Abstract:
A process cartridge detachably mountable to a main assembly of the apparatus of an image forming apparatus, the process cartridge includes a first unit provided with a photosensitive drum; and a second unit provided with a developer carrying member and connected with the first unit so as to be movable between a contact position in which the developer carrying member is contacted with the drum and a spacing position in which the developer carrying member is spaced from the drum, and the second unit including a first contact portion for contacting to a main assembly electrical contact provided in the main assembly and for receiving a first contact force therefrom when the process cartridge is mounted to the main assembly and the second unit is positioned in the spacing position, and a second contact portion for contacting to the main assembly electrical contact and for receiving a second contact force therefrom to electrically connect with the main assembly electrical contact when the process cartridge is mounted to the main assembly and the second unit is positioned in the contact position; wherein the second contact force has a component oriented in a moving direction of moving the second unit away from the spacing position toward the contact position, and the component is greater than that of the first contact force.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to an image forming apparatus having a function to form an image on recording medium such as a sheet of paper. It relates also to a process cartridge which is removably mountable in an image forming apparatus. 
         [0002]    A process cartridge has long been used in the field of an electrophotographic image forming apparatus. A process cartridge is removably mountable in the main assembly of an electrophotographic image forming apparatus. It comprises: an electrophotographic photosensitive drum; one or more means for processing the photosensitive drum; and a shell (cartridge) in which the electrophotographic photosensitive drum and processing means are integrally placed. A process cartridge makes it possible for a user to maintain an image forming apparatus without relying on a service person. Thus, it can substantially increase an image forming apparatus in operational efficiency. This is why a process cartridge has been widely used in the field of an image forming apparatus. An electrophotographic image forming apparatus which employs a process cartridge has to, be enabled to make electrical connection between the process cartridge and its main assembly (for example, Japanese Laid-open Patent Application 2007-213018 (P.9, P.7, and  FIG. 11 ) when voltage has to be applied to the charging member of a process cartridge to charge the electrophotographic photosensitive drum of the process cartridge, and when voltage has to be applied to the developing means of the process cartridge of the process cartridge to develop an electrostatic latent image formed on the electrophotographic photosensitive drum. 
         [0003]    Some electrophotographic color image forming apparatuses of the so-called inline type employ multiple process cartridges which are aligned in parallel in the main assembly of the image forming apparatus. As the developing method usable by a process cartridge employed by an electrophotographic color image forming apparatus such as those described above, there area contact developing method and a non-contact developing method. A contact developing method is such a developing method that a development roller is placed in contact with an electrophotographic photosensitive drum in order to develop an electrostatic latent image on the drum. In the case of this developing method, a development roller has to be placed in contact with an electrophotographic photosensitive drum so that a preset amount of pressure is maintained between the roller and drum. Thus, during an image forming operation, the development roller is kept pressed upon the electrophotographic photosensitive drum. Therefore, if an electrophotographic image forming apparatus which employs a contact developing method is kept in a state in which the development roller is in contact with the electrophotographic photosensitive drum, for a substantial length of time, it is liable for the elastic layer of the development roller to be deformed by the pressure which it receives from the electrophotographic photosensitive drum. If the elastic layer of the development roller remains deformed, it is liable that the developed electrostatic latent image will suffer from nonuniformity in terms of density, the pattern of which corresponds to the rotational frequency of the development roller. 
         [0004]    There have been proposed various solutions to this problem. One of these solutions is to provide an electrophotographic image forming apparatus and the process cartridge therefor with a mechanism for keeping the electrophotographic photosensitive drum and development roller separated while the apparatus is not being used for image formation (Japanese Laid-open Patent Application 2001-337511 (P.5, P.6, and  FIG. 2 ), for example). Another of these solutions is to provide an electrophotographic image forming apparatus and the process cartridge therefor with such a mechanism that keeps the development roller of the process cartridge separated from the electrophotographic photosensitive drum of the process cartridge until the process cartridge is mounted into the main assembly of an image forming apparatus, and then, places the development roller in contact with the photosensitive drum as the process cartridge is mounted into the main assembly of the image forming apparatus (Japanese Laid-open Patent Application 2006-276190 (for example, P.9-P.11,  FIGS. 6-8 )). 
       SUMMARY OF THE INVENTION 
       [0005]    However, the conventional structural solutions, such as those described above, to the problem suffer from the following problems. That is, when a development roller is placed in contact with an electrophotographic photosensitive drum, a process cartridge comes into contact with the electrical contacts of the main assembly of an electrophotographic image forming apparatus. Thus, if the amount of pressure applied to keep the development roller in contact with the electrophotographic photosensitive drum is small, it is liable that the friction between the process cartridge and the electrical contacts of the electrophotographic image forming apparatus prevents the development roller from remaining properly in contact with the electrophotographic photosensitive drum. Thus, in the case of the structural solutions such as those described above, the pressure applied to keep the development roller properly in contact with the photosensitive drum had to be substantial. However, increasing the amount of pressure between the development roller and electrophotographic photosensitive drum resulted in increase in the amount of load to which the mechanism for keeping the development roller and photosensitive drum separated from each other is subjected while the image forming apparatus was on standby. Thus, the mechanism for keeping the development roller and photosensitive drum separated from each other had to be increased in strength. The present invention was made in consideration of problems such as those described above, Thus, the primary object of the present invention is to provide a process cartridge, the image bearing member and developer bearing member of which are separable from each other, and which is more stable in the state of contact between the image bearing member and developer bearing member than any of the process cartridge in accordance with the prior art, and also, an image forming apparatus which is compatible with the process cartridge which is in accordance with the present invention. 
         [0006]    According to an aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of the apparatus of an image forming apparatus, said process cartridge comprising a first unit provided with an image bearing member; and a second unit which is provided with a developer carrying member for carrying a developer and which is connected with said first unit so as to be movable between a contact position in which said developer carrying member is contacted with said image bearing member and a spacing position in which said developer carrying member is spaced from said image bearing member, and said second unit including a first contact portion for contacting to a main assembly electrical contact provided in the main assembly of is the apparatus and for receiving a first contact force therefrom when said process cartridge is mounted to the main assembly of the apparatus and said second unit is positioned in the spacing position, and a second contact portion for contacting to the main assembly electrical contact and for receiving a second contact force therefrom to electrically connect with the main assembly electrical contact when said process cartridge is mounted to the main assembly of the apparatus and said second unit is positioned in the contact position, wherein the second contact force has a component oriented in a moving direction of moving said second unit away from the spacing position toward the contact position, and the component is greater than that of the first contact force. 
         [0007]    According to another aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of the apparatus of an image forming apparatus, said process cartridge comprising a first unit provided with an image bearing member; and a second unit which is provided with a developer carrying member for carrying a developer and which is connected with said first unit so as to be movable between a contact position in which said developer carrying member is contacted with said image bearing member and a spacing position in which said developer carrying member is spaced from said image bearing member, said second unit including a recess or opening into which a main assembly electrical contact provided in said main assembly of the apparatus to apply a voltage to said process cartridge when said process cartridge is mounted to said main assembly of the apparatus and second unit is positioned in the spacing position. 
         [0008]    According to another aspect of the present invention, there is provided an image forming apparatus to which a process cartridge is detachably mountable, wherein said process cartridge includes a first unit provided with an image bearing member and a second unit which is provided with a developer carrying member for carrying a developer and which is connected with said first unit so as to be movable between a contact position in which said developer carrying member is contacted with said image bearing member and a spacing position in which said developer carrying member is spaced from said image bearing member, said apparatus comprising a main assembly electrical contact for contacting to and applying a first contact force to a first contact portion provided in said second unit when said second unit is in the spacing position, and for contacting to a second contact portion provided in said second unit to electrically connect with said second contact portion, wherein the second contact force has a component oriented in a direction of moving said second unit away from the spacing position toward the contact position, and the component is greater than that of the first contact force. 
         [0009]    According to a further aspect of the present invention, there is provided an image forming apparatus to which a process cartridge is demountable, wherein said process cartridge includes a first unit provided with an image bearing member and a second unit which is provided with a developer carrying member for carrying a developer and which is connected with said first unit so as to be movable between a contact position in which said developer carrying member is contacted with said image bearing member and a spacing position in which said developer carrying member is spaced from said image bearing member, said apparatus comprising a main assembly electrical contact, capable of entering a recess or opening provided in said second unit, for applying a voltage to said process cartridge when said second unit is in the spacing position. 
         [0010]    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 THE DRAWINGS 
         [0011]      FIG. 1  is a drawing for describing the electrical contacts of the process cartridge, and the electrical contacts of the main assembly of the image forming apparatus, in the first preferred embodiment of the present invention. 
           [0012]      FIG. 2  is a schematic sectional view of the image forming apparatus in the first preferred embodiment of the present invention, and shows the general structure of the apparatus. 
