JP7790177B2 - Fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a fixing device and an image forming apparatus.

Conventionally, a known fixing device includes a fixing frame that supports a heating roller, a fixing cover that rotates relative to the fixing frame, and a lock lever for locking the fixing cover to the fixing frame (see Patent Document 1). In this technology, the lock lever is rotatable between a lock position that locks the fixing cover and an unlock position that unlocks the fixing cover. The fixing device also includes a spring that biases the lock lever toward the lock position.

The lock lever has an engaging portion. The fixation cover has an engaged portion that engages with the engaging portion. The engaged portion has a roughly triangular shape that convex toward the lock lever when the fixation cover is closed. The engaged portion has an upstream inclined surface that contacts the engaging portion when the fixation cover is closed, a downstream inclined surface located downstream of the upstream inclined surface in the direction in which the fixation cover closes, and an apex located between the upstream inclined surface and the downstream inclined surface.

With this technology, for example, when a user closes an open fuser cover, the downstream inclined surface first comes into contact with the engagement portion. This causes the downstream inclined surface to rotate the lock lever against the biasing force of the spring.

When the angle of the fuser cover reaches a predetermined angle, the apex of the engaged portion overcomes the engaging portion, and the spring's biasing force causes the engaging portion of the lock lever to press against the upstream inclined surface. This transmits the spring's biasing force to the fuser cover via the lock lever, and the fuser cover closes due to the biasing force of the spring even when the user is not touching the fuser cover. Even when the fuser cover is closed, the engaging portion of the lock lever contacts the upstream inclined surface, maintaining the fuser cover in a closed state.

Here, the angle of the fixing cover refers to the angle of the fixing cover relative to the fixing cover when it is closed, and in the following explanation, this will also be referred to as the "opening angle." Furthermore, in the following explanation, the maximum opening angle when the spring force acts in the direction of closing the fixing cover will also be referred to as the "retraction angle."

JP 2010-079049 A

Increasing the retraction angle is desirable to reduce the operational burden on the user. However, with conventional technology, the upstream inclined surface that transmits the spring force to the fixing cover is a single flat surface, making it difficult to increase the retraction angle.

The present invention therefore aims to provide a fixing device and image forming apparatus that can increase the retraction angle of the fixing cover.

In order to solve the above problem, the fixing device of the present invention comprises a heating element for heating a sheet, a fixing frame for supporting the heating element, a fixing cover that is rotatable relative to the fixing frame, a lock lever having an engagement portion, and a spring.
The fixation cover is rotatable between a first closed position where it overlaps with the fixation frame and a first open position where it is farther from the fixation frame than the first closed position.
The lock lever is rotatable between a lock position where the fixation cover is locked in the first closed position and a release position where the fixation cover is unlocked.
The spring biases the lock lever from the release position toward the lock position.
One of the fixation frame and the fixation cover rotatably supports the lock lever.
The other of the fixation frame and the fixation cover has an engaged portion that engages with the engaging portion of the lock lever.
One of the engaging portion and the engaged portion has a first surface and a second surface that can contact the other portion, and the first surface and the second surface have different angles relative to a direction perpendicular to the rotation axis of the lock lever.
When the first surface contacts the other portion, the spring force causes the lock lever to rotate from the release position toward the lock position, and the fixing cover to rotate from the first open position toward the first closed position.
When the fuser cover is located at the first closed position, the lock lever is located at the lock position and the second surface is in contact with the other portion.

With this configuration, by setting the angles of the first and second surfaces to different angles, the fixing cover can be rotated toward the first closed position by utilizing the biasing force of the first surface and the spring, even when the opening angle of the fixing cover is relatively large, thereby increasing the retraction angle. Furthermore, the second surface, which is at a different angle from the first surface, can lock the fixing cover in the first closed position.

Furthermore, the angle between the first surface and the second surface may be an obtuse angle.

The engagement portion may also have the first surface and the second surface.

The engaged portion may also be a protrusion that is convex on the engaging portion side.

