JP2019018959A - Sheet conveying apparatus and image forming apparatus including the same - Google Patents

Abstract

To provide a sheet conveying apparatus capable of stably conveying various kinds of sheets without deteriorating durability thereof even when a conveying rotary member pair is a soft roller.SOLUTION: In a sheet conveying device (300), a rotary body (31) and a roller (32) form a nip, to at least one of which a rotary drive unit (31M) applies rotary force. The roller includes a cylindrical elastic body (322). A pushing force (FP) is applied by a pushing portion (34) with a pushing member (341) against an end face (324) of the elastic body in an axial direction to displace the end face in the axial direction. When the end face is displaced inward in the axial direction, nip pressure (FV) rises in a grip portion (51B) of the nip due to the viscoelasticity of an elastic layer.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a sheet conveyance technique, and more particularly to a nip conveyance.

  The “nip conveyance” is one of methods for conveying a sheet such as paper, a film, a cloth, and a thin plate using a rotating body such as a roller and a belt. In the nip conveyance, a pair of rotating bodies having parallel rotation axes sandwich a sheet to be conveyed between the outer peripheral surfaces, and rotate in opposite directions in that state. Since the tangential speed of the outer peripheral surface is the same in the contact portion between both rotating bodies, that is, the nip, the frictional force applied to the sheet by the outer peripheral surface acts on the sheet as a conveying force that is drawn into the nip and sent from the opposite side. . Nip transport is used in many systems that process sheets, including image forming devices such as printers and copiers, scanners, vending machines, automatic teller machines (ATMs), automatic ticket vending machines, automatic ticket gates, etc. Is done.

  In these systems, a sheet conveying apparatus generally uses a soft roller as a rotating body itself or as a roller (hereinafter referred to as “pulley”) that drives or tensions a belt that is a rotating body. The “soft roller” refers to a roller in which a metal or high-hardness resin cylinder or column (hereinafter referred to as “core metal”) is covered with a cylindrical elastic body such as a rubber tube. On the other hand, a roller including only a core metal and not including an elastic body is referred to as a “hard roller”. The soft roller is advantageous in comparison with the hard roller, for example, in that the noise is low, the sheet is not easily damaged, and a sheet having a large paper thickness or material such as an IC card can be conveyed. The soft roller also has a high elasticity on the outer peripheral surface, so that the nip width is increased and the outer peripheral surface is easily adhered to the sheet. Accordingly, the soft roller is often used in a fixing unit or a transfer unit of an electrophotographic image forming apparatus such as a laser printer (see, for example, Patent Documents 1 and 2). The higher the adhesion between the rotating body and the sheet, the higher the effect of both fixing and transfer. Therefore, the soft roller is advantageous for improving the quality of the toner image.

  On the other hand, when the soft roller receives a pressing force, that is, a nip pressure, from the counterpart rotating body, an expansion pressure is generated on the end surface in the axial direction of the elastic body. Since the height of the expansion pressure changes every time the sheet passes through the nip, there is a risk that the end surface may be damaged or cracked due to fatigue if the end surface of the elastic body is left free to be deformed. As a device for reducing this risk, for example, the soft roller disclosed in Patent Document 2 includes a member that suppresses expansion of the end face of the elastic body, that is, a regulating plate at both ends of the cored bar.

JP 2014-202897 A JP 2006-330064 A

  In general, a rotating body pair (hereinafter referred to as a “conveying rotating body pair”) used for nip conveyance is rotated by the torque of a motor, and a rotational force generated in the nip (hereinafter referred to as “grip force”). The other is driven to rotate. In the portion of the nip through which the sheet passes (hereinafter referred to as a “sheet passing portion”), one of the pair of conveying rotators receives a frictional force from the other through the sheet. The grip force is determined by the product of the dynamic friction coefficient and the sum of the nip pressures at the sheet passing portion. On the other hand, at the portion where both rotating bodies are in direct contact with each other outside the paper passing section (hereinafter referred to as “grip section”), the frictional force that one of the conveying rotating body pair receives directly from the other, that is, between the two rotating bodies. The grip force is determined by the product of the dynamic friction coefficient of the nip and the total nip pressure at the grip portion. As the grip force increases, slippage is less likely to occur between the pair of conveying rotators, that is, the followability between the pair of conveying rotators is higher, so that the sheet conveyance is more stable. When at least one of the pair of conveying rotators is a soft roller, the viscoelastic force of the elastic body accompanying the deformation at the nip acts so as to increase the gripping force, so that the sheet conveying stability is further improved.

  However, diversification of sheets in recent years is making it difficult to maintain high stability of sheet conveyance in the conveyance rotating body pair. This is due to the following reason. In the sheet to be conveyed, there are an increasing number of paper types such as thin paper and coated paper (coated paper) that have a lower coefficient of friction than plain paper, and paper types that are wider than standard sizes such as A3 and B4. Furthermore, paper types whose basis weight or coefficient of friction varies depending on environmental conditions, such as humidity control paper whose water content changes according to the ambient humidity. The decrease in the friction coefficient of the sheet weakens the frictional force that the rotating body receives in the sheet passing portion. The expansion of the sheet width widens the paper passing portion while narrowing the grip portion, so that the frictional force received by the rotating body is strengthened at the paper portion but weakened at the grip portion. Since the friction coefficient of the sheet is considerably lower than that of the rotating body, the friction force applied to the rotating body is weakened in the entire nip. If the purpose is to stably convey these sheets to the conveying rotating body pair, the nip pressure may be increased to the rotating body pair. However, when at least one of the pair of conveying rotators is a soft roller, an increase in the nip pressure involves a risk of accelerating fatigue of the elastic body as described below. Since each of the pair of conveying rotators has a higher coefficient of friction than the sheet, the frictional force received by each rotator is stronger in the grip portion than in the sheet passing portion. The difference in frictional force between the paper passing portion and the grip portion causes torsional stress in the portion of the elastic body facing the nip. The higher the nip pressure, the greater the difference in friction force, so the torsional stress is stronger. Therefore, an excessive increase in the nip pressure can accelerate the fatigue of the elastic body.

  An object of the present invention is to solve the above-described problems, and in particular, even when at least one of the pair of rotating conveyance bodies is a soft roller, various sheets can be stably conveyed without impairing durability. An object of the present invention is to provide a possible sheet conveying apparatus.

  A sheet conveying apparatus according to one aspect of the present invention is a sheet conveying apparatus that performs nip conveyance with respect to a sheet, and a core metal that is rotatably supported, and a cylindrical elastic body that covers an outer circumferential surface of the core metal. A rotating body that is supported rotatably around an axis parallel to the core of the roller, and that forms a nip by bringing the surface into contact with the outer peripheral surface of the roller, and the roller and the rotating body. A rotation drive unit that applies a rotational force to at least one of the rollers, and a pushing unit that pushes a cylindrical end surface of the elastic body of the roller to displace it in the axial direction.

  The pressing portion may include a pressing member that moves in the axial direction on the outer peripheral surface of the core metal of the roller and presses the end surface of the elastic body of the roller. The pressing member has a plate shape at least in contact with the end surface of the elastic body of the roller, and the contact portion includes a through hole through which the core metal of the roller passes on the plate surface, and the inner diameter of the through hole is outside the core metal. The diameter may be equal to the extent that the pressing member can slide in the axial direction on the outer peripheral surface of the cored bar. The elastic body of the roller may include an adhesive portion with the outer peripheral surface of the core metal of the roller. In the edge of the through hole of the pressing member, the distance from the outer peripheral surface of the core metal may be larger than the thickness in the radial direction of the bonded portion of the elastic body. The through hole of the pressing member may include a tapered portion that extends inward from the edge. The taper portion may have a larger inclination with respect to the axial direction of the through hole as it is closer to the edge of the through hole.

  The contact portion of the pressing member with respect to the end surface of the elastic body of the roller may have a position in the circumferential direction of the roller within the range of the nip between the roller and the rotating body. The elastic body of the roller may include an adhesive portion with the outer peripheral surface of the core metal of the roller. In the contact portion of the pressing member with respect to the end surface of the elastic body of the roller, the distance from the outer peripheral surface of the core metal of the roller may be larger than the thickness in the radial direction of the bonded portion of the elastic body. The elastic body of the roller includes an adhesive portion with the outer peripheral surface of the core metal of the roller inside the end surface, and a range from the end surface to the adhesive portion in the axial direction may not be bonded to the outer peripheral surface of the core metal.

