Patent Publication Number: US-7721859-B2

Title: Rotary force controlling apparatus and image forming apparatus including the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2005-0028513, filed on Apr. 6, 2005, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus. More particularly, the present invention relates to a rotary force controlling apparatus of an image forming apparatus that controls a rotary force transferred to a rotary body mounted on a shaft. 
   2. Description of the Related Art 
   Generally, an image forming apparatus, such as a laser printer, an LED printer, a digital copier, or a facsimile machine, transfers an image signal according to a digital signal input from a computer or a scanner onto a recording medium in a visible image form. This image forming apparatus includes an image forming unit for forming an image on a sheet, and a feed device for feeding the sheet to the image forming unit. The feed device and other devices used in the image forming apparatus use a rotary force controlling apparatus for controlling a rotary force transferred to a rotary body that is mounted on a rotary shaft. A conventional rotary force controlling apparatus used in a feed device of an image forming apparatus is described as an example. 
     FIG. 1  is a perspective view of a feed device of an image forming apparatus using a conventional rotary force controlling apparatus.  FIG. 2  is an elevational view of the conventional rotary force controlling apparatus of  FIG. 1 .  FIG. 3  illustrates the operation of the conventional rotary force controlling apparatus. 
   Referring to  FIG. 1 , a conventional feed device  1  includes a driving shaft  3  that is rotated by a driving source (not shown), such as a motor. A roller device  20  includes a driving roller  2  connected to and rotated by the driving shaft  3  and a driven roller  5  tightly attached to and rotated by the driving roller  2 . The driven roller  5  is pivoted on levers  10   b  around a hinge shaft  7  to press against the driving roller  2  under the force of a pressing spring  8 . The levers  10   b  are coupled to and rotate on the hinge shaft  7 . One of the levers  10   b  has a mechanical interrupter  10   a  that follows a rotary cam  12 . The feed device  1  includes the rotary cam  12  to actuate the interrupter  10   a  and to retract the driven roller  5  from the driving roller  2 . When necessary, the rotary cam  12  acts as a clutch  14  for rotating the rotary cam  12 . 
   When the driving roller  2  of the feed device  1  rotates, the driven roller  5  rotates and a sheet passes between the driving roller  2  and the driven roller  5  to an image forming unit (not shown) to form an image on the sheet. The roller device  20  has a pressure for conveying the sheet. Accordingly, when the rear end of the sheet leaves the roller device  20 , a sudden impact is applied to the sheet that may distort the image. To prevent such distortion, when the rear end of the sheet leaves the roller device  20 , the rotary cam  12  rotates to press the interrupter  10   a  and to separate the driven roller  5  from the driving roller  2 . 
   The conventional feed device  1  includes a rotary force controlling apparatus  30  having the rotary cam  12  and the clutch  14  to separate the driving roller  2  and the driven roller  5 . 
   Referring to  FIGS. 2 and 3 , the conventional rotary force controlling apparatus  30  includes a rotary shaft  10 , a clutch unit  20  mounted on the rotary shaft  10 , and a power transferring member  22  that receives a driving force from a driving source (not shown) to rotate the rotary shaft  10 . 
   A rotary body  12 , such as a cam, is mounted on one end of the rotary shaft  10 . The clutch unit  20  is mounted around the periphery of the rotary shaft  10  and controls the rotary force transferred from the driving source (not shown) to control the rotation of the rotary shaft  10 . The clutch unit  20  includes a clutch  32  mounted around the periphery of the rotary shaft  10  and a rotation controlling unit  50  for controlling the rotation of the rotary shaft  10 . 
   The clutch  32  includes a first positioning unit  33  and a second positioning unit  34  for stopping the rotary body  12  at a predetermined location. The first and second positioning units  33  and  34  protrude from the circumference of the rotary body  12  and are spaced apart from each other. 
   The rotation controlling unit  50  interferes with the first and second positioning units  33  and  34  to control the rotation of the rotary shaft  10 , and includes a bracket  60 , an interfering unit  65 , and an elastic member  90 . 
   A solenoid unit  70 , which is turned on and off by an electrical signal, is mounted on the bracket  60 . When the solenoid unit  70  is turned on by the electrical signal, a magnetic force is generated and the interfering unit  65  is attracted to a predetermined location. 
   One side of interfering unit  65  is mounted on the bracket  60 , and the interfering unit  65  interferes with or is released from the first and second positioning units  33  and  34  when the solenoid unit  70  is turned on or off. That is, the interfering unit  65  interferes with the first and second positioning units  33  and  34  mounted on the clutch  32  to control the rotation of the clutch  32 . An armature  80  having an engaging unit  82  for interfering with the first and second positioning units  33  and  34  is mounted on one end of the interfering unit  65 . 
   One end of the elastic member  90  is mounted on the bracket  65 , and the other end is mounted on the interfering unit  65 . The elastic member  90  provides an elastic force to the interfering unit  65  such that the armature  80  is coupled to and released from the first and second positioning units  33  and  34 . 
   By the action of the solenoid unit  70 , the armature  80  moves and interferes with the first and second positioning units  33  and  34  to stop the rotation of the rotary body  12  that is mounted on the rotary shaft  10 . When the solenoid unit  70  is turned on, the interfering unit  65  moves so that the armature  80  interferes with the first positioning unit  33 . When the solenoid unit  70  is turned off, the interfering unit  65  is returned to its original location by the elastic force of the elastic member  90 , and is released from the first positioning unit  33  and interferes with the second positioning unit  34 . That is, the action of the solenoid unit  70  and the elastic force of the elastic member  90  moves the interfering unit  65  back and forth between the first and second positioning units  33  and  34 . 