Furthermore, the rotation axis of the lock lever may be parallel to the rotation axis of the fixing cover.

Furthermore, the fixing cover may rotatably support the lock lever, and the fixing frame may have the engaged portion.

Furthermore, the fixing frame may rotatably support the lock lever, and the fixing cover may have the engaged portion.

The heating member may also include a heating roller and a heater that heats the heating roller.

The spring may also be a torsion coil spring having a coil portion, arranged so that the rotation axis of the lock lever is located inside the coil portion, one end of the torsion coil spring being fixed to the lock lever, and the other end of the torsion coil spring being fixed to one of the fixing frame and the fixing cover.

The image forming apparatus according to the present invention includes the fixing device, a main body housing having an opening for exposing the fixing cover, and a main body cover.
The main body cover is rotatable between a second closed position in which the opening is closed and a second open position in which the opening is opened.
When the main body cover is positioned in the second open position and the fixing cover is positioned in the first open position and the main body cover rotates toward the second closed position, the main body cover pushes the fixing cover, causing the fixing cover to rotate toward the first closed position.
When the rotating main body cover reaches the second closed position, the first surface comes into contact with the other portion, and the fixing cover rotates toward the first closed position due to the biasing force of the spring.

With this configuration, when the main body cover is rotated to the second closed position, the first surface comes into contact with the other part. Therefore, after the main body cover is rotated to the second closed position, the fixing cover can be rotated to the first closed position by the biasing force of the spring.

This invention allows for a larger retraction angle for the fixing cover.

1 is a cross-sectional view showing a laser printer according to a first embodiment of the present invention. 10A is a side view showing the fixing device, in which FIG. 10A shows the state in which the lock lever is in the lock position and the second surface is in contact with the engaged portion, and FIG. 10B is an enlarged view showing the structure around the engaging portion. 10A and 10B are diagrams illustrating a state in which the fixing cover is in a first open position and the rear cover is in a second open position. 10A and 10B are views showing a state in which the downstream surface comes into contact with the engaged portion during the process of closing the rear cover. 10A and 10B are diagrams showing a state in which the apex has climbed over the engaged portion during the process of closing the rear cover. 10A and 10B are diagrams illustrating a state in which the first surface comes into contact with the engagement portion, causing the fixation cover to rotate due to the biasing force of the spring. 1A and 1B are diagrams illustrating a comparative example to the first embodiment. 10A and 10B are diagrams showing a fixing device according to a second embodiment. 10A and 10B are diagrams illustrating a comparative example to the second embodiment. 10A and 10B are diagrams showing a fixing device according to a third embodiment.

Next, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.
As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main body 2, a sheet supply unit 3, and an image forming unit 4.

The main body housing 2 has a discharge tray 21 on its top surface. The main body housing 2 has a first opening H1 on its front surface. The main body housing 2 has a second opening H2 on its rear surface. The first opening H1 is an opening through which the process cartridge 10 (described later) can pass. The second opening H2 is an opening for exposing the fixing cover 85 (described later) to the outside of the main body housing 2.

The laser printer 1 further includes a front cover 2A and a rear cover 2B, which is an example of a main body cover. The front cover 2A opens and closes the first opening H1. The rear cover 2B opens and closes the second opening H2. Specifically, the rear cover 2B is rotatable between a second closed position (position shown in Figure 1) in which it closes the second opening H2, and a second open position (position shown in Figure 3) in which it opens the second opening H2.

The sheet supply unit 3 includes a supply tray 31 and a supply mechanism 32. The supply mechanism 32 supplies the sheet S in the supply tray 31 to the image forming unit 4.

The image forming unit 4 includes an exposure device 5, a process cartridge 10, and a fixing device 8.

The exposure device 5 includes a laser emitter, a polygon mirror, a lens, a reflecting mirror, and other components (not shown). The exposure device 5 exposes the surface of the photosensitive drum 61 (described below) with a laser beam.