  The sheet conveying apparatus may further include a control unit that determines a target position in the axial direction of the end surface of the elastic body of the roller in accordance with the type, size, or number of sheets to be conveyed and instructs the pushing unit. . When the type of the sheet to be conveyed is thin paper, coated paper, or humidity control paper, or when the sheet width exceeds the upper limit, the control unit sets the target position of the end surface of the elastic body of the roller from the standard position. It may be set inward in the axial direction. When the number of sheets continuously conveyed reaches the upper limit with the end surface of the elastic body of the roller displaced inward in the axial direction from the standard position in the pushing section, or the temperature of the roller falls below the lower limit. In this case, the target position of the end face may be returned outward in the axial direction. The roller may further include a surface layer that covers and protects the same range in the axial direction as the paper passing portion of the nip between the outer peripheral surface of the elastic body and the rotating body. The control unit gives the target position in the axial direction of the end surface of the elastic body of the roller in the radial direction of the roller when the exposed portion of the outer peripheral surface of the elastic body that is not covered with the surface layer is compressed in the axial direction by the end surface. You may determine based on the height of expansion pressure.

A fixing device according to one aspect of the present invention is mounted on an electrophotographic image forming apparatus, and includes the above-described sheet conveying device that nip conveys a sheet on which a toner image is formed by the image forming device, a roller, and a rotating body. A heating unit that applies heat to at least one of the above, and a pressing unit that presses one of the roller and the rotating body against the other.
An image forming apparatus according to one aspect of the present invention includes an image forming unit that forms a toner image on a sheet, and the above-described fixing device that thermally fixes the toner image on the sheet.

  In the sheet conveying apparatus according to the present invention, the end face in the axial direction of the elastic body of the roller that forms the nip with the rotating body is pushed and displaced in the axial direction. When this end face is displaced inward in the axial direction, the nip pressure increases due to the viscoelasticity of the elastic body. The amount of increase in the nip pressure at this time can be adjusted by the amount of displacement of the end face of the elastic body. In this way, this sheet conveying apparatus can convey various sheets stably without impairing the durability of the soft roller.

FIG. 1A is a perspective view illustrating an appearance of a printer that is an image forming apparatus according to an embodiment of the present invention. (B) is a schematic cross-sectional view of the printer along the line bb shown in (a). FIG. 2 is a block diagram illustrating a configuration of an electronic control system of the printer illustrated in FIG. 1. (A) is a typical exploded view of a pressure roller and a pressure pad shown in (b) of FIG. 1, and (b) is a cross-sectional view along a line bb shown in (a). is there. It is a block diagram of the electronic control system of the sheet conveying apparatus by embodiment of this invention. (A), (b) is a fragmentary sectional view which shows the end of the nip between the pressure roller and press pad along the straight line VV which (a) of FIG. 3 shows. (C), (d) is a perspective view of the nip vicinity which (a), (b) respectively shows. (A) is a perspective view of the regulating plate according to the first modification, and (b) is between the pressure roller and the pressure pad when the regulating plate pushes the end face of the elastic body layer of the pressure roller. It is a fragmentary sectional view which shows the end of nip of. (C) is a perspective view of the restriction plate according to the second modification, and (d) is a space between the pressure roller and the pressure pad when the restriction plate pushes the end face of the elastic body layer of the pressure roller. It is a fragmentary sectional view which shows the end of nip of. (A) is a perspective view of the regulating plate according to the third modified example, and (b) is between the pressure roller and the pressure pad when the regulating plate pushes the end face of the elastic body layer of the pressure roller. It is a fragmentary sectional view which shows the end of nip of. (C) is a perspective view of a regulating plate according to a fourth modified example, and (d) is a space between the pressure roller and the pressure pad when the regulating plate pushes the end surface of the elastic body layer of the pressure roller. It is a fragmentary sectional view which shows the end of nip of. It is a fragmentary sectional view which shows the end of the nip between a pressure roller and a press pad in case the control board by a 1st modification is pushing in the end surface of the elastic body layer of the pressure roller by a modification.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Appearance of image forming apparatus]
FIG. 1A is a perspective view showing an external appearance of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 is a printer. A sheet discharge tray 41 is provided on the upper surface of the casing, and accommodates sheets discharged from a sheet discharge opening 42 opened in the back thereof. An operation panel 51 is embedded in front of the paper discharge tray 41. A paper feed cassette 11 is attached to the bottom of the printer 100 so that it can be pulled out.

[Structure of image forming apparatus]
FIG. 1B is a schematic cross-sectional view of the printer 100 along the line bb shown in FIG. The printer 100 is an electrophotographic color printer, and includes a feeding unit 10, an image forming unit 20, a fixing unit 30, and a paper discharge unit 40.
First, the feeding unit 10 uses the pickup roller 12 to separate the sheets one by one from the bundle of sheets stored in the sheet feeding cassette 11. The feeding unit 10 sends the separated sheet SH <b> 1 to the image forming unit 20 using the timing roller 13. “Sheet” refers to a thin film or thin plate material, article, or printed matter. The material of the sheet that can be printed by the printer 100 includes paper or resin. The types of sheets that can be stored in the paper feed cassette 11, that is, the paper types, include plain paper, high-quality paper, color paper, or coated paper, and the size includes standard sizes defined by JIS standards, such as A3-A7. , B4-B7, business cards, bookmarks, tickets, postcards, envelopes, photos (L version). Furthermore, the posture of the sheet can be set to either vertical or horizontal.

  The image forming unit 20 is, for example, an intermediate transfer system, and includes a photoreceptor unit 20Y, 20M, 20C, 20K, an intermediate transfer belt 21, a primary transfer roller 22Y, 22M, 22C, 22K, and a secondary transfer roller 23. . The intermediate transfer belt 21 is rotatably spanned between a driven pulley 21L and a driving pulley 21R. Between these pulleys 21L and 21R, four photoreceptor units 20Y-20K and four primary transfer rollers 22Y-22K are arranged in pairs, and the intermediate transfer belt 21 is interposed therebetween. Opposite across (tandem arrangement). The secondary transfer roller 23 forms a nip with the drive pulley 21R with the intermediate transfer belt 21 interposed therebetween. The sheet SH2 sent from the timing roller 13 is passed through this nip.

  In the photoreceptor units 20Y-20K, the photoreceptor drums 24Y-24K are in contact with the opposing primary transfer rollers 22Y-22K with the intermediate transfer belt 21 interposed therebetween to form a nip. While the intermediate transfer belt 21 rotates in one direction (counterclockwise in FIG. 1B), the same surface portion of the photosensitive unit 20Y-20K has the primary transfer roller 22Y-22K and the photosensitive drum 24Y-. When passing through the nip with 24K, a toner image of one color different from yellow (Y), magenta (M), cyan (C), and black (K) is formed on the surface portion. These four color toner images are superimposed on the surface portion to form one color toner image. The sheet SH2 is passed from the timing roller 13 to the nip at the timing when the color toner image passes through the nip between the driving pulley 21R and the secondary transfer roller 23. As a result, the color toner image is transferred from the intermediate transfer belt 21 to the sheet SH2 at the nip.

  The fixing unit 30 thermally fixes the toner image on the sheet SH <b> 3 sent from the image forming unit 20. Specifically, the fixing unit 30 is, for example, a belt type, and a nip is formed between the pressure roller 32 and the pressing pad 35 with the fixing belt 31 interposed therebetween, and the sheet SH3 is passed through the nip. The fixing belt 31 is rotatably spanned between the pressing pad 35 and the heating roller 36, and transfers heat received from the heater 37 built in the heating roller 36 to the surface of the sheet SH3. The pressure roller 32 applies pressure to the heated portion of the sheet SH3 and presses it against the pressing pad 35 through the fixing belt 31. The toner image is fixed on the surface of the sheet SH <b> 3 by the heat from the fixing belt 31 and the pressure from the pressure roller 32. The fixing unit 30 further sends the sheet SH3 to the paper discharge unit 40 by the rotation of the fixing belt 31 and the pressure roller 32.

