Fixation device and image formation device

Abstract

To solve problems that for contact / separation operation control of a pair of rollers of a fixation device, a configuration for inhibiting overrun is complicated and inefficient, and further nip release and lock release operation by lever operation does not concurrently serve as contact / separation operation by automatic operation.SOLUTION: A fixation device comprises: a holding lever 70 biasing a pressure roller 34; a cam 56 displacing the holding lever 70; a first engagement clutch 58 rotating integrally with the cam 56; a second engagement clutch 59 held rotatably and axially movably; a first cam part 58b included in the first engagement clutch 58; and a second cam part 59b included in the second engagement clutch 59, the second cam part acting in a direction away from the first engagement clutch 58 by rotation of the first engagement clutch 58. A rotation angle region in which acceleration torque by biasing force of the holding lever 70 is received within a rotation angle region in which brake torque when the first engagement clutch 58 moves the second engagement clutch in the separation direction is received.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a fixing device, and more particularly to a configuration relating to nipping and releasing operations of a pair of rollers in a fixing device. [Background technology]

[0002] In the past, in order to suppress the transmission of load to the motor due to overrun of a cam used when contacting or separating a rotating roller or belt, etc., to change the state between nip and nip release, there have been devices that spring-load a gear midway through the gear train in the thrust direction (axial direction), constantly applying a frictional braking load to suppress cam overrun and use a motor with an output that can be driven even when this braking load is constantly applied (see, for example, Patent Document 1), and devices that link the operation of releasing the nip between the lock lever of the fixing unit and the roller pair (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-16734 A (Page 8, Figure 4) [Patent Document 2] JP 2018-13637 A (page 8, Figure 8) Summary of the Invention [Problem to be solved by the invention]

[0004] However, the conventional technology for suppressing cam overrun used in nip change operations placed a heavy load on the machine, and there was a need to reduce the load and provide satisfactory operability. [Means for solving the problem]

[0005] The fixing device according to the present invention comprises: a biasing arm portion that biases one of a first rotating body and a second rotating body used in fixing a medium toward the other to form a nip; a cam that acts on the biasing arm portion and can displace the biasing arm portion against the biasing force by rotating in one direction relative to an axis until the nip is released; a first clutch that rotates coaxially with the cam and rotates integrally with the cam; a second clutch that is held by the axis so as to be rotatable and axially movable and is biased toward the first clutch; an engaging portion formed on one of the first clutch and the second clutch; and a first cam portion that is formed on the other of the first clutch and the second clutch and engages with the engaging portion, and has a first slope that acts in a direction in which the second clutch moves away from the first clutch due to the rotation of the first clutch in one direction; The present invention is characterized in that the rotation angle range of the shaft in which the cam receives an acceleration torque in one direction due to the biasing force of the biasing arm portion is configured so that it falls within the rotation angle range of the shaft in which the first clutch receives a braking torque when moving the second clutch in the direction of separation.

[0006] An image forming apparatus according to the present invention is an image forming apparatus to which the above-described fixing device is detachably attached, the fixing device includes a lock lever whose movement in the axial direction is restricted and which is held rotatably integrally with the second clutch, and a gear formed integrally with the shaft, which is rotationally driven in the one direction by a rotation drive unit of the image forming apparatus main body when the fixing device is attached to the image forming apparatus main body, and the first cam portion has an abutment surface that abuts against the engagement portion and transmits the rotation of the second clutch, which is caused by the rotation of the lock lever in the one direction, to the first clutch, The first rotating body and the second rotating body are in a nipped state and a released nip state while the shaft rotates once in the one direction. [Effects of the Invention]

[0007] According to the present invention, a fixing device can be provided that can efficiently suppress the occurrence of overrun with a simple configuration, and when operating a lock lever that locks the fixing device to the image forming device main body, the lock release and nip release are linked, and nip and nip release can also be performed by a rotation drive unit. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a configuration of a main part of an image forming apparatus according to a first embodiment of the present invention, which employs a fixing unit according to the present invention; [Figure 2] FIG. 2 is a perspective view of the appearance of the image forming apparatus with the top cover closed. [Figure 3] FIG. 2 is a perspective view of the appearance of the image forming apparatus with the top cover open. [Figure 4] 1 is an explanatory diagram showing a frame in the image forming apparatus main body, a fixing unit mounted on the frame, and a fixing unit removed from the frame and pulled out upward; FIG. [Figure 5] 10A and 10B are diagrams showing the engagement state of an engagement guide groove formed in the left wall of the frame and a locking cam portion provided on the fixing unit, where (a) shows the released state and (b) shows the locked state. [Figure 6] FIG. 2 is a perspective view showing the internal configuration around the left lock lever of the fixing unit. [Figure 7] FIG. 2 is an exploded perspective view of the internal configuration around the left lock lever of the fixing unit. [Figure 8] An explanatory diagram for explaining the configuration of the gear and the first engagement clutch, where (a) is an external oblique view of the gear and the first engagement clutch fixed to the shaft, seen from above, (b) is a front view of these as seen from the positive side of the Y direction, and (c) is a left side view thereof. [Figure 9] An explanatory diagram for explaining the configuration of the second engagement clutch, where (a) is an external oblique view of the second engagement clutch mounted on the shaft as seen from below, (b) is a front view of these as seen from the negative side of the Y direction, and (c) is a right side view thereof. [Figure 10]10A and 10B are diagrams illustrating the contact and separation of the heating roller and pressure roller as the cam rotates, in which (a) shows the nip state in which the cam is separated from the cam contact surface of the pressure roller holding lever, (b) shows the nip state at the start of contact, (c) shows the nip released state immediately after the start of the stop zone, and (d) shows the nip released state immediately after the stop zone ends. [Figure 11] This is an explanatory diagram of the operation used to explain the displacement of each part in each of steps 1 to 7 as the shaft rotates once from a rotation angle of 0° to 360°. It is an oblique view of the vicinity of the left lock lever seen from diagonally below, and (a) to (d) correspond to steps 1 to 4. [Figure 12] This is an explanatory diagram of the operation used to explain the displacement of each part in each of steps 1 to 7 as the shaft rotates once from a rotation angle of 0° to 360°. It is an oblique view of the vicinity of the left lock lever seen from diagonally below, and (a) to (c) correspond to steps 5 to 7. [Figure 13] The graph shows the relationship between the rotation angle and the numerical values ​​(torque, nip pressure) at each part, with torque and nip pressure on the vertical axis and the rotation angle of the shaft on the horizontal axis. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiment 1 FIG. 1 is a diagram showing the essential configuration of an image forming apparatus 1 according to a first embodiment, which employs a fixing device 32 according to the present invention.

