Abstract:
A process cartridge detachably mountable to a main assembly of an apparatus, includes a drum, a developing member, a cartridge frame including a developer accommodating portion, a first light guide adjacent one end of the cartridge frame and a leading end with respect to a cartridge mounting direction and including a light entrance portion opposed to an emitting portion to receive detecting light when the process cartridge is mounted to the main assembly and guiding the detecting light to cross with a developer accommodating space in the developer accommodating container, a second light guide adjacent the one end and the leading end, and including a light exit portion and directing, the detecting light having passed through the developer accommodating space to the light receiving portion, and a memory member communicatable with the main assembly and adjacent the one end o and the leading and including a cartridge electrical contact.

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to a process cartridge, and an electrophotographic image forming apparatus in which a process cartridge is removably mountable. 
   Here, an electrophotographic image forming apparatus is an apparatus for forming an image on a recording medium (for example, recording paper, OHP sheet, etc.), with the use of an electrophotographic image forming method. As examples of an electrophotographic image forming apparatus, there are an electrophotographic copying machine, an electrophotographic printer (for example, a laser printer, an LED printer, etc.), a facsimile machine, a word processor, a multifunction apparatus capable of performing the tasks of two or more of the preceding machines (multifunction printer, etc.), etc. 
   A process cartridge (which hereinafter will be referred to simply as a “cartridge”) is a cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus, and in which a minimum of a developing means (developing member) and an electrophotographic photosensitive drum are integrally placed. 
   It has been a common practice to employ the combination of a developing apparatus and developer to develop an electrostatic latent image formed on an electrophotographic photosensitive drum (which hereinafter will be referred to simply as a “photosensitive drum”) of an electrophotographic image forming apparatus (which hereinafter will be referred to as an “image forming apparatus”). 
   An image forming apparatus which employs a process cartridge can be maintained by an operator alone. In other words, the employment of a cartridge system can drastically improve an image forming apparatus in operational efficiency. 
   As the technologies for making an image forming apparatus easier to use, various developer remainder detecting means capable of informing an operator of the amount of the developer remaining in the developer storage portion of a cartridge have been devised. Some of these developer remainder detecting means detect the amount of the developer remaining in the developer storage portion, by measuring the length of time a beam of light is allowed to travel through the developer storage portion of the cartridge during a predetermined length of time. 
   A developer remainder detecting means (which hereinafter will be referred to simply as a “remainder detecting means”) of a transmission type such as the aforementioned ones, comprises, for example: the combination of a beam emitting portion and a beam receiving portion, disposed on the main assembly side of an image forming apparatus; a beam transmitting portion with which the developer storage portion is provided; and a beam guide for guiding a beam of light emitted from the beam emitting portion, from the beam emitting portion to the beam transmitting portion, and then, to the beam receiving portion. 
   In the case of a developer remainder detecting means structured as described above, the length of time the detection beam is allowed to travel through the developer storage portion is dependent upon the amount of the developer remaining therein. In other words, the greater the amount of the remaining developer, the shorter the time; the smaller the amount of the remaining developer, the longer the time. Therefore, it is possible to estimate the amount of the developer remaining in the developer storage portion, by measuring the length of time the detection beam is allowed to travel through the developer storage portion, with the use of a measuring means on the main assembly side of the image forming apparatus (Japanese Laid-open Patent Application 10-186822). 
   As the technologies of another type for making it easier for an operator to use an image forming apparatus of a cartridge type, various methods for providing a cartridge with a storage element (storage member) have been devised. Between this storage element and the apparatus main assembly, information regarding image quality, the cartridge itself (manufacture, length of service life (for example, amount of remaining developer), the operational state of the apparatus main assembly, etc.) are exchanged, making it easier to maintain the image forming apparatus, or the cartridge (U.S. Pat. No. 5,937,239). 
   In recent years, demand has been increasing for an image forming apparatus which is not only easier to use, but also, smaller. In order to reduce an image forming apparatus in size, it is necessary to create a cartridge smaller in the space it occupies in the main assembly of an image forming apparatus. In the case of a color image forming apparatus, this need for cartridge size reduction is a very serious issue. 
   The issue of cartridge size reduction is just as important to a cartridge comprising the above-described developer remainder amount detecting means and storage element for making it easier for an operator to use a cartridge, and an image forming apparatus employing such a cartridge, as it is to a color image forming apparatus. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a process cartridge substantially smaller than a process cartridge in accordance with the prior art, and an electrophotographic image forming apparatus in which said process cartridge is removably mountable. 
   Another object of the present invention is to provide a process cartridge which is substantially smaller than a process cartridge in accordance with the prior art, and in which a storage member is positioned between the point of its first light guide through which the beam of detection light enters the first light guide, and the point of its second light guide through which the beam of detection light exits from the second light guide, and an electrophotographic image forming apparatus in which the process cartridge is removably mountable. 
   Another object of the present invention is to provide an electrophotographic image forming apparatus, in which the beam emitting portion, beam receiving portion for receiving the detection beam emitted from the beam emitting portion, and electrical contacts on the main assembly side, are compactly disposed on the same substrate, and a process cartridge removably mountable in the electrophotographic image forming apparatus. 
   Another object of the present invention is to provide a process cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus, in which the beam emitting portion, the beam receiving portion for receiving the detection beam emitted from the beam emitting portion, and electrical contacts on the main assembly side, are compactly disposed on the same substrate, comprising: an electrophotographic photosensitive drum; a developing member for developing an electrostatic latent image formed on the photosensitive drum; a frame having a developer storage portion for storing the developer used by the developing member to develop the electrostatic latent image; a first beam guide which is located at one end of the frame in terms of a direction parallel to the axial line of the electrophotographic photosensitive drum, and at the front end of the process cartridge, in terms of the direction in which the process cartridge is inserted into the main assembly of an electrophotographic image forming apparatus, and which has a beam entrance portion which is positioned directly opposite to the beam emitting portion, and through which the detection beam emitted from the beam emitting portion is guided into the developer storage portion so that the detection beam travels through the internal space of the developer storage portion, when the process cartridge is in the main assembly of the image forming apparatus; a second beam guide which is located at the same end of the frame, in terms of the direction parallel to the axial line of the electrophotographic photosensitive drum, as the end of the frame at which the first beam guide is located, and at the front end of the process cartridge, in terms of the direction in which the process cartridge is inserted into the main assembly of an electrophotographic image forming apparatus, and which has a beam exit portion which is positioned directly opposite to the beam receiving portion, and through which the detection beam having traveled through the internal space of the developer storage portion is guided toward the beam receiving portion, when the process cartridge is in the main assembly of the image forming apparatus; a storage member which is located at the same end of the frame, in terms of the direction parallel to the axial line of the electrophotographic photosensitive drum, as the end of the frame at which the first and second beam guides are located, and at the front end of the frame, in terms of the direction in which the process cartridge is inserted into the main assembly of the image forming apparatus, is enable to communicate with the main assembly of the image forming apparatus, and is located so that it is positioned between a horizontal plane coinciding with the center of the beam entrance portion, and a horizontal plane coinciding with the center of the beam exit portion, when the process cartridge is in the main assembly of the image forming apparatus. It is also an object of the present invention to provide an electrophotographic image forming apparatus in which such a process cartridge is removably mountable. 
   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 
       FIG. 1  is a sectional view of the process cartridge in a preferred embodiment of the present invention. 
       FIG. 2  is a schematic sectional view of a color laser printer, in the preferred embodiment, which is an example of an image forming apparatus employing one of the electrophotographic processes. 
       FIG. 3  is a sectional view of the process cartridge, depicting the general structure thereof. 
       FIG. 4  is a perspective view of the process cartridge in a partially disassembled state, showing the general structure thereof. 
       FIG. 5  is a perspective view of the portion of the process cartridge, in the preferred embodiment, equipped with a transmission-type developer remainder amount detecting means, showing the state of the process cartridge, in which the beam of detection light has reached the beam receiving portion. 
