Patent ID: 12197152

DESCRIPTION OF THE EMBODIMENTS

As an example configuration of an image forming apparatus according to the present disclosure, an embodiment in which the present disclosure is applied to an electrophotographic laser printer will be specifically described. First, an overall configuration of the image forming apparatus will be described, and next, a configuration of a fixing device of the image forming apparatus will be described.

FIG.1illustrates an example of an image forming apparatus according to a first exemplary embodiment.FIG.1is a cross-section diagram illustrating a configuration of an electrophotographic laser printer having a two-sided image forming function. However, dimensions, materials, shapes, and their relative arrangements of components described in the present exemplary embodiment are not intended to limit the range of the present disclosure only to the exemplary embodiments unless otherwise specifically described. The image forming apparatus according to the present disclosure is not limited to the laser printer, and the present disclosure may be applied to other image forming apparatuses such as a copying machine and a facsimile machine.

An image forming apparatus101illustrated inFIG.1includes a sheet feeding unit, an image forming unit for forming an image on a sheet, a fixing unit, a discharge-sheet reversing unit, and a two-sided conveyance unit, as main components.

The image forming apparatus101includes a process cartridge1attachable to and detachable from an apparatus main body. The process cartridge1is a process unit required for forming a toner image on a sheet using an electrophotographic process, and includes a photosensitive drum2, and a process unit such as a developing unit and a charging roller (not illustrated). A scanner unit3is disposed in a vertically upward direction of the process cartridge1, to expose the photosensitive drum2to light based on an image signal. The photosensitive drum2is charged to a predetermined negative potential by a charging roller (not illustrated). Then, the scanner unit3scans the photosensitive drum2with a laser beam to form an electrostatic latent image on the photosensitive drum2. The electrostatic latent image is subjected to a reversal development by a developing unit (not illustrated) included in the process cartridge1, and negatively charged toner is caused to adhere onto a sheet. In this way, a toner image is formed on the sheet.

The sheet feeding unit includes a sheet feeding roller4disposed in the image forming apparatus101, and a sheet cassette5for storing sheets, which is attachable to and detachable from the image forming apparatus101. Sheets S stored in the sheet cassette5are separated and fed one by one from the sheet cassette5by the sheet feeding roller4being rotated due to the power of a sheet feeding drive unit (not illustrated). A fed sheet S is conveyed by a conveyance roller pair6to a registration roller pair7to be subjected to a skew correction, and conveyed to a transfer unit.

In the transfer unit, a positive polarity bias is applied to a transfer roller8by a bias application unit (not illustrated). With this configuration, a toner image is transferred onto the sheet S conveyed to the transfer unit.

The sheet S with the toner image transferred thereon is conveyed to a fixing device9disposed downstream of the transfer unit in a conveyance direction. The fixing device9is a device to fix the toner image transferred on the sheet S to the sheet S, and includes a heating unit10provided with a heater serving as a heating means (not illustrated), and a pressure roller11serving as a pressure member rotating in contact with the heating unit10. The sheet S with the toner image formed thereon is nipped and conveyed by a nip portion formed by the heating unit10and the pressure roller11, and heat and pressure are applied to the toner image so that the toner image is fixed onto the surface of the sheet S.

The sheet S with the toner image fixed thereon is conveyed from the fixing device9to the discharge-sheet reversing unit. The discharge-sheet reversing unit includes a two-sided flapper12and three rollers including a sheet-discharge roller13, a sheet discharge roller14, and a reversing roller15. In a case where an image is formed on one side of a sheet (one-sided printing), the two-sided flapper12is located at a position to guide the sheet S toward a discharge-sheet nip portion formed by the sheet-discharge roller13and the sheet discharge roller14so that the sheet S is discharged onto a discharge tray16by the sheet-discharge roller13and the sheet discharge roller14.

In a case where an image is formed on two sides of a sheet (two-sided printing), the two-sided flapper12is located at a position (indicated by a dotted line) to guide the sheet S toward a reversing nip portion formed by the sheet-discharge roller13and the reversing roller15so that the sheet S is conveyed toward the reversing nip portion by the fixing device9. The sheet-discharge roller13inversely rotates by a rotation direction switching unit (not illustrated) at a timing at which the rear end of the sheet S reaches a predetermined position. In this way, the sheet S with its trailing edge changed to the leading edge passes through a two-sided conveyance roller pair17and a sheet-refeeding roller pair18, to be reconveyed to the registration roller pair7with its front-surface and back-surface reversed. Then, in a way similar to a case where the one-sided printing is performed, a second surface (back surface) of the sheet S is subjected to the transfer by the transfer roller8, and the fixing by the fixing device9, and the sheet S is discharged to the discharge tray16by the sheet-discharge roller13and the sheet discharge roller14. In this way, the two-sided printing is completed.

