JP2018072802A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device which prevents excessive temperature rise in the non-rotation state of a fixation member without damaging a component of the fixation device.SOLUTION: A fixation device includes: a fixation member 21 which is rotatable; a heat source 23 which heats the fixation member; a facing member 22 which is brought into contact with an outer peripheral surface of the fixation member to form a fixing nip part N; and one or a plurality of rotors 11, 12, 32, 36 which convey a recording medium to the fixing nip part. The fixation device fixes a toner image on the recording medium by rotating the fixation member in the normal rotation direction. The fixation device stops the heat source at the occurrence of abnormality during the operation of the fixation device and then, rotates the fixation member in the prescribed direction. When the fixing nip part and one or the plurality of rotors simultaneously sandwich one recording medium at the occurrence of abnormality during the operation of the fixation device, the fixation device decides the prescribed direction of the fixation member to the normal rotation direction or to the reverse direction reverse to the normal rotation direction in accordance with one or the plurality of rotors sandwiching the recording medium.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a fixing device and an image forming apparatus.

  2. Description of the Related Art Image forming apparatuses such as copiers, printers, facsimiles, and multifunction peripherals thereof are provided with a fixing device that fixes a toner image carried on a recording medium such as paper.

  In general, a fixing device includes a fixing member that is heated by radiant heat from a heating source such as a heater, and an opposing member that contacts the fixing member to form a nip portion. When the image forming operation is started in the image forming apparatus and the toner image is transferred to the sheet, the sheet passes through the nip portion between the fixing member heated to a predetermined temperature and the opposing member. Then, the toner carried on the paper is heated and melted to fix the image.

  Among image forming apparatuses, the fixing apparatus has a large amount of power consumption and a large room for energy saving, and various proposals have been made. For example, an endless fixing member (for example, a fixing belt) that is thin in a film shape with a low heat capacity is directly heated without using a metal heat conductor that also serves as a support, and is mounted on a high-production image forming apparatus. However, a fixing device capable of obtaining good fixing properties is known (see, for example, Patent Document 1). In this fixing device, the pressure roller arranged on the outer peripheral side of the endless fixing belt and the nip forming member fixedly arranged inside the fixing belt (in the loop) are pressed and fixed through the fixing belt. A nip is formed.

  However, in the direct heating configuration, since the fixing member is very thin and the response to the radiant heat from the heating source is very good, when the fixing member is in a non-rotating state and irradiated with the radiant heat from the heating source, the fixing member If the temperature rises too much, it may exceed the heat resistance temperature of the silicone rubber or fluororubber used for the fixing member or the pressure member, leading to damage.

  On the other hand, at the end of the normal image forming operation, after the energization of the heating source is stopped, the fixing member is further rotated in the normal direction for a predetermined time and then the fixing member is stopped from rotating (high temperature avoiding normal rotation operation). It is known that the temperature in the circumferential direction of the fixing member is made uniform to prevent the fixing member and the pressure member from being damaged due to excessive temperature rise (see, for example, Patent Document 2).

  In addition, recording medium detection means are provided on the upstream side and the downstream side of the recording medium conveyance path in the nip portion, respectively, and after the energization of the heating source is stopped, the fixing member is further reversely rotated for a predetermined time, and then the fixing member is rotated. It is known to prevent damage due to excessive temperature rise of the fixing member and the pressure member even when a jam occurs by performing control to stop the operation (high temperature avoidance reverse operation) (see, for example, Patent Document 2). .

  However, the apparatus disclosed in Patent Document 2 is an image forming apparatus that is caused by an abnormality such as a jam when there is no recording medium between the recording medium detection means on the upstream side and the downstream side of the recording medium conveyance path in the nip portion. When the emergency stop occurs, the high temperature avoidance forward rotation operation is executed. As a result, the device described in Patent Document 2 damages components such as a fixing member constituting the fixing device even if a predetermined high-temperature avoidance forward rotation operation is performed depending on the state of the recording medium and the fixing device during an emergency stop. There is a fear.

  An object of the present invention is to provide a fixing device that prevents an excessive temperature rise in a non-rotating state of a fixing member without damaging components of the fixing device.

In order to solve the above-described problem, a fixing device according to a first aspect of the present invention includes:
A rotatable fixing member;
A heating source for heating the fixing member;
An opposing member that contacts the outer peripheral surface of the fixing member to form a fixing nip portion;
One or a plurality of rotating bodies that convey the recording medium to the fixing nip portion,
In the fixing device for fixing the toner image to the recording medium by rotating the fixing member in the normal rotation direction,
A fixing device that stops the heating source when an abnormality occurs during operation of the fixing device, and then rotates the fixing member in a predetermined direction;
When an abnormality occurs during the operation of the fixing device, when the fixing nip portion and the one or more rotating bodies sandwich one recording medium at the same time, the one or more sandwiching the recording medium The predetermined direction of the fixing member is determined as the forward rotation direction or the reverse rotation direction opposite to the forward rotation direction according to the rotating body.

  According to the present invention, it is possible to provide a fixing device that prevents an excessive temperature rise in the non-rotating state of the fixing member without damaging the components of the fixing device.

1 is a configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a configuration diagram illustrating an embodiment of a fixing device according to the present invention. 1 is a configuration diagram illustrating an embodiment of a fixing device according to the present invention. FIG. 4 is a perspective view showing a fixing device according to FIG. 3. FIG. 4 is an explanatory diagram illustrating a support structure for a shielding member of the fixing device according to FIG. 3. It is explanatory drawing explaining the drive means of the shielding member of the fixing device which concerns on FIG. It is a side view which shows schematic structure of the switching means, (a) shows a depressurization state, (b) shows a pressurization state. 6 is a timing chart showing an operation sequence of each part of the fixing device after completion of normal image formation. FIG. 6 is an explanatory diagram illustrating a deformed fixing belt. 6 is a timing chart showing an operation sequence of each part of the fixing device when the fixing belt rotates forward when an abnormality occurs. 6 is a flowchart for describing control for selecting whether the fixing belt is rotating forward or reverse when an abnormality occurs. 6 is a timing chart showing an operation sequence of each part of the fixing device when the fixing belt reversely rotates when an abnormality occurs. It is a block diagram which shows the structure which judges normal rotation or reverse rotation which concerns on 2nd Embodiment. 12 is a flowchart for explaining control for selecting whether the fixing belt is rotating forward or reverse in the second embodiment. It is explanatory drawing explaining the structure which judges normal rotation or reverse rotation which concerns on 3rd Embodiment. 10 is a flowchart illustrating control for selecting whether the fixing belt is rotating forward or rotating backward in the third embodiment. FIG. 6 is a schematic cross-sectional configuration diagram showing another embodiment of a fixing device. It is a perspective view which shows the basic composition of a nip formation unit. It is a perspective view which shows the structure of a nip formation unit and a halogen heater. It is a schematic diagram which shows arrangement | positioning of the heat-emitting part of a halogen heater and an edge part heater.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

  First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

  An image forming apparatus 1 shown in FIG. 1 is a color laser printer. In the center of the main body of the color laser printer, four image forming units 4Y, 4M, 4C, and 4K are provided. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photosensitive member 5 as a latent image carrier and a charging device 6 that charges the surface of the photosensitive member 5. In addition, each of the image forming units 4Y, 4M, 4C, and 4K includes a developing device 7 that supplies toner to the surface of the photoconductor 5, a cleaning device 8 that cleans the surface of the photoconductor 5, and the like. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. In addition, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Each primary transfer roller 31 is connected to a known power source, and a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a known power source is connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A known waste toner transfer hose extending from the belt cleaning device 35 is connected to the entrance of a known waste toner container.