   The power transferring member  22  is mounted around the clutch unit  20 , and receives the rotary force from the driving source (not shown) to rotate the rotary shaft  10 . The power transferring member  22  is preferably a gear. The rotary force transferred by the power transferring member  22  is selectively transferred to the rotary shaft  10  by the clutch unit  20 . 
   The conventional rotary force controlling apparatus  30  includes two positioning units  33  and  34 . The locations of the two positioning units  33  and  34  are spaced apart from each other so that the two positioning units  33  and  34  are controlled when the solenoid unit  70  is turned on and off to control the location of the rotary body  12 . Accordingly, when the rotary body  12  is continuously held at any one location, the solenoid unit  70  must stay in the ON state or the OFF state. 
   When the solenoid unit  70  is continuously OFF, there is no problem. However, when the solenoid unit  70  is continuously ON, it continuously draws power and can become overheated. This can weaken its magnetic force and attracting force. Accordingly, the force for attracting the armature  80  is weakened, and thus the armature  80  may not accurately interfere with the two positioning units  33  and  34 . 
   Also, heat generated in the solenoid unit  70  can shorten its life span or damage other components. 
   Furthermore, when the solenoid unit  70  is in the ON state for a long time, the armature  80  can be magnetized. Thus, when the solenoid unit  70  is turned off, the armature  80  does not immediately separate from the solenoid unit  70 . That is, a time delay occurs and the operation of the rotary body  12  cannot accurately be controlled. 
   Also, since only two positioning units are used, the rotary body  12  cannot stop at three or more locations. Moreover, when the solenoid unit  70  is turned off and then on, the engaging unit  82  of the armature  80  is engaged with the first positioning unit  33  by the time delay. Thus, the rotary body  12  cannot rotate. 
   Accordingly, a need exists for an improved rotary force controlling apparatus for an image forming apparatus that controls a rotary force transferred to a rotary body mounted on a shaft. 
   SUMMARY OF THE INVENTION 
   The present invention provides a rotary force controlling apparatus and an image forming apparatus including the same that stops a rotary body at a predetermined location when a solenoid unit is turned OFF. 
   The present invention also provides a rotary force controlling apparatus and an image forming apparatus including the same that is adapted to stop a rotary body at a plurality of locations. 
   The present invention also provides a rotary force controlling apparatus and an image forming apparatus including the same that easily changes the location of a rotary body. 
   According to an aspect of the present invention, a rotary force controlling apparatus of an image forming apparatus includes a clutch device having a shaft and a rotary body mounted at one end of the shaft. A housing receives and rotates together with the shaft. A power transferring member is rotatably mounted in the housing and selectively rotates the housing by a clutch inserted between the housing and the power transferring member. A positioning unit protrudes from the periphery of the housing and positions a stop location of the rotary body. A solenoid unit is spaced apart from the clutch device and is selectively turned on and off. The positioning unit includes a first positioning unit that positions an initial location of the rotary body when the solenoid unit is turned on. A plurality of second positioning units are separated from the first positioning unit and stop the rotary body at a predetermined location when the solenoid unit is turned off. 
   The solenoid unit may include a bracket having a solenoid mounted thereon. The solenoid operates by an electrical signal. An armature mounted on the bracket has an interfering unit that interferes with the first positioning unit when the solenoid is turned on and interferes with the second positioning units when the solenoid is turned off. An elastic member connected between the bracket and the armature provides a biasing force to the armature such that the interfering unit interferes with or is released from the first and second positioning units. 
   The interfering unit may include a first interfering unit that interferes with the first positioning unit when the solenoid is turned on. A second interfering unit is spaced apart from the first interfering unit and interferes with the second positioning units when the solenoid is turned off. 
   The clutch may be a spring clutch. 
   The second positioning units may be located on substantially the same circumference around the surface of the housing. 
   The second positioning units may have substantially the same height, which is different from that of the first positioning unit, such that the first positioning unit interferes with the interfering unit only when the when the solenoid is turned on. 
   The first positioning unit may include a first portion protruding from the surface of the housing and a second portion extending from the first portion in the axial direction of the housing that interferes with the interfering unit when the solenoid is turned on. 
   The second positioning units may form a pair and are symmetrical around the center of the housing. The first positioning unit is positioned at 90° from each of the second positioning units around the center of the housing. 
   Interference between the interfering unit and any one of the second positioning units may be released by the instantaneous ON and OFF operation of the solenoid unit. 
   According to another aspect of the present invention, a rotary force controlling apparatus of an image forming apparatus includes a clutch device having a shaft and a rotary body mounted at one end of the shaft. A housing receives and rotates together with the shaft. A power transferring member is rotatably mounted in the housing and selectively rotates the housing by a clutch inserted between the housing and the power transferring member. A positioning unit protrudes from the periphery of the housing and has a first positioning unit that positions an initial location of the rotary body and a plurality of second positioning units that stop the rotary body at a predetermined location. A solenoid unit includes a bracket on which a solenoid is mounted. An armature is mounted on the bracket and has an interfering unit that interferes with the first positioning unit when the solenoid is turned on and interferes with the second positioning unit when the solenoid is turned off. An elastic member connected between the bracket and the armature provides a biasing force to the armature such that the interfering unit interferes with or is released from the first and second positioning units. A stopper is mounted on the bracket and controls the motion of the armature such that the interfering unit interferes with the second positioning units when the solenoid is turned off. The solenoid is operated by an electrical signal. 
   The clutch device and the solenoid unit may be spaced apart from each other. 
   The apparatus may further include a connecting member for integrally assembling the clutch device and the solenoid unit together. 