The process cartridge 10 is detachably attached to the main body casing 2 through the first opening H1. The process cartridge 10 includes a drum cartridge 6 and a developer cartridge 7.

The drum cartridge 6 includes a photosensitive drum 61, a charger 62, and a transfer roller 63.

The developing cartridge 7 is detachably attached to the drum cartridge 6. The developing cartridge 7 includes a developing roller 71 and a toner storage compartment 72.

The charger 62 charges the surface of the photosensitive drum 61. The exposure device 5 then exposes the surface of the photosensitive drum 61 to light, forming an electrostatic latent image on the surface of the photosensitive drum 61.

The developing roller 71 supplies toner from the toner storage section 72 to the electrostatic latent image on the photosensitive drum 61. This forms a toner image on the photosensitive drum 61. When the sheet S is then transported between the photosensitive drum 61 and the transfer roller 63, the toner image on the photosensitive drum 61 is transferred to the sheet S.

The fixing device 8 includes a heating member 81, a pressure roller 82, and a conveying roller 83. The heating member 81 includes a heating roller 81A and a heater 81B that heats the heating roller 81A. The pressure roller 82 is pressed against the heating roller 81A.

The transport roller 83 transports the sheet S heated by the heating member 81. Of the rollers located downstream of the heating roller 81A in the transport direction of the sheet S, the transport roller 83 is located closest to the heating roller 81A. The transport roller 83 has a drive roller 83A to which a driving force is input from a drive source (not shown), and a driven roller 83B that sandwiches the sheet S between the drive roller 83A and the drive roller 83A.

In the fixing device 8, the toner image transferred onto the sheet S is thermally fixed as the sheet S passes through the nip portion NP between the heating roller 81A and the pressure roller 82. The sheet S with the thermally fixed toner image is discharged from the fixing device 8 by the transport roller 83. The sheet S discharged from the fixing device 8 is then discharged onto the discharge tray 21 by the discharge roller R.

As shown in FIG. 2(a), the fixing device 8 further includes a fixing frame 84, a fixing cover 85, a lock lever 90, and a spring 100.

The fixing frame 84 supports the heating member 81. The fixing frame 84 is fixed to the main body housing 2.

As shown in FIG. 1, the fixing cover 85 supports at least the drive roller 83A of the drive roller 83A and driven roller 83B that make up the conveying roller 83. The driven roller 83B may be supported by the fixing frame 84 or by the fixing cover 85.

The fixing cover 85 is rotatable relative to the fixing frame 84 about a rotation axis X1 between a first closed position shown in FIG. 2 and a first open position shown in FIG. 3. The fixing cover 85 may be rotatably supported on the fixing frame 84, or may be rotatably supported on the main body housing 2.

When the fixing cover 85 is in the first closed position, the fixing cover 85 overlaps the fixing frame 84. When the fixing cover 85 is in the first closed position, the conveying roller 83 is capable of conveying the sheet S.

When the fixing cover 85 is in the first open position, it is farther from the fixing frame 84 than when it is in the first closed position. When the fixing cover 85 is in the first open position, at least the drive roller 83A of the conveying rollers 83 is positioned so that it cannot convey the sheet S.

The fixation cover 85 has a first contact surface 85A. The fixation frame 84 has a second contact surface 84A. The second contact surface 84A functions to position the fixation cover 85 in the first closed position. When the fixation cover 85 is positioned in the first closed position, the first contact surface 85A comes into contact with the second contact surface 84A. The second contact surface may also be provided on the main body housing 2.

The fixing cover 85 rotatably supports the lock lever 90. The rotation axis X2 of the lock lever is parallel to the rotation axis X1 of the fixing cover 85.

The lock lever 90 functions to lock the fixing cover 85 in the first closed position. The lock lever 90 is rotatable between the locked position shown by the solid line in Figure 2 and the unlocked position shown by the two-dot chain line in Figure 2.

