JP2018072792A - Contact/separation mechanism, fixing device, transfer device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: it is difficult to ensure a large distance for members to approach/separate from each other, while reducing the inclination of a cam surface.SOLUTION: A contact/separation mechanism includes a cam member 41 and rotates the cam member 41 to cause a contact/separation member 19 to approach/separate from an opposite member 18. The cam member 41 includes a cam surface 41a in which the distance from the center of rotation gradually increases over an area larger than that of a half round in the direction of rotation, and can rotate in one direction and a direction opposite thereto.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a contact / separation mechanism, a fixing device, a transfer device, and an image forming apparatus.

  2. Description of the Related Art Known fixing devices and transfer devices used in image forming apparatuses such as copying machines and printers are provided with a contact / separation mechanism that moves members closer to and away from each other.

  For example, in the fixing device, in order to change the contact pressure between the fixing rotator and the pressure rotator, a contact / separation mechanism is provided to approach and separate these rotators. Further, in the transfer device, a contact / separation mechanism that separates the primary transfer member from a color image photosensitive member that is not used at the time of monochrome image formation, or paper entering the contact portion between the intermediate transfer member and the secondary transfer member. In order to suppress a decrease in the speed of the intermediate transfer member, a contact / separation mechanism for separating the secondary transfer member from the intermediate transfer member is provided.

  Generally, the contact / separation mechanism includes a cam member that rotates and moves the contact / separation member toward and away from the counterpart member. For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2006-85438), by rotating an elliptical cam member in one direction, the other roller is moved closer to and away from one roller, The structure which changes the pressing amount of the other roller with respect to a roller is disclosed.

  By the way, the cam surface of the cam member rotates so that the cam member pushes and moves the contacting / separating member or the member interlocking with it when the gradient (change rate of the distance from the rotation center with respect to the length in the rotation direction) is gentler. Rotational torque is reduced, and the load on the device can be reduced. In addition, when the cam member rotates in the direction opposite to the rotation direction that pushes the contacting / separating member or the member interlocking therewith, the cam member is rotated more slowly when the cam surface has a gentler gradient of the cam surface due to a sudden release of the pressing force. The increase in speed can be suppressed, and the generation of operating noise (abnormal noise) can be suppressed.

  However, in the conventional configuration in which the elliptical cam member is rotated in one direction, the cam surface whose distance from the rotation center gradually increases in the rotation direction and the cam whose distance from the rotation center gradually decreases in the rotation direction. There is a restriction that the range in which the surface can be secured is at most half the circumference of the cam member. For this reason, when the gradient of the cam surface is made gentle, the maximum height difference of the gradient is reduced correspondingly, and there arises a problem that a distance for moving the members closer to each other cannot be obtained sufficiently.

  As described above, in the conventional configuration, there is a trade-off relationship between making the slope of the cam surface gentle and ensuring a large approaching / separating distance between members, and it has been difficult to achieve both. .

  In order to solve the above-described problems, the present invention is a contact / separation mechanism that includes a cam member and rotates the cam member to move the contact / separation member closer to and away from the counterpart member, the cam member rotating The cam surface has a gradually increasing distance from the rotation center over a region larger than a half circumference of the direction, and is capable of rotating in one direction and in the opposite direction.

  According to the present invention, the cam member is configured to be rotatable in one direction and in the opposite direction, so that the same cam surface is used when the contacting / separating member is moved toward and away from the counterpart member. be able to. For this reason, the cam member is not subject to the restriction that the range in which the cam surface can be secured is at most half of the rotation direction as in the conventional case (a configuration in which the cam member is rotated only in one direction). It can be provided over a region larger than a half circumference in the rotation direction. And, by providing the cam surface over a region larger than a half circumference in the rotational direction, even if the gradient of the cam surface is gentle, it is possible to avoid a decrease in the maximum height difference of the gradient. It is possible to suppress the increase in rotational torque and the generation of operating noise (abnormal noise) by making the gradient of the cam surface gentle while ensuring a sufficient approach / separation distance of the contact / separation member with respect to the counterpart member.

1 is a schematic configuration diagram of a monochrome image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of a fixing device according to an exemplary embodiment. It is a figure which extracts and shows a cam member, a light shielding member, and an optical sensor. It is a schematic block diagram of the drive system of the contact-separation mechanism which concerns on this embodiment. It is a block diagram of the control system of the contacting / separating mechanism according to the present embodiment. It is a figure for demonstrating the separation operation | movement of the pressure roller by a cam member. It is a figure for demonstrating the approaching operation of the pressure roller by a cam member. It is a figure for demonstrating the rotation control method at the time of a depressurization operation | movement. It is a flowchart of rotation control at the time of pressure release operation. It is a figure for demonstrating the time required to switch to the light-shielding state after switching to the light transmission state. It is a figure for demonstrating an abnormal state. It is a figure for demonstrating the rotation control method at the time of pressurization operation | movement. It is a flowchart of rotation control at the time of pressurization operation. It is a figure for demonstrating the state different from normal. It is a figure which shows other embodiment of a light-shielding member. It is a figure for demonstrating the rotation control method at the time of a depressurization operation | movement. It is a figure for demonstrating the rotation control method at the time of pressurization operation | movement. It is a figure of the cam member which has the cam surface in which the flat surface was formed in part. It is a figure of the light shielding member which replaced the light shielding part and the translucent part. It is a figure of a reflection member. It is a schematic block diagram of the contact-and-separation mechanism using two optical sensors. It is a figure for demonstrating the rotation control method at the time of a depressurization operation | movement. It is a flowchart of rotation control at the time of pressure release operation. It is a figure for demonstrating the rotation control method at the time of pressurization operation | movement. It is a flowchart of rotation control at the time of pressurization operation. It is a schematic block diagram of the contacting / separating mechanism using a DC brushless motor. It is a flowchart of rotation control at the time of pressure release operation. It is a flowchart of rotation control at the time of pressurization operation. It is a schematic block diagram of the contacting / separating mechanism using a DC brushless motor and further using two optical sensors. It is a flowchart of rotation control at the time of pressure release operation. It is a flowchart of rotation control at the time of pressurization operation. It is a schematic block diagram of the contacting / separating mechanism using a stepping motor. It is a figure for demonstrating the rotation control method at the time of a depressurization operation | movement. It is a flowchart of rotation control at the time of pressure release operation. It is a figure for demonstrating the rotation control method at the time of pressurization operation | movement. It is a flowchart of rotation control at the time of pressurization operation. FIG. 2 is a schematic configuration diagram of a fixing device including a fixing belt. FIG. 3 is a schematic configuration diagram of a fixing device in which a fixing roller approaches and separates from a counter roller. 1 is a schematic configuration diagram of a color image forming apparatus of a lateral conveyance type. It is a schematic block diagram of the contact-and-separation mechanism which approaches and separates a secondary transfer roller. 1 is a schematic configuration diagram of a vertical conveyance type color image forming apparatus. It is a schematic block diagram of a transfer apparatus. It is a schematic block diagram of the contact-and-separation mechanism which approaches and separates a primary transfer roller.

  Hereinafter, the present invention will be described with reference to the accompanying drawings. In the drawings for explaining the present invention, components such as members and components having the same function or shape are denoted by the same reference numerals as much as possible, and once described, the description will be given. Omitted.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
First, the overall configuration and operation of the image forming apparatus will be described with reference to FIG. The image forming apparatus to which the present invention is applied includes, in addition to a printer, a copying machine, a facsimile alone, or a multifunction machine having at least two functions of a copying machine, a printer, a facsimile, and a scanner.

  The image forming apparatus shown in FIG. 1 is a monochrome image forming apparatus. A process unit 1 as an image forming unit is detachably mounted on the apparatus main body (image forming apparatus main body) 100. The process unit 1 visualizes a photoreceptor 2 as an image carrier that carries an image on the surface, a charging roller 3 as a charging unit that charges the surface of the photoreceptor 2, and a latent image on the photoreceptor 2. A developing device 4 as a developing unit and a cleaning blade 5 as a cleaning unit for cleaning the surface of the photoreceptor 2 are provided. Further, an LED head array 6 as an exposure unit that exposes the surface of the photoconductor 2 is disposed at a position facing the photoconductor 2.

  The process unit 1 is detachably mounted with a toner cartridge 7 as a powder container for storing toner, which is powder for image formation. The toner cartridge 7 includes an unused toner storage unit 8 that stores unused toner, and a waste toner storage unit 9 that stores used waste toner.

  In addition, the image forming apparatus includes a transfer device 10 that transfers an image to a sheet as a recording medium, a paper feeding device 11 that supplies the sheet, a fixing device 12 that fixes the image transferred to the sheet, and a sheet outside the apparatus. And a pair of registration rollers 17 as timing rollers.

  The transfer device 10 includes a transfer roller 14 as a transfer member. The transfer roller 14 is disposed so as to come into contact with the photoreceptor 2 in a state where the process unit 1 is mounted on the apparatus main body 100. The transfer roller 14 is connected to a power source (not shown) so that a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied.

  The paper feeding device 11 includes a paper feeding cassette 15 that stores paper P and a paper feeding roller 16 that feeds the paper P stored in the paper feeding cassette 15. In addition to plain paper, the paper P includes thick paper, thin paper, postcard, envelope, coated paper (coated paper, art paper, etc.), tracing paper, and the like. Furthermore, in addition to paper, an OHP sheet, an OHP film, or the like can be used as a recording medium.

  The fixing device 12 includes a pair of rotating bodies facing each other. One rotating body is a fixing roller 18 as a fixing rotating body that fixes an image on a sheet, and the other rotating body is a pressure roller 19 as a pressure rotating body that pressurizes the fixing roller 18. is there. The fixing roller 18 is provided with a halogen heater 22 as a heating means. The fixing roller 18 and the pressure roller 19 are in contact with each other, and a fixing nip is formed between the rollers 18 and 19.

  The paper discharge device 13 includes a pair of paper discharge rollers 20 that discharge the paper to the outside of the device. Further, a paper discharge tray 21 for placing the paper discharged by the paper discharge roller 20 is formed on the upper surface of the exterior of the apparatus main body 100.

  Further, in the apparatus main body 100, a paper discharge roller 20 is supplied from a paper feed cassette 15 through a registration roller 17, an image transfer portion (transfer nip) between the transfer roller 14 and the photoreceptor 2, and a fixing device 12. A transport path R1 for transporting the paper P is provided. Further, in the image forming apparatus 100, a double-sided conveyance path R2 is provided for conveying the paper P that has passed through the fixing device 12 to the image transfer unit again when performing double-sided printing.

Next, an image forming operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the photosensitive member 2 is rotationally driven, and the surface of the photosensitive member 2 is uniformly charged to a predetermined polarity by the charging roller 3. Next, the LED head array 6 exposes the charged surface of the photoreceptor 2 based on image information from a reader or a computer, and an electrostatic latent image is formed. Then, the toner is supplied to the electrostatic latent image on the photoconductor 2 by the developing device 4, whereby the electrostatic latent image is visualized (visualized) as a toner image.

  When the image forming operation is started, the paper feed roller 16 starts to rotate and the paper P is sent out from the paper feed cassette 15. The fed paper P is temporarily stopped by the registration roller 17. Thereafter, rotation of the registration roller 17 is started at a predetermined timing, and the paper P is conveyed to the image transfer unit in accordance with the timing at which the toner image on the photoconductor 2 reaches the image transfer unit.

  Then, when the paper P is conveyed to the image transfer unit, the toner image on the photosensitive member 2 is transferred onto the paper P by a transfer electric field generated by applying a predetermined voltage to the transfer roller 14. At this time, the toner on the photosensitive member 2 that has not been transferred to the paper P is removed by the cleaning blade 5 and collected in the waste toner container 9 of the toner cartridge 7.

  The paper P on which the toner image has been transferred is conveyed to the fixing device 12 and heated and pressurized by passing through a fixing nip formed by the fixing roller 18 and the pressure roller 19, and the toner on the paper P The image is fixed. Then, the paper P is discharged out of the apparatus by the paper discharge roller 20 and placed on the paper discharge tray 21.

