the movable frame 23, and the other end is fixed to an engagement piece 21a formed on the side frame 21. The biasing member 24 biases the movable frame 23 in the direction indicated by the arrow C1 in Fig. 5.

[0051] A fixing gear 41 serving as a first helical gear is attached to the shaft portion 18e of the pressure roller 18 in the +X direction. A drive gear 42 serving as a second helical gear is engaged with the fixing gear 41. The drive gear 42 is supported by a support portion provided within the housing of the image forming apparatus 1. Rotation is transmitted to the drive gear 42 from a fixing motor 43 described later. Both the fixing gear 41 and the drive gear 42 are helical gears.

[0052] The fixing gear 41 has a module of 1, a number of teeth of 27, a pressure angle of 20 degrees, a twist angle of 20 degrees, and a right-handed twist direction. The drive gear 42 has a module of 1, a number of teeth of 31, a pressure angle of 20 degrees, a twist angle of 20 degrees, and a left-handed twist direction.

[0053] Since both the fixing gear 41 and the driving gear 42 are helical gears, a force in the X direction (thrust direction) acts between them when they rotate. Also, each shaft portion 18e of the pressure roller 18 has a length sufficient to cover a predetermined amount of movement in the X direction. Here, the amount of movement of the pressure roller 18 in the X direction is 6 mm.

[0054] In order to prevent disengagement between the fixing gear 41 and the driving gear 42 even when the pressure roller 18 moves in the X direction, the width of the driving gear 42 in the X direction is set to be wider than the width of the fixing gear 41 in the X direction. If the amount of movement of the pressure roller 18 in the X direction is 6 mm, the width of the fixing gear 41 is 8 mm and the width of the driving gear 42 is 18 mm.

[0055] Fig. 7 is a side view showing the fixing device 10. Fig. 8 is an exploded perspective view showing the mounting structure of the bearing 25 in the side frame 21. Fig. 9 is a perspective view showing the shape of the bearing 25. Fig. 10 is a cross-sectional view showing the mounting structure of the bearing 25 in the side frame 21.

[0056] 7 and 8, each shaft portion 18e of the pressure roller 18 is supported on the side frame 21 by a bearing 25. The bearing 25 is attached to a groove portion 21b (FIG. 8) formed in the side frame 21.

[0057] As shown in FIG. 9, the bearing 25 has a pair of flange portions 25a, 25b facing each other in the axial direction (X direction) of the pressure roller 18, and a body portion 25c disposed therebetween.

[0058] The flanges 25a and 25b protrude outward from the outer periphery of the body 25c. The flanges 25a and 25b and the body 25c are all square, but are not limited to this. The distance between the flanges 25a and 25b in the X direction is slightly wider than the thickness of the side frame 21.

[0059] 10, when the bearing 25 is attached to the groove 21b of the side frame 21, the body 25c of the bearing 25 engages with the groove 21b, and the flanges 25a and 25b sandwich the side frame 21 from both sides in the X direction. Therefore, even if the pressure roller 18 moves in the X direction, the bearing 25 will not come out of the groove 21b of the side frame 21.

[0060] 5, the fixing device 10 includes a thermistor 30 as a sensor (temperature sensor) that detects the surface temperature of the pressure roller 18. The thermistor 30 includes a temperature detection portion 31 which is an element, a contact portion 32 which holds the temperature detection portion 31, a leaf spring portion 33 which supports the contact portion 32 in a cantilever shape, and a housing portion 34 which supports the lower end of the leaf spring portion 33.

[0061] The housing 34 of the thermistor 30 is fixed to the mounting edge 20a (FIG. 8) of the bottom frame 20 of the fixing device 10. The leaf spring portion 33 extends in the +Z direction from the housing 34. The contact portion 32 is made of a heat-resistant and insulating polyimide resin tape, and sandwiches the element that is the temperature detection portion 31 from both sides. The contact width between the contact portion 32 and the pressure roller 18 is 5 mm in the X direction.

[0062] Considering the spring characteristics of the leaf spring portion 33, the housing portion 34 is fixed to the bottom frame 20 so that the temperature detection portion 31 of the contact portion 32 is pressed against the surface of the pressure roller 18 with a constant pressure. The housing portion 34 incorporates a lead wire that outputs a detection signal to the heater control portion 113 (FIG. 12).

[0063] 11(A) and (B) are diagrams for explaining the operation of gears 41 and 42. Fig. 11(A) shows a state in which fixing belt 11 and pressure roller 18 rotate in the forward direction. Fig. 11(B) shows a state in which fixing belt 11 and pressure roller 18 rotate in the reverse direction.

[0064] Here, the forward direction refers to the rotation direction of the fixing belt 11 and the pressure roller 18 during image formation (printing operation). The reverse direction refers to the direction opposite to the forward direction.

[0065] In addition, if the side where unfixed medium P is brought into the fixing device 10 is defined as the upstream side, and the side where fixed medium P is discharged is defined as the downstream side, the rotation direction of the pressure roller 18 when transporting medium P from the upstream side to the downstream side is referred to as the positive direction.

[0066] 11A and 11B, the forward direction of rotation of the pressure roller 18 is indicated by an arrow R1, and the reverse direction is indicated by an arrow R2. Hereinafter, the forward direction is referred to as the R1 direction, and the reverse direction is referred to as the R2 direction.

[0067] As described above, the fixing gear 41 is fixed to the shaft portion 18e of the pressure roller 18, and the fixing gear 41 meshes with the drive gear 42. The drive gear 42 rotates due to the rotation of the fixing motor 43 (FIG. 12), and the fixing gear 41 meshed with the drive gear 42 rotates, causing the pressure roller 18 to rotate.

[0068] As shown in FIG. 11A, when the pressure roller 18 rotates in the R1 direction, a force in the -X direction acts on the fixing gear 41, which is a helical gear, due to the engagement between the fixing gear 41 and the drive gear 42, and the pressure roller 18 is urged in the -X direction.

[0069] This biasing force causes the pressure roller 18 to move in the -X direction, and the position of the pressure roller 18 in the X direction is determined by the stopper surface 18f on the -X side of the pressure roller 18 abutting against the bearing 25. The position of the pressure roller 18 in the X direction at this time is referred to as the normal position.

[0070] When the pressure roller 18 is in the normal position, the distance in the X direction from the end of the pressure roller 18 in the -X direction to the thermistor 30 is distance D1 (first distance). The fixing operation during image formation is performed with the pressure roller 18 in the normal position. The relative position between the pressure roller 18 and thermistor 30 when the pressure roller 18 is in the normal position is referred to as the first relative position.

[0071] As shown in FIG. 11B, when the pressure roller 18 rotates in the R2 direction, a force in the +X direction acts on the fixing gear 41 due to the engagement between the fixing gear 41 and the drive gear 42, and the pressure roller 18 is biased in the +X direction.

[0072] This biasing force causes the pressure roller 18 to move in the +X direction, and the position of the pressure roller 18 in the X direction is determined by the stopper surface 18f on the +X side of the pressure roller 18 abutting against the bearing 25. The position of the pressure roller 18 in the X direction at this time is referred to as the cleaning position.

[0073] When the pressure roller 18 is in the cleaning position, the distance in the X direction from the end of the pressure roller 18 in the -X direction to the thermistor 30 is distance D2 (second distance). The relative position between the pressure roller 18 and thermistor 30 when the pressure roller 18 is in the cleaning position is referred to as a second relative position.

[0074] 11(A) and (B), since the fixing belt 11 is fixed to the movable frame 23 and the thermistor 30 is fixed to the bottom frame 20, even if the pressure roller 18 moves in the X direction, the fixing belt 11 and thermistor 30 do not move in the X direction. In other words, the relative positions of the pressure roller 18, the fixing belt 11, and thermistor 30 in the X direction change.

[0075] The fixing gear 41 and the drive gear 42 constitute a position changing unit that changes the relative position in the X direction between the pressure roller 18 and thermistor 30. The fixing gear 41 and the drive gear 42, together with the fixing motor 43, constitute a rotating unit that rotates the pressure roller 18.

[0076] In addition, in Figures 11(A) and (B), distances D1 and D2 are shown as the X-direction distances from the -X-direction end of the roller portion of pressure roller 18 to the thermistor 30, but they may also be the X-direction distances from the -X-direction end of shaft portion 18e of pressure roller 18 to the thermistor 30.

[0077] <Image forming device control system> Next, we will explain the control system of the image forming apparatus 1. Fig. 12 is a block diagram showing the control system of the image forming apparatus 1. In Fig. 12, the part of the control system of the image forming apparatus 1 that is related to receiving and processing print commands and print data from a higher-level device is omitted.

