PROCESS UNIT FOR AN IMAGING APPARATUS

Abstract: A cassette (12) for an electrophotographic imaging machine (10) contains a photoreceptor, such as an endless belt photoreceptor (20) and optionally one or more process means, such as a charge corotron, as development device, a transfer corotron and a cleaning device. The photoreceptor (20) is loosely held in an open loop, for example by means of belt retaining strips (21), within the cassette when the cassette is out of the main machine (10). When the cassette (12) is inserted into a suitably shaped aperture (11) in the main machine, the photoreceptor engages over a pair of support rollers (22). Either or both of the rollers are movable so as to space them further apart, thereby tensioning the photoreceptor belt and accurately locating the belt within the machine. One of the support rollers (22) may also be a drive roller for the belt.

Description: This invention relates generally to an imaging apparatus, and is particularly, although not exclusively, concerned with a xerographic copying apparatus. The invention is more especially concerned with a xerographic process cassette adapted to be removably mounted in a main assembly of a xerographic imaging apparatus, the cassette including an imaging member in the form of a rigid cylinder or a flexible endless belt having an electrically photosensitive surface, and optionally one or more process means. Such a cassette might comprise a xerographic process cassette of the kind which includes only the photoreceptor, or the photoreceptor and at least one of the process means such as a charge corotron, a development device, a transfer corotron, and a cleaning device. An example of such a xerographic process cassette is described in US Patent No. 3 985 436. The use of a cassette of this kind enables the easy replacement of those parts of a xerographic machine which are most likely to deteriorate with use, especially the photoreceptor, but also the development and cleaning systems as well as the corotron wires. A further advantage of containing the major xerographic process elements within a cassette is that interchangeable cassettes may be used in a given copying machine, to provide different development characteristics, or different coloured development. It is advantageous to make the insertion and withdrawal operations as simple and reliable as possible, without the need for elaborate mechanisms to ensure that the photoreceptor arrives at exactly the correct position for an in-focus image to be formed on it by the optical system of the machine. This becomes especially important when considering interchangeable cassettes because of the possibility of frequent changes of cassette. Furthermore, it would be advantageous if the cassette contained the minimum of mechanical components associated with the xerographic processor and of the kind which do not rapidly deteriorate, so as to make the cassette as inexpensive as possible. One service option with a very low cost cassette is to make it a truly "throw-away" item once one or more of its components has deteriorated to such an extent as to be no longer useful. The present invention is intended to provide a xerographic process cassette for an imaging apparatus which has these advantageous features. The cassette of the invention is characterised by the image bearing member being loosely retained in the cassette when the cassette is removed from the main assembly, and being adapted to be supported in an operative position by support means forming part of the main assembly when the cassette is inserted into the main assembly. In a preferred form of the invention, the imaging member comprises an endless photosensitive belt. When the cassette is inserted into the main assembly, the belt is engaged by spaced holding members forming part of the main assembly. The holding members are then operated to move them to a position which tensions the belt. This arrangement makes it possible to provide a cassette in which no driving mechanisms are needed, in which insertion and withdrawal of the cassette are simple operations, and in which accurate positioning of the photosensitive member relative to the optics of the machine is automatically achieved. The photoreceptor supporting and driving arrangements are mounted in the main machine, thus simplifying and reducing the number of components in the cassette, and also avoiding the probelm of accurate positioning of the photoreceptor within the machine. The invention can be applied to drum photoreceptors as well as to endless belts. Various embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figures 1 to 3 are diagrammatic representations showing the basic principle of operation of three embodiments of the invention; Figures 4 and 5 are cross sectional views of a cassette showing two alternative ways in which a photoreceptor belt may be retained in a cassette; Figure 6 is a cross sectional side view of a further embodiment of a cassette, installed in a machine; Figure 7 is a cross sectional, partial plan view of the cassette of Figure 6; and Figures 8, 9 and 10 are diagrammatic sectional views showing guiding systems for the photoreceptor belt. Referring to the drawings, the simplest example of the invention is when applied to a hard cylindrical (drum) photoreceptor as shown in Figure 1. A xerographic machine 10 has an aperture 11 to accept the cassette 12, and within the aperture 11 is located a drive and location shaft 13 for the photoreceptor which is cantilevered from the rear of the machine. The shaft 13 has a tapered end 14 to aid engagement of the photoreceptor over the shaft, and could be of the expanding mandrel type. The cassette 12 has a loosely held, hollow, cylindrical photoreceptor 15 located within an open ended cavity to enable engagement of the drive and location shaft 13 into the photoreceptor 15. When the cassette is inserted into the machine, the photoreceptor 15 is located by the drive and location shaft 13, thus minimising location errors between the photoreceptor and the imaging unit of