The paper discharge unit 40 discharges the sheet SH3 on which the toner image is fixed from the paper discharge port 42 to the paper discharge tray 41. Specifically, the paper discharge unit 40 uses the paper discharge roller 43 disposed inside the paper discharge port 42 to discharge the sheet SH3 that has moved from the upper part of the fixing unit 30 to the paper discharge port 42. And put it on the paper discharge tray 41.
-Sheet transport path-
Between these elements 10-40 included in the printer 100, a sheet conveyance path is formed by a guide plate or the like. In FIG. 1B, the conveyance path starts from the paper feed cassette 11, the conveyance rollers 12 and 13 of the feeding unit 10, the pair of the driving roller 21 </ b> R and the secondary transfer roller 23 of the intermediate transfer belt 21, and the fixing belt 31. And the pressure roller 32 and the paper discharge roller 43 of the paper discharge unit 40 in order to extend to the paper discharge port 42 which is the end. A motor for driving the transport roller and a plurality of paper passing sensors are installed around the transport path (not shown). The motor is, for example, a direct current brushless (BLDC) motor, and applies a rotational force to a conveyance roller to be driven through a transmission system such as a gear and a belt. The paper passing sensor is, for example, an optical type, and irradiates light to a monitoring area set on the conveyance path, and measures the amount of light transmitted through the area or the amount of light reflected from the area. When the sheet passes through the monitoring area, the irradiation light of the sheet passing sensor is blocked or reflected by the sheet, so that the measurement value of the light amount changes. From this change, the paper passing sensor detects passage of the monitoring area by the sheet.

[Electronic control system of image forming apparatus]
FIG. 2 is a block diagram illustrating the configuration of the electronic control system of the printer 100. In this system, in addition to the paper feeding unit 10, the image forming unit 20, the fixing unit 30, and the paper discharge unit 40, an operation unit 50 and a main control unit 60 are connected to each other through a bus 90 so as to communicate with each other.
−Driver−
The paper feeding unit 10, the image forming unit 20, the fixing unit 30, and the paper discharge unit 40 are respectively provided with motors 10A, 20A, 30A, 40A, driving units 10D, 20D, 30D, 40D, and sensors 10S, 20S, 30S, 40S. Including. The motors 10A-40A include actuators that drive movable members such as the photosensitive drums 24Y-24K, in addition to the motors that rotate the transport rollers 12, 13, 21R, 23, 31, 32, 36, 43. Each of the drive units 10D-40D is an electronic circuit mounted on a single printed circuit board built in the printer 100, and includes a control circuit and a drive circuit for the motors 10A-40A. The control circuit is a logic circuit such as a microprocessor (MPU / CPU), an application specific integrated circuit (ASIC), or a programmable integrated circuit (FPGA), and sets a target value for the rotational speed of the motor to drive the circuit. To instruct. Specifically, for example, the actual value of the rotational speed fed back from the motor is compared with the target value, and the target value of the voltage applied to the motor is instructed to the drive circuit so that the difference between them is reduced. The drive circuit is an inverter and supplies power to the motor using a switching element such as a power transistor (FET). At this time, when the drive circuit matches the voltage applied to the motor to the target value, the rotational speed of the motor is substantially maintained at the target value (that is, within an allowable error range).

  The sensor 10S-40S measures a physical quantity necessary for monitoring the operation state of the element 10-40 of the printer 100 and the sheet conveyance state, and provides the measured physical amount to the driving unit 10D-40D. For example, the sensor 10S-40S includes a position sensor that detects the position or posture of the movable members such as the photosensitive drums 24Y-24K and the intermediate transfer belt 21 in addition to the above-described sheet passing sensor, an actuator that drives these movable members, It includes a temperature sensor that detects overheating of the drive circuit, a sensor that detects a running out of paper in the paper feed cassette 11, and a toner sensor that detects toner shortage in the image forming units 20Y-20K. The drive unit 10D-40D controls the movable member in the element 10-40 according to the state indicated by the measurement value of the sensor 10S-40S. Further, when the drive unit 10D-40D detects a failure of the element 10-40 from the measured value of the sensor 10S-40S, the drive unit 10D-40D notifies the failure to the main control unit 60. In particular, the drive unit 30D of the fixing unit 30 monitors the temperature of the fixing belt 31 or the heating roller 36 through a temperature sensor installed in the fixing unit 30, and adjusts the amount of heat generated by the heater 37 according to the change in the temperature.

-Operation part-
The operation unit 50 includes an operation panel 51 and an external interface (I / F) 52, which accepts a job request and image data to be printed through user operation or communication with an external electronic device. Tell the main controller 60. As shown in FIG. 1A, the operation panel 51 includes a push button, a touch panel, and a display. The operation panel 51 displays a graphics user interface (GUI) screen such as an operation screen and an input screen for various parameters on a display. The operation panel 51 also identifies a push button pressed by the user or detects a position on the touch panel touched by the user, and transmits information related to the identification or detection to the main control unit 60 as operation information. In particular, when the input screen for a print job is displayed on the display, the operation panel 51 displays the size of the sheet to be printed, the type of paper, the orientation (separately between portrait and landscape), the number of copies, color / monochrome, Print conditions such as image quality are received from the user, and items indicating these conditions are incorporated into the operation information. The external I / F 52 includes a USB port or a memory card slot, through which image data to be printed is read directly from an external storage device such as a USB memory or HDD. The external I / F 52 is also wired or wirelessly connected to an external network (not shown) and receives image data to be printed from other electronic devices on the network.

−Main control unit−
The main control unit 60 is an integrated circuit mounted on a single printed circuit board built in the printer 100, and includes a CPU 61, a RAM 62, and a ROM 63. The CPU 61 is constituted by one MPU, and implements various functions as a control subject for the other elements 10-40 by executing various firmware. For example, the CPU 61 displays a GUI screen such as an operation screen on the operation unit 50 to accept a user input operation. In response to this input operation, the CPU 61 selects an operation mode such as an operation mode, a standby mode, or a sleep mode, and instructs the element 10-40 to perform processing corresponding to the operation mode. The RAM 62 is a volatile semiconductor memory device such as a DRAM or an SRAM, and provides a work area when the CPU 61 executes firmware to the CPU 61 and stores image data to be printed received by the operation unit 50. In particular, the RAM 62 displays the printing conditions indicated by the operation information from the operation unit 50, the operation mode selected by the CPU 61, and the environmental conditions such as temperature and humidity detected by the CPU 61 through the sensors in the printer 100 from other elements 10-40. Hold for reference. The ROM 63 is configured by a combination of a non-writable nonvolatile storage device and a rewritable nonvolatile storage device. The former stores firmware. The latter includes a semiconductor memory device such as EEPROM, flash memory, SSD, or HDD, and provides the CPU 61 with a storage area for environment variables and the like.

  When the operation unit 50 receives a print job from the user, the main control unit 60 first causes the operation unit 50 to transfer image data to be printed to the RAM 62. Next, the main control unit 60 designates the type of sheet to be fed and the timing of feeding in accordance with the printing conditions indicated by the job, and the toner to be formed in the image forming unit 20. Image data representing the image is provided. In particular, the main control unit 60 selects a target value of the sheet conveyance speed according to the image quality, power consumption, or sheet type indicated by the printing conditions, and instructs the element 10-40 of the printer 100. For example, when the paper type to be printed is thick paper, the sheet conveyance speed is set lower than the value for plain paper. The correspondence between the printing conditions and the target value of the conveyance speed is determined in advance by experiments or simulations, and is stored in the ROM 63 in the form of a numerical table or a mathematical expression. The CPU 61 retrieves a target value corresponding to the printing condition from this table or calculates it according to this equation. By adjusting the actual conveyance speed to the target value obtained in this way, the drive unit 10D-40D of the element 10-40 stabilizes the power consumption of the motor regardless of the basis weight of the sheet to be conveyed. The main control unit 60 further notifies the drive unit 30D of the fixing unit 30 of the operating conditions. The operating conditions include, for example, the target temperature of the fixing belt 31 or the heating roller 36, the paper type, size, and number of sheets to be printed.

