Fixing device and image forming apparatus

Abstract

To provide a fixing device that can achieve both prevention of damage to a cam receiving member and a reduction in space and cost.SOLUTION: A fixing device comprises: a swingable plate-like pressure lever member 31 that presses one of a pair of rollers to the other; a cam member 41 that displaces the pressure lever member 31 between a position for maintaining the pressure contact state of the pair of rollers and a position for releasing the state; and a cam receiving member 32 that is disposed at a position of the pressure lever member 31 facing the cam member 41, and transmits a pressing force from the cam member 41 to the pressure lever member 31. When the thickness of the pressure lever member 31 is defined as t, the dimension of the cam receiving member 32 in the thickness direction of the pressure lever member 31, the dimension being the length of a surface in contact with the cam member 41 as W, and the dimension of the cam receiving member 32 in a direction orthogonal to the thickness direction of the pressure lever member 31, the dimension being the length from the contact position with the cam member 41 to one side face as L1, the relationship of L1≥0.6×(W-t) / 2+0.2 is satisfied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] A known fixing device installed in an image forming apparatus such as a copier, printer, or facsimile machine is equipped with a heating roller and a pressure roller, and the recording medium is passed through a fixing nip formed by the pressing of the heating roller and the pressure roller, and the image on the recording medium is fixed by heat and pressure. Such a fixing device is provided with a contact / separation mechanism that moves the heating roller and the pressure roller toward and away from each other.

[0003] The contacting / separating mechanism generally includes a cam member that rotates to move the contacting / separating member toward or away from the contacting / separating member (see, for example, Patent Document 1). Patent Document 1 discloses a contact / separation mechanism that moves a contact member closer and further away by rotating a cam member, in which the cam member has a cam surface whose distance from the center of rotation gradually increases over an area greater than halfway around the rotational direction, and is rotatable in one direction and the opposite direction. Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for space saving and cost reduction in image forming apparatuses, and the same is true for the fixing devices installed therein. One way to achieve space savings and cost reductions is to make the components smaller and thinner. For example, as in the fixing device of Patent Document 1, space savings can be achieved by using a flat pressure lever member that does not require complex processing. Also, by using an easily processable resin material for the cam member and the member that contacts the cam member and by miniaturizing the parts, the amount of material used can be reduced, thereby achieving cost reductions.

[0005] However, the constraints imposed on making components thinner and more compact can lead to a decrease in the strength of the components. In particular, the cam receiving member, which is pressed by the cam member, can be deformed by repeated loads and can break over time.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device that can prevent damage to a cam receiving member while simultaneously realizing space saving and cost reduction. [Means for solving the problem]

[0007] In order to solve the above problems, the fixing device of the present invention comprises a pair of rollers that are in pressure contact with each other so as to be able to move toward or away from each other and that sandwich and transport a recording medium, a plate-like pressure lever member that is pivotally supported at one end and has an elastic member engaged at the other end and that presses one of the pair of rollers against the other, a cam member that displaces the pressure lever member between a position that maintains the pressure contact state of the pair of rollers and a position that releases the pressure contact state, and a cam receiving member that is disposed at a position on the pressure lever member opposite the cam member and that transmits the pressing force from the cam member to the pressure lever member, the cam receiving member is a member having a substantially U-shaped cross section, and is fitted to cover a pressed surface of the pressure lever member that receives a pressing force from the cam member and at least a portion of both side surfaces of the pressure lever member in a thickness direction, The thickness of the pressure lever member is t (mm) The dimension of the cam receiving member in the thickness direction of the pressure lever member is W, and the length of the surface that abuts against the cam member is W (mm) and the dimension of the cam receiving member in a direction perpendicular to the thickness direction of the pressure lever member is The other end of the pressure lever member The length to the side of L1 (mm) When the thickness of the portion of the cam receiving member that covers at least a part of both side surfaces of the pressure lever member in the thickness direction is (Wt) / 2 on both sides, L1≧0.6×(Wt) / 2+0.2 (mm), and L1≦1.3×(Wt) / 2+1.25(mm) The above relationship is satisfied. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a fixing device that can prevent damage to a cam receiving member while simultaneously realizing space saving and cost reduction. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of a monochrome image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a fixing device according to the present embodiment. [Figure 3] FIG. 2 is a diagram illustrating a cam member, a light blocking member, and an optical sensor. [Figure 4] FIG. 2 is a schematic configuration diagram of a drive system of the contact / separation mechanism according to the embodiment. [Figure 5] FIG. 2 is a block diagram of a control system for the contact / separation mechanism according to the present embodiment. [Figure 6] 10A and 10B are diagrams illustrating a separating operation of the pressure roller by the cam member. [Figure 7] 10A and 10B are diagrams illustrating an approaching operation of the pressure roller caused by the cam member. [Figure 8] FIG. 4 is a cam diagram showing the relationship between the rotation angle and the radius of the cam member. [Figure 9] FIG. 10 is a perspective view showing an example of a cam receiving member disposed on the pressure lever member. [Figure 10] 10 is an explanatory view showing a state in which the cam member and the cam receiving member are in contact with each other; FIG. [Figure 11] 5A and 5B are explanatory diagrams of loads and stresses acting on a cam receiving member. [Figure 12] 10 is an explanatory diagram of the dimensions of the cam receiving member in the thickness direction of the pressure lever member. FIG. [Figure 13] 10A is a graph showing the position where the load is received on the cam receiving member, and FIG. 10B is a graph showing the stress distribution on the cam receiving member. [Figure 14] 10 is a graph showing changes in stress value when a load position on a cam receiving member is changed. [Figure 15] 10 is a graph showing the results of a stress analysis simulation for combinations of values ​​of Δt and L1. [Figure 16] 5A and 5B are explanatory diagrams illustrating an example of a cam receiving member. [Figure 17] 10 is a graph showing the results of a stress analysis simulation for the R shape of the cam receiving member. [Figure 18]10 is an explanatory diagram showing an unstable contact state between the pressure lever member and the cam receiving member. FIG. [Figure 19] 10A and 10B are explanatory views showing an example of an engagement structure between a cam receiving member and a pressure lever member. [Figure 20] 10 is a perspective view showing an example of an engagement structure between a cam receiving member and a pressure lever member. FIG. [Figure 21] 10 is a perspective view showing an example of fitting between a pressure lever member having a wall portion and a cam receiving member. FIG. [Figure 22] 10 is an explanatory view showing an example of fitting between a pressure lever member having a wall portion and a cam receiving member. FIG. [Figure 23] 10A and 10B are diagrams illustrating the tilt of the posture caused by the gap between the pressure lever member and the cam receiving member. [Figure 24] 10 is a perspective view showing an example of a cam receiving member that fits into a pressure lever member having a wall portion. FIG. [Figure 25] 10 is an explanatory diagram of the dimensions of a cam receiving member that fits into a pressure lever member having a wall portion. FIG. [Figure 26] 10 is a graph showing the results of a stress analysis simulation for combinations of values ​​of Δt and L2. [Figure 27] FIG. 10 is a perspective view showing an example of a cam receiving member disposed on the pressure lever member. [Figure 28] 10A and 10B are explanatory diagrams showing the R-shape and stress of the bottom surface of the recessed portion of the cam receiving member. [Figure 29] 10 is a perspective view showing an example of the shape of a contact surface of a cam receiving member with a cam member; FIG. [Figure 30] 5A and 5B are cross-sectional views showing examples of the shape of a contact surface of a cam receiving member with a cam member. [Figure 31] FIG. 1 is a schematic diagram illustrating the configuration of a fixing device including a fixing belt. [Figure 32] FIG. 2 is a schematic diagram illustrating the configuration of a fixing device in which a fixing roller moves toward and away from an opposing roller. DETAILED DESCRIPTION OF THE INVENTION

[0010] The fixing device and image forming apparatus according to the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments, and can be modified, added, modified, deleted, or otherwise altered within the scope of what can be conceived by a person skilled in the art. Any embodiment that achieves the functions and effects of the present invention is within the scope of the present invention.