  A bottle container 2 is provided in the upper part of the printer body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. . A known replenishment path is provided between each of the toner bottles 2Y, 2M, 2C, and 2K and each of the developing devices 7, and each development from each toner bottle 2Y, 2M, 2C, and 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 containing the recording medium P, a paper feed roller 11 for carrying the recording medium P out of the paper feed tray 10, and the like are provided. In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. A manual paper feed mechanism may be provided.

  In the printer main body, a conveyance path R is provided for discharging the recording medium P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of timing rollers 12 serving as timing rollers for transporting the recording medium P to the secondary transfer nip at the transport timing is arranged upstream of the position of the secondary transfer roller 36 in the recording medium transport direction. It is installed.

  Further, a fixing device 20 for fixing the unfixed toner image transferred to the recording medium P is disposed downstream of the position of the secondary transfer roller 36 in the recording medium conveyance direction. Further, a pair of paper discharge rollers 13 for discharging the recording medium to the outside of the apparatus is provided downstream of the fixing device 20 in the recording medium conveyance direction on the conveyance path R. A discharge tray 14 for stocking the recording medium discharged outside the apparatus is provided on the upper surface of the printer main body.

  The image forming apparatus is provided with a control device 90 that controls the entire apparatus, and controls driving of each device based on a control program stored in the control device.

  Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG. When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise in the drawing by a known driving device, and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity.

  The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Further, by applying a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current to each primary transfer roller 31, the primary transfer nip between each primary transfer roller 31 and each photoreceptor 5 is applied. A transfer electric field is formed.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30.

  Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by a known neutralization device, and the surface potential is initialized.

  In the lower part of the printer, the paper feed roller 11 starts to rotate, and the recording medium P is sent out from the paper feed tray 10 to the transport path R. The recording medium P sent to the conveyance path R is temporarily stopped by the timing roller 12.

  Thereafter, rotation of the timing roller 12 is started at a predetermined timing, and the recording medium P is conveyed to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. .

  Then, the toner image on the intermediate transfer belt 30 is collectively transferred onto the recording medium P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the recording medium P is removed by the belt cleaning device 35, and the removed toner is conveyed to a known waste toner container and collected. .

  Thereafter, the recording medium P is conveyed to the fixing device 20, and the toner image on the recording medium P is fixed to the recording medium P by the fixing device 20. Then, the recording medium P is discharged out of the apparatus by the discharge roller 13 and stocked on the discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a recording medium. In addition to this full-color image, for example, a single-color image is formed using any one of four image forming units 4Y, 4M, 4C, and 4K, or two colors are formed using two or three image forming units. Alternatively, it is possible to form an image of three colors.

  Hereinafter, the configuration of the fixing device 20 will be described with reference to FIGS. FIG. 2 is a configuration diagram showing an embodiment of a fixing device according to the present invention. FIG. 3 is a configuration diagram showing an embodiment of a fixing device according to the present invention.

  As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a pressure roller 22 as an opposing member that contacts the outer peripheral surface of the fixing belt 21, and a heating source that heats the fixing belt 21. A halogen heater 23, a nip forming member 24 that contacts the pressure roller 22 from the inner peripheral side of the fixing belt 21 to form a fixing nip portion N, a stay 25 as a support member that supports the nip forming member 24, a halogen A reflection member 26 that reflects heat from the heater 23 to the fixing belt 21, a temperature sensor 28 as first temperature detection means for detecting the temperature of the fixing belt 21, a medium detection sensor 29 as medium detection means, and the like are provided. In addition, the fixing device 20 of the present embodiment has a configuration in which a shielding member 27 that shields heat from a heating source is provided in the non-sheet passing region of the fixing belt 21.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes an inner peripheral base material and an outer peripheral release layer. The inner peripheral base is formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI). The release layer on the outer peripheral side is formed of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE). Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven glossiness is formed on the solid portion of the image. It can happen. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided.

  In the present embodiment, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is thin and has a small diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less.

  The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a switching unit 60 described later, and is in contact with the nip forming member 24 via the fixing belt 21.

  At the location where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a fixing nip portion N having a predetermined width. Note that the fixing belt 21 and the pressure roller 22 are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

  The pressure roller 22 is configured to be rotationally driven by a driving source such as a known fixing motor provided in the printer body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the fixing nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but it may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  The halogen heater 23 is disposed on the inner peripheral side of the fixing belt 21 and on the upstream side of the fixing nip N in the recording medium conveyance direction. Specifically, in FIG. 2, assuming that a virtual straight line passing through the center Q of the fixing nip N in the recording medium conveyance direction and the rotation center O of the pressure roller 22 is L, the halogen heater 23 is more than the virtual straight line L. It is arranged on the upstream side (lower side in FIG. 2) in the transport direction.

  The halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 28. Is called. By such output control of the halogen heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  Instead of the temperature sensor that detects the temperature of the fixing belt 21, a temperature sensor that detects the temperature of the pressure roller 22 is provided, and the temperature of the fixing belt 21 is predicted based on the temperature detected by the temperature sensor. Also good.

  In the present embodiment, two halogen heaters 23 are provided, but the number of halogen heaters 23 may be one or three or more according to the size of the recording medium used in the printer. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater, or the like can be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 includes a base pad 241 and a low friction sliding sheet 240 provided on a surface of the base pad 241 facing the fixing belt 21. The base pad 241 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22.

  The shape of the fixing nip portion N is determined by the base pad 241 receiving pressure from the pressure roller 22. In the present embodiment, the fixing nip portion N has a flat shape, but may have a concave shape or other shapes.

  The sliding sheet 240 is provided to reduce sliding friction when the fixing belt 21 rotates. Note that when the base pad 241 itself is formed of a low-friction member, the sliding sheet 240 may not be provided.

  The base pad 241 is made of a heat resistant material having a heat resistant temperature of 200 ° C. or higher. With such a configuration, the nip forming member 24 is prevented from being deformed by heat in the toner fixing temperature region, and a stable state of the fixing nip portion N is secured to stabilize the output image quality.

  In addition, the base pad 241 is required to have appropriate rigidity to ensure strength. The material of the base pad 241 that satisfies the above conditions includes polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone. A resin such as (PEEK) can be used. In addition, the base pad 241 can be formed of metal or ceramic.

  The base pad 241 is fixedly supported by the stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending.

  The reflection member 26 is fixedly supported by the stay 25 so as to face the halogen heater 23. By reflecting the radiant heat from the halogen heater 23 to the fixing belt 21 by the reflection member 26, heat is prevented from being transmitted to the stay 25 and the like, thereby efficiently heating the fixing belt 21 and saving energy. Yes. As the material of the reflecting member 26, aluminum, stainless steel or the like is used. In particular, in the case of using a material obtained by vapor-depositing silver having a low emissivity (high reflectivity) on an aluminum base material, the heating efficiency of the fixing belt 21 can be improved.