[Fixing part structure]
FIG. 3A is a schematic exploded view of the pressure roller 32 and the pressure pad 35, and FIG. 3B is a cross-sectional view taken along a line bb shown in FIG. The fixing unit 30 includes a fixing belt 31, a pressure roller 32, driving mechanisms 33 and 34, a pressing pad 35, a heating roller 36, a heater 37, and a holding member 38.

-Fixing belt-
The fixing belt 31 is a cylindrical endless belt having a length of several tens of centimeters, a diameter of several tens of millimeters to several hundreds of millimeters, and a thickness of several hundreds of micrometers to several millimeters, and rotates between the pressing pad 35 and the heating roller 36. It is spanned as possible. The fixing belt 31 includes a base layer, an elastic layer, and a surface layer in order from the inner peripheral side (not shown). The base layer is made of a high-strength heat-resistant resin film such as polyimide (PI) or a metal foil such as stainless steel (SUS) or nickel. The elastic layer is formed of a highly elastic heat-resistant resin film such as silicone rubber covering the outside of the base layer, and the elasticity of the elastic layer deforms the outer peripheral surface of the fixing belt 31 in accordance with the fine irregularities on the surface of the sheet SH3. This makes the gloss of the toner image uniform. The surface layer is made of a fluororesin film such as polytetrafluoroethylene (PFA) covering the outside of the elastic layer, and the toner melted in the high-temperature and high-pressure nip NP is transferred from the surface of the sheet SH3 to the outer peripheral surface of the fixing belt 31. Prevent (offset).

-Pressure roller-
The pressure roller 32 includes a cored bar 321, an elastic body layer 322, and a surface layer 323. The core metal 321 is an elongated cylindrical member having a length of several tens of centimeters and a diameter of several millimeters to several tens of millimeters, and is made of a highly rigid metal such as aluminum, iron, or SUS. The cored bar 321 is rotatably supported around its own central axis by bearings (not shown) at both ends in the longitudinal direction (Z-axis direction in the figure). These bearings are supported by the frame of the fixing unit 30 so as to be slidable in a direction in which the core metal 321 approaches the pressing pad 35 (in the negative direction of the X axis in the drawing). The elastic body layer 322 is a cylindrical member having a thickness of several tens to several hundreds of millimeters arranged coaxially on the outside of the cored bar 321 and is made of a highly elastic heat-resistant resin such as silicone rubber. The elastic body layer 322 has an inner peripheral surface that is in contact with the outer peripheral surface of the cored bar 321 over the entire circumferential direction, and is bonded to the outer peripheral surface with an adhesive. The surface layer 323 is a fluororesin film such as PFA having a thickness of several hundred μm to several mm, and covers the outer peripheral surface of the elastic layer 322 over the entire circumferential direction. The surface layer 323 is a portion of the nip NP between the fixing belt 31 and the pressure roller 32 (hereinafter referred to as “sheet passing portion”) and the longitudinal direction of the cored bar 321 (Z-axis direction). , The toner is transferred (offset) from the surface of the sheet SH3 to the outer peripheral surface of the elastic layer 322. In the nip NP, the outer portion (hereinafter referred to as “grip portion”) in the longitudinal direction (Z-axis direction) of the sheet passing portion is exposed without being covered with the surface layer 323. Therefore, it comes into direct contact with the fixing belt 31.

-Drive mechanism-
The drive mechanism is the entire combination of a movable member included in the fixing unit 30 and an actuator for the movable member, and includes a pressure drive unit, a rotation drive unit 33, and a push-in unit 34.
The pressure driving unit applies a force in a direction to press the outer peripheral surface of the pressure roller 32 against the plate surface of the pressing pad 35. Specifically, the pressure driving unit is an actuator (not shown) such as a solenoid or a motor, and the cored bar 321 is pressed to the press pad 35 with respect to the bearing that supports the cored bar 321 of the pressure roller 32. On the other hand, a force in a direction to approach the pressing pad 35 while being parallel (in the drawing, the negative direction of the X axis) is applied. When this force is transmitted to the cored bar 321 through the bearing, the outer peripheral surface of the pressure roller 32 is located on the plate surface of the pressing pad 35 with the portion located at the nip NP sandwiching the fixing belt 31 therebetween, the paper passing portion, the grip portion, and the like. Is pressed with a uniform pressure, for example, a pressure of the order of 10 ⁶ Pa.

  The rotation drive unit 33 applies a rotational force to the cored bar 321 of the pressure roller 32. Specifically, the rotation drive unit 33 includes a first motor 31M and a torque transmission mechanism 331. The first motor 31M is one of the motors 30M provided in the driving unit 30D of the fixing unit 30. The torque transmission mechanism 331 is a combination of a gear, a belt, and the like, and transmits the torque of the first motor 31M to one end in the longitudinal direction of the cored bar 321 to rotate the cored bar 321 around the central axis.

  When the pressure driving unit presses the outer peripheral surface of the pressure roller 32 against the plate surface of the pressing pad 35 through the fixing belt 31, the elastic body layer 322 is softer than the pressing pad 35. In the NP, it is substantially flat (that is, within an allowable range of error), and is recessed flat along the plate surface of the pressing pad 35. When the rotation driving unit 33 rotates the cored bar 321 around the central axis in this state, the frictional force that the outer peripheral surface of the elastic layer 322 applies to the fixing belt 31 in the nip NP and the viscoelastic force of the elastic layer 322, that is, the elasticity The fixing belt 31 is driven to rotate by the force that the body layer 322 expands in the circumferential direction along with the radial compression and pushes the fixing belt 31 in the circumferential direction.

  The pushing portion 34 pushes the cylindrical end surface 324 in the elastic body layer 322 of the pressure roller 32 to displace it in the axial direction (that is, “push”). Specifically, the pressing portion 34 is a combination of the second motor 32M and a pressing member, and one set is installed on each side of the pressing roller 32 in the longitudinal direction (Z-axis direction). The second motor 32M is one of the motors 30M included in the driving unit 30D of the fixing unit 30, and applies a driving force to the pressing member. The pressing member is a combination of a plurality of members formed from a highly rigid metal such as aluminum, iron, or SUS, or a resin having high mechanical strength, and includes a restriction plate 341, a cam 342, and a driven node 343. The restriction plate 341 is an annular plate-like member having a diameter of several tens mm and a thickness of several mm, for example, and the inner diameter of the central through hole is substantially equal to the outer diameter of the cored bar 321. The restricting plate 341 is arranged at one end at each end in the longitudinal direction (Z-axis direction) of the core bar 321, with the end passing through the through hole, and from the end 328 of the core bar 321 in the longitudinal direction to the elastic layer. It is slidably attached to the end surface 324 of 322. The cam 342 is a plate member having a smooth outer periphery and a rotationally asymmetric shape, and is rotatably supported around a rotation shaft 344 that penetrates the plate surface. Since the rotating shaft 344 is connected to the shaft of the second motor 32M directly or via some gears or belts (not shown), the cam 342 receives torque from the second motor 32M. Rotate. The driven node 343 is, for example, an elongated rod-like member, and extends in parallel to the longitudinal direction (Z-axis direction) of the cored bar 321 from the base end 345 fixed to the outer plate surface of the regulating plate 341. In a state where the inner plate surface of the regulating plate 341 is in contact with the end surface 324 of the elastic body layer 322, the elastic plate receives elastic force outwardly (in the positive direction of the Z axis) from the elastic body layer 322 through the regulating plate 341 and follows the follower node. The length of the follower 343 is designed so that the tip 346 of the 343 is pressed against the outer peripheral surface of the cam 342. Thereby, when the cam 342 rotates, the tip 346 of the driven node 343 follows the outer peripheral surface of the cam 342 so that the entire driven node 343 maintains a posture parallel to the longitudinal direction (Z-axis direction) of the cored bar 321. Slide. Since this outer peripheral surface is asymmetrical around the rotation shaft 344, the entire follower 343 moves parallel to the longitudinal direction (Z-axis direction) with respect to the cored bar 321 including the proximal end 345 and the distal end 346. With this parallel movement, the regulating plate 341 slides on the outer peripheral surface of the cored bar 321 in the longitudinal direction (Z-axis direction). The sliding range is such that when the elastic layer 322 returns to its original length in the longitudinal direction (Z-axis direction), the position of the regulating plate 341 with the inner plate surface in contact with the end surface 324 is the outer side. It is designed to be a boundary. When the cam 342 rotates from the posture when the regulating plate 341 is positioned at this boundary, the regulating plate 341 is displaced inward in the longitudinal direction (Z-axis direction) and pushes the end surface 324 of the elastic body layer 322. Due to this displacement, the restricting plate 341 can compress the elastic body layer 322 to a maximum of several mm, for example. The amount of compression of the elastic layer 322 is determined according to the position of the restricting plate 341, that is, the rotation angle of the cam 342. On the other hand, with the compression of the elastic body layer 322, the exposed portion of the elastic body layer 322 expands in the radial direction by the viscoelasticity without being covered by the surface layer 323 in the grip portion. Since the expansion pressure of the exposed portion increases the nip pressure, the grip force received by the fixing belt 31 is increased.

