PROCESS UNIT FOR AN IMAGING APPARATUS

Abstract: A process unit (1) which can be removably mounted in a main assembly (100) of a reproducing machine such as a xerographic copier. The unit 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 unit also comprises an integral transfer corotron (7) which has one end (21) hingedly mounted on the housing enabling the corotron to be pivoted open for jam clearance. Preferably, the end (22) of the corotron remote from the pivoted end (21) is retained in the unit by a latch (26) which is opened automatically to release the corotron when the unit is inserted into the main assembly. A flexure (49) within the main assembly normally urges the corotron to its operative position when the unit is inserted in the main assembly, but the flexure may be withdrawn so that the corotron pivots open about its hinged end (21) to permit jam clearance. When the unit is withdrawn from the main assembly the corotron is automatically latched back into the unit housing.

Description: This invention relates to a process unit adapted to be removably mounted in a main assembly of a reproducing machine, the process unit comprising at least an imaging member and a charging device. The invention also relates to a reproducing machine, particularly a xerographic copying machine, including 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 effects 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 US patents mentioned above the transfer charging device, i.e. 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. In particular, 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. By contrast, however, our Euorpean patent application publication No.0272093 proposes incorporating the transfer charging device (a corotron) in a process unit with an imaging member so that the corotron shield forms part of the housing of the process unit. That has the advantage that the corotron itself shields and protects the imaging member from light exposure, damage, and contamination even when the process unit is removed from the main assembly of the copying machine, thus dispensing with the need for a separate protecting cover. An additional advantage of having the transfer corotron integral with the process unit housing is that it will be replaced automatically whenever the process unit is exchanged for a fresh one without having to change the transfer corotron separately. As the transfer corotron is incorporated in the process unit, a copy sheet actually has to enter the process unit in order to have an image transferred thereto from the imaging member. With this arrangement it may be a difficult and delicate operation to clear a copy sheet if it becomes jammed in the process unit in the vicinity of the transfer corotron without damaging the photoreceptor. Although a transfer charging device which can be moved relative to the imaging member in a reproducing machine has been described (JP-A-60 140264 and JP-A-56 109371), the problem of jam clearance in a process unit which incorporates both an image member and a transfer corotron remains. According to a first apect of the present invention, there is provided a process unit adapted to be removably mounted in a main assembly of a reproducing machine, comprising a housing enclosing an imaging member and an elongate transfer corotron, characterised in that the transfer corotron is hingedly mounted at one end so that its second, opposite, end is movable away from the imaging member, the second end being releasably retained in the process unit by latch means. The hinged mounting enables the transfer corotron to be pivoted to an open position away from the imaging member when the process unit is in the reproducing machine to facilitate jam clearance without damaging the imaging member. Preferably, the latch means are adapted to release the corotron automatically when the process unit is inserted into the main assembly. According to a further aspect of the present invention, there is provided a reproducing machine comprising a main assembly, and a process unit in accordance with the first aspect of the invention adapted to be removably mounted in said main assembly. The main assembly suitably comprises means for supporting the corotron in a predetermined location relative to the main assembly when the process unit is inserted therein. The support means may comprise resilient flexures. In one embodiment, respective support means may be provided at each of the two ends of the corotron, the support means at the latch end being withdrawable from the main assembly whereby the corotron is pivotable about the hinged end. Normally, both of the support means act to hold the corotron in an operative position when the process unit is fully inserted in the main assembly. It is only when the withdrawable support is actually withdrawn from the main assembly that the corotron can be pivoted open about its hinged end. Additionally, a member may be included in the main assembly which provides an abutment to limit the pivotal movement of the corotron. In a preferred form the withdrawable support means at the latch end of the corotron comprises a double sided ramp member in back-to-back configuration defining an apex therebetween, wherein the latch end of the charging device is supported by the apex when both the ramp member and the process unit are fully inserted in the main assembly. 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; 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; Figure 4 is a sectional view of the process unit of Figure 2 partially inserted in the main assembly of a xerographic copier; Figure 5 is a perspective view of a ramp flexure member which supports the transfer corotron in the main assembly; Figure 6 is a perspective view of the latch in the closed position when the process unit is partially inserted into the main assembly; Figure 7 is a cross section showing detail of the latch mechanism of Figure 2, but with the latch in the open position; Figure 8 is a sectional view of the process unit of Figure 2 fully inserted in the main assembly; Figure 9 is a perspective view of the transfer corotron, and Figure 10 is a sectional view of the process unit of Figure 8 when it is fully inserted in the main assembly with the transfer corotron in its hinged-open position. It is noted that, for the sake of clarity, the Figures are not drawn to scale. In particular in the sectional views the dimensions in the vertical direction have been exaggerated. The same features are denoted by the same reference numerals in each of the Figures. In the drawings the main assembly of the copier is depicted only insofar as its features are relevant to the subject matter of the present invention. The process unit or cassette 1 shown in Figure 1 is designed to be removably mounted in the main assembly 100 of a xerographic copier as described, for example, in the aforementioned US patents and also in EP-A-0 244 104 to which reference is invited for further details. 