JP2012128222A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device equipped with a fixing device capable of certainly changing nip pressure with a simple structure.SOLUTION: An image forming device 10 comprises an elastic member 53 energizing first and second abutting portions 51a and 52a in a direction separating them from each other, a first arm member 51 abutting on one end portion of the elastic member 53 at the first abutting portion 51a, and a second arm member 52 abutting on the other end portion of the elastic member 53 at the second abutting portion 52a. The image forming device 10 also comprises a roller 61 provided at the second arm member 52, and an eccentric cam 62 abutting on the roller 61 and changing a distance from a rotation center to an outer peripheral surface. An aligning direction of a center axis of the roller 61 and the rotation center of the eccentric cam 62 is generally the same as a direction of energizing force of the elastic member 53 which acts on the second abutting portion 52a.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and more particularly, an image including a fixing device capable of changing a nip pressure between a heating member and a pressure member. The present invention relates to a forming apparatus.

  Conventionally, an image forming apparatus is provided with a fixing device for fixing a toner image transferred from an image carrier onto a recording material. As this fixing device, a roller system including a heating roller and a pressure roller rotating in contact with each other, a belt system using an endless fixing belt as a heating member, and the like are known. For example, a roller-type fixing device heats and presses a toner image carried on a recording material at a nip portion between a pressure-contacting fixing roller and a pressure roller and fixes the toner image on the recording material.

  In the above-described fixing device, the temperature of the heating member and the nip pressure at the nip portion are set in consideration of the toner fixing property to the recording material. However, when fixing a toner image on a recording material such as an envelope of a different type under heating / pressurization conditions set in consideration of toner fixing properties to a sheet-like recording material such as plain paper, Wrinkles are likely to occur on the recording material. Therefore, there is a fixing device in which the pressure of the heating member and the pressure member is made variable in accordance with the type of the recording material on which the toner image is fixed. In some cases, the nip pressure is released due to the jam processing of the recording material, and the nip pressure is lower during the conveyance of the image forming apparatus than during the fixing process.

  In order to change the nip pressure between such a heating member and a pressure member, for example, the fixing devices described in Patent Documents 1 and 2 manually operate the lever member to change the pressure member and the heating member. The pressing force between the pressing member and the heating member is released or relaxed against the biasing force of the biasing members that are in pressure contact with each other.

  In order to change the nip pressure, for example, the fixing device described in Patent Document 3 uses a sensor that detects the state of the nip pressure and a motor that drives the variable nip pressure member. When a jam occurs, the sensor detects the state of the nip pressure, and based on the detection result, the motor drives the nip pressure variable member to release the nip pressure.

JP-A-8-328406 (paragraphs [0060] to [0063], FIG. 3) JP 2003-186340 A (paragraphs [0020] to [0021], FIG. 1) JP 2010-26447 A (paragraphs [0027] to [0028], FIG. 3)

  However, in Patent Documents 1 and 2 described above, the lever member must be manually operated in order to change the nip pressure, and the operation of changing the nip pressure becomes complicated. In Patent Document 3, the nip pressure is changed. In order to detect this state, a sensor is required, and the apparatus is inconveniently expensive.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus including a fixing device that can surely change the nip pressure with a simple configuration.

  In order to achieve the above object, an image forming apparatus of a first invention has a heating member and a pressure member pressed against the heating member, and heats and presses a toner image carried on the recording material. A fixing unit that fixes the recording material, a pressure mechanism that applies a nip pressure to a nip portion where the pressure member and the heating member are in pressure contact, and a nip pressure switching unit that changes the nip pressure of the nip portion. A first arm member that is supported so as to be swingable about a support shaft and that has a first contact portion and holds one member of the pressure member and the heating member; A second arm member having a second abutting part, and one end abutting on the first abutting part and the other end abutting on the second abutting part, and the first and second abutting parts An elastic member that applies nip pressure to the nip portion by urging the portions in a direction to separate them from each other The nip pressure switching unit includes a roller provided on the second arm member, an eccentric cam that abuts on the roller and changes a distance from a rotation center to an outer peripheral surface, and the eccentric cam. A rotating drive unit, and the alignment direction of the center axis of the roller and the rotation center of the eccentric cam is substantially the same as the direction of the urging force of the elastic member acting on the second contact portion It is characterized by becoming.

  According to a second aspect of the present invention, in the above-described image forming apparatus, the eccentric cam is formed such that the first concave portion and the second concave portion that selectively engage with the roller are formed at different circumferential positions from the rotation center. When the first recess engages with the roller, the distance between the first and second contact portions is a predetermined distance, and when the second recess engages with the roller, The distance between the first and second contact portions is larger than a predetermined distance.

  According to a third aspect of the present invention, in the above image forming apparatus, the first concave portion and the second concave portion of the eccentric cam are arranged at positions facing the rotation center.

  According to a fourth aspect of the present invention, in the above image forming apparatus, the drive unit is disposed in a motor that can rotate forward and backward and a gear train that transmits the rotational driving force of the motor to the eccentric cam. A tooth missing gear having a number of tooth missing parts, a motor side gear that can mesh with the tooth missing gear, and a tooth missing part of the tooth missing gear when the motor side gear rotates forward or backward. A return spring that urges the tooth missing gear in a direction away from the motor side gear, and the motor side gear rotates in one direction so that the tooth missing portion of the tooth missing gear is the motor side gear. The tooth missing gear is urged by the return spring and cannot engage with the motor side gear at the tooth missing portion, causing the tooth missing gear to idle and the motor side gear to move in the other direction. Times Then, the tooth missing portion other than the toothless portion of the gear that is possible the motor-side gear and meshed, the tooth breaking gear is rotated, is characterized by rotating the eccentric cam.

  According to a fifth aspect of the present invention, in the image forming apparatus, when the image formation is started, the motor is rotated in a direction in which the first recess of the eccentric cam engages the roller, and the image formation is completed at the end of the image formation. The second concave portion of the lead cam is provided with a control unit that controls the motor to rotate in a direction to engage the roller.

