Image forming apparatus

Radius increased areas, radius decreased areas, and rotation stop areas are arranged in peripheral surfaces of first and second cams. In a state in which a portion in the peripheral surface of the first cam to which the first cam follower is contacting is positioned at an upstream end portion of the radius increased area, θ1 is a rotation amount of the first cam from the end portion needed until the first cam follower contacts the rotation stop area, and in a state in which a portion in the peripheral surface of the second cam to which the second cam follower is contacting is positioned at an upstream end portion of the radius increased area, θ2 is a rotation amount of the second cam from the end portion needed until the second cam follower contacts the rotation stop area. θ1<θ2 is satisfied.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to an electrophotographic system image forming apparatus, such as an electrophotographic copying machine, an electrophotographic printer (an LED printer, a laser printer, etc.), a facsimile machine, or a word processor.

Description of the Related Art

In an electrophotographic system image forming apparatus, there is a contact developing system in which development is performed during an image-forming period by having a photosensitive drum and a development roller contact each other. From the viewpoint of stabilizing image quality and increasing lives of the photosensitive drum and the development roller, it is desirable that, in the contact developing system, the photosensitive drum and the development roller be separated from each other during a non-image-forming period.

A patent literature, International Publication No. WO2016/157285, discloses a configuration in which an apparatus main body includes cams provided in vicinities of two end portions of a development roller in an axial direction, in which the development roller is pressed against a photosensitive drum and is separated from the photosensitive drum by way of rotational movements of the cams. In the apparatus in the patent literature, the cams are fixed to a shaft rotatably provided on a frame member. Furthermore, by driving a gear provided on one end of the shaft and by rotational movement of the shaft and the cams in an integral manner, cam followers engaged with a frame that supports the development roller are moved to perform the pressing and separation of the development roller. Furthermore, by stopping and maintaining the cams at predetermined stop positions, the development roller can be positioned while being pressed against or separated from the photosensitive drum.

However, when the development roller is pressed against or separated from the photosensitive drum, since loads are, through cam followers, applied to the two cams disposed in the vicinities of the two end portions of the cam shaft in the axial direction, the cam shaft becomes elastically deformed and twisted. Particularly, due to the twisting, the rotation of the cam that is farther away from a drive portion and that has a long driving force transmission path becomes delayed relative to the rotation of the cam that is near the drive portion and that has a short driving force transmission path. As a result, a concern that the cam with the long driving force transmission path cannot reach the stop position is encountered.

Furthermore, the cams are abutted against rotation restricting portions provided in the cam followers or the like to stop the cams at predetermined stop positions. After the cam shaft is twisted and elastically deformed with the loads, when the elastic deformation is released, the speed of the cam increases. Accordingly, when the cam, the speed of which has been increased, abuts against the rotation restricting portion, sound of the cam impinging against the rotation restricting portion may become increased when the cam is stopped at the desired stop position.

SUMMARY OF THE INVENTION

The present disclosure provides an image forming apparatus capable of, in a case in which a rotation of a first cam between two cams becomes delayed relative to a rotation of a second cam, preventing a first cam from not reaching a stop position, and/or preventing a cam from coming into contact with a rotation restricting portion in a state in which the speed of the cam is high.

The present disclosure is an image forming apparatus that forms an image on a recording material, the image forming apparatus including a drive source, a first cam that comes in contact with a first cam follower, the first cam moving the first cam follower by being rotated by driving force transmitted thereto from the drive source, and a second cam that comes in contact with a second cam follower, the second cam moving the second cam follower by being rotated by driving force transmitted thereto from the drive source. In the image forming apparatus, peripheral surfaces of the first and second cams each include, a radius increased area in which a distance between a portion to which a relevant one of the first and second cam follower comes in contact and a rotation center of a relevant one of the first and second cam becomes larger as a relevant one of the first or second cam rotates, a radius decreased area in which a distance between a portion to which a relevant cam follower comes in contact and the rotation center of a relevant one of the first and second cam becomes smaller as a relevant one of the first or second cam rotates, and a rotation stop area that is capable of stopping a relevant one of the first and second cam by coming into contact with a relevant cam follower, in which the radius increased area, the radius decreased area, and the rotation stop area are arranged on the peripheral surface of the first or second cam so as to be aligned in that order from a downstream side towards an upstream side in a rotation direction of the first or second cam, in which a second driving force transmission path through which the driving force is transmitted from the drive source to the second cam is longer than a first driving force transmission path through which the driving force is transmitted from the drive source to the first cam, and in which θ1<θ2 is satisfied, where in a state in which a portion in the peripheral surface of the first cam to which the first cam follower is in contact is positioned at an end portion of the radius increased area on an upstream side in the rotation direction, when the end portion is a starting point, a rotation amount of the first cam needed until the first cam follower comes in contact with the rotation stop area is θ1, and in a state in which a portion in the peripheral surface of the second cam to which the second cam follower is in contact is positioned at an end portion of the radius increased area on an upstream side in the rotation direction, when the end portion is a starting point, a rotation amount of the second cam needed until the second cam follower comes in contact with the rotation stop area is θ2.

Further features and aspects of the disclosure will become apparent from the following description of numerous example embodiments with reference to the attached drawings.

DESCRIPTION OF THE EMBODIMENTS

First Example Embodiment

Referring first toFIG. 1, an overall configuration of the present example embodiment will be described.FIG. 1is a cross-sectional view of an image forming apparatus1inside of which a process cartridge50is mounted. On the basis of image information received from an external device such as a personal computer, the image forming apparatus1forms an image on a recording material P (recording paper, an OHP sheet, or fabric, for example) with developer through an electrophotographic image forming process.FIG. 1illustrates a state in which the process cartridge50including a drum cartridge60and a developing cartridge70is mounted in an apparatus main body1A.

Configuration of Example Image Forming Apparatus

A structure of the image forming apparatus1will be described with reference toFIG. 1. By rotating a photosensitive drum (a photosensitive member)2in an arrow A direction, a surface of the photosensitive drum2is uniformly charged with a charge roller3serving as a charging device. The photosensitive drum2is irradiated with a laser beam L from an optical member (an exposing device)4in accordance with image information so that an electrostatic latent image according to the image information is formed on the photosensitive drum2. A toner image (a developer image) is formed by supplying (developing) toner (developer) t carried on a development roller71, serving as a developer bearing member, to the electrostatic latent image on the photosensitive drum2.

