Image forming device

Abstract

To prevent printing from being started in a state in which a sheet remains wound around a roller.SOLUTION: An image forming apparatus comprises: a fixing device including a first fixing member 81 that has a roller and a second fixing member 82 that sandwiches a sheet P between the first fixing member 81 and itself to form a nip part NP; a motor M that rotates the first fixing member 81; a rotation detection member (Hall element M1) that detects the rotation of the motor M; and a control unit 100. When the control unit 100 determines that the sheet P is wound around the first fixing member 81 during printing, it determines that a winding jam error occurs, stops supply of current for driving to the motor M, based on a signal from the rotation detection member, determines whether the motor M not supplied with the current for driving is rotated, when determining that the motor M is not rotated, does not cancel the winding jam error, and when determining that the motor M is rotated, cancels the winding jam error.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a fixing device. [Background technology]

[0002] Conventionally, a fixing device for an image forming apparatus is known that includes a heating roller, a pressure roller that sandwiches a sheet between the heating roller, and an operating member that can manually rotate the heating roller (see Patent Document 1). With this technology, when a sheet has wrapped around the heating roller, the operating member can be operated to remove the sheet that has wrapped around the heating roller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-043446 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional technology, since it is not determined whether the sheet wrapped around the heating roller has been removed, there is a risk that printing will start with the sheet still wrapped around the heating roller.

[0005] Therefore, an object of the present invention is to prevent printing from starting while the sheet is still wrapped around the roller. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the image forming apparatus of the present invention comprises a main body housing, a developer image forming unit that forms a developer image on a sheet, a fixing device that fixes the developer image to the sheet, the fixing device including a first fixing member having a roller and a second fixing member that sandwiches the sheet between the first fixing member and forms a nip portion, a motor that rotates the first fixing member, a rotation detection member that detects the rotation of the motor, and a control unit. When the control unit determines that a sheet has wrapped around the first fixing member during printing, it determines that a wrap-around jam error has occurred and stops the supply of driving current to the motor, and determines whether the motor is rotating in a state where no driving current is being supplied based on a signal from the rotation detection member.If it determines that the motor is not rotating, it does not cancel the wrap-around jam error, and if it determines that the motor is rotating, it cancels the wrap-around jam error.

[0007] According to this configuration, when a user pulls out a sheet sandwiched between the first and second fixing members, the first fixing member and the motor are rotated by an external force, and the rotation detection member detects the rotation of the motor. Also, if the sheet sandwiched between the first and second fixing members is not pulled out, the first fixing member and the motor do not rotate, and the rotation detection member does not detect the rotation of the motor. Therefore, if the sheet remains wrapped around the first fixing member, the rotation detection member does not detect the rotation of the motor, and the control unit does not release the wrap jam error, so it is possible to prevent printing from starting with the sheet wrapped around the first fixing member.

[0008] The motor may include a Hall element as the rotation detection member, and the control unit may determine that the motor is being rotated based on a signal from the Hall element.

[0009] According to this configuration, the Hall element used for controlling the drive of the motor is used to detect the rotation of the motor when a winding jam error occurs, thereby reducing costs compared to, for example, a configuration that uses a separate sensor that is not used for controlling the drive of the motor.

[0010] In addition, the image forming device may be equipped with a switching mechanism that can switch the nip state of the first fixing member and the second fixing member between a strong nip state and a weak nip state in which the nip pressure is lower than that of the strong nip state, and the control unit may change the nip state to the weak nip state when it determines that the winding jam error has occurred.

[0011] According to this configuration, by changing the nip state to a weak nip state when a wraparound jam error occurs, less force is required to pull the sheet out from between the first and second fixing members, making it easier to pull out the sheet. Also, compared to a method of leaving a gap between the first and second fixing members when a wraparound jam error occurs, a weak nip state, that is, a state in which the first and second fixing members are in contact, when a wraparound jam error occurs allows the first fixing member to rotate smoothly as the sheet is pulled out.

[0012] In addition, the image forming device may be provided with a transmission mechanism that transmits a driving force from the motor to the developer image forming unit, the transmission mechanism being capable of cutting off the transmission of the driving force from the motor to the developer image forming unit, and the control unit may cut off the driving force from the motor to the developer image forming unit when it determines that the winding jam error has occurred.

[0013] According to this configuration, when a sheet becomes wrapped around the first fixing member, the driving force from the motor to the developer image forming unit is cut off, and the developer image forming unit, which is a load when turning the motor, is disconnected from the motor, thereby reducing the force required to pull out the sheet from between the first and second fixing members.

[0014] The image forming apparatus may further include a temperature sensor for detecting the temperature of the first fixing member, the temperature sensor being positioned within the width of the smallest sheet that can be fixed by the fixing device, and the control unit may determine that the sheet has been wrapped around the first fixing member based on a decrease in the detected temperature detected by the temperature sensor.

[0015] According to this configuration, since the temperature sensor can be used to determine whether the sheet has wrapped around the first fixing member, costs can be reduced compared to, for example, a method of determining whether the sheet has wrapped around the first fixing member using a sensor other than a temperature sensor. Also, since a decrease in the detected temperature can be determined when the sheet reaches the position of the temperature sensor, it is possible to prevent the sheet from wrapping around the first fixing member multiple times.

[0016] In addition, the control unit may cancel the winding jam error when the motor is rotated a rotational phase angle of the motor or more corresponding to the rotational phase angle of the first fixing member when the portion of the first fixing member facing the temperature sensor is rotated to the nip portion.

[0017] According to this configuration, the winding jam error is cleared after the leading edge of the sheet wrapped around the first fixing member moves from the temperature sensor to the nip portion and is pulled out of the nip portion, thereby further preventing printing from starting with the sheet wrapped around the first fixing member.

[0018] In addition, the image forming apparatus may be provided with a cover for opening and closing an opening of the main body housing, and the control unit may cancel the winding jam error when it determines that the motor is rotated with the cover open.

[0019] According to this configuration, by determining that the motor is rotated with the cover open, it is possible to more reliably determine whether or not the sheet sandwiched between the first and second fixing members has been pulled out. Effect of the Invention

[0020] According to the present invention, it is possible to prevent printing from starting while the sheet is still wrapped around the roller. [Brief description of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view showing a color printer according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing the fixing device. [Diagram 3] FIG. [Figure 4] 1A is a cross-sectional view showing a switching mechanism when the nip state is a strong nip state, and FIG. 1B is a cross-sectional view showing a structure around the nip portion. [Diagram 5] 1A is a cross-sectional view showing a switching mechanism when the nip state is a medium nip state, and FIG. 1B is a cross-sectional view showing a structure around the nip portion. [Figure 6] 1A is a cross-sectional view showing a switching mechanism when the nip state is a weak nip state, and FIG. 1B is a cross-sectional view showing a structure around the nip portion. [Figure 7] FIG. 4A is a diagram showing a state in which a sheet is wrapped around a first fixing member, and FIG. 4B is a diagram showing the relationship between a sheet with a minimum width and a temperature sensor. [Figure 8] 11 is a graph showing a change in temperature detected by a temperature sensor from when a sheet is wrapped around a first fixing member until a user removes the sheet. [Figure 9] 4 is a flowchart showing a printing process. [Figure 10] 10 is a flowchart showing a jam error determination process. [Figure 11] 13 is a flowchart showing an error release process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. As shown in FIG. 1, a color printer 1, as an example of an image forming apparatus, includes a main body housing 10, a supply section 20 that supplies a sheet P, an image forming section 30 that forms an image on the sheet P, a conveying section 90 that ejects the sheet P on which the image has been formed, and a control section 100.

[0023] The main body housing 10 has an opening 10A and a cover 11 that opens and closes the opening 10A. The opening 10A is an opening through which a unit U, which will be described later, can pass. The cover 11 is rotatable between an open position where the opening 10A is opened and a closed position where the opening 10A is closed.

[0024] The supply section 20 includes a supply tray 21 that stores the sheet P, and a sheet transport mechanism 22 that transports the sheet P from the supply tray 21 to the image forming section 30.

[0025] The image forming section 30 includes a scanner unit 40, a unit U, a transfer unit 70, and a fixing device 80. The scanner unit 40, the unit U, and the transfer unit 70 correspond to a developer image forming section that forms a developer image on the sheet P.

[0026] The scanner unit 40 includes a laser emitting unit, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). The scanner unit 40 irradiates the surface of each photosensitive drum 61 with a laser beam.

[0027] The unit U can be pulled out from the main body housing 10 through the opening 10A. The unit U includes four cartridges 50 and a drawer 60.

[0028] The cartridges 50 are detachably attached to the drawer 60. The cartridges 50 include a storage section 51 that stores toner as an example of a developer, a developing roller 52, and a layer thickness regulating blade 53 that contacts the developing roller 52 to regulate the layer thickness of the toner on the developing roller 52. The storage sections 51 of the four cartridges 50 store toner of each of the colors yellow, magenta, cyan, and black.

[0029] The cartridges 50 are indicated by reference characters 50Y, 50M, 50C, and 50K containing toner of yellow, magenta, cyan, and black, respectively, and are arranged in this order from the upstream in the conveying direction of the sheet P.

