PATENT DOCUMENT

Abstract:
A process cartridge detachably mountable to a main assembly of an image forming apparatus, wherein the main assembly includes a main assembly electrical contact, a movable member movable between a protecting position for covering the main assembly electrical contact and an exposing position for exposing the main assembly electrical contact, and a locking member movable between a locking position for limiting an operation of the movable member and a releasing position for permitting the operation of the movable member, the cartridge includes an electrophotographic photosensitive drum; process means actable on the drum; a first engaging portion for moving the locking member from the locking position to the releasing position in midstream of mounting the cartridge to the main assembly of the apparatus; a second engaging portion for moving the movable member from the protecting position to the exposing position in midstream of mounting the cartridge to the main assembly of the apparatus; and a cartridge contact for electrically connecting with the main assembly electrical contact when the cartridge is mounted to the main assembly of the apparatus.

Full Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to a process cartridge and an electrophotographic image forming apparatus 
   Here, an electrophotographic image forming apparatus means an apparatus for forming an image on recording medium with the use of one of the electrophotographic image forming methods. As for examples of an electrophotographic image forming apparatus, an electrophotographic copying machine, an electrophotographic printer (for example, LED printer, laser beam printer, etc.), an electrophotographic facsimileing machine, an electrophotographic wordprocessor, etc., are included. 
   Here, a process cartridge means a cartridge in which an electrophotographic photosensitive member, and at least one of the charging member and a developing member, as a processing means, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
   It also means a cartridge in which a charging means, a developing means or cleaning means, and an electrophotographic photosensitive member, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus, a cartridge in which at least one among a charging means, a developing means, and a cleaning means, and an electrophotographic photosensitive member, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. Further, it means a cartridge in which at least a developing means, and an electrophotographic photosensitive member, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
   (1) An electrophotographic image forming apparatus employing a process cartridge system enables a user to mount a process cartridge into the apparatus main assembly, or dismount it therefrom, without relying on a service person, drastically improving an electrophotographic image forming apparatus in operability. 
   In order to form an image with the use of an electrophotographic image forming apparatus, it is necessary to apply voltage to the charging member to charge the electrophotographic photosensitive member (which hereinafter will be referred to as photosensitive drum) of a process cartridge, the developing member for developing an electrostatic latent image formed on the photosensitive drum, and the like. 
   For the above described purpose, that is, in order to establish electrical connection between a process cartridge and the main assembly of an electrophotographic image forming apparatus, the frame of a cartridge and the frame of the main assembly are provided with electrical contacts. Thus, as a cartridge is mounted into the main assembly, the electrical contacts of the cartridge come into contact with the electrical contacts of the main assembly, respectively, making it possible for the cartridge to be supplied with the voltage from the main assembly. 
   More concretely, the following structural arrangement has been known. 
   The main assembly of an electrophotographic image forming apparatus is provided with a movably protective plate for covering the electrodes (electrical contacts of main assembly), preventing thereby an operator and/or tools from coming into contact with the electrodes while maintaining a printer (image forming apparatus). The protective plate is retracted into its retreat, by the insertion of a cartridge into the apparatus main assembly, allowing thereby electrical connection to be established between the electrodes on the main assembly side and the electrodes (electrical contacts) of the cartridge (Japanese Laid-open Patent Application 7-77921: FIGS. 1-3). 
   Further, as the unit is removed from the apparatus main assembly, the connector pins (electrical contacts of apparatus main assembly) are retracted behind the partition wall, preventing thereby a service person or a user from contacting the connector pins, whereas, as the unit is removed from the apparatus main assembly, the connector pins are made to project into the cartridge compartment, into which the unit is mounted, allowing thereby electrical connection to be established between the connector pins and the connector portions (electrical contact on cartridge side) of the unit (Japanese Laid-open Patent Application 62-215278 (line 15 of bottom left section of page 4—line 15 of top left section of page 6). 
   The electrodes (electrical contact of main assembly) are enabled to move between their retreat positions and normal positions, enabling thereby the electrical contacts of the cartridge and the electrodes of the apparatus main assembly to properly contact each other. More specifically, the removal of the cartridge from the apparatus main assembly causes the electrodes (electrical contacts of apparatus main assembly) to retract into their retreats (prior to the insertion of the cartridge into the apparatus main assembly, the electrodes are in their retreats), whereas the insertion of the cartridge into the apparatus main assembly causes the electrodes to move back into the normal positions, allowing electrical connection to be established between the electrodes and electrical contacts (Japanese Laid-open Patent Application 9-68833). 
   (2) In recent years, various products employing a cartridge having a memory (storage element) in which various service and/or process data are stored have been realized. With the utilization of the data stored in the memory of the cartridge, an electrophotographic image forming apparatus has been further improved in maintenance. The utilization of the data is made possible by the electrical communication between the memory of a cartridge and the main assembly of an electrophotographic image forming apparatus, which is made possible by the electrical connection between the connectors of the cartridge and apparatus main assembly. 
   Even an electrophotographic image forming apparatus employing a process cartridge removably mountable in the main assembly of the electrophotographic image forming apparatus sometimes suffers from the problem that recording medium such as recording paper becomes stuck in the main assembly. If this problem occurs, a user takes the process cartridge out of the apparatus main assembly, and removes the stuck recording paper. Then, the user reinserts the process cartridge. If the removed process cartridge has static electricity, it is possible that as the process cartridge is reinserted into the apparatus main assembly, electrical discharge occurs between the process cartridge and the exposed electrical contacts in the apparatus main assembly. Thus, in order to prevent the problem that this kind of electrical charge will generate electrostatic noises in the electrical circuit in the image forming apparatus, some image forming apparatuses are provided with a static electricity discharging member (Japanese Laid-open Patent Application 10-63166). 
   SUMMARY OF THE INVENTION 
   The present invention is one of the further developments of the above described prior art. 
   The primary object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus, superior to those in accordance with the prior art, in terms of the reliability in the electrical connection which occurs between the electrical contacts of the process cartridge(s) and the electrical contacts of the main assembly of the electrophotographic image forming apparatus as the process cartridge(s) is mounted into the main assembly of the electrophotographic image forming apparatus. 
   Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus, which are structured so that as the process cartridge is inserted into the main assembly of the electrophotographic image forming apparatus, the member with which the main assembly of the electrophotographic image forming apparatus is provided to protect the electrical contacts of the main assembly is moved from the position in which it protects the electrical contacts of the main assembly, to the position in which it exposes them. 
   Another object of the present invention is to provide an electrophotographic image forming apparatus which employs a process cartridge(s) removably mountable in the main assembly of the electrophotographic image forming apparatus, and in which when the process cartridge(s) is mounted into the electrophotographic image forming apparatus main assembly, static electricity discharge does not occur between the electrical contacts of the process cartridge and the electrical contacts of the apparatus main assembly. 
   Another object of the present invention is to provide an electrophotographic image forming apparatus, the electrical circuit of the main assembly of which is not subject to damage. 
   Another object of the present invention is to provide an electrophotographic image forming apparatus superior to that in accordance with the prior art, in terms of the reliability in the electrical connection which occurs between the electrical contacts of a process cartridge(s) and the electrical contacts of the main assembly of the electrophotographic image forming apparatus as the process cartridge(s) is mounted into the main assembly of the electrophotographic image forming apparatus. 
   According to an aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein said main assembly includes a main assembly electrical contact, a movable member movable between a protecting position for covering the main assembly electrical contact and an exposing position for exposing the main assembly electrical contact, and a locking member movable between a locking position for limiting an operation of the movable member and a releasing position for permitting the operation of the movable member, said process cartridge comprising: an electrophotographic photosensitive drum; process means actable on said electrophotographic photosensitive drum; a first engaging portion for moving the locking member from the locking position to the releasing position in midstream of mounting said process cartridge to the main assembly of the apparatus; a second engaging portion for moving the movable member from the protecting position to the exposing position in midstream of mounting said process cartridge to the main assembly of the apparatus; and a cartridge contact for electrically connecting with the main assembly electrical contact when said process cartridge is mounted to the main assembly of the apparatus. 
   According to another aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, to which a process cartridge is detachably mountable, said apparatus comprising: (a) a main assembly electrical contact; (b) a movable member movable between a protecting position for covering the main assembly electrical contact and an exposing position for exposing the main assembly electrical contact; (c) a locking member movable between a locking position for limiting an operation of the movable member and a releasing position for permitting the operation of the movable member; (d) a mounting member for detachably mounting said process cartridge, said process cartridge including, an electrophotographic photosensitive drum, process means actable on said electrophotographic photosensitive drum, a first engaging portion for moving the locking member from the locking position to the releasing position in midstream of mounting said process cartridge to the main assembly of the apparatus, a second engaging portion for moving the movable member from the protecting position to the exposing position in midstream of mounting said process cartridge to the main assembly of the apparatus, and a cartridge contact for electrically connecting with the main assembly electrical contact when said process cartridge is mounted to the main assembly of the apparatus; (e) feeding means for feeding said recording material. 
   According to a further aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein said main assembly includes a main assembly electrical contact, an electroconductive member movable between a first position for electrically connecting with a ground and a second position for electrically disconnecting with the ground, and a locking member movable between a locking position for limiting an operation of said electroconductive member and a releasing position for permitting the operation of said electroconductive member, said process cartridge comprising: an electrophotographic photosensitive drum; process means actable on said electrophotographic photosensitive drum; a first engaging portion for moving the locking member from the locking position to the releasing position in midstream of mounting said process cartridge to the main assembly of the apparatus; a second engaging portion for moving the movable member from the protecting position to the exposing position in midstream of mounting said process cartridge to the main assembly of the apparatus; and a cartridge contact for electrically connecting with the main assembly electrical contact when said process cartridge is mounted to the main assembly of the apparatus. 
   According to a further aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, to which a process cartridge is detachably mountable, said apparatus comprising: (a) (a) a main assembly electrical contact; (b) an electroconductive member movable between a first position for electrically connecting with a ground and a second position for electrically disconnecting with the ground, (c) a locking member movable between a locking position for limiting an operation of the movable member and a releasing position for permitting the operation of the movable member; (d) a mounting member for detachably mounting said process cartridge, said process cartridge including, an electrophotographic photosensitive drum; process means actable on said electrophotographic photosensitive drum; a first engaging portion for moving the locking member from the locking position to the releasing position in midstream of mounting said process cartridge to the main assembly of the apparatus, a second engaging portion for moving the movable member from the protecting position to the exposing position in midstream of mounting said process cartridge to the main assembly of the apparatus; and a cartridge contact for electrically connecting with the main assembly electrical contact when said process cartridge is mounted to the main assembly of the apparatus; (e) feeding means for feeding said recording material. 
   These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a sectional view of the process cartridge in the first embodiment of the present invention. 
       FIG. 2  is a schematic drawing of the image forming apparatus in the first embodiment, showing the general structure thereof. 
       FIG. 3  is a perspective view of the image forming apparatus. 
       FIG. 4  is a drawing of the process cartridge compartment of the main assembly of the image forming apparatus, and its adjacencies (No. 1). 
       FIG. 5  is a drawing of the process cartridge compartment of the main assembly of the image forming apparatus, and its adjacencies (No. 2). 
       FIG. 6  is a perspective view of the process cartridge (No. 1). 
       FIG. 7  is a perspective view of the process cartridge (No. 2). 
       FIG. 8  is a drawing showing the positioning of the various components of the electrical contact protection mechanism of the process cartridge. 
       FIG. 9  is an exploded view of the electrical contact protection mechanism of the process cartridge, and the components related thereto, showing the structures thereof. 
       FIG. 10  is a perspective view of one of the lengthwise end portions of the process cartridge. 
       FIG. 11  is a perspective view of the electrical contact protection mechanism of the image forming apparatus main assembly, showing the structures thereof (No. 1). 
       FIG. 12  is a perspective view of the electrical contact protection mechanism of the image forming apparatus main assembly, showing the structures thereof (No. 2). 
       FIG. 13  is a perspective view of the electrical contact protection mechanism of the image forming apparatus main assembly, showing the structures thereof (No. 3). 
       FIG. 14  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 1). 
       FIG. 15  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 2). 
       FIG. 16  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 3). 
       FIG. 17  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 4). 
       FIG. 18  is a perspective view of the electrical contact protection mechanism, and the components in its adjacencies, of the main assembly of the image forming apparatus, showing the structures thereof. 