Meanwhile, synchronizing with the formation of the toner image, the recording materials P set on a feeding cassette6is separated and fed sheet by sheet with a pickup roller7and a pressure contact member9that is in pressure contact therewith. Furthermore, the recording material P is conveyed along a conveyance guide8to a transfer roller10serving as a transfer device. Subsequently, the recording material P passes through a transfer nip portion15formed between the photosensitive drum2and the transfer roller10to which a specific voltage is applied. In the above process, the toner image formed on the photosensitive drum2is transferred onto the recording material P. The recording material P to which the toner image has been transferred is conveyed towards a fixing device12with a conveyance guide11. The fixing device12includes a driving roller12a, and a fixing roller12cbuilt in with a heater12b. Heat and pressure are applied to the recording material P passing through a fixing nip portion16formed between the fixing roller12cand the driving roller12ato fix the transferred toner image to the recording material P. Subsequently, the recording material P is conveyed with a pair of discharge rollers13and is discharged to a discharge tray14.

Configuration of Process Cartridge

Referring next toFIGS. 2 and 3, the process cartridge50, which is detachably attachable to the apparatus main body1A of the image forming apparatus1of the present example embodiment, will be described.FIG. 2is a cross-sectional view illustrating a configuration of the process cartridge50.

As illustrated inFIG. 2, the process cartridge50includes the drum cartridge60including the photosensitive drum2, the charge roller3, and a cleaning blade61, and the development cartridge70including the development roller71. The drum cartridge60and the developing cartridge70are each separately detachably attachable to the apparatus main body1A.

FIG. 3illustrates a perspective view of the process cartridge50. The photosensitive drum2is attached in a rotatable manner to a cleaning frame62of the drum cartridge60through a drive-side drum bearing63and a nondrive-side drum bearing64. A drive input portion2aprovided in a longitudinally drive-side end portion of the photosensitive drum2engages with a drive output portion (not shown) of the apparatus main body1A, and receives driving force of a drive source (not shown) to the apparatus main body1A. With the above, the photosensitive drum2is rotationally driven in the arrow A direction in accordance with the image forming operation. Note that in the present example embodiment, the drive input portion2ahas a shape of a triangular prism twisted slightly; however, the shape thereof is not limited to such a shape.

A development frame member (a developing frame)72of the developing cartridge70includes a drive-side development-roller bearing73and a nondrive-side development-roller bearing74. The development roller71is rotationally supported by the drive-side development-roller bearing73and the nondrive-side development-roller bearing74. A pressed member75is attached to each of the drive-side development-roller bearing73and the nondrive-side development-roller bearing74. Furthermore, pressurizing springs76that bias the pressed members75are each provided between the drive-side development-roller bearing73and the pressed member75and between the nondrive-side development-roller bearing74and the pressed member75.

Configuration of Guiding Device of Process Cartridge

Referring next toFIG. 4, a configuration of a guiding device used when attaching and detaching the process cartridge50to and from the apparatus main body1A will be described. Note thatFIG. 4is a side view of the process cartridge50and a cartridge guide20in a state in which the process cartridge50is mounted in the apparatus main body1A. The cartridge guides20that are guiding devices that guide the process cartridge50are provided in the apparatus main body1A so as to oppose each other at the drive side and the nondrive side. WhileFIG. 4illustrates the drive-side cartridge guide20, since the cartridge guides20are provided so as to have similar configurations on the drive side and the nondrive side in a symmetrical manner, detailed description of the nondrive-side cartridge guide20will be omitted.

As described above, the process cartridge50includes the drum cartridge60and the developing cartridge70. As illustrated inFIG. 4, the cartridge guides20that serve as guiding devices when the process cartridge50is mounted inside the apparatus main body1A are provided in the apparatus main body1A. The cartridge guides20are provided inside the apparatus main body1A on the drive side and on the nondrive side. Moreover, the cartridge guides20are each divided into a fixed guide21and a movable guide22. The fixed guides21are fixed inside the apparatus main body1A and serve as guiding devices when the drum cartridge60is mounted inside the apparatus main body1A. The movable guide22are supported by the fixed guides21in a rotatable manner about a rotational axis X and serve as guiding devices when the developing cartridge70is mounted inside the apparatus main body1A.

Furthermore, as illustrated inFIG. 4, a guide spring23is provided between the fixed guide21and the movable guide22of each cartridge guide20. The guide springs23biases the fixed guides21to the movable guides22. The developing cartridge70and the movable guides22are pivoted about the rotational axis X in a photosensitive drum direction Y1with the guide springs23so as to be biased against the photosensitive drum2. Accordingly, when in a state in which the drum cartridge60is mounted in the fixed guide21and the developing cartridge70is mounted in the movable guide22, the development frame member72is rotatable relative to the photosensitive drum2. Furthermore, in a state in which the developing cartridge70is not mounted as well, the movable guides22are pivoted about the rotational axis X in the photosensitive drum direction Y1and is biased by the guide springs23.

Abutting and Separating Configuration of Process Cartridge

An abutting and separating configuration of the photosensitive drum2and the development roller71of the process cartridge50will be described next. In the image forming apparatus1, the photosensitive drum2and the development roller71are abutted against each other only when an image is formed on the recording material P and other than that, the photosensitive drum2and the development roller71are separated from each other. A configuration changing the position of the development roller71with respect to the photosensitive drum2to perform an abutment and separation operation is illustrated inFIGS. 5A and 5B.FIG. 5Aillustrates a state in which the drum cartridge60is mounted in the fixed guide21, and the developing cartridge70is mounted in the movable guide22.FIG. 5Ais a perspective view illustrating a separated state of the process cartridge50in the abutting and separating configuration, andFIG. 5Bis a diagram of the separated state of the process cartridge50in the abutting and separating configuration viewed in a rotational axis direction of the cam shaft30from the drive side towards the nondrive side.

As illustrated inFIG. 5A, the cam shaft (shaft)30is rotationally provided in the apparatus main body1A, and a gear32is attached to a gear engagement portion30aat a first end portion of the cam shaft30. For the sake of description, in the rotational axis direction of the cam shaft30, a first end side is referred to as a drive side (DS), and a second end side is referred to as a nondrive side (NS). The rotational axis direction of the cam shaft30is parallel to a rotational axis of the development roller71of the developing cartridge70mounted in the apparatus main body1A and to a rotational axis of the photosensitive drum2of the drum cartridge60mounted in the apparatus main body1A.

