JP2019139012A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device including an opening/closing member that can appropriately open/close an entrance of a pressure area without using a special driving source.SOLUTION: A fixing device 9 applies heat and pressure to a sheet conveyed to a pressure area N2 formed between a fixing member 33 and a pressure member 35 to fix a toner image to the sheet. The fixing device 9 comprises: a pressure changing unit 37 that moves the pressure member 35 in a direction to approach or separate from the fixing member 33 to change the pressure in the pressure area N2; and an opening/closing member 39 that opens/closes an entrance 41 for the sheet to the pressure area N2. The opening/closing member 39 is displaced from an opening attitude for opening the entrance 41 to a closing attitude for closing the entrance 41 in conjunction with an operation of the pressure changing unit 37 to reduce the pressure in the pressure area N2 from a normal pressure corresponding to plain paper.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet and an image forming apparatus including the fixing device.

  In the fixing device, a pressure region is formed between the fixing member and the pressure member, and when the paper is conveyed to the pressure region, the toner is heated and pressurized and fixed on the paper. The fixing member is maintained at a constant temperature, so that even in a standby state where the printing operation is not performed, the printing operation can be performed immediately when a print job occurs.

  On the other hand, the entrance of the sheet to the pressurizing area is always open, so that the heat around the fixing member can easily escape from the entrance. When there is a large amount of heat dissipation, there is a problem that power consumption increases or heat that escapes from the inlet raises the temperature of components near the inlet and causes deformation or deterioration.

  To solve such a problem, the fixing device disclosed in Patent Document 1 opens and closes the openings on the inlet side and the outlet side using an outer peripheral plate formed of a bimetal that deforms according to temperature. In the fixing device disclosed in Patent Document 2, the paper supply / discharge port is opened and closed by a guide that is rotated by a drive source.

JP-A-6-95544 Japanese Patent Laid-Open No. 2002-365932

  However, the fixing device described in Patent Document 1 has a problem that the bimetal is expensive, or the countermeasure against static electricity is required because it is a metal. Further, since the fixing device described in Patent Document 2 requires a drive source for rotating the guide, there is a problem that the number of parts increases, and the fixing device becomes larger and costs increase.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a fixing device and an image forming apparatus including an opening / closing member that can appropriately open and close an entrance of a pressure region without using a dedicated drive source.

  In order to solve the above problems, a fixing device of the present invention fixes a toner image on a sheet by heating and pressing a sheet conveyed to a pressure region formed between the fixing member and the pressure member. A pressure changing section for changing one of the fixing member and the pressure member in a direction approaching or separating from the other to change the pressure in the pressure area; and a paper inlet to the pressure area. An opening / closing member that opens and closes, and the pressure changing unit depresses the pressure in the pressurizing region from the normal pressure corresponding to plain paper, and the opening / closing member opens the inlet from the open posture. It is characterized by being displaced to a closed posture.

  In the fixing device according to the aspect of the invention, the pressure changing unit supports the pressure member, a holder member that swings in a direction in which the pressure member approaches or separates from the fixing member, and one end fixed to the holder member. A spring that urges the holder member in a direction in which the pressure member approaches the fixing member, and a lever that changes the length of the spring by swinging with the other end of the spring fixed. A member and a cam that rotates while contacting the lever member to swing the lever member, and by rotating the cam, the lever member is swung to change the length of the spring, The spring is provided so as to change the pressure of the pressurizing region by changing a biasing force that biases the holder member, and the opening / closing member is provided to be rotatable about the same axis as the cam, The pressure in the pressure area Serial usually in conjunction with the rotation of the cam in the direction of reduced pressure pressure, it may be characterized in that pivots from said open position to said closed position.

  In the fixing device of the present invention, the opening / closing member may have a heat insulating layer.

  In the fixing device according to the aspect of the invention, the elastic member includes an elastic member that urges the opening / closing member to the closed position, and the elastic member is elastically deformed when the opening / closing member contacts the paper when the paper is present at the entrance. Then, the rotation of the opening / closing member to the closing posture may be restricted.

  In the fixing device according to the aspect of the invention, the pressure changing unit may set the pressure in the pressure region to a first reduced pressure value lower than the normal pressure, and a second reduced pressure value lower than the first reduced pressure value, In the changing operation from the normal pressure to the first reduced pressure value, the opening / closing member is not displaced from the open position to the closed position, and the first reduced pressure value is changed to the second reduced pressure value. The opening / closing member may be displaced from the open posture to the closed posture in conjunction with the change operation to the value.