  Further, when performing duplex printing, the paper P that has passed through the fixing device 12 is switched back without being discharged out of the device, and is sent to the duplex conveyance path R2. The paper P passes through the double-sided conveyance path R2 and is sent to the conveyance path R1 on the near side of the registration roller 17, and is conveyed again to the image transfer unit by the registration roller 17. Then, after the image is transferred to the back surface of the paper P and the image on the back surface side is fixed by the fixing device 12, the paper P is discharged out of the device.

FIG. 2 is a schematic configuration diagram of the fixing device according to the present embodiment.
Hereinafter, the fixing device 12 according to the present embodiment will be described in detail with reference to FIG.

  Both end portions of the fixing roller 18 and the pressure roller 19 are rotatably supported by a pair of support members 25 via bearings 23 and 24. When a driving force is transmitted from the driving source provided in the apparatus main body to the fixing roller 18, the fixing roller 18 is rotationally driven in a direction indicated by an arrow A in FIG. 2 in the direction indicated by the arrow B in FIG. In contrast to this embodiment, the pressure roller 19 may be a driving roller and the fixing roller 18 may be a driven roller.

  When the sheet enters the fixing nip N from the direction indicated by the arrow C1 in FIG. 2 in a state where the fixing roller 18 is heated to a predetermined temperature by the radiant heat generated from the halogen heater 22, the rotating fixing roller 18 and the pressure are pressed. The sheet is conveyed while being nipped by the roller 19. At this time, the unfixed image on the paper is heated by the heat of the fixing roller 18 and is pressed by the fixing roller 18 and the pressure roller 19, whereby the image is fixed on the paper. Then, the sheet on which the image is fixed is discharged from the fixing nip N in the direction of arrow C2 in FIG.

  The pressure roller 19 is supported by the support member 25 so as to be able to approach and separate from the fixing roller 18 in the direction of arrow D in FIG. Specifically, a bearing 24 that supports the pressure roller 19 is fitted into a bearing guide portion 25b that is a rectangular hole provided in the support member 25, and the bearing 24 is moved along the bearing guide portion 25b. By being guided, the pressure roller 19 approaches and separates from the fixing roller 18. On the other hand, the bearing 23 that supports the fixing roller 18 is fitted in a bearing fitting portion 25a that is a circular hole provided in each support member 25, and the axial position of the fixing roller 18 is perpendicular to the axial direction. It has been fixed so as not to move.

  Further, the fixing device 12 according to the present embodiment includes a pressure lever 31 as a pressure member that presses the pressure roller 19 against the fixing roller 18 and a biasing force that biases the pressure lever 31 in the pressure direction. And a pressure spring 32 as a member. One pressure lever 31 and one pressure spring 32 are provided on each side of the pressure roller 19. One end 31 a of the pressure lever 31 is attached to a support shaft 33 provided below the support member 25, and is configured to be rotatable about the support shaft 33 in the direction of arrow E in FIG. 2. Each pressure spring 32 is attached by being hooked to hooks 31 c and 25 c provided on the other end 31 b side of the pressure lever 31 and the upper portion of the support member 25. As a result, the other end 31b of the pressure lever 31 is held in a state of being always pulled upward in FIG. The pressure lever 31 presses the bearing 24 that supports the pressure roller 19 through the pad 34 fitted in the bearing guide portion 25 b of the support member 25, and applies the pressure roller 19 toward the fixing roller 18. Pressure.

  In addition, the fixing device 12 according to the present embodiment includes a cam member 41 as a contact / separation mechanism that moves the pressure roller 19 toward and away from the fixing roller 18. The cam member 41 is provided on each end of the rotating shaft 42 that is rotatably supported by the pair of support members 25. When the rotating shaft 42 rotates, the pair of cam members 41 rotate integrally with the rotating shaft 42. The cam member 41 has a cam surface 41a whose distance from the rotation center changes in the rotation direction. When the pressure lever 31 is pulled by the pressure spring 32, the cam receiving portion 31d provided on the pressure lever 31 is held in contact with the cam surface 41a. In this state, when the cam member 41 rotates in one direction, the pressure lever 31 is pushed downward by the cam surface 41a in FIG. 2, whereby the pressure roller 19 is separated from the fixing roller 18, and the cam member When 41 reversely rotates, the pressure lever 31 is returned upward in FIG. 2 so that the pressure roller 19 approaches the fixing roller 18. The detailed contact / separation operation by the cam member 41 will be described later.

  In addition, the fixing device 12 according to the present embodiment includes an optical sensor 51 and a light shielding member 52 as rotational position detection means for detecting the rotational position (rotation angle) of the cam member 41. The optical sensor 51 is a transmissive optical sensor and includes a light projecting unit that emits light and a light receiving unit that receives light emitted from the light projecting unit. The light shielding member 52 is a member to be detected whose rotational position is detected by the optical sensor 51 by rotating integrally with the cam member 41 to shield or transmit the irradiation light of the optical sensor 51 and switching the presence or absence of light reception. is there. The optical sensor 51 and the light shielding member 52 are provided only on one cam member 41 side of the two cam members 41.

FIG. 3 is a diagram illustrating the cam member, the light shielding member, and the optical sensor.
As shown in FIG. 3, the cam surface 41a provided on the cam member 41 is formed such that the distance from the rotation center gradually increases in the clockwise direction in the figure. The cam surface 41a is provided over a region larger than a half circumference (180 °) in the rotation direction. Specifically, in the present embodiment, the range from the lowest point e1 having the smallest distance from the rotation center of the cam surface 41a to the highest point e2 having the largest distance from the rotation center of the cam surface 41a is in a range of about 270 °. It is provided across.

  The light shielding member 52 is long in the rotational direction (the length in the rotational direction is X1) as a detection region, and is shorter in the rotational direction than the long light shielding portion 52a (the length in the rotational direction is X2). And a short light-shielding portion 52b as a detected region. Both the long light-shielding part 52a and the short light-shielding part 52b shield the irradiation light by passing through the light irradiation part L of the optical sensor 51 with rotation. In addition, a hole (translucent part) 52j that transmits the light emitted from the optical sensor 51 is formed between the long light-shielding part 52a and the short light-shielding part 52b.

FIG. 4 is a schematic configuration diagram of a drive system of the contact / separation mechanism according to the present embodiment.
As shown in FIG. 4, the drive system includes a motor 43 as a drive source and a gear train 44 that transmits the drive force from the motor 43 to the cam member 41 and the light shielding member 52. In the present embodiment, a small and inexpensive DC brush motor is used as the motor 43. The gear train 44 includes a first worm gear 45 attached to the output shaft of the motor 43, a second worm gear 46 that meshes with the first worm gear 45, and a first flat gear provided integrally with the second worm gear 46. A gear 47 and a second spur gear 48 that meshes with the first spur gear 47 and is provided integrally with the light shielding member 52 are configured. When the output shaft of the motor 43 rotates in one direction or in the opposite direction, the worm gears 45 and 46 and the spur gears 47 and 48 rotate, and the second spur gear 48 and the light shielding member 52 rotate integrally. Thus, each cam member 41 rotates in one direction (the direction indicated by arrow F in FIG. 3) or the opposite direction (the direction indicated by arrow G in FIG. 3) via the rotation shaft 42.

FIG. 5 is a block diagram of a control system of the contact / separation mechanism according to the present embodiment.
As shown in FIG. 5, the control system measures the rotation time of the control unit 60 that controls the rotation of the cam member 41, the optical sensor 51 for detecting the rotation position of the cam member 41, and the cam member 41. Timer 70 is provided. The control unit 60 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like provided in the image forming apparatus main body. The control unit 60 controls the rotation of the cam member 41 by controlling the driving of the motor 43 based on the signal detected by the optical sensor 51 and the time measured by the timer 70. The control unit 60 is also set to control the timing of the time measurement start by the timer 70 and the timing of the time measurement stop based on the signal detected by the optical sensor 51.

  By the way, when two sheets of paper such as envelopes are passed through the fixing nip, if the fixing roller and the pressure roller are pressed with the same pressure as when plain paper is passed, the paper is wrinkled. there is a possibility. For this reason, when a sheet such as an envelope is passed, it is preferable to form the fixing nip with a pressing force smaller than a normal pressing force when passing plain paper.

  Therefore, in the fixing device according to the present embodiment, as described above, the pressure roller can be moved toward and away from the fixing roller, so that the pressing force in the fixing nip can be changed according to the paper type. . Hereinafter, the depressurization operation when depressurizing from the normal pressurization force and the pressurization operation when returning to the normal pressurization force will be described.

First, the contact / separation operation of the pressure roller 19 by the cam member 41 will be described.
6A shows a state where the cam receiving portion 31d of the pressure lever is in contact with the cam surface 41a on the lowest point e1 side. In this state, the pressure roller approaches the fixing roller and is pressurized with a normal pressure.

  When the cam member 41 is rotated counterclockwise as shown in FIG. 6B from the state shown in FIG. 6A, the cam surface 41a slides relative to the cam receiving portion 31d. The contact position of the cam receiving portion 31d with respect to the cam surface 41a relatively moves from the lowest point e1 side to the highest point e2 side. Along with this, the cam receiving portion 31d is pushed downward by the cam surface 41a and the pressure lever is retracted from the bearing of the pressure roller, so that the pressure roller is separated from the fixing roller. Moving.

  Then, as shown in FIG. 6C, when the contact position of the cam receiving portion 31d with respect to the cam surface 41a reaches the uppermost point e2, the separation operation of the pressure roller with respect to the fixing roller is completed, and the addition at the fixing nip is completed. A depressurized state in which the pressure is smaller than the normal pressure is obtained. At this time, the rotation of the cam member 41 is stopped.

  On the contrary, from the depressurized state shown in FIG. 7A, the cam member 41 is rotated in the clockwise direction in the drawing as shown in FIG. 7B (the direction opposite to the rotational direction at the time of the depressurizing transition). When rotating, the cam surface 41a slides relative to the cam receiving portion 31d, and the contact position of the cam receiving portion 31d with respect to the cam surface 41a relatively moves from the uppermost point e2 side to the lowermost point e1 side. Along with this, the cam receiving portion 31d is pulled upward in the drawing by the urging force of the pressure spring, and the pressure lever presses the bearing of the pressure roller so that the pressure roller approaches the fixing roller. Move in the direction.

  As shown in FIG. 7C, when the contact position of the cam receiving portion 31d with the cam surface 41a reaches the lowest point e1, the approaching operation of the pressure roller with respect to the fixing roller is completed, and the fixing nip is completed. The pressure is returned to the normal pressurization state where the applied pressure is increased. At this time, the rotation of the cam member 41 is stopped.

  Thus, in the fixing device according to the present embodiment, the cam member 41 is rotated in one direction when the pressure roller is separated, and the cam member 41 is rotated in the reverse direction when the pressure roller is approached. Then, the pressing lever is pushed and moved using the same cam surface 41a. That is, in this embodiment, unlike the conventional configuration in which the cam member is rotated only in one direction, the cam surface whose distance from the rotation center gradually increases in the rotation direction and the distance from the rotation center in the rotation direction. Are not separated from the gradually decreasing cam surfaces, so that the range in which the respective cam surfaces can be secured is not limited to a half circumference in the rotational direction even at the maximum. For this reason, in the cam member 41 which concerns on this embodiment, the cam surface 41a can be provided over an area | region larger than the half periphery of a rotation direction. Accordingly, even if the gradient of the cam surface 41a is made gentle, it is possible to avoid a decrease in the maximum height difference of the gradient, so that the cam surface can be secured while ensuring a sufficient distance between the pressure roller and the fixing roller. It is possible to moderate the slope of 41a and suppress the increase in rotational torque and the generation of operating noise (abnormal noise).

  Next, a cam member rotation control method will be described.