In a case where a paper jam occurs in the fixing device9while the sheet S is being conveyed, a front door19or a rear door20is opened at a position of the jam occurrence, so that a jam clearance operation is to be performed.

The fixing device9will be described with reference toFIGS.2to11A and11B. In the description hereinbelow, fastener members such as screws are not illustrated in the drawings.FIG.2is a schematic diagram of the fixing device9according to the first exemplary embodiment. The fixing device9includes a first side plate21, a second side plate22, an upper stay23, and a lower stay24. The pressure roller11is rotatably supported by the first side plate21and the second side plate22each via a ball bearing25and a bearing26. The heating unit10is attached to the first side plate21and the second side plate22each via a flange member28. The pressure roller11is disposed on the opposing side of the heating unit10to form the nip portion to nip the sheet S.

FIG.3is a cross-section diagram illustrating a configuration of the heating unit10. The heating unit10mainly includes a heater30, a pressure stay29, a fixing film31, and a film guide32. The fixing film31is a cylindrically formed (endless belt-like shape or sleeve-like shape) flexible film, and is externally fitted loosely to the film guide32. The heater30serving as a heat source is fitted and fixed in a depressed groove portion provided along a lengthwise direction of the film guide32. The pressure stay29has a U-shaped cross-section, is arranged inside the film guide32, and presses the film guide32and the heater30toward the pressure roller11when receiving a pressing force.

FIGS.4A and4Bare side views of the fixing device9inFIG.2seen in an A direction, and schematic diagrams of a pressure application mechanism and a pressure release mechanism of the fixing device9.FIG.4Ais a diagram illustrating a contact state where a predetermined pressure force is applied by the heating unit10being urged to the pressure roller11, andFIG.4Bis a diagram illustrating a pressure release state where the pressure force of the heating unit10to the pressure roller11is weaker (including zero) than that in the contact state. The urging force is transmitted to the heating unit10via the flange member28by a pressure spring33urging a pressure plate27, and the heating unit10is urged to the pressure roller11to apply a pressure force to the nip portion.

The pressure release mechanism of the fixing device9includes a front cam34that rotates in conjunction with the open and close of the front door19, and a rear cam35that rotates in conjunction with the open and close of the rear door20. Further, the pressure release mechanism of the fixing device9includes a pressure release arm36for adjusting the pressure plate27between the contact state and the pressure release state, and a pressure release arm holder40for holding the pressure release arm36. The fixing device9is configured to be switched from the contact state inFIG.4Ato the pressure release state inFIG.4B, by the front cam34and the rear cam35rotating in conjunction with the change of the front door19or the rear door20from the closed state to the open stated.FIG.4Billustrates the pressure release state where both of the front door19and the rear door20are open, and both of the front cam34and the rear cam35are rotated. In a case where only one of the front door19and the rear door20is opened, the cam corresponding to the open door is in the rotated state. The front cam34, the rear cam35, the pressure release arm36, and the pressure release arm holder40are arranged on each side of the fixing device9in a lengthwise direction.

The pressure release arm36may include a plurality of components, or may include a power transmission system such as a plurality of gears.

FIG.5is a perspective view of the pressure release mechanism in the fixing device9. The pressure release arm36contacts the front cam34and the rear cam35to convert a variation amount in a radial direction caused by the rotation of any of the front cam34and the rear cam35into a variation amount in a Y direction. In this way, the pressure plate27is pushed up by the pressure release arm36moving in the Y direction, so that the pressure force by the pressure spring33is to be adjusted.

