Corona discharging device

Abstract: A corona discharging device (1) in which an engaging member (11) engaging with one of slits (23) of a control grid (20) is provided on a cover (6) of one end block (3) provided in a case (2). When mounting the control grid (20) on the corona discharging device (1), one end of the control grid (20) is at first attached to the device, and the slit (23) formed in the other end of the control grid (20) is engaged with the engaging member (11) on the cover (6). Subsequently, the cover (6) is mounted on the end block (3) with its one end serving as a fulcrum.

Description: BACKGROUND OF THE INVENTION: The present invention is directed to a corona discharging device for use with an image forming apparatus such as a copying machine or the like. Such an image forming apparatus like a copying machine comprises a corona discharging device for electrifying a photosensitive body. For the purpose of stabilizing an electrifying potential on the photosensitive body, conventionally a corona discharging device of the so-called scorotron type is used in which a mesh-like grid plate defined as a control grid is interposed between the photosensitive body and a corona wire. The grid plate is typically mounted on the corona discharging device and is so constructed as to be attachable to and detachable from the copying machine body together with the corona discharging device. A long lasting use of the corona discharging device, however, causes adhesion of foreign matters to the corona wire or contamination in the interior of a shield case, which in turn require periodic cleaning. On that occasion, an easier work needs removal of the grid plate attached to the corona discharging device. The grid plate removed has to be, as a matter of course, remounted on the corona discharging device. In order to facilitate the attachment and detachment of the grid plate with respect to the corona discharging device, a variety of proposals have hitherto been made. For instance, as disclosed in JP-U-143961/1987, end blocks for holding the corona wire are fixedly provided at both ends of the corona discharging device, engaging members integrally stand erect on the end blocks. One of the engaging members is arranged to be elastically deformable, whereby the engaging members engage with slits conceived as engaged parts of the grid plate. As is also disclosed in JP-U-30268/1987, an engagement portion formed on a U-shaped spring member detachably mounted on a discharging body engages with a slit formed in the grid plate. The first of the prior art corona discharging devices, however, presents the following problems. The grid plate is stretched with a tension due to the elasticity of one of the engaging members, and hence a distance between the engaging members disposed at both ends of the corona discharging device in the longitudinal direction has to be longer than between the slits formed on both ends of the grid plate. As a result, when fitting the grid plate to the thus constructed corona discharging device, the engagement portion formed by an elastic protrusion has to be deformed beforehand, or alternatively the grid plate is required to be pulled inwards to the greatest possible extent. Therefore, the attachment thereof is quite troublesome. Besides, dismounting the grid plate involves operations reversed to the above, so that the troublesome situation is the same. The second of the prior art corona discharging devices is attended with the following problems. It is difficult to insert the U-shaped spring member into the discharging body, against the resilient force thereof. Even if inserted, the spring member has a tendency to spring out of the discharging body due to its resilient force. In addition, the configuration of the corona discharging device becomes intricate, and its assembly is also troublesome. The document US-A-4 550 253 discloses a corona charger of scorotron type wherein a corona wire is detachably secured to a base frame made of insulating material and a control grid is also detachably secured to a grid frame made of insulating material. In this conventional construction, the corona wire is secured to a base frame so that it is stretched out resiliently between two end portions. A grid frame, provided to cover the corona wire, can be detachably fixed to the base frame by means of a pair of screws. At one end of the grid frame, there is provided a slide plate which can be slidably moved in a longitudinal direction. For this purpose, the slide plate is biased by means of a coiled spring. On this grid frame, a control grid is provided which is fixed to the grid frame by means of openings co-operating with projections of the grid frame. The proper function of this conventional device depends on a sufficient bias force of the coiled spring biasing the slide plate. If this spring is broken or worn out, the proper positioning and function of the control grid cannot be ensured. SUMMARY OF THE INVENTION The object underlying the present invention is to provide a corona discharging device which is capable of facilitating the attachment and detachment of a grid plate with a simple construction. According to a first aspect of the invention, there is provided a corona discharging device comprising: a body; a corona wire stretched within the body; a control grid having receiving portions formed at two ends thereof, for covering at least a part of the corona wire; engaging members engaging with the receiving portions of the control grid; and support members for supporting the engaging members, at least one of the support