First, the rotation control method during the depressurization operation will be described.
FIG. 8 is a diagram for explaining the rotation control method during the depressurization operation. The upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows the optical position. The timing chart by which the irradiation light of a sensor is interrupted | blocked or permeate | transmitted is shown. In addition, (a), (b), (c), and (d) in the upper, middle, and lower stages correspond to each other. FIG. 9 is a flowchart of the rotation control during the depressurization operation.

  8A, the cam receiving portion 31d of the pressure lever is in contact with the cam surface 41a on the lowest point e1 side, and the pressure roller is pressed with the pressure roller approaching the fixing roller. Normal pressure state. Further, in this state, the optical sensor 51 is in a light shielding state because the long light shielding portion 52a is disposed so as to overlap the light irradiation portion L.

  When an instruction to rotate the cam member 41 is issued from the control unit so as to change from this state to the depressurized state, the motor starts driving, and as shown in FIG. Starts to rotate counterclockwise (positive direction) at (S1 in FIG. 9). As a result, the cam receiving portion 31d is pushed downward by the cam member 41 in the figure.

  As the cam member 41 rotates, the light shielding member 52 also starts to rotate in the same direction (positive direction). Then, if normal, then, as shown in FIG. 8B, the optical sensor 51 is switched to the translucent state when the rear end portion in the rotation direction of the long light shielding portion 52a passes through the light irradiation portion L. It is done.

  However, here, when an abnormality occurs such that the light shielding member 52 does not rotate normally, there is a possibility that the light transmission state shown in FIG. Therefore, the control unit determines whether or not the switching to the light-transmitting state shown in FIG. 8B is performed within a preset time h1 after the rotation of the cam member 41 is started. (S2 in FIG. 9). In the present embodiment, the time h1 is a time obtained by adding a grace time α to a timer setting time T described later.

  As a result, when the light-transmitting state is switched within the preset time h1, it is determined that there is no abnormality, and the rotation of the cam member 41 is continued as it is (S3 in FIG. 9). On the other hand, if it does not switch to the translucent state even after the preset time h1, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue any more (S4 in FIG. 9). When the rotation of the cam member 41 is continued, the translucent state continues for a while after that, and the cam receiving portion 31d is pushed further downward by the cam member 41.

  Then, as shown in FIG. 8C, when the front end portion of the short light shielding portion 52b in the rotation direction reaches the light irradiation portion L as the light shielding member 52 rotates, the optical sensor 51 is switched to the light shielding state. (S5 in FIG. 9). At this time, a time t1 required for switching from the light transmission state shown in FIG. 8B to the light shielding state shown in FIG. 8C is calculated by the control unit, and this time t1 is calculated. It is determined whether or not it is longer than a preset time h2 (S6 in FIG. 9). Here, the preset time h2 is a normal time assumed to be required for switching from the light transmission state shown in FIG. 8B to the light shielding state shown in FIG. 8C. is there. In short, the portion from the rear end portion J in the rotation direction of the long light-shielding portion 52a shown in FIG. 10 to the front end portion K in the rotation direction of the short light-shielding portion 52b becomes the light irradiation portion L. This is the time that is expected to pass.

  As a result of the above determination, when the time t1 is equal to or longer than the preset time h2, the rotation of the cam member 41 is continued (S7 in FIG. 9). On the other hand, when the time t1 is shorter than the preset time h2, it is determined that there is an abnormality in the rotational position of the light shielding member 52, and the rotation of the cam member 41 is stopped (S8 in FIG. 9).

  Specifically, the abnormality here is that the decompression operation is not performed from the normal initial position where the long light shielding portion 52a overlaps the light irradiation portion L as shown in FIG. It is assumed that the short light-shielding part 52b as shown in FIG. In this case, the time t1 from switching to the light-transmitting state until switching to the light-blocking state corresponds to the passage time of the hole (light-transmitting portion) 52j, and thus becomes shorter than the preset time h2. In the case of an abnormality due to such an initial position shift of the light shielding member 52, the image forming apparatus is turned off and then turned on again, so that the light shielding member 52 has a normal initial position (a) shown in FIG. Therefore, the depressurization operation can be performed again from this state.

  When the rotation of the cam member 41 is continued from the state shown in FIG. 8 (c), as usual, immediately after that, as shown in FIG. Since the rear end portion passes through the light irradiation portion L, the optical sensor 51 is returned to the translucent state.

  Also here, the control unit determines whether or not there is an abnormality in the rotation of the light shielding member 52 or the like. Specifically, whether or not switching to the light transmission state shown in FIG. 8D is performed within a preset time h3 after switching to the light shielding state shown in FIG. Is determined by the control unit (S9 in FIG. 9). In the present embodiment, the time h3 is set to the same time (T + α) as the time h1.

  As a result, if the light-transmitting state is switched within the preset time h3, it is determined that there is no abnormality, and at the timing when the optical sensor 51 detects this switching to the light-transmitting state, the cam member An instruction to stop the rotation of 41 is issued (S10 in FIG. 9). As a result, the motor stops driving, and the rotation of the cam member 41 is stopped. On the other hand, if it does not switch to the translucent state even after the preset time h3, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue any more (S11 in FIG. 9).

  Here, there is a slight time difference from the instruction to stop the rotation of the cam member to the actual stop of the rotation of the cam member. At that time, if the rotation speed of the motor increases due to a change in the current value of the motor, a change in the load torque of the cam member, or other disturbance, the cam member is in a normal decompression state shown in FIG. It is conceivable that the motor further rotates beyond the stop position and shifts to a pressurized state. Therefore, in this embodiment, in order to determine whether or not there is such an abnormality, the control unit determines whether or not the light-transmitting state continues for a predetermined time h6 after instructing rotation stop of the cam member. Is confirmed (S12 in FIG. 9).

  When the light transmission state continues for a predetermined time h6, the depressurization operation is completed assuming that there is no abnormality (S13 in FIG. 9). On the other hand, when the translucent state does not continue for the predetermined time h6, the control unit determines that the cam member is stopped abnormally (S14 in FIG. 9). That is, in this case, as the rotational speed of the motor increases, the light shielding member 52 further rotates counterclockwise in the drawing from the light transmitting state shown in FIG. This is a case where the part 52a is in a light-shielding state overlapping the light irradiation part L. In this state, it is assumed that the cam member has shifted to the pressurized state beyond the stop position in the normal decompressed state. Therefore, when the translucent state does not continue for the predetermined time h6, measures such as notifying abnormality and repeating the depressurization operation again are taken.

Subsequently, a method for controlling the rotation of the cam member during the pressurizing operation for returning to the normal pressure will be described.
FIG. 12 is a diagram for explaining a cam member rotation control method during a pressurizing operation. The upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, The lower part shows a timing chart in which the light emitted from the optical sensor is blocked or transmitted. Further, (a), (b), (c), (d), and (e) of the upper, middle, and lower stages correspond to each other. FIG. 13 is a flowchart of the rotation control during the pressurizing operation.

  12A shows a depressurized state where the pressure roller is separated from the fixing roller. In this state, the cam member 41 and the light shielding member 52 are in a position where the rotation operation is normally stopped by the control during the depressurization operation. That is, the cam receiving portion 31d of the pressure lever is in contact with the cam surface 41a on the uppermost point e2 side, and the optical sensor 51 is configured such that the hole (translucent portion) 52j overlaps the light irradiation portion L. It is in a translucent state.

  When an instruction to rotate the cam member 41 is issued from the controller so that the depressurized state becomes a normal pressurized state, the motor starts driving, and as shown in FIG. The member 41 starts to rotate clockwise (reverse direction) in the drawing (S1 in FIG. 13). As a result, the cam receiving portion 31d is pulled upward in the figure by the urging force of the pressurizing spring, contrary to the transition to the depressurization transition.

  As the cam member 41 rotates, the light blocking member 52 also starts to rotate in the same direction (reverse direction). Then, if normal, immediately after that, as shown in FIG. 12B, the optical sensor 51 is switched to the light shielding state by the front end portion in the rotation direction of the short light shielding portion 52 b overlapping the light irradiation portion L. .

  Also in this case, in order to check whether there is an abnormality in the rotation of the light shielding member 52 or the like, the light shielding state shown in FIG. 12B is changed in advance after the rotation of the cam member 41 is started. It is judged by the control part whether it is performed within the set time h4 (S2 in FIG. 13). In the present embodiment, this time h4 is set to a time required for the cam member 41 to make one rotation.

  As a result, when switching to the light shielding state within a preset time h4, it is determined that there is no abnormality, the rotation of the cam member 41 is continued as it is, and the timing at which switching to the light shielding state is detected. Thus, time measurement by the timer is started (S3 in FIG. 13). On the other hand, if it does not switch to the light-shielded state even after the preset time h4, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue any more (S4 in FIG. 13).

  Here, the time measured by the timer is set in advance, and a signal for stopping the cam member is issued from the control unit when the timer finishes measuring the preset time. However, the time measurement by the timer continues as long as the light shielding state of the optical sensor continues, but if the timer switches from the light shielding state to the translucent state before completing the time measurement, the time measurement by the timer is halfway. Is set to be canceled.

  With respect to the timer set in this way, the short light-shielding part 52b is formed so that the passing time passing through the light irradiation part L during rotation is shorter than the set time T of the timer. Therefore, usually, after switching to the light shielding state shown in FIG. 12 (b), the short light shielding part 52b immediately passes through the light irradiation part L as shown in FIG. 12 (c). The light shielding duration t2 at is shorter than the set time T of the timer. However, it is also conceivable that the light shielding duration t2 here becomes longer due to some abnormality.

  Therefore, in this embodiment, the control unit determines whether or not the light shielding duration t2 is shorter than the set time T of the timer (S5 in FIG. 13). As a result, when the light shielding duration t2 is shorter than the timer setting time T, it is determined that there is no abnormality, and the rotation of the cam member 41 is continued (S6 in FIG. 13). In this case, since the timer is switched to the translucent state before measuring the set time T, the time measurement by the timer is canceled halfway as described above (S6 in FIG. 13).

  On the other hand, when the light shielding duration t2 continues for the set time T of the timer, the pressurizing operation is not performed from the normal depressurization position as shown in FIG. 14A but in FIG. 14B. The case where it starts from the non-regular position as shown is assumed. In this case, not the short light shielding part 52b but the long light shielding part 52a passes through the light irradiation part L.

  The long light-shielding part 52a is formed so that the transit time passing through the light irradiation part L during rotation is longer than the set time T of the timer. Therefore, the light blocking state by the long light blocking unit 52a continues during the time measurement by the timer. For this reason, when the timer finishes measuring the set time T, a signal for stopping the cam member 41 is issued from the control unit, and the rotation of the cam member 41 is stopped (S7 in FIG. 13). In this case, as a result, the cam member 41 is stopped at the normal stop position (pressurized state).

  As described above, when the time measurement by the timer is canceled by the passage of the short light-shielding portion 52b, the translucent state continues for a while, and the cam receiving portion 31d further moves upward as the cam member 41 rotates. Be raised. Thereafter, as shown in FIG. 12D, when the front end portion in the rotation direction of the long light-shielding portion 52a reaches the light irradiation portion L, the light-shielding state is switched again.

  Also in this case, in order to confirm whether or not an abnormality occurs in the rotation of the light shielding member 52, the light transmission state shown in FIG. 12C is switched to the light shielding state shown in FIG. It is determined by the control unit whether or not it is performed within a preset time h5 after switching to (S8 in FIG. 13). In the present embodiment, the time h5 is set to a time required for the cam member 41 to make one rotation, similarly to the time h4.

  As a result, when the light-shielding state is switched within the preset time h5, it is determined that there is no abnormality, the rotation of the cam member 41 is continued as it is, and the timing when the switching to the light-shielding state is detected. Thus, the time measurement by the timer is started again from the beginning (S9 in FIG. 13). On the other hand, if it does not switch to the light-shielding state even after the preset time h5, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue (S10 in FIG. 13).

