Image forming apparatus and spring-type biasing device

Abstract

To provide a configuration that can obtain a more stable urging force when using a pulling coil spring.SOLUTION: An image forming apparatus has: a pulling coil spring; and a moving member that has an acting part acting on an action target part and an engagement target part engaged with the pulling coil spring, and is moved by an urging force of the pulling coil spring to cause the acting part to act on the action target part. The pulling coil spring has a coil part and a hook part. The hook part has: a first extension part in which a wire extends from an end of the coil part in a first direction; a second extension part in which the wire extends in a second direction opposite to the first direction; and a connection part that connects the first extension part and the second extension part to each other and is engaged with the engagement target part. A leading end in the second direction of the second extension part is inserted into the coil part through an opening on a side of the first direction of the coil part.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a recording material, and a spring type biasing device using a tension coil spring.

Background Art

[0002] Image forming apparatuses such as printers, copiers, and multifunction devices may be configured to move or position movable members by a mechanism including a spring member. Patent Documents 1 and 2 describe configurations having a compression coil spring or a tension coil spring in a mechanism for bringing a developing roller into contact with and separating it from a photosensitive drum. In addition to the developing roller, an image forming apparatus also has a mechanism for bringing a transfer roller into contact with and separating it from a transfer belt, a mechanism for bringing a pair of rollers for conveying a recording material into contact with and separating them, etc., and spring members are also arranged in these mechanisms.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when using a tension coil spring, the position where the hook portion of the tension coil spring engages with the attached engagement portion and the position of the boundary portion between the coil portion and the hook portion are offset, so that the hook portion may deform starting from the boundary portion. And due to the deformation of the hook portion, there is a possibility that the magnitude of the biasing force acting on the member to be biased from the tension coil spring may fluctuate. In addition, due to the deformation of the hook portion, there is a possibility that the wire material may break due to fatigue at the boundary portion while the tension coil spring is repeatedly stretched and contracted.

[0005] Therefore, the present invention aims to provide a configuration that can obtain a more stable biasing force. [Means for solving the problem]

[0006] One aspect of the present invention is an image forming apparatus having a tension coil spring, an acting part that acts on a workpiece, and an engaged part that engages with the tension coil spring, and a movable member that moves so as to cause the acting part to act on the workpiece by the biasing force of the tension coil spring, wherein the tension coil spring has a coil portion in which a wire is wound in a spiral shape, and a hook portion that protrudes from the coil portion in a first direction along the central axis of the coil portion, the hook portion has a first extended portion in which the wire extends from the end of the coil portion in the first direction, a second extended portion in which the wire extends in a second direction opposite to the first direction, and a connecting portion that connects the first extended portion and the second extended portion and engages with the engaged part, the tip of the second extended portion in the second direction being inserted into the inside of the coil portion through an opening on the first direction side of the coil portion Ori , The movable member is rotatable about a pivot axis extending in a direction intersecting the central axis of the coil portion, the length of the hook portion in the direction along the central axis is the distance from the boundary between the coil portion and the first extension portion to the point of application where the connecting portion engages with the engaged portion, and the length of the hook portion is set such that, when viewed in the direction along the pivot axis of the movable member, the position of the coil portion in the state in which the tension coil spring is most extended when the movable member moves within the range of movement of the movable member does not overlap with the movement trajectory of the movable member. This is an image forming apparatus characterized by the following features.

[0007] Another aspect of the present invention is a spring-type biasing device comprising: a tension coil spring; an acting part that acts on a workpiece; and a movable member that engages with the tension coil spring, wherein the movable member moves to cause the acting part to act on the workpiece by the biasing force of the tension coil spring, the tension coil spring having a coil portion in which a wire is wound in a spiral shape; and a hook portion projecting from the coil portion in a first direction along the central axis of the coil portion, the hook portion having a first extension portion in which the wire extends from the end of the coil portion in the first direction; a second extension portion in which the wire extends in a second direction opposite to the first direction; and a connecting portion that connects the first extension portion and the second extension portion and engages with the engaged portion, the tip of the second extension portion in the second direction being inserted into the inside of the coil portion through an opening on the first direction side of the coil portion Ori , The movable member is rotatable about a pivot axis extending in a direction intersecting the central axis of the coil portion, the length of the hook portion in the direction along the central axis is the distance from the boundary between the coil portion and the first extension portion to the point of application where the connecting portion engages with the engaged portion, and the length of the hook portion is set such that, when viewed in the direction along the pivot axis of the movable member, the position of the coil portion in the state in which the tension coil spring is most extended when the movable member moves within the range of movement of the movable member does not overlap with the movement trajectory of the movable member. This is a spring-type biasing device characterized by the following: [Effects of the Invention]

[0008] According to the present invention, a more stable biasing force can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram of an image forming apparatus according to the first embodiment. [Figure 2] A perspective view of a process cartridge according to the first embodiment. [Figure 3] Plan view (a, b) of the developing and separating mechanism according to the first embodiment. [Figure 4] A perspective view of the developing and separating mechanism according to the first embodiment. [Figure 5] A perspective view of the developing and separating mechanism according to the first embodiment. [Figure 6] Enlarged views (a, b) of the developing and separating mechanism according to the first embodiment. [Figure 7] A cross-sectional view of the developing and separating mechanism according to the first embodiment. [Figure 8] A cross-sectional view of the developing and separating mechanism according to the first embodiment. [Figure 9] A perspective view of a tension coil spring according to the first embodiment. [Figure 10] Figures (a, b) illustrating the operation of the tension coil spring according to the first embodiment. [Figure 11] A schematic diagram of an image forming apparatus according to the second embodiment. [Figure 12] Perspective views (a, b) of the discharge roller unit according to the second embodiment. [Modes for carrying out the invention]

[0010] The embodiments relating to this disclosure will be described below with reference to the drawings.

[0011] 《First Embodiment》 The image forming apparatus according to the first embodiment will be described with reference to FIGS. 1 to 10. The "image forming apparatus" is an apparatus that forms an image on a recording material by an image forming means such as an electrophotographic method, and includes a copying machine, a laser beam printer, and a facsimile apparatus.

[0012] (Image forming apparatus) FIG. 1 is a schematic diagram showing a cross-sectional configuration when the image forming apparatus 100 in the present embodiment is viewed from the front side. The image forming apparatus 100 is a tandem type color laser beam printer in which four process cartridges 7Y, 7M, 7C, and 7K are arranged in a line. The image forming apparatus 100 forms an image on a sheet S as a recording material using toner based on image information received from the outside. As the sheet S, various sheet materials having different sizes and materials can be used, such as paper such as plain paper and thick paper, plastic film, cloth, sheet materials with surface treatment such as coated paper, and special-shaped sheet materials such as envelopes and index papers.

[0013] The image forming apparatus 100 generally includes process cartridges 7Y, 7M, 7C, 7K, an intermediate transfer unit 12, a secondary transfer roller 16, a fixing device 14, and a feeding device 13. The process cartridges 7Y, 且M, 7C, 7K, the intermediate transfer unit 12, and the secondary transfer roller 16 constitute an image forming unit 102 as an image forming means for forming an image on the sheet S.

[0014] The process cartridges 7Y, 7M, 7C, 7K have substantially the same configuration except that the colors of the toner used for development are different. Each process cartridge 7Y, 7M, 7C, 7K includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging means, a developing roller 24 as a developing means, and a cleaning member 8 as a cleaning means. Each process cartridge 7Y, 7M, 7C, 7K further includes a toner container 25 and a waste toner container 26. Further, a laser scanner unit 3 as an exposure means is disposed below the process cartridges 7Y, 7M, 7C, 7K.

[0015] A process cartridge is a cartridge in which a photosensitive drum 1 and at least one process means acting on the photosensitive drum 1 are integrated as a unit that can be attached to and detached together from the main body 101 of the image forming apparatus 100. The charging roller 2, developing unit 4, and cleaning member 8 are examples of process means that act on the photosensitive drum 1 in the electrophotographic process. In this embodiment, "main body of apparatus" refers to the part of the image forming apparatus 100 excluding the process cartridges 7Y, 7M, 7C, 7K and the cassette 11 described later. In this embodiment, the process cartridges 7Y, 7M, 7C, and 7K can be attached to and detached from the main body 101 of the image forming apparatus 100 from the front side.

[0016] The photosensitive drum 1 is a photoreceptor formed in a drum shape (cylindrical shape). The photosensitive drum 1 is made, for example, by coating the outer surface of an aluminum cylinder with an organic photoconductor layer (OPC), and both ends are rotatably supported by bearings. A gear or coupling that receives driving force from a motor is provided at one end of the photosensitive drum 1.

[0017] The charging roller 2 is a conductive roller formed in a roller shape and is positioned in contact with the surface of the photosensitive drum 1. The toner container 25 contains toner as a developer. The developing roller 24 is a developer carrier that carries the developer and supplies it to the photosensitive drum 1, developing a developer image on the surface of the photosensitive drum 1 (on the image carrier). The four toner containers 25 each contain yellow, magenta, cyan, and black toner. The developing roller 24 is positioned close to the photosensitive drum 1 and is movable to contact and separate from the photosensitive drum 1 by a developing contact / separation mechanism 41, which will be described later. This embodiment employs a contact developing method in which development is performed with the developing roller 24 (developer carrier) in contact with the photosensitive drum 1 (image carrier). As the developer, a one-component developer consisting of, for example, toner is used.