           [0013]      FIG. 3  is a schematic sectional view of the process cartridge (which contains toner) in the first preferred embodiment of the present invention, and shows the general structure of the cartridge. 
           [0014]      FIG. 4  is a schematic perspective view of the process cartridge in the first preferred embodiment of the present invention. 
           [0015]      FIG. 5  is a schematic perspective view of the development unit in the first preferred embodiment of the present invention. 
           [0016]      FIG. 6  is a drawing for describing the operation for mounting the process cartridge into the main assembly of the image forming apparatus. 
           [0017]      FIG. 7  is a drawing for describing the operation for separating the photosensitive drum and development roller from each other, or placing them in contact with each other, in the first preferred embodiment of the present invention. 
           [0018]      FIG. 8  is a schematic perspective view of the process cartridge in the first preferred embodiment of the present invention. 
           [0019]      FIG. 9  is a drawing for describing the movement of the member of the process cartridge in the first preferred embodiment, which is for keeping the development roller separated from the photosensitive drum. 
           [0020]      FIG. 10  is a drawing for describing the electrical contacts of the main assembly of the image forming apparatus in the first preferred embodiment of the present invention. 
           [0021]      FIG. 11  is drawing for describing the electrical contacts of the process cartridge, and those of the main assembly of the image forming apparatus, in the first preferred embodiment of the present invention. 
           [0022]      FIG. 12  is a drawing for describing the electrical contacts of the development roller, about their structure. 
           [0023]      FIG. 13  is a drawing for describing the electrical contacts of the process cartridge, and those of the main assembly of the image forming apparatus, in the first preferred embodiment of the present invention. 
           [0024]      FIG. 14  is a drawing for describing the electrical contacts of the process cartridge, and those of the main assembly of the image forming apparatus, in the fourth preferred embodiment of the present invention. 
           [0025]      FIG. 15  also is a drawing for describing the electrical contacts of the process cartridge, and those of the main assembly of the image forming apparatus, in the fourth preferred embodiment of the present invention. 
           [0026]      FIG. 16  is a drawing for describing the electrical contacts of the development roller in the second preferred embodiment of the present invention, about their structure. 
           [0027]      FIG. 17  is a drawing for describing the electrical contacts of the development roller in the third preferred embodiment of the present invention, about their structure.  FIG. 18  is a drawing for describing the electrical contacts of the development roller in the fourth preferred embodiment of the present invention, about their structure. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Hereinafter, the preferred embodiments of the present invention are described in detail with reference to the appended drawings. However, the measurements, material, and shapes of the structural components of the image forming apparatus and process cartridge in the following preferred embodiments of the present invention, and their positional relationship, are to be modified as necessary according to the structure of the apparatus to which the present invention is applied, and also, according to various conditions under which the present invention is applied to the apparatus. That is, the following preferred embodiments of the present invention are not intended to limit the present invention in scope. 
         [0029]    The present invention relates to the structure of the electrical contacts of an image forming apparatus, and the structure of the electrical contacts of a process cartridge for the image forming apparatus. In this specification, an “image forming apparatus” means an electrophotographic image forming apparatus which forms an image on recording medium with the use of an electrophotographic image forming method. Examples of an electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for example, laser beam printer, LED printer, and the like), a facsimile apparatus, a word processor, etc. A “process cartridge” means a cartridge which comprises a drum unit and a development unit, which are integrally connected to each other. The drum unit has an electrophotographic photosensitive drum, whereas the development unit has one or more developing means. The process cartridge is structured so that it can be removably mounted in the main assembly of the electrophotographic image forming apparatus. Incidentally, a process cartridge may be provided with a processing means for processing the electrophotographic photosensitive drum. Examples of the processing means include a charging means, a cleaning means, a developer supplying member for supplying the development roller with developer, a developer regulating member for regulating the layer of the developer on the peripheral surface of the development roller, in the amount (thickness), in addition to the development roller. 
       EMBODIMENT 1 
       [0030]    First, the first preferred embodiment of the present invention is described. 
       (General Structure of Image Forming Apparatus) 
       [0031]    First, referring to  FIG. 2 , the overall structure of the electrophotographic image forming apparatus  100  (which hereafter will be referred to simply as image forming apparatus) in this embodiment. 
         [0032]      FIG. 2  is a schematic sectional view of the image forming apparatus  100  in this embodiment, and shows the general structure of the apparatus. The image forming apparatus  100  employs four process cartridges  7  ( 7   a,    7   b,    7   c,  and  7   d ), which are removably mountable in the main assembly of the apparatus  100  with the use of a process cartridge mounting member (unshown), as shown in  FIG. 2 . Referring to  FIG. 2 , the process cartridges  7  ( 7   a,    7   b,    7   c,  and  7   d ) are positioned in the main assembly  100 A of the image forming apparatus  100  (which hereafter will be referred to simply as apparatus main assembly  100 A) in parallel at a preset angle relative to the horizontal direction of the apparatus main assembly  100 A. The four process cartridges  7  are practically the same in structure and operation, except that they are different in the color of the developer (which hereafter will be referred to as toner) which they use. Therefore, in the following description of the preferred embodiments of the present invention, unless it is necessary to differentiate them, the suffixes a, b, c, and d, which indicate the color of the developers, one for one, will not be shown. 
         [0033]    Each process cartridge  7  has an electrophotographic photosensitive drum  1  as an image bearing member (which hereafter will be referred to simply as photosensitive drum  1 ), and processing means, more specifically, a charge roller  2 , a development roller  25 , a cleaning means, etc., which are in the adjacencies of the peripheral surface of the photosensitive drum  1 . The charge roller  2  is for uniformly charging the peripheral surface of the photosensitive drum  1 . The development roller  25 , which is a developer bearing member, is for bearing toner, and developing a latent image formed on the peripheral surface of the photosensitive drum  1  into a visible image with the use of the toner. The cleaning member  6  is for removing the toner remaining on the peripheral surface of the photosensitive drum  1  after the transfer of a toner image (developer image) formed on the peripheral surface of the photosensitive drum  1 , onto recording medium. The apparatus main assembly  100 A is provided with a scanner unit  3  for forming a latent image on the photosensitive drum  1  by selectively exposing numerous points of the peripheral surface of the photosensitive drum  1 , based on the information of the image to be formed. The scanner unit  3  is below the space for the process cartridges  7  in the apparatus main assembly  100 A. 
         [0034]    The apparatus main assembly  100 A is provided with a space for a cassette  17  which contains sheets S of recording medium. The space is in the bottom portion of the apparatus main assembly  100 A. The apparatus main assembly  100 A is also provided with a recording medium conveying means, which is positioned so that the sheet S of recording medium is conveyed upward from the cassette  17  by way of a second transfer roller  70  and a fixing portion  74 . The recording conveying means comprises: a feed roller  54  which feeds each of the sheets S of recording medium in the cassette  17  into the apparatus main assembly  100 A while separating it from the rest; a pair of recording medium conveying rollers  76  for conveying each sheet S of recording medium further into the apparatus main assembly  100 A; a pair of registration rollers  76  for synchronizing the movement of a latent image formed on the peripheral surface of the photosensitive drum  1 , with the movement of the sheet S of recording medium. Further, the apparatus main assembly  100 A is provided with an intermediary transfer unit  5  as an intermediary means for transferring a toner image formed on the peripheral surface of the photosensitive drum  1 , from the photosensitive drum  1  onto the sheet. S of recording medium. The intermediary transfer unit  5  is above the space for the process cartridge  7 . The intermediary transfer unit  5  has a driver roller  56 , a follower roller  57 , four first transfer rollers  58 , a second transfer roller  70 , a backup roller  59 , and a transfer belt  9 . The four first transfer rollers  58  correspond in position to the four photosensitive drums  1 , one for one. The backup roller  59  corresponds in position to the second transfer roller  70 . The transfer belt  9  wraps around these rollers, being thereby suspended and kept stretched, by them. 
         [0035]    The transfer belt  9  is circularly moved in such a manner that it faces all the photosensitive drums  1  and comes into contact with them. As voltage is applied to the first transfer roller  58 , the toner on the photosensitive drum  1  is transferred (first transfer) onto the transfer belt  9 . Then, as voltage is applied between the backup roller  59  (which is on inward side of loop which transfer belt  9  forms) and the second transfer roller  70 , the toner on the transfer belt  9  is transferred (second transfer) onto the sheet S of recording medium. 