[0078] The image forming apparatus 1 has a control unit 100. The control unit 100 has a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, a timer, etc. The control unit 100 performs a printing operation of the image forming apparatus 1 based on a print command and print data received from a higher-level device. The control unit 100 also has a print count storage unit 101 and a cleaning count storage unit 102, which will be described later.

[0079] The image forming apparatus 1 further includes a sensor group 103, an operation unit 104, a display unit 105, a charging voltage control unit 106, a developing voltage control unit 107, a transfer voltage control unit 108, a head control unit 109, a main motor control unit 110, a fixing control unit 111, a conveying motor control unit 114, and a belt drive control unit 115.

[0080] The sensor group 103 includes sensors for detecting the position of the medium P on the transport path, specifically, a paper feed sensor M1, a writing sensor M2, a fixing IN sensor M3, and a fixing OUT sensor M4. The sensor group 103 also includes a temperature sensor, a humidity sensor, a concentration sensor, and the like, which are not shown.

[0081] The operation unit 104 has switches, keys, etc. for an operator to input instructions. The display unit 105 has a display (e.g., an LED) that displays the state of the image forming apparatus 1. The operation unit 104 and the display unit 105 are arranged on the upper cover 1B, etc., as, for example, an operation panel.

[0082] The charging voltage control unit 106 controls the charging voltage applied to the charging roller 62. The charging voltage applied to the charging roller 62 causes the surface of the photoconductor drum 61 to be uniformly charged.

[0083] The developing voltage control unit 107 controls the developing voltage applied to the developing roller 64. The electrostatic latent image on the surface of the photoconductor drum 61 is developed by the developing voltage applied to the developing roller 64.

[0084] The transfer voltage control unit 108 controls the developing voltage applied to the transfer roller 71. The toner image on the photosensitive drum 61 is transferred onto the medium P on the transfer belt 72 by the developing voltage applied to the transfer roller 71.

[0085] Based on the image data for each color, the head control unit 109 controls the light emission of the exposure head 63. The surface of the photoconductor drum 61 is exposed to the light emitted by the exposure head 63, and an electrostatic latent image is formed.

[0086] The main motor control unit 110 controls the rotation of a main motor 120 that drives and rotates the photosensitive drum 61. The rotation of the main motor 120 is transmitted to the photosensitive drum 61, as well as to the developing roller 64 and the supply roller 65.

[0087] The fixing control unit 111 has a motor control unit 112 and a heater control unit 113. The motor control unit 112 controls the rotation of the fixing motor 43 that rotates the pressure roller 18. The motor control unit 112 also receives an output signal from the thermistor 30, and calculates a speed correction value that reflects the amount of thermal expansion of the outer diameter of the pressure roller 18 from the detected value of the surface temperature of the pressure roller 18.

[0088] The motor control unit 112 controls the fixing motor 43 so that the rotation speed of the pressure roller 18, which corresponds to the printing speed, is adjusted by adding the above-mentioned speed correction value. The rotation of the fixing motor 43 is transmitted to the pressure roller 18 via the above-mentioned drive gear 42 and fixing gear 41. The pair of discharge rollers 91, 92 are also rotated by the rotation transmitted from the fixing motor 43.

[0089] The heater control unit 113 of the fixing control unit 111 receives the output signal of the heater sensor 14. The heater control unit 113 calculates an optimal heater heating amount so that the temperature detected by the heater sensor 14 becomes the target temperature, and controls the heat generation of the heater 15.

[0090] The transport motor control unit 114 controls the rotation of a transport motor 121 for transporting the medium P. By the rotation of the transport motor 121, the feed roller 82 and the transport roller pair 83 each rotate at a predetermined timing, and transport the medium P along the transport path.

[0091] The belt drive control unit 115 controls the rotation of a belt drive motor 122 for driving the transfer belt 72. The rotation of the belt drive motor 122 rotates the belt drive roller 73, causing the transfer belt 72 to move.

[0092] <Operation of the image forming device> Next, the operation of the image forming apparatus 1 will be described with reference to Figures 1 and 12. When the control unit 100 of the image forming apparatus 1 receives a print command and print data from a higher-level device, it starts image formation (printing operation).

[0093] First, the control unit 100 drives the conveying motor 121 via the conveying motor control unit 114. This rotates the feed roller 82, which feeds the medium P stored in the paper feed tray 81 one by one onto the conveying path. Furthermore, the conveying roller pair 83 conveys the medium P along the conveying path to the transfer unit 70.

[0094] In the transfer unit 70, the transfer belt 72 runs due to the rotation of the belt drive roller 73, and attracts, holds, and transports the medium P. The medium P passes through the image forming units 60K, 60Y, 60M, and 60C in this order.

[0095] The control unit 100 forms a toner image in each image forming unit 60. That is, a charging voltage is applied to the charging roller 62 by voltage control units 106 and 107, and a developing voltage is applied to the developing roller 64.

[0096] Furthermore, the main motor control unit 110 rotates the main motor 120, which rotates the photosensitive drum 61. Accordingly, the charging roller 62, the developing roller 64, and the supply roller 65 also rotate. The charging roller 62 uniformly charges the surface of the photosensitive drum 61 with its charging voltage.

[0097] Furthermore, the head control unit 109 causes the exposure head 63 to emit light based on the image data for each color. The exposure head 63 exposes the uniformly charged surface of the photoconductor drum 61 to light, whereby an electrostatic latent image is formed on the surface of the photoconductor drum 61.

[0098] The electrostatic latent image formed on the surface of the photoconductor drum 61 is developed by the toner attached to the developing roller 64, and a toner image is formed on the surface of the photoconductor drum 61. When the toner image approaches the surface of the transfer belt 72 due to the rotation of the photoconductor drum 61, a transfer voltage is applied to the transfer roller 71 by the transfer voltage control unit 108. As a result, the toner image formed on the photoconductor drum 61 is transferred to the medium P on the transfer belt 72. The toner that has not been transferred to the medium P is scraped off by the cleaning member 67.

[0099] In this manner, the toner images of each color formed by each image forming unit 60K, 60Y, 60M, and 60C are transferred sequentially onto the medium P and superimposed on each other. The medium P onto which the toner images of each color have been transferred is further transported by the transfer belt 72 and reaches the fixing device 10.

[0100] In the fixing device 10, the pressure roller 18 rotates due to the rotation of the fixing motor 43 driven by the motor control unit 112, and the fixing belt 11 rotates accordingly. In addition, the heater 15 is heated by the heater control unit 113 and reaches a predetermined fixing temperature. The medium P conveyed to the fixing device 10 is heated and pressurized between the fixing belt 11 and the pressure roller 18, and the toner image is fixed to the medium P.

[0101] The medium P on which the toner image has been fixed is discharged to the outside of the image forming apparatus 1 by the pair of discharge rollers 91, 92, and is stacked on the stacker unit 93. This completes the formation of a color image on the medium P.

[0102] <Fixing Operation of the Fixing Device> Next, the operation of the fixing device 10 in the above printing operation will be described. Fig. 13 is a timing chart showing the operation of the fixing device 10 during the printing operation. After the operator turns on the power switch of the image forming apparatus 1, the operator performs a process to start a print job (timing a1 in Fig. 13). The process to start a print job is, for example, the transmission of a print job from a higher-level device such as a personal computer.

[0103] When a print job starts, the heater control unit 113 of the fixing control unit 111 supplies power to the heater 15 (timing a2). The heater control unit 113 controls the power supply to the heater 15 based on the temperatures detected by the heater sensor 14 and the thermistor 30.

[0104] Furthermore, the motor control unit 112 of the fixing control unit 111 rotates the fixing motor 43 (timing a3). The rotation of the fixing motor 43 is transmitted to the fixing gear 41 via the drive gear 42, and the pressure roller 18 rotates in the R1 direction (forward direction). When the pressure roller 18 rotates in the R1 direction, the fixing belt 11 in contact with the pressure roller 18 also rotates accordingly.

[0105] The biasing force of the biasing member 24 (FIG. 2) described above presses the fixing belt 11 against the pressure roller 18, forming a fixing nip between them. The medium P, which is supplied from the medium supply section 80 and has a toner image transferred thereto by the transfer unit 70, reaches the fixing device 10 and is sent into the fixing nip between the pressure roller 18 and the fixing belt 11. Timing a4 in FIG. 13 is the timing when the leading edge of the medium P passes through the fixing IN sensor M3.

[0106] Then, the toner image on the surface of the medium P is melted by the heat from the fixing belt 11 heated by the heater 15 and the pressure between the fixing belt 11 and the pressure roller 18, and is fixed to the medium P. The medium P with the fixed toner image is discharged from the fixing device 10 and headed toward the medium discharge section 90.