  In the fixing device according to the aspect of the invention, the opening / closing member may include a guide unit that guides the sheet to the pressure area in the open posture.

  An image forming apparatus according to the present invention includes an image forming unit that forms a toner image on a sheet, and the fixing device described above that fixes the toner image on the sheet.

  According to the present invention, since the opening / closing member is rotated in conjunction with the operation of the pressure changing unit that changes the pressure in the pressurizing region, the inlet of the pressurizing region is opened by the opening / closing member without using a dedicated drive source. Can be opened and closed.

1 is a front view schematically showing an internal configuration of a printer according to an embodiment of the present invention. In the fixing device according to an embodiment of the present invention, FIG. In the fixing device according to an embodiment of the present invention, FIG. FIG. 3 is a front view showing an opening / closing member of the fixing device according to the embodiment of the present invention. FIG. 3 is a side view showing an opening / closing member of a fixing device according to an embodiment of the present invention. FIG. 5 is a perspective view of the fixing device according to the embodiment of the present invention, as viewed from below, in a state in which the opening / closing member is displaced to the open posture. FIG. 6 is a perspective view of the fixing device according to the embodiment of the present invention, as viewed from below, in a state where the opening / closing member is displaced to the closing posture. In the fixing device according to an embodiment of the present invention, FIG. In the fixing device according to an embodiment of the present invention, FIG. FIG. 3 is a front view showing an opening / closing member when a paper jam occurs in the fixing device according to the embodiment of the present disclosure. FIG. 4 is a front view illustrating a part of the fixing device and the image forming unit in a state where the opening / closing member is displaced to the open posture in the printer according to the embodiment of the present disclosure. FIG. 4 is a front view illustrating a part of the fixing device and the image forming unit in a state where the opening / closing member is displaced to the closing posture in the printer according to the embodiment of the present disclosure. FIG. 4 is a perspective view showing a cam and an opening / closing member at normal pressure in the fixing device according to the embodiment of the present invention. FIG. 3 is a perspective view showing a cam and an opening / closing member during a first pressure reduction in the fixing device according to the embodiment of the present invention. FIG. 6 is a perspective view showing a cam and an opening / closing member during second decompression in the fixing device according to the embodiment of the present invention.

  Hereinafter, an image forming apparatus and a fixing device of the present invention will be described with reference to the drawings.

  First, the overall configuration of a color printer as an image forming apparatus will be described with reference to FIG. FIG. 1 is a front view schematically showing the internal configuration of the color printer 1. In the following description, the front side of the paper surface in FIG. 1 is the front side (front side) of the color printer 1, and the left and right directions will be described with reference to the direction when the color printer 1 is viewed from the front. L and R of each figure show the left direction and the right direction, respectively.

  The apparatus main body 2 of the color printer 1 includes a paper feeding cassette 3 that stores paper, a paper feeding device 5 that feeds paper from the paper feeding cassette 3, an image forming unit 7 that forms a toner image on the paper, and a toner image. A fixing device 9 for fixing the paper to the paper, a paper discharge device 11 for discharging the paper, and a paper discharge tray 13 on which the discharged paper is stacked.

  The image forming unit 7 includes an intermediate transfer belt 17, four image forming units 19, four primary transfer rollers 21, an exposure device 23, a toner container 25, and a secondary transfer roller 27. . The intermediate transfer belt 17 is stretched between rollers 17a and 17b arranged on the left and right sides and travels in the counterclockwise direction of FIG. The four image forming units 19 and the four primary transfer rollers 21 face each other across the lower track of the intermediate transfer belt 17. The secondary transfer roller 27 faces the right roller 17b with the intermediate transfer belt 17 in between, and forms a transfer nip N1 with the intermediate transfer belt 17.

  The exposure device 23 irradiates each image forming unit 19 with laser light, and forms a latent image according to the image to be formed. The four image forming units 19 develop the illuminated image into a toner image using toners supplied from the toner containers 25 corresponding to the four colors (yellow, magenta, cyan, and black), respectively. The four primary transfer rollers 21 transfer the toner images formed on the four image forming units 19 to the intermediate transfer belt 17 to form a full-color toner image on the intermediate transfer belt 17. The full-color toner image is transferred onto the sheet by the secondary transfer roller 27 in the transfer nip N1.

