Patent Publication Number: US-7215909-B2

Title: Developing device, and process cartridge maintaining position of developing roller, and image forming apparatus using these

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a divisional application of application Ser. No. 10/403,282, filed Apr. 1, 2003 now U.S. Pat. No. 7,024,137. 

   This application claims the right of priority under 35 U.S.C. § 119 based on Japanese Patent Application No. JP 2002-161808 which is hereby incorporated by reference herein in its entirety as if fully set forth herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a developing device, a developing cartridge, a process cartridge, and an image forming apparatus using these, which are applicable to an electrophotographic copying machine, printer or the like. 
   2. Description of the Related Art 
   Conventionally, an image forming apparatus using the electrophotographic image forming process adopts a process cartridge system, in which the image bearing member and the process means acting thereon are integrated into a cartridge, which is detachable with respect to the image forming apparatus main body. In this process cartridge system, the user can perform maintenance on the apparatus without relying on a serviceman, thus achieving a substantial improvement in terms of operability. As a result, this process cartridge system has come to be widely adopted in image forming apparatuses. 
     FIG. 17  shows an example of an image forming apparatus adopting this cartridge system, comprising an in-line type color printer  200  in which a plurality of process cartridges are arranged in a row. Regarding the developing means of process cartridges  207  ( 207   a – 207   d ) used in the image forming apparatus, two systems are generally known: a contact type development system in which development is performed with a developing roller  240  ( 240   a – 240   d ) being in contact with a photosensitive drum  201  ( 201   a – 201   d ) serving as the image bearing member, and a non-contact type development system in which development is performed with the developing roller being spaced apart from the photosensitive drum by a predetermined gap. 
   As an example of the developing device of a process cartridge, a developing device as shown in  FIG. 18  has been proposed and put into practical use. The conventional developing device  207  shown in  FIG. 18  has a developer container  245  containing a non-magnetic mono-component toner and equipped with a developing roller  240  serving as a developer carrying member, a developing blade  244  serving as a developer regulating member, and an application roller  243  serving as a developer applying member. The toner supplied to the developing roller  240  is conveyed to the portion where it abuts the developing blade  244  as the developing roller  240  rotates. Here, the toner on the developing roller  240  is turned into a uniform thin layer (toner coat) by the developing blade  244 . 
   A developing bias is applied to the developing roller  240 , and the toner on the developing roller  240  moves in correspondence with an electrostatic latent image formed on the photosensitive drum  201 , visualizing a toner image on the photosensitive drum  201 . 
     FIG. 19  is a longitudinal sectional view of the process cartridge. Here, the sectional view is taken along a plane passing the center of the developing roller  240 . 
   As shown in  FIG. 19 , the developing roller  240  is rotatably mounted to bearing portions  247   a  and  248   a  of retaining members  247  and  248 . Here, at one end of the developing roller  240 , there is provided a regulating portion  240   c  for regulating the longitudinal moving amount of the developing roller  240 . Further, mounted to the end surface on the opposite side is a helical gear  279  serving as a driving force transmission member for driving the developing roller. The torsional direction of the helical gear  279  is such that the thrust force generated when the driving force is applied to the developing roller  240  causes the developing roller  240  to move in the direction of the arrow C in the drawing. 
   Thus, in the state in which driving force is being applied to the developing roller  240 , the developing roller  240  is constantly held at a fixed position by the thrust force of the helical gear and the regulating portion  240   c , and it is possible to prevent image deficiency (so-called out of color registration generated when a number of colors are superimposed one upon the other) due to oscillation of the developing roller  240  in the thrust direction (the y-direction in the drawing). 
   However, in the conventional construction, it is necessary to provide play in the thrust direction of the developing roller  240  in order to absorb expansion and contraction of the developer container, etc., due to environmental fluctuation and the tolerance of each component. Thus, when no driving force is being applied to the developing roller  240 , the developing roller  240  is movable in the thrust direction with respect to the developer container  245  and the developing blade  244 . 
   Here, it is to be expected that during its transportation, the process cartridge suffers from vibrations in various directions. When it suffers from vibration in the longitudinal direction of the developing roller, it can happen that the developing roller  240  vibrates in the thrust direction within the process cartridge  207 . At this time, the developing roller  240  and the developing blade  244  are rubbed against each other, with the result that the developing roller  240  undergoes deformation. Further, also when the developing roller  240  is moved by the thrust force generated by the helical gear  279 , the developing roller  240  may suffer from a similar deformation. 
   Furthermore, the positional relationship between the point of contact  276  through which bias is supplied to the developing roller  240  and the developing roller  240  is not fixed. When a driving force is applied to the developing roller  240 , the developing roller  240  moves to the regulating position due to the thrust force generated through meshing of the helical gear  279 . However, the contact pressure immediately after the application of the driving force to the developing roller  240  is not fixed. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus in which the position of the developing roller in the thrust direction can remain constant. 
   Another object of the present invention is to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus in which the position of the developing roller in the thrust direction can remain constant not only during image formation, but also during transportation. 
   Still another object of the present invention is to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus in which the position of the developing roller in the thrust direction can remain constant not only during image formation, but also during the attachment of a developing device, a developing cartridge, and a process cartridge to the image formation apparatus. 
   A further object of the present invention is to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus in which the positional relationship between the developing roller and the developing blade in the thrust direction can remain constant. 