When the lock lever 90 is in the locked position, the lock lever 90 locks the fixing cover 85 in the first closed position. When the lock lever 90 is in the unlocked position, the lock lever 90 unlocks the fixing cover 85.

The spring 100 functions to bias the lock lever 90 from the release position toward the lock position. The spring 100 is a torsion coil spring having a coil portion 110. The spring 100 is positioned so that the rotation axis X2 of the lock lever 90 is located inside the coil portion 110. Specifically, the center of the coil portion 110 approximately coincides with the rotation axis X2.

One end of the spring 100 is fixed to the lock lever 90. The other end of the spring 100 is fixed to the fixing cover 85.

The lock lever 90 has a base portion 91 extending from the rotation axis X2 in a direction perpendicular to the rotation axis X2, and an engagement portion 92 protruding from the base portion 91. The portion of the base portion 91 that extends away from the rotation axis X2 beyond the engagement portion 92 serves as an operating portion that is operated by the user.

The fixing frame 84 has an engaged portion 84B that engages with the engaging portion 92 of the lock lever 90. The engaged portion 84B is a protrusion that is convex on the engaging portion 92 side. The tip of the engaged portion 84B is curved and can come into contact with the engaging portion 92.

The engaging portion 92 protrudes from the base portion 91 so as to be convex in the opposite direction to the engaged portion 84B. As shown in Figure 2(b), the engaging portion 92 has a downstream surface Fd, an upstream surface Fu, and a vertex P located between the downstream surface Fd and the upstream surface Fu.

In the direction in which the fixing cover 85 moves from the first open position to the first closed position, the downstream surface Fd is located downstream of the apex P. In the direction in which the fixing cover 85 moves from the first open position to the first closed position, the upstream surface Fu is located upstream of the apex P.

As shown in FIG. 4, the downstream surface Fd is the surface that comes into contact with the engaged portion 84B before the upstream surface Fu does when the fixing cover 85 is rotated from the first open position to the first closed position. The downstream surface Fd is formed at an angle such that the reaction force received from the engaged portion 84B when the downstream surface Fd comes into contact with the engaged portion 84B causes the lock lever 90 to rotate from the locked position to the unlocked position against the biasing force of the spring 100. The downstream surface Fd is a flat surface.

The upstream surface Fu has a first surface F1 extending from the downstream surface Fd and a second surface F2 extending from the first surface F1. The first surface F1 and the second surface F2 are each flat.

As shown in FIG. 6, the first surface F1 is the surface that comes into contact with the engaged portion 84B next after the downstream surface Fd during the process of rotating the fuser cover 85 from the first open position to the first closed position. The first surface F1 is formed at an angle such that, when it comes into contact with the engaged portion 84B, the biasing force of the spring 100 causes the lock lever 90 to rotate from the released position toward the locked position, and the fuser cover 85 to rotate from the first open position toward the first closed position.

Like the first surface F1, the second surface F2 is angled so that when it comes into contact with the engaged portion 84B, the force of the spring 100 causes the lock lever 90 to rotate from the released position toward the locked position, and the fuser cover 85 to rotate from the first open position toward the first closed position. As shown in FIG. 2(b), the second surface F2 comes into contact with the engaged portion 84B when the fuser cover 85 is in the first closed position and the lock lever 90 is in the locked position. The first surface F1 and the second surface F2 have different angles relative to the direction perpendicular to the rotation axis X2 of the lock lever 90. Here, the direction perpendicular to the rotation axis X2 may be any direction, but an example will be described below.

In the example shown in Figure 2(b), the direction perpendicular to the rotation axis X2 is the direction along the first straight line L1 shown by the two-dot chain line. Here, the circle C shown by the two-dot chain line is a circle that has its center at the rotation axis X1 of the fixing cover 85 and passes through the point of contact TP between the second surface F2 and the engaged portion 84B when the fixing cover 85 is positioned in the first closed position. The first straight line L1 is a tangent to the circle C at the point of contact TP. Furthermore, the second straight line L2 is a line connecting the point of contact TP and the rotation axis X1.