[0018] The intermediate transfer unit 12 comprises an intermediate transfer belt 12e as an intermediate transfer body, a drive roller 12f, a driven roller 12g, a primary transfer roller 12a as a primary transfer means, a secondary transfer inner roller 12b, and a cleaning device 22. The intermediate transfer belt 12e is an endless belt member and is stretched over the drive roller 12f, the driven roller 12g, and the secondary transfer inner roller 12b. The driven roller 12g is biased in the direction of arrow 1A in Figure 1 by a biasing means, applying a predetermined tension to the intermediate transfer belt 12e. The drive roller 12f is rotationally driven by the driving force of a motor, rotating the intermediate transfer belt 12e at a predetermined speed in the direction of arrow B in Figure 1. The primary transfer roller 12a is positioned inside the intermediate transfer belt 12e. A total of four primary transfer rollers 12a are positioned on either side of the intermediate transfer belt 12e, facing the photosensitive drum 1 of each process cartridge 7Y, 7M, 7C, and 7K.

[0019] The secondary transfer roller 16 is positioned opposite the secondary transfer inner roller 12b, with the intermediate transfer belt 12e in between. The secondary transfer section 15 is formed as a nip between the secondary transfer roller 16 and the secondary transfer inner roller 12b.

[0020] The fixing device 14 includes a fixing film 14a as a heating element, a pressure roller 14b as a pressurizing element, a heating element 14c, and a pair of discharge rollers 20. The fixing film 14a is an endless (tubular) building. The outer surface of the fixing film 14a is the surface that contacts the image on the sheet S. The heating element 14c is positioned inside the fixing film 14a. The pressure roller 14b presses the fixing film 14a against the heating element. A fixing nip is formed between the heating element 14c and the fixing film 14a.

[0021] The discharge roller pair 20 is positioned downstream of the fixing nip in the sheet conveying direction. The discharge roller pair 20 is a discharge means for discharging the sheet S from the device body 101. A discharge tray 21 is provided on the upper part of the device body 101. The discharge tray 21 has an inclined surface 21a that is tilted with respect to the horizontal. The inclined surface 21a is tilted such that the upstream side in the sheet discharge direction is lower and the downstream side is higher.

[0022] The feeding device 13 is located at the bottom of the main body 101 of the device. The feeding device 13 includes a cassette 11 for storing the sheets S, a feeding roller 9 as a feeding means, a pair of separating rollers 23 as a separating means, and a pair of registration rollers 17. The cassette 11 is configured to allow for replenishment or replacement of the sheets S by pulling it out from the main body 101 of the device.

[0023] (Image formation process) The image forming operation of the image forming apparatus 100 will now be described. The image forming apparatus 100 starts the image forming operation when it receives image information from an external source. During the image forming operation, the rotational drive of the photosensitive drum 1 and intermediate transfer belt 12e of each process cartridge 7Y, 7M, 7C, and 7K is started. The charging roller 2 uniformly charges the surface of the photosensitive drum 1. The laser scanner unit 3 irradiates each photosensitive drum 1 with a laser beam modulated based on the image information to perform exposure and form an electrostatic latent image on the surface of the photosensitive drum 1. The developing unit 4 develops the electrostatic latent image by having the developing roller 24 carry toner from the toner container 25 and supply it to the photosensitive drum 1, thereby visualizing the toner image.

[0024] The toner images of each color formed on the surfaces of the four photosensitive drums 1 are sequentially transferred to the intermediate transfer belt 12e by the primary transfer roller 12a. At this time, the toner images of each color overlap each other to form a full-color toner image (hereinafter simply referred to as the image). The image carried on the intermediate transfer belt 12e is transported toward the secondary transfer section 15. Toner remaining on the surface of the photosensitive drums 1 that is not transferred to the intermediate transfer belt 12e is removed by the cleaning member 8 and collected in the waste toner container 26.

[0025] In parallel with the creation of the images described above, the sheets S are fed one by one by the feeding device 13. The feeding roller 9 unloads the sheets S loaded on the cassette 11. The separation roller pair 23 separates the sheets S one by one by frictional force and transports them to the registration roller pair 17. After correcting the skew of the sheets S, the registration roller pair 17 transports the sheets S to the secondary transfer section 15 in synchronization with the timing when the images supported on the intermediate transfer belt 12e reach the secondary transfer section 15.

[0026] In the secondary transfer section 15, a bias voltage is applied to the secondary transfer roller 16, and the image on the intermediate transfer belt 12e is transferred to the sheet S. Toner that remains on the surface of the intermediate transfer belt 12e without being transferred to the sheet S is removed by the cleaning device 22 and collected in a waste toner container (not shown).

[0027] In the fixing device 14, the pressure roller 14b is rotationally driven by a driving force transmitted from the drive source, and the fixing film 14a rotates in accordance with the rotation of the pressure roller 14b. In addition, the power supply to the heating element 14c is controlled so that the fixing film 14a reaches a predetermined target temperature. At the fixing nip, the fixing film 14a holds the sheet S between the fixing film 14a and the pressure roller 14b and transports it, heating the image on the sheet S with the fixing film 14a heated by the heating element 14c. As a result, the image is fixed to the sheet S.

[0028] The sheet S that has passed through the fixing nip is gripped by the discharge roller pair 20 and discharged to the outside of the device body 101. The discharged sheet S is loaded onto the discharge tray 21 as an output. Since the discharge tray 21 has an inclined surface 21a, the sheet S loaded on the discharge tray 21 moves along the inclined surface 21a by gravity and aligns.

[0029] (cartridge) The configuration of the process cartridges will now be explained. Since each of the process cartridges 7Y, 7M, 7C, and 7K has a substantially common configuration except for the color of the toner contained in the toner container 25, any one of the process cartridges 7Y, 7M, 7C, and 7K will be described below as process cartridge 7.

[0030] Furthermore, the direction along the rotation axis of the developing roller 24, from the front side to the back side of the image forming apparatus 100, is defined as the X direction. The vertically upward direction when the image forming apparatus 100 is installed on a horizontal plane is defined as the Z direction. The horizontal direction perpendicular to the X direction is defined as the Y direction. Preferably, the X, Y, and Z directions are perpendicular to each other. If necessary, the directions opposite to the directions of the arrows shown in the figure are defined as the -X direction, -Y direction, and -Z direction. In addition, the shape and arrangement of the components of the process cartridge 7 will be described based on the state in which the process cartridge 7 is mounted on the apparatus body 101.

[0031] Figure 2 is a perspective view showing the external appearance of the process cartridge 7. The process cartridge 7 is an assembly whose longitudinal direction is the rotation axis direction (X direction) of the photosensitive drum 1. The process cartridge 7 includes a developing unit 4 and a cleaning unit 5. The developing unit 4 has a developing roller 24 and a toner container 25. The cleaning unit 5 has a photosensitive drum 1, a charging roller 2, a cleaning member 8 and a waste toner container 26.

[0032] The toner container 25 is the frame of the developing unit 4. The developing roller 24 is rotatably supported by the toner container 25. The toner container 25 is provided with a pressed portion 31 that is pressed by the pressing member 30 (Figure 7) of the developing contact / separation mechanism 41, which will be described later.

[0033] The waste toner container 26 is the frame of the cleaning unit 5. The photosensitive drum 1 is rotatably supported by the waste toner container 26. The cleaning member 8 and the charging roller 2, supported by the waste toner container 26, are positioned in contact with the photosensitive drum 1 (Figure 7).

[0034] The developing unit 4 is supported by the cleaning unit 5 so as to be rotatable in the directions of arrows D1 and D2, around a pivot axis 27 extending in the longitudinal direction (X direction). When no external force is acting on the process cartridge 7, the developing unit 4 is configured to be biased to rotate in the direction of D1 around the pivot axis 27 by its own weight or by a biasing means (not shown). In other words, the process cartridge 7 is configured so that the developing roller 24 remains separated from the photosensitive drum 1 when the developing unit 4 is not receiving force from the developing contact / separation mechanism 41 (Figure 8).

[0035] To bias the developing unit 4 in the D1 direction by its own weight, the center of gravity of the developing unit 4 should be located to the left in Figures 7 and 8 relative to the rotation axis 27 when viewed in the direction along the rotation axis 27. To bias the developing unit 4 in the D1 direction by its own weight using a biasing means, for example, a torsion coil spring can be arranged around the rotation axis 27, with one arm hooked onto the cleaning unit 5 and the other arm hooked onto the developing unit 4.

[0036] The support configuration when the process cartridge 7 is mounted on the main body 101 will be explained using Figures 7 and 8. Figures 7 and 8 are cross-sectional views of the process cartridge 7 mounted on the main body 101, cut by a virtual plane perpendicular to the longitudinal direction (X direction).

[0037] As shown in Figures 7 and 8, when the process cartridge 7 is mounted on the main body 101, the waste toner container 26 of the cleaning unit 5 is positioned by the support member 155 provided on the main body 101. Also, when the process cartridge 7 is mounted on the main body 101, if the pressing member 30 of the developing contact / separation mechanism 41 (described later) presses against the pressed portion 31 of the developing unit 4, the developing unit 4 rotates in the D2 direction, opposite to the D1 direction (Figure 7). As a result, the developing roller 24 comes into contact with the photosensitive drum 1 with a predetermined contact pressure.