   A further object of the present invention is to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus in which the positional relationship between the developing roller and the developing blade in the thrust direction can remain constant, whereby it is possible to prevent deformation of the elastic roller portion of the developing roller due to movement of the developing roller in the thrust direction. 
   A further object of the present invention is to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus in which the electrical contact for supplying developing bias to the developing roller from the image forming apparatus main body can be kept in stable contact with the developing roller. 
   A further object of the present invention is to provide a developing device, a developing cartridge, a process cartridge, and an image forming apparatus which are easy to assemble. 
   A further object of the present invention is to provide a developing device installed in an image forming apparatus main body, including:
     a frame member;   a developing roller supported by the frame member and adapted to develop a latent image formed on an electrophotographic photosensitive member;   a developing blade adapted to regulate the thickness of a toner layer borne by the developing roller;   a helical gear provided at one end of the developing roller in an axial direction thereof and adapted to transmit a driving force to the developing roller; and   an urging unit that axially urges the developing roller, the urging unit urging the developing roller in a direction of movement of the developing roller by a thrust force of the helical gear when the driving force is transmitted to the developing roller.   

   A further object of the present invention is to provide a process cartridge detachable with respect to an image forming apparatus main body, including:
     an electrophotographic photosensitive member;   a frame member;   a developing roller supported by the frame member and adapted to develop a latent image formed on the electrophotographic photosensitive member;   a developing blade adapted to regulate the thickness of a toner layer borne by the developing roller;   a helical gear provided at one end of the developing roller in an axial direction thereof and adapted to transmit a driving force to the developing roller; and   an urging unit that axially urges the developing roller, the urging unit urging the developing roller in a direction of movement of the developing roller by a thrust force of the helical gear when the driving force is transmitted to the developing roller.   

   A further object of the present invention is to provide a developing cartridge detachable with respect to an image forming apparatus main body, including:
     a frame member;   a developing roller supported by the frame member and adapted to develop a latent image formed on an electrophotographic photosensitive member;   a developing blade adapted to regulate the thickness of a toner layer borne by the developing roller;   a helical gear provided at one end of the developing roller in an axial direction thereof and adapted to transmit a driving force to the developing roller; and   an urging unit that axially urges the developing roller, the urging unit urging the developing roller in a direction of movement of the developing roller by a thrust force of the helical gear when the driving force is transmitted to the developing roller.   

   A further object of the present invention is to provide an image forming apparatus which forms an image on a recording medium, including:
     (i) a developing device including:   a frame member;   a developing roller supported by the frame member and adapted to develop a latent image formed on an electrophotographic photosensitive member;   a developing blade adapted to regulate the thickness of a toner layer borne by the developing roller;   a helical gear provided at one end of the developing roller in an axial direction thereof and adapted to transmit a driving force to the developing roller; and   an urging unit that axially urges the developing roller, the urging unit urging the developing roller in a direction of movement of the developing roller by a thrust force of the helical gear when the driving force is transmitted to the developing roller; and   (ii) a conveying unit that conveys the recording medium.   

   A further object of the present invention is to provide an image forming apparatus to which a process cartridge is detachably attached and which forms an image on a recording medium, including:
     (i) an attachment portion;   (ii) a process cartridge detachably attached to the attachment portion and including:   an electrophotographic photosensitive member;   a frame member;   a developing roller supported by the frame member and adapted to develop a latent image formed on the electrophotographic photosensitive member;   a developing blade adapted to regulate the thickness of a toner layer borne by the developing roller;   a helical gear provided at one end of the developing roller in an axial direction thereof and adapted to transmit a driving force to the developing roller; and   an urging unit that axially urges the developing roller, the urging unit urging the developing roller in a direction of movement of the developing roller by a thrust force of the helical gear when the driving force is transmitted to the developing roller; and   (iii) a conveying unit that conveys the recording medium.   

   A further object of the present invention is to provide an image forming apparatus to which a developing cartridge is detachably attached and which forms an image on a recording medium, including:
     (i) an attachment portion;   (ii) a developing cartridge detachably attached to the attachment portion and including:   a frame member;   a developing roller supported by the frame member and adapted to develop a latent image formed on an electrophotographic photosensitive member;   a developing blade adapted to regulate the thickness of a toner layer borne by the developing roller;   a helical gear provided at one end of the developing roller in an axial direction thereof and adapted to transmit a driving force to the developing roller; and   an urging unit that axially urges the developing roller, the urging unit urging the developing roller in a direction of movement of the developing roller by a thrust force of the helical gear when the driving force is transmitted to the developing roller; and   (iii) a conveying unit that conveys the recording medium.   

