Abstract:
Provided is an image forming apparatus for printing a desired image. The image forming apparatus comprises a first developing unit comprising a first fixed power transmission unit, a second developing unit comprising a second fixed power transmission unit, a first sliding power transmission unit comprising a first interconnection portion placed slidably along a first axis of the first fixed power transmission unit, a second sliding power transmission unit comprising a second interconnection portion placed slidably along a second axis of the second fixed power transmission unit, and a clutching unit comprising a rotating element having a plurality of pushing bosses protruding towards at least one of the first and second sliding power transmission units, at least one of the pushing bosses selectively contacting at least one of the first and second sliding power transmission units when the rotating element is rotated, so that at least one of the first and second sliding power transmission units is slid towards at least one of the first and second fixed power transmission units to couple with or separate from at least one of the first and second fixed power transmission units, respectively.

Description:
BACKGROUND OF THE INVENTION 
     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2005-0032764, filed on Apr. 20, 2005 in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference. 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus having a power controlling device that controls power supplied to a plurality of color developers. 
     2. Description of the Related Art 
     Image forming apparatuses print a desired image by receiving a digital image signal and forming an electrostatic latent image on a photosensitive medium coated with a conductive material by using an exposure unit such as a laser scanning unit. The electrostatic latent image is develop into a toner image using toner by transferring the toner image to a recording medium, and fusing the toner image on the recording medium by applying heat and pressure thereto. 
     Image forming apparatuses generally are classified into dry and wet apparatuses according to a state of toner and carrier being used. Furthermore, the dry apparatuses can be classified into a 1-component developing unit and a 2-component developing unit. 
     In the 1-component developing unit, an image is formed using only toner. In the 2-component developing unit, an image is formed using a mixture of toner. 
     In the 1-component developing unit, the toner is provided to the photosensitive medium to develop the toner image. The toner remaining on a surface of the photosensitive medium is removed by a cleaning blade and collected by a collecting unit for reuse. In the 2-component developing unit, the carrier is collected without being provided to the photosensitive medium and only the toner particles are provided to the photosensitive medium to develop the toner image. As a result, the toner particles remaining on the surface of the photosensitive medium are removed by the cleaning blade and collected by the collecting unit for reuse. The above descriptions relate to a case of forming a black and white image. It is difficult to reuse the toner remaining on the photosensitive medium when a color image is formed, because a color toner image on the surface of the photosensitive medium is a mixture of toners of various colors. 
     In order to form a color image, an image forming apparatus needs four toner cartridges, such as, yellow (Y), magenta (M), cyan (C), and black (K). Developing rollers provided in each of the four toner cartridges supply toners to an electrostatic latent image formed on a photosensitive medium, and develops the electrostatic latent image into a toner image by supplying the toners to the electrostatic latent image. 
     The developing rollers provided in each of the four toner cartridges are actuated by a driving motor. Since the developing rollers do not need to operate simultaneously, an electrical clutch is used to power the developing rollers selectively. 
     However, such electrical clutch is expensive and increases the overall size of the image forming apparatus. In addition, the electrical clutch frequently malfunctions and does not operate precisely. 
     Accordingly, there is a need for an improved image forming apparatus that is reduced in size and has a power controlling device that controls power to the toner cartridges. 
     SUMMARY OF THE INVENTION 
     An aspect of embodiments of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of embodiments of the present invention is to provide an image forming apparatus including a power controlling device that can more timely and precisely control a developing roller. 
     According to an aspect of the present invention, there is provided an image forming apparatus, the image forming apparatus comprising: a first developing unit comprising a first fixed power transmission unit; a second developing unit comprising a second fixed power transmission unit; a first sliding power transmission unit comprising a first interconnection portion placed slidably along a first axis of the first fixed power transmission unit; a second sliding power transmission unit comprising a second interconnection portion placed slidably along a second axis of the second fixed power transmission unit; and a clutching unit comprising a rotating element having a plurality of pushing bosses protruding towards at least one of the first and second sliding power transmission units, at least one of the pushing bosses selectively contacting at least one of the first and second sliding power transmission units when the rotating element is rotated, so that at least one of the first and second sliding power transmission units is slid towards at least one of the first and second fixed power transmission units to couple with or separate from at least one of the first and second fixed power transmission units, respectively. 
     Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of an image forming apparatus using a power controlling device according to an exemplary embodiment of the present invention; 
         FIG. 2  is a diagram illustrating a power transmission process of the power controlling device of  FIG. 1  according to an exemplary embodiment of the present invention; 
         FIG. 3  is a side view of the power controlling device in  FIG. 2 ; 
         FIG. 4  is a plane view of a clutching unit illustrated in  FIG. 3 ; 
         FIG. 5  is a side view of the clutching unit illustrated in  FIG. 3 ; 
         FIG. 6  is a plane view of a clutching unit according to an exemplary embodiment of the present invention placed in a home position; and 
         FIG. 7  is a side view of a power controlling device according to an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
     Referring to  FIG. 1 , an image forming apparatus  100 , according to an exemplary embodiment of the present invention, includes paper cassettes  110 , an exposure unit  130 , a photosensitive drum  140 , black  141 K, cyan  141 C, magenta  141 M, and yellow  141 Y color developing units, an intermediate transfer unit  160 , a transfer roller  170 , a fusing unit  180 , and a paper eject unit  190 . 
     The paper cassettes  110  store sheets of printing paper S and are detachably installed in a main body  101 . Pickup rollers  111  and  112 , which pick up the printing paper S one by one, are rotatably installed in the main body  101  above the paper cassettes  110 , respectively. Reference number  120  includes a multi-purpose paper stacking tray which stores sheets of printing paper S. The multi-purpose paper stacking tray  120  is pivotably installed to the main body  101  and in an exemplary implementation folds in and out, with respect to the main body  101 . A pickup roller  121 , which picks up the sheets of printing paper S one by one, is installed above the multi-purpose paper stacking tray  120 . 
     The exposure unit  130  emits a ray, corresponding to image information, onto the photosensitive drum  140  charged with a uniform electrostatic potential in order to form an electrostatic latent image thereon. 
     An optical conductive layer is formed on an outer circumference of the photosensitive drum  140 , which is cylindrical in shape and made of metal. 
     The black  141 K, cyan  141 C, magenta  141 M, and yellow  141 Y color developing units each include solid powder toners of black K, cyan C, magenta M, and yellow Y colors. The black  141 K, cyan  141 C, magenta  141 M, and yellow  141 Y color developing units each include developing rollers  1411  for supplying the toners to the electrostatic latent image formed on the photosensitive drum  140  in order to form a toner image. The black  141 K, cyan  141 C, magenta  141 M, and yellow  141 Y color developing units are installed so that the developing rollers  1411  are a predetermined distance away from the outer circumference of the photosensitive drum  140 . 
     The transfer roller  170  is installed in the main body  101  facing a transfer belt  161 . The transfer roller  170  separates from the transfer belt  161  when a color toner image transfers to the transfer belt  161 . After the color toner image is completely transferred to the transfer belt  161 , the transfer roller  170  provides the transfer belt  161  with a predetermined pressure in order to transfer the color toner image onto the printing paper S. 
     The fusing unit  180  includes a pair of rollers that are meshed with each other. The fusing unit  180  heats and applies pressure to the color toner image in order to fuse and fix the color toner image on the printing paper S passing therebetween. A heating element (not shown) may be installed on one or both rollers. 
     The paper eject unit  190  includes a pair of rollers for ejecting the printing paper S in which the color toner image is formed, and pile the sheets of printing paper S in an exit tray  191 . 
     A charging roller  143  charges the photosensitive drum  140  with a uniform electrostatic potential. The charging roller  143  rotates while making or not making contact with the outer circumference of the photosensitive drum  140 , and supplies electric charges to uniformly charge the outer circumference of the photosensitive drum  140 . 
     A pre-transfer eraser  142  removes charges in a region where the toner image on the photosensitive drum  140  is not formed (that is, a non-image region). 
     Referring to  FIG. 2 , the image forming apparatus  100  includes a power controlling device  150  for selectively transmitting power to the black  141 K, cyan  141 C, magenta  141 M, and yellow  141 Y color developing units. 
     The power controlling device  150  includes black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units; black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y sliding power transmission units; and a clutching unit  153 . 
     The black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units are rotatably installed on the main body  101  via bushings  1512 , and each includes a developing roller driving gear  1511 . The black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units are respectively connected to the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units via axes  1514 . A plurality of claws  1513  are respectively formed on the side of the black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units. Each of the plurality of claws  1513  face the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. The plurality of claws  1513  are formed to, for example, interconnect with claws  1522  formed on an end of the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units so that they can mesh with each other and transmit rotation power to the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. The claws  1513  and  1522  are exemplary elements for transmitting power. However other elements that interconnect can be used for transmitting power. 
     The black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units are installed in the main body  101  via bushings  1512  to, for example, slide in a Z direction along the axes  1514 . Passive gears  1523  are each placed at a side of the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units facing the clutching unit  153  to be connected to power transmitting gears  210  installed in the main body  101 , as illustrated in  FIG. 3 . The power transmitting gears  210  receive power from a driving source  230  and a second power transmitting gear  220 . When the driving source  230  operates, the power transmitting gears  210  also rotate, thereby rotating each of the passive gears  1523  of the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. 
