Unit comprising an image bearing member

Abstract: A support structure for an image bearing member is provided in which the tip portions (16a, 26a) of support pins (16, 26) inwardly projecting from side plates (2) of a housing, come in contact with the bottoms of support-pin introducing holes (13c, 23c) in the image bearing member, so that tension applied to a grid electrode (4) disposed opposite the image bearing member (3) is rigidly received by the image bearing member (3) and the support-pins (6). Predetermined gaps (S) are formed between the side plates (2) and the flange portions (3a) of the image bearing member.

Description: The present invention relates to a unit for supporting an image bearing member, and more particularly to an image bearing unit in an image forming apparatus, in which the image bearing member is supported, at opposite sides thereof, by a pair of side plates formed in a housing of the image bearing unit, and in which a grid electrode for a corona discharger is installed between the side plates. An image forming apparatus such as a copying machine, a laser beam printer or the like, may comprise an image bearing unit in which an image bearing member such as a photoreceptor drum or the like is rotatably held in the housing of the image bearing unit. In an image forming apparatus having such an image bearing unit, upon completion of a predetermined amount of image forming operations, the image bearing unit can be removed from the main body of the image forming apparatus and replaced with a new image bearing unit. This advantageously facilitates the mounting of a new image bearing unit. The Patent Abstracts of Japan, Vol. 13, No. 276 (P-890) (3624), June 26, 1989 and JP-A-01-065573 disclose an electrifying device for a photosensitive body. A corona discharge and a grid electrode are supported by supporting plates of a support housing. Pins project inwardly from the supporting plate to support the photosensitive drum therebetween. The separation distance of the supporting plates is maintained by connection to a bottom plate located adjacent the photosensitive drum opposite the grid electrode. The image bearing unit with a similar arrangement has been also proposed. An image bearing member is interposed between a pair of side plates formed on the housing of the image bearing unit with predetermined gaps formed between the image bearing member and the side plates, and shafts inwardly projecting from the side plates are inserted in and passed through flange portions of the image bearing member at opposite sides thereof so that the image bearing member is rotatably supported. Further, a grid electrode of the scorotron type for a corona discharger is installed between the pair of side plates with a predetermined tension applied to the grid electrode. In this image bearing unit, the image bearing member is arranged such that the shafts inwardly projecting from the side plates are inserted in and passed through the flange portions of the image bearing member. Accordingly, the tension applied to the grid electrode may cause the side plates to be inwardly deformed and come in slide contact with the opposing sides of the image bearing member. This disadvantageously increases the driving torque of the image bearing member and generates noise. In view of these problems, the object of the present invention is to provide a support unit for an image bearing member which prevents the side plates holding the image bearing member from being inwardly deformed, and allows better exposure of the image bearing member. In accordance with the present invention, an image bearing unit for an image forming apparatus is provided as defined in the claims. The image bearing member is supported, at opposite sides thereof, by a pair of side plates formed in a housing. A grid electrode for a corona discharger is installed between the side plates. Support pins, restrained from being axially moved, inwardly project from the side plates and are introduced into support-pin introducing holes formed in flange portions of the image bearing member at opposite sides thereof, so that the image bearing member is rotatably supported. The tip portions of the support-pins come in contact with the bottoms of the support-pin introducing holes with gaps formed between the side plates and the flange portions. The support structure for an image bearing member having the arrangement above-mentioned, prevents the side plates of the housing from coming in slide contact with the flange portions of the image bearing member, thus preventing an increase in the driving torque of the image bearing member, as well as generation of noise. Preferably, one of the side plates has an engagement projection with which one end of the grid electrode is engaged, and the other side plate has a resilient member which applies tension to the grid electrode with the other end of the grid electrode held by the resilient member. With this arrangement, a desired tension can be applied to the grid electrode by the biasing force of the resilient member. Preferably, the side plates have grid-electrode positioning surfaces, and the resilient member applies a biasing force such that the grid electrode is pressed onto the positioning surfaces. With this arrangement, the ends of the grid electrode are pressed onto the positioning surfaces, thus precisely positioning the grid electrode. Accordingly, the distance between the grid electrode and the image bearing surface of the image bearing member can be uniformly maintained. Preferably, the resilient member is formed by a leaf spring, and the support pins inwardly projecting from the side plates have flange portions which are fixed, together with the leaf spring, to the side plates with screws. With this arrangement above-mentioned, the same screws are used for fixing the support pins and the leaf spring to the side plates, thus