  Further, a sheet conveyance path 29 is formed in the apparatus main body 2 from the sheet feeding device 5 to the sheet discharge device 11 through the transfer nip N1 and the fixing device 9 of the image forming unit 7.

  The sheet fed from the sheet feeding cassette 3 by the sheet feeding device 5 is transported along the transport path 29 to the transfer nip N1 of the image forming unit 7, and a full-color toner image is transferred onto the sheet. The sheet is conveyed to the fixing device 9 along the conveyance path 29, and the toner image is fixed on the sheet. The paper on which the toner image is fixed is discharged from the paper discharge device 11 and stacked on the paper discharge tray 13.

  Next, the fixing device 9 will be described with reference to FIGS. 2 and 3 are front views showing the fixing device.

  The fixing device 9 holds a fixing housing 31, a fixing roller 33 as a fixing member, a pressure roller 35 as a pressure member that forms a pressure region N <b> 2 between the fixing roller 33, and the pressure roller 35. A pressure changing portion 37 that opens and closes and an opening and closing member 39 that opens and closes the inlet of the pressurizing region N2.

  The fixing housing 31 is a hollow box-shaped member that is long in the width direction (front-rear direction) intersecting the sheet conveyance direction. A paper inlet 41 is formed in the lower surface of the fixing housing 31 along the width direction. A paper outlet 43 is formed on the upper surface of the fixing housing 31 along the width direction. A paper transport path 29 is formed from the inlet 41 toward the outlet 43. A fixing roller accommodating portion 31a that accommodates the fixing roller 33 is formed on one side (left side) of the conveyance path 29, and a pressure roller accommodating that the pressure roller 35 is accommodated on the other side (right side). A portion 31b is formed.

  The fixing roller 33 has a cylindrical cored bar and a release layer provided on the outer peripheral surface of the cored bar via an adhesive layer. A halogen heater 45 is accommodated in the hollow portion of the fixing roller 33. The halogen heater 45 radiates heat to the inner peripheral surface of the fixing roller 33 to heat the fixing roller 33. The fixing roller 33 is rotatably supported by the fixing roller housing portion 31 a of the fixing housing 31. The fixing roller 33 is driven by a motor (not shown) and rotates counterclockwise in FIGS.

  The pressure roller 35 has a rotating shaft 35a, an elastic layer provided on the outer peripheral surface of the rotating shaft 35a, and a release layer provided on the outer peripheral surface of the elastic layer via an adhesive layer. As described above, the pressure roller 35 is supported by the pressure roller accommodating portion 31 b of the fixing housing 31 by the pressure changing portion 37.

  The pressure changing unit 37 includes a holder member 51 that supports both ends of the rotating shaft 35a of the pressure roller 35, a coil spring 53 that is fixed at one end to the holder member 51, and a lever that is fixed at the other end of the coil spring 53. A member 55 and a cam 57 that rotates in contact with the lever member 55 are provided.

  The holder member 51 is a substantially rectangular plate-like member that is long in the vertical direction. On one side (left side) of the holder member 51, a groove 51a is formed which is cut out in a direction (right side) substantially perpendicular to the side edge. The end of the rotating shaft 35a of the pressure roller 35 is engaged with the groove 51a. Further, a hook portion 51b protruding to the other (right side) is formed above the groove 51a. The hook portion 51b is engaged with a protruding piece 31c provided in the pressure roller housing portion 31b. As the hook portion 51b engages with the protrusion 31c in this way, the pressure roller 35 comes into contact with the fixing roller 33 obliquely from above, and the pressure region N2 is interposed between the pressure roller 35 and the fixing roller 33. Is forming.

  When the fixing roller 33 rotates in the counterclockwise direction in FIGS. 2 and 3, the pressure roller 35 follows the fixing roller 33 and rotates in the clockwise direction. As a result, the sheet conveyed to the pressurizing area N2 is conveyed along the conveyance path 29. When the holder member 51 is swung in the clockwise direction in FIGS. 2 and 3 around the contact point between the hook portion 51b and the protruding piece 31c, the pressure roller 35 is pressed against the fixing roller 33 to apply pressure. The pressure in the region N2 increases. Conversely, when the holder member 51 is swung counterclockwise in FIGS. 2 and 3 around the contact point between the hook portion 51b and the protruding piece 31c, the pressure in the pressurizing region N2 is lowered.