[0010] As shown in the figure, image forming apparatus 1 has the configuration of an electrophotographic printer, and paper feed tray 12 has recording paper 40 stacked therein as a recording medium, and is detachably attached to the bottom of the main body of image forming apparatus 1. Pickup roller 15 as a feeding member constitutes paper feed section 35 together with paper feed roller 16 and separation roller 17, which are arranged in pair in contact with each other. Pickup roller 15 and paper feed roller 16 are driven to rotate by a drive motor (not shown), and separation roller 17 generates torque in the counter-rotational direction by torque generating means (not shown).

[0011] Therefore, the pickup roller 15 picks up the uppermost recording paper 40 that it contacts from the paper feed tray 12, and the paper feed roller 16 and separation roller 17 separate the recording paper 40 one by one and feed them sequentially onto the transport path, even when, for example, multiple sheets of recording paper 40 are pulled out at the same time.

[0012] A pair of conveying rollers 18 and a pair of registration rollers 19 are arranged in this order on the conveyance path downstream of the paper feed unit 35 in the conveyance direction of the recording paper 40. The pair of conveying rollers 18 conveys the recording paper 40 to the pair of registration rollers 19, and the pair of registration rollers 19 starts conveying the recording paper 40 after it comes into contact with the pair of registration rollers 19 based on the paper detection timing of a paper sensor 36 that detects the passage of the recording paper 40, thereby correcting any skew of the recording paper 40 and sending it to the image forming unit 11.

[0013] The image forming unit 11 includes an image drum 30 that rotates in the direction of the arrow and on whose peripheral surface a toner development is formed, and a transfer roller 31 that is positioned opposite the image drum 30 so as to be in pressure contact therewith and transfers the toner development onto recording paper 40.

[0014] As recording paper 40 fed into image forming unit 11 passes through the pressure contact area between image drum 30 and transfer roller 31, the toner development formed on the circumferential surface of image drum 30 is transferred onto the paper surface by transfer roller 31, to which a predetermined transfer voltage is applied. Image forming unit 11 starts the process of forming toner development on the circumferential surface of image drum 30 based on the paper detection timing of paper sensor 37, which detects recording paper 40 after it has passed through pair of registration rollers 19.

[0015] The fixing unit 32 has a heating roller 33 that rotates in the direction of the arrow and a pressure roller 34 that is arranged to be in pressure contact with the heating roller 33, and applies heat and pressure to the recording paper 40 to which the toner development has been transferred as it passes through the nip formed by these rollers, thereby fixing the toner development to the recording paper 40. The printed recording paper 40 is sent out along the conveyance path from the fixing unit 32 and is sent to the discharge roller pair 21 via the conveyance roller pair 20, and is then discharged by the discharge roller pair 21 into the stacker unit 22. The fixing unit 32 will be described in detail later.

[0016] 1, the X-direction is the conveyance direction of the recording paper 40 as it passes through the pressure-contact portion between the image drum 30 and the transfer roller, the Y-direction is the direction of the rotational axis of the image drum 30, and the Z-direction is the direction perpendicular to both axes. Furthermore, when the X-, Y-, and Z-directions are shown in other figures described later, these directions refer to the same directions. That is, the X-, Y-, and Z-directions in each figure indicate the arrangement direction of the depicted parts in each figure when configuring the image forming apparatus 1 shown in FIG. 1. Here, the Z-direction is assumed to be approximately vertical.

[0017] FIG. 2 is an external perspective view of the image forming apparatus 1 with the top cover 5 closed, and FIG. 3 is an external perspective view of the image forming apparatus 1 with the top cover 5 open.

[0018] In each of these figures, the top cover 5 rotates around coaxial rotation shafts (not shown) located on the left and right sides of the upper rear of the image forming apparatus 1, and when opening, the front half is folded over the rear half at the center in the front-to-rear direction, and as shown in Fig. 3, these are rotated in an overlapping state, opening the top of the image forming apparatus 1. As mentioned above, the top, bottom, left, right, front and back may be identified by viewing the image forming apparatus 1 from the direction of arrow A (X direction) shown in Fig. 2.

[0019] 3, the area 7 surrounded by a dotted line corresponds to the upper part of the fixing unit 32 shown in Fig. 1, and this fixing unit 32 is moved up and down (in the direction of the outline arrow) by an operator holding its grip portion 51 (Fig. 4), thereby being attached to or detached from the main body of the image forming apparatus 1. As mentioned above, for each of the detachable or movable components, such as the fixing unit 32 of the image forming apparatus 1, the part excluding that component may be referred to as the main body of the apparatus.

[0020] Figure 4 is an explanatory diagram showing the frame 41 inside the main body of the image forming apparatus 1, the fixing unit 32 attached to the frame 41, and the fixing unit 32 removed from the frame 41 and pulled out upward. Figure 5 is a diagram showing the engagement state between the engagement guide groove 44 formed in the left wall portion 42 of the frame 41 and the locking cam portion 54 provided on the fixing unit 32, where (a) shows the released state and (b) shows the locked state.