FIGS.6to8are diagrams each illustrating details of a member of the pressure release mechanism, andFIG.6illustrates the front cam34,FIG.7illustrates the rear cam35, andFIG.8illustrates the pressure release arm36. As illustrated inFIG.6, the front cam34includes a surface34A that contacts the pressure release arm36when the nip portion is in the contact state illustrated inFIG.4A, and an arc portion34B that contacts the pressure release arm36when the nip portion is in the pressure release state illustrated inFIG.4B. The center of the arc portion34B is coincident with the center of the rotational shaft of the cams, and the distance between the arc portion34B and the rotational shaft of the cams is longer than the distance between the surface34A and the rotational shaft of the cams. The front cam34includes a boss portion34C to interlock with the open and close of the front door19, and a bearing portion34D with an approximately circular shape for supporting the rear cam35.

As illustrated inFIG.7, the rear cam35includes an arc portion35A, an arc portion35B, and an arc portion35C. The arc portion35A contacts the pressure release arm36in the contact state illustrated inFIG.4A. The arc portion35B contacts the pressure release arm36in the pressure release state illustrated inFIG.4B. The arc portion35C has a shape to apply a rotational force to the rear cam35by the pressing force at the fixing time.

The centers of the arc portion35A and the arc portion35B are coincident with the rotational shaft of the cams, and the arc portion35B is larger than the arc portion35A in curvature radius. The arc portion35C is different from the rotational shaft of the cams in center position, and the distance between the rotational shafts of the arc portion35C and the rear cam35is longer than the distance between the rotational shafts of the arc portion35B and the rear cam35. The rear cam35includes an inner circumferential surface35D and an engaging portion35E. The inner circumferential surface35D has an approximately circular shape to fit a bearing portion34D of the front cam34therein. The engaging portion35E is provided to interlock with the open and close of the rear door20. As illustrated inFIG.8, the pressure release arm36includes a first contact surface36A to contact the front cam34, a second contact surface36B to contact the rear cam35, and a pressure plate contact portion36C to contact the pressure plate27.

FIGS.9A and9Bare diagrams illustrating a relationship between the front cam34and the rear cam35.FIG.9Ais a perspective view, andFIG.9Bis a cross-section diagram cut along the rotational shaft center of the front cam34and the rear cam35. As illustrated inFIG.9A, the front cam34and the rear cam35are arranged on each side of the fixing device9in a lengthwise direction, and have a common rotational shaft. Because the rotational shaft of the two different types of cams is common, the two cams can be arranged in a space smaller than that when the rotational shafts are provided separately. As illustrated inFIG.9B, a shaft member37is a shaft with an approximately circular basic cross-section shape, and a D-cut shape37A is provided at a shaft end on each side. The front cam34is provided with a D-cut groove34E, and the front cam34and the shaft member37interlock with each other at the D-cut portion, and the front cams34at the respective ends rotate in conjunction with each other. The inner circumferential surface35D of the rear cam35is arranged on the bearing portion34D of the front cam34, and the rear cam35is configured to rotate independently from the front cam34. Because the rear cam35rotating independently from the front cam34is not fastened to the shaft member37, the rear cams35at the respective ends are configured to be rotatable independently from each other.

Like the relationship between the front cam34and the rear cam35illustrated inFIG.9B, the front cam34also acts as the bearing of the rear cam35. With this configuration, the front cam34and the rear cam35are provided in an overlapped manner in the rotational shaft direction of the cams, and thus the two cams can be arranged in a space smaller than that when the cams are not provided in an overlapped manner.

With reference toFIGS.10,11A, and11B, the pressure release method interlocking with the front door19will be described.FIG.10is a perspective view illustrating the pressure release method performed interlocking with the front door19, andFIGS.11A and11Bare diagrams illustrating an operation of the pressure release mechanism of the fixing device9in conjunction with the open and close of the front door19, when the pressure release mechanism is seen in a B direction inFIG.10. InFIGS.10to19, components not necessary to describe the pressure release mechanism operating interlocking with the front door19are not illustrated. The image forming apparatus101includes a connecting member to rotate the front cam34in conjunction with the open and close of the front door19. The connecting member includes a front door connecting member38connecting with the front door19, and a cam side connecting member39to contact and rotate the front cam34. The front cam34is rotated in conjunction with the open and close of the front door19because the front door connecting member38and the cam side connecting member39are connected. With reference toFIGS.11A and11B, the operation of the pressure release mechanism of the fixing device9when the front door19is opened and closed will be described. InFIG.11A, the front door19is closed, and the nip portion is in the contact state inFIG.4A. InFIG.11B, the front door19is open, and the nip portion is in the pressure release state inFIG.4B. The cam side connecting member39includes an engaging hole39A to engage with the boss portion34C of the front cam34. When the front door19is being opened from the closed state as inFIG.11Atoward the open state as inFIG.11B, the cam side connecting member39moves toward the front side of the image forming apparatus101(C direction inFIG.11B) interlocking with the front door19. When the cam side connecting member39moves in the C direction, the boss portion34C is pushed by the engaging hole39A to rotate the front cam34in a counterclockwise direction. When the front door19is completely opened, the pressure release mechanism turns into the state inFIG.11B. At this time, in the process of the front door19being opened, the surface of the front cam34contacting the pressure release arm36shifts from the surface34A to the arc portion34B. Because the distance of the arc portion34B from the rotational shaft of the cams is longer than that of the surface34A from the rotational shaft of the cams, the pressure release arm36is pushed up when the front door19is opened, and the nip portion is switched from the contact state inFIG.4Ato the pressure release state inFIG.4B. At this time, because the rear cam35and the front cam34are configured to rotate independently from each other, the rear cam35has not rotated from the rotational phase inFIG.11Awhen the front cam34is switched to the pressure release state.