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a main portion of a developing device according to a first embodiment of the present invention; 
       FIG. 2  is a schematic diagram showing the overall construction of an image forming apparatus; 
       FIG. 3  is an explanatory, longitudinal sectional view of a process cartridge; 
       FIG. 4  is an exploded perspective view of the process cartridge; 
       FIG. 5  illustrates how the process cartridge is mounted to the image forming apparatus; 
       FIG. 6  illustrates how positioning is effected on the process cartridge inside the image forming apparatus; 
       FIG. 7  illustrates bow positioning is effected on the process cartridge inside the image forming apparatus; 
       FIG. 8  illustrates the construction of a retaining member; 
       FIG. 9  is a perspective view illustrating how a developing unit is assembled; 
       FIG. 10  is a perspective view illustrating how the developing unit is assembled; 
       FIG. 11  is an exploded perspective view illustrating how an urging means according to the embodiment of the present invention is assembled; 
       FIG. 12  is a main-portion sectional view of a second embodiment of the present invention; 
       FIG. 13  is an exploded perspective view of the second embodiment of the present invention; 
       FIG. 14  is an exploded perspective view of the second embodiment of the present invention; 
       FIG. 15  is a main-portion sectional view of a third embodiment of the present invention; 
       FIG. 16  is an exploded perspective view of the third embodiment of the present invention; 
       FIG. 17  is a general schematic diagram illustrating a conventional image forming apparatus; 
       FIG. 18  is a sectional view illustrating a conventional developing device; and 
       FIG. 19  is a main-portion sectional view illustrating the conventional developing device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of this invention will now be described in detail with reference to the drawings. Note that, unless otherwise specified, the sizes, materials, configurations, and positional relationship of the components of these embodiments should not be construed restrictively. 
   (First Embodiment) 
   A developing device, a developing cartridge, a process cartridge, and an image forming apparatus according to a first embodiment of the present invention will be described with reference to  FIGS. 1 through 11 . 
   (General Construction of the Image Forming Apparatus) 
   First, the general construction of the image forming apparatus will be schematically described with reference to  FIG. 2 . The image forming apparatus  100  shown in  FIG. 2  is equipped with four photosensitive drums  1   a  through  1   d  serving as the image bearing members arranged side by side in the vertical direction. The photosensitive drums  1   a  through  1   d  are rotated counterclockwise as seen in the drawing by a driving means (not shown). 
   Respectively arranged around the photosensitive drums  1   a  through  1   d , successively in the rotating direction thereof, are charging devices  2   a  through  2   d  for uniformly charging the surfaces of the photosensitive drums  1   a  through  1   d , scanner units  3   a  through  3   d  adapted to apply laser beams based on image information to form electrostatic latent images on the photosensitive drums  1   a  through  1   d , developing units  4   a  through  4   d  causing toners serving as developers to adhere to the electrostatic latent images to develop them into toner images, an electrostatic transfer device  5  for transferring the toner images on the photosensitive drums  1   a  through  1   d  onto a transfer sheet S, cleaning devices  60   a  through  60   d  for removing residual toner from the surfaces of the photosensitive drums  1   a  through  1   d  after transfer, etc. 
   The photosensitive drums  1   a  through  1   d , the charging devices  2   a  through  2   d , the developing units  4   a  through  4   d , and the cleaning devices  60   a  through  60   d  are integrated into process cartridges  7   a  through  7   d.    
   The photosensitive drums  1   a  through  1   d  consist of aluminum cylinders with a diameter, for example, of 30 mm, to the outer peripheral surfaces of which an organic photoconductor (OPC photosensitive material) is applied. The photosensitive drums  1   a  through  1   d  are rotatably supported at their ends by support members. And, a driving force from a driving motor (not shown) is transmitted to one end of each of the photosensitive drums  1   a  through  1   d , whereby the photosensitive drums  1   a  through  1   d  are rotated counterclockwise. 
   The charging device  2  may be of a contact charging type as shown in  FIG. 3 . In this embodiment, the charging device  2  is constituted of a conductive roller, which is brought into contact with the surface of the photosensitive drum  1  and to which a charging bias voltage is applied, whereby the surface of the photosensitive drum  1  is uniformly charged. 
   The scanner units  3   a  through  3   d  are arranged substantially in the horizontal extensions of the photosensitive drums  1   a  through  1   d . Laser diodes (not shown) apply image beams corresponding to image signals to polygon mirrors  9   a  through  9   d  rotated at high speed by scanner motors (not shown). The image beams reflected by the polygon mirrors  9   a  through  9   d  are transmitted through image formation lenses  10   a  through  10   d  to be used for selective exposure of the charged surfaces of the photosensitive drums  1   a  through  1   d  to form electrostatic latent images. 
   Further, as shown in  FIG. 5 , the scanner units  3   a  through  3   d  have a longitudinal dimension larger than the pitch between right and left side plates  32  and are mounted such that their protrusions  33  project outwardly through openings  35   a  through  35   h  of the side plates  32 . As shown in  FIG. 6 , in the mounting process, each scanner unit is pressurized downwardly approximately 45 degrees with a force of approximately 9.8 N by a compression spring  36 , whereby the scanner is reliably pressed against the abutment portions of the side plate  32  and positioning is effected thereon. 
   As shown in  FIG. 3 , the developing units  4   a  through  4   d  are composed of toner containers  41  respectively containing yellow, magenta, cyan, and black toners and developing frames  45 . And, the toner in each of the toner containers  41  is fed to a toner supply roller  43  by a toner feeding mechanism  42 . And, the toner is applied to the outer periphery of a developing roller  40  rotating clockwise by a toner supply roller  43  rotating clockwise and a developing blade  44  in press contact with the outer periphery of the developing roller  40 . 
   And, by applying developing bias to the developing roller  40  opposed to the photosensitive drum  1  with a latent image formed thereon, toner development in conformity with the latent image is effected on the photosensitive drum  1  (as will be described in detail below). 