-Press pad-
The pressing pad 35 is a plate-like member that is elongated in the axial direction of the pressure roller 32 (Z-axis direction in the figure), and is made of, for example, a heat-resistant resin such as liquid crystal polymer (LCP) or polyphenylene sulfide (PPS). The pressing pad 35 receives a pressing force from the outer peripheral surface of the pressure roller 32 through the fixing belt 31 on one side, and forms a nip NP therebetween. Compared to the elastic layer 322, the pressure of the pressing pad 35 is so low that the elasticity is negligible, so that the outer peripheral surface of the pressure roller 32 is flattened along the plate surface of the pressing pad 35 at the nip NP. Due to this deformation, the nip NP expands on the plate surface of the pressing pad 35 with a width of several mm in the conveying direction (vertical direction in the drawing) of the sheet SH3 as shown in FIG.

-Heating roller and heater-
The heating roller 36 includes a core bar 361 and an elastic body layer 362. The cored bar 361 is a cylindrical member having a diameter of several tens mm, for example, and is made of a metal such as aluminum or iron. The elastic body layer 362 is made of a highly elastic heat-resistant resin such as silicone rubber, and covers the outer peripheral surface of the cored bar 361 with a thickness of less than 1 mm, for example. A heater 37 is installed in a hollow portion inside the cored bar 361. The heater 37 is, for example, a rod-shaped halogen heater elongated in the axial direction (Z-axis direction) of the pressure roller 32, and heats the core 361 from the inside by heat radiation accompanying light emission. Since this heat is transmitted to the outer peripheral surface through the elastic body layer 362, the temperature is maintained in the range of hundreds of degrees C. to hundreds of degrees C.

-Holding member-
The holding member 38 is a plate-like member that is long in the axial direction (Z-axis direction) of the pressure roller 32. For example, a grooved steel plate (cross section) made of a metal such as electrogalvanized steel (SECC), SUS, or aluminum. Is a steel plate having a U shape. The holding member 38 is bonded to the plate surface of the pressing pad 35 on the side opposite to the pressing roller 32 with respect to the pressing pad 35, and both end portions in the longitudinal direction are attached to the frame (not shown) of the fixing unit 30. It is fixed. The holding member 38 holds the pressing pad 35 at the same position with respect to this frame.

[Sheet Conveying Device with Fixing Unit]
FIG. 4 is a block diagram of an electronic control system of the sheet conveying apparatus 300 according to the embodiment of the present invention. The sheet conveying apparatus 300 includes a driving unit 30 </ b> D, a fixing belt 31, a pressure roller 32, driving mechanisms 33 and 34, a pressing pad 35, and a heating roller 36 among the elements of the fixing unit 30. The drive unit 30D includes a rotation speed actual measurement unit 301, a temperature sensor 302, a humidity sensor 303, a control unit 310, a first drive circuit 311, and a second drive circuit 312.

  The rotational speed actual measurement unit 301 monitors the output signal FGP of the encoder built in the first motor 31M, calculates the actual rotational speed Nms of the first motor 31M from these signals FGP, and feeds it back to the control unit 310. . The temperature sensor 302 is, for example, a non-contact type using a thermopile, and measures the temperature of the surface according to the output of the thermopile according to the heat radiation from the surface of the fixing belt 31, the heating roller 36, or the pressure roller 32, The measurement value is notified to the control unit 310. The humidity sensor 303 measures the humidity of the atmosphere in the space surrounded by the frame of the fixing unit 30 and notifies the control unit 310 of the measured value.

  The control unit 310 includes a logic circuit such as an MPU / CPU, ASIC, or FPGA, a ROM that stores firmware, and a RAM that provides a work area when the firmware is executed. The controller 310 sets a target value for the rotation speed of the first motor 31M according to the firmware and instructs the first drive circuit 311. Specifically, when the control unit 310 is first instructed to execute the fixing process from the main control unit 60, the first motor is determined from the paper type, size, and conveyance speed target values of the sheet to be printed indicated by the instruction. A target value for the rotational speed of 31M is set. Next, the control unit 310 compares the target value with the actual measurement value Nms fed back from the rotational speed actual measurement unit 301, and calculates the amount of power to be supplied to the first motor 31M so that the difference therebetween is reduced. The first drive circuit 311 is instructed. The first drive circuit 311 is an inverter, and supplies power to the first motor 31M using a switching element such as an FET. By making this amount of electric power coincide with the value instructed by the first drive circuit 311, the rotation speed of the first motor 31M is maintained substantially equal to the target value (that is, within an allowable error range), and the pressure roller The sheet conveyance speed by 32 substantially matches the target value.

  The control unit 310 sets a target value for the control amount such as the rotation speed of the second motor 32M and the amount of power according to another firmware and instructs the second drive circuit 312. Specifically, the control unit 310 first acquires parameter values that affect the stability of conveyance at the start of nip conveyance by the fixing belt 31 and the pressure roller 32, for example. For example, the temperature sensor 302 determines the temperature of the fixing belt 31, the heating roller 36, and the pressure roller 32, the humidity sensor 303 indicates the humidity of the atmosphere in the fixing unit 30, and the main control unit 60 indicates the sheet to be printed. The paper type, size, and number of sheets are acquired. The control unit 310 stores a correspondence relationship between the values of these parameters and the target value of the rotation angle of the cam 342 in the form of a numerical table or a mathematical expression. Next, the control unit 310 retrieves the target value of the rotation angle of the cam 342 associated with the acquired parameter value from this table or calculates it according to this equation. The controller 310 calculates the amount of electric power of the second motor 32M required to rotate the cam 342 to the target value obtained in this way, and instructs the second drive circuit 312. The second drive circuit 312 is an inverter and supplies power to the second motor 32M using a switching element such as an FET. The second drive circuit 312 matches the electric energy of the second motor 32M with the instructed value, so that the rotation angle of the cam 342 substantially matches the target value (that is, within an allowable error range).

[Adjustment of grip force that the pressure roller should apply to the fixing belt]
5A and 5B are partial cross-sectional views showing one end of the nip between the pressure roller 32 and the pressure pad 35 along the line VV shown in FIG. 3A. FIG. 5A shows a case where the rotation angle of the cam 342 is set so that the regulating plate 341 is positioned at the outer boundary OBN in the sliding range MVR in the axial direction of the pressure roller 32. b) shows a case where the rotation angle of the cam 342 is changed so that the restricting plate 341 is located inside the case. FIGS. 5C and 5D are perspective views in the vicinity of the nip shown in FIGS. 5A and 5B, respectively.

