Patent Publication Number: US-6904247-B2

Title: High voltage switching equipment of developing device for color image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2002-38467, filed Jul. 3, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrophotographic color image forming apparatus, and more particularly to a high voltage switching equipment sequentially supplying a high developing voltage (referred to as a ‘high voltage’ hereinafter) to color developing devices which develop an electrostatic latent image on a photoconductive medium using toner. 
     2. Description of the Related Art 
     For example, an electrophotographic color image forming apparatus, such as a color laser printer, a duplicating machine, etc., sequentially develops an electrostatic latent image on a photoconductive medium using color developing devices, i.e., a yellow toner developing device, a magenta toner developing device, a cyan toner developing device and a black toner developing device, and then transcribes and prints a visible image on a paper. 
     In a printing process mentioned above, a developing process adopts a method where a toner of a developing device is transferred to a photoconductive medium by a voltage difference between the photoconductive medium and the developing device and in order to perform such method, a high voltage should be supplied to one selected developing device or the above four color developing devices in sequence. 
     A typical example for a high voltage switching equipment of a developing device, adopted in a general electrophotographic color image forming apparatus, is illustrated in  FIGS. 1 and 2 , which will be briefly described in the following. 
     In  FIGS. 1 and 2 , the high voltage switching equipment includes a photoconductive drum  80 , a developing device  82 , a driving unit  83 . Before description, it should be noted that a general color image forming apparatus has four color developing devices as shown in FIG.  1 . Since the four developing devices have the same structure and operate in the same manner, description for only one developing device will be made for convenience. 
     As shown in  FIG. 1 , the four developing devices  82  are installed to contact the photoconductive drum  80  selectively or sequentially. Such respective developing device  82  has a developing roller  90  and a toner supplying roller  92  as shown in FIG.  2 . 
     The driving unit  83  has a motor  86  and a cam  84  and is disposed in a rear end of each developing device  82 . The driving unit  83  moves a relevant developing device  82  back and forth with respect to a side of the photoconductive drum  80 , thereby the developing roller  90  become close on the photoconductive drum  80  so that toner on the developing roller  90  is transferred to the photoconductive drum  80 . A curved contact  94  is disposed at the rear end of each developing device  82  to contact the cam  84  of the driving unit  83 . 
     In the meantime, a high voltage terminal  88  generating a voltage difference necessary for development at the photoconductive drum  80  and the developing roller  90  is fixedly installed in a frame not shown. Therefore, when the developing device  82  is moved forth toward the side of the photoconductive drum  80  by the driving unit  83 , a shaft of the developing roller  90  and the high voltage terminal  88  come in contact with each other, whereby the high voltage is supplied and the toner on a relevant developing device  82  is transferred to the photoconductive drum  80 . After that, the developing device  82  is moved back by a restoring spring installed in its rear end, and another developing device  82  is moved forth by the driving unit  83 , whereby development by toner of another color is performed. By such series of successive operations, the color developing devices are moved back and forth in sequence and the electrostatic latent image on the photoconductive drum  80  is developed using the color toners. 
     But the above-mentioned general high voltage switching equipment for the developing device adopted in the color image forming apparatus, operates in a manner such that the developing device  82  is moved back and forth with respect to the side of the photoconductive drum  80  using the driving unit  83  having the motor  86  and the cam  84 . Accordingly, vibration due to a movement of the developing device  82  and a load variation upon a rotation of the photoconductive drum  80  are generated since the developing device  82  contacts the photoconductive drum  80  periodically. Such factors cause a change in a velocity of the photoconductive drum  80  in the long run, thereby generating a jitter that is fatal to an image quality of a color image. 
     Further, the above mentioned high voltage switching equipment of a conventional movement type developing device maintains a proper developing nip to obtain a stable image quality only if a movement distance of the developing device is always constant. But when the movement distance of the driving unit  83  is changed due to deterioration and abrasion of the driving unit  83  upon use for a long period of time and the movement distance of the developing device  82  is changed, a constant developing leaf can not be maintained accordingly, whereby a problem of deterioration in the image quality occurs. 
     Still further, the high voltage switching equipment of the conventional developing device requires the motor  86  or the cam  84  necessary for movement of the developing device  82 , and a sensor for sequentially driving color developing devices. Therefore, a problem that increases a manufacturing cost inevitably occurs. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve at least the above and other problems and/or disadvantages and to provide at least the advantages described hereinafter. 
     Accordingly, an object of the present invention is to solve the foregoing and other problems by providing a high voltage switching equipment of a developing device for a color image forming apparatus capable of preventing deterioration in an image quality due to a load variation of a photoconductive drum which occurs in a conventional movement type developing device, and by adopting a fixed developing device type sequentially supplying a high voltage to each developing device. 