[0021] As shown in Fig. 4, the fixing unit 32 serving as a fixing device is provided with a lock lever 52 having a locking cam portion 54 on the left side and a lock lever 53 having a locking cam portion (not shown) on the right side at its upper left and right sides. When the fixing unit 32 is attached to the main body of the image forming apparatus 1, the left locking cam portion 54 is guided by an engagement guide groove 44 formed in the left wall portion 42 of the frame 41, and at the same time, the right locking cam portion (not shown) is guided by an engagement guide groove 45 formed in the right wall portion 43 of the frame 41 and moves downward in a parallel manner. For reference, the locking cam portion 54 of the fixing unit 32 in the attached position is shown by a dotted line in Fig. 4.

[0022] 5, locking cam portion 54 is formed to be rotatable about a rotation axis, as will be described later, and has an outer shape consisting of a cylindrical portion 54a formed in an arc shape and a pair of cutout portions 54b formed parallel to and facing each other in a cross section perpendicular to the rotation axis. Meanwhile, engagement guide groove 44 has, at its lower end, locking portion 44a having an inner diameter slightly larger than the outer diameter of the cylindrical portion of locking cam portion 54, and restricting portion 44b formed adjacent to locking portion 44a and facing each other, the restricting portion 44b being narrower than the outer diameter of cylindrical portion 54a and having a gap slightly wider than the width of pair of cutout portions 54b.

[0023] 4 and 5(a), the locking cam portion 54 of the fixing unit 32 is in a rotational position (hereinafter sometimes referred to as a released state) in which the plane of the notch portion 54b is parallel to the side surface of the restricting portion 44b of the engagement guide groove 44. This allows the locking cam portion 54 to pass through the restricting portion 44b, making it possible to attach and detach the fixing unit 32 to and from the image forming apparatus 1 main body.

[0024] On the other hand, the fixing device 32 is restricted to an installation position where the locking cam portion 54 abuts the bottom of the engagement guide groove 44 formed in the frame 41 as shown in Figure 5(a), but as shown in Figure 5(b), by further rotating to a rotation position (hereinafter sometimes referred to as the locked state) where the plane of the notch portion 54b is inclined relative to the side of the regulating portion 44b of the engagement guide groove 44, the locking cam portion 54 can no longer pass through the regulating portion 44b and is locked in the installation position.

[0025] The rotation of the locking cam portion 54 is linked to the operation of the lock levers 52 and 53 by the operator, the positional movement of the pressure roller 34 inside the fixing unit 32, etc., and these configurations will be described below.

[0026] Fig. 6 is a perspective view showing the internal structure around the lock lever 52 on the left side of the fixing unit 32, and Fig. 7 is an exploded perspective view of the same part as seen from the same direction. Note that the cover of the fixing unit 32 is removed in these figures.

[0027] 6 and 7, the internal configuration around the left lock lever 52 is similarly configured around the right lock lever 53 (FIG. 4), and is formed in a substantially plane-symmetrical manner with respect to a virtual reference plane (XZ plane) that intersects at the center of the fixing unit 32 in the Y direction. Therefore, since the configurations and operations of these plane-symmetrical components are symmetrical, only the left side will be described, and the right side will also be mentioned as necessary. The shaft 55 is a through shaft that is integrated on both the left and right sides.

[0028] In these figures, the shaft 55 and the heating roller 33 extend in the longitudinal direction of the fixing unit 32 (the Y direction when installed), and are rotatably held by the main body of the fixing unit 32. On the shaft 55 as an axis, a cam 56, a gear 57, a first engagement clutch 58 as a first clutch, a second engagement clutch 59 as a second clutch, and a lock lever 52 are arranged in this order from the inside (the center side of the shaft 55), with the shaft 55 as a rotation axis or a turning axis.

[0029] Of these, the cam 56, gear 57, and first engagement clutch 58 are fixed to the shaft 55, the second engagement clutch 59 is arranged so that it can move axially and rotate freely, and the lock lever 52 is arranged so that it can rotate freely but its axial movement is restricted.

[0030] Figure 8 is an explanatory diagram for explaining the configuration of the gear 57 and the first engagement clutch 58, where Figure 8(a) is an external perspective view of the gear 57 and the first engagement clutch 58 fixedly arranged on the shaft 55, seen from above, Figure 8(b) is a front view of these as seen from the positive side of the Y direction, and Figure 8(c) is a left side view thereof.

[0031] As shown in these figures, the gear 57 and the first engagement clutch 58 are configured as an integral unit, and the first engagement clutch 58 has a first cylindrical circumferential surface portion 58a disposed in contact with a gear side surface 57a of the gear 57, and a first cam portion 58b formed in contact with the gear side surface 57a and protruding from the first cylindrical circumferential surface portion 58a. Note that, although the gear 57 and the first engagement clutch 58 are described here as being formed as an integral unit, they may also be configured as being formed separately and each fixedly disposed on the shaft 55.

[0032] 8(c), first cam portion 58b has first cam portion inclined surface 58c inclined with respect to gear side surface 57a, and first cam portion abutment surface 58d perpendicular to gear side surface 57a and first cylindrical circumferential surface portion 58a, and the formation area of ​​first cam portion inclined surface 58c is formed over a range of rotation angle θ1 in terms of the rotation angle of shaft 55, as shown in FIG. 8(b). Gear 57 and first engagement clutch 58, which are integrally formed, are fixed to shaft 55 by a locking pin 60 disposed so as to penetrate gear 57 and shaft 55.

[0033] Figure 9 is an explanatory diagram for explaining the configuration of the second engagement clutch 59, where Figure 9(a) is an external perspective view of the second engagement clutch 59 mounted on the shaft 55 as seen from below, Figure 9(b) is a front view of these as seen from the negative side in the Y direction, and Figure 9(c) is a right side view thereof.