  The lever member 55 is a member having an L-shaped cross section, and includes a support piece 55a and a contact piece 55b that bends at a substantially right angle from the support piece 55a. The upper end portion of the support piece 55a is supported so as to be rotatable about a support shaft 31d provided in the fixing roller accommodating portion 31a. The abutting piece 55 b faces the inlet 41 of the fixing housing 31. The lever member 55 is urged by a torsion coil spring (not shown) so that the contact piece 55b swings in a direction close to the inlet 41 (counterclockwise direction in FIGS. 2 and 3).

  The coil spring 53 is interposed between the lower end portion of the holder member 51 and the lower end portion of the support piece 55 a of the lever member 55.

  The cam 57 has a rotating shaft 61 and a cam body 63. The rotating shaft 61 has a D-cut surface 61a in which a part of the outer peripheral surface is cut out in parallel with the axial direction. The rotating shaft 61 is driven to rotate by a driving gear 62 (not shown in FIGS. 2 and 3; see FIGS. 5 and 6). The cam body 63 is an eccentric cam having a substantially egg-shaped outer frame 63x and a substantially cross-shaped inner frame 63y fixed to the inner peripheral surface of the outer frame 63x. The rotating shaft 61 is fixed near the intersection of the inner frame 63y. The outer peripheral surface of the outer frame 63x is formed so that the diameter gradually decreases along the circumferential direction from the maximum outer peripheral surface 63a that maximizes the distance (diameter) to the axis of the rotation shaft 61. The maximum outer peripheral surface 63a has a relatively small curvature. The maximum outer circumferential surface 63 a is formed at the same position as the D-cut surface 61 a of the rotation shaft 61 and the circumferential direction of the rotation shaft 61. One end of the inner frame 63y is fixed to the inner peripheral surface corresponding to the maximum outer peripheral surface 63a of the outer frame 63x.

  The rotation shaft 61 is rotatably supported between the contact piece 55 b of the lever member 55 and the inlet 41. The contact piece 55b of the lever member 55 biased by the torsion coil spring is in contact with the outer peripheral surface of the outer frame 63x of the cam body 63. When the rotary shaft 61 rotates while the outer peripheral surface of the outer frame 63x of the cam body 63 contacts the contact piece 55b, the lever member 55 swings around the support shaft 31d. As the lever member 55 swings in this way, the length of the coil spring 53 changes.

  For example, as shown in FIG. 2, when the maximum outer peripheral surface 63 a of the outer frame 63 x of the cam body 63 is in contact with the contact piece 55 b of the lever member 55, the lever member 55 is separated from the holder member 51. It swings the most (to the left). That is, the length L1 of the coil spring 53 is the longest, and the force for swinging the holder member 51 in the clockwise direction in FIGS. 2 and 3 is increased. The pressure roller 35 held by the holder member 51 is the fixing roller. 33 is pressed with the strongest pressure. The pressure in the pressurizing area N2 at this time is set to a normal pressure corresponding to plain paper. Further, the curvature of the maximum outer peripheral surface 63a is relatively small, and the outer frame 63x of the cam body 63 and the contact piece 55b of the lever member 55 are in contact with each other on a relatively wide surface, so that the lever member 55 is securely held. I can keep it.

  On the other hand, as shown in FIG. 3, the rotating shaft 61 of the cam 57 rotates about 90 degrees, and the outer peripheral surface 63b having a smaller diameter than the maximum outer peripheral surface 63a of the outer frame 63x of the cam body 63 When coming into contact with the contact piece 55b, the lever member 55 swings in the direction approaching the holder member 51 (right direction). Then, the length L2 of the coil spring 53 is shorter than the length L1, and the force for swinging the holder member 51 in the clockwise direction in FIGS. 2 and 3 is reduced. Thereby, the force which presses the pressure roller 35 against the fixing roller 33 is reduced, and the pressure in the pressure region N2 is lower than the normal pressure. At this time, the pressure roller 35 may be completely separated from the fixing roller 33. Further, since the outer peripheral surface of the outer frame 63x is formed so that the diameter gradually decreases along the circumferential direction from the maximum outer peripheral surface 63a, the lever member 55 is rotated when the outer frame 63x of the cam main body 63 rotates. Rotates smoothly, and the pressure in the pressurizing region N2 can be gradually reduced. Further, when the rotation shaft 61 of the cam 57 rotates about 90 degrees, the outer peripheral surface 63b that contacts the contact piece 55b of the lever member 55 also has a relatively small curvature, so that the contact surface between the cam body 63 and the lever member 55 , And the lever member 55 can be securely held.