  As shown in FIG. 5A, when the regulating plate 341 is positioned at the boundary OBN outside the sliding range MVR, the elastic body layer 322 of the pressure roller 32 is the original length in the longitudinal direction (Z-axis direction). Returning to this, the radius is uniform over its entire length except for the part facing the nip, and the deformation at the nip is also uniform over its entire length. Therefore, the nip pressure is substantially uniform (that is, within an allowable error range) between the sheet passing portion 50A and the grip portion 51A. In this case, the difference between the grip force FRH received by the fixing belt 31 at the paper passing portion 50A and the grip force GRH received by the grip portion 51A (see the arrow shown in FIG. 5C) is the difference between the elastic layer 322. This is the difference between the frictional forces received by each of the sheet passing portion 50A and the grip portion 51A. This difference causes a torsional stress in the elastic layer 322, and repetition of this torsional stress causes the elastic layer 322 to fatigue. The nip between the fixing belt 31 and the pressure roller 32 is designed so that the driven rotation of the fixing belt 31 stably follows the rotation of the pressure roller 32 and the durability of the elastic layer 322 is not impaired. ing. In particular, the height of the friction coefficient between the elastic body layer 322 and the fixing belt 31 with respect to the friction coefficient between the elastic body layer 322 and the sheet HMS is offset by the narrow width of the grip portion 51A with respect to the paper passing portion 50A. Is done. For example, when the sheet HMS is plain paper, the nip is designed so that the restricting plate 341 may be positioned at the boundary OBN outside the sliding range MVR. In this sense, the outer boundary OBN of the sliding range MVR is hereinafter referred to as “standard position”. When the sheet HMS is plain paper and the regulation plate 341 is maintained at the standard position OBN, the sum of the gripping forces FRH + GRH between the paper passing portion 50A and the grip portion 51A substantially causes the fixing belt 31 to slip. (Ie, the slip frequency and magnitude are maintained within an allowable range), and the rotation level is maintained. On the other hand, the difference GRH−FRH between these gripping forces remains at a level where the torsional stress generated in the elastic body layer 322 is sufficiently lower than the allowable upper limit.

  As shown in FIG. 5B, when the regulation plate 341 is pushed inward from the standard position OBN, the elastic body layer 322 of the pressure roller 32 receives the pressing force FP from the regulation plate 341 on the end surface 324. Compressed in the longitudinal direction (Z-axis direction). At this time, in the sheet passing portion 50B, the elastic body layer 322 is assisted by the high rigidity of the surface layer 323 and the sheet SH3, and resists compression against the pressing force from the regulating plate 341. As a result, the portion of the elastic body layer 322 located in the grip portion 51B, that is, the portion exposed without being covered by the surface layer 323 is formed in the longitudinal direction (Z-axis) by the portion located in the paper passing portion 50B and the regulating plate 341. Since it is compressed by the pressing force FP from both sides in the direction), it expands in the radial direction (in the XY plane) by viscoelasticity. Since the nip pressure is increased by the expansion pressure FV of the exposed portion, the gripping force GRL received by the fixing belt 31 in the grip portion 51B shown in FIG. 5D is the grip portion 51A shown in FIG. It is stronger than the grip power GRH.

  The grip force GRL at the grip part 51B is stronger as the restriction plate 341 is positioned inside the sliding range MVR. Therefore, when the gripping force FRL at the paper passing portion 50B shown in FIG. 5D is weaker than the gripping force FRH at the paper passing portion 50A shown in FIG. 5C (FRL <FRH), the pushing portion 34 Moves the restricting plate 341 inward and pushes the end face 324 of the elastic layer 322 into it. The insufficient grip force FRL at the paper passing portion 50B is compensated by the strengthening of the grip force GRL at the grip portion 51B. That is, the sum of the gripping forces FRL + GRL between the sheet passing portion 50B and the grip portion 51B is maintained at a level at which the fixing belt 31 can be rotated without substantially slipping.

  The difference GRL-FRL between the gripping forces shown in FIG. 5D is larger than the difference GRH-FRH between the gripping forces shown in FIG. 5C, so that the difference is generated in the elastic layer 322. The torsional stress is stronger in (d) of FIG. 5 than in (c) of FIG. Therefore, the control unit 310 performs the pushing operation of the end surface 324 of the elastic body layer 322 by the pushing portion 34 so that the fatigue of the elastic body layer 322 due to the repetition of the torsional stress is delayed as much as possible. Restrict if FRL is insufficient. Specifically, as described in the description of FIG. 4, the control unit 310 represents the target value of the rotation angle of the cam 342 associated with the value of the parameter that affects the stability of the nip conveyance. Or in accordance with a mathematical formula and instructing the pushing unit 34. In this numerical table or mathematical expression, when the target value of the rotation angle of the cam 342 represents the pushing of the end surface 324 of the elastic body layer 322, the value of the above parameter represents the shortage of the grip force FRL at the sheet passing portion 50B. Corresponding to These cases include, for example, a case where any one of conditions (1) to (5) listed below is satisfied. (1) The sheet to be transported is a paper type having a lower friction coefficient than plain paper, such as thin paper, coated paper, and humidity-controlled paper. (2) The sheet width exceeds the upper limit, for example, standard sizes such as A3, B4, and A4. (3) The humidity of the atmosphere in the fixing unit 30 is higher than the upper limit. (4) The temperature of the pressure roller 32 is equal to or higher than the lower limit. (5) The number of continuously conveyed sheets is less than the upper limit. Condition (1) represents a lack of frictional force at the paper passing portion. Condition (2) represents that the frictional force is insufficient in the entire nip due to the shortening of the grip part accompanying the extension of the sheet passing part. In condition (3), since the moisture content of the sheet is high due to the high humidity, the decrease in the nip pressure due to the water vapor pressure on the sheet surface due to heating at the nip cannot be ignored, and the frictional force at the sheet passing portion is insufficient. Represents what to do. Condition (4) represents that the temperature of the pressure roller 32 is high, so the hardness of the elastic body layer 322 is low, and the viscoelastic force of the elastic body layer 322 at the paper passing portion 50B is insufficient. Condition (5) represents the following. When the number of sheets to be continuously conveyed is less than the upper limit, for example, 10 sheets, the amount of heat taken away from the pressure roller 32 by the sheet during continuous conveyance is small. Therefore, during continuous conveyance, the temperature of the pressure roller 32 remains high, the hardness of the elastic body layer 322 is low, and the viscoelastic force of the elastic body layer 322 at the paper passing portion 50B is insufficient. Specific numerical values of parameters satisfying these conditions and the target value of the rotation angle of the cam 342, that is, the displacement amount of the restricting plate 341 are determined by experiment or simulation. In this way, when the target value of the rotation angle of the cam 342 represents the pushing of the end surface 324 of the elastic layer 322, it is limited when the grip force FRL at the sheet passing portion 50B is insufficient, so that the elastic layer 322 has a torsional stress. It is only in that case. As a result, the occurrence frequency of torsional stress is low, and the progress of fatigue of the elastic body layer 322 is slow, so that the durability of the elastic body layer 322 is not impaired, that is, its life is sufficiently long.

[Advantages of the embodiment]
In the sheet conveying apparatus 300 according to the embodiment of the present invention, as described above, the pressing portion 34 displaces the regulating plate 341 in the axial direction along the outer peripheral surface of the cored bar 321 of the pressure roller 32, and the elasticity of the pressure roller 32. The end surface 324 in the axial direction of the body layer 322 is pushed and displaced in the axial direction. When the end face 324 is pushed in in this way, the nip pressure increases due to the viscoelasticity of the elastic body layer 322 in the grip portion 51B. The amount of increase in the nip pressure at this time can be adjusted by the amount of displacement of the end surface 324 of the elastic layer 322. The control unit 310 affects the stability of the nip conveyance such that the sheet to be conveyed is a low friction coefficient paper type such as thin paper, coated paper, humidity control paper, or the width of the sheet exceeds the standard size. When the value of the parameter represents a shortage of the grip force FRL at the sheet passing portion 50B, the end surface 324 of the elastic layer 322 is pushed into the pushing portion 34. Along with this, the nip pressure increases in the grip portion 51B, so that the shortage of the grip force FRL in the paper passing portion 50B is compensated, and the driven rotation of the fixing belt 31 stably follows the rotation of the pressure roller 32. Furthermore, the pushing of the end surface 324 of the elastic body layer 322 is limited when the grip force FRL at the paper passing portion 50B is insufficient, so the torsional stress is generated less frequently and the fatigue of the elastic body layer 322 progresses slowly. Thus, the sheet conveying apparatus 300 has a width smaller than that of a standard size and a paper type having a low friction coefficient such as a thin paper, a coated paper, and a humidity-controlled paper, without impairing the durability of the pressure roller 32. Various sheets including a wide sheet can be stably conveyed.