[0034] As shown in these figures, the second engagement clutch 59 comprises a clutch portion 59a having a reference plane 59e with a circular outer shape, a second cam portion 59b formed along the outer edge of the reference plane 59e, and a cylindrical portion 59g formed integrally adjacent to the clutch portion 59a and having a pair of engagement posts 59h formed opposite each other and protruding from its peripheral surface.

[0035] The second engagement clutch 59 has an axial hole 59f formed in the center of its reference plane 59e, which is formed along the center of the rotation axis of the second engagement clutch 59, and the shaft 55 is fitted into this axial hole 59f, so that the second engagement clutch 59 is rotatable about the shaft 55 as the rotation axis and movable in the axial direction. In this case, the reference plane 59e is perpendicular to the shaft 55, and the pair of engagement posts 59h protrude radially from the shaft 55.

[0036] Furthermore, the second cam portion 59b has a second cam portion inclined surface 59c inclined with respect to the reference plane 59e as shown in Figure 9(c), and a second cam portion abutment surface 59d extending radially and perpendicular to the reference plane 59e, and the formation area of ​​the second cam portion inclined surface 59c is formed over a range of rotation angle θ2 in terms of the rotation angle of the shaft 55 as shown in Figure 9(b).

[0037] One of first cam portion 58b and second cam portion 59b corresponds to the engagement portion, and the other of first cam portion 58b and second cam portion 59b corresponds to the first cam portion having a first inclined surface. Furthermore, one of second cam portion inclined surface 59c and first cam portion inclined surface 58c corresponds to the first inclined surface, and the other corresponds to the second inclined surface. Furthermore, second cam portion abutment surface 59d or first cam portion abutment surface 58d corresponds to the abutment surface. Furthermore, first cam portion 58b or second cam portion 59b corresponds to the second cam portion.

[0038] 6 and 7, the gear 57, first engagement clutch 58, and second engagement clutch 59 configured as described above are arranged with respect to the first engagement clutch 58 fixed to the shaft 55 so that the second cam portion inclined surface 59c of the gear 57 faces and is capable of contacting the first cam portion inclined surface 58c of the first engagement clutch 58. At this time, the first cylindrical circumferential surface portion 58a of the first engagement clutch 58 faces the arc-shaped inner circumferential surface 59i of the second cam portion 59b of the second engagement clutch 59 so as not to come into contact with each other.

[0039] The lock lever 52 comprises a cylindrical portion 52b having a locking cam portion 54 formed therein and one end closed by an end wall, and a lever portion 52a extending radially from the outer peripheral surface of the cylindrical portion 52b. A pair of guide holes 52c extending in the central axis direction are formed in the outer peripheral wall of the cylindrical portion 52b at opposing positions. As shown in Figures 6 and 7, the lock lever 52 is arranged so that a cylindrical portion 59g of the second engagement clutch 59 is fitted inside the cylindrical portion 52b, and further, a pair of engagement posts 59h formed on the cylindrical portion 59g are fitted into and guided by two guide holes 52c. The lock lever 52 is configured so that the central axis of the cylindrical portion 52b and the rotation axis of the locking cam portion 54 coincide with each other.

[0040] At this time, a compression spring 62 is interposed between the cylindrical portion 59g and the tubular portion 52b, and the second engagement clutch 59 and the lock lever 52 are arranged so that the compression spring 62 urges the second engagement clutch 59 and the lock lever 52 in directions separating from each other along the shaft 55. This brings the reference plane 59e of the second engagement clutch 59 into contact with the tip of the first cam portion 58b of the first engagement clutch 58, or simultaneously the gear side surface 57a of the gear 57 into contact with the tip of the second cam portion 59b of the second engagement clutch 59. The axial movement of the lock lever 52 is restricted by a step 55a formed on the shaft 55 and an E-ring 61 attached to the end of the shaft 55 that penetrates the axial center of the locking cam portion 54.

[0041] Therefore, for example, when the lock lever 52 is rotated counterclockwise from the state shown in Figure 6 when viewed from the positive side of the Y direction, the reference plane 59e of the second engagement clutch 59 slides against the tip of the first cam portion 58b of the first engagement clutch 58, and the lock lever 52 and the second engagement clutch 59 can be rotated in the same direction without rotating the shaft 55 until the first cam portion abutment surface 58d of the first engagement clutch 58 and the second cam portion abutment surface 59d of the second engagement clutch 59 abut.

[0042] On the other hand, both ends of the rotation shaft of the pressure roller 34 are held by a pair of pressure roller holding levers 70 arranged on the left and right sides inside the fixing unit 32. As shown in Fig. 6, the left pressure roller holding lever 70 has a flat bearing portion 70a formed with a rotation shaft hole 70d into which the rotation shaft end portion 34a of the pressure roller 34 is fitted, and a cam abutment surface 70b formed at a right angle to the bearing portion 70a and which receives the action of the cam 56.

[0043] A rotation shaft hole 70c into which a rotation shaft (not shown) formed in the main body of the fixing device 32 is fitted is formed in the bearing portion 70a of the pressure roller holding lever 70. The pair of left and right pressure roller holding levers 70 are rotatably held by the main body of the fixing device 32 around the rotation shaft fitted in the rotation shaft hole 70c at a position where the pressure roller 34 faces the heat roller 33 as shown in Fig. 6. The heat roller 33 corresponds to either the first rotating body or the second rotating body, and the pressure roller 34 corresponds to the other of the first rotating body or the second rotating body.

[0044] Furthermore, the pressure roller holding lever 70 is biased in the counterclockwise direction about the rotation axis by a biasing means (not shown) that is hung between it and the main body of the fixing unit 32. Therefore, in a natural state, this biasing force causes the pressure roller 34 to contact the heat roller 33, and at a predetermined rotation position where an appropriate nip is formed, rotation in the same direction is restricted by a rotation restricting member (not shown).