         [0036]    The image forming operation of the image forming apparatus  100  is as follows: While each photosensitive drum  1  is rotated, the peripheral surface of the photosensitive drum  1  is uniformly charged by the charge roller  2 . Then, the numerous points of the uniformly charged portion of the peripheral surface of the photosensitive drum  1  are selectively exposed by the scanner unit  3 . Consequently, an electrostatic latent image is formed on the photosensitive drum  1 . This latent image is developed by the development roller  25 . Thus, four monochromatic toner images, different in color, are formed on the four photosensitive drums  1 , one for one. In synchronism with the formation of the toner images, a sheet S of recording medium is conveyed by the pair of registration rollers  55 , to the second transfer position, in which the backup roller  59  and second transfer roller  70  are kept in contact with each other, with the presence of the transfer belt  9  between the two rollers  59  and  70 . Then, transfer bias voltage is applied to the second transfer roller  7  while the sheet S of recording medium is conveyed through the second transfer position. Thus, the four monochromatic toner images, different in color, on the transfer belt  9  are transferred (second transfer) onto the sheet S of recording medium. This is how a multicolor image is formed on the sheet S of recording medium. After the formation of a multicolor image on the sheet S of recording medium, the sheet S is conveyed through the fixing portion  74 . While the sheet S is conveyed through the fixing portion  74 , the multicolor image is subjected to heat and pressure, whereby it becomes fixed to the sheet S. Thereafter, the sheet S is discharged into a delivery tray  75  by a pair of discharge roller  72 . Incidentally, the fixing portion  74  is in the top portion of the apparatus main assembly  100 A. 
       (Process Cartridge) 
       [0037]    Next, referring to  FIGS. 3-5 , the process cartridge  7  in this embodiment is described.  FIG. 3  is a schematic sectional view of the process cartridge  7 , which stores toner. Incidentally, the process cartridges  7   a,    7   b,    7   c,  and  7   d,  which store yellow, magenta, cyan, and black toners, respectively, are the same in structure.  FIG. 4(   a ) is a schematic perspective view of the process cartridge  7  in this embodiment, prior to the mounting of the process cartridge  7  into the apparatus main assembly  100 A, and shows the general structure of the process cartridge  7 .  FIG. 4(   b ) is a schematic perspective view of the process cartridge  7  in this embodiment after the proper positioning of the process cartridge  7  in the apparatus main assembly  100 A.  FIG. 5  is a schematic perspective view of the development unit in this embodiment. The process cartridge  7  has: a drum unit  26  as the first unit; and a development unit  4  as the second unit. The drum unit  26  has the photosensitive drum  1 , charge roller  2 , and cleaning member  6 . The development unit  4  has the development roller  25 . 
         [0038]    The drum unit  26  has a cleaning means frame  27 , to which the photosensitive drum  1  is rotatably attached with the presence of a front drum bearing  10  and a rear drum bearing  11  between the photosensitive drum  1  and cleaning means frame  27 . One of the lengthwise end portions of the photosensitive drum  1  is provided with a drum coupling  16 , and the other is provided with a flange  85  ( FIG. 4 ). The charge roller  2  and cleaning member  6  are in the adjacencies of the peripheral surface of the photosensitive drum  1 , as described above, and are in contact with the peripheral surface of the photosensitive drum  1 . As the residual toner on the peripheral surface of the photosensitive drum  1  is removed by the cleaning member  6 , it falls into the waste toner chamber  27   a . As the driving force from a motor (unshown) of the apparatus main assembly  100 A, which is the source of the drum driving force, is transmitted to the drum unit  26 , the photosensitive drum  1  is rotated in synchronism with the progression of the on-going image forming operation. The charge roller  2  is rotatably attached to the cleaning means frame  27  with the presence of a pair of charge roller bearings  28  between the charge roller  2  and frame  27 . The charge roller  2  is kept pressed upon the photosensitive drum  1  by a charging roller pressing member  46 , and is rotated by the rotation of the photosensitive drum  1 . 
         [0039]    The development unit  4  comprises: the development roller  25  which rotates in contact with the photosensitive drum  1  in the direction indicated by an arrow mark B in  FIG. 3 ; and a development unit frame  31  which supports the development roller  25 . The development roller  25  is rotatably supported by the development unit frame  31 . More specifically, the front and rear walls of the development unit frame  31  are provided with front and rear development roller bearings  12  and  13 , respectively, by which the development roller  25  is supported ( FIG. 5 ). Further, the development unit  4  is provided with a toner supply roller  34  and a development blade  35 , which are in the adjacencies of the peripheral surface of the development roller  25 . The toner supply roller  34  is in contact with the peripheral surface of the development roller  25  and rotates in the direction indicated by an arrow mark C in  FIG. 3 . The toner supply roller  34  is a member for supplying the peripheral surface of the development roller  25  with developer (toner). The development blade  35  is for regulating the layer of toner on the peripheral surface of the development roller  25 . It is a member for regulating the amount by which developer (toner) is borne on the peripheral surface of the development roller  25  per unit area of the peripheral surface of the development roller  25 . Further, the development unit  4  is provided with a toner conveying member  36  which is in the toner storage chamber  31   a  of the development unit frame  31 . The toner conveying member is for conveying toner in the toner storage chamber  31   a,  to the toner supply roller  34  while stirring the toner. 
         [0040]    Referring to  FIG. 3 , the development unit  4  is attached to the drum unit  26  in such a manner that the development unit  4  is rotationally movable relative to the drum unit  26 . More specifically, development unit supporting front and rear pins  14  and  15  are pressed into the holes of the cleaning means frame  27 , and then, are fitted in the holes  12   a  and  13   a  of the aforementioned front and rear development roller bearings  12  and  13 , respectively, of the development unit  4 . Thus, the development unit  4  is rotationally movable relative to the cleaning means frame  27  about the development unit supporting pins  14  and  15  ( FIG. 3 ). Further, the cleaning means frame  27  is provided with front and rear drum bearings  10  and  11 , respectively, which rotatably support the photosensitive drum  1 . The rear drum bearing  11  supports the drum coupling  16  which is in connection to the photosensitive drum  1 , whereas the front drum bearing  10  supports the flange  85 . The drum coupling  16  is for transmitting rotational driving force (first rotational driving force) from the apparatus main assembly  100 A to the photosensitive drum  1  ( FIG. 4 ). 
         [0041]    The process cartridge  7  is structured so that when the process cartridge  7  is being used for image formation, the development unit  4 , which is shown in  FIG. 5 , is kept pressed toward the drum unit  26  by a compression spring  38 , with which the development unit frame  31  is provided, and a tension spring  39  with which the front development roller bearing  12  is provided. The compression spring  38  is for providing the pressure for keeping the development roller  25  in contact with the photosensitive drum  1 . The compression spring  38  is between the cleaning means frame  27  and development unit frame  31 , and remains compressed. One end of the tension spring  39  is attached to front development roller bearing  12 , whereas the other end is attached to the front drum bearing  10 . The forces generated by the compression spring  38  and tension spring  39  keep the development roller  25  in contact with the photosensitive drum  1 . 
         [0042]    The front end of the development unit  4  is provided with an electrical contact  40  for the development roller  25  (which hereafter is referred to as development roller contact  40 ), an electrical contact  41  for the toner supply roller  34  (which hereafter is referred to as toner supply roller contact  41 ), and an electrical contact  42  for the development blade  35  (which hereafter is referred to as development blade contact  42 ). The development roller contact  40  is for applying bias voltage to the development roller  25 . The toner supply roller contact  41  is for applying bias voltage to the toner supply roller  34 . The development blade contact  42  is for applying bias voltage to the development blade  35 . In a case where the image forming apparatus  100  is of the contact development type which places the development roller  25  in contact with the photosensitive drum  1  to develop a latent image on the photosensitive drum  1 , it is desired that the photosensitive drum  1  is a rigid member, whereas the development roller  25  is an elastic roller, that is, a roller having an elastic layer. As the development roller  25 , a roller having a single layer of solid rubber, a roller having a solid rubber layer and a resin layer coated on the solid rubber layer in consideration of the charging of toner by the roller, or the like roller, is usable. 
         [0043]    Next, the image formation sequence of the process cartridge  7  is described ( FIGS. 2 and 3 ). As the information of the image to be formed is sent to the image forming apparatus  100 , the motor (unshown) of the apparatus main assembly  100 A begins to rotate, whereby rotational driving force is transmitted to the development roller  25 , toner supply roller  34 , and toner conveying member  36 . Then, the charge bias is applied to the charge roller  2  from the apparatus main assembly  100 A, whereby the peripheral surface of the photosensitive drum  1  is uniformly charged. Then, the uniformly charged portion of the peripheral surface of the photosensitive drum  1  is exposed to the beam of light projected from the scanner unit  3  while being modulated with the information of the image to be formed. Consequently, a latent image is formed on the photosensitive drum  1 . 
