Abstract:
An image forming apparatus is provided. The image forming apparatus includes a photosensitive body unit including a photosensitive body, at least one developing unit including a developing roller that is configured to contact the photosensitive body or to be separated from the photosensitive body, and a press device to press the developing unit in order to contact or separate the photosensitive body and the developing roller to/from each other. The press device includes at least one lever configured to rotate about an end portion thereof and press the developing unit by rotation, and at least one cam configured to allow the lever to rotate by rotation thereof. Since the lever gradually rotates by rotation of the cam, force applied to the developing unit through the lever is also gradually and smoothly increased or decreased. Accordingly, shock, which may occur by rough movement of the developing unit, is remarkably reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to, and claims the priority benefit of, Korean Patent Application No. 10-2013-0052047, filed on May 8, 2013 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments relate to an image forming apparatus having a structure capable of contacting or separating developing rollers and photosensitive bodies to/from each other. 
     2. Description of the Related Art 
     An image forming apparatus refers to an apparatus that prints an image on a printing medium according to input signals. An image forming apparatus may be classified as a printer, a copying machine, a fax machine, a multi-function printer that has multiple functions including printing, scanning, copying and faxing, and the like. 
     An image forming apparatus comprises a photosensitive body unit including a photosensitive body therein, a laser scanning unit to form an electrostatic latent image on the photosensitive body, and a developing unit including a developing roller to form a visible image by supplying developers to the photosensitive body on which an electrostatic latent image is formed. 
     An image forming apparatus having a structure of supplying developers by contacting a developing roller to a photosensitive body operates such that a developing roller and a photosensitive body contact each other while an image forming process is performed, but are separated from each other to avoid interference therebetween while an image forming process is not being performed. 
     SUMMARY 
     It is an aspect of an exemplary embodiment to provide an image forming apparatus capable of reducing shock, which may occur during operation of a developing unit, by gradually increasing or decreasing force applied to the developing unit. 
     Additional aspects are set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with an aspect of an embodiment, an image forming apparatus includes a photosensitive body unit including a photosensitive body, at least one developing unit including a developing roller that is configured to contact the photosensitive body or to be separated from the photosensitive body, and a press device to press the developing unit in order to contact or separate the photosensitive body and the developing roller to/from each other. The press device includes at least one lever configured to rotate about an end portion thereof and press the developing unit by rotation, and at least one cam configured to allow the lever to rotate by rotation thereof. 
     The cam may include a cam portion that extends in a circumferential direction thereof, and the lever may include a guide part that interacts with the cam portion so that the lever rotates in an axial direction of the cam. 
     The cam portion may include a cam recess that is concavely formed at an outer peripheral surface of the cam, and the guide part may include a guide protrusion that protrudes from the lever and is inserted into the cam recess. 
     The cam portion may include a cam protrusion that is convexly formed at an outer peripheral surface of the cam, and the guide part may include a pair of guide protrusions that protrude from the lever and between which the cam protrusion is inserted. 
     The cam portion may include a first cam portion that extends obliquely in a first direction and a second cam portion that extends obliquely in a second direction that is opposite to the first direction. 
     The at least one developing unit may include plural developing units. The at least one lever may include plural levers to respectively press the plural developing units. The at least one cam may include plural cams that respectively correspond to the plural levers. The cam portion of each of the plural cams may be shaped such that the first cam portion and the second cam portion are connected in order in a circumferential direction of the cam. 
     The first cam portion and the second cam portion may respectively extend by an angle of 180 degrees in a circumferential direction of the cam. 
     The cam portion may further include a third cam portion that extends in parallel with a rotating direction of the cam. 
     The at least one developing unit may include a first developing unit for a black and white developing process and plural second developing units for a color developing process. The at least one lever may include a first lever to press the first developing unit and plural second levers to respectively press the plural second developing units. The at least one cam may include a first cam to rotate the first lever and plural second cams to respectively rotate the plural second levers. The cam portion of the first cam may be shaped such that the first cam portion, the third cam portion and the second cam portion are connected in order in a circumferential direction of the first cam. The cam portion of each of the plural second cams may be shaped such that the first cam portion, the second cam portion and the third cam portion are connected in order in a circumferential direction of the second cams. 
