Patent Publication Number: US-6671477-B2

Title: Developing device, process cartridge and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a developing device for use in an image forming apparatus of the electrophotographic type, a process cartridge having the same, and an image forming apparatus having the process cartridge. 
     2. Description of Related Art 
     The construction of a process cartridge using a developing device according to the conventional art will be described below. In a photosensitive member unit of the process cartridge, there are disposed a photosensitive drum which is an image bearing member on which an electrostatic latent image is formed, charging means for uniformly charging the surface of a photoconductive layer of the photosensitive drum, and cleaning means for scraping off any residual toner not transferred to a recording medium but adhering to the photosensitive drum, and storing the scraped-off toner in a waste toner container. 
     Also, in a developing unit, there are disposed a toner container containing a toner therein, a developing roller for supplying the toner to the electrostatic latent image formed on the photosensitive drum and forming a visible image, a developing blade for giving triboelectrification charges to the toner and forming a toner layer on the surface of the developing roller, and a jet preventing sheet for preventing the leakage of the toner in the radial direction of the developing roller. The developing unit and the photosensitive member unit are rotatably connected together by an engagement pin. The engagement pin is provided at a location at which the developing roller supported by the developing unit and the photosensitive member supported by the photosensitive drum unit are movable. A biasing spring is provided between the developing unit and the photosensitive member unit so as to urge the developing roller toward the photosensitive drum. 
     In the above-described developing unit according to the conventional art, however, the developing unit and the photosensitive member unit are rotatably connected and therefore, the weight of the toner in the toner container is added to the pressure force urging the developing roller toward the photosensitive drum. Consequently, the pressure force pressing the developing roller toward the photosensitive drum fluctuates due to the consumption of the toner during image formation. The driving torque of the developing unit also fluctuates with the fluctuation of the pressure force. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a developing device in which the pressure force of a developing roller toward an image bearing member can be stabilized, a process cartridge having the developing device, and an image forming apparatus having the process cartridge. 
     It is another object of the present invention to provide a developing device in which the pressure force of a developing roller toward an image bearing member can be stabilized independently of the amount of developer in a developer containing portion, a process cartridge having the developing device, and an image forming apparatus having the process cartridge. 
     It is another object of the present invention to provide a developing device in which the pressure force of a developing roller toward an image bearing member can be stabilized and at the same time, an improvement in the assembling property has been realized, a process cartridge having the developing device, and an image forming apparatus having the process cartridge. 
     It is another object of the present invention to provide a developing device having: 
     a developing roller for developing an electrostatic latent image formed on an image bearing drum; 
     a developer containing portion for containing therein a developer to be supplied to the developing roller; 
     a first frame for supporting the developing roller; 
     a second frame for movably supporting the first frame, and supporting the developer containing portion; and 
     an urging member for urging the developing roller toward the image bearing drum, 
     a process cartridge having the developing device, and an image forming apparatus having the process cartridge. 
    
    
     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 cross-sectional view illustrating a process cartridge. 
     FIG. 2 is a perspective view illustrating a first frame. 
     FIG. 3 is a cross-sectional view illustrating the first frame. 
     FIG. 4 is a perspective view illustrating the process cartridge. 
     FIG. 5A is an enlarged view of essential portions illustrating a slide frame. 
     FIG. 5B is an enlarged view of essential portions illustrating a slide frame. 
     FIG. 6 is a view of the first frame illustrating a toner seal construction. 
     FIG. 7 is a view of a second frame illustrating the toner seal construction. 
     FIG. 8 is a cross-sectional view illustrating the direction of compression of the toner seal. 
     FIG. 9 illustrates the construction of the toner seals on the opposite end portions of a developing roller. 
     FIG. 10 is a schematic view of a driving system for the developing roller. 
     FIG. 11 shows the construction in which the developing roller is driven on the slide frame side. 
     FIG. 12 shows the general construction of an image forming apparatus according to the present embodiment. 
     FIG. 13 is a perspective view illustrating the construction of a process cartridge. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of an image forming apparatus according to the present invention will hereinafter be described with reference to the accompanying drawings. FIG. 12 shows the general construction of the image forming apparatus according to the present embodiment. 