         [0044]    The toner in the toner storage portion  31   a  is conveyed to the toner supply roller  34  by the rotation of the toner conveying member  36 . To the toner supply roller  34 , the bias voltage is applied. As the toner supply roller  34  is rotated, the peripheral surface of the rotating development roller  25  is supplied with the toner from the toner supply roller  34 . After being supplied to the peripheral surface of the development roller  25 , the toner on the peripheral surface of the development roller  25  is frictionally charged by the development blade  35  to which the bias voltage is being applied. Further, to the development roller  25 , the development bias is applied from the apparatus main assembly  100 A, whereby the electrostatic latent image formed on the photosensitive drum  1  is developed. 
         [0045]    The development roller  25  is positioned so that its peripheral surface squarely faces the peripheral surface of the photosensitive drum  1 . Further, the development unit  4  is structured so that the development roller  25  develops the electrostatic latent image formed on the peripheral surface of the photosensitive drum  1 , by being placed in contact with the peripheral surface of the photosensitive drum  1 . 
         [0000]    (Mechanism for Mounting Process Cartridge into Main Assembly of Image Forming Apparatus) 
         [0046]    Next, referring to  FIG. 6 , the mechanism for to mounting the process cartridge  7  into the apparatus main assembly  100 A is described.  FIG. 6  is a schematic drawing for describing the operation for mounting the process cartridge  7  into the apparatus main assembly  100 A.  FIG. 6(   a ) is a drawing for describing the process cartridge  7  which is in the state prior to its mounting into the apparatus main assembly  100 A. Referring to  FIG. 6(   a ), the process cartridge  7  is inserted into the apparatus main assembly  100 A in the direction indicated by an arrow mark E through the opening  82   a  with which the front plate  82  of the apparatus main assembly  100 A is provided. During the insertion of the process cartridge  7 , the process cartridge  7  is guided by the process cartridge guiding member  81  of the apparatus main assembly  100 A; a cartridge guiding portion  27   b , which is an integral part of the cleaning means frame  27  of the process cartridge  7 , is guided by the cartridge guiding member  81  by being rested on the guiding member  81 . The process cartridge guiding member  81 , that is, the process cartridge guiding member on the main assembly side, is the member for removably mounting the process cartridge  7  into the apparatus main assembly  100 A. 
         [0047]      FIG. 6(   b ) is a drawing for describing the process cartridge  7  which is being mounted into the apparatus main assembly  100 A. The cartridge guiding member  81  of the apparatus main assembly  100 A is provided with a slanted surface  81   a,  which is at the downstream end of the guiding member  81  in terms of the direction in which the process cartridge  7  is inserted into the apparatus main assembly  100 A. The slanted surface  81   a  inclines upward in terms of the cartridge insertion direction. Further, the cleaning means frame  27  is provided with a slanted surface  27   c , which is at the upstream end of the cleaning means frame  27 . The slanted surface  27   c  inclines downward in terms of the opposite direction to the cartridge insertion direction. As the process cartridge  7  is inserted into the apparatus main assembly  100 A, the guiding portion  27   b  of the cleaning means frame  27  comes into contact with the slanted surface  81   a,  and slides diagonally upward by being guided by the slanted surface  81   a,  whereas the slanted surface  27   c  comes into contact with the cartridge guiding member  81 , whereby the trailing end portion of the process cartridge  7  slides diagonally upward by being guided by the slanted surface  27   c.  Thus, the process cartridge  7  is moved toward the intermediary transfer unit  5  (upward). 
         [0048]      FIG. 6(   c ) is a drawing for describing the process cartridge  7  after it is properly positioned in the apparatus main assembly  100 A. As the process cartridge  7  is inserted further into the apparatus main assembly  100 A after it is moved toward the intermediary transfer unit  5 , a stopper  27   d,  which is an integral part of the cleaning means frame  27  comes into contact with the rear plate  83  of the apparatus main assembly  100 A, which completes the mounting of the process cartridge  7  into the apparatus main assembly  100 A. When the process cartridge  7  is in the state shown in  FIG. 6(   c ), the bearing positioning portion  11   a  of the rear drum bearing  11  is in contact with the bearing pressing (positioning) member  91  of the rear plate  83 , which is under the upward pressure generated by a compression spring  92 . Therefore, the rear drum bearing  11  is kept pressed upward. Further, the cartridge positioning portion  11   b,  which is a part of the top portion of the rear drum bearing  11 , is in contact with the cartridge positioning portion  83   a  of the rear plate  83 . Therefore, the rear end of the process cartridge  7  is properly positioned relative to the apparatus main assembly  100 A. 
         [0049]    Also right before the cartridge stopper portion  27   d  comes into contact with the rear plate  83  of the apparatus main assembly  100 A, the bearing pulling member  93  of the front plate  82  fits into the hole of the bearing pulling portion of the front drum bearing  10 . Thus, the bearing pulling portion  10   a  of the front drum bearing  10  is moved upward by the bearing pulling portion  93  which is under the upward pressure generated by the tension spring  94  of the front plate  82 . Therefore, the stopper portion  10   b  of the front drum bearing  10 , which is the cartridge positioning portion of the front drum bearing  10 , is placed in contact with the bearing positioning portion  82   b  of the front plate  82 , whereby the front end of the process cartridge  7  is precisely positioned relative to the apparatus main assembly  100 A. 
         [0050]    Next, referring to  FIG. 4(   b ), the cartridge positioning portion  83   a  (contoured by two-dot chain line in  FIG. 4(   b )) has a roughly V-shaped groove, into which the bearing positioning portion  11   b  of the rear drum bearing  11  fits. The cartridge  7  is structured so that as the bearing pulling member  93  of the front plate  82  fits into the hole of bearing pulling portion  10   a  of the front drum bearing  10 , the front drum bearing  10  is pulled in the direction indicated by an arrow mark P. Further, regarding the positioning of the front drum bearing  10 , the front drum bearing  10  fits into the V-shaped groove of the drum positioning portion  82   b  (contoured by double-dot chain line in  FIG. 4(   b )) of the front plate  82 . Further, the pressure necessary for precisely positioning the front and rear drum bearings  10  and  11  are applied in the direction indicated by the arrow marks P and R from the apparatus main assembly  100 A. Therefore, the front and rear drum bearings  10  and  11  to which rotatably support the photosensitive drum  1 , and by which the process cartridge  7  is precisely positioned relative to the apparatus main assembly  100 A, are accurately positioned relative to the apparatus main assembly  100 A. Further, one of the lateral plates of the cleaning means frame  27  is provided with a boss  27   g  which functions as a stopper for preventing the process cartridge  7  from rotating. The boss  27   g  fits into the groove of the process cartridge rotation controlling member  51  of the apparatus main assembly  100 A, whereby the process cartridge  7  is prevented from rotating in the apparatus main assembly  100 A. 
         [0000]    (Mechanism for Separating Photosensitive Drum and Development Roller of Process Cartridge from Each Other, or Placing Them in Contact with Each Other) 
         [0051]    Next, referring to  FIG. 7 , the mechanism for separating the photosensitive drum  1 . (drum unit  26 ) and development roller  25  (development unit  4 ) of the process cartridge  7  from each other, or placing them in contact with each other, is described. Hereafter, this mechanism may be referred to simply as “separation-contact mechanism”,  FIG. 7(   a ) is a schematic sectional view of the process cartridge  7  in this embodiment, which is for describing how the photosensitive drum  1  and development roller  25  are separated from each other, and kept separated from each other.  FIG. 7(   b ) is a schematic sectional view of the process cartridge  7  in this embodiment, which is for describing how the photosensitive drum  1  and development roller  25  are placed in contact with each other, and kept in contact with each other. Referring to  FIG. 7(   a ), the image forming apparatus  100  has a member  8  for keeping the development roller  25  separated from the photosensitive drum  1 . Hereafter, the member  8  is referred to as the separation member As soon as an image forming operation is ended, the separation member  8  is moved in the direction indicated by an arrow mark N, and the separation force catching portion  31   b  of the development unit  4  of the process cartridge  7  is pressed by the separation member  8 . Thus, the development unit  4  is rotationally moved into the position in which it keeps the development roller  25  separated from the photosensitive drum  1 . Hereafter, this position of the development unit  4  is referred to as the “separation position”. 
         [0052]    Next, referring to  FIG. 7(   b ), as the separation member  8  separates from the separating force catching portion  31   b  by being moved in the direction indicated by an arrow mark M, the development unit  4  is rotationally moved in the direction indicated by an arrow mark T, about the axial lines of the holes  12   a  and  13   a  of the front and rear development unit bearings  12  and  13 , respectively, by the resiliency of the compression spring  38 , and the resiliency of the tension spring  39 . As the development unit  4  is moved as described above, the development roller  25  comes into contact with the photosensitive drum  1 . Hereafter, the position in which the development unit  4  is when the development roller  25  is kept in contact with the photosensitive drum  1  is referred to as the “contact position”. Since the image forming apparatus  100  and process cartridge  7  are structured so that the development roller  25  is separated from, or placed in contact with, the photosensitive drum  1  as described above, the development unit  4  can be kept in the separation position (shown in  FIG. 7(   a )) except for during image formation. Therefore, the development roller  25  is unlikely to be deformed by the contact between the development roller  25  and photosensitive drum  1 . Therefore, the image forming apparatus  100  in this embodiment is unlikely to output low quality images, the low quality of which is attributable to the deformation of the development roller  25 . 