[0107] In the medium discharge section 90, the medium P is transported by a pair of discharge rollers 91, 92, discharged to the outside of the image forming apparatus 1, and placed on a stacker section 93. Timing a5 in Figure 13 is the timing when the rear end of the medium P passes by the fixing OUT sensor M4.

[0108] When the medium P is discharged from the fixing device 10, the motor control unit 112 stops the rotation of the fixing motor 43 after a predetermined time (timing a6), and the heater control unit 113 stops the power supply to the heater 15 (timing a7). This completes one print job (timing a8).

[0109] <Cleaning operation> Next, a cleaning operation of the fixing device 10 in the present embodiment will be described below with reference to a timing chart shown in FIG.

[0110] The control unit 100 of the image forming apparatus 1 executes the cleaning operation when the above-mentioned print job (FIG. 13) is not being performed. During the cleaning operation, the power supply to the heater 15 is always off, and the medium P is not transported to the fixing device 10.

[0111] With the start of the cleaning operation, the motor control unit 112 of the fixing control unit 111 rotates the fixing motor 43 in the R2 direction (timing t1). The rotation of the fixing motor 43 is transmitted to the fixing gear 41 via the drive gear 42, and the pressure roller 18 rotates in the R2 direction (reverse direction) as shown in FIG. 11B.

[0112] A force in the +X direction is generated by the engagement between the fixing gear 41 and the drive gear 42, and the pressure roller 18 moves in the +X direction (timing t1 to t2).

[0113] When the stopper surface 18f of the pressure roller 18 abuts against the bearing 25, the movement of the pressure roller 18 in the +X direction stops (timing t2). That is, the pressure roller 18 reaches the cleaning position. The operation from timing t1 to t2 corresponds to the first operation.

[0114] In this state, the motor control unit 112 continues to rotate the fixing motor 43 in the R2 direction (timing t2 to t3). That is, the pressure roller 18 further rotates in the R2 direction at the cleaning position. The operation from timing t2 to t3 corresponds to the second operation.

[0115] Next, the motor control unit 112 temporarily stops the rotation of the fixing motor 43 (timing t3 to t4).

[0116] Next, the motor control unit 112 rotates the fixing motor 43 in the R1 direction (timing t4), which causes the pressure roller 18 to rotate in the R1 direction (forward direction) as shown in FIG.

[0117] The engagement between the fixing gear 41 and the drive gear 42 generates a force in the -X direction, and the pressure roller 18 moves in the -X direction (timing t4 to t5). The operation from timing t4 to t5 corresponds to the third operation.

[0118] When the stopper surface 18f of the pressure roller 18 abuts against the bearing 25, the movement of the pressure roller 18 in the -X direction stops (timing t5). That is, the pressure roller 18 reaches the normal position.

[0119] In this state, the motor control unit 112 continues to rotate the fixing motor 43 in the R1 direction (timing t5 to t6). That is, the pressure roller 18 continues to rotate in the R1 direction at the normal position. The operation from timing t5 to t6 corresponds to the fourth operation.

[0120] Thereafter, the motor control unit 112 stops the rotation of the fixing motor 43 (timing t6), thereby completing the cleaning operation.

[0121] When the cleaning operation is completed, the pressure roller 18 has returned to its normal position in the X direction, so the fixing device 10 is ready to start the fixing operation.

[0122] In the above cleaning operation, the time (timing t1 to t2) during which the pressure roller 18 rotates in the R2 direction while moving in the +X direction is 3 seconds. The time (timing t2 to t3) during which the pressure roller 18 rotates in the R2 direction at the cleaning position is 1 second.

[0123] The time (timing t4 to t5) during which the pressure roller 18 rotates in the R1 direction while moving in the -X direction is 3 seconds. The time (timing t5 to t6) during which the pressure roller 18 rotates in the R1 direction at the normal position is 3 seconds.

[0124] In this example, the total time T1 for rotating the pressure roller 18 in the R2 direction is 4 seconds. The total time T2 for rotating the pressure roller 18 in the R1 direction is 6 seconds. The ratio of time T1 to time T2 is T1:T2=1:1.5.

[0125] Fig. 15 is a timing chart showing a cleaning sequence in which multiple cleaning operations are performed. One cleaning operation corresponds to the operation at timings t1 to t6 described with reference to Fig. 14. It is preferable that the control unit 100 of the image forming apparatus 1 performs n cleaning operations P1, P2...Pn when no print job is being performed. The number n of cleaning operations included in the cleaning sequence will be described later.

[0126] 16(A) and (B) are schematic diagrams for explaining the function of the cleaning operation. As described above, the thermistor 30 is disposed so that the contact portion 32 including the temperature detection portion 31 is pressed against the surface of the pressure roller 18.

[0127] As the printing operation continues, as shown in FIG. 16A, adhesions T such as paper powder or toner on the surface of the pressure roller 18 accumulate between the contact portion 32 of the thermistor 30 and the surface of the pressure roller 18.

[0128] Since the rotation direction of the pressure roller 18 during the printing operation is the R1 direction (positive direction), the deposit T tends to accumulate in the area below the contact portion 32 of the thermistor 30 in the figure.

[0129] As shown in FIG. 16(B), when the pressure roller 18 is rotated in the R2 direction during the cleaning operation, the adhesion T that has accumulated on the contact portion 32 of the thermistor 30 moves away from the contact portion 32 of the thermistor 30, following the surface of the pressure roller 18.

[0130] Furthermore, since the pressure roller 18 also moves in the thrust direction (+X direction) while rotating in the R2 direction, the deposit T also moves away in the X direction from the contact portion 32 of the thermistor 30. This allows the deposit T that has accumulated on the contact portion 32 of the thermistor 30 to be dispersed over the surface of the pressure roller 18.

[0131] Fig. 17(A) is a schematic diagram for explaining the contact trajectory of contact portion 32 of thermistor 30 on pressure roller 18 during cleaning operation. Note that in reality, the thermistor 30 is stationary and pressure roller 18 moves and rotates, but Fig. 17(A) shows the trajectory of contact portion 32 of thermistor 30 with respect to the surface of pressure roller 18.

[0132] When the pressure roller 18 moves in the +X direction while rotating in the R2 direction (reverse direction) (timing t1 to t2 in FIG. 14), the contact portion 32 of the thermistor 30 moves relatively in the R1 direction and the -X direction on the pressure roller 18. This trajectory is called trajectory E1. The deposit T that has accumulated on the contact portion 32 of the thermistor 30 disperses along the trajectory E1.

[0133] When the pressure roller 18 reaches the cleaning position, which is the limit of its movement in the +X direction, and continues to rotate (timing t2 to t3), the contact portion 32 of the thermistor 30 moves relatively in the R1 direction on the pressure roller 18. This trajectory is referred to as trajectory E2. The deposit T remaining on the contact portion 32 of the thermistor 30 disperses along the trajectory E2.

[0134] Thereafter, when the pressure roller 18 moves in the -X direction while rotating in the R1 direction (positive direction) (timing t4 to t5), the contact portion 32 of the thermistor 30 moves relatively in the R2 direction and the +X direction on the pressure roller 18. This trajectory is referred to as trajectory E3. At this point, almost no deposit T remains on the contact portion 32 of the thermistor 30, so almost no deposit T is dispersed on trajectory E3.

[0135] In addition, since the trajectory E3 does not overlap with the trajectory E1, the deposits T dispersed on the trajectory E1 are prevented from adhering again to the contact portion 32 of the thermistor 30.

[0136] When the pressure roller 18 reaches the normal position, which is the movement limit in the -X direction, and continues to rotate (timing t5 to t6), the contact portion 32 of thermistor 30 moves relatively in the R2 direction on the pressure roller 18. This trajectory is referred to as trajectory E4.

[0137] The time interval between timings t5 and t6 (eg, 3 seconds) shown in Fig. 14 is longer than the time interval between timings t2 and t3 (eg, 1 second). Therefore, the trajectory E4 is longer than the trajectory E2 by a distance e.

[0138] Therefore, the contact portion 32 of thermistor 30 reaches position G, which is overrun in the direction R2 by a distance e from the starting point at the start of the cleaning operation, and the cleaning operation ends there. The above-mentioned four trajectories E1 to E4 form the movement locus (loop) of the contact portion 32 of thermistor 30 in one cleaning operation.