     General Construction of the Image Forming Apparatus 
     The general construction of the image forming apparatus will first be described with reference to FIG. 12. A laser beam printer P forms an image on a recording medium  4  (such as recording paper, an OHP sheet or cloth) by an electrophotographic image forming process. 
     The surface of a photosensitive drum  10  which is a drum-shaped electrophotographic photosensitive member as an image bearing member is uniformly charged by charging means  11 . A laser beam L containing image information is applied from optical means  1  to the photosensitive drum  10  to thereby form an electrostatic latent image conforming to the image information on the photosensitive drum  10 . The thus formed electrostatic latent image on the photosensitive drum  10  is developed by developing means which will be described later to thereby form a toner image. 
     On the other hand, in synchronism with the formation of the toner image, the recording medium  4  set on a feed cassette  6   a  is conveyed and surface-reversed (turned-over) by a pickup roller  6   b , a conveying guide  6   c  and a pair of registration rollers  6   e . The recording medium  4  then passes through a nip portion formed by the photosensitive drum  10  and a transferring roller  3  to which a constant voltage is applied. At this time, the toner image developed on the photosensitive drum  10  is transferred to the recording medium  4 . The recording medium  4  which has been subjected to the transfer of the toner image is conveyed to fixing means  5  by a conveying guide  6   f . The fixing means  5  has a driving roller  5   c  and a fixing roller  5   b  having a heater  5   a  therein, and applies heat and pressure to the recording medium  4  as the recording medium  4  passes through the nip portion of the fixing means S, thereby fixing the transferred toner image. Thereafter, the recording medium  4  is conveyed by a pair of delivery rollers  6   i  and is delivered to a delivery tray  7 . 
     Process Cartridge 
     A process cartridge C will now be described. The process cartridge C is detachably and mountably supported by a supporting means (not shown) of the image forming apparatus as shown in FIG.  12 . As shown in FIG. 1, in a photosensitive member unit B of the process cartridge C, there are disposed the photosensitive drum  10  for forming an electrostatic latent image thereon, the charging means  11  for uniformly charging the surface of a photoconductive layer of the photosensitive drum  10 , and cleaning means  14  for scraping off from the surface of the photosensitive drum  10  any residual toner not transferred to the recording medium  4  but adhering on the photosensitive drum  10 , and storing the scraped-off toner in a waste toner container  12 . 
     Also, in a developing unit A, there are disposed a toner container  21  containing toner therein, a developing roller  20  for supplying the toner to the electrostatic latent image formed on the photosensitive drum  10  to thereby form a visible image, and a developing blade  22  for giving triboelectrification charges to the toner to thereby form a toner layer on the surface of the developing roller  20 . Also, in lower openings between the developing roller  20  and a first frame  40  and between the developing roller  20  and a second frame  50 , there are provided jet preventing seals  25  for sealing the lower openings, and these seals  25  have the function of preventing the leakage of the toner in the radial direction of the developing roller  20 . 
     The developing unit A and the photosensitive member unit B, as shown in FIG. 13, have their lengthwisely opposite sides integrally connected together and fixed by a side cover  100  and a side cover  101 . Thus, they constitute the process cartridge C. The side cover  100  is provided with a pin  100   a  for positioning with respect to the developing unit A, and an aperture  100   b  for positioning with respect to the photosensitive member unit B, and the pin  100   a  and the aperture  100   b  are fitted to a positioning hole Al formed in the developing unit A and a photosensitive drum bearing  10   a  of the photosensitive member unit B, respectively. Thereby, the relative position of the developing unit A and the photosensitive member unit B is determined. Likewise, the side cover  101  is provided with a pin  101   a  for positioning with respect to the developing unit A, and an aperture  101   b  for positioning with respect to the photosensitive member unit B. The pin  101   a  and the aperture  101   b  are fitted to a positioning hole (not shown) formed in the developing unit A and the photosensitive drum bearing (not shown) of the photosensitive member unit B, whereby the two units are positioned and connected together. 