   The interfering unit may include a first interfering unit that interferes with the first positioning unit when the solenoid is turned on. A second interfering unit is spaced from the first interfering unit and interferes with the second positioning units when the solenoid is turned off. 
   The second positioning units may be located on substantially the same circumference around the surface of the housing. 
   The second positioning units may have substantially the same height, which is different from that of the first positioning unit, such that the first positioning unit interferes with the interfering unit only when the solenoid is turned on. 
   The first positioning unit may include a first portion protruding from the surface of the housing and a second portion extending from the first portion in the axial direction of the housing and interferes with the interfering unit when the solenoid is turned on. 
   The second positioning units may form a pair and are symmetrical around the center of the housing. The first positioning unit is positioned at 90° from each of the second positioning units around the center of the housing. 
   Interference between the interfering unit and any one of the second positioning units may be released by the instantaneous ON and OFF operation of the solenoid unit. 
   According to another aspect of the present invention, an image forming apparatus includes the above-mentioned rotary force controlling apparatus, 
   Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a perspective view of a feed device of an image forming apparatus having a conventional rotary force controlling apparatus; 
       FIG. 2  is an elevational view of the conventional rotary force controlling apparatus of  FIG. 1 ; 
       FIG. 3  illustrates the operation of the conventional rotary force controlling apparatus; 
       FIG. 4  is a schematic elevational view in partial cross section of an image forming apparatus according to an exemplary embodiment of the present invention; 
       FIG. 5  is a perspective view of a rotary force controlling apparatus according to an exemplary embodiment of the present invention; 
       FIG. 6  is an elevational view in cross section taken along line I-I′ of a clutch device of the rotary force controlling apparatus of  FIG. 5 ; 
       FIG. 7  illustrates the relationship between a clutch device and a solenoid unit when the solenoid unit is turned off; 
       FIGS. 8A through 8C  illustrate the operation when a clutch device rotates and stops when the solenoid unit is turned off; 
       FIG. 9  illustrates the relationship between a clutch device and a solenoid unit when the solenoid unit is turned on; 
       FIGS. 10A through 10C  illustrate the operation when the clutch device rotates and stops when the solenoid unit is turned on; 
       FIG. 11  is a perspective view of a rotary force controlling apparatus according to another exemplary embodiment of the present invention; 
       FIG. 12  is a side elevational view of the rotary force controlling apparatus of  FIG. 11 ; 
       FIG. 13  is a front elevational view of the rotary force controlling apparatus of  FIG. 11 ; 
       FIG. 14  is a front elevational view of a rotary force controlling apparatus according to another exemplary embodiment of the present invention; 
       FIG. 15  is a front elevational view of a rotary force controlling apparatus according to another exemplary embodiment of the present invention; and 
       FIG. 16  is a front elevational view of a rotary force controlling apparatus according to another exemplary embodiment of the present invention. 
   

   Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The present invention is described more fully with reference to the accompanying drawings in which exemplary embodiments of the present invention are shown. The invention may, however, be embodied in many different forms, and should not be construed as being limited to the exemplary embodiments set forth herein; rather, these exemplary embodiments are provided so that this disclosure is thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of lines and the size of components are exaggerated for clarity. 
   First, an image forming apparatus is described first. An electrophotographic type printer is used as an example, but the present invention is not limited to this exemplary embodiment. For example, the present invention may be used in an image forming apparatus, such as a facsimile machine or a copier. 
     FIG. 4  is a schematic elevational view in cross section of an image forming apparatus according to an exemplary embodiment of the present invention. 
   The image forming apparatus  100  includes a photosensitive body  101 , a charging roller  102 , a light scanning unit  103 , four developer units  104 , and a transfer belt  105 . 
   The photosensitive body  101  is coated by deposition with a photoconductive material layer around a cylindrical metal drum, and a portion of the surface thereof is exposed. The photosensitive body  101  rotates while an electrostatic latent image corresponding to an image to be printed is formed on the surface of the photosensitive body  101  by the light irradiated by the light scanning unit  103 . 
   The charging roller  102  is an example of a charging unit for charging the photosensitive body  101  to a uniform potential. The charging roller  102  supplies charge to the photosensitive body  101  while rotating in or out of contact with the photosensitive body  101 , thereby charging the surface of the photosensitive body  101  to a uniform potential. A charging bias voltage or a corona charging unit (not shown) provide the charge. 
   The light scanning unit  103  is provided below the photosensitive body  101 , and irradiates the light for forming the electrostatic latent image onto the surface of the photosensitive body  101  according to a computer signal. The light scanning unit  103  includes a light source (not shown) for irradiating a laser beam, and a beam deflector for deflecting the laser beam. The light scanning unit  103  generally uses a laser scanning unit (LSU) having a laser diode light source. 
   Four cartridge type developers  104 C,  104 M,  104 Y, and  104 K are detachably mounted in the frame  140 , and four powdered color toners, cyan (C), magenta (M), yellow (Y) and black (K) toners, are respectively stored in the developers  104 C,  104 M,  104 Y, and  104 K. The developers  104 C,  104 M, and  104 Y, and  104 K include development rollers  125  for supplying the color toners to the electrostatic latent image formed on the photosensitive body  101  to form toner images. The developers  104 C,  104 M,  104 Y, and  104 K maybe refilled when their color toner is exhausted. 
   The development rollers  125  apply the color toners to the electrostatic latent image formed on the photosensitive body  101  to develop a toner image. A development bias voltage is applied to the development rollers  125  to supply the color toners to the photosensitive body  101 . 