[0038] (Developing and disengaging mechanism) The developing contact / separation mechanism that brings the developing roller 24 into contact with and separates it from the photosensitive drum 1 will be described below. As shown in Figure 1, the main body 101 of the image forming apparatus 100 is provided with four developing contact / separation mechanisms 41 corresponding to the process cartridges 7Y, 7M, 7C, and 7K. Since the configuration of each developing contact / separation mechanism 41 is substantially the same, any one of the developing contact / separation mechanisms 41 will be described below.

[0039] Hereinafter, the "development contact state" of the process cartridge 7 refers to the state in which the developing roller 24 is in contact with the photosensitive drum 1 and it is possible to develop the electrostatic latent image on the photosensitive drum 1 (a state in which an image can be formed). The "development separation state" of the process cartridge 7 refers to the state in which the developing roller 24 is separated from the photosensitive drum 1.

[0040] In a configuration using a contact developing roller 24, if the developing roller 24 is always in contact with the photosensitive drum 1, including during periods when no image forming is taking place (non-image forming time), the following problems may occur. Specifically, friction between the developing roller 24 and the photosensitive drum 1 may shorten the lifespan of both the developing roller 24 and the photosensitive drum 1. Also, if the developer adheres to the photosensitive drum 1 during non-image forming time, the developer may be wasted, or toner may contaminate the recording material during image forming. Furthermore, if the same part of the developing roller 24 continues to contact the photosensitive drum 1 for a long period of time during the shutdown period of the image forming apparatus, deformation or deterioration of the developing roller 24 may occur. In contrast, by configuring the developing roller 24 to be able to contact and separate from the photosensitive drum 1, and separating it from the photosensitive drum 1 during non-image forming time, the possibility of the above problems occurring can be reduced.

[0041] Figure 3(a) is a plan view showing the development contact / detachment mechanism 41 (slider 33 and cam mechanism omitted) corresponding to the development contact state. Figure 3(b) is a plan view showing the development contact / detachment mechanism 41 (slider 33 and cam mechanism omitted) corresponding to the development separation state. Figure 4 is a perspective view of the development contact / detachment mechanism 41 corresponding to the development contact state. Figure 5 is a perspective view of the development contact / detachment mechanism 41 corresponding to the development separation state. Figure 6(a) is an enlarged plan view of a part of the development contact / detachment mechanism 41 corresponding to the development contact state. Figure 6(b) is an enlarged plan view of a part of the development contact / detachment mechanism 41 corresponding to the development contact state.

[0042] As shown in Figures 3(a, b), 4, and 5, the developing and releasing mechanism 41 includes two pressing members 30, two tension coil springs 32, a slider 33, a lever 34, a cam 35, and a stay 36. As will be explained below, the developing and releasing mechanism 41 is configured such that the lever 34 and the slider 33 move in accordance with the rotation of the cam 35, thereby moving the pressing members 30 relative to the pressed portion 31.

[0043] As shown in Figures 3(a, b), the stay 36 is a plate-shaped member that extends elongated in the X direction. The stay 36 is fixed to the frame member of the main body 101 of the image forming apparatus 100.

[0044] As shown in Figures 4 and 5, the cam 35 is positioned at the X-direction end of the stay 36. The cam 35 is rotatable about an axis extending in the X direction. The cam 35 is rotationally driven in a predetermined rotational direction (arrow M) by a driving force transmitted from the motor M1, which is the drive source. The cam 35 has a cam surface 35a that contacts the lever 34.

[0045] The lever 34 is supported by a stay 36 and is rotatable within a predetermined range around a pivot axis 36c (see Figure 6(a, b)) provided on the stay 36. The range of rotation of the lever 34 is defined, for example, by the shape of the cam surface 35a of the cam 35. The lever 34 has an arm portion 34a that contacts the cam surface 35a of the cam 35 and a connecting portion 34b that connects to the slider 33. The lever 34 is a fan-shaped member centered on the pivot axis 36c, with the arm portion 34a positioned at one end of the fan shape in the circumferential direction and the connecting portion 34b positioned at the other end.

[0046] The slider 33 is supported by a stay 36. The slider 33 is a plate-shaped member that extends elongated in the X direction, and the main surface of the slider 33 faces the main surface of the stay 36 in the Z direction (Figure 7). The stay 36 is provided with a guide portion 36b that guides the slider 33. The slider 33 is provided with a guide hole 33b into which the guide portion 36b fits. Guided by the fitting of the guide portion 36b and the guide hole 33b, the slider 33 can slide relative to the stay 36 in the X direction and the -X direction.

[0047] The slider 33 is connected to the connecting portion 34b of the lever 34 at its end in the X direction. As shown in Figure 6(a, b), the lever 34 rotates in conjunction with the rotation of the cam 35, and the slider 33 slides in the X direction and the -X direction in conjunction with the rotation of the lever 34. In other words, the cam 35, lever 34, and slider 33 constitute a mechanism that converts rotational motion transmitted from the motor M1 into linear motion.

[0048] As shown in Figures 3(a, b), the two pressing members 30 are positioned apart from each other in the X direction of the stay 36. Each pressing member 30 is rotatable within a predetermined range in both clockwise and counterclockwise directions in the figure, around a pivot axis 36a provided on the stay 36. Details of the pressing unit 30U, including the pressing members 30, will be described later.

[0049] Each pressing member 30 has a pressing portion 30a (Figures 7 and 8) that presses against the pressed portion 31 of the developing unit 4, and a protruding portion 30b that engages with the hook portion (U-hook 32c, described later) of the tension coil spring 32. The pressing portion 30a functions as an actuating portion that acts on the pressed portion 31, which is the actuating portion. The pressing member 30 is also an example of a movable member that moves so that the actuating portion acts on the actuating portion by the biasing force of the tension coil spring. The pressing portion 30a protrudes in the -Z direction from the stay 36 through a fan-shaped groove 36f (see also Figures 3(b) and 10(a,b)) provided in the stay 36 (Figure 7). The groove 36f is a hole that penetrates the stay 36 in the Z direction and extends in an arc direction centered on the rotation axis of the pressing member 30. The protruding portion 30b, which is the engaged portion in this embodiment, is a cylindrical projection extending in the Z direction.

[0050] The slider 33 is provided with a contact surface 33a that contacts the contacted portion of the pressing member 30 (Figure 4). The pressing member 30 is configured to rotate in conjunction with the slider 33 when the contact surface 33a is in contact with the contacted portion of the pressing member 30. In this embodiment, the contacted portion of the pressing member 30 is part of the protrusion 30b that engages with the tension coil spring 32. In other words, in this embodiment, the protrusion 30b of the pressing member 30 serves as both the engaged portion that engages with the hook portion of the tension coil spring 32 and the contacted portion that contacts the slider 33.

[0051] The two tension coil springs 32 are also positioned at locations separated from each other in the X direction, corresponding to the two pressing members 30. Each tension coil spring 32 is positioned such that the axial direction (extension direction) of the spiral of the coil portion 32a is approximately parallel to the X direction. In addition, a portion of the pressing member 30 and the tension coil springs 32 are positioned in the space between the stay 36 and the slider 33, which are facing each other in the Z direction (Figure 7). Note that the slider 33 is not shown in Figures 3(a, b).

[0052] The tension coil spring 32 is a biasing member that applies a biasing force (elastic force) to the pressing member 30. The detailed configuration of the tension coil spring 32 will be described later. In this embodiment, the direction of the force received by the pressing member 30 from the tension coil spring 32 is generally in the X direction.

[0053] On the other hand, the direction in which the slider 33 slides when the lever 34 is pressed against the cam 35 (the direction in which the contact surface 33a of the slider 33 presses against the pressing member 30) is the -X direction. Therefore, the pressing member 30 can rotate in the direction of arrow G in Figure 3(b) against the biasing force of the tension coil spring 32 by receiving the driving force of the motor M1 via the cam 35, etc. Also, when the pressing member 30 is not receiving the driving force of the motor M1, it can rotate in the direction of arrow E in Figure 3(a) according to the biasing force of the tension coil spring 32.

[0054] Furthermore, by using a tension coil spring 32 as the biasing member, the coil portion 32a naturally lies on the straight line connecting the fixed and movable engaged portions (the central axis Ax in Figure 10(a)) due to the tension. Therefore, compared to, for example, using a compression coil spring as the biasing member, it is easier to obtain a stable biasing force.

[0055] (Operation of the developing mechanism) The operation of the developing contact / separation mechanism 41 will be described below. First, the operation when transitioning from the developing contact state to the developing separation state will be explained.

[0056] In the developing contact state, the cam 35 is held at a rotation angle in which the cam surface 35a does not contact the lever 34 (Figures 4 and 6(a)). Therefore, a moment in the direction of arrow E in Figure 3(a) acts on the pressing member 30 due to the biasing force of the tension coil spring 32. Then, as shown in Figure 7, the pressing portion 30a of the pressing member 30 comes into contact with the pressed portion 31 of the developing unit 4, pressing the pressed portion 31 in the direction of arrow F in the figure. This maintains the state in which the developing roller 24 is in contact with the photosensitive drum 1.