simplifying the assembling steps. Preferably, the side plates extend as projecting from the housing such that the image bearing surface of the image bearing member is exposed to the outside from the housing. With this arrangement, the corona discharger can be attached at the outside of the image bearing unit, i.e., arranged in the main body of an image forming apparatus adjacent to the image bearing unit. Accordingly, the image bearing unit can be composed of disposable parts only. The grid electrode is preferably installed between the side plates at the free end sides thereof. In a further embodiment the tip portions of the support pins are preferably semi-spherical and the bottoms of the support-pin introducing holes are semi-spherical accommodating the spherical surfaces of the tip portions of the support-pins. The arrangement advantageously reduces the slide resistance between the tip portions of the support pins and the bottoms of the support-pin introducing holes. For the same reason, in another embodiment the tip portions of the support pins are tapered and that the bottoms of the support-pin introducing holes are tapered to accommodate the tapering surfaces of the tip portions of the support pins. Preferably, the image bearing member has a casing main body and flange portions formed at both ends of the main body, the flange portions being made separately from the main body. These and other objects and advantages of the present invention will be more fully apparent from the following detailed description set forth below when taken in conjunction with the accompanying drawings and wherein: Figure 1 is a section view of a drum unit serving as an image bearing unit employing the structure of supporting an image bearing member according to an embodiment of the present invention; Figure 2 is a perspective view of the drum unit shown in Figure 1; Figure 3 is a section view of main portions of another embodiment of the present invention; and Figure 4 is a section view of main portions of a further embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a detailed description of the present invention with reference to the attached drawings illustrating embodiments thereof. Fig. 1 is a sectional view of a drum unit serving as an image bearing unit with the support structure according to an embodiment of the present invention. Fig. 2 is a perspective view of the drum unit shown in Fig. 1. In the drum unit, a photoreceptor drum 3 serving as the image bearing member is rotatably supported between a pair of side plates 2 formed as part of a housing 1 with a predetermined space provided between the side plates 2. The photoreceptor drum 3 in this embodiment has a casing main body 3c and flange portions 3a respectively formed at both ends of the main body 3c, the flange portions 3a being formed separately from the main body 3c. A grid electrode 4 for a corona discharger (not shown) is disposed between the pair of side plates 2. The housing 1 is a molded integral structure made of synthetic resin. The side plates 2 project from the housing 1 such that the image bearing surface of the photoreceptor drum 3 extends from the housing 1 and is exposed. In this embodiment, the corona discharger can be mounted separate from the image bearing unit or photoreceptor drum 3, i.e. arranged in the main body of an image forming apparatus proximate the photoreceptor drum 3. Accordingly, the image bearing unit can be composed of separately exchangeable parts. In the housing 1, one of the side plates 2 is provided on the top thereof with an engagement projection 2a with which one end of the grid electrode 4 is engaged, and the other side plate 2 is provided at the outer side surface thereof with a leaf spring 5 serving as a resilient member with which the other end of the grid electrode 4 is engaged. The grid electrode 4 is arranged between the side plates 2 at the free end sides thereof. A predetermined tension is applied to the grid electrode 4 by the resilient force of the leaf spring 5. Thus, a desired tension can be applied to the grid electrode 4 by the biasing force of the leaf spring 5. The side plates 2 preferably have positioning surfaces 2b for the grid electrode 4. The leaf spring 5 applies tension to the grid electrode 4 and at the same time exerts a biasing force in such a direction that the ends of the grid electrode 4 are pressed onto the positioning surfaces 2b. As a result, the grid electrode 4 can be precisely positioned. Accordingly, the distance between the grid electrode 4 and the image bearing surface of the photoreceptor drum 3 can be uniformly maintained. Support pins 6 for rotatably supporting the photoreceptor drum 3 are respectively inserted into and pass through the pair of side plates 2. Each of the support pins 6 has a shank portion 6a and a flange portion 6b at the base end of the shank 6a. The tips of the shanks 6a project inwardly of the side plates 2. The flange portions 6b are fixed to the side plates 2 with screws 7, thus securing the support pins 6 against movement in the axial direction. The support pins 6 are fitted into support-pin introducing holes 3b formed in the flange portions 3a of the photoreceptor drum 3 at the opposite sides thereof such that the drum is rotatable. The tips of the support pins 6 come in contact with the bottoms of the support-pin introducing holes 3b. With the tips of the pins 6 in contact with the bottoms of the holes 3b, predetermined spacing gaps S are formed between the flange portions 3a and the side plates 2. The resilient member, preferably leaf spring 5 is preferably mounted between the flange portion 6b of one support pin 6 and one side plate 2. The spring 5 together with the one support pin 6 are preferably fixed to the one side plate 2 with the screws 7. Thus, the same screws 7 can be used for fixing the flange portion 6b of the one support pin 6 and the leaf