[Modification]
(A) The image forming apparatus 100 according to the above embodiment of the present invention is an electrophotographic color printer. In addition, the image forming apparatus according to the embodiment of the present invention may be a single-function device such as a monochrome printer, a copier, or a fax machine, or may be a multifunction device (MFP).
(B) The fixing belt 31 is a tension belt that is stretched between the pressing pad 35 and the heating roller 36. In addition, the fixing belt may be a non-stretch belt (free belt). Further, a driven roller may be used instead of the pressing pad 35. In this case, either the pressure roller or the driven roller may be a soft roller, or both may be a soft roller.

The fixing belt 31 applies heat from a heater 37 built in the heating roller 36 to the sheet. The heater 37 is a halogen heater. In addition, the heater may be an induction heating device.
The fixing belt 31 heats the sheet, and the pressure roller 32 presses the sheet. In addition, the structure may be such that the driving roller heats the sheet and the pressing pad directly presses the sheet against the driving roller through the belt or the driven roller directly.

  (C) The control unit 310 may update the target values of the respective rotational speeds of the first motor 31M and the second motor 32M for each job or each sheet. In particular, the control unit 310 continues to monitor parameter values that affect the stability of the nip conveyance even during continuous conveyance of the sheet, and continues to update the target value of the rotation angle of the cam 342 in accordance with the change in the value. Also good. Thereby, the period during which the end surface 324 of the elastic body layer 322 is pushed in corresponds to the period when the grip force is insufficient in the paper passing portion more quickly, so the frequency of occurrence of torsional stress is further reduced. For example, in the following cases (α) and (β), the control unit 310 may immediately update the target value of the rotation angle of the cam 342 so that the end face 324 of the elastic body layer 322 returns outward in the axial direction. . (Α) Since the temperature of the pressure roller 32 is equal to or higher than the lower limit indicated by the condition (4) at the start of the print job, the regulation plate 341 is pushed inward from the standard position OBN, and the pressure roller is being processed during the processing of the job. When the temperature of 32 falls below the lower limit. (Β) When any one of the conditions (1) to (4) is satisfied at the start of the print job, the regulation plate 341 is pushed inward from the standard position OBN, and the number of sheets continuously conveyed in that state is When the upper limit indicated by condition (5) is reached.

  (D) The regulation plate 341 shown in FIGS. 3 and 5 is in the shape of an annular plate, and the inner diameter of the central through hole is the outer diameter of the cored bar 321 and the regulation plate 341 is axially on the outer peripheral surface of the cored bar 321. It is equal to the extent that it can slide. The restriction plate may have other shapes. For example, the contact portion of the pressure roller 32 with the end surface 324 of the elastic body layer 322 may be a polygonal plate shape or an asymmetric shape with respect to the core metal 321. Further, the edge of the through hole may be wider than the inner diameter.

  6A is a perspective view of the restriction plate 441 according to the first modification, and FIG. 6B is an additional view when the restriction plate 441 pushes the end surface 324 of the elastic body layer 322 of the pressure roller 32. 3 is a partial cross-sectional view showing one end of a nip between a pressure roller 32 and a pressing pad 35. FIG. In the restriction plate 441, the diameter Rr of the edge 442 of the through hole opened in the contact surface with the end surface 324 of the elastic body layer 322 of the pressure roller 32 is larger than the inner diameter Ri of the through hole: Rr> Ri. In particular, the difference Rr−Ri between them is a portion 32H in which the elastic body layer 322 is bonded to the outer peripheral surface of the core metal 321 of the pressure roller 32 (that is, the adhesive layer and the elastic body layer in which the adhesive penetrates). Larger than twice the thickness Th in the radial direction of the entire 322 portion: Rr−Ri> 2 × Th. The through hole of the restriction plate 441 further includes a tapered portion 443 that extends inward from the edge 442. As shown in FIG. 6B by a broken line, the inner surface of the tapered portion 443 has a constant inclination θ with respect to the central axis Cx of the through hole. 6B, when the regulating plate 441 pushes the end surface 324 of the elastic body layer 322 as shown in FIG. 6B, a portion of the end surface 324 located outside the edge 442 of the through hole is the regulating plate. It is pushed by the plate surface 441 and displaced. On the other hand, the portion located on the inner side of the edge 442 is not substantially pushed by the taper portion 443 but remains deformed along the inner surface. In particular, the adhesive portion 32 </ b> H of the elastic body layer 322 does not receive a pressing force from the tapered portion 443. Therefore, damage and peeling of the adhesion portion 32H accompanying the pressing of the regulation plate 441 are prevented.

  FIG. 6C is a perspective view of the restriction plate 541 according to the second modification, and FIG. 6D is an additional view when the restriction plate 541 pushes the end surface 324 of the elastic body layer 322 of the pressure roller 32. 3 is a partial cross-sectional view showing one end of a nip between a pressure roller 32 and a pressing pad 35. FIG. In the restriction plate 541, the diameter Rr of the edge 542 of the through hole is larger than the inner diameter Ri of the through hole, and the difference Rr−Ri between them is the same as the restriction plate 441 according to the first modification shown in FIG. It is larger than twice the thickness Th of the adhesive portion 32H of the elastic layer 322: Rr−Ri> 2 × Th. On the other hand, the restricting plate 541 according to the second modified example is different from the restricting plate 441 according to the first modified example, and the inner surface of the tapered portion 543 of the through hole has an edge of the through hole as shown in FIG. The closer to 542, the greater the inclination φ with respect to the central axis Cx of the through hole. Due to the distribution of the inclination φ, as shown in FIG. 6D, when the regulating plate 541 pushes the end surface 324 of the elastic body layer 322, the end portion 324 has a pressing force applied from the taper portion 543 to the adhesive portion 32 </ b> H. Not only is it not received, but the portion closer to the edge 542 of the through hole receives a stronger pressing force from the regulating plate 541. Since the elastic layer 322 is more easily elastically deformed as it is closer to the edge 542 of the through hole, the effect of increasing the nip pressure at the grip portion 51 </ b> C due to the pressing of the regulating plate 541 is high.

  FIG. 7A is a perspective view of a restriction plate 641 according to the third modification, and FIG. 7B is an additional view when the restriction plate 641 pushes the end surface 324 of the elastic body layer 322 of the pressure roller 32. 3 is a partial cross-sectional view showing one end of a nip between a pressure roller 32 and a pressing pad 35. FIG. The regulation plate 641 has a donut (torus) shape as shown in FIG. 7A, and the diameter of the edge 642 of the through hole is the same as the regulation plate 541 according to the second modification shown in FIG. Rr is larger than the inner diameter Ri of the through hole, and the difference Rr-Ri between them is larger than twice the thickness Th of the adhesive portion 32H of the elastic body layer 322: Rr-Ri> 2 × Th. Further, as with the restricting plate 541 according to the second modified example, as the inner surface of the through hole is closer to the edge 642 of the through hole as shown in FIG. ψ is large. Due to the distribution of the inclination ψ, when the regulating plate 641 pushes the end surface 324 of the elastic body layer 322 as shown in FIG. 7B, the end surface 324 is pressed by the adhesive portion 32H from the inner surface of the through hole. In addition, the portion closer to the edge 642 of the through hole receives a stronger pressing force from the regulating plate 641. Since the elastic layer 322 is more easily elastically deformed as the portion is closer to the edge 642 of the through hole, the effect of increasing the nip pressure at the grip portion 51 </ b> D accompanying the pressing of the regulating plate 641 is high.

