Structure for switching developing unit to developmentposition and release position

Abstract

A process cartridge includes a photoconductive unit, a developing unit coupled to the photoconductive unit and pivotable to a development position and a release position, and an elastic member to bias the development unit toward the development position. A nip control member is switchable to a nip separation position at which the developing unit is maintained at the release position and to a nip formation position that allows the developing unit to pivot to the development position. A switching member switches the nip control member from the nip separation position to the nip formation position when a developing roller of the developing unit is rotated in an image forming direction. Transmission of rotation power between the switching member and the developing roller is blocked or reduced by a rotation power control member when the nip control member is switched from the nip formation position to the nip separation position.

Description

STRUCTURE FOR SWITCHING DEVELOPING UNIT TO DEVELOPMENT POSITION AND RELEASE POSITIONBACKGROUND

[0001] An electrophotographic image forming apparatus forms a visible toner image on a photoconductor by providing toner on an electrostatic latent image formed on the photoconductor, transfers the toner image to a print medium, fixes the transferred toner image on the print medium, and prints an image on the print medium. A developing device includes a developing roller that receives toner and supplies the toner to an electrostatic latent image formed on a photoconductor.

[0002] A process cartridge is an assembly of parts for forming a visible toner image and may be detached from a main body of an image forming apparatus. The cartridge may include a unit for a development member (developing roller) or units for a development member and a photoconductive member (photoconductor) which is operatively connected to the development member. The process cartridge is a consumable that is replaced when its lifespan has elapsed. In the case of a process cartridge employing a contact developing method, a developing roller and a photoconductor come into contact with each other to form a development nip. When a long period of time elapses in a state in which the development nip is formed, there is a concern of deformation of the developing roller and damage to the photoconductor. Deformation of the developing roller and damage to the photoconductor may cause a change in the development nip and thus have a negative effect on image quality.BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. l is a schematic side view of an example of a process cartridge according to the disclosure, which shows a state in which a developing unit is positioned at a development position and a development nip separating member is positioned at a home position;

[0004] FIG. 2 shows a state in which the development nip separating member is in contact with a nip control member in the example of the process cartridge shown in FIG. 1;

[0005] FIG. 3 shows a state in which the developing unit is positioned at a release position and the development nip separating member is positioned at a switching position in the example of the process cartridge shown in FIG. 1;

[0006] FIG. 4 shows a state in which the developing unit is positioned at the release position and the development nip separating member is positioned at the home position in the example of the process cartridge shown in FIG. 1;

[0007] FIG. 5 is a schematic exploded perspective view of an example of a structure for switching the nip control member from a nip separation position to a nip formation position in the example of the process cartridge shown in FIG. 1;

[0008] FIG. 6 is a view illustrating an operation of an example of a rotation power control member shown in FIG. 5, which shows a state in which the nip control member is positioned at the nip formation position;

[0009] FIG. 7 is a view illustrating an operation of an example of the rotation power control member shown in FIG. 5, which shows a state in which the nip control member is positioned at the nip separation position;

[0010] FIG. 8 is a schematic exploded perspective view illustrating an example of a rotation power control member;

[0011] FIG. 9 is a schematic perspective view of an example of a development nip formation / separation structure employing a one-way power transmission member as a rotation power control member;

[0012] FIG. 10 is a schematic exploded perspective view of the example of the development nip formation / separation structure shown in FIG. 9;

[0013] FIG. 11 is a schematic side view of an example of a process cartridge to which the development nip formation / separation structure shown in FIGS. 9 and 10 is applied, which shows a state in which a developing unit is positioned at a development position and a development nip separating member is positioned at a home position;

[0014] FIG. 12 is a schematic side view of an example of a process cartridge to which the development nip formation / separation structure shown in FIGS. 9 and 10 is applied, which shows a state in which a developing unit is positioned at a release position and a development nip separating member is positioned at a switching position;

[0015] FIG. 13 is a schematic side view of an example of a process cartridge to which the development nip formation / separation structure shown in FIGS. 9 and 10 is applied, which shows a state in which a developing unit is positioned at a release position and a development nip separating member is positioned at a home position;

[0016] FIG. 14 is a schematic side view of an example of a process cartridge, which shows a state in which a developing unit is positioned at a development position and a development nip separating member is positioned at a home position;

[0017] FIG. 15 shows a state in which the developing unit is positioned at an over-rotation position in the example of the process cartridge shown in FIG. 14;

[0018] FIG. 16 shows a state in which a nip control member is positioned at a nip separation position in the example of the process cartridge shown in FIG. 14;

[0019] FIG. 17 shows a state in which the developing unit is positioned at the release position and the development nip separating member is positioned at the home position in the example of the process cartridge shown in FIG. 14; and

[0020] FIG. 18 is a schematic configuration diagram of an example of an electrophotographic image forming apparatus.DETAILED DESCRIPTION OF EXAMPLES

[0021] An image forming apparatus that prints an image on a print medium by an electrophotographic method may include a process cartridge. The process cartridge may include a photoconductive unit including a photoconductive drum and a developing unit including a developing roller. The process cartridge may include a gear train for driving the developing roller. During image formation, the developing roller comes into contact with the photoconductive drum to form a development nip. The developing roller supplies toner accommodated inside the developing unit to an electrostatic latent image formed on the photoconductive drum to visually develop the electrostatic latent image into a toner image. When an image forming operation is not performed, the developing roller is spaced from the photoconductive drum so that the development nip may be released. The developing unit may be coupled to the photoconductive unit so as to be pivotable to a development position at which the development nip is formed and to a release position at which the development nip is released. The developing unit may be elastically biased by an elastic member to be pivoted in a direction toward the development position.

[0022] For example, a separating member may be pivotable to a nip separation position that maintains the developing unit at the release position and to a nip formation position that allows the developing unit to be pivoted from the release position to the development position. Switching of the separating member from the nip separation position to the nip formation position may be implemented by driving the gear train in an image forming direction. To this end, the separating member is directly or indirectly connected to the gear train. When the separating member is pivoted from the nip formation position to the nip separation position, the rotation power of the separating member is transmitted to the gear train, and thus, the geartrain is driven in the opposite direction to the image forming direction. Then, rotation members of the developing unit connected to the gear train, for example, a developing roller, a supply roller, etc. are rotated in the opposite direction to the image forming direction. Because the rotation members act as a rotation load when the separating member is pivoted from the nip formation position to the nip separation position, large rotation power is required to pivot the separating member from the nip formation position to the nip separation position. Also, the process cartridge may include various members such as a sealing member for preventing leakage of toner, and some of the various members are in contact with the rotation members. When the rotation members are rotated in the opposite direction to the image forming direction, sealing members in contact with the rotation members may be deformed or damaged, which may cause problems such as leakage of toner and surface damage of the rotation members.

[0023] The disclosure provides a process cartridge having a structure capable of switching a separating member from a nip formation position to a nip separation position with a relatively small force, and an image forming apparatus employing the process cartridge. The disclosure provides a process cartridge having a structure capable of reducing the risk of deformation / damage to rotation members of the process cartridge and members in contact therewith during a process of forming / releasing a development nip, and an image forming apparatus employing the process cartridge.

[0024] A process cartridge according to the disclosure may include a photoconductive unit including a photoconductive drum and a developing unit including a developing roller. The developing unit may be coupled to the photoconductive unit so as to be pivotable to a release position at which the developing roller is spaced apart from the photoconductive drum and to a development position at which the developing roller comes into contact with the photoconductive drum to form a development nip. An elastic member applies an elastic force to the developing unit biasing the development unit toward the development position. A nip control member is switchable between a nip separation position and a nip formation position. The nip separation position is a position at which the developing unit is maintained at the release position. The nip formation position is a position allowing the developing unit to be pivoted to the development position from the release position by the elastic force of the elastic member. A switching member is rotated in conjunction with a rotation of the developing roller when the developing roller is rotated in a first direction, which is the image forming direction, to switch the nip control member from the nip separation position to the nip formation position. A rotation power control member blocks or reduces transmission of rotation powerbetween the switching member and the developing roller when the nip control member is switched from the nip formation position to the nip separation position.

[0025] When the nip control member is switched from the nip formation position to the nip separation position, the switching member is rotated in a second direction which is the opposite direction to the image forming direction. At this time, the rotation power control member blocks or reduces the rotation power of the switching member in the second direction so as not to be transmitted to the developing roller. Accordingly, the rotation power control member may prevent the rotation members of the developing unit, such as the developing roller and the supply roller connected thereto, from being rotated in the opposite direction to the image forming direction, thereby switching the nip control member from the nip formation position to the nip separation position with a low driving force, and reducing the risk of deformation / damage of the rotation members and various members in contact therewith.

[0026] As an example, a developing roller gear may be coupled to a rotation shaft of the developing roller. The switching member may include a switching gear rotatably supported on the rotation shaft of the developing roller and opposite the developing roller gear in an axial direction. The nip control member may include a partial gear portion engaged with the switching gear. The rotation control member may be disposed between the developing roller gear and the switching gear.