     While the power transmitting gears  210  and the passive gears  1532  are connected to each other, the passive gears  1523  may slide, for example, while making contact with the power transmitting gears  210 . Therefore, the power transmitting gears  210  and the passive gears  1532  may be spur gears. 
     The black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units may apply elastic forces towards the clutching unit  153  via elastic members  1524  placed on each of the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. After the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units are respectively coupled with the black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units, each of the color sliding power transmission units separates from the clutching unit  153  by the elastic forces of the elastic members  1524  and then returns to an original position. 
     Referring to  FIGS. 2 through 5 , the clutching unit  153  selectively couples the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units with the black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units. The clutching unit  153  includes a rotating element  1531 , a pushing boss  1532 , black  1533 K, cyan  1533 C, magenta  1533 M, and yellow  1533 Y color location setting hooks or devices, a home position hook or device  1534 , and an actuator  1535 . As applied to elements  1533  and  1534 , the term “hook(s)” shall be understood to be interchangeable with “device(s)”. 
     The rotating element  1531  is rotatably installed in the main body  101 , and is connected to a power transmitting gear  240  that is connected to power from the driving source  230 . The power transmitted to the rotating element  1531  can be blocked by a clutch  1538  installed between the rotating element  1531  and the power transmitting gear  240 . The rotating element  1531  rotates by receiving the power transmitted from the driving source  230  via the clutch  1538 . Therefore, the rotating element  1531  rotates when the driving source  230  operates unless an external torque is applied. 
     The clutch  1538  preferably transmits power in only one direction. Thus, the clutch  1538  transmits power so that the rotating element  1531  rotates preferably in an anti-clockwise direction as illustrated in  FIG. 4 . If the rotating element  1531  needs to rotate in a clockwise direction, a clutch can be used that transmits the power preferably in the clockwise direction. 
     The pushing boss  1532  protrudes from a surface  1531   a  of the rotating element  1531  facing the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. When the rotating element  1531  rotates, the pushing boss  1532  comes in contact with a bottom surface of one of the passive gears  1523 . The pushing boss  1532  then pushes one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units towards a corresponding black  151 K, cyan  151 C, magenta  151 M, or yellow  151 Y color fixed power transmission units to connect the corresponding color sliding power transmission units and color fixed power transmission units together. Accordingly, power is transmitted from one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units to the corresponding black  151 K, cyan  151 C, magenta  151 M, or yellow  151 Y color fixed power transmission units. One side of the pushing boss  1532  may be slanted to easily come in contact with the bottom surface of the passive gear  1523 . 
     The black  1533 K, cyan  1533 C, magenta  1533 M, and yellow  1533 Y color location setting devices protrude from a surface  1531   b  connected to the clutch  1538  at predetermined intervals to correspond to the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. The black  1533 K, cyan  1533 C, magenta  1533 M, and yellow  1533 Y color location setting devices control the position of the pushing boss  1532  together with the actuator  1535  so that the pushing boss  1532  contacts one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units in order to connect with one of the corresponding black  151 K, cyan  151 C, magenta  151 M, or yellow  151 Y color fixed power transmission units. 
     Similarly to the black  1533 K, cyan  1533 C, magenta  1533 M, and yellow  1533 Y color location setting devices, the home position hook  1534  protrudes from the surface  1531   b , which is connected to the clutch  1538 . The home position device  1534  controls the position of the pushing boss  1532  together with the actuator  1535 . As a result, the pushing boss  1532  is located in a home position and does not make contact with any one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units. 
     The actuator  1535 , installed in the main body  101 , ascends and descends an actuator arm  1536  in the Z direction in order to lock the rotating element  1531  by contacting one of the black  1533 K, cyan  1533 C, magenta  1533 M, or yellow  1533 Y color location setting devices, and the home position device  1534 . 
     Referring to  FIG. 6 , the clutching unit  153  further includes a home position mark  1537  formed on the rotating element  1531  and a sensor  250 . The home position mark  1537  indicates the home position of the pushing boss  1532  in order to help locate where the pushing boss  1532  does not make contact with any one of the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. The sensor  250  installed in the main body  101  senses the home position mark  1537 . 
     When the sensor  250  senses the home position mark  1537 , the actuator  1535  contacts the home position device  1534  and locks the rotating element  1531 . As a result, the pushing boss  1532  is located in the home position, not contacting any of the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. 