     In FIG. 1, the photosensitive drum  10  is rotated clockwise. The charging means  11  has a constant voltage applied thereto, and the charging means  11  and the photosensitive drum  10  contact each other and the surface of the photoconductive layer of the photosensitive drum  10  is uniformly charged. Then, the laser beam L conforming to the image information from the optical means  1  is applied to the photosensitive drum  10  through an exposure opening portion  2  to thereby form an electrostatic latent image on the photosensitive drum  10 . Thereafter, a toner image is formed on the photosensitive drum  10  by the developing means. 
     The developing means feeds the toner in the toner container  21  to the developing roller  20  by the rotation of a toner feeding member  23 . The developing roller  20  having a stationary magnet therein is rotated and also, a toner layer, having had triboelectrification charges given thereto by the developing blade  22 , is formed on the surface of the developing roller  20 . The developing roller  20  is urged against the photosensitive drum  10  by a biasing spring  32  (see FIGS. 4 and 10) while keeping a constant clearance through spacer runners  26 . The toner layer formed on the surface of the developing roller  20  is supplied to the developing area of the photosensitive drum  10 . The toner is shifted to the photosensitive drum  10  in accordance with the electrostatic latent image thereon to thereby form a toner image. The developing blade  22  regulates the amount of toner on the peripheral surface of the developing roller  20  and gives triboelectrification charges. Also, in the vicinity of the developing roller  20 , there is rotatably attached a toner agitating member  24  for circulating the toner in a developing chamber. 
     A voltage opposite in polarity to the toner image is applied to the transferring roller  3  provided in the main body of the image forming apparatus to thereby transfer the toner image formed on the photosensitive drum  10  to the recording medium  4 . Thereafter, any residual toner on the photosensitive drum  10  is removed by the cleaning means  14 . The cleaning means  14  scrapes off the toner residual on the photosensitive drum  10  by an elastic cleaning blade  14 a provided in contact with the photosensitive drum  10  and collects the scraped-off toner into the waste toner container  12 . 
     As shown in FIG. 1, the developing unit A is comprised of the first frame  40  and the second frame  50 . As shown in FIGS. 2 and 3, the first frame  40  is comprised of a movably supported frame (hereinafter referred to as the movable frame)  41 , a rockably supported frame (hereinafter referred to as the rockable frame)  42  and a slidably supported frame (hereinafter referred to as the slide frame)  43 , disposed at the opposite ends thereof, and the first frame  40  is generally supported for movement relative to the second frame  50 . Also, the first frame  40  holds the developing roller  20  and the developing blade  22 . The developing roller  20  has its opposite ends rotatably supported by the rockable frames  42  and the slide frames  43  through bearings  27 . Also, the spacer runners  26  substantially concentric with the developing roller  20  and having an outer diameter larger by a predetermined gap than the outer diameter of the developing roller  20  are slidably provided at the opposite ends of the developing roller  20 . The developing blade  22  as regulating means for regulating the amount of toner on the developing roller  20  is formed integrally with or adhesively secured to a developing blade metal plate  28 . The developing blade metal plate  28  is fixed to the movable frame  41 , and the distal end of the developing blade  22  abuts against the developing roller  20 . 
     As shown in FIG. 4, the first frame  40  is installed in the second frame  50 . 
     The second frame  50  is fixed to the toner container  21 . The rockable frame  42  of the first frame  40  is provided with a rockable arm  46  having a rocking hole  47  in the end portion thereof, and the second frame  50  is provided with a supporting arm  55  having a fixing hole  56  in the end portion thereof, and the rockable frame  42  and the second frame  50  are rockably engaged with each other by an engagement pin  80 . The rocking hole  47  of the rockable frame  42  and the engagement pin  80  are slidable relative to each other, and the fixing hole  56  of the second frame  50  and the engagement pin  80  are force-fitted to each other. The biasing springs  32  are provided between the first frame  40  and the second frame  50 . (Specifically, the biasing springs (see FIGS. 4 and 10, the biasing spring on the spring receiving portion  51   f  side being not shown) are attached to spring receiving portions  51   e  and  51   f  of the second frame  50 .) The developing roller  20  provided in the first frame  40  is urged against the photosensitive drum  10  with a constant clearance by the spacer runners  26 . By the biasing springs  32  being thus disposed, the developing device can be made compact. While in the present embodiment, the second frame  50  is fixed to the toner container  21 , the second frame  50  may be formed integrally with the toner container  21  (by integral molding). 