The biasing force of spring 100 acts on engaged portion 84B in a direction perpendicular to second surface F2 from contact point TP. As a result, second surface F2 receives a reaction force from engaged portion 84B as indicated by the arrow in the figure. When the reaction force faces downstream of second straight line L2 in the closing direction of fixation cover 85, it acts as a force to close fixation cover 85. When the reaction force faces upstream of second straight line L2 in the closing direction of fixation cover 85, it acts as a force to open fixation cover 85.

The greater the angle of the reaction force relative to the second line L2, the greater the component of the force that rotates the fuser cover 85. Therefore, the greater the angle θ2 of the second surface F2 relative to the first line L1, the stronger the force pressing the fuser cover 85 against the second contact surface 84A, allowing the fuser cover 85 to be locked more firmly. In this embodiment, the angle θ2 of the second surface F2 relative to the first line L1 is greater than the angle θ1 of the first surface F1 relative to the first line L1. As a result, in this embodiment, the fuser cover 85 can be locked more firmly than when the angle of the second surface F2 relative to the first line L1 is the same as angle θ1.

Furthermore, by making the angle θ1 of the first surface F1 smaller than the angle θ2 of the second surface F2, the distance from the contact point TP to the apex P can be increased without increasing the height h of the engagement portion 92, compared to a structure in which the upstream surface Fu2 is a single plane, such as that shown in Figure 7(a). In other words, the retraction angle θ3 of this embodiment shown in Figure 5 can be made larger than the retraction angle θ4 of the comparative example shown in Figure 7(b).

The comparative example shown in Figure 7 differs from this embodiment only in the configuration of the upstream surface Fu2; other structures are substantially the same as this embodiment. Therefore, components that are substantially the same as this embodiment are assigned the same reference numerals and descriptions thereof are omitted.

As shown in Figure 2, the angle between the first surface F1 and the second surface F2 is an obtuse angle. The angle between the downstream surface Fd and the first surface F1 is also an obtuse angle.

The rear cover 2B has a pressing portion 2C. The pressing portion 2C has the function of pressing the fuser cover 85 from the first open position toward the first closed position when the rear cover 2B rotates from the second open position to the second closed position. More specifically, as shown in FIG. 3, when the rear cover 2B is positioned in the second open position and the fuser cover 85 is positioned in the first open position, and the rear cover 2B rotates toward the second closed position, the pressing portion 2C of the rear cover 2B presses the fuser cover 85, causing the fuser cover 85 to rotate toward the first closed position, as shown in FIG. 4.

As shown in FIG. 5, when the rotating rear cover 2B reaches the second closed position, the first surface F1 comes into contact with the engaged portion 84B. As a result, after the rear cover 2B stops at the second closed position, the fixing cover 85 rotates toward the first closed position due to the biasing force of the spring 100. Therefore, as shown in FIG. 2(a), when the rear cover 2B is located at the second closed position and the fixing cover 85 is located at the first closed position, the fixing cover 85 is separated from the pressing portion 2C.

Next, we will explain in detail the operation of the lock lever 90 and the fixing cover 85 when closing the rear cover 2B while the rear cover 2B is in the second open position and the fixing cover 85 is in the first open position.

As shown in FIG. 3, when the rear cover 2B rotates from the second open position to the second closed position, the pressing portion 2C of the rear cover 2B comes into contact with the fuser cover 85, as indicated by the two-dot chain line in the figure. After the pressing portion 2C comes into contact with the fuser cover 85, when the rear cover 2B rotates further toward the second closed position, the fuser cover 85 is pressed by the pressing portion 2C, causing the fuser cover 85 to rotate together with the rear cover 2B.

As shown in FIG. 4, when the downstream surface Fd of the lock lever 90 comes into contact with the engaged portion 84B as the fixing cover 85 rotates, the engaged portion 84B relatively pushes the lock lever 90 clockwise as shown, causing the lock lever 90 to rotate from the locked position toward the unlocked position against the biasing force of the spring 100. Then, just before the rear cover 2B reaches the second closed position, the apex P of the lock lever 90 clears the engaged portion 84B, and the biasing force of the spring 100 causes the lock lever 90 to begin rotating toward the locked position.