[0139] 17(B) is a schematic diagram for explaining the movement trajectory of contact portion 32 of thermistor 30 on pressure roller 18 when multiple cleaning operations are performed. F1 is the movement trajectory in the first cleaning operation (i.e., trajectories E1 to E4). F2 is the movement trajectory in the second cleaning operation. F3 is the movement trajectory in the third cleaning operation.

[0140] As described above, between the start and end of one cleaning operation, the contact portion 32 of the thermistor 30 moves relative to the surface of the pressure roller 18 in the R2 direction by the distance e.

[0141] Therefore, when three cleaning operations are performed, the relative position of contact portion 32 of thermistor 30 with respect to pressure roller 18 at the start of the first, second, and third cleaning operations changes as shown by symbols 32(1), 32(2), and 32(3) in FIG. 17(B).

[0142] The movement trajectories F1, F2, and F3 of the three cleaning operations are set so as not to overlap each other. By making the movement trajectories F1, F2, and F3 not overlap, the deposits T dispersed on the surface of the pressure roller 18 from the contact portion 32 of the thermistor 30 are prevented from adhering again to the contact portion 32.

[0143] FIG. 17B shows a case where the cleaning operation is performed three times, but the same applies to a case where the cleaning operation is performed three or more times.

[0144] <Cleaning sequence> Next, a specific example of a cleaning sequence in which multiple cleaning operations are performed will be described. If the number of cleaning operations is too small, the accumulation of the deposits T on the contact portion 32 of the thermistor 30 cannot be sufficiently reduced, which may result in a decrease in detection accuracy. On the other hand, if the number of cleaning operations is too large, the deposits T dispersed from the contact portion 32 of the thermistor 30 spread over the entire surface of the pressure roller 18, increasing the possibility of the deposits T re-adhering to the contact portion 32 of the thermistor 30.

[0145] Therefore, the number of cleaning operations in one cleaning sequence is determined as follows: Here, the contact width in the circumferential direction between the contact portion 32 of the thermistor 30 and the pressure roller 18 is set to 5 mm, and the circumferential length of the pressure roller 18 is set to 79 mm.

[0146] In order to prevent the paths E1 and E3 shown in FIG. 17(A) from overlapping, the upper limit value V of the cleaning operation is the circumference of the pressure roller 18 (79 mm) divided by twice the contact width (5 mm) of the contact portion 32 of the thermistor 30, that is, 79 ÷ (5 × 2) ≒ 7 times.

[0147] Furthermore, the greater the number of pages printed per print job (print volume), the more likely it is that deposits T will accumulate on contact portion 32 of the thermistor 30. Therefore, control unit 100 executes two cleaning sequences A and B, which differ in the number of cleaning operations, according to the print count included in the print job.

[0148] In cleaning sequence A, for example, one cleaning operation is performed, whereas in cleaning sequence B, for example, seven cleaning operations are performed. These numbers are merely examples and can be changed as appropriate.

[0149] The control unit 100 has a print count storage unit 101 and a cleaning count storage unit 102. The print count storage unit 101 adds and stores one count each time a medium P of a predetermined size passes through the fixing device 10. Here, one count is added and stored each time a medium P of 216 mm in length, which corresponds to one page of A4 paper, passes through the fixing device 10.

[0150] The cleaning count storage unit 102 stores the added print count since the previous cleaning sequence was executed as the cleaning count N. When the cleaning sequence ends, the cleaning count N is reset.

[0151] The control unit 100 also stores a cleaning count threshold Nc, which corresponds to the interval at which the cleaning sequence is executed. The control unit 100 compares the cleaning count N with the cleaning count threshold Nc to determine whether or not to execute a cleaning sequence and whether to execute either cleaning sequence A or B.

[0152] 18 is a flowchart showing the flow of the cleaning sequence. When the image forming apparatus 1 performs a printing operation based on a print job, the control unit 100 increments the print count C and the cleaning count N by 1 each time a 216 mm medium P passes through the fixing device 10 (step S101).

[0153] When the print job is completed (Yes in step S102), it is determined whether the cleaning count N has exceeded the cleaning count threshold Nc. If the cleaning count N is equal to or less than the cleaning count threshold Nc (No in step S103), the process moves to a standby state. The cleaning count threshold Nc is also referred to as the first threshold.

[0154] If the cleaning count N exceeds the cleaning count threshold Nc (Yes in step S103), it is determined whether the cleaning count N exceeds 1.5 times the cleaning count threshold Nc (Nc×1.5) (step S104). Note that Nc×1.5 is also referred to as a second threshold.

[0155] If the cleaning count N exceeds 1.5 times the cleaning count threshold Nc (Yes in step S104), cleaning sequence B is executed (step S105). In cleaning sequence B, for example, seven cleaning operations are executed. When cleaning sequence B is completed, cleaning count N is reset (step S106) and the system goes into a standby state.

[0156] On the other hand, if the cleaning count N is equal to or less than 1.5 times the cleaning count threshold Nc (No in step S104), cleaning sequence A is executed (step S107). In cleaning sequence A, for example, one cleaning operation is executed. When cleaning sequence A is completed, cleaning count N is reset (step S108) and the system transitions to a standby state.

[0157] If the cleaning count threshold Nc is set too high, the amount of deposit T on the contact portion 32 of the thermistor 30 before the cleaning sequence is executed increases, and the deposit T may adhere to the contact portion 32, making cleaning difficult. For this reason, the cleaning count threshold Nc is determined taking into consideration the degree of paper dust generation of the medium P used, the average amount of toner used in the printed image, etc.

[0158] Cleaning sequence B is executed when the number of printed pages per print job is large and the cleaning count N greatly exceeds the cleaning count threshold Nc at the end of the print job, i.e., when it is assumed that a large amount of deposits T has accumulated on the contact portion 32 of the thermistor 30. Cleaning sequence B has a higher cleaning effect than cleaning sequence A because it has a greater number of cleaning operations, but it takes a longer time to complete.

[0159] The deposits T separated from the contact portion 32 of the thermistor 30 by the above cleaning operation may adhere to the surface of the pressure roller 18, as well as to the surface of the fixing belt 11. These deposits T adhere to the medium P passing through the fixing device 10 in the print job after the cleaning sequence is completed, and are discharged to the outside of the fixing device 10 together with the medium P.

[0160] In this case as well, the amount of deposit T removed from the contact portion 32 of the thermistor 30 in the cleaning sequence is small relative to the toner image on the medium P and is not noticeable, so that the effect on the print image quality is minimal.

[0161] In the above description, due to the torsion angles of gears 41 and 42, which are helical gears, pressure roller 18 moves in the -X direction while rotating in the R1 direction, and moves in the +X direction while rotating in the R2 direction (FIGS. 11A and 11B). However, the -X direction and the +X direction may be reversed.

[0162] <Comparative Example> 19(A) and (B) are a perspective view and a front view showing a fixing device 10F of a comparative example. In the fixing device 10F of the comparative example, a fixing gear 45, which is a spur gear, is attached to the pressure roller 18. A driving gear 46, which is also a spur gear, is engaged with the fixing gear 45. The pressure roller 18 is attached to the side frame 21 so as not to move in the X direction. Except for these points, the fixing device 10F is configured similarly to the fixing device 10 of the first embodiment.

[0163] In the fixing device 10F of the comparative example, the pressure roller 18 does not move in the X direction, and therefore the relative positions in the X direction between the pressure roller 18 and the thermistor 30 do not change. Therefore, even if the pressure roller 18 is rotated in the R2 direction ( FIG. 19(B) ) during the cleaning operation to transfer the deposits accumulated on the contact portion 32 of the thermistor 30 to the pressure roller 18, the deposits remain in the same position as the thermistor 30 in the X direction, and there is a high possibility that they will re-adhere to the thermistor 30.

[0164] In contrast, in the first embodiment, the pressure roller 18 moves in the X direction while rotating in the R1 and R2 directions, so that the X-direction positions of the pressure roller 18 and the thermistor 30 change. Therefore, the adhesion T can be dispersed over a wide area of ​​the pressure roller 18, and the adhesion T is less likely to re-adhere to the thermistor 30.

[0165] <Effects of the embodiment> As described above, the first embodiment includes the pressure roller 18 (rotating member), a drive unit (fixing gear 41, drive gear 42, and fixation motor 43) that rotates the pressure roller 18 in the R1 direction (forward direction) and the R2 direction (reverse direction), the thermistor 30 (sensor) that contacts the surface of the pressure roller 18, and a position change unit (fixing gear 41 and drive gear 42) that changes the relative position in the X direction between the pressure roller 18 and thermistor 30. The position change unit rotates the pressure roller 18 in the R2 direction, and changes the relative position between the pressure roller 18 and thermistor 30 from a first relative position where the distance between one end of the width direction of the pressure roller 18 (one end in the -X direction) and thermistor 30 is distance D1 to a second relative position where the distance is distance D2.