     The following is a description of the operation of the power controlling device  150  having the above-described structure. 
     Referring to  FIG. 1 , when the black  141 K, cyan  141 C, magenta  141 M, and yellow  141 Y color developing units are installed in the main body  101 , the corresponding color developing units are respectively connected to the developing roller driving gears  1511 . 
     Referring to  FIGS. 2 through 6 , the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units rotate in connection with the passive gears  1523 . Before the electrostatic latent image is developed, the home position device  1534  contacts the actuator arm  1536 . In this instance, the rotating element  1531  is locked by the actuator arm  1536  and power is not transmitted to the rotating element  1531 . Additionally, the pushing boss  1532  does not contact any one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units, and thus power is not transmitted to any one of the color sliding power transmission units. 
     In order to transmit power to the cyan color developing unit  141 C to print a cyan color image, the actuator arm  1536  contacts the cyan color location setting device  1533 C and locks the rotation of the rotating element  1531  while the pushing boss  1532  contacts the cyan sliding power transmission unit  152 C, as illustrated in  FIG. 4 . The cyan color sliding power transmission unit  152 C slides in the Z direction along the axis  1514  and connects the cyan color fixed power transmission unit  151 C, thereby transmitting the rotation power of the cyan color sliding power transmission unit  152 C to the cyan color fixed power transmission unit  151 C. Thereafter, the cyan color developing roller  141 C, as shown in  FIG. 1 , contacts the photosensitive drum  140  and the electrostatic latent image formed on the outer circumference of the photosensitive drum  140  is developed into the cyan color image. 
     As described above, when the actuator arm  1536  contacts the cyan color location setting device  1533 C, the clutch  1538  blocks the rotation power of the power transmitting gear  240 . 
     In order to develop a magenta color image after developing the electrostatic latent image into the cyan color image, the actuator arm  1536  unlocks the cyan color location setting device  1533 C and locks the magenta color location setting device  1533 M. Then, consistent with operations for developing the cyan color image as described above, the magenta color sliding power transmission unit  152 M contacts the magenta color fixed power transmission unit  151 M, as shown in  FIG. 1 , to transmit power. Accordingly, the electrostatic latent image is developed into the magenta color image. 
     A black color image and a yellow color image are developed by repeating the same operations described above. 
     When the printing operation restarts, after the developing of the electrostatic latent image is completed or power of the image forming apparatus  100  is turned off, the sensor  250  senses the home position mark  1537  and the actuator arm  1536  locks the home position device  1534 , thereby locating the pushing boss  1532  in the home position. 
     Referring to  FIG. 7 , a power controlling device  260 , according to an exemplary embodiment of the present invention, has a similar structure with the power controlling device  150  of an exemplary embodiment. The power controlling device  260  includes black  151 K, cyan  151 C, magenta  151 M, and yellow  151 Y color fixed power transmission units; and black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. The power controlling device  260  includes a clutching unit  263 . 
     The clutching unit  263  includes a rotatably installed rotating element  2631 , and a pushing boss  2632  protruding from a surface of the rotating element  2631  facing the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. The clutching unit further includes a motor  2633  for rotating the rotating element  2631  so that the pushing boss  2632  contacts one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units. 
     Passive gears  1523  rotate in connection with a driving source  230  and power transmitted gears  210  and  220 , as illustrated in  FIG. 3 . The rotating element  2631  is rotated by a separate motor  2633 . Accordingly, the rotating element  2631  and the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units are operated by different power sources. 
     The clutching unit  263  further includes a home position mark  1537  and a sensor  250 . The home position mark  1537  formed on the rotating element  2631  indicates a home position of the pushing boss  2632  in order to help locate where the pushing boss  2632  does not contact any one of the black  152 K, cyan  152 C, magenta  152 M, or yellow  152 Y color sliding power transmission units. The sensor  250  installed in the main body  101  senses the home position mark  1537 . 
     When the sensor  250  senses the home position mark  1537 , the motor  2633  rotates the rotating element  2631  so that the pushing boss  2632  is placed in the home position, and makes no contact with the black  152 K, cyan  152 C, magenta  152 M, and yellow  152 Y color sliding power transmission units. 
     A description of the operations of the power controlling device  260  will be omitted in exemplary embodiments of the present invention since the power controlling device  260  functions similarly to the power controlling device  150  described previously. 
     As described above, an image forming apparatus according to exemplary embodiments of the present invention has improved reliability since power is transmitted via the meshed fixed power transmission units and sliding power transmission units, and the fixed power transmission units and sliding power transmission units make contact with each other without slipping. 
     While the invention has been shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.