     The at least one developing unit may include a first developing unit for a black and white developing process and plural second developing units for a color developing process. The at least one lever may include a first lever to press the first developing unit and plural second levers to respectively press the plural second developing units. The at least one cam may include a first cam to rotate the first lever and plural second cams to respectively rotate the plural second levers. The cam portion of the first cam may be shaped such that the first cam portion, the third cam portion and the second cam portion are connected in order in a circumferential direction of the first cam. The cam portion of each of the plural second cams may be shaped such that the third cam portion, the first cam portion and the second cam portion are connected in order in a circumferential direction of the second cams. 
     The first cam portion, the second cam portion and the third cam portion may respectively extend by an angle of 120 degrees in a circumferential direction of the cam. 
     The image forming apparatus may further include a drive shaft. The at least one cam may include plural cams coupled to the drive shaft and arranged apart from each other in an axial direction of the drive shaft. 
     The press device may include a worm configured to rotate by receiving rotational force and a worm wheel that is coupled to the drive shaft and tooth-engaged with the worm. 
     The developing unit may be rotatably coupled to the photosensitive body unit, and the press unit may press the developing unit to rotate the same so that the developing roller comes into contact with the photosensitive body. 
     The developing unit may include a protruding part that protrudes upward therefrom and is configured to be pressed by a lower end portion of the lever. 
     The image forming apparatus may further include an elastic element by which the developing unit is elastically supported to the photosensitive body unit. 
     In accordance with an aspect of an exemplary embodiment, an image forming apparatus includes four photosensitive body units, each of which includes a photosensitive body, four developing units that are respectively rotatably mounted to the four photosensitive body units and each of that includes a developing roller configured to contact the photosensitive body or to be separated from the photosensitive body according to rotation thereof, and a press device to press the four developing units to rotate the same. The four developing units include a first developing unit for a black and white image developing process and three second developing units for a color image developing process. The press device includes a first lever to press the first developing unit by rotation thereof, three second levers to respectively press the three second developing units by rotation thereof, a first cam to allow the first lever to rotate by interaction with the first lever, and three second cams to respectively allow the three second levers to rotate by respective interaction with the three second levers. 
     Since the lever configured to apply force to the developing unit gradually rotates by rotation of the cam, the force applied to the developing unit may also be gradually and smoothly increased or decreased. Accordingly, shock, which may occur by rough movement of the developing unit, for example, is remarkably reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates an image forming apparatus according to an embodiment; 
         FIG. 2  illustrates a developing unit, a photosensitive body unit and a press device of an image forming apparatus according to an embodiment; 
         FIG. 3  illustrates a press device of an image forming apparatus according to an embodiment; 
         FIGS. 4 and 5  illustrate exemplary operational states of a press device of an image forming apparatus according to an embodiment; 
         FIG. 6  illustrates an exemplary embodiment of cams of an image forming apparatus according to an embodiment; 
         FIG. 7  illustrates an exemplary embodiment of cams of an image forming apparatus according to an embodiment; 
         FIG. 8  illustrates an exemplary embodiment of cams of an image forming apparatus according to an embodiment; and 
         FIG. 9  illustrates an exemplary embodiment of a lever and a cam of an image forming apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  illustrates an image forming apparatus according to an embodiment. 
     As illustrated in  FIG. 1 , an image forming apparatus  1  comprises a main body  10 , a printing medium feeding unit  20 , a laser scanning unit  30 , a developing unit  40 , a photosensitive body unit  50 , a transfer unit  60 , a fusing unit  70  and a printing medium discharge unit  80 . 
     The main body  10  forms an exterior appearance of the image forming apparatus  1 , and supports components mounted therein. 
     The printing medium feeding unit  20  includes a cassette  21  to store a printing medium S, a pickup roller  22  to pick up the printing medium S in the cassette  21  sheet by sheet, and a feeding roller  23  to feed the picked-up printing medium toward the transfer unit  60 . 