       FIG. 19  is a perspective view of the electrical contact protection mechanism, and its adjacencies, of the main assembly of the image forming apparatus, in the second embodiment of the present invention, showing the structures thereof. 
       FIG. 20  is an exploded view of the electrical contact protection mechanism of the image forming apparatus main assembly, and the components related thereto, showing the structures thereof. 
       FIG. 21  is a perspective view of one of the lengthwise ends of the process cartridge. 
       FIG. 22  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 1). 
       FIG. 23  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 2). 
       FIG. 24  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 3). 
       FIG. 25  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 4). 
       FIG. 26  is a schematic drawing depicting the movements of the electrical contact protection mechanism (No. 5). 
       FIG. 27  is a schematic drawing the electrical contact protection mechanism, and its adjacencies, in the third embodiment of the present invention, showing the structures and movements thereof. 
       FIG. 28  is a perspective drawing depicting the structure of the electrical contact protection mechanism. 
       FIG. 29  is a schematic drawing depicting the movements of the electrical contact protection mechanism, which occur as the process cartridge is mounted into the apparatus main assembly (No.1). 
       FIG. 30  is a schematic drawing depicting the movements of the electrical contact protection mechanism, which occur as the process cartridge is mounted into the apparatus main assembly (No.2). 
       FIG. 31  is a schematic drawing depicting the movements of the electrical contact protection mechanism, which occur as the process cartridge is mounted into the apparatus main assembly (No.3). 
       FIG. 32  is a schematic drawing depicting the movements of the electrical contact protection mechanism, which occur as the process cartridge is mounted into the apparatus main assembly (No.4). 
       FIG. 33  is a schematic sectional view of the electrophotographic image forming apparatus (laser beam printer), showing the general structure thereof. 
       FIG. 34  is a schematic sectional view of the process cartridge removably mountable in the main assembly of the electrophotographic image forming apparatus, showing the general structures of the electrical contact protection mechanism of the process cartridge. 
       FIG. 35  is a perspective view of the electrophotographic image forming apparatus, the cartridge access door of which is open for mounting or dismounting the process cartridge. 
       FIG. 36  is a perspective view of one of the lengthwise ends of the top end portion of the apparatus main assembly, showing the process cartridge mounting means of the apparatus main assembly (No. 1). 
       FIG. 37  is a perspective view of the other lengthwise end of the top end portion of the apparatus main assembly, showing the process cartridge mounting means of the apparatus main assembly (No. 2). 
       FIG. 38  is a schematic perspective view of the process cartridge (No. 1). 
       FIG. 39  is a schematic perspective view of the process cartridge (No. 2). 
       FIG. 40  is a schematic perspective view of the electrical contact protection mechanism of the apparatus main assembly (before mounting of cartridge). 
       FIG. 41  is a schematic perspective view of the electrical contact protection mechanism of the apparatus main assembly (after mounting of cartridge). 
       FIG. 42  is a drawing of the electrical contact protection mechanism of the apparatus main assembly, as seen from the opposite direction from the direction in which it is seen in  FIG. 40 . 
       FIG. 43  is a schematic drawing of the electrical contact protection mechanism, showing the movements thereof during one of the steps of the cartridge insertion sequence in the fifth embodiment of the present invention (No. 1). 
       FIG. 44  is a schematic drawing of the electrical contact protection mechanism, showing the movements thereof during another step of the cartridge insertion sequence in the fifth embodiment of the present invention (No. 2). 
       FIG. 45  is a schematic drawing of the electrical contact protection mechanism, showing the movements thereof during another step of the cartridge insertion sequence in the sixth embodiment of the present invention (No. 1). 
       FIG. 46  is a schematic drawing of the electrical contact protection mechanism, showing the movements thereof during another step of the cartridge insertion sequence in the sixth embodiment of the present invention (No. 2). 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, the process cartridge, image forming apparatus, and electrical contact protection mechanism, in accordance with the present invention, will be described in detail with reference to the appended drawings. 
   Embodiment 1 
   (1) General Description of Process Cartridge 
   First, referring to  FIG. 1 , the process cartridge B (which hereinafter will be referred to simply as cartridge) in the first embodiment of the present invention will be described.  FIG. 1  is a sectional view of the cartridge B. 
   Referring to  FIG. 1 , the cartridge B has an electrophotographic photosensitive drum  107  (which hereinafter will be referred to simply as photosensitive drum). With the cartridge B mounted in the electrophotographic image forming apparatus A (which hereinafter will be referred to simply as apparatus main assembly) as shown in  FIG. 2 , the photosensitive drum  107  rotates as it receives driving force from the apparatus main assembly A. 
   The apparatus main assembly A is provided with a charge roller  108  as a charging member, which is disposed in the immediate adjacencies of the peripheral surface of the photosensitive drum  107 . To the charge roller  108 , voltage is applied from the apparatus main assembly A to charge the photosensitive drum  107 . The charge roller  108  is kept in contact with the peripheral surface of the photosensitive drum  107 , and is rotated by the rotation of the photosensitive drum  107 . 
   With the cartridge B mounted in the apparatus main assembly A, the charge roller  108  receives voltage from the apparatus main assembly A, and as it receives the voltage, it charges the photosensitive drum  107 . 
   The cartridge B is provided with a development roller  110  as a developing member for supplying the portion of the peripheral surface of the photosensitive drum  107 , in the development range, with developer t. The development roller  110  develops an electrostatic latent image formed on the photosensitive drum  107  with the use of the developer t. It internally holds a magnetic roller (stationary magnet). 
   With the cartridge B mounted in the apparatus main assembly A, the development roller  110  receives voltage from the apparatus main assembly A through a development bias transmission electrical contact  161  ( FIG. 11(   b )) as one of the electrical contacts on the main assembly side, and a development bias reception electrical contact  160  ( FIG. 8)  as one of the electrical contacts on the cartridge side. As the development roller  110  receives this voltage, it develops the aforementioned electrostatic latent image. 
   The apparatus main assembly A is provided with a development blade  112 , which is disposed in the adjacencies of the peripheral surface of the development roller  110 , being disposed in contact with the peripheral surface of the development roller  110 . The development blade  112  regulates the amount by which the developer t having adhered to the peripheral surface of the development roller  110  is allowed to be conveyed to the aforementioned development area. It also frictionally charges the developer t. 
   The developer t stored in a developer storage portion  114   a  is sent out by the rotation of a stirring member  115  to a development chamber  113   a . Meanwhile, the development roller  110  receiving the aforementioned voltage through the electrical contacts  160  rotates by receiving driving force from the apparatus main assembly A. As a result, a layer of developer t having been frictionally charged by the development blade is formed on the peripheral surface of the development roller  110 . Then, the developer t on the peripheral surface of the development roller  110  is transferred onto the peripheral surface of the photosensitive drum  107  in the pattern of the latent image; in other words, the latent image is developed into an image formed of the developer t (which hereinafter will be referred to simply as developer image). 
   The developer image formed on the photosensitive drum  107  is transferred by a transfer roller  104  ( FIG. 2 ) onto a recording medium  102 . 
   The apparatus main assembly A is also provided with an elastic cleaning blade  117   a , which is disposed in the adjacencies of the peripheral surface of the photosensitive drum  107 , with its free edges disposed in contact with the peripheral surface of the photosensitive drum  107 . The cleaning blade  117   a  removes the developer t remaining on the peripheral surface of the photosensitive drum  107  after the transfer of the developer image onto the recording medium  102 . After being removed from the peripheral surface of the photosensitive drum  107  by the cleaning blade  117   a , the removed developer t is stored in a bin  117   b  for the removed developer t. 
   The cartridge B comprises a development unit  119  and a drum unit  20  integrally connected to each other. 
   The development unit  119  comprises a top frame  114  which constitutes a part of the cartridge frame, and a bottom frame  113  which also constitutes a part of the cartridge frame. The development unit  119  has the development roller  110 , development blade  112 , development chamber  113   a , developer storage chamber  114   a , and stirring member  115 . It is also provided with the aforementioned development bias reception electrical contact, which will be described later. 
   The drum unit  120  comprises a drum frame  118 , which also constitutes a part of the cartridge frame. It has the photosensitive drum  107 , cleaning blade  117   a , bin  117   b  for removed developer, and charge roller  108 . 
   As will be evident from  FIG. 6 , the drum unit  120  is provided with a cartridge guide  140 R 1  and a cartridge guide  140 R 2 , which are located at the lengthwise end  120   a  of the drum unit  120 . Referring to  FIG. 7 , the other lengthwise end  120   a  of the drum unit  120  is provided with a cartridge guide  140 L 1  and a cartridge guide  140 L 2 . 
   The development unit  119  and drum unit  120  are connected to each other so that they can be pivoted relative to each other, and also, so that the development roller  110  is kept pressed upon the photosensitive drum  107 . 
   (2) Description of Electrophotographic Image Forming Apparatus 
   Next, referring to  FIG. 2 , the electrophotographic image forming apparatus  100  comprising the above described apparatus main assembly A and cartridge B will be described.  FIG. 2  is a schematic drawing of the electrophotographic image forming apparatus  100  (which hereinafter will be referred to simply as image forming apparatus), depicting the general structure thereof. In the following description of the image forming apparatus  100 , the image forming apparatus  100  will be described as a laser beam printer. 
   As the image forming operation of the image forming apparatus  100  begins, the peripheral surface of the rotating photosensitive drum  107  is uniformly charged by the charge roller  108 . Next, a beam of laser light L is projected onto the peripheral surface of the photosensitive drum  107 , while being modulated by image formation data, from an optical means  101  comprising a laser diode, a polygon mirror, a lens, and a deflection mirror (none of which are shown). As a result, an electrostatic latent image reflecting the image formation data is formed on the peripheral surface of the photosensitive drum  107 . This latent image is developed by the abovementioned development roller  110 . 
   Meanwhile, in synchronism with the progression of the developer image formation, the recording medium  102  stored in a cassette  103   a  is sent out of the cassette  103   a , into the apparatus main assembly A by a feeding roller  103   b , and is conveyed to the transfer location by a pair of conveyance rollers  103   c  and a pair of conveyance rollers  103   d.    
   At the transfer location, a transfer roller  104  as a transferring means is disposed. As voltage is applied to the transfer roller  104 , the developer image on the photosensitive drum  107  is transferred onto the recording medium  102 . 
   After the transfer of the developer image onto the recording medium  102 , the recording medium  102  is guided by the guide  103   f  to a fixing means  105 , which comprises a driver roller  105   c  and a fixation roller  105   b . The fixation roller  105   b  internally holds an unshown heater. As the recording medium  102  is conveyed through the fixing means  105 , heat and pressure are applied to the recording medium  102 . As a result, the developer image is permanently fixed to the recording medium  102 . Thereafter, the recording medium  102  is further conveyed, and is discharged into a delivery tray  106 , by a pair of conveyance rollers  103   g  and a pair of conveyance rollers  103   h . The abovementioned roller  103   b , pairs of conveyer rollers  103   c  and  103   d , guide  103   f , and pairs of rollers  103   g  and  103   h , etc., constitute a conveying means  103  for conveying the recording medium  102 . 
   The cartridge B is mounted into, or dismounted from, the apparatus main assembly A, as will be described next. 
   Referring to  FIG. 3 , first, a door  109  of the apparatus main assembly A is to be opened by an operator in order to allow the cartridge B to be removably mounted into the cartridge mounting means  130  of the apparatus main assembly A. 
   Referring to  FIGS. 4 and 5 , the cartridge mounting means  130  in this embodiment comprises guides  130 R 1 ,  130 R 2 ,  130 L 1 , and  130 L 2 , which are parts of apparatus main assembly A. As for the method for mounting the cartridge B into the apparatus main assembly A, the cartridge B is to be inserted into the apparatus main assembly A, into the cartridge compartment  130   a , that is, the internal space of the apparatus main assembly A for the cartridge B, so that the cartridge guides  140 R 1  and  140 R 2  ( FIG. 6 ) as the cartridge guide portions of the cartridge B are engaged with the guides  130 R 1  and  130 R 2 , respectively, of the apparatus main assembly A, and the cartridge guides  140 L 1  and  140 L 2  of the cartridge B are engaged with the cartridge guides  130 L 1  and  130 L 2 , respectively, of the apparatus main assembly A. 