[0030] The drawer 60 can be pulled out from the image formation position of the main body housing 10 in a direction perpendicular to the up-down direction. Here, the image formation position refers to the position of the drawer 60 when an image is formed. The drawer 60 includes a photosensitive drum 61, a charger (not shown), a frame 62 that detachably holds the four cartridges 50, an internal temperature sensor SE1, and a first contact CN1. Four photosensitive drums 61 and chargers are provided on the frame 62 corresponding to the four developing rollers 52.

[0031] The frame 62 is supported by the main body housing 10 so as to be movable in a direction perpendicular to the up-down direction. The internal temperature sensor SE1 is, for example, a thermistor, and acquires an internal temperature, which is the temperature inside the main body housing 10. The first contact CN1 is electrically connected to the internal temperature sensor SE1 via a wire.

[0032] The main body housing 10 has a second contact CN2 that is electrically connected to the control unit 100 via a wire. The first contact CN1 is connected to the second contact CN2 when the drawer 60 is placed in the image formation position of the main body housing 10. More specifically, when the drawer 60 is placed in the image formation position, the first contact CN1 is connected to the second contact CN2.

[0033] Furthermore, the first contact CN1 is separated from the second contact CN2 when the drawer 60 is pulled out from the main housing 10. More specifically, when the drawer 60 is removed from the image forming position, the first contact CN1 is separated from the second contact CN2.

[0034] The transfer unit 70 includes a drive roller 71, a driven roller 72, a conveyor belt 73, and a transfer roller 74. The conveyor belt 73 is an endless belt. The drive roller 71 and the driven roller 72 are rollers that rotate the conveyor belt 73. The transfer rollers 74 are rollers that hold the conveyor belt 73 between themselves and the corresponding photosensitive drums 61, and four of them are disposed opposite each photosensitive drum 61.

[0035] The fixing device 80 is a device that fixes a toner image onto a sheet P. The fixing device 80 includes a heater 110, a first fixing member 81 that is heated by the heater 110, and a second fixing member 82 that sandwiches the sheet P between the first fixing member 81 and the second fixing member 82. The fixing device 80 will be described in detail later.

[0036] When the drawer 60 is in the image forming position of the main body housing 10, the color printer 1 is capable of forming an image. The image forming position is a position where the photosensitive drum 61 and the transfer unit 70 are in contact with each other, and where the scanner unit 40 can expose a predetermined position of the photosensitive drum 61. In the image forming section 30, the surface of each photosensitive drum 61 is first uniformly charged by a charger, and then exposed by the scanner unit 40. As a result, an electrostatic latent image based on image data is formed on each photosensitive drum 61. Thereafter, the toner in the storage section 51 is supplied by the developing roller 52 to the electrostatic latent image on the photosensitive drum 61, thereby forming a toner image on the photosensitive drum 61.

[0037] Next, the sheet P supplied onto the conveyor belt 73 passes between each photosensitive drum 61 and each transfer roller 74, so that the toner images formed on each photosensitive drum 61 are transferred onto the sheet P. Thereafter, the toner images transferred onto the sheet P are thermally fixed by the fixing device 80.

[0038] The conveying section 90 functions as a discharge mechanism that discharges the sheet P discharged from the image forming section 30 onto the discharge tray 13 of the main body housing 10, and also functions as a re-conveying means that re-conveys the sheet P, one side of which has an image formed by the image forming section 30, to the image forming section 30 in a state in which the sheet P is turned over. Specifically, the conveying section 90 mainly includes a conveying path 91, discharge rollers 92, and a re-conveying path 93.

[0039] The transport path 91 is a path that guides the sheet P from the fixing device 80 toward the discharge tray 13 .

[0040] The discharge roller 92 is configured to be rotatable in both forward and reverse directions. When rotating forward, the discharge roller 92 discharges the sheet P conveyed out from the image forming unit 30 toward the discharge tray 13, and when rotating reversely, the discharge roller 92 transports the sheet P so as to be drawn into the main housing 10.

[0041] The re-conveying path 93 is configured to guide the sheet P, one side of which has an image formed by the image forming unit 30, through under the supply unit 20 back to the image forming unit 30.

[0042] The color printer 1 further includes a cover open / close sensor SE2, a first sheet sensor SE3, a second sheet sensor SE4, a temperature sensor SE5, a motor M, a transmission mechanism TM, and a second transmission mechanism TM2.

[0043] The cover opening / closing sensor SE2 is a sensor that detects the opening and closing of the cover 11. When the cover 11 is closed, a part of the cover 11 comes into contact with the cover opening / closing sensor SE2 and outputs an ON signal to the control unit 100. When the cover 11 is open, the cover 11 moves away from the cover opening / closing sensor SE2 and outputs an OFF signal to the control unit 100.

[0044] The first sheet sensor SE3 and the second sheet sensor SE4 are sensors that detect the presence or absence of a sheet. The first sheet sensor SE3 and the second sheet sensor SE4 have, for example, a rocking member that rocks by contacting the sheet P, and an optical sensor that detects the rocking of the rocking member. In this embodiment, each of the sheet sensors SE3 and SE4 outputs an ON signal when the rocking member is tilted by the sheet P, and outputs an OFF signal when the rocking member is not tilted.

[0045] The first sheet sensor SE3 is located upstream of the photosensitive drum 61 in the transport direction of the sheet P. The second sheet sensor SE4 is located downstream of the first sheet sensor SE3, specifically, downstream of the first fixing member 81 in the transport direction of the sheet P.

[0046] The temperature sensor SE5 is a sensor that detects the temperature of the first fixing member 81 in a non-contact manner. The temperature sensor SE5 faces the outer circumferential surface of the first fixing member 81 in a non-contact manner. The temperature sensor SE5 has a thermistor that detects infrared rays from the first fixing member 81. The temperature sensor SE5 is mainly used as a sensor for controlling the temperature of the heater 110.

[0047] The motor M is a motor that rotates the first fixing member 81. The motor M includes a Hall element M1 as a rotation detection member that detects the rotation of the motor M. The Hall element M1 is mainly used as a sensor for controlling the rotation speed of the motor M.

[0048] The transmission mechanism TM is a mechanism that transmits driving force from the motor M to the developer image forming unit, such as the drive roller 71 and the photosensitive drum 61, and is capable of blocking the transmission of driving force from the motor M to the developer image forming unit. More specifically, the transmission mechanism TM includes a clutch CL that is capable of blocking the transmission of driving force.

[0049] The second transmission mechanism TM2 is a mechanism that transmits driving force from the motor M to the first fixing member 81. The second transmission mechanism TM2 is a gear train without a one-way clutch. This allows the motor M to rotate regardless of the direction in which the first fixing member 81 is rotated.

[0050] The control unit 100 has a CPU, a ROM, a RAM, etc., and is configured to execute various processes in response to receiving a print command, etc., according to a previously prepared program, etc. The control unit 100 is capable of acquiring signals from each of the sensors SE1 to SE5.

[0051] 2, the fixing device 80 includes a heater 110, a first fixing member 81, a second fixing member 82, and a temperature sensor SE5. The first fixing member 81 includes a roller 120.

[0052] Heater 110 is a halogen lamp that emits light and generates heat when energized, and uses radiant heat to heat roller 120. Heater 110 is disposed so as to pass through the inside of roller 120 along the rotation axis of roller 120. Here, the direction along the rotation axis of roller 120 is the axial direction of first fixing member 81, and hereinafter may also be referred to simply as the "axial direction."

[0053] The roller 120 is a cylindrical roller and is heated by the heater 110. The roller 120 has an element tube 121 made of metal or the like, and an elastic layer 122 covering the outer circumferential surface of the element tube 121. The elastic layer 122 is made of rubber such as silicone rubber. In this embodiment, the roller 120 has a concave shape in which the outer diameter at both ends in the axial direction is larger than the outer diameter at the axial center, and the outer diameter gradually increases from the axial center toward both ends. However, the shape of the roller 120 is not limited to this. The roller 120 may be, for example, a cylindrical roller with a uniform outer diameter in the axial direction. The roller 120 may also be a crown-shaped roller whose outer diameter gradually decreases from the axial center toward both ends.

[0054] Both axial ends of the roller 120 are rotatably supported by a frame FL, described later, more specifically, a side frame 83 (see FIG. 3), and are driven to rotate counterclockwise in FIG. 2 by inputting a driving force from a motor M.

[0055] The second fixing member 82 is capable of linear movement in a predetermined direction, which is a direction in which the second fixing member 82 approaches or moves away from the first fixing member 81. The predetermined direction is perpendicular to the axial direction. The second fixing member 82 is biased toward the first fixing member 81 by a switching mechanism 300 (see FIG. 3), which will be described later.

[0056] The second fixing member 82 includes an endless belt 130, a nip forming member N, a holder 140, a stay 200, a belt guide G, and a sliding sheet 150.