The gear engagement portion30aof the cam shaft30is the drive input portion that is where driving force transmitted from a motor M (described later, seeFIG. 5B) is input to the cam shaft30through the gear32. A DS cam (a first cam)31aand an NS cam (a second cam)31bare fixed to the cam shaft30at positions that correspond to the two pressed members75attached to the two end portions of the developing cartridge70. In the rotational axis direction of the cam shaft30, the NS cam31bis disposed at a position that is farther away from the gear engagement portion30athan the DS cam31a. Note that the DS cam31aand the NS cam31bwill be referred to as cams31aand31bwhen referred collectively.

Furthermore, a DS slider (a first cam follower)33aand an NS slider (a second cam follower)33bare provided in the apparatus main body1A at positions corresponding to the two pressed members75so as to be movable in a parallel manner in a B1direction. Note that the DS slider33aand the NS slider33bare referred to as sliders31aand31bwhen referred collectively. The two pressed members75of the developing cartridge70mounted in the apparatus main body1A are engaged to recesses38aand38bof the DS slider33aand the NS slider33b, and the abutment and separation operation of the developing cartridge70can be performed by moving the sliders33aand33bhorizontally. Furthermore, the DS slider33aand the NS slider33binterlocking with the rotational movements of the DS cam31aand the NS cam31bin an arrow C1direction move parallelly in the B1direction.

Shapes (profiles of cam surfaces) of the cams31aand31bwill be described next.FIG. 9Ais a diagram of the DS cam31aviewed in a direction of a rotational axis R of the cam shaft30, andFIG. 9Bis a diagram of the NS cam31bviewed in a rotational axis R direction of the cam shaft30.FIG. 10is a diagram illustrating the DS cam31aand the NS cam31bin an overlapped state in the rotational axis R direction of the cam shaft30. For the sake of description, the DS cam31ais illustrated by a broken line and the NS cam31bis illustrated by a solid line.

A peripheral surface of the DS cam31aincludes an area that comes into contact with the DS slider33a. The area that comes into contact with the DS slider33aincludes a radius increased area a3, a radius decreased area a2, and a rotation stop area a1, which are arranged side by side in the above order from the downstream side towards the upstream side in a C1direction in which the DS cam31arotates. A peripheral surface of the NS cam31bincludes an area that comes into contact with the NS slider33b. The area that comes into contact with the NS slider33bincludes a radius increased area b3, a radius uniform area b4, a radius decreased area b2, and a rotation stop area b1, which are arranged side by side in the above order from the downstream side towards the upstream side in a C1direction in which the NS cam31brotates. The cams31aand31brotate in the C1direction with the rotation of the cam shaft30. Accordingly, contact points CPa and CPb that are portions in the peripheral surfaces of the cams31aand31b, with which the sliders33aand33bcome into contact, move along the peripheral surfaces of the cams31aand31bin a direction opposite to the C1direction when the cams31aand31brotate in the C1direction.FIGS. 9A and 9Billustrate, as examples of the contact points CPa and CPb, states in which the contact points CPa and CPb are situated in the radius increased areas a3and b3.

The radius increased areas a3and b3are areas in which the distances (radii to the cam surfaces) between the contact points CPa and CPb and the rotational axis (a rotation center) R increase as the cams31aand31brotate in the C1direction. When the contact points CPa and CPb are in the radius increased areas a3and b3, the sliders33aand33bare biased towards the cams31aand31b. Accordingly, the radius increased areas a3and b3receive, from the sliders33aand33b, force (loads) that rotates the cams31aand31bin a direction opposite to a rotation direction C1.

The radius decreased areas a2and b2are areas in which the distances (the radii to the cam surfaces) between the contact points CPa and CPb and the rotational axis (the rotation center) R decrease as the cams31aand31brotate in the C1direction. When the contact points CPa and CPb are in the radius decreased area a2and b2, since the sliders33aand33bare biased towards the cams31aand31b, the radius decreased area a2and b2receive, from the sliders33aand33b, force that rotates the cams31aand31bin the rotation direction C1.

The rotation stop areas a1and b1are areas that stop the rotations of the cams31aand31b. By having the sliders33aand33b, which are biased towards the cams31aand31b, contact both the radius decreased areas a2and b2and the rotation stop areas a1and b1, the rotations of the cams31aand31brelative to the sliders33aand33bin the C1direction and the direction opposite to the C1direction are restricted. The above state is a state in which the cams31aand31bare at home positions (stop positions), and is a state in which the contact points CPa and CPb are situated in the rotation stop areas a1and b1and in the radius decreased areas a2and b2, and the cams31aand31band the sliders33aand33bengage with each other. The radius uniform area b4is an area that is provided on the peripheral surface of the NS cam31band between the radius increased area b3and the radius decreased area b2in the rotation direction C1. The radius uniform area b4is an area in which the distance (the radius to the cam surface) between a contact point CPb and the rotational axis (the rotation center) R is practically uniform (does not change) with the rotation of the NS cam31bin the C1direction.

As illustrated inFIG. 10, in a state (a natural state) in which the cam shaft30is not twisted, the DS cam31aand the NS cam31bare fixed to the cam shaft30so that the rotation stop area a1and the rotation stop area b1are in the same phase in the rotation direction C1. Accordingly, in the natural state, the radius increased area b3of the NS cam31bis disposed downstream of the radius increased area a3of the DS cam31ain the rotation direction C1in proportion to the length of the radius uniform area b4.

Furthermore, in a state in which a contact point CPa to which the DS slider33ais in contact is positioned at an upstream end portion (a boundary point between the radius increased area a3and the radius decreased area a2) Pa1of the radius increased area a3in the direction C1(the rotation direction), when the end portion is a starting point, θ1 is a rotation amount of the DS cam31aneeded for the slider33ato contact the rotation stop area a1. In the present example embodiment, θ1 is an angle formed between a line segment ra1connecting the boundary point Pa1between the radius increased area a3and the radius decreased area a2and the rotational axis R, and a line segment ra2connecting a boundary point Pa2between the radius decreased area a2and the rotation stop area a1and the rotational axis R.