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 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 40 forming part of the main assembly (see especially Figure 8). A cassette having this kind of loosely retained photoreceptor arrangement forms the subject of our aforementioned EP-A-0244 104. 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 tranfer charging device 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. 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 laterally-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, two such sockets being provided, one on each side of the end cap 21. The pin and socket arrangement is such as to allow the corotron a small amount of vertical movement, typically 2 mm, at its pivoted end. At the opposite end of the corotron 7, the other end cap 22 has a longitudinally projecting tab 25 which engages in a latch mechanism 26 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 2, 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 more clearly in Figures 2 and 6. 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 6). When the cassette is outside the main assembly of the copying machine, the jaws 27a, 27b of the latch 26 are closed to grip tab 25 and so 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 and also enables the corotron to be hinged open about pivot pin 23 to allow for clearance of jammed copy sheets, as described in more detail below. As can be seen from Figures 1 and 2, the outside of the corotron shield 8 forms part of the external wall of the cassette housing 2. Figure 4 shows the situation as the cassette 1 is almost, but not quite, fully inserted into its operative position in the main assembly 100 of a reproducing machine. For the sake of clarity the whole of the machine main assembly is not shown in this Figure. As the cassette is first inserted into the main assembly, the support member 40, which is integral with the main assembly, enters the cassette 1 through aperture 2a in the housing 2 and threads through the belt photoreceptor 3. To facilitate this threading operation the support 40 is provided with a chamfered leading end face 40a. Extending from the end face 40a is a spigot 41, the purpose of which is to actuate the latch mechanism 26 when the cassette is fully inserted in the main assembly as explained in more detail below. With the cassette in the position shown in Figure 4, electrical connection is about to be made with the corotron 7 by means of compression spring 45 which is fastened to block 44 of the main machine assembly. The spring 45 is electrically connected to a high voltage source. As the cassette approaches the position shown in Figure 4, the spring 45 enters the tape bore of socket member 46 projecting from the leading face of the corotron end cap 21. In Figure 4, the socket member is cut-away for enhanced clarity of the features being discussed here. As the cassette continues to be inserted the spring 45 engages around electrical contact 47 protruding within the socket 46. Contact 47 is tapered in such a manner as to permit the spring 45 to thread over it easily and to ensure intimate electrical contact therewith. The contact 47 is electrically connected to corona wire 9. With the cassette at the position shown in Figure 4, the underside of leading end cap 21 has just engaged leaf spring 46 which extends cantilever-fashion from the block 44 of the main assembly 100. Spring 46 acts to urge the corotron 7 up towards the support 40 until a projection 48 provided on the upper surface of end cap 21 abuts the underside of support member 40. Projection 48 thus acts as a spacer. At the same time the end cap 22 at the trailing end of the corotron approaches ramp flexure 49 fastened on a surface 50 which may be withdrawn from the main assembly of the reproducing machine as discussed in more detail below. The ramp flexure 49 which is shown in more detail in Figure 5 is made of plastics material, for example polypropylene and comprises a double ramp 51, 52 in back-to-back configuration defining an apex 53 therebetween. The inwardly extending ramp 51 comprises a lower sloping portion 51a and an integral upper portion 51b which is more steeply inclined. The ramp 51 is slightly wider than the corotron end cap 22 and is provided with upstanding wall portions 54 at its edges, thus presenting a guide channel for the corotron. Extending from the underside of lower ramp portion 51a is a T-shaped lug 55 which extends through a slot 56 in the surface 50 to lock the ramp member 49 thereto. The ramp member is further fastened to the surface 50 by a bifurcated barbed member 57 extending through a slot 58 in the surface 50. The outwardly extending ramp portion 52 is shorter than the inwardly extending portion 51 and at its lower end curves inwardly and terminates in a block 58 which is bolted to an upstanding flange 50a at the outside edge of surface 50. The ramp portion 52 provides a guide surface for the leading end cap 21 of corotron 7 when the cassette is first inserted into the main assembly 100. As the cassette is inserted further, the spigot 41 of the support member 40 approaches the latch mechanism 26. Referring to Figure 6, it can be seen that the spigot 41 is aligned with two substantially semicircular boss members 60, 61 at the facing edges of the two jaws 27a, 27b. The boss members 60, 61 are each chamfered at their inwardly directed faces 60a, 61a respectively. As the cassette approaches its fully inserted position within the main assembly 100 the spigot 41 engages the bosses 60, 61 at their chamfered surfaces 60a, 61a and prizes them apart against the bias of spring 28, thus forcing the jaws 27a, 27b to move apart thereby releasing tab 25 of corotron end cap 22 as shown in Figure 7. At this stage the trailing end of the corotron will drop slightly under its own weight until it abuts ramp portion 52 of ramp flexure 49. The cassette is then pushed all the way to its fully inserted position in which the underside of end cap 22 is supported by the apex 53 of ramp flexure 49, as shown in Figure 