  Then, when the rotation of the cam member 41 is continued and the time measurement by the timer is started again from the beginning, the light shielding state by the long light shielding unit 52a is continued, so the light shielding state continues during the time measurement by the timer. As a result, as shown in FIG. 12E, when the timer finishes measuring the set time T, a signal for stopping the cam member 41 is issued from the control unit (S11 in FIG. 13). Then, upon receiving this stop instruction, the motor stops driving, and the rotation of the cam member 41 is completely stopped. As a result, the pressure roller is held in a normal pressure state approaching the fixing roller, and the pressure operation is completed.

  As described above, in this embodiment, the rotation of the cam member during the decompression operation is stopped based on the detection timing of the optical sensor (see S10 in FIG. 9). The rotation of the member is stopped based on the timing of time measurement by a timer (see S11 in FIG. 13). That is, in this embodiment, the timing determination means for controlling the stop position of each cam member at the time of decompression operation and pressurization operation is divided into an optical sensor and a timer. On the other hand, when performing rotation control at the time of depressurization operation and pressurization operation only by position detection by the optical sensor, an optical sensor for detecting the rotational position of the cam member at the time of depressurization operation, and pressurization operation It is necessary to separately provide an optical sensor for detecting the rotational position of the cam member. Therefore, as in the present embodiment, one of the optical sensors can be omitted by performing one control during the pressurizing operation and the depressurizing operation by measuring the time with a timer, and the configuration in which two optical sensors are provided Compared to the above, there is an advantage that cost and size can be reduced.

  In this embodiment, since a small and inexpensive DC brush motor is used as a motor for driving the cam member to rotate, it is advantageous for cost reduction and size reduction. However, in the case of using a DC brush motor, during the pressure-removing operation in which the pressure lever is pushed by the cam member, the rotational torque increases as the pressure roller approaches the pressure-removal position, thereby increasing the variation in the rotation speed of the motor. There is a problem. Therefore, in this embodiment, the rotation stop control of the cam member during the depressurization operation is performed based on the detection timing by the optical sensor so that the rotation stop position of the cam member is not affected by the variation in the rotation speed of the motor. I am doing so. By detecting the rotational position of the light shielding member by the optical sensor, the cam member can be reliably stopped at the predetermined rotational position regardless of variations in the rotational speed of the motor, so the accuracy of the rotational stop position of the cam member is improved. improves.

  On the other hand, during the pressurizing operation, the pressurizing lever is not pushed and moved by the cam member, so that the influence of the variation in the motor rotation speed due to the increase in rotational torque is small. For this reason, during the pressurizing operation, the rotational position of the cam member is controlled not by an optical sensor but by a timer. However, during the pressing operation, when the pressing force by the cam member is released, a force in the direction of accelerating the rotation is applied from the pressing lever to the cam member. Thereby, when the rotation speed of the cam member changes, there is a possibility that the rotation stop position of the cam member may vary during the pressurizing operation in which the rotation of the cam member is controlled by measuring time with a timer. For this reason, in this embodiment, a worm gear is used as the driving force transmission means for transmitting the rotational driving force to the cam member (see FIG. 4). The worm gear has a so-called self-locking function that does not rotate the input side gear even when the rotational force is input from the output side gear. For this reason, even if the force which tries to speed up rotation acts with respect to a cam member, the acceleration of a cam member can be prevented by the self-lock function of a worm gear. Thereby, the dispersion | variation in the rotation stop position accompanying the change of the rotational speed of a cam member can be suppressed, and the precision of the rotation stop position of a cam member improves. Moreover, generation | occurrence | production of the operation sound (abnormal noise) accompanying a cam member's acceleration can also be suppressed.

  There is also some variation in time measurement by the timer. Since this variation increases as the measurement time continues, it is desirable that the measurement time be as short as possible. Therefore, in the present embodiment, in order to shorten the measurement time by the timer during the pressurizing operation, the short light shielding unit 52b is provided, and the time measurement started at the light shielding timing of the short light shielding unit 52b is canceled. Yes. That is, the time measurement started at the light shielding timing by the short light shielding unit 52b is canceled halfway, and then the time measurement from the light shielding timing by the long light shielding unit 52a to the rotation stop timing is performed, thereby the short light shielding unit 52b to the long light shielding unit. It is possible to prevent time measurement from continuing until 52a. As a result, the measurement time can be shortened compared to the case where the time measurement is continuously performed from the first light shielding timing to the rotation stop timing, so that variations in time measurement by the timer are reduced, and the rotational position control of the cam member is reduced. Accuracy can be improved.

FIG. 15 is a diagram showing another embodiment of the light shielding member.
The light shielding member 52 shown in FIG. 15 has a plurality of short light shielding portions 52b to 52i in the rotation direction. The lengths X2 to X9 in the rotation direction of the respective short light shielding portions 52b to 52i are set so that the passing time with respect to the light irradiation unit L during rotation is shorter than the set time T of the timer, as in the above embodiment. Yes. On the other hand, the length X1 in the rotation direction of the long light-shielding part 52a is set so that the passing time with respect to the light irradiation part L during rotation is longer than the set time T of the timer.

  Hereinafter, a method for controlling the rotation of the cam member when the light shielding member according to another embodiment is used will be described.

First, the rotation control method during the depressurization operation will be described.
FIG. 16 is a diagram for explaining the rotation control method during the depressurization operation. The upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows the optical position. The timing chart by which the irradiation light of a sensor is interrupted | blocked or permeate | transmitted is shown. Also, (a), (b), (c), (d), (l), and (m) in the upper, middle, and lower stages correspond to each other.

  When the cam member 41 starts rotating counterclockwise (positive direction) in the drawing from the normal pressurization state shown in FIG. 16A, the cam receiving portion 31d is moved as shown in FIG. The cam member 41 is pushed downward in the figure. Simultaneously with the start of rotation of the cam member 41, the light shielding member 52 also rotates in the same direction (forward direction), and the rear end portion in the rotational direction of the long light shielding portion 52a is irradiated with light as shown in FIG. The light passing through the portion L is switched from the light shielding state to the light transmitting state.

  Then, as shown in FIGS. 16C and 16D, when the first short light-shielding part 52b reaches the light irradiation part L, it is switched to the light-shielding state, and then the short light-shielding part 52b is changed to the light irradiation part L. It can be switched to the translucent state by passing through. Thereafter, each time the second and subsequent short light-shielding parts 52c to 52i pass through the light irradiation part L, the light-shielding state and the light-transmitting state are repeated in the same manner.

  Then, as shown in (l) and (m) of FIG. 16, when the last short light-shielding part 52i reaches the light irradiation part L and is switched from the light-shielding state to the light-transmitting state, the cam is reached at this timing. An instruction to stop the rotation of the member 41 is issued. As a result, the rotation of the cam member 41 is stopped, and the pressure roller enters a pressure-removed state in which the pressure roller is separated from the fixing roller. In this depressurization operation as well, as in the flow described with reference to FIG. 9 above, the presence or absence of abnormality is determined by the control unit, but the description thereof is omitted here.

  In the control in the case where the light shielding member according to the other embodiment is used, the rotation stop instruction of the cam member 41 is performed based on the light transmission switching timing by the last short light shielding unit 52i. It is also possible to stop the cam member 41 based on the light transmission switching timing by 52b to 52h. That is, the cam member 41 can be stopped based on any one of timings (d) to (k) in addition to the timing shown in (m) of FIG.

  As described above, in another embodiment of the present invention, by providing a plurality of short light shielding portions, one of these is selected, and the selected short light shielding portion switches the light shielding state to the light transmitting state. The cam member can be stopped at the same timing. Thereby, the rotation stop position of the cam member can be finely adjusted, and the applied pressure in the fixing nip can be changed in multiple stages.

Then, the rotation control method at the time of the pressurization operation | movement at the time of using the light shielding member which concerns on other embodiment is demonstrated.
FIG. 17 is a diagram for explaining a rotation control method during a pressurizing operation. The upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows the optical position. The timing chart by which the irradiation light of a sensor is interrupted | blocked or permeate | transmitted is shown. In addition, (a), (b), (c), (k), and (l) in the upper, middle, and lower stages correspond to each other.

  When the cam member 41 starts rotating in the clockwise direction (reverse direction) in the drawing from the depressurized state shown in FIG. 17A, as shown in FIG. The cam receiving portion 31d is pulled upward in the figure by the urging force of the pressure spring. Further, simultaneously with the start of rotation of the cam member 41, the light shielding member 52 also rotates in the same direction (reverse direction), and the first short light shielding portion 52i becomes the light irradiation portion L as shown in FIGS. The short light-shielding portion 52i is switched to the light-transmitting state by passing through the light irradiation portion L immediately thereafter.

  At this time, the time measurement by the timer is started at the timing when the light-shielding state shown in FIG. 17B is switched, but the light-shielding duration by the short light-shielding part 52i is based on a preset timer setting time T. Since it is short, the time measurement by the timer is canceled halfway as in the above embodiment. Thereafter, each time the second and subsequent short light-shielding parts 52h to 52b pass through the light irradiation part L, the light-shielding state and the light-transmitting state are repeated, and the time measurement started at the light-shielding timing by these short light-shielding parts 52h to 52b is also the same. Canceled by

  Then, as shown in FIG. 17 (k), when the long light shielding portion 52a reaches the light irradiation portion L, the light shielding portion 52a is switched to the light shielding state. Be started. At this time, since the light shielding duration time by the long light shielding unit 52a is longer than the preset timer setting time T, the light shielding state continues during the time measurement by the timer. Then, as shown in (l) of FIG. 17, when the timer finishes measuring the set time T, an instruction to stop the rotation of the cam member 41 is issued. As a result, the rotation of the cam member 41 is stopped, and a pressure state is reached in which the pressure roller approaches the fixing roller. Note that the flow for determining whether or not there is an abnormality in the pressurizing operation is basically the same as the flow described with reference to FIG.

  Thus, also in other embodiments, the measurement time by the timer can be shortened as in the above embodiment by canceling the time measurement started at the light shielding timing by each of the short light shielding units 52b to 52i. it can. Thereby, the variation in time measurement by the timer is reduced, and the accuracy of the rotational position control of the cam member can be improved.

  Further, as described above, when the pressing force in the fixing nip can be changed in multiple stages, as shown in the example shown in FIG. 18, between the lowest point e1 and the highest point e2 of the cam surface 41a, One or a plurality of flat surfaces 41b orthogonal to the radial direction may be provided. Each flat surface 41b is disposed at a position where the pressure lever (cam receiving portion) contacts the cam surface 41a when the rotation of the cam member 41 is stopped. By providing such a flat surface 41b, the pressure applied from the pressure lever is likely to act in the direction perpendicular to the rotation direction (radial direction), and therefore the rotational force applied to the cam member 41 can be increased. Thus, the position of the cam member 41 in the rotational direction can be more reliably held.

  In the above embodiment, the light shielding member is provided with the long light shielding portion and the short light shielding portion, and the rotation of the cam member is controlled by the optical sensor detecting the switching between the light shielding and the light transmission by these. The rotation of the cam member can be similarly controlled by reversing the light shielding portion and the light transmitting portion.

  In the example shown in FIG. 19, the light shielding part and the light transmitting part of the light shielding member 52 shown in FIG. 3 are interchanged. That is, the light shielding member 52 shown in FIG. 19 has a long light transmitting portion 52m long in the rotation direction and a short light transmitting portion 52n short in the rotation direction instead of the long light shielding portion 52a and the short light shielding portion 52b shown in FIG. doing. The other part is a light shielding part that shields the irradiated light when intervening in the light irradiation part L. When the light shielding member 52 is used, the light shielding timing and the light transmission timing are opposite to those in the above embodiment. Therefore, if the “light shielding” and “translucent” are switched and controlled, the rotation control of the cam member can be performed using the same control method. Further, such a light shielding member in which the light shielding portion and the light transmitting portion are interchanged may be configured to have a plurality of short light transmitting portions following the light shielding member 52 shown in FIG.