With reference toFIGS.12,13A,13B,13C, and13D, the pressure release method performed interlocking with the rear door20will be described.FIG.12is a perspective view illustrating a configuration of the rear door20, andFIGS.13A,13B,13C, and13Dare cross-section diagrams cut at the rear cam portion, and illustrating the operation of the pressure release mechanism of the fixing device9in conjunction with the open and close of the rear door20. As illustrated inFIG.12, the rear door20includes protruding portions20A at both ends of the rear door20to release the pressure of the fixing device9. This is because the rear cams35arranged at both of the ends in the lengthwise direction of the fixing device9are configured to be rotatable independently from each other, and the rear cams35at both of the ends can be rotated by the corresponding two protruding portions20A.

With reference toFIGS.13A,13B,13C, and13D, the operation of the pressure release mechanism of the fixing device9when the rear door20is opened and closed will be described.FIG.13Aillustrates a state where the rear door20is closed and the nip portion is in the contact state as inFIG.4A.FIG.13Billustrates a state where the pressure release arm36is in contact with the arc portion35C, and the rear cam35receives a force to rotate in a direction in which the rear door20is closed, by an urging force of the pressure spring33transmitted from the pressure release arm36.FIG.13Cillustrates a state where the pressure release arm36is in contact with the arc portion35C, and the rear cam35receives a force to rotate in a direction in which the rear door20is opened by the urging force of the pressure spring33transmitted from the pressure release arm36. As described above, since the arc center of the arc portion35C is different from the rotational shaft center of the rear cam35, the direction in which the rear cam35is rotated changes by the urging force of the pressure spring33transmitted from the pressure release arm36, depending on the contact position of the arc portion35C to the pressure release arm36.FIG.13Dillustrates a state where the rear door20is open, and the nip portion is in the pressure release state. When the rear door20starts to open as illustrated inFIG.13A, the protruding portion20A of the rear door20rotates on a rotational locus L, and contacts a surface35F of the engaging portion35E of the rear cam35. In this way, the rear cam35rotates in conjunction with the open and close of the rear door20. A force is applied to the rear cam35in a direction in which the rear door20is closed until the state in FIG.13B, because the direction of the pressure force applied to the rear cam35from the pressure release arm36is directing toward the rear door20from the rotational center of the rear cam35. Accordingly, until the state inFIG.13B, the protruding portion20A of the rear door20continues to rotate the rear cam35.

Then, when the rear cam35rotates beyond the state inFIG.13B, and the contact position of the arc portion35C and the pressure release arm36changes as illustrated inFIG.13C, a force in an arrow direction illustrated inFIG.13Cis applied to the rear cam35by the pressure force from the pressure release arm36. With this operation, the rear cam35is in a state where the rotation force to open the rear door20is applied. In this way, in and after the state inFIG.13C, because the rear cam35is precedingly rotated by the pressure received from the pressure release arm36, the rear cam35does not rotate due to the engagement of the rear door20and the rear cam35. As illustrated inFIG.13D, the rear cam35stops rotating at the arc portion35B that has a circular shape concentric with the rotational shaft of the cams. With the preceding-rotation of the rear cam35, the pressure force from the pressure release arm36is not applied to the user's operation at and after the preceding-rotation. At the same time, in a state where the rear door20is open, since the engagement of the protruding portions20A of the rear door20and the engaging portion35E of the rear cam35is released, the pressure force of the fixing device9is not applied to the protruding portion20A of the rear door20via the pressure release arm36. Thus, there is no possibility of creep of the protruding portions20A of the rear door20. In this state, because the rear cam35receives the pressure force from the pressure release arm36at a surface of the arc portion35B, a certain degree of large contact area can be secured, and the force applied to a unit area is reduced. Accordingly, there is no possibility of creep of the rear cam35. In the state inFIG.13D, the surface35F of the rear cam35stops with a gap kept to the rotational locus L of the protruding portions20A of the rear door20. Accordingly, when the rear door20is closed from the state inFIG.13D, the protruding portion20A is prevented from being caught by the surface35F.