[0166] Therefore, the deposits T accumulated on the thermistor 30 can be dispersed on the surface of the pressure roller 18, improving the detection accuracy of the thermistor 30. As a result, the accuracy of temperature control in the fixing device 10 can be improved, and the print quality can be improved.

[0167] In particular, since the fixing gear 41 and the drive gear 42 are helical gears and the pressure roller 18 is configured to be movable in the X direction, the pressure roller 18 can be moved in the X direction while being rotated with a simple configuration.

[0168] Furthermore, since the pressure roller 18 is further rotated when the pressure roller 18 has reached the cleaning position and the normal position, it is possible to prevent the deposit T from adhering again to the thermistor 30 from the surface of the pressure roller 18.

[0169] In addition, since the amount of rotation of the pressure roller 18 when the pressure roller 18 is in the cleaning position is different from the amount of rotation of the pressure roller 18 when the pressure roller 18 is in the normal position, re-adhesion of the deposit T from the surface of the pressure roller 18 to the thermistor 30 is unlikely to occur even if the cleaning operation is repeated multiple times.

[0170] In addition, the decision as to whether or not to perform a cleaning operation and the number of cleaning operations to be performed are based on the number of print pages included in the print job, so that appropriate cleaning can be performed according to the accumulation status of deposits T on the thermistor 30.

[0171] Embodiment 2 Next, a description will be given of embodiment 2. Fig. 20 is a cross-sectional view showing a fixing device 10A of an image forming apparatus according to embodiment 2. Fixing device 10A is provided with a contact / separation mechanism that brings fixing belt 11 and pressure roller 18 into contact with or separates them from each other.

[0172] As described above, the fixing belt 11 and each of its inner peripheral members (the stay 12, the heater support member 13, the heater sensor 14, and the heater 15) are attached to the movable frame 23. The movable frame 23 is rotatably attached to the side frame 21 by the support shaft 22.

[0173] Fixing device 10A of the second embodiment includes cam 28 that presses movable frame 23 to rotate it around support shaft 22. Cam 28 has shaft portion 28b that is a rotation shaft in the X direction, and shaft portion 28b is rotatably supported by each side frame 21.

[0174] The cam 28 is an eccentric cam in which the distance from the rotation center (the center of the shaft portion 28b) to the outer circumferential surface 28a changes in the circumferential direction. The outer circumferential surface 28a of the cam 28 abuts against a contact piece 23c formed on the movable frame 23.

[0175] The cam 28 rotates by the rotation transmitted from a separation / contact motor 44 (FIG. 21). The cam 28 and the separation / contact motor 44 constitute a separation / contact mechanism.

[0176] During the fixing operation, the cam 28 is in a position where it presses the contact piece 23c of the movable frame 23 with the least force. In this case, the movable frame 23 rotates about the support shaft 22 in the direction indicated by the arrow C1 due to the biasing force of the biasing member 24, and a fixing nip is formed between the fixing belt 11 and the pressure roller 18.

[0177] On the other hand, when the cam 28 rotates clockwise around the shaft portion 28b, the outer peripheral surface 28a of the cam 28 presses the contact piece 23c of the movable frame 23 in the direction indicated by the arrow F in the figure. This causes the movable frame 23 to rotate in the direction indicated by the arrow C2 in the figure around the support shaft 22 against the biasing force of the biasing member 24. When the movable frame 23 rotates in the direction indicated by the arrow C2, the fixing belt 11 separates from the surface of the pressure roller 18 and rises.

[0178] Fig. 21 is a block diagram showing a control system of image forming apparatus 1 of embodiment 2. As shown in Fig. 21, the control system of embodiment 2 is obtained by adding a separation motor 44 that rotates cam 28 and a separation motor control unit 116 that controls the rotation of the separation motor 44 to the control system of embodiment 1.

[0179] The separation / contact motor control unit 116 controls the rotation of the separation / contact motor 44 under the control of the control unit 100, and brings the fixing belt 11 and the pressure roller 18 into contact with or separates them from each other. The control system of the second embodiment is configured similarly to the control system of the first embodiment, except for the separation / contact motor 44 and the separation / contact motor control unit 116.

[0180] Fig. 22 is a timing chart showing the cleaning operation in embodiment 2. As shown in Fig. 22, in embodiment 2, an operation to open the fixing nip is performed (timing t0) before the start of the cleaning operation (timing t1).

[0181] That is, the separation / removal motor control unit 116 rotates the separation / removal motor 44, and the cam 28 rotates and presses the contact piece 23c of the movable frame 23. As a result, the movable frame 23 rotates in the direction indicated by the arrow C2 in FIG.

[0182] Thereafter, a cleaning operation is performed (timings t1 to t6) in the same manner as in embodiment 1. After the cleaning operation is completed, an operation for forming a fixing nip is performed (timing t7).

[0183] That is, the separation / removal motor control unit 116 rotates the separation / removal motor 44, and the cam 28 rotates to a position where the amount of pressure applied to the contact piece 23c of the movable frame 23 is minimized. As a result, the movable frame 23 rotates in the direction indicated by the arrow C1 in Fig. 21 due to the biasing force of the biasing member 24, and the fixing belt 11 comes into contact with the surface of the pressure roller 18, forming a fixing nip.

[0184] Furthermore, when a cleaning sequence including multiple cleaning operations (see FIG. 15) is executed, the fixing nip is opened before the start of the cleaning sequence, i.e., before the start of the first cleaning operation P1, and then, after the cleaning sequence is completed, i.e., after the completion of the last cleaning operation Pn, the fixing nip is formed.

[0185] In the above-described first embodiment, during the cleaning operation, the pressure roller 18 is moved in the X direction with a fixing nip formed between the fixing belt 11 and the pressure roller 18, so that external forces such as frictional forces acting on the pressure roller 18 are relatively large.

[0186] In contrast, in the second embodiment, the pressure roller 18 is not in contact with the fixing belt 11 during the cleaning operation, so that external forces such as frictional forces acting on the pressure roller 18 are small, and therefore the pressure roller 18 can move smoothly in the X direction.

[0187] Furthermore, since the movement of the pressure roller 18 in the X direction is not hindered by an external force, re-adhesion of the adhering matter T to the thermistor 30 due to overlapping of the trajectories, etc., can be suppressed.

[0188] As described above, in the second embodiment, a separation mechanism (cam 28 and separation motor 44) is provided that moves pressure roller 18 and fixing belt 11 toward and away from each other, and the cleaning operation is performed in a state in which fixing belt 11 and pressure roller 18 are separated from each other. Therefore, the external force acting on pressure roller 18 during the cleaning operation is small, and the movement of pressure roller 18 in the X direction can be performed smoothly.

[0189] In this embodiment, the cam 28 and the motor 44 are used to separate and contact the pressure roller 18 and the fixing belt 11, but other mechanisms may be used to separate and contact the pressure roller 18 and the fixing belt 11.

[0190] In the above-described first and second embodiments, during cleaning operation, the pressure roller 18 is moved in the X direction while rotating using the helical gears 41 and 42, thereby changing the relative position of the pressure roller 18 and thermistor 30 in the X direction.

[0191] However, the present disclosure is not limited to such a configuration, and it is sufficient to rotate a rotating member (e.g., pressure roller 18) in a direction opposite to the rotation direction during the fixing operation, and to change the relative position in the width direction (X direction) between the rotating member and a sensor (e.g., thermistor 30) from a first relative position where the distance between one end of the rotating member in the width direction and the sensor is distance D1 (first distance) to a second relative position where the distance between the one end of the rotating member and the sensor is distance D2 (second distance).

[0192] Furthermore, the present invention is not limited to a configuration in which the rotating member is moved in the width direction (X direction) using a helical gear, and the rotating member may be moved in the width direction using another mechanism (Modification 1 described later).

[0193] Further, the configuration is not limited to moving the rotating member in the width direction (X direction), and the sensor may be moved in the width direction (Modification 2 described later).

[0194] Furthermore, the rotating member is not limited to the pressure roller 18, but may be, for example, the fixing belt 11 (Modification 3 to be described later).

[0195] Furthermore, two rotation transmission mechanisms may be provided in accordance with the rotation direction of the pressure roller 18 (Modification 4 described later).

[0196] Furthermore, the sensor is not limited to the thermistor 30, but may be another type of sensor as long as it is in contact with the rotating member.

[0197] Modifications 1 to 4 will be explained below.