In a state in which a contact point CPb to which the NS slider33bis in contact is positioned at an upstream end portion Pb1(a boundary point between the radius increased area b3and the radius uniform area b4) of the radius increased area b3in the direction C1(the rotation direction), when the boundary point is a starting point, θ2 is a rotation amount of the NS cam31bneeded for the slider33bto contact the rotation stop area b1. In the present example embodiment, θ2 is an angle formed between a line segment rb1connecting the boundary point Pb1between the radius increased area b3and the radius uniform area b4and the rotational axis R, and a line segment rb2connecting a boundary point Pb2between the radius decreased area b2and the rotation stop area b1and the rotational axis R. Furthermore, the rotation amount θ2 is larger than the rotation amount θ1 (θ1<θ2).

Referring next toFIG. 5B, a drive structure of the cam shaft30to which the cams31aand31bare fixed will be described. The drive structure of the cam shaft30includes the gear32attached to the cam shaft30, a partially-toothless gear35that transmits driving force to the gear32, and a driving gear36that receives driving force from the motor M serving as a drive source and that transmits the driving force to the partially-toothless gear35. The partially-toothless gear35is a two-step gear including a gear portion that meshes with the driving gear and a gear portion that meshes with the gear32. When the partially-toothless gear35rotates a single turn, the gear32rotates half a turn. In other words, the gear ratio between the partially-toothless gear35and the gear32is 1:2. Furthermore, the partially-toothless gear35and the apparatus main body1A are connected to each other through a partially-toothless gear spring37. A solenoid34provided on the apparatus main body1A engages with the partially-toothless gear35. When the solenoid34is operated, the partially-toothless gear35is meshed with the driving gear36with the partially-toothless gear spring37and is rotated one turn so that the gear32and the cam shaft30rotate half a turn in an integral manner.

When the cams31aand31bare in separated positions, the sliders33aand33bare in separated positions, and the development roller71is separated from the photosensitive drum2. When the cams31aand31bare in contact positions, the sliders33aand33bare in contact positions, and the development roller71is abutted against the photosensitive drum2and is urged against the photosensitive drum2at a desired pressure. When the cams31aand31bare in the separated positions and in the contact positions, the toothless portion of the partially-toothless gear35opposes the driving gear36, and the partially-toothless gear35is not meshed with the driving gear36. Accordingly, a state in which there is no drive transmitted between the partially-toothless gear35and the driving gear36is obtained (a state in which the drive is off is obtained). The above state is a state in which the cams31aand31bare in the home positions. In such a case, as described above, the cams31aand31breceiving force from the sliders33aand33bare positioned so that the contact points CPa and CPb are situated in the rotation stop areas a1and b1and the radius decreased areas a2and b2, and so that the tips of the teeth of the partially-toothless gear35and those of the driving gear36do not contact each other.

Driving force is transmitted to both the cams31aand31bfrom a drive source M through a driving force transmission path including the driving gear36, the partially-toothless gear35, the gear32, and the cam shaft30. However, in the cam shaft30, a portion between the gear32and the NS cam31bis longer than a portion between the gear32and the DS cam31a. Accordingly, the driving force transmission path from the gear32to the NS cam31bis longer than the driving force transmission path from the gear32to the DS cam31a. Due to the above difference in length between the driving force transmission paths, the driving force transmission path from the motor M to the NS cam31bis longer than the driving force transmission path from the motor M to the DS cam31a.

Abutment and Separation Operation of Process Cartridge

An abutment and separation operation of the photosensitive drum2and the development roller71of the process cartridge50will be described with reference toFIGS. 6A and 6B.FIG. 6Aillustrates a contact state of the process cartridge50.FIG. 6Billustrates a separated state of the process cartridge50and is a diagram of a can shaft30viewed in the rotational axis direction.

As illustrated inFIG. 6B, first, the image forming apparatus1is stopped in a state in which the photosensitive drum2and the development roller71are separated from each other. Subsequently, when a print start signal is input to the apparatus main body1A, the solenoid34illustrated inFIG. 5Bis operated, the partially-toothless gear35is meshed with the driving gear36with the partially-toothless gear spring37, and the cam shaft30integral with the gear32, and the cams31aand31brotate in the C1direction. When the cams31aand31brotate in the C1direction, the sliders33aand33binterlocked with the cams31aand31bmove in an arrow B1direction. Subsequently, the sliders33aand33bbias the pressed members75supported by the developing cartridge70, and the biasing force is transmitted to the developing cartridge70through the pressurizing springs76. By so doing, the developing cartridge70having received the biasing force pivots in a Y1direction together with the movable guides22about the movable guide rotational axis X to abut the development roller71and the photosensitive drum2against each other. When the cams31aand31brotate half a turn in the C1direction and stop, the contact state of the process cartridge50illustrated inFIG. 6Ais reached which allows a toner image to be formed on the photosensitive drum2. In the above, the cams31aand31bstop at the contact position.

Subsequently, after the transfer of an image to the recording material P is completed, a print end signal is input to the apparatus main body1A, the solenoid34illustrated inFIG. 5Bis operated, and the partially-toothless gear35is meshed with the driving gear36with the partially-toothless gear spring37. Subsequently, the cam shaft30integral with the gear32and the cams31aand31brotate half a turn (turn 180°) in the C1direction illustrated inFIG. 6A. When the cams31aand31brotate half a turn in the C1direction, the sliders33aand33binterlocked with the cams31aand31bmove in an arrow B2direction. Subsequently, the sliders33aand33bbias the pressed member75supported by the developing cartridge70, the developing cartridge70and the movable guides22pivot in a Y2direction about the movable guide rotational axis X, and the development roller71and the photosensitive drum2become separated from each other. When half a turn of the cams31aand31bin the C1direction is completed, the separated state of the process cartridge50illustrated inFIG. 6Bis reached, and the printing operation is completed. In the above, the cams31aand31bstop at the separated position.

As described above, the operation of transitioning from the separated state illustrated inFIG. 6Bto the contact state illustrated inFIG. 6Ais performed before the printing, and the operation of transitioning from the contact state illustrated inFIG. 6Ato the separated state illustrated inFIG. 6Bis performed after the printing. The above sequential operation is repeated each time a print job signal is input.