   As shown in  FIG. 2 , arranged in the image forming apparatus is an electrostatic transfer belt  11  circulating so as to be opposed to and held in contact with all the photosensitive drums  1   a  through  1   d . The electrostatic transfer belt  11  is formed of an approximately 150 μm thick film-like member having a volume resistivity of 10 11  to 10 14  Ω·cm. This electrostatic transfer belt  11  is vertically supported by four rollers  13 ,  15 ,  14   a , and  14   b ; its outer peripheral surface on the left-hand side as seen in the drawing electrostatically attracts the transfer sheet S, and circulates so as to bring it into contact with the photosensitive drums  1   a  through  1   d . In this way, the transfer sheet S is conveyed to transfer positions by the electrostatic transfer belt  11  to undergo toner image transfer from the photosensitive drums  1   a  through  1   d.    
   Transfer rollers  12   a  through  12   d  are arranged side by side so as to abut the inner side of the electrostatic transfer belt  11  and to be opposed to the four photosensitive drums  1   a  through  1   d . A charge of positive polarity is applied from these transfer rollers  12   a  through  12   d  to the transfer sheet S through the electrostatic transfer belt  11 . And, due to the electric field formed by this charge, toner images of negative polarity on the photosensitive drums  1   a  through  1   d  are successively transferred to the sheet as it successively comes into contact with the photosensitive drums  1   a  through  1   d.    
   The electrostatic transfer belt  11  is constituted of a belt approximately 700 mm round and approximately 150 μm thick. And, the electrostatic transfer belt  11  is stretched between the four rollers of the driving roller  13 , the driven rollers  14   a  and  14   b , and the tension roller  15 , and runs in the direction of the arrow in  FIG. 2 , whereby the above-described electrostatic transfer belt  11  circulates to effect toner image transfer as the transfer sheet S is conveyed from the driven roller  14   a  side to the driving roller  13  side. 
   A feeding portion  16  feeds the transfer sheet S to the image forming portions and has a feeding cassette  17  containing a plurality of transfer sheets S. When an image is to be formed, a feeding roller  18  (semilunar roller) and a registration roller pair  19  rotate in accordance with the image forming operation. And, the feeding roller  18  feeds one by one the transfer sheets S in the feeding cassette  17 . And, the leading edge of each transfer sheet S abuts the registration roller pair  19  to stop temporarily, and, after having formed a loop, is fed to the electrostatic transfer belt  11  by the registration roller pair  19 , with the running of the electrostatic transfer belt  11  and the image write position being in synchronism with each other. 
   A fixing portion  20  serves to fix a toner image in a plurality of colors transferred to the transfer sheet S, and is composed of a fixing roller pair comprising a rotary heating roller  21   a  and a pressurizing roller  21   b  in press contact therewith and adapted to impart heat and pressure to the transfer sheet S. That is, as it passes through the fixing portion  20 , the transfer sheet S to which the toner images on the photosensitive drums  1   a  through  1   d  have been transferred is conveyed by the fixing roller pair and receives heat and pressure from the fixing roller pair, whereby a toner image in a plurality of colors is fixed to the surface of the transfer sheet S. 
   In the image forming operation, the process cartridges  7   a  through  7   d  are successively driven in synchronism with the image formation operation, and, upon their driving, the photosensitive drums  1   a  through  1   d  are rotated counterclockwise. And, the scanner units  3   a  through  3   d  corresponding to the process cartridges  7   a  through  7   d  are successively driven. When the process cartridges are thus driven, the charging devices  2   a  through  2   d  impart uniform charge to the peripheral surfaces of the photosensitive drums  1   a  through  1   d , and the scanner units  3   a  through  3   d  perform exposure on the peripheral surfaces of the photosensitive drums  1   a  through  1   d  in accordance with image signals to thereby form electrostatic latent images on the peripheral surfaces of the photosensitive drums  1   a  through  1   d . The developing rollers  40  in the developing units  4   a  through  4   d  transfer toner to the low-potential portions of the electrostatic latent images to thereby form (develop) toner images on the peripheral surfaces of the photosensitive drums  1   a  through  1   d.    
   In order that the toner image on the peripheral surface of the photosensitive drum  1   a  may be transferred to a predetermined position on the transfer sheet S, the registration roller pair  19  starts to rotate to feed the transfer sheet S to the electrostatic transfer belt  11 . That is, while being held between the electrostatic attraction roller  22  and the electrostatic transfer belt  11 , the transfer sheet S is brought into press contact with the outer periphery of the electrostatic transfer belt  11 . Further, by applying voltage between the electrostatic transfer belt  11  and the electrostatic attraction roller  22 , charge is induced in the dielectric transfer sheet S and the dielectric layer of the electrostatic transfer belt  11 , thereby electrostatically attracting the transfer sheet to the outer periphery of the electrostatic transfer belt  11 . In this way, the transfer sheet S is attracted to the electrostatic transfer belt  11  in a stable manner, and conveyed to the transfer portion consisting of the photosensitive drum  1   a  and the transfer roller  12   a.    
   While the transfer sheet S is being thus conveyed, the toner images on the photosensitive drums  1   a  through  1   d  are successively transferred to the transfer sheet S due to the electric fields formed between the photosensitive drums  1   a  through  1   d  and the transfer rollers  12   a  through  12   d . The transfer sheet S, to which the toner images in four colors have been transferred, is separated from the electrostatic transfer belt  11  due to the curvature of the driving roller  13 , and sent into the fixing portion  20 . In the fixing portion  20 , the toner image is thermally fixed to the transfer sheet S, which is then discharged with the image face down to the exterior of the main body through a discharge portion  24  by a discharge roller pair  23 . 