   The development rollers  125  may contact the photosensitive body  101  or be spaced from its surface by a development gap (Dg). A force directed from the photosensitive body  101  to the development roller  125  is generated by an electric field, and the charged toner is conveyed in a development region formed by the development gap (Dg). 
   A developer driving apparatus  104 A selectively drives the developers  104 C,  104 M,  104 Y, and  104 K and is disposed on one side of the developers  104 C,  104 M,  104 Y, and  104 K. The rotary force controlling apparatus of the exemplary embodiments of the present invention may be used to selectively drive the corresponding developers  104 C,  104 M,  104 Y, and  104 K. For example, the developer may be driven so that the rotary body coupled to the shaft of the rotary force controlling apparatus selectively interferes with each of the developers. 
   In the present exemplary embodiment, the developers  104 C,  104 M,  104 Y, and  104 K are arranged in the color order of cyan, magenta, yellow, and black. A pre-transfer erasing unit  110  is provided on the developer  104 K. A light scanning unit  103  and an erasing lamp  107  are provided below the photosensitive body  101 . A sheet conveying unit  120  is provided opposite the developers  104 C,  104 M,  104 Y, and  104 K with respect to the photosensitive body  101 . 
   The toner images cyan (C), magenta (M), yellow (Y), and black (K) that are sequentially formed on the photosensitive body  101  are sequentially transferred and superimposed onto the transfer belt  105  to form a color toner image. Generally, the length of the transfer belt  105  is equal to or greater than that of a sheet (S) on which the color toner image is finally formed. 
   A plurality of supporting rollers are provided at the inner surface of the transfer belt  105  to support and move the transfer belt  105 . A nip roller  105   a  is provided at the inner surface of the transfer belt  105 , such that the photosensitive body  101  and the transfer belt  105  form a nip of length (A). A middle transfer roller  105   b  receives a first transfer bias voltage so that the color toner images formed on the photosensitive body  101  are transferred onto the transfer belt  105 . 
   The transfer belt  105  faces the photosensitive body  101  in the section between the middle transfer roller  105   b  and the nip roller  105   a,  such that the color toner images developed on the photosensitive body  101  are transferred onto the transfer belt  105 . That is, the transfer belt  105  is supported by the plurality of supporting rollers and rotates while the color toner images developed on the photosensitive body  101  are transferred onto the transfer belt  105 . 
   A first cleaning unit  106  includes a first blade  106   a,  which contacts the surface of the photosensitive body  101  and scrapes remaining waste toner off the surface of the photosensitive body  101  after the transfer process is complete, and a first conveying means  106   b  for conveying the waste toner to a waste toner storing unit (not shown). The first conveying means  106  is preferably an auger. 
   A second cleaning unit  109  removes remaining waste toner from the transfer belt  105  after the color toner images are transferred onto the sheet (S). The second cleaning unit  109  includes a second blade  109   a  for scraping the waste toner from the surface of the transfer belt  105 , and a second conveying means  109   b  for conveying the waste toner to the waste toner storing unit (not shown). The second conveying means  109   b  is preferably an auger. 
   A transfer roller  112  faces the surface of the transfer belt  105  having the color toner images, and receives a transfer bias voltage of opposite polarity to the color toner images so that the color toner images are transferred from the transfer belt  105  onto the sheet (S). The color toner images are transferred onto the sheet (S) by an electrostatic force generated between the transfer belt  105  and the transfer roller  112 . The transfer roller  112  is spaced from the transfer belt  105  when the color toner images are transferred onto the transfer belt  105 . After the color toner images are completely transferred onto the transfer belt  105 , the transfer roller  112  contacts the transfer belt  105  to transfer the color toner images onto the sheet (S). Also, the color toner images transferred onto the outer side of the transfer belt  105  may be transferred onto the sheet (S) passing between the transfer roller  112  and the transfer belt  105  by the contact pressure between the transfer belt  105  and the transfer roller  112 . The rotary force controlling apparatus of the present invention may be used for controlling the operation of the transfer roller  112 . The rotary force controlling apparatus is described later in detail. 
   A pre-transfer erasing unit  110  removes charge from areas (non-image regions) of the photosensitive body  101  on which no toner images are formed before transferring the color toner images from the photosensitive body  101  onto the transfer belt  105 . The pre-transfer erasing unit  110  improves the transfer efficiency from the photosensitive body  101  to the transfer belt  105 . 
   An erasing lamp  107  is an example of an eraser for removing the remaining charge from the surface of the photosensitive body  101  before performing the charging operation. The erasing lamp  107  irradiates light onto the surface of the photosensitive body  101  to remove the charge remaining on its surface. 
   A high voltage power supply unit  108  provides a voltage to components of the image forming apparatus  100 , such as a development bias voltage for developing the color toner from the developers  104 C,  104 M,  104 Y, and  104 K onto the photosensitive body  101 , a development preventing bias voltage for preventing the color toner from being attached to the photosensitive body  101 , a first transfer bias voltage for transferring the color toner images from the photosensitive body  101  onto the transfer belt  105 , a second transfer bias voltage for transferring the toner image from the transfer belt  105  onto the sheet (S), and a charging voltage provided to the charging roller  102 . 
   The fixing unit  111  includes a heat roller  123  and a pressing roller  124  that faces the heat roller  123  and fixes the color toner image onto the sheet (S) by applying heat and pressure to the color toner images transferred onto the sheet (S). The heat roller  123  is a heat source for permanently fixing the color toner images, and faces the pressing roller  124  in an axial direction. The pressing roller  124  faces the heat roller  123  and applies a high pressure to the sheet (S) to fix the color toner images onto the sheet (S). 