Elastic Deformation of Twisted Cam Shaft

When performing the abutment and separation operation on the process cartridge50, since the sliders33aand33breceives a load (a resistance) from the developing cartridge70in a direction that is opposite to the moving direction, there are cases in which the cam shaft30becomes twisted and elastic deformed. Regarding such twisting and elastic deformation, twisting and elastic deformation of a cam shaft230occurring when the abutment and separation operation of the developing cartridge70is performed will be described using a conventional abutting and separating configuration.FIG. 7Ais a diagram illustrating sliders233aand233bof the conventional art transitioning from a separated state to a contact state.FIG. 7Bis a perspective view illustrating the twisting and elastic deformation of the cam shaft when the sliders233aand233bof the conventional art are moved.FIG. 8is a diagram of cams231aand231bof the conventional art viewed in a rotational axis R direction.

As illustrated inFIG. 8, the DS cam231aand the NS cam231bhave the same shape and have the same shape as the DS cam31aof the present example embodiment. Accordingly, radius increased areas2a3and2b3, radius decreased areas2a2and2b2, rotation stop areas2a1and2b1of the DS cam231aand the NS cam231bhave the same shapes as the radius increased area a3, the radius decreased area a2, and the rotation stop area a1of the DS cam31a, respectively.

Note that in the conventional art, the configuration and control other than those of the cams231aand231bdescribed above are similar to the abutting and separating configuration of the present disclosure described above; accordingly, detailed description thereof is omitted.

As illustrated inFIG. 7A, in a case in which the sliders233aand233bperform movement for abutment in the B1direction from the separated position towards the contact position, the sliders233aand233bare biased in a direction opposite to the B1direction with a pressurizing spring276of a developing cartridge270. Accordingly, when the radius increased areas2a3and2b3come into contact with the sliders233aand233b, the radius increased areas2a3and2b3receive loads that resist the rotation of the cams231aand231bin the C1direction.

There are cases in which the cam shaft230becomes twisted and elastically deformed, depending on the torsional rigidity of the cam shaft230. Note that as illustrated inFIG. 7B, the NS cam231bis farther away from a gear232than the DS cam231ain the rotational axis direction of the cam shaft230, and the NS cam231bhas a driving force transmission path from the gear232that is longer than that of the DS cam231a. Accordingly, the NS cam231bis more effected by the twisting of the cam shaft230than the DS cam231aand, accordingly, the driving force from the gear232is not easily transmitted to the NS cam231b. As a result, the rotation of the NS cam231bis delayed with respect to the rotation of the DS cam231a.

Furthermore, even in a case in which the sliders233aand233bperform movement for separation in the B2direction from the contact position towards the separated position, the sliders233aand233bare biased to a direction (the B1direction) opposite to the B2direction with the guide springs223attached to the movable guides222. Accordingly, when the radius increased areas2a3and2b3come into contact with the sliders233aand233b, the radius increased areas2a3and2b3receive loads that resist the rotation of the cams231aand231bin the C1direction, and similar to the movement for abutment, twisting and elastic deformation occurs in the cam shaft230.

Since the shapes of the DS cam231aand the NS cam231bare the same, and the attached phases with respect to the cam shaft230are the same, when the cams231aand231breceive loads and the cam shaft230becomes twisted, unconformity occurs between the movement of the DS slider233aand that of the NS slider233b. Specifically, the NS cam231bthat is father away from the gear232becomes delayed relative to the DS cam231aand, due to that, the NS slider233bbecomes delayed relative to the DS slider233a. In some cases, there will be a concern that the NS cam231bmay not be able to reach the home position although the DS cam231ahas reached the home position, due to the twisting of the cam shaft230not being released and the contact point CPb not passing through the radius increased area2b3.

Furthermore, even if the NS slider233bwere to reach the home position, there is a concern that the following phenomenon may occur. That is, in a state in which the contact point CPb is situated in the radius decreased area2b2and the NS cam230bis receiving C1direction rotating force, the twist of the cam shaft230may be released. In such a case, in addition to the force from the NS slider233bin contact with the radius decreased area2b2, restorative force that releases the twist of the cam shaft230is received; accordingly, the rotation speed of the NS cam231bin the C1direction is increased significantly. Furthermore, the impinging sound generated when the NS slider233bcomes into contact with the rotation stop area2a1of the NS cam231bwith increased speed may increase and the operation sound of the NS cam231bmay increase. As described above, when the timing at which the twisting of the cam shaft230is released and the timing at which the NS slider233bcomes into contact with the rotation stop area2a1coincides each other, the impinging sound when the NS slider233bcomes into contact becomes large and the quietness of the image forming apparatus1may become compromised.

Movements of Cams31aand31bDuring Abutting Operation

Movements of the cams31aand31bmoving from the separated position to the contact position when the process cartridge50is transitioned from the separated state to the contact state will be described next.FIGS. 13A to 13CandFIGS. 14A and 14Bare diagrams of portions of the cams31aand31band the sliders33aand33bwhen viewed in the rotational axis R direction. For the sake of description, the cam31ais depicted by a broken line and the cam31bis depicted by a solid line.

When the cam shaft30is rotated about 130° in the C1direction from the separated state illustrated inFIG. 6B, a state illustrated inFIG. 13Ais reached in which the radius increased area b3of the NS cam31bstarts to come in contact with the NS slider33b. As described above, in the natural state, the radius increased area b3of the NS cam31bis disposed downstream of the radius increased area a3of the DS cam31ain the rotation direction C1in proportion to the length of the radius uniform area b4. Accordingly, in the above state, the DS cam31ais not in contact with the DS slider33a, and the cam shaft30is not twisted.

Furthermore, when the cam shaft30is rotated in the C1direction, as illustrated inFIG. 13B, a state is reached in which the radius increased area a3of the DS cam31astarts to come in contact with the DS slider33a. In other words, the clock time (first timing) at which the radius increased area a3of the DS cam31astarts to come in contact with the DS slider33ais later than the clock time (second timing) at which the radius increased area b3of the NS cam31bstarts to come in contact with the NS slider33b. When the NS cam31bis further rotated in the C1direction after the radius increased area b3has come into contact with the NS slider33b, the NS cam31battempts to move the NS slider33bin the B1direction. However, since the NS slider33breceives biasing force from the developing cartridge70in the B2direction, owing to the biasing force, the NS cam31breceives a load that obstructs the rotation in the C1direction. By being affected by the above loads, the cam shaft30is twisted in an elastically deformed manner to the degree that the radius increased area a3of the DS cam31acomes into contact with the DS slider33asuch that, compared with the natural state, the phase of the NS cam31bis deviated towards the upstream side with respect to the DS cam31ain the C1direction. Accordingly, in the state illustrated inFIG. 13B, the cam shaft30is twisted.