  The shielding member 27 is configured by forming a metal plate having a thickness of 0.1 mm to 1.0 mm into an arc-shaped cross-sectional shape along the inner peripheral surface of the fixing belt 21. The shielding member 27 is movable between the fixing belt 21 and the halogen heater 23 in the circumferential direction.

  As a result, in this embodiment, as shown in FIG. 3, a heating region α that is directly heated by the halogen heater 23 and a non-heating region β that is not directly heated by the halogen heater 23 are formed in the circumferential region of the fixing belt 21. It is formed. The heating region α is opposed to the front surface of the halogen heater 23. The non-heated region β is not directly heated by the halogen heater 23 because other members (such as the reflection member 26, the stay 25, and the nip forming member 24) fixed to the side plate are interposed between the non-heated region β and the halogen heater 23.

  When it is necessary to thermally shield the fixing belt 21 from the halogen heater 23, as shown in FIG. 2, the shielding member 27 is disposed at one or a plurality of shielding positions set on the heated region α side. On the other hand, when there is no need for heat shielding, as shown in FIG. 3, the shielding member 27 is moved to the non-heating region β side, and the entire shielding member 27 is retracted to the back side of the reflecting member 26 and the stay 25. It is possible.

  By rotating the shielding member 27 in this manner, the area of the heated region α of the fixing belt 21 is changed, and the amount of radiant heat applied to the fixing belt 21 from the halogen heater 23 is adjusted. Since the shielding member 27 requires heat resistance, it is preferable to use a metal material such as aluminum, iron, stainless steel, or ceramic as the material.

  The medium detection sensor 29 is disposed downstream of the fixing nip portion N in the conveyance direction of the recording medium as the recording medium. The medium detection sensor 29 detects the presence / absence of a recording medium, and can be composed of, for example, a photo interrupter.

  FIG. 4 is a perspective view showing the fixing device according to FIG. As shown in FIG. 4, flange members 40 as belt holding members are inserted into the inner circumferences of both ends of the fixing belt 21, and the fixing belt 21 is rotatably held by the flange members 40. . Each flange member 40, halogen heater 23 and stay 25 are fixedly supported by a pair of side plates of the fixing device 20.

  FIG. 5 is an explanatory diagram for explaining a support structure of the shielding member of the fixing device according to FIG. 3. As shown in FIG. 5, the shielding member 27 is supported via an arcuate slide member 41 attached to the flange member 40.

  Specifically, the projection 27 a provided at the end of the shielding member 27 is inserted into the hole 41 a provided in the slide member 41, so that the shielding member 27 is attached to the slide member 41. The slide member 41 is provided with a convex portion 41b. By inserting the convex portion 41b into an arc-shaped groove portion 40a provided in the flange member 40, the slide member 41 can be slid along the groove portion 40a.

  Thereby, the shielding member 27 can rotate and move integrally with the slide member 41 in the circumferential direction of the flange member 40. In the present embodiment, the flange member 40 and the slide member 41 are made of resin.

  In FIG. 5, only the support structure of one end portion is shown, but the other end portion is similarly held rotatably via the slide member 41.

  FIG. 6 is an explanatory diagram illustrating a driving unit of the shielding member of the fixing device according to FIG. As shown in FIG. 6, the present embodiment includes a motor 42 as a drive source and a power transmission mechanism 46 having a gear train made up of a plurality of gears 43, 44, 45 as a drive mechanism for the shielding member 27.

  In the gear train, the gear 43 on one end side is connected to the motor 42, and the gear 45 on the other end side is connected to a gear portion 41 c provided in the circumferential direction of the slide member 41. When the motor 42 is driven, the driving force is transmitted to the slide member 41 through the gear train. The shielding member 27 is rotationally moved in the forward direction (the rotational direction from the non-heated region β toward the heated region α) and in the reverse direction (the rotational direction from the heated region α toward the non-heated region β). . The motor 42 can be constituted by a stepping motor, for example. In this case, the position control of the shielding member 27 can be performed by changing the number of drive pulses. As the motor 42, a DC motor or the like can be used instead of the stepping motor.

  The shielding member 27 is configured to detect the temperature at the center and the end in the longitudinal direction of the fixing belt 21 using a temperature sensor 28 that detects the temperature of the fixing belt 21 and control the shielding range based on the temperature and the temperature difference. However, detailed description of the operation is omitted here.

  Next, switching means for switching the fixing nip N between a pressurized state and a depressurized state will be described. FIG. 7 is a side view showing a schematic configuration of the switching means, where (a) shows a depressurized state and (b) shows a pressurized state. The switching means (nip pressure switching means) 60 presses the pressure roller 22 against the fixing belt 21 to place the fixing nip portion N in a pressurized state and separates the pressure roller 22 from the fixing belt 21 to fix. This is a mechanism for bringing the nip portion N into a depressurized state.

  The switching unit 60 also has a function of detecting whether the fixing nip N is in a pressurized state or a depressurized state. The switching unit 60 includes a lever member 61, a cam 62, an elastic member 63, a filler 64 as a member to be detected, and a detection sensor 65 as a detection unit as main components.

  The lever member 61 is supported rotatably about a support shaft O1 provided at one end thereof, and the cam surface of the cam 62 is in contact with the other end of the lever member 61. A cored bar 22 a protrudes from the shaft end of the pressure roller 22, and the cored bar 22 a is in contact with the intermediate part of the lever member 61.

  The cam 62 is supported rotatably about a support shaft O2 provided at an eccentric position, and is driven to rotate by a driving source such as a known motor (pressure / decompression motor). The lever member 61 is pressed against the cam surface of the cam 62 by the elastic force of the elastic member 63 made of a tension spring or the like.

  The pressure roller 22 is supported so as to be slidable in the horizontal direction in the figure so as to be able to approach and separate from the fixing belt 21. As shown in FIG. 7A, in a state where the small-diameter cam surface of the cam 62 is in contact with the lever member 61, the lever member 61 is separated from the cored bar 22a of the pressure roller 22 by the elastic force of the elastic member 63. Be energized by.

  Therefore, the pressure roller 22 moves in a direction away from the fixing belt 21, and the fixing nip portion is in a depressurized state. On the other hand, as shown in FIG. 7B, when the large-diameter cam surface of the cam 62 is in contact with the lever member 61, the lever member 61 is pressed against the pressure roller 22 by the pressing force received from the cam 62. 22a is pushed into the side closer to the fixing belt 21. As a result, the fixing nip N is in a pressurized state.

  Next, the operation sequence of each part of the fixing device after completion of normal image formation will be described based on the timing chart of FIG. FIG. 8 is a timing chart showing the operation sequence of each part of the fixing device after completion of normal image formation.

  The control device 90 of the image forming apparatus transmits a stop signal to the fixing device 20 at the timing when the trailing edge of the final recording medium escapes from the fixing nip N. After receiving the stop signal, the halogen heater 23 is turned off first, and then the heater relay is turned off. When the shielding member 27 is provided, the shielding member 27 then returns to the initial position (HP).

  The fixing belt 21 continues to rotate so far, but after a predetermined time t1 has elapsed since the shielding member 27 returned to the initial position, the fixing motor is stopped. After the fixing motor is stopped, the fixing nip N is depressurized by the switching means 60 shown in FIG.