As shown in FIG. 5, when the rear cover 2B reaches the second closed position, the first surface F1 of the lock lever 90 comes into contact with the engaged portion 84B. As a result, the reaction force from the engaged portion 84B against the biasing force of the spring 100 acts on the fuser cover 85 via the lock lever 90, and as shown in FIG. 6, the biasing force of the spring 100 causes the fuser cover 85 to rotate toward the first closed position.

Then, as shown in FIG. 2, when the fuser cover 85 reaches the first closed position, the second surface F2 of the lock lever 90 comes into contact with the engaged portion 84B. This causes the reaction force from the engaged portion 84B to press the fuser cover 85 firmly against the second contact surface 84A, thereby firmly locking the fuser cover 85.

As described above, the following effects can be obtained in this embodiment.
By setting the angles of the first surface F1 and the second surface F2 to different angles, even if the opening angle of the fixing cover 85 is increased, the fixing cover 85 can be rotated toward the first closed position by utilizing the biasing force of the first surface F1 and the spring 100, thereby increasing the retraction angle. In addition, the second surface F2, which has an angle different from that of the first surface F1, can firmly lock the fixing cover 85 in the first closed position.

When the rear cover 2B is rotated to the second closed position, the first surface F1 comes into contact with the engaged portion 84B. Therefore, after the rear cover 2B is rotated to the second closed position, the fixing cover 85 can be rotated to the first closed position by the biasing force of the spring 100.

The present invention is not limited to the above-described embodiment, but can be used in various forms, as exemplified below. In the following description, components with substantially the same structure as those in the previously described embodiment will be assigned the same reference numerals, and their description will be omitted.

As shown in Figures 8(a) and (b), the fixing device 200 according to the second embodiment includes a fixing frame 210, a fixing cover 220, a lock lever 230, and a spring 100 that is substantially the same as that of the first embodiment. Unlike the first embodiment, the fixing frame 210 rotatably supports the lock lever 230. The other configuration of the fixing frame 210 is substantially the same as that of the first embodiment.

The spring 100 is positioned so that the rotation axis X2 of the lock lever 230 is located inside the coil portion 110. One end of the spring 100 is fixed to the lock lever 230. The other end of the spring 100 is fixed to the fixing frame 210.

Unlike the first embodiment, the fuser cover 220 has an engaged portion 221. The rest of the configuration of the fuser cover 220 is substantially the same as that of the fuser cover 85 of the first embodiment. The engaged portion 221 is a protrusion that protrudes toward the lock lever 230. The tip of the engaged portion 221 is curved.

The lock lever 230 has an engaging portion 231 that is different from that in the first embodiment. The engaging portion 231 has a vertex P, a first surface F11, a second surface F12, and a third surface F13. The first surface F11, the second surface F12, and the third surface F13 are each flat. The first surface F11, the second surface F12, and the third surface F13 are each capable of contacting the engaged portion 221.

The first surface F11, second surface F12, and third surface F13 are arranged so that, in the process of rotating the fuser cover 220 from the first open position to the first closed position, the engaged portion 221 of the fuser cover 220 comes into contact with the third surface F13, the first surface F11, and the second surface F12 in that order. The vertex P is located between the first surface F11 and the third surface F13.

The third surface F13 is formed at an angle such that when it comes into contact with the engaged portion 221, the reaction force received from the engaged portion 221 causes the lock lever 230 to rotate from the locked position to the unlocked position against the biasing force of the spring 100.

The first surface F11 is formed at an angle such that, when it comes into contact with the engaged portion 221, the biasing force of the spring 100 causes the lock lever 230 to rotate from the release position toward the lock position, and the fixing cover 220 to rotate from the first open position toward the first closed position.