[0045] Here, the first engagement clutch 58 is configured to have a first cam portion 58b having a first cam portion inclined surface 58c, and the second engagement clutch 59 is configured to have a second cam portion 59b having a second cam portion inclined surface 59c, but either the first engagement clutch 58 or the second engagement clutch 59 may have an engagement portion such as a protrusion that engages with the cam portion inclined surface (58c or 59c) and cam portion abutment surface (58d or 59d) of the other.

[0046] In the above configuration, the operation of the cam 56 and the lock lever 52, which rotate or turn in conjunction with each other, will be described.

[0047] Figure 10 is an explanatory diagram illustrating the contact and separation operations of the heating roller 33 and pressure roller 34 as the cam 56 rotates, i.e., the transition to a nip state and the transition to a nip release state. Figure 10(a) shows the nip state in which the cam 56 is separated from the cam contact surface 70b of the pressure roller holding lever 70, Figure 10(b) shows the nip state at the start of contact, Figure 10(c) shows the nip release state immediately after the start of the stop zone, and Figure 10(d) shows the nip release state immediately after the stop zone ends.

[0048] First, the contact and separation operations, nip state, and nip release state of the heating roller 33 and the pressure roller 34 caused by the rotation of the cam 56 will be described with reference to FIG.

[0049] As shown in Figure 1A, when the notch 56a of the cam 56 is at a rotation angle facing the cam contact surface 70b of the pressure roller holding lever 70, the cam 56 is spaced from the cam contact surface 70b of the pressure roller holding lever 70, and the pressure roller holding lever 70 presses the pressure roller 34 against the heating roller 33 with a biasing force in the direction of arrow B from a biasing means (not shown), creating a nip between them. At this time, the pressure roller holding lever 70 is restricted from further rotation in the counterclockwise direction by a restricting means (not shown). The biasing means that biases in the direction of arrow B and the pressure roller holding lever 70 correspond to a biasing arm.

[0050] 10(b) shows the state immediately after the cam 56 rotates counterclockwise and the end of the notch 56a of the cam 56 abuts against the cam abutment surface 70b of the pressure roller holding lever 70. At this stage, the pressure roller holding lever 70 has not yet rotated counterclockwise, so the nipped state is maintained.

[0051] As will be described later, the cam 56 rotates in the counterclockwise direction when the gear 57 is rotationally driven in the counterclockwise direction by a drive motor (not shown) or when an operator operates the lock lever 52 to unlock the lock. Hereinafter, the counterclockwise rotation direction around the axis of the shaft 55 as viewed from the positive side of the Y direction may be referred to as the "predetermined direction."

[0052] 10C shows the state immediately after the cross-sectional arc portion 56b comes into contact with the cam contact surface 70b. At this time, the contact position 70e of the cam contact surface 70b is the position where a perpendicular line passing through the center of rotation of the cam 56 intersects with the contact position 70e.

[0053] Here, the abutment position 70e is defined as a reference position on the cam abutment surface 70b, and L1 is the upstream distance from the abutment position where the cam 56 abuts against the cam abutment surface 70b upstream of the reference position in the rotation direction of the cam 56 to the reference position, and L2 is the downstream distance from the abutment position where the cam 56 abuts against the cam abutment surface 70b downstream of the reference position in the rotation direction of the cam 56 to the reference position. As described above, when the cam abutment surface 70b is viewed from the positive side in the Y direction, the side closer to the pivot shaft hole 70c than the reference position (abutment position 70e) may be referred to as the upstream side in the rotation direction, and the opposite side may be referred to as the downstream side in the rotation direction.

[0054] Therefore, from the time when the end of the notched portion 56a of the cam 56 abuts against the cam abutment surface 70b of the pressure roller holding lever 70 as shown in Figure 12(b), until the upstream distance L1 becomes zero (=L3) and the abutment portion moves to the cross-sectional arc portion 56b as shown in Figure 12(c), the urging force in the direction of arrow B acts as a moment that rotates the cam 56 counterclockwise. Therefore, during this time, the cam 56, which rotates in the predetermined direction, rotates while receiving the above-mentioned reaction force, and rotates the pressure roller holding lever 70 clockwise.

[0055] When the cam 56 rotates to the position shown in FIG. 10(c), the pressure roller holding lever 70 rotates clockwise to a maximum extent, and the pressure roller 34 separates from the heat roller 33, resulting in a nip release state.

[0056] 10(d) shows the state immediately after the contact portion of the cam 56 has disengaged from the cross-sectional arc portion 56b. While the cross-sectional arc portion 56b is in contact with the cam contact surface 70b, the cam 56 continues to contact the cam contact surface 70b at contact position 70e (reference position). Therefore, the cam 56 rotates without receiving a moment caused by the biasing force in the direction of arrow B, and maintains the nip release state without changing the rotational position of the pressure roller holding lever 70. The rotation region of the cam 56 where the cross-sectional arc portion 56b is in contact with the cam contact surface 70b is sometimes referred to as the cam stop region.

[0057] As shown in Fig. 1(d), when the cam 56 rotates counterclockwise beyond the cam stop area, it comes into contact with the cam contact surface 70b at downstream distance L2. In this way, when the contact position becomes downstream of the reference position (contact position 70e), the urging force in the direction of arrow B acts as a moment that rotates the cam 56 in the predetermined direction. Therefore, the force acts to promote (accelerate) the rotation of the cam 56 rotating in the predetermined direction, and the cam 56 rotates in an overrun state while receiving this moment, and the pressure roller holding lever 70 rapidly rotates in the predetermined direction, returning to the state shown in Fig. 1(a), thereby establishing the nip state again.

[0058] Next, the interlocking operation of the lock lever 52, the first engagement clutch 58, the second engagement clutch 59, the cam 56, and the pressure roller holding lever 70 will be described.