[0011] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. The configuration of the fixing device according to the present invention can be applied to both electrophotographic and inkjet image forming apparatuses. An example of a fixing device mounted in an electrophotographic image forming apparatus will be described below, but in an inkjet image forming apparatus, the fixing device can be applied, for example, as a means for heating a recording medium with a heating roller to dry the ink.

[0012] In the following embodiments, the "recording medium" will be described as "paper," but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper (paper), but also overhead projector sheets, fabric, metal sheets, plastic films, and prepreg sheets made of carbon fiber pre-impregnated with resin. Media to which developer or ink can be attached, recording paper, and recording sheets are all included in the "recording medium." Furthermore, "paper" includes not only plain paper, but also cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

[0013] Furthermore, the term "image formation" used in the following description refers not only to the application of meaningful images such as letters and figures to a medium, but also to the application of meaningless images such as patterns to a medium.

[0014] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. First, the overall configuration and operation of an image forming apparatus will be described with reference to Figure 1. Note that image forming apparatuses to which the present invention is applicable include printers, as well as single copy machines and facsimiles, or multifunction machines that combine at least two of the functions of a copy machine, printer, facsimile, and scanner.

[0015] The image forming apparatus shown in Fig. 1 is a monochrome image forming apparatus. A process unit 1 serving as an imaging unit is detachably mounted in the apparatus main body (image forming apparatus main body) 100. The process unit 1 includes a photoconductor 2 serving as an image carrier that carries an image on its surface, a charging roller 3 serving as charging means for charging the surface of the photoconductor 2, a developing device 4 serving as developing means that visualizes the latent image on the photoconductor 2, and a cleaning blade 5 serving as cleaning means that cleans the surface of the photoconductor 2. An LED head array 6 serving as exposure means that exposes the surface of the photoconductor 2 is also disposed opposite the photoconductor 2.

[0016] A toner cartridge 7 serving as a powder container for containing toner, which is powder for image formation, is removably attached to the process unit 1. The toner cartridge 7 has an unused toner storage section 8 for storing unused toner, and a waste toner storage section 9 for storing used waste toner.

[0017] The image forming apparatus also includes a transfer device 10 that transfers an image onto paper as a recording medium, a paper feed device 11 that supplies paper, a fixing device 12 that fixes the image transferred onto the paper, a paper discharge device 13 that discharges the paper outside the apparatus, and a pair of registration rollers 17 that serve as timing rollers.

[0018] The transfer device 10 includes a transfer roller 14 as a transfer member. The transfer roller 14 is arranged so as to come into contact with the photosensitive element 2 when the process unit 1 is attached to the device main body 100. The transfer roller 14 is also connected to a power source (not shown) so that a predetermined direct current (DC) and / or alternating current (AC) voltage is applied to it.

[0019] The paper feed device 11 includes a paper feed cassette 15 that stores paper P as a recording medium, and a paper feed roller 16 that feeds the paper P stored in the paper feed cassette 15. In addition to plain paper, the paper P also includes cardboard, thin paper, postcards, envelopes, coated paper (coated paper, art paper, etc.), tracing paper, etc. Furthermore, in addition to paper, it is also possible to use overhead projector sheets, overhead projector film, etc. as recording media.

[0020] The fixing device 12 includes a pair of rotating bodies facing each other. One of the rotating bodies is a fixing roller 18 that serves as a fixing rotating body for fixing an image onto paper, and the other is a pressure roller 19 that serves as a pressure rotating body that applies pressure to the fixing roller 18. The fixing roller 18 is provided with a heating means (e.g., a halogen heater) 22 inside. The fixing roller 18 and the pressure roller 19 are in contact with each other, and a fixing nip is formed between the rollers 18 and 19.

[0021] The paper discharge device 13 includes a pair of paper discharge rollers 20 that discharge paper outside the device. In addition, a paper discharge tray 21 is formed on the upper surface of the exterior of the device main body 100, on which paper discharged by the paper discharge rollers 20 is placed.

[0022] Also provided within the apparatus main body 100 is a conveying path 101 for conveying paper P from the paper feed cassette 15 through the registration roller 17, the image transfer section (transfer nip) between the transfer roller 14 and the photosensitive member 2, and the fixing device 12 to the paper discharge roller 20. Furthermore, also provided within the image forming apparatus 100 is a double-sided conveying path 102 for conveying paper P that has passed through the fixing device 12 again to the image transfer section when double-sided printing is performed.

[0023] Next, the image forming operation of the image forming apparatus according to this embodiment will be described with reference to FIG. When the image formation operation starts, the photoconductor 2 is rotated, and the surface of the photoconductor 2 is uniformly charged to a predetermined polarity by the charging roller 3. Next, the LED head array 6 exposes the charged surface of the photoconductor 2 to light based on image information from a reading device or a computer, etc., and an electrostatic latent image is formed. Then, the developing device 4 supplies toner to the electrostatic latent image on the photoconductor 2, thereby developing (visualizing) the electrostatic latent image as a toner image.

[0024] When the image forming operation is started, the paper feed roller 16 starts to rotate and feeds the paper P from the paper feed cassette 15. The conveyance of the fed paper P is temporarily stopped by the registration roller 17. Thereafter, the registration roller 17 starts to rotate at a predetermined timing, and the paper P is transferred to the image transfer unit in time with the toner image on the photosensitive member 2 reaching the image transfer unit. Transport to the photo section.

[0025] When the paper P is transported to the image transfer section, a predetermined voltage is applied to the transfer roller 14, generating a transfer electric field that transfers the toner image on the photoreceptor 2 onto the paper P. Any toner remaining on the photoreceptor 2 that has not been transferred to the paper P is removed by the cleaning blade 5 and collected in the waste toner storage section 9 of the toner cartridge 7.

[0026] The paper P onto which the toner image has been transferred is transported to the fixing device 12, where it is heated and pressed as it passes through the fixing nip formed by the fixing roller 18 and the pressure roller 19, thereby fixing the toner image on the paper P. The paper P is then ejected out of the device by the paper ejection rollers 20 and placed on the paper ejection tray 21.

[0027] Furthermore, when double-sided printing is performed, the paper P that has passed through the fixing device 12 is not discharged outside the device but is switched back and sent to the double-sided conveying path 102. The paper P passes through the double-sided conveying path 102 and is sent into the conveying path 101 just before the registration rollers 17, and is conveyed again to the image transfer section by the registration rollers 17. An image is then transferred to the back side of the paper P, and after the image on the back side is fixed by the fixing device 12, the paper P is discharged outside the device.