Like the first surface F11, the second surface F12 is angled so that when it comes into contact with the engaged portion 221, the spring force of the spring 100 causes the lock lever 230 to rotate from the released position toward the locked position, and the fuser cover 220 to rotate from the first open position toward the first closed position. As shown in FIG. 8(a), the second surface F12 comes into contact with the engaged portion 221 when the fuser cover 220 is in the first closed position and the lock lever 230 is in the locked position. The first surface F11 and the second surface F12 have different angles relative to the direction perpendicular to the rotation axis X2 of the lock lever 230.

Even in this second embodiment, the distance from the contact point TP to the apex P can be made larger than in a structure in which the first surface F11 and the second surface F12 of the engagement portion 231 in the second embodiment are combined into a single plane F14, as shown in FIG. 9(a). This allows the retraction angle θ5 in the second embodiment, shown in FIG. 8(b), to be larger than the retraction angle θ6 of the comparative example, shown in FIG. 9(b).

As shown in Figure 10(a), the third embodiment is a partial modification of the second embodiment. In the third embodiment, components that are substantially the same as those in the second embodiment are assigned the same reference numerals and will not be described again.

The fixing device 300 according to the third embodiment has a fixing cover 320 and a lock lever 330 that are different from those in the second embodiment. The fixing cover 320 has an engaged portion 321 that is different from that in the second embodiment. The lock lever 330 has an engaging portion 331 that is different from that in the second embodiment.

The engaging portion 331 is a protrusion that protrudes toward the engaged portion 321. The tip of the engaging portion 331 is curved and can come into contact with the engaged portion 321.

The engaged portion 321 is a protrusion that protrudes in the opposite direction to the engaging portion 331. The engaged portion 321 has a vertex P, a first surface F21, a second surface F22, and a third surface F23. The first surface F21, the second surface F22, and the third surface F23 are each flat. The first surface F21, the second surface F22, and the third surface F23 are each capable of contacting the engaging portion 331.

The first surface F21, second surface F22, and third surface F23 are positioned so that, during the process of rotating the fixing cover 320 from the first open position to the first closed position, the engagement portion 331 of the lock lever 330 contacts the third surface F23, the first surface F21, and the second surface F22 in that order. The vertex P is located between the first surface F21 and the third surface F23.

The third surface F23 is formed at an angle such that, when it comes into contact with the engagement portion 331, it rotates the lock lever 330 from the locked position to the unlocked position against the biasing force of the spring 100.

The first surface F21 is formed at an angle such that, when it comes into contact with the engagement portion 331, the biasing force of the spring 100 causes the lock lever 330 to rotate from the release position toward the lock position, and the fixing cover 320 to rotate from the first open position toward the first closed position.

Like the first surface F21, the second surface F22 is formed at an angle such that, when it comes into contact with the engaging portion 331, the biasing force of the spring 100 causes the lock lever 330 to rotate from the released position toward the locked position, and the fixing cover 320 to rotate from the first open position toward the first closed position. As shown in FIG. 10(a), the second surface F22 comes into contact with the engaging portion 331 when the fixing cover 320 is located in the first closed position and the lock lever 330 is located in the locked position. The first surface F21 and the second surface F22 have different angles relative to the direction perpendicular to the rotation axis X2 of the lock lever 330.

Even in this third embodiment, the distance from the contact point TP to the apex P can be made larger compared to an engaged portion 221 having a shape similar to that of the second embodiment, as shown by the two-dot chain line in Figure 10. This allows the retraction angle θ7 in the third embodiment to be made larger than the retraction angle θ8 of the fixing cover 220, which serves as a comparative example and is shown by the two-dot chain line.

In the above embodiment, the rear cover 2B was used as an example of the main body cover, but for example, if the opening exposing the fixing cover is located on one of the left and right sides of the main body housing, the main body cover may also be a side cover located on one of the left and right sides of the main body housing.