   A discharge roller  117  discharges the sheet (S) having the fixed toner image from the image forming apparatus  100  into a discharge tray  180 . 
   Also, the image forming apparatus  100  includes a feeding cassette  113   a  in which sheets (S) are loaded. The feeding cassette  113   a  is an example of a loading means for loading the sheets (S). The loading means may include a multi-purpose feeder (MPF)  113   c.  The MPF  113   c  is mainly used for conveying an overhead presentation (OHP) sheet or a non-standard sheet (S). 
   The pickup rollers  115   a  and  115   c  are placed above the sheet feeding cassettes  113   a  and  113   c,  and convey the sheet (S) from the sheet feeding cassettes  113   a  and  113   c  to a feed roller  116 . 
   The feed roller  116  conveys the sheet (S) from the sheet feeding cassettes  113   a  and  113   c  to the sheet conveying unit  120  by pickup rollers  115   a  and  115   c.    
   The sheet conveying unit  120  includes a sheet feeding path  121  for guiding the sheet (S) between the feed roller  116  and the fixing unit  111 , and a duplex path  122  for duplex printing. The sheet conveying unit  120  is provided with a registration roller  118 . The registration roller  118  registers the sheet (S) such that the color toner images may be transferred onto the desired portion of the sheet (S) before the sheet (S) passes from the feed roller  116  between the transfer belt  105  and the transfer roller  112 . The sheet (S) passes between the transfer belt  105  and the transfer roller  112  such that the color toner images are transferred onto the sheet (S). The toner image is fixed to the sheet (S) by the fixing unit  111 , and the sheet (S) is discharged from the image forming apparatus  100  by the discharge roller  117 . 
   When duplex printing, the discharge roller  117  rotates in reverse and conveys the sheet (S) along the duplex path  122 . Thereby, the sheet (S) is reversed such that an image is printed on its back surface. The reversed sheet (S) is conveyed along the sheet feeding path  121  by the feed roller  116  to receive the image on its back surface. 
   Hereinafter, the operation of the image forming apparatus  100  according to an exemplary embodiment of the present invention is described in detail. 
   Color image information is composed by mixing corresponding information on cyan (C), magenta (M), yellow (M), and black (K) colors. In the present exemplary embodiment, the color toner images may be superimposed on the transfer belt  105  in order of cyan (C), magenta (M), yellow (M) and black (K), and may be transferred and fixed onto the sheet (S) to form the color image. 
   The surface of the photosensitive body  101  is charged with a uniform potential by the charging roller  102 . An optical signal corresponding to the image information on cyan is scanned onto the rotating photosensitive body  101  by the light scanning unit  103 , thereby reducing the resistance of the portion onto which the light is scanned and removing the charge adhering to the surface of the photosensitive body  101 . Accordingly, a potential difference is generated between the portion onto which the light is scanned and the portion onto which no light is scanned, and thus the electrostatic latent image is formed on the surface of the photosensitive body  101 . 
   When the electrostatic latent image approaches the cyan developer  104 C by the rotation of the photosensitive body  101 , the development roller  125  of the cyan developer  104 C begins to rotate and the development bias voltage is applied from the high voltage power supply unit  108  to the development roller  125  of the cyan developer  104 C. Also, the development preventing bias voltage for preventing image development is applied to the development rollers  125  of the other developers  104 M,  104 Y, and  104 K. Then, only the cyan toner traverses the development gap (Dg) to adhere to the electrostatic latent image that is formed on the surface of the photosensitive body  101 , thereby forming the cyan (C) toner image. 
   When the cyan (C) toner image is brought to the transfer belt  105  by the rotation of the photosensitive body  101 , the toner image is transferred onto the transfer belt  105  by the first transfer bias voltage or the contact pressure between the photosensitive body  101  and the transfer belt  105 . 
   After the cyan toner image is completely transferred onto the transfer belt  105 , the toner images of magenta (M), yellow (M), and black (K) colors are superimposed and transferred onto the transfer belt  105  in a similar way. At this time, the developer driving apparatus  200  ( FIG. 5 ) drives the developers  104 C,  104 M,  104 Y, and  104 K to develop the image. 
   In the above-mentioned process, the transfer roller  112  is spaced from the transfer belt  105 . Since four color toner images are transferred and superimposed onto the transfer belt  105  to form the color toner image on the transfer belt  105 , the transfer roller  112  contacts the transfer belt  105  to transfer the color toner images to the sheet (S). At this time, the rotary force controlling apparatus according to exemplary embodiments of the present invention acts on one side of the transfer roller  112  such that the transfer roller  112  contacts the transfer belt  105  for a predetermined time. 
   The sheet (S) is supplied from the sheet feeding cassette  113   a  (or the MPF  113   c ) such that the leading edge of the sheet (S) approaches the point where the transfer belt  105  contacts the transfer roller  112  when the top end of the color toner image formed on the transfer belt  105  approaches the point where the transfer belt  105  contacts the transfer roller  112 . When the sheet passes between the transfer belt  105  and the transfer roller  112 , the color toner image is transferred onto the sheet (S) by the second transfer bias voltage and then fixed on the sheet (S) by the heat and pressure of the fixing unit  111 . Then, the sheet (S) having the color image is discharged, thereby finishing the color image forming process. 
   For the next printing, the first and second cleaning units  106  and  109  remove the waste toner remaining on the photosensitive body  101  and the transfer belt  105 , and the erasing lamp  107  irradiates light onto the photosensitive body  101  to remove any charge remaining on the photosensitive body  101 . 