members being detachably attached to the body, which corona discharging device is characterized in that said at least one support member is arranged so that, when being attached, an end of said support member on the side of the control grid abuts upon a part of the body and that the support member is rotated with the end thereof serving as a fulcrum, and in that lock means are provided for locking said one of the support members when it is attached to the body. According to a second aspect of the invention, there is provided a corona discharging device comprising: a shield case; end blocks formed with openings and provided at both ends of the shield case; cover members detachably mounted on the end blocks to cover the openings; a corona wire stretched between the end blocks; and a control grid, formed at its both ends with receiving portions, for covering at least a part of the corona wire, wherein at least one of engaging members engaging with the receiving portions is provided on one of the cover members and at least one of the engaging members is elastically deformable in a stretching direction of the control grid, which corona discharging device is characterized in that said corona discharging device further comprises lock means for locking the cover member, when being set in the opening of the end block wherein said lock means consists of a second engaging member provided on the cover member and a second receiving portion formed in the end block, arranged to effect locking by abutting an inner end of the cover member against an inner end of the end block and by engaging the second engaging member with the second receiving portion while rotating the cover member with the abutting part thereof serving as a fulcrum. Further developments of the corona discharging device according to the invention have been defined in the subclaims wherein these developments relate to the two different aspects of the invention. Other objects, features and advantages of the present invention will be come readily apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially exploded perspective view illustrating a corona discharging device of a first embodiment of the present invention; Fig. 2 is a sectional view showing an assembled state of the corona discharging device depicted in Fig. 1; Fig. 3 is a side view illustrating a method of assembling the corona discharging device depicted in Figs. 1 and 2; Fig. 4 is a sectional view illustrating the corona discharging device of another embodiment of the invention; and Fig. 5 is a perspective view showing a part of the corona discharging device of still another embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION: Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. Turning first to Figs. 1 and 2, the numeral 1 designates a corona discharging device mainly comprising the following components: a shield case 2; end blocks 3; a corona wire 4; a cover 6 constituting a support member; and a grid plate 20 which forms a control grid. More specifically, the shield case 2 is formed of a conductive material to assume a substantially C-like configuration, wherein the shield case may have sidewalls 2a and 2b and a bottom wall 2c. Provided at both ends of the shield case 2 are the end blocks 3, each made of an insulating material, which are combined with the shield case 2 to constitute a discharging body. Stretched between the end blocks 3 is the corona wire 4 for electrifying a photosensitive body (not illustrated) with a predetermined tension by proper means like machine screws 25. The corona wire 4 may pass through suitable apertures in respective end walls of the end blocks 3 and is electrically connected to a connector terminal 26 provided on an end surface of one of the end blocks 3 by known means. Formed in the end blocks 3 are openings 5 for performing screw-fastening when stretching the corona wire 4. When a high voltage is impressed after inserting the corona discharging device 1 into a copying machine body with the openings 5 wearing no cover, an inconvenient situation like a leak due to lacking protection arises. For this reason, a cover 6 made of an insulating material is generally attached. The cover 6 is provided with a stopper 7 forming a second engaging member, the stopper 7 protruding therefrom, as shown in Fig. 1. The end block 3 corresponding thereto is formed with a notch 8 conceived as a receiving portion to be engaged with the stopper 7. The stopper 7 is inserted and fitted into the notch 8, thereby engaging the cover 6 with the end block 3. It is useful to have two pairs of notches 8 and stoppers 7, especially when they are provided in the sides of the end blocks 3; however, one pair of one stopper 7 and a complementary notch 8 may be sufficient, especially when provided in the end wall of the end block 3. As illustrated in Figs. 1 and 2, a substantially central portion of the cover 6 is provided with an engaging member 11 consisting of a base 9 having a thickness smaller than that of the cover 6 and of a hook-like portion 10 formed in continuation of the base 9. The hook-like portion 10 is relatively and sufficiently thin to be elastically deformed by a force acting in a direction as indicated by an arrow A in Fig. 1 and Fig. 2. Through-holes 12 are perforated in the circumference of the base 9, thereby further facilitating the elastic deformation of the hook-like portion 10 of the engaging member 11. As will be explained hereinafter, a height regulating member 13 for regulating the height of the grid plate 20 is provided in continuation of the cover 6 on one side of a