  The reason why the fixing belt 21 continues to rotate for the time t1 after the shielding member 27 returns to the initial position is to prevent the fixing belt 21 from being locally heated by residual heat and causing a temperature deviation in the fixing belt 21. Because. This time t1 is set in anticipation of the time during which the fixing belt 21 is soaked. For example, the end of t1 can be determined from the temperature information detected by the temperature sensor 28, or the time when a predetermined time has passed can be set as the end of t1.

  When the jam processing is performed while the fixing nip N is in a pressurized state, the recording medium sandwiched between the fixing nip N is pulled out, so that the fixing belt 21 and the pressure roller 22 are damaged or the recording medium is removed. There is a risk that it will be broken and it will be difficult for the user to handle the jam. On the other hand, if the fixing nip portion is depressurized before the rotation of the fixing belt 21 stops, the fixing belt 21 slips, the fixing belt 21 partially rises in temperature, and the fixing belt 21 may be deformed. Therefore, after the fixing belt 21 is stopped, the fixing nip portion N is switched to the depressurized state.

  The above is the operation sequence when the image forming operation is completed normally. However, during image formation (between the input of the image signal and the discharge of the fixed recording medium to the discharge tray), the conveyance is performed. The image forming apparatus may stop urgently due to the occurrence of a jam on the path R (see FIG. 1) or an abnormality of each part in the image forming apparatus. If the rotation of the fixing belt 21 is stopped immediately at the time of emergency stop, the fixing belt 21 is heated by residual heat, and temperature fluctuations may occur, causing the fixing belt 21 to be deformed (see region Q in FIG. 9).

  The operation of each part of the fixing device at the time of occurrence of an abnormality can be considered in two ways: when the fixing belt 21 rotates in the forward direction and when it rotates in the reverse direction.

  Since the fixing device 20 is normally rotated during normal image formation and is not configured to be reversely rotated, damage to the fixing device 20 is less caused by normal rotation even during an emergency stop.

  Even when there is remaining paper (remaining recording medium) in the transport path when a jam occurs, if the leading end of the recording medium passes through the fixing nip N and is separated from the fixing belt 21, the fixing belt 21. Is further rotated forward (rotation in a direction in which the recording medium is sent downstream in the transport direction), the recording medium does not wrap around the fixing belt 21.

  Even when the remaining paper on the conveyance path at the time of jam occurrence has not passed through the fixing nip N, the recording medium is removed from the fixing belt 21 by the separating member provided on the fixing nip N exit side of the fixing device 20. Therefore, even if the fixing belt 21 is further rotated forward, the recording medium is not wound around the fixing belt 21. Therefore, it is desirable to select more stable forward rotation as the operation of the fixing belt 21 after the heater is turned off in the normal operation procedure at the time of emergency stop.

  Next, the order of the operation of each part of the fixing device (normal rotation operation at the time of abnormality) when the fixing belt 21 rotates forward when an abnormality occurs will be described based on the timing chart of FIG. FIG. 10 is a timing chart showing the operation sequence of each part of the fixing device when the fixing belt rotates normally when an abnormality occurs.

  When an abnormality detection signal is transmitted from the image forming apparatus, the halogen heater 23 is turned off, and then the heater relay is turned off. After the heater relay is turned off, the image forming linear speed is reduced and switched to a low linear speed, and the fixing belt 21 is rotated forward for a predetermined time Ta in a low speed state. After a lapse of time Ta, the fixing belt 21 is stopped, and thereafter, when the switching means 60 is provided, the fixing nip portion N is switched to the depressurized state. After these operations are completed, a notification means (display on the operation panel, lighting of an abnormality display lamp, generation of an alarm sound, etc.) provided in the image forming apparatus notifies the occurrence of abnormality to the outside. Use of the fixing device 20 is prohibited after notification of the occurrence of an abnormality.

  During normal rotation of the fixing belt 21 after the heater is turned off, a region not covered by the shielding member 27 in the heated region α (see FIG. 2) of the fixing belt 21 is heated by the residual heat of the halogen heater 23. It becomes. At this time, as the fixing belt 21 rotates forward, the recording medium P passes through the fixing nip portion N, and the heat of the fixing belt 21 is taken away by the recording medium, so that a large temperature deviation does not occur in the fixing belt 21. . Accordingly, it is possible to prevent occurrence of temperature spots on the fixing belt 21 and further deformation of the fixing belt 21.

  During the forward rotation Ta of the fixing belt 21, the entire circumference of the fixing belt 21 passes through the fixing nip portion N to move the heat of the fixing belt 21 to the recording medium. It is necessary to set the time sufficient for moving to 22. As a guideline, it is preferable that the fixing belt 21 rotate once. The purpose of switching the rotational linear speed during normal rotation of the fixing belt 21 to a low speed is to efficiently move the heat of the fixing belt 21 to the recording medium P, thereby minimizing the temperature deviation generated in the fixing belt 21.

  Next, a case where it is desirable to select reverse rotation of the fixing belt 21 when an abnormality occurs will be described.

  In recent years, recording media (transfer paper) used in image forming apparatuses have been diversified. For example, there are an increasing number of cases where images are formed on long sheets such as those posted at mass retailers. Long paper has a variety of paper thicknesses, desired lengths, paper types, and paper surface properties, depending on the application, and is more likely to cause transport jams, including user setting errors. It has become.

  When a conveyance jam occurs in a long sheet, the sheet feeding roller 11 as the rotating body, the timing roller 12 as the rotating body, the secondary transfer roller 36 as the rotating body, and the secondary transfer as the rotating body in FIG. There are cases where the backup roller 32 and the fixing nip N sandwich the recording medium at the same time. In such a case, the recording medium is pinched with a plurality of strong forces upstream of the fixing nip portion N, so that the load for driving the fixing belt 21 is too large even if the fixing belt 21 is rotated forward. The fixing belt 21 may not be able to rotate. Therefore, there is a problem that the fixing belt 21 is heated by residual heat and temperature spots are generated. In addition to the long sheet, the load of the fixing belt 21 (fixing driving load) is increased depending on the paper type, the paper thickness, and the like at the time of the occurrence of the conveyance jam, and the fixing belt 21 may not be able to rotate. .

  Specifically, for example, the timing roller 12 has a large driving torque and a strong force for pinching the recording medium. Therefore, when the fixing nip N and the timing roller 12 sandwich the recording medium at the same time when an abnormality occurs, the recording medium conveyance force by the fixing belt 21 becomes smaller than the recording medium conveyance force by the timing roller 12. Even if the fixing belt 21 is rotated forward, it cannot be rotated as intended. Therefore, it is necessary to determine the rotation direction of the fixing belt 21 as the reverse rotation direction opposite to the normal rotation direction.

  On the other hand, when the abnormality occurs, the timing roller 12 does not pinch the recording medium, and only the conveyance nip between the fixing nip portion N and the secondary transfer roller 36 and the secondary transfer backup roller 32 pinches the recording medium. Therefore, the conveyance force of the recording medium by the fixing belt 21 is larger than the conveyance force of the recording medium by the conveyance nip. Therefore, it is possible to rotate the fixing belt 21 in the forward rotation direction as intended, and in this case, the rotation direction of the fixing belt 21 needs to be determined as the forward rotation direction.