  Further, as the rotation position detecting means for detecting the rotation position of the cam member, a reflection type optical sensor can be used in addition to the transmission type optical sensor. In this case, a cam member that uses the same control method as in the above embodiment by using a reflective member that reflects light in the same shape as the light shielding member 52 shown in FIG. 3 as the reflective member that reflects the irradiation light of the optical sensor. It is possible to perform rotation control. That is, if the reflecting member 53 having the long reflecting portion 53a that is long in the rotating direction and the short reflecting portion 53b that is short in the rotating direction as shown in FIG. 20 is used, the “light shielding” in the control flow is simply changed to “reflecting”. Similarly, it is possible to control the rotation of the cam member. Further, the reflecting member may be configured to have a plurality of short reflecting portions, following the light shielding member 52 shown in FIG.

  In the above embodiment, in order to omit the optical sensor, the rotation control of the cam member is performed using a timer. However, the rotation control of the cam member may be performed using two optical sensors.

FIG. 21 is a schematic configuration diagram of a contact / separation mechanism using two optical sensors.
The contact / separation mechanism shown in FIG. 21 includes a depressurization position sensor (first optical sensor) 49 for detecting the rotational position of the cam member 41 during the depressurization operation, and the rotational position of the cam member 41 during the pressurization operation. And a pressure position sensor (second optical sensor) 50 for detecting the above. The light shielding member 52 used here does not have a long light shielding portion or a short light shielding portion like the light shielding member according to the above-described embodiment, and may be in a general shape such as a sector shape or a rectangular shape. The drive system is the same as the drive system (see FIG. 4) according to the above embodiment.

  With reference to FIG. 22 and FIG. 23, the rotation control method of the cam member at the time of the depressurization operation when two optical sensors are used will be described. In FIG. 22, the upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows that the irradiation light of the pressurization position sensor and the decompression position sensor is blocked or blocked. The transmitted timing chart is shown. In addition, (a), (b), and (c) of the upper, middle, and lower stages correspond to each other.

  In the normal pressurization state shown in FIG. 22A, the pressurization position sensor 50 is switched to the light-shielding state by the light-shielding member 52. From this state, as shown in FIG. 22B, when the cam member 41 rotates counterclockwise (positive direction) in the drawing (S1 in FIG. 23), the light shielding member 52 also rotates in the same direction, and the light shielding member. The rear end portion in the rotation direction of 52 passes through the light irradiation portion L of the pressurizing position sensor 50 and is switched to the light transmitting state. Further, at this time, the control unit determines whether or not the switching to the translucent state is performed within a preset time h7 after the rotation of the cam member 41 is started (S2 in FIG. 23). ).

  As a result, when the pressurization position sensor 50 switches to the translucent state within the preset time h7, it is determined that there is no abnormality and the rotation of the cam member 41 is continued as it is (S3 in FIG. 23). . On the other hand, if the pressure position sensor 50 does not switch to the translucent state even after a preset time h7, it is determined that there is an abnormality and the cam member 41 is stopped so as not to continue rotating ( S4 in FIG.

  Thereafter, the rotation of the cam member 41 is continued. As shown in FIG. 22C, when the front end portion of the light shielding member 52 in the rotation direction overlaps the light irradiation part L of the pressure release position sensor 49, the pressure release position sensor. 49 is switched from the light transmitting state to the light blocking state. Further, at this time, whether or not to switch to the light shielding state is performed within a preset time h8 after the pressure position sensor 50 shown in FIG. 22B switches to the light transmitting state. The determination is made by the control unit (S5 in FIG. 23).

  When the depressurization position sensor 49 switches to the light shielding state within a preset time h8, it is determined that there is no abnormality, and at the timing when the switch to the light shielding state is detected, the control unit detects the cam member. An instruction to stop the rotation of 41 is issued (S6 in FIG. 23). Thereby, the rotation of the cam member 41 is stopped and the depressurization operation is completed. On the other hand, if the depressurization position sensor 49 does not switch to the light-shielding state even after a preset time h8, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue (see FIG. 23 S7).

  Next, a method for controlling the rotation of the cam member during the pressurizing operation when two optical sensors are used will be described with reference to FIGS. In FIG. 24, the upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows that each irradiation light of the pressurization position sensor and the decompression position sensor is blocked The transmitted timing chart is shown. In addition, (a), (b), and (c) of the upper, middle, and lower stages correspond to each other.

  When the cam member 41 rotates in the clockwise direction (reverse direction) in the drawing (S1 in FIG. 25) from the depressurized state shown in FIG. 24 (a), as shown in FIG. Rotating in the same direction, the rear end portion of the light shielding member 52 in the rotational direction passes through the light irradiation part L of the decompression position sensor 49, so that the light transmission state is switched. Further, at this time, the control unit determines whether or not switching to the translucent state is performed within a preset time h9 after the rotation of the cam member 41 is started (S2 in FIG. 25). ).

  As a result, if the depressurization position sensor 49 switches to the light transmitting state within a preset time h9, it is determined that there is no abnormality, and the rotation of the cam member 41 is continued as it is (S3 in FIG. 25). . On the other hand, if the depressurization position sensor 49 does not switch to the translucent state even after a preset time h9, it is determined that there is an abnormality and the cam member 41 is stopped so as not to continue rotating ( S4 in FIG.

  Thereafter, the rotation of the cam member 41 is continued, and when the front end portion of the light shielding member 52 in the rotation direction overlaps the light irradiation portion L of the pressure position sensor 50 as shown in FIG. 50 is switched from the light transmitting state to the light blocking state. Further, at this time, whether or not to switch to the light shielding state is performed within a preset time h10 after the depressurization position sensor 49 shown in FIG. 24 (b) switches to the light transmitting state. The determination is made by the control unit (S5 in FIG. 25).

  When the pressure position sensor 50 is switched to the light shielding state within a preset time h10, it is determined that there is no abnormality, and at the timing when the switching to the light shielding state is detected, the control unit detects the cam member. An instruction to stop the rotation of 41 is issued (S6 in FIG. 25). Thereby, the rotation of the cam member 41 is stopped and the pressurizing operation is completed. On the other hand, if the pressure position sensor 50 does not switch to the light-shielding state even after the preset time h10 has elapsed, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue (see FIG. 25 S7).

  As described above, when two optical sensors are used, the rotation of the cam member can be controlled without using a timer. Therefore, the configuration using two optical sensors is disadvantageous in terms of cost reduction and downsizing compared to the configuration using a timer and one optical sensor, but there is no influence of variations in time measurement by the timer. There is an advantage that the rotation stop position accuracy of the cam member is improved and the control can be easily performed.

  In the above embodiment, a small and inexpensive DC brush motor is used as a drive source for the contact / separation mechanism. However, a DC brushless motor may be used instead of the DC brush motor.

FIG. 26 shows a schematic configuration of a contact / separation mechanism using a DC brushless motor.
In the configuration shown in FIG. 26, two electromagnetic clutches as drive transmission switching means are provided (electromagnetic clutches 62, 63) so that the driving force of the DC brushless motor 61 can be switched and transmitted to the contact / separation mechanism and the other devices. I have to. In order to transmit the driving force to the contact / separation mechanism, the electromagnetic clutch 62 for the contact / separation mechanism is switched to a transmittable state where the driving force can be transmitted, and the electromagnetic clutch 63 for the other device is switched to a disconnected state where the driving force is not transmitted. In this case, the driving force of the DC brushless motor 61 is transmitted to the electromagnetic clutch 62 for the contact / separation mechanism after the transmission direction is changed by 90 ° by the motion conversion mechanism 64 including a pair of helical gears or a pair of bevel gears meshing with each other. Is done. The driving force is transmitted from the electromagnetic clutch 62 for the contact / separation mechanism to the light shielding member 52 and the cam member 41 via the worm gear 65. On the other hand, in order to transmit the driving force to another device, the electromagnetic clutch 62 for the contact / separation mechanism is switched to a shut-off state in which the driving force is not transmitted and the electromagnetic clutch 63 for the other device is transmitted to the other device. Switch to a possible transmission state.

  Thus, when a DC brushless motor is used as a drive source for the contact / separation mechanism, the drive source for the contact / separation mechanism can be shared with a drive source for a device other than the contact / separation mechanism, thereby saving power. I can plan. Further, since the rotation speed of the DC brushless motor can be controlled, the rotation stop position accuracy of the cam member is improved as compared with the case where the DC brush motor is used.

  FIG. 27 and FIG. 28 show control flowcharts when a DC brushless motor is used. FIG. 27 is a flowchart during the depressurization operation, and FIG. 28 is a flowchart during the pressurization operation.

  The depressurization operation shown in FIG. 27 and the pressurization operation shown in FIG. 28 are basically the same as the control (control shown in FIGS. 9 and 13) when the DC brush motor is used. However, in the configuration using the DC brushless motor, in order to perform switching of the electromagnetic clutch, a portion indicated by a dotted frame in each of FIGS. 27 and 28 is added. That is, before starting the depressurization operation or pressurization operation, the DC brushless motor is stopped, the electromagnetic clutch for the other device is switched to the disconnected state, and the electromagnetic clutch for the contact / separation mechanism is switched to the transmittable state. Depressurization operation or pressurization operation is started. Thereafter, when the depressurization operation or pressurization operation is completed, the electromagnetic clutch for the contact / separation mechanism is returned to the disconnected state.

  Further, in a configuration using a DC brushless motor, rotation control of the cam member may be performed using two optical sensors.

FIG. 29 shows a schematic configuration of a contact / separation mechanism using a DC brushless motor as a drive source and further using two optical sensors.
In FIG. 29, reference numeral 49 denotes a depressurization position sensor (first optical sensor) for detecting the rotation position of the cam member 41 during the depressurization operation, and reference numeral 50 denotes the rotation position of the cam member 41 during the pressurization operation. This is a pressure position sensor (second optical sensor) for detection. The light shielding member 52 used here may be of a general shape. The drive system is the same as the drive system shown in FIG.

  FIG. 30 and FIG. 31 show flowcharts of control when a DC brushless motor is used and two optical sensors are used. FIG. 30 is a flowchart during the depressurization operation, and FIG. 31 is a flowchart during the pressurization operation.

  The depressurization operation shown in FIG. 30 and the pressurization operation shown in FIG. 31 are basically the same as the control (control shown in FIGS. 23 and 25) in the case of using the two optical sensors. However, in the configuration using the DC brushless motor, in order to switch the electromagnetic clutch, a portion indicated by a dotted frame in each of FIGS. 30 and 31 is added. That is, before starting the depressurization operation or pressurization operation, the DC brushless motor is stopped, the electromagnetic clutch for the other device is switched to the disconnected state, and the electromagnetic clutch for the contact / separation mechanism is switched to the transmittable state. Depressurization operation or pressurization operation is started. Thereafter, when the depressurization operation or pressurization operation is completed, the electromagnetic clutch for the contact / separation mechanism is returned to the disconnected state.

  Even when a DC brushless motor is used, the rotation of the cam member can be controlled without using a timer by using two optical sensors. Therefore, compared to a configuration using a timer and one optical sensor, it is disadvantageous in terms of cost reduction and miniaturization, but since there is no influence of variation in time measurement by the timer, the rotation stop position accuracy of the cam member is improved. In addition, control can be easily performed.

  Moreover, in the said embodiment, although the worm gear was used in order to prevent the speed change of a cam member, it can also be set as the structure which does not use a worm gear. Specifically, by using a stepping motor instead of the DC brush motor, it is possible to realize a configuration that does not use a worm gear.

FIG. 32 is a schematic configuration diagram of a drive system of a contact / separation mechanism using a stepping motor.
When the stepping motor is energized, the stepping motor can hold the rotational position by the exciting force. For this reason, if a stepping motor is used, acceleration of the cam member can be prevented without using the worm gear, even if a force to accelerate the rotation is applied to the cam member. Therefore, as shown in FIG. 32, in the configuration using the stepping motor 55, the gear train 56 that interlocks and connects the stepping motor 55, the cam member 41, and the light shielding member 52 is configured by only a plurality of spur gears 57 to 59. can do. As described above, in the configuration using the stepping motor, the worm gear need not be used in order to prevent the speed change of the cam member, so that the design becomes easy.