The arc portion35B is not limited to a circle concentric with the rotational shaft of the cams, and may have any shape as long as the rotation of the pressure release arm36can be stopped by the rear cam35supporting the pressure release arm36as illustrated inFIG.13D.

Because the rear cam35is arranged at each of the ends of the fixing device9in the lengthwise direction of the fixing device9and the protruding portion20A of the rear door20is also arranged at each of the ends of the fixing device9in the lengthwise direction of the fixing device9, the nip portion uniformly turns into the pressure release state when the rear door20is opened. Because the rear cam35and the front cam34are configured to rotate independently from each other, the front cam34keeps the rotation phase corresponding to the contact state inFIG.13A, when the rear cam35turns into the pressure release state.

The rear cams35arranged at both of the ends of the fixing device9in the lengthwise direction are configured to rotate independently from each other. With this configuration, there are following advantages compared with a case where the rear cams35at both of the ends rotate in conjunction with each other. In the case where the rear cams35at both of the ends rotate in conjunction with each other, the pressure release operation is performed only by one of the rear cams35contacting the corresponding protruding portion20A of the rear door20first when timings at which the protruding portions20A of the rear door20contact the rear cams35at both of the ends are different, due to the variation of components or the like. Thus, because the pressure force of the fixing device9acts on the rear cam35at one end, the user's operation force increases. On the other hand, in the configuration in which the rear cams35at both of the ends rotate independently from each other, the protruding portions20A of the rear door20contact the rear cams35at both of the ends without fail. Accordingly, because the pressure release operation is performed by the rear cams35at both of the ends and the pressure force of the fixing device9is divided to both of the ends, the user's operation force becomes smaller and more stable than that when the rear cams35at both of the ends rotate in conjunction with each other.

The components of the fixing device9can be arranged in a small space with a simple configuration by arranging the rotation centers of the rear cams35and the rotation centers of the front cams34coaxially, and enabling the rear cams35arranged at both of the ends of the fixing device9in the lengthwise direction to rotate independently from each other and to rotate independently from the front cams34.

The configuration according to the present exemplary embodiment can provide an image forming apparatus capable of achieving reductions of apparatus size and cost, and a stable pressure release mechanism.

With reference toFIGS.14to16, a second exemplary embodiment according to the present disclosure will be described. In the present exemplary embodiment, the descriptions of the portions common with the first exemplary embodiment are omitted. The present exemplary embodiment is different from the first exemplary embodiment in the configuration of a shaft member137for interlocking front cams134on both ends in the lengthwise direction.

FIG.14is a diagram illustrating a shape of the shaft member137,FIG.15is a diagram illustrating a shape of the front cam134, andFIG.16is a side view illustrating an interlocking configuration of the shaft member137and the front cam134. With reference toFIG.14, the shaft member137is an approximately V-shaped rotational shaft formed by bending a sheet metal. The angle of the bending portion of the shaft member137is less than 90°. With reference toFIG.15, the front cam134includes an engaging portion134A configured to engage with an approximately V-shaped portion, which is a cross-section shape of the shaft member137. With reference toFIG.16, the front cam134and the shaft member137are configured to rotate in an interlocked manner, by the engaging portion134A of the front cam134and the V-shaped portion, which is a cross-section shape of the shaft member137, engaging with each other.

As described above, because the shaft member137is a rotational shaft formed by bending the sheet metal in the V-shape at only one portion, it is possible to reduce the cost compared with the turning processed shaft with an approximately circular shape in the first exemplary embodiment.