  Therefore, in the present invention, when an abnormality occurs, the fixing nip portion and one or more rotating bodies sandwich one recording medium at the same time, depending on the one or more rotating bodies sandwiching the recording medium. Thus, the predetermined direction of the fixing member is determined as the forward rotation direction or the reverse rotation direction opposite to the normal rotation direction. More specifically, in the present invention, when the conveyance nip other than the fixing nip portion N holds the recording medium, the rotational load of the fixing belt 21 and the presence / absence (position) of the recording medium by the recording medium detection unit. And / or based on the rotation detection at the start of rotation by the speed detection means, it is determined whether the fixing belt 21 is rotated in the forward direction or the reverse direction.

[First Embodiment]
The first embodiment of the present invention includes rotational load detection means for measuring the fixing driving load (rotational load) of the fixing belt 21 in order to prevent the occurrence of temperature spots due to such a cause. The fixing driving load of the fixing belt 21 to be rotated is measured, and when the fixing driving load is equal to or greater than a predetermined value, the fixing belt 21 is reversed instead of forward rotation. As a result, even if the recording medium is pinched upstream from the fixing nip N, the recording belt is loosened by the reverse rotation of the fixing belt 21, so that the fixing belt can be operated with a small fixing driving force. 21 can be rotated, and the occurrence of temperature spots can be prevented.

  Next, the control for selecting whether the fixing belt 21 rotates forward or reverse when an abnormality occurs will be described with reference to the flowchart of FIG. FIG. 11 is a flowchart for explaining the control for the fixing belt to select normal rotation or reverse rotation when an abnormality occurs.

  When the control device 90 of the image forming apparatus detects the conveyance jam, the control device 90 turns off the halogen heater 23 (step S10), and then turns off the heater relay (step S11). After the heater relay is turned off, the control device 90 slews down the imaging linear velocity and switches to a low linear velocity (step S12). Next, the control device 90 causes the rotational load detecting means for measuring the fixing driving load of the fixing belt 21 to measure the fixing driving load during the low speed linear speed (while the fixing belt 21 is rotated forward for a predetermined time Ta) ( Step S13). Here, the rotational load detection means is a device that measures the driving torque of the fixing belt 21. The rotational load detection means is not limited to this mode, and may be a device that calculates the drive torque by measuring the current value of the fixing motor. Next, the control device 90 determines whether or not the fixing driving load is a predetermined value (for example, X [Nm]) or more (Step S14).

  If the control device 90 determines in step S14 that the fixing driving load is equal to or greater than a predetermined value (YES in step S14), the control device 90 may not be able to rotate the fixing belt 21 due to a large load on the fixing unit. Judge that there is. Then, the control device 90 brakes the fixing motor (step S20) and stops driving the fixing belt 21 (step S21). Next, after the driving of the fixing belt 21 is stopped, the control device 90 reverses the fixing belt 21 and continues the rotation for a predetermined time (Td) (step S22). Next, after stopping the fixing motor, the control device 90 switches the fixing nip portion N from the pressurized state to the depressurized state by the switching means 60 and ends the reverse rotation operation when the fixing belt 21 is abnormal (step S23). End control.

  In step S14, when the control device 90 determines that the fixing driving load is not equal to or greater than the predetermined value (NO in step S14), the control device 90 determines that the fixing belt 21 is in a forward-rotatable state. Then, as shown in FIG. 10, the control device 90 executes the forward rotation operation when the fixing belt 21 is abnormal (step S15). Next, after stopping the fixing motor, the control device 90 switches the fixing nip portion N from the pressurized state to the depressurized state by the switching means 60, and ends the forward rotation operation when the fixing belt 21 is abnormal (step S16). ), The control is terminated.

  Next, the order of the operation of each part of the fixing device (reverse operation at the time of abnormality) when the fixing belt 21 reverses when an abnormality occurs will be described based on the timing chart of FIG. FIG. 12 is a timing chart showing the operation sequence of each part of the fixing device when the fixing belt reversely rotates when an abnormality occurs.

  When an abnormality detection signal is transmitted from the image forming apparatus, the halogen heater 23 is turned off, and then the heater relay is turned off. After the heater relay is turned off, the imaging linear velocity is reduced and switched to the low linear velocity. The fixing driving load is measured during the low speed linear speed (while the fixing belt 21 is rotated forward for a predetermined time Ta). When the fixing driving load becomes a predetermined value (for example, X [Nm]) or more, the fixing motor is immediately turned on. The brake is controlled for a predetermined time Tb, and the fixing belt 21 is stopped.

  After the fixing motor is forcibly stopped for a predetermined time Tc, the fixing motor is switched in the reverse direction and driven, and after the predetermined time Td has elapsed, the fixing motor is stopped. Thereafter, when the switching means 60 is provided, the fixing nip portion N is switched to the depressurized state. After these operations are completed, a notification means provided in the image forming apparatus notifies the occurrence of abnormality to the outside. Use of the fixing device 20 is prohibited after notification of the occurrence of an abnormality.

  The reverse rotation time Td is preferably set to a time that the fixing belt 21 rotates once. Further, it is preferable that the rotation linear velocity of the fixing belt 21 driven in the reverse rotation direction when an abnormality occurs is switched to a lower speed than the rotation linear velocity of the fixing belt 21 driven in the normal rotation direction when normal. Thus, the temperature deviation generated in the fixing belt 21 is minimized by efficiently transferring the heat of the fixing belt 21 to the recording medium P.

  During the reverse rotation of the fixing motor, the area not covered by the shielding member 27 in the heated area α of the fixing belt 21 is heated by the residual heat of the halogen heater 23. Also in this case, the recording medium P passes through the fixing nip portion N in the reverse direction (upstream in the recording medium conveyance direction) as the fixing belt 21 rotates in the reverse direction. Therefore, the heat of the fixing belt 21 is taken away by the recording medium. As a result, a large temperature deviation does not occur in the fixing belt 21, and temperature spots can be prevented, and further, deformation of the fixing belt 21 can be prevented.

  By adopting such forward rotation or reverse rotation control, when an abnormality occurs in the image forming apparatus, the fixing device 20 and the image forming apparatus can be stopped in a short time, thereby reducing damage to each part of the image forming apparatus. can do. Further, it is possible to prevent temperature spots on the fixing belt 21 and deformation of the fixing belt 21.

  In the operation procedure shown in FIG. 12, the brake control and the forced stop are performed before the fixing motor reversely rotates, in order to prevent the fixing motor from being damaged when switching from the normal rotation to the reverse rotation. When using a fixing motor that can switch from forward rotation to reverse rotation without requiring brake control or forced stop, it is not necessary to perform brake control and forced stop.

[Second Embodiment]
Next, forward / reverse determination according to the second embodiment will be described. FIG. 13 is a configuration diagram illustrating a configuration for determining forward rotation or reverse rotation according to the second embodiment.

  In the second embodiment, it is determined whether the fixing belt 21 is rotated forward or backward by a recording medium detection unit provided in the conveyance path.

