Patent Publication Number: US-8538292-B2

Title: Image forming apparatus with supporting member set and force-exerting member set interacting with each other

Description:
This application claims priority of No. 099109793 filed in Taiwan R.O.C. on Mar. 31, 2010 under 35 USC 119, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to an image forming apparatus, and more particularly to an image forming apparatus with a top-mounted photosensitive drum and being capable of reducing wear of the photosensitive drum. 
     2. Related Art 
     In a conventional printer, the photosensitive drum, which is mounted at the side of or under the developing unit, constantly withstands a weight or a lateral locking force of the developing unit, especially when the developing unit contains a toner supplier. Therefore, the pressing contact between the photosensitive drum and the developing roller of the developing unit produces excessive friction therebetween. Consequently, the increase in friction causes rapid wear of the photosensitive film of the photosensitive drum and shortens the life of the photosensitive drum. 
     The toners inside the toner supplier gradually decrease as the amount of usage increases, and therefore, the toner supplier becomes lighter in weight. To maintain the contact between the developing roller and the photosensitive drum even when the least amount of the toners remains in the toner supplier, the developing roller is usually designed to press against the photosensitive drum at a high level of pressure in the case of a full tank of toners. However such high level of pressure on the photosensitive drum only accelerates a deterioration of the photosensitive drum and consequent impact on images is liable to occur. 
     In addition, in the situation where the developing unit is mounted in a case with a lock device pushing the developing unit towards the photosensitive drum, the increase in the pressure applied on the photosensitive drum causes the expedited deterioration as well. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been proposed to solve the problems of the prior art, and it is an object of the present invention to provide an image forming apparatus with a top-mounted photosensitive drum and a resilient member, for example, a compression spring, for counteracting the weight of a developing cartridge, in order to maintain steady contact pressure between the developing roller and the photosensitive drum and to reduce the wear of the photosensitive drum. 
     To achieve the above-identified object, the present invention provides an image forming apparatus including a case, a photosensitive drum, a developing cartridge and a resilient member. The photosensitive drum, disposed over the developing cartridge, forms a toner image. The developing cartridge is movably disposed within the case and includes a developing tank and a developing roller. The developing roller is mounted on the developing tank and positioned opposite the photosensitive drum. The developing roller transfers toners to the photosensitive drum. The resilient member, disposed between the developing tank and the case, provides a restoring force for counteracting a weight of the developing tank and urging the developing roller towards the photosensitive drum. 
     The image forming apparatus of the present invention maintains a steady and tight contact between the top-mounted photosensitive drum and the developing roller without applying excessive pressure on the photosensitive drum. Therefore, no abnormal tear and wear will be produced on the photosensitive drum, and endurability of the photosensitive drum is remarkably improved. 
     Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded pictorial view of an image forming apparatus according to a first embodiment of the present invention. 
         FIG. 2  is an exploded side view of the image forming apparatus according to the first embodiment of the present invention. 
         FIG. 3  is a simplified drawing of  FIG. 2 . 
         FIG. 4  is a side view of the image forming apparatus according to the first embodiment of the present invention. 
         FIG. 5  is a partial pictorial view of the image forming apparatus according to the first embodiment of the present invention. 
         FIG. 6  is a side view of an image forming apparatus according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is an exploded pictorial view of an image forming apparatus  1  according to a first embodiment of the present invention. Referring to  FIG. 1 , the image forming apparatus  1  includes a case  10 , a photosensitive drum  20  and a developing cartridge  30 . The photosensitive drum  20 , disposed over the developing cartridge  30 , forms a toner image. The developing cartridge  30  is accommodated within a chamber  11  of the case  10 . A roller  52  is rotatable and mounted on a sidewall of the chamber  11 . 
       FIG. 2  is an exploded side view of the image forming apparatus  1  according to the first embodiment of the present invention. As shown in  FIG. 2 , the roller  52  is depicted in dashed lines.  FIG. 3  is a simplified drawing of  FIG. 2 . In  FIG. 3 , the case  10  is shown in a simplified form, omitting parts of its structure non-essential in this present invention, in order to improve visibility of a supporting member set  50  (to be described later) depicted in phantom lines of  FIG. 2 . In addition, for the convenience of illustration of the interactions between the roller  52  and a first force-exerting member  62  of a force-exerting member set  60  and between a guiding block  54  and a second force-exerting member  64  of the force-exerting member set  60 , the roller  52  and the guiding block  54  of the supporting member set  50  are drawn together on the developing cartridge  30  instead. 
       FIG. 4  is a side view of the image forming apparatus  1  according to the first embodiment of the present invention, where the developing cartridge  30  is movably disposed within the case  10 .  FIG. 5  is a partial pictorial view of the image forming apparatus  1  according to the first embodiment of the present invention. As shown in  FIG. 4 , the case  10  is represented by a frame, for the sake of illustration. The image forming apparatus  1  of this embodiment includes the case  10 , the photosensitive drum  20 , the developing cartridge  30  and a resilient member  40 . 
     The image forming apparatus  1  for printing data on a sheet may be installed in a printer, a copier or a multi-function device, for example. The photosensitive drum  20  is rotatable and mounted on the case  10 . 