   The rotary force controlling apparatus according to an exemplary embodiment of the present invention is described with reference to the accompanying drawings. As mentioned above, the rotary force controlling apparatus may be used for controlling the operation of the transfer roller  112 . The rotary force controlling apparatus according to the exemplary embodiment of the present invention controls the rotating position of the rotary body mounted on one side of the shaft. 
     FIG. 5  is a perspective view of a rotary force controlling apparatus according to an exemplary embodiment of the present invention.  FIG. 6  is a cross-sectional view taken along line I-I′ of a clutch device of the rotary force controlling apparatus shown in  FIG. 5 . 
   Referring to  FIGS. 5 and 6 , the rotary force controlling apparatus  200  according to an exemplary embodiment of the present invention includes a clutch device  210  and a solenoid unit  260 . The clutch device  210  and the solenoid unit  260  are preferably spaced apart from each other. Although in the present exemplary embodiment the clutch device  210  and the solenoid unit  260  are spaced apart from each other, the present invention is not limited to this, and various modifications may be made. For example, the clutch device  210  and the solenoid unit  260  may be integrally assembled using a frame. 
   The clutch device  210  includes a shaft  212  having a rotary body  214  mounted at the one end thereof, a clutch  220  for controlling the rotation of the shaft  212 , a housing  230  for wrapping the clutch  220 , a positioning unit  240  for positioning the stop location of the rotary body  214  by the operation of the solenoid unit  260 , and a power transferring member  250  for receiving a rotary force from a driving source (not shown). 
   The shaft  212  is inserted into an axis hole of the housing  230 , and rotates together with the housing  230 . The rotary body  214 , such as a cam, is fixed to one side of the shaft  212 . The rotary body  214  is used for interfering with or being released from the component mounted on the image forming apparatus at a certain location. For example, the rotary body  214  interferes with one side of the transfer roller  112  at a certain location by the control of the clutch  220 , and thus the transfer roller  112  contacts the transfer belt  105 . The housing  230  is rotatably mounted on a support frame (not shown). 
   The clutch  220  is disposed between the housing  230  and the power transferring member  250 . The clutch  220  selectively transfers the rotary force transferred from the driving source to the housing  230 . That is, the clutch  220  selectively controls the rotary force transferred from the driving source (not shown) to rotate the housing  230 . Accordingly, when a load is applied to the housing  230 , the power transferring member  250  slips. The clutch  220  is preferably a spring clutch. Since the structure and operation of the spring clutch are widely known in the art, their description is omitted here. 
   The power transferring member  250  is rotatably mounted in the housing  230  and selectively rotates the housing  230  through the clutch  220 . Power from the driving source rotates the power transferring member  250 . The power transferring member  250  is preferably a gear. Also, the driving source may be a driving motor. The rotary force transferred by the power transferring member  250  is selectively transferred to the rotary body  214  through the clutch  220 . 
   Referring to  FIG. 6 , the positioning unit  240  protrudes from the periphery of the housing  230  and positions a stop location of the rotary body  214 . The positioning unit  240  includes a first positioning unit  246  for positioning an initial location of the rotary body  214  and a plurality of second positioning units  242  and  244  for stopping the rotary body  214  at a certain location. 
   The first positioning unit  246  positions the initial location of the rotary body  214  when the solenoid unit  260  is turned on. The first positioning unit  246  includes a first portion  246   a  protruding from the peripheral surface of the housing  230 , and a second portion  246   b  that extends from the first portion  246   a  in the axial direction of the housing  230 . The second portion  246   b  interferes with (or engages) an interfering unit  282  (which is described later) when the solenoid unit  260  is turned on, but not when the solenoid unit  260  is turned off. That is, the second portion  246   b  preferably interferes with the interfering unit  282  only when the solenoid unit  260  is turned on. For example, the first positioning unit  246  may be formed in a reversed z, 900  -shape (or substantially L-shaped). 
   The plurality of second positioning units  242  and  244  are spaced from the first positioning unit  246 . The second positioning units  242  and  244  interfere with the interfering unit  282  and stop the rotary body  214  at certain locations when the solenoid unit  260  is turned off. Preferably, the plurality of second positioning units  242  and  244  are provided at locations such that the rotary body  214  stops at a desired, predetermined location. 
   In the present exemplary embodiment, for clarity, two second positioning units are used. Preferably, the second positioning units  242  and  244  are located on substantially the same circumference around the peripheral surface of the housing  230 . Also, the second positioning units  242  and  244  have substantially the same height, which is different from that of the first positioning unit  246 , such that the first positioning unit  246  interferes with the interfering unit  282  only the solenoid unit  260  is turned on. As shown in  FIG. 6 , the second positioning units  242  and  244  form a pair, and are positioned symmetrically around the center of the housing  230 . Preferably, the first positioning unit  246  is positioned at 90° from each of the second positioning units  242  and  244 . 
   Referring back to  FIG. 5 , the solenoid unit  260  is spaced from the clutch device  210 . When the solenoid unit  260  is turned on, the positioning unit  240  interferes with the interfering unit  282  to control the stopping location of the rotary body  214 . The solenoid unit  260  includes a bracket  264 , an armature  280  that is reciprocal-movably mounted on the bracket  264 , and an elastic member  270  for providing an elastic biasing force to the armature  280 . Also, a solenoid  262  is mounted on the bracket  264  and is turned on and off by an electrical signal. 