     Another object of the present invention is to provide a high voltage switching equipment of a developing device for a color image forming apparatus whose structure is simple, and which selectively supplies and switches a high voltage to each developing device, thereby achieving reduction in a manufacturing cost and improvement in reliability. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
     The foregoing and other objects and advantages are achieved by providing a high voltage switching equipment of a developing device in a color image forming apparatus, which sequentially supplies a high voltage to color developing devices fixed on a frame of the color image forming apparatus to develop an electrostatic latent image formed on a photoconductive medium of the color image forming apparatus using color toner. The equipment includes high voltage applying terminals respectively formed in rear ends of the fixed color developing devices contacting the photoconductive medium, a high voltage applying substrate, within which a high voltage circuit is installed, and on which connector terminal strips connected to the each high voltage applying terminal is provided on one side, and on which first terminal strips connected to the high voltage circuit and second terminal strips connected to the connector terminal strips are arranged in pairs and spaced apart from each other by a constant distance, and a high voltage connecting unit connecting the first terminal strips and the second terminal strips arranged on the high voltage applying substrate, so that the high voltage is supplied to on a relevant developing device. 
     The high voltage connecting unit includes a contact member having a first and a second contact end portions corresponding to the first and the second terminal strips of the high voltage applying substrate, a holder supporting the contact member, and a holder moving member bringing the first and the second contact end portions into contact with the first and the second terminal strips selectively, by moving the holder back and forth with respect to the high voltage applying substrate. 
     Here, the contact member is a contact spring, and the holder moving member is a solenoid. 
     According to an aspect of the present invention, the connector terminal strips on the high voltage applying substrate and the high voltage applying terminal of the developing device, are closely connected by a spring connector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantageous of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a cross-sectional view schematically representing a high voltage switching equipment of a developing device adopted to a conventional color image forming apparatus; 
         FIG. 2  is an enlarged, cross-sectional view explaining a structure and an operation of the high voltage switching equipment of the developing device as shown in  FIG. 1 ; 
         FIGS. 3 and 4  are drawings representing a status before and after a high voltage is supplied, in a high voltage switching equipment of a developing device for a color image forming apparatus according to one embodiment of the present invention; and 
         FIG. 5  is a plan view of the high voltage switching equipment of the developing device in a color image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described in order to explain the present invention by referring to the figures. 
     The following detailed description will present a high voltage switching equipment of a developing device according to a preferred embodiment of the invention in reference to the accompanying drawings. 
     As shown in  FIGS. 3 through 5 , the high voltage switching equipment of the developing device for a color image forming apparatus according to an embodiment of the present invention, comprises developing devices  10 , i.e., a yellow developing device, a magenta developing device, a cyan developing device, and a black developing device respectively fixed by a frame of the color image forming apparatus such that each developing device comes in contact with a photoconductive medium  80  with a constant developing nip. Here, each developing device  10  has a developing roller and a toner supplying roller as is the case of a conventional developing device (refer to FIG.  2 ). 
     A high voltage applying terminal  12  is formed in rear end portions of each developing device  10 . In  FIGS. 3 and 4 , an example that three high voltage applying terminals  12   a ,  12   b ,  12   c  are formed for each developing device  10 , is represented. 
     A high voltage applying substrate  16  is disposed in a rear side of each developing device  10 . This high voltage applying substrate  16  includes a high voltage circuit and has a plurality of connector terminal strips  22  ( 22   a ,  22   b ,  22   c ) connected to a plurality of the high voltage applying terminals  12  ( 12   a ,  12   b ,  12   c ) on its one side, and has first terminal strips  18  ( 18   a ,  18   b ,  18   c ) and second terminal strips  20  ( 20   a ,  20   b ,  20   c ) which are formed in pairs and spaced-apart from each other by a constant distance, on its rear side. The first terminal strips  18  are connected to the high voltage applying circuit installed within the high voltage applying substrate  16 , and the second terminal strips  20  are connected to the connector terminal strips  22 , respectively. 
     Also, the high voltage applying terminals  12  and the connector terminal strips  22  are connected to each other by using spring connectors  14  ( 14   a,    14   b,    14   c ) disposed to be connected between the high voltage applying terminals  12  and the connector terminal strips  22 . 
     A high voltage connecting unit  23  (as four high voltage connecting units are the same in their structure, description will be made only for one of the high voltage connecting units), is disposed on the rear side of the high voltage applying substrate  16  and comprises contact members  24  ( 24   a,    24   b,    24   c ), a holder  26  supporting the contact members  24  ( 24   a,    24   b,    24   c ), and a solenoid  28  moving back and forth the holder  26  with respect to the high voltage applying substrate  16 . 