     The developing cartridge  30 , movably disposed within the case  10 , includes a developing tank  32 , a developing roller  34  and a rotation shaft  38 . The developing roller  34 , mounted on the developing tank  32  and positioned opposite the photosensitive drum  20 , transfers toners  36  to the photosensitive drum  20 . The toners  36 , stored in a toner supplier (not shown) attached to the developing tank  32 , are transferred to the photosensitive drum  20  by the rotating developing roller  34 . 
     The resilient member  40 , which may be a compression spring, is disposed between the developing tank  32  and the case  10 . One or more resilient member  40  may be provided. In this embodiment, two resilient members  40  are disposed at the two opposite ends of the developing tank  32 , as shown in  FIG. 5 . The resilient members  40  are disposed under a bottom  32 A of the developing tank  32 . The resilient member  40  provides a restoring force F for counteracting a weight W of the developing tank  32  and urging the developing roller  34  towards the photosensitive drum  20 . The resilient members  40  are disposed to one side of the center of gravity CG of the developing tank  32  and on the same side as the developing roller  34 . Such a configuration alleviates the load, caused by the weight of the developing tank  32 , on the photosensitive drum  20  and effectively reduces the wear of the photosensitive drum  20 . 
     The force-exerting member set  60  interacts with the supporting member set  50  to maintain steady contact pressure between the developing roller  34  and the photosensitive drum  20 . The supporting member set  50 , disposed on an inner wall  10 A of the case  10  (see  FIG. 1 ), includes a first supporting member  52  and a second supporting member  54 . The force-exerting member set  60  is disposed on an outer wall  32 B of the developing tank  32 . The first force-exerting member  62  and the second force-exerting member  64  are positioned correspondingly to the positions of the first supporting member  52  and the second supporting member  54 , respectively. The image forming apparatus  1  may further include a transfer roller  70  for transferring the toner image to a medium M transported past the nip between the transfer roller  70  and the photosensitive drum  20 . 
     In this embodiment, the first supporting member  52  is the roller  52  and the second supporting member  54  is the guiding block  54 ; and the first force-exerting member  62  is a guiding block  62  and the second force-exerting member  64  is a roller  64 . When the developing tank  32  is swinging, the guiding block  62  and the roller  64  respectively exert forces on the roller  52  and the guiding block  54 . The guiding block  54  and the roller  64  respectively have guiding structures  50 G and  60 G. The guiding structure  50 G may be a track disposed or formed on the walls of the case  10 . The roller  52  and the guiding block  62  may roll or slide on the guiding structures  60 G and  50 G. In this embodiment, each of the supporting member set  50  and the force-exerting member set  60  includes a guiding structure and a roller, but the invention is not restricted thereto. In another embodiment, the supporting member set  50  may include two guiding structures, and the force-exerting member set  60  may include two rollers, working in conjunction with the two guiding structures of the supporting member set  50 . Alternatively, another type of component, such as sliding blocks, may also be used as long as the same function is achieved. 
     The resilient member  40  serves as a fulcrum for the developing tank  32 . The weight W of the developing tank  32  produces a clockwise moment, which causes the force-exerting member set  60  to exert a force on the supporting member set  50  of the case  10 . However, a reaction force by the supporting member set  50  with respect to the force exerted by the force-exerting member set  60  counterbalances the moment induced by the weight W of the developing tank  32 . In other words, the interactions between the first force-exerting member  62  and the first supporting member  52  and between the second force-exerting member  64  and the second supporting member  54  counterbalance the moment induced by the weight W of the developing tank  32 , to keep the case  10  and the developing cartridge  30  in the equilibrium state. 
     The rotation shaft  38 , inserted through the developing tank  32 , supports the developing tank  32  and drives the developing roller  34  to rotate and supply the toners  36  to the photosensitive drum  20 . The rotation shaft  38  is the rotation axis of the developing tank  32 , and the resilient member  40  is located on the rotation axis. 
       FIG. 6  is a side view of an image forming apparatus  1 ′ according to a second embodiment of the present invention. As shown in  FIG. 6 , this embodiment is similar to the first embodiment except for the following differences. In the first embodiment, the guiding structure  50 G of the supporting member set  50  includes an inclined guiding plane, and the roller  64  of the force-exerting member set  60  exerts the force on the inclined guiding plane, and rolls or slides on the inclined guiding plane. In the second embodiment, however, the guiding structure  50 G of the supporting member set  50  includes a guiding plane extending in the direction of gravity, and the roller  64  of the force-exerting member set  60  exerts a force on the guiding plane and rolls or slides on the surface in the direction of gravity. 
     Therefore, the top-mounted photosensitive drum of the present invention is different from the conventional photosensitive drum mounted at the side of or under the developing unit, and is free from the problem of the unstable contact condition of the photosensitive drum and the developing roller caused by the weight of the developing tank or the improper support to the developing tank. The image forming apparatus of the present invention reduces the wear of the photosensitive drum and improves the endurability of the photosensitive drum. 
     While the present invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that the present invention is not limited thereto. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.