   (Process Cartridge) 
   Next, a process cartridge according to an embodiment of the present invention will be described in detail with reference to  FIGS. 3 and 4 .  FIG. 3  is a longitudinal sectional view of a process cartridge  7  containing toner, and  FIG. 4  is an exploded perspective view of the process cartridge  7 . Process cartridges  7   a  through  7   d  are of the same construction but respectively contain yellow, magenta, cyan, and black toners. 
   The process cartridge  7  is composed of an image bearing member unit  50  equipped with a drum-shaped photosensitive member  1  serving as an image bearing member, a charging means, and a cleaning means, and a developing unit  4  having a developing means for developing an electrostatic latent image on the photosensitive drum  1 . 
   In the image bearing member unit  50 , the photosensitive drum  1  is rotatably mounted to a cleaning frame member  51  through the intermediation of bearings  31   a  and  31   b . Arranged around the photosensitive drum  1  are a charging device  2  for uniformly charging the surface of the photosensitive drum  1 , and a cleaning blade  60  serving as a cleaning device for removing residual developer (toner) on the photosensitive drum  1 . The residual toner removed from the surface of the photosensitive drum  1  by the cleaning blade  60  is successively sent to a waste toner chamber  53  provided at the rear of the cleaning frame member  51  by a toner feeding mechanism  52 . 
   And, by transmitting the driving force of a driving motor (not shown) to the rear end as seen in the drawing, the photosensitive drum  1  is rotated counterclockwise in accordance with an image forming operation. 
   The developing unit  4  has a developing roller  40  in contact with the photosensitive drum  1  and adapted to rotate in the direction of the arrow Y, a toner container  41  containing toner, and a developing frame member  45 . The developing roller  40  is rotatably supported by the developing frame member  45  through the intermediation of retaining members  47  and  48 . Further, in the periphery of the developing roller  40 , there are arranged a toner supply roller  43  in contact with the developing roller  40  and adapted to rotate in the direction of the arrow Z, and a developing blade  44 . Further, in the toner container  41 , there is provided a toner feeding mechanism  42  for agitating the toner accommodated in the toner container  41  and feeding the toner to the toner supply roller  43 . 
   And, the developing unit  4  has a suspension structure in which the entire developing unit  4  is supported so as to be capable of oscillating with respect to the image bearing member unit  50  around a support axis  49  by means of pins  49   a  respectively provided in the retaining members  47  and  48  mounted at the ends of the developing unit  4 . And, in the state in which the process cartridge  7  is left alone (i.e., in the state in which it is not attached to the printer main body), the developing unit  4  is constantly urged by a pressurizing spring  54  serving as an urging member so as to bring the developing roller  40  into contact with the photosensitive drum  1  due to the rotational moment around the support axis  49 . 
   When development is to be performed, the toner contained in container  41  is fed to the toner supply roller  43  by the toner feeding mechanism  42 . And, the toner supply roller  43 , rotating in the direction of the arrow Y, is rubbed against the developing roller  40  rotating in the direction of the arrow Z, to thereby supply the toner to the developing roller  40 , causing the toner to be borne by the same. 
   As the developing roller  40  rotates, the toner borne by the developing roller  40  reaches the developing blade  44 , which regulates the toner to form a predetermined thin toner layer. As the developing roller  40  rotates, the regulated toner reaches a developer charging roller  70  serving as a developer charging means and is charged to a desired degree. Further, the thin toner layer on the developing roller  40  is fed to the developing portion where the photosensitive drum  1  and the developing roller  40  are in contact with each other. And, in the developing portion, due to DC development bias applied to the developing roller  40  from a power source (not shown), the toner adheres to an electrostatic latent image formed on the surface of the photosensitive drum  1  to thereby develop the latent image. 
   The portion of the toner left on the surface of the developing roller  40  without contributing to the development is returned to the interior of the developing frame member  45  as the developing roller  40  rotates, and is recovered after being separated from the developing roller  40  at the position where the developing roller  40  and the toner supply roller  43  are rubbed against each other. The recovered toner is mixed through agitation with the residual toner by the toner feeding mechanism  42 . 
   As in this embodiment, in the contact development system, in which the photosensitive drum  1  and the developing roller  40  are held in contact with each other for development, it is desirable that the photosensitive drum  1  be rigid, and that the developing roller  40  be a roller having a resilient portion. The resilient portion may consist, for example, of a monolayer solid rubber or a monolayer of solid rubber coated with resin taking into account the toner charging property. 
   (Positioning of the Process Cartridge) 
   As shown in  FIG. 5 , in attaching the process cartridge  7  to the apparatus main body  100 , the bearings  31   a  and  31   b  supporting the photosensitive drum  1  are inserted from the direction of the arrow along the first guide grooves  34 . And, as shown in  FIG. 7 , by pressing the bearings  31   a  and  31   b  against abutment surfaces  37  and  38  of the guide grooves  34 , the positioning of the process cartridge  7  is effected. 