  According to a sixth aspect of the present invention, in the above image forming apparatus, the fixing unit is disposed opposite to the heating member, generates a magnetic flux, and induction heats the induction heating layer provided on the heating member by the magnetic flux. The induction heating unit is further provided, and the one member is a pressure member.

  According to the first invention, the elastic member urges the first and second abutting portions in the direction in which they are separated from each other, so that a nip pressure is applied to the nip portion, and the fixing process can be performed by the fixing portion. It becomes. At this time, since the direction of rotation of the eccentric cam and the roller is substantially the same as the direction of the urging force of the elastic member acting on the second contact portion, the engagement portion between the roller and the eccentric cam Substantially all the urging force of the elastic member acts, and the roller and the eccentric cam are securely locked, so that the nip pressure in the nip portion is stabilized.

  According to the second invention, when the drive unit rotates the eccentric cam and the first recess of the eccentric cam engages the roller, the biasing force according to the interval between the first and second contact portions is The elastic member applies a nip pressure to the nip portion, and the fixing process can be performed by the fixing portion. At this time, the direction in which the rotation center of the eccentric cam and the roller are aligned is substantially the same as the direction of the urging force of the elastic member acting on the second contact portion. Substantially all of the urging force of the elastic member acts, and the roller and the first recess are reliably locked, so that the nip pressure in the nip portion is stabilized. Further, when the second concave portion of the eccentric cam engages the roller, the distance between the first and second contact portions becomes larger than a predetermined distance, and the elastic member is moved to the nip portion by an urging force that is smaller than that during the fixing process. A nip pressure is applied to. At this time, the direction in which the rotation center of the eccentric cam and the roller are aligned is substantially the same as the direction of the urging force of the elastic member acting on the second contact portion. Substantially all of the urging force of the elastic member acts, and the roller and the second recess are securely locked, so that the nip pressure in the nip portion is stabilized. Therefore, the nip pressure can be changed easily and reliably.

  According to the third aspect of the invention, when the eccentric cam is rotated halfway, the engagement is switched from one of the first and second recesses to the other recess, and the drive unit needs to be greatly decelerated. In addition, the output torque of a drive source such as a motor can be reduced.

  Further, according to the fourth invention, when the motor side gear rotates in one direction due to the normal rotation of the motor and the tooth missing portion of the tooth missing gear faces the motor side gear, the motor rotates. The tooth missing gear is idling and the eccentric cam is stopped. For example, the first concave portion of the eccentric cam is engaged with the roller. Next, when the motor is rotated in the reverse direction, the motor side gear rotates in the other direction, and the portion other than the tooth missing portion of the tooth missing gear meshes with the motor side gear, whereby the tooth missing gear rotates. The eccentric cam rotates. Due to the rotation of the eccentric cam, the second concave portion of the eccentric cam is engaged with the roller, and the urging member is changed to a smaller urging force than that during the fixing process. That is, the nip pressure is changed. Even if the motor continues to rotate in the reverse direction, the tooth missing portion of the tooth missing gear maintains the position facing the motor side gear by the biasing force of the return spring. Therefore, when the motor rotates in the forward direction, the state where the nip pressure is large is maintained, while when the motor rotates in the reverse direction, the state where the nip pressure is small is maintained. Accordingly, the nip pressure can be easily and inexpensively switched without providing a special member such as a sensor.

  According to the fifth aspect of the invention, if the motor rotation direction and the nip pressure state are correlated and the motor rotation direction is switched according to the operation mode, for example, when no image is formed. The pressure load between the pressure member and the heating member is easily reduced, and the durability of the pressure member and the heating member is improved.

  According to the sixth aspect of the present invention, in the electromagnetic induction heating type fixing device including the induction heating unit, the induction heating unit and the nip pressure switching unit are disposed on the pressure member side by disposing the pressure mechanism and the nip pressure switching unit. The peripheral member can be appropriately disposed on the heating member side.

Sectional drawing which shows the image forming apparatus which concerns on embodiment of this invention Sectional drawing which shows the fixing device used for the image forming apparatus which concerns on embodiment. The perspective view which shows the fixing device which concerns on embodiment The side view which shows the normal pressurization state (a) and pressure reduction state (b) of the fixing device which concerns on embodiment. The perspective view which shows the normal pressurization state of the drive part of the fixing device which concerns on embodiment The perspective view which shows the pressure reduction state of the drive part of the fixing device which concerns on embodiment The figure which shows the state (a) at the time of normal pressurization of the chipped gear which concerns on embodiment, and the state (b) at the time of pressure reduction of a chipped gear The block diagram which shows the control part which concerns on embodiment, and its periphery

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Further, the use of the invention and the terms shown here are not limited thereto.

  FIG. 1 is a cross-sectional view showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 10 is a tandem type color copier of an in-body discharge type, and includes a lower apparatus main body 11 and an upper apparatus main body 16.

  The lower apparatus main body 11 is provided with a paper feeding section 14, an image forming section 12, and a fixing device 13, and the upper apparatus main body 16 is provided with an image reading section 20 for reading a document image. Is done. A paper discharge space 15 is formed between the lower apparatus main body 11 and the upper apparatus main body 11, and the paper P after the fixing process is discharged into the paper discharge space 15.

  The image forming unit 12 forms a toner image on the paper P fed from the paper feeding unit 14, and includes a magenta unit 12M and a cyan from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 125. A unit 12C for yellow, a unit 12Y for yellow, and a unit 12K for black are disposed.

  Each of the image forming units 12M, 12C, 12Y, and 12K is provided with a photoconductor 121 as an image carrier, and around the photoconductor 121, a developing device 122, an exposure unit 124, a charger 123, and a cleaning device 126 are provided. Arranged.

  The developing device 122 is arranged to face the right side of the photoconductor 121 and supplies toner to the photoconductor 121. The charging device 123 is disposed on the upstream side of the developing device 122 with respect to the rotation direction of the photosensitive member and opposed to the surface of the photosensitive member 121, and uniformly charges the surface of the photosensitive member 121.