   As the cartridge B is inserted, the cartridge guide  140 R 1  fits into the positioning portion  13 OR 1   a  of the guide  130 R 1  of the apparatus main assembly A, and the cartridge guide  140 R 2  fits into the positioning portion  130 R 2   a  of the guide  130 R 2  of the apparatus main assembly A. Further, the cartridge guides  140 L 1  and  140 L 2  fit into the positioning portions  130 L 1   a  and  130 L 2   a  of the cartridge guides  130 L 1  and  130 L 2  of the apparatus main assembly, respectively. As a result, the cartridge B is removably mounted into the cartridge compartment  130   a  by the cartridge mounting means  130 , being thereby readied for image forming operation. 
   While the cartridge B is mounted into the apparatus main assembly A, a coupling  134  ( FIG. 3 ) as a driving force transmitting portion remains retracted, and therefore, does not interfere with the mounting of the cartridge B. Then, as the cover  109  is closed, the coupling  107   a  ( FIG. 6 ), as a driving force receiving portion, of the cartridge B engages with the abovementioned coupling  134  on the main assembly A side, making it possible for the cartridge B to receive from the apparatus main assembly A the force for driving the photosensitive drum  107 . 
   (3) Electrical Contact Protection Mechanism of Process Cartridge 
   Next, the electrical contact protection mechanism on the process cartridge side, in accordance with the present invention, will be described. 
     FIG. 8  is a perspective view of one of the lengthwise ends of the cartridge B, showing the positioning of the development bias reception electrical contact thereof. The development bias reception electrical contact  160 , that is, one of the electrical contacts on the cartridge side, is attached to a part of the end cover  121  of the development unit  119 . It has a contact portion  160   a , by which it contacts the counterpart of the apparatus main assembly A. 
     FIG. 9  is an exploded drawing of the electrical contact protection mechanism of the cartridge B, and the components related thereto, showing the structures thereof through which development bias is applied to the development roller  110 . Referring to  FIG. 9(   a ), the development unit  119  is provided with a developer roller spring  122  and a flange  123 . The developer roller spring  122  is fixed to the flange  123 , and the flange  123  is attached to one of the lengthwise ends of the development roller  110  by pressing or the like means, with one end  122   a  of the development roller spring  122  held between the internal surface of the development roller  110  and flange  123 , establishing thereby electrical connection between the development roller  110  and development roller spring  122 . The flange  123  is rotatably supported by a bearing  124 . As will be evident from  FIG. 9(   b ), the development bias reception electrical contact  160  is fixed to the end cover  121 . Further, the shaft  121   a  of the end cover  121  is fitted in the hole  124   a  of the bearing member  124 ; in other words, the end cover  121  is supported by the bearing member  124  to support the development roller  110 . After the bearing member  124  and development bias reception electrical contact  160  are sandwiched between the top frame  114  ( FIG. 7)  and end cover  121 , the end cover  121  is fixed to the top frame  114  with fixing means such as small screws. 
   With the end cover  121  fixed to the top frame  114 , the end portion  122   b  of the development roller spring  122  (coil spring), that is, the end opposite to the end portion  122   a  of the development roller spring  122 , is in contact with the contact portion  160   b  ( FIG. 9(   b )) of the development bias reception electrical contact  160   a  fixed to the cover  121 , establishing electrical connection between the two. Because of the resiliency of the coil spring, a predetermined amount of contact pressure is maintained between the development roller spring  122  and development bias reception electrical contact  160 . With the provision of the above described structural arrangement, electrical connection is maintained between the development bias reception electrical contact  160  and development roller  110 . 
   Next, the engaging portion and retaining portion of the cartridge B will be described. The engaging portion and retaining portion of the cartridge B function as actuators for the retaining member of the apparatus main assembly and the movable member of the apparatus main assembly A, respectively. 
     FIG. 10  is a perspective view of the cartridge B. The drum frame  118  holds the photosensitive drum  107 , charge roller  108 , cleaning blade  117   a , etc., which were integrally disposed therein. One end of the photosensitive drum  107  is rotatably supported by a drum shaft  130 . The drum shaft  130  is rotatably fitted in the center hole of the cartridge guide  140 L 1 , by which the cartridge B is supported by the counterpart on the apparatus main assembly A when the cartridge B is mounted into the apparatus main assembly A. The contact portion  140 L 1   a , as a first engaging portion, which is a part of the cartridge guide  140 L 1 , has the function of engaging with the movable member of the apparatus main assembly A. The cartridge guide L 1  is provided with a plurality of radial ribs  140 L 1   b , which extend from the edge of the center hole of the cartridge guide  140 L 1  toward the peripheral edge of the cartridge guide  140 L 1 . The cartridge guide L 1  is also provided with an extension  141 , which extends from the peripheral edge portion of the cartridge guide  104 L 1  toward the end cover  121 . The outward primary surface of the extension  141  functions as contact area  141   a  as a first retaining portion for holding the retaining member in the release position. In other words, the first retaining portion for holding the retaining member movable between the releasing position in which the retaining member does not retains the movable member, and the retaining position in which it retains the movable member, is located at one of the lengthwise ends of the process cartridge. The top surface of the extension  141  functions as a portion  141   b  for regulating the attitudes of the cartridge B when cartridge B is mounted into the apparatus main assembly A. Further, the drum frame  118  is provided with a projection  142 , which projects downward. The projection  142  functions as a second engaging portion of the process cartridge, which engages with the movable member of the apparatus main assembly A, which will be described later, and also, as a second retaining portion for retaining the moving member in the exposing portion. 
   (4) Electrical Contact Protection Mechanism on Apparatus Main Assembly Side 
   Next, the structure of the electrophotographic image forming apparatus in accordance with the present invention will be described in detail. 
     FIGS. 11-13  are perspective views of the main assembly of the electrophotographic image forming apparatus, depicting the structure thereof.  FIG. 11(   a ) shows the apparatus main assembly in which the cartridge B is yet to be mounted, whereas  FIG. 11(   b ) shows the apparatus main assembly in which the cartridge B is present, although the cartridge B itself is not drawn. Referring to  FIG. 11(   a ), the apparatus main assembly A is provided with the guides  130 L 1  and  130 L 2  for facilitating the mounting of the cartridge B into the apparatus main assembly A. It is also provided with: a retention spring  143  for retaining the cartridge B after the mounting of the cartridge B into the image formation position; a ground contact  144  which is placed in contact with the drum shaft  139  ( FIG. 10)  to ground the photo-sensitive drum  107 ; an electrical contact protecting movable member  162  movable between the protective position in which it covers the development bias transmission electrical contact  161  ( FIG. 11(   b )) as one of the electrical contacts on the main assembly side, and the exposing position in which it leaves the development bias transmission electrical contact  161  exposed; and a retaining member  163  for retaining the movable member  162 . 
   To the development bias transmission electrical contact  161  as one of the electrical contacts on the main assembly side, development voltage is applied from an electrical power source (unshown) with predetermined control timing. 
   Next, the structures of the movable member  162  and retaining member  163  will be described in more detail. Referring to  FIG. 12 , the movable member  162  is rotatably supported by the shaft  162   a , and the movable member  162  is kept pressured by a spring in the direction to be rotated into the protective position shown in  FIG. 11(   a ). The rotational axis of the movable member  162  is parallel to the axial line of the photosensitive drum  107  in the cartridge B, and is rotatably movable relative to the apparatus main assembly A. As for the movement of the movable member  162  into the exposing position ( FIG. 11(   b )) in which it keeps the development bias transmission electrical contact  161  exposed, the movable member  162  is moved into the exposing position by the insertion of the cartridge B into the apparatus main assembly A. To describe in more detail, which will be repeated later, during the insertion of the cartridge B into the apparatus main assembly A, the projection  142  ( FIG. 10)  as the second engaging portion of the cartridge B engages with the engaging portion  162   b , which is a part of the movable member  162  ( FIG. 12 ). As the cartridge B is inserted into the image forming position, the projection  142  as the second retaining portion retains the movable member  162  by the surface  162   c , retaining the movable member  162  in the exposing position ( FIG. 11(   b )). As a result, the development bias transmission electrical contact  161  is exposed and remains exposed through the slit  162   d  of the movable member  162 . The internal plate  145  is provided with a small hole  145   a , through which the retaining member  163  for retaining the movable member  162  partially projects ( FIG. 11(   a )). Not only does the projection  142  function as the first engaging portion, but also, as the first retaining portion. 
     FIG. 13  is a drawing of the same portions of the image forming apparatus shown in  FIG. 11 , except that in  FIG. 13 , they are seen from the opposite direction from the direction in which they are seen in  FIG. 11 . Referring to  FIG. 13(   a ), the retaining member  163  is rotatably supported by the shaft  163   a . Referring to  FIG. 12 , there is an elastic member  164  as a first elastic member between the surface  163   b  of the retaining member  163  and an unshown internal plate  145 , and the retaining member  163  is kept pressured by the elastic member  164  in the direction indicated by an arrow mark a. Thus, as will be understood from  FIG. 13(   b ), the engaging portion  163   c  of the retaining member  163  slips into the underside of the movable member  162 , preventing the movable member  162  from rotating into the exposing position. 
   (5) Description of Movements of Electrical Contact Protection Mechanism 
   Next, the movement of the electrical contact protection mechanism will be described in detail.  FIGS. 14-16  are drawings for describing the movements of the electrical contact protection mechanism, which occur as the cartridge B is inserted (advanced) into the apparatus main assembly A. 
     FIGS. 14(   a ),  15 ( a ), and  16 ( a ) are drawings of the electrical contact protection mechanism, as seen from the cartridge compartment  130   a  side toward the internal plate  145  (as seen from direction indicated by arrow mark Y in  FIG. 11(   a )).  FIGS. 14(   b ),  15 ( b ), and  16 ( b ) are drawings of the electrical contact protection mechanism, as seen from the direction indicated by an arrow mark Z in  FIGS. 14(   a ),  15 ( a ), and  16 ( a ). In  FIGS. 14(   a ),  15 ( a ), and  16 ( a ), the cartridge B is outlined with broken lines for ease of understanding. Further, for the purpose of showing the development bias transmission electrical contact  161 , a part of the movable member  162  is not drawn. 
   The development bias transmission electrical contact  161  as one of the electrical contacts on the main assembly side is supported by the shaft  166 , being enabled to rotate. That is, with the cartridge B mounted in the apparatus main assembly A, the rotational axis of the development bias transmission electrical contact  161  is parallel to the axial line of the photosensitive drum  107  of the cartridge B, and is rotatable relative to the apparatus main assembly A. 
   Further, in terms of the direction parallel to the axial line of the photosensitive drum  107 , the movable member  162 , and the development bias transmission electrical contact  161  as one of the electrical contacts on the main assembly side, overlap with each other. 
     FIGS. 14(   a ) and  14 ( b ) show the states of the electrical contact protection mechanism during the mounting of the cartridge B into the apparatus main assembly A. The movable member  162  is in the position in which it covers the development bias transmission electrical contact  161 , and the retaining member  163  is in the position in which it retains the movable member  162 . The movable member  162  is kept pressured in the direction indicated by an arrow mark b by the elastic member  165  as the second elastic member ( FIG. 14(   a )). As described above, the retaining member  163  is kept pressured in the arrow a direction by the elastic member  164  ( FIG. 14(   b )). Thus, the engaging portion  163   c  of the retaining member  163  is projecting into the cartridge compartment  130   a  through the hole of the internal plate  145  as shown in  FIG. 14(   b ), having slipped into the underside of the movable member  162 , preventing thereby the movable member  162  from rotating. Also, the projection  163   d  of the retaining member  163  is projecting into the cartridge compartment  130   a . In other words, when the retaining member  163  is in the retaining position, it prevents the movable member  162  from moving from the protective position to the exposing position. 
     FIGS. 15(   a ) and  15 (B) show the states of the electrical contact protection mechanism, in which the cartridge B has been advanced deeper into the apparatus main assembly than the state shown in  FIGS. 14(   a ) and  14 ( b ), respectively. They show the very moment when the projection  142  as the second engaging portion of the cartridge B has just engaged with the engaging portion  162   b  of the movable member  162  of the apparatus main assembly A ( FIG. 15(   a )). In this state, the projection  163   d  of the retaining member  163  has engaged with the engaging portion  140 L 1   a  as the first engaging portion, that is, a part of the cartridge guide  140 L 1  which engages with the engaging portion retaining member  163 , and rotates the retaining member  163  in the direction indicated by an arrow mark c about the shaft  163   a , and therefore, the retaining member  163  has been moved into the releasing position ( FIG. 15(   b )). When the retaining member  163  is in the releasing position, the engaging portion  163   c  of the retaining member  163  is away from the position in which it prevents the movable member  162  from rotating. Therefore, the movable member  162  is allowed to rotate. In other words, when the retaining member  163  is in the releasing position, it allows the movable member  162  to rotate. The elastic member  164  is disposed in the compressed state. 