   Inside the printer main body, the process cartridge  7  is pressurized as follows. As shown in  FIG. 6 , a shaft  39  is crimped to the side plate  32 , and a torsion coil spring  30  is supported by the shaft  39 , an end portion  30   a  thereof being fitted into the hole  32   a  in the side plate for fixation. In the state in which no process cartridge  7  is attached, the torsion coil spring  30  is regulated in the rotating direction by a raised portion  32   b  of the side plate  32 . 
   The side plate  32  is provided at either end of the apparatus main body  100 . 
   And, when the process cartridge  7  is inserted, the torsion coil spring  30  rotates counterclockwise against its force; when the bearings  31   a  and  31   b  are got over, it is positioned as shown in  FIG. 6 , exerting a pressurizing force of approximately 9.8 N in the direction of the arrow. 
   (Developing Device) 
   Next, the construction of and the mounting method for the developing roller of the developing device, which is a main component of this embodiment of the present invention, and an urging means for the developing roller, will be described with reference to  FIGS. 1 , and  8  through  11 . 
   As shown in  FIG. 1 , the developing roller  40  is a conductive roller formed by a metal core  40   a  and a conductive material  40   b . The core ends  40   d  and  40   e  of the developing roller  40  are rotatably supported by retaining members  47  and  48  constituting the frame member. 
   The mounting of the developing roller  40  and the retaining members  47  and  48  to the developing container  45  is executed by the following procedures. 
   As shown in  FIG. 9 , the toner container  41  is attached to the developing container  45  by thermal welding or the like. Further, the toner supply roller  43  and a seal member (not shown) for preventing leakage of toner to the exterior of the developing container  45  are mounted to the developing container  45 . Further, the developing blade  44  is fixed to the developing container  45  by means of a screw  90 . 
   Provided in a longitudinal side surface of the developing container  45  are holes  45   h  for positioning with respect to the retaining member  48  and lower holes  45   i  for securing the retaining member by screws. As shown in  FIG. 8 , the retaining member  48  has at positions corresponding to the holes  45   h  provided in the side surface of the developing container  45  positioning bosses  48   e  and holes  48   f  through which screws are to be passed. 
   The longitudinally opposite side (the side where the retaining member  47  is mounted) of the developing container  45  exhibits the same construction. 
   As shown in  FIG. 9 , the developing roller  40  is placed on the developing container  45  with the developing blade  44  mounted thereto. And, to both sides of the developing container  45 , the retaining members  47  and  48  are attached in conformity with the positioning holes  45   h , and the developing roller  40  and the toner supply roller  43  are assembled so as to be mated with the bearing portions  47   a ,  47   b ,  48   a , and  48   b  of the retaining members  47  and  48  to fix the retaining members  47  and  48  to the developing container  45  by means of screws. 
   (Details on the Urging Means) 
   In the following the construction of portion A (the non-drive side of the developing unit) in  FIG. 1  will be described. 
   As shown in  FIG. 1 , at an end of the developing roller  40 , there is provided a regulating portion  40   c  for regulating the developing roller  40  in the thrust direction (the direction of the arrow y in the drawing). At the same time, the retaining member  48  has a regulating portion  48   g  at a position corresponding to the regulating portion of the developing roller  40 . In this embodiment, for regulation in the thrust direction, the core  40   a  of the developing roller is equipped with portions with different outer diameters, and the step due to the difference in diameter and a wall surface provided on the developing roller bearing  48   a  of the retaining member  48  are used as the thrust regulating portion for the developing roller (see  FIG. 8 ). 
   Further, the retaining member  48  has on the outer side a side cover  73 , into which a contact plate  76  serving as a means for supplying electricity to the developing roller  40  is incorporated beforehand. Here, the contact plate  76  constitutes a part of the electricity supply path for applying bias from the image forming apparatus main body; electricity supply becomes possible upon incorporation of the developing device into the image forming apparatus (not shown). 
   In the following, the construction of portion B (the drive side of the developing unit) in  FIG. 1  will be described. 
   The mounting method for the retaining member  47  is the same as that for the non-drive side of the developing unit described above. 
   As shown in  FIG. 1 , the retaining member  47  is equipped with a developing roller bearing portion  47   a . In this embodiment, the bearing portion  47   a  is a through-hole of a fixed diameter. On the drive side, there is play in the thrust direction between the developing roller  40  and the retaining member  47 . 
   Mounted through fitting to the developing roller end portion  40   f  is a helical gear  79  serving as the driving force transmission means for the developing roller  40 . Further, the helical gear  79  and the developing roller end portion  40   f  are shaped through D-cut or relieving in order to prevent idle rotation of the helical gear  79 . Here, the torsional direction of the helical gear  79  is determined such that the thrust force generated upon application of a driving force is applied in the non-drive-side direction (the direction of the arrow C in the drawing). And, when the developing roller  40  is being driven to rotate, that is, during image formation, the developing roller  40  rotates while undergoing positioning on the non-drive side by the regulating portion  40   c  on the non-drive side described above. 
   On the longitudinal outer side of the helical gear  79 , a side cover  77  is provided. As shown in  FIG. 10 , the side cover  77  is mounted by connecting a side cover mounting boss  47   b  of the retaining member  47  and a mounting portion  77   b  of the side cover  77  by a fixing means like a screw. As shown in  FIGS. 1 and 11 , mounted to the side cover  77  are a pressurizing spring  80  serving as an urging means, a sliding member  81  mounted to a forward end portion of the pressurizing spring and adapted to abut the developing roller core end portion  40   g  and slide thereon, and a spring case  82  for temporarily attaching the pressurizing spring  80  and the sliding member  81  to the side cover  77 . 