[0057] The belt 130 is a long cylindrical member and has flexibility. Although not shown, the belt 130 has a base material made of metal, resin, or the like, and a release layer covering the outer peripheral surface of the base material. When the roller 120 rotates, the belt 130 rotates clockwise in FIG. 2 due to friction with the roller 120 or the sheet P. A lubricant such as grease is applied to the inner peripheral surface of the belt 130. A nip forming member N, a holder 140, a stay 200, a belt guide G, and a sliding sheet 150 are arranged inside the belt 130.

[0058] The nip forming member N is a member that forms a nip portion NP by nipping the belt 130 between itself and the roller 120. The nip forming member N includes a first nip forming member N1 and a second nip forming member N2.

[0059] The first nip forming member N1 has a first pad P1 and a first fixed plate B1. The first pad P1 is a rectangular parallelepiped member. The first pad P1 is made of rubber such as silicone rubber. The first pad P1 and the roller 120 sandwich the belt 130 therebetween to form an upstream nip portion NP1.

[0060] In the following description, the movement direction of the belt 130 in the upstream nip portion NP1 and the nip portion NP described in detail later will be simply referred to as the "movement direction". In this embodiment, the movement direction is along the outer circumferential surface of the roller 120, but since this direction is roughly along a direction perpendicular to the predetermined direction and the axial direction, it will be illustrated as a direction perpendicular to the predetermined direction and the axial direction. The movement direction is the same as the conveying direction of the sheet P in the nip portion NP. In the following description, the upstream and downstream of the movement direction will also be simply referred to as "upstream and downstream".

[0061] The first pad P1 is fixed to the surface of the first fixed plate B1 facing the roller 120. The first pad P1 protrudes slightly upstream in the moving direction beyond the upstream end of the first fixed plate B1. This allows the first pad P1 to come into contact with the holder 140 on the upstream side.

[0062] The first fixing plate B1 is made of a material harder than the first pad P1, such as a metal.

[0063] The second nip forming member N2 is disposed downstream in the movement direction relative to the first nip forming member N1 with a gap therebetween. In other words, the second nip forming member N2 is separated from the first nip forming member N1 in the transport direction of the sheet P. The second nip forming member N2 has a second pad P2 and a second fixed plate B2.

[0064] The second pad P2 is a rectangular parallelepiped member. The second pad P2 is made of rubber such as silicone rubber. The second pad P2 forms a downstream nip portion NP2 by sandwiching the belt 130 between the second pad P2 and the roller 120. The second pad P2 is separated from the first pad P1 in the movement direction.

[0065] Therefore, between the upstream nip portion NP1 and the downstream nip portion NP2, there is an intermediate nip portion NP3 where the pressure from the second fixing member 82 does not directly act. In this intermediate nip portion NP3, the belt 130 contacts the roller 120, but there is no member that sandwiches the belt 130 between the roller 120 and the intermediate nip portion NP3, so almost no pressure is applied. Therefore, the sheet P passes through the intermediate nip portion NP3 while being heated by the roller 120 and almost without being pressurized. In this embodiment, the region from the upstream end of the upstream nip portion NP1 to the downstream end of the downstream nip portion NP2, that is, the entire region where the outer circumferential surface of the belt 130 and the roller 120 contact each other, is referred to as the nip portion NP. In other words, in this embodiment, the nip portion NP includes a portion where the pressing force from the first pad P1 and the second pad P2 is not applied.

[0066] The second pad P2 is fixed to the surface of the second fixed plate B2 on the roller 120 side. The second pad P2 protrudes slightly downstream in the moving direction from the downstream end of the second fixed plate B2. This allows the second pad P2 to contact the holder 140 on the downstream side. As shown in Fig. 6, the dimension of the second pad P2 in a predetermined direction is smaller than the dimension of the first pad P1.

[0067] The second fixed plate B2 is made of a material harder than the second pad P2, such as metal, etc. In a predetermined direction, the dimension of the second fixed plate B2 is the same as that of the first fixed plate B1.

[0068] The hardness of the first pad P1 is greater than the hardness of the elastic layer 122 of the roller 120. The hardness of the second pad P2 is greater than the hardness of the first pad P1. In other words, the first pad P1 is softer than the second pad P2.

[0069] Here, the hardness refers to the durometer hardness defined in ISO 7619-1. The durometer hardness is a value obtained from the depth of a specified indenter when the specified indenter is pressed into a test piece under specified conditions. For example, when the durometer hardness of the elastic layer 122 is 5, it is preferable that the durometer hardness of the first pad P1 is 6 to 10, and the durometer hardness of the second pad P2 is 70 to 90.

[0070] The hardness of silicone rubber can be adjusted by changing the ratio of additives (silica-based fillers and carbon-based fillers) added during manufacturing. Specifically, increasing the ratio of additives increases the hardness of the rubber. Hardness can also be reduced by adding silicone oil. Liquid injection molding and extrusion molding can be used as methods for manufacturing rubber. Generally, liquid injection molding is suitable for low hardness rubber, and extrusion molding is suitable for high hardness rubber.

[0071] The holder 140 is a member that holds the nip formation member N. In other words, the first nip formation member N1 and the second nip formation member N2 are supported by one holder 140. The holder 140 is supported by a stay 200.

[0072] The holder 140 has a first support surface 141A that supports the surface of the first nip forming member N1 opposite to the first fixing member 81, and a second support surface 141B that supports the surface of the second nip forming member N2 opposite to the first fixing member 81. The first support surface 141A and the second support surface 141B are located at the same position in a predetermined direction.

[0073] 6, the first nip forming member N1 protrudes closer to the first fixing member 81 than the second nip forming member N2. In other words, a first tip surface N11, which is the surface of the first nip forming member N1 facing the first fixing member 81, is located closer to the first fixing member 81 in a predetermined direction than a second tip surface N21, which is the surface of the second nip forming member N2 facing the first fixing member 81. In more detail, when the nip forming members N1 and N2 are not pressed against the first fixing member 81, the first tip surface N11 is located closer to the first fixing member 81 than the second tip surface N21.

[0074] Here, in the state of FIG. 6, only a part of the first tip surface N11 of the first nip forming member N1 is in pressure contact with the first fixing member 81, and no pressure is applied to the other part of the first tip surface N11 and the second tip surface N21. Therefore, the positions of the other part of the first tip surface N11 and the second tip surface N21 are the same as when each of the nip forming members N1 and N2 is not in pressure contact with the first fixing member 81. In other words, the other part of the first tip surface N11 is located closer to the first fixing member 81 than the second tip surface N21. In other words, in a predetermined direction, the shortest distance D1 between the part of the first tip surface N11 to which pressure is not applied and the outer circumferential surface of the first fixing member 81 is smaller than the shortest distance D2 between the second tip surface N21 to which pressure is not applied and the outer circumferential surface of the first fixing member 81.

[0075] The stay 200 is a member that is located on the opposite side of the holder 140 from the nip forming member N and supports the holder 140. The stay 200 is made of metal or the like. A buffer member BF (see FIG. 4) made of resin or the like is attached to the axial end of the stay 200. The buffer member BF is a member for suppressing friction between the metallic stay 200 and a metallic arm 310 (see FIG. 4) described later.

[0076] The belt guide G is a member that guides an inner circumferential surface 131 of the belt 130. The belt guide G is made of a heat-resistant resin or the like. The belt guide G has an upstream guide G1 and a downstream guide G2.

[0077] The sliding sheet 150 is a rectangular sheet for reducing frictional resistance between each of the pads P1, P2 and the belt 130. The sliding sheet 150 is sandwiched between the inner circumferential surface 131 of the belt 130 and each of the pads P1, P2 at the nip portion NP. The sliding sheet 150 is made of an elastically deformable material. Note that the sliding sheet 150 may be made of any material, but in this embodiment, a resin sheet containing polyimide is used.

[0078] 3, the fixing device 80 further includes a frame FL and a switching mechanism 300. The frame FL is a frame that supports the first fixing member 81 and the second fixing member 82, and is made of metal or the like. The frame FL includes side frames 83 and brackets 84 that are disposed on both sides of the first fixing member 81 and the second fixing member 82 in the axial direction, and connection frames 85 that are connected to each side frame 83.

[0079] The side frame 83 is a frame that supports the first fixing member 81 and the second fixing member 82. The side frame 83 has a spring engagement portion 83A that engages with one end of a first spring 320, which will be described later.

[0080] The brackets 84 are members that support the second fixing member 82 so as to be movable in a predetermined direction, and are fixed to the side frames 83. More specifically, the brackets 84 arranged on both sides in the axial direction have first elongated holes 84A that support the axial end portion 142 of the holder 140 so as to be movable in the predetermined direction. The first elongated holes 84A are elongated holes that extend in the predetermined direction.

[0081] Here, the first long hole 84A corresponds to a groove serving as a guide. Each end 142 in the axial direction of the holder 140 is inserted into the first long hole 84A on both sides in the axial direction, and the second fixing member 82 is supported so as to be movable in a predetermined direction. Note that the groove serving as a guide may be a groove with a bottom.