   An interfering unit  282  for interfering with the positioning unit  240  is mounted on one side of the armature  280 . The interfering unit  282  interferes with the first positioning unit  246  when the solenoid  262  is turned on, and interferes with the second positioning units  242  and  244  when the solenoid  262  is turned off. When the solenoid  262  is turned on by the electrical signal, a magnetic force is generated and thus the armature  280  is attracted. At this time, the interfering unit  282  mounted on the armature  280  moves to a location for interfering with the first positioning unit  246 . When the solenoid  262  is turned off, the magnetic force disappears and thus the armature  280  is separated from the solenoid  262 . At this time, the interfering unit  282  moves to a location for interfering with the second positioning units  242  and  244 . That is, the interfering unit  282  moves between the location for interfering with the first positioning unit  246  and the location for interfering with the second positioning units  242  and  244 , as the solenoid  262  is turned on and off. 
   As shown in  FIG. 14 , the interfering unit  282  may include a first interfering unit  284  for interfering with the first positioning unit  246  when the solenoid  262  is turned on, and a second interfering unit  286  for interfering with the second positioning units  242  and  244  when the solenoid  262  is turned off. These are described later in detail. 
   As mentioned above, the interfering unit  282  interferes with or is released from the first positioning unit  246  and the second positioning units  242  and  244  to control the rotation of the rotary body  214  when the solenoid  262  is turned on and off. That is, the interfering unit  282  interferes with the first positioning unit  246  and the second positioning units  242  and  244  to control the rotation of the rotary body  214 . 
   One end of the elastic member  270  is attached to the bracket  264 , and the other end is attached to the armature  280 . The elastic member  270  provides an elastic biasing force to the armature  280  such that the interfering unit  282  interferes with or is released from the first positioning unit  246  and the second positioning units  242  and  244 . That is, the interfering unit  282  is attracted to the solenoid  262  by the magnetic force when the solenoid  262  is turned on. At this time, the interfering unit  282  interferes with the first positioning unit  246  and positions an initial location of the rotary body  214 . When the solenoid  262  is turned off, the elastic force of the elastic member  270  moves the interfering unit  282  to a location for interfering with the second positioning units  242  and  244 . At this time, the interfering unit  282  interferes with the second positioning units  242  and  244  and stops the rotary body  214  at a certain location. That is, the solenoid  262  and the elastic force of the elastic member  270  move the interfering unit  282  between two locations so that it interferes with or is released from the first positioning unit  246  and the second positioning units  242  and  244 . As mentioned above, the interference of the interfering unit  282  and the first positioning unit  246  or the second positioning units  242  and  244  is released by an instantaneous ON and OFF operation of the solenoid  262 . 
   Hereinafter, the operation of the rotary force controlling apparatus according to an exemplary embodiment of the present invention is described in detail with reference to the accompanying drawings. 
     FIG. 7  illustrates the relationship between the clutch device and the solenoid unit when the solenoid unit is turned off.  FIGS. 8A through 8C  illustrate the operation when the clutch device rotates and stops when the solenoid unit is turned off.  FIG. 9  illustrates the relationship between the clutch device and the solenoid unit when the solenoid unit is turned on.  FIGS. 10A through 10C  illustrate the operation when the clutch device rotates and stops when the solenoid unit is turned on. 
   As shown in  FIG. 7 , when the solenoid  262  is turned off, the armature  280  is separated from the solenoid  262  by the elastic member  270 . As shown in  FIGS. 7 and 8A , the interfering unit  282  is placed below the second portion  246   b.  When the rotary force is transferred to the housing  230  by the power transferring member  250 , the housing  230  rotates in the direction shown by the arrows with the first positioning unit  246  mounted thereon. At this time, as shown in  FIGS. 7 and 8A , since the interfering unit  282  is placed below the second portion  246   b  of the first positioning unit  246 , it does not interfere with the first positioning unit  246 . When the housing  230  continuously rotates in the direction of the arrow, the second positioning unit  244  interferes with the interfering unit  282 , as shown in  FIG. 8B . Since the power transferring member  250  slips by the operation of the clutch  220 , the rotary force of the power transferring member  250  is not transferred to the housing  230 . Accordingly, the rotary body  214  mounted on the shaft  212  stops rotating. When the solenoid  262  is instantaneously turned on, the interference between the interfering unit  282  and the second positioning unit  244  is released. Then, when the solenoid  262  is turned off, the second positioning unit  242  interferes with the interfering unit  282 , as shown in  FIG. 8C . That is, the interfering unit  282  interferes with the second positioning units  242  and  244  and stops the rotary body  214  at a certain location when the solenoid  262  is turned off. 
   When the solenoid  262  is turned on, the magnetic force is generated in the solenoid  262  and thus the armature  280  moves toward the solenoid  262 , as shown in  FIG. 9 . The interfering unit  282  moves to a location where it interferes with the second portion  246   b  of the first positioning unit  246 , as shown in  FIGS. 9 and 10A . That is, when the solenoid  262  is turned on, the solenoid  262  attracts the armature  280  and the interfering unit  282  is moved to a location where it interferes with the first positioning unit  246  by the magnetic force of the solenoid  262 . When the interfering unit  282  interferes with the first positioning unit  246 , the power transferring member  250  slips by the operation of the clutch  220 , and thus the rotary force of the power transferring member  250  is not transferred to the housing  230 . That is, the rotary body  214  mounted on one end of the shaft  212  stops rotating. When the solenoid  262  is instantaneously turned off and then turned on, the interference between the interfering unit  282  and the first positioning unit  264  is released. As shown in  FIGS. 10B and 10C , the interfering unit  282  does not interfere with the second positioning units  242  and  244  when the solenoid  262  is turned on. Accordingly, since the first positioning unit  246  interferes with the interfering unit  282  only when the solenoid  262  is turned on, it is used for setting the initial location of the rotary body  214 . 
   Hereinafter, a rotary force controlling apparatus according to another exemplary embodiment of the present invention is described with reference to the accompanying drawings. For clarity, components having the same operation and effect as in the above exemplary embodiment are indicated by the same reference numerals. 