With reference toFIGS.17to19, a third exemplary embodiment according to the present disclosure will be described. In the present exemplary embodiment, the descriptions of the portions common with the first exemplary embodiment are omitted. The configuration of the shaft member to interlock front cams234provided at both of the ends in the lengthwise direction thereof is similar to that in the second exemplary embodiment, and the description thereof is omitted. The present exemplary embodiment is different from the first and second exemplary embodiments in shapes of a surface236A of a pressure release arm236, and a surface234A and an arc portion234B of the front cam234.

FIG.17is a diagram illustrating a shape of the pressure release arm236. The pressure release arm236includes the common surface236A to contact both of the front cam234and a rear cam235. A pressure plate contact portion236C to contact the pressure plate27is similar to that in the first exemplary embodiment.

FIGS.18A and18Bare diagrams illustrating a shape of the front cam234, andFIG.18Ais a perspective view, andFIG.18Bis a side view when the front cam234inFIG.18Ais seen in an A direction. The front cam234includes the surface234A that contacts the surface236A of the pressure release arm236in the contact state inFIG.4A, and the arc portion234B that contacts the surface236A of the pressure release arm236in the pressure release state inFIG.4B. The arc portion234B has a circular shape concentric with the rotational shaft of the cams, and the distance between the arc portion234B and the rotational shaft of the cams is longer than the distance between the surface234A and the rotational shaft of the cams. A boss portion234C to interlock with the open and close of the front door, and a bearing portion234D with an approximately circular shape to support the rear cam235are similar to those in the first exemplary embodiment.

FIG.19is a schematic diagram illustrating a pressure application mechanism and a pressure release mechanism of the fixing device9according to the present exemplary when the fixing device9inFIG.2is seen in the A direction. InFIG.19, the front cam234is not illustrated for the simplification of the description. As illustrated by an A portion inFIG.19, the pressure release arm236and the rear cam235do not overlap when seen from the side surface.

In the present exemplary embodiment, because the shaft member is a rotational shaft formed by bending the sheet metal in the V-shape at only one portion, similar to that in the second exemplary embodiment, it is possible to reduce the cost compared with the first exemplary embodiment.

In the present exemplary embodiment, the surface236A of the pressure release arm236has a cam shape common to the front cam234and the rear cam235. With this configuration, because the pressure release arm236and the rear cam235do not overlap when seen from the side surface, it is not necessary to assemble the rear cam35while lifting up the pressure release arm36to avoid the pressure release arm36like the configuration according to the first exemplary embodiment when the rear cam35is assembled. In the present exemplary embodiment, because the rear cam235can be assembled without avoiding the pressure release arm236, it is possible to improve the assemblability compared with the first exemplary embodiment.

With reference toFIGS.20,21, and22A to22E, a fourth exemplary embodiment according to the present disclosure will be described. In the present exemplary embodiment, the descriptions of the portions common with the first and second exemplary embodiments are omitted. The configuration of the shaft member to interlock the front cams provided at both of the ends of the shaft member is similar to that according to the second exemplary embodiment, and the description of the configuration is omitted. The present exemplary embodiment is different from the first and second exemplary embodiments in the configuration of the pressure release mechanism of the fixing device9when a rear door320is opened and closed.

FIG.20is a diagram illustrating a shape of a protruding portion of the rear door320to rotate a rear cam335. The rear door320includes a first engaging portion320A and a second engaging portion320B for engaging with the rear cam335to rotate the rear cam335.

FIG.21is a diagram illustrating a shape of the rear cam335. The rear cam335includes an arc portion335A that contacts the pressure release arm336in the contact state inFIG.4A, an arc portion335B that contacts a pressure release arm336in the pressure release state inFIG.4B, and an arc portion335C that smoothly connects the arc portion335A and the arc portion335B. The arc portion335A and the arc portion335B each have a circular shape concentric with the rotational shaft of the cams, and the arc portion335C has a center position of the arc different from the rotational shaft center position of the rear cam335. The rear cam335further includes a first engaged portion335E to be engaged with the first engaging portion320A of the rear door320, and a second engaged portion335F to be engaged with the second engaging portion320B.