  Thus, the pressure changing unit 37 can change the pressure in the pressurizing region N2 from the normal pressure to a pressure lower than the normal pressure by rotating the rotating shaft 61 of the cam 57 by about 90 degrees.

  Next, the opening / closing member 39 will be described with reference to FIGS. 4A and 4B and FIGS. 4A is a front view of the opening / closing member, FIG. 4B is a side view of the opening / closing member, FIGS. 5 and 6 are perspective views of the fixing device, and FIGS. 7 to 9 are front views showing the opening / closing member.

  As shown in FIGS. 4A and 4B, the opening / closing member 39 includes a hollow main body 71 and a pair of rotating cylinders 73. The main body 71 has a length equivalent to the length of the inlet 41 in the width direction W, and has a fan-shaped (substantially quarter-circular) side shape that is approximately ¼ of a circle, as shown in FIG. 4B. ing. The main body 71 forms a hollow portion S surrounded by a pair of side walls 71a facing the width direction W, an outer peripheral wall 71b, and a pair of end walls 71c facing the fan-shaped circumferential direction. A corner portion between the outer peripheral wall 71 b and one end wall 71 c is obliquely cut out along the width direction W. A triangular recess 75 is formed along the width direction W in the cut-out corner as viewed from the side. In the recess 75, a plurality of ribs 77 are formed in parallel along a direction orthogonal to the width direction W.

  Each of the pair of rotating cylinders 73 has an inner diameter that can be fitted to the rotating shaft 61 of the cam 57. On the inner peripheral surface of each rotary cylinder 73, a quadrant (protrusion of a quarter of a circle) projection 81 is formed. The pair of rotary cylinders 73 are fixed to positions on the side walls 71a of the main body 71 that are the center of the fan shape. In the circumferential direction of the rotating cylinder 73, the protrusion 81 and the side wall 71a are formed at substantially the same position.

  As shown in FIGS. 5 and 7 to 9, the opening / closing member 39 is in a posture in which the concave portion 75 faces the inlet 41 side, and each rotary cylinder 73 is fitted to the rotary shaft 61 of the cam 57. The protrusion 81 of the rotating cylinder 73 enters the D-cut space of the rotating shaft 61.

  7 to 9, a torsion coil spring 91 is interposed between the opening / closing member 39 and the fixing roller accommodating portion 31a. The coil portion 91a of the torsion coil spring 91 is fitted into the rotating cylinder 73 of the opening / closing member 39, one arm portion 91b is fixed to the side wall 71a of the body portion 71 of the opening / closing member 39, and the other arm portion 91c is the fixing roller housing portion. It is fixed to 31a. The torsion coil spring 91 urges the opening / closing member 39 in the direction of closing the inlet 41 (counterclockwise direction in FIGS. 7 to 9). As a result, as shown in FIG. 7, the protrusion 81 of the rotating cylinder 73 of the opening / closing member 39 abuts on the D-cut surface 61 a of the rotating shaft 61 of the cam 57.

  The fixing operation of the fixing device 6 having the above configuration will be described with reference to FIGS. 10 and 11 are front views showing a conveyance path between the transfer nip N1 and the fixing device.

  When the paper is plain paper, the pressure in the pressure region N2 is set to normal pressure. That is, in the pressure changing portion 37, as shown in FIG. 2, the maximum outer peripheral surface 63a of the cam body 63 of the cam 57 contacts the contact piece 55b of the lever member 55, and the lever member 55 is moved away from the holder member 51 most. It is swung in the direction of separation. Since the maximum outer peripheral surface 63 a of the cam body 63 is in contact with the contact piece 55 b of the lever member 55, the D-cut surface 61 b of the rotating shaft 61 faces in the direction opposite to the inlet 41.