[0028] FIG. 2 is a schematic diagram of the fixing device according to this embodiment. The fixing device 12 to which the present invention is applied will be described in detail below with reference to FIG. Both ends of the fixing roller 18 and the pressure roller 19 are rotatably supported by a pair of support members 25 via bearings 23 and 24. When a driving force is transmitted to the fixing roller 18 from a driving source provided in the main body of the apparatus, the fixing roller 18 is driven to rotate in the direction indicated by arrow A in Fig. 2, and accordingly the pressure roller 19 is driven to rotate in the direction indicated by arrow B1 in Fig. 2. Note that, contrary to this embodiment, the pressure roller 19 may be the driving roller and the fixing roller 18 may be the driven roller.

[0029] When the fixing roller 18 is heated to a predetermined temperature by radiant heat emitted from the heating means 22 and the paper enters the fixing nip 80 in the direction indicated by the arrow C1 in Fig. 2, the paper is conveyed while being sandwiched between the rotating fixing roller 18 and the pressure roller 19. At this time, the unfixed image on the paper is heated by the heat of the fixing roller 18 and is pressed by the fixing roller 18 and the pressure roller 19, thereby fixing the image to the paper. The paper with the fixed image is then discharged from the fixing nip 80 in the direction indicated by the arrow C2 in Fig. 2.

[0030] 2, the pressure roller 19 is supported by the support members 25 so as to be movable toward or away from the fuser roller 18 in the direction of arrow B2. Specifically, the bearings 24 that support the pressure roller 19 are fitted into bearing guide portions 25b, which are rectangular holes provided in the support members 25, and the pressure roller 19 moves toward or away from the fuser roller 18 as the bearings 24 are guided along the bearing guide portions 25b. Meanwhile, the bearings 23 that support the fuser roller 18 are fitted into bearing fitting portions 25a, which are circular holes provided in the support members 25, and the fuser roller 18 is fixed so that its axial position does not move in a direction perpendicular to the axial direction.

[0031] The fixing device 12 according to this embodiment also includes a pressure lever member 31 that presses the pressure roller 19 against the fixing roller 18, and a pressure spring 36 that acts as a biasing member that biases the pressure lever member 31 in the pressure direction. The pressure lever member 31 and the elastic member (hereinafter also referred to as "pressure spring") 36 are provided on both ends of the pressure roller 19, one on each side. One end 31d of the pressure lever member 31 is attached to a support shaft 33 provided at the bottom of the support member 25, and is configured to be rotatable around the support shaft 33 in the direction of arrow α in FIG. 2. Each pressure spring 36 is attached by being hooked onto hooks 31c, 25c provided on the other end 31b of the pressure lever member 31 and on the upper part of the support member 25. As a result, the other end 31b of the pressure lever member 31 is constantly held in a state of being pulled upward in the figure by the pressure spring 36. The pressure lever member 31 presses the bearing 24 supporting the pressure roller 19 via the pad 34 fitted in the bearing guide portion 25 b of the support member 25 , thereby pressing the pressure roller 19 toward the fixing roller 18 .

[0032] The fixing device 12 according to this embodiment also includes a cam member 41 as a contact / separation mechanism for moving the pressure roller 19 toward or away from the fixing roller 18. The cam members 41 are provided on both ends of a rotary shaft 42, which is rotatably supported by a pair of support members 25. When the rotary shaft 42 rotates, the pair of cam members 41 rotate integrally with the rotary shaft 42. The cam member 41 also has a cam surface 41a whose distance from the center of rotation changes in the direction of rotation. When the pressure lever member 31 is pulled by the pressure spring 36, the cam receiver member 32 provided on the pressure lever member 31 is held in contact with the cam surface 41a. When the cam member 41 rotates in one direction in this state, the pressure lever member 31 is pushed downward in the figure by the cam surface 41a, causing the pressure roller 19 to move away from the fuser roller 18. When the cam member 41 rotates in the reverse direction, the pressure lever member 31 is returned upward in the figure, causing the pressure roller 19 to approach the fuser roller 18. The contact and separation operation by the cam member 41 will be described in detail later.

[0033] Furthermore, the fixing device 12 according to this embodiment includes an optical sensor 51 and a light-shielding member 52 as rotational position detection means for detecting the rotational position (rotation angle) of the cam member 41. The optical sensor 51 is a transmission-type optical sensor and includes a light-emitting portion that emits light and a light-receiving portion that receives the light emitted from the light-emitting portion. The light-shielding member 52 is a detectable member that rotates integrally with the cam member 41 to block or transmit the light emitted by the optical sensor 51, and switches between receiving and not receiving light, thereby detecting the rotational position of the optical sensor 51. The optical sensor 51 and the light-shielding member 52 are provided on only one of the two cam members 41.

[0034] FIG. 3 is a diagram showing the cam member, the light blocking member, and the optical sensor. 3, cam surface 41a provided on cam member 41 is formed so that the distance from the center of rotation gradually increases clockwise in the figure. Cam surface 41a is provided over an area that is greater than half the circumference (180°) in the rotation direction. Specifically, in this embodiment, cam surface 41a is provided over a range of approximately 270° from the lowest point e1, which is the shortest distance from the center of rotation of cam surface 41a, to the highest point e2, which is the longest distance from the center of rotation of cam surface 41a.

[0035] The light-shielding member 52 has a long light-shielding portion 52a as a detection area that is long in the rotational direction (having a length J1 in the rotational direction), and a short light-shielding portion 52b as a detection area that is shorter in the rotational direction than the long light-shielding portion 52a (having a length J2 in the rotational direction). Both the long light-shielding portion 52a and the short light-shielding portion 52b pass through the light-irradiating portion H of the optical sensor 51 as the member rotates, thereby blocking the irradiated light. In addition, a hole portion (translucent portion) 52j that transmits the irradiated light from the optical sensor 51 is formed between the long light-shielding portion 52a and the short light-shielding portion 52b.

[0036] FIG. 4 is a schematic diagram of the drive system of the contact / separation mechanism according to this embodiment. 4, the drive system includes a motor 43 as a drive source and a gear train 44 that transmits the drive force from the motor 43 to the cam member 41 and the light blocking member 52. In this embodiment, a small, inexpensive DC brush motor is used as the motor 43. The gear train 44 includes a first worm gear 45 attached to the output shaft of the motor 43, a second worm gear 46 that meshes with the first worm gear 45, a first spur gear 47 that is integral with the second worm gear 46, and a second spur gear 48 that meshes with the first spur gear 47 and is integral with the light blocking member 52. When the output shaft of the motor 43 rotates in one direction or the opposite direction, each worm gear 45, 46 and each spur gear 47, 48 rotate, and the second spur gear 48 and the light-shielding member 52 rotate integrally, causing each cam member 41 to rotate in one direction (the direction indicated by arrow F in Figure 3) or the opposite direction (the direction indicated by arrow G in Figure 3) via the rotating shaft 42.