  The exposure unit 124 is for scanning and exposing the photosensitive member 121 based on image data such as characters and patterns read by the image reading unit 20, and is provided below the photosensitive member 121. The exposure unit 124 is provided with a laser light source, a polygon mirror, and the like (not shown), and laser light emitted from the laser light source passes through the polygon mirror from the downstream side of the charger 123 in the rotation direction of the photosensitive member 121. Irradiate the surface. An electrostatic latent image is formed on the surface of the photosensitive member 121 by the irradiated laser light, and the electrostatic latent image is developed into a toner image by the developing device 122.

  The endless intermediate transfer belt 125 is stretched around a driving roller 125a and a tension roller 125b. The driving roller 125a is rotationally driven by a motor (not shown), and the intermediate transfer belt 125 is circulated and driven by the rotation of the driving roller 125a.

  Photoconductors 121 are arranged below the intermediate transfer belt 125 so as to be in contact with the intermediate transfer belt 125 along the conveyance direction. The primary transfer roller 125c faces the photoconductor 121 with the intermediate transfer belt 125 interposed therebetween, and presses against the intermediate transfer belt 125 to form a primary transfer portion. In the primary transfer portion, the toner images on the photosensitive members 121 are sequentially transferred to the intermediate transfer belt 125 at a predetermined timing as the intermediate transfer belt 125 rotates. As a result, a toner image is formed on the surface of the intermediate transfer belt 125 by superimposing toner images of four colors of magenta, cyan, yellow, and black.

  The secondary transfer roller 113 faces the driving roller 125a with the intermediate transfer belt 125 interposed therebetween, and presses against the intermediate transfer belt 125 to form a secondary transfer portion. In this secondary transfer portion, the toner image on the surface of the intermediate transfer belt 125 is transferred onto the paper P. After the transfer, a belt cleaning device (not shown) cleans the toner remaining on the intermediate transfer belt 125.

  A paper feed unit 14 is disposed below the image forming apparatus 10, and a paper tray 141 that accommodates the paper P and is detachably attached to the apparatus main body 11 is provided in the paper feed unit 14. On the left side of the paper supply unit 14, a first paper transport path 111 is provided that transports the paper P fed from the paper tray 141 by the pickup roller 142 to the secondary transfer unit of the intermediate transfer belt 125 by the transport roller 112. The Further, on the upper left side of the apparatus main body 11, a fixing device 13 that performs a fixing process on the sheet P on which an image is formed, and a second sheet conveyance path that conveys the sheet on which the fixing process has been performed to the sheet discharge tray 151. 114 is disposed.

  The sheet P is conveyed to the secondary transfer unit at the timing of the image forming operation and the sheet feeding operation on the intermediate transfer belt 125. The toner image on the intermediate transfer belt 125 is secondarily transferred to the sheet P conveyed to the secondary transfer unit by the secondary transfer roller 113 to which a bias potential is applied, and is conveyed to the fixing device 13.

  The fixing device 13 includes a fixing roller 131 that is heated by a heat source, and a pressure roller 132 that is disposed in pressure contact with the fixing roller 131. The fixing device 13 is fixed by heating and pressing the paper P on which the toner image is transferred. Process. The sheet P on which the toner image is fixed passes through the second sheet conveyance path 114 and is discharged to the sheet discharge tray 151 by the discharge roller.

  FIG. 2 is a cross-sectional view showing the fixing device, as seen from the back side of FIG. The fixing device 13 includes a fixing roller 131 that is a heating member and a pressure roller 132 that is a pressure member, and further includes an induction heating unit 133 and a temperature sensor 134, and these members constitute a fixing unit. .

  The fixing device 13 is a fixing method using a heat source of an electromagnetic induction heating method, and includes an induction heating unit 133 disposed facing the outer periphery of the fixing roller 131, a thermistor that detects the temperature of the surface of the fixing roller 131, and the like. The induction heating unit 133 and the temperature sensor 134 are fixedly held on the apparatus main body 11, while the fixing roller 131 and the pressure roller 132 are rotatably held on the apparatus main body 11.

  The fixing roller 131 includes a base material 131a made of cylindrical stainless steel, and an elastic layer 131d made of silicon rubber sponge for improving elasticity and releasability to the nip portion N in pressure contact with the pressure roller 132. Between the 131a and the elastic layer 131d, a heat insulating layer 131b and an induction heat generating layer 131c are provided in this order from the base material side.

  The pressure roller 132 includes a base material 132a made of an aluminum cored bar, an elastic layer 132b made of silicon rubber formed on the base material 132a to impart elasticity to the nip portion N, and undetermined at the nip portion N. A release layer 132c made of a fluororesin tube covering the surface of the elastic layer 132b is provided in order to improve the release property when the toner image is fused and fixed.

  The pressure roller 132 is driven to rotate by a drive source (not shown) such as a motor, and further pressurizes the fixing roller 131 in the center direction. As a result, when the pressure roller 132 comes into pressure contact with the fixing roller 131 and the pressure roller 132 rotates, the fixing roller 131 is driven to rotate in the same direction in the nip portion N.

  The temperature sensor 134 has axially (widthwise) central sheet passing areas on the surface of the fixing roller 131 and both axial ends that are non-sheet passing areas when a small size sheet or A4 vertical sheet is passed. It arrange | positions so that it may oppose to a part, and the temperature of each area | region is detected. Based on the temperature detected by the temperature sensor 134, the electric power of the induction heating unit 133 is controlled, and the surface of the fixing roller 131 is held at a predetermined temperature.

  The induction heating unit 133 includes an exciting coil 133a, a hobbin 133b, and a core 133c, and heats the fixing roller 131 by electromagnetic induction. The induction heating unit 133 extends in the axial direction of the fixing roller 131 and is a part of the outer periphery of the fixing roller 131. So as to surround each other.

  The exciting coil 133a made of a copper wire is wound around the hobbin 133b and spirally arranged over a part of the outer periphery of the fixing roller 131 so as to circulate around the central portion of the core 133c in the axial direction. The exciting coil 133a is connected to a power source (not shown) and generates a magnetic flux by a high frequency current supplied from the power source. A magnetic flux generated from the induction heating unit 133 is generated in a direction parallel to the paper surface of FIG. 2 and penetrates the induction heating layer 131 c of the fixing roller 131. An eddy current is generated around the magnetic flux of the induction heat generating layer 131c. When the eddy current flows, Joule heat is generated by the electric resistance in the induction heat generating layer 131c, and the induction heat generating layer 131c generates heat.