When the cam shaft30further rotates in the C1direction from the state illustrated inFIG. 13B, the cam shaft30rotates in the C1direction while maintaining the balance between the restorative force that returns the twisted cam shaft30to the natural state and the load that the NS cam31breceives. In due time, as illustrated inFIG. 13C, the contact point of the NS cam31bin contact with the NS slider33breaches the boundary between the radius increased area b3and the radius uniform area b4. In the above moment, while the twisted amount of the cam shaft30is maintained at a constant amount, the contact point of the DS cam31ain contact with the DS slider33ais situated immediately before the boundary between the radius increased area a3and the radius decreased area a2.

Subsequently, when the contact point of the NS cam31bin contact with the NS slider33benters the radius uniform area b4, the load exerted in the direction that obstructs the rotation towards the C1direction and that is, from the NS slider33b, received by the NS cam31bbecomes smaller; accordingly, the twist of the cam shaft30is substantially released by the restorative force. The above state is the state illustrated inFIG. 14A, and is a state in which the contact point of the NS cam31bin contact with the NS slider has reached the boundary between the radius uniform area b4and the radius decreased area b2. Furthermore, the contact point of the DS cam31ain contact with the DS slider33ais at the boundary between the radius increased area a3and the radius decreased area a2.

From the above state, when the cam shaft30rotates further in the C1direction, the contact point of the NS cam31bin contact with the NS slider33bmoves to the radius decreased area b2, and the contact point of the DS cam31ain contact with the DS slider33amoves to the radius decreased area a2. The DS slider33aand the NS slider33breceive biasing force in the B2direction from the developing cartridge70; accordingly, the biasing force becomes the pressing force that presses the NS cam31band the DS cam31a. Furthermore, the above pressing force includes a force (rotary force) component that acts on the NS cam31band the DS cam31aso that the NS cam31band the DS cam31aare rotated in the C1direction.

When the NS slider33bis in contact with the radius decreased area b2and the DS slider33ais in contact with the radius decreased area a2, the toothless portion of the partially-toothless gear35rotates to a position opposing the gear36so that the cam shaft30cannot receive rotary force from the gear32in the C1direction. However, the NS cam31band the DS cam31aare rotated in the C1direction with the rotary force from the DS slider33aand the NS slider33b. As a result, as illustrated inFIG. 14B, the NS slider33bcomes in contact with the rotation stop area b1of the NS cam31b, and the DS slider33acomes in contact with the rotation stop area a1of the DS cam31a; accordingly, the rotations are stopped. In so doing, the NS slider33balso comes in contact with the radius decreased area b2of the NS cam31b, and the DS slider33aalso comes in contact with the radius decreased area a2of the DS cam31a; accordingly, the NS cam31band the DS cam31aare positioned at the above positions. The NS cam31band the DS cam31aare positioned in the contact positions (the home positions) in the above manner, and the process cartridge50is maintained in the contact state. The clock time (third timing) at which the DS slider33acomes in contact with the rotation stop area a1of the DS cam31aand the clock time (fourth timing) at which the NS slider33bcomes in contact with the rotation stop area b1of the NS cam31bare the same. However, as long as the time difference (absolute value) between the third timing and the fourth timing is shorter than the time difference (absolute value) between the first timing and the second timing described above, the third timing and the fourth timing do not have to be the same.

The movements of the cams31aand31bmoving from the contact position to the separated position when the operation process cartridge50is transitioned from the contact state to the separated state is a movement similar to that described above; accordingly, description thereof is omitted.

As described above, in the present example embodiment, the radius decreased area a2is provided adjacent to the radius increased area a3in the C1direction and on the peripheral surface of the DS cam31aand, meanwhile, the radius uniform area b4is provided between the radius increased area b3and the radius decreased area b2in the C1direction and on the peripheral surface of the NS cam31b. With the above, the rotation amount θ2 is set larger than the rotation amount θ1 (θ1<θ2). Accordingly, after passing through the radius increased area b3, when the contact point CPb of the NS cam31bin contact with the NS slider33benters the radius uniform area b4, the twist of the cam shaft30becomes substantially released.

In a state in which the contact point CPb is at the upstream end portion Pb1of the radius increased area b3in the C1direction, when the end portion is the starting point, the rotation amount of the NS cam31bneeded to substantially release the twist of the cam shaft30is denoted as θ3. In the peripheral surface of the NS cam31b, an area from the upstream end portion Pb1, serving as a starting point, to where the contact point CPb comes in contact after moving rotation amount θ3 in the C1direction is referred to as a twist releasing area bx. Regarding the distance in which the contact point CPb moves on the peripheral surface of the NS cam31b, the distance of the radius uniform area b4is set so that the distance of the twist releasing area bx is the same or shorter than the distance of the radius uniform area b4.

Accordingly, the twist of the cam shaft30is substantially released when the contact point of the NS cam31bin contact with the NS slider33bis situated in the radius uniform area b4and, subsequently, the contact point of the DS cam31ain contact with the DS slider33areaches the radius decreased area a2. Accordingly, situations such as the DS cam31areaching the home position before the twist of the cam shaft30is released and the NS cam31bnot being able to reach the home position can be prevented.

Furthermore, the contact point of the NS cam31bin contact with the NS slider33breaches the radius decreased area b2after the twist of the cam shaft30has been substantially released. Accordingly, when the NS cam31bis rotating in the C1direction while the NS slider33bis in contact with the radius decreased area b2, there will be no increase in the speed of the NS cam31bdue to the release of the twist of the cam shaft30. Accordingly, an increase in the impinging sound when the NS slider33bcomes in contact with the rotation stop area b1of the NS cam31bcan be suppressed, and the decrease in the quietness of the image forming apparatus1can be suppressed.

Second Example Embodiment

Description of a second example embodiment will be given next. In the second example embodiment, a modification example of the cam shape of the NS cam31bwill be described.FIG. 11is a diagram illustrating a shape of the NS cam31b, and is a diagram viewed in the rotational axis R direction.FIG. 11illustrates, as an example of the contact point CPb, a state in which the contact point CPb is situated in the radius increased area b3.