[0037] FIG. 5 is a block diagram of a control system for the contact / separation mechanism according to this embodiment. As shown in Figure 5, the control system includes a control unit 60 that controls the rotation of the cam member 41, the optical sensor 51 for detecting the rotation position of the cam member 41, and a timer 70 that measures the rotation time of the cam member 41. The control unit 60 is configured, for example, with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., which are provided in the image forming apparatus main body. The control unit 60 controls the rotation of the cam member 41 by controlling the drive of the motor 43 based on a signal detected by the optical sensor 51 and the time measured by the timer 70. The control unit 60 is also configured to control the timing of when the timer 70 starts and stops measuring time based on the signal detected by the optical sensor 51.

[0038] In the fixing device according to this embodiment, the pressure roller 19 can be moved toward or away from the fixing roller 18, so that the pressure applied in the fixing nip 80 can be changed. Hereinafter, the contact and separation operation of the pressure roller 19 by the cam member 41 (pressure release operation when releasing the normal pressure and pressure operation when returning to the normal pressure) will be described with reference to FIGS.

[0039] 6A shows a state in which the cam receiving member 32 disposed on the pressure lever member 31 is in contact with the cam surface 41a at the lowest point e1 side. In this state, the pressure roller 19 shown in FIG. 2 approaches the fixing roller 18 and is pressed with a normal pressure.

[0040] 6(B), when cam member 41 is rotated counterclockwise in the figure from the state shown in Fig. 6(A), cam surface 41a slides against cam receiver member 32, and the contact position of cam receiver member 32 with cam surface 41a moves relatively from the lowest point e1 side to the highest point e2 side. Accordingly, cam receiver member 32 is pushed downward in the figure by cam surface 41a, and pressure lever member 31 retracts from the bearing of pressure roller 19, so that pressure roller 19 moves in a direction away from fuser roller 18.

[0041] 6(C), when the contact position of the cam receiving member 32 with the cam surface 41a reaches the highest point e2, the pressure roller 19 completes its separation from the fixing roller 18, and the pressure applied to the fixing nip becomes smaller than normal pressure, resulting in a depressurized state. At this point, the rotation of the cam member 41 is stopped.

[0042] 7(B), when cam member 41 is rotated clockwise in the figure (the opposite direction to the rotation direction during the transition to depressurization) from the depressurized state shown in Fig. 7(A), cam surface 41a slides against cam receiver member 32, and the contact position of cam receiver member 32 with cam surface 41a moves relatively from the uppermost point e2 side to the lowermost point e1 side. Accordingly, cam receiver member 32 is pulled upward in the figure by the biasing force of pressure spring 36, and pressure lever member 31 presses the bearing of the pressure roller, so that pressure roller 19 moves in a direction approaching fuser roller 18.

[0043] 7(C), when the contact position of the cam receiving member 32 with the cam surface 41a reaches the lowest point e1, the pressure roller 19 completes its approach to the fixing roller 18, and the pressure in the fixing nip 80 returns to the normal pressure state where the pressure is increased. At this point, the rotation of the cam member 41 is stopped.

[0044] In this way, in the fixing device of this embodiment, when the pressure roller 19 and the fixing roller 18 are separated, the cam member 41 is rotated in one direction, and when the pressure roller 19 is brought closer to the fixing roller 18, the cam member 41 is rotated in the opposite direction, so that the pressure lever member 31 is pushed and returned using the same cam surface 41a.

[0045] FIG. 8 is a cam diagram showing the relationship between the rotation angle and radius of the cam member 41. To ensure smooth operation of cam member 41, cam surface 41a is generally configured to have a sinusoidal curve as shown in Fig. 8. In this way, by reducing the amount of change in cam surface 41a as the load on cam surface 41a increases, it is possible to prevent sudden load fluctuations, stabilize operation, reduce the load on the drive motor, and prevent the generation of abnormal noise. The curvature of the cam surface 41a is large when the load is small and is small when the load is large, and therefore, in the cam diagram of FIG. 8, it can be seen that the inclination decreases as the outer diameter of the cam member 41 increases.

[0046] The cam receiving member 32 provided in the fixing device according to the present invention is designed to have a compact size and shape while still providing the necessary strength, based on the contact portion with the cam member 41 and the contact portion with the pressure lever member 31. This allows the size and arrangement of the components to be optimized, and by selecting an appropriate material, space savings, cost reductions, and improved durability can be achieved. The following describes the design configuration of the cam receiving member 32 of the fixing device according to the present invention.

[0047] The fixing device according to the present invention comprises a pair of rollers (for example, pressure roller 19 and fixing roller 18 shown in FIG. 2) that are in contact with and separate from each other with pressure and that sandwich and transport a recording medium, a plate-like pressure lever member 31 that is pivotally supported at one end and has an elastic member (pressure spring) 36 engaged at the other end and that presses one of the pair of rollers against the other, a cam member 41 that displaces pressure lever member 31 between a position that maintains the pressure contact state of the pair of rollers and a position that releases the pressure contact state of the pair of rollers, and a lever member that faces cam member 41 of pressure lever member 31. and a cam receiving member 32 disposed at a position corresponding to the pressure applied by the cam member 41 and transmitting the pressing force from the cam member 41 to the pressure applying lever member 31, wherein the relationship of the following formula (1) is satisfied when the thickness of the pressure applying lever member 31 is taken as t, the dimension of the cam receiving member 32 in the thickness direction of the pressure applying lever member 31, which is the length of the surface that abuts against the cam member 41, is taken as W, and the dimension of the cam receiving member 32 in the direction perpendicular to the thickness direction of the pressure applying lever member 31, which is the length from the abutment position with the cam member 41 to one side surface, is taken as L1. L1≧0.6×(Wt) / 2+0.2····Formula (1)

[0048] The symbols in equation (1) will be explained below with reference to FIGS. FIG. 10 is an explanatory diagram showing a state in which the cam member 41 and the cam receiving member 32 are in contact with each other, and FIG. 11 is an explanatory diagram showing the load and stress acting on the cam receiving member 32. As shown in FIG. 10, the cam receiving member 32 receives a load M at the contact position 32b with the cam member 41 from above, and receives a load N at the contact surface with the pressure lever member 31 from below. In addition, in Figure 10, the installation surface of the cam receiving member 32 and the contact surface with the pressure lever member 31 are shown as inclined based on the installation mode in the fixing device 12 shown in Figure 2, but in the following explanation, these will be described using a diagram showing them horizontally.

[0049] As shown in FIG. 11, "D" is the overall length of the cam receiving member 32 in the direction perpendicular to the thickness direction of the pressure lever member 31 (x direction in the drawing). "L1" is the dimension of the cam receiving member 32 in a direction perpendicular to the thickness direction of the pressure lever member 31 (X direction in the figure), and is the length from the contact position 32a with the cam member 41 to one side surface (left side surface 32c in Figure 11). In addition, when the contact area between the cam receiving member 32 and the cam member 41 has a width in a direction perpendicular to the thickness direction of the pressure lever member 31 (X direction in the figure), the contact position 32a is based on the center of the X direction of the area that contacts the cam member 41.