  The power of the power source is controlled based on the temperature detected by the temperature sensor 134 so that the fixing roller 131 reaches a predetermined temperature by the induction heating unit 133. When the fixing roller 131 is heated and heated to a predetermined temperature, the paper P sandwiched by the nip portion N is heated and pressed by the pressure roller 132, whereby the powder on the paper P is heated. The toner in the state is melted and fixed.

  FIG. 3 is a perspective view showing the fixing device. The fixing device 13 includes a pressure mechanism 50 and a nip pressure switching unit 60 in addition to the fixing unit 30 including the fixing roller 131 and the pressure roller 132 described above. In FIG. 3, only the fixing unit 30, the pressure mechanism 50, and the nip pressure switching unit 60 are illustrated for convenience of explanation.

  The fixing roller 131 and the pressure roller 132 are rotatably supported at both ends in the longitudinal direction, and a pressure mechanism 50 and a nip pressure switching unit 60 are disposed at both ends of the pressure roller 132.

  The pressure mechanism 50 presses the pressure roller 132 and the fixing roller 131 and generates a nip pressure at a nip portion N (see FIG. 2) where the pressure roller 132 and the fixing roller 131 are in pressure contact. The first arm member 51 and the second arm member 52 and an elastic member 53, and a pair of pressure rollers 132 are disposed on both ends.

  The nip pressure switching unit 60 makes the urging force of the elastic member 53 variable, and includes a drive unit 70 composed of a motor, a gear train, etc., an eccentric cam 62, and a roller 61 that engages with the eccentric cam 62. And a rotation connecting shaft 63. The drive unit 70 is disposed on the right side of the pressure roller 132, and a pair of the eccentric cam 62 and the roller 61 are disposed on both ends of the pressure roller 132. The rotary connecting shaft 63 is provided integrally with the eccentric cams 62 on both sides, and transmits the rotational driving force of the drive unit 70 to the right eccentric cam 62 and the left eccentric cam 62. Accordingly, the nip pressure switching unit 60 changes the urging force of the elastic members 53 on both sides of the pressure roller 132 at the same time.

  4A and 4B are side views showing the pressurizing mechanism and the nip pressure switching unit. FIG. 4A shows a normal pressurizing state and FIG. 4B shows a depressurized state.

  As shown in FIG. 4A, the first arm member 51 is formed in a predetermined shape with a metal plate such as iron. A pressure roller 132 is rotatably supported at a substantially central portion of the first arm member 51. A hole is formed in the lower portion of the first arm member 51 so as to be fitted to a support shaft 54 fixed to the apparatus main body, and the first arm member 51 is swingably held in the left-right direction around the support shaft 54. Is done. One end of a fixed shaft 55 extending in the left direction is fixed to the upper portion of the first arm member 51, and a first contact portion 51a formed to extend to the left from a portion where the fixed shaft 55 is fixed. Is formed. The first contact portion 51a has a flat plate shape, and the other end of the fixed shaft 55 is fixed to the first contact portion 51a. An elastic member 53 is wound around the fixed shaft 55, and one end of the elastic member 53 is in contact with the first contact portion 51a.

  The second arm member 52 is formed in a predetermined shape with a metal plate such as iron. A second contact portion 52 a having a flat plate shape is formed on the right side portion of the second arm member 52. The second contact portion 52 a has a hole that penetrates the fixed shaft 55 so as to face the first contact portion 51 a of the first arm member 51 and to be movable in the left-right direction with respect to the fixed shaft 55. . Further, the other end of the elastic member 53 is in contact with the second contact portion 52a.

  The elastic member 53 is for applying a nip pressure to the nip portion N, and is composed of a compression coil spring. In a contracted state, both ends of the elastic member 53 abut against the first abutment portion 51a and the second abutment portion 52a. ing. For this reason, a leftward biasing force acts on the first abutting portion 51a, and a rightward biasing force acts on the second abutting portion 52a. The abutting portions 52a are urged away from each other, and the pressure roller 132 is in pressure contact with the fixing roller 131.

  The second arm member 52 is formed to extend to the left from the second contact portion 52a, and a cylindrical roller 61 is rotatably attached to the left end portion thereof.

  An eccentric cam 62 is engaged with the roller 61. The eccentric cam 62 is rotatable around the rotation center of the rotary connecting shaft 63 (see also FIG. 3), and is formed such that the distance from the rotation center to the outer peripheral edge differs on the circumference. A concave first concave portion 62 a and a second concave portion 62 b are formed on the outer peripheral edge of the eccentric cam 62. The first recess 62a and the second recess 62b are provided at different circumferential surface positions from the rotation center, and the distance from the rotation center of the first recess 62a is larger than the distance from the rotation center of the second recess 62b. Is set. The first recess 62 a and the second recess 62 b can be engaged with the roller 61, and when the rotary connecting shaft 63 is rotated by a driving unit 70 described later, the first recess 62 a shown in FIG. The engaged state and the state where the second recess 62b shown in FIG. 4B is engaged with the roller 61 are switched.

  When the first recess 62 a shown in FIG. 4A is engaged with the roller 61, the second contact portion 52 a of the second arm member 52 and the first contact portion 51 a of the first arm member 51 Is at a predetermined distance, and the elastic member 53 is reduced by a predetermined amount. When the second recess 62b shown in FIG. 4B is engaged with the roller 61, the second arm member 52 is displaced in the right direction with respect to the state of FIG. The distance between the contact part 52a and the first contact part 51a is increased, and the elastic member 53 is extended.

  Therefore, in the state of FIG. 4B, the urging force by the elastic member 53 becomes smaller than in the state of FIG. 4A, and accordingly, the nip pressure of the nip portion N becomes smaller and the pressure is reduced. . In addition, since the nip pressure of the nip portion N is reduced, the first arm member 51 is slightly rotated in the right direction around the support shaft 54.