[0027] As an example, the developing roller gear may include a first protrusion, and the switching gear may include a second protrusion opposite the first protrusion in a circumferential direction. The rotation power control member may include a compression spring disposed between the first protrusion and the second protrusion. When the nip control member is rotated from the nip formation position to the nip separation position, the partial gear portion may engage with the switching gear so that the switching gear rotates in the second direction which is the opposite direction to the first direction, and the compression spring may be compressed between the first protrusion and the second protrusion. A torque acting on the developing roller by the compressed compression spring may be less than a rotation load torque of the developing roller in the second direction. Therefore, even though the switching gear is rotated in the second direction by the nip control member rotated from the nip formation position to the nip separation position, a rotation amount of the switching gear in the second direction is absorbed by a compression displacement of the compression spring. Therefore, the developing roller gear is not rotated. When the developing roller is rotated in the first direction to switch the nip control member from the nip separation position to the nip formation position before performing an image forming operation, the firstprotrusion of the developing roller gear pushes the compression spring so that the switching gear is rotated in the first direction, and the switching gear and the partial gear portion are engaged so that the nip control member is rotated from the nip separation position to the nip formation position. When the nip control member reaches the nip formation position, the engagement between the switching gear and the partial gear portion is released, and the compression spring returns to a relaxed state.

[0028] As an example, the rotation power control member may include a friction member disposed between the developing roller gear and the switching gear to provide a friction torque. The friction torque of the friction member may be less than the rotation load torque of the developing roller in the second direction which is the opposite direction to the image forming direction, and may be greater than the rotation load torque of the nip control member from the nip separation position to the nip formation position. Therefore, even though the switching gear is rotated in the second direction as the nip control member is rotated from the nip formation position to the nip separation position, the developing roller gear is not rotated. When the developing roller gear is rotated in the first direction, the switching gear is rotated in the first direction so that the nip control member may be rotated from the nip separation position to the nip formation position.

[0029] As an example, the developing roller gear may be rotatably supported on the rotation shaft of the developing roller. The switching member may be rotatably supported on the rotation shaft of the developing roller while receiving rotation power in the first direction from the developing roller gear. The rotation power control member may include a one-way power transmission member disposed between the rotation shaft of the developing roller and the switching member to transmit the rotation power of the switching member in the first direction to the rotation shaft of the developing roller. The one-way power transmission member blocks the rotation power of the switching member in the second direction from being transmitted to the rotation shaft of the developing roller. Therefore, the developing roller is not rotated while the nip control member is rotated from the nip formation position to the nip separation position.

[0030] As an example, the nip control member may include a first interfering portion. The nip control member may include a second interfering portion that interferes with the first interfering portion so that the nip control member is switched from the nip separation position to the nip formation position when the switching member is rotated in the first direction. When the switching member is rotated in the first direction in accordance with the rotation of the developing roller in the first direction, the second interfering portion may push the firstinterfering portion so that the nip control member may be switched from the nip separation position to the nip formation position.

[0031] A process cartridge according to the disclosure may include a photoconductive unit including a photoconductive drum, a developing unit including a developing roller, and a gear train for rotating the developing roller. The developing unit may be coupled to the photoconductive unit so as to be pivotable to a release position at which the developing roller is spaced apart from the photoconductive drum and to a development position at which the developing roller comes into contact with the photoconductive drum to form a development nip. An elastic member applies an elastic force to the photoconductive unit and the developing unit biasing the development unit toward the development position. The gear train includes one or more gears including a pinion. A nip control member includes a rack gear portion. The nip control member is switchable to a nip separation position at which the developing unit is maintained at a release position in a state in which the rack gear portion is engaged with the pinion and to a nip formation position that allows the developing unit to be pivoted to the development position by an elastic force of an elastic member when the gear train is driven in an image forming direction.

[0032] As an example, the pinion may be provided in the developing unit and the nip control member may be provided in the photoconductive unit. As an example, the developing unit may have an over-rotation position further pivoted beyond the release position such that the pinion is spaced apart from the rack gear portion of the nip control member positioned at the nip formation position. When the developing unit is positioned at the over-rotation position, the nip control member may be moved from the nip formation position to the nip separation position. As an example, when the developing unit is positioned at the over-rotation position, the nip control member may be switched from the nip formation position to the nip separation position by gravity or by an elastic force of a second elastic member.

[0033] An image forming apparatus according to the disclosure may include the abovedescribed process cartridge, a development nip separating member switching a nip control member from a nip formation position to a nip separation position, and a driving unit driving the development nip separating member. The cartridge may include a developing unit including a developing roller. The developing unit may be coupled to a photoconductive unit so as to be pivotable to a release position at which the developing roller is spaced apart from a photoconductive drum provided in the photoconductive unit and to a development position at which the developing roller comes into contact with the photoconductive drum to form a development nip. An elastic member applies an elastic force to the developing unit biasingthe development unit toward the development position. A nip control member is switchable between a nip separation position and a nip formation position. The nip separation position is a position at which the developing unit is maintained at the release position. The nip formation position is a position allowing the developing unit to be pivoted to the development position from the release position by the elastic force of the elastic member. A switching member is rotated in conjunction with a rotation of the developing roller when the developing roller is rotated in a first direction, which is the image forming direction, to switch the nip control member from the nip separation position to the nip formation position. A rotation power control member blocks or reduces transmission of rotation power between the switching member and the developing roller when the nip control member is switched from the nip formation position to the nip separation position.

[0034] As an example, when the nip control member is positioned at the nip separation position, the driving unit may return the development nip separating member to a home position spaced apart from the nip control member.

[0035] Hereinafter, examples of a process cartridge and an image forming apparatus according to the disclosure will be described in detail with reference to drawings. In order to more clearly describe the characteristics of the present examples, detailed descriptions of matters widely known to those skilled in the art to which the following examples belong are omitted.

[0036] FIGS. 1 to 4 are schematic side views of an example of a process cartridge 2. FIG. 1 shows a state in which a developing unit 200 is positioned at a development position and a development nip separating member 3 is positioned at a home position. FIG. 2 shows a state in which the development nip separating member 3 is in contact with the nip control member 4. FIG. 3 shows a state in which the developing unit 200 is positioned at a release position and the development nip separating member 3 is positioned at a switching position. FIG. 4 shows a state in which the developing unit 200 is positioned at the release position and the development nip separating member 3 is positioned at the home position.

[0037] Referring to FIGS. 1 to 4, the process cartridge 2 may include a developing unit 200. The process cartridge 2 may include a photoconductive unit 100 and the developing unit 200. The photoconductive unit 100 may include a photoconductive drum 21. The developing unit 200 may include a developing roller 22. The developing unit 200 may be coupled to the photoconductive unit 100 so as to be pivotable to a release position (FIG. 4) at which the developing roller 22 is spaced apart from the photoconductive drum 21 and a development position (FIG. 1) at which the developing roller 22 comes into contact with thephotoconductive drum 21 to form a development nip N. An elastic member 300 applies an elastic force to the developing unit 200 biasing the development unit toward the development position from the release position. The process cartridge 2 may include a nip control member 4, a switching member 5, and a rotation power control member 6. The nip control member 4 is switchable between a nip separation position (FIG. 4) at which the developing unit 200 is maintained at the release position and a nip formation position (FIG. 1) allowing the developing unit 200 to be pivoted to the development position by the elastic force of the elastic member 300. The switching member 5 is rotated in conjunction with the rotation of the developing roller 22 when the developing roller 22 is rotated in a first direction Al, which is an image forming direction, to switch the nip control member 4 from the nip separation position to the nip formation position. The rotation power control member 6 blocks or reduces transmission of rotation power between the switching member 5 and the developing roller 22 when the nip control member 4 is switched from the nip formation position to the nip separation position. The process cartridge 2 may include a gear train 230 connecting the developing roller 22 and rotation members of the process cartridge 2 (e.g., a supply roller 27, an agitator, etc.). The rotation power control member 6 blocks or reduces transmission of rotation power between the switching member 5 and the gear train 230 when the nip control member 4 is switched from the nip formation position to the nip separation position.

[0038] Hereinafter, the “image forming direction” indicating a rotation direction of the rotation members of the process cartridge 2, excluding the developing roller 22 and rotation members installed on a rotation shaft 22a of the developing roller 22, indicates a direction in which the rotation members are rotated when the developing roller 22 is rotated in the first direction Al. The “opposite direction to the image forming direction” indicating the rotation direction of the rotation members of the process cartridge 2, excluding the developing roller 22 and rotation members installed on the rotation shaft 22a of the developing roller 22, indicates a direction in which the rotation members are rotated when the developing roller 22 is rotated in a second direction A2.