  Further, as shown in FIG. 7, the opening / closing member 39 is urged by a torsion coil spring 91 in a direction to close the inlet 41, so that the protrusion 81 of the rotating cylinder 73 contacts the D-cut surface 61 a of the rotating shaft 61 of the cam 57. Touching. That is, the protrusion 81 is located obliquely lower left with respect to the center of the rotating cylinder 73. Since the protrusion 81 and the side wall 71a are formed at substantially the same position in the circumferential direction of the rotating cylinder 73, the side wall 71a, that is, the main body 71 is also positioned obliquely lower left with respect to the center of the rotating cylinder 73, The inlet 41 is open. The posture of the opening / closing member 39 at this time is an open posture. In the open position, as shown in FIGS. 5 and 7, the recess 75 of the opening / closing member 39 faces obliquely downward to the right.

  As shown in FIG. 10, after passing through the transfer nip N <b> 1 of the image forming unit 7, the sheet is conveyed to the pressure area N <b> 2 through the inlet 41 of the fixing housing 31 of the fixing device 9. While the sheet is conveyed through the pressurizing area N2, the toner image is heated and pressurized and fixed to the sheet. When the paper that has passed through the pressurizing region N2 is transported in the direction along the rotational direction of the roller 17b after being removed from the transport path 29, the leading edge of the paper comes into contact with the rib 77 of the recess 75 of the opening / closing member 39. , Guided to the inlet 41 along the rib 77.

  On the other hand, when the color printer 1 is on standby or the power is turned off, the pressure in the pressure region N2 needs to be set lower than the normal pressure in order to prevent deformation of the pressure roller 35 due to heat.

  When the pressure in the pressurizing region N2 is reduced from the normal pressure, the cam 57 is rotated about 90 degrees counterclockwise in FIG. Then, as shown in FIG. 3, the outer peripheral surface having a diameter smaller than the maximum outer peripheral surface 63 a of the cam main body 63 comes into contact with the contact piece 55 b of the lever member 55, and the lever member 55 approaches the holder member 51. Rocks. Thereby, as described above, the length of the coil spring 53 is shortened, the force for pressing the pressure roller 35 held by the holder member 51 against the fixing roller 33 is decreased, and the pressure in the pressure region N2 is higher than the normal pressure. Also lower. Further, by rotating the cam 57 by about 90 degrees, the D-cut surface 61a of the rotating shaft 61 of the cam 57 faces downward.

  Since the opening / closing member 39 is urged by the torsion coil spring 91, the projection 81 of the rotary cylinder 73 follows the change in the direction of the D-cut surface 61a, and as shown in FIG. Rotate degrees. Then, as shown in FIGS. 6 and 8, the inlet 41 of the fixing housing 31 is closed by the main body 71 of the opening / closing member 39. The posture of the opening / closing member 39 at this time is a closing posture. By closing the inlet 41 in this way, as shown in FIG. 11, leakage of heated air near the fixing roller 33 from the inlet 41 can be prevented.

  Also, when the paper jam of the fixing device 9 is handled, the pressure in the pressurizing region N2 is reduced from the normal pressure in order to facilitate the removal of the paper. At this time, as described above, the opening / closing member 39 also rotates from the open posture to the closed posture in conjunction with the rotation of the cam 57. Since the sheet is sandwiched between the transfer nip N1 and the pressure region N2 and crosses the inlet 41, the opening / closing member 39 interferes with the sandwiched sheet when rotating from the open position to the closed position. However, as shown in FIG. 9, when the opening / closing member 39 interferes with the paper, the torsion coil spring 91 is compressed and elastically deformed (both arm portions 91 b and 91 c are close to each other), and the opening / closing member 39 rotates with respect to the cam 57. Therefore, the opening / closing member 39 can be rotated only to a position in contact with the jammed paper.

  As described above, according to the fixing device 9 of the present invention, the inlet 41 of the fixing housing 31 is opened and closed by the opening / closing member 39 in conjunction with the operation of the pressure changing unit 37 that changes the pressure in the pressure region N2. Specifically, the opening / closing member 39 rotates from the open position to the closed position in conjunction with the rotation of the cam 57 for reducing the pressure in the pressurizing region N2 from the normal pressure. Thus, the opening / closing member 39 can be rotated without using a dedicated drive source. Therefore, heat dissipation from the fixing housing 31 can be prevented with a simple configuration.