spring 5 to the one side plate 2, thus simplifying the assembling steps. According to the arrangement above-mentioned, since the tips of the support-pins 6 fixed to the side plates 2 come in contact with the bottoms of the support-pin introducing holes 3b in the photoreceptor drum 3, the support-pins 6 are restrained from being axially displaced. Accordingly, the tension applied to the grid electrode 4 can be received by the rigidity of the photoreceptor drum 3 and the support pins 6 fixed to the side plates 2. This prevents inward bending of the side plates 2, so that the gaps S between the flange portions 3a of the photoreceptor drum 3 and the side plates 2 can be maintained constant at all times. This also prevents the side plates 2 from coming into slide contact with the flange portions 3a, thus avoiding an increase in the required driving torque of the photoreceptor drum 3, as well as avoiding the generation of noise. By providing that the side plates 2 are not bent, the grid electrode 4 is prevented from being loosened or improperly positioned on the grid electrode positioning surfaces 2b. This ensures that images formed by the photoreceptor drum 3 are not lowered in quality. The drum unit may be further embodied as having, in a unitary structure, processing components such as a cleaner for collecting a toner remaining on the photoreceptor drum 3. The support structure for an image bearing member should not be limited to the embodiment described above. For example, as shown in Fig. 3, the support-pin 16 may have a semi-spherical tip portion 16a, and a flange portion 13a in which a support-pin introducing hole 13b has a bottom 13c which is semi-spherical accommodating the spherical surface of the tip portion 16a of the support pin 16. Further, as shown in Fig. 4, the support-pin 26 may have a tapering tip portion 26a, and a flange portion 23a in which a support-pin introducing hole 23b has a bottom 23c which is tapered to accommodate the tapering surface of the tip portion 26a of the support-pin 26. The arrangements shown in Figs. 3 and 4 advantageously lower the slide resistance between the tip portions 16a, 26a of the support-pins 16, 26 and the bottoms 13c, 23c of the support-pin introducing holes 13b, 23b. Alternatively, the image bearing member may be made in the form of a photoreceptor belt instead of the photoreceptor drum 3, or the support pins 6 may be thread connected directly to the side plates 2.

Claims: An image bearing unit for an image forming machine, comprising an image bearing member (3) supported at opposite ends by a pair of side plates (2) formed in a housing (1) and a grid electrode (4) for a corona discharger arranged between said side plates (2), wherein support pins (6) project inwardly from said side plates (2) and are fitted into flange portions (3a) at opposite ends respectively of the image bearing member (3), so as to rotatably support said image bearing member (3), characterized in that said support pins (6) are mounted to be restrained against axial movement with respect to the side plates (2), the tip portions (16a, 26a) of said support pins (6) are adapted to contact the bottoms of support-pin introducing holes (3b) provided in said flange portions (3a), such that predetermined gaps are formed between said side plates (2) and said flange portions (3a). The image bearing unit according to Claim 1, wherein one of the side plates (2) has an engagement projection (2a) with which one end of the grid electrode (4) is engaged, and the other side plate (2) has a resilient member (5) which applies tension to said grid electrode (4) with the other end of said grid electrode held by said resilient member (5). The image bearing unit according to Claim 2, wherein the side plates (2) have grid-electrode positioning surfaces (2b), and the resilient member (5) applies a biasing force in such a direction that the grid electrode (4) is pressed onto said positioning surfaces (2b). The image bearing unit according to Claim 2 or 3, wherein the resilient member (5) is formed by a leaf spring, and the support pins (6) have integral flange portions (6b) which are secured, together with said leaf spring, to said other side plate (2) with screws (7). The image bearing unit according to any one of the Claims 1 to 4, wherein the side plates (2) project from the housing (1) such that the image bearing surface of the image bearing member (3) extends from said housing (1) and is exposed. The image bearing unit according to Claim 5, wherein the grid electrode (4) arranged between the side plates (2) is mounted on free end sides of the respective side plates (2). The image bearing unit according to any one of the Claims 1 to 6, wherein the tip portions (16a) of the support pins (16) are semi-spherical and the bottoms (13c) of the support-pin introducing holes (13b) are semi-spherical and accommodate the spherical surfaces of said tip portions (16a) of said support pins (16). The image bearing unit according to any one of the Claims 1 to 6, wherein the tip portions (26a) of the support pins (26) are tapered and the bottoms (23c) of the support-pin introducing holes (23b) are tapered to accommodate the tapered surfaces of said tip portions (26a) of said support pins (26). The image bearing unit according to any one of the Claims 1 to 8, wherein the image bearing member has a casing main body (3c) and said flange portions (3a) formed at either end of said main body, said flange portions (3a) being formed separately from said main body (3c). The image bearing unit of any one of the Claims 1 to 9, wherein the image bearing member (3) is a drum unit.

Inventors: KUBOTA HIROSHI, TANIGUCHI SUSUMU, KUBOTA, HIROSHI, TANIGUCHI, SUSUMU, KUBOTA, HIROSHI, C/O MITA INDUSTRIAL CO., LTD., TANIGUCHI, SUSUMU, C/O MITA INDUSTRIAL CO., LTD.
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G03G15
IPC codes: G03G21, G03G15