[0039] The photoconductive unit 100 may include a first frame 101. The photoconductive drum 21 may be rotatably supported on the first frame 101. The developing unit 200 may include a second frame 201. The developing roller 22 may be rotatably supported on the second frame 201. Because the position of the photoconductive drum 21 is related to positions of transfer-related members provided on a main body of an image forming apparatus to be described below, when the process cartridge 2 is mounted on the main body, the position of the photoconductive drum 21 is fixed, and the developing unit 200 may be pivoted around ahinge axis HA to switch between the development position and the release position. The development position is the position of the developing unit 200 when an image forming operation is performed by the process cartridge 2, and the release position is the position of the developing unit 200 when the image forming operation by the process cartridge 2 is not being performed.

[0040] The elastic member 300 provides an elastic (e.g., tensile) force in a direction of forming the development nip N to the photoconductive unit 100 and the developing unit 200. The elastic member 300 provides the elastic force to the developing unit 200 so as to be pivoted in the direction of forming the development nip N. By the elastic force of the elastic member 300, the developing unit 200 is pivoted about the hinge axis HA so that the developing roller 22 comes into contact with the photoconductive drum 21, and accordingly, the development nip N may be formed as shown in FIG. 1. FIGS. 1 to 4 show, as an example of the elastic member 300, a tension coil spring having one end and the other end supported by the photoconductive unit 100 and the developing unit 200, respectively. An example of the elastic member 300 is not limited thereto. For example, various types of members such as a torsion coil spring, a leaf spring, etc. may be used as the elastic member 300.

[0041] As an example, the nip control member 4 may be supported on the developing unit 200, for example, the second frame 201, so as to be pivotable to the nip separation position and the nip formation position around the pivot shaft 41. The nip control member 4 may include a nip separating portion 42 contacting the photoconductive unit 100 (e.g., the first frame 100), interfering with the rotation of the developing unit 200 toward the photoconductive unit 100 when switched from the nip formation position to the nip separation position, as shown in FIGS. 3 and 4. When the nip control member 4 is positioned at the nip formation position, the nip separating portion 42 may be spaced apart from the photoconductive unit 100, as shown in FIGS 1 and 2. The nip control member 4 may be pivoted from the nip formation position to the nip separation position or from the nip separation position to the nip formation position, and thus, the developing unit 200 may be pivoted to the release position and the development position.

[0042] As an example, the switching of the nip control member 4 from the nip formation position to the nip separation position may be performed by the development nip separating member 3. The development nip separating member 3 may be provided in the main body of the image forming apparatus in which the process cartridge 2 is mounted. A driving unit 35 driving the development nip separating member 3 may be provided in the main body of the image forming apparatus. While moving from the home position (FIG. 1) to the switchingposition (FIG. 3), the development nip separating member 3 may contact and move the nip control member 4 to allow the nip control member 4 to be pivoted and switched from the nip formation position to the nip separation position. When the nip control member 4 is positioned at the nip separation position, the driving unit 35 may return the development nip separating member 3 to the home position (FIG. 4). For example, the development nip separating member 3 may be linearly moved between the home position and the switching position. The driving unit 35 may include an actuator, for example, a driving motor, and a power conversion mechanism that converts rotation power of the driving motor into linear motion of the development nip separating member 3. The power conversion mechanism may be implemented by, for example, a rack-and-pinion mechanism, a cam-slider mechanism, etc. A first manipulating portion 43 capable of contacting the development nip separating member3 when the development nip separating member 3 is moved from the home position to the switching position may be provided in the nip control member 4.

[0043] As an example, switching of the nip control member 4 from the nip separation position to the nip formation position may be implemented by rotating the developing roller 22 in the first direction Al . The rotation power of the developing roller 22 in the first direction Al may be transmitted to the nip control member 4 by the switching member 5. FIG. 5 is a schematic exploded perspective view of an example of a structure for switching the nip control member4 from a nip separation position to a nip formation position.

[0044] Referring to FIG. 5, a developing roller gear 210 is coupled to a rotation shaft 22a of the developing roller 22. The developing roller gear 210 is coupled to the rotation shaft 22a of the developing roller 22 so as to rotate together with the developing roller 22. The switching member 5 may include a switching gear 51 rotatable coaxially with the rotation shaft 22a of the developing roller 22. The switching gear 51 may be adjacent the developing roller gear 210 in an axial direction. In the present example, a cylindrical supporting portion 211 protruding in the axial direction so as to be coaxial with the rotation shaft 22a of the developing roller 22 may be provided in the developing roller gear 210, and the switching gear 51 may be rotatably supported on the cylindrical supporting portion 211. Although not shown in the drawings, the rotation shaft 22a of the developing roller 22 may extend in the axial direction beyond the developing roller gear 210, and the switching gear 51 may be rotatably supported on the rotation shaft 22a of the developing roller 22.

[0045] The switching gear 51 may be rotated in connection with the developing roller gear 210. The developing roller gear 210 may include a first protrusion 212. The first protrusion 212 may protrude from the developing roller gear 210 toward the switching gear 51 in theaxial direction. The switching gear 51 may include a second protrusion 51a. The second protrusion 51a may protrude from the switching gear 51 toward the developing roller gear 210 in the axial direction. The second protrusion 51a may face the first protrusion 212 in a circumferential direction.

[0046] The nip control member 4 may include a partial gear portion 44 engageable with the switching gear 51. As shown in FIG. 1, in a state in which the nip control member 4 is positioned at the nip formation position, the partial gear portion 44 remains spaced apart from the switching gear 51. As shown in FIG. 4, in a state in which the nip control member 4 is positioned at the nip separation position, the partial gear portion 44 remains engaged with the switching gear 51.

[0047] The rotation power control member 6 transmits rotation power of the developing roller 22 to the switching gear 51 when the developing roller 22 is rotated in the first direction Al. When the nip control member 4 is switched from the nip formation position to the nip separation position, the switching gear 51 is rotated in the second direction A2, which is the opposite direction to the first direction Al, by the engagement between the partial gear portion 44 and the switching gear 51. The rotation power control member 6 blocks or reduces the transmission of the rotation power in the second direction A2 transmitted from the nip control member 4 to the switching gear 51 to the developing roller 22. The rotation power control member 6 may be disposed between the developing roller gear 210 and the switching gear 51. As an example, the rotation power control member 6 may include a compression spring 61 disposed between the first protrusion 212 of the developing roller gear 210 and the second protrusion 5 la of the switching gear 51. One end and the other end of the compression spring 61 are supported on the first protrusion 212 of the developing roller gear 210 and the second protrusion 51a of the switching gear 51, respectively A displacement difference between the free length of the compression spring 61 (i.e., without load applied) and the maximum deflection length of the compression spring 61 (i.e., at maximum compression) may be equal to or greater than a formation angle of the partial gear portion 44. When a compression displacement of the compression spring 61 is maximum, a torque acting on the developing roller 22 by the compression spring 61 is less than a rotation load torque of the developing roller 22 in the second direction A2. The rotation load torque of the developing roller 22 may be provided by rotation members connected to the developing roller 22 by the gear train 230 and rotated, for example, the supply roller 27, an agitator, etc.

[0048] FIGS. 6 and 7 are diagrams illustrating operations of the rotation power control member 6 shown in FIG. 5. FIG. 6 illustrates a state in which the nip control member 4 ispositioned at a nip formation position. FIG. 7 illustrates a state in which the nip control member 4 is positioned at a nip separation position. Referring to FIGS. 1 to 7, a process of forming / releasing the development nip N is described.

[0049] First, referring to FIG. 1, the nip control member 4 is positioned at the nip formation position. The nip separating portion 42 is spaced apart from the photoconductive unit 100, for example, the first frame 101. The photoconductive drum 21 and the developing roller 22 contact each other to form the development nip N. The developing unit 200 is maintained at the development position by an elastic force of the elastic member 300. The development nip separating member 3 is positioned at a home position spaced apart from the first manipulating portion 43 of the nip control member 4. Referring to FIG. 6, the partial gear portion 44 of the nip control member 4 is not engaged with the switching gear 51. The compression spring 61 is relaxed (e.g., at minimum compression) between the first protrusion 212 of the developing roller gear 210 and the second protrusion 51a of the switching gear 51.

[0050] An image forming operation may be performed in a state shown in FIG. 1. The developing roller 22 is rotated in an image forming direction. In other words, the developing roller gear 210 connected to a developing coupler 220 is rotated in the first direction Al so that the developing roller 22 is rotated in the first direction Al . The supply roller 27 is rotated in connection with the developing roller gear 210 or the developing roller 22 through the gear train 230 of FIG. 5. The first protrusion 212 of the developing roller gear 210 pushes the compression spring 61 in the first direction Al, and the second protrusion 51a is pushed by the compression spring 61 in the first direction Al. The switching gear 51 is rotated in the first direction Al. Because the the partial gear portion 44 of the nip control member 4 is not engaged with the switching gear 51, the nip control member 4 is not rotated and is maintained at the nip formation position. Thus, the developing unit 200 is maintained at the development position.