the machine. Referring now to Figures 2 and 3, there are shown two embodiments of the invention using flexible, endless photoreceptor belts. The Figure 2 embodiment uses a two-roller support arrangement, whereas that shown in Figure 3 has three rollers. In Figure 2, the belt 20 is loosely held in the cassette 12 by means of belt retaining strips 21 to be described below. As in the Figure 1 embodiment, the cassette 12 is inserted into an aperture 11 in the machine 10, the belt 20 being so positioned as to slide over two support rollers 22. Either or both of the rollers may be movable such as to space them further apart, operable after insertion of the cassette, to locate and tension the belt 20. Once it is positioned and tensioned over the rollers 22, the belt 20 runs out of contact with the belt retaining strips 21, and may be driven around the rollers, for example by one or both of the rollers, or by other drive means cooperating with the belt. One of the rollers may be replaced by a skid member (e.g. a non-rotating cylinder), or in the case where some other drive means is used, both the rollers may be replaced by skid members. The space between the rollers may be vacant, or substantially filled, or, preferably, may contain processor elements. The rollers 22 may have tapered end portions 23 to assist in the initial location of the rollers into the loop formed by the belt. Figure 3 shows a three-roller embodiment, which operates in substantially the same way as the Figure 2 embodiment. The belt 30 in the cassette 12 is loosely held in a generally triangular configuration by belt retaining strips 31, and the rollers 32 in the machine are spaced apart in a triangular configuration for receiving the belt 30. The rollers 32 may be provided with tapering ends, or a tapering triangular member 33 may be supported by the rollers 32 to assist in locating the belt 30 over the rollers. In the Figures 2 and 3 embodiments, the cassette includes a housing member which cooperates with the photoreceptor belt to constrain the external contour of the belt to the desired configuration. A suitable ribbed housing for this purpose is shown in Figure 4, with the photoreceptor belt 20 loosely retained between the ribs 37 and a set of belt retaining strips 21. Lateral movement of the belt is prevented by the upturned ends of the belt retaining strips 21 on the upper run of the belt, and by larger ribs 38, at each side of the base of the housing. The upturned ends of the belt retaining strips 21 are secured by sets of clamping ribs 39 to the roof of the housing. In this way, the upper belt run of the belt 20 is loosely defined, while the remainder of the belt hangs freely below it in a loop. Belt retaining strips, not shown, may also be provided for the lower run of the belt. When a cassette of this construction is inserted into the main assembly of the copying machine, its open end 40 allows the support rollers to locate inside the loop of the photoreceptor belt 20 in the same way as shown in Figure 2. Once the belt has been tensioned (by moving the support rollers apart) its upper run lies between the ribs 37 and the belt retaining strips 21. In the case where the space between the tensioning rollers is filled, with a casing extending between the rollers, the casing may be formed with recesses or grooves to accommodate the belt retaining strips when the cassette is in the machine. Referring now to Figure 5, there is shown an alternative arrangement for supporting the photoreceptor belt 20 within a cassette. The upper run of the belt is loosely retained betweeen belt retaining strips 21 and the roof of the cassette, with the lower run of the belt hanging down in a loop. The lower run of the belt occupies a position near the mid-plane of the cassette, and cannot therefore be supported or guided by the floor of the cassette. In order to ensure that the belt loop is always open and ready to receive the tensioning rollers, a set of flexures 42 are provided, secured at one end to the belt retaining strips 21, and contacting the inside surface of the belt 20 with their free ends so as to resiliently urge the belt into the desired open loop configuration. In this arrangement, the tensioning rollers are mounted at each end of a drive module 43 which substantially fills the space between the rollers. On insertion of the cassette into the machine, the drive module 43 slides into the space inside the photoreceptor belt loop, engaging the flexures 42 as it does so, and pushing them upwards. The drive module 43 is grooved to accommodate the flexures 42. Once the cassette is fully engaged, the tensioning rollers in the drive module 43 are urged apart to tension the belt. This tensioning may be done manually, e. g. by operation of a suitable lever, or automatically, upon location of the cassette into its fully inserted position. On removal of the cassette, (after first releasing the tension in the belt) the flexures spring back and hold the photoreceptor belt loop open again. Another way of holding the photoreceptor belt open when the cassette is out of the machine is shown in Figures 6 and 7. In this arrangement, the inside of the photoreceptor belt 20 is constrained into the shape of the belt drive assembly by a sliding former 44 that can slide inside the photoreceptor belt in the cassette on rods 45, or on a similar guide rail arrangement. When the cassette is outside the machine the sliding former 44 is at the rear of the unit, holding open the photoreceptor belt loop. On insertion of the cassette into the machine, the former 44 is pushed through the photoreceptor belt loop by the belt drive assembly, as indicated by arrows 46, until it passes out of the front end of the photoreceptor belt loop, whereafter the belt can be tensioned. On removal of the cassette, after releasing the belt tension, a latching arrangement pulls the former 44 back inside the photoreceptor loop, aided by the tapered shape 47 of the former, and the former is returned to its original position at the rear of the cassette when the latching