       FIG. 6  is a sectional view of the portion of the process cartridge, in the first embodiment, equipped with a transmission-type developer remainder amount detecting means, showing the state of the process cartridge, in which the beam of detection light has not reached the beam receiving portion. 
       FIG. 7  is a perspective view of the process cartridge, in the preferred embodiment, comprising a storage means. 
       FIG. 8  is a perspective view of a part of the process cartridge in the preferred embodiment, showing the positioning of the light guides and storage unit. 
       FIG. 9  is a schematic sectional view of the process cartridge in accordance with the present invention, and its adjacencies, in an image forming apparatus, showing the state of the process cartridge in the image forming apparatus. 
       FIG. 10  is a view of the component of the image forming apparatus in the preferred embodiment of the present invention, having the beam emitting portion, beam receiving portion, and communicating means. 
       FIG. 11  is a sectional view of a cartridge showing the structure of its developer remainder amount detecting means of a transmission type. 
       FIG. 12  is also a sectional view of a process cartridge, showing the structure of its developer remainder amount detecting means of a transmission type. 
       FIG. 13  is a rear view of the process cartridge, showing the structures and positioning of the beam guides and storage means thereof. 
       FIG. 14  is a sectional view of the process cartridges in the preferred embodiment of the present invention, and a part of an image forming apparatus in the preferred embodiment, which are holding the process cartridges. 
       FIG. 15  is a perspective view of the beam emitting portion, the beam receiving portion, and communicating means, of an image forming apparatus in the preferred embodiment of the present invention. 
       FIG. 16  is a sectional view of the process cartridge in the preferred embodiment. 
       FIG. 17  shows a cartridge, illustrating arrangement of a light guide and a memory unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, some of the preferred embodiments of the present invention will be described with reference to the appended drawings. Incidentally, the materials and shapes of the structural components, and the positional relations among them, which come up in the following descriptions of the preferred embodiment of the present invention, are not intended to limit the scope of the present invention, unless specifically noted. Further, if a component similar to a given component which came up in the description of one of the preceding embodiments comes up in the descriptions of the following embodiments, it is similar in material and shape to those in the preceding embodiments, unless specifically noted. 
   Referring to  FIGS. 1–15 , the cartridge and image forming apparatus, in accordance with the present invention, will be described. 
   [General Description of Image Forming Apparatus] 
   First, referring to  FIG. 2 , the general structure of a color image forming apparatus will be described.  FIG. 2  is a schematic sectional view of a color laser printer, which is an example of an image forming apparatus, in accordance with the present invention, employing one of the electrophotographic processes. 
   As shown in  FIG. 2 , the color laser printer  100  (which hereinafter may be referred to simply as the “printer”) has a cartridge compartment section  100 A comprising a plurality of cartridge compartments in which a yellow cartridge ( 7 Y) containing developer of yellow color (Y), a magenta cartridge ( 7 M) containing developer of magenta color (M), a cyan cartridge ( 7 C) containing developer of cyan color (C), and a black cartridge ( 7 K) containing developer of black color (K), are removably mountable, one for one. The color laser printer  100  also has an intermediary transferring member  5 , which holds a plurality of developer images different in color after the developer images developed by the cartridges  7  in the cartridge compartment section  100 A are transferred in layers onto the intermediary transferring member  5 , and from which the color images are transferred onto a recording medium P delivered from a recording medium feeding section. 
   The electrophotographic photosensitive drum  1  ( 1 Y,  1 M,  1 C, or  1 K, which hereinafter may be referred to simply as the “photosensitive drum”) is rotationally driven by a driving means (unshown) in the counterclockwise direction indicated by an arrow mark in  FIG. 2 . 
   Located around the peripheral surface of the photosensitive drum  1  are a charge roller  2 , for example, charge roller  2 K as a charging member for uniformly charging the peripheral surface of the photosensitive drum  1 , and scanner units ( 3 Y,  3 M,  3 C, and  3 K) for projecting a beam of laser light, while modulating it with image formation data, in order to form an electrostatic latent image, on the peripheral surface of the photosensitive drum  1  charged by the charge roller  2 . In terms of the rotational direction of the photosensitive drum  1 , the charge roller  2  is on the upstream side of the scanner units. Also located around the peripheral surface of the photosensitive drum  1  are: a second frame  4  ( 4 Y,  4 M,  4 C, and  4 K) which holds a developing means for developing the latent image; primary transfer rollers ( 12 Y,  12 M,  12 C, and  12 K) for transferring the developer image on the peripheral surface of the photosensitive drum  1 , onto the intermediary transferring member  5 , in the primary transfer station T 1 ; and a first frame  6  ( 6 Y,  6 M,  6 C, and  6 K) holding a cleaning blade  60  for removing the developer remaining on the peripheral surface of the photosensitive drum  1  after the transfer of the developer image. The transfer rollers are on the main assembly A side of the image forming apparatus. 
   After being transferred onto the intermediary transferring member  5 , the developer images are transferred by a secondary transfer roller  13  onto the recording or transfer medium P, in the second transfer station T 2 . Then, the transfer medium P is conveyed through a fixing device  8 , in which the developer images on the recording medium P are fixed to the recording medium P. Then, the recording medium P is discharged by a pair of discharge rollers  25  onto the delivery tray  26 , which constitutes a part of the top surface of the apparatus main assembly. 
   The cartridge  7  comprises the above-described photosensitive drum  1 , the charging member  2 , the second frame  4 , and the first frame  6 . The printer  100  has a hinged cover  11  ( FIG. 6 ) to which the intermediary transferring member  5  is attached. With the cover  11  opened, the cartridge  7  is mounted into, or removed from, the printer  100 , from the photosensitive drum side thereof. 
   Next, referring to  FIGS. 1–3 , various portions of the printer  100  and the cartridge  7  will be described. 
     FIG. 3  is a sectional view of the cartridge  7 , depicting the structure thereof. Here, only the cartridge  7  containing the yellow developer will be described, since all the cartridges  7  different in the color of the developers they contain are the same in structure; the cartridges  7  containing the developer different in color from yellow developer will not be described. 
   First, the various portions of the cartridge  7  containing the yellow developer will be described. 
   [Photosensitive Drum] 
   The photosensitive drum  1  ( 1 Y) comprises a substrate, for example, an aluminum cylinder, and a layer of organic photoconductive substance (OPC) coated on the peripheral surface of the substrate. The photosensitive drum  1  is rotatably supported at its lengthwise end portions, by a pair of supporting members, which are supported by the first frame  6 . 
   [Charging Member] 
   The charge roller  2  is a charging member based on one of the contact charging systems. It is an electrically conductive roller, to which charge bias is applied while it is placed in contact with the peripheral surface of the photosensitive drum  1 . With the application of the charge bias, the peripheral surface of the photosensitive drum  1  is uniformly charged. The charge roller  2  also is supported by the first frame  6 . 
   [Second Frame] 
   Referring to  FIG. 3 , the second frame  4  ( 4 Y) has a developer storage portion  41  in which the developer of yellow color for developing the aforementioned latent image into a visible image is stored. It holds a development roller  40  as a latent image developing member, a developer conveying member  42 , a developer supplying roller  43 , and a development blade  44 . In other words, the second frame  4  supports the development roller  40 , and has the developer storage portion  41  in which the developer t used for the development of the latent image is stored. The second frame  4  is connected to the first frame  6  so that they can pivot relative to each other. 
   The developer in the developer storage portion  41  is sent to the developer supplying roller  43  by rotating the developer conveying member  42  in the counterclockwise direction (indicated by arrow mark X in  FIG. 3 ); the developer supplying roller  43  is a member for supplying the development roller  40  with the developer. As the development roller  40  ( FIG. 3 ) is rotated in the clockwise direction (indicated by arrow Y in  FIG. 3 ), the developer is coated on the peripheral surface of the development roller  40  by the supply roller  43 , and the development blade  44  is kept pressed on the peripheral surface of the development roller  40 . The supply roller  43  is an elastic roller comprising a metallic core, and a spongy layer formed around the peripheral surface of the metallic core. 