8. The ramp flexure 49 acts to urge the trailing end of the corotron up towards the support 40 until two flange-like projections 62 provided on the top side of end cap 22 abut the underside of support member 40 and thus act as spacers. Thus the projection 48 on end cap 21 and the two projections 62 on end cap 22 which can be seen most clearly in Figure 9 act as spacers which accurately locate the corotron 7 relative to the support member 40. As described in our aforementioned copending EP-A-0244 104 the photoreceptor belt 3 may be tensioned after the cassette has been fully inserted in the main assembly, e.g. by using a pair of rollers (not shown here) which can be moved apart, whereupon the belt 3 will adopt an operative position in which it conforms closely with the support member 40. It follows, therefore, that by acurately locating the corotron 7 relative to the support member 40 it is also located accurately relative to the photoreceptor, as required. Although the ramp flexure 49 may itself be sufficiently resilient to urge the corotron 7 against the support member 40 additional bias may be provided by threading a compression spring 39 over bifurcated member 57 so that it buts against the apex 53 of the flexure 49 at its upper end and against the surface 50 at its lower end. As shown in figure 1, 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 and is 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 16 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, but for the sake of clarity they are not depicted in the accompanying drawings. 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 sheet 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. In case a copy sheet becomes jammed while it passes through the cassette 2, surface 50 with the ramp flexure 49 mounted thereon may be withdrawn manually from the main assembly 100 of the reproducing machine when the cassette is fully inserted therein, as shown in Figure 10. As the surface 50 and ramp 49 are withdrawn the end cap 22 of corotron 7 will begin to descend the ramp 51 of ramp flexure 49, because it is no longer retained by latch 26. The end cap 22 is guided down the ramp 51 by edge wall portions 54. As the free end of the corotron descends, it pivots about hinge pin 23 at the other end cap 21. Leaf spring 46 is displaced against subjacent platform 68 extending from the block 44 in the main assembly 100. As the surface 50 continues to be withdrawn, the corotron end cap 22 continues to descend ramp portion 51 until it engages the surface 50 which limits the corotron's pivotal movement. Figure 10 shows the corotron 7 hinged in its fully open position away from the photoreceptor to permit access to the transfer region of the cassette, especially for clearing copy sheets which may have jammed there without damaging the photoreceptor. Once the jam has been cleared, the corotron 7 is returned to its former operative position simply by reinserting surface 50. Initially the end cap 22 will slide along the surface 50 until the ramp flexure 49 approaches when it will begin to ascend ramp portion 51 again guided by edge wall portions 54. For this purpose, end cap 22 is flanked by a pair of wings 66 with outwardly extending sloping faces 67 complementary to ramp 51 to facilitate sliding thereover. When the surface 50 is returned to its fully inserted position, the corotron end cap 22 reverts to its former position at the apex 53 of ramp flexure 49 with the projecting flanges 62 abutting the supporting member 40 of the main assembly 100, as shown in figure 8. When it comes to removing the cassette 1 from the main assembly 2 the spigot 41 of support 40 disengages from the latch 26 whereby the jaws 27a, 27b of the latch close together under the bias of spring 28 to regrip the tab 25 of corotron end cap 22. Thus, when the casette is removed from the main assembly the transfer corotron is automatically latched back into, and as such again becomes an integral part of, the cassette housing 2. From the foregoing it will be evident that various modifications may be made within the scope of the present invention as claimed. Thus, 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 (100) of a reproducing machine, comprising a housing (2) enclosing an imaging member (3) and an elongate transfer corotron (7), characterized in that the transfer corotron is hingedly mounted at a first end (21) so that the second, opposite, end (22) thereof is movable away from the imaging member, the said second end being releasably retained by latch means (26). A process unit as claimed in claim 1, wherein the latch means comprises a pair of jaw members (27a, b) which are mutually biased together to grip the second end of the corotron when the process unit is withdrawn from the main assembly. A process unit as claimed in claim 2, wherein the second end of the corotron is provided with a projecting tab (25) adapted to be gripped by the jaw members when the process unit is withdrawn from the main assembly. A process unit as claimed in any preceding claim, wherein the latch means is adapted to release the corotron when the process unit is inserted into the main assembly. A reproducing machine comprising a main assembly, and a process unit as claimed in any preceding claim adapted to be removably mounted in said main assembly. A reproducing machine as claimed in claim 5, wherein the main assembly comprises means (46, 53) for supporting the corotron in a predetermined location relative to the main assembly when the process unit is inserted therein. A reproducing machine as claimed in claim 8, wherein the support means comprise resilient flexures (49). A reproducing machine as claimed in claim 6 or claim 7, wherein respective support means are provided at each of the two ends of the corotron, the support means at the second end of the corotron being withdrawable from the main assembly whereby the corotron is pivotable about the hinged end. A reproducing machine as claimed in claim 8, comprising a member (50) providing an abutment which limits the pivotal movement of the corotron. A reproducing machine as claimed in claim 8 or claim 9, wherein the withdrawable support means at the second end of the corotron comprises a double sided ramp member (51, 52) in back-to-back configuration defining an apex (53) therebetween, wherein the second end of the corotron is supported by the apex when both the ramp member and the process unit are fully inserted in the main assembly.

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