[0082] Switching mechanism 300 is a mechanism that is driven by control unit 100 and can switch the nip state of first fixing member 81 and second fixing member 82 between a strong nip state, a medium nip state in which the nip pressure is lower than that of the strong nip state, and a weak nip state in which the nip pressure is lower than that of the medium nip state. Here, in any of the strong nip state, medium nip state, and weak nip state, belt 130 is sandwiched between at least one of pads P1, P2 and first fixing member 81.

[0083] 4(a), the switching mechanism 300 includes an arm 310, a first spring 320 as an example of a spring, a second spring 330, a cam 340, and a second motor 360 that drives the cam 340. The arm 310, the first spring 320, the second spring 330, and the cam 340 are provided at one end side and the other end side of the frame FL in the axial direction, respectively.

[0084] The arm 310 is a member for pressing the stay 200 toward the first fixing member 81 via the buffer member BF. The arm 310 supports the second fixing member 82, and is supported by the side frame 83 so as to be rotatable.

[0085] The arm 310 has an arm body 311 and a cam follower 350. The arm body 311 is an L-shaped plate-like member made of metal or the like.

[0086] The side frame 83 has a boss 83X that rotatably supports the arm body 311. The arm body 311 has one end 311A ​​that is rotatably supported by the boss 83X of the side frame 83, the other end 311B to which the first spring 320 is connected, and an engagement hole 311C that supports the second fixing member 82. The engagement hole 311C is disposed between the one end 311A ​​and the other end 311B, and engages with the buffer member BF.

[0087] Moreover, the arm body 311 further has a guide protrusion 312 extending towards the cam 340. The guide protrusion 312 is disposed between the other end 311B and the engagement hole 311C in the direction from the other end 311B towards the engagement hole 311C.

[0088] Cam follower 350 is attached movably relative to guide protrusion 312 of arm body 311, and is capable of contacting cam 340. Cam follower 350 is made of resin or the like, and has a cylindrical portion 351 that fits into guide protrusion 312, a contact portion 352 provided at one end of cylindrical portion 351, and a flange portion 353 provided at the other end of cylindrical portion 351.

[0089] Cylindrical portion 351 is supported by guide protrusion 312 so as to be movable in the extending direction of guide protrusion 312. Contact portion 352 is a wall that closes an opening at the end portion of cylindrical portion 351 on the cam 340 side, and is disposed between cam 340 and the tip of guide protrusion 312. Flange portion 353 protrudes from the other end of cylindrical portion 351 in a direction perpendicular to the moving direction of cam follower 350.

[0090] In addition, a second spring 330 is disposed between the cylindrical portion 351 and the arm body 311. This allows the arm body 311 to be biased by the first spring 320 and also biased by the second spring 330.

[0091] The first spring 320 is a spring that applies a load to the nip portion NP by applying a first biasing force to the second fixing member 82. In detail, the first spring 320 applies the first biasing force to the second fixing member 82 via the arm body 311.

[0092] More specifically, the first spring 320 biases the first pad P1 and the second pad P2 toward the roller 120 via the arm body 311, the buffer member BF, the stay 200, and the holder 140. The first spring 320 is a tension coil spring made of metal or the like, and has one end connected to the spring engagement portion 83A of the side frame 83 and the other end connected to the other end portion 311B of the arm body 311.

[0093] The second spring 330 is a spring capable of applying a second biasing force in a direction opposite to the first biasing force to the second fixing member 82. In detail, the second spring 330 is capable of applying the second biasing force to the second fixing member 82 via the arm main body 311. The second spring 330 is a compression coil spring made of metal or the like, and is disposed between the tubular portion 351 and the arm main body 311 with the guide protrusion 312 inserted in the space surrounded by the compression coil spring.

[0094] The cam 340 is a member that presses the arm 310 via the cam follower 350 to move the second fixing member 82 in a predetermined direction. The cam 340 also has a function of changing the expansion and contraction state of the second spring 330 to a first expansion and contraction state in which the second biasing force is not applied to the second fixing member 82, a second expansion and contraction state in which the second biasing force is applied to the second fixing member 82, and a third expansion and contraction state in which the second fixing member 82 is more deformed than the second expansion and contraction state. The cam 340 is supported by the side frame 83 so as to be rotatable between a first cam position shown in FIG. 4(a), a second cam position shown in FIG. 5(a), and a third cam position shown in FIG. 6(a). In detail, the cam 340 is configured to rotate to each cam position by intermittently supplying the driving force of the second motor 360 to the cam 340 by the control unit 100. The intermittent supply of driving force from the second motor 360 to the cam 340 may be achieved by controlling a driving force transmission switching mechanism, such as a clutch, that switches the transmission of driving force from the second motor 360 to the cam 340 using the control unit 100, or may be achieved by switching between driving and stopping the second motor 360 using the control unit 100.

[0095] Cam 340 is made of resin or the like, and has first portion 341, second portion 342, and third portion 343. First portion 341, second portion 342, and third portion 343 are located on the outer circumferential surface of cam 340.

[0096] The first portion 341 is the portion closest to the cam follower 350 when the cam 340 is located at the first cam position. As shown in Fig. 4(a) , when the cam 340 is located at the first cam position, the first portion 341 is separated from the cam follower 350.

[0097] The second portion 342 is a portion that comes into contact with the cam follower 350 when the cam 340 is located at the second cam position. More specifically, the second portion 342 is a portion that comes into contact with the cam follower 350 when the cam 340 rotates approximately 90 degrees clockwise from the first cam position as shown in Fig. 5(a). The distance from the second portion 342 to the rotation center of the cam 340 is greater than the distance from the first portion 341 to the rotation center of the cam 340.

[0098] The third portion 343 is a portion that comes into contact with the cam follower 350 when the cam 340 is located at the third cam position. More specifically, the third portion 343 is a portion that comes into contact with the cam follower 350 when the cam 340 rotates approximately 270 degrees in the clockwise direction from the first cam position, in other words, when the cam 340 rotates approximately 180 degrees in the clockwise direction from the second cam position, as shown in Fig. 6(a). The distance from the third portion 343 to the rotation center of the cam 340 is greater than the distance from the second portion 342 to the rotation center of the cam 340.

[0099] When the cam 340 is located at the first cam position, the cam 340 is separated from the cam follower 350, and the second spring 330 is in the first extended / contracted state. When the cam 340 causes the second spring 330 to be in the first extended / contracted state in this manner, the arm main body 311 is in the first posture shown in FIG. 4(a).

[0100] In detail, when the cam 340 sets the second spring 330 in the first contraction state, the cam 340 is separated from the cam follower 350, so that the second biasing force of the second spring 330 is not applied to the second fixing member 82 via the arm body 311, and only the first biasing force of the first spring 320 is applied to each pad P1, P2 of the second fixing member 82 via the arm body 311. When the first biasing force is applied to the second fixing member 82 by the first spring 320 in this manner and the second biasing force is not applied to the second fixing member 82 by the second spring 330, the nip state is a strong nip state and the nip pressure is the first nip pressure. In the strong nip state, the belt 130 is sandwiched between each pad P1, P2 and the first fixing member 81.

[0101] 5(a) from the first cam position shown in Fig. 4(a) to the second cam position shown in Fig. 5(a), the cam 340 comes into contact with the cam follower 350 and moves the cam follower 350 a predetermined amount relative to the arm body 311. As a result, when the cam 340 is located at the second cam position, the second spring 330 is in a second expanded / contracted state that is more deformed than the first expanded / contracted state.

[0102] When the cam 340 is located at the second cam position, the cam follower 350 is supported by the cam 340, and therefore the second biasing force of the second spring 330 is applied to the second fixing member 82 via the arm body 311 in the opposite direction to the first biasing force. Therefore, when the first biasing force is applied to the second fixing member 82 by the first spring 320 and the second biasing force is applied to the second fixing member 82 by the second spring 330, the nip state is a medium nip state, and the nip pressure is a second nip pressure that is smaller than the first nip pressure. In the medium nip state, the belt 130 is sandwiched between each of the pads P1, P2 and the first fixing member 81.

[0103] When the cam 340 sets the second spring 330 in the second contraction state, the arm body 311 remains in the first position described above. Here, the second pad P2 is pressed against the roller 120, that is, when a load is applied to the second pad P2, it is not substantially deformed regardless of the magnitude of the load. Since the second pad P2 is not substantially deformed, the position of the stay 200 supporting the second pad P2 and the arm 310 supporting the stay 200 are also kept substantially constant regardless of the magnitude of the load. Furthermore, since the position of the first pad P1 is determined by the position of the second pad P2, when the second pad P2 is not substantially deformed and its position is not deformed, the position of the first pad P1 does not change. Therefore, in either the strong nip (first nip pressure) or medium nip (second nip pressure), the total nip width (the length from the entrance of the upstream nip portion NP1 to the exit of the downstream nip portion NP2) remains the same, and the posture of the arm 310 is kept approximately constant. Both the strong nip state and the medium nip state are full nip states in which the belt 130 is sandwiched between each of the pads P1, P2 and the first fixing member 81. The reason why the second pad P2 does not deform is because the hardness of the second pad P2 is sufficiently higher than the hardness of the first pad P1 and the elastic layer 122 of the roller 120. More specifically, the second pad P2 has a hardness that is such that it is hardly deformed by a nip pressure within the range from the maximum nip pressure (downstream nip pressure at the time of strong nip) to the minimum nip pressure (downstream nip pressure at the time of weak nip) required at the downstream nip portion NP2. In other words, the maximum nip pressure and the minimum nip pressure required in the downstream nip are set to a value that causes almost no deformation of the second pad P2. Here, "the second pad P2 is almost not deformed" includes the second pad P2 deforming to an extent that the deformation amount of the nip width (length and position of the nip in the belt movement direction) of the downstream nip portion NP2 formed by the second pad P2 does not affect image quality or paper transport (the deformation amount of the downstream nip width is not zero).