   As development bias is applied to the development roller  40 , a visible image, which reflects the pattern of the electrostatic latent image, is formed of the developer, on the peripheral surface of the photosensitive drum  1 . In other words, the development roller  40  develops the electrostatic latent image formed on the peripheral surface of the photosensitive drum  1 . 
   Next, the various portions of the main assembly A of the image forming apparatus will be described. 
   [Exposing Means] 
   The scanner unit as an exposing means comprises a laser diode (unshown), to which image formation signals are given. As the image formation signals are given to the laser diode, the laser diode emits a beam of image formation light which reflects the image formation signals, onto one of the polygon mirrors ( 9 Y,  9 M,  9 C, and  9 K), which are being rotated at a high velocity by a scanner motor (unshown). As a result, the beam of image formation light is deflected by one of the mirrors ( 9 Y,  9 M,  9 C, and  9 K) toward a focal lens (unshown), and is transmitted through the focal lens, being thereby focused on the peripheral surface of the photosensitive drum  1 , which is being rotated at a predetermined constant peripheral velocity. As a result, the numerous points of the peripheral surface of the photosensitive drum  1  are selectively exposed, forming thereby an electrostatic latent image, on the peripheral surface of the photosensitive drum  1 . 
   [Intermediary Transferring Member] 
   The intermediary transferring member  5  is a member onto which a plurality of images formed of the developer, on the peripheral surfaces of the photosensitive drums  1 , by the development rollers  40 , one for one, are transferred in layers during the color image formation process. The intermediary transferring member  5  is circularly rotated in the clockwise direction ( FIG. 2 ) at the same peripheral velocity as those of the photosensitive drums  1 . 
   The images formed of the developer (which hereinafter will be referred to as the developer image), on the photosensitive drums  1 , are transferred in layers onto the intermediary transferring member  5 , in the primary transfer stations T 1 , by the primary transfer rollers ( 12 Y,  12 M,  12 C, and  12 K) which are kept pressed against the peripheral surfaces of the photosensitive drums  1 , with the intermediary transferring member  5  kept pinched between the transfer rollers and photosensitive drums  1 , and to which voltage is being applied. The primary transfer stations T 1  are where the peripheral surfaces of the primary transfer rollers are kept pressed against the peripheral surface of the photosensitive drums  1 , with the intermediary transferring member  5  kept pinched between the two surfaces. 
   After the multilayer transfer of the developer images, the intermediary transferring member  5  is moved through the secondary transfer station T 2 , through which the recording medium P is conveyed while remaining pinched between the secondary transfer roller  13  to which voltage is being applied, and the intermediary transferring member  5 , so that the developer images on the intermediary transferring member  5  are transferred all at once onto the recording medium P. 
   The intermediary transferring member  5  in accordance with the present invention is an endless and seamless belt formed of resin. It is stretched around a driving roller  14 , a counter roller  15 , and a tension roller  16 , being thereby supported by the three rollers. 
   Further, the intermediary transferring member  5  is attached to the apparatus main assembly A at the driving roller  14 . As the driving force is transmitted to one of the lengthwise ends of the driving roller  14  from a motor (unshown) in coordination with an image forming operation, the driving roller  14  is rotated in the clockwise direction indicated in the drawing. 
   [Sheet Conveying Portion] 
   The sheet conveying portion is a portion for conveying a recording medium P to the photosensitive drum  1 . It comprises a cassette  17  storing multiple recording media P, a feed roller  18 , a separation pad  19 , and a pair of registration rollers  21 . 
   During an image forming operation, the roller  18  is rotationally driven in synchronism with the image forming operation, feeding the recording media P in the cassette  17 , out into the apparatus main assembly A, one by one. Each recording medium P is conveyed to the pair of registration rollers  21  by way of the sheet conveying rollers (unshown). The pair of registration rollers  21  carries out a non-rotational operation which keeps the recording medium P on standby, and a rotational operation which releases the recording medium P toward the intermediary transferring member  5 , following a predetermined sequence, in order to align the developer images with the recording medium P, for the transfer process. 
   [Transfer Station] 
   The transfer station comprises the secondary transfer roller  13 , which is movable roughly in the vertical direction; it is moved by a cam (unshown), with the timing for transferring the developer images, to the top position in which it transfers the developer images onto the recording medium P, that is, the position in which it is kept pressed against the intermediary transferring member  5 , with the recording medium P kept pinched between the transfer roller  13  and intermediary transferring member  5 . While the transfer roller  13  is kept pressed against the intermediary transferring member  5 , bias is continuously applied to the transfer roller  13 . As a result, the developer images on the intermediary transferring member  5  are transferred onto the recording medium P. 
   The intermediary transferring member  5  and the transfer roller  13  are individually driven. Therefore, the recording medium P is conveyed in the leftward direction, in  FIG. 2 , at a predetermined speed, while remaining pinched between the intermediary transferring member  5  and transfer roller  13 . Then, the recording medium P is further conveyed by the conveyer belt  22  toward the fixation station. 
   [Fixation Station] 
   The fixing device  8  fixes the developer images which have just been transferred onto the recording medium P from the intermediary transferring member  5 . To describe in more detail, the fixing device  8  comprises: a film guide unit  23  containing a ceramic heater for heating the recording medium P, and a pressure roller  24  for keeping the recording medium P pressed against the film guide unit  23 . In other words, heat and pressure are applied to the recording medium P bearing the developer images, while the recording medium P is conveyed by the film guide unit  23  and the pressure roller  24 . As a result, the developer images on the recording medium P are fixed to the recording medium P. 
   [Image Forming Operation] 
   Next, the image forming operation carried out by the apparatus structured as described above will be described. 
   First, the roller  18  ( FIG. 2 ) is rotated to separate one of the recording media P in the cassette  17  from the rest, and conveys it to the pair of registration rollers  21 . 
   Meanwhile, the photosensitive drum  1  and the intermediary transferring member  5  are rotated at a predetermined peripheral velocity (which hereinafter may be referred to as process speed) in the direction indicated by an arrow mark in  FIG. 2 . 
   After the peripheral surface of the photosensitive drum  1  is uniformly charged by the charge roller  2 , it is exposed to the aforementioned beam of exposure light. As a result, a latent image is formed on the peripheral surface of the photosensitive drum  1 . Since all the cartridges are the same in terms of their image forming operation, only the operation for forming an image of yellow color will be described, here. 
   [Formation of Yellow Image] 
   An electrostatic image which reflects the yellow component of an intended color image is formed on the peripheral surface of the photosensitive drum  1 Y, by projecting a beam of laser light emitted from the scanner unit  3 Y which corresponds to the yellow component of the intended image. In synchronism with the formation of the latent image, the developing means held in the second frame  4 Y is made to operate to adhere the yellow developer to the peripheral surface of the photosensitive drum  1 , in the pattern of the latent image; the developing means is operated to develop the latent image. The developer image formed on the peripheral surface of the photosensitive drum  1 Y is transferred onto the outwardly facing surface of the intermediary transferring member  5 , by applying to the intermediary transferring member  5 , a voltage opposite in polarity to the yellow developer, in the transfer station T 1  located on the downstream side of the development station. 
   Next, the latent images reflecting the magenta, cyan, and black components of the intended color image, are formed and are developed into the magenta, cyan, and black developer images, in the mentioned order. Then, the magenta, cyan, and, black developer images are sequentially transferred onto the intermediary transferring member  5 . As a result, a full color image is formed of four developer images, that is, the yellow, magenta, cyan, and black developer images, on the intermediary transferring member  5 . 
   Before the leading edge of the full-color image formed on the intermediary transferring member  5  reaches the secondary transfer station T 2 , the recording medium P kept on standby by the aforementioned pair of registration rollers  21  is released so that the leading end of the recording medium P will arrive at the secondary transfer station T 2  at the same time as the leading edge of the full-color image. 