[0051] When the image forming operation is completed or the process cartridge 2 is not used for the image forming operation, the developing unit 200 may be pivoted to the release position. To this end, the nip control member 4 may be rotated from the nip formation position to the nip separation position by driving the development nip separating member 3. For example, the driving unit 35 moves the development nip separating member 3 from the home position toward the switching position. As shown in FIG. 2, the nip control member 4 is maintained at the nip formation position until the development nip separating member 3 comes into contact with the first manipulating portion 43 of the nip control member 4, and the developing unit 200 is maintained at the development position.

[0052] When the development nip separating member 3 is further moved toward the switching position after the development nip separating member 3 comes into contact with the first manipulating portion 43 of the nip control member 4, the development nip separating member 3 pushes the first manipulating portion 43, and the nip control member 4 is rotated from the nip formation position to the nip separation position. When the partial gear portion 44 is engaged with the switching gear 51, the switching gear 51 is rotated in the second direction A2. The second protrusion 51a of the switching gear 51 pushes the compression spring 61 in the second direction A2, and the compression spring 61 pushes the first protrusion 212 of the developing roller gear 210 in the second direction A2. The developing roller gear 210 is coupled to the developing roller 22. Because the developing roller 22 is coupled to a rotation member such as the supply roller 27, the rotation load of the developing roller 22 is greater than the torque applied to the first protrusion 212 by the compression spring 61. The developing roller 22 is not rotated, and the switching gear 51 is rotated in the second direction A2, and accordingly, the compression spring 61 is compressed between the first protrusion 212 and the second protrusion 51a. The rotation displacement of the switching gear 51 while the nip control member 4 reaches the nip separation position is stored in the compression spring 61.

[0053] As the nip control member 4 is rotated from the nip formation position to the nip separation position, the nip separating portion 42 of the nip control member 4 pushes the photoconductive unit 100, for example, the first frame 101. Because the photoconductive unit 100 has a fixed position, the developing unit 200 is pivoted around the hinge axis HA in the opposite direction to the elastic force of the elastic member 300, that is, in a direction Bl (e.g., counterclockwise as shown in FIGS. 1-4). Then, the developing roller 22 is spaced from the photoconductive drum 21, and the development nip N is released. When the development nip separating member 3 reaches the switching position, the nip control member 4 is positioned at the nip separation position, and the developing unit 200 is positioned at the release position, as shown in FIG. 3. The partial gear portion 44 of the nip control member 4 remains engaged with the switching gear 51. The compression spring 61 is maintained in a compressed state between the first protrusion 212 of the developing roller gear 210 and the second protrusion 51a of the switching gear 51. The driving unit 35 may return the development nip separating member 3 from the switching position to the home position shown in FIG. 4.

[0054] As described above, in a process of switching the developing unit 200 from the development position to the release position, the rotation power in the second direction A2 is applied to the developing roller 22 by the switching gear 51. When the developing roller 22is rotated in the second direction A2, rotation members of the developing unit 200 connected to the developing roller 22, for example, the supply roller 27 and an agitator (not shown), are rotated in the opposite direction to an image forming direction, which is the opposite direction to a rotation direction during the image forming operation. Sealing members for preventing leakage of toner are in contact with the developing roller 22 and the supply roller 27. Reverse rotations of the developing roller 22 and the supply roller 27 may cause damage to surfaces of the developing roller 22 and the supply roller 27 and damage to the sealing members, which may cause deterioration of image quality. A reverse rotation of the agitator may cause damage to a film forming the agitator, etc. In addition, in the process of switching the developing unit 200 from the development position to the release position, when the rotation members of the developing unit 200 are rotated, a driving motor with a large driving torque needs to be employed as a driving motor of the driving unit 35 for driving the development nip separating member 3. This may result in an increase in manufacturing cost of an image forming apparatus.

[0055] According to the present example, the rotation power of the switching gear 51 in the second direction A2 is blocked, reisisted, or reduced by the rotation power control member 6, for example, the compression spring 61, and is not transmitted to the developing roller gear 210 and the gear train 230 including the developing roller gear 210. That is, the rotation power of the switching gear 51 in the second direction A2 is stored in the compression spring 61 in the form of compression energy by compression deformation of the compression spring 61. Therefore, the developing roller 22, the supply roller 27, and the agitator are not reversely rotated. Accordingly, damage to the surfaces of the developing roller 22 and the supply roller 27, damage to the sealing members, and the like, which cause deterioration of image quality, may be prevented. In addition, a driving motor with a relatively small driving torque may be employed as the driving motor of the driving unit 35 for driving the development nip separating member 3, and thus, the manufacturing cost of the image forming apparatus may be reduced.

[0056] Before performing the image forming operation, the developing unit 200 may be switched from the release position to the development position. To this end, the nip control member 4 may be switched from the nip separation position to the nip formation position. According to the present example, the nip control member 4 is pivoted from the nip separation position to the nip formation position by the rotation power of the developing roller 22 driven in the first direction Al. In the state shown in FIG. 4, when the developing roller gear 210 is rotated in the first direction Al by the rotation power transmitted from the main body of theimage forming apparatus to the developing coupler 220, the developing roller 22 is rotated in the first direction Al . The supply roller 27 and the agitator connected to the developing roller 22 by the gear train 230 are rotated in the rotation direction for image formation (the image forming direction).

[0057] As shown in FIG. 7, the compression spring 61 is in a compressed state between the first protrusion 212 of the developing roller gear 210 and the second protrusion 51a of the switching gear 51. The first protrusion 212 of the developing roller gear 210 pushes the compression spring 61 in the first direction Al, and the compression spring 61 pushes the second protrusion 51a of the switching gear 51 in the first direction Al. The switching gear 51 is rotated in the first direction Al. Because the partial gear portion 44 of the nip control member 4 and the switching gear 51 are engaged, the nip control member 4 is rotated from the nip separation position to the nip formation position. As shown in FIG. 4, because the development nip separating member 3 is positioned at the home position, the first manipulating portion 43 of the nip control member 4 does not contact the development nip separating member 3, and the development nip separating member 3 does not interfere with the rotation of the nip control member 4. The nip separating portion 42 of the nip control member 4 is spaced apart from the photoconductive unit 100, for example, the first frame 101, and the developing unit 200 is pivoted in a direction B2 (e.g., clockwise as shown in FIGS 1- 4) around the hinge shaft HA by the elastic force of the elastic member 300. The developing roller 22 is in contact with the photoconductive drum 21. As shown in FIG. 1, when the nip control member 4 reaches the nip formation position, the developing unit 200 is positioned at the development position, and the development nip N where the photoconductive drum 21 and the developing roller 22 are in contact with each other is formed. The partial gear portion 44 of the nip control member 4 is disengaged from the switching gear 51. The compression spring 61 is relaxed. Therefore, even though the developing roller gear 210 is rotated in the first direction Al while the image forming operation is being performed, the nip control member 4 may not be rotated and may be maintained at the nip formation position.

[0058] FIG. 8 is a schematic exploded perspective view illustrating an example of the rotation power control member 6. The present example differs from the example shown in FIGS. 1 to 7 in that the first and second protrusions 51a and 212 and the compression spring 61 are replaced with a friction member 62. Therefore, the description of FIGS. 1 to 7 may be applied to the example shown in FIG. 8 unless contradictory, and the differences are mainly described.

[0059] Referring to FIG. 8, the rotation power control member 6 may include the friction member 62. The friction member 62 may be disposed between the switching gear 51 and thedeveloping roller gear 210 disposed opposite to the rotation shaft 22a of the developing roller 22 in an axial direction. For example, the switching gear 51 may be rotatably supported on the cylindrical supporting portion 211 of the developing roller gear 210. The friction member 62 provides a friction torque between the developing roller gear 210 and the switching gear 51. The friction member 62 functions as a torque limiter or a clutch. The friction member 62 may be implemented by, for example, a disc spring, felt, etc. The friction torque provided by the friction member 62 may be less than a rotation load torque of the developing roller 22 in the second direction A2 and may be greater than a rotation load torque of the nip control member 4 from the nip separation position to the nip formation position. To satisfy this condition, the magnitude of an elastic (e.g., compressive) force of the friction member 62, a material of the friction member 62, etc. may be appropriately determined.

[0060] As described above, the nip control member 4 is rotated from the nip formation position to the nip separation position by the development nip separating member 3 to switch the developing unit 200 from the development position to the release position. Then, while the partial gear portion 44 of the nip control member 4 and the switching gear 51 are engaged with each other, the switching gear 51 is rotated in the second direction A2. At this time, the friction torque is applied to the switching gear 51 and the developing roller gear 210 by the friction member 62. Because the friction torque is less than the rotation load torque of the developing roller 22 in the second direction A2, a slip occurs between the switching gear 51 and the developing roller gear 210 and the friction member 62. The developing roller gear 210 and the developing roller 22 are not rotated in the second direction A2. Because the gear train 230 also is not rotated, other rotation members of the developing unit 200 also are not rotated.