[0104] In this way, whether the second spring 330 is in the first or second contraction state, the posture of the arm body 311 is the first posture, so that, as shown in Figures 4(b) and 5(b), in both states where the nip pressure is the first nip pressure and where the nip pressure is the second nip pressure, the first pad P1 and the second pad P2 sandwich the belt 130 between themselves and the roller 120. In more detail, in each state, the position of the second fixing member 82 relative to the roller 120 is substantially the same, so that the width (length in the movement direction) of the nip portion NP in each state is substantially the same.

[0105] 6(a) from the second cam position shown in Fig. 5(a), the cam 340 moves the cam follower 350 further relative to the arm body 311, and then presses the arm body 311 via the cam follower 350. As a result, the contracted state of the second spring 330 becomes a third contracted state in which the second contracted state is more deformed than the second contracted state, and the arm body 311 rotates from the first posture to a second posture different from the first posture.

[0106] Specifically, in the first stage of the process of rotating the cam 340 from the second cam position to the third cam position, the cam follower 350 moves relative to the arm body 311 so that the contact portion 352 of the cam follower 350 approaches the tip of the guide protrusion 312. When the contact portion 352 comes into contact with the tip of the guide protrusion 312, the contracted state of the second spring 330 becomes the third contracted state. When the cam 340 makes the contracted state of the second spring 330 the third contracted state in this manner, the contact portion 352, which is a part of the cam follower 350, is sandwiched between the cam 340 and the guide protrusion 312. In other words, the contact portion 352 comes into contact with the cam 340 and also with the guide protrusion 312. Thereafter, when the cam 340 is further rotated, the cam 340 presses the guide projection 312 via the contact portion 352, so that the arm body 311 rotates from the first position to the second position against the biasing force of the first spring 320.

[0107] As a result, when the arm body 311 is in the second position, the second fixing member 82 is disposed at a position (position in FIG. 6(b)) farther from the roller 120 than the position (position in FIG. 5(b)) when the arm body 311 is in the first position. In this way, the position of the second fixing member 82 with respect to the roller 120 changes, and as shown in FIG. 6(b), when the arm body 311 is in the second position, the width of the nip portion NP becomes smaller than that in the first position, and the nip pressure becomes a third nip pressure that is smaller than the second nip pressure, as shown in FIG. 6(b). In other words, the position of the arm 310 is changed by the cam 340, so that the nip pressure and the nip width change. In more detail, when the arm 310 is in the second position, the nip state is a weak nip state in which the belt 130 is sandwiched only between the first pad P1 and the roller 120, and the belt 130 is not sandwiched between the second pad P2 and the roller 120. As a result, when the arm 310 is in the second posture, the upstream nip pressure and the upstream nip width become small, and the downstream nip pressure disappears. In addition, in the weak nip state, the biasing force of the first spring 320 is received by the cam 340 via the arm body 311 and the contact portion 352 of the cam follower 350, so that the biasing force of the first spring 320 is not applied to the first pad P1. In other words, in the weak nip state, the nip portion NP is formed only by the deformation of the first pad P1. The weak nip state is a partial nip state in which the belt 130 is sandwiched between the pad P1 and the first fixing member 81, and the belt 130 is not sandwiched between the pad P2 and the first fixing member 81.

[0108] 7(a), the temperature sensor SE5 is disposed at a position shifted a predetermined angle θ downstream from the upstream end of the nip portion NP in the rotation direction of the first fixing member 81 during printing. In other words, the angle between a line L1 connecting the upstream end of the nip portion NP and the rotation center of the first fixing member 81 and a line L2 connecting the temperature sensor SE5 and the rotation center of the first fixing member 81, and the angle in the range from the line L1 to the downstream side in the rotation direction of the first fixing member 81 and from the line L2 to the upstream side in the rotation direction of the first fixing member 81, is the predetermined angle θ.

[0109] 7(b), the temperature sensor SE5 is located within the width of the sheet Pmin, which is the minimum width that can be fixed by the fixing device 80. This allows the sheet P to enter between the temperature sensor SE5 and the first fixing member 81, regardless of the size of the sheet P that is wrapped around the first fixing member 81, as shown in FIG.

[0110] The control unit 100 has a function of determining whether or not a jam error has occurred in which the sheet P stops during printing. In detail, the control unit 100 can determine a first jam error in which the sheet P gets stuck near the first sheet sensor SE3, a second jam error in which the sheet P gets stuck between the first sheet sensor SE3 and the second sheet sensor SE4, a third jam error in which the sheet P gets stuck near the second sheet sensor SE4, and a wraparound jam error in which the sheet P gets stuck by wrapping around the first fixing member 81.

[0111] The control unit 100 determines that a first jam error has occurred when the time during which the first sheet sensor SE3 outputs an ON signal exceeds the sheet length time, that is, when the sheet P is jammed near the first sheet sensor SE3 and the first sheet sensor SE3 remains tilted. Here, the sheet length time is a time corresponding to the length of the sheet P. When the sheet P passes through the first sheet sensor SE3 normally, the first sheet sensor SE3 is ON for a time obtained by dividing the length of the sheet P by the conveying speed of the sheet P, so the sheet length time is set to a time longer than this time.

[0112] The control unit 100 determines that a second jam error has occurred if the second sheet sensor SE4 does not detect a specific sheet P within a specific time after the first sheet sensor SE3 detects the specific sheet P, that is, if the sheet P passes the first sheet sensor SE3 normally but gets stuck before reaching the second sheet sensor SE4. The control unit 100 also determines that a third jam error has occurred if the time during which the ON signal is output from the second sheet sensor SE4 exceeds the sheet length time, that is, if the sheet P gets stuck near the second sheet sensor SE4 and the second sheet sensor SE4 remains tilted.

[0113] The control unit 100 determines that the sheet P has wrapped around the first fixing member 81 based on a drop in the detected temperature detected by the temperature sensor SE5. Here, the detected temperature is maintained near the target temperature of the first fixing member 81 during printing (time t1-t2) as shown in FIG. 8. However, as shown in FIG. 7(a), when the sheet P wrapped around the first fixing member 81 enters between the temperature sensor SE5 and the first fixing member 81, the detected temperature drops suddenly as shown at time t2 in FIG. 8. When the amount of decrease in the detected temperature per unit time is greater than a first predetermined amount, the control unit 100 determines that the sheet P has wrapped around the first fixing member 81 and determines that a winding error has occurred.

[0114] Furthermore, the control unit 100 has a function of determining whether the sheet P wrapped around the first fixing member 81 has been removed based on a change in the detected temperature after determining that the sheet P has been wrapped around the first fixing member 81. Here, the detected temperature, which dropped suddenly at time t2, gradually rises thereafter as the sheet P wrapped around the first fixing member 81 is warmed by the heat of the first fixing member 81. Then, when the user pulls the sheet P in the direction opposite to the conveying direction, the leading edge of the sheet P leaves between the temperature sensor SE5 and the first fixing member 81, and the warmed air between the temperature sensor SE5 and the first fixing member 81 leaves between the temperature sensor SE5 and the first fixing member 81, causing the detected temperature to drop suddenly as shown at time t3 in FIG. When the control unit 100 determines that the sheet P has wrapped around the first fixing member 81 and then determines that the decrease in the detected temperature per unit time is greater than a second predetermined amount, it determines that the sheet P wrapped around the first fixing member 81 has been removed, and with this determination as a condition, cancels the wrapping jam error.

[0115] Here, the rectangular waveform shown in Fig. 8 is a waveform indicating that a sheet P has passed through the second sheet sensor SE4. The example in Fig. 8 shows an example in which it is determined that wrapping has occurred when the second sheet sensor SE4 is ON at time t2. This example shows an example in which two sheets P enter the fixing device 80 in an overlapping state, and one of the two sheets P wraps around the first fixing member 81, while the other sheet P passes through the second sheet sensor SE4 normally.

[0116] Even if it is not possible to determine the occurrence of a jam error based on the signal of the second sheet sensor SE4 in this manner, it is possible to accurately determine a wrap-around jam error caused by wrap-around by determining the wrap-around around the first fixing member 81. Note that when one sheet P enters the fixing device 80 and wraps around the first fixing member 81, the second sheet sensor SE4 does not turn ON within a predetermined time from the first sheet sensor SE3 turning ON. In this case, the control unit 100 determines that a second jam error has occurred, and also determines that a wrap-around error has occurred based on the wrap-around determination.