  On the other hand, the configuration using the worm gear has an advantage that electric energy can be saved because acceleration of the cam member can be prevented by the self-locking function even when the power is not supplied as in the stepping motor. In addition, the use of the worm gear can reduce the number of gears that ensure the reduction ratio, which is advantageous for cost reduction and size reduction.

  In addition to the characteristics that can maintain the rotational position as described above, the stepping motor rotates in units of steps determined by periodically applying pulse signals, so the rotation angle and rotation speed of the cam member can be controlled with high accuracy. can do. Therefore, it is possible to eliminate a sensor for controlling the rotation stop position of the cam member during the depressurization operation and the pressurization operation. However, in the example shown in FIG. 32, when the cam member stops rotating at a position different from the normal because the power of the image forming apparatus is turned off during the operation of the cam member, An optical sensor 54 for returning to the initial position is provided.

  With reference to FIG. 33 and FIG. 34, the rotation control method of the cam member at the time of the depressurization operation when the stepping motor is used will be described. 33, the upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows a timing chart where the light emitted from the optical sensor is blocked or transmitted. Further, (a) and (b) in the upper, middle, and lower stages correspond to each other.

  In the normal pressure state shown in FIG. 33A, the optical sensor 54 is not shielded by the light shielding member 52 and is in a light-transmitting state. From this state, as shown in FIG. 33 (b), when the cam member 41 rotates counterclockwise (positive direction) in the figure (S1 in FIG. 34), the light shielding member 52 also rotates in the same direction. The front end portion in the rotation direction of 52 overlaps with the light irradiation portion L of the optical sensor 54, so that the light shielding state is switched. Further, at this time, the control unit determines whether or not switching to the light shielding state is performed within a preset time h11 after the rotation of the cam member 41 is started (S2 in FIG. 34). .

  As a result, when the light-shielding state is switched within the preset time h11, it is determined that there is no abnormality, and an instruction to stop the rotation of the cam member 41 is issued from the control unit at the timing when the light-shielding state is switched. (S3 in FIG. 34). Thereby, the rotation of the cam member 41 is stopped and the depressurization operation is completed. On the other hand, if it does not switch to the light-shielding state even after the preset time h11, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue any more (S4 in FIG. 34).

  Next, with reference to FIG. 35 and FIG. 36, a method for controlling the rotation of the cam member during the pressurizing operation when the stepping motor is used will be described. 35, the upper part of the figure shows the rotational position of the light shielding member, the middle part of the figure shows the rotational position of the cam member, and the lower part of the figure shows a timing chart in which the light emitted from the optical sensor is blocked or transmitted. In addition, (a), (b), and (c) of the upper, middle, and lower stages correspond to each other.

  When the cam member 41 rotates in the clockwise direction (reverse direction) in the drawing (S1 in FIG. 36) from the depressurized state shown in FIG. 35 (a), as shown in FIG. The light is rotated in the same direction, and the rear end portion of the light shielding member 52 in the rotational direction passes through the light irradiation portion L of the optical sensor 54 to be switched to the light transmitting state. Further, at this time, the control unit determines whether or not the switching to the translucent state is performed within a preset time h12 after the rotation of the cam member 41 is started (S2 in FIG. 36). ).

  As a result, if the light-transmitting state is switched within the preset time h12, it is determined that there is no abnormality, and the rotation of the cam member 41 is continued as it is (S3 in FIG. 36). On the other hand, if it does not switch to the translucent state after the preset time h12, it is determined that there is an abnormality and the rotation of the cam member 41 is stopped so as not to continue (S4 in FIG. 36).

  When the rotation of the cam member 41 is continued, the motor is driven a predetermined number of steps after the light transmission state. Then, at the timing when the motor is driven by a predetermined number of steps, an instruction to stop the rotation of the cam member 41 is issued from the control unit (S5 in FIG. 36). Thereby, the rotation of the cam member 41 is stopped and the pressurizing operation is completed.

  As described above, when the stepping motor is used, the cam member can be stopped at a desired rotational position without using the optical sensor by driving the stepping motor a predetermined number of steps. Further, since the rotation of the cam member can be controlled without using a timer, the rotation stop position accuracy of the cam member is improved. In the above flow, an optical sensor is used to detect the decompression position, but the cam member is stopped at a predetermined decompression position by managing the number of steps of the stepping motor without using the optical sensor. It is also possible to make it.

  In the above embodiment, the case where the present invention is applied to a fixing device that changes the pressure depending on the paper type is given as an example, but the present invention is not limited to the case where the pressure is changed for such a purpose. For example, in the present invention, the pressure is reduced in order to make it easier to remove the jammed paper from the fixing nip, or the pressure is reduced after passing to suppress plastic deformation of the pressure roller and the fixing roller due to the pressure. This is also applicable to cases where The present invention can also be applied to a fixing device in which the pressure roller is completely separated from the fixing roller (non-contact state) when the pressure is released.

  The fixing device to which the present invention is applied is not limited to a fixing device including a pair of rollers (a fixing roller and a pressure roller) as in the above embodiment. For example, a fixing device 80 including an endless fixing belt 83 may be used instead of the fixing roller as shown in FIG. In this example, a heating source 82 and a nip forming member 81 are disposed on the inner peripheral side of the fixing belt 83, and the pressure roller 84 is pressed against the fixing belt 83 at the position of the nip forming member 81. A fixing nip N is formed.

  Furthermore, the fixing device to which the present invention is applied is not limited to the fixing device in which the pressure roller approaches and separates from the fixing roller as in the above-described embodiment, and the fixing roller 91 is the same as the example shown in FIG. A fixing device 90 that approaches and separates from the opposing counter roller 92 may be used.

  The contact / separation mechanism according to the present invention is applicable not only to a fixing device but also to a transfer device that transfers an image to a recording medium such as paper.

FIG. 39 is a schematic configuration diagram of a color image forming apparatus equipped with a transfer device having a contact / separation mechanism.
First, the overall configuration and operation of the image forming apparatus will be described with reference to FIG.

  An image forming apparatus 200 shown in FIG. 39 includes an image forming unit 201, a paper feeding unit 202, a scanner unit 203, a transfer device 206, a conveyance belt 207, a fixing device 208, a paper discharge unit 230, an automatic document conveyance device 204, and the like.

  The image forming unit 201 includes four process units 210Y and 210M for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to color separation components of a color image. , 210C, 210K. Each of the process units 210Y, 210M, 210C, and 210K has the same configuration except that it contains developers of different colors.

  Specifically, each of the process units 210Y, 210M, 210C, and 210K includes a drum-shaped photosensitive member 211 as a latent image carrier, a charging device 212 that charges the surface of the photosensitive member 211, and a latent image on the photosensitive member 211. A developing device 213 for supplying a developer to the photosensitive member 211, a cleaning device 214 for cleaning the surface of the photosensitive member 211, and the like. In FIG. 1, only the photoconductor 211, the charging device 212, the developing device 213, and the cleaning device 214 included in the yellow process unit 210 </ b> Y are denoted by reference numerals, and the other process units 210 </ b> M, 210 </ b> C, and 210 </ b> K are denoted by reference numerals. Omitted.

  Further, the image forming unit 201 includes an optical writing unit 205. The optical writing unit 205 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and is configured to irradiate the surface of each photoconductor 211 with laser light based on image data.

  The transfer device 206 includes an intermediate transfer belt 216 as an intermediate transfer member, a belt cleaning device 220, a stretching roller 217, a driving roller 218, a secondary transfer backup roller 219 as a secondary transfer counter member, and four primary transfer members. A primary transfer roller 221 and a secondary transfer roller 222 as a secondary transfer member are included. The intermediate transfer belt 216 is stretched while being tensioned by a plurality of rollers including a stretching roller 217.

  The four primary transfer rollers 221 are in contact with the photosensitive member 211 via the intermediate transfer belt 216, respectively. As a result, the intermediate transfer belt 216 and each photoconductor 211 come into contact with each other, and a primary transfer nip is formed between them.

  The secondary transfer roller 222 is in contact with the secondary transfer backup roller 219 via the intermediate transfer belt 216. As a result, a secondary transfer nip is formed between the secondary transfer roller 222 and the intermediate transfer belt 216.

  The paper feed unit 202 is provided with a plurality of paper feed cassettes 224 that can store a plurality of sheets as sheet-like recording media. Each paper feed cassette 224 is provided with a paper feed roller 225 that feeds the top sheet of the paper bundle to the paper feed path 226 and a separation roller 228 that separates the fed paper one by one.

  The paper feed path 226 is provided with a plurality of conveying roller pairs 227 and a registration roller pair 215 that conveys the sheet conveyed by the conveying roller pair 227 to the secondary transfer nip.

  The fixing device 208 includes a fixing belt 234 that is stretched by two rollers, and a pressure roller 235 that is pressed toward one roller that stretches the fixing belt 234. The fixing belt 234 and the pressure roller 235 are in contact with each other to form a fixing nip. Of the two rollers that stretch the fixing belt 234, the roller that is pressed from the pressure roller 235 has a heat source inside, and the fixing belt 234 is heated by the generated heat.

  The paper discharge unit 230 is provided with a paper discharge roller pair 236 that discharges paper to the outside of the machine and a paper discharge tray 237 that stocks the paper discharged outside the machine.

  The scanner unit 203 includes a first traveling body 238 and a second traveling body 239 each provided with a mirror, a contact glass 240, an imaging lens 241, a reading sensor 242, and the like. An automatic document feeder 204 provided above the scanner unit 203 is provided with a document table 243 for setting a document.

Next, the operation of the image forming apparatus shown in FIG. 39 will be described.
When making a copy of a document, set the document on the document table 243 of the automatic document feeder 204 or open the automatic document feeder 204 and set the document on the contact glass 240 of the scanner unit 203. The automatic document feeder 204 is closed to hold the document.

  When the copy start switch is pressed after the original is set in this way, the original reading operation by the scanner unit 203 is started. In the document reading operation, first, the first traveling body 238 and the second traveling body 239 start traveling together, and light is emitted from a light source provided in the first traveling body 238. Then, the reflected light from the document surface is reflected by a mirror provided in the second traveling body 239, passes through the imaging lens 241, and then enters the reading sensor 242. The reading sensor 242 constructs image information based on incident light.

  In parallel with the document reading operation as described above, each device in each of the process units 210Y, 210M, 210C, and 210K, the transfer device 206, the conveyance belt 207, the fixing device 208, and the like start driving.

  In each process unit 210Y, 210M, 210C, 210K, each photoconductor 211 is rotationally driven counterclockwise in the figure, and the surface of each photoconductor 211 is uniformly charged to a predetermined polarity by the charging device 212. Based on the image information constructed by the reading sensor 242, laser light is irradiated from the optical writing unit 205 to the charging surface of each photosensitive member 211. Then, the potential of the irradiation part (exposure part) is attenuated, whereby an electrostatic latent image is formed on the surface of each photoconductor 211. At this time, the image information to be exposed on each photoconductor 211 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Then, by supplying toner as a developer from each developing device 213 to the electrostatic latent image on each photoconductor 211, the electrostatic latent image is visualized (visualized) as a toner image.

  In the transfer device 206, the drive roller 218 that stretches the intermediate transfer belt 216 is driven to rotate, whereby the intermediate transfer belt 216 rotates in the direction of the arrow in the drawing. In addition, a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current is applied to each primary transfer roller 221, so that the primary transfer nip between each primary transfer roller 221 and each photoconductor 211. A transfer electric field is formed. Then, the toner images of the respective colors on the respective photoconductors 211 are primarily transferred by being sequentially superimposed on the intermediate transfer belt 216 by the transfer electric field formed in the primary transfer nip. Thus, a full color toner image is carried on the intermediate transfer belt 216. Further, residual toner on each photoconductor 211 that could not be transferred to the intermediate transfer belt 216 is removed by the cleaning device 214.