     As shown in FIG. 5A, slide flat surfaces  43   a  and  43   b  for determining the slide direction are provided on the substantially upper and lower surfaces of the slide frame  43  parallel to each other. On the other hand, guide flat surfaces  51   a  and  51   b  are provided at regions opposed to the slide flat surfaces  43   a  and  43   b  of the slide frame  43 , with a minute clearance provided therebetween, when the first frame  40  is installed in the second frame  50 . Further, in order to effect the lengthwise positioning of the second frame  50  and the first frame  40 , a positioning boss  52  is provided on the second frame  50 , and a positioning slot  41   a  for determining only the lengthwise direction is formed in the movable frame  41 . The slide frame  43  can be slid in a predetermined direction by the slide flat surfaces  43   a ,  43   b  and the guide flat surfaces  51   a ,  51   b . As an alternative construction, as shown in FIG. 5B, slide rail convex portions  43   c  and  43   d  for determining the slide direction are provided on the substantially upper and lower surfaces of the slide frame  43 , and slide rail concave portions  51   c  and  51   d  are provided at the opposed regions of the second frame  50 . The rail fitting portion of the slide frame  43  may be made of a construction for positioning the lengthwise direction of the slide frame  43  and the second frame  50 . 
     FIG. 6 shows a toner seal construction for the first frame  40  and the second frame  50 . Elastic seal members  44  and an elastic seal member  45  are fixed to the shorter side portions at the opposite ends and the upper longer side portion, respectively, of the first frame  40  by adhesive-double-coated-tapes, and are compressed by the receiving surfaces  57  and  58  of the second frame  50  shown in FIG. 7 to thereby provide the sealing effect of preventing the leakage of the toner. In FIG. 8, the double-headed arrows “s” and “t” indicate the directions of compression of the elastic seal members  44  on the shorter side portions at the opposite ends and the elastic seal member  45  on the upper longer side portion, respectively. Here, the direction of compression of the elastic seal member  45  is set so as to be a direction substantially perpendicular to the direction of movement of the first frame  40 . By doing so, it is possible to decrease the influence of the repulsive force of the elastic seal member  45 , which is larger in a compression area, upon the pressure force with which the developing roller  20  is urged against the photosensitive drum  10  and stabilize the pressure force. 
     Also, a jet preventing sheet  25  is fixed to the lower longer side portion  54  of the second frame  50  by an adhesive-double-coated tape so as to abut against the developing roller  20  and prevents the leakage of the toner in the radial direction of the lower portion of the developing roller  20 . By doing this, it is unnecessary to adopt a construction in which an elastic seal member is disposed on the lengthwise lower surface of the first frame  40 , and it is possible to realize the compactness of the apparatus. 
     FIG. 9 shows toner seals on the opposite end portions of the developing roller  20 . A magnetic seal  60  is provided with a plurality of magnetic poles on the surface  60   a  thereof opposed to the surface of the developing roller  20 , and is sealing means for adsorbing the toner by the magnetic curtain between itself and the developing roller  20 . The magnetic seal  60  is inserted and positioned in a recess (not shown) formed in the movable frame  41 , and is urged and fixed by the developing blade metal plate  28 . The developing roller  20  and the magnetic seal  60  are fixed to the same first frame  40 . Consequently, even if the developing roller follows the outer periphery of the photosensitive drum  10  and the first frame  40  moves, the clearance between the developing roller  20  and the magnetic seal  60  can be accurately set constantly. Therefore, the toner sealing of the opposite end portions of the developing roller  20  by the magnetic seal  60  can be done well. 