In the first example embodiment described above, the peripheral surface of the NS cam31bis provided with the radius increased area b3, the radius uniform area b4, the radius decreased area b2, and the rotation stop area b1. In the NS cam31bof the present example embodiment, as illustrated inFIG. 11, the portions in the first example embodiment where the radius uniform area b4and the radius decreased area b2are provided is a radius decreased area b22. In other words, in the peripheral surface of the NS cam31b, the radius decreased area b22is disposed adjacent to the radius increased area b3in the C1direction. Other configurations are the same as those of the first example embodiment; accordingly, description thereof is omitted.

In a state in which the contact point CPb is situated at a boundary point Pb21between the radius increased area b3and the radius decreased area b22, when the boundary point is a starting point, θ2 is a rotation amount of the NS cam31bneeded for the slider33bto contact the rotation stop area b1. θ2 is an angle formed between a line segment rb21connecting the boundary point Pb21between the radius increased area b3and the radius decreased area b22and the rotational axis R, and a line segment rb22connecting a boundary point Pb22between the radius decreased area b22and the rotation stop area b1and the rotational axis R. Furthermore, the rotation amount θ2 is larger than the rotation amount θ1 (θ1<θ2). In other words, regarding the distances along the peripheral surfaces of the cams31aand31b, the radius decreased area b22is longer than the radius decreased area a2.

Accordingly, after passing through the radius increased area b3, when the contact point CPb of the NS cam31bin contact with the NS slider33benters the radius decreased area b22, the twist of the cam shaft30becomes substantially released. In a state in which the contact point CPb is at the upstream end portion Pb21of the radius increased area b3in the C1direction, when the end portion is starting point, the rotation amount of the NS cam31bneeded to substantially release the twist of the cam shaft30is denoted as θ3. Then, the rotation amount θ2 is set so that the rotation amount θ2 is larger than the rotation amount θ3 (θ3<θ2). In the peripheral surface of the NS cam31b, an area from the upstream end portion Pb21, serving as a starting point, to where the contact point CPb comes in contact after moving rotation amount θ3 in the C1direction is referred to as the twist releasing area bx. By providing the twist releasing area bx in the radius decreased area b22in the above manner, the NS cam31breceives, from the NS slider33b, force in the direction releasing the twist of the cam shaft30; accordingly, the twist of the cam shaft30can be released in a more reliable manner.

Note that the rotation amount θ2 in the present example embodiment is set to have the same value as the rotation amount θ2 of the first example embodiment; however, the rotation amount θ2 may be any value that satisfies θ1<θ2 and θ3<θ2 described above.

As described above, in the present example embodiment, the radius decreased area a2is provided adjacent to the radius increased area a3in the C1direction and on the peripheral surface of the DS cam31a, and the radius decreased area b22is provided adjacent to the radius increased area b3in the C1direction and on the peripheral surface of the NS cam31b. Furthermore, the shapes of the radius decreased area a2and the radius decreased area b22are set so that the rotation amount θ2 is larger than the rotation amount θ1 (θ1<θ2).

Accordingly, after passing through the radius increased area b3, when the contact point CPb enters the radius decreased area b22, the twist of the cam shaft30becomes substantially released in the twist releasing area bx. Subsequently, the contact point of the DS cam31ain contact with the DS slider33acan be made to reach the radius decreased area a2. Accordingly, situations such as the DS cam31areaching the home position before the twist of the cam shaft30is released and the NS cam31bnot being able to reach the home position can be prevented.

Furthermore, even after the contact point CPb passes through the twist releasing area bx, the radius decreased area b22continues. Accordingly, after the contact point CPb has passed through the twist releasing area bx, when the contact point CPb is situated in the radius decreased area b22, there will be no increase in the speed of the NS cam31bdue to the release of the twist of the cam shaft30. Accordingly, an increase in the impinging sound when the NS slider33bcomes in contact with the rotation stop area b1of the NS cam31bcan be suppressed, and the decrease in the quietness of the image forming apparatus1can be suppressed.

Third Example Embodiment

Description of a third example embodiment will be given next. In the third example embodiment, a modification example of the cam shape of the NS cam31bwill be described.FIG. 12is a diagram illustrating a shape of the NS cam31b, and is a diagram viewed in the rotational axis R direction.FIG. 12illustrates, as an example of the contact point CPb, a state in which the contact point CPb is situated in the radius increased area b3.

In the first example embodiment described above, the peripheral surface of the NS cam31bis provided with the radius increased area b3, the radius uniform area b4, the radius decreased area b2, and the rotation stop area b1. In the NS cam31bof the present example embodiment, as illustrated inFIG. 12, a radius decreased area b32and a radius uniform area b34are provided by switching positions of the radius uniform area b4and the radius decreased area b2of the first example embodiment with each other. In other words, the radius increased area b3, the radius decreased area b32, the radius uniform area b34, and the rotation stop area b1are arranged on the peripheral surface of the NS cam31bin that order in the C1direction. Other configurations are the same as those of the first example embodiment; accordingly, description thereof is omitted.

In a state in which contact point CPb is situated at an upstream end portion Pb31(a boundary point between the radius increased area b3and the radius decreased area b32) of the radius increased area b3in the C1direction (the rotation direction), when the boundary point is a starting point, θ2 is a rotation amount of the NS cam31bneeded for the slider33bto contact the rotation stop area b1. θ2 is an angle formed between a line segment rb31connecting the boundary point Pb31between the radius increased area b3and the radius decreased area b32and the rotational axis R, and a line segment rb32connecting a boundary point Pb32between the radius uniform area b34and the rotation stop area b1and the rotational axis R. Furthermore, the rotation amount θ2 is larger than the rotation amount θ1 (θ1<θ2). In other words, regarding the distances along the peripheral surfaces of the cams31aand31b, a sum of the radius decreased area b32and the radius uniform area b34is longer than the radius decreased area a2.

Accordingly, after passing through the radius increased area b3, when the contact point CPb of the NS cam31bin contact with the NS slider33benters the radius decreased area b32, the twist of the cam shaft30becomes substantially released. In a state in which the contact point CPb is at the upstream end portion Pb31of the radius increased area b3in the C1direction, when end portion is the starting point, the rotation amount of the NS cam31bneeded to substantially release the twist of the cam shaft30is denoted as θ3. Then, the rotation amount θ2 is set so that the rotation amount θ2 is larger than the rotation amount θ3 (θ3<θ2). In the peripheral surface of the NS cam31b, an area from the upstream end portion Pb31, serving as a starting point, to where the contact point CPb comes in contact after moving rotation amount θ3 in the C1direction is referred to as the twist releasing area bx. By providing the twist releasing area bx in the radius decreased area b32in the above manner, the NS cam31breceives, from the NS slider33b, force in the direction releasing the twist of the cam shaft30; accordingly, the twist of the cam shaft30can be released in a more reliable manner.