  Almost simultaneously with the start of the document reading operation, the paper feeding operation is started in the paper feeding unit 202. In this paper feeding operation, one of the paper feeding rollers 225 is selectively rotated, and the paper is sent out from one of the paper feeding cassettes 224. The fed paper is separated one by one by the separation roller 228 and enters the paper feed path 226, and is then transported toward the secondary transfer nip by the transport roller pair 227.

  The sheet conveyed from the sheet feeding cassette 224 is sent to the secondary transfer nip by the registration roller pair 215 so as to be synchronized with the four-color toner image on the intermediate transfer belt 216. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image is applied to the secondary transfer roller 222, thereby forming a transfer electric field in the secondary transfer nip. Then, the toner image on the intermediate transfer belt 216 is secondarily transferred collectively onto the paper by the transfer electric field formed in the secondary transfer nip. Further, the toner remaining on the intermediate transfer belt 216 after the secondary transfer is removed by the belt cleaning device 220.

  The sheet on which the toner image is secondarily transferred as described above is sent to the fixing device 208 by the transport belt 207. Then, the sheet is fed into a fixing nip between the fixing belt 234 and the pressure roller 235, where the sheet is heated and pressed to fix the toner image on the sheet. Thereafter, the sheet is fed out by the rotating fixing belt 234 and the pressure roller 235, then discharged out of the apparatus by the pair of discharge rollers 236 and stocked on the discharge tray 237.

  The above description relates to the image forming operation when forming a full-color image. However, one of the four process units 210Y, 210M, 210C, and 210K is used to form a single-color image, or two or It is also possible to form a two-color or three-color image using three process units.

  By the way, in the transfer device having the intermediate transfer belt as described above, when the thick paper enters the secondary transfer nip, the intermediate transfer belt and the roller are subjected to a sudden load by the impact at that time, and the rotation speed of the intermediate transfer belt is increased. May drop instantaneously. If the rotational speed of the intermediate transfer belt decreases and a rotational speed difference occurs between the photosensitive member and the intermediate transfer belt, the dots of the image transferred to the intermediate transfer belt are stretched in the rotational direction of the photosensitive member. , The image quality is degraded. Therefore, in the transfer apparatus according to the present embodiment, the secondary transfer roller is moved from the intermediate transfer belt (or the secondary transfer backup roller) in order to suppress a sudden load caused by the thick paper entering the secondary transfer nip. An approach / separation mechanism for approaching and separating is provided.

FIG. 40 is a schematic configuration diagram of a contact / separation mechanism for approaching and separating the secondary transfer roller.
As shown in FIG. 40, the secondary transfer roller 222 is held by a holding member 251 that rotates about a support shaft 250 in the direction of arrow M in the drawing. When the holding member 251 rotates about the support shaft 250, the secondary transfer roller 222 approaches and separates from the intermediate transfer belt 216. The holding member 251 is urged upward in the figure by a pressure spring 252 as an urging member. For this reason, the secondary transfer roller 222 is held in a state of being pressed against the intermediate transfer belt 216. Further, an idling roller 253 is relatively rotatably provided on the rotation shaft 222a of the secondary transfer roller 222.

  The secondary transfer backup roller 219 is provided with a cam member 41 similar to that provided in the fixing device according to the above embodiment. Further, the transfer device according to the present embodiment is provided with the same optical sensor 51 and the light shielding member 52 as the rotational position detecting means for detecting the rotational position of the cam member 41.

  In the state shown in FIG. 40, the idling roller 253 is in contact with the cam surface 41a on the lowest point e1 side by the urging force of the pressure spring 252. In this state, the secondary transfer roller 222 is held at a position close to the intermediate transfer belt 216, and the pressure applied at the secondary transfer nip is a normal pressure when passing plain paper. .

  In order to change from this state to the depressurized state (depressurized state) when passing thick paper, the cam member 41 is rotated counterclockwise in FIG. As a result, the contact position of the idling roller 253 with respect to the cam surface 41a relatively moves from the lowest point e1 side to the uppermost point e2 side, and the idling roller 253 is pushed downward by the cam member 41 in the figure. Along with this, the secondary transfer roller 222 is also pushed downward. As a result, the secondary transfer roller 222 moves to a position separated from the intermediate transfer belt 216, and the pressure is reduced in the secondary transfer nip.

  Moreover, when returning to a normal pressurization state, what is necessary is just to rotate the cam member 41 in the reverse direction from the said depressurization state. As a result, the contact position of the idling roller 253 with respect to the cam surface 41 a relatively moves from the uppermost point e2 side to the lowermost point e1 side, and the idling roller 253 approaches the cam member 41. Along with this, the secondary transfer roller 222 approaches the intermediate transfer belt 216 and is returned to the normal pressure state in which the pressurizing force in the secondary transfer nip is increased. A control method similar to the cam member control method in the fixing device can be applied to the rotation control of the cam member during the pressurizing operation and the depressurizing operation.

  As described above, the contact / separation mechanism according to the present invention can also be applied to the contact / separation mechanism that moves the secondary transfer roller toward and away from the intermediate transfer belt. Further, by applying the cam member according to the present invention to the contact / separation mechanism of the transfer device, the same effect as that of the fixing device can be obtained. That is, as shown in FIG. 40, since the cam surface 41a can be provided over a region larger than a half circumference in the rotation direction, even if the gradient of the cam surface 41a is made gentle, the maximum difference in gradient is reduced. Can be avoided. As a result, it is possible to suppress an increase in rotational torque and generation of operating noise (abnormal noise) while ensuring a sufficient distance between the secondary transfer roller and the intermediate transfer belt.

  In the example shown in FIG. 40, the contact / separation mechanism of the embodiment shown in FIG. 2 or FIG. 3 is applied to the transfer device, but other configurations according to the above-described embodiment can be similarly applied. In the transfer device, the secondary transfer roller is separated when the thick paper is passed through the secondary transfer nip. However, in the present invention, in addition to this, the secondary transfer roller is connected to the intermediate transfer belt. In order to suppress plastic deformation and toner adhesion due to constant pressurization, the present invention can also be applied to a configuration in which the secondary transfer roller is separated at a timing other than at the time of transfer.

  In addition, the example shown in FIG. 39 is a transfer device in which the paper is conveyed in the horizontal direction (horizontal direction) with respect to the secondary transfer nip. However, as shown in FIG. The contact / separation mechanism according to the present invention can also be applied to the transfer device 306 in which the sheet is conveyed in the vertical direction (vertical direction). In this case, the contact / separation mechanism for moving the secondary transfer roller 322 shown in FIG. 41 closer to and away from the intermediate transfer belt 316 by arranging the contact / separation mechanism shown in FIG. Can be configured. In FIG. 41, 300 is an image forming apparatus, 301 is an image forming unit including a plurality of photoconductors 311, 321 is a primary transfer roller, 302 is a paper feeding unit, 308 is a fixing device, and 330 is a paper discharging unit. Since these basic configurations and operations are the same as those of the image forming apparatus 200 shown in FIG.

  The contact / separation mechanism according to the present invention can also be applied to a transfer device 406 that moves the primary transfer roller closer to and away from the photosensitive member as shown in FIG. Here, at the time of monochrome image formation, the corresponding primary transfer rollers 421Y, 421M, 421C are separated from the photoconductors 411Y, 411M, 411C for color images that do not contribute to image formation (state indicated by dotted lines in FIG. 42). The photosensitive members 411Y, 411M, and 411C and the intermediate transfer belt 416 are prevented from unnecessary wear and power consumption. In FIG. 42, reference numeral 422 denotes a secondary transfer roller.

FIG. 43 is a schematic configuration diagram of a contact / separation mechanism for approaching and separating the primary transfer roller.
In FIG. 43, only one primary transfer roller is shown among the three primary transfer rollers that approach and separate from each other, but the contact / separation mechanism relating to any primary transfer roller is also configured in the same manner, so that it relates to one primary transfer roller. An approach / separation mechanism will be described as an example.

  As shown in FIG. 43A, the primary transfer roller 421Y is held by a holding member 451 that rotates about a support shaft 450 in the direction of arrow Q in the drawing. The holding member 451 is configured to engage with the link member 452 that linearly moves in the direction of the arrow W in the drawing and to be interlocked with the link member 452. In addition, one end portion (left end portion in the drawing) of the link member 452 is pressurized toward the other end portion side (right direction in the drawing) by a pressure spring 453 as an urging member. Thereby, the other end of the link member 452 is held in contact with the cam surface 41 a of the cam member 41. The cam member 41 is configured in the same manner as that provided in the fixing device according to the embodiment. Further, the transfer device is provided with an optical sensor 51 and a light shielding member 52 as rotational position detection means for detecting the rotational position of the cam member 41, as in the fixing device.

  When the cam member 41 rotates clockwise in the drawing from the state shown in FIG. 43A, the contact position of the link member 452 with respect to the cam surface 41a relatively moves from the uppermost point e2 side to the lowermost point e1 side. . Accordingly, as shown in FIG. 43B, the link member 452 is pushed by the pressure spring 453 and moves to the right side in the drawing. As the link member 452 moves, the holding member 451 rotates counterclockwise in the drawing, and the primary transfer roller 421Y moves away from the photoreceptor 411Y. As a result, the intermediate transfer belt 416 is held in a state of being separated from the color image photoreceptor 411Y.

  Further, in order to bring the primary transfer roller 421Y closer to the photoreceptor 411Y, the cam member 41 may be rotated in the direction opposite to the above from the state shown in FIG. Thereby, the contact position of the link member 452 with respect to the cam surface 41a relatively moves from the lowest point e1 side to the highest point e2 side, and the link member 452 is pushed to the left side in the figure by the cam member 41. Along with this, the holding member 451 rotates clockwise in the drawing. As a result, as shown in FIG. 43A, the secondary transfer roller 222 is returned to the state of approaching the intermediate transfer belt 416.

  As described above, the contact / separation mechanism according to the present invention can also be applied to the contact / separation mechanism that moves the primary transfer roller toward and away from the photosensitive member. In addition, by applying the cam member according to the present invention to the contact / separation mechanism that moves the primary transfer roller closer to and away from the primary transfer roller, the maximum height of the gradient can be reduced even if the gradient of the cam surface is moderated as in the case of the fixing device and the transfer device. It can be avoided that the difference becomes small. Accordingly, it is possible to suppress an increase in rotational torque and generation of operating noise (abnormal noise) while ensuring a sufficient distance between the primary transfer roller and the photosensitive member. In the example shown in FIG. 43, the contact / separation mechanism of the embodiment shown in FIG. 2 or FIG. 3 is applied to the transfer device, but other configurations according to the above-described embodiment can be similarly applied.

  The configuration, operation, and effects of the embodiment of the present invention described above are summarized as follows.

  The contact / separation mechanism according to the above embodiment includes a cam member, and rotates the cam member to move the contact / separation member toward and away from the mating member, the cam member rotating in the rotation direction. The cam surface has a gradually increasing distance from the center of rotation over a region larger than a half circumference of the shaft, and is configured to be rotatable in one direction and in the opposite direction.

  By configuring the cam member to be rotatable in one direction and in the opposite direction, the same cam surface can be used when the contact / separation member is moved closer to and away from the counterpart member. For this reason, the cam member is not subject to the restriction that the range in which the cam surface can be secured is at most half of the rotation direction as in the conventional case (a configuration in which the cam member is rotated only in one direction). It can be provided over a region larger than a half circumference in the rotation direction. And, by providing the cam surface over a region larger than a half circumference in the rotational direction, even if the gradient of the cam surface is gentle, it is possible to avoid a decrease in the maximum height difference of the gradient. It is possible to suppress the increase in rotational torque and the generation of operating noise (abnormal noise) by making the gradient of the cam surface gentle while ensuring a sufficient approach / separation distance of the contact / separation member with respect to the counterpart member.

  The cam surface whose distance from the center of rotation gradually increases, as in the example shown in FIG. 3, the cam surface 41a is continuously from the lowest point e1 to the highest point e2 (without going through the flat surface 41b). In addition to the case of increasing gradually, the case of increasing gradually via the flat surface 41b in the middle from the lowest point e1 to the highest point e2 as in the example shown in FIG. 18 is also included.