     FIG. 10 is a schematic view of a driving system for the developing roller  20  in the present embodiment. A drum gear  71  provided at an end portion of the photosensitive drum  10  has a driving force transmitted thereto from the image forming apparatus (not shown) through a driving gear  70 , and rotatably drives the photosensitive drum  10 . On the other hand, the drum gear  71  rotatably drives a developing roller gear  72  provided coaxially with the developing roller  20 . In FIG. 10, the arrow “a” indicates the direction of an acting force acting on the developing roller gear  72  when the drive is transmitted from the drum gear  71  to the developing roller gear  72 . The arrow “b” in FIG. 10 is a line linking the center of the rocking movement of the rockable frame  42  and the acting point (the meshing point on a pitch circle) of the acting force acting on the developing roller gear  72  together. When the angle formed by the arrow “a” with the horizontal line is defined as θa and the angle formed by the arrow “b” with the horizontal line is defined as θb, the following relation is established therebetween: θa≧θb. As a result, the acting force acting on the developing roller gear  72  acts in a direction to urge the developing roller  20  against the photosensitive drum  10 . Therefore, the pressure between the developing roller  20  and the photosensitive drum  10  is not decreased under the influence of the acting force, and the spacer runners  26  are not spaced apart from the photosensitive drum  10  by the action of a slight extraneous force. 
     As described above, the design is made such that driving is effected on the rockable frame side, whereby an increase in a frictional resistance force on the slide surface, created by the influence of a force acting during the transmission of a driving force when sliding movement is adopted, can be avoided. Also, on the slide side at the other end, such parts as a member constituting a rocking shaft and a rockable arm can be curtailed and therefore, there can be provided a compact and low-cost developing device. 
     FIG. 11 shows a construction which is another embodiment in which the developing roller  20  is driven on the slide frame side. In this construction, the developing roller gear  72  is disposed on the slide frame side. In FIG. 1, the arrow “a” indicates the direction of an acting force acting on the developing roller gear  72  when a driving force is transmitted from the drum gear  71  to the developing roller gear  72 . The angle of the slide flat surfaces  43   a  and  43   b  of the slide frame  43  may be a right angle with respect to the arrow “a”, or may be set to an angle at which, when an acting force acts on the slide flat surfaces  43   a  and  43   b , the force urges the first frame  40  toward the photosensitive drum  10 . In FIG. 11, the reference letter “F” designates a force created by the acting force acting on the developing roller gear  72 . The reference letters “Fy” denote a component force in a direction perpendicular to the guide flat surface  51   b  for the force F, and the reference letters “Fx” designate a component force in a direction parallel to the guide flat surface  51   b  for the force F. The component force Fx is directed to the photosensitive drum  10 . By doing this, under the influence of the acting force from the gear  72  when the developing roller  20  is driven, the pressure between the developing roller  20  and the photosensitive drum  10  is not decreased and the spacer runners  26  are not spaced apart from the photosensitive drum  10  by the action of a slight extraneous force. 
     Also, in the present embodiment, as previously described, the first frame  40  has one end thereof in the lengthwise direction (the axial direction of the developing roller  20 ) supported for rotation relative to the second frame  50  and the other end thereof in the lengthwise direction slidably supported. However, as another embodiment, both ends in the lengthwise direction may be rotatably supported or both ends in the lengthwise direction may be slidably supported. 
     Also, in the present embodiment, as previously described, the developing unit A is a unit having the first frame  40  for supporting the developing roller  20 , the second frame  50  for movably supporting the first frame  40 , and supporting the toner container  21 , and the biasing spring  32 . Also, the photosensitive member unit B has the photosensitive drum  10 , the charging means  11 , the waste toner container  12  and the cleaning means  14 . Consequently, the connecting and assembly of the developing unit A movably supported by the first frame  40  and the photosensitive member unit B can be done easily. 
     As described above, the effect of the present invention is to provide the capability of stabilizing the pressure force of the developing roller  20  toward the photosensitive drum or the image bearing member  10 . Particularly, it has become possible to stabilize the pressure force of the developing roller  20  toward the image bearing member  10  independently of the amount of developer in the developer containing portion. 
     Also, the developing unit A has the developing roller  20  for developing the electrostatic latent image formed on the image bearing member 10 , the developer containing portion for containing therein the developer to be supplied to the developing roller  20 , the first frame  40  for supporting the developing roller  20 , the second frame  50  for movably supporting the first frame  40 , and supporting the developer containing portion, and the biasing spring or urging member  32  for urging the developing roller  20  toward the image bearing drum member  10 , whereby the pressure force of the developing roller toward the image bearing member  10  can be stabilized and at the same time, the assembling property of the process cartridge C can be improved. 
     While the invention has been described with reference to the structure 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.