  Furthermore, since the opening / closing member 39 has a hollow shape, the hollow portion becomes a heat insulating layer, and an effect of preventing heat dissipation can be obtained. The hollow portion S may be filled with a heat insulating resin such as sponge.

  Further, when a paper jam occurs in the fixing device 9, the pressure in the pressure region N2 is reduced from the normal pressure. At this time, the opening / closing member 39 is also rotated to the closed posture. However, when the opening / closing member 39 interferes with the sheet sandwiched, the torsion coil spring 91 is compressed to prevent the rotation to the open position. Therefore, the opening / closing member 39 is not damaged by receiving a load from the paper.

  Further, since the opening / closing member 39 has a rib 77 as a guide portion for guiding the paper to the inlet 41 in the open posture, the paper can be conveyed to the inlet 41.

  Further, since the lever member 55 smoothly rotates in accordance with the rotation of the cam 57 in the pressure changing unit 37, the pressure in the pressurizing region N2 can be gradually reduced. Furthermore, since the area of the contact surface between the cam 57 and the lever member 55 can be increased, the lever member 55 can be reliably held at a predetermined rotational position.

  Next, another embodiment of the fixing device 9 of the present invention will be described with reference to FIGS. 12A to 12C. 12A to 12C are perspective views showing the cam and the opening / closing member. In this embodiment, the pressure changing unit 37 changes the pressure in the pressurizing region N2 to a first reduced pressure value lower than the normal pressure and a second reduced pressure value lower than the first reduced pressure value. . For example, the first reduced pressure value corresponds to thick paper such as an envelope, and the second reduced pressure value corresponds to the case where the color printer 1 is on standby or the power is turned off.

  As described above, the pressure changing unit 37 changes the pressure in the pressurizing region N <b> 2 according to the length of the coil spring 53. In other words, the pressure in the pressurizing region N2 is changed according to the swinging amount of the lever member 55, that is, the rotation angle of the cam 57. In this embodiment, when the cam 57 rotates about 45 degrees relative to the normal pressure, the pressure is reduced to the first reduced pressure value, and when the cam 57 rotates about 90 degrees, the pressure is reduced to the second reduced pressure value.

  In this embodiment, a convex portion 95 is formed on the outer peripheral surface of the cam body 63 of the cam 57. One arm portion 91b of the torsion coil spring 91 is fixed to the side wall 71a of the main body portion 71 of the opening / closing member 39, and the other arm portion 91c is free. A distal end portion 91 d of the free arm portion 91 c is bent along the outer peripheral surface of the cam body 63.

  As shown in FIG. 12A, in the case of normal pressure, the bent tip portion 91 d of the torsion coil spring 91 is separated from the convex portion 95 in the rotational direction of the cam 57 by a predetermined interval. At normal pressure, the opening / closing member 39 is rotated by its own weight until the projection 81 of the rotating cylinder 73 of the opening / closing member 39 comes into contact with the D-cut surface 61a of the rotating shaft 61 of the cam 57. .

  When the cam 57 is rotated counterclockwise in FIG. 12A when changing from the normal pressure to the first reduced pressure value, the lever member 55 swings and the spring length of the coil spring 53 changes as described above. The pressure in the pressurizing region N2 is changed from the normal pressure to the first reduced pressure value. As shown in FIG. 12B, the cam 57 rotates until the convex portion 95 contacts the tip end portion 91 d of the torsion coil spring 91. During this time, since the opening / closing member 39 is independent of the cam 57, the opening / closing member 39 does not rotate from the open posture even if the cam 57 rotates. That is, since the inlet 41 is open, a thick sheet can be conveyed to the pressurizing region N2.

  When the cam 57 is further rotated in the counterclockwise direction in FIG. 12B when changing from the first reduced pressure value to the second reduced pressure value, the lever member 55 swings as described above, and the spring of the coil spring 53 is rotated. The length changes, and the pressure in the pressurization region N2 is changed from the first reduced pressure value to the second reduced pressure value. On the other hand, since the convex portion 95 of the cam 57 is engaged with the distal end portion 91d of the torsion coil spring 91, when the cam 57 rotates, the distal end portion 91d of the torsion coil spring 91 is pushed by the convex portion 95, and the torsion coil spring 91 is moved. It rotates with the cam 57. As a result, as shown in FIG. 12C, the main body 71 to which one arm 91b of the torsion coil spring 91 is fixed rotates, and the opening / closing member 39 rotates from the open position to the closed position to close the inlet 41. To do.