  The contact / separation mechanism according to the embodiment includes a rotation position detection unit that detects the rotation position of the cam member, and a timer that measures the rotation time of the cam member. When the cam member rotates in one direction, the rotation of the cam member is stopped at a timing when a predetermined rotation position is detected by the rotation position detection means, and when the cam member rotates in the reverse direction. The cam member is controlled to stop rotating at a timing when a predetermined time is measured by the timer.

  In this way, by dividing the timing determination means for controlling the stop position of the cam member into a rotation position detection means and a timer when the cam member rotates in one direction and when it rotates in the opposite direction, Since it is not necessary to provide two rotational position detecting means, the cost and size can be reduced.

  In the contact / separation mechanism according to the embodiment, when the cam member rotates so as to push and move the contact / separation member or a member interlocked therewith, a predetermined rotation position is detected by the rotation position detection unit. When the rotation of the cam member is stopped at the timing and the cam member rotates in a direction opposite to the rotation direction for pushing the contact / separation member or a member interlocked therewith, a predetermined time is measured by the timer. The cam member is controlled to stop rotating at the timing. In this case, a worm gear is used as the driving force transmission means for transmitting the rotational driving force to the cam member.

  When the cam member rotates so as to push and move the contacting / separating member or the member interlocking therewith, there is a possibility that the rotational speed of the cam member varies due to an increase in the rotational torque. However, even if such rotational speed variations occur, the rotational position detecting means detects the rotational position of the cam member, as described above, so that the cam member can be reliably set to a predetermined value regardless of the rotational speed variation. It can be stopped at the rotational position. Thereby, the accuracy of the rotation stop position of the cam member is improved.

  On the other hand, when the cam member rotates in the direction opposite to the rotation direction that pushes the contact / separation member or the member interlocked therewith, the influence of the variation in the rotational speed of the cam member due to the increase in the rotational torque is small. Therefore, in this case, the rotational position of the cam member can be controlled not by the rotational position detecting means but by the timer. However, in this case, when the pressing force by the cam member is released, a force in the direction of accelerating the rotation of the cam member is applied, and the rotation stop position of the cam member may vary. For this reason, as described above, by using the worm gear as the driving force transmission means, the cam member can be prevented from being accelerated by the self-locking function of the worm gear. Thereby, the dispersion | variation in the rotation stop position accompanying the change of the rotational speed of a cam member can be suppressed, and the precision of the rotation stop position of a cam member improves. In addition, it is possible to suppress the generation of operating noise (abnormal noise) that accompanies acceleration of the cam member.

  In the above-described embodiment, the rotational position detecting means shields or transmits the irradiation light of the optical sensor by rotating integrally with the optical sensor that irradiates light and receives the irradiation light and the cam member. And a member to be detected whose rotational position is detected by the optical sensor by switching the presence or absence of light reflected. Further, the detected member includes a long detected region formed so that a passing time passing through the light irradiation part of the optical sensor during rotation is longer than a preset measurement time of the timer, and the detected member during rotation. And a short detection area formed so that a transit time passing through the light irradiation part of the optical sensor is shorter than a preset measurement time of the timer. In addition, the timer starts time measurement at a timing when the presence or absence of light reception by the optical sensor is switched, and when the measurement of the preset time is completed while the state of the presence or absence of light reception continues. If the presence or absence of light reception by the optical sensor is switched before the rotation of the cam member is stopped and the measurement of the preset time is completed, the time measurement is controlled to be canceled halfway.

  In this case, the time measurement by the timer started at the light reception switching timing by the short detected area is canceled halfway because the state of the presence or absence of light reception at this time does not continue until the time measurement by the timer is completed. On the other hand, when the time measurement is started at the light reception switching timing in the long detection area, the presence or absence of the light reception continues until the time measurement is completed, so that the rotation of the cam member is stopped by the completion of the time measurement. . Thus, the time measurement started at the light reception switching timing by the short detection area is canceled in the middle, and the rotation stop position of the cam member is controlled by the time measurement started at the light reception switching timing by the long detection area. Thus, the measurement time by the timer can be shortened. Thereby, the variation in time measurement by the timer is reduced, and the accuracy of the rotational position control of the cam member can be improved.

  In the above embodiment, when the cam member rotates in one direction, the cam member rotates at the timing when the short detection region passes through the light irradiation part of the optical sensor and the presence or absence of light reception is switched. When the cam member rotates in the reverse direction, the timer starts measuring time when the long detection area reaches the light irradiation part of the optical sensor and the presence or absence of light reception is switched. The rotation of the cam member is stopped at the timing when the timer measures the preset measurement time while the state of the presence or absence of light reception continues.

  By performing such control, the cam member can be stopped at a predetermined position using an optical sensor and a timer in a configuration using a detection member having a short detection region and a long detection region.

  Further, as in the contact / separation mechanism according to the above-described embodiment, when the light shielding member has a plurality of the short detection regions in the rotation direction and the cam member rotates in one direction, the plurality of the short detection regions One of the detected areas is selected, and the rotation of the cam member is stopped at a timing when the selected short detected area passes through the light irradiation unit of the optical sensor and the presence or absence of light reception is switched. You may control as follows.

  In this way, by selecting one of the plurality of short detected areas and stopping the rotation of the cam member at the light reception switching timing by the selected short detected area, the rotation stop position of the cam member is set. It will be possible to make fine adjustments.

  The contact / separation mechanism according to the embodiment includes a pair of rotating members facing each other, and passes a recording medium carrying an unfixed image between the rotating members to pass the unfixed image to the recording medium. The fixing device can be applied to a fixing device that includes a contact / separation mechanism for approaching / separating the other rotating body that is a contact / separation member with respect to one rotating body that is a counterpart member.

  The contact / separation mechanism according to the embodiment includes an intermediate transfer member, a plurality of primary transfer members that transfer images formed on a plurality of photosensitive members to the intermediate transfer member, and an image transferred to the intermediate transfer member. A transfer device including a secondary transfer member that transfers the image to a recording medium, the transfer device including a contact / separation mechanism that moves the primary transfer member that is a contact / separation member closer to and away from the photosensitive member that is a counterpart member It can also be applied.

  The contact / separation mechanism according to the embodiment includes an intermediate transfer member, a plurality of primary transfer members that transfer images formed on a plurality of photosensitive members to the intermediate transfer member, and an image transferred to the intermediate transfer member. A transfer device including a secondary transfer member that transfers the image to a recording medium, the transfer device including a contact / separation mechanism that moves the secondary transfer member that is a contact / separation member closer to and away from the intermediate transfer member that is a counterpart member It can also be applied to a device.

  The contact / separation mechanism according to the embodiment can be used for an image forming apparatus.

12 Fixing device 18 Fixing roller (rotating body)
19 Pressure roller (rotating body)
41 cam member 41a cam surface 45 first worm gear 46 second worm gear 50 optical sensor (rotational position detecting means)
52 Shading member (detected member)
52a Long light shielding part (long detection area)
52b to 52i Short light shielding part (short detected area)
70 Timer 206 Transfer Device 211 Photoconductor 216 Intermediate Transfer Belt (Intermediate Transfer Member)
221 Primary transfer roller (primary transfer member)
222 Secondary transfer roller (secondary transfer member)
306 Transfer device 311 Photoconductor 316 Intermediate transfer belt (intermediate transfer member)
321 Primary transfer roller (primary transfer member)
322 Secondary transfer roller (secondary transfer member)
406 Transfer device 411Y, 411M, 411C, 411K Photoconductor 416 Intermediate transfer belt (intermediate transfer member)
421Y, 421M, 421C, 421K Primary transfer roller (primary transfer member)
422 Secondary transfer roller (secondary transfer member)

JP-A-2006-85438

Claims (10)

A cam member,
An approach / separation mechanism for rotating the cam member to approach and separate the contact / separation member with respect to the counterpart member,
The cam member has a cam surface whose distance from the rotation center gradually increases over a region larger than a half circumference in the rotation direction, and is capable of rotating in one direction and the opposite direction. mechanism. Rotational position detecting means for detecting the rotational position of the cam member;
A timer for measuring the rotation time of the cam member,
When the cam member rotates in one direction, the rotation of the cam member is stopped at a timing when a predetermined rotation position is detected by the rotation position detection means,
The contact / separation mechanism according to claim 1, wherein when the cam member rotates in the reverse direction, the rotation of the cam member is stopped at a timing when a predetermined time is measured by the timer. When the cam member rotates so as to push and move the contact / separation member or a member interlocked therewith, the rotation of the cam member is stopped at a timing when a predetermined rotation position is detected by the rotation position detection means,
When the cam member rotates in a direction opposite to the rotation direction that pushes the contact / separation member or a member interlocked therewith, the rotation of the cam member is stopped at a timing when a predetermined time is measured by the timer. West,
The contact / separation mechanism according to claim 2, wherein a worm gear is used as a driving force transmission unit that transmits a rotational driving force to the cam member. The rotational position detection means is configured to detect whether light is received by irradiating light and receiving the irradiated light, and rotating integrally with the cam member to shield, transmit or reflect the irradiated light of the optical sensor. A detected member whose rotational position is detected by the optical sensor by switching,
The detected member includes a long detected region formed so that a passing time passing through the light irradiation part of the optical sensor during rotation is longer than a preset measurement time of the timer, and the optical sensor during rotation. And a short detection area formed so that the transit time passing through the light irradiation unit is shorter than the preset measurement time of the timer,
The timer starts time measurement at the timing when the presence or absence of light reception by the optical sensor is switched, and when the measurement of the preset time is completed while the state of presence or absence of light reception continues, the cam member The control is performed so that the time measurement is canceled in the middle when the presence or absence of light reception by the optical sensor is switched before the measurement of the preset time is completed. The contact / separation mechanism described. When the cam member rotates in one direction, the rotation of the cam member is stopped at a timing when the short detection region passes through the light irradiation part of the optical sensor and the presence or absence of light reception is switched,
When the cam member rotates in the reverse direction, the timer starts measuring time when the long detection area reaches the light irradiation part of the optical sensor and the presence or absence of light reception is switched. The contact / separation mechanism according to claim 4, wherein the rotation of the cam member is stopped at a timing when the timer measures a preset measurement time while the presence / absence state is continued. The light shielding member has a plurality of the short detection areas in the rotation direction,
When the cam member rotates in one direction, one of the plurality of short detection areas is selected, and the selected short detection area passes through the light irradiation unit of the optical sensor and receives light. The contact / separation mechanism according to claim 5, wherein rotation of the cam member is stopped at a timing when the presence or absence of the switch is switched. A pair of rotating bodies facing each other,
A fixing device for passing a recording medium carrying an unfixed image between the rotating bodies and fixing the unfixed image on the recording medium;
The contact / separation mechanism according to any one of claims 1 to 6 is provided as an approach / separation mechanism for approaching / separating the other rotation body, which is a contact / separation member, to one rotation body, which is a counterpart member. A fixing device characterized by the above. An intermediate transfer member, a plurality of primary transfer members that transfer the images formed on the plurality of photosensitive members to the intermediate transfer member, and a secondary transfer member that transfers the image transferred to the intermediate transfer member to a recording medium. A transfer device comprising:
7. The contact / separation mechanism according to claim 1, wherein the contact / separation mechanism is configured to approach and separate the primary transfer member, which is a contact / separation member, with respect to the photoconductor, which is a counterpart member. Transfer device. An intermediate transfer member, a plurality of primary transfer members that transfer the images formed on the plurality of photosensitive members to the intermediate transfer member, and a secondary transfer member that transfers the image transferred to the intermediate transfer member to a recording medium. A transfer device comprising:
7. The contact / separation mechanism according to claim 1, wherein the contact / separation mechanism is configured to approach and separate the secondary transfer member, which is a contact / separation member, with respect to the intermediate transfer member, which is a counterpart member. Characteristic transfer device.   An image forming apparatus comprising the contact / separation mechanism according to claim 1.

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