     FIGS. 16(   a ) and  16 ( b ) show the state of the electrical contact protection mechanism, in which the cartridge B has been advanced even further into the apparatus main assembly A from the position shown in  FIGS. 15(   a ) and  15 ( b ), respectively. The retaining member  163  is kept in the same attitude as that shown in  FIGS. 15(   a ) and  15 ( b ), by the plurality of ribs  140 L 1   b  radially extending from the center ring portion of the cartridge guide  140 L 1  to the periphery of the cartridge guide  140 L 1 . As for the movable member  162 , it is pressed by the projection  142 , being therefore rotated in the direction indicated by an arrow mark d about the shaft  162   a , against the resiliency of the elastic member  165 . 
     FIGS. 17(   a ) and  17 ( b ) show the state of the electrical contact protection mechanism, in which the cartridge B has been inserted into the image forming position. In this state, the cartridge guide  140 L 1  is engaged with the positioning portion  130 L 1   a  of the guide  130 l 1  on the main assembly side, being precisely positioned relative to the apparatus main assembly A. As for the top portion of the cartridge guide  140 L 1 , it is in contact with a retainer spring  143 , being thereby pressured downward by the spring  143 . The retaining member  163  is held by the contact portion  141   a  as the first retaining portion of the extension portion  141  ( FIG. 10)  of the cartridge B. Further, the movable member  162  is retained by the projection  142  as the second retaining portion, in the exposing position in which it keeps the development bias transmission electrical contact  161  exposed. As the cartridge B is inserted into this position, the contact portion  161   a  of the development bias transmission electrical contact  161  comes into contact with the contact portion  160   a  of the development bias reception electrical contact  160 , establishing electrical connection between the electrical power source on the apparatus main assembly A side and the cartridge B. The image forming operation is carried out when the cartridge B is in this state. 
   In summary, this embodiment of the present invention can yield the following effects. 
   1) Even if an operator inserts his hand into the image forming apparatus main assembly A to take care of a paper jam or the like problem after removing the process cartridge B from the image forming apparatus main assembly A, the hand does not easily come into contact with the electrical contact  162  on the main assembly side, because the electrical contact  1621  is not projecting inward of the apparatus main assembly A. Therefore, it does not occur that a bad electrical connection occurs between the process cartridge B and apparatus main assembly A due to the adhesion of human sweat and/or the internal grease of the apparatus main assembly A to the electrical contact  161 . 
   2) The electrical contact protecting movable member is moved by the movement of the cartridge B, making it unnecessary for an operator to perform an operation dedicated to the establishment of electrical connection between the cartridge B and apparatus main assembly A. 
   3) The apparatus main assembly A is provided with the retaining member  163  for preventing the movable member  162  from moving into the exposing position in which the movable member  162  keeps the electrical contact of the apparatus main assembly A exposed, while no cartridge B is in the apparatus main assembly A. In other words, in order for an operator to touch the electrical contact  161  of the apparatus main assembly A, the movable member  162  must be moved into the electrical contact exposing position while retaining the retaining member  163  in the releasing position. Therefore, even if an operator inserts his hand into the apparatus main assembly A in order to maintain the image forming apparatus, for example, to deal with paper jam or the like problem, the hand of the operator is far less likely to accidentally touch the electrical contact  161 , compared to the case in which an operator inserts his hand into the main assembly of an image forming apparatus in accordance with the prior art. 
   4) The surface  141   a  as the first retaining portion is provided as a part of the extension portion  141  of the cartridge guide  140 L 1 , and the cartridge guide  140 L 1  is the portion for precisely positioning the cartridge B. Therefore, the surface  141   a  is stable in position, being therefore reliable in function. 
   5) The movable member  162  is moved by the projection  142  projecting downward from the cartridge B, into the position in which the movable member  162  keeps the electrical contact on the main assembly side exposed, while the retaining member  163  is retained by one of the lateral surfaces of the cartridge B. Therefore, while the cartridge B is inserted, the retaining member  163  is kept in the position in which it does not retain the movable member  162  until the end of the insertion of the cartridge B into the apparatus main assembly A. Therefore, it is assured that the movable member  162  is moved into the exposing position in which it keeps exposed the electrical contact on the main assembly side. 
   6) The apparatus main assembly A and cartridge B are structured so that when the cartridge B is in the apparatus main assembly A, the rotational axis of the movable member  162  is parallel to the axial line of the photosensitive drum  107 , and the movable member  162  is rotatable relative to the apparatus main assembly A; that when the cartridge B is in the apparatus main assembly A, the rotational axis of the development bias transmission electrical contact  161  as one of the electrical contacts on the main assembly side is parallel to the axial line of the photosensitive drum  107 , and the development bias transmission electrical contact  161  rotates relative to the apparatus main assembly A; and that the movable member  162 , and the development bias transmission electrical contact  161  as one of the electrical contacts of the main assembly A, are disposed in a manner of overlapping in the direction parallel to the aforementioned axial line, contributing to space saving. 
   Embodiment 2  
   Next, the second embodiment of the present invention will be described. The structure of the image forming apparatus  100  in this embodiment is similar to that of the image forming apparatus in the first embodiment described above. Here, therefore, only the structural features different from those of the image forming apparatus in the first embodiment will be described. Further, the components of the image forming apparatus in this embodiment, which are identical in structural feature and function to the counterparts in the first embodiment, will be given the same referential symbols so that the descriptions of the counterparts in the first embodiment can be referred to. 
   (1) Structures of Apparatus Main Assembly and Cartridge 
     FIGS. 18-20  are drawings depicting the retaining member and movable member of the apparatus main assembly A in this embodiment. 
     FIG. 18(   a ) shows the cartridge compartment of the apparatus main assembly A, in which the cartridge B is not present, and  FIG. 18(   b ) shows the cartridge compart of the apparatus main assembly A, in which the cartridge B is present, although the cartridge B is not illustrated. When the cartridge B is not in the apparatus main assembly A as shown in  FIG. 18(   a ), the development bias transmission electrical contact  161  is covered with the movable member  162 , whereas when the cartridge B is in the apparatus main assembly A as shown in  FIG. 18(   b ), the development bias transmission electrical contact  161  is exposed; it is not covered with the movable member  162 . 
   Like the apparatus main assembly A in the first embodiment described with reference to the  FIGS. 11(   a ) and  11 ( b ), the apparatus main assembly A in this embodiment is also provided with the development bias transmission electrical contact  161 , movable member  162  for covering the development bias transmission electrical contact  161 , and retaining member  163  for retaining the movable member  162 . 
   This embodiment is different from the first embodiment in that the apparatus main assembly A in this embodiment is also provided with a releasing member  200  which moves with the movable member  162  and retaining member  163 . When the apparatus main assembly A is in the state shown in  FIG. 18(   a ), the releasing member  200  remains retracted in a recess of the guide  130 L 1  of the apparatus main assembly A. Also, this embodiment is different from the first embodiment, in the structural arrangement regarding how the movable member  162  is retained by the retaining member  163 . Next, these differences will be described in detail. 
     FIG. 19  is a perspective view of the cartridge compartment of the apparatus main assembly A as seen from the direction indicated by an arrow mark Y 2  in  FIG. 18 . The retaining member  163  in  FIG. 19  is rotatably supported like the retaining member in the first embodiment. The apparatus main assembly A in this embodiment is also provided with a linking member  201  and an elastic member  202 . The linking member  201  connects the releasing member  200 , shown in  FIGS. 18(   a ) and  18 ( b ), and the movable member  162 . 
     FIG. 20  is an exploded view of the releasing member and movable member  162 , as well as the components related thereto, showing the structures thereof. The guide  130 L 1  of the main assembly is provided with a shaft  130 L for rotatably supporting the releasing member  200 . The releasing member  200  is provided with a shaft  200   a , which is fitted in the hole  201   a  of the linking member  201 , rotatably supporting the linking member  201 . Further, one end of the elastic member  202  is hooked to the shaft  200   a  of the releasing member  200 , and the other end of the elastic member  202  is hooked to the shaft  145   a  ( FIG. 19 ) projecting from the internal plate  145 . Further, the linking member  201  is provided with a hole  202   b , in which the shaft  162   d  of the movable member  162  is fitted, rotationally supporting thereby the linking member  201 . The releasing member  200  and movable member  162  are connected with the provision of the above described structural arrangement. 
     FIG. 21  is a perspective view of the cartridge B in this embodiment. Like the cartridge B in the first embodiment, the cartridge B in this embodiment also has the cartridge guide  140 L 1 , and first engaging portion  140 L 1   a  as a part of the cartridge guide  140 L 1 , as well as the projection  142  projecting downward from the drum frame  119 . However, the extension portion  141  is stepped (the extension portion  141  has two sections: a section level with the cartridge guide  140 L 1 , and a section  141   a  recessed toward the cartridge frame). Therefore, the surface  141   a  of the cartridge guide  140 L 1 , that is, the surface of the section recessed toward the cartridge frame, does not have the function of retaining the retaining member  163  in the releasing position. This is different from the first embodiment. 
   (2) Description of Movement of Electrical Contact Protection Mechanism 
   Next, the movements of the electrical contact protection mechanism in this embodiment will be described in detail.  FIGS. 22-25  are schematic drawings depicting the movements of the electrical contact protection mechanism, which occur as the cartridge B is inserted (advanced) into the apparatus main assembly A. 
     FIGS. 22(   a )- 25 ( a ) are drawings of the electrical contact protection mechanism as seen from the direction indicated by the arrow mark Y in  FIG. 18(   a ).  FIGS. 22(   b )- 25 ( b ) are drawings of the electrical contact protection mechanism as seen from the direction indicated by the arrow mark Y 2  in  FIG. 18(   a ).  FIGS. 22(   c )- 25 ( c ) are drawings of the electrical contact protection mechanism as seen from the direction indicated by the arrow mark Z 2  in  FIG. 22(   b ). These drawings are provided for the understanding of the movement of the retaining member  163 . 
     FIGS. 22(   a )- 22 ( c ) show the states of the electrical contact protection mechanism in various stages of the cartridge B insertion into the apparatus main assembly A. Referring to  FIG. 22(   a ), the movable member  162  is in the protective position in which it covers the development bias transmission electrical contact  161 , and the retaining member  163  is in the retaining position in which it retains the movable member  162 . When the retaining member  163  is in the retaining position, it prevents the movable member  162  from moving from the protective position to the exposing position. The retaining member  163  is kept pressured by the elastic member  164  in the direction indicated by an arrow mark a. The retaining portion  163   c  of the retaining member  163  does not directly retain the movable member  162 ; the linking member  201  rotatably connected to the movable member  162  is retained by the retaining portion  163   c . As for the releasing member  200 , referring to  FIG. 22(   b ), it has been rotated about the shaft  130 L 1   a  in the clockwise direction (direction indicated by arrow mark e); it has been retracted into the recess of the guide  130 L 1  of the apparatus main assembly A. The elastic member  202  is disposed so that its resiliency acts in the direction to rotate the releasing member  200  in the arrow e direction. 
     FIGS. 23(   a )- 23 ( c ) show the state of the electrical contact protection mechanism in a more advanced stage in the insertion of the cartridge B into the apparatus main assembly A than that shown in  FIG. 22 . In this stage, the engaging portion  140 L 1   a  as the first engaging portion of the cartridge B has engaged with the projection  163   d  of the retaining member  163 , and has rotated the retaining member  163  about the shaft  163   c  in the direction indicated by an arrow mark c, having thereby moved the retaining member  163  into the releasing position, as shown in  FIG. 23(   c ). When the retaining member  163  is in the releasing position, the retaining portion  163   c  of the retaining member  163  is away from the position in which it prevents the linking member  201  from moving. Therefore, the movable member  162  is rotatable. In this stage, however, the movable member  162  has not come into contact with the projection  142  of the drum frame, as shown in  FIG. 23(   a ). Therefore, the releasing member  200  and linking member  201  remain in the same attitudes as they are in  FIG. 22  ( FIG. 23(   b ). 