[0117] 7(a), the control unit 100 also has a function of determining whether the motor M, which is not supplied with a driving current, has been rotated based on a signal from the Hall element M1, and determining that the sheet P wrapped around the first fixing member 81 has been removed on condition that it has been determined that the motor M has been rotated. Specifically, when the user pulls the sheet P in the direction opposite to the conveying direction, the first fixing member 81 in contact with the sheet P rotates clockwise as shown in the figure, and the motor M connected to the first fixing member 81 also rotates. When the motor M rotates, the Hall element M1 detects the rotation and outputs a signal, and the control unit 100 determines that the motor M has been rotated based on this signal.

[0118] When the control unit 100 determines that the motor M is not rotated, the control unit 100 does not cancel the winding jam error, and when the control unit 100 determines that the motor M is rotated, the control unit 100 cancels the winding jam error. In detail, when the motor M is rotated by a rotation phase angle θ2 of the motor M or more corresponding to the rotation phase angle θ1 of the first fixing member 81 when the part of the first fixing member 81 facing the temperature sensor SE5 is rotated to the nip portion NP, the rotation phase angle θ1 of the first fixing member 81 corresponds to the above-mentioned predetermined angle θ. In addition, the rotation phase angle θ2 of the motor M corresponding to the rotation phase angle θ1 of the first fixing member 81 is determined by the gear ratio between the gear provided at the end of the first fixing member 81 in the axial direction and the gear provided on the output shaft of the motor M.

[0119] In this embodiment, in addition to the two conditions described above, the conditions for clearing the wrap jam error also include a condition for opening and closing the cover 11 and a condition for inserting and removing the drawer 60. In detail, when the control unit 100 determines that the motor M has rotated by rotation phase angle θ2 or more based on a signal from the Hall element M1 with the cover 11 open and the drawer 60 pulled out from the image forming position, or when it determines that the sheet P has been removed based on a change in the temperature detected by the temperature sensor SE5, the control unit 100 clears the wrap jam error.

[0120] The conditions for clearing all jam errors including the wraparound jam error include the above-mentioned conditions of opening and closing the cover 11 and the conditions of inserting and removing the drawer 60, as well as the sheet sensors SE3 and SE4 being OFF.

[0121] The control unit 100 has a function of changing the nip state to a weak nip state when it is determined that a jam error has occurred. In more detail, if the nip state is a strong nip state when it is determined that a jam error has occurred, the control unit 100 executes stopping the rotation of the first fixing member 81, stopping the heater 110, and switching from the strong nip state to the weak nip state. More specifically, the control unit 100 executes stopping the rotation of the first fixing member 81 and stopping the heater 110, and then executes switching from the strong nip state to the weak nip state.

[0122] Here, the rotation of first fixing member 81 is stopped by stopping the supply of driving current to motor M. The heater 110 is stopped by stopping the supply of current to heater 110. Switching from the strong nip state to the weak nip state is performed by switching the position of cam 340 of switching mechanism 300.

[0123] Furthermore, the control unit 100 has a function of cutting off the driving force from the motor M to the developer image forming unit when it is determined that a jam error has occurred. Here, the cutting off of the driving force from the motor M to the developer image forming unit is performed by disengaging the clutch CL.

[0124] Next, the operation of the control unit 100 will be described in detail. When the control unit 100 receives a print command, it executes the print process shown in FIG.

[0125] In the printing process, the control unit 100 first sets the nip state according to the type of the sheet P (S1). For example, if the type of the sheet P is a sheet of a first thickness, such as plain paper, the control unit 100 positions the cam 340 at the first cam position to set the nip state to a strong nip state. If the type of the sheet P is a sheet of a second thickness, such as cardboard, which is thicker than the first thickness, the control unit 100 positions the cam 340 at the second cam position to set the nip state to a medium nip state. If the type of the sheet P is a sheet of a third thickness, such as an envelope, which is thicker than the second thickness, the control unit 100 positions the cam 340 at the third cam position to set the nip state to a weak nip state.

[0126] After step S1, the control unit 100 starts printing (S2). After step S2, the control unit 100 executes a jam error determination process (S3). The jam error determination process will be described in detail later.

[0127] After step S3, the control unit 100 determines whether a jam error has occurred, more specifically, whether a jam error has occurred in the jam error determination process (S4). If it is determined in step S4 that a jam error has occurred (Yes), the control unit 100 stops printing (S5). More specifically, in step S5, the control unit 100 stops the rotation of the first fixing member 81, stops the heater 110, and disengages the clutch CL.

[0128] After step S5, the control unit 100 determines whether the nip state is other than the weak nip state (S6). If it is determined in step S6 that the nip state is other than the weak nip state, that is, the medium nip state or the strong nip state (Yes), the control unit 100 drives the switching mechanism 300 to switch the nip state to the weak nip state (S7). Specifically, the control unit 100 drives the second motor 360 to rotate the cam 340 from the first cam position or the second cam position to the third cam position.

[0129] After step S7, or if the result of the determination in step S6 is No, the control unit 100 executes an error reset process (S8). Note that the error reset process will be described in detail later.

[0130] After step S8, the control unit 100 determines whether the jam error has been cleared in the error clearing process (S9). If it is determined in step S9 that the jam error has not been cleared (No), the control unit 100 returns to the process of step S8.

[0131] If it is determined in step S9 that the jam error has been cleared (Yes), the control unit 100 resumes printing (S10). After step S10, or if it is determined No in step S4, the control unit 100 determines whether printing has ended (S11).

[0132] If it is determined in step S11 that printing has not finished (No), the control unit 100 returns to the process of step S3. If it is determined in step S11 that printing has finished (Yes), the control unit 100 ends this process.

[0133] 10, in the jam error determination process, the control unit 100 first determines whether the first sheet sensor SE3 is ON (S31). If it is determined in step S31 that the first sheet sensor SE3 is not ON (No), the control unit 100 ends this process.

[0134] If it is determined in step S31 that the first sheet sensor SE3 is ON (Yes), the control unit 100 determines whether the ON time of the first sheet sensor SE3 has exceeded the sheet length time (S32). If it is determined in step S32 that the ON time of the first sheet sensor SE3 has exceeded the sheet length time (Yes), the control unit 100 determines that a first jam error has occurred (S33) and ends this process.

[0135] When it is determined in step S32 that the ON time of the first sheet sensor SE3 does not exceed the sheet length time (No), the control section 100 determines whether the first sheet sensor SE3 has turned OFF (S34).

[0136] If it is determined in step S34 that the first sheet sensor SE3 is not turned OFF (No), the control unit 100 returns to the process of step S32. If it is determined in step S34 that the first sheet sensor SE3 is turned OFF (Yes), the control unit 100 determines whether the second sheet sensor SE4 is turned ON within a predetermined time after the first sheet sensor SE3 is turned ON (S35).

[0137] If it is determined in step S35 that the second sheet sensor SE4 has not turned ON within the predetermined time from the ON of the first sheet sensor SE3 (No), the control unit 100 determines that a second jam error has occurred (S36). If it is determined in step S35 that it is Yes, or after step S36, the control unit 100 determines whether the temperature detected by the temperature sensor SE5 has decreased (S37). More specifically, in step S37, the control unit 100 determines whether the amount of decrease in the detected temperature per unit time is greater than a first predetermined amount.

[0138] If it is determined in step S37 that the detected temperature has decreased (Yes), the control unit 100 determines that a wrap jam error has occurred (S38), and sets a wrap flag F indicating that the sheet P has wrapped around the first fixing member 81 to 1 (S39). After step S39, or if it is determined No in step S37, the control unit 100 determines whether the ON time of the second sheet sensor SE4 has exceeded the sheet length time (S40).

[0139] If it is determined in step S40 that the ON time of the second sheet sensor SE4 has exceeded the sheet length time (Yes), the control unit 100 determines that a third jam error has occurred (S41) and ends this process. If it is determined in step S40 that the result is No, the control unit 100 determines whether the second sheet sensor SE4 has turned OFF (S42).

[0140] If it is determined in step S42 that the second sheet sensor SE4 is not turned OFF (No), the control unit 100 returns to the process of step S40. If it is determined in step S42 that the second sheet sensor SE4 is turned OFF (Yes), the control unit 100 ends this process.

[0141] 11, in the error reset process, the control unit 100 first determines whether the cover 11 is opened based on a signal from the cover open / close sensor SE2 (S61). If it is determined in step S61 that the cover 11 is not opened (No), the control unit 100 ends this process without resetting the jam error.

[0142] If it is determined in step S61 that cover 11 has been opened (Yes), control unit 100 determines whether or not drawer 60 has been pulled out from the image forming position based on the connection state of first contact CN1 and second contact CN2 (S62). More specifically, in step S62, control unit 100 determines whether or not there is a response from internal temperature sensor SE1 provided in drawer 60, and if there is no response, determines that drawer 60 has been pulled out from the image forming position. If it is determined in step S62 that drawer 60 has not been pulled out (No), control unit 100 ends this process without resetting the jam error.