     The laser scanning unit  30  is configured to irradiate light corresponding to image information to photosensitive bodies  52 , thereby forming electrostatic latent images on surfaces of the photosensitive bodies  52 . 
     The developing unit  40  includes a first developing unit  40 K to develop a black and white image and three second developing units  40 Y,  40 M and  40 C to develop a color image. The developing unit  40 K stores a black (K) developer therein, and the other developing units  40 Y,  40 M and  40 C store yellow (Y), magenta (M) and cyan (C) developers therein, respectively. 
     Each of the developing units  40 Y,  40 M,  40 C and  40 K includes a developing roller  41  and a supply roller  46 . The supply roller  46  supplies the developers to the developing roller  41 . The developing roller  41  attaches the developers to a surface of the photosensitive body  52 , on which an electrostatic latent image is formed, to form a visible image. 
     The photosensitive body unit  50  includes plural photosensitive body units  50 Y,  50 M,  50 C and  50 K that respectively correspond to the plural developing units  40 Y,  40 M,  40 C and  40 K. Each of the photosensitive body units  50 Y,  50 M,  50 C and  50 K includes a photosensitive body  52  and a charger  53 . The photosensitive body  52  is charged to a predetermined electric potential by the charger  53 . An electrostatic latent image is formed on the surface of the photosensitive body  52  charged by the charger  53 . According to an embodiment, the photosensitive body unit  50  includes a first photosensitive body unit  50 K to form a black and white image and three second photosensitive body units  50 Y,  50 M and  50 C to form a color image. 
     The transfer unit  60  includes a transfer belt  61 , a drive roller  62 , a driven roller  63 , four first transfer rollers  64 Y,  64 M,  64 C and  64 K, a second transfer roller  65 . The transfer belt  61  circulates in contact with the photosensitive body  52  of each of the photosensitive body units  50 Y,  50 M,  50 C and  50 K. The drive roller  62  drives the transfer belt  61  to circulate the same. The driven roller  63  rotates by receiving rotational force through the transfer belt  61 . The visible image formed on the photosensitive body  52  of each of the photosensitive body units  50 Y,  50 M,  50 C and  50 K is transferred onto the transfer belt  61  by the first transfer rollers  64 Y,  64 M,  64 C and  64 K. The second transfer roller  65  opposes the drive roller  62  while the transfer belt  61  is interposed therebetween. The visible image on the transfer belt  61  is transferred onto a printing medium by the second transfer roller  65 . 
     The fusing unit  70  includes a heating roller  71  having a heat source and a press roller  72  that opposes the heating roller  71 . A printing medium onto which an image has been transferred passes between the heating roller  71  and the press roller  72 . The image may be fused to the printing medium by heat transmitted from the heating roller  71  and a pressure generated between the heating roller  71  and the press roller  72 . 
     The printing medium discharge unit  80  includes a discharge roller  81 . A printing medium passing through the fusing unit  70  is guided to the printing medium discharge unit  80 , and then may be discharged to the outside of the main body  10  by the discharge roller  81 . 
     When image formation is performed, the developing roller  41  of each of the developing units  40 Y,  40 M,  40 C and  40 K is in contact with the photosensitive body  52  in order to supply the developers to the photosensitive body  52 . However, when the image forming is not performed, the developing roller  41  is separated from the photosensitive body  52 . 
     To achieve this, the developing units  40 Y,  40 M,  40 C and  40 K are rotatably mounted to the photosensitive body units  50 Y,  50 M,  50 C and  50 K, and a press device  90  is disposed above the developing units  40 Y,  40 M,  40 C and  40 K so as to apply force to the developing units  40 Y,  40 M,  40 C and  40 K to rotate the same. 