  The image forming apparatus includes a manual feed tray 100, a manual feed tray paper feed roller 111, and a recording medium detection unit. The recording medium detection means for detecting the presence / absence of a recording medium includes a remaining paper sensor 101 after tray feeding, a remaining paper sensor 102 after manual tray feeding, a remaining sensor 103 before timing roller, a remaining sensor 104 after timing roller, and a fixing. It is composed of one or more of the pre-apparatus remaining paper sensors 105.

  The remaining paper sensor 101 after the tray feed, the remaining paper sensor 102 after the manual feed tray, the remaining sensor 103 before the timing roller, the remaining sensor 104 after the timing roller, and the remaining sensor 105 before the fixing device are the fixing nip portion N. Is arranged upstream of the recording medium conveyance direction and detects the presence or absence of the recording medium in each rotating body.

  When a paper jam occurs in the long paper as described above, the remaining paper sensor 102 after feeding the manual feed tray, the remaining paper sensor 103 before the timing roller, the remaining paper sensor 104 after the timing roller, and the remaining paper before the fixing device If all the sensors 105 determine that “remaining paper is present”, the fixing driving load of the fixing belt 21 increases. In this case, the control device 90 drives the fixing belt 21 in the reverse direction. Note that the determination of the presence or absence of the recording medium by the recording medium detection means may be determined in combination with the setting of the recording medium size by the user.

  Next, the control for selecting whether the fixing belt 21 rotates forward or backward when an abnormality occurs will be described based on the flowchart of FIG. FIG. 14 is a flowchart for describing control for selecting whether the fixing belt is rotating forward or reverse in the second embodiment.

  In the second embodiment, after passing through the same steps as steps S10 to S13 shown in FIG. 11, the control device 90 performs the remaining paper sensor 102 after the manual tray feeding, the remaining paper sensor 103 before the timing roller, and the timing. It is determined whether all of the post-roller residual sensor 104 and the pre-fixing apparatus residual sensor 105 are “remaining” (step S114).

  In step S <b> 114, the control device 90 determines that all the remaining paper sensors 102 after the manual feed tray, the remaining paper sensor 103 before the timing roller, the remaining paper sensor 104 after the timing roller, and the remaining paper sensor 105 before the fixing device are “ If it is determined that there is a remaining sheet (YES in step S114), the control device 90 determines that there is a possibility that the fixing belt 21 cannot rotate due to a large load on the fixing unit. Then, the control is terminated through the same steps as steps S20 to S23 of FIG.

  In step S <b> 114, the control device 90 determines that all the remaining paper sensors 102 after the manual feed tray, the remaining paper sensor 103 before the timing roller, the remaining paper sensor 104 after the timing roller, and the remaining paper sensor 105 before the fixing device are “ If it is determined that there is no remaining sheet (NO in step S114), the control device 90 determines that the fixing belt 21 is in a state in which the fixing belt 21 can rotate forward. Then, the control is terminated through the same steps as steps S15 to S16 in FIG.

  By adopting such forward rotation or reverse rotation control, when an abnormality occurs in the image forming apparatus, the fixing device 20 and the image forming apparatus can be stopped in a short time, thereby reducing damage to each part of the image forming apparatus. can do. Further, it is possible to prevent temperature spots on the fixing belt 21 and deformation of the fixing belt 21.

  It should be noted that the position at which the sensor is provided and the combination of the sensors to be determined includes a part specific to the model, and can be arbitrarily set depending on the size of each model and the transport layout.

[Third Embodiment]
Next, forward / reverse determination according to the third embodiment will be described. FIG. 15 is an explanatory diagram illustrating a configuration for determining forward rotation or reverse rotation according to the third embodiment.

  In the third embodiment, whether the rotation of the fixing belt 21 is normal or reverse is determined by speed detection means that can detect the rotation speed of the fixing belt 21.

  A marking 106 having a reflectance different from that of the surface of the fixing belt 21 is provided at an end portion in the longitudinal direction of the fixing belt 21. A change in reflectance accompanying rotation of the fixing belt 21 is detected by a reflective sensor 107 serving as a speed detecting means provided in the vicinity of the fixing belt 21. When the period of the marking 106 detected by the reflective sensor 107 is longer than a predetermined period, that is, when the rotation speed of the fixing belt 21 detected by the speed detection means is equal to or lower than the predetermined speed, the fixing belt 21 is at the target rotation speed. Without rotation, the fixing driving load of the fixing belt 21 increases. In this case, the control device 90 drives the fixing belt 21 in the reverse direction.

  Next, the control for selecting whether the fixing belt 21 rotates forward or backward when an abnormality occurs will be described with reference to the flowchart of FIG. FIG. 16 is a flowchart for explaining the control for selecting whether the fixing belt is rotating forward or reverse in the third embodiment.

  In the third embodiment, after passing through steps similar to steps S10 to S13 shown in FIG. 11, the control device 90 detects that the detection information by the reflective sensor 107 has a predetermined change rate of reflectance (for example, V [ms ]) It is determined whether or not the following is true (step S214).

  In step S214, when the control device 90 determines that the detection information by the reflective sensor 107 is equal to or lower than the predetermined change rate of the reflectance (YES in step S214), the control device 90 has a large load on the fixing unit and the fixing belt 21. Judging that may not be able to rotate. Then, the control is terminated through the same steps as steps S20 to S23 of FIG.

  When the control device 90 determines in step S114 that the detection information by the reflective sensor 107 is not less than or equal to the predetermined change rate of the reflectance (NO in step S214), the control device 90 is in a state where the fixing belt 21 can rotate forward. It is judged that. Then, the control is terminated through the same steps as steps S15 to S16 in FIG.

  By adopting such forward rotation or reverse rotation control, when an abnormality occurs in the image forming apparatus, the fixing device 20 and the image forming apparatus can be stopped in a short time, thereby reducing damage to each part of the image forming apparatus. can do. Further, it is possible to prevent temperature spots on the fixing belt 21 and deformation of the fixing belt 21.

[Fixing Device According to Another Embodiment]
The determination of forward rotation or reverse rotation according to the above-described embodiment can be applied to a fixing device having an end heater. FIG. 17 is a schematic cross-sectional configuration diagram showing another embodiment of the fixing device.

  The fixing device 120 includes an endless fixing belt 121 that is a thin and flexible cylindrical fixing member, and a pressure roller 122 that is a pressure member that abuts from the outer peripheral side of the fixing belt 121. ing. The fixing belt 121 is heated by the radiant heat of halogen heaters 123A and 123B (hereinafter also referred to as first halogen heater 123A and second halogen heater 123B) as a plurality of fixing heat sources arranged inside (in the loop). The halogen heater represents a radiant heat source as a fixing heat source which is a main heat source.

  Further, inside the fixing belt 121, a nip forming member 124 that forms a fixing nip portion N with the pressure roller 122 via the fixing belt 121, and a stay member 125 (support member) that supports the nip forming member 124. Is arranged.

  The nip forming member 124 arranged in the width direction of the fixing belt 121 is fixedly supported by the stay member 125, thereby preventing the nip forming member 124 from being bent by the pressure from the pressure roller 122, A uniform nip width is obtained over the axial direction (longitudinal direction) of the pressure roller 122. The nip forming member 124 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly heat-resistant resins such as polyimide (PI) resin, polyether ether ketone (PEEK) resin, and reinforced them with glass fiber. Is made up of. This prevents deformation of the nip forming member 124 due to heat in the toner fixing temperature region, ensures a stable state of the fixing nip portion, and stabilizes the output image quality.