[0050] FIG. 12 is an explanatory diagram of the dimensions of the cam receiving member 32 in the thickness direction of the pressure lever member 31. As shown in FIG. 12, "W" is the overall length of the surface (contact area) of the cam receiving member 32 that abuts against the cam member 41 in the thickness direction of the pressure lever member 31 (Y direction in the drawing). Note that the area of ​​contact with the cam member 41 varies depending on the shape of the surface of the cam receiving member 32 facing the cam member 41, so the value of "W" does not necessarily coincide with the overall length of the cam receiving member in the Y direction. "t" is the thickness of the pressure lever member 31. The thickness of the pressure lever member 31 refers to the thickness of the flat plate-shaped sheet metal member that constitutes the pressure lever member 31. "Δt" is a variable expressed as "(Wt) / 2" in equation (1), and is the length of one side in the Y direction of the area (length W) that abuts against the cam member 41, which corresponds to the outer part of the area 32f that abuts against the pressure lever member 31.

[0051] "Sc" in FIG. 11 is the load stress value occurring at the contact position 32a of the cam receiving member 32 with the cam member 41, and is a value calculated by simulation. Furthermore, "St" is the load stress value occurring at the upper corner of the left end face 32c of the cam receiving member 32, i.e., the area where cracks are likely to occur and which becomes the starting point for member damage, and is a value calculated by simulation. The graphs relating to these simulations are shown in FIG.

[0052] FIG. 13(A) is a diagram for explaining the positions (M1, M2, M3) of the cam receiving member 32 where the load is received in the simulation, and FIG. 13(B) is a graph showing the stress distribution corresponding to each position. As shown in Figure 13(A), the load at the contact position 32a with the cam member 41 at the center in the left-right direction in the X direction (length D) is indicated as M1, the load at the vicinity of one end (left side surface 32c) is indicated as M3, and the load at the intermediate position between these is indicated as M2. Note that the loads M1, M2, and M3 are all equal. Figure 13(B) shows the stress distribution over the X direction (length D).

[0053] 13(B), in all cases, the stress value "Sc" is highest at the contact position 32a with the cam member 41. Also, although the loads of M1, M2, and M3 are the same, it can be seen that the stress increases in the order of the contact position 32a being closer to the end in the X direction (M1 being the largest). Furthermore, the stress value "St" is the value at the leftmost side in the graph (the value at the upper corner of the left side surface 32c), and similar to Sc, it can be seen that the stress increases (M1 is the largest) as the contact position 32a approaches the end side in the X direction.

[0054] 14 is a graph showing the change in stress value when the contact position 32a of the cam receiving member 32 with the cam member 41 (position of the load M) is changed from the left end to the right end in the X direction. The value of the load is constant. The horizontal axis L is the length from the contact position 32a of the cam receiving member 32 with the cam member 41 to the left end (left side surface 32c), and when the contact position 32a is at the left end (left side surface 32c), L=0, and the value of L increases as the contact position 32a moves toward the right end (right side surface 32d) of the contact position 32a. As can be seen from the graph in Figure 14, the values ​​of Sc and St are maximum near L = 0, and the values ​​of Sc and St are close to each other. The value of Sc decreases as the value of L increases, and remains constant at the value enclosed by the dashed circle after Lx. The value of St also decreases as the value of L increases, and becomes even smaller than the value enclosed by the dashed circle after Lx. In other words, the difference between the values ​​of Sc and St becomes larger at positions after Lx.

[0055] When the occurrence of cracks in the actual cam receiving member 32 was investigated, early crack occurrence was observed in the range of L from 0 to Lx. This is thought to be because a high stress state is maintained in the region from the contact position 32a of the cam receiving member 32 with the cam member 41 to the upper corner of the left end face 32c, making creep fatigue more likely to progress. Therefore, it is believed that by providing the contact position 32a of the cam member 41 at a position where L is larger than the range of L (0 to Lx) where the values ​​of Sc and St are close to each other, it is possible to prevent the occurrence of cracks and creep failure of the member.

[0056] On the other hand, the value of "Δt" shown in Fig. 12 contributes to the condition (threshold) that determines whether the value of Sc and the value of St deviate or not, depending on L. "Δt" is a variable expressed as "(Wt) / 2" in equation (1). Figure 15 shows the results of stress analysis simulation for combinations of Δt and L values.

[0057] In the graph of Figure 15, the horizontal axis is Δt (= (Wt) / 2) and the vertical axis is L, and the value of L (for example, Lx in Figure 14) at which the value of Sc and the value of St begin to diverge is plotted and indicated by "●". The line obtained from the "●" is approximated as the following formula (2). L=0.6×Δt+0.2...Equation (2)

[0058] In designing the cam receiving member 32, if the value of Δt is determined from the thickness t of the pressure lever member 31, which is made of a flat sheet metal member, then the occurrence of cracks can be prevented by setting the contact position 32a with the cam member 41 at a position greater than L calculated by equation (2) from one end face of the cam receiving member 32 (one side face in a direction perpendicular to the thickness direction of the pressure lever member). That is, in the fixing device of this embodiment, when the length from the contact position 32a with the cam member 41 to one side is L1, the occurrence of cracks can be prevented by making L1≧0.6×(Wt) / 2+0.2.

[0059] As shown in equation (2), the variable Δt determines the deviation between the values ​​of Sc and St, so the optimal shape can be determined by focusing only on the relationship between the contact position 32a of the cam receiver member 32 and the cam member 41. After determining the optimal shape, it is only necessary to consider the material that constitutes the cam receiver member 32 and the magnitude of the stress that it receives from the cam member 41. As a result, it is no longer necessary to select and use a material that is stronger than necessary, and it is possible to prevent an increase in costs.

[0060] As shown in the graph in Figure 14, the value of St decreases as the value of L increases, and is nearly 0 near the maximum value of L. When the value of St is close to 0, the possibility of cracks occurring in the cam receiving member 32 is extremely low, so there is no need to increase the value of L any further in the design. Figure 15 shows the results of stress analysis simulation for combinations of L values ​​when the value of St is 0.

[0061] In the graph of Figure 15, the horizontal axis is Δt (= (Wt) / 2) and the vertical axis is L, and the value of L at which the value of St becomes 0 is plotted and indicated by "▲". The line obtained from "▲" can be approximated as the following formula (3). L=1.3×Δt+1.25...Equation (3)

[0062] In FIG. 15, the range La enclosed by the straight line of formula (2) and the straight line of formula (3) is the appropriate range for Δt.

[0063] In designing the cam receiving member 32, once the value of Δt is determined from the thickness t of the pressure lever member 31, which is made up of a flat sheet metal member, the contact position 32a with the cam member 41 can be set at a position that is smaller than L calculated by equation (3) and larger than L calculated by equation (2) from one end face of the cam receiving member 32 (one side face in a direction perpendicular to the thickness direction of the pressure lever member), thereby making it possible to prevent cracks from occurring and to make the member more compact. That is, in the fixing device of this embodiment, when the length from the contact position 32a with the cam member 41 to one side is L1, by further satisfying the relationship L1≦1.3×(Wt) / 2+1.25, it is possible to prevent cracks from occurring and to reduce the size of the component at the same time.

[0064] In FIG. 15, the range La enclosed by the straight line of formula (2) and the straight line of formula (3) is the appropriate range for Δt.