     The contact member  24  has first and a second contact end portions  24 - 1 ,  24 - 2  coming in contact with the first and the second terminal strips  18 ,  20 , respectively. Accordingly, if the holder  26  is moved by the solenoid  28 , that is, the holder  26  is moved forth, the first and the second contact end portions  24 - 1 ,  24 - 2  of the contact member  24  come into contact with the first and the second terminal strips  18 ,  20  of the high voltage applying substrate  16 , so the first and the second terminal strips  18 ,  20  are connected electrically, whereby a high voltage could be supplied to a relevant developing device  10 . For the contact member  24 , a contact spring is preferably used, but there is no definite restriction to a material used for the contact member  24 . 
     The solenoid  28  is one embodiment of a holder moving member moving the holder  26 . For the holder moving member, not only the solenoid but also variety of embodiments are possible. In  FIGS. 3 and 4 , a reference numeral  30  represents a bracket supporting the solenoid. 
     An operation of the high voltage switching equipment of the developing device for a color image forming apparatus having the foregoing constitution according to the present invention, will be described hereinafter with reference to  FIGS. 3 and 4 . 
       FIG. 3  represents a status in which a power supply is not supplied to the solenoid  28 , namely, a status in which a high voltage is not supplied to a relevant developing device  10 . As is illustrated, the contact member  24  is moved back from the high voltage applying substrate  16 , and the first and the second terminal strips  18 ,  20  on the high voltage applying substrate  16  are separated accordingly. Therefore, the high voltage is not supplied to the relevant developing device  10 . In that case, the developing device  10  of  FIG. 3  is in a status of non-development and only one of the three developing devices except that developing device  10  of  FIG. 3  is in a status of development. Namely, to other developing devices  10  of  FIG. 3  except the developing device  10  of  FIG. 4  under a development status, the high voltage is not supplied as shown in a non-contact status of FIG.  3 . 
     After that, when a turn comes for the developing device of  FIG. 3  that was in the nondevelopment status, the power supply is applied to the solenoid  28 , the holder  26  is moved forth to a side of the high voltage applying substrate  16 . Accordingly, as shown in  FIG. 4 , the first and the second contact end portions  24 - 1 ,  24 - 2  of the contact member  24  supported by the holder  26  come into contact with the first and the second terminal strips  18 ,  20  of the high voltage applying substrate  16 , whereby the first and the second terminal strips  18 ,  20  are connected electrically. Namely, as the high voltage circuit installed within the high voltage applying substrate  16  is electrically connected to the high applying terminal  12   a  ( 12   b ,  12   c ), the high voltage is supplied to the relevant developing device  10 . 
     In the meantime, when development is completed for a relevant color by the developing device  10 , the power supply for the solenoid  28  becomes off and, instead, the power supply is supplied to the solenoid  28  of other developing device  10 , the development for other color is performed. 
     With the foregoing process performed repeatedly, an electrostatic latent image formed on the photoconductive medium, is developed into a visible color image. At the moment, in the foregoing development process, the high voltage is sequentially supplied to the color developing devices  10 . Therefore, a problem of deterioration in image quality due to a load variation of the photoconductive medium  80  occurring in a conventional movement type developing device could be resolved. 
     As is apparent from the foregoing, according to the present invention, the high voltage switching equipment of a developing device which is a fixed type, is possibly constructed, and a change in rotational velocity and a change in a load of the photoconductive medium are not generated, so a stable image quality could be achieved accordingly. 
     Further, according to the present invention, elements, such as a motor or cam as was necessary in the conventional case, moving the developing device, could be eliminated, which makes it possible to construct the high voltage switching equipment of simple structure and to prevent a poor development, and a development interval between the developing device and the photoconductive medium is maintained almost constant. 
     Still further, for realization of the fixed type developing device, the solenoid is used for direct contact in order to supply the high voltage to the developing device, whereby a high voltage section through which the high voltage is transferred from the high voltage applying substrate to each developing device, could be minimized, and reliability for a high voltage contact point could be improved using a direct contact point. 
     Another still further, in an equipment supplying the high voltage to the developing device of four colors for realizing color printing, a high voltage control for each developing device could be constructed in a simply manner. 
     While the invention has been shown and described with reference to certain preferred 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 invention as defined by the appended claims and their equivalents. 
     Namely, a high voltage switching equipment according to the present invention, could be used not only for a color laser printer but also for a variety of printers, duplicating machines, and multifunction machines, etc., which require sequential control of voltage supplied to the developing device.