Abstract:
A process cartridge detachably mountable to a main assembly of an image forming apparatus, includes a plurality of process device including at least one member having an electrically conductive cylinder; a supporting frame for supporting as a unit the plural process devices; and an electrode, in the supporting frame, having a first portion electrically contactable to the main assembly and a second portion press-contacted to an end surface of the cylindrical member.

Description:
This application is a continuation of application Ser. No. 07/727,126 filed Jul. 9, 1991 now abandoned. 
    
    
     FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, an electrostatic recording apparatus or a laser beam printer and to a process cartridge detachably mountable to such an image forming apparatus. 
     It is known that an image forming apparatus is loaded with a process cartridge which contains an image bearing member, a charging device, a developing device, and a cleaning device supported on a common frame as a unit. The process cartridge is detachably mountable to the main assembly of the image forming apparatus, so that the maintenance and servicing operations are made easier. 
     When the process cartridge is set in the main assembly of the image forming apparatus, electric connections are to be established between the process cartridge and the main assembly so as to electrically ground the image bearing member in the form of a photosensitive drum and so as to supply developing bias voltage to a developer (toner) carrying member in the form of a developing sleeve. 
     Referring first to FIGS. 5, 6, 7 and 8, there are shown the grounding mechanism for the photosensitive drum (FIGS. 5 and 6) and an electric connection of the developing sleeve (FIGS. 7 and 8), in exemplary structures. 
     As shown in FIGS. 5 and 6, the photosensitive drum 10 comprises a base member in the form of a conductive cylinder and a photoconductive layer thereon. A longitudinal end thereof is provided with a flange 104 which supports the photosensitive drum 10 on a supporting shaft 103 and which has an integral gear (made of resin material) for driving the drum 10. A conductive metal grounding plate in the form of a leaf spring is mounted to the gear flange 104. The grounding plate 8 has pawls 8a and 8b at its outside portion, and the pawls 8a and 8b are press-contacted to the internal peripheral surface of the photosensitive drum 10. By doing so, the electric connection of the drum 10 is established. In the middle portion of the grounding plate 8, a contact portion 8c is formed. The contact portion 8c is contacted to an end surface of the supporting shaft 103 for the photosensitive drum 10 by the resiliency of the grounding plate 8 itself. The supporting shaft 103 is disposed in the cartridge and is made of conductive material. When the process cartridge is positioned in place in the main assembly of the image forming apparatus, the supporting shaft 103 is contacted to the contact portion (not shown) of the main assembly of the image forming apparatus. 
     As shown in FIGS. 7 and 8, a bias plate 210 is disposed in the developing sleeve 112. The bias plate 210 has outer pawls 210a, 210b, 210c and 210d, which contact the internal surface of the developing sleeve 112, so that it is fixed therein with the electric connection established with the developing sleeve 112. The bias plate 210 has arms 210e and 210f, which are contacted to an electrode plate 211 mounted in the housing 14a of the process cartridge. The electrode plate 211, similarly to the grounding contact for the photosensitive drum 10, is contacted to a developing bias contact (not shown) of the main assembly of the image forming apparatus so that it is supplied with a bias voltage from an unshown developing bias supply device in the main assembly, when the process cartridge is positioned in place in the main assembly of the image forming apparatus. 
     However, in the conventional examples, when the gear flange 104 having the grounding plate 8 is bonded to the photosensitive drum 10, it is liable for the bonding material flows to the contact portion of the grounding plate 8 to disturb the electric contact. Therefore, the quantity of the bonding agent and the drying conditions or the like must be strictly controlled. 
     On the other hand, the size of the process cartridge must generally be small, and in order to meet this demand, the diameter of the photosensitive drum 10 must be small. This prevents increase of the pressing force at the contact portion 8c of the grounding plate 8. As a result, the contact of the contact portion 8c with the supporting shaft 103 becomes destabalized. If the photosensitive drum 10 is moved in the housing 14a in the thrust direction by the distance corresponding to the clearance between the housing 14a and the photosensitive drum 10 upon the driving of the photosensitive drum 10, the pressing force between the grounding plate 8 and the supporting shaft 103 changes with the result of destabalized contact therebetween. 
     With respect to the developing sleeve 112, in order to maintain a constant pressing force between the electrode plate 211 and the arms 210e and 210f of the bias plate 210, the position of the bias plate 210 from the end of the developing sleeve 112 is required to be highly accurate during the assembling. Similarly to the case of the photosensitive drum 10, when the developing sleeve 112 is moved in the thrust direction by the distance corresponding to the clearance from the housing 14a, the contact between the bias plate 210 and the electrode plate 211 is easily destabalized. Furthermore, by the sliding resistance due to the contact between the electrode plate 211 and the arms 210e and 210f of the bias plate 210, the engagement between the developing sleeve 112 and the pawls 210a, 210b, 210c and 210d of the bias plate 210, becomes weaker, with the result that the bias plate 210 does possibly not rotate integrally with the developing sleeve 112. If this occurs, the relative sliding between the bias plate 210 and the developing sleeve 112 produces electric noise, and therefore, the main assembly of the image forming apparatus operates improperly. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to provide a process cartridge and an image forming apparatus usable therewith wherein the electric connection between an image bearing member in the process cartridge and the main assembly of the image forming apparatus is assured. 