[0061] As described above, to switch the developing unit 200 from the release position to the development position, the developing roller 22 and the developing roller gear 210 are rotated in the first direction Al. The friction torque is applied to the switching gear 51 and the developing roller gear 210 by the friction member 62. Because the friction torque is greater than the rotation load torque of the nip control member 4 from the nip separation position to the nip formation position, the switching gear 51 is rotated in the first direction Al, and the rotation power of the switching gear 51 is transmitted to the nip control member 4 through the partial gear portion 44. The nip control member 4 may be rotated from the nip separation position to the nip formation position. When the nip control member 4 reaches the nip formation position, the engagement between the partial gear portion 44 of the nip control member 4 and the switching gear 51 is released. Therefore, even though the developing rollergear 210 is rotated in the first direction Al while the image forming operation is being performed, the nip control member 4 may be maintained at the nip formation position.

[0062] As an example, the rotation power control member 6 may be implemented by a oneway power transmission member. FIG. 9 is a schematic perspective view of an example of a development nip formation / separation structure employing a one-way power transmission member 63 as the rotation power control member 6. FIG. 10 is a schematic exploded perspective view of an example of the development nip formation / separation structure shown in FIG. 9. The development nip formation / separation structure of the present example differs from the example shown in FIGS. 1 to 7 in that a switching member 53, the one-way power transmission member 63, and a nip control member 4a including a first interfering portion 45 are employed, instead of the switching gear 51, the compression spring 61, and the nip control member 4 including the partial gear portion 44 of the example shown in FIGS. 1 to 7. Therefore, the descriptions of FIGS. 1 to 7 may be applied to the example of the development nip formation / separation structure shown in FIGS. 9 and 10 unless contradictory, and differences are mainly described.

[0063] Referring to FIGS. 9 and 10, the developing roller gear 210 is rotatably supported on the rotation shaft 22a of the developing roller 22. The developing roller gear 210 is rotated in connection with the developing coupler 220. The switching member 53 is rotatably supported on the rotation shaft 22a of the developing roller 22. The switching member 53 is engaged with the developing roller gear 210 in an axial direction. The switching member 53 receives a rotation power in the first direction Al from the developing roller gear 210. For example, as shown in FIG. 10, a first power transmission portion 213 in a sawtooth shape is provided in the developing roller gear 210. A second power transmission portion 53b having a shape complementary to that of the first power transmission portion 213 is provided in the switching member 53. The rotation power of the developing roller gear 210 in the first direction Al is transmitted to the switching member 53 through the first power transmission portion 213 and the second power transmission portion 53b.

[0064] The rotation power control member 6 includes the one-way power transmission member 63 disposed between the rotation shaft 22a of the developing roller 22 and the switching member 53 and transmitting the rotation power of the switching member 53 in the first direction Al to the rotation shaft 22a of the developing roller 22. The one-way power transmission member 63 may be implemented in various forms, such as a one-way clutch, a one-way bearing, a one-way gear assembly using a satellite gear, etc. In the present example, a one-way bearing is employed as the one-way power transmission member 63. When arotation power in a power transmission direction is applied to the one-way bearing, for example, a cylindrical bearing is locked to a shaft, the one-way bearing and the shaft are rotated together in the power transmission direction. When a rotation power in the opposite direction to the power transmission direction acts is applied to the one-way bearing, for example, the locking of the cylindrical bearing and the shaft is released, the shaft is not rotated, and the one-way bearing is rotated in the opposite direction to the power transmission direction.

[0065] The one-way power transmission member 63 is connected to the switching member 53 to rotate together with the switching member 53. The switching member 53 may function as a housing in which the one-way power transmission member 63 is accommodated. For example, when the one-way bearing is employed as the one-way power transmission member 63, the switching member 53 may be a bearing housing accommodating the one-way bearing. When the developing roller gear 210 is rotated in the first direction Al, the switching member 53 and the one-way power transmission member 63 are rotated together in the first direction Al. Because the switching member 53 and the rotation shaft 22a of the developing roller 22 are connected to each other by the one-way power transmission member 63, the developing roller 22 is rotated in the first direction Al. A connecting gear 231 is coupled to the rotation shaft 22a of the developing roller 22. The connecting gear 231 is rotated together with the developing roller 22. The rotation power of the developing roller 22 in the first direction Al may be transmitted to rotation members of the developing unit 200, for example, the supply roller 27 and an agitator (not shown) through the gear train 230 including the connecting gear 231. When the switching member 53 is rotated in the second direction A2, the connection between the switching member 53 and the rotation shaft 22a of the developing roller 22 is released by the one-way power transmission member 63, and the developing roller 22 is not rotated. Therefore, the gear train 230 including the connecting gear 231 is not rotated in the opposite direction to an image forming direction, and the rotation members of the developing unit 200, for example, the supply roller 27, and the agitator (not shown), also are not rotated in the opposite direction to the image forming direction. The developing roller gear 210 is rotated in the second direction A2.

[0066] The nip control member 4a of the present example is different from the nip control member 4 shown in FIG. 1 in that the first interfering portion 45 is provided instead of the partial gear portion 44. The nip control member 4a may be supported on the developing unit 200, for example, the second frame 201, so as to be pivotable to a nip formation position (FIG. 11) and a nip separation position (FIGS. 12 and 13). The nip control member 4a may includea nip separating portion 42 that contacts the photoconductive unit 100 and interferes with the rotation of the developing unit 200 when positioned at the nip separation position, and a first manipulating portion 43 that contacts and is pushed by the development nip separating member 3 that moves from the home position to the switching position. The nip control member 4a may further include the first interfering portion 45. The switching member 53 includes a second interfering portion 53a that contacts the first interfering portion 45 when rotated in the first direction Al so that the nip control member 4a is switched from the nip separation position to the nip formation position. For example, the second interfering portion 53a may protrude from the switching member 53 in an axial direction. When the nip control member 4a is rotated from the nip formation position to the nip separation position, the second interfering portion 53a may contact the first interfering portion 45. Then, the switching member 53 is rotated in the second direction A2. The rotation power of the switching member 53 in the second direction A2 is blocked by the one-way power transmission member 63. Therefore, the developing roller 22 is not rotated. As shown in FIG. 9, the nip separating portion 42 is formed stepwise from the first interfering portion 45 in the axial direction. Therefore, when the switching member 53 is rotated, the nip separating portion 42 and the second interfering portion 53a do not interfere with each other.

[0067] FIGS. 11 to 13 are schematic side views of an example of the process cartridge 2 to which the development nip formation / separation structure shown in FIGS. 9 and 10 is applied. FIG. 11 illustrates a state in which the developing unit 200 is positioned at a development position and the development nip separating member 3 is positioned at a home position. FIG. 12 illustrates a state in which the developing unit 200 is positioned at a release position and the development nip separating member 3 is positioned at a switching position. FIG. 13 illustrates a state in which the developing unit 200 is positioned at the release position and the development nip separating member 3 is positioned at the home position. A process of forming / releasing the development nip N is described with reference to FIGS. 9 to 13.

[0068] First, referring to FIG. 11, the nip control member 4a is positioned at the nip formation position. The nip separating portion 42 is spaced apart from the photoconductive unit 100, for example, the first frame 101. The photoconductive drum 21 and the developing roller 22 contact each other to form the development nip N. The developing unit 200 is maintained at the development position by an elastic (e.g., tensile) force of the elastic member 300. The development nip separating member 3 is positioned at the home position spaced apart from the first manipulating portion 43 of the nip control member 4a.

[0069] An image forming operation may be performed in the state shown in FIG. 11. The developing roller 22 is rotated in the first direction Al. In other words, when the developing roller gear 210 connected to the developing coupler 220 is rotated in the first direction Al, the switching member 53 is rotated in the first direction Al. The rotation power of the switching member 53 in the first direction Al is transmitted to the rotation shaft 22a of the developing roller 22 by the one-way power transmission member 63, and the developing roller 22 is rotated in the first direction Al. The connecting gear 231 is rotated in the first direction Al together with the developing roller 22, and rotation members of the developing unit 200, for example, the supply roller 27 and an agitator, are rotated in an image forming direction by the gear train 230 including the connecting gear 231. The second interfering portion 53a of the switching member 53 does not contact the nip separating portion 42 and the first interfering portion 45 of the nip control member 4a. Thus, the nip control member 4a is maintained at the nip formation position, and the developing unit 200 is maintained at the development position.

[0070] When the image forming operation is completed or the process cartridge 2 is not used for the image forming operation, the developing unit 200 may be pivoted to the release position. To this end, the nip control member 4a may be rotated from the nip formation position to the nip separation position by driving the development nip separating member 3. For example, the driving unit 35 moves the development nip separating member 3 from the home position shown in FIG. 11 toward the switching position shown in FIG. 12. The nip control member 4a is maintained at the nip formation position until the development nip separating member 3 comes into contact with the first manipulating portion 43 of the nip control member 4a, and the developing unit 200 is maintained at the development position.