[0065] Furthermore, in equation (3), it is sufficient to consider the variable Δt, just as in equation (2), and the optimum shape can be determined by focusing only on the relationship between the contact position 32a of the cam receiver member 32 and the cam member 41. After determining the optimum shape, it is sufficient to consider the material that constitutes the cam receiver member 32 and the magnitude of the stress that it receives from the cam member 41. As a result, it is no longer necessary to select and use a material that has more strength than necessary, and it is possible to prevent an increase in costs. When further narrowing down the optimum range of the value of L, the strength of the material of the cam receiving member 32 and the magnitude of the stress received from the cam member 41 can be taken into consideration.

[0066] In this way, by considering the relationship between L and Δt, it is possible to avoid designing the cam receiving member 32 to be larger than necessary, and in a pressure / release mechanism with a simple configuration, it is possible to select a material that is appropriate for cost and strength, and to achieve optimization of the size and placement of parts, thereby realizing space savings and cost reductions.Furthermore, by preventing damage to parts, it is possible to achieve improved durability of the fixing device.

[0067] Next, examples of the external shape of the cam receiving member 32 will be described. (First embodiment) An example of this embodiment is shown in FIG. FIG. 16 is a side view showing an example of the outer shape of the cam receiving member 32. In FIG. It is preferable that at least one of the corners (32h, 32g) of the cam receiving member 32 formed by the surface facing the cam member 41 and the left and right outer surfaces in the thickness direction of the pressing lever member 31 is rounded. The corner that is rounded is preferably an upper corner 32h of the left end face 32c as shown in FIG. 16, that is, a corner that is prone to cracking and serves as a starting point for damage to the member.

[0068] FIG. 17 is a graph showing the results of a stress analysis simulation performed on the change in the applied stress St when the magnitude of the R shape of the corner 32h shown in FIG. 16 is changed. The magnitude of the load M from the cam member 41 and the position of the load (contact position 32a with the cam member 41) are constant. 17, it can be seen that the stress generated at the corner 32h in the range of R0.5 to R2 is smaller than when there is no R shape. By making the corner R shaped in this way, it is possible to reduce the load stress St at the location where cracks are likely to occur.

[0069] (Second embodiment) The arrangement of this embodiment is shown in FIGS. Fig. 9 is a perspective view showing an example of the cam receiving member 32 disposed on the pressure lever member 31. Fig. 12 shows a cross-sectional view of the cam receiving member 32 in Fig. 9 in the thickness direction of the pressure lever member 31. 9 and 12, the cam receiving member 32 is a member having a generally U-shaped cross section, and is preferably shaped to fit over a pressed surface 41a that receives the pressing force from the cam member 41 of the pressing lever member 31 and at least a portion of both thickness-wise side surfaces of the pressing lever member 31. In addition, it is preferable that there is little difference between the width of the recess of the generally U-shaped cross section of the cam receiving member 32 and the thickness of the pressing lever member 31.

[0070] FIG. 18 is an explanatory diagram showing an example of an unstable contact state between the pressure lever member 31 and the cam receiving member 32. In FIG. 18(A), the cam receiving member 32 may not have a shape that covers both sides of the pressure lever member 31 in the thickness direction, or may have a covering shape but a large gap between the pressure lever member 31 and the cam receiving member 32, as shown in FIG. 18(B), which may result in unstable contact with the pressure lever member 31. As a result of partial contact, a local load is applied to the contact area indicated by 32j in the figure, which may lead to breakage starting from that area.

[0071] By giving the cam receiving member 32 the shape shown in Figures 9 and 12, there is no rattle when it is fitted to the pressure lever member 31, and it is in a stable mounted state, so that the occurrence of abnormal stress loads and the occurrence of defects such as early breakage can be prevented. Furthermore, it is possible to prevent problems such as parts falling off not only when the device is in use but also when parts are being assembled.

[0072] (Third embodiment) An example of this embodiment is shown in FIGS. 19 and 20 are explanatory views showing an example of an engagement structure 35 between the cam receiving member 32 and the pressure lever member 31. Fig. 19 is a cross-sectional view in the thickness direction of the pressure lever member 31, and Fig. 20 is a perspective view of the embodiment of Fig. 19(B). The cam receiving member 32 and the pressure lever member 31 preferably have an engagement structure 35 for engaging with each other. The engagement structure 35 functions as, for example, a mechanism for preventing disengagement.

[0073] 19 shows the state in which the cam receiving member 32 and the pressure lever member 31 are fitted together in the upper part, and the state before the cam receiving member 32 and the pressure lever member 31 are fitted together in the lower part. 19(A) and 19(B) show an example in which the pressure lever member 31 has an engaging recess 35b, which engages with the engaging protrusion 35a of the cam receiving member 32. In FIG. 19(C) and 19(D) show an example in which the engaging protrusion 35a of the cam receiving member 32 engages with the bottom of the pressing lever member 31. In FIG.

[0074] The shape of the engagement recess 35b provided in the pressure lever member 31 is not particularly limited as long as it engages with the engagement protrusion 35a of the cam receiving member 32, and may be an opening that penetrates the thickness direction of the pressure lever member 31, or may have a groove-like structure. Furthermore, the shape of the engaging protrusion 35a provided on the cam receiving member 32 is not particularly limited, and may be a protrusion as shown in Figures 19(A) and 19(C), or a claw-like shape with a triangular cross section as shown in Figures 19(B) and 19(C). Regardless of the shape, it is preferable that the strength of the member is not reduced and that complicated processing is not required.

[0075] The structure in this embodiment in which the cam receiving member 32 and the pressure lever member 31 engage with each other results in a stable mounting state, as in the second embodiment described above, which prevents the occurrence of abnormal stress loads and prevents problems such as early breakage, and also prevents problems such as parts falling off not only when the device is in use but also when assembling the parts.

[0076] (Fourth embodiment) An example of this embodiment is shown in FIGS. 21, the pressing lever member 31 can be shaped to have a wall portion 31k that protrudes vertically relative to the pressed surface 31a that receives the pressing force from the cam member 41. The cam receiving member 32 can be shaped to have a shape that fits into the wall portion 31k (wall portion fitting portion 32k). As in the second embodiment, the cam receiving member 32 is preferably shaped to fit into the pressing lever member 31 so as to cover at least a portion of both side surfaces in the thickness direction.

[0077] The cam receiving member 32 engages with the pressed surface 31a in the thickness direction of the pressure lever member 31 and with the wall portion 31k in a direction perpendicular to the thickness direction of the pressure lever member 31, making the mounting state more stable, preventing the occurrence of abnormal stress loads, and preventing the occurrence of defects such as early breakage.

[0078] Figure 22(A) is a cross-sectional view taken in the X direction in Figure 21, and Figure 22(B) is the same cross-sectional view showing a state in which the cam receiving member 32 is attached to the pressure lever member 31. Figure 22(C) is a cross-sectional view of an example of the second embodiment shown for comparison. As shown in FIG. 22(B), the wall fitting portion 32k of the cam receiving member 32 and the wall portion 31k of the pressing lever member 31 overlap over a length K2 that is longer than K1 in the vertical direction of the figure.

[0079] Figure 23 is a cross-sectional view in the Y direction of Figures 21 and 22(B), illustrating the tilt of the posture due to the gap u between the pressure lever member 31 and the cam receiving member 32. Figures 23(A) and 23(B) are cross-sectional views seen from the left side of Figure 22(B), and Figures 23(C) and 23(D) are cross-sectional views seen from the right side of Figure 22(B). It is preferable that the gap u that occurs when the pressure lever member 31 and the cam receiver member 32 are fitted together is small. If there is no gap at all, there is a risk that they will not function properly, so it is preferable that a certain amount of gap u is provided in the fitted state, taking into consideration dimensional variations between the parts, etc.