   The side cover  77 , the pressurizing spring  80 , the sliding member  81 , and the spring case  82  are assembled by the following procedures (See  FIG. 11 ). 
   First, the sliding member  81  is fitted to the pressurizing spring  80 . The sliding member  81  is a member formed of a resin material having slidability (such as POM), and has a fitting or abutment portion  81   a  with a diameter slightly larger than the inner diameter of the pressurizing spring  80 . By fitting the pressurizing spring  80  into this fitting portion  81   a , it is possible to handle the pressurizing spring  80  and the sliding member  81  integrally. 
   The spring case  82  is a member formed of a resin material (PS, POM, ABS or the like), and has an inner diameter larger than the outer diameter of the pressurizing spring  80  so as not to hinder the expansion and contraction of the pressurizing spring  80 . Further, the spring case  82  is equipped with a wall portion  82   a , surrounding the abutment portion  81   a  allowing the sliding member  81  to abut against and slide on the developing roller  40 , and a hole  82   b . Thus, the sliding member  81  is always joined to a portion near the rotation shaft center of the developing roller core end portion  40   g.    
   Subsequently, an integral unit consisting of the pressurizing spring  80  and the sliding member  81  is fitted into the spring case  82 . In this embodiment, the side cover  77  is equipped with a hole  77   c , and the spring case  82  is equipped with a snap-fit-shaped portion  82   c , the mounting being completed through their engagement. 
   Further, the central axes of the spring case  82 , the pressurizing spring  80 , and the sliding member  81  are substantially matched with the rotation shaft center of the developing roller  40 . 
   By mounting the side cover  77  assembled by the above procedures to the retaining member  47 , the sliding member  81  abuts the developing roller core end portion  40   g  to urge the developing roller  40 . 
   Here, a round hole  79   a  is provided in the portion of the end surface of the helical gear near the developing roller shaft center, and the sliding member  81  directly urges the developing roller core end portion  40   g . The reason for taking this measure is as follows. In this embodiment, the helical gear  79  is formed of a resin material having slidability, so that it is necessary to prevent heat generation when the gear and the sliding member  81  are rubbed against each other, which leads to their wear. Further, when the sliding member  81  directly urges the developing roller  40 , it is possible to restrain a variation in the urging force due to building-up of a dimensional tolerance. 
   Further, the spring force of the pressurizing spring  80  is larger than the abutment force of the contact plate  76 , and not less than double the weight X (g) of the developing roller. That is, it is not less than 0.0196 X (N). This value is determined based on actual measurement of the value of impact applied to the developing roller  40  due to the vibration during transportation. 
   In this embodiment, the weight of the developing roller  40  is 150 g, and the spring force of the pressurizing spring  80  is set at not less than 3.43 N. In this embodiment, the abutment force of the contact plate  76  is approximately 1.47 N, so that the spring force of the pressurizing spring  80  is larger than the spring force of the contact plate  76 . 
   Due to this arrangement, even if a vibration in the longitudinal direction of the developing roller is applied to the process cartridge  7 , the positional relationship between the developing roller  40 , the developing container  45 , and the developing blade  44  is always maintained, making it possible to prevent deformation of the developing roller when the developing roller  40  moves in the thrust direction to be rubbed against the developing blade  44 . Further, even when no driving force is being applied to the developing roller  40 , the developing roller  40  is always pressurized by the developing roller longitudinal regulating portion  48   g  of the retaining member  48  to be thereby stabilized in position. Further, even immediately after the drive input to the developing roller  40 , the abutment pressure for the developing roller contact point is secured, making it possible to supply bias in a stable manner. 
   Further, the forward end portion of the sliding member  81  has a spherical configuration or the area of the surface portion thereof coming into contact with the developing roller  40  is small, whereby even when urging is effected on the developing roller  40  by the urging means, the load torque generated at the portion where the sliding member  81  slides on the developing roller core end portion  40   g  is very small, and does not adversely affect the requisite motor output necessary for driving the developing device. 
   (Second Embodiment) 
     FIGS. 12 through 14  show a second embodiment of the present invention. The general construction of the image forming apparatus is the same as that of the first embodiment described above. The following description will focus on the features of the second embodiment, and a description of the components which are the same as those of the first embodiment will be omitted as appropriate. 
   (Construction of the Process Cartridge) 
   The general construction of the cleaning unit and the developing unit is the same as that of the first embodiment. 
   (Details on the Urging Means) 
     FIGS. 12 through 14  show the urging means of this embodiment in detail. The constructions of the developing roller  40  and the retaining members  47  and  48  are the same as those of the first embodiment. 
   As shown in  FIGS. 12 through 14 , the side cover  77  is equipped with a cylindrical portion  77   d  for mounting the pressurizing spring  80  and the sliding member  81  from the outside with respect to the longitudinal direction of the developing roller  40 . This cylindrical portion  77   d  has an inner diameter larger than the outer diameter of the pressurizing spring  80  and the outer diameter of the sliding member  81 , so that it does not hinder the expansion and contraction of the pressurizing spring  80  and the movement of the sliding member  81 . 
   Further, a cap member  83  for retaining the pressurizing spring  80  is mounted to the outer side surface of the side cover  77 . 