  As described above, the pressure in the pressurizing region N2 is set to the normal pressure corresponding to the plain paper, the first reduced pressure value corresponding to the paper thicker than the plain paper, the second corresponding to the power-off time or the standby time. In the case of changing to the reduced pressure value, the inlet 41 is opened at the time of the normal pressure and the first reduced pressure so that the sheet can be conveyed. As described above, since the pressure in the pressurizing area N2 is set according to the thickness of the sheet, sheets having different thicknesses can be stably passed through the pressurizing area N2. On the other hand, at the time of the second pressure reduction, the inlet 41 can be closed to prevent heat dissipation.

  Furthermore, since the above description of the embodiments of the present invention describes preferred embodiments of the fixing device and the image forming apparatus according to the present invention, various technically preferable limitations may be imposed. However, the technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention. That is, the above-described components in the embodiment of the present invention can be appropriately replaced with existing components and the like, and various variations including combinations with other existing components are possible. The description of the embodiment of the present invention described above does not limit the contents of the invention described in the claims.

1 Color printer (image forming device)
7 Image forming unit 9 Fixing device 33 Fixing roller (fixing member)
35 Pressure roller (pressure member)
37 Pressure changing portion 39 Opening / closing member 41 Inlet 51 Holder member 53 Coil spring (spring)
55 Lever member 57 Cam 77 Rib (guide part)
91 Torsion coil spring (elastic member)
N2 pressure area

Claims (7)

A fixing device for fixing a toner image on a sheet by heating and pressing a sheet conveyed to a pressure region formed between a fixing member and a pressure member,
A pressure changing unit that changes the pressure in the pressure region by moving one of the fixing member and the pressure member in a direction approaching or separating from the other;
An opening and closing member that opens and closes the entrance of the sheet to the pressurizing region,
The opening / closing member is displaced from an open posture to open the inlet to a closed posture to close the inlet in conjunction with an operation in which the pressure changing unit reduces the pressure in the pressurizing region from the normal pressure corresponding to plain paper. A fixing device characterized. The pressure changing unit is
A holder member that supports the pressure member and swings in a direction in which the pressure member approaches or separates from the fixing member;
A spring having one end fixed to the holder member and biasing the holder member in a direction in which the pressure member is close to the fixing member;
A lever member that fixes the other end of the spring and swings to change the length of the spring;
A cam that rotates while contacting the lever member to swing the lever member,
The lever member is swung by rotating the cam to change the length of the spring, and the biasing force by which the spring biases the holder member is changed to change the pressure in the pressurizing region. Provided in
The opening / closing member is provided so as to be rotatable about the same axis as the cam, and in conjunction with the rotation of the cam in the direction of reducing the pressure in the pressurizing region from the normal pressure, The fixing device according to claim 1, wherein the fixing device rotates to a closed posture.   The fixing device according to claim 1, wherein the opening / closing member includes a heat insulating layer. An elastic member that urges the opening and closing member to the closed posture;
The elastic member is elastically deformed and the rotation of the opening / closing member to the closing posture is restricted when the opening / closing member abuts on the sheet when paper is present at the entrance. The fixing device according to any one of 1 to 3. The pressure changing unit can change the pressure in the pressurization region to a first reduced pressure value lower than the normal pressure and a second reduced pressure value lower than the first reduced pressure value,
In the changing operation from the normal pressure to the first reduced pressure value, the opening / closing member is not displaced from the open posture to the closed posture, and the changing operation from the first reduced pressure value to the second reduced pressure value is performed. The fixing device according to claim 1, wherein the opening / closing member is displaced from the open posture to the closed posture in conjunction with the fixing device.   The fixing device according to claim 1, wherein the opening / closing member includes a guide unit that guides a sheet to the pressure area in the open posture. An image forming unit that forms a toner image on paper;
An image forming apparatus comprising: the fixing device according to claim 1, wherein the toner image is fixed on the sheet.

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