[0080] On the other hand, if the gap u is large, tilting occurs as shown in Figures 23(B) and 23(D), and local stress may be applied to the area indicated by the arrow in the figure. The amount of this tilting is determined by the length of overlap between the cam receiving member 32 and the pressure lever member 31, indicated by K1 and K2 in the vertical direction in Figures 23(A) and 23(C). As the overlap length changes from K1 to K2, the inclination is reduced, and as a result, the local stress indicated by the arrow in the figure is also reduced.

[0081] FIG. 24 is a perspective view of the cam receiving member 32 of this embodiment, and FIG. 24(B) is a view seen from the rear (wall portion 31k side) in FIG. 24(A). 25(A) is a cross-sectional view of the cam receiving member 32 in the X direction in this embodiment, and FIG. 25(B) is a plan view of the surface of the cam receiving member 32 in this embodiment that faces the cam member 41. In this embodiment, the shape of the surface of the cam receiving member 32 that receives the load from the cam member 41 has a recessed portion whose horizontal cross section is approximately U-shaped due to the extending wall fitting portion 32k, and corners 32m are provided on both sides of the bottom surface of the recessed portion. In the drawing, the portion other than the corners of the upper end corners of the wall fitting portion 32k is represented by 32n.

[0082] In the cam receiving member 32 of this embodiment, a stress analysis simulation was performed for the same combinations of values ​​of Δt and L as those shown in FIG. The value of L, which is the threshold at which the value of Sc and the value of St, which change depending on the value of Δt, deviate, is different between the corner 32m and the other part 32n at the upper end corner of the wall fitting portion 32k, with the value being larger at the corner 32m.

[0083] The results of the simulation are shown in FIG. The horizontal axis is Δt (= (Wt) / 2) and the vertical axis is L, and the L value at which the Sc value and the St value begin to diverge is plotted and indicated by "■". The line obtained from "■" can be approximated as the following equation (4). L=0.5×Δt+0.9...Equation (4)

[0084] In designing the cam receiving member 32, if the value of Δt is determined from the thickness t of the pressure lever member 31, which is made of a flat sheet metal member, the occurrence of cracks can be prevented by setting the contact position 32a with the cam member 41 at a position greater than L calculated by equation (4) from the side surface of the cam receiving member 32 facing the wall portion 31k in a direction perpendicular to the thickness direction of the pressure lever member. The "side surface facing" of the cam receiving member 31 to the wall portion 31k refers to the side surface facing or abutting against the wall portion 31k when the cam receiving member 31 is installed on the pressure lever member 31. In other words, when the dimension of the cam receiving member 32 in a direction perpendicular to the thickness direction of the pressure lever member 31, namely the length from the contact position 32a with the cam member 41 to the side surface facing the wall portion 31k, is defined as L2, the occurrence of cracks at the corner portion 32m can be prevented by making L2 ≧ 0.5 × (Wt) / 2 + 0.9.

[0085] Similarly, it is only necessary to consider the variable Δt in equation (4), and the optimum shape can be determined by focusing only on the relationship between the contact position 32a of the cam receiver member 32 and the cam member 41. After determining the optimum shape, it is only necessary to consider the material that constitutes the cam receiver member 32 and the magnitude of the stress that it receives from the cam member 41. As a result, it is no longer necessary to select and use a material that is stronger than necessary, and it is possible to prevent an increase in costs.

[0086] (Fifth embodiment) An example of this embodiment is shown in Figures 27 and 28. The upper part of Figure 28 is a schematic cross-sectional view of the cam receiver member 32 and the pressure lever member 31 in a fitted state, and the lower part of Figure 28 is an enlarged view of the contact portion between the cam receiver member and the pressure lever member 31. As shown in Figures 27 and 28(A), the cam receiving member 32 has a shape having a depressed surface 31a that receives the pressing force from the cam member 41 of the pressure lever member 31 and a recess that fits to cover at least a portion of both side surfaces in the thickness direction of the pressure lever member 31, and it is preferable that the bottom surface of the recess that abuts against the depressed surface 31a extends horizontally on both sides and has a groove portion 32r with an R-shaped end.

[0087] As in the second embodiment described above, the cam receiving member 32 is a member having a generally U-shaped cross section. In a cam receiving member 32 having such a shape, the corners of the region 32f (bottom surface of the recess) that contacts the pressure lever member 31 are subject to high stress, making them prone to breakage. If an R-shape is provided to reduce stress in these areas, depending on the shape, the problem may not be solved and other problems may occur.

[0088] Figure 27(C) shows an example in which both ends of the bottom surface of the recess are rounded. As a result of a stress analysis simulation of the example in Figure 27(C), it was found that the generated stress was reduced by about 30% compared to the unprocessed example. However, in the example of Figure 27(C), the corners of the contact surface of the pressure lever member 31 interfere with the rounded shape 32r of the cam receiver member 32, making it necessary to widen the width of the recess of the cam receiver member 32 that fits with the pressure lever member 31. This causes a problem, as shown in the examples of Figures 23(A) and 23(B), in that it becomes difficult to achieve posture stability between the cam receiver member 32 and the pressure lever member 31. Furthermore, high stress may be generated at both ends 32q of the region 32f that contacts the pressure lever member 31, which may make them more susceptible to breakage.

[0089] On the other hand, Figure 27(B) shows an example in which an R-shape that protrudes upward is provided on both ends of the bottom surface of the recess. As a result of performing a stress analysis simulation on the example in Figure 27(B), it was found that, as with (C), the generated stress was reduced by about 30% compared to the unprocessed example. However, in the example of Figure 27(B), although the corners of the contact surface of the pressure lever member 31 do not interfere, high stress may be generated in the areas indicated by both end portions 32q of the area 32f that contacts the pressure lever member 31, which may make breakage more likely to occur.

[0090] In FIG. 28(A), the bottom surface of the recess has grooves 32r that extend to both sides in the horizontal direction and have semicircular R-shaped ends, so-called relief-shaped grooves. By adopting the shape shown in FIG. 28(A), the side surface of the pressure lever member 31 and the contact surface of the cam receiving member 32 can come into contact with each other with an appropriate gap and width, and the positional relationship between them is stable. As shown in the lower part of Figure 28(A), the bottom surface has flat portions 32p extending horizontally on both sides of the area 32f that abuts against the pressure lever member 31, and is sufficiently longer than the width t of the pressure lever member 31, thereby preventing the occurrence of areas with locally high stress.

[0091] A stress analysis simulation of the example shown in Figure 27(A) revealed that the stress generated was reduced by 84% compared to an unprocessed example. This is thought to be because the long flat portion of the bottom of the recess prevents stress concentration and maintains low stress across the entire bottom surface. Therefore, in this embodiment, it is preferable that the cam receiving member 32 have the shape shown in Figure 27(A). In this way, by using a shape that can reduce load stress in areas where damage is likely to occur, early component damage can be prevented and durability can be improved.