     FIGS. 24(   a )- 24 ( c ) show the state of the electrical contact protection mechanism in a more advanced stage in the insertion of the cartridge B into the apparatus main assembly A than that shown in  FIG. 23 . In this stage, the projection  142  of the drum frame has engaged with the engaging portion  162   d  of the movable member  162 , as shown in  FIG. 24(   a ), placing therefore the movable member  162  under the pressure which acts to rotate the movable member  162  in the direction indicated by an arrow mark d. As the movable member  162  is rotated, the linking member  201  is moved as shown in  FIG. 24(   b ). The movement of the linking member  201  causes the releasing member  200  to rotated about the shaft  130 L 1   a  in the direction indicated by an arrow mark f. As a result, a part of the releasing member  200  projects from the recess of the guide  130 L 1  of the apparatus main assembly A as shown in  FIG. 24(   a ). Further, the movement of the linking member  201  causes the surface  201   a  of the linking member  201  to come into contact with the engaging surface  163   d  of the retaining member  163 . 
     FIGS. 25(   a )- 25 ( c ) show the state of the electrical contact protection mechanism in the stage in which the cartridge B has settled in the image forming position. Referring to  FIG. 25(   a ), the movable member  162  has rotated further in the arrow d direction from its position shown in  FIG. 24 , exposing thereby the development bias transmission electrical contact  161 . As the cartridge B was mounted into this position, the actual contact portion  161   a  of the development bias transmission electrical contact  161  and actual contact portion  160   a  of the development bias reception electrical contact  160  came into contact with each other, establishing electrical connection between the apparatus main assembly A and cartridge B. The image formation is carried out in this stage. As for the releasing member  200 , it has been rotated further in the arrow f direction from its position shown in  FIG. 24 , into the position shown in  FIG. 25 . Referring to  FIG. 25(   b ), the rotation of the movable member  162  moves the linking member  201  further, causing the releasing member  200  to move into the position shown in the drawing. As a result, the shaft  200   a  to which the elastic member  202  is hooked is positioned below the rotational axis  130 L 1   a  of the releasing member  200 , causing the resiliency of the elastic member  202  to act in the direction to rotate the releasing member  200  in the arrow f direction. Therefore, unlike the projection  142  of the drum frame in the first embodiment, the projection  142  of the drum frame in this embodiment does not retain the movable member  162 , by the engaging portion  162   d , as will be evident from in  FIG. 25(   a ). Referring to  FIG. 25(   c ), the surface  201   a  of the linking member  201  catches the surface  163   d  of the retaining member  163 , preventing thereby the retaining member  163  from rotating in the arrow a direction. In other words, in this embodiment, the portion  141   a  ( FIG. 21) , that is, recessed portion, of the extension portion  141  of the drum frame is not structured to retain the retaining member  163 . 
     FIGS. 26(   a ) and  26 ( b ) are drawings showing the movements of the electrical contact protection mechanism which occur during the extraction of the cartridge B from the apparatus main assembly A. Referring to  FIG. 26(   a ), when the cartridge B is extracted from the apparatus main assembly A, the guide  140 L 1  of the cartridge is guided by the guide  130 L 1  of the apparatus main assembly A. As has been described above, the releasing member  200  rotatably supported by the guide  130 L 1  of the apparatus main assembly A is projecting from the recess of the guide  130 L 1  of the apparatus main assembly A. Thus, as the cartridge B is pulled outward, the guide  140 L 1  of the cartridge B comes into contact with the releasing member  200 , causing the releasing member  200  to rotate in the direction indicated by an arrow mark g. When the releasing member  200  is in the position shown in  FIG. 26(   a ), the movable member  162  is in the exposing position in which it keeps the development bias transmission electrical contact  161  exposed, and also, the retaining member  163  is kept in the releasing position. In this stage of the extraction, the relationship between the retaining member  163  and linking member  201  is as shown in  FIGS. 25(   b ) and  25 ( c ). In other words, the surface  163   d  of the retaining member  163  and the surface  201   a  of the linking member  201  are in contact with each other, as shown in  FIG. 25(   c ). 
     FIG. 26(   b ) shows the state of the electrical contact protection mechanism, in which the releasing member  200  has come into contact with the guide  140 L 1  of the cartridge B, and has been made to retract into the recess of the guide  130 L 1  of the apparatus main assembly A. The releasing member  200  rotates, through the linking member  201 , which has already been described, the movable member  162  in the arrow b direction, moving thereby the movable member  162  into the protective position in which the movable member  162  covers the development bias transmission electrical contact  161 . As the releasing member  200  is moved into the position shown in  FIG. 26(   b ), the retaining member  163  is moved into the retaining position. In this stage, the relationship between the retaining member  163  and linking member  201  is as shown in  FIGS. 22(   b ) and  22 ( c ). In other words, the linking member  201  has rotated upward, having thereby caused the surface  201   a  of the linking member  201  to disengage from the surface  163   d  of the retaining member  163 , as shown in  FIG. 22(   c ). As a result the retaining member  163  has been rotated by the elastic member  164  in the arrow a direction, causing thereby the retaining portion  163   c  to prevent the linking member  201  from moving. 
   In summary, this embodiment can yield the following effects. 
   1) Even if an operator inserts his hand into the image forming apparatus main assembly A to take care of a paper jam or the like problem after removing the process cartridge B from the image forming apparatus main assembly A, the hand does not easily come into contact with the electrical contact  161  on the main assembly side, because the electrical contact  161  is not projecting inward of the apparatus main assembly A. Therefore, it does not occur that a bad electrical connection occurs between the process cartridge B and apparatus main assembly A due to the adhesion of human sweat and/or the internal grease of the apparatus main assembly A to the electrical contact  161 . 
   2) The electrical contact protecting movable member is moved by the movement of the cartridge B, making it unnecessary for an operator to perform an operation dedicated to the establishment of electrical connection between the cartridge B and apparatus main assembly A. 
   3) The apparatus main assembly A is provided with the retaining member  163  for preventing the movable member  162  from moving into the exposing position in which the movable member  162  keeps the electrical contact of the apparatus main assembly A exposed, while no cartridge B is in the apparatus main assembly A. In other words, in order for an operator to touch the electrical contact  161  of the apparatus main assembly A, the movable member  162  must be moved into the electrical contact exposing position while retaining the retaining member  163  in the releasing position. Therefore, even if an operator inserts his hand into the apparatus main assembly A in order to maintain the image forming apparatus, for example, to deal with paper jam or the like problem, it is far less likely for the hand of the operator to accidentally touch the electrical contact  161 , compared to the case in which an operator inserts his hand into the main assembly of an image forming apparatus in accordance with the prior art. 
   6) The apparatus main assembly A and cartridge B are structured so that when the cartridge B is in the apparatus main assembly A, the rotational axis of the movable member  162  is parallel to the axial line of the photosensitive drum  107 , and the movable member  162  is rotatable relative to the apparatus main assembly A; that when the cartridge B is in the apparatus main assembly A, the rotational axis of the development bias transmission electrical contact  161  as one of the electrical contacts on the main assembly side is parallel to the axial line of the photosensitive drum  107 , and the development bias transmission electrical contact  161  rotates relative to the apparatus main assembly A; and that the movable member  162 , and the development bias transmission electrical contact  161  as one of the electrical contacts of the main assembly A, are disposed in a manner of overlapping in the direction parallel to the aforementioned axial line, contributing to space saving. 
   Embodiment 3 
   Next, the third embodiment of the present invention will be described. The structure of the image forming apparatus  100  in this embodiment is similar to that of the image forming apparatus in the first and second embodiments described above. Here, therefore, only the structural features different from those of the image forming apparatus in the preceding embodiments will be described. Further, the components of the image forming apparatus in this embodiment, which are identical in structural feature and function to the counterparts in the preceding embodiments, will be given the same referential symbols so that the descriptions of the counterparts in the first and second embodiments can be referred to. 
     FIG. 27  is a schematic sectional view of the image forming apparatus  100  in this embodiment. It shows the image forming apparatus  100  as seen from the same direction as that from which the image forming apparatuses in the first and second embodiments are seen (from direction indicated by arrow mark Y in  FIG. 18(   a )). 
   The cartridge B is inserted into the apparatus main assembly A, with its guide  104 L 1  supported by the guide  130 L 1  of the apparatus main assembly A.  FIG. 27(   a ) shows the state of the electrical contact protection mechanism, in the early stage of the cartridge insertion, in which the movable member  162  is in the protective position in which it covers the development bias transmission electrical contact  161 , and is retained by the retaining member  163 ; the movable member  162  is prevented by the retaining portion  163   c  of the retaining member  163  from rotating in the arrow d direction. The retaining member  163  is kept pressured by the elastic member  203  to rotate about the shaft  204  in the direction indicated by an arrow mark h. Further, the movable member  162  is kept pressured by the elastic member  165  to rotate in the direction indicated by the arrow mark b. 
     FIG. 27(   b ) shows the state of the electrical contact protection mechanism, in which the cartridge has been moved into the image forming position. While the cartridge B was moved into the image forming position, the projection  142  of the cartridge B came into contact with the engaging portion  163   d  of the retaining member  163 , rotating thereby the retaining member  163  in the direction indicated by an arrow mark i. When the cartridge B is in the image forming position ( FIG. 27(   b )), the engaging portion  163   d  and projection  142  remain in contact with each other. In other words, in this embodiment, the projection  142  has the functions of the first engaging portion and first retaining portion. 
   As the retaining member  163  is rotated in the arrow i direction, the movable member  162  is released by the retaining member  163 , and the engaging portion  205  of the cartridge B engages with the surface  162   c  of the movable member  162 , retaining thereby the movable member  162 . In other words, the engaging portion  205  has the functions of the second engaging portion and second retaining portion, and the surface  162   c  of the movable member  162  is the surface by which the movable member  162  is retained by the second retaining portion. Shortly before the cartridge B has settled in this position, the actual contact portion  161   a  of the development bias transmission electrical contact  161  came into contact with the actual contact portion  160   a  of the development bias reception electrical contact  160 , establishing electrical connection between the apparatus main assembly A and cartridge B. The image formation is carried out in this state. As the cartridge B is extracted from the apparatus main assembly A, the movable member  162  and retaining member  163  return to the positions shown in  FIG. 27(   a ); the movable member  162  and retaining member  163  return to the protective and retaining positions, respectively. 
     FIG. 28  is a perspective drawing depicting the states of the movable member  162  and retaining member  163  when the cartridge B is in the image forming position. When the cartridge B is in the image forming position, the projection  142  of the cartridge B is in contact with the engaging portion  163   d  of the retaining member  163 , retaining thereby the retaining member  163  by the engaging portion  163   d . Further, the engaging portion  205  of the cartridge B is in contact with the surface  162   c  of the movable member  162 , retaining thereby the movable member  162  by the surface  162   c . In this state, the development bias transmission electrical contact  161  and development bias reception electrical contact  160  are in contact with each other, maintaining electrical contact between the apparatus main assembly A and cartridge B. 
   With the employment of the above described structural arrangement, effects similar to those yielded by the second embodiment are yielded. 
   1) Even if an operator inserts his hand into the image forming apparatus main assembly A to take care of a paper jam or the like problem after removing the process cartridge B from the image forming apparatus main assembly A, the hand does not easily come into contact with the electrical contact  162  on the main assembly side, because the electrical contact  162  is not projecting inward of the apparatus main assembly A. Therefore, it does not occur that a bad electrical connection occurs between the process cartridge B and apparatus main assembly A due to the adhesion of human sweat and/or the internal grease of the apparatus main assembly A to the electrical contact  161 . 
   2) The electrical contact protecting movable member is moved by the movement of the cartridge B, making it unnecessary for an operator to perform an operation dedicated to the establishment of electrical connection between the cartridge B and apparatus main assembly A. 
   3) The apparatus main assembly A is provided with the retaining member  163  for preventing the movable member  162  from moving into the exposing position in which the movable member  162  keeps the electrical contact of the apparatus main assembly A exposed, while no cartridge B is in the apparatus main assembly A. In other words, in order for an operator to touch the electrical contact  161  of the apparatus main assembly A, the movable member  162  must be moved into the electrical contact exposing position while retaining the retaining member  163  in the releasing position. Therefore, even if an operator inserts his hand into the apparatus main assembly A in order to maintain the image forming apparatus, for example, to deal with paper jam or the like problem, the hand of the operator is far less likely to accidentally touch the electrical contact  161 , compared to the case in which an operator inserts his hand into the main assembly of an image forming apparatus in accordance with the prior art. 