     It is another object of the present invention to provide a process cartridge and an image forming apparatus usable therewith wherein an electric connection between a developer carrying member in the process cartridge and the main assembly of the image bearing member is assured. 
     According to an embodiment of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an image forming apparatus, comprising: a plurality of process means including at least one member having an electrically conductive cylinder; supporting means for supporting as a unit said plural process means; and an electrode, in said supporting means, having a first portion electrically contactable to the main assembly and a second portion press-contacted to an end surface of said cylindrical member. 
     Then, the size of process cartridge and/or the image forming apparatus can be reduced. In addition, the positional accuracy is improved by normally urging a constituent element of the process means in one direction. 
     These and other objects, features and advantages of the present invention will become more apparent upon a 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 top plan view in cross-section of a process cartridge according to an embodiment of the present invention. 
     FIG. 2 is a perspective view of a major part of the process cartridge. 
     FIG. 3 is a perspective view illustrating mounting of the process cartridge in the image forming apparatus. 
     FIG. 4 is a sectional view of an image forming apparatus. 
     FIGS. 5 and 6 are a sectional view and a perspective view illustrating an example of a photosensitive drum grounding structure. 
     FIGS. 7 and 8 are a sectional view and a perspective view illustrating an electric connection structure for a developing sleeve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings. 
     Referring to FIG. 4, there is shown an image forming apparatus in the form of an electrophotographic copying apparatus. It comprises a photosensitive drum 10 (image bearing member) which comprises a photoconductive layer and a conductive cylindrical member supporting the photoconductive layer. Around the photosensitive drum 10, there are provided a developing device 11, a charger 12, a cleaning device 13 and other process means actable on the photosensitive drum 10 for image formation. The photosensitive drum 10 and these process means are supported as a unit on a frame of a process cartridge casing 14a, so that a process cartridge 14 detachable from a main assembly 1 of the image forming apparatus, is constituted. 
     Below the photosensitive drum 10, there is a transfer charger 15. At a sheet feeding side of the transfer charger 15, there are disposed a sheet feeding tray 16, a sheet feeding roller 17 and a registration rollers 18. At the sheet discharge side thereof, there are a sheet guide 19, an image fixing device 20, a sheet discharging roller 21 and a sheet discharging tray 22. 
     Above the process cartridge 14 in the main assembly of the image forming apparatus, there are an illumination lamp 23 for illuminating the original and a short focus optical element array 24 for projecting on the photosensitive drum 10 the light from the illumination lamp 23 and reflected by an original. At an upper position of the main assembly 1, an original carriage 25 reciprocable in the directions indicated by an arrow 25a is provided. 
     In operation, the photosensitive drum 10 is uniformly charged by a charger 12 and is exposed to light image of the original on the original carriage 25 by the illumination lamp 23 and through the short focus optical element array 24, so that an electrostatic latent image is formed on the photosensitive drum 10. The electrostatic latent image is carried on the photosensitive drum 10 to the developing device 11, where the latent image receives toner t by the developing device 11 and is visualized into a toner image. A transfer sheet P is supplied from the sheet supply tray 16 by the sheet feeding roller 17 to the registration roller 18. The registration roller 18 further feeds the transfer material P to between the photosensitive drum 10 and the transfer charger 15 in timed relation with the image on the photosensitive drum 10. Then, the toner image is transferred from the photosensitive drum 10 onto the transfer sheet P. The transfer sheet P now carrying the toner image is fed into the fixing device 20, where the toner image is fixed into a permanent image. Then, the transfer sheet P is discharged onto a discharge tray 22 by the discharging rollers 21. After the completion of the image transfer operation, the photosensitive drum 10 is cleaned by the cleaning device 13 so that the residual toner thereon is removed so as to be prepared for the next image forming operation. 
     Referring to FIGS. 1 and 2, the description will be made as to the process cartridge according to an embodiment of the present invention which has a photosensitive drum and a developing sleeve for carrying toner. 
     As shown in the Figures, the photosensitive drum 10 is in the form of a cylinder and is made of aluminum, stainless steel or brass. To a longitudinal end of the photosensitive drum 10, a flange 104 made of resin material and having an integral gear is mounted. The gear engages a driving gear mounted in the main assembly (not shown) of the image forming apparatus to receive a driving force, so that it is rotated in the direction indicated by an arrow at a predetermined rotational speed. It is rotatably supported on a rotational shaft 103 mounted to a part of the casing 14a of the process cartridge. 
     The other end of the photosensitive drum 10 is rotatably supported by a bearing 6a which partly encloses the peripheral surface of the drum 10 with the aid of a holder 6. 
     In the developing sleeve 112 in the form of a cylinder and made of aluminum alloy or stainless steel, there is a magnet roller 115, and the developing sleeve 112 is rotatably supported by bearings 117a and 117b. The gear 119 at the end is normally meshed with the photosensitive drum, so that the photosensitive drum is rotated. 