         [0000]    (Member for Separating, and Keeping Separated, Development Roller from Photosensitive Drum) 
         [0053]      FIG. 8(   a ) is a schematic perspective view of the process cartridge  7  prior to the mounting (insertion) of the process cartridge  7  into the apparatus main assembly  100 A. The process cartridge  7  is provided with a member  64  for keeping the development unit  4  locked in the separation position. Hereafter, the member  64  is referred to as a cartridge locking member  64 . When the process cartridge  7  is in the state shown in  FIG. 8(   a ), the cartridge locking member  64  is in the hole  27   e  of the lateral plate of the cleaning means frame  27 , and keeps the development roller  25  separated from the photosensitive drum  1 . The position of the cartridge locking member  64 , which is shown in  FIG. 8(   a ), is referred to as the “engagement position”. 
         [0054]      FIG. 8(   b ) is a schematic perspective view of the process cartridge  7  after the disengagement of the cartridge locking member  64  has allowed the development roller  25  to come into contact with the photosensitive drum  1 . Referring to  FIG. 8(   b ), the apparatus main assembly  100 A is provided with a member  65  which is for disengaging the cartridge locking member  64 , and comes into contact with the cartridge locking member  64  when the process cartridge  7  is mounted into the apparatus main assembly  100 A. More specifically, the apparatus main assembly  100 A and process cartridge  7  are structured so that as the process cartridge  7  is inserted into the apparatus main assembly  100 A, the member  65  for disengaging the cartridge locking member  64  disengaging the cartridge locking member  64  from the hole  27   e  by coming into contact, and pressing on, the cartridge locking member  64  right before the process cartridge  7  is precisely positioned relative to the apparatus main assembly  100 A by the cartridge positioning portions  82   b  and  83   a  ( FIG. 6)  of the apparatus main assembly  100 A. The position of the cartridge locking member  64  after its disengagement from the hole  27   e,  which is shown in  FIG. 8(   b ), is referred to as the disengagement position of the cartridge locking member  64 . As the cartridge locking member  64  is moved out of the hole  27   e,  it becomes possible for the development roller  25  to come into contact with the photosensitive drum  1 . However, the apparatus main assembly  100 A is structured so that when the process cartridge  7  is in its image forming position in the apparatus main assembly  100 A, the separation member  8  of the apparatus main assembly  100 A is in the position in which it presses on the separation force catching portion  31   b  of the development unit frame  31  ( FIG. 7(   a )). Therefore, even if the cartridge locking member  64  is moved out of the hole  27   e  by the mounting of the process cartridge  7  into the apparatus main assembly  100 A, the development roller  25  does not immediately come into contact with the photosensitive drum  1  ( FIG. 7(   a )). 
         [0055]    Next, referring to  FIG. 9 , the method for disengaging the cartridge locking member  64  of the process cartridge  7  is described.  FIG. 9(   a ) is a schematic drawing of the cartridge locking member  64 , cartridge locking member disengaging member  65 , and cleaning means frame  27 , when the cartridge locking member  64  is in engagement with the cleaning means frame  27 .  FIG. 9(   b ) is a schematic drawing of the cartridge locking member  64 , cartridge locking member disengaging member  65 , and cleaning means frame  27  when the cartridge locking member disengaging member  65  is pressing on the cartridge locking member  64 .  FIG. 9(   c ) is a schematic drawing of the cartridge locking member  64 , cartridge locking member disengaging member  65 , and cleaning frame  27  when the cartridge locking member  64  has been disengaged from the cleaning means frame  27  by the cartridge locking member disengaging member  65 .  FIG. 9(   a ) shows a boss  64   a  with which the cartridge locking member  64  is provided. The boss  64   a  is in the groove  31   c  of the development unit frame  31 , and is rotatably supported by the development unit frame  31 . It remains in the groove  31   c  by being kept pressed by the boss pressing portion  48   b  of the side cover  48 . The engaging portion  64   b  of the cartridge locking member  64  is in the hole  27   e  of the cleaning means frame  27 . 
         [0056]    Next, referring to  FIG. 9(   b ), as the process cartridge  7  is moved in the direction indicated by the arrow mark E when the cartridge locking member  64  is in the state shown in  FIG. 9(   a ), the cartridge locking member disengaging member  65  comes into contact with the cartridge locking member  64 . Then, the cartridge locking member disengaging member  65  is moved into the hole  27   e  while pressing on the cartridge locking member  64 . Thus, the cartridge locking member  64  is rotated about the boss  64   a  by the cartridge locking member disengaging member  65 , being thereby disengaged from the cleaning member  27 . 
         [0057]    Consequently, it becomes possible for the development unit frame  31  to be moved in the direction indicated by an arrow mark L, that is, the direction for placing the development roller  25  in contact with the photosensitive drum  1 . 
         [0058]    As an image forming operation is started by a print signal after the completion of the mounting of the process cartridge  7 , the separation member  8  ( FIG. 7(   b )) is moved in the direction indicated by the arrow mark M in synchronism with the timing with which the development operation is started. Thus, the separation member  8  moves away from the separation force catching portion  31   b.  Therefore, the development unit  4  is moved into the contact position by the resiliency of the compression spring  38  and the resiliency of the tension spring  39  ( FIG. 7(   b )), whereby the development roller  25  is placed in contact with the photosensitive drum  1 , being enabled to develop the latent image on the photosensitive drum  1 . 
         [0059]    As soon as the development of the latent image on the photosensitive drum  1  ends, the separation member  8  is moved in the direction indicated by the arrow mark N in  FIG. 7(   a ), pressing thereby on the separation force catching portion  31   b.  Consequently, the development unit  4  is moved back into the separation position where the development roller  25  is kept separated from the photosensitive drum  1 . Unless the development unit  4  is being used for image formation, it is kept in the separation position, that is, the position in which the development roller  25  is kept separated from the photosensitive drum  1 . 
         [0060]    As described above, in this embodiment, the development unit  4  can be easily placed in the state in which the development roller  25  is kept separated from the photosensitive drum  1 , or the state in which the development roller  25  is kept in contact with the photosensitive drum  1 . Therefore, it is unnecessary to strictly select the material for the elastic layer of the development roller  25  in order to prevent the deformation of the elastic layer. 
       (Structure of Electrical Contacts of Process Cartridge and Apparatus Main Assembly) 
       [0061]    Next, the structure of the electrical contacts of the process cartridge  7  and apparatus main assembly  100 A is described.  FIG. 10(   a ) is a schematic perspective view of the electrical contacts, and their adjacencies, of the apparatus main assembly  100 A in this embodiment.  FIG. 10(   b ) is a schematic drawing of the electric contacts of the apparatus main assembly  100 A in this embodiment. The primary characteristic feature of this embodiment is that the contact pressure between the electrical contacts of the apparatus main assembly  100 A and the electrical contacts of the process cartridge  7  is utilized as an additional force for keeping the development roller  25  pressed on the photosensitive drum  1 . Next, this feature is described in detail. 
         [0062]    The process cartridge  7  has the above described electrical contact  40  for the development roller  25 , electrical contact  41  for the toner supply roller  34 , and electrical contact  42  for the development blade  35  ( FIG. 5 ). These electrical contacts are at one of the lengthwise ends of the process cartridge  7  in terms of the lengthwise direction of the development roller  25 . Referring to  FIG. 10(   a ), the electrical contacts of the apparatus main assembly  100 A are on the inward surface of the rear plate  83 , which is on the downstream side of the apparatus main assembly  100 A in terms of the direction in which the process cartridge  7  is inserted into the apparatus main assembly  100 A. The development bias contact  43 , toner supply roller bias contact  44 , and development blade bias contact  45 , which are the electrical contacts of the apparatus main assembly  100 A, are supported by the electrical contact holder  49 , which has a cover  50 . The electrical contacts of the apparatus main assembly  100 A are in connection to the high voltage circuit (unshown) in the apparatus main assembly  100 A, so that they can be supplied with bias voltage from the high voltage circuit. 