discharging region, projecting from an edge of the cover 6. Namely, the height regulating member 13 serves to keep constant a spacing between a surface of the photosensitive body and the grid plate 20. The grid plate 20 consists mainly of a mesh 21 and a frame 22. Slits 23 serving as receiving portions to be engaged with the hook-like portion 10 are formed in both ends of the frame 22 in the longitudinal direction thereof. The respective slit 23 is caught by the hook-like portion 10 of the engaging member 11, whereby the grid plate 20 is held by the cover 6, which in turn is engaged with the end block 3. Both ends of the frame 22 in the longitudinal direction abut against the height regulating member 13, thereby regulating the height and the spacing of the grid plate 20 with respect to the shield case 2. Based on the constitution of the foregoing embodiment, there will be explained the operation of mounting the grid plate 20 on the corona discharging device body in which the corona wire 4 is stretched with an adequate tension. To start with, the first cover 6 is mounted on the first end block 3 depicted at an upper right portion in Figs. 2 and 3 by engaging the stopper 7 provided on the first cover 6 with the notch 8 formed in the right end block 3. Subsequent to this step, the slit 23 formed at the right end of the grid plate 20 is caught by the hook-like portion 10 of the right engaging member 11 provided on the first cover 6 attached to the right end block 3. The slit 23 formed in the left end of the grid plate 20 is caught by the hook-like portion 10 of the left engaging member 11 provided on the second cover 6. At this time, the second cover 6 is not yet engaged with the left end block 3 as shown in Figs. 2 and 3. Thereafter, the second cover 6 is attached to the left end block 3 as shown in Fig. 3. As illustrated in detail in Fig. 3, the end of the left cover 6 on the side of the height regulating member 13 (adjacent to the grid plate 20) is placed on the grid-side end of the left end block 3, while the other end of the second cover 6 is set afloat above the left end block 3. At this time, the grid plate 20 is retained with no slack between the two engaging hook-like portions 10. In this state, the two hook-like portions 10 of the two engaging members 11 are not yet elastically deformed. Subsequently, the second cover 6 is rotated in a direction indicated by an arrow B to engage the stopper 7 thereof with the notch 8 of the left end block 3 to assume a configuration depicted in Fig. 3, wherein the fulcrum is the end of the second cover 6 mounted on the left end block 3 on the side of the height regulating member 13. When pivoting the respective cover 6, the two hook-like portions 10 of the two engaging members 11 provided on the two covers 6 are elastically deformed in such a direction as to gradually narrow a spacing therebetween in accordance with the length of the grid plate 20. Eventually, as depicted in Fig. 2, the two engaging members 11 provided with the hook-like portions 10 undergo the elastic deformation corresponding to the length of the grid plate 20, and the lower part of the frame 22 of the grid plate 20 abuts against the two height regulating members 13, thus regulating the height and spacing of the grid plate 20. Simultaneously, the grid plate 20 can be stretch-retained with a proper tension. On the occasion of periodic cleaning of the corona wire 4 and the interior of the shield case 2 or of replacement of the corona wire 4, it is desirable that the workability be improved by removing the grid plate 20. On that occasion, the reversed operations are performed. That is, the grid plate 20 can be removed simply by dismounting one cover 6 from the respective end block 3. Another embodiment of the invention will be explained with reference to Fig. 4. The arrangement of this further embodiment differs from the preceding embodiment in that one engaging member is attached to the end block instead of the cover, and the other engaging member has no elasticity. More specifically and as shown in Fig. 4, the first cover 6a mounted on the right end block 3a includes only the height regulating member 13 of the grid plate 20 but does not have any stopper and notch for engagement, Rather, in this embodiment, the right engaging member 11a for holding the right end of the grid plate 20 is provided on the right end block 3a fixed to the shield case 2. The configuration of the right engaging member 11a is identical with that shown in the previous embodiment, and the explanation is therefore omitted. The second cover 6b fitted to the left end block 3b is provided with a left engaging member 11b having no elasticity. The description will next be focused on the operation of mounting the grid plate 20 on the corona discharging device 1 on the basis of the above-described construction. A slit formed in the right end of the grid plate 20 has to be engaged with the right engaging member 11a provided on the right end block 3a. The second cover 6b is taken off from the left end block 3b, in which state a slit formed in the left end of the grid plate 20 is engaged with the left engaging member 11b. Hence, there is no necessity for previously causing any elastic deformation of the engaging members or pulling the grid plate. Consequently, hooking can be made between the two engaging members 11a and 11b. Thereafter, the second cover 6b is mounted on the left end block 3b in the same manner as that of the embodiment discussed above. In accordance with this embodiment, the grid plate 20 can be stretched with an adequate tension, because