[0071] When the development nip separating member 3 is further moved toward the switching position after the development nip separating member 3 comes into contact with the first manipulating portion 43 of the nip control member 4a, the development nip separating member 3 pushes the first manipulating portion 43, and the nip control member 4a is rotated from the nip formation position to the nip separation position. As the nip control member 4a is rotated from the nip formation position to the nip separation position, the nip separating portion 42 of the nip control member 4a pushes the photoconductive unit 100, for example, the first frame 101. Because the photoconductive unit 100 has a fixed position, the developing unit 200 is rotated around the hinge axis HA in the opposite direction to an elastic force of the elastic member 300, that is, in the direction Bl. Then, the developing roller 22 is spaced from the photoconductive drum 21 and the development nip N is released. While thenip control member 4a is rotated from the nip formation position to the nip separation position, the first interfering portion 45 may interfere with the second interfering portion 53a. At this time, the first interfering portion 45 pushes the second interfering portion 53a in the second direction A2. Then, the switching member 53 is rotated in the second direction A2. The rotation power of the switching member 53 in the second direction A2 is blocked by the oneway power transmission member 63 and is not transmitted to the rotation shaft 22a of the developing roller 22. Therefore, the developing roller 22 is not rotated, and the rotation members of the developing unit 200 also are not rotated. When the development nip separating member 3 reaches the switching position, as shown in FIG. 12, the nip control member 4a is positioned at the nip separation position, and the developing unit 200 is positioned at the release position. The driving unit 35 may return the development nip separating member 3 from the switch position to the home position shown in FIG. 13.

[0072] According to the present example, the rotation power of the switching member 53 in the second direction A2 is blocked by the rotation power control member 6, for example, the one-way power transmission member 63, and is not transmitted to the developing roller 22. Therefore, the developing roller 22, the supply roller 27, and the agitator are not reversely rotated. Accordingly, damage to the surfaces of the developing roller 22 and the supply roller 27, damage to the sealing members, and the like, which cause deterioration of image quality, may be prevented. In addition, a driving motor with a relatively small driving torque may be employed as the driving motor of the driving unit 35 for driving the development nip separating member 3, and thus, the manufacturing cost of the image forming apparatus may be reduced.

[0073] Before performing the image forming operation, the developing unit 200 may be switched from the release position to the development position. To this end, the nip control member 4a may be switched from the nip separation position to the nip formation position. According to the present example, the nip control member 4a is pivoted from the nip separation position to the nip formation position by the rotation power of the developing roller 22 driven in the first direction Al. In the state shown in FIG. 13, when the developing roller gear 210 is rotated in the first direction Al by the rotation power transmitted from a main body of an image forming apparatus to the developing coupler 220, the switching member 53 is rotated in the first direction Al . The rotation power of the switching member 53 in the first direction Al is transmitted to the rotation shaft 22a of the developing roller 22 by the oneway power transmission member 63, and the developing roller 22 is rotated. The supply roller27 connected to the developing roller 22 and the agitator are rotated in the image forming direction through the gear train 230 including the connecting gear 231.

[0074] The second interfering portion 53a of the switching member 53 pushes the first interfering portion 45 of the nip control member 4a. Then, the nip control member 4a is rotated from the nip separation position to the nip formation position. As shown in FIG. 13, because the development nip separating member 3 is positioned at the home position, the first manipulating portion 43 of the nip control member 4a does not contact the development nip separating member 3, and the development nip separating member 3 does not interfere with the rotation of the nip control member 4a. The nip separating portion 42 of the nip control member 4a is spaced apart from the photoconductive unit 100, for example, the first frame 101, and the developing unit 200 is pivoted in the direction B2 around the hinge shaft HA by the elastic force of the elastic member 300. The developing roller 22 is in contact with the photoconductive drum 21. As shown in FIG. 11, when the nip control member 4a reaches the nip formation position, the developing unit 200 is positioned at the development position, and the development nip N where the photoconductive drum 21 and the developing roller 22 are in contact with each other is formed. The contact between the first interfering portion 45 of the nip control member 4a and the second interfering portion 53a of the switching member 53 ends. Even though the developing roller gear 210 is rotated in the first direction Al while the image forming operation is being performed, the nip control member 4a is not rotated and may be maintained at the nip formation position.

[0075] FIGS. 14 to 17 are schematic side views of an example of a process cartridge. FIG. 14 illustrates a state in which the developing unit 200 is positioned at a development position and the development nip separating member 3 is positioned at a home position. FIG. 15 illustrates a state in which the developing unit 200 is positioned at an over-rotation position. FIG. 16 illustrates a state in which a nip control member is positioned at a nip separation position. FIG. 17 illustrates a state in which the developing unit 200 is positioned at a release position and the development nip separating member 3 is positioned at the home position.

[0076] Referring to FIGS. 14 to 17, the photoconductive unit 100 including the photoconductive drum 21 and the developing unit 200 including the developing roller 22 are shown. The developing unit 200 may be coupled to the photoconductive unit 100 so as to be pivotable to a development position (FIG. 14) where the developing roller 22 contacts the photoconductive drum 21 to form the development nip N and to a release position (FIG. 17) at which the developing roller 22 is spaced apart from the photoconductive drum 21. For example, the developing unit 200 may be pivotable to the development position and therelease position around the hinge shaft HA. The elastic member 300 applies an elastic force to the photoconductive unit 100 and the developing unit 200 biasing the development unit toward the development position.

[0077] The gear train 230 is for rotating the developing roller 22. The gear train 230 may be connected to the developing coupler 220 that receives rotation power from a main body of an image forming apparatus when the process cartridge 2 is mounted on the main body of the image forming apparatus. The gear train 230 may include one or more gears including a pinion. As an example, the gear train 230 may include a gear 221 provided in the developing coupler 220, the developing roller gear 210 coupled to the rotation shaft 22a of the developing roller 22 and connecting gears 232 and 233 connecting the gear 221 to the developing roller gear 210. The gear train 230 includes a pinion. In the present example, the gear train 230 is provided in the developing unit 200, and the gear 221 is used as the pinion. Hereinafter, the gear 221 is referred to as a pinion 221.

[0078] A nip control member 4b includes a rack gear portion 46. The nip control member 4b is switchable between the nip formation position (FIG. 14) and the nip separation position (FIG. 17). The nip separation position is a position at which the rack gear portion 46 maintains the developing unit 200 at the release position while engaged with the pinion 221. The nip separation position is a position allowing the developing unit 200 to be pivoted to the development position by the elastic force of the elastic member 300 when the gear train 230 is driven in an image forming direction. In the present example, the nip control member 4b is provided on the photoconductive unit 100.

[0079] As an example, the nip control member 4b may be linearly moved to the nip formation position and the nip separation position. Guide pins 121 and 122 may be provided in the photoconductive unit 100. A guide slot 48 into which the guide pins 121 and 122 are inserted may be provided in the nip control member 4b. The nip control member 4b may be guided by the guide pins 121 and 122 and linearly moved to the nip formation position and the nip separation position. Movement of the nip control member 4b from the nip separation position to the nip formation position may be implemented by driving the gear train 230 in the image forming direction. When the nip control member 4b is positioned at the nip separation position, the pinion 221 is engaged with the rack gear portion 46. In this state, when the gear train 230 is driven in the image forming direction, the nip control member 4b may be moved from the nip separation position to the nip formation position. When the nip control member 4b reaches the nip formation position, the pinion 221 may disengage from the rack gear portion 46. An opposing portion 47 that faces the pinion 221 when the pinion 221 isdisengaged from the rack gear portion 46 is provided in the nip control member 4b when the nip control member 4b is positioned at the nip formation position. The opposing portion 47 is formed to be more recessed than the rack gear portion 46 away from the pinion 221. Therefore, when the rack gear portion 46 disengages from the pinion 221, and the pinion 221 faces the opposing portion 47, the developing unit 200 may be pivoted in a direction of the elastic force of the elastic member 300 and reach the development position.

[0080] As an example, the switching of the nip control member 4b from the nip formation position to the nip separation position may be performed by moving the development nip separating member 3. The development nip separating member 3 may be provided in the main body of the image forming apparatus in which the process cartridge 2 is mounted. The driving unit 35 for driving the development nip separating member 3 may be provided in the main body of the image forming apparatus. For example, the development nip separating member 3 may be linearly moved between the home position and the switching position. The driving unit 35 may include an actuator, for example, a driving motor, and a power conversion mechanism that converts rotation power of the driving motor into linear motion of the development nip separating member 3. The power conversion mechanism may be implemented by, for example, a rack-and-pinion mechanism, a cam-slider mechanism, etc. A first manipulating portion 203 capable of contacting the development nip separating member 3 moved from the home position may be provided in the developing unit 200.