     The bearings 117a and 117b supporting the longitudinal end of the sleeve 112 are provided with compression springs 118a and 118b to normally urge the developing sleeve 112 toward the photosensitive drum 10. The developing sleeve 112 is provided with spacer rings 116a and 116b, each of the rings extending around the entire circumference, so as to maintain a constant clearance between the photosensitive drum 10 and the surface of the developing sleeve 112. 
     On the side wall surface of the holder 6, a grounding electrode plate (grounding plate) 3 made of metal such as phosphor bronze or spring stainless steel and a voltage applying electrode (bias plate) 4, are mounted. End portions of the plates 3 and 4 are in sliding press-contact with longitudinal end surfaces of the photosensitive drum 10 and the developing sleeve 112. A clearance is deliberately provided in the thrust direction for the photosensitive drum 10 and for the developing sleeve 112 so as to permit smooth rotation thereof and for the purpose of permitting manufacturing tolerances. The clearances, however, may make the thrust direction positions of the photosensitive drum 10 and the developing sleeve 112 destabalized. In this embodiment, however, the grounding plate 3 and the bias plate 4 urges the photosensitive drum 10 and the developing sleeve 112 in one thrust direction so as to prevent the movement thereof in the thrust direction, so that the rotations thereof are stabilized. 
     Additionally, reference numeral 114 designates a pull tab for pulling out a toner seal 113. 
     As shown in FIG. 3, the process cartridge 14 is mounted in the direction indicated by an arrow to a top cover 2 of the main assembly of the image forming apparatus. The process cartridge 14 is pushed along guides 2a to the correct position, and thereafter, the top cover 2 is closed. As shown in FIG. 2, when the process cartridge 14 is mounted in the main assembly 1 of the image forming apparatus, the grounding plate 3 and the bias plate 4 are press-contacted to an elastic grounding electrode 31 and bias electrode 41 fixedly mounted in the main assembly 1 of the image forming apparatus, so that the electric contacts are established therebetween, respectively. 
     With the above-described structure, the grounding plate 3 functioning as a grounding electrode for the photosensitive drum 10 is directly press-contacted to an end surface of the photosensitive drum 10, and therefore, the conventional necessity for the drum flange 104, the grounding plate 8 and the supporting shaft 103 or the like (FIGS. 5 and 6), is eliminated, so that the number of parts is reduced. Since the drum flange is not used, the bonding of the flange to the drum is not required. Therefore, the problem unstable electric contact due to the bonding material having flown into between the grounding plate 3 and the photosensitive drum 10), can be eliminated, by which the reliability of the apparatus is improved. 
     Additionally, the length and width of the spring contact portion of the grounding plate 3 can be increased irrespective of the size of the photosensitive drum 10, and therefore, the pressing force can be increased. Therefore, the contact between the contact portion and the photosensitive drum 10 is assured, while permitting reduction of the diameter of the photosensitive drum 10. 
     In the developing sleeve 112, the bias plate 4 is directly press-contacted to the end surface of the developing sleeve 112. The conventional necessity for the bias plate 210 (FIGS. 7 and 8) in the developing sleeve 112, is eliminated so that the number of parts can be reduced and the highly accurate assembling step can be eliminated. 
     Similarly to the case of the photosensitive drum 10, the length and width of the spring contact portion of the bias plate 4 can be selected irrespective of the diameter of the developing sleeve 112, and therefore, the pressing force at the contact portion can be increased. Since the developing sleeve 112 is normally urged in the thrust direction by the bias plate 4, and therefore, the stabilized contact therebetween can be accomplished. This is preferable from the standpoint of reduction of the developing sleeve diameter. 
     In addition, no bias plate is provided in the developing sleeve 112, and therefore, the conventional inconveniences (the electric noise produced by failure in the fixing between the pawls of the bias plate and the developing sleeve 112) can be eliminated. This also improves the reliability of the apparatus. 
     In the foregoing embodiments, the photosensitive drum 10 has a diameter of 24 mm and a thickness of 0.5 mm and is made of aluminum. The developing sleeve 112 has a diameter of 12 mm and a thickness of 0.5 mm and is made of aluminum. The electrodes 3 and 4 are made of phosphor bronze and are press-contacted with the force of 70-250 g (preferably 150-200 g). The pressing force can be determined properly by one skilled in the art by consideration of the degree of deflection, free length elastically deformable, width of the electrode, elasticity coefficient of the material. 
     The process cartridge may contain the photosensitive drum and the sleeve as a unit, or may contain as a unit the cleaning device and the photosensitive drum, or may contain as a unit the charger, the cleaning device and the photosensitive drum, or may contain as a unit the charger and the developing device. 
     The photosensitive member contained in the cartridge may be in the form of the drum or an electrophotographic photosensitive belt supported on plural conductive cylindrical members. 
     As described in the foregoing, according to the present invention, the photosensitive member or the sleeve contained in the process cartridge is urged in the thrust direction by an electrode press-contacted to a longitudinal end surface thereof, and therefore, the position of the photosensitive member and/or the sleeve in the cartridge when the cartridge is mounted in the main assembly of the image forming apparatus, is stabilized, and in addition, the electric contact therebetween can be assured. 
     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.