   The transfer roller  13  kept on standby below the counter roller  15 , that is, in the aforementioned bottom position, while the aforementioned four developer images different in color are formed, is moved upward into the aforementioned top position by the cam (unshown), pressing thereby the recording medium P upon the intermediary transferring member  5 , in the transfer station T 2 . Then, a bias opposite in polarity from the developer is applied to the transfer roller  13 . As a result, the four developer images, which make up the single full-color image, are transferred all at once onto the recording medium P. 
   After being conveyed through the transfer station T 2 , the recording medium P is conveyed to the fixing apparatus  8 , in which the developer images are fixed. Thereafter, the recording medium P is discharged by the pair of discharge rollers  25  onto the delivery tray  26  on top of the apparatus main assembly A, concluding the printing of a single copy. 
   [Process Cartridge Structure] 
   Next, referring to  FIGS. 3–5 , the structure of the cartridge  7  will be described.  FIG. 3  is a sectional view of the essential portion of the cartridge  7  containing the developer t, and  FIG. 4  is a perspective view of the cartridge  7 . In  FIG. 4 , the second and first frames  4  and  6  are separated from each other.  FIG. 5  is a perspective view of the cartridge  7 , as seen from the opposite side from the photosensitive drum  1 . More specifically,  FIG. 5  is a perspective view of the lengthwise ends of the frames  4  and  6 , on their front sides in terms of the direction in which the cartridge  7  is inserted into the apparatus main assembly A. 
   Referring to  FIG. 3 , the housing of the cartridge  7  comprises the first frame  6  and second frame  4 , which can be separated from each other. The first frame  6  holds the electrophotographic photosensitive drum  1 , that is, an electrophotographic photosensitive member in the form of a drum, the charge roller  2 , and the cleaning blade  60 , whereas the second frame  4  holds the development roller  40  for developing an electrostatic latent image on the photosensitive drum  1 . 
   To the first frame  6 , the photosensitive drum  1  is rotatably attached, with a pair of bearings  31  (cartridge positioning members) placed between the photosensitive drum  1  and the first frame  6 . Around the peripheral surface of the photosensitive drum  1 , the charge roller  2  for uniformly charging the peripheral surface of the photosensitive drum  1 , and the cleaning blade  60  for removing the developer remaining on the peripheral surface of the photosensitive drum  1 , are placed in contact with the peripheral surface of the photosensitive drum  1 . 
   As the developer remaining on the peripheral surface of the photosensitive drum  1  is cleaned by the cleaning blade  60 , it is conveyed by the developer conveying mechanism  62  to a waste developer chamber  63  located in the rear portion of the drum unit frame  61 . To the helical gear  46  located at the other lengthwise end of the second frame  4 , the driving force of a motor (unshown) is transmitted. In other words, the helical gear  46  is the gear which receives from the apparatus main assembly A the force for rotating the development roller  40 , the developer supplying roller  43 , and the developer conveying member  42 , while the cartridge  7  is in the apparatus main assembly A. Also, the photosensitive drum  1  is rotationally driven (in counterclockwise direction) in synchronism with an image forming operation, by the force transmitted from the apparatus main assembly A. The lengthwise end portions of the axle of the photosensitive drum  1  are fitted with the aforementioned pair of bearings  31 , and in order to precisely position the cartridge  7  relative to the image forming apparatus main assembly A, the cartridge  7  is positioned relative to the side plates  106  of the image forming apparatus main assembly A, with the pair of bearings  31  positioned between the side plates  106 , and lengthwise ends of the axle of the photosensitive drum  1 , one for one. 
   The second frame  4  holds the development roller  40 , which is rotated (in the direction indicated by arrow Y) in contact with the photosensitive drum  1 . It also has the developer storage portion  41  which contains the developer. Further, it has a developing means container  45 . The development roller  40  is rotatably supported by the developing means container  45 , with the development roller bearings  47  and  48  placed between the development roller  40  and the developing means container  45 . In the adjacencies of the peripheral surface of the development roller  40 , the developer supplying roller  43 , which is rotated (in the direction indicated by arrow mark Z) while being pressed against the development roller  40 , and development blade  44 , are located. Further, within the developer storage portion  41 , the developer conveying mechanism  42  for conveying the developer, while stirring it, to the developer supplying roller  43  is provided. 
   Next, referring to  FIG. 4 , the second frame  4  is attached to the first frame  6  in such a manner that it can be pivoted about the pair of pins  49   a  fitted in the hole  49  of the development roller bearing  47  and the hole  49  of the development roller bearing  48 , one for one. 
   When the cartridge  7  is not in the apparatus main assembly A, the second frame  4  is kept constantly pressed by a pair of compression springs  64  in the direction to be rotated about the pair of pins  49   a  so that the development roller  40  is kept pressured toward the photosensitive drum  1  by the moment generated by the pair of compression springs  64 . 
   During development, the developer in the developer storage portion  41  is conveyed by the developer stirring member  42  to the developer supplying roller  43 , which is being rotated (in the direction indicated by arrow mark Z) while rubbing against the development roller  40  which is also being rotated (in the direction indicated by arrow mark Y). As a result, the developer is supplied to the peripheral surface of the development roller  40 , being thereby borne on the peripheral surface of the development roller  40 . Then, the developer borne on the peripheral surface of the development roller  40  is delivered by the rotation of the development roller  40  to the development blade  44 , which forms the body of developer on the peripheral surface of the development roller  40  into a thin layer of the developer with a predetermined thickness, while charging the developer. Then, the thin layer of the developer is delivered by the rotation of the development roller  40  to the development station, in which the peripheral surface of the photosensitive drum  1  is in contact with the peripheral surface of the development roller  40 , and development bias (DC voltage) is applied to the development roller  40  from the power source (unshown) of the image forming apparatus  100  by way of a development power supply contact  92 , so that the developer particles in the thin layer of the developer are adhered to the peripheral surface of the photosensitive drum  1 , in the pattern of the electrostatic latent image on the peripheral surface of the photosensitive drum  1 , developing thereby the latent image into a visible image. 
   The developer which did not contribute to the development, that is, the developer remaining on the peripheral surface of the development roller  40 , is returned by the rotation of the development roller  40  to the developing means container  45 , in which the developer is stripped (it is recovered) from the peripheral surface of the development roller  40  by the developer supplying roller  43  which is being rotated while rubbing the development roller  40 . The recovered developer is stirred and mixed with the developer in the developing means container  45 , by the developer stirring mechanism  42 . 
   The cartridge  7  is provided with a charge bias electrical contact  91  for supplying the charge roller  2  with high voltage from the power source (unshown) on the main assembly side, a development bias electrical contact  92  for supplying the development roller  40  and the developer supplying roller  43  with high voltage from the power source (unshown) on the main assembly side, and a blade bias electrical contact  93  for supplying the development blade  44  with high voltage. These electrical contacts  91 ,  92 , and  93  are attached to one of the lengthwise end walls, that is, the walls perpendicular to the direction parallel to the axial direction of the photosensitive drum  1 . More specifically, the charge bias electrical contact  91  is attached to one of the lengthwise end walls (in terms of the direction parallel to the aforementioned axial line) of the first frame  6  supporting the charge roller  2 . 
   The electrical contact  92  for supplying the development roller and the developer supplying roller with bias, and the blade bias electrical contact  93 , are attached to one of the lengthwise end walls (in terms of the direction parallel to the aforementioned axial line) of the second frame  4  supporting the development roller  40 , the developer supplying roller  43 , and the development blade  44 . In other words, the electrical contacts  91 ,  92 , and  93  are attached to the lengthwise end walls  4   a  and  6   a  of the second and first frames  4  and  6 , respectively, in terms of the lengthwise direction of the frames, being exposed from the end walls  4   a  and  6   a , which are on the same end of the cartridge  7  in terms of the lengthwise direction of the cartridge  7 . 