[0198] Variation 1. First, a description will be given of Modification 1. Figures 23(A) and (B) are diagrams showing a fixing device 10B of Modification 1. In the above-described first and second embodiments, the pressure roller 18 is moved in the X direction using the gears 41 and 42, which are helical gears, but in this Modification 1, the pressure roller 18 is moved in the X direction using a cam 47.

[0199] A spur gear fixing gear 45 is attached to the pressure roller 18 instead of the helical gear fixing gear 41. A spur gear driving gear 46 is engaged with this fixing gear 45.

[0200] The widths of the fixing gear 45 and the drive gear 46 in the X direction are similar to those of the fixing gear 41 and the drive gear 42 in embodiment 1. Like the fixing gear 41 and the drive gear 42 in embodiment 1, the fixing gear 45 and the drive gear 46 receive rotation from the fixing motor 43 (FIG. 12).

[0201] Cam 47, which serves as a rotating member moving mechanism (position changing unit), is provided so as to come into contact with an end face of shaft portion 18e on the +X side of pressure roller 18. Cam 47 has shaft portion 47a, which is a rotation shaft in the Y direction, for example. Shaft portion 47a is supported by a support portion within the housing of image forming apparatus 1, and is rotationally driven by a motor or the like.

[0202] Cam 47 is an eccentric cam in which the distance from the rotation center (center of shaft portion 47a) to the outer circumferential surface changes depending on the circumferential position. Cam 47 abuts against the end face of shaft portion 18e of pressure roller 18. As cam 47 rotates, the amount of push-out of pressure roller 18 in the -X direction changes.

[0203] The pressure roller 18 is attached so as to be movable in the X direction, similarly to the first embodiment. In addition, a coil spring 48 is provided between the end of the pressure roller 18 in the -X direction and the side frame 21 as a biasing part that biases the pressure roller 18 in the +X direction.

[0204] Therefore, the position of pressure roller 18 in the X direction is determined by the amount of push-out of cam 47 in the -X direction relative to pressure roller 18. The outer circumferential surface (i.e., the contour) of cam 47 is formed so that the position of pressure roller 18 in the X direction gradually changes as cam 47 rotates.

[0205] 23A, the pressure roller 18 is at its normal position, having moved the furthest in the -X direction. At this time, the distance in the X direction from the -X direction end of the pressure roller 18 to the thermistor 30 is distance D1 (first distance).

[0206] 23(B), the pressure roller 18 is at the cleaning position, having moved the furthest in the +X direction. At this time, the distance in the X direction from the -X direction end of the pressure roller 18 to the thermistor 30 is distance D2 (second distance). Here, D1>D2, but it may be reversed.

[0207] During the cleaning operation, at timings t1 to t2 shown in Fig. 14, the pressure roller 18 is moved in the +X direction by the cam 47 as shown in Fig. 23(B). This causes the pressure roller 18 to move to the cleaning position. In addition, the fixing motor 43 rotates the pressure roller 18 in the R2 direction.

[0208] During the cleaning operation, at timings t4 to t5 shown in Fig. 14, the pressure roller 18 is moved in the -X direction by the cam 47 as shown in Fig. 23(A). This causes the pressure roller 18 to move to the normal position. Also, the fixing motor 43 rotates the pressure roller 18 in the R1 direction.

[0209] The cleaning operation in the first modification is similar to that in the first embodiment, except that the pressure roller 18 is moved in the X direction by the cam 47. After the cleaning operation is completed, the fixing operation is performed in the state shown in FIG.

[0210] As described above, according to the first modification, the pressure roller 18 is moved in the X direction by the cam 47, so that the movement range of the pressure roller 18 in the X direction can be set to be wide. Therefore, the deposits T accumulated on the thermistor 30 can be dispersed over a wide range of the pressure roller 18, and cleaning efficiency can be improved.

[0211] Although the pressure roller 18 is moved in the X direction by using the cam 47 here, the pressure roller 18 may be moved in the X direction by using another mechanism.

[0212] Variation 2. Next, a description will be given of Modification 2. Figures 24(A) and (B) are diagrams showing a fixing device 10C of Modification 2. In the above-described Embodiments 1 and 2 and Modification 1, the pressure roller 18 is moved in the X direction, but in Modification 2, the thermistor 30 is moved in the X direction.

[0213] The thermistor 30 is supported by, for example, a feed screw mechanism 35 serving as a sensor moving mechanism (position changing unit). The feed screw mechanism 35 has a feed screw 37 whose axial direction is in the X direction, a movable body 36 that screws into the feed screw 37 and moves in the X direction, and a motor 38 that rotates the feed screw 37. The feed screw mechanism 35 is attached to the bottom frame 20.

[0214] A housing 34 of the thermistor 30 is fixed to a movable body 36. The position of the thermistor 30 in the X direction is determined by the rotation of a motor 38.

[0215] 24A, the thermistor 30 is at its normal position, having moved the furthest in the +X direction. The distance in the X direction from the -X direction end of the pressure roller 18 to the thermistor 30 at this time is distance D1 (first distance).

[0216] 24(B), the thermistor 30 is at the cleaning position, having moved the furthest in the -X direction. At this time, the distance in the X direction from the -X direction end of the pressure roller 18 to the thermistor 30 is distance D2 (second distance). Here, D1>D2, but the opposite is also possible.

[0217] As in the first modification, the rotation of the fixing motor 43 is transmitted to the pressure roller 18 via a fixing gear 45, which is a spur gear, and a drive gear 46. The pressure roller 18 rotates in the R1 direction and the R2 direction. However, in the second modification, the pressure roller 18 is attached to the side frame 21 so as not to move in the X direction.

[0218] During the cleaning operation, between timings t1 and t2 shown in Fig. 14, the thermistor 30 moves in the -X direction by the feed screw mechanism 35 and reaches the cleaning position as shown in Fig. 24(B). Also, the fixing motor 43 rotates the pressure roller 18 in the R2 direction.

[0219] During the cleaning operation, between timings t4 and t5 shown in Fig. 14, the feed screw mechanism 35 moves the thermistor 30 in the +X direction and reaches the normal position as shown in Fig. 24(A). Also, the fixing motor 43 rotates the pressure roller 18 in the R1 direction.

[0220] The cleaning operation in the second modification is similar to that in the first embodiment, except that the thermistor 30 is moved in the X direction instead of the pressure roller 18. In addition, the fixing operation after the cleaning operation is performed in the state shown in FIG.

[0221] As described above, according to the second modification, the deposits T accumulated on the thermistor 30 can be dispersed onto the surface of the pressure roller 18 by moving the thermistor 30 in the X direction.

[0222] Although the feed screw mechanism 35 is used to move the thermistor 30 in the X direction here, thermistor 30 may be moved in the X direction using another mechanism.

[0223] Variation 3. Next, Modification 3 will be described. Figures 25(A) and (B) are diagrams showing a fixing device 10D of Modification 3. In the above-mentioned embodiments 1 and 2 and Modification 1, the pressure roller 18 is moved in the X direction, and in Modification 2, the thermistor 30 is moved in the X direction. In contrast, in Modification 3, the thermistor 30 is in contact with the fixing belt 11, and a unit including the fixing belt 11 (movable unit 50) is moved in the X direction.

[0224] To support the thermistor 30, the fixing device 10D has an upper frame 29 that connects the pair of side frames 21. A housing 34 of the thermistor 30 is fixed to a predetermined position (for example, the center in the X direction) of the upper frame 29. The leaf spring 33 extends from the housing 34 in the -Z direction, and a contact portion 32 is attached to its tip. The contact portion 32 is pressed against the surface of the fixing belt 11 with a constant pressing force.

[0225] As described in the first embodiment, the fixing belt 11 and each of its inner peripheral members (the stay 12, the heater support member 13, the heater sensor 14, and the heater 15) are attached to the movable frame 23. The movable frame 23 is rotatably attached to each side frame 21 by the support shaft 51.

[0226] The support shaft 51 of the third modification is longer in the X direction than the support shaft 22 of the first embodiment. The movable frame 23 is supported along the support shaft 51 so as to be movable in the X direction. The support shaft 51 has a shaft portion 51a that is long in the X direction, and stopper portions 51b, 51c formed on both ends of the shaft portion 51a in the X direction. The stopper portions 51b, 51c restrict the movement range of the movable frame 23 in the X direction.

[0227] The pair of movable frames 23 and the members sandwiched therebetween (the fixing belt 11, the stay 12, the heater support member 13, the heater sensor 14, and the heater 15) constitute a movable unit 50. The movable unit 50 is movable in the X direction along a support shaft 51 between the pair of side frames 21.

[0228] Further, a coil spring 52 serving as a biasing member is provided between the -X side movable frame 23 of the pair of movable frames 23 and the side frame 21. The coil spring 52 biases the movable unit 50 in the +X direction.