   4) The apparatus main assembly A and cartridge B are structured so that when the cartridge B is in the apparatus main assembly A, the rotational axis of the movable member  162  is parallel to the axial line of the photosensitive drum  107 , and the movable member  162  is rotatable relative to the apparatus main assembly A; that when the cartridge B is in the apparatus main assembly A, the rotational axis of the development bias transmission electrical contact  161  as one of the electrical contacts on the main assembly side is parallel to the axial line of the photosensitive drum  107 , and the development bias transmission electrical contact  161  rotates relative to the apparatus main assembly A; and that the movable member  162 , and the development bias transmission electrical contact  161  as one of the electrical contacts of the main assembly A, are disposed in a manner of overlapping in the direction parallel to the aforementioned axial line, contributing to space saving. 
   Embodiment 4 
   Next, the fourth embodiment of the present invention will be described. 
   (General Structure of Electrophotographic Image Forming Apparatus and Structure of Process Cartridge) 
   First, referring to  FIGS. 33 and 34 , the electrophotographic image forming apparatus employing a process cartridge removably mountable in the main assembly of the image forming apparatus will be described regarding its general structure, along with the structure of the cartridge. 
     FIG. 33  is a schematic sectional view of the electrophotographic image forming apparatus (which in this embodiment is a laser beam printer), showing the general structure thereof, and  FIG. 34  is a schematic sectional view of the process cartridge removably mountable in the main assembly of the image forming apparatus, and the electrical contacts thereof, showing the general structures thereof. 
   First, referring to  FIG. 33 , the general structure of the image forming apparatus will be described following the movement of a sheet of recording medium S in the apparatus main assembly. The laser beam printer E forms an image with the use of one of the electrophotographic image forming methods. A sheet of recording medium S is conveyed by a recording medium feeding and conveying means to an image forming means, and a toner image is transferred onto the sheet of recording medium S. Then, the sheet of recording medium S is conveyed to a fixing means, in which the toner image is fixed. Then, the sheet of recording medium S is discharged into a delivery tray portion. More specifically, a cassette  111  in which a plurality of sheets of recording medium S are stored in layers is mounted in the bottom portion of the main assembly of the image forming apparatus. The sheets of recording medium S stored in the cassette  111  of a recording medium feeding portion  1  are sequentially drawn out of the cassette  111  by a feed roller  112 , starting from the topmost sheet, and are sent to an image forming portion  2  by a pair of conveyance rollers  113  and a pair of conveyance rollers  114 . In the image forming portion  2 , a beam of laser light is projected by a laser scanner  121 , while being modulated with image formation data, onto the peripheral surface of the photosensitive drum  151  being rotated in the clockwise direction. As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum  151 . This electrostatic latent image is developed with toner, in a developing portion in the process cartridge P; it is developed into an image formed of toner (which hereinafter will be referred to simply as toner image). This toner image is transferred, as an unfixed image, by a transfer roller  124  onto the sheet of recording medium S. Then, the sheet of recording medium S is sent to a fixing portion  3 , through which the sheet of recording medium S is conveyed. While the sheet of recording medium S is conveyed through the fixing portion  3 , the toner image is fixed to the sheet of recording medium S. Thereafter, the sheet of recording medium S is conveyed further, and is discharged from the main assembly of the image forming apparatus, by a pair of discharge rollers  133 . Designated by a referential number  4  is an electrical portion comprising the electrical power source and the control circuit for controlling the image forming apparatus. 
   To describe the process of recording on both surfaces of the sheet of recording medium S, after the sheet of recording medium S, on the top surface of which an image has been formed, is passed through the fixing portion  3 , it is switched back by the reversal driving of the pair of conveyance-discharge rollers  133  and the pair of conveyance rollers  131 , and then, is conveyed by a pair of conveyance rollers  141  and a pair of conveyance rollers  142  to the image forming portion, for the second time. Then, an image is formed on the bottom side of the sheet of the recording medium S. Then, the sheet of recording medium S is discharged from the image forming apparatus. 
   Referring to  FIG. 34 , as for the process cartridge P, the photosensitive drum  151  is rotated, and as the photosensitive drum  151  is rotated, its peripheral surface is uniformly charged by the voltage applied to a charge roller  152  as a charging means. The voltage to be applied to the charge roller  152  is supplied to the charge roller  152  from the electrical portion  4  of the apparatus main assembly through the electrical contact  125  on the main assembly side, and the electrical contact  153  on the cartridge side. Next, a latent image is formed on the peripheral surface of the photosensitive drum  151  by projecting a beam of laser light L onto the peripheral surface of the photosensitive drum  151  from the laser scanner  121 , while modulating it with image formation data. This latent image is developed by a developing means, which uses toner. 
   To describe in more detail, the charge roller  152  is disposed in contact with the photosensitive drum  151 , and charges the photosensitive drum  151 . The charge roller  152  is rotated by the rotation of the photosensitive drum  151 . The developing means develops the latent image, formed on the photosensitive drum  151 , by supplying with toner the portion of the peripheral surface of the photosensitive drum  151 , which is in the development range. 
   The developing means sends the toner in the toner container  154  into the development chamber  156  by the rotation of a stirring member  155 . It also rotates a development roller  157  in which a magnetic roller (stationary magnet) is disposed, and forms a layer of frictionally charged toner on the peripheral surface of the development roller  157 , by a development blade  158 . It develops the latent image on the photosensitive drum  157  by transferring the toner on the peripheral surface of the development roller  157  onto the peripheral surface of the photosensitive drum  151 , in the pattern of the latent image, by applying voltage to the development roller  157 ; it develops the latent image into a visible image, that is, an image formed of toner. As for the application of voltage to the development roller  157 , voltage is supplied from the electrical portion  4  of the apparatus main assembly to the development roller  157  through the development bias transmission electrical contact  126  on the main assembly side to the development bias reception electrical contact  158  on the process cartridge side. Not only does the development blade  158  regulate in amount the toner on the peripheral surface of the development roller  157 , but also, it frictionally charges the toner on the peripheral surface of the development roller  157 . 
   After the transfer of the toner image onto the sheet of recording medium S by the transfer roller  24 , the photosensitive drum  151  is cleared by a cleaning means, of the toner remaining thereon. Then, the cleared portion of the peripheral surface of the photosensitive drum  151  is used for the following image formation process. The cleaning means scrapes down the toner remaining on the peripheral surface of the photosensitive drum  151 , by its elastic cleaning blade  159  disposed in contact with the peripheral surface of the photosensitive drum  151 , and collects the scraped toner into a waste toner bin  160 . 
   The process cartridge P is provided with a memory tag  6  as an information storage medium, which is attached to the surface of the process cartridge P. The memory tag  6  communicates with the apparatus main assembly by being electrically connected to the electrical contact  71  with which the connector  7  of the main assembly is provided. 
   Designated by a referential numeral  161  is a drum shutter. When the process cartridge P is out of the apparatus main assembly, the drum shutter  161  is kept in the position in which it covers the hole of the process cartridge P, through which the photosensitive drum  151  is partially exposed, in order to protect the photosensitive drum  151 . As the process cartridge P is mounted into the apparatus main assembly, the drum shutter  161  is moved into the open position and kept therein, allowing the photosensitive drum  151  to be exposed across the bottom area, as shown in  FIGS. 33 and 34 . 
   Next, the frame of the process cartridge P will be described. Referring to  FIG. 34 , the photosensitive drum  151 , charge roller  152 , cleaning means such as the elastic cleaning blade  159  or the like, are attached to a drum frame  162 , that is, one of the sub-frames of the frame of the process cartridge P, making up the photosensitive member unit. The developing means unit is made up of the toner container  154 , development roller  157 , development blade  158 , and the developing means supporting frame  164  to which the preceding components are attached. The photosensitive member unit and developing means unit are connected to each other with the use of connector pins (unshown), being enabled to be pivoted relative to each other. In other words, the process cartridge P is made up of the photosensitive member unit and developing means unit. 
   (Structural Arrangement for Mounting or Dismounting Process Cartridge, and Process Cartridge Compartment) 
   Referring to  FIGS. 35-39 , the guides for mounting or dismounting the process cartridge P, and the process cartridge compartment, will be described regarding their structures.  FIG. 35  is a perspective view of the main assembly of the image forming apparatus, the cartridge access door of which is open for mounting or dismounting the process cartridge, showing the general structure thereof.  FIGS. 36 and 37  are perspective views of the process cartridge compartment of the apparatus main assembly, showing the process cartridge mounting (dismounting) means of the apparatus main assembly.  FIGS. 38 and 39  are schematic perspective views of the process cartridge. 
   In order to mount the process cartridge P into the apparatus main assembly E, the cartridge access door D ( FIG. 35 ) of the apparatus main assembly E must be opened by a user, and then, the process cartridge P is to be placed on the cartridge mounting means of the apparatus main assembly E so that the process cartridge P is removably mounted into the cartridge compartment of the apparatus main assembly E. 
   First, the guiding members or the like with which the process cartridge P is provided will be described. The process cartridge P is provided with a pair of guiding members  190  and  191  ( FIGS. 38 and 39 ), which are roughly cylindrical and project from the end surfaces of the process cartridge P, one for one. The process cartridge P is also provided with a rotation control projections  191  and  193 , which are also on the end surfaces of the process cartridge P, one for one, being located so that when the process cartridge P is in the apparatus main assembly E, they will be at the top edge of the end surfaces of the process cartridge P. 
   Next, the guiding members with which the apparatus main assembly E is provided will be described. The apparatus main assembly E is provided with guiding members  181 - 189  ( FIGS. 36 and 37 ). The guiding members  181  and  186  are tilted relative to the direction in which the process cartridge P is inserted into the apparatus main assembly E, and are connected to the guiding portions  185  and  189 , respectively. When the process cartridge P is inserted into the apparatus main assembly E, the guiding portions  192  and  190  of the process cartridge P are engaged with the guiding members  181  and  186 , respectively. The guiding members  183 ,  182 , and  187  are also tilted relative to the direction in which the process cartridge P is mounted into the apparatus main assembly E. When the process cartridge P is inserted into the apparatus main assembly E, the rotation control projections  191  and  193  of the process cartridge P are engaged with the guiding members  183 ,  182 , and  187 , respectively. The drum shutter  161  is opened or closed as the cylindrical portion  197  ( FIG. 39 ) is guided by the guiding portions  182  and  184  of the apparatus main assembly E. 
   The engaging portion  194  and retaining portion  195  of the process cartridge P, which will be described later in detail, have the functions of moving the retaining member and movable member, respectively, of the apparatus main assembly E. 
   (Structure of Electrical Contact Protection Mechanism) 
   Next, the electrical contacts of the main assembly of the electrophotographic image forming apparatus, and the structure of the mechanism for protecting the electrical contacts, will be described in detail.  FIGS. 40-42  are perspective views of various portions of the apparatus main assembly of the electrophotographic image forming apparatus, showing the structures thereof. They are the internal views of the cartridge compartment of the apparatus main assembly E as seen through the opening through which the process cartridge P is to be mounted or dismounted.  FIG. 40  is a perspective view of the cartridge compartment in which the process cartridge P is not present, and  FIG. 41  is a perspective view of the cartridge compartment in which the process cartridge P is present, although the process cartridge P is not shown. Referring to  FIG. 40 , the apparatus main assembly E is provided with guides  186  and  187  for facilitating the mounting of the process cartridge P. It is also provided with a retainer spring  188  for keeping the process cartridge P in place after the mounting of the process cartridge P into the apparatus main assembly E, and grounding contact  201  which is placed in contact with the drum shaft  196  ( FIG. 38 ) to ground the photosensitive drum  151 . In addition, the apparatus main assembly E has: a movable member  202  movable between the protective position in which it covers a development bias transmission electrical contact  126  ( FIG. 40  (broken line)) as one of the electrical contacts on the main assembly side, and the exposing position ( FIG. 41 ) in which it exposes the electrical contact  126 ; a retaining member  203  ( FIG. 42 ) for retaining the movable member  202 ; and an electrically conductive member  204  attached to the movable member  202  and movable with the movable member  202 . 
   The electrically conductive member  204  is disposed next to the electrical contact  126 . It is disposed inside the cartridge compartment of the apparatus main assembly. 