   As the cartridge  7  is inserted into the apparatus main assembly A, these electrical contacts  91 ,  92 , and  93  come into contact with the charge bias electrical contacts (for example,  111 Y, and  111 K), the development bias electrical contacts (for example,  112 Y, and  112 K), and the blade bias electrical contacts (for example,  113 Y, and  113 K) of the apparatus main assembly A, being thereby enabled to supply the corresponding components of the cartridge  7  with electric power. The electrical contacts  91 ,  92 , and  93  are electrically connected to the corresponding components in the cartridge  7 , and so are the electrical contacts  111 Y,  111 K,  112 Y,  112 K,  113 Y, and  113 K of the apparatus main assembly A. 
   More specifically, the first frame  6  holds the charge roller  2  for charging the photosensitive drum  1 . The end wall  6   a  of the first frame  6 , located at one of the lengthwise ends of the first frame  6  in terms of the direction parallel to the axial direction of the photosensitive drum  1 , is provided with the charge bias electrical contact  91 , through which voltage is supplied to the charge roller  2  from the apparatus main assembly A when the cartridge  7  is in the apparatus main assembly A. 
   The second frame  4  holds the development roller  40  as a latent image developing member, the development blade  44  for regulating the amount of the developer to be kept adhered to the peripheral surface of the development roller  40 , and the developer supplying roller  43  for supplying the peripheral surface of the development roller  40  with the developer. The lengthwise end wall  4   a  of the second frame  4 , located at one of the lengthwise ends of the second frame  6  in terms of the direction parallel to the axial line of the electrophotographic photosensitive drum, is provided with the blade bias electrical contact  92  for supplying the development blade  44  with voltage from the image forming apparatus main assembly A when the cartridge  7  is in the apparatus main assembly A. The end wall  4   a  of the second frame  4  is also provided with the development bias electrical contact  92  (developer supplying bias electrical contact) through which the development voltage, and the voltage for the developer supplying roller  43 , are supplied to the development roller  40  and the developer supplying roller  43 , from the image forming apparatus main assembly A, when the cartridge  7  is in the image forming apparatus main assembly A. 
   With the employment of the above-described structural arrangement, all the electrical contacts of the cartridge  7  are placed at one of the lengthwise ends of the cartridge  7 , making it possible to place all the electrical contacts of the apparatus main assembly A on the same end of the apparatus main assembly A. In other words, the electrical junction of the apparatus main assembly A can be placed at one end of the electrical circuit board of the apparatus main assembly A. 
   [Cartridge Supporting Structure of Image Forming Apparatus] 
   Next, referring to  FIGS. 6–10 , the cartridge supporting structure of the image forming apparatus  100  will be described.  FIG. 6  is a sectional view of the image forming apparatus, the hinged cover  11  of which is open, and  FIG. 7  is a perspective view of the same image forming apparatus.  FIG. 8  is a perspective view of the cartridge supporting portion (plate) of the image forming apparatus, depicting the structure thereof, and  FIG. 9  is a drawing for depicting the structure of the cartridge positioning portion of the image forming apparatus main assembly A for positioning the cartridge  7  as the cartridge  7  is inserted into one of the cartridge compartments of the apparatus main assembly A.  FIG. 10  is a drawing for depicting the cartridge  7  in the apparatus main assembly A after the precise positioning of the cartridge  7  in the apparatus main assembly A by closing the hinged cover  11 . Incidentally,  FIGS. 9 and 10  show the cartridge in the top cartridge compartment of the image forming apparatus main assembly A; the other cartridge compartments of the image forming apparatus main assembly A, that is, the cartridge compartments for the cartridges  7  for the colors different from the one shown in  FIGS. 9 and 10 , which are the same in structure as the cartridge compartment shown in  FIGS. 9 and 10 , are not shown. 
   The rotational axis of the hinged cover  11  is located in the bottom portion of the image forming apparatus  100 . To the hinged cover  11 , the aforementioned intermediary transferring member  5  is attached. Therefore, opening the hinged cover  11  makes it possible for an operator to access the cartridges  7 Y,  7 M,  7 C, and  7 K. What is holding the cartridges  7 Y,  7 M,  7 C, and  7 K is a cartridge holding member  101 , the rotational axis  101   a–b  of which, that is, the axis of the cartridge holding member supporting member, is located in the top portion of the apparatus main assembly A. 
   The cartridge holding member  101  is connected to the hinged cover  11  by a linkage (unshown). Thus, opening the hinged cover  11  makes the cartridge holding member  101  rotate (roughly 45 degrees in this embodiment) about the pivot  101   a–b , thereby causing the cartridges  7  in the cartridge holding member  11  to orbitally move through a predetermined angle (roughly 40 degrees in this embodiment) about the pivot  101   a–b . In other words, opening the hinged cover  11  makes it easier to insert the cartridges  7  into the apparatus main assembly A, or remove them therefrom. 
   In this embodiment, for cost reduction, the left- and right-hand portions ( 101   a  and  101   b ) of the cartridge holding member  101  are separately formed, and then, are joined. However, the cartridge holding member  101  may be formed as a single-piece member. When the left- and right-hand portions are separately formed, the two portions are solidly held together by a linking member. Therefore, the two-piece cartridge holding member  101  is virtually the same in structure as a single-piece cartridge holding member  101 . 
   Referring to  FIG. 8 , the portion  101   b  of the cartridge holding member  101  is provided with four sets of the charge bias electrical contacts, development bias-development supply bias electrical contacts, and development blade bias electrical contacts, one set for each of the four cartridge compartments, as the electrical contacts for supplying the cartridges  7  with the aforementioned high voltages. Thus, as the cartridge  7  is inserted into the cartridge holding member  101  in the direction indicated by an arrow mark in the drawing, the aforementioned charge bias electrical contact  91 , development bias-developer supplying bias electrical contact  92 , and blade bias electrical contact  93  of the cartridge  7  come into contact with the charge bias, development bias-development supply bias, and development blade bias electrical contacts of the portion  101   b  of the cartridge holding member  101 , respectively. Incidentally, the direction in which the cartridge  7  is inserted into the image forming apparatus  100  is the direction perpendicular to the lengthwise direction (axial direction) of the photosensitive drum  1 . 
   Next, the cartridge  7  and the cartridge holding member  101  will be described regarding their structures for making the closing of the hinged cover  11  precisely position the cartridge  7  relative to the cartridge holding member  101 . 
   After the cartridge holding member  101  is rotated outward roughly 45 degrees from the position in which it is kept when forming an image, the cartridge  7  can be effortlessly inserted into the apparatus main assembly A. 
   Referring to  FIG. 9 , as the cartridge  7  is inserted into the first position, which is the deepest position for the cartridge  7  in the cartridge holding member  101 , the cartridge regulating portion  81  of the cartridge  7  comes into contact with the cartridge regulating portion  101   a–f  of the apparatus main assembly A, which is a part of the cartridge holding portion  101 . 
   Next, the hinged cover  11  is to be closed. As the hinged cover  11  is closed, the cartridge holding member  101  is moved into the image forming apparatus main assembly A by the linkage connected to the hinged cover  11  and cartridge holding member  101 , causing the cartridge  7  to move into the second position, as shown in  FIG. 10 , in which the cartridge  7  can be used for image formation. As the cartridge  7  is moved into the second position, the drum shaft bearings  31  (first and second cartridge positioning portions) fitted around the lengthwise end portions of the photosensitive drum  1  and projecting outward from the lengthwise ends of the first frame  6  in the axial direction of the photosensitive drum  1 , fit into the positioning portions  106   a  (first and second positioning portions), one for one, of the side plates  106  of the image forming apparatus main assembly A, and each of the bearings  31  is pressed against the two surfaces  106   a   1  and  106   a   2  of the side plate  106 , on the corresponding side, facing rearward, in terms of the cartridge insertion direction, and upward, respectively. 
   Also as the cartridge  7  is moved into the second position in the apparatus main assembly A, the cartridge regulating portion  81  of the cartridge  7  comes into contact with the cartridge regulating portion  101   a–f  of the apparatus main assembly A. 