[0057] When transitioning from the developing contact state to the developing separation state, the cam 35 is driven by the driving force of the motor M1, and the cam surface 35a comes into contact with the arm portion 34a of the lever 34 (Figure 6(b)). As a result, the lever 34 rotates in the direction of arrow N in Figure 6(b). In conjunction with the rotation of the lever 34, the slider 33 slides in the direction of arrow P (-X direction) in Figures 5 and 6(b), and the contact surface 33a of the slider 33 presses against the protrusion 30c of the pressing member 30. As a result, the pressing member 30 rotates in the direction of arrow G in Figure 3(b), while extending the tension coil spring 32.

[0058] As the pressing member 30 rotates in the direction of arrow G, the pressing portion 30a moves away from the pressed portion 31 (in the Y direction), as shown in Figure 8. As a result, the developing unit 4 rotates in the direction of arrow D1 so that the developing roller 24 moves away from the photosensitive drum 1, and stops at a position where the pressed portion 31 contacts the pressing portion 30a. This causes the process cartridge 7 to transition from the developing contact state to the developing separation state.

[0059] In this way, by using the driving force of the motor M1 to move the pressing member 30 against the biasing force of the tension coil spring 32, a switch from the developing contact state to the developing separation state is achieved.

[0060] In the development-separated state, the protrusion 30c of the pressing member 30 contacts the contact surface 33a of the slider 33, which is moved in the X direction by the cam 35 and the slider 33, thereby receiving the biasing force of the tension coil spring 32. In other words, the contact surface 33a functions as a restricting surface that receives the biasing force of the tension coil spring 32 and restricts the movement of the pressing member 30.

[0061] When transitioning from the developing distance state to the developing contact state, the cam 35 is driven by the driving force of the motor M1, and the cam surface 35a moves away from the arm portion 34a of the lever 34 (Figure 6(a)). As a result, the restriction by the contact surface 33a of the slider 33 is released, and the pressing member 30 rotates in the direction of arrow E shown in Figure 3(a) according to the biasing force of the tension coil spring 32. As the pressing member 30 rotates in the direction of arrow E, the slider 33 slides in the direction of arrow K (X direction) in Figures 4 and 6(a), and the lever 34 rotates in the direction of arrow L in Figure 6(a). Also, as the pressing member 30 rotates in the direction of arrow E, the tension coil spring 32 contracts.

[0062] As the pressing member 30 rotates in the direction of arrow E, the pressing portion 30a moves in the direction of arrow F (-Y direction) as shown in Figure 7. As a result, the developing unit 4 rotates in the direction of arrow D2 until the developing roller 24 contacts the photosensitive drum 1. This causes the process cartridge 7 to transition from the developing-away state to the developing-contact state.

[0063] In this way, the biasing force of the tension coil spring 32 moves the pressing member 30, thereby enabling a switch from the developing separation state to the developing contact state.

[0064] Furthermore, in the developing contact state, there is a gap between the cam 35 and the lever 34, as shown in Figure 6(a). That is, the slider 33 does not restrict the rotation of the pressing member 30 and does not receive the biasing force of the tension coil spring 32.

[0065] In the developing contact state, the biasing force of the tension coil spring 32 is received by the pressed portion 31 of the developing unit 4, which is in contact with the pressing portion 30a of the pressing member 30 (Figure 7). In other words, in this embodiment, the biasing force of the tension coil spring 32 defines the contact pressure between the developing roller 24 and the photosensitive drum 1 in the developing contact state.

[0066] In this embodiment, as described above, the developing unit 4 is pressed by two pressing members 30 that are spaced apart from each other in the longitudinal direction (X direction, the direction of the rotation axis of the developing roller 24) of the developing roller 24. This makes it possible to make the contact pressure of the developing roller 24 with respect to the photosensitive drum 1 and the distance between the developing roller 24 and the photosensitive drum 1 more uniform in the longitudinal direction. Depending on the degree to which uniformity of contact pressure and distance is required, for example, a configuration in which one pressing member presses one point (the center) in the longitudinal direction of the developing unit 4 may be used. In that case, one tension coil spring 32 is sufficient.

[0067] (Details of the pressing unit) The pressing member 30 and tension coil spring 32 of the developing contact / separation mechanism 41, as well as the pivot shaft 36a and engaged portion 36d of the stay 36, constitute a pressing unit 30U as an acting means that acts on the developing unit 4, which is a movable member. The pressing unit 30U is a pressing means that presses the pressed portion 31 of the developing unit 4. In this embodiment, two sets of pressing units 30U (a first pressing unit and a second pressing unit) are provided. The configuration of the pressing unit 30U will be described below.

[0068] Figure 9 is a perspective view of the pressing unit 30U. Figure 10(a) is a cross-sectional view of the pressing unit 30U corresponding to the developing contact state. Figure 10(b) is a cross-sectional view of the pressing unit 30U corresponding to the developing contact state. In the following, the configuration of the pressing unit 30U on the -X side (lower side in Figure 3(a)) will be described, but the pressing unit 30U on the X side (upper side in Figure 3(a)) can be substantially the same.

[0069] As shown in Figures 9 and 10(a, b), the pressing unit includes a pressing member 30, a tension coil spring 32, and a pivot shaft 36a and an engaged portion 36d of the stay 36.

[0070] The stay 36 is a support member that rotatably supports the pressing member 30 by a pivot shaft 36a. In this embodiment, the stay 36 engages with the hook portion (round hook 32b, described later) on the fixed end side of the tension coil spring 32 at the engaged portion 36d. The pivot shaft 36a and the engaged portion 36d may be provided on a separate member.

[0071] As described above, the pressing member 30 has a pressing portion 30a and a protrusion 30b. The axial direction of rotation is at least intersecting the direction along the central axis of the tension coil spring 32, and in this embodiment, it is substantially perpendicular to the direction along the central axis (Z direction). The pressing portion 30a and the protrusion 30b are positioned at different locations (for example, 90 degrees apart) with respect to the circumferential direction of a virtual circle centered on the rotation axis 36a. This allows the linear motion of the stay 36 along the X direction to be converted into the movement of the pressing portion 30a in the Y direction (movement of the pressed portion 31 in the pressing direction). Furthermore, the force in the approximately X direction received by the protrusion 30b from the tension coil spring 32 can be converted into a force that the pressing portion 30a exerts on the pressed portion 31 in the pressing direction.

[0072] The tension coil spring 32 has a coil portion 32a in which a wire is wound in a spiral shape, and hook portions formed by wires extending from both ends of the coil portion 32a. In this embodiment, the hook portion at one end (fixed end) is a circular round hook 32b, and the hook portion at the other end (movable end) is a U-shaped U-hook 32c extending in the direction along the central axis Ax of the coil portion 32a. The round hook 32b is, for example, an arc shape (semicircular or nearly circular) with the same radius as the coil portion 32a. The round hook 32b, coil portion 32a, and U-hook 32c are formed by bending a single wire (wire forming).

[0073] The boundary between the coil portion 32a and the U-hook 32c is defined as the switching portion 32d. In this embodiment, the switching portion 32d is a bent portion where the first extension portion 32c1 of the U-hook 32c is bent in a direction substantially parallel to the central axis Ax from the end of the coil portion 32a, which is spirally wound along a virtual cylindrical surface centered on the central axis Ax. The boundary between the coil portion 32a and the round hook 32b is defined as the switching portion 32h. When the shape changes continuously from the coil portion 32a to the hook portion, the range in which the wire is formed in a shape different from the spiral shape of the coil portion is determined. Within the above range of the tension coil spring 32, the position closest to the coil portion in the portion located at the opposite angle to the contact portion 32e (described later) with respect to the central axis Ax is defined as the boundary between the coil portion and the hook portion. This is because if the contact portion 32e does not contact the inner surface of the coil portion 32a, deformation of the hook portion may occur starting from the vicinity of the above switching portion (boundary portion).

[0074] Hereinafter, the direction from the round hook 32b to the U-hook 32c along the central axis Ax will be referred to as the first direction Ax1, and the opposite direction (the direction from the U-hook 32c to the round hook 32b along the central axis Ax) will be referred to as the second direction Ax2.

[0075] The U-hook 32c has a first extension portion 32c1, a connecting portion 32c2, and a second extension portion 32c3. The first extension portion 32c1 extends from the switching portion 32d in the first direction Ax1. The connecting portion 32c2 is a connecting portion that connects the end of the first extension portion 32c1 in the first direction Ax1 to the end of the second extension portion 32c3 in the first direction Ax1 and engages with the convex portion 30b (engaged portion) of the pressing member 30. The second extension portion 32c3 extends from the connecting portion 32c2 toward the second direction Ax2, that is, toward the coil portion 32a. The extension directions of the first extension portion 32c1 and the second extension portion 32c3 can be substantially parallel to the central axis Ax.

[0076] The connecting portion 32c2 connects the end of the first extension portion 32c1 in the first direction Ax1 to the end of the second extension portion 32c3 in the second direction Ax2. In this embodiment, the connecting portion 32c2 is a bent portion that is substantially bent in a semicircular shape from the extension direction of the first extension portion 32c1 (first direction Ax1) to the extension direction of the second extension portion 32c3 (second direction Ax2). The inner diameter of the connecting portion 32c2 is set to be slightly larger than the outer diameter of the protrusion 30b (engaged portion) of the stay 36.

