PROCESS UNIT FOR AN IMAGING APPARATUS

Abstract: A process unit (1) which can be removably mounted in a main assembly of an electrostatographic copying machine. The unit (1) comprises a housing (2) enclosing an imaging member (3) and, optionally, other processing means such as a development device (4), a cleaner (5), and a charge corotron (6). The transfer corotron (7), for transferring a toner image from the photoreceptor (3) to a copy sheet is incorporated in the cassette housing (2), thus avoiding the need to provide a separate movable cover to protect the imaging member from contamination, physical damage, and light exposure when the cassette is removed from the main assembly of the copier.

Description: This invention relates to a process unit adapted to be removably mounted in a main assembly of an electrostatographic copying machine, the unit comprising a housing and an imaging member inside the housing. The invention also relates to an electrostatographic copying machine employing such a process unit. In the art of electrostatographic copying there is a trend to incorporate the imaging member, i.e. the photoreceptor, together with other process means such as a charge corotron, a development device, and a cleaning device in a removable process unit or so-called cassette as disclosed for example, in US Patent No. 3 985 436. The use of such a cassette enables the easy replacement of those parts of the copying machine which are most likely to deteriorate with use, especially the photoreceptor, but also the development and cleaning systems as well as the charge corotron wire. A further advantage of containing the major 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. A problem with the cassette disclosed in US Patent No. 3 985 436 is that when it is removed from the main assembly of the copying machine the part of the imaging member where image transfer occurs in the copying machine is unprotected and is therefore susceptible to damage or contamination, and also to light exposure which can result in premature deterioration of the photosensitive material on the imaging member. Needless to say, these adverse affects are likely to impair the quality of image formation. With a view to overcoming this problem it has been proposed to provide a cassette with a retractable cover for shielding and protecting the imaging member. For example US Patent No. 4 470 689 discloses a cassette with a movable cover mounted below the cassette housing, but integral therewith. An actuating device is included whereby the cover is automatically rotated to a closed position to shield the imaging member when the cassette is removed from the main assembly of the copying machine, and when the cassette is inserted into the main assembly the cover is automatically rotated to an open position to expose the imaging member at the area where image transfer occurs. The arrangement is such that the cover remains open during normal operation of the machine. A drawback with this arrangement is that it employs a relatively elaborate mounting and actuating mechanism for the cover which is likely to result in increased cost and diminished reliability. It is noted that in both the US patents mentioned above the transfer corotron is present in the main assembly of the copying machine. The possibility of a transfer corotron being contained in a removable process unit of a copying machine has also been suggested. An abstract of JP-A-61-97663 (Patent Abstracts of Japan, Vol. 10 No. 274 (P-498) [2330], 18 September 1986) describes a process unit for an electrostatic recorder, containing an intermediate image carrying body, and appears also to show an image transfer corotron incorporated in the unit; and US-A-4 609 276 describes a process unit for an electrophotographic copying apparatus, containing a photosensitive drum, and mentions the possibility of a transfer discharger being integrally incorporated in the unit. According to a first aspect of the present invention there is provided a process unit adapted to be removably mounted in a main assembly of an electrostatographic copying machine, the unit comprising a substantially closed housing, having apertures through which a copy sheet may enter or exit the process unit, an imaging member inside the housing, and a transfer corotron for transferring an image from the imaging member to a copy sheet, characterised in that the shield of the corotron forms part of said housing. Inclusion of the charging shield as part of the housing of the process unit has the advantage that the corotron itself shields and protects the imaging member from light exposure, damage, and contamination even when the unit is removed from the main assembly of the copying machine, thus dispensing with the need for a separate protection cover. An additional advantage of having the corotron integral with the process unit is that the corotron will be replaced automatically whenever the process unit is exchanged for a fresh one without having to change the corotron separately. The aperture through which a copy sheet may enter the process unit is, preferably adjacent the corotron. It is noted however that this aperture merely provides an entrance for the copy sheet and as such may be formed by a relatively narrow slot. In fact the slot may be so narrow that it can be left uncovered while still affording adequate protection for the photoreceptor. Alternatively, a simple resilient cover member may be provided which is readily displaced by the action of a entering copy sheet bearing against it as disclosed and claimed in our UK Patent Application publication No. 2207885. In one embodiment, a guide member formed integrally with the housing is also included for guiding a copy sheet to the aperture through which the copy sheet may enter the process unit. This guide member may comprise an extended portion of the corotron shield. According to a further aspect of the invention there is provided an electrostatographic copying machine employing a process unit in accordance with the first aspect of the invention. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic cross section of a process unit having an integral transfer corotron in accordance with the invention, Figure 2 is a schematic cross section of the process unit taken on the line II-II in Figure 1, and Figure 3 is a cross section showing detail of a latch mechanism for retaining the corotron in the process unit taken on the line III-III in Figure 2. It is noted that for the sake of clarity the Figures are not drawn to scale. In particular, in Figure 2, the dimensions in the vertical direction have been exaggerated. The same features are denoted by the same reference numerals in each of the Figures. The process unit or cassette 1 shown in Figure 1 is designed to be removably mounted in the main assembly of a xerographic copier as described, for example, in the aforementioned US Patents and also in our EP-A-0 244 104. As the interaction between the cassette and the main assembly of the copying machine is adequately described in the aforementioned documents no further details need be given here and for the same reason the main assembly of the copying machine is not depicted in the present Figures. The cassette 1 comprises a housing 2 made for example, primarily of polystyrene which encloses an imaging member in the form of a belt photoreceptor 3 in addition to various process means, in particular a development device 4, a cleaner 5, and a charge corotron 6. These processing means are not directly relevant to the subject matter of the present invention and so no further details are given here. The belt photoreceptor is an endless flexible belt 3 having a photosensitive surface. In the arrangement shown, when the cassette 1 is removed from the main assembly of the copier the belt is only loosely retained in the cassette, but when the cassette is inserted into the main assembly of the copying machine the photoreceptor belt is supported in an operative position by a member (not shown) forming part of the main assembly. A cassette having this kind of loosely retained photoreceptor arrangement forms the subject of our EP-A-0 244 104 to which reference is invited for further details. Returning to Figure 1, a transfer charging device 7 is included in the cassette housing in the vicinity of the photoreceptor belt at the area where a toner image is to be transferred from the belt to a copy sheet. The technique of actually transferring a toner image is well known to those skilled in the art and no further details need be given here. The transfer charging device 7 is in the form of a corotron having an outer shield 8 which, as is conventional, is substantially U-shaped and made for example of stainless steel. A corona wire 9 extends the full length of the shield 8 and is spaced apart from the walls thereof in the usual manner. At its upper end the shield has extended portions 10 and 11 on its left- and right-hand sides respectively, as viewed in the drawing. These portions 10 and 11 define the path which a copy sheet follows as it passes through the cassette for the purposes of having a toner image transferred thereto, as described in more detail below. The manner in which the transfer corotron 7 is fixed to the cassette housing 2 will now be described. As shown in Figure 2, the corotron 7 has end caps 21,22 fastened to opposite ends of shield 8. The end caps 21,22 are made of a plastics material. End cap 21 has a projecting pin 23 extending from its side faces both into and out of the plane of Figure 2. The pin 23 is accommodated in sockets 24 formed integrally in the cassette housing 2. Two such sockets 24 are provided, one on each side of the end cap 21. At the opposite end of the corotron 7, the other end cap 22 has a projecting tab 25 which engages in a latch mechanism 26 as shown more clearly in Figure 3. The tab 25 is held by two jaws 27a, 27b of the latch which are biased together by an inverted keyhole-shaped spring 28. The spring 28 is held in place by pairs of tabs 29a, 29b; 30a, 30b formed integrally on the inward face of the jaws 27a, 27b. The upper portion of each jaw 27a, 27b is provided with a protruding post 31a, 31b with an enlarged head 33a, 33b extending from the outward face. The posts 31a, 31b are accommodated in slots 32a, 32b respectively in the cassette housing, thus providing a pivotal mounting for the jaws. The enlarged heads 33a, 33b which act to retain the latch in its own plane are present on the outside of the cassette housing as can be seen most clearly in Figure 2. The latch is also held in place by two bail bars 34a, 34b formed on a recessed portion of the internal wall of the cassette housing 