   In other words, the cartridge  7  is provided with a first cartridge positioning portion comprising the bearing  31 , which is located at one of the lengthwise ends of the first frame  6 , and which comes into contact with a first cartridge positioning portion comprising the positioning portion  106   a  of the image forming apparatus main assembly A to precisely position the cartridge  7  relative to the apparatus main assembly A when the cartridge  7  is inserted into the image forming apparatus main assembly A. The cartridge  7  is also provided with a second cartridge positioning portion comprising another bearing  31 , which is located at the other lengthwise end of the first frame  6 , and which comes into contact with a second cartridge positioning portion comprising another positioning portion  106   a  of the image forming apparatus main assembly A in order to precisely position the cartridge  7  relative to the image forming apparatus main assembly A as the cartridge  7  is inserted into the image forming apparatus main assembly A. Further, the cartridge  7  is provided with the cartridge regulating portion  81 , which is a part of the first frame  6 , and which comes into contact with the cartridge regulating portion  101   a–f  of the image forming apparatus main assembly A, thereby regulating the rotation of the cartridge  7  about the first and second cartridge positioning portions  31  of the cartridge  7 , when the cartridge  7  receives the driving force transmitted from the image forming apparatus main assembly A. 
   Next, the reception, by the cartridge  7 , of the diving force transmitted from the image forming apparatus  100  will be described. 
   The cartridge  7  is provided with a driving force receiving portion  30  (coupler) connected to one of the lengthwise ends of the supporting shaft of the photosensitive drum  1 . As the driving force receiving portion  30  is engaged with the driving force transmitting means (unshown) of the apparatus main assembly A, the driving force is transmitted to the photosensitive drum  1 , thereby rotating the photosensitive drum  1  in the clockwise direction ( FIG. 10 ). As the photosensitive drum  1  receives the driving force, the first frame  6  is subjected to such a moment that acts in the direction to rotate the first frame  6  in the direction indicated by the arrow mark, about the line which coincides with the axial lines of the pair of bearings  31  as the first and second cartridge positioning portions. As a result, the first frame  6  is rotated in the direction indicated by the arrow mark, thereby causing the cartridge regulating portion  81  as the third cartridge positioning portion to come into contact with the cartridge regulating portion  101   a–f  of the apparatus main assembly A. The contact between the cartridge regulating portion  81  and the cartridge regulating portion  101   a–f  caused by the moment fixes the attitude of the cartridge  7  in terms of the direction in which the cartridge  7  is pivoted by the moment generated as the photosensitive drum  1  is rotationally driven by the driving force from the apparatus main assembly A. As a result, the cartridge  7 , in particular, the photosensitive drum  1  in the cartridge  7 , is precisely positioned relative to the apparatus main assembly A. 
   [Structure of Stirring Member, and Detection of Developer Remainder Amount by Beam Transmission] 
   Next, referring to  FIGS. 11 and 12 , the detection of the developer remainder amount by beam transmission will be described.  FIG. 11  is a sectional view of the cartridge  7 , in accordance with the present invention, equipped with a transmission-type developer remainder amount detecting means, in which the beam of detection light has reached the beam receiving portion, and  FIG. 12  is a sectional view of the transmission-type developer remainder amount detecting means, in which the beam of detection light has not reached the beam receiving portion. 
   Referring to  FIG. 11 , within the developer storage portion  41 , a developer stirring member  42  is positioned. The rotation of the developer stirring member  42  in the direction indicated by the arrow mark X conveys the developer to the developer supplying roller  43 . The stirring member  42  comprises a shaft  42   a , and a flexible sheet  42   b  for conveying the developer while stirring it. 
   The force for driving the stirring member  42  is transmitted thereto by a driving gear (unshown) inserted through the hole in one of the side walls of the developer storage portion  41 . 
   The developer storage portion  41  is provided with first and second beam guides  51  and  52 , each of which is the integral combination of a transparent window and a beam guiding portion. The first light guide  51  is on the side from which the beam of detection light enters. The first and second light guide  51  and  52  are near the aforementioned end walls  4   a  and  6   a  ( FIG. 5 ), respectively, in terms of the lengthwise direction of the cartridge  7 . The first light guide  51  is for guiding the beam L of the developer remainder amount detection light emitted from a beam emitting portion  53  (LED) located in the image forming apparatus main assembly A, into the developer storage portion  41 . After passing through the developer storage portion  41 , the detection beam L is guided by the second beam guide to the beam receiving portion  54  (photo-transistor) located also in the image forming apparatus main assembly A. As the aforementioned flexible sheet  42   b  of the developer stirring member  42  is rotated, not only does it interrupt the detection beam L, but also cleans the inward surface  51   b  of the first light guide  51 , and the inward surface  52   b  of the second light guide  52 . 
   In this embodiment, incidentally, the outward surface  52   a  of the second light guide  52 , from which the detection beam L exits, is located a predetermined distance forward, in terms of the direction in which the cartridge  7  is inserted into the image forming apparatus main assembly A (leftward in  FIGS. 11 and 12 ), relative to the outward surface  51   a  of the first light guide  51 , from which the detection beam L is guided into the developer storage portion  41 . 
     FIG. 11  shows the state of the cartridge  7  immediately after the cleaning of the beam transmission surface  51   b  of the first light guide  51  by the flexible sheet  42   b . The amount of the developer remainder in the developer storage portion  41  shown in  FIG. 11  is relatively small. Thus, the detection beam L is allowed to uninterruptedly travel through the developer storage portion  41  to be transmitted through the second light guide  52 , and is detected by the beam receiving portion  54 . In comparison,  FIG. 12  shows the state of the cartridge  7  immediately before the flexible sheet  42   b  begins to clean the detection beam transmission surface  51   b . When the cartridge  7  is in the state shown in  FIG. 12 , the detection beam L is blocked by the developer stirring member  42  as well as the developer in the developer storage portion  41 , being therefore prevented from reaching the second beam guide  52 ; in other words, the detection beam L is not detected by the beam receiving portion  54  located in the image forming apparatus main assembly A. 
   When the cartridge  7  is structured as described above, it is possible to detect the length of time the detection beam L is allowed to freely travel through the developer storage portion  41  per rotation of the stirring member  42 . This length of time is processed by the control portion of the apparatus main assembly A following a predetermined procedure in order to estimate the amount of the remaining developer remaining in the developer storage portion  41 . With the employment of this procedure, the amount of the remaining developer remaining in the developer storage portion  41  can be reasonably precisely estimated when the amount of the developer remaining in the developer storage portion  41  is in the range of 0%–25% of the effective developer capacity of the developer storage portion  41 . 
   To summarize, the second frame  4  of the cartridge  7  is provided with the first and second beam guides  51  and  52 , which are located near one of the lengthwise ends in terms of the direction parallel to the axial line of the photosensitive drum  1 , and at the front end in terms of the direction in which the cartridge  7  is mounted. The first beam guide  51  is positioned so that when the cartridge  7  is in the apparatus main assembly A, the beam entrance surface  51   a  of the first beam guide  51  directly faces the aforementioned beam emitting portion  53  located in the apparatus main assembly A, and the second beam guide  52  is positioned so that when the cartridge  7  is in the apparatus main assembly A, the beam exit surface  52   a  of the second beam guide  52  directly faces the aforementioned beam receiving portion  54 . 
   Further, when the cartridge  7  is in the apparatus main assembly A, the first frame  6  is located on top of the second frame  4 , and the first beam guide  51  is located under the developer storage portion  41 , guiding the detection beam L emitted from the beam emitting portion  53 , into the developer storage portion  41 ; the detection beam L enters the first beam guide  51  and is transmitted into the developer storage portion  41  through the detection beam guide  51 , whereas the second beam guide  52  is located on top of the developer storage portion  41 , guiding the detection beam L to the beam receiving portion  54  after the detection beam L travels through the developer storage portion  41 ; the detection beam L exits from the beam exit surface  52   a  and reaches the beam receiving portion  54 . Incidentally, “at one of the lengthwise ends” means “nearer to one of the lengthwise ends than to the center of the second frame in terms of the direction parallel to the axial direction of the photosensitive drum  1 ”. 