   Further, the apparatus main assembly E is provided with a conveyance guide (bottom)  205  and a conveyance guide (top)  206  (outlined by broken lines in  FIGS. 40 and 41 ), which constitute parts of the recording medium path. These guides  205  and  206  are always grounded, and so is an internal plate  207 , which is located on the inward side of the electrical contact  126  when the cartridge compartment is seen through the opening of the apparatus main assembly E. 
   Next, the structures of the movable member  202 , electrically conductive member  204 , and retaining member  203  will be described in more detail. Referring to  FIG. 42 , the movable member  202  is rotatably supported by a shaft  202   a , and is kept pressured by a spring to rotate into the protective position shown in  FIG. 40 . The conductive member  204  is attached to the movable member  202 . All that is necessary to move the movable member  202  and electrically conductive member  204  into the exposing position ( FIG. 41 ) in which the movable member  202  exposes the electrical contact  126  is to mount the process cartridge P into the apparatus main assembly E. As for the process of mounting the process cartridge P into the apparatus main assembly E, which will be described again later, while the process cartridge P is mounted into the apparatus main assembly E, the engaging portion  194  ( FIG. 38 ) of the cartridge P engages with the engaging portion  202   b , which is a part of the movable member  202  ( FIG. 40 ). As the cartridge P is mounted into the image forming position, the engaging portion  194  ( FIG. 38 ) of the cartridge P comes into contact with the surface area  202   c  of the movable member  202 , retaining thereby the movable member  202  and electrically conductive member  204  in the exposing position ( FIG. 41 ), in which the movable member  202  allows the electrical contact  126  to be exposed through the slit  202   d  of the movable member  202 . The internal plate  207  is provided with a hole  207   a , through which the engaging portion  203   b  of the retaining member  203  for retaining the movable member  202  is allowed to partially project into the cartridge compartment ( FIG. 42 ).  FIG. 42  is a perspective view of the electrical contact protection mechanism as seen from the direction opposite to the direction from which the cartridge compartment is seen in  FIG. 40 . Referring to  FIG. 42(   a ), the retaining member  203  is rotatably supported by a shaft  203   a , and is kept pressured in the direction indicated by an arrow mark a by an elastic member (unshown) disposed between the remaining member  203  and internal plate  207 . Thus, the engaging portion  203   b  of the remaining member  203  is made to slip into the underside of the movable member  202 , preventing thereby the movable member  202  from rotating into the exposing position, as will be understood from  FIG. 42(   b ). 
   (Description of Structure and Movements of Electrical Contact Protection Mechanism) 
   Next, the movements of the electrical contact protection mechanism will be described in detail.  FIGS. 29-32  are schematic drawings for describing the movements of the electrical contact protection mechanism, which occur as the cartridge P is inserted (advanced) into the apparatus main assembly E. 
     FIGS. 29(   a ),  30 ( a ),  31 ( a ), and  32 ( a ) are drawings of the electrical contact protection mechanism, and the components related thereto, as seen from where the guiding members  181  and  182  of the apparatus main assembly E are present, toward the internal plate  207  (as seen from direction indicated by arrow mark Y in  FIG. 40) .  FIGS. 29 ) b ),  30 ( b ),  31 ( b ), and  32 ( b ) are drawings of the same portions as those shown in  FIG. 29(   a ),  30 ( a ),  31 ( a ), and  32 ( a ), as seen from the direction indicated by an arrow mark Z. In  FIGS. 29(   a ),  30 ( a ),  31 ( a ), and  32 ( a ), the cartridge P is outlined in the broken line for ease of understanding. Further, for the purpose of showing the development bias transmission electrical contact  161 , a part of the movable member  202  and a part of the conductive member  204 , are not shown. Further, In  FIGS. 29(   b )- 32 ( b ), the conductive member  204  are hatched for ease of understanding. The development bias transmission electrical contact  126  is supported by a shaft  208 , being thereby rendered rotatable. 
     FIGS. 29(   a ) and  29 ( b ) show the states of the electrical contact protection mechanism and its adjacencies, during or prior to the mounting of the cartridge P into the apparatus main assembly A. The movable member  202  and conductive member  204  are in the position in which they cover the development bias transmission electrical contact  126 , and the retaining member  203  is in the position in which it retains the movable member  202 . The springy portion  204   a  of the conductive member is kept pressed upon the conductive member seat portion  205   a  of the conveyance guide (bottom)  205 , grounding thereby the conductive member  204 . With the springy portion  204   a  being resiliently bent, a predetermined amount of contact pressure is present. The movable member  202  is kept pressured in the direction indicated by an arrow mark b by the elastic member  209 . As described above, the retaining member  203  is kept pressured in the arrow a direction by an elastic member (unshown). Thus, the engaging portion  203   c  of the retaining member  203  is projecting into the cartridge compartment through the hole  207   a  of the internal plate  207  as shown in  FIG. 42 , having slipped into the underside of the movable member  202 , preventing thereby the movable member  202  and conductive member  204  from rotating. 
   With the employment of the above described structural arrangement, if the hand of a user, which has accumulated static electricity prior to the insertion of the cartridge P, is placed in the adjacencies of the electrical contact  126 , the static electricity of the hand is discharged to the conductive member  204 , and therefore, it does not discharge to the electrical contact  126 . 
     FIGS. 30(   a ) and  30 ( b ) show the states of the electrical contact protection mechanism, in which the cartridge P has been advanced deeper in the apparatus main assembly E from the position shown in  FIGS. 29(   a ) and  29 ( b ), respectively. They show the very moment when the engaging portion  194  of the cartridge P has just engaged with the engaging portion  202   b  of the movable member  202  of the apparatus main assembly E ( FIG. 30(   a )). In this state, the projection  203   c  of the retaining member  203  has come into contact with the end surface of the guiding portion  190 , being thereby pressed by the guiding portion  190 . As a result, the retaining member  203  has rotated about the shaft  203   a  in the direction indicated by an arrow mark c, having been thereby moved into the releasing position ( FIG. 30(   b )). When the retaining member  203  is in the releasing position, the engaging portion  203   b  of the retaining member  203  is away from the position in which it prevents the movable member  202  from rotating. Therefore, the movable member  202  is allowed to rotate. In other words, when the retaining member  203  is in the releasing position, it allows the movable member  202  to rotate. The elastic member for pressing the retaining member  203  is disposed in the compressed state. 
     FIGS. 31(   a ) and  31 ( b ) show the state of the electrical contact protection mechanism and its adjacencies, in which the cartridge P has been advanced even further into the apparatus main assembly E from the position shown in  FIGS. 30(   a ) and  30 ( b ), respectively. The retaining member  203  is kept in the same attitude as that shown in  FIGS. 30(   a ) and  30 ( b ), by the end surface of the guiding portion  190  of the cartridge P. As for the movable member  202 , it is pressed by the engaging portion  194 , being therefore rotated in the direction indicated by an arrow mark d about the shaft  202   a , against the resiliency of the elastic member  209 . 
     FIGS. 32(   a ) and  32 ( b ) show the state of the electrical contact protection mechanism, in which the cartridge P has been inserted into the image forming position. In this state, the guiding portion  190  is engaged with the positioning portion  189  of the guiding portion of the apparatus main assembly E, being precisely positioned relative to the apparatus main assembly E. As for the top portion of the guiding portion  190 , it is in contact with a retainer spring  188 , being thereby pressured downward by the spring  188 . The retaining member  203  is held by the retaining portion  195  ( FIG. 38)  of the cartridge P, by its engaging portion  203   c . Further, the movable member  202  and conductive member  204  are retained by the engaging portion  194 , in the exposing position in which they keep the development bias transmission electrical contact  126  exposed. As the cartridge P is inserted into this position, the springy portion  204   a  of the conductive member  204  is separated from the conductive member seat portion  205   a  of the conveyance guide (bottom)  205 , ceasing thereby the grounding of the conductive member  204 . Further, the development bias transmission electrical contact  126  comes into contact with the development bias reception electrical contact  158 , establishing electrical connection between the apparatus main assembly E and the cartridge P. The image forming operation is carried when the cartridge P is in this state. When the development bias transmission electrical contact  126  becomes electrically connected to the electrical contact  158  of the cartridge P, high voltage with a voltage level of several thousands is applied from the electrical power source on the main assembly side. Although the development bias transmission electrical contact  126  and conductive member  204  are disposed close to each other, it is ensured that the conductive member  204  remains electrically separated from the conveyance guide (bottom)  205  (grounded). 
   In summary, this embodiment of the present invention can yield the following effects. 
   1) If a user looks into the cartridge compartment of the image forming apparatus, while standing in the position in which the user mounts the process cartridge into the apparatus main assembly E, when the process cartridge is not in the main assembly of the image forming apparatus, the electrical contact  126  is directly behind the conductive member  204 . Thus, even if the hand of a user has static electricity when an operator inserts his hand into the adjacencies of the electrical contact  126  in the image forming apparatus main assembly E to take care of a paper jam or the like problem after removing the process cartridge P from the image forming apparatus main assembly A, the static electricity discharges to the conductive member  204 . Therefore, it does not occur that electrostatic noises are applied to the electrical contact  126  of the image forming apparatus main assembly. Therefore, it does not occur that the elements of the electrical circuit are affected by the static electricity. 
   2) While the process cartridge is in the main assembly of the image forming apparatus, the conductive member  204  is not grounded, being thereby definitely electrically separated from the grounded components. Therefore, the process cartridge and image forming apparatus in this embodiment are superior to a process cartridge and an image forming apparatus in accordance with the prior art, in terms of the reliability of the connection between the electrical contact of the apparatus main assembly and the electrical contact of the process cartridge, and also, in the supplying of electrical power from the electrical contact of the apparatus main assembly to the electrical contact of the process cartridge. 
   3) The conductive member is moved by the movement of the process cartridge, which occurs as the process cartridge is mounted or dismounted. Therefore, it is unnecessary for a user to carry out an operation dedicated to the movement of the conductive member. 
   Embodiment 5 
   Next, the fifth embodiment of the present invention will be described. The components in the fifth embodiment similar in structure and function to those in the fourth embodiment will be given identical referential symbols as those given for the description of the fourth embodiment, and will not be described. In other words, this embodiment will be described only regarding its features that characterize this embodiment. 
   (Description of Structure and Movements of Electrical Contact Protection Mechanism) 
   Next, the structure and movements of the electrical contact protection mechanism in this embodiment will be described in detail.  FIGS. 43 and 44  are schematic drawings depicting the movements of the electrical contact protection mechanism, which occur as the cartridge P is inserted (advanced) into the apparatus main assembly E. 
     FIGS. 43(   a ) and  44 ( a ) are drawings of the electrical contact protection mechanism, and the components related thereto, as seen from the side where the guiding members  181  and  182  of the apparatus main assembly E are present, toward the internal plate  207  (as seen from direction indicated by arrow mark Y in  FIG. 40) .  FIGS. 43(   b ) and  44 ( b ) are drawings of the same portions as those shown in  FIG. 43(   a ) and  44 ( a ), as seen from the direction indicated by an arrow mark Z. In  FIGS. 43(   a ) and  44 ( a ), the cartridge P is outlined in the broken line for ease of understanding. Further, for the purpose of showing the development bias transmission electrical contact  126 , a part of the movable member  202  and a part of the coil portion of the electrical contact  126 , are not shown. The development bias transmission electrical contact  126  is supported by a shaft  208 , being thereby rendered rotatable. A connective contact spring  210  is connected to the electrical portion  4  (unshown). 
     FIGS. 43(   a ) and  43 ( b ) show the states of the electrical contact protection mechanism and its adjacencies, during or prior to the mounting of the cartridge P into the apparatus main assembly E. The movable member  202  is in the position in which it is prior to the cartridge insertion, and the retaining member  203  is in the retaining position in which it retains the movable member  202 . The grounding portion  126   a  and connective portion  126   b  of the electrical contact  126  are hooked to the hook portion  202   e  of the movable member  202 . The movable member  202  is kept pressured in the direction indicated by an arrow mark b by the elastic member  209 . Therefore, the grounding portion  126   a  of the electrical contact  126  is pressed upon the portion  205   a  of the conveyance guide (bottom)  205 , grounding thereby the electrical contact  126 . As described above, the retaining member  203  is kept pressured in the arrow a direction by an elastic member (unshown). Thus, the engaging portion  203   c  of the retaining member  203  is projecting into the cartridge compartment through the hole of the internal plate  207  as shown in  FIG. 42 , having slipped into the underside of the movable member  202 , preventing thereby the movable member  202  and conductive member  204  from rotating. 