[0077] The tip portion 32c4 of the second extension portion 32c3 is inserted into the inside of the coil portion 32a through the opening on the first direction Ax1 side of the coil portion 32a. Here, the inside of the coil portion 32a refers to the inside of the coil portion 32a with respect to the radial direction with respect to the central axis Ax, and the space between the switching portions 32d and 32h with respect to the direction along the central axis Ax. In other words, the U-hook 32c has a portion that includes the edge 32c5 of the wire material constituting the tension coil spring 32 and is housed in the internal space of the coil portion 32a.

[0078] The tip portion 32c4 includes a contact portion 32e extending along the inner surface of the coil portion 32a in a direction along the central axis Ax, and a non-contact portion 32f formed away from the inner surface of the coil portion 32a. The non-contact portion 32f is bent relative to the contact portion 32e so that it is directed radially inward from the inner surface of the coil portion 32a, centered on the central axis Ax, as it moves toward the second direction Ax2. The non-contact portion 32f includes the edge 32c5 of the wire. The contact portion 32e is located on the side of the first direction Ax1 (the end side of the coil portion 32a) relative to the non-contact portion 32f.

[0079] The contact portion 32e is positioned so as to be in contact with the inner surface of the coil portion 32a when the tension coil spring 32 is not under tensile load, or at least in contact with the inner surface of the coil portion 32a when the tension coil spring 32 is under tensile load. The non-contact portion 32f is formed to maintain a state of being separated from the inner surface of the coil portion 32a even when the contact portion 32e is in contact with the inner surface of the coil portion 32a. When viewed in the direction along the central axis Ax, it is preferable that the contact portion 32e is located on the opposite side of the central axis Ax from the switching portion 32d between the coil portion 32a and the first extension portion 32c1. This effectively restricts deformation that would cause the gap W of the U-hooks 32c (Figure 10(a)), which will be described later, to widen.

[0080] As shown in Figure 9, the round hook 32b of the tension coil spring 32 engages with the engaged portion 36d of the stay 36, and the U-hook 32c engages with the convex portion 30b (engaged portion) of the pressing member 30. At this time, the tension coil spring 32 engages with the engaged portion 36d and the convex portion 30b when it is extended from the unloaded state (free length state). As a result, the biasing force (tension) of the tension coil spring 32 acts on the pressing member 30.

[0081] The biasing force of the tension coil spring 32 causes a moment of force in the direction of arrow E to act on the pressing member 30 around the pivot axis 36a. This moment of force biases the pressing portion 30a in the pressing direction (-Y direction) relative to the pressed portion 31 of the developing unit 4.

[0082] The point at which the force of the tension coil spring 32 acts from the U-hook 32c to the protrusion 30b of the pressing member 30 is defined as 32g. Specifically, the point at which the force acts, 32g, is the contact point between the inner surface of the connecting portion 32c2 of the U-hook 32c and the surface of the protrusion 30b on the first direction Ax1 side.

[0083] When viewed along the central axis Ax of the coil portion 32a, the point of application 32g of the force from the tension coil spring 32 to the pressing member 30 is located closer to the central axis Ax than to the inner surface of the coil portion 32a. Preferably, the point of application 32g is located on the central axis Ax. In other words, the switching portion 32d of the coil portion 32a and the U-hook 32c and the point of application 32g of the force from the tension coil spring 32 to the pressing member 30 are offset with respect to the radial direction of a virtual circle centered on the central axis Ax.

[0084] Therefore, in the comparative example where the tip of the U-hook 32c' is not inserted inside the coil portion 32a, as shown by the dashed line in Figure 10(a), the U-hook 32c' may deform so that the connecting portion 32c2 is displaced in the direction of arrow R relative to the switching portion 32d. That is, the tension (f1) from the coil portion 32a that the U-hook 32c' receives at the switching portion 32d and the reaction force (f2) that the U-hook 32c' receives from the convex portion 30b at the point of application 32g are not on the same straight line. Therefore, a force moment in the counterclockwise direction in the figure acts on the U-hook 32c'. At that time, the U-hook 32c' deforms so that the gap W between the first extension portion 32c1 and the second extension portion 32c3 widens, allowing the U-hook 32c' to contact the convex portion 30b at a point closer to the second extension portion 32c3 than the initial contact point with the convex portion 30b. As a result, in the comparative example, displacement of the U-hook 32c' in the direction of arrow R may be permissible.

[0085] In the above comparative example, the deformation of the U-hook 32c' so that the gap W widens may cause the magnitude of the biasing force actually acting on the pressing member 30 from the tension coil spring 32 to deviate from the design value.

[0086] Furthermore, as the amount of deformation of the U-hook 32c' originating from the switching section 32d changes according to the magnitude of the tensile load, metal fatigue of the switching section 32d progresses as the tension coil spring 32 is repeatedly expanded and contracted. In other words, even if the deformation of the U-hook 32c' shown by the dashed line in Figure 10(a) occurs within the elastic range, the deformation of the U-hook 32c' occurs when the tension coil spring 32 expands and contracts, which increases the amount of deformation of the switching section 32d and accelerates metal fatigue. Consequently, if the contact and separation operation of the developing roller 24 is repeatedly performed over a long period of time as shown in Figures 10(a, b), the switching section 32d may break, potentially causing malfunction of the developing contact / separation mechanism 41 (such as a one-sided pressing state where one of the two pressing members 30 does not function).

[0087] In contrast, in this embodiment, the tip portion 32c4 of the U-hook 32c is located inside the coil portion 32a. Therefore, even though the switching portion 32d of the coil portion 32a and the U-hook 32c, and the point of application of force 32g from the tension coil spring 32 to the pressing member 30 are offset, the displacement of the U-hook 32c in the direction of arrow R is restricted. That is, because the contact portion 32e contacts the inner surface of the coil portion 32a, deformation of the U-hook 32c that would widen the gap W between the first extension portion 32c1 and the second extension portion 32c3 is restricted. In other words, the planar shape of the U-hook 32c when viewed in the Z direction is fixed at three points: the switching portion 32d, the contact portion 32e, and the point of application 32g. Therefore, movement of the U-hook 32c in the direction of arrow R relative to the convex portion 30b is restricted, and deformation of the U-hook 32c originating from the switching portion 32d is suppressed.

[0088] According to this embodiment, even when a tensile load is applied to the tension coil spring 32, deformation of the U-hook 32C is restricted so that the contact area of ​​the U-hook 32c with the protrusion 30b (engaged portion) changes as the gap W widens. Therefore, it is possible to reduce the deviation of the magnitude of the biasing force actually applied from the tension coil spring 32 to the pressing member 30 from the design value.

[0089] Furthermore, even if the tension coil spring 32 is repeatedly stretched and compressed, the amount of deformation of the U-hook itself is kept small, thus reducing the progression of metal fatigue in the switching section 32d. Therefore, even if the developing roller 24 is repeatedly brought into contact with and separated from the surface over a long period of time, breakage of the switching section 32d becomes less likely, and the possibility of malfunction of the developing contact / separation mechanism 41 is reduced.

[0090] Thus, the pressing unit 30U as a spring-type biasing device according to this embodiment can generate a more stable biasing force.

[0091] Furthermore, the pressing unit 30U of this embodiment constitutes part of the developing contact / separation mechanism 41 that brings the developing roller 24 into contact with and separates it from the photosensitive drum 1. Therefore, by using the pressing unit 30U of this embodiment, the contact pressure of the developing roller 24 with respect to the photosensitive drum 1 can be stabilized over a long period of time. This reduces the possibility of image defects caused by fluctuations in the contact pressure of the developing roller 24 in the contact developing method.

[0092] Image defects caused by fluctuations in the contact pressure of the developing roller 24 include unevenness in the image density in the longitudinal direction (main scanning direction during image formation) due to uneven contact pressure in the longitudinal direction of the developing roller 24. Therefore, by arranging at least two of the pressing units 30U of this embodiment (first pressing unit, second pressing unit) on one end and the other end in the longitudinal direction of the developing roller 24, unevenness in density in the longitudinal direction can be reduced. Furthermore, when using the pressing units 30U of this embodiment to bring a cylindrical rotating member other than the developing roller 24 (including hollow cylindrical members) into contact with another member (see (Other Embodiments) below), there is also the advantage of uniform contact pressure in the longitudinal direction.

[0093] Furthermore, in this embodiment, the tip of the tip portion 32c4 of the U-hook 32c is formed as a non-contact portion 32f so as not to come into contact with the inner surface of the coil portion 32a. Therefore, the possibility of the wire edge 32c5 getting caught on the coil portion 32a when the coil portion 32a expands and contracts can be reduced, and the possibility of deformation or malfunction of the tension coil spring 32 due to the edge 32c5 getting caught can be reduced.

[0094] Furthermore, the contact portion 32e of the U-hook 32c may be positioned with a gap between it and the inner surface of the coil portion 32a if necessary for manufacturing. In other words, a gap may exist between the contact portion 32e and the inner surface of the coil portion 32a when no tensile load is acting on the tension coil spring 32. Even in this case, it is sufficient that the contact portion 32e contacts the inner surface of the coil portion 32a at least when the coil portion 32a is most extended due to the movement of the pressing member 30 (in this embodiment, the fully separated state). This reduces deformation of the U-hook 32c and allows the tension coil spring 32 to apply a stable biasing force to the pressing member 30 over a long period of time.