  In the present embodiment, the first and second recesses 62a and 62b of the eccentric cam 62 are disposed at positions facing each other with respect to the rotation center (position shifted by 180 ° phase). Thus, when the eccentric cam 62 is rotated 180 °, the first recess 62a is engaged with the roller 61, whereas when the eccentric cam 62 is rotated reversely 180 °, the second recess 62b is engaged with the roller 61. To do.

  As shown in FIG. 4A, when the first recess 62 a of the eccentric cam 62 is engaged with the roller 61, the second abutting portion 52 a of the second arm member 52 is moved to the arrow by the elastic member 53. A biasing force in the A direction acts. In this embodiment, the alignment direction of the central axis of the roller 61 and the rotation center of the eccentric cam 62 is set to be substantially the same in the direction of the arrow A. With this setting, substantially all of the urging force in the direction of arrow A acts on the engaging portion between the roller 61 and the first recess 62 a, and the roller 61 and the first recess 62 a are reliably locked by the elastic member 53. The

  When the eccentric cam 62 is rotated 180 ° from the state of FIG. 4A and the second recess 62b of the eccentric cam 62 is engaged with the roller 61 as shown in FIG. A biasing force in the direction of arrow A smaller than the state of FIG. 4A acts on the second contact portion 52a of the two-arm member 52 by the elastic member 53. The alignment direction of the center axis of the roller 61 and the rotation center of the eccentric cam 62 (hereinafter sometimes referred to as “the alignment direction of the roller 61 and the eccentric cam 62”) is substantially the same in the arrow A direction. It is set as follows. With this setting, substantially all of the urging force in the direction of arrow A acts on the engaging portion between the roller 61 and the second recess 62b, and the roller 61 and the second recess 62b are securely locked by the elastic member 53. The

  If the alignment direction of the roller 61 and the eccentric cam 62 coincides with the arrow A direction, all the urging force in the arrow A direction acts on the engaging portion between the roller 61 and the second recess 62b. However, even if the direction of alignment of the roller 61 and the eccentric cam 62 is inclined by about 10 ° with respect to the direction of the arrow A, even if it does not coincide with the direction of the arrow A, the engagement between the roller 61 and the first recess 62a. If the component force of the urging force in the A direction facing the direction in which the roller 61 and the eccentric cam 62 are arranged is sufficiently larger than the component force in the direction perpendicular to the component force, the roller 61 and the first recess 62a Are securely locked by the elastic member 53. This also applies when the second recess 62b engages with the roller 61.

  A drive unit 70 is provided to rotate the eccentric cam 62 forward and backward. 5 to 7 are views showing the drive unit 70 in detail, FIG. 5 is a perspective view showing a normal pressure state of the drive unit, FIG. 6 is a perspective view showing a reduced pressure state of the drive unit, and FIG. 8 is a diagram showing a state (a) when the tooth missing gear is normally pressurized and a state (b) when the tooth missing gear is depressurized. 5 and 6 show some gears removed from the gear train for convenience.

  As shown in FIG. 5, the drive unit 70 includes a motor 72, a motor gear 73, gear trains 74 to 80, a return spring 82, and a base plate 71 fixed to the apparatus main body.

  The motor 72 is a DC motor, for example, and is attached to the base plate 71. When the motor 72 is rotated forward and backward by a motor drive circuit described later, the eccentric cam 62 (see FIG. 4) rotates forward or backward via the gear trains 74 to 80 and the rotary connecting shaft 63. A motor gear 73 made of worm is attached to the rotating shaft of the motor 72.

  The gear trains 74 to 80 are a first gear 74 made of a wheel meshing with the motor gear 73, a second gear 75 made of a spur gear, a third gear 76, a fourth gear 77, and a spur gear and having a predetermined number of teeth. It has a tooth missing gear 78 having a tooth missing portion 78a, a fifth gear 79 and a sixth gear 80 made of spur gears, and the rotational driving force of the motor 72 is the first to fourth gears 74 to 77, and the tooth missing gear. 78, the fifth gear 79, and the sixth gear 80 are sequentially transmitted.

  The first and second gears 74 and 75 are integrally provided on the rotation shaft and are rotatably supported by the base plate 71. The third gear 76 meshes with the second gear 75 and is provided integrally with the fourth gear 77. The third and fourth gears 76 and 77 are rotatably supported by a rotation shaft 63 a extending from the rotation connecting shaft 63. The tooth missing gear 78 meshes with the fourth gear 77 which is a motor side gear, is provided integrally with the fifth gear 79 and is rotatably supported by the base plate 71. The sixth gear 80 meshes with the fifth gear 79 and is provided integrally with the rotation shaft 63a.

  Here, when the motor 72 rotates forward, the gear trains 74 to 80 are in the state shown in FIG. 5, and when the motor 72 rotates reversely a predetermined number of times from this state, the gear trains 74 to 80 change to the state shown in FIG. The state shown in FIG. 5 is a normal pressure state, that is, a case where the first recess 62a of the eccentric cam 62 is engaged with the roller 61 (see FIG. 4A). The state shown in FIG. 6 is a reduced pressure state, that is, a case where the second recess 62b of the eccentric cam 62 is engaged with the roller 61 (see FIG. 4A).

  In the gear trains 74 to 80 in the state shown in FIG. 5, the tooth missing gear 78 is arranged and set so that the right end of the tooth missing portion 78 a faces the fourth gear 77. Specifically, as shown in FIG. 7A, the fourth gear 77 faces the tooth missing portion 78 a so as to mesh with the tooth portion 78 b at the right end of the tooth missing portion 78 a in the tooth missing gear 78.

  Further, when the motor 72 rotates reversely a predetermined number of times from the state shown in FIG. 5, the sixth gear 80 rotates 180 °, that is, the engagement with the roller 61 starts from the first recess 62 a of the eccentric cam 62. The reduction ratio of the gear trains 74 to 80 is set so as to switch to the second recess 62b (see FIG. 4). In addition, when the motor 72 rotates reversely a predetermined number of times in the reduction ratios of the gear trains 74 to 80, as shown in FIG. 6, the tooth missing gear 78 has the fourth gear 77 at the left end of the tooth missing portion 78a. The tooth-missing portion 78a is set to a predetermined number of teeth so as to be opposed to each other. Specifically, as shown in FIG. 7B, the fourth gear 77 faces the tooth missing portion 78 a so as to mesh with the tooth portion 78 c at the left end portion of the tooth missing portion 78 a in the tooth missing gear 78.