After the contact point CPb passes through the twist releasing area bx, the contact point CPb passes at least the radius uniform area b34. In the above, the NS cam31bcannot receive, from the NS slider33b, rotary force that rotates the NS cam31bin the C1direction. However, in the above, since the contact portion of the DS cam31ais situated in the radius decreased area a2, the DS cam31arotates in the C1direction with the rotary force from the DS slider33a(seeFIGS. 9A and 14A). Accordingly, since the rotary force is transmitted to the NS cam31bthrough the cam shaft30, the NS cam31bcan rotate until the NS slider33bcomes into contact with the rotation stop area b1.

Note that the rotation amount θ2 in the present example embodiment is set to have the same value as the rotation amount θ2 of the first example embodiment; however, the rotation amount θ2 may be any value that satisfies θ1<θ2 and θ3<θ2 described above. Furthermore inFIG. 12, regarding the distance along the peripheral surface of the NS cam31b, the radius decreased area b32is set so that the radius decreased area b32is longer than the twist releasing area bx. However, not limited to the above, as long as θ1<θ2 and θ3<θ2 described above are satisfied, regarding the distance along the peripheral surface of the NS cam31b, the radius decreased area b32may be set so that the radius decreased area b32is shorter than the twist releasing area bx.

According to the present example embodiment, after passing through the radius increased area b3, when the contact point CPb enters the radius decreased area b32, the twist of the cam shaft30becomes substantially released in the twist releasing area bx. Subsequently, the contact point of the DS cam31ain contact with the DS slider33acan be made to reach the radius decreased area a2. Accordingly, situations such as the DS cam31areaching the home position before the twist of the cam shaft30is released and the NS cam31bnot being able to reach the home position can be prevented.

Furthermore, even after the contact point CPb passes through the twist releasing area bx, there is at least the radius uniform area b34. Accordingly, after the contact point CPb has passed through the twist releasing area bx, when the contact point CPb is situated in the radius uniform area b34, there will be no increase in the speed of the NS cam31bdue to the release of the twist of the cam shaft30. Accordingly, an increase in the impinging sound when the NS slider33bcomes in contact with the rotation stop area b1of the NS cam31bcan be suppressed, and the decrease in the quietness of the image forming apparatus1can be suppressed.

Fourth Example Embodiment

Description of a fourth example embodiment will be given next. In the fourth example embodiment, a modification example of the cam shape of the DS cam31awill be described.FIG. 15is a diagram illustrating a shape of the DS cam31a, and is a diagram viewed in the rotational axis R direction.FIG. 15illustrates, as an example of the contact point CPa, a state in which the contact point CPa is situated in the radius increased area a3.

In the first example embodiment described above, the peripheral surface of the DS cam31ais provided with the radius increased area a3, the radius decreased area a2, and the rotation stop area a1. As illustrated inFIG. 15, in the DS cam31bof the present example embodiment, the DS cam31aincludes a radius uniform area a4between the radius increased area a3and the radius decreased area a2in the C1direction. Other configurations are the same as those of the first example embodiment; accordingly, description thereof is omitted.

The radius uniform area a4is an area in which the distance (the radius to the cam surface) between a contact point CPb and the rotational axis (the rotation center) R is practically uniform (does not change) with the rotation of the DS cam31ain the C1direction. In a state in which a slider33ais in contact with an upstream end portion Pa21(the boundary point between the radius increased area a3and the radius uniform area a4) of the radius increased area a3in the C1direction (the rotation direction), when the boundary is a starting point, θ1 is a rotation amount of the DS cam31aneeded for the slider33ato contact the rotation stop area a1. In the present example embodiment, θ1 is an angle formed between a line segment ra21connecting the boundary point Pa21between the radius increased area a3and the radius uniform area a2and the rotational axis R, and a line segment ra22connecting a boundary point Pa22between the radius decreased area a2and the rotation stop area a1and the rotational axis R. Furthermore, the radius uniform area a4and the radius decreased area a2are set so that the rotation amount θ1 is smaller than the rotation amount θ2 (θ1<θ2).

Note that the rotation amount θ1 in the present example embodiment is set to have the same value as the rotation amount θ1 of the first example embodiment; however, the rotation amount θ1 may be any value that satisfies θ1<θ2 described above.

In the present example embodiment, the shapes of the radius uniform area a4and the radius decreased area a2are set so that the rotation amount θ2 is larger than the rotation amount θ1 (θ1<θ2) while providing, on the peripheral surface of the DS cam31a, the radius uniform area a4between radius increased area a3and the radius decreased area a2in the C1direction.

By providing the radius uniform area a4in the DS cam31ain the above manner, the contact point of the DS cam31ain contact with the DS slider33acan be made to reach the radius decreased area a2in a more reliable manner after the twisting of the cam shaft30has been substantially released. Accordingly, situations such as the DS cam31areaching the home position before the twist of the cam shaft30is released and the NS cam31bnot being able to reach the home position can be prevented.

Furthermore, similar to the first example embodiment, the contact point of the NS cam31bin contact with the NS slider33breaches the radius decreased area b2after the twist of the cam shaft30has been substantially released. Accordingly, when the NS cam31bis rotating in the C1direction while the NS slider33bis in contact with the radius decreased area b2, there will be no increase in the speed of the NS cam31bdue to the release of the twist of the cam shaft30. Accordingly, an increase in the impinging sound when the NS slider33bcomes in contact with the rotation stop area b1of the NS cam31bcan be suppressed, and the decrease in the quietness of the image forming apparatus1can be suppressed.

Note that the modification example of the cam shape of the DS cam31adescribed in the fourth example embodiment can be applied to the second example embodiment and the third example embodiment as well. In such a case as well, an advantage similar to the advantage described above can be obtained.

The present disclosure is capable of, in a case in which a rotation of a first cam between two cams becomes delayed relative to a rotation of a second cam, preventing a first cam from not reaching a stop position, and/or preventing a cam from coming into contact with a rotation restricting portion in a state in which the speed of the cam has been increased.

This application claims the benefit of Japanese Patent Application No. 2017-147661 filed Jul. 31, 2017, which is hereby incorporated by reference herein in its entirety.