[0081] The home position of the development nip separating member 3 is a position at which the first manipulating portion 203 does not contact the development nip separating member 3 or interfere with the rotation of the developing unit 200. The switching position of the development nip separating member 3 is a position at which the developing unit 200 is positioned at an over-rotation position (FIG. 15). The over-rotation position of the developing unit 200 is a position at which the developing unit 200 is further pivoted beyond the release position. The over-rotation position of the developing unit 200 is a position at which the rack gear portion 46 and the pinion 221 are spaced apart from each other so that the nip control member 4b positioned at the nip formation position may be movable to the nip separation position. When the rack gear portion 46 and the pinion 221 are spaced apart from each other, the nip control member 4b may be moved from the nip formation position to the nip separation position, for example, by gravity. As indicated by dotted lines in FIGS. 14 to 17, a second elastic member 49 applying an elastic (e.g., compressive) force in a direction in which the nip control member 4b is moved from the nip formation position to the nip separation position may be provided. For example, the second elastic member 49 may be implemented in variousforms such as a coil spring, a leaf spring, etc. When the rack gear portion 46 and the pinion 221 are spaced apart from each other, the nip control member 4b may be moved from the nip formation position to the nip separation position by the elastic force of the second elastic member 49.

[0082] Referring to FIGS. 14 to 17, a process of forming / releasing the development nip N is described. First, referring to FIG. 14, the nip control member 4b is positioned at the nip formation position. The photoconductive drum 21 and the developing roller 22 contact each other to form the development nip N. The developing unit 200 is maintained at the development position by the elastic force of the elastic member 300. The development nip separating member 3 is positioned at the home position spaced apart from the first manipulating portion 203 of the developing unit 200. The rack gear portion 46 of the nip control member 4b is spaced apart from the pinion 221. That is, the rack gear portion 46 is not engaged with the pinion 221.

[0083] An image forming operation may be performed in the state shown in FIG. 14. Even though the gear train 230 is rotated in the image forming direction, the nip control member 4b is maintained at the nip formation position because the rack gear portion 46 is not engaged with the pinion 221. Thus, the developing unit 200 is maintained at the development position. When the image forming operation is completed or the process cartridge 2 is not used for the image forming operation, the developing unit 200 may be pivotable to the release position. To this end, the developing unit 200 may be pivotable from the development position to the over-rotation position by driving the development nip separating member 3. For example, the driving unit 35 moves the development nip separating member 3 from the home position to the switching position. The development nip separating member 3 pushes the first manipulating portion 203 of the developing unit 200. As shown in FIG. 15, when the development nip separating member 3 reaches the switching position, the developing unit 200 reaches the over-rotation position at which the developing unit 200 is further pivoted in the direction Bl beyond the release position. When the developing unit 200 is positioned at the over-rotation position, the pinion 221 is positioned at a position at which the pinion 221 does not contact the rack gear portion 46 when the nip control member 4b is moved from the nip formation position to the nip separation position. As shown in FIG. 16, the nip control member 4b is moved to the nip separation position by sliding in a direction Cl by gravity or by the elastic force of the second elastic member 49. When the guide pin 122 is hung on an upper end of the guide slot 48, the nip control member 4b reaches the nip separation position. The guide pin 122 functions as a stopper to prevent the nip control member 4b from furthermoving beyond the nip separation position. The driving unit 35 may return the development nip separating member 3 from the switching position to the home position. As the development nip separating member 3 is moved toward the home position, the developing unit 200 is pivoted in a direction of the elastic force of the elastic member 300, that is, in the direction B2. When the pinion 221 is engaged with the rack gear portion 46, the developing unit 200 stops being pivoted in the direction B2, and the developing unit 200 reaches the release position as shown in FIG. 17. The development nip separating member 3 reaches the home position.

[0084] According to the present example, the gear train 230 is not rotated in a process of moving the nip control member 4b from the nip formation position to the nip separation position. Therefore, the developing roller 22, the supply roller 27, and an agitator are not reversely rotated. Accordingly, damage to the surfaces of the developing roller 22 and the supply roller 27, damage to a sealing member, and the like, which cause deterioration of image quality, may be prevented. In addition, a driving motor with a relatively small driving torque may be employed as the driving motor of the driving unit 35 for driving the development nip separating member 3, and thus, the manufacturing cost of the image forming apparatus may be reduced.

[0085] Before performing the image forming operation, the developing unit 200 may be switched from the release position to the development position. To this end, the nip control member 4b may be switched from the nip separation position to the nip formation position. According to the present example, the nip control member 4b is pivotable from the nip separation position to the nip formation position by the rotation power of the gear train 230 driven in the image forming direction. In the state shown in FIG. 17, the gear train 230 is driven in the image forming direction by rotation power transmitted from the main body of the image forming apparatus to the developing coupler 220. Because the pinion 221 and the rack gear portion 46 are engaged, as the pinion 221 rotates, the nip control member 4b is moved from the nip separation position to the nip formation position. When the engagement between the pinion 221 and the rack gear portion 46 is released, the pinion 221 faces the concave opposing portion 47 of the nip control member 4b. The developing unit 200 is pivotable in the direction B2 by the elastic force of the elastic member 300, the developing unit 200 reaches the development position shown in FIG. 14, and the development nip N is formed. Even though the gear train 230 is driven in the image forming direction while the image forming operation is being performed, because the pinion 221 is disengaged from therack gear portion 46, the nip control member 4b may be maintained at the nip formation position.

[0086] FIG. 18 is a schematic configuration diagram of an example of an electrophotographic image forming apparatus. The image forming apparatus of the present example prints a color image on a print medium P by an electrophotographic method. Referring to FIG. 1, the image forming apparatus may include a main body 1 and a plurality of process cartridges 2. The plurality of process cartridges 2 are attached to and detached from the main body 1. An exposure device 11, a transfer unit, and a fixing unit 15 are provided in the main body 1. In addition, a print medium transporting unit for loading and transporting the print medium P on which an image is to be formed is provided in the main body 1.

[0087] For color printing, the plurality of process cartridges 2 may include four process cartridges 2 for developing images of, for example, cyan C, magenta M, yellow Y, and black K colors. Each of the four process cartridges 2 may contain developers, for example, toners, of cyan C, magenta M, yellow Y, and black K colors. Although not shown in the drawings, the toners of cyan C, magenta M, yellow Y, and black K colors may be contained in four toner supply containers, respectively, and may be supplied from the four toner supply containers to the four process cartridges 2, respectively. The image forming apparatus may further include the process cartridge 2 for containing and developing toners of various colors, such as light magenta and white, in addition to the above-described colors. Hereinafter, the image forming apparatus including the four process cartridges 2 is described. Unless otherwise specified, reference numerals denoted by C, M, Y, and K respectively refer to components for developing images of cyan C, magenta M, yellow Y, and black K colors. The process cartridges 2C, 2M, 2Y, and 2K may be attached to and detached from the main body 1 through a door not shown.

[0088] The process cartridge 2 of the present example is an integrated process cartridge. The process cartridge 2 may have the structure described with reference to FIGS. 1 to 17. The process cartridge 2 may include the photoconductive unit 100 and the developing unit 200. The photoconductive unit 100 includes the photoconductive drum 21. The photoconductive drum 21 is an example of a photoconductor on which an electrostatic latent image is formed and may include a conductive metal pipe and a photosensitive layer formed on its outer circumference. A charging roller 23 is an example of a charger that charges the photoconductive drum 21 to have a uniform surface electric potential. Instead of the charging roller 23, a charging brush, a corona charger, etc. may be employed. The photoconductive unit 100 may further include a cleaning roller (not shown) for removing foreign substancesfrom a surface of the charging roller 23. A cleaning blade 25 is an example of a cleaning means for removing toner and foreign substances remaining on the surface of the photoconductive drum 21 after a transfer process described below. Instead of the cleaning blade 25, another type of cleaning device such as a rotating brush may be employed.

[0089] The developing unit 200 includes a toner container 209. The developing unit 200 supplies the toner contained in the toner container 209 to the electrostatic latent image formed on the photoconductive drum 21 to develop the electrostatic latent image into a visible toner image. Developing methods include a one-component developing method using toner and a two-component developing method using toner and carrier. The process cartridge 2 of the present example employs the one-component developing method. The developing roller 22 is for supplying toner to the photoconductive drum 21. A developing bias voltage for supplying toner to the photoconductive drum 21 may be applied to the developing roller 22. In the present example, a contact developing method is employed in which the developing roller 22 and the photoconductive drum 21 come into contact with each other to form the development nip N. The supply roller 27 supplies the toner in the toner container 209 to the surface of the developing roller 22. To this end, a supply bias voltage may be applied to the supply roller 27. The developing unit 200 may further include a regulating member 28 for regulating an amount of toner supplied to the development nip N where the photoconductive drum 21 and the developing roller 22 come into contact with each other. The regulating member 28 may be, for example, a doctor blade that elastically comes into contact with the surface of the developing roller 22. The developing unit 200 may further include a lower sealing member 29 that contacts the developing roller 22 on the opposite side of the regulating member 28 to prevent leakage of toner. The lower sealing member 29 may be, for example, a film contacting the developing roller 22.

[0090] An exposure device 11 irradiates the photoconductive drum 21 with light modulated corresponding to image information to form an electrostatic latent image on the photoconductive drum 21. As the exposure device 11, a laser scanning unit (LSU) using a laser diode as a light source, a light emitting diode (LED) exposure device using an LED as a light source, etc. may be employed.