  Returning to FIG. 5, the return spring 82 is a coil spring hung between the sixth gear 80 and the base plate 71, and applies a biasing force to the tooth missing gear 78 via the sixth gear 80 and the fifth gear 79. Has been granted. In the state shown in FIG. 5, the return spring 82 urges the sixth gear 80 clockwise, and when the motor 72 rotates in the reverse direction, the return spring 82 counteracts the sixth gear 80 as shown in FIG. It is energized clockwise. Each urging force of the return spring 82 in FIGS. 5 and 6 acts on the tooth missing gear 78 in the direction F1 of FIG. 7A via the sixth gear 80 and the fifth gear 79. The gear 78 acts in the direction F2 in FIG.

  Accordingly, as shown in FIG. 7A, the fourth gear 77 rotates in the direction of arrow B due to the forward rotation of the motor 72, and the fourth gear 77 meshes with the tooth portion 78 b of the tooth missing gear 78. When the fourth gear 77 further rotates in the direction of the arrow B in the state of facing the 78 a, a rotational driving force in the clockwise direction is transmitted to the tooth missing gear 78 by the fourth gear 77. However, a biasing force in the direction opposite to the rotational driving force is also applied to the tooth missing gear 78 by the return spring 82. For this reason, in the state where the tooth missing portion 78 a of the tooth missing gear 78 faces the fourth gear 77, the tooth missing gear 78 rotates idly. In this way, even if the motor 72 further rotates forward, the tooth-missing gear 78 rotates idly, so that the eccentric cam 62 (see FIG. 4) does not rotate via the rear gear train and the rotation connecting shaft 63. The first recess 62a of the eccentric cam 62 is engaged with the roller 61, and the normal pressure state is maintained.

  When the motor 72 rotates backward a predetermined number of times from the state of FIG. 7A, the fourth gear 77 rotates in the opposite direction to the arrow B direction, and the tooth missing gear 78 rotates counterclockwise. Next, the eccentric cam 62 (see FIG. 4) rotates through 180 ° via the rear stage gear train and the rotary connecting shaft 63, and the second recess 62b of the eccentric cam 62 engages with the roller 61, and FIG. It changes to the reduced pressure state shown in b). In the state of FIG. 7B, the fourth gear 77 meshes with the tooth part 78c of the tooth missing gear 78 and faces the tooth missing part 78a. In this state, when the motor 72 further rotates in the reverse direction and the fourth gear 77 further rotates in the direction of arrow C, the fourth gear 77 transmits a rotational driving force in the counterclockwise direction to the tooth missing gear 78. However, the tooth missing gear 78 is also subjected to a biasing force in the direction opposite to the rotational driving force by the return spring 82, and the tooth missing part 78 a of the tooth missing gear 78 faces the fourth gear 77. The gear 78 will idle. As described above, even if the motor 72 rotates reversely a predetermined number of times or more, the tooth-missing gear 78 rotates idly, so that the eccentric cam 62 (see FIG. 4) is moved via the rear gear train and the rotary connecting shaft 63. Without rotation, the second recess 62b of the eccentric cam 62 engages with the roller 61 and maintains the reduced pressure state.

  In addition, since the urging force in the direction opposite to the rotational driving force acts on the tooth missing gear 78 by the return spring 82, when the rotation direction of the motor 72 is switched, the tooth portion 78b located at the end of the tooth missing portion 78a or 78 c is disposed at a position where it meshes with the fourth gear 77. Therefore, the rotational driving force from the fourth gear 77 can be reliably transmitted to the tooth missing gear 78.

  FIG. 8 is a block diagram showing a control unit for controlling the motor 72 and its periphery. The switching control unit 101 serving as a control unit includes a motor drive circuit 103 that drives the motor 72, a power switch 105 that turns on and off the power of the image forming apparatus 10 including the fixing device 13, an on / off operation of the power switch 105, and printing. An operation panel 104 is connected to perform operations such as mode and jam release, and display of the operations.

  The switching control unit 101 includes a microcomputer, a storage element such as a RAM and a ROM, and controls input / output according to a program set in the storage element. Specifically, based on a signal from the power switch 105 and a signal input from the operation panel 104, the switching control unit 101 controls the motor drive circuit 103 so that the motor 72 rotates forward or backward a predetermined number of times. Control. By this control, the fixing device 13 is switched between the normal pressure state and the pressure reduction state.

  When an ON signal is input from the power switch 105, the switching control unit 101 rotates the motor 72 reversely a predetermined number of times via the motor drive circuit 103 and then stops the rotation of the motor 72. As a result, the second recess 62b of the eccentric cam 62 (see FIG. 4) is engaged with the roller 61 via the gear trains 74 to 80 (see FIG. 5), and the fixing device 13 is in a decompressed state. When the print mode is set, a print start signal is input from the operation panel 104, and the switching control unit 101 rotates the motor 72 forward by a predetermined number of times via the motor drive circuit 103 based on the print start signal. Thereafter, the rotation of the motor 72 is stopped. As a result, the first recess 62a of the eccentric cam 62 (see FIG. 4) is engaged with the roller 61 via the gear trains 74 to 80 (see FIG. 5), and the fixing device 13 is in a normal pressure state. Thus, the fixing process can be performed. Further, when printing is completed, the switching control unit 101 reversely rotates the motor 72 a predetermined number of times via the motor drive circuit 103 based on the print end signal, and then stops the rotation of the motor 72, thereby fixing the fixing device. 13 is in a reduced pressure state. Further, when a jam processing signal is input from the operation panel 104 during the fixing process, the switching control unit 101 rotates the motor 72 reversely a predetermined number of times via the motor drive circuit 103 and then stops the rotation of the motor 72. To do. As a result, the fixing device 13 is changed from the normal pressure state to the pressure reduction state, and jamming can be performed.