In the above embodiment, the main body cover is configured to directly push the fuser cover when closing, but the present invention is not limited to this, and the main body cover may push the fuser cover via another member. For example, in a structure in which a sheet guide that is rotatable relative to the main body housing is connected to the main body cover via a link, and the sheet guide rotates in conjunction with the rotation of the main body cover, the sheet guide may push the fuser cover.

The heating member is not limited to a structure including a heating roller, but may also include, for example, a cylindrical film, a nip plate that sandwiches the film between a pressure roller, and a heater that heats the nip plate.

The spring is not limited to a torsion coil spring, but may also be, for example, a leaf spring or a wire spring.

In the above embodiment, the present invention is applied to a monochrome laser printer 1, but the present invention is not limited to this and may also be applied to other image forming devices, such as color printers, copiers, and multifunction devices.

The elements described in the above embodiments and variations may be implemented in any combination.

8 Fixing device 81 Heating member 84 Fixing frame 84B Engaged portion 85 Fixing cover 90 Lock lever 92 Engaging portion 100 Spring F1 First surface F2 Second surface S Sheet X2 Rotating shaft

Claims (10)

a heating element for heating the sheet;
a fixing frame supporting the heating member;
a fixation cover that is rotatable with respect to the fixation frame between a first closed position where the fixation cover overlaps the fixation frame and a first open position that is farther away from the fixation frame than the first closed position;
a lock lever that is rotatable between a lock position that locks the fuser cover at the first closed position and an unlock position that unlocks the fuser cover, the lock lever having an engagement portion;
a spring that biases the lock lever from the release position toward the lock position,
one of the fixation frame and the fixation cover rotatably supports the lock lever;
the other of the fixation frame and the fixation cover has an engaged portion that engages with the engaging portion of the lock lever,
one of the engaging portion and the engaged portion has a first surface and a second surface that can come into contact with the other of the engaging portion and the engaged portion, the first surface and the second surface having mutually different angles with respect to a direction perpendicular to the rotation axis of the lock lever;
When the first surface comes into contact with the other portion, the lock lever rotates from the release position toward the lock position due to the biasing force of the spring, and the fixing cover rotates from the first open position toward the first closed position,
a lock lever positioned at the lock position and the second surface contacting the other portion when the fixing cover is positioned at the first closed position; The fixing device described in claim 1, characterized in that the angle formed between the first surface and the second surface is an obtuse angle. The fixing device described in claim 1 or claim 2, characterized in that the engagement portion has the first surface and the second surface. The fixing device described in claim 3, characterized in that the engaged portion is a protrusion that is convex on the engaging portion side. The fixing device described in any one of claims 1 to 4, characterized in that the rotation axis of the lock lever is parallel to the rotation axis of the fixing cover. the fixing cover rotatably supports the lock lever,
6. The fixing device according to claim 1, wherein the fixing frame has the engagement portion. the fixing frame rotatably supports the lock lever;
6. The fixing device according to claim 1, wherein the fixing cover has the engagement portion. A fixing device according to any one of claims 1 to 7, characterized in that the heating member comprises a heating roller and a heater that heats the heating roller. the spring is a torsion coil spring having a coil portion, and is arranged so that the rotation axis of the lock lever is located inside the coil portion;
9. The fixing device according to claim 1, wherein one end of the torsion coil spring is fixed to a lock lever, and the other end of the torsion coil spring is fixed to the one of the fixing frame and the fixing cover. An image forming apparatus comprising the fixing device according to any one of claims 1 to 9,
a main body housing having an opening for exposing the fixing cover;
a main body cover that is rotatable between a second closed position that closes the opening and a second open position that opens the opening,
When the main body cover is positioned at the second open position and the fuser cover is positioned at the first open position, if the main body cover rotates toward the second closed position, the main body cover pushes the fuser cover, causing the fuser cover to rotate toward the first closed position,
An image forming apparatus characterized in that when the rotating main body cover reaches the second closed position, the first surface comes into contact with the other part, and the spring force causes the fixing cover to rotate toward the first closed position.