[0059] 11 and 12 are operation explanatory diagrams illustrating the displacement of each part during steps 1 to 7 as shaft 55 rotates from a rotation angle of 0° to 360°. These are perspective views of the vicinity of left-side lock lever 52 viewed from diagonally below, with Figs. 11(a) to 11(d) corresponding to steps 1 to 4 and Figs. 12(a) to 12(c) corresponding to steps 5 to 7. Fig. 13 is a graph showing the relationship between the rotation angle and the numerical values ​​(torque, nip pressure) of each part, with torque and nip pressure on the vertical axis and the rotation angle of shaft 55 on the horizontal axis. Note that in Fig. 13, the rotation angles corresponding to steps 1 to 7 are indicated by arrows.

[0060] In process 1 of Figure 11(a), the locking cam portion 54 is in a released state (see Figure 5(a)), and the rotational position of the lock lever 52 at this time may be referred to as the release position. With the lock lever 52 in this release position, the fixing unit 32 is attached to or detached from the main body of the image forming apparatus 1. In this process 1, it is assumed that the fixing unit 32 is in the attached position relative to the main body of the image forming apparatus 1.

[0061] At this time, first cam portion abutment surface 58d of first engagement clutch 58 fixed to shaft 55 abuts against second cam portion abutment surface 59d of second engagement clutch 59, and the rotation angle of shaft 55 at this time is 75° (see FIG. 13). At this rotation angle (= 75°), cam 56 fixed to shaft 55 is in a state where its cross-sectional arc portion 56b abuts against cam abutment surface 70b, as shown in FIG. 10(c), and the pressure roller 34 and heating roller 33 are in a released nip state.

[0062] In step 2 of FIG. 11(b), the operator rotates the lock lever 52 clockwise by 75° as viewed from the positive side of the Y direction, and the locking cam portion 54 is in a locked state (see FIG. 5(b)). The rotational position of the lock lever 52 at this time may be referred to as the locked position. At this time, the second engagement clutch 59 rotates in the same direction as the rotation of the lock lever 52, but the first engagement clutch 58 remains stopped, and the rotational angle of the shaft 55 also remains at 75°. Therefore, the pressure roller 34 and the heat roller 33 remain in a nip-released state.

[0063] In process 3 of Figure 11(c), with the fixing unit 32 attached to the image forming apparatus 1 main body, the gear 57 is rotated in a predetermined direction by a rotation drive unit (not shown) provided within the apparatus, and has rotated to a position just before the first cam portion inclined surface 58c of the first engagement clutch 58 and the second cam portion inclined surface 59c of the second engagement clutch 59 come into contact with each other.

[0064] At this time, cam 56, which rotates integrally with gear 57 via shaft 55, is configured so that its cam stop area abuts against cam contact surface 70b of pressure roller holding lever 70, so pressure roller holding lever 70 does not move and the nip release state is maintained. The rotation angle of shaft 55 from process 2 to process 3 in the cam stop area corresponds to 75° to 240° as shown in Figure 13.

[0065] In process 4 of Figure 11(d), gear 57 is further rotated from process 3, and first cam portion 58b of first engagement clutch 58, which rotates integrally with gear 57, moves second engagement clutch 59 in the +Y direction, which is the axial direction. At this time, second engagement clutch 59 is guided by guide hole 52c formed in lock lever 52, and moves in the direction of arrow Y (axial direction) against the bias of compression spring 62 (Figure 7). At this time, a force acts on lock lever 52 in the counterclockwise rotation direction, but rotation in the same direction is prevented by a locking means (not shown) provided on top cover 5 (see Figure 1) or the like.

[0066] The rotation angle of shaft 55 from process 3 to process 4, in which second engagement clutch 59 moves in the direction of arrow Y (axial direction) against the force of compression spring 62 (Figure 7), corresponds to 240° to 345° as shown in Figure 13.

[0067] During this time, when the cam 56 completes the cam stop region up to around 285°, slightly past the state of Process 3, it comes into contact with the cam contact surface 70b at the downstream distance L2 as explained in Figure 10(d). As a result, the cam 56 is subjected to a moment that rotates in a predetermined direction by a biasing means (not shown) that biases the pressure roller holding lever 70 in the direction of arrow B.

[0068] Here, with reference to the graph in FIG. 13, the torque and nip pressure generated in response to the rotation angle of shaft 55, which is rotated in a predetermined direction via gear 57 by a rotation drive unit (not shown), will be described.

[0069] Tc, Tcl, Tco, and Pn shown in the graph are as follows: Tc: The torque required to rotate the shaft 55 in a predetermined direction (counterclockwise when viewed from the positive side of the Y direction), which may be referred to here as the required cam torque. Tcl: the torque required to move the second engagement clutch 59 in the direction of arrow Y against the bias of the compression spring 62 by the rotation of the first engagement clutch 58, and may be referred to herein as the braking torque. Tco: As shown in FIG. 10(d), this is a torque equivalent to the moment that rotates the cam 56 in the forward direction by a biasing means (not shown) that biases the cam 56 in the direction of arrow B, and may be referred to here as the acceleration torque. Pn: Nip pressure generated in the nip between the heating roller 33 and the pressure roller 34

[0070] 13, in the operation from process 1 to process 2 described above, shaft 55 does not rotate and remains at a rotation angle of 75°. Between process 2 and process 3, shaft 55 rotates from a rotation angle of 75° to a rotation angle of 240°, but because the cam is in a stationary region, the required cam torque Tc is 0. Note that even while the cam is stationary, loads due to friction are generated between cam 56 and cam contact surface 70b of pressure roller holding lever 70, and between first engagement clutch 58 and second engagement clutch 59; however, the frictional resistance is assumed to be sufficiently low due to grease lubrication, and is not taken into consideration here.