[0095] By the way, it is preferable that the length T of the U-hook 32c be set to a length such that, when viewed in the direction of the rotation axis of the pressing member 30, the position of the coil portion 32a in the state in which the coil portion 32a is most extended due to the movement of the pressing member 30 does not overlap with the movement trajectory of the pressing member 30 when it rotates. (See Figure 10(b).) Here, the length T of the U-hook 32c is the distance from the switching portion 32d to the point of application 32g in the direction along the central axis Ax of the coil portion 32a (for example, the first direction Ax1). Furthermore, the state in which the coil portion 32a is most extended due to the movement of the pressing member 30 is the state in which the coil portion 32a is most extended when the pressing member 30 moves within the range of movement of the pressing member 30, and in this embodiment corresponds to the developed separated state (Figure 10(b)).

[0096] By setting the U-hook 32c to the length T described above, the coil portion 32a can be prevented from interfering with the pressing member 30 even when the tension coil spring 32 expands or contracts. This makes it possible to save space in the pressing unit 30U without hindering the expansion or contraction of the tension coil spring 32.

[0097] Furthermore, in this embodiment, the pressing member 30 and the U-hook 32c overlap when viewed along the rotation axis of the pressing member 30. In addition, the pressing member 30 and the coil portion 32a overlap when viewed along the central axis Ax of the coil portion 32a (see Figure 7). Overlap means that the positions of the two members overlap at least partially. This arrangement makes it possible to save space in the pressing unit 30U.

[0098] 《Second Embodiment》 In the first embodiment, as an example of a spring-type biasing device, a configuration was described in which a developing roller 24 is moved between a contact position and a separated position relative to the photosensitive drum 1. In the second embodiment, as another example of a spring-type biasing device, a configuration is described in which a pair of rollers for transporting recording material is opened and closed. Hereinafter, elements denoted by the same reference numerals as in the first embodiment have substantially the same configuration and operation as those described in the first embodiment, and only the parts that differ from the first embodiment will be described.

[0099] Figure 11 is a schematic diagram of the image forming apparatus 200 according to this embodiment. The image forming apparatus 200 of this embodiment includes an image forming apparatus body 201 with the same configuration as the image forming apparatus 100 of the first embodiment, and a sheet processing device 202 installed on the upper part of the image forming apparatus body 201.

[0100] The sheet processing apparatus 202 includes a discharge roller pair 51, a transport roller pair 52, a sheet transport path 53, a loading section 54, and an alignment member 59. The sheet processing apparatus 202 transports sheets on which images have been formed from the image forming apparatus body 201 to the sheet transport path 53 using the transport roller pair 52 and loads them. After aligning multiple sheets with the alignment member 59, the sheets are stapled together. The stapled sheet bundle is then discharged by the discharge roller pair 51 and loaded into the loading section 54. The details of the sheet processing apparatus 202 can be the same as those described in, for example, Japanese Patent No. 4759185.

[0101] In the sheet processing device 202, while multiple sheets are loaded onto the sheet transport path 53 and aligned, the discharge roller pair 51 is kept in a separated state so as not to hinder sheet alignment. Once the sheet alignment and binding process is complete, the discharge roller pair 51 returns to a contact state where it can grip and transport the sheet bundle. Therefore, the discharge roller pair 51 is configured to be able to contact and separate.

[0102] The discharge roller unit 50 will be explained using Figures 12(a, b). Figure 12(a) is a perspective view of the discharge roller unit 50 in the contact state of the discharge roller pair 51. Figure 12(b) is a perspective view of the discharge roller unit 50 in the separated state of the discharge roller pair 51.

[0103] The discharge roller unit 50 includes a drive roller 51a and a driven roller 51b constituting a discharge roller pair 51, a tension coil spring 55, a support frame 56, a bearing member 57, and a cam 58.

[0104] The drive roller 51a is an example of a first roller, and the driven roller 51b is an example of a second roller that can contact and separate from the first roller. The rotation axis direction of the drive roller 51a and the driven roller 51b is the longitudinal direction of the discharge roller pair 51.

[0105] The drive roller 51a is rotatably supported at both ends in the longitudinal direction by two support frames 56. The drive roller 51a rotates (forward rotation) when a driving force is input from a motor (not shown). The driven roller 51b is rotatably supported at both ends in the longitudinal direction by two bearing members 57. The driven roller 51b can rotate in accordance with the drive roller 51a.

[0106] The pressing unit 57U (roller contact / separation mechanism), consisting of a tension coil spring 55, a support frame 56, a bearing member 57, and a cam 58, is arranged one on each side in the longitudinal direction. The following description will focus on the pressing unit 57U on the front side in Figure 12(a, b), but the pressing unit on the back side has substantially the same configuration.

[0107] The cams 58 are positioned at both ends in the longitudinal direction of the drive roller 51a. For example, the rotation angle of the cams 58 changes when the motor reverses direction. The cams 58 have a cam surface capable of pressing against the bearing member 57.

[0108] The bearing member 57 is an example of a roller support member that rotatably supports the second roller and moves the second roller relative to the first roller. The bearing member 57 is rotatably supported on the shaft portion 56a of the support frame 56. The bearing member 57 has a bearing portion 57a ​​as an acting portion that acts on the roller axis (acted portion) of the driven roller 51b when the discharge roller pair 51 comes into contact with and separates from each other. The bearing member 57 further has an engaged portion 57b at the end furthest from the shaft portion 56a that engages with the hook portion of the tension coil spring 55. The bearing member 57 is rotatable about its longitudinal axis so that the rotation axis of the driven roller 51b approaches and separates from the rotation axis of the drive roller 51a (i.e., up and down in the figure).

[0109] The tension coil spring 55 has a coil portion 55a in which a metal wire is wound spirally, and a round hook 55b and a U-hook 55c that protrude from the coil portion 55a toward one side and the other side in the direction along the central axis of the coil portion 55a, respectively. The round hook 55b, which is the hook portion on the fixed end side, engages with the engaged portion 56d of the support frame 56. The U-hook 55c, which is the hook portion on the movable end side, engages with the engaged portion 57b of the bearing member 57. The direction of the biasing force of the tension coil spring 55 acting on the bearing member 57 is in the direction that brings the driven roller 51b closer to and presses against the drive roller 51a (i.e., downward in the figure).

[0110] Here, the tip of the U-hook 55c of the tension coil spring 55 is inserted into the space inside the coil portion 55a through the opening on the U-hook 55c side of the coil portion 55a, similar to the tension coil spring 32 of the first embodiment. The tip of the U-hook 55c also has a contact portion that can contact the inner surface of the coil portion 55a, and a non-contact portion that is bent away from the inner surface of the coil portion 55a on the tip side of the contact portion.

[0111] Next, the operation of the discharge roller pair 51 will be described. As shown in Figure 12(a), when the discharge roller pair 51 is in contact, the cam 58 is not pressing against the bearing member 57. Therefore, the bearing member 57 is in the lower position in the figure according to the biasing force of the tension coil spring 55, and the driven roller 51b is pressed against the drive roller 51a by the biasing force of the tension coil spring 55. In this contact state where the discharge roller pair 51 is in contact due to the biasing force of the tension coil spring 55, when the drive roller 51a is rotated, the discharge roller pair 51 grips and conveys the sheet or sheet bundle.

[0112] When the discharge roller pair 51 is separated, the cam 58 is rotationally driven, and as shown in Figure 12(b), the cam surface presses against the bearing member 57. As a result, the bearing member 57 rotates against the biasing force of the tension coil spring 55, and the discharge roller pair 51 enters a separated state in which the driven roller 51b is separated from the driving roller 51a.

[0113] When the discharge roller pair 51 is brought into contact, the cam 58 is driven to rotate again, and the cam surface retracts from the bearing member 57 as shown in Figure 12(a). As a result, the bearing member 57 rotates according to the biasing force of the tension coil spring 55, and the discharge roller pair 51 enters a contact state in which the driven roller 51b is in contact with the driving roller 51a.

[0114] As described above, since the tip of the U-hook 55c is inserted inside the coil portion 55a, deformation of the U-hook 55c starting from the switching portion (boundary) between the U-hook 55c and the coil portion 55a is restricted. In other words, even when a tensile load is applied to the tension coil spring 55, the U-hook 55c deforms in such a way that the distance W between the first extension portion and the second extension portion widens, and the contact portion of the U-hook 55c with the engaged portion 57b is restricted from changing.

[0115] Therefore, according to this embodiment, it is possible to reduce the deviation of the magnitude of the biasing force actually acting from the tension coil spring 55 to the bearing member 57 from the design value.

[0116] Furthermore, even if the tension coil spring 55 is repeatedly stretched and compressed, the amount of deformation of the U-hook itself is kept small, thus reducing the progression of metal fatigue in the switching section 55d. Therefore, even if the contact and separation operation of the discharge roller pair 51 is repeatedly performed over a long period of time, breakage of the switching section 55d becomes less likely, and the possibility of malfunction of the discharge roller pair 51 is reduced.

[0117] Thus, the pressing unit 57U as a spring biasing device according to this embodiment can generate a more stable biasing force.

[0118] Furthermore, the pressing unit 57U of this embodiment constitutes a mechanism for bringing the discharge roller pair 51 into contact with and separating from each other. Therefore, by using the pressing unit 57U of this embodiment, the contact pressure (nip pressure) of the discharge roller pair 51 can be stabilized over a long period of time. This reduces the possibility of sheet conveying failures due to fluctuations in the contact pressure of the discharge roller pair 51.