     An exemplary mounting structure of the first developing unit  40 K, the first photosensitive body unit  50 K and a first lever  91 A and a first cam  92 A of the press device  90  is illustrated in  FIG. 2 . Although not illustrated in the drawings, the mounting structure of the second developing units  40 Y,  40 M and  40 C, the second photosensitive body units  50 Y,  50 M and  50 C and a second lever  91 B and a second cam  92 B of the press device  90  is the same as illustrated in  FIG. 2 . 
     An elastic element  42  may be mounted between each of the photosensitive body units  50 K,  50 Y,  50 M and  50 C and each of the developing units  40 K,  40 Y,  40 M and  40 C. The elastic element  42  serves to elastically bias the developing units  40 K,  40 Y,  40 M and  40 C toward the photosensitive body units  50 K,  50 Y,  50 M and  50 C, so that the developing units  40 K,  40 Y,  40 M and  40 C return to original positions after being rotated by the press device  90 . Each of the developing units  40 K,  40 Y,  40 M and  40 C may be provided with a protruding part  43  at a top portion thereof to receive force from the press device  90 . 
     As illustrated in  FIGS. 2 and 3 , the press device  90  includes levers  91 A and  91 B that are rotatably mounted thereto and apply force to the protruding parts  43  of the developing units  40 K,  40 Y,  40 M and  40 C by rotation, and cams  92 A and  92 B that are rotatably mounted thereto and allow the levers  91 A and  91 B to rotate. According to an embodiment, the number of the levers  91 A and  91 B and the number of the cams  92 A and  92 B are respectively four in order to independently operate the four developing units  40 K,  40 Y,  40 M and  40 C. The four levers  91 A and  91 B may be rotatably mounted to a support bracket  97  that is mounted in the main body  10 . 
     The press device  90  includes a drive shaft  93  rotatably mounted to the support bracket  97 , on which the four cams  92 A and  92 B may be arranged apart from each other in an axial direction thereof, a worm  94  configured to rotate by receiving rotational force from a drive motor (not shown), and a worm wheel  95  coupled to the drive shaft  93  and tooth-engaged with the worm  94  so as to rotate the drive shaft  93  by being rotated by the worm  94 . 
     Upper end portions of the levers  91 A and  91 B may be rotatably mounted to the support bracket  97 . Accordingly, while rotating about the upper end portions thereof, lower end portions of the levers  91 A and  91 B apply force to the protruding parts  43 . One of the levers  91 A and  91 B is a first lever  91 A to press the first developing unit  40 K, and the others are three second levers  91 B to respectively press the second developing units  40 Y,  40 M and  40 C. 
     The levers  91 A and  91 B respectively include guide parts  911  that are respectively guided by the cams  92 A and  92 B corresponding to the levers  91 A and  91 B. According to an embodiment, each of the guide parts  911  may be a guide protrusion that protrudes from a lateral surface of each of the levers  91 A and  91 B. 
     One of the cams  92 A and  92 B is a first cam  92 A to rotate the first lever  91 A configured to press the first developing unit  40 K, and the others are three second cams  92 B to respectively rotate the three second levers  91 B configured to respectively press the three second developing units  40 Y,  40 M and  40 C. 
     Each of the cams  92 A and  92 B includes a cam portion  921  that is formed in a circumferential direction thereof to guide each of the guide parts  911 . According to an embodiment, the cam portion  921  is a cam recess having a concave shape into which the guide part  911  (guide protrusion) may be inserted. 
     The cam portion  921 , as illustrated in  FIGS. 4 through 6 , includes a first cam portion  921   a , a second cam portion  921   b  and a third cam portion  921   c . The first cam portion  921   a  extends obliquely in a first direction to guide the guide part  911  in the first direction, thereby rotating each of the levers  91 A and  91 B in the first direction. The second cam portion  921   b  extends obliquely in a second direction, which is opposite to the first direction, to guide the guide part  911  in the second direction, thereby rotating each of the levers  91 A and  91 B in the second direction. The third cam portion  921   c  extends in parallel with the rotating direction of each of the cams  92 A and  92 B, so that each of the levers  91 A and  91 B is kept in a stationary state even though each of the cams  92 A and  92 B rotates. According to an embodiment, as each of the levers  91 A and  91 B rotates in the first direction, the developing roller  41  is in contact with the photosensitive body  52 . As each of the levers  91 A and  91 B rotates in the second direction, the developing roller  41  is separated from the photosensitive body  52 . 