   The side cover  77 , the pressurizing spring  80 , the sliding member  81 , and the cap member  83  are assembled by the following procedures. 
   The procedure for attaching the sliding member  81  to the pressurizing spring  80  is the same as that in the first embodiment. 
   Next, the integral unit consisting of the pressurizing spring  80  and the sliding member  81  is incorporated into the cylindrical portion  77   d  of the side cover  77 . 
   Thereafter, the cap member  83  is mounted to the side cover  77 . The cap member  83  is equipped with a snap-fit-shaped portion  83   a , and the side cover  77  is equipped with a hole  77   c . The mounting is completed through their engagement. 
   By mounting the side cover  77  assembled by the above procedures to the retaining member  47 , the sliding member  81  abuts the developing roller core end portion  40   g  to urge the developing roller  40 . 
   In this embodiment, it is possible to reverse the procedure for attaching the side cover  77  to the retaining member  47  and the procedure for mounting the pressurizing spring  80 , the sliding member  81 , and the cap member  83  to the side cover  77 . 
   The load of the pressurizing spring  80 , the forward end configuration of the sliding member  81 , etc., are the same as those of the first embodiment described above. 
   (Third Embodiment) 
     FIGS. 15 and 16  show a third embodiment of the present invention. The general construction of the image forming apparatus is the same as that of the first embodiment described above. The following description will focus on the features of the third embodiment, and a description of the components which are the same as those of the first embodiment will be omitted as appropriate. 
   (Construction of the Process Cartridge) 
   The general construction of the cleaning unit and the developing unit is the same as that of the first embodiment. 
   (Details on the Urging Means) 
     FIGS. 15 and 16  show the urging means of this embodiment in detail. The constructions of the developing roller  40  and the retaining member  47  are the same as those of the first embodiment. 
   As shown in  FIGS. 15 and 16 , the side cover  77  is equipped with a retaining portion  77   e  for retaining the sliding member  81 . Around the retaining portion  77   e , there is provided a guide wall  77   f  having a diameter larger than the outer diameter of the sliding member  81 . Further, a guide pin  77   g  is provided in the portion of the side cover  77  where the pressurizing spring  80  is mounted. Further, the sliding member  81  is equipped with a claw portion  81   b  to be engaged with the retaining portion  77   e  of the side cover  77 . 
   The mounting of the pressurizing spring  80  and the sliding member  81  to the side cover  77  is conducted by the following procedures. 
   The pressurizing spring  80  is temporarily fitted onto the guide pin  77   g  provided on the side cover  77 . Thereafter, the sliding member  81  is fitted into the side cover  77  while guiding the pressurizing spring  80  by the interior of the sliding member  81 . The sliding member  81  is pushed in until its claw portion  81   b  passes the retaining portion  77   e  of the side cover  77 , thereby engaging the claw portion  81   b  with the retaining portion  77   e , whereby the mounting of the sliding member  81  and the pressurizing spring  80  to the side cover  77  is completed. 
   By mounting the side cover  77  assembled by the above procedures to the retaining member  47 , the sliding member  81  abuts the developing roller core end portion  40   g  to urge the developing roller  40 . 
   The load of the pressurizing spring  80 , the forward end configuration of the sliding member  81 , etc. are the same as those of the first embodiment described above. 
   (Other Embodiments) 
   While in the above-described embodiments the present invention is applied to a process cartridge having a developing device according to an embodiment of the present invention and an image forming apparatus to which this process cartridge is detachably attached, this should not be construed restrictively. The present invention provides the same advantages if applied to a developing device installed in an image forming apparatus, a developing cartridge of which the developing device alone is detachable, etc. 
   As described above, in accordance with the embodiments described above, the developing roller core portion is urged by an urging means superior in assembly property, always keeping the developing roller at the regulated position. Due to this arrangement, the positional relationship between the developing roller and the developing blade can be fixed even under vibration, etc., applied mainly during transportation, thereby preventing rubbing between them and preventing an image deficiency. Further, by fixing the positional relationship between the developing roller and the contact member, it is always possible to make the contact pressure applied to the developing roller constant. Thus, it is possible to prevent the contact pressure from becoming unstable immediately after a start operation. 
   Thus, as described above, in accordance with the present invention, there is provided an urging means provided in the frame body and adapted to urge the developing roller in the axial direction, wherein when a driving force is transmitted to the developing roller, the developing roller is urged by the thrust force of the helical gear in the same direction in which the developing roller moves, whereby it is always possible to make the position of the developing roller in the thrust direction constant. Further, not only during image formation, transportation, and the attachment of a developing device, a developing cartridge, and a process cartridge to the image formation apparatus, it is always possible to make the positional relationship of the developing roller in the thrust direction constant, thereby always making the positional relationship in the thrust direction between the developing roller and the electrophotographic photosensitive member constant. Thus, it is possible to prevent deformation of the resilient member of the developing roller due to movement of the developing roller in the thrust direction. 
   Further, in the developing device having a developing blade, the developing cartridge, and the process cartridge, it is always possible to make the positional relationship in the thrust direction between the developing roller and the developing blade constant. 
   Further, according to another aspect of the present invention, it is always possible to stabilize the contact between the electrical contact for supplying development bias to the developing roller from the image forming apparatus main body and the developing roller. 
   Further, according to still another aspect of the present invention, due to the provision of the urging means in the side cover, the assembly is facilitated.