[0143] If it is determined in step S62 that the drawer 60 has been pulled out (Yes), the controller 100 determines whether the wrapping flag F is 1 (S63). If it is determined in step S63 that F=1 (Yes), the controller 100 determines whether the wrapping of the sheet P around the first fixing member 81 has been resolved, that is, whether the sheet P wrapped around the first fixing member 81 has been removed, based on a change in the temperature detected by the temperature sensor SE5 or a signal from the Hall element M1 (S64).

[0144] More specifically, in step S64, the control unit 100 determines that the winding has been eliminated when it determines that the amount of decrease in the detected temperature per unit time is greater than a second predetermined amount, or when it determines that the motor M has been rotated by the rotation phase angle θ2 or more based on the signal from the Hall element M1. If the control unit 100 determines that the winding has been eliminated in step S64 (Yes), it sets the winding flag F to 0 (S65).

[0145] After step S65, or if the determination in step S64 is No, the control unit 100 determines whether or not the drawer 60 is placed at the image forming position based on the connection state of the first contact CN1 and the second contact CN2 (S66). More specifically, in step S66, the control unit 100 determines whether or not there is a response from the internal temperature sensor SE1 provided in the drawer 60, and if there is a response, determines that the drawer 60 is placed at the image forming position.

[0146] If it is determined in step S66 that drawer 60 is not located at the image forming position (No), control unit 100 returns to the process of step S63. If it is determined in step S66 that drawer 60 is located at the image forming position (Yes), control unit 100 determines whether cover 11 is closed or not based on a signal from cover open / close sensor SE2 (S67).

[0147] If it is determined in step S67 that the cover 11 is not closed (No), the control unit 100 returns to the process of step S63. If it is determined in step S67 that the cover 11 is closed (Yes), the control unit 100 determines whether the winding flag F is 0 (S68).

[0148] If it is determined in step S68 that F=0 (Yes), the control unit 100 determines whether the sheet P that is holding the rocking member of the first sheet sensor SE3 or the second sheet sensor SE4 in the tilted state has been removed by determining whether each sheet sensor SE3, SE4 is OFF (S69). Note that the process of step S69 is particularly effective when the first jam error or the third jam error occurs, but it is also effective when the second jam error or the wrapping error occurs, because a sheet P other than the sheet P causing each error may be stopped with the rocking member in the tilted state.

[0149] If it is determined in step S69 that the sheet sensors SE3 and SE4 are OFF (Yes), the control unit 100 clears the jam error (S70) and ends this process. If it is determined in steps S68 and S69 that the control unit 100 is No, the control unit 100 does not clear the jam error and ends this process.

[0150] Next, an example of the operation of the control unit 100 will be described in detail. 7A, when the sheet P wraps around the first fixing member 81 during printing, the leading edge of the sheet P wrapped around the first fixing member 81 approaches the temperature sensor SE5 as the first fixing member 81 rotates. When the leading edge of the sheet P enters between the temperature sensor SE5 and the first fixing member 81, the detected temperature drops suddenly as shown at time t2 in FIG 8. When the detected temperature drops suddenly in this manner, the control unit 100 determines that a wrap jam error has occurred in the jam error determination process shown in FIG 10 (S37: Yes -> S38).

[0151] 9, the control unit 100 determines Yes, stops the rotation of the first fixing member 81, stops the heater 110, and disconnects the clutch CL to stop printing (S5). By stopping the rotation of the first fixing member 81 in this way, the bending of the sheet P is prevented from becoming severe, and the leading edge of the sheet P can be kept in the vicinity of the temperature sensor SE5.

[0152] Moreover, by stopping the heater 110, it is possible to suppress unnecessary heating of the sheet P. Furthermore, by disengaging the clutch CL, the developer image forming unit, which is a load when rotating the motor M, is separated from the motor M.

[0153] After step S5, if the nip state is, for example, a strong nip state, the control unit 100 switches the nip state from the strong nip state to a weak nip state (S6: Yes→S7). This reduces the nip pressure between the first fixing member 81 and the second fixing member 82, making it easier for the user to pull out the sheet P from between the first fixing member 81 and the second fixing member 82.

[0154] When a wrap jam error occurs and printing is stopped, the user opens the cover 11 and pulls out the drawer 60 to remove the sheet P jammed inside the main body housing 10. This causes the control unit 100 to determine Yes in each of steps S61 and S62 in the error release process in FIG.

[0155] When a user inserts his / her hand through opening 10A of main body housing 10 and pulls out sheet P jammed in fixing device 80 in the opposite direction to the conveying direction as shown in Fig. 7(a), the leading edge of sheet P leaves temperature sensor SE5 and first fixing member 81, causing the temperature detected by temperature sensor SE5 to drop suddenly as shown at time t3 in Fig. 8. When the detected temperature drops suddenly in this manner, control unit 100 determines that the wrapping has been resolved in the error release process in Fig. 11 (S64: Yes) and sets wrapping flag F to 0 (S65).

[0156] Furthermore, even if the condition for the detected temperature is not satisfied in step S64, the control unit 100 determines that the wrapping has been resolved if the condition for the signal from the Hall element M1 is satisfied. In more detail, as the user pulls out the sheet P, the first fixing member 81 in contact with the sheet P rotates, and the motor M rotates in conjunction with the rotation of the first fixing member 81. When the leading edge of the sheet P leaves the nip portion NP, the first fixing member 81 rotates by a rotation phase angle θ1 (=θ) or more, and the motor M rotates by a rotation phase angle θ2 corresponding to θ1 or more.

[0157] While motor M is rotating, hall element M1 continues to output a signal to control unit 100, and therefore when control unit 100 receives a signal from hall element M1 for a specified time or longer, it determines that motor M has rotated by rotation phase angle θ2 or more and that the winding has been resolved. After the user pulls out sheet P that is jammed in fixing device 80, the user returns drawer 60 to the image formation position and closes cover 11 to resume the suspended printing.

[0158] As a result, the control unit 100 determines Yes in each of steps S66 and S67 in the error release process of Fig. 11. After that, after determining Yes in step S68, the control unit 100 determines whether or not each of the sheet sensors SE3 and SE4 is OFF (S69).

[0159] In step S69, if the sheet P is not jammed at the positions of the sheet sensors SE3 and SE4, the control unit 100 determines Yes and releases the winding error (S70). As a result, step S9 in FIG. 9 is determined as Yes, and printing is resumed (S10).

[0160] As described above, the following effects can be obtained in this embodiment. If a jam error occurs during printing in the strong nip state, the strong nip state is switched to a weak nip state, so that the sheet P between the first fixing member 81 and the second fixing member 82 can be easily pulled out.

[0161] Since the rotation of the first fixing member 81 is stopped in advance before switching from the strong nip state to the weak nip state, it is possible to prevent the sheet P from becoming difficult to pull out due to severe bending of the sheet P. Also, since the heater 110 is stopped in advance before switching from the strong nip state to the weak nip state, it is possible to prevent the sheet P from being heated unnecessarily after the occurrence of a jam error.

[0162] If a specified sheet P is not detected by the second sheet sensor SE4 within a specified time after the specified sheet P is detected by the first sheet sensor SE3, it is determined that a jam error has occurred.Therefore, a second jam error caused by the sheet P stopping between the first sheet sensor SE3 and the second sheet sensor SE4 can be accurately determined by the two sheet sensors SE3 and SE4.

[0163] Since the temperature sensor SE5 used to control the heater 110 is used to determine whether the sheet P has wrapped around the first fixing member 81, costs can be reduced compared to determining whether the sheet P has wrapped around the first fixing member 81 using a sensor other than a temperature sensor. Also, since a decrease in the detected temperature can be determined when the sheet P reaches the position of the temperature sensor SE5, the sheet P can be prevented from wrapping around the first fixing member 81 multiple times.

[0164] Since the wrap jam error is not released unless the sheet P wrapped around the first fixing member 81 is removed, it is possible to prevent the printing operation from being started with the sheet P still wrapped around the first fixing member 81. In addition, it is possible to easily determine that the wrap has been removed based on a change in the detected temperature.

[0165] Based on the signal from the Hall element M1, it is determined that the motor M is rotating without being supplied with a driving current, and then it is determined that the sheet P wrapped around the first fixing member 81 has been removed. Therefore, it is possible to accurately determine that the wrapping has been eliminated by the rotation of the motor M.

[0166] In the weak nip state, the nip portion NP is formed by only the deformation of the first nip forming member N1, so that the force required to pull out the sheet P is small, and the sheet P can be easily pulled out.

[0167] Since the first nip forming member N1 and the second nip forming member N2 are spaced apart in the transport direction, in a weak nip state, the nip width in the transport direction can be made small, and the resistance when the sheet P is pulled out can be reduced.

[0168] In the weak nip state, the nip portion NP is formed by the softer first nip forming member N1, so that the resistance when the sheet P is pulled out can be reduced.