[0071] In the operation from process 3 to process 4, once the rotation angle of shaft 55 exceeds 240°, braking torque Tcl increases approximately in proportion to the increase in the rotation angle. This is because the reaction force of compression spring 62 increases in proportion to the movement of second engagement clutch 59 in the direction of arrow Y. Furthermore, once the rotation angle of shaft 55 passes process 3 and approaches 285°, as shown in FIG. 10(d), cam 56 abuts against cam abutment surface 70b at a downstream distance L2 from the reference position, and therefore, cam 56 receives acceleration torque Tco equivalent to a moment that rotates cam 56 in a predetermined direction (counterclockwise) due to the biasing force in the direction of arrow B.

[0072] This acceleration torque Tco is generated until a little past a rotation angle of 345°, when the cam 56 reaches process 4, where it separates from the cam contact surface 70b of the pressure roller holding lever 70, and reaches a maximum at a rotation angle of about 325°. This acceleration torque Tco is a factor that causes overrun, and here, as shown in the graph of FIG. Tc=Tcl-Tco>0 (1) Since the required cam torque Tc is set to be negative, no overrun occurs. Note that the state in which the required cam torque Tc becomes negative is sometimes referred to as overrun.

[0073] That is, the braking force due to the braking torque Tcl generated by moving the second engagement clutch 59 in the direction of the arrow Y suppresses the acceleration torque Tco that causes overrun, thereby preventing the occurrence of overrun.

[0074] The braking torque Tcl that determines the braking force is determined by the slope angles of the first cam portion slope 58c of the first engagement clutch 58 and the second cam portion slope 59c of the second engagement clutch 59, the spring pressure of the compression spring 62, the friction coefficient of the slopes, etc. Tcl>Tco (2) The relationship is appropriately set as follows.

[0075] Between process 3 and process 4, as the pressure roller holding lever 70 rotates counterclockwise around the rotation axis (not shown) that fits into the rotation axis hole 70c, the heating roller 33 and the pressure roller 34 transition from a nip release state to a nip state in which a predetermined nip pressure is generated.

[0076] 12(a), first engagement clutch 58 further rotates in the predetermined direction from the state in process 4, thereby disengaging first cam portion inclined surface 58c of first engagement clutch 58 from second cam portion inclined surface 59c of second engagement clutch 59. This causes second engagement clutch 59 to move in the −Y direction (axial direction), and, for example, gear side surface 57a of gear 57 and the tip end of second cam portion 59b of second engagement clutch 59 come into contact with each other.

[0077] Here, the rotational drive by the rotational drive unit is temporarily stopped. As a result, the cam 56 is stabilized in a state separated from the cam abutment surface 70b of the pressure roller holding lever 70, and the heating roller 33 and the pressure roller 34 maintain a nip state. Note that process 5 corresponds to a state where the rotation angle is 360° as shown in the graph of FIG. 13.

[0078] In addition, the braking torque Tcl satisfies inequality (2) with respect to the generated acceleration torque Tco, and is configured to be generated within the minimum necessary rotational angle range, including the rotational angle range in which the acceleration torque Tco is generated. The generation range of the braking torque Tcl here is 240° to 360°, compared to the rotational angle range in which the acceleration torque Tco is generated, which is 275° to 350°. Therefore, the generation range of the braking torque Tcl is limited to one-third of one rotation of the cam 56.

[0079] Process 6 in Figure 12(b) corresponds to a rotation angle of 0° (=360°) as shown in the graph in Figure 13, and shows the same state as process 5 in Figure 12(a), and printing is performed in this state.

[0080] 12(c), in process 7, the operator rotates the lock lever 52 counterclockwise by 75° as viewed from the positive side of the Y direction in order to remove the fixing unit 32 attached to the main body of the image forming apparatus 1. As the lock lever 52 rotates from process 6 to process 7, the second engagement clutch 59, the first engagement clutch 58, the gear 57, and the cam 56 rotate integrally in the same direction. As a result, the locking cam portion 54 enters a released state, and the cross-sectional arc portion 56b of the cam 56 abuts against the cam abutment surface 70b of the pressure roller holding lever 70, thereby releasing the nip between the pressure roller 34 and the heating roller 33.

[0081] 13, between process 6 and process 7, as explained above with reference to Figures 10(a) to 10(c), cam 56 rotates while receiving a reaction force based on the urging force in the direction of arrow B, so the required cam torque Tc increases from a peak at a rotation angle of about 30°. Also, during this time, pressure roller holding lever 70 rotates clockwise, so pressure roller 34 separates from heat roller 33, resulting in a nip release state.

[0082] Furthermore, this process 7 is the same as the state in process 1 when the fixing unit 32 is placed in the mounting position of the image forming apparatus 1 main body, and the operator can simply remove it from the apparatus by holding the grip portion 51 as shown in Figure 4.

[0083] Here, an example has been shown in which the operator rotates the lock lever 52 counterclockwise from step 6 to step 7 to release the lock cam portion 54 and set the nip to a released state, thereby removing the fixing unit 32 from the device. However, it is also possible to set the nip between the pressure roller 34 and the heating roller 33 to a released state without operating the lock lever 52, while keeping the lock cam portion 54 in the locked state.

[0084] That is, from the state of process 6 shown in FIG. 12(b), by rotating the cam 56 in a predetermined direction (counterclockwise) to a rotation angle of 75° by a rotation drive unit (not shown) that drives the gear 57, it is possible to directly transition to process 2 shown in FIG. 11(b), which is the nip release state, without going through process 7 (= process 1) of operating the lock lever 52.

[0085] As described above, in the image forming apparatus 1 of the present embodiment 1, when the fixing device 32 is attached, the rotation drive unit (not shown) rotates the gear 57 once in a predetermined direction, during which the rotation angle position of the cam 56 in the state of process 3 (240°) is set as the nip release position, and the rotation angle position of the cam 56 in the state of process 5 (= process 6) (0°=360°) is stopped as the nip position, and the nip and nip release of the fixing device 32 are controlled by repeating this unidirectional rotation.