   Structuring the cartridge  7  as described above makes it possible to avoid positioning the beam emitting portion  53  so that it overlaps with the photosensitive drum  1  in terms of the direction perpendicular to the axial line of the photosensitive drum  1 . Therefore, it prevents the photosensitive drum  1  from being exposed to the detection beam L, raising thereby the level of image quality at which an image is formed. 
   As seen from the direction parallel to the axial line of the photosensitive drum  1  held by the second frame  4 , the second beam guide  52  is located forward of the first beam guide  51  in terms of the direction in which the cartridge  7  is inserted into the apparatus main assembly A; the beam exit surface  52   a  is forward of the beam entrance surface  51   a.    
   [Structure of Storage Means of Process Cartridge] 
   Next, referring to  FIGS. 1 and 13 , the storage means of the cartridge  7  will be described regarding the structure of and communication with the image forming apparatus main assembly A.  FIG. 13  is a rear view of the cartridge  7  having a storage means, in accordance with the present invention. 
   The storage means  55  (which hereinafter may be referred to as a memory unit) is located at the front end of the cartridge  7  in terms of the cartridge insertion direction. The memory unit  55  comprises a memory  55   b , first and second electrical contacts  55   d   1  and  55   d   2  as electrical contacts on the cartridge side, a pair of conductive areas  55   c   1  and  55   c   2 , and a dielectric substrate  55   a , on which the preceding portions are placed. The first and second contacts  55   d   1  and  55   d   2  are within the conductive areas  55   c   1  and  55   c   2 , respectively, which are positioned in a manner to sandwich the memory  55   b  from the left and right sides, respectively. 
   The cartridge  7  is provided with an electrical contact, which is located at one end of the first frame  6  in terms of the direction parallel to the axial direction of the photosensitive drum  1 , and at the front end of the cartridge  7  in terms of the cartridge mounting direction, and which comes into contact with the electrical contact  56   a  of the image forming apparatus main assembly A, thereby transmitting the data stored in the memory  55   b  to the image forming apparatus main assembly A, as the cartridge  7  is mounted into the image forming apparatus main assembly A. 
   The memory  55   b , the first conductive area  55   c   1  having the first electrical contact  55   d   1  as the electrical contact on the cartridge side, and the second conductive area  55   c   2  having the second electrical contact  55   d   2  as the electrical contact on the cartridge side, are on the same substrate  55   a . Listing from the inward side of the cartridge  7  in terms of the aforementioned direction parallel to the axial line of the photosensitive drum  1 , the first conductive area  55   c   1 , the memory  55   b , and the second conductive area  55   c   2  are disposed on the substrate  55   a . Further, the straight line S 1  ( FIG. 13 ) connecting the outward edge of the beam entrance portion (surface)  51   a  in terms of the direction parallel to the axial line of the photosensitive drum  1  held by the second frame  4 , and the outward edge of the beam exit portion (surface)  52   a , overlaps with at least a part of the substrate  55   a , as seen from the direction perpendicular to the drawing. In this embodiment, the straight line S 1  crosses the first conductive area  55   c   1 , which is on the inward side of the memory  55   b  in terms of the direction parallel to the axial line of the photosensitive drum  1 . 
   Structuring the cartridge  7  as described above makes it possible to utilize the space between the first and second beam guides, which otherwise is a dead space. In particular, it makes it possible to reduce the dimension of the cartridge  7  in terms of the direction parallel to the axial line of the photosensitive drum  1 . 
   Referring to  FIG. 13 , in this embodiment, the cartridge  7  is provided with two first electrical contacts  55   d   1 , which are located in the first conductive area  55   c   1 , and two second electrical contacts  55   d   2 , which are located in the second conductive area  55   c   2 , improving the cartridge  7  in reliability of electrical connection. The image forming apparatus main assembly A is provided with a communication unit  56  (shown in  FIG. 14 ) as a communicating means connected to the controller (unshown). As the cartridge  7  is inserted into the apparatus main assembly A, the electrical contacts  55   d   1  and  55   d   2  of the memory unit  55 , within the first and second conductive areas  55   c   1  and  55   c   2 , respectively, come into contact with the communication contacts  56   a  (electrical contacts on the main assembly side shown in  FIG. 15 ), making possible the communication between the memory  55   b  of the memory unit  55 , and a controller of the apparatus main assembly A (making it possible to read data in memory  55   b , or write data into memory  55   b ). 
   The data to be stored in the memory  55   b  are one or more of various parameters showing the state of the cartridge  7 , for example, the types of the electrophotographic photosensitive drum  1  and the developer t in the cartridge  7 , the lot number, the history of cartridge usage, the number of performed image forming operations, etc. 
   Another datum stored in the memory  55   b  is datum regarding the amount of the developer remaining in the developer storage portion  41 , which is transmitted from the apparatus main assembly A through the electrical contacts  55   d   1  and  55   d   2  on the cartridge side. In this embodiment, a minimum of the datum regarding the amount of the remaining developer detected by the developer remainder amount detecting means is stored in the memory  55   b . Having the data regarding the amount of the remaining developer stored in the memory  55   b  makes it possible to properly manage a cartridge  7  in terms of service life, even when the cartridge  7  is transferred from one apparatus to another during its usage. 
   The memory unit  55  is attached to the first frame  6  with the use of one of such means as a piece of two-sided adhesive tape, adhesive, thermal crimping, ultrasonic welding, snap fit, etc., and is precisely positioned relative to the apparatus main assembly A by the first and second cartridge positioning portions  31  (bearings) of the first frame of the cartridge  7 . Therefore, the memory unit  55  attached to the first frame  6  is precisely positioned relative to the apparatus main assembly A, being thereby precisely positioned relative to the communication unit  56  of the apparatus main assembly A. 
   The communication unit  56  is provided with four sets of conductive electrical contacts  56   a . Each set has two electrical contacts  56   a , which are placed in contact with the two conductive areas  55   c   1  and  55   c   2  of the corresponding memory unit  55 . 
   Providing each of the conductive areas  55   c   1  and  55   c   2  with two electrical contacts, in other words, providing the conductive area  55   c   1  with two first electrical contacts  55   d   1 , and the conductive area  55   c   2  with two second electrical contacts  55   d   2 , as described before, improves communication reliability. In reality, the first and second electrical contacts  55   d   1  and  55   d   2  mean nothing but the scratch marks which the electrical contacts  56   a  on the apparatus main assembly side make on the conductive areas ( 55   c   1  and  55   c   2 ) as the cartridge  7  is inserted into the apparatus main assembly A. 
   Next, referring to  FIGS. 14 and 15 , the state of the cartridge  7  mounted in the apparatus main assembly A will be described.  FIG. 14  is a schematic sectional view of the cartridge holding portion of the color image forming apparatus  100 , and the cartridges  7  therein, in accordance with the present invention, showing the structures thereof.  FIG. 15  is a perspective view of the dielectric substrate  57  of the apparatus main assembly A, on which the beam emitting portion  53 , the beam receiving portion, and the communication unit  56   a  (electrical contacts on main assembly side) are mounted. 
   The image forming apparatus  100  is capable of holding four cartridges  7 , which are inserted into the apparatus main assembly A, so that the photosensitive drum  1  of each cartridge  7  is located on the intermediate transferring member side, and also, so that the four cartridges  7  are vertically stacked. More specifically, the image forming apparatus  100  is provided with multiple (four) vertically stacked cartridge compartments  7   t  into which the cartridges  7 Y,  7 M,  7 C, and  7 K different in the color of the developer they store are removably mountable. The beam entrance portion  51   a  of the first beam guide  51 , and the beam exit portion (surface)  52   a  of the second beam guide  52 , are located at the front end of the cartridge  7  in terms of the cartridge insertion direction, as shown in  FIG. 1 . The beam entrance surface  51   a  and beam exit surface  52   a  are vertically spaced apart by a distance equal to the height of the developer storage portion  41 , and are parallel to each other. Therefore, the space between the beam entrance surface  51   a  and beam exit surface  52   a  constitutes a dead space. In the case of the cartridge  7  in this embodiment, the memory unit  55  for communicating with the main assembly of the printer  100  is placed in this space. 