[0229] Further, a cam mechanism 53 serving as a unit moving mechanism (position changing unit) is provided to face movable frame 23 on the +X side. Cam mechanism 53 has a pin 54 that abuts against movable frame 23, and a cam 55 that abuts against this pin 54.

[0230] The pin 54 is attached to, for example, the side frame 21 on the +X side so as to be movable in the X direction. One end of the pin 54 abuts against the movable frame 23, and the other end abuts against a cam 55.

[0231] Cam 55 has shaft 55a which is a rotation axis in the Y direction. Shaft 55a is supported by a support part in the housing of image forming apparatus 1 and rotated by a motor or the like. Cam 55 is an eccentric cam in which the distance from the center of rotation (center of shaft 55a) to the outer circumferential surface changes depending on the circumferential position. Cam 55 abuts against the end face of pin 54. As cam 55 rotates, the push-out amount of pin 54 in the -X direction changes.

[0232] As described above, movable unit 50 is biased in the +X direction by coil spring 52. Therefore, the position of movable unit 50 in the X direction is determined by the amount of pushing of pin 54 in the -X direction. The outer circumferential surface of cam 55 is formed so that the position of movable unit 50 in the X direction gradually changes with the rotation of cam 55 (pushing of pin 54).

[0233] 25A, movable unit 50 is at a normal position located at the furthest position in the +X direction. The distance in the X direction from the -X direction end of fixing belt 11 to thermistor 30 is distance D1 (first distance).

[0234] In FIG. 25(B), the movable unit 50 is at the cleaning position located most in the -X direction. The distance in the X direction from the -X direction end of the fixing belt 11 to the thermistor 30 is the distance D2 (the second distance). Here, D1 < D2, but the reverse may also be true.

[0235] Similar to Modifications 1 and 2, the rotation of the fixing motor 43 is transmitted to the pressure roller 18 via the fixing gear 45 and the drive gear 46, which are spur gears. The pressure roller 18 rotates in the R1 direction and the R2 direction. However, in this Modification 3, the pressure roller 18 is attached to the side frame 21 so as not to move in the X direction.

[0236] During the cleaning operation, at the timings t1 to t2 shown in FIG. 14, as shown in FIG. 25(B), the cam 55 gradually pushes out the pin 54 in the -X direction. As a result, the movable unit 50 moves in the -X direction, and the fixing belt 11 reaches the cleaning position. Also, the fixing motor 43 rotates the pressure roller 18 in the R2 direction.

[0237] Also, during the cleaning operation, at the timings t4 to t5 shown in FIG. 14, as shown in FIG. 25(A), the amount of extrusion of the pin 54 in the -X direction by the cam 55 is gradually decreased. As a result, the movable unit 50 moves in the +X direction, and the fixing belt 11 reaches the normal position. Also, the fixing motor 43 rotates the pressure roller 18 in the R1 direction.

[0238] The cleaning operation in Modification 3 is the same as the cleaning operation in Embodiment 1, except that the movable unit 50 is moved in the X direction by the cam mechanism 53 (the pin 54 and the cam 55) as described above, and the pressure roller 18 is not moved in the X direction. Also, the fixing operation is performed in the state shown in FIG. 25(A).

[0239] As described above, in this Modification 3, by moving the fixing belt 11 in the X direction while rotating the pressure roller 18, the deposits T accumulated on the thermistor 30 can be dispersed on the surface of the fixing belt 11.

[0240] Furthermore, since the movable unit 50 including the fixing belt 11 is moved in the X direction, the fixing belt 11, which does not have a rotation shaft, can be moved in the X direction.

[0241] Here, the movable unit 50 is moved in the X direction using the cam mechanism 53, but the movable unit 50 may be moved in the X direction using another mechanism.

[0242] Here, the thermistor 30 is supported by the upper frame 29 of the fixing device 10D, but the thermistor 30 may be supported by another member as long as it can support the thermistor 30 in a position that does not interfere with the transport of the medium P. For example, the thermistor 30 may be supported by a lid that is detachably attached to the side frame 21. Alternatively, the thermistor 30 may be supported by a member provided on the housing of the image forming apparatus 1 outside the fixing device 10D.

[0243] Variation 4. Next, a description will be given of Modification 4. Figures 26A and 26B are diagrams showing the configuration and operation of a fixing device 10E according to Modification 4.

[0244] In the above-described first to fourth embodiments, the pressure roller 18 is rotated using a single gear train consisting of the fixing gear 41 and the drive gear 42 (or the fixing gear 45 and the drive gear 46), but in this fourth variant, the pressure roller 18 is rotated using two gear trains (rotation transmission mechanisms) depending on the direction of rotation.

[0245] As in the first modification, a fixing gear 45 is attached to the shaft portion 18e on the -X side of the pressure roller 18, and a driving gear 46 is provided to mesh with the fixing gear 45. The width of the driving gear 46 in the X direction is wider than the width of the fixing gear 45 in the X direction by the amount of movement of the pressure roller 18 in the X direction. The fixing gear 45 and the driving gear 46 form a first rotation transmission mechanism used when rotating the pressure roller 18 in the R1 direction.

[0246] A fixing gear 203 is attached to shaft portion 18e on the -X side of pressure roller 18, and a drive gear 204 is provided to mesh with this fixing gear 203. The fixing gear 203 is rotatably supported by a support portion within the housing of image forming apparatus 1. The width of drive gear 204 in the X direction is wider than the width of fixing gear 203 in the X direction by the amount of movement of pressure roller 18 in the X direction. The fixing gear 203 and drive gear 204 form a second rotation transmission mechanism used when rotating pressure roller 18 in the R2 direction.

[0247] Also provided is a switching mechanism 200 that selectively transmits the rotation of the fixing motor 43 to either the drive gear 46 or the drive gear 204. The switching mechanism 200 selects between the first rotation transmission mechanism and the second rotation transmission mechanism.

[0248] Furthermore, a solenoid 201 is provided as a rotating member moving mechanism (position changing unit) so as to bias the end face of the shaft portion 18e on the +X side of the pressure roller 18. The solenoid 201 has a plunger 202 that protrudes in the -X direction. The solenoid 201 is disposed so that the tip of the plunger 202 abuts against the end face of the shaft portion 18e.

[0249] Further, on the -X side of the pressure roller 18 (the opposite side to the solenoid 201), a coil spring 205 is provided as a biasing member that biases the end face of the shaft portion 18e of the pressure roller 18 in the +X direction.

[0250] As shown in FIG. 26(A), the plunger 202 of the solenoid 201 + In the X direction Evacuate Then, the plunger 202 is biased to the pressure roller 18. +X The pressure roller 18 moves in the direction of the -X direction. At this time, the pressure roller 18 is in the normal position. The distance in the X direction from the -X direction end of the pressure roller 18 to the thermistor 30 is a distance D1 (first distance).

[0251] When the pressure roller 18 is in the normal position, the rotation of the fixing motor 43 is transmitted to the drive gear 46 by the switching mechanism 200, and is further transmitted to the fixing gear 45. The pressure roller 18 rotates in the R1 direction (forward direction).

[0252] As shown in FIG. 26(B), the plunger 202 of the solenoid 201 - In the X direction protrusion Then, the pressure roller 18 is biased by the force of the coil spring 205. -X The pressure roller 18 moves in the cleaning position. The pressure roller 18 is positioned at the cleaning position. The distance in the X direction from the -X direction end of the pressure roller 18 to the thermistor 30 is a distance D2 (a second distance).

[0253] When the pressure roller 18 is in the cleaning position, the rotation of the fixing motor 43 is transmitted to the drive gear 204 by the switching mechanism 200, and is further transmitted to the fixing gear 203. The pressure roller 18 rotates in the R2 direction (reverse direction).

[0254] During the cleaning operation, from timing t1 to t2 shown in Fig. 14, the plunger 202 of the solenoid 201 is protruded in the -X direction as shown in Fig. 26(B). This causes the pressure roller 18 to move in the -X direction and reach the cleaning position. After that, from timing t2 to t3, the fixing motor 43 rotates the pressure roller 18 in the R2 direction.

[0255] During the cleaning operation, the solenoid 201 is retracted in the +X direction as shown in Fig. 26(A) from timing t4 to t5 shown in Fig. 14. This causes the pressure roller 18 to move in the +X direction and reach its normal position. After that, from timing t5 to t6, the fixing motor 43 rotates the pressure roller 18 in the R1 direction.