     According to an embodiment, during one rotation of the drive shaft  93 , the image forming apparatus performs a stand-by mode, a color print mode and a black and white print mode, for example, in order. In the stand-by mode, all the developing rollers  41  may be spaced apart from the photosensitive bodies  52 . In the color print mode, all the developing rollers  41  may be in contact with the photosensitive bodies  52  to print a color image. In the black and white print mode, only the first developing roller  41  may be in contact with the photosensitive body  52  and the other second developing rollers  41  may be spaced apart from the photosensitive bodies  52  to print a black and white image. In other words, the operational mode of the developing units  40 K,  40 Y,  40 M and  40 C is repeatedly changed to the stand-by mode, the color print mode and the black and white print mode, for example, in order according to the rotation of the drive shaft  93 . 
     To achieve such sequential change of the operational mode of the developing units  40 K,  40 Y,  40 M and  40 C (i.e., the stand-by mode, the color print mode and the black and white print mode), the cam portion  921  formed at the first cam  92 A may be shaped such that the first cam portion  921   a , the third cam portion  921   c  and the second cam portion  921   b  are connected in order in a circumferential direction of the first cam  92 A. However, the cam portion  921  formed at each of the second cams  92 B may be shaped such that the first cam portion  921   a , the second cam portion  921   b  and the third cam portion  921   c  are connected in order in a circumferential direction of the second cams  92 B. According to an embodiment, the first cam portion  921   a , the second cam portion  921   b  and the third cam portion  921   c  respectively extend by an angle of 120 degrees. 
     An exemplary operation of an image forming apparatus according to an embodiment is described. 
     At an initial stage, the developing rollers  41  of all the developing units  40 K,  40 Y,  40 M and  40 C may be separated from the photosensitive bodies  52 . Therefore, the image forming apparatus is in a state incapable of performing an image forming process. When image formation is required, if the drive shaft  93  is rotated, for example, by an angle of 120 degrees by the drive motor  96 , the cams  92 A and  92 B also rotate, for example, by an angle of 120 degrees according to the rotation of the drive shaft  93 . 
     According to the rotation of the cams  92 A and  92 B, the guide parts  911  provided at the levers  91 A and  91 B may be guided in the first direction by the first cam portions  921   a  formed at the cams  92 A and  92 B. Accordingly, the levers  91 A and  91 B rotate in the first direction, and the force applied to the developing units  40 K,  40 Y,  40 M and  40 C is removed. If the force applied to the developing units  40 K,  40 Y,  40 M and  40 C is removed, the developing units  40 K,  40 Y,  40 M and  40 C rotate by elastic restoring force of the elastic elements  42 , and the developing rollers  41  provided at the developing units  40 K,  40 Y,  40 M and  40 C come into contact with the photosensitive bodies  52  provided at the photosensitive body units  50 K,  50 Y,  50 M and  50 C, respectively. As a result, the operational mode of the image forming apparatus is switched to a mode capable of forming a color image. 
     If the drive shaft  93  is rotated another 120 degrees, the guide part  911  provided at the first lever  91 A is kept in a stationary state, after being guided in the first direction, by the third cam portion  921   c  formed at the first cam  92 A. Therefore, the developing roller  41  of the first developing unit  40 K is kept in contact with the photosensitive body  52  of the first photosensitive body unit  50 K. 
     The guide parts  911  provided at the second levers  91 B may be guided in the second direction by the second cam portions  921   b  formed at the second cams  92 B. Accordingly, the second levers  91 B rotate in the second direction and apply force to the second developing units  40 Y,  40 M and  40 C. 
     If force is applied to the second developing units  40 Y,  40 M and  40 C by the second levers  91 B, the second developing units  40 Y,  40 M and  40 C rotate such that the developing rollers  41  provided at the second developing units  40 Y,  40 M and  40 C are separated from the photosensitive bodies  52  provided at the second photosensitive body units  50 Y,  50 M and  50 C. Accordingly, color image formation is not achieved. 