  According to the embodiment, the image forming apparatus 10 includes the pressurizing mechanism 50 that applies a nip pressure to the nip portion N, and the nip pressure switching unit 60 that changes the nip pressure of the nip portion N. The pressurizing mechanism 50 includes an elastic member 53 that urges the first and second contact portions 51a and 52a in a direction away from each other, and a first contact portion that contacts the one end portion of the elastic member 53 at the first contact portion 51a. It has the arm member 51 and the 2nd arm member 52 which contact | abuts the other end part of the elastic member 53 in the 2nd contact part 52a. The nip pressure switching unit 60 includes a roller 61 provided on the second arm member 52 and an eccentric cam 62 that contacts the roller 61 and changes the distance from the rotation center to the outer peripheral surface. The alignment direction of the central axis of the roller 61 and the rotation center of the eccentric cam 62 is substantially the same as the direction of the urging force of the elastic member 53 acting on the second contact portion 52a.

  According to this configuration, the elastic member 53 urges the first and second abutting portions 51 a and 52 a in the direction in which they are separated from each other, thereby applying a nip pressure to the nip portion N and performing a fixing process by the fixing portion 30. It becomes possible. At this time, since the direction in which the rotation center of the eccentric cam 62 and the roller 61 are aligned is substantially the same as the direction of the urging force of the elastic member 53 acting on the second contact portion 52a, the roller 61 and the eccentric cam 62 are aligned. Nearly all the urging force of the elastic member 53 acts on the engaging portion, and the roller 61 and the eccentric cam 62 are securely locked, so that the nip pressure at the nip portion N is stabilized.

  Moreover, according to the said embodiment, the eccentric cam 62 is formed in the circumferential surface position from which the 1st recessed part 62a and the 2nd recessed part 62b which selectively engage with the roller 61 differ from a rotation center. When the recess 62a engages with the roller 61, the distance between the first and second contact portions 51a and 52a is a predetermined distance, and when the second recess 62b engages with the roller 61, the first and Second contact portion 51a

  According to this configuration, when the first recess 62a of the eccentric cam 62 is engaged with the roller 61, the elastic member 53 is applied to the nip portion N by the biasing force according to the distance between the first and second contact portions 51a and 52a. By applying a nip pressure, the fixing unit 30 can perform a fixing process. At this time, since the direction in which the rotation center of the eccentric cam 62 and the roller 61 are aligned is substantially the same as the direction of the urging force of the elastic member 53 acting on the second contact portion 52a, the roller 61 and the first recess 62a. Nearly all the urging force of the elastic member 53 acts on the engaging portion, and the roller 61 and the first concave portion 62a are reliably locked, so that the nip pressure in the nip portion N is stabilized. Further, when the second recess 62b of the eccentric cam 62 is engaged with the roller 61, the distance between the first and second contact portions 51a and 52a is larger than a predetermined distance, and the biasing force is smaller than that during the fixing process. The elastic member 53 applies a nip pressure to the nip portion N. At this time, since the direction in which the rotation center of the eccentric cam 62 and the roller 61 are aligned is substantially the same as the direction of the urging force of the elastic member 53 acting on the second contact portion 52a, the roller 61 and the second recess 62b. Nearly all the urging force of the elastic member 53 acts on the engaging portion, and the roller 61 and the second recessed portion 62b are securely locked, so that the nip pressure at the nip portion N is stabilized. Therefore, the nip pressure can be changed easily and reliably.

  Further, according to the above embodiment, the drive unit 70 is disposed in the gear trains 74 to 80 that transmit the rotational driving force of the motor 72 that can rotate forward and backward to the eccentric cam 62 and has a predetermined number of teeth missing portions. A tooth missing gear 78 having 78a, a fourth gear 77 (motor side gear) that can mesh with the tooth missing gear 78, and a tooth missing portion of the tooth missing gear 78 when the fourth gear 77 rotates forward or backward. And a return spring 82 that urges the tooth-missing gear 78 in a direction away from the fourth gear 77. When the fourth gear 77 rotates in one direction and faces the tooth missing portion 78a of the tooth missing gear 78, the tooth missing portion 78a of the tooth missing gear 78 is urged by the return spring 82 and the tooth missing portion 78a causes the first tooth missing portion 78a. When the toothless gear 78 is idled and the fourth gear 77 rotates in the other direction by being unable to mesh with the 4th gear 77, the part other than the toothless part 78a of the toothless gear 78 can mesh with the 4th gear 77. As a result, the tooth missing gear 78 rotates and the eccentric cam 62 rotates.

  According to this configuration, when the fourth gear 77 rotates in one direction due to the normal rotation of the motor 72 and the tooth missing portion 78a of the tooth missing gear 78 faces the fourth gear 77, the motor 72 rotates. Also, the tooth missing gear 78 is idling, the eccentric cam 62 is stopped, and the first recess 62 a of the eccentric cam 62 is engaged with the roller 61. Next, when the motor 72 is rotated in the reverse direction, the fourth gear 77 rotates in the other direction, and the portion other than the tooth missing portion 78a of the tooth missing gear 78 meshes with the fourth gear 77. As a result, the eccentric cam 62 rotates. By the rotation of the eccentric cam 62, the second recess 62b of the eccentric cam 62 is engaged with the roller 61, and the elastic member 53 is changed to a smaller urging force than that at the time of fixing processing. That is, the nip pressure is changed. Even if the motor 72 continues to rotate in the reverse direction, the tooth missing portion 78 a of the tooth missing gear 78 is positioned to face the fourth gear 77 due to the urging force of the return spring 82. Therefore, when the motor 72 rotates forward, the nip pressure is kept high. On the other hand, when the motor 72 rotates backward, the nip pressure is kept low. If these are correlated, the nip pressure can be easily and inexpensively switched without providing a special member such as a sensor.

  Moreover, according to the said embodiment, when the eccentric cam 62 is made to rotate half a half by arrange | positioning the 1st recessed part 62a and the 2nd recessed part 62b of the eccentric cam 62 in the position which opposes with respect to a rotation center, Engagement is switched from one recess of the first and second recesses 62a, 62b to the other recess, and the rotation angle of the toothless gear 78 is set large without greatly decelerating the gear trains 74-80. As a result, the output torque of the motor 72 can be reduced.