arrangement releases to free the cassette from the machine. The cassette of the present invention is particularly advantageous when the photoreceptor belt is transparent or translucent. In these circumstances, the photosensitive surface of the photoreceptor belt may be exposed to light, either for imaging (e.g by means of a LED writing array) or discharge (e.g. for intercopy and edge fadeout), by exposure means located inside the belt drive module, thus further simplifying the cassette. As well as containing the photoreceptor, the cassette may also contain one or more other xerographic process assemblies, such as charging, erasing, development, transfer, or cleaning assemblies. In the case of a cassette containing a flexible belt photoreceptor, various methods may be employed for tracking or steering the belt, some examples of which will be described with reference to Figures 8 to 10. Referring to Figure 8, an edge force on the edges of the photoreceptor belt may be used to guide the belt, the edge force being provided by edge guides 50. The edge guides 50 may be provided as ribs on the inside of the cassette housing at a position adjacent one of the tension rolls. The tension roll, which is mounted in the belt drive module of the main assembly of the machine, is cammed into engagement between the edge guides. In this arrangement, the tension roll is preferably a slotted roll, i.e. a roll in the form of a succession of spaced discs of a resilient material, that has low lateral shear characteristics, or can alternatively be a low shear modulus material (e.g. a foamed resilient plastics material). Alternatively, a non-rotational skid may be substituted for the tension roll, and such a skid can act as a camming member since it offers no frictional resistance to sideways movement of the photoreceptor belt. An alternative guidance arrangement is shown in Figure 9. In this arrangement, the belt drive module is arranged so as to always drive the photoreceptor belt into the cassette (i.e. away from its open end) and for this purpose the camming roller or skid has a flange 51 which limits the outward motion of the photoreceptor belt. This arrangement is in other respects similar to the Figure 8 embodiment. Figure 10 shows a further refinement to the arrangement of Figure 9. In this arrangement, the tension roller is allowed to travel laterally under the influence of the edge force, and the lateral motion is used to steer the roller, thus reducing the edge force to a low level. The roll bearing 52 is urged by a spring 53 into engagement with an inclined support 54. In a cassette which uses a delicate photoreceptor belt, or one for which considerable use is anticipated, it is advantageous to avoid using edge forces altogether for controlling the belt steering system. This can be achieved by optically sensing the photoreceptor belt position, and steering a roll or skid with a servo motor or solenoid. Here again, the additional complexity required is in the belt driving module of the machine, and the cassette is of simple construction. In order to protect the photoreceptor belt from damage in the environment, for example by over exposure to light, dust, or handling, it is advantageous to have a cover at the open end of the cassette. This can be a simple spring-loaded flap 55 (Figure 5) that is pushed open by the belt drive module 43 of the machine when the cassette is inserted.

Claims: Xerographic process cassette (12) adapted to be removably mounted in a main assembly (10) of a xerographic imaging apparatus, the cassette including an image bearing member in the form of a rigid cylinder (15) or a flexible endless belt (20) having an electrically photosensitive surface, and optionally one or more process means, characterised in that the image bearing member (15 or 20) is loosely retained in the cassette (12) when the cassette is removed from the main assembly, and is adapted to be supported in an operative position by support means (13 or 22) forming part of the main assembly when the cassette is inserted into the main assembly. The cassette of claim 1 wherein the image bearing member is a belt photoreceptor, and including means (21) to retain the belt photoreceptor in the cassette, when the cassette is out of the main assembly, in an open loop configuration. The cassette of claim 2, wherein said belt retaining means comprises a plurality of guiding surfaces (37) within the cassette to limit outward movement of the belt, and a plurality of retaining members (21) inside the belt to limit inward movement of the belt. The cassette of claim 2 wherein said belt retaining means comprises a guiding surface (37) within the cassette to limit outward movement of a first run of the belt, and a plurality of retaining means (21) inside the belt to limit inward movement of said first run of the belt, and resilient means (42) urging a second run of the belt away from said first run so as to maintain said open loop configuration. Xerographic imaging apparatus comprising a main assembly and a cassette according to any one of claims 1 to 4. The imaging apparatus of claim 5, wherein the image bearing member is a drum photoreceptor and wherein a drive shaft (13) for the drum is mounted within the main assembly and includes means for releasably securing the drum around it. The imaging apparatus of claim 5, wherein the image bearing member is an endless flexible belt, and wherein a plurality of belt holding members (22) are mounted within the main assembly, and wherein at least one of said belt holding members is movable to tension the belt so as to permit the belt to be driven, optionally by one of the belt holding members, around said belt holding members. The imaging apparatus of claim 7 wherein the belt holding members (22) comprise two rollers, at least one of which is movable away from the other to tension the belt, and at least one of which is a drive roller for the belt.

Inventors: CARTER, ROBERT ALBERT
Applicants: XEROX CORPORATION
Application year: 1987
Main classification: G03G15
IPC codes: G03G21, G03G15