     An operational mode of the image forming apparatus may be switched to a mode capable of forming only a black and white image, in which the developing roller  41  of the first developing unit  40 K for black and white image forming is in contact with the photosensitive body  52  of the first photosensitive body unit  50 K and the developing rollers  41  of the second developing units  40 Y,  40 M and  40 C for color image forming are separated from the photosensitive bodies  52  of the second photosensitive body units  50 Y,  50 M and  50 C. 
     From such an operational mode, if the drive shaft  93  is rotated, for example, another 120 degrees, the guide part  911  provided at the first lever  91 A may be guided in the second direction by the second cam portion  921   b  formed at the first cam  92 A. Accordingly, the first lever  91 A rotates in the second direction and applies force to the first developing unit  40 K. If force is applied to the first developing unit  40 K by the first lever  91 A, the first developing unit  40 K rotates such that the developing roller  41  provided at the first developing unit  40 K is separated from the photosensitive body  52  provided at the first photosensitive body unit  50 K. Accordingly, black and white image formation is not achieved. 
     The second levers  91 B may be kept in a stationary state, after rotating in the second direction, by the third cam portions  921   c  formed at the second cams  92 B. Therefore, the developing rollers  41  of the second developing units  40 Y,  40 M and  40 C may be kept separated from the photosensitive bodies  52  of the second photosensitive body units  50 Y,  50 M and  50 C. Accordingly, color image formation is not achieved. 
     An image forming apparatus may return to the state incapable of performing an image forming process, in which the developing rollers  41  of all the developing units  40 K,  40 Y,  40 M and  40 C are separated from the photosensitive bodies  52  of the photosensitive body units  50 K,  50 Y,  50 M and  50 C. 
     According to an embodiment, the operational mode of the image forming apparatus may be repeatedly changed to the stand-by mode, the color print mode and the black and white print mode in order according to the rotation of the drive shaft  93 . According to an embodiment, the operational mode may be changed to the stand-by mode, the black and white print mode and the color print mode in order. 
     To achieve such sequential change of the operational mode, i.e., the stand-by mode, the black and white print mode and the color print mode, of the developing units  40 K,  40 Y,  40 M and  40 C, as illustrated in  FIG. 7 , the cam portion  921  formed at the first cam  92 A 1  is shaped such that the first cam portion  921   a , the third cam portion  921   c  and the second cam portion  921   b  are connected in order in a circumferential direction of the first cam  92 A 1 . The cam portion  921  formed at each of the second cams  92 B 1  may be shaped such that the third cam portion  921   c , the first cam portion  921   a  and the second cam portion  921   b  are connected in order in a circumferential direction of the second cams  92 B 1 . According to an embodiment, the first cam portion  921   a , the second cam portion  921   b  and the third cam portion  921   c  respectively extend, for example, by an angle of 120 degrees. 
     According to an embodiment, an operational mode of the developing units  40 K,  40 Y,  40 M and  40 C may be changed to the stand-by mode and the color print mode alternately according to the rotation of the drive shaft  93 . 
     As illustrated in  FIG. 8 , each of the cam portions  921  formed at the cams  92 A 2  and  92 B 2  may be shaped such that the first cam portion  921   a  and the second cam portion  921   b  are connected in order in a circumferential direction of the cams. The first cam portion  921   a  and the second cam portion  921   b  respectively extend, for example, by an angle of 180 degrees. 
     According to an embodiment, a guide part  911  is a single guide protrusion and the cam portion  921  is a cam recess into which the guide part  911  is inserted. However, as illustrated in  FIG. 9 , an exemplary embodiment includes a guide part  911   a  that includes a pair of guide protrusions that are provided at a lever  91 P and spaced apart from each other and a cam portion  921 P of a cam  92 P is a cam protrusion that may be inserted between the pair of guide protrusions of the guide part  911   a.    
     Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.