  FIG. 7C is a perspective view of the restriction plate 741 according to the fourth modified example, and FIG. 7D is an additional view when the restriction plate 741 pushes the end surface 324 of the elastic body layer 322 of the pressure roller 32. 3 is a partial cross-sectional view showing one end of a nip between a pressure roller 32 and a pressing pad 35. FIG. As shown in FIG. 7C, the restricting plate 741 is coaxial with a shaft 744 extending perpendicularly to the longitudinal direction from the tip 743 of the rod-like member 742, and the shaft 744 It is supported so that it can rotate around. As shown in FIG. 7D, the rod-shaped member 742 can move in parallel with the core bar 321 through the gap between the core bar 321 and the pressing pad 35. Due to this parallel movement, the outer peripheral surface of the regulating plate 741 is located within the nip within the end surface 324 of the elastic body layer 322 in the circumferential direction, and the distance Ds from the outer peripheral surface of the core metal 321 is the elastic body layer 322. The part 32T is larger than the thickness Th of the adhesive part 32H, and the part 32T is pushed in. At this time, the regulation plate 741 is driven to rotate around the shaft 744 as the pressure roller 32 rotates, so that the frictional force between the outer peripheral surface of the regulation plate 741 and the end surface 324 of the elastic body layer 322 is sufficiently weak. . As shown in FIG. 7D, the deformation of the end surface 324 of the elastic body layer 322 due to the pressing of the regulation plate 741 is limited to the vicinity of the nip. The load on the motor 32M can be small.

  (E) When the restricting plates 441-741 according to the modification shown in FIGS. 6 and 7 are used, the elastic body layer 322 of the pressure roller 32 has an adhesive portion with the outer peripheral surface of the cored bar 321 on the inner side of the end surface 324. And the range from the end surface 324 to the bonded portion in the axial direction may not be bonded to the outer peripheral surface of the cored bar 321. As a result, the adhesive portion is more difficult to receive the pressing force associated with the pressing of the regulating plate, and the risk of damage and peeling is further reduced.

  FIG. 8 shows an end of the nip between the pressure roller 62 and the pressure pad 35 when the restriction plate 441 according to the first modification pushes the end surface 324 of the elastic body layer 622 of the pressure roller 62 according to the modification. It is a fragmentary sectional view shown. The elastic body layer 622 of the pressure roller 62 includes an adhesion portion 62H with the outer peripheral surface of the core metal 321 on the inner side of the end surface 324, and a range 62T from the end surface 324 to the adhesion portion 62H in the axial direction is the core metal 321. It is not bonded to the outer peripheral surface. Therefore, as shown by a two-dot chain line in FIG. 8, when the regulating plate 441 pushes the end surface 324 of the elastic body layer 622, the inside of the edge 442 of the through hole of the regulating plate 441 is inside the end surface 324 of the elastic body layer 622. Small deformation. In other words, a portion of the end surface 324 near the outer peripheral surface of the cored bar 321 has a small distortion due to the pressing of the restriction plate 441. In this way, the risk of damage and peeling of the adhesive portion 62H accompanying the pressing of the regulating plate 441 is further reduced.

  (F) The sheet conveying apparatus 300 according to the above embodiment targets the fixing belt 31 and the pressure roller 32. In addition, the sheet conveying apparatus may be any of a pair of rotating bodies that perform nip conveyance, such as the intermediate transfer belt 21, the secondary transfer roller 23, the timing roller 13, and the paper discharge roller 43.

  The present invention relates to a soft roller used for nip conveyance, and as described above, pushes the end surface 324 of the elastic body layer 322 with the restriction plate 341, thereby increasing the grip force. Thus, the present invention is clearly industrially applicable.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 30 Fixing part 300 Sheet conveying apparatus 31 Fixing belt 32 Pressure roller 321 Core metal 322 Elastic body layer 323 Surface layer 324 End surface of elastic body layer 34 Pushing part 32M 2nd motor 341 Restriction plate 342 Cam 343 Driven joint 344 Cam 345 Rotating shaft 345 Proximal end of driven node 346 Front end of driven node 35 Pressure pad MVR Sliding range of restricting plate OBN Standard position of restricting plate 50A, 50B Nip passing portion 51A, 51B Nip grip portion FP Elastic layer Compressive force applied to the exposed part FV Expansion pressure of the exposed part of the elastic layer HMS, LMS sheet FRH, FRL Grip force in the paper passing part GRH, GRL Grip force in the grip part

Claims (15)

A sheet conveying device that performs nip conveyance for a sheet,
A roller including a core metal supported rotatably and a cylindrical elastic body covering an outer peripheral surface of the core metal;
A rotating body that is rotatably supported around an axis parallel to the core of the roller, and that forms a nip by bringing the surface into contact with the outer peripheral surface of the roller;
A rotation drive unit that applies a rotational force to at least one of the roller and the rotating body;
The sheet conveying apparatus provided with the pushing part which presses the end surface in the axial direction of a cylindrical shape among the elastic bodies of the roller, and displaces it in the axial direction. The pushing portion is
The sheet conveying apparatus according to claim 1, further comprising: a pressing member that moves in an axial direction on an outer peripheral surface of the core metal of the roller and presses an end surface of the elastic body of the roller. The pressing member has a plate-shaped contact portion with at least an end face of the elastic body of the roller,
The contact portion includes a through hole in the plate surface through which the core metal of the roller passes.
3. The sheet conveying apparatus according to claim 2, wherein an inner diameter of the through hole is equal to an outer diameter of the cored bar and an extent that the pressing member can slide in an axial direction on an outer peripheral surface of the cored bar. . The elastic body of the roller includes an adhesive portion with the outer peripheral surface of the core metal of the roller,
The sheet conveying apparatus according to claim 3, wherein the edge of the through hole of the pressing member has a distance from the outer peripheral surface of the core metal that is larger than a thickness in a radial direction of an adhesion portion of the elastic body.   The sheet conveying apparatus according to claim 4, wherein the through hole of the pressing member includes a tapered portion that extends inward from the edge.   6. The sheet conveying apparatus according to claim 5, wherein the taper portion has a greater inclination with respect to an axial direction of the through hole as a portion is closer to an edge of the through hole.   The contact portion of the pressing member with respect to an end surface of the elastic body of the roller has a position in the circumferential direction of the roller within a range of a nip between the roller and the rotating body. Sheet transport device. The elastic body of the roller includes an adhesive portion with the outer peripheral surface of the core metal of the roller,
The contact portion of the pressing member with respect to the end surface of the elastic body of the roller has a distance from the outer peripheral surface of the core metal of the roller that is larger than the thickness in the radial direction of the bonded portion of the elastic body. The sheet conveying apparatus according to 1. The elastic body of the roller is
An adhesive portion with the outer peripheral surface of the core metal of the roller is included inside the end surface,
The sheet conveying apparatus according to any one of claims 1 to 8, wherein a range from the end surface to the bonding portion in the axial direction is not bonded to the outer peripheral surface of the cored bar. 10. The apparatus according to claim 1, further comprising a control unit that determines a target position in an axial direction of an end face of the elastic body of the roller according to a type, a size, or a number of sheets to be conveyed, and instructs the pushing unit. The sheet conveying apparatus according to any of the above.   When the type of sheet to be transported is thin paper, coated paper, or humidity control paper, or when the width of the sheet exceeds the upper limit, the control unit sets the target position of the end surface of the elastic body of the roller as a standard position. The sheet conveying apparatus according to claim 10, wherein the sheet conveying apparatus is set inward in the axial direction.   The control unit is configured such that when the number of sheets continuously conveyed reaches the upper limit in a state where the end surface of the elastic body of the roller is displaced inward in the axial direction from the standard position to the pressing unit, or The sheet conveying apparatus according to claim 11, wherein when the temperature falls below a lower limit, the target position of the end face is returned outward in the axial direction. The roller is
The outer surface of the elastic body further includes a surface layer that covers and protects the same range in the axial direction as the paper passing portion of the nip with the rotating body,
The control unit sets the target position in the axial direction of the end surface of the elastic body of the roller when the exposed portion of the outer peripheral surface of the elastic body that is not covered with the surface layer is compressed in the axial direction by the end surface. The sheet conveying device according to claim 10, wherein the sheet conveying device is determined based on a height of an expansion pressure applied in a radial direction of the roller. A fixing device mounted on an electrophotographic image forming apparatus;
A sheet conveying apparatus according to any one of claims 1 to 13, wherein a sheet on which a toner image is formed by the image forming apparatus is nipped.
A heating unit that applies heat to at least one of the roller and the rotating body;
A fixing device including a pressure unit that presses one of the roller and the rotating body against the other. An image forming unit for forming a toner image on a sheet;
An image forming apparatus comprising: the fixing device according to claim 14, wherein the toner image is thermally fixed on the sheet.

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