         [0063]    Next, the structure of the development roller contact  40  of the process cartridge  7  and the development bias contact  43  of the apparatus main assembly  100 A are described as the examples of the structure of the electrical contacts in this embodiment. That is, in this embodiment, the structure of the toner supply roller contact  41 , the structure of the toner supply bias contact  44 , and the structural relationship between the contacts  41  and  44 , are the same as those of the development roller contact  40  and development bias contact  43 , and so are those of the development blade contact  42  and development blade bias contact  45 . In terms of practicality, all that is necessary is that at least one of the electrical contacts mentioned above is structured as will be described next. 
         [0064]    Referring to  FIG. 10(   b ), the development bias contact  43  in the apparatus main assembly  100 A comprises: a compression spring  43   a  for providing the pressure for keeping the development bias contact  43  in contact with the development roller contact  40 ; and a portion  43   b  which actually contacts the development roller contact  40 . In other words, the development bias contact  43  is structured so that as the development bias contact  43  is placed in contact with (pressed upon) the development roller contact  40  of the process cartridge  7 , a preset amount of contact pressure is generated between the development bias contact  43  and development roller contact  40  by the resiliency of the compression spring  43   a.  Further, the development bias contact  43  is provided with a portion  43   c  by which the development bias contact  40  contacts the high voltage circuit (unshown) to be supplied with electrical power. 
         [0065]    Next, the state of the process cartridge  7 , in which the electrical contacts of the process cartridge  7  are in contact with the corresponding electrical contacts of the apparatus main assembly  100 A, is described.  FIG. 11(   a ) is a schematic perspective view of the process cartridge  7  when the development unit  4  is in the separation position. It is for describing the state of the electrical contacts of the process cartridge  7  and those of the apparatus main assembly  100 A when the development unit  4  is in the separation position.  FIG. 11(   b ) is a schematic perspective view of the process cartridge  7  when the development unit  4  is in the contact position. It is for describing the state of the electrical contacts of the process cartridge and those of the apparatus main assembly  100 A when the development unit  4  is in the contact position. For the sake of convenience in terms of description,  FIG. 11  does not show the rear plate  83 . 
         [0066]    Referring to  FIG. 11(   a ), at the completion of the mounting of the process cartridge  7  into the apparatus main assembly  100 A, the separation member  8  of the apparatus main assembly  100 A is in contact with the separation force catching portion  31   b,  and the development unit  4  is in the separation position, that is, the position in which the development roller  25  is kept separated from the photosensitive drum  1 . When the development unit  4  is in the separation position, the development bias contact  43  of the apparatus main assembly  100 A is in contact with the area  48   a,  as the first electrical contact (hatched portion in drawing) of the process cartridge  7 , which is on the outward surface of the side cover  48  of the peripheral surface  7 . The toner supply roller bias contact  44  is in contact with the area  48   c  (hatched portion in drawing) of the side cover  48 . Further, the development blade bias contact  45  is in contact with the unshown area of the side cover  48 . 
         [0067]    The apparatus main assembly  100 A and process cartridge  7  are structured so that the area  48   a  is flat, and the plane of the area  48   a  of the side cover  48  is perpendicular to the direction in which the compression spring  43   a  of the development bias contact  43  is kept compressed. That is, the plane of the area is  48   a  is not parallel to the direction in which the pressure is applied to place the development roller  25  in contact with the photosensitive drum  1 . In this embodiment, the area  48   a  is flat, and is perpendicular to the rotational axis of the development roller  25 . Further, the area with which the toner supply roller bias contact  44  comes into contact, and the area with which the development blade bias contact  45  comes into contact, are similar to the area  48   a.    
         [0068]    Next, referring to  FIG. 11(   b ), prior to the starting of an image forming apparatus, the separation member  8  is moved in the direction indicated by the arrow mark M, being thereby separated from the separation force catching portion  31   b.  Thus, the development unit  4  is rotationally moved in the direction indicated by the arrow mark T, being thereby placed in the contact position. Thus, the development roller  25  is placed in contact with the photosensitive drum  1 . It is when the development unit  4  is in the contact position that the development roller contact  40  of the development unit  4 , which is the second electrical contact of the development unit  4 , is placed in contact with the development bias contact  43  to provide electrical connection between the two electrical contacts  40  and  43 . 
         [0069]    It should be noted here that because bias voltage has to begin to be applied to the development roller  25  before the development roller  25  comes into contact with the photosensitive drum  1 , the development roller contact  40  is positioned so that it comes into contact with the development bias contact  43  while the development unit  4  is moved from the separation position to the contact position. If the development roller  25  comes into contact with the photosensitive drum  1  while bias voltage is not being applied to the development roller  25 , it is liable that toner particles with no electrical charge might be transferred from the development roller  25  onto the photosensitive drum  1 . This is why the image forming apparatus  100  and process cartridge  7  are structured so that the development bias contact  43  and development roller contact  40  come into contact with each other before the development roller  25  comes into contact with the photosensitive drum  1 . 
         [0070]    Next, the development roller contact  40  and side cover  48  of the process cartridge  7  are described about their structures.  FIG. 12  is a schematic sectional view of one of the lengthwise end portions of the process cartridge  7 , which is for describing the structure of the development roller contact  40  and the structure of the side cover  48 . Referring to  FIG. 12 , the development roller  25  has a metallic core  25   a,  which is rotatably supported by the development roller bearings  13 . One of the lengthwise ends of the metallic core  25   a  of the development roller  25  is fitted with an Oldham&#39;s coupling  23  through which driving force is transmitted to the development roller  25  from the apparatus main assembly  100 A. The development roller contact  40  is on the rear development roller bearing  13 . It has: an area  40   b,  by which it contacts the metallic core  25   a;  and an area  40   a,  as the second electrical contact of the developer roller contact  40 , by which the developer roller contact  40  contacts the development bias contact  43 . 
         [0071]    The side cover  48  is provided with the area  48   a  of electrical contact of the process cartridge  7 , on which the portion  43   b  of the development bias contact  43  slides. The process cartridge  7  is designed so that the normal line of the area  48   a  of electrical contact of the process cartridge  7  is parallel to the rotational axis  25   c  of the development roller  25 , and also, so that the normal line H 2  of the area  40   a  of the development roller contact  40  is angled relative to the normal line H 1  of the area  48   a  of electrical contact (parallel to direction in which development unit  4  is moved from contact position to separation position). 
         [0072]    Next, referring to  FIGS. 13 and 1 , the positional relationship between development bias contact  43  and development roller contact  40  when the development unit  4  is in the separation position, and the state of contact between the development bias contact  43  and development roller contact  40  when the development unit  4  is in the contact position, and the contact pressure which is present between the development bias contact  43  and development roller contact  40  when the development unit  4  is in the contact position, are described.  FIG. 13  is a schematic sectional view of the electrical contacts of the process cartridge  7 , electrical contacts of the apparatus main assembly  100 A, and their adjacencies. It is for describing the electrical contacts.  FIG. 1  is a schematic sectional view of the electrical contacts of the process cartridge  7 , electrical contacts of the apparatus main assembly  100 A, and their adjacencies. It is for describing the state of contact between the electrical contacts of the process cartridge  7  and the electrical contacts of the apparatus main assembly  100 A. 
         [0073]    Referring to  FIG. 13 , when the development unit  4  is in the separation position, that is, the position in which the development roller  25  is kept separated from the photosensitive drum  1 , the area  48   a  of electrical contact is in contact with the portion  43   b  of the development bias contact  43 , and is subjected to the contact pressure P 1  generated between the portion  43   b  and area  438   a  by the resiliency of the compressed compression spring  43   a.  The direction of the contact pressure P 1  does not coincide with the direction in which the development roller  25  is moved to be placed in contact with the photosensitive drum  1 . That is, the process cartridge  7  is structured so that the direction of the contact pressure P 1  to which the area  48   a  of electrical contact is subjected by the development bias contact  43  is not parallel to the direction (indicated by arrow mark T in drawings) in which the development unit  4  is moved from the separation position to the contact position. 
         [0074]    In this embodiment, the direction of the contact pressure P 1  is perpendicular to the lengthwise direction of the process cartridge  7  (rotational axis of development roller  25  and rotational axis of photosensitive drum  1 ), that is, the direction in which the development unit  4  is moved to place the development roller  25  in contact with the photosensitive drum  1 . When the process cartridge  7  is not being used for image formation, the development unit  4  is kept in the separation position by the separation member  8  in the apparatus main assembly  100 A. Since the contact pressure P 1  which the development bias contact  43  generates is parallel to the lengthwise direction of the process cartridge  7 , it is different in direction from the force applied for placing the development unit  4  development roller  25  in contact with the photosensitive drum  1 . Therefore, the separation member  8  is not subjected to the contact pressure P 1 . 