[0091] The transfer unit may include an intermediate transfer belt 12, intermediate transfer rollers 13, and a transfer roller 14. A toner image developed on the photoconductive drum 21 of each of the process cartridges 2C, 2M, 2Y, and 2K is temporarily transferred to the intermediate transfer belt 12. The intermediate transfer belt 12 is supported by support rollers 12a, 12b, and 12c and is circulated. Four intermediate transfer rollers 13 are respectivelydisposed at positions facing the photoconductive drums 21 of the process cartridge 2C, 2M, 2Y, and 2K with the intermediate transfer belt 12 disposed therebetween. An intermediate transfer bias voltage for transferring the toner image developed on the photoconductive drum 21 to the intermediate transfer belt 12 is applied to the four intermediate transfer rollers 13. Instead of the intermediate transfer roller 13, a corona transfer unit or a pin scorotron type transfer unit may be employed. The transfer roller 14 is positioned to face the intermediate transfer belt 12. A transfer bias voltage for transferring the toner image primarily transferred on the intermediate transfer belt 12 to the print medium P is applied to the transfer roller 14.

[0092] When a print command is received from a host (not shown), a control unit (not shown) charges the surface of the photoconductive drum 21 with a uniform electric potential by using the charging roller 23. The exposure device 11 scans the photoconductive drums 21 of the process cartridges 2C, 2M, 2Y, and 2K with four light beams modulated to be equal to the image information of each color to form electrostatic latent images on the photoconductive drum 21. The developing rollers 22 of the process cartridges 2C, 2M, 2Y, and 2K supply the toners of C, M, Y, and K to the corresponding photoconductive drums 21, respectively, to develop the electrostatic latent images into visible toner images. The developed toner images are primarily transferred to the intermediate transfer belt 12. The print media P loaded on a loading table 17 is withdrawn from one by one by a pick-up roller 16, and is transferred to a transfer nip, by a feed roller 18, formed by the transfer roller 14 and the intermediate transfer belt 12. The toner images primarily transferred on the intermediate transfer belt 12 are transferred to the print medium P by a secondarily transferred bias voltage applied to the transfer roller 14. When the print medium P passes through the fixing unit 15, the toner images are fixed on the print medium P by heat and pressure. The completely fixed print medium P is discharged to the outside by a discharge roller 19.

[0093] According to the above configuration, the developing unit 200 is positioned at a release position while an image forming operation is not being performed, so that the developing roller 22 may be spaced from the photoconductive drum 21. Before performing the image forming operation, the developing unit 200 is positioned at a development position by driving the developing roller 22 in the first direction Al, which is an image forming direction, so that the developing roller 22 may contact the photoconductive drum 21 to form the development nip N.

[0094] Although the disclosure has been described with reference to the examples shown in the drawings, it will be understood that this is merely exemplary, and that various modifications and equivalent other examples are possible therefrom by those of ordinary skillin the art. Accordingly, the true technical protection scope of the disclosure should be defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A cartridge comprising: a photoconductive unit comprising a photoconductive drum; a developing unit comprising a developing roller and coupled to the photoconductive unit so as to be pivotable to a release position at which the developing roller is spaced apart from the photoconductive drum and to a development position at which the developing roller comes into contact with the photoconductive drum to form a development nip; an elastic member to apply an elastic force to the photoconductive unit and the developing unit biasing the developing unit toward the development position; a nip control member switchable to a nip separation position at which the developing unit is maintained at the release position and to a nip formation position that allows the developing unit to be pivoted to the development position by the elastic force of the elastic member; a switching member rotated in conjunction with a rotation of the developing roller to switch the nip control member from the nip separation position to the nip formation position in a case where the developing roller is rotated in a first direction that is an image forming direction; and a rotation power control member to block or reduce transmission of rotation power between the switching member and the developing roller in a case where the nip control member is switched from the nip formation position to the nip separation position.

2. The cartridge of claim 1, comprising: a developing roller gear coupled to a rotation shaft of the developing roller, wherein the switching member includes a switching gear rotatably supported on the rotation shaft of the developing roller and opposite the developing roller gear in an axial direction, the nip control member includes a partial gear portion to engage with the switching gear, and the rotation power control member is disposed between the developing roller gear and the switching gear.

3. The cartridge of claim 2, wherein the developing roller gear includes a first protrusion,the switching gear includes a second protrusion opposite to the second protrusion in a circumferential direction, and the rotation power control member includes a compression spring disposed between the first protrusion and the second protrusion.

4. The cartridge of claim 3, wherein, in a case where the nip control member is rotated from the nip formation position to the nip separation position, the partial gear portion is engaged with the switching gear so that the switching gear is rotated in a second direction opposite to the first direction, and the compression spring is compressed between the first protrusion and the second protrusion, and a torque acting on the developing roller by the compressed compression spring is less than a rotation load torque of the developing roller in the second direction.

5. The cartridge of claim 3, wherein, in a case where the developing roller is rotated in the first direction, the first protrusion of the developing roller gear pushes the compression spring so that the switching gear is rotated in the first direction, and the switching gear and the partial gear portion are engaged with each other so that the nip control member is rotated from the nip separation position to the nip formation position, and in a case where the nip control member reaches the nip formation position, the switching gear is disengaged from the partial gear portion, and the compression spring returns to a relaxed state.

6. The cartridge of claim 2, wherein the rotation power control member includes a friction member disposed between the developing roller gear and the switching gear to provide a friction torque, and the friction torque of the friction member is less than a rotation load torque of the developing roller in a second direction opposite to the first direction and is greater than a rotation load torque of the nip control member from the nip separation position to the nip formation position.

7. The cartridge of claim 1, comprising: a developing roller gear rotatably supported on a rotation shaft of the developing roller,wherein the switching member receives rotation power in the first direction from the developing roller gear and is rotatably supported on the rotation shaft of the developing roller, and the rotation power control member includes a one-way power transmission member disposed between the rotation shaft of the developing roller and the switching member to transmit the rotation power of the switching member in the first direction to the rotation shaft of the developing roller.

8. The cartridge of claim 7, wherein the nip control member includes a first interfering portion, and the switching member includes a second interfering portion that contacts the first interfering portion such that the nip control member is switched from the nip separation position to the nip formation position in a case where the switching member is rotated in the image forming direction.

9. A cartridge comprising: a photoconductive unit comprising a photoconductive drum; a developing unit comprising a developing roller and coupled to the photoconductive unit so as to be pivotable to a development position at which the developing roller comes into contact with the photoconductive drum to form a development nip and to a release position at which the developing roller is spaced apart from the photoconductive drum; an elastic member to apply an elastic force to the photoconductive unit and the developing unit biasing the developing unit toward the development position; a gear train to rotate the developing roller and comprising one or more gears comprising a pinion; and a nip control member comprising a rack gear portion and switchable to a nip separation position at which the developing unit is maintained at the release position in a state in which the rack gear portion is engaged with the pinion and to a nip formation position that allows the developing unit to be pivoted to the development position by the elastic force of the elastic member, wherein, in a case where the nip control member is positioned at the nip formation position, the rack gear portion is disengaged from the pinion.

10. The cartridge of claim 9, wherein the pinion is provided in the developing unit, and the nip control member is provided in the photoconductive unit.

11. The cartridge of claim 9, wherein the developing unit includes an over-rotation position at which the developing unit is further rotated beyond the release position such that the pinion is spaced apart from the rack gear portion of the nip control member positioned at the nip formation position, and in a case where the developing unit is positioned at the over-rotation position, the nip control member is moved from the nip formation position to the nip separation position.

12. The cartridge of claim 11, wherein in a case where the developing unit is positioned at the over-rotation position, the nip control member is switched from the nip formation position to the nip separation position by gravity.

13. The cartridge of claim 11, comprising: a second elastic member to apply an elastic force to the nip control member in a direction toward the nip separation position.

14. An image forming apparatus comprising: a cartridge comprising a developing unit comprising a developing roller and coupled to a photoconductive unit so as to be pivotable to a release position at which the developing roller is spaced apart from a photoconductive drum in the photoconductive unit and to a development position at which the developing roller comes into contact with the photoconductive drum to form a development nip; an elastic member to apply an elastic force to the photoconductive unit and the developing unit biasing the development unit toward the development position; a nip control member switchable to a nip separation position at which the developing unit is maintained at the release position and a nip formation position that allows the developing unit to be pivoted to the development position by the elastic force of the elastic member; a switching member rotated in conjunction with a rotation of the developing roller to switch the nip control member from the nip separation position to the nip formation position in a case where the developing roller is rotated in a first direction that is an image forming direction;a rotation power control member to block or reduce transmission of rotation power between the switching member and the developing roller in a case where the nip control member is switched from the nip formation position to the nip separation position; a development nip separating member to switch the nip control member from the nip formation position to the nip separation position; and a driving unit to drive the development nip separating member.

15. The image forming apparatus of claim 14, wherein, in a case where the nip control member is positioned at the nip separation position, the driving unit returns the development nip separating member to a home position spaced apart from the nip control member.

Images