one engaging member has the necessary elasticity. Referring next to Fig. 5, there is shown still another embodiment of the engaging member according to the present invention. The above-described two embodiments adopt an arrangement where the engaging member is formed integrally with the cover or the end block. However, in this embodiment, an engaging member separate from the cover is attached thereto. In this embodiment, an engaging member 110 involves the use of a leaf spring formed by bending, e.g., a thin metal plate. Describing the configuration in greater detail, the engaging member 110 includes a hook portion 100, corresponding to the hook-like portion 10 used in the previous embodiments, and a base plate 90 corresponding to the base 9. The engaging member 110 is mounted on a cover 60 in the following manner. To begin with, the base plate 90 is notched to form a tongue piece 91. Subsequently, a pin 61 standing upright on the cover 60 is fitted into the notched portion of the base plate 90, in which case the tongue piece 91 abuts against the pin 61 from the opposite side to the grid plate 20. The pin 61 is formed with a notch 62 into which the tip of the tongue piece 91 is inserted, thus preventing the engaging member 110 from coming off upwards in Fig. 5. A slit 23 perforated in an end part of the grid plate 20 is caught by the hook portion 100 of the thus constructed engaging member 110. At this time, a tension is imparted to the grid plate 20 because of the spring property of the hook portion 100. Note that in this embodiment the tongue piece 91 also has a spring property adaptive more elastically to a pulling force acting in a direction indicated by an arrow C in Fig. 5. In the embodiments discussed above, the shield case 2 is formed to assume a substantially C-like configuration in section, wherein the corona wire 4 may be surrounded by three wall elements 2a, 2b and 2c in Fig. 1. However, the three wall elements are not necessarily provided. There may be adopted a combination of the wall elements 2a and 2b, or 2a and 2c; or one wall element, e.g., 2c may be sufficient. In short, the configuration of the shield case 2 may be properly selected to be adapted to the respective type of a copying machine. There are offered process units for use with small-sized copying machines which have spread over in recent years. This type of process unit is an image forming unit including a photosensitive body, an electrifying part, a developing part and a cleaning part. A casing for accommodating these components is typically formed of a resin. A shield case of the electrifying part and end blocks are formed integrally with the resinous casing, and a conductive plate is installed on the rear surface opposite to a discharge opening formed in the side of the photosensitive body. The present invention can be applied even to the thus constructed process units on condition that at least one end block is fitted with a cover for blocking the opening. The above embodiments deal with an arrangement where the height regulating member 13 of the grid plate 20 is provided in continuation of the respective cover 6. The height regulating member 13 may be attached to the end block or formed integrally with the end block. The configuration of the height regulating member 13 can be varied as the case may be. In the embodiments given in the description of the present invention, there are exemplified only two arrangements where in one case both of the covers 6 are equipped with engaging members 11 each exhibiting an elasticity, while in another case one engaging member 11a having the elasticity is provided on a fixed body, whereas the other engaging member 11b having no elasticity is attached to the cover 6b. However, at least one of the engaging members is mounted on an attachable/detachable support member like a cover and has the necessary elasticity. By utilizing such combinations, the present invention can be embodied. If the dimension or distance between the receiving and engaged portions of the grid plate 20 is virtually equalized to that between the two respective engaging members, it is permitted that the two engaging members do not have elastic properties. Even in this case, when mounting the support member, as illustrated in Fig. 3, on the corona discharging device 1 with one end of the support member for supporting one engaging member serving as a fulcrum, the grid plate 20 can readily be stretched between the respective engaging members.

Claims: A corona discharging device comprising: a body (2); a corona wire (4) stretched within the body (2); a control grid (20) having receiving portions (23) formed at two ends thereof, for covering at least a part of the corona wire (4); engaging members (11, 11a, 11b, 110) engaging with the receiving portions (23) of the control grid (20); and support members (6, 6a, 6b, 60) for supporting the engaging members (11, 11a, 11b, 110), at least one (6, 6b, 60) of the support members being detachably attached to the body (2), characterized in that said at least one support member is arranged so that, when being attached, an end of said support member (6, 6b, 60) on the side of the control grid (20) abuts upon a part of the body (2) and that the support member (6, 6b, 60) is rotated with the end thereof serving as a fulcrum, and in that lock means (7, 8) are provided for locking said one of the support members (6, 6b, 60) when it is attached to the body (2). The corona discharging device as set forth in claim 1, characterized in that at least one (11, 11a, 110) of the engaging members (11, 11a