         [0075]    While the development unit  4  is moved from the separation position to the contact position, the development unit  4  remains in contact with the portion  43   b  of the development bias contact  43 , creating thereby a frictional resistance Q. If the amount of force applied to place the development roller  25  in contact with the photosensitive drum  1  is relatively small, this friction resistance Q interferes with the movement of the development unit  4 , making it impossible to ensure that the development roller  25  is placed in contact with the photosensitive drum  1 . Thus, one of the characteristic features of this embodiment is that the area  40   a  of the development roller contact  40  is angled relative to the direction in which the development bias contact  43  comes into contact with the development unit  4  (area  40   a ). Therefore, when the development bias contact  43  comes into contact with the area  40   a  of the development roller contact  40 , the effect of the frictional resistance Q which occurs between the development bias contact  43  and area  40   a  is significantly smaller than the effect of the comparable frictional resistance in any process cartridge in accordance with the prior art. 
         [0076]    As described above, the area  40   a  of the development roller contact  40  is angled relative to the direction in which the development bias contact  43  comes into contact with the development unit  4  (area  40   a ). More specifically, the area  40   a  of the development roller contact  40  is angled so that the upstream end of the area  40   a,  in terms of the direction in which the development unit  4  is moved from the separation position to the contact position, is farther from the development bias contact  43  than the downstream end of the area  40   a.  Next, referring to  FIG. 1 , as the development bias contact  43  comes into contact, and presses on, the area  40   a  of the development roller contact  40  while the development unit  4  is moved from the separation position to the contact position, the area  40   a  of the development roller contact  40  is subjected to a contact pressure P 2  from the development bias contact  43 . A referential code P 3  stands for a component of the contact pressure P 2 , the direction of which is parallel to the lengthwise direction of the process cartridge  7 , and a referential code P 4  stands for a component of the contact pressure P 2 , which is perpendicular to the component P 3 . In this embodiment, the component P 4  is parallel to the direction in which the development roller  25  is moved to be placed in contact with the photosensitive drum  1 . 
         [0077]    That is, the process cartridge  7  is structured so that the component P 4  of the contact pressure P 2 , to which the area  40   a  of the development roller contact  40  is subjected by the development bias contact  43  when the development roller  25  is placed in contact with the photosensitive drum  1  for image formation, is parallel to the direction in which the development roller  25  is moved to be placed in contact with the photosensitive drum  1 . That is, the process cartridge  7  is structured so that the force to which the area  40   a  of the development roller contact  40  is subjected by the development bias contact  43  as the development bias contact  43  comes into contact with, and presses on, the area  40   a  of the development roller contact  40  while the development unit  4  is moved into the contact position, is parallel to the direction in which the development unit  4  is moved from the separation position to the contact position. 
         [0078]    In a case where the area of the electrical contact of the development roller is parallel to the electrical contact portion of the side cover as in the case of a conventional process cartridge, it is liable that the development roller is prevented by the frictional resistance between the area of the electrical contact of the development roller, and the development bias contact, from being properly pressed upon the photosensitive drum. Further, in consideration of the frictional resistance between the area of the electrical contact of the development roller, and the spring of the development bias contact of the apparatus main assembly  10 A, the spring with which the process cartridge is provided to press the development roller upon photosensitive drum has to be substantial in resiliency. However, if this spring is substantial in resiliency, the force to which the separation member for separating the development roller from the photosensitive drum is subjected when the development roller is separated from the photosensitive drum is substantial, making it necessary to increase the separation member in strength. 
         [0079]    In this embodiment, however, the component P 4  of the contact pressure P 2  to which the area  40   a  of the development roller contact  40  is subjected by the development bias contact  43  of the apparatus main assembly  100 A is utilized as an additional force for placing the development roller  25  in contact with the photosensitive drum  1 . Therefore, the force applied to place the development roller  25  in contact with the photosensitive drum  1  is prevented from being substantially robbed by the friction resistance between the area  40   a  of the development roller contact  40  and the development bias contact  43 . Further, the compression spring  38  and tension spring  39 , which are necessary to keep the development roller  25  in contact with the photosensitive drum  1 , may be substantially smaller in resiliency. Thus, the amount of the load to which the separation member  8  and separation force catching portion  31   b  are subjected when the photosensitive drum  25  is separated from the photosensitive drum  1  is smaller than in the case of a conventional image forming apparatus and process cartridge therefor. Therefore, it is unlikely for the process cartridge  7  to be deformed by the force from the compression spring  38  and the force applied by the separation member  8 . Further, the strength required of the separation member  8  and process cartridge  7  is smaller. 
         [0080]    Also in this embodiment, in order to prevent the development unit  4  from being moved from the separation position to the contact position by the contact pressure. P 1  ( FIG. 13 ) to which the area  48   a  of the side cover  48  is subjected by the development bias contact  43 , the process cartridge is structured so that the area  48   a  of the side cover  48  is perpendicular to the rotational axis  25   c  of the development roller  25  (parallel to direction in which development unit  4  is moved from separation position to contact position). However, it is not mandatory that the process cartridge  7  is structured so that the area  48   a  is perpendicular to the rotational axis  25   c  of the development roller  25 . That is, the process cartridge  7  may be structured so that the inclination of the area  48   a  of the side cover  48  relative to the direction in which the development unit  4  is moved from the contact position to the separation position, is gentler than the inclination of the area  40   a  of the development roller contact  40  relative to the moving direction of the development unit  4 . Since the process cartridge  7  is structured as described above, the component of the contact pressure P 1  between the development bias contact  43  and development roller contact  40 , which works in the direction in which the development unit  4  is moved from the separation position to the contact position, is the smaller than the contact pressure P 2  to which the area  40   a  is subjected by the development bias contact  43 . Therefore, the separation member  8 , which keeps the development unit  4  in the separation position is prevented from being subjected to the full force of contact pressure P 1  while the development roller  25  is kept separated from the photosensitive drum  1 . 
         [0081]    To summarize, according to this embodiment, it is possible to minimize the amount of the load to which the separation member  8  is subjected by the development bias contact  43  while the image forming apparatus  100  is not being used for image formation, and also, to ensure that while the image forming apparatus  100  is being used for image formation, the development roller  25  is kept properly in contact with the photosensitive drum  1 . 
       EMBODIMENT 2  
       [0082]    Next, referring to  FIG. 16 , the second embodiment of the present invention is described. The components, portions, and the like, of the image forming apparatus and process cartridge in this embodiment, which are similar to the counterparts in the first embodiment are given the same referential codes as those given to the counterparts in the first embodiment, and will not be described here.  FIG. 16  is a schematic sectional view of the electrical contacts of the process cartridge  7 , electrical contacts of the apparatus main assembly  100 A, and their adjacencies in this embodiment when the development unit  4  is in the separation position. 
         [0083]    Referring to  FIG. 16 , the primary characteristic feature of this embodiment is that when the development unit  4  is in the separation position, that is, the position in which the development roller  25  is kept separated from the photosensitive drum  1 , the compression spring  43   a  of the development bias contact  43  is in contact with the electrical contact area  48   b  of the side cover  48  of the process cartridge  7 . The plane of the electrical contact area  48   b  is inclined relative to the direction in which the development unit  4  is moved be placed in contact with the development bias contact  43 . That is, the area  48   b  is flat, and is inclined so that the downstream end of the area  48   b,  in terms of the direction in which the development unit  4  is moved from the separation position to the contact position, is farther from the upstream end of the area  48   b.  Therefore, the contact pressure P 5 , to which the area  48   b  is subjected by the development bias contact  43  when the development bias contact  43  comes into contact, and remains in contact, with the area  48   b  works in the direction parallel to the direction in which the development unit  4  is moved from the contact position to the separation position. 
         [0084]    That is, the component P 7  of the contact pressure P 5 , the direction of which is perpendicular to the component P 6  of the contact pressure P 5 , the direction of which is parallel to the lengthwise direction of the process cartridge  7 , is parallel to the direction in which the development roller  25  is separated from the photosensitive drum  1 . Therefore, the contact pressure P 5  to which the area  48   b  of electrical contact is subjected by the development bias contact  43  reduces the amount of the force which has to be applied to the process cartridge  7  by the separation member  8  ( FIG. 7 ) to keep the development roller  25  separated from the photosensitive drum  1  when no image is being formed by the image forming apparatus  100 . 
         [0085]    On the other hand, the area  40   a  of the development roller contact  40  is inclined so that its upstream end in terms of the direction in which the development unit  4  is moved from the separation position to the contact position, is farther from the development bias contact  43  than its downstream end. That is, the force to which the area  40   a  of the development roller contact  40  is subjected by the development bias contact  43  when the development unit  4  is in the contact position works in the direction to keep the development roller  25  in contact with the photosensitive drum  1 . Therefore, the image forming apparatus  100  and process cartridge  7  in this embodiment are smaller in the amount of the force (load) necessary to keep the development roller  25  separated from the photosensitive drum  1  when the image forming apparatus  100  is not forming an image, whereas they are more stable in the state of contact between the development roller  25  and photosensitive drum  1  when they are being used for image formation. 