[0092] (Sixth embodiment) An example of this embodiment is shown in FIGS. 29 is a perspective view showing an example of the shape of the contact surface of cam receiver member 32 with cam member 41. As shown in Fig. 29, it is preferable that the surface of cam receiver member 32 facing cam member 41 has a cross section in the thickness direction (Y direction) of pressure lever member 31 that is a substantially arc-shaped surface that protrudes toward cam member 41.

[0093] 29(A) and 29(C) show a shape in which the center in the Y direction of the surface facing the cam member 41 is convex toward the cam member 41. By using such a shape, the length W in the Y direction of the surface (area) that comes into contact with the cam member 41 becomes smaller compared to when the entire facing surface is flat. 29(B) and 29(D), both ends in the Y direction of the surface that faces the cam member 41 are rounded. By using such a shape, the length W in the Y direction of the surface (area) that comes into contact with the cam member 41 becomes smaller than when the facing surface is flat, as in Figures 29(A) and (C).

[0094] In either case, as W decreases, Δt decreases, and the value of L obtained from the above equations (1) to (4) also decreases. In other words, setting a smaller L can prevent cracks from occurring in the cam receiving member 32. However, while W becomes smaller (the contact area of ​​the cam member 41 becomes smaller), there is a problem that the contact pressure increases. Therefore, it may be necessary to take measures considering the risk of early component damage due to the increase in contact pressure and the effects of wear caused by the cam member 41.

[0095] Figure 30 is a cross-sectional view in the Y direction showing the state in which the cam member 41, the cam receiving member 32, and the pressure lever member 31 are in contact with each other. Figure 30(B) corresponds to Figure 29(A), Figure 30(C) corresponds to Figure 29(B), Figure 30(E) corresponds to Figure 29(C), and Figure 30(F) corresponds to Figure 29(B). For comparison, Figures 30(A) and 30(D) show an example in which the surface facing the cam member 41 is flat. In both examples, the surface of the cam receiving member 32 facing the cam member 41 has a shape that protrudes toward the cam member 41, particularly an approximately arc shape, so that the length W in the Y direction of the surface (area) that abuts against the cam member 41 is small.

[0096] 30(B) and 30(E), cam receiving member 32 has a generally arcuate shape that protrudes toward cam member 41, and theoretically contacts cam member 41 at one point in the center, but because it is a resin member, the length W in the Y direction of the surface (area) that contacts cam member 41 may change due to the influence of rigidity, wear, etc. However, compared to when contact occurs on a flat surface as in Figures 30(A) and 30(D), W is a sufficiently small value, and it is believed that reducing W will have an effect.

[0097] The fixing device of this embodiment can change the pressure of the pressure roller with the above-mentioned configuration. The pressure of the pressure roller is not limited to being changed according to the paper type, but can also be applied to cases such as reducing the pressure to make it easier to remove jammed paper from the fixing nip, or reducing the pressure after paper has passed through to suppress plastic deformation of the pressure roller and fixing roller due to pressure. The fixing device can also be applied to a fixing device in which the pressure roller is completely separated from the fixing roller (non-contact state) when in a depressurized state.

[0098] Furthermore, the fixing device to which the present invention can be applied is not limited to the fixing device having a pair of rollers (fixing roller and pressure roller) as shown in FIG. For example, as shown in Fig. 31, the fixing device 12 may include an endless fixing belt 83 instead of a fixing roller. In the configuration shown in Fig. 31, the heating means 22 and the nip forming member 81 are disposed on the inner circumferential side of the fixing belt 83, and the pressure roller 19 presses the fixing belt 83 at the position of the nip forming member 81, thereby forming the fixing nip 80.

[0099] Furthermore, the fixing device to which the present invention can be applied is not limited to the fixing device in which the pressure roller moves toward and away from the fixing roller as shown in FIG. For example, as shown in FIG. 32, the fixing device 12 may be one in which the fixing roller 18 moves toward and away from an opposing roller 82 facing the fixing roller 18. Furthermore, the contact / separation mechanism according to the present invention can be applied not only to a fixing device but also to a transfer device that transfers an image onto a recording medium such as paper. [Explanation of symbols]

[0100] 12 Fixing device 31 Pressure lever member 32 Cam receiving member 35 Engagement structure 41 Cam member 100 Image forming device [Prior art documents] [Patent documents]

[0101] [Patent Document 1] Japanese Patent Application Publication No. 2018-072792

Claims

1. a pair of rollers that are in contact with and separate from each other and press against each other to sandwich and transport a recording medium; a plate-shaped pressure lever member that is pivotally supported at one end and has an elastic member engaged at the other end, and that is capable of swinging to press one of the pair of rollers toward the other; a cam member that displaces the pressure lever member between a position that maintains the pressure contact state of the pair of rollers and a position that releases the pressure contact state; a cam receiving member disposed at a position of the pressure lever member facing the cam member and transmitting a pressing force from the cam member to the pressure lever member, The cam receiving member is a member having a substantially U-shaped cross section, the pressure lever member is fitted to cover a pressed surface that receives a pressing force from the cam member and at least a part of both side surfaces of the pressure lever member in a thickness direction, The thickness of the pressure lever member is t (mm), The dimension of the cam receiving member in the thickness direction of the pressure lever member is defined as W (mm), where W is the length of the surface that abuts against the cam member, The dimension of the cam receiving member in a direction perpendicular to the thickness direction of the pressure lever member is L1 (mm), where L1 is the length from the contact position with the cam member to the side surface on the other end side of the pressure lever member. a thickness of a portion of the cam receiving member that covers at least a part of both side surfaces of the pressure lever member in the thickness direction is (W-t) / 2 on both sides, L1≧0.6×(W−t) / 2+0.2 (mm), and L1≦1.3×(W-t) / 2+1.25(mm) A fixing device characterized in that the following relationship is satisfied.

2. The cam receiving member is 2. The fixing device according to claim 1, wherein at least one of the corners formed by the surface facing the cam member and the side surface of the pressure lever member in a direction perpendicular to the thickness direction thereof is rounded.

3. 3. The fixing device according to claim 1, wherein the cam receiving member and the pressure lever member have an engagement structure for engaging with each other.

4. the pressure lever member has a wall portion that protrudes in a direction perpendicular to a pressure-receiving surface that receives a pressing force from the cam member, 4. The fixing device according to claim 1, wherein the cam receiving member has a shape that fits into the wall portion.

5. When the dimension of the cam receiving member in a direction perpendicular to the thickness direction of the pressure lever member, that is, the length from the contact position with the cam member to the side surface facing the wall portion, is L2 (mm), L2≧0.5×(W-t) / 2+0.9(mm) 5. The fixing device according to claim 4, wherein the following relationship is satisfied:

6. The cam receiving member is 6. The fixing device according to claim 1, wherein the pressure lever member has a surface that receives a pressing force from the cam member and a recess that fits to cover at least a portion of both sides of the pressure lever member in the thickness direction, and the bottom surface of the recess that abuts against the pressure lever surface extends horizontally on both sides and has a groove portion with an R-shaped end.

7. 7. The fixing device according to claim 1, wherein a surface of the cam receiving member facing the cam member has a cross section in a thickness direction of the pressure lever member that is substantially arc-shaped and protrudes toward the cam member.

8. An image forming apparatus comprising the fixing device according to any one of claims 1 to 7.

Images