[0169] When the user pulls out the sheet P sandwiched between the first fixing member 81 and the second fixing member 82, the first fixing member 81 and the motor M are rotated by an external force, and the Hall element M1 detects the rotation of the motor M. Also, if the sheet P sandwiched between the first fixing member 81 and the second fixing member 82 is not pulled out, the first fixing member 81 and the motor M do not rotate, and the Hall element M1 does not detect the rotation of the motor M. Therefore, if the sheet P remains wrapped around the first fixing member 81, the Hall element M1 does not detect the rotation of the motor M, and therefore the control unit 100 does not release the wrap jam error, and therefore it is possible to prevent printing from starting with the sheet P wrapped around the first fixing member 81.

[0170] The Hall element M1 used for driving control of the motor M is used to detect the rotation of the motor M when a winding jam error occurs, thereby reducing costs compared to, for example, using a separate sensor that is not used for driving control of the motor.

[0171] For example, compared to a method in which a gap is provided between the first and second fixing members when a wrap-around jam error occurs, a weak nip state, i.e., the first fixing member 81 and the second fixing member 82 are in contact with each other, is created when a wrap-around jam error occurs, so that the first fixing member 81 can be rotated smoothly as the sheet P is pulled out.

[0172] When the sheet P is wrapped around the first fixing member 81, the driving force from the motor M to the developer image forming unit is cut off, so that the developer image forming unit, which is a load when rotating the motor M, is disconnected from the motor M, thereby reducing the force required to pull out the sheet P from between the first fixing member 81 and the second fixing member 82.

[0173] By configuring the motor M to cancel the winding error when it is determined that it has been rotated by more than the rotational phase angle θ2, the winding jam error is canceled after the leading edge of the sheet P wrapped around the first fixing member 81 moves from the temperature sensor SE5 to the nip portion NP and is pulled out of the nip portion NP, thereby further preventing printing from starting with the sheet P wrapped around the first fixing member 81.

[0174] By determining that the motor M has been rotated with the cover 11 open, it is possible to more reliably determine whether or not the sheet has been pulled out from between the first fixing member 81 and the second fixing member 82.

[0175] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below. In the following description, the same reference numerals are used to designate components having substantially the same structures as those in the above-described embodiment, and the description thereof will be omitted.

[0176] In the above embodiment, the Hall element M1 is exemplified as the rotation detection member, but the present invention is not limited to this, and the rotation detection member may be, for example, a rotary encoder that detects the rotation of a motor.

[0177] In the above embodiment, the winding is determined based on the temperature detected by the temperature sensor SE5, but the present invention is not limited to this. For example, the winding may be determined by a sensor other than the temperature sensor.

[0178] In the above embodiment, it is determined whether the winding has been released based on the temperature detected by the temperature sensor SE5 and the signal from the Hall element M1. However, the present invention is not limited to this. For example, it may be determined whether the winding has been released based only on the temperature detected by the temperature sensor, or it may be determined whether the winding has been released based only on the signal from the Hall element.

[0179] In the above embodiment, the nip state is configured to be switched between three stages: a strong nip state, a medium nip state, and a weak nip state; however, the present invention is not limited to this, and the nip state may be configured to be switched between two stages: a strong nip state and a weak nip state, or may be configured to be switched between four or more stages including a strong nip state and a weak nip state.

[0180] The determination of the occurrence of a jam error is not limited to the above embodiment. For example, the occurrence of a jam error may be determined based on the time from when a sheet is picked up until when the first sheet sensor turns ON.

[0181] In the above embodiment, the clutch CL is configured to block the transmission of driving force from the motor M to the developer image forming unit. However, the present invention is not limited to this. For example, the transmission of driving force from the motor to the developer image forming unit may be blocked by a pendulum gear or a planetary gear mechanism.

[0182] In the above embodiment, the present invention is applied to a color printer 1, but the present invention is not limited to this and may be applied to other image forming devices, such as monochrome printers, copiers, and multifunction machines.

[0183] In the embodiment described above, the control unit 100 is configured to execute weak nip processing when the sheet P is an envelope, but it may be configured to execute strong nip processing, medium nip processing, or weak nip processing as desired regardless of the type of sheet P. Also, it may be configured to selectively execute strong nip processing, medium nip processing, or weak nip processing under specific conditions regardless of the type of sheet.

[0184] In the embodiment described above, the second fixing member 82 is configured to move relative to the first fixing member 81, but the present invention is not limited to this, and the first fixing member may be moved relative to the second fixing member.

[0185] The heater may be any type of heater, for example, a carbon heater, etc. Also, the number of heaters may be multiple.

[0186] In the above embodiment, the nip forming member is configured by a pad and a fixed plate, but the present invention is not limited to this, and the nip forming member may be configured by, for example, only a pad.

[0187] In the above embodiment, the second spring 330 and the cam follower 350 are provided, but the present invention is not limited to this, and the second spring and the cam follower may be omitted. In other words, a configuration in which the cam directly presses the arm body may be used.

[0188] In the above embodiment, the first spring is a tension coil spring and the second spring is a compression coil spring, but the present invention is not limited to this. For example, the first spring may be a compression coil spring and the second spring may be a tension coil spring.

[0189] In the embodiment described above, the biasing force of the first spring 320 and the second spring 330 is applied to the second fixing member 82 via the arm 310, but the present invention is not limited to this. For example, the biasing force of the first spring and the second spring may be applied directly to the second fixing member.

[0190] The first spring and the second spring are not limited to the coil spring described above, and may be, for example, a torsion spring, a leaf spring, or the like.

[0191] The method of heating the first fixing member with a heater may be, for example, an external heating method in which a heater is disposed outside the first fixing member and heats the outer peripheral surface of the first fixing member, or an IH (Induction Heating) method.

[0192] In the above embodiment, the second fixing member 82 is moved by a rotatable cam 340, but the present invention is not limited to this. For example, the second fixing member may be moved by a linearly movable cam, or the second fixing member may be moved by advancing and retreating a rod of an air cylinder.

[0193] In the above embodiment, the first pad P1 and the second pad P2 are made of rubber, but the present invention is not limited to this, and the pads may be made of a hard material such as resin or metal that does not elastically deform even when pressure is applied.

[0194] In the above embodiment, the developer image forming unit is configured to include a photosensitive drum, a charger, etc., but the present invention is not limited to this, and the developer image forming unit may include, for example, a belt-shaped photosensitive body, a charging roller, etc.

[0195] In the above embodiment, the second fixing member 82 including the belt 130 and the pads P1 and P2 is exemplified as the second fixing member, but the present invention is not limited thereto. For example, the second fixing member may be a pressure roller having a cylindrical rubber layer.

[0196] In the embodiment, the heater 110 heats the first fixing member 81, but the present invention is not limited to this, and the heater may heat the second fixing member. Also, a heater may be provided on the second fixing member to indirectly heat the first fixing member that contacts the outer peripheral surface of the second fixing member. Also, the first fixing member and the second fixing member may each have a built-in heater.

[0197] The elements described in the above-mentioned embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0198] 1. Color printer 10 Main unit housing 40 Scanner unit 70 Transcription Unit 80 Fixing device 81 First fixing member 82 Second fixing member 100 Control section 120 Lola Medium motor M1 Hall element P-sheet U-Unit

Claims

1. A main body housing; a developer image forming section for forming a developer image on a sheet; a fixing device for fixing a developer image onto a sheet, the fixing device including a first fixing member having a roller, and a second fixing member for sandwiching the sheet between the first fixing member and a second fixing member to form a nip portion; a motor that rotates the first fixing member; a rotation detection member for detecting rotation of the motor, the rotation detection member being used for driving control of the motor; a temperature sensor for detecting a temperature of the first fixing member, the temperature sensor being located within a width of a minimum sheet that can be fixed by the fixing device; A control unit, The control unit is determining that a sheet has been wrapped around the first fixing member based on a decrease in the detected temperature detected by the temperature sensor during printing; When it is determined that the sheet has wrapped around the first fixing member, it is determined that a wrapping jam error has occurred, and the supply of a driving current to the motor is stopped; based on a signal from the rotation detection member, it is determined whether or not the motor, to which no driving current is supplied, has been rotated by an amount equal to or greater than a rotation phase angle of the motor corresponding to a rotation phase angle of the first fixing member at a time when a portion of the first fixing member facing the temperature sensor is rotated to the nip portion; If it is determined that the motor is not rotating, the wrapping jam error is not cleared, When it is determined that the motor has been rotated, the image forming apparatus releases the wrapping jam error.

2. the motor includes a Hall element as the rotation detection member, 2. The image forming apparatus according to claim 1, wherein the control unit determines whether the motor is rotated based on a signal from the Hall element.

3. a switching mechanism that switches a nip state between the first fixing member and the second fixing member between a strong nip state and a weak nip state in which a nip pressure is lower than that of the strong nip state, The control unit is 3. The image forming apparatus according to claim 1, wherein when it is determined that the wraparound jam error has occurred, the nip state is changed to the weak nip state.

4. a transmission mechanism for transmitting a driving force from the motor to the developer image forming unit, the transmission mechanism being capable of interrupting transmission of the driving force from the motor to the developer image forming unit; The control unit is 4. The image forming apparatus according to claim 1, wherein, when it is determined that the winding jam error has occurred, the driving force from the motor to the developer image forming unit is cut off.

Images