       EMBODIMENT 3  
       [0086]    Next, referring to  FIG. 17 , the third preferred embodiment of the present invention is described. The components, parts, etc. of the image forming apparatus and process cartridge in this embodiment, which are similar to the counterparts in the preceding embodiments are given the same referential codes as those for the counterparts, and are not described.  FIG. 17  is a schematic sectional view of the electrical contacts of the process cartridge  7  and the electrical contacts of the apparatus main assembly  100 A in this embodiment, when the development unit  4  is in the separation position. 
         [0087]    The primary characteristic feature of this embodiment is that when the development unit  4  is in the separation position, that is, the position in which the development roller  25  is kept separated from the photosensitive drum  1 , the compression spring  43   a  of the development bias contact  43  is not in contact with the process cartridge  7 , as shown in  FIG. 17 . 
         [0088]    More specifically, the side cover  48  of the development unit  4  has a recess  48   c,  which is positioned so that as the development unit  4  is moved into the separation position, the compression spring  34   a  of the development bias contact  43  enters the recess  48   c,  and therefore, does not come into contact with the process cartridge  7 . Thus, it does not occur that when the development roller  25  is kept separated from the photosensitive drum  1 , the separation member  8  is subjected to the force generated by the resiliency of the development bias contact  43 . When the development unit  4  is moved from the separation position to the contact position, first, the compression spring  43   a  rides onto the bent portion  40   d  of the development roller contact  40 . Then, as the development unit  4  is moved further toward the contact position, the compression spring  43   a  comes into contact with the area  40   a  of the development roller contact  40 . Thus, as the development unit  4  is moved further toward the contact position, the development unit  4  is pressed toward the contact position by the development bias contact  43 . Therefore, it is ensured that the development unit  4  places the development roller  25  in contact with the photosensitive drum  1 , and keeps the development roller  25  in contact with the photosensitive drum  1 . 
         [0089]    Incidentally, the gist of this embodiment is that when the development unit  4  is in the separation position, the development bias contact  43  is not in contact with the development unit  4 . Thus, the side cover  48  may be provided with a through hole or the like, instead of the recess  48   c.    
       EMBODIMENT 4  
       [0090]    Next, the fourth preferred embodiment of the present invention is described with reference to  FIGS. 14 and 15 .  FIG. 14  is a schematic perspective view of the electrical contacts of the process cartridge  7  and the electrical contacts of the apparatus main assembly  100 A in this embodiment when the development unit  4  is in the separation position.  FIG. 15  is a schematic perspective view of the electrical contacts of the process cartridge  7  and the electrical contacts of the apparatus main assembly  100 A in this embodiment when the development unit  4  is in the contact position. This embodiment is described only about the structural components, parts, etc., of the image forming apparatus and process cartridge in this embodiment, which are different from the counterparts in the first embodiment. Those which are similar to the counterparts in the first embodiment are not going to be described. 
         [0091]    The image forming apparatus  100  and process cartridge  7  in the first embodiment described above are structured so that when the development unit  4  is in the separation position, that is, the position in which it keeps the development roller  25  separated from the photosensitive drum  1 , the development bias contact  43  is in contact with the area  48   a  of the side cover  48 . Referring to  FIG. 14 , in comparison, in this embodiment, when the development unit  4  is in the separation position, that is, the position in which it keeps the development roller  25  separated from the photosensitive drum  1 , the development bias contact  43  is in contact with the area  40   c  (first area of contact) of the development roller contact  40 . More concretely, in this embodiment, the development roller contact  40 , which is one of the components which can be placed in electrical connection to the development bias contact  43 , is provided with an area  40   c  (as first area of electrical contact) and an area  40   a  (second area of electrical contact). The area  40   c , which is shown in  FIG. 18 , is flat and perpendicular to the rotational axis of the development roller  25  like the area  48   a  of the side plate  48  in the first preferred embodiment. 
         [0092]    Referring to  FIG. 15 , at the starting of an image forming operation, the development unit  4  is rotationally moved in the direction indicated by the arrow mark T in order to place the development roller  25  in contact with the photosensitive drum  1 . While the development unit  4  is rotationally moved, the development bias contact  43  comes into contact with the area  40   c  of the development roller contact  40 , and slides on the area  40   c.  Then, right before the completion of the rotational movement of the development unit  4 , the development bias contact  43  comes into contact with the area  40   a  of the development roller contact  40 . However, bias voltage has to be applied to the development roller  25  before the development roller  25  comes into contact with the photosensitive drum  1  as described before, for the reason that if the development roller  25  comes into contact with the photosensitive drum  1  when bias voltage is not being applied to the development roller  25 , it is liable that the toner particles with no electrical charge may be transferred from the development roller  25  onto the photosensitive drum  1 . 
         [0093]    In this embodiment, however, the development bias contact  43  and development roller contact  40  are in contact with each other even when the development unit  4  is in the separation position. Therefore, a certain amount of latitude can be afforded for the timing with which bias voltage has to be applied to the development roller  25 . That is, this embodiment also can provide the same effects as those which can be provided by the first embodiment. Moreover, this embodiment ensures better than the first embodiment, that the toner particles with no electrical charge are not transferred from the development roller  25  onto the photosensitive drum  1 . 
         [0094]    Although in this embodiment, in order to prevent the development unit  4  from being moved to the contact position by the contact pressure which the area  40   c  of the development roller contact  40  receives from the development bias contact  43 , the area  40   c  is made perpendicular to the rotational axis of the development roller  25 . This setup, however, is not mandatory. That is, all that is necessary is that, relative to the direction in which the development unit  4  is moved from the separation position to the contact position, the inclination of the area  40   a  is gentler than the inclination of the area  40   c.    
         [0095]    That is, the area  40   c  of the development roller contact  40  may be inclined so that in terms of the direction in which the development unit  4  is moved from the separation position to the contact position, the downstream end of the area  40   c  is farther from than development bias contact  43  than the upstream end of the area  40   c.  In this embodiment, therefore, the amount of the force applied to the area  40   c  by the development bias contact  43  works in the same direction as the direction in which the development unit  4  is moved from the contact position to the separation position. Thus, this embodiment can reduce the amount of the force necessary to be applied to the process cartridge  7  by the separation member  8  ( FIG. 7 ) to separate the development roller  25  from the photosensitive drum  1 . 
       [Miscellaneous Embodiments] 
       [0096]    In each of the preferred embodiments of the present invention, four process cartridges were used. However, the preceding embodiments are not intended to limit the present invention in process cartridge count. That is, the process cartridge count may be set as necessary. Also in the preceding embodiments, the image forming apparatus was a printer. However, the preceding embodiments are not intended to limit the present invention in terms of the image forming apparatus to which the present invention is applicable. That is, the present invention is applicable to various image forming apparatuses other than a printer. For example, the present invention is applicable to a copying machine, a facsimile machine, etc., and a multifunction image forming apparatus capable of performing two or more functions of the preceding machines. Also in the preceding preferred embodiments, the image forming apparatus was such an image forming apparatus that employs an intermediary transfer member; transfers multiple monochromatic toner images, different in color, onto the intermediary transferring member; and transfers all at once the multiple monochromatic toner images from the intermediary transfer member onto recording medium. However, these preferred embodiments are not intended to limit the present invention in terms of the image forming apparatus to which the present invention is applicable. For example, the present invention is also applicable to an image forming apparatus which employs a recording medium bearing member, and sequentially transfers multiple monochromatic toner images, different in color, onto the recording medium borne on the recording medium bearing member. The application of the present invention to these image forming apparatuses other than those in the preceding preferred embodiments provides the same effects as those provided by the preferred embodiments. 
         [0097]    Further, the preceding preferred embodiments were described with reference to the structure of the development roller contact  40 , structure of the development bias contact  43 , and the positional relationship between the development roller contact  40  and development bias contact  43 . However, the preferred embodiments are not intended to limit the present invention in scope. That is, the present invention is applicable to other electrical contact (connection) between the process cartridge  7  and apparatus main assembly  100 A than between the development roller contact  40  and development bias contact  43 , as effectively as in the preferred embodiments. In a case where each of the process cartridge  7  and apparatus main assembly  100 A has multiple (two) electrical contacts through which electrical connection is made between the process cartridge  7  and  100 A, it is desired that the process cartridge  7  is provided with the first and second areas (points) of electrical contact, which correspond to the multiple (two) electrical contacts of the apparatus main assembly  100 A, one for one. 
         [0098]    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. 
         [0099]    This application claims priority from Japanese Patent Applications Nos. 112208/2010 and 097427/2011 filed May 14, 2010 and Apr. 25, 2011, respectively, which are hereby incorporated by reference.