  The stay member 125 and the halogen heaters 123A and 123B are fixedly held at both ends in the longitudinal direction by a side plate of the fixing device 120 or a separately provided holder.

  End heaters 126a and 126b as end heat sources different from the main heat source (fixing heat source) are integrally attached to both ends of the nip forming member 124 in the longitudinal direction. As the end heater, a contact heat transfer type heat source that is a resistance heating element such as a ceramic saver is generally used.

  A heat transfer auxiliary member 127, also referred to as a soaking member, that facilitates heat transfer in the longitudinal direction of the fixing belt 121, faces the inner peripheral surface of the fixing belt 121 of each of the nip forming member 124 and the end heater 126. It is arranged to cover. This prevents heat from staying in the end region of the fixing belt 121 when small-size paper is passed or when the end heater 126 is turned on, and positively changes the width of the fixing belt 121, that is, the heat transfer assisting member 127. In the longitudinal direction, heat is moved to eliminate the temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer auxiliary member 127 is formed of a material having high thermal conductivity that enables heat transfer in a short time, such as copper (398 W / mk) or aluminum (236 W / mk).

  In the depiction of FIG. 17, the surface of the heat transfer assisting member 127 that faces the inner peripheral surface of the fixing belt 121 is a surface that directly contacts the fixing belt 121 and is a nip forming surface that is formed in a flat shape. However, it may be a concave shape or other shapes. When the nip forming surface has a concave shape, the discharge direction of the leading end of the recording medium is closer to the pressure roller, and the separation property is improved and the occurrence of jam is suppressed.

  As is well known, a temperature sensor 129 for detecting the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 121, for example, upstream of the fixing nip portion in the belt rotation direction. A separation member 141 that separates the recording medium P from the fixing belt 121 is disposed on the downstream side in the direction. Further, releasable pressure means for pressing the pressure roller 122 to the fixing belt 121 is also provided.

  In order to reduce the heat capacity, the endless fixing belt 121, which is thin and has a small diameter like a film, has the same configuration as the fixing belt 21 of FIG. 2 described above, and thus description thereof is omitted here.

  The stay member 125 having a T-shaped cross section has an upright portion 125a that is upright on the side opposite to the fixing nip portion N, and is arranged so that halogen heaters 123A and 123B as main heat sources are separated by the upright portion 125a. Yes.

  One of the halogen heaters 123A and 123B has a heat generating portion at the center in the longitudinal direction corresponding to the small size paper, and the other has a heat generating portion at both longitudinal ends corresponding to the large size paper. The halogen heaters 123 </ b> A and 123 </ b> B are configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed on the belt surface by a temperature sensor 129 provided on the outer periphery of the fixing belt 121. This is performed based on the temperature detection result. By such heater output control, the temperature of the fixing belt 121 (fixing temperature) can be set to a desired temperature.

  Reflecting members 128A and 128B are disposed between the stay member 125 and the halogen heaters 123A and 123B. Accordingly, the heating efficiency of the halogen heaters 123A and 123B with respect to the fixing belt 121 is increased, and wasteful energy consumption due to the stay member 125 being heated by the radiant heat from the halogen heaters 123A and 123B can be suppressed. The same effect can be obtained by performing heat insulation or mirror treatment on the surface of the stay member 125 instead of providing the reflecting members 128A and 128B.

  The pressure roller 122 has the same configuration as that of the pressure roller 22 shown in FIG. 2 and the configuration of the rotational drive transmission method and the like are the same as those of the fixing device 20 shown in FIG. Description is omitted.

  FIG. 18 is a perspective view showing the basic configuration of the nip forming unit. As shown in FIG. 18, the nip forming unit includes a nip forming member 124, a stay member 125, a heat transfer assisting member 127, and end heaters 126a and 126b. In the nip forming unit, the surface of the nip forming member 124 opposite to the fixing nip portion N side is integrated with the flat surface of the stay member 125 on the fixing nip portion N side. At this time, uneven shapes such as bosses and pins may be formed on the respective surfaces, and these may be fitted in a shape-constrained manner.

  The heat transfer auxiliary member 127 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 124 that faces the inner peripheral surface of the fixing belt 121. The heat transfer assisting member 127 and the nip forming member 124 may be integrated with each other by providing a nail or the like, but may be bonded or the like.

  Concave portions 124a and 124b as stepped portions are formed at both ends in the longitudinal direction of the nip forming member 124, and end heaters 126a and 126b are accommodated and fixed at these portions. The positional relationship between the end heaters 126a and 126b and the halogen heaters 123A and 123B will be described later.

  The surface of the heat transfer assisting member 127 that faces the inner peripheral surface of the fixing belt 121 is configured as a belt sliding contact surface 127a. However, in terms of mechanical strength, the nip forming surface substantially becomes the nip forming surface. It is a surface 124 c facing the pressure roller 122.

  As described above, in the present embodiment, the end heaters 126a and 126b are integrally provided on the nip forming member 124 necessary for forming the fixing nip portion. Therefore, the end heaters 126a and 126b are provided on the fixing belt 121. It can be placed inside the space-saving.

  Further, the surface of the end heaters 126a and 126b that faces the inner surface of the fixing belt 121 and the surface of the nip forming member 124 that faces the fixing belt 121 are positioned at the same height (on the same plane). Sufficient pressure by 122 is given through the heat transfer auxiliary member 127.

  Thereby, the fixing belt 121 is in a state of being in intimate contact with the end heaters 126a and 126b, so that stable belt running can be performed. Further, the fixing belt 121 and the end heaters 126a and 126b are in contact with each other with a sufficient contact pressure, and good heating is maintained. With these configurations, the reliability of the fixing device 120 is improved.

  Further, the heating portion of the fixing belt 121 by the end heaters 126a and 126b is in the nip region. Therefore, heating at a site different from the fixing nip portion N does not cause a problem that untransferred toner is remelted and quality is deteriorated.

  FIG. 19 is a perspective view showing configurations of the nip forming unit and the halogen heater. As shown in FIG. 19, the stay member 125 is composed of a first member 125A and a second member 125B having a substantially L-shaped section, and the section is configured to be a substantially T-shaped section. Therefore, the rigidity is high and the nip forming member 124 can be prevented from being bent by the stress from the pressure roller 122. The stay members 125 (the first member 125 </ b> A and the second member 125 </ b> B) extend linearly in the longitudinal direction of the nip forming member 124 and are fixed to the nip forming member 124. Therefore, a good nip forming surface can be maintained over the entire longitudinal direction of the fixing nip portion N.

  A first halogen heater 123A and a second halogen heater 123B are disposed on both sides of the standing portion 125a in the short-side direction, respectively. That is, the first and second halogen heaters 123A and 123B are shielded from each other by the standing portion 125a. Therefore, since the glass tubes are not heated when the heater is turned on, the heating efficiency is not lowered. Further, since the first and second halogen heaters 123A and 123B are not surrounded by the stay member 125 (the center of each halogen heater 123 is outside the space surrounded by the stay member 125), the irradiation angles α and β (see FIG. 17) becomes obtuse and heating efficiency can be improved.