2. The bail bars 34a, 34b are both joined to the cassette housing at each of their two ends, thereby providing a slot between the bars and the cassette housing through which the jaws 27a, 27b are threaded, thereby limiting their pivotal movement as well as holding them in their own plane (see Figure 3). When the cassette is outside the main assembly of the copying machine the jaws 27a, 27b of the latch 26 are closed to support the corotron as shown in Figure 3. However, the latch is adapted to be opened automatically to release the corotron when the cassette is inserted into the main assembly of a copying machine, which enables the corotron to be located accurately relative to the photoreceptor when it is in the operative position in the machine and also enables the corotron to be hinged open about pivot pin 23 to allow for clearance of jammed copy sheets. These features are the subject of our UK patent application No. 2199537 and our European patent application No. 0272094, to which reference is invited for further details. It is noted, however, that it is not necessary for the transfer corotron 7 to have a hinge and latch mounting as described above. Instead the transfer corotron 7 may, for example simply be fixed rigidly at each of its two ends to the side walls of the cassette housing 2. As can be seen from Figures 1 and 2, the outside of the corotron shield 8 forms part of the external wall of the housing 2. An aperture 14 is present between the right-hand extension 11 of corotron shield 8 and the main part of the cassette housing to enable a copy sheet to enter the process unit for the purpose of transferring an image thereto from the photoreceptor belt 3 in the vicinity of the transfer corotron when the cassette is inserted into the main assembly of the copying machine. The aperture 14 is in the form of a slot extending substantially the full width of the cassette but being relatively narrow, for example 2 mm wide. Thus the slot is sufficiently wide to permit a copy sheet to enter the cassette, but narrow enough to provide appreciable protection for the photoreceptor from damage, contamination, and light exposure thus prolonging the useful life of the photoreceptor. The path which a copy sheet follows as it passes through the cassette for image transfer purposes is denoted by an arrow in Figure 1. The external wall portion 15 of the main part of the cassette housing is shaped so as to deflect and guide the approaching copy sheets towards the aperture 14. Furthermore, the extreme right-hand side of the extended portion 11 of corotron shield 8 has a downturned lip 16 inclined obtusely relative to the adjacent plateau portion 17. The downturned lip thus also acts to guide approaching copy sheets towards the aperture 14. It is noted here that the means for feeding the copy sheets form part of the main assembly of the copying machine, as is usual, and as such they are not depicted in the accompanying drawing. As the copy sheet enters the cassette it follows the path defined between the photoreceptor belt 3 and the plateau portion 17 of the corotron shield extension 11. The copy sheet then passes over the main part (i.e. the shield 8 and the wire 9) of the transfer corotron 7 where the toner image is transferred from the photoreceptor belt to the copy sheet itself in known manner. From there the copy sheet traverses the slightly upwardly inclined ramp 18 forming part of the shield extension 10 on the left-hand side of the corotron 7, and thence to aperture 20 in the cassette housing where the copy sheets exits the cassette for further processing, in particular for the toner image to be fixed permanently to the copy sheet using techniques well known to persons skilled in the art. From the foregoing it will be evident that various modifications may be made within the scope of the present invention as claimed. For example, instead of a flexible belt the imaging member may comprise a photoreceptor drum as commonly used in xerographic machines. Moreover, apart from the transfer corotron, the cassette may enclose additional or alternative processing means to those described above.

Claims: A process unit (1) adapted to be removably mounted in a main assembly of an electrostatographic copying machine, the unit comprising a substantially closed housing (2) having apertures (14,20) through which a copy sheet may enter or exit the process unit, an imaging member (3) inside the housing, and a transfer corotron (7) for transferring an image from the imaging member to a copy sheet, characterised in that the shield (8) of the corotron(7) forms part of said housing. A process unit as claimed in claim 1, wherein the housing further comprises an integral guide member (15,16) for guiding the copy sheet to the aperture (14) through which a copy sheet may enter the process unit. A process unit as claimed in claim 1 or claim 2, in which the shield of the corotron has an extended portion (10) defining the path of a copy sheet though the process unit. An electrostatographic copying machine comprising a main assembly, and a process unit as claimed in any preceding claim adapted to be removably mounted in said main assembly.

Inventors: HOWARD, ALAN CHARLES RICHARD, NEWBURY, DAVID MICHAEL, DR.
Applicants: XEROX CORPORATION
Application year: 1987
Main classification: G03G15
IPC codes: G03G21, G03G15