FIGS.22A to22Eare diagrams illustrating a pressure release method performed in conjunction with the open and close of the rear door320. InFIG.22A, the rear door320is closed and the nip portion is in the contact state inFIG.4A.FIG.22Billustrates a timing at which the rotation of the rear cam335by the first engaging portion320A of the rear door320ends.FIG.22Cillustrates a timing at which the rotation of the rear cam335by the second engaging portion320B of the rear door320starts. InFIG.22D, the rear door320is open, and the nip portion is in the pressure release state inFIG.4B. When the rear door320starts opening from the state inFIG.22A, the first engaging portion320A of the rear door320contacts the surface of the first engaged portion335E of the rear cam335to rotate the rear cam335up to the state inFIG.22B. In the state inFIG.22B, the first engaging portion320A of the rear door320and the first engaged portion335E of the rear cam335disengages. At this time, because the rear cam335is in contact with the pressure release arm336at the arc portion335B with a circular shape concentric with the rotational shaft of the cams, the rear door320rotates to the state inFIG.22C, while the rear cam335stops rotating. From the state inFIG.22C, the second engaging portion320B of the rear door320contacts the second engaged portion335F of the rear cam335to rotate the rear cam335to the state inFIG.22D, and to rotate the nip portion to the pressure release state inFIG.4B. In the state inFIG.22D, a front edge335G of the rear cam335stops with a gap kept to a rotational locus L2 of the first engaging portion320A of the rear door320. Accordingly, when the rear door320is closed from the state inFIG.22D, the first engaging portion320A is configured to avoid being caught by the front edge335G.

In the state inFIG.22B, when the first engaging portion320A of the rear door320and the first engaged portion335E of the rear cam335disengage, the state of the rotation of the rear cam335is not limited to the stopped state. For example, the rear cam335may have a shape to be rotated in a direction in which the second engaged portion335F approaches the second engaging portion320B of the rear door320.

FIG.22Eis a diagram illustrating a timing at which a preceding-rotation of the rear cam335preceding the rotation caused by the engagement of the rear door320starts when the rear door320is closed from the open state. When the rear door320is closed from the state inFIG.22D, as in the state inFIG.22E, the preceding-rotation of the rear cam335starts in a state where the rear cam335contacts the pressure release arm336at the arc portion335C of the rear cam335. This is because the pressure force applied to the rear cam335from the pressure release arm336is directed toward the rear door320more than the rotation center of the rear cam335, and the rear cam335receives a force in a direction in which the rear door320is closed. As inFIG.22E, at the timing at which the preceding-rotation is caused, the gap between the first engaging portion320A and the first engaged portion335E is very small or the first engaging portion320A and the first engaged portion335E are already engaged. In the present exemplary embodiment, similar to the second exemplary embodiment, because the shaft member is a rotational shaft formed by bending a sheet metal in the V-shape only at one position, it is possible to reduce the cost compared with the first exemplary embodiment. In the present exemplary embodiment, the rear door320is provided with the first engaging portion320A and the second engaging portion320B, and the second engaging portion320B rotates the front edge335G of the rear cam335to the state with the gap kept with respect to the rotational locus L2 of the first engaging portion320A. With this configuration, in the process of opening the rear door320, the rear door320does not move over the preceding-rotation, different from the first and second exemplary embodiments. Thus, the force required to open the rear door320is smaller than that in the first exemplary embodiment, and the operability is improved. Further, in the present exemplary embodiment, in the process of closing the rear door320, at the timing at which the preceding-rotation of the rear cam335starts, the space between the first engaging portion320A and the first engaged portion335E is very small or the first engaging portion320A and the first engaged portion335E are already engaged. Thus, it is possible to reduce the collision energy of the rear cam335by the preceding-rotation against the first engaging portion320A of the rear door320, and to decrease the collision noise, compared with the first exemplary embodiment.

The exemplary embodiments of the present disclosure are specifically described above, but the present disclosure is not limited to the above-described exemplary embodiments, and the exemplary embodiments can be modified in various manners within the technical concept according to the present disclosure.

According to the exemplary embodiments of the present disclosure, in an image forming apparatus including a pressure force release mechanism of a fixing device operating in conjunction with an open and close of a plurality of doors, it is possible to provide the image forming apparatus in a smaller size.

Embodiments of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described Embodiments and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described Embodiments, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described Embodiments and/or controlling the one or more circuits to perform the functions of one or more of the above-described Embodiments. The computer may include one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc™ (BD)), a flash memory device, a memory card, and the like.

While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2022-134629, filed Aug. 26, 2022, which is hereby incorporated by reference herein in its entirety.