   To describe these features in more detail with reference to  FIG. 16 , the memory unit  55  is attached to the cartridge  7  so that when the cartridge  7  is in the main assembly of the printer  100 , the memory unit  55  is positioned between the horizontal plane A 1  coinciding with the center of the beam entrance portion (surface)  51   a , and the horizontal plane A 2  coinciding with the center of the exist portion (surface)  52   a . Further, referring to  FIG. 17 , the memory  55  is placed so that the vertical plane A 3  coinciding with the centers of the beam entrance portion (surface)  51   a  and beam exit portion (surface)  52   a , and perpendicular to the rotational axis R of the photosensitive drum  1 , crosses a part of the memory unit  55 . 
   In other words, the memory unit  55  is placed so that the beam entrance portion  51   a , the memory unit  55 , and the beam exit portion  52   a  appear vertically aligned as seen from the direction perpendicular to the drawing. Therefore, the first beam guide  55 , the second beam guide  52 , and the memory  55  can be compactly placed in the cartridge  7 , making it possible to reduce the dimension of the cartridge  7  in terms of the direction parallel to the axial direction of the photosensitive drum  1 , and therefore, making it possible to reduce the size of the printer  100  in which the cartridge  7  is removably mountable. 
   Further, the memory unit  55  on the printer side, the first beam guide  51 , and the second beam guide  52 , are placed close to each other, and the communication unit  56  is attached to the main assembly of the printer  100  so that when the cartridge  7  is in the printer  100 , the communication unit  56  is placed between the horizontal plane A 1  coinciding with the center of the LED  53 , and the horizontal plane A 2  coinciding the center of the photo-transistor  54 , as shown in  FIG. 16 . 
   Therefore, the LED  53 , the photo-transistor  54 , and the communication unit  56  can be placed on the same substrate. Further, the means for controlling these components can also be placed on the same substrate, making it unnecessary to distribute these components and controlling units among multiple substrates, and therefore, making it possible to reduce the component count of the apparatus main assembly A as well as the size of the apparatus main assembly A. 
   The cartridge  7 , the memory unit  55  of which is attached thereto so that the beam entrance portion  51   a , the beam exit portion  52   a , and the memory unit  55  of the cartridge  7  vertically align as seen from the direction perpendicular to the drawing, is preferable as the cartridge for the color printer  100  in which multiple cartridges are vertically stacked, as shown in  FIG. 14 . 
   Further, the LED  53  for detecting the amount of the remaining developer, the photo-transistor  54 , the communication unit  56  as the electrical contact on the main assembly side, which are attached to the apparatus main assembly A so that they directly face the first beam guide  51 , the second beam guide  52 , and the memory unit  55 , can be compactly disposed in a single area. 
   Therefore, the LED  53 , the photo-transistor  54 , and the communication unit  56  can be compactly placed on the same rectangular substrate  57  as shown in  FIG. 15 , making it possible to substantially reduce the electrical wiring and compactly place the components, contributing thereby to the reduction of the size of the printer  100  which employs multiple cartridges  7 . 
   As described above, in this embodiment, the memory unit  55  is placed in the aforementioned dead space. More specifically, referring to  FIGS. 1 and 13 , the beam entrance surface  51   a  and the beam exit surface  52   a  are located at the front end of the cartridge  7  in terms of the cartridge insertion direction, and at the same location in terms of the lengthwise direction (parallel to the axial line of photosensitive drum  1 ). Further, the memory unit  55  is attached to the cartridge  7  so that a part of the memory unit  55  is crossed by the straight line S 1  connecting the outward edges of the beam entrance portion (surface)  51   a  and the beam exit portion (surface)  52   a . More specifically, in this embodiment, the cartridge  7  is structured so that the straight line S 1  crosses the conductive area  55   c   1  of the memory unit  55 . 
   Therefore, it is possible to make the dimension of the cartridge  7 , in particular, the first frame  6 , smaller, in terms of the lengthwise direction, than the dimension of a process cartridge in accordance with the prior art, the beam entrance portion  51   a  and the beam exit portion  52   a  of which are located apart from each other, in terms of the lengthwise direction, in order to prevent the developer remainder amount detection beam from interfering with the beam for forming a latent image on the peripheral surface of the photosensitive drum  1 . Therefore, it is possible to reduce the overall size of the cartridge  7 . 
   Further, the beam entrance portion  51   a , the beam exit portion  52   a , and the memory unit  55  are attached to the cartridge  7  so that they vertically align as they are seen from the direction perpendicular to the drawing, and also, so that they are located close to each other. Therefore, the beam emitting portion (LED)  53 , the beam receiving portion (photo-transistor)  54 , and the communication unit  56  for detecting the amount of the remaining developer can be attached to the main assembly of the image forming apparatus  100 , employing the cartridge  7  structured as described, so that they are positioned close to each other. 
   Therefore, the beam emitting portion  53  ( 53 Y,  53 M,  53 C, and  53 K), the beam receiving portion  54  ( 54 Y,  54 M,  54 C, and  54 K), and the communication unit  56  ( 56 Y,  56 M,  56 C, and  56 K) can be placed on the same substrate  57 . Further, the means for controlling these components can also be placed on the same substrate  57 . Therefore, it is unnecessary to distribute the aforementioned components and controlling means among multiple substrates. Therefore, it is possible to reduce the component count and the size of the apparatus main assembly A. 
   Further, the beam emitting portion  53 , the beam receiving portion  54 , and the communication unit  56  of the color image forming apparatus  100  which employs multiple cartridges  7 , the beam entrance portion  51   a , the beam exit portion  52   a , and the memory unit  55  of which are attached to the cartridge  7  so that they are positioned close to each other, and also, so that they appear to vertically align as seen from the direction perpendicular to the drawing ( FIG. 13 ), and in which the multiple cartridges  7  are vertically stacked as shown in  FIG. 14 , can be placed on the same rectangular substrate  57  for sensors, which extends in the vertical direction ( FIG. 15 ). 
   Therefore, it is unnecessary to distribute the aforementioned components and controlling means among multiple substrates, making it possible to substantially reduce wiring and compactly place them. Therefore, it is possible to reduce the component count and size of the image forming apparatus  100 . 
   Incidentally, the cartridge  7  in this embodiment is structured so that the aforementioned line S 1  crosses the conductive area  55   c   1  of the memory unit  55 . The line S 1 , however, may cross any part of the memory unit  55  as long as it crosses the memory unit  55 . Even if the line S 1  crosses a portion of the memory unit  55  different from the portion which the line S 1  crosses in this embodiment, the effects of the present invention are the same as those described above. 
   Further, in this embodiment, the electrical contacts  91 ,  92 , and  93  of the cartridge  7  are located at the same end of the cartridge  7  as the end at which the first and second beam guides  51  and  52 , and the memory unit  55 , are located, in terms of the lengthwise direction (parallel to axial line of photosensitive drum  1 ), as shown in  FIG. 5 . Therefore, the components of the apparatus main assembly A and the cartridge  7 , which electrically connect the apparatus main assembly A and cartridge  7 , can be compactly placed, making it possible to shorten the wiring between the power source (unshown) and electrical substrates of the apparatus main assembly A. 
   While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
   This application claims priority from Japanese Patent Application Nos. 349466/2003, 398939/2003 and 161219/2004, filed Oct. 8, 2003, filed Nov. 28, 2003 filed May 31, 2004, which are hereby incorporated by reference.