  Further, according to the above-described embodiment, the switching control unit 101 rotates the motor 72 in the direction in which the first recess 62a of the eccentric cam 62 engages the roller 61 at the start of image formation (printing), thereby performing image formation. At the end, the motor 72 is controlled to rotate in the direction in which the second recess 62b of the eccentric cam 62 is engaged with the roller 61. Thus, if the rotation direction of the motor 72 is correlated with the state of the nip pressure and the rotation direction of the motor 72 is switched according to the operation mode, for example, when no image is formed, the pressure roller The pressure load between the pressure roller 132 and the fixing roller 131 is easily reduced, and the durability of the pressure roller 132 and the fixing roller 131 is improved.

  In addition, according to the embodiment, the fixing unit 30 is disposed to face the fixing roller 131, generates a magnetic flux, and induces and heats the induction heating layer 131 c provided on the fixing roller 131 by the magnetic flux. Is further provided. Accordingly, in the electromagnetic induction heating type fixing device including the induction heating unit 133, the pressure mechanism 50 and the nip pressure switching unit 60 can be appropriately disposed on the pressure roller 132 side, and the induction heating unit 133, In addition, the peripheral members can be appropriately arranged on the fixing roller 131 side.

  In the above embodiment, an example in which the present invention is applied to a roller type fixing device has been described. However, the present invention is not limited to this, and a belt type using an endless fixing belt as a heating member or a heating member is fixedly supported. Further, the present invention may be applied to a fixing device having a heating body and a heat-resistant film that slides in close contact with the heating body and presses the heating body and a pressure roller through the heat-resistant film. Further, a heater may be used as the heat source, and a pressurizing mechanism may be provided on the heating member side.

  In the above-described embodiment, the configuration in which the eccentric cam 62 is provided with the first and second recesses 62a and 62b is shown. However, the present invention is not limited to this, and the roller 61 is provided with a recess to You may make it the structure which provides the 1st protrusion and 2nd protrusion which engage with this recessed part. In this case as well, the same effects as in the above embodiment can be obtained.

  INDUSTRIAL APPLICABILITY The present invention can be used for an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, a fixing device capable of changing a nip pressure between a heating member and a pressure member. Can be used in an image forming apparatus equipped with

10 Image forming apparatus
11 Device body 13 Fixing device 131 Fixing roller (heating member)
132 Pressure roller (Pressure member)
133 Induction heating unit 30 Fixing unit 50 Pressure mechanism 51 First arm member 51a First contact unit 52 Second arm member 52a Second contact unit 53 Elastic member 54 Support shaft 55 Fixed shaft 60 Nip pressure switching unit 61 Roller 62 Eccentric cam 62a 1st recessed part 62b 2nd recessed part 63 Rotation connection shaft 70 Drive part 71 Base plate 72 Motor 73 Motor gear 74-80 Gear train 77 4th gear (motor side gear)
78 tooth missing gear 78a tooth missing part 82 return spring 101 switching control part (control part)
103 Motor drive circuit 104 Operation panel 105 Power switch

Claims (6)

A fixing unit configured to heat and press a toner image carried on the recording material and fix the toner image on the recording material; and the pressure member and the heating member. A pressure mechanism that applies a nip pressure to the nip portion that is in pressure contact, and a nip pressure switching portion that changes the nip pressure of the nip portion,
The pressurizing mechanism is supported so as to be swingable about a support shaft, has a first abutting portion, holds a first arm member that holds one member of the pressurizing member and the heating member, and a second A second arm member having an abutting portion, and one end abutting against the first abutting portion and the other end abutting against the second abutting portion, wherein the first and second abutting portions are arranged An elastic member that applies a nip pressure to the nip portion by urging in a direction in which the nip portions are separated from each other;
The nip pressure switching unit includes a roller provided on the second arm member, an eccentric cam that contacts the roller and changes a distance from a rotation center to an outer peripheral surface, and a drive unit that rotationally drives the eccentric cam. And having
2. An image forming apparatus according to claim 1, wherein an alignment direction of a center axis of the roller and a rotation center of the eccentric cam is substantially the same as a direction of a biasing force of the elastic member acting on the second contact portion. In the eccentric cam, the first recess and the second recess that selectively engage with the roller are formed at different circumferential surface positions from the rotation center,
When the first recess engages with the roller, the distance between the first and second contact portions is a predetermined distance, and when the second recess engages with the roller, the first recess The image forming apparatus according to claim 1, wherein a distance between the first contact portion and the second contact portion is larger than a predetermined distance.   The image forming apparatus according to claim 2, wherein the first concave portion and the second concave portion of the eccentric cam are disposed at positions facing the rotation center. The drive unit includes a motor capable of rotating in the forward and reverse directions, a tooth missing gear disposed in a gear train that transmits a rotational driving force of the motor to the eccentric cam, and a tooth missing portion having a predetermined number of teeth; A motor-side gear that can mesh with the chipped gear, and the tooth-missed gear in a direction in which the tooth-missed portion of the tooth-missed gear is separated from the motor-side gear when the motor-side gear rotates forward or backward. A return spring for biasing,
When the motor side gear rotates in one direction and the tooth missing portion of the tooth missing gear faces the motor side gear, the tooth missing gear is biased by the return spring and at the tooth missing portion on the motor side. By becoming unable to mesh with the gear, the toothless gear idles,
When the motor side gear rotates in the other direction, portions other than the tooth missing portion of the tooth missing gear can mesh with the motor side gear, so that the tooth missing gear rotates and rotates the eccentric cam. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The motor is rotated in a direction in which the first concave portion of the eccentric cam engages the roller at the start of image formation, and the second concave portion of the eccentric cam engages in the roller at the end of image formation. The image forming apparatus according to claim 4, further comprising a control unit that controls the motor to rotate.   The fixing unit further includes an induction heating unit that is arranged to face the heating member, generates an magnetic flux, and induction-heats an induction heating layer provided on the heating member by the magnetic flux, and the one member is pressurized The image forming apparatus according to claim 1, wherein the image forming apparatus is a member.

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