     FIG. 11  is a perspective view of a rotary force controlling apparatus according to another exemplary embodiment of the present invention.  FIG. 12  is an elevational view of the rotary force controlling apparatus shown in  FIG. 11 .  FIG. 13  is a front elevational view of the rotary force controlling apparatus shown in  FIG. 11 .  FIGS. 14 through 16  are front elevational views of a rotary force controlling apparatus according to other exemplary embodiments of the present invention. 
   When the solenoid  262  is turned off, the armature  280  is spaced apart from the solenoid  262  by the elastic force of the elastic member  270 . At this time, the interfering unit  282  mounted on the armature  280  may bump against the housing  230 . When the housing  230  rotates while the interfering unit  282  contacts the housing  230 , noise or abrasion of the equipment may be caused. To prevent the interfering unit  282 , from contacting the housing  282 , a stopper  295  is included to control the motion of the armature  280 . 
   Referring to  FIGS. 11 through 13 , the rotary force controlling apparatus according to another exemplary embodiment of the present invention further includes a stopper  295  for controlling the motion of the armature  280 , unlike the above-mentioned exemplary embodiment. One end of the stopper  295  is fixed to the bracket  264 . The other end of the stopper  295  has a coupling hook  296  for controlling the motion of the armature  280 . When the solenoid  262  is turned off, the stopper  295  controls the motion of the armature  280  such that the interfering unit  282  interferes with the second positioning member  242  and  244 . When the solenoid  262  is turned off, the armature  280  moves away from the solenoid  262  and engages the stopper  295 . Accordingly, movement of the armature  280  away from the solenoid  262  is not unrestricted. That is, the armature  280  interferes with the stopper  295  and stops at a location where the interfering unit  282  interferes with the second positioning units  242  and  244 . Also, in the present exemplary embodiment, the interfering unit  282  must not interfere with the first positioning unit  246  when the housing  230  rotates when the solenoid  262  is OFF. Accordingly, the interfering unit  282  may take various shapes so that it interferes with or is released from the first positioning unit  246  and the second positioning units  242  and  244 . 
   As shown in  FIGS. 11 through 13 , the interfering unit  282  includes a second interfering unit  282   a  that is angled from the armature  280  and a first interfering unit  282   b  that extends from the second interfering unit  282   a  in the axial direction of the housing  230 . The first interfering unit  282   b  interferes with the first positioning unit  246  only when the solenoid  262  is turned on, and the second interfering unit  282   a  interferes with the second positioning units  242  and  244  only when the solenoid  262  is turned off. 
   Alternatively, as shown in  FIG. 14 , the interfering unit  282  includes a first interfering unit  284  that is angled from the armature  280  and interferes with the first positioning unit  246  only when the solenoid  262  is turned on, and a second interfering unit  286  that is angled from the armature  280  and spaced from the first interfering unit  284  and interferes with the second positioning units  242  and  244  only when the solenoid  262  is turned off. 
   As shown in  FIGS. 13 and 14 , the interfering unit  282  may take various shapes. These modifications do not limit the scope of the present invention. Since the structure and operation of the rotary force controlling apparatus shown in  FIGS. 11 through 14  are similar to that of the above-mentioned exemplary embodiments, except that the stopper  295  is mounted on the bracket  264 , their description is omitted. 
   Referring to  FIG. 15 , the rotary force controlling apparatus according to the exemplary embodiments of the present invention may further include a connecting member  298  for integrally assembling the clutch device  210  and the solenoid unit  260 . The connecting member  298  supports one side of each of the clutch device  210  and the solenoid unit  260 . As shown in  FIG. 16 , the connecting member  298  may also be provided on both sides of the clutch device  210  and the solenoid unit  260 . Since the structure and operation of rotary force controlling apparatus shown in  FIGS. 15 and 16  are similar to that of the above-mentioned exemplary embodiments, their description is omitted. 
   According to the rotary force controlling apparatus and the image forming apparatus of the exemplary embodiments of the present invention, the initial location of the rotary body  214  is positioned when the solenoid unit  260  is turned on, and the rotary body  214  stops at a certain location when the solenoid unit  260  is turned off. Also, by mounting the plurality of second positioning units on the surface of the housing  230 , the rotary body  214  may be stopped at a desired location. Also, by mounting the stopper  295 , the location of the interfering unit  282  may be controlled. 
   As mentioned above, the rotary force controlling apparatus and the image forming apparatus according to the exemplary embodiments of the present invention, the solenoid unit is turned on only when the initial location of the rotary body is set, or when the rotary body rotates to a certain location. When the rotary body stops at a certain location, the solenoid unit is turned off. Since the solenoid unit is turned off while the rotary body is stopped, the solenoid unit is prevented from being overheated. 
   Furthermore, according to the exemplary embodiments of the present invention, the plurality of second positioning units may stop the rotary body at a desired location, and thus the operation of the rotary body may be easily controlled. 
   Also, the location of the rotary body may be smoothly changed by allowing the interfering unit to interfere with the first positioning unit when the solenoid unit is turned on and to interfere with the second positioning units when the solenoid unit is turned off. That is, since the interfering unit is located adjacent to the surface of the housing when the solenoid unit is turned off, it does not interfere with the first positioning unit when the housing rotates. Accordingly, by instantaneously turning the solenoid unit on and off, the location of the rotary body may be more smoothly changed. 
   Further, by providing the stopper, the interfering unit may be prevented from contacting the housing when the solenoid is turned off, and thus noise or abrasion of the equipment may be prevented. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.