  The cross-sectional shape of the stay member 125 is not limited to a substantially T shape. The first and second halogen heaters 123A and 123B may be arranged so as to partition each other with the upright portion 125a interposed therebetween, and the first member 125A and the second member 125B extend in the longitudinal direction of the halogen heater in a curved manner. May be. Further, the first member 125A and the second member 125B may be raised in an oblique direction with respect to the nip forming surface of the nip forming member 124.

  Next, the arrangement of heat sources that can be used for recording materials of special sizes such as A3 Novi will be described. FIG. 20 is a schematic diagram showing the arrangement of the heat generating portions of the halogen heater and the end heater. As shown in FIG. 20, a first halogen heater 123A having a dense light distribution at the center in the longitudinal direction and a second halogen heater 123B having a dense light distribution at both ends in the longitudinal direction are arranged. Yes. That is, the first halogen heater 123A heats the central range of the fixing belt 121, and the second halogen heater 123B heats the side range of the fixing belt 121.

  The heat generating portion 140A of the first halogen heater 123A corresponds to a recording material of a small size such as A4 vertical size, for example, and the heat generating portion 140B of the second halogen heater 123B is an A3 vertical size that cannot be covered by the first halogen heater 123A. Covers the side area of the largest standard size recording material that can be used. That is, the heat generating unit 140 including the heat generating units 140A and 140B of both halogen heaters corresponds to the maximum standard size paper width and does not cover the nobi size paper width larger than the maximum standard size.

  On the other hand, the end heaters 126a and 126b are located at positions corresponding to both ends in the longitudinal direction of the second halogen heater 123B, and have heating portions 142a and 142b that heat both ends of the nobi size paper width larger than the maximum regular size. Further, part of the heat generating portions 142a and 142b of the end heaters 126a and 126b overlap with the heat generating portion 140B of the halogen heater 123B. As a result, the fixing device 120 can cope with both ends of a nobi size paper width larger than the maximum standard size.

  By the way, the end heaters 126a and 126b are arranged so as to cover each surface facing the inner peripheral surface of the fixing belt 121 through a heat transfer auxiliary member 127 made of copper or aluminum having high thermal conductivity. Yes. Therefore, even when the end heaters 126a and 126b are turned off immediately when an abnormality occurs, the high temperature may be maintained for a predetermined time due to overshoot or the like. As a result, if the fixing belt 121 is in a stopped state, temperature spots and deformation of the fixing belt 121 may occur.

  Even when such a highly energy-saving fixing device 120 is used, by adopting the forward rotation or reverse rotation control of the present invention, when an abnormality occurs in the image forming apparatus, the fixing device 120 and the image can be quickly processed. The forming apparatus can be stopped, and damage to each part of the image forming apparatus can be reduced. In addition, temperature spots on the fixing belt 121 and deformation of the fixing belt 121 can be prevented.

  As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can add a various change in the range which is not restricted to the above-mentioned embodiment and does not deviate from the summary of this invention. Note that the manner in which the fixing nip portion and one or a plurality of rotating bodies determine that one recording medium is sandwiched at the same time when an abnormality occurs is not limited to the embodiment described above, and the fixing nip portion Any one or a plurality of rotating bodies may be used as long as it can be determined that one recording medium is sandwiched at the same time. Further, the image forming apparatus equipped with the fixing device according to the present invention is not limited to the printer as shown in FIG. 1, but can be a copying machine, a facsimile, or a complex machine thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Paper feed roller (an example of a rotary body)
12 Timing roller (an example of a rotating body)
20,120 Fixing device 21 Fixing belt (an example of a fixing member)
23 Halogen heater (an example of a heating source)
22 Pressure roller (an example of a counter member)
24, 124 Nip forming member 32 Secondary transfer backup roller (an example of rotating body)
36 Secondary transfer roller (an example of a rotating body)
101 Remaining paper sensor after tray feeding (an example of a recording medium detection unit)
102 Remaining sheet sensor after manual tray feeding (an example of a recording medium detecting unit)
103 Remaining sheet sensor before timing roller (an example of a recording medium detection unit)
104 Remaining sheet sensor after timing roller (an example of recording medium detection means)
105 Remaining sheet sensor before fixing device (an example of a recording medium detection unit)
107 reflective sensor (an example of speed detection means)
126a, 126b End heater (an example of a contact heat transfer type heat source)
127 Heat transfer auxiliary member N Fixing nip

JP 2010-32631 A JP 2013-178487 A

Claims (8)

A rotatable fixing member;
A heating source for heating the fixing member;
An opposing member that contacts the outer peripheral surface of the fixing member to form a fixing nip portion;
One or a plurality of rotating bodies that convey the recording medium to the fixing nip portion,
In the fixing device for fixing the toner image to the recording medium by rotating the fixing member in the normal rotation direction,
A fixing device that stops the heating source when an abnormality occurs during operation of the fixing device, and then rotates the fixing member in a predetermined direction;
When an abnormality occurs during the operation of the fixing device, when the fixing nip portion and the one or more rotating bodies sandwich one recording medium at the same time, the one or more sandwiching the recording medium The fixing device determines the predetermined direction of the fixing member as the forward rotation direction or a reverse rotation direction opposite to the normal rotation direction according to the rotating body. A nip forming member provided inside the fixing member and forming the fixing nip portion between the fixing member and the opposing member;
A plurality of contact heat transfer type heat sources provided at both longitudinal ends of the nip forming member and respectively heating the longitudinal ends of the fixing member;
A heat transfer auxiliary member that covers each surface of the nip forming member and the plurality of contact heat transfer type heat sources that faces the fixing member and moves heat in a longitudinal direction of the fixing member. The fixing device according to claim 1. A rotation load detecting means for detecting a rotation load of the fixing member;
When an abnormality occurs during operation of the fixing device and the rotational load detected by the rotational load detection means is a predetermined value or more, the fixing member is rotated in a reverse rotation direction opposite to the normal rotation direction. The fixing device according to claim 1 or 2. Having one or more recording medium detecting means for detecting the presence or absence of the recording medium,
When all of the one recording medium detection unit or the plurality of recording medium detection units detect the presence of a recording medium when an abnormality occurs during the operation of the fixing device, the fixing member is reverse to the normal rotation direction. The fixing device according to claim 1, wherein the fixing device rotates in a reverse direction. Having a speed detection means for detecting the rotation speed of the fixing member;
When an abnormality occurs during operation of the fixing device, if the rotation speed detected by the speed detection means is equal to or lower than a predetermined speed, the fixing member is rotated in a reverse rotation direction opposite to the normal rotation direction. The fixing device according to claim 1 or 2.   The linear velocity of the fixing member that rotates in the reverse rotation direction when an abnormality occurs during operation of the fixing device is slower than the linear velocity of the fixing member that rotates in the normal rotation direction during normal operation. Item 6. The fixing device according to any one of Items 3 to 5. It is possible to switch between a pressurized state in which the opposing member is pressed against the fixing member and a depressurized state in which the opposing member is depressurized from the fixing member,
The fixing device according to claim 1, wherein after the rotation of the fixing member is stopped, the fixing member is switched to the depressurized state.   An image forming apparatus comprising the fixing device according to claim 1.

Images