[0119] Furthermore, in this embodiment as well, a non-contact portion is provided at the tip of the U-hook 55c. This reduces the possibility of the wire edge getting caught on the coil portion 32a when the coil portion 55a expands and contracts, thereby reducing the possibility of deformation or malfunction of the tension coil spring 55 due to edge catching.

[0120] Furthermore, it is preferable that the length of the U-hook 55c be such that, when viewed in the direction of the rotation axis of the bearing member 57, the position of the coil portion 55a in the state in which the coil portion 32a is most extended due to the movement of the bearing member 57 does not overlap with the movement trajectory of the bearing member 57 during rotation. (See Figure 12(b).) In this embodiment, the state in which the coil portion 32a is most extended due to the movement of the bearing member 57 corresponds to the separated state of the discharge roller pair 51 (Figure 10(b)). By setting the U-hook 55c to the length described above, it is possible to save space in the pressing unit 57U without hindering the expansion and contraction of the tension coil spring 55.

[0121] Furthermore, it is preferable that the bearing member 57 and the U-hook 55c overlap when viewed along the rotation axis of the bearing member 57, and that the bearing member 57 and the coil portion 55a overlap when viewed along the central axis of the coil portion 55a. This arrangement makes it possible to save space in the pressing unit 30U.

[0122] (Other embodiments) In the embodiments described above, a U-shaped hook was explained as an example of the hook portion of a tension coil spring. The shape of the hook portion is not limited to this, and for example, a hook shape with two approximately right-angle bends at the connecting portion (square hook) or a hook shape with an elliptical connecting portion may also be used. Even when using these hook shapes, by inserting the tip of the hook portion inside the coil portion, the deformation of the hook portion starting from the boundary between the coil portion and the hook portion can be restricted, and a more stable biasing force can be obtained.

[0123] Furthermore, in the above-described embodiment, the force acting from the working part to the working part due to the biasing force of the tension coil spring acted in a direction that pressed one member (developing roller 24, driven roller 51b) against the other member (photosensitive drum 1, drive roller 51a). However, the configuration may be such that the force acting from the working part to the working part due to the biasing force of the tension coil spring acts in a direction that pulls one member away from the other member.

[0124] Furthermore, in the embodiments described above, a spring-type biasing device was exemplified as a mechanism that brings the developing roller 24 or the pair of discharge rollers 51 into contact with and separates them. However, the spring-type biasing device of this disclosure may also be used as a biasing mechanism for other movable members of an image forming apparatus.

[0125] For example, a mechanism is known that brings a transfer member (a primary transfer roller 12a and a secondary transfer roller 16 in the example of the first embodiment) into contact with and separates from an image carrier or an intermediate transfer body. If a transfer member in a stationary state is in contact with the mating member for a long period of time, deformation or deterioration may occur in the transfer member or the mating member, potentially leading to image defects. Therefore, the transfer member is separated from the mating member when not forming an image. The mechanism described in the above-described embodiment can be used as a mechanism for bringing the transfer member into contact with and separating it in this way.

[0126] In addition, the mechanism described in the above-described embodiment can be used as a mechanism for moving a flap-shaped guide member to switch the transport path of recording material inside the image forming apparatus. For example, the guide member 60 in Figure 11 can move between a position that guides the sheet discharged from the fixing device 14 toward the sheet processing device 202 (solid line) and a position that guides it toward the discharge roller pair 20 (dashed line).

[0127] Furthermore, the spring-type biasing device of this disclosure is not limited to image forming apparatuses, but can be used as a mechanism for mechanically biasing movable parts in general industrial products.

[0128] This disclosure includes at least the following configuration:

[0129] (Composition 1) A tension coil spring, A movable member having an acting portion that acts on the object to be acted upon, and an engaged portion that engages with the tension coil spring, wherein the acting portion is moved by the biasing force of the tension coil spring to act on the object to be acted upon, An image forming apparatus having, The tension coil spring has a coil portion in which a wire is wound in a spiral shape, and a hook portion that protrudes from the coil portion in a first direction along the central axis of the coil portion. The hook portion has a first extension portion from which the wire extends in the first direction from the end of the coil portion, a second extension portion from which the wire extends in the second direction opposite to the first direction, and a connecting portion that connects the first extension portion and the second extension portion and engages with the engaged portion. The tip of the second extension in the second direction is inserted into the inside of the coil portion through the opening on the first direction side of the coil portion. An image forming apparatus characterized by the following:

[0130] (Configuration 2) The second extension portion has a contact portion that contacts the inner surface of the coil portion when the tension coil spring is in its most extended state when the moving member moves within the range of movement of the moving member. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus.

[0131] (Composition 3) The second extension portion is a non-contact portion provided on the tip side of the second extension portion in the second direction compared to the contact portion, and further comprises a non-contact portion that is bent relative to the contact portion so as it approaches the tip of the second extension portion, it moves further away from the inner surface of the coil portion. The image forming apparatus according to configuration 2, characterized in that...

[0132] (Composition 4) The contact portion is in contact with the inner surface of the coil portion when the tension coil spring is not subjected to a tensile load. The image forming apparatus according to configuration 2 or 3, characterized by the above.

[0133] (Composition 5) The contact portion has a gap between it and the inner surface of the coil portion when the tension coil spring is not subjected to a tensile load. The image forming apparatus according to configuration 2 or 3, characterized by the above.

[0134] (Composition 6) When viewed in the direction along the central axis, the contact portion is located on the opposite side of the central axis from the boundary between the coil portion and the first extension portion. An image forming apparatus according to any one of configurations 2 to 5, characterized by the above.

[0135] (Composition 7) The moving member is a member that can rotate about a rotation axis in a direction intersecting the central axis. An image forming apparatus according to any one of configurations 1 to 6 characterized by the above.

[0136] (Composition 8) When viewed in the direction along the pivot axis of the moving member, the length of the hook portion in the direction along the central axis is set such that the position of the coil portion when the tension coil spring is most extended when the moving member moves within the range of motion of the moving member does not coincide with the movement trajectory of the moving member. The image forming apparatus according to configuration 7, characterized by the features described above.

[0137] (Composition 9) When viewed in the direction along the rotation axis of the moving member, the moving member and the hook portion overlap. When viewed in the direction along the central axis of the coil portion, the moving member and the coil portion overlap. The image forming apparatus according to configuration 7 or 8, characterized by the above.

[0138] (Composition 10) With respect to the circumferential direction of a virtual circle centered on the rotation axis, the position of the working part and the position of the engaged part are different. The direction of the force acting from the acting part to the acted part is perpendicular to the direction of the biasing force received by the acting part from the tension coil spring. An image forming apparatus according to any one of configurations 7 to 9, characterized by the features described herein.

[0139] (Composition 11) The system further includes a support member that rotatably supports the aforementioned movable member, The support member has a hole formed in it that penetrates the support member in a direction along the rotation axis and extends in an arc direction centered on the rotation axis of the moving member. The acting portion protrudes through the hole toward the side opposite to the side on which the tension coil spring is positioned relative to the support member. An image forming apparatus according to any one of configurations 7 to 10, characterized by the above.

[0140] (Composition 12) A cam that rotates with the driving force of the drive source, A slider positioned opposite the support member in a direction along the rotation axis, the slider slides relative to the support member in conjunction with the rotation of the cam, so as to move the moving member against the biasing force of the tension coil spring, It further possesses, The tension coil spring is positioned in the space between the support member and the slider in a direction along the rotation axis. The image forming apparatus according to configuration 11, characterized by the features described above.

[0141] (Composition 13) The connecting portion is formed to connect the end of the first extension portion in the first direction and the end of the second extension portion in the second direction in a semicircular manner. An image forming apparatus according to any one of configurations 1 to 12, characterized by the above.

[0142] (Composition 14) A rotatable cylindrical rotating member, A first pressing unit is provided at one end of the rotating member in the longitudinal direction of the rotating member, which presses the part to be acted upon in order to bring the rotating member into contact with another member. A second pressing unit is provided at the other end of the rotating member in the longitudinal direction, which presses the part to be acted upon in order to bring the rotating member into contact with the other member. Furthermore, Each of the first pressing unit and the second pressing unit has the moving member and the tension coil spring, An image forming apparatus according to any one of configurations 1 to 13, characterized by the above.

[0143] (Composition 15) Image carrier and, A developing unit comprising: a developer carrier that carries a developer and rotates to develop a developer image on the image carrier; a frame that rotatably supports the developer carrier, and a developing unit that is movable between a contact position where the developer carrier abuts the image carrier and a separated position where the developer carrier is separated from the image carrier, Furthermore, The moving member moves the developing unit from the separated position to the contact position by pressing the actuated portion provided on the frame of the developing unit with the actuated portion. An image forming apparatus according to any one of configurations 1 to 13, characterized by the above.

[0144] (Composition 16) When the developing unit is in the contact position, the biasing force of the tension coil spring generates contact pressure between the developer carrier and the image carrier. The image forming apparatus according to configuration 15, characterized in that...

[0145] (Composition 17) A first pressing unit that presses the part to be worked on at one end of the developer carrier in the longitudinal direction of the developer carrier, A second pressing unit that presses the part to be worked on with the other end of the developer carrier in the longitudinal direction, Furthermore, Each of the first pressing unit and the second pressing unit has the moving member and the tension coil spring, The image forming apparatus according to configuration 15 or 16, characterized by the above.