[0256] In this fourth modification, too, the rotation of the pressure roller 18 in the R2 direction during the cleaning operation can disperse the deposits T accumulated on the contact portion 32 of the thermistor 30. Furthermore, the fixing operation after the cleaning operation is completed is performed in the state shown in FIG.

[0257] In the first and second embodiments and the first to third modifications, the pressure roller 18 is rotated in the R1 and R2 directions while being moved in the axial direction. In contrast, in the fourth modification, the pressure roller 18 is moved in the -X direction and then rotated in the R2 direction, and the pressure roller 18 is moved in the +X direction and then rotated in the R1 direction.

[0258] 27, the paths E1 and E3 of the movement of contact portion 32 of thermistor 30 on the surface of pressure roller 18 are parallel to the X direction. Therefore, in terms of effectively dispersing deposit T accumulated on contact portion 32 of thermistor 30 over a wide range, Embodiments 1 and 2 and Modifications 1 to 3 are superior to Modification 4.

[0259] As described above, according to the fourth modification, even in a configuration using two rotation transmission mechanisms according to the rotation direction of the pressure roller 18, the deposits T accumulated on the contact portion 32 of the thermistor 30 can be dispersed.

[0260] Here, the rotation of the fixing motor 43 is transmitted to either the drive gear 46 or 204 via the switching mechanism 200, but the rotation of the fixing motor 43 may be transmitted to both the drive gears 46 and 204 at the same time. With this configuration, the rotation is transmitted to both ends of the pressure roller 18 in the X direction, so that the pressure roller 18 is less likely to twist compared to the case where the rotation is transmitted to only one end of the pressure roller 18. Therefore, there is an advantage in that the effect of the twist of the pressure roller 18 on image quality can be suppressed.

[0261] Further, in this embodiment, the solenoid 201 is used to move the pressure roller 18 in the X direction, but the mechanism is not limited to the solenoid 201 and may be another mechanism to move the pressure roller 18 in the X direction.

[0262] 27 can also be realized in fixing devices 10B, 10C, and 10D of Modifications 1 to 3. For example, in Modification 1 (FIGS. 23(A) and 23(B)), cam 47 may move pressure roller 18 in the +X direction, and then fixing motor 43 may rotate pressure roller 18 in the R2 direction, and cam 47 may move pressure roller 18 in the -X direction, and then fixing motor 43 may rotate pressure roller 18 in the R1 direction.

[0263] In the above embodiments, the image forming apparatus for forming a color image has been described, but the present disclosure can also be applied to an image forming apparatus for forming a single-color (monochrome) image. In addition, the present disclosure can be used, for example, in an image forming apparatus (such as a copier, facsimile, printer, multifunction machine, etc.) that forms an image on a medium using an electrophotographic method. [Explanation of symbols]

[0264] 1 image forming apparatus, 10, 10A, 10B, 10C, 10D, 10E fixing device, 11 fixing belt (rotating member), 12 stay, 13 heater support member, 14 temperature sensor, 15 heater, 18 pressure roller (rotating member), 20 bottom frame, 21 side frame, 22 support shaft, 23 movable frame, 24 biasing member, 25 bearing, 28 cam, 30 thermistor (sensor, temperature sensor), 31 temperature detection portion (element portion), 32 contact portion, 33 leaf spring portion, 34 housing portion, 35 feed screw mechanism (sensor moving mechanism), 41 fixing gear, 42 drive gear, 43 fixing motor, 45 fixing gear, 46 drive gear, 47 cam (rotating member moving mechanism), 48 Coil spring (pressing member), 49 Contact / separation motor (contact / separation mechanism), 50 Movable unit, 51 Coil spring (pressing member), 52 Support shaft, 53 Cam mechanism (unit moving mechanism), 60, 60K, 60Y, 60M, 60C Image forming unit (image forming section), 61 Photoconductor drum (image carrier), 62 Charge roller (charging member), 63 Exposure head (exposure device), 64 Development roller (developer carrier), 65 Supply roller (supply member), 70 Transfer unit, 80 Medium supply section, 90 Medium discharge section, 100 Control section, 101 Print count memory section, 102 Cleaning count memory section, 111 Fixing control section, 112 Motor control section, 113 Heater control section, 200 Rotation transmission mechanism, 201 Solenoid, 202 plunger, 203 fixing gear, 204 drive gear, 211 heater control section, D1 distance (first distance), D2 distance (second distance), E1 to E4 orbits, N cleaning count, Nc cleaning count threshold.

Claims

1. a rotating member extending in the width direction and rotatably provided to transport the medium; a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction; A sensor that contacts a surface of the rotating member; a position changing unit that changes a relative position between the rotation member and the sensor in the width direction, the position changing unit includes a rotation member moving mechanism that moves the rotation member in the width direction, A first operation is performed in which the driving unit rotates the rotating member in the reverse direction and the rotating member moving mechanism moves the rotating member in the width direction, thereby changing a relative position between the rotating member and the sensor in the width direction from a first relative position in which a distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position in which a distance between the one end of the rotating member and the sensor is a second distance.

1. An image forming apparatus comprising:

2. After performing the first operation, performing a second operation in which the drive unit rotates the rotation member in the reverse direction while maintaining the second relative position; Furthermore, a third operation is executed in which the drive unit rotates the rotating member in the forward direction and the rotating member moving mechanism moves the rotating member in the width direction, thereby changing the relative position between the rotating member and the sensor in the width direction from the second relative position to the first relative position.

2. The image forming apparatus according to claim 1,

3. The first operation, the second operation, the third operation, and a fourth operation in which the driving unit rotates the rotating member in the forward direction while maintaining the first relative position; an image forming unit that forms an image based on a print job; When the image forming unit performs printing in which the number of printed pages included in the print job exceeds a first threshold, the cleaning operation is executed.

3. The image forming apparatus according to claim 2,

4. When the image forming unit performs printing in which the number of printed pages included in the print job exceeds a second threshold, the cleaning operation is performed a plurality of times.

4. The image forming apparatus according to claim 3.

5. The amount of rotation by which the drive unit rotates the rotating member in the forward direction in the fourth operation is greater than the amount of rotation by which the drive unit rotates the rotating member in the reverse direction in the second operation.

5. The image forming apparatus according to claim 3, wherein the image forming apparatus is a multi-color image forming apparatus.

6. a fixing member that contacts the rotating member to form a nip, a contact / separation mechanism that brings the rotating member and the fixing member into contact with each other and separates them from each other, Before performing the first operation, the rotating member and the fixing member are separated from each other by the separation mechanism.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. A rotating member extending in a width direction and rotatably provided to transport a medium; a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction; A sensor that contacts a surface of the rotating member; a position changing unit that changes a relative position between the rotation member and the sensor in the width direction, The position change unit is a first helical gear to which rotation of the drive unit is transmitted; a second helical gear connected to the rotating member, meshing with the first helical gear to transmit rotation of the first helical gear to the rotating member; having a first operation is performed in which the driving unit rotates the rotating member in the reverse direction and moves the rotating member in the width direction by the rotation of the driving unit, thereby changing a relative position between the rotating member and the sensor in the width direction from a first relative position in which a distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position in which a distance between the one end of the rotating member and the sensor is a second distance; 1. An image forming apparatus comprising:

8. A rotating member extending in a width direction and rotatably provided to transport a medium; a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction; A sensor that contacts a surface of the rotating member; a position changing unit that changes a relative position between the rotation member and the sensor in the width direction; a fixing member that contacts the rotating member to form a nip; a contact / separation mechanism that brings the rotating member and the fixing member into contact with each other and separates them from each other, After the rotating member and the fixing member are separated from each other by the separation mechanism, A first operation is performed in which the driving unit rotates the rotating member in the reverse direction, and the position changing unit changes a relative position between the rotating member and the sensor in the width direction from a first relative position in which a distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position in which a distance between the one end of the rotating member and the sensor is a second distance.

1. An image forming apparatus comprising:

9. a rotating member extending in the width direction and rotatably provided to transport the medium; a drive unit that rotates the rotating member in a forward direction in which the medium is transported during image formation and in a reverse direction opposite to the forward direction; A sensor that contacts a surface of the rotating member; a position changing unit that changes a relative position between the rotating member and the sensor in the width direction by moving the rotating member in the width direction, a first operation in which the position change unit moves the rotating member in the width direction to change a relative position between the rotating member and the sensor in the width direction from a first relative position in which a distance between one end of the rotating member in the width direction and the sensor is a first distance to a second relative position in which a distance between the one end of the rotating member and the sensor is a second distance; and performing a second operation in which the drive unit rotates the rotating member in the reverse direction while maintaining the second relative position.

1. An image forming apparatus comprising:

Images