[0086] Furthermore, when removing the fixing unit 32 from the main body of the image forming apparatus 1, the operator rotates the lock lever 52 counterclockwise from the nip position in step 6, thereby releasing the nip and shifting to step 7 (= step 1) where the locking cam portion 54 is in the released state, thereby enabling the fixing unit to be removed. The operation after reattachment is as described above.

[0087] As described above, according to the image forming apparatus 1 of this embodiment, the occurrence of overrun can be suppressed when the drive motor drives the nip between the heat roller 33 and the pressure roller 34 and the nip release. Furthermore, since the braking torque Tcl can be configured to be generated only in the minimum necessary range within one rotation of the shaft, the burden on the rotation drive unit is reduced, enabling efficient operation. Furthermore, when the fixing unit 32 is attached to or detached from the main body of the image forming apparatus 1, the cam 56 moves away from the pressure roller holding lever 70, allowing the gear 57 to rotate almost freely. This allows the gear 57 to mesh smoothly with the gear provided on the main body of the image forming apparatus 1, improving the operability when attaching or detaching the fixing unit 32.

[0088] Furthermore, when the lock lever 52 is rotated to change the locking cam portion 54 from the locked state to the released state, the state between the heating roller 33 and the pressure roller 34 can be simultaneously changed from the nipped state to the nipped release state, which simplifies the operation for removing the fixing unit 32.

[0089] Furthermore, the transition from the nip state between the heating roller 33 and the pressure roller 34 to the nip release state can be performed automatically (by a rotation drive unit) or manually (by operating the lock lever 52) using a substantially common mechanism, thereby simplifying the device.

[0090] Furthermore, in the description of the above embodiment, terms such as "upper," "lower," "left," "right," "front," and "rear" are used for convenience and do not limit the absolute positional relationship in the state in which the image forming apparatus 1 or the fixing unit 32 is positioned. [Industrial Applicability]

[0091] In this embodiment, a monochrome printer has been used as the image forming apparatus, but the present invention can also be applied to a color printer, a copying machine, a fax machine, and a multifunction machine that combines these. [Explanation of symbols]

[0092] 1 image forming apparatus, 5 top cover, 7 area, 11 image forming section, 12 paper feed tray, 15 pickup roller, 16 paper feed roller, 17 separation roller, 18 conveying roller pair, 19 registration roller pair, 20 conveying roller pair, 21 discharge roller pair, 22 stacker section, 30 image drum, 31 transfer roller, 32 fuser unit, 33 heating roller, 34 pressure roller, 35 paper feed section, 36 paper sensor, 37 paper sensor, 40 recording paper, 41 frame, 42 wall section, 43 wall section, 44 engagement guide groove, 44a locking section, 44b regulating section, 45 engagement guide groove, 51 gripping section, 52 lock lever, 52a lever section, 52b cylindrical section, 52c guide hole, 53 lock lever, 54 locking cam portion, 54a cylindrical portion, 54b notch portion, 55 shaft, 56 cam, 56a notch portion, 56b cross-sectional arc portion, 57 gear, 57a gear side surface, 58 first engagement clutch, 58a first cylindrical peripheral surface portion, 58b first cam portion, 58c first cam portion inclined surface, 58d first cam portion contact surface, 59 second engagement clutch, 59a clutch portion, 59b second cam portion, 59c second cam portion inclined surface, 59d second cam portion contact surface, 59e reference plane, 59f shaft hole, 59g cylindrical portion, 59h engagement post, 59i arc-shaped inner peripheral surface, 60 locking pin, 61 E-ring, 62 compression spring.

Claims

1. a biasing arm portion that biases one of the first rotating body and the second rotating body used in fixing the medium toward the other to form a nip; a cam that acts on the biasing arm portion and can displace the biasing arm portion by rotating in one direction relative to a shaft against the biasing force until the nip is released; a first clutch that is coaxial with the cam and rotates integrally with the cam; a second clutch held by the shaft so as to be rotatable and axially movable, and biased toward the first clutch; an engaging portion formed on one of the first clutch and the second clutch; a first cam portion formed on the other of the first clutch and the second clutch, which is engaged with the engaging portion, and which has a first slope that acts in a direction in which the second clutch moves away from the first clutch due to the rotation of the first clutch in one direction; and a fixing device configured such that a rotation angle region of the shaft in which the cam receives an acceleration torque in one direction due to the biasing force of the biasing arm portion is within a rotation angle region of the shaft in which the first clutch receives a braking torque when moving the second clutch in the direction of separation,

2. When the braking torque is Tcl and the acceleration torque is Tco, regardless of the rotation angle, Tcl>Tco 2. The fixing device according to claim 1, wherein the fixing device is configured such that:

3. 3. The fixing device according to claim 1, wherein the engaging portion is a second cam portion having a second inclined surface that can be brought into contact with the first inclined surface.

4. a lock lever whose movement in the axial direction is restricted and which is held rotatably integrally with the second clutch, 3. The fixing device according to claim 1, wherein the first cam portion has a contact surface that contacts the engagement portion to transmit the rotation of the second clutch accompanying the rotation of the lock lever in one direction to the first clutch.

5. 5. An image forming apparatus in which the fixing device according to claim 4 is detachably mounted, the fixing device has a gear formed integrally with the shaft, the gear being rotationally driven in the one direction by a rotation drive unit of the image forming apparatus body when the fixing device is attached to the image forming apparatus body; an image forming apparatus, characterized in that the first rotating body and the second rotating body are in a nipped state and a released nip state while the shaft makes one rotation in the one direction;

6. 6. The image forming apparatus according to claim 5, wherein the rotation of the lock lever in one direction releases the fixing device from the image forming apparatus main body and changes the first rotating body and the second rotating body from the nip state to the nip release state.

7. The image forming apparatus according to claim 6, characterized in that the lock lever has a locking cam portion that rotates integrally, and when the lock lever rotates in one direction, the locking cam portion is released from its fixed state to the locking portion of the engagement guide groove formed in the image forming apparatus main body.

Images