[0146] (Composition 18) First Laura and, A second roller, which grips and transports the recording material together with the first roller, A roller support member that rotatably supports the second roller and moves the second roller between a contact position in which the second roller abuts the first roller and a separation position in which the second roller is separated from the first roller, Furthermore, The moving member moves the second roller from the separated position to the contact position by pressing the acted-on portion provided on the roller support member with the actuating portion. An image forming apparatus according to any one of configurations 1 to 13, characterized by the above.

[0147] (Composition 19) A tension coil spring, A movable member having an acting portion that acts on the object to be acted upon, and an engaged portion that engages with the tension coil spring, wherein the acting portion is moved by the biasing force of the tension coil spring to act on the object to be acted upon, A spring-type biasing device having, The tension coil spring has a coil portion in which a wire is wound in a spiral shape, and a hook portion that protrudes from the coil portion in a first direction along the central axis of the coil portion. The hook portion has a first extension portion from which the wire extends in the first direction from the end of the coil portion, a second extension portion from which the wire extends in the second direction opposite to the first direction, and a connecting portion that connects the first extension portion and the second extension portion and engages with the engaged portion. The tip of the second extension in the second direction is inserted into the inside of the coil portion through the opening on the first direction side of the coil portion. A spring-type biasing device characterized by the following features. [Explanation of Symbols]

[0148] 30, 57…Moving member (pressing member, bearing member) / 30a, 57a…Acting part (pressing part, bearing part) / 31…Actuated part (pressed part) / 32, 55…Tension coil spring / 32a, 55a…Coil part / 32c, 55c…Hook part (U-hook) / 32c1…First extension part / 32c2…Connecting part / 32c3…Second extension part / 32c4…Tip part / 32e…Contact part / 32f…Non-contact part

Claims

1. A tension coil spring, A movable member having an acting portion that acts on the object to be acted upon, and an engaged portion that engages with the tension coil spring, wherein the acting portion is moved by the biasing force of the tension coil spring to act on the object to be acted upon, An image forming apparatus having, The tension coil spring has a coil portion in which a wire is wound in a spiral shape, and a hook portion that protrudes from the coil portion in a first direction along the central axis of the coil portion. The hook portion has a first extension portion from which the wire extends in a first direction from the end of the coil portion, a second extension portion from which the wire extends in a second direction opposite to the first direction, and a connecting portion that connects the first extension portion and the second extension portion and engages with the engaged portion. The tip of the second extension in the second direction is inserted into the inside of the coil portion through the opening on the first direction side of the coil portion. The moving member is rotatable about a pivot axis that extends in a direction intersecting the central axis of the coil portion. The length of the hook portion in the direction along the central axis is the distance from the boundary between the coil portion and the first extension portion to the point of application where the connecting portion engages with the engaged portion. The length of the hook portion is set such that, when viewed in the direction along the pivot axis of the moving member, the position of the coil portion when the tension coil spring is most extended within the range of movement of the moving member does not overlap with the movement trajectory of the moving member. An image forming apparatus characterized by the following features.

2. The second extension portion has a contact portion that contacts the inner surface of the coil portion when the tension coil spring is in its most extended state when the moving member moves within the range of movement of the moving member. The image forming apparatus according to feature 1.

3. The second extension portion is a non-contact portion provided on the tip side of the second extension portion in the second direction compared to the contact portion, and further comprises a non-contact portion that is bent relative to the contact portion so as it approaches the tip of the second extension portion, it moves further away from the inner surface of the coil portion. The image forming apparatus according to feature 2.

4. The contact portion is in contact with the inner surface of the coil portion when the tension coil spring is not subjected to a tensile load. The image forming apparatus according to feature 2.

5. The contact portion has a gap between it and the inner surface of the coil portion when the tension coil spring is not subjected to a tensile load. The image forming apparatus according to feature 2.

6. When viewed in the direction along the central axis, the contact portion is located on the opposite side of the central axis from the boundary between the coil portion and the first extension portion. The image forming apparatus according to feature 2.

7. When viewed in the direction along the rotation axis of the moving member, the moving member and the hook portion overlap. When viewed in the direction along the central axis of the coil portion, the moving member and the coil portion overlap. The image forming apparatus according to feature 1.

8. When the tension coil spring is in the most extended state, the point of action is located on the opposite side of the coil portion from the rotation axis with respect to the direction along the central axis of the coil portion, The image forming apparatus according to feature 1.

9. The position of the acting part and the position of the engaged part are different with respect to the circumferential direction of a virtual circle centered on the rotation axis, and the acting part is configured to press the engaged part in a direction intersecting the direction of the biasing force received by the engaged part from the tension coil spring, When the acting part presses against the acted part, the tension coil spring is contracted more than in its most extended state. When viewed in the direction along the rotation axis of the moving member, when the acting part presses against the acted part, the rotation axis and the acting part are aligned in the direction along the central axis, and the rotation axis and the acted part are aligned in the direction perpendicular to the central axis. The image forming apparatus according to feature 8.

10. When the acting part presses the acted part, the direction of the force acting from the acting part to the acted part is perpendicular to the direction of the biasing force received by the engaged part from the tension coil spring. The image forming apparatus according to feature 9.

11. The system further includes a support member that rotatably supports the aforementioned movable member, The support member has a hole formed in it that penetrates the support member in a direction along the rotation axis and extends in an arc direction centered on the rotation axis of the moving member. The acting portion protrudes through the hole toward the side opposite to the side on which the tension coil spring is positioned relative to the support member. The image forming apparatus according to feature 1.

12. A cam that rotates with the driving force of the drive source, A slider positioned opposite the support member in a direction along the rotation axis, the slider slides relative to the support member in conjunction with the rotation of the cam, so as to move the moving member against the biasing force of the tension coil spring, It further possesses, The tension coil spring is positioned in the space between the support member and the slider in a direction along the rotation axis. The image forming apparatus according to feature 11.

13. The connecting portion is formed to connect the end of the first extension portion in the first direction and the end of the second extension portion in the second direction in a semicircular manner. The image forming apparatus according to feature 1.

14. A rotatable cylindrical rotating member, A first pressing unit is provided at one end of the rotating member in the longitudinal direction of the rotating member, which presses the part to be acted upon in order to bring the rotating member into contact with another member. A second pressing unit is provided at the other end of the rotating member in the longitudinal direction, which presses the part to be acted upon in order to bring the rotating member into contact with the other member. Furthermore, Each of the first pressing unit and the second pressing unit has the moving member and the tension coil spring, The image forming apparatus according to any one of claims 1 to 13.

15. Image carrier and, A developing unit comprising: a developer carrier that carries a developer and rotates to develop a developer image on the image carrier; a frame that rotatably supports the developer carrier, and a developing unit that is movable between a contact position where the developer carrier abuts the image carrier and a separated position where the developer carrier is separated from the image carrier, Furthermore, The moving member moves the developing unit from the separated position to the contact position by pressing the actuated portion provided on the frame of the developing unit with the actuated portion. The image forming apparatus according to any one of claims 1 to 13.

16. When the developing unit is in the contact position, the biasing force of the tension coil spring generates contact pressure between the developer carrier and the image carrier. The image forming apparatus according to feature 15.

17. A first pressing unit that presses the part to be worked on at one end of the developer carrier in the longitudinal direction of the developer carrier, A second pressing unit presses the part to be worked on at the other end of the developer carrier in the longitudinal direction, Furthermore, Each of the first pressing unit and the second pressing unit has the moving member and the tension coil spring, The image forming apparatus according to feature 15.

18. First Laura and, A second roller, which grips and transports the recording material together with the first roller, A roller support member that rotatably supports the second roller and moves the second roller between a contact position in which the second roller contacts the first roller and a separation position in which the second roller is separated from the first roller, Furthermore, The moving member moves the second roller from the separated position to the contact position by pressing the acted-on portion provided on the roller support member with the actuating portion. The image forming apparatus according to any one of claims 1 to 13.

19. A tension coil spring, A movable member having an acting portion that acts on the object to be acted upon, and an engaged portion that engages with the tension coil spring, wherein the acting portion is moved by the biasing force of the tension coil spring to act on the object to be acted upon, A spring-type biasing device having, The tension coil spring has a coil portion in which a wire is wound in a spiral shape, and a hook portion that protrudes from the coil portion in a first direction along the central axis of the coil portion. The hook portion has a first extension portion from which the wire extends in a first direction from the end of the coil portion, a second extension portion from which the wire extends in a second direction opposite to the first direction, and a connecting portion that connects the first extension portion and the second extension portion and engages with the engaged portion. The tip of the second extension in the second direction is inserted into the inside of the coil portion through the opening on the first direction side of the coil portion. The moving member is rotatable about a pivot axis that extends in a direction intersecting the central axis of the coil portion. The length of the hook portion in the direction along the central axis is the distance from the boundary between the coil portion and the first extension portion to the point of application where the connecting portion engages with the engaged portion. The length of the hook portion is set such that, when viewed in the direction along the pivot axis of the moving member, the position of the coil portion when the tension coil spring is most extended within the range of movement of the moving member does not overlap with the movement trajectory of the moving member. A spring-type biasing device characterized by the following features.

Images