   With the employment of the above described structural arrangement, if the hand of a user, which has accumulated static electricity prior to the insertion of the cartridge P, is placed in the adjacencies of the electrical contact  126 , and the static electricity discharges from the hand, the static electricity of the hand is discharged to the ground, and therefore, it does not discharge to the electrical portion  4 . 
     FIGS. 44(   a ) and  44 ( b ) show the states of the electrical contact protection mechanism, in which the cartridge P has been inserted into the image forming position. The movements of the movable member  202  and retaining member  203 , which occur up to this point during the insertion of the cartridge P, are the same as those which occur during the insertion of the cartridge P in the fourth embodiment, and therefore, will not be described. In this state, the guiding portion  190  is engaged with the positioning portion  189  of the guiding portion of the apparatus main assembly E, being precisely positioned relative to the apparatus main assembly E. As for the top portion of the guiding portion  190 , it is in contact with a retainer spring  188 , being thereby pressured downward by the spring  188 . The retaining member  203  is held by the retaining portion  195  ( FIG. 38)  of the cartridge P, by its engaging portion  203   c . Further, the grounding portion  126   a  and connective portion  126   b  of the electrical contact  126 , are separated, in terms of electrical connection, from the hook portion  202   e  of the movable member  202 . As the cartridge P is inserted into this position, the grounding portion  126   a  of the electrical contact  126  is separated from the portion  205   a  of the conveyance guide (bottom)  205 , eliminating the connection to the ground. Further, the connective portion  126   b  of the electrical contact  126  comes into contact with the connective portion  210   a  of the connective contact spring  210 . Also as the cartridge P is moved into this position, the development bias transmission electrical contact  126  comes into contact with the electrical contact  158  of the cartridge P, and the connective portion  126   b  of the electrical contact  126  comes into contact with the connective portion  210   a  of the connective contact spring  210 , establishing electrical connection between the apparatus main assembly E and cartridge P. The image forming operation is carried when the cartridge P is in this state. When the development bias transmission electrical contact  126  becomes electrically connected to the electrical contact  158  of the cartridge P, high voltage with a voltage level of several thousands is applied. However, the grounding portion  126   a  of the electrical contact  126  is definitely not in contact with the portion  205   a  (grounded) of the conveyance guide (bottom)  205 . Thus, this embodiment yields the following effects. 
   1) If a user inserts his hand into the adjacencies of the electrical contact  126  in the main assembly of the image forming apparatus in order to deal with a paper jam or the like problem, and the hand happens to have accumulated static electricity, static noises are applied to the electrical contact  126  of the apparatus main assembly E. However, when the process cartridge is not in the main assembly of the image forming apparatus, the electrical contact  126  is grounded. Therefore, the static noises are not applied to the electrical circuit. Therefore, the electrical circuit is not affected by the static noises. 
   2) As the process cartridge is mounted into the apparatus main assembly E, the electrical contact  126  is connected to the connective contact spring  210 , being thereby connected to the electrical portion  4  of the apparatus main assembly E. Further, the electrical contact  126  is disconnected from the ground, being ensured that it is electrically separated from the grounded components. Therefore, the process cartridge and image forming apparatus in this embodiment are superior to a process cartridge and an image forming apparatus in accordance with the prior art, in terms of the reliability of the connection between the electrical contact of the apparatus main assembly and the electrical contact of the process cartridge, and also, in the supplying of electrical power from the electrical contact of the apparatus main assembly to the electrical contact of the process cartridge. 
   3) The electrical connection is automatically switched by the movement of the process cartridge, which occurs as the process cartridge is mounted or dismounted. Therefore, it is unnecessary for a user to carry out an operation dedicated to the switching of the electrical connection. 
   Embodiment 6 
   Next, the sixth embodiment of the present invention will be described. The components in the sixth embodiment similar in structure to those in the fourth embodiment will be given referential symbols identical to those given for the description of the fourth embodiment, and will not be described. In other words, this embodiment will be described only regarding its features that characterize this embodiment. 
   (Description of Structure and Movements of Electrical Contact Protection Mechanism) 
   Next, the structure and movements of the electrical contact protection mechanism in this embodiment will be described in detail.  FIGS. 45 and 46  are schematic drawings depicting the movements of the electrical contact protection mechanism, which occur as the cartridge P is inserted (advanced) into the apparatus main assembly E. 
     FIGS. 45(   a ) and  46 ( a ) are drawings of the electrical contact protection mechanism, and the components related to, as seen from the side where the guiding members  181  and  182  of the apparatus main assembly E are present, toward the internal plate  207  (as seen from direction indicated by arrow mark Y in  FIG. 40) .  FIGS. 45(   b ) and  46 ( b ) are drawings of the same portions as those shown in  FIG. 45(   a ) and  46 ( a ), as seen from the direction indicated by an arrow mark Z. In  FIGS. 45(   a ) and  46 ( a ), the cartridge P is outlined in the broken line for ease of understanding. The development bias transmission electrical contact  126  is supported by a shaft  208 , being thereby rendered rotatable. A connective contact spring  210  is connected to the electrical portion  4  (unshown). 
     FIGS. 45(   a ) and  45 ( b ) show the states of the electrical contact protection mechanism and its adjacencies, during or prior to the mounting of the cartridge P into the apparatus main assembly E. The movable member  202  is in the position in which it is prior to the cartridge insertion, and the retaining member  203  is in the retaining position in which it retains the movable member  202 . The connective portion  210   a  of the connective contact spring  210  is hooked to the hook portion  202   e  of the movable member  202 . The movable member  202  is kept pressured in the direction indicated by an arrow mark b by the elastic member  209 . Therefore, the connective portion  210   a  of the connective contact spring  210  is kept separated from the connective portion  126   b  of the electrical contact  126 , keeping the electrical contact  126  floating in terms of electrical connection. As described above, the retaining member  203  is kept pressured in the arrow a direction by an elastic member (unshown). Thus, the engaging portion  203   c  of the retaining member  203  is projecting into the cartridge compartment through the hole of the internal plate  207  as shown in  FIG. 42 , having slipped into the underside of the movable member  202 , preventing thereby the movable member  202  and conductive member  204  from rotating. 
   With the employment of the above described structural arrangement, when the cartridge P is not in the apparatus main assembly E, the electrical contact  126  is afloat in terms of electrical connection. Therefore, even if the hand of a user, which has accumulated static electricity prior to the insertion of the cartridge P, is placed in the adjacencies of the electrical contact  126 , the static electricity of the hand is not discharged to the electrical contact  126 , and therefore, it is not applied to the electrical portion  4 . 
     FIGS. 46(   a ) and  46 ( b ) show the states of the electrical contact protection mechanism, in which the cartridge P has been inserted into the image forming position. The movements of the movable member  202  and retaining member  203 , which occur up to this point during the insertion of the cartridge P, are the same as those which occur during the insertion of the cartridge P in the fourth embodiment, and therefore, will not be described. In this state, the guiding portion  190  is engaged with the positioning portion  189  of the guiding portion of the apparatus main assembly E, being precisely positioned relative to the apparatus main assembly E. As for the top portion of the guiding portion  190 , it has come into contact with a retainer spring  188 , being thereby pressured downward by the spring  188 . The retaining member  203  is held by the retaining portion  195  ( FIG. 38)  of the cartridge P, by its engaging portion  203   c . Further, the connective portion  210   a  of the connective contact spring  210  has been separated from the hook portion  202   e  of the movable member  202 . As this separation has occurred, the connective portion  126   b  of the electrical contact  126  has come into contact with the connective portion  210   a  of the connective contact spring  210 . As the cartridge P is inserted into this position, the connective portion  126   b  of the electrical contact  126  comes into contact with the connective portion  210   a  of the connective contact spring  210 . Also as the cartridge P is moved into this position, the development bias transmission electrical contact  126  comes into contact with the electrical contact  158  of the cartridge P, and the connective portion  126   b  of the electrical contact  126  comes into contact with the connective portion  210   a  of the connective contact spring  210 , establishing electrical connection between the apparatus main assembly E and cartridge P. The image forming operation is carried out when the cartridge P is in this state. When the development bias transmission electrical contact  126  becomes electrically connected to the electrical contact  158  of the cartridge P, high voltage with a voltage level of several thousands is applied. At the moment of this application of high voltage, however, there is no grounded component in the adjacencies of the electrical contact  126 . 
   Thus, this embodiment yields the following effects. 
   1) When the process cartridge is not in the main assembly of the image forming apparatus, the electrical contact  126  is afloat in terms of electrical connection. Therefore, even if a user inserts his hand into the adjacencies of the electrical contact  126  in the main assembly of the image forming apparatus in order to deal with a paper jam or the like problem, and the hand happens to have accumulated static-electricity, static noises are not applied to the electrical contact  126  of the apparatus main assembly E. Therefore, the static noises are not applied to the electrical circuit. Therefore, the elements of the electrical circuit are not affected by the static noises. 
   2) As the process cartridge is mounted into the apparatus main assembly E, the electrical contact  126  is connected to the connective contact spring  210 , being thereby connected to the electrical portion  4  of the apparatus main assembly E. Therefore, the process cartridge and image forming apparatus in this embodiment are superior to a process cartridge and an image forming apparatus in accordance with the prior art, in terms of the reliability of the connection between the electrical contact of the apparatus main assembly and the electrical contact of the process cartridge, and also, in the supplying of electrical power. 
   3) The electrical connection is switched by the movement of the process cartridge, which occurs as the process cartridge is mounted or dismounted. Therefore, it is unnecessary for a user to carry out an operation dedicated to the switching of the electrical connection. 
   In the above, the first to sixth embodiments were described with reference to the electrical contacts for development bias. Obviously, however, the present invention is also applicable to the electrical contacts of a process cartridge and the main assembly of an image forming apparatus other than the development bias contacts, for example, the electrical contacts for charge bias, electrical contacts for a memory (storage element), and the like. 
   Further, the preceding embodiments were described with reference to the laser beam printer as an example of an electrophotographic image forming apparatus. It is obvious, however, that the above described structural arrangement in accordance with the present invention is also compatible with an image forming apparatus, other than the laser beam printer, which forms an image on recording medium, such as recording paper, OHP sheet, fabric, etc., with the use of one of the electrophotographic image forming methods, for example, an electrophotographic copying machine, an electrophotographic printer (for example, LED printer, laser beam printer, etc.), an electrophotographic facsimileing machine, an electrophotographic wordprocessor, etc. 
   According to the above described present invention, it is possible to improve a process cartridge and an electrophotographic image forming apparatus in terms of the reliability in the electrical connection which occurs between the electrical contacts of the process cartridge and the electrical contacts of the main assembly of the electrophotographic image forming apparatus as the process cartridge is mounted into the main assembly of the electrophotographic image forming apparatus. 
   Also according to the present invention, even if the hand of a user happens to have accumulated static electricity when the user places his hand in the adjacencies of the electrical contacts in the main assembly of an electrophotographic image forming apparatus, the static electricity discharges to the electrical conductive member. Therefore, the electrical contacts of the main assembly are not affected by the static electricity. Further, when the process cartridge is in the main assembly, the conductive member is not grounded. Therefore, the process cartridge and main assembly are superior to those in accordance with the prior art in terms of the reliability of the electrical connection between the electrical contacts of the main assembly and the electrical contacts of the process cartridge for supplying the process cartridge with electrical power from the apparatus main assembly. Further, the conductive member is moved by the movement of the process cartridge, which occurs as the process cartridge is mounted or dismounted. Therefore, it is unnecessary for a user to perform an operation dedicated to the movement of the conductive member. 
   Further, only as the process cartridge is mounted into the apparatus main assembly, do the electrical contacts of the apparatus main assembly become ready to be connected for supplying electrical power, improving thereby the image forming apparatus in terms of the reliability in electrical connection between the process cartridge and main assembly. Further, the electrical connection is switched by the movement of the process cartridge, which occurs as the process cartridge is mounted or dismounted. Therefore, it is unnecessary for a user to carry out an operation dedicated to the switching of the electrical connection. 
   While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
   This application claims priority from Japanese Patent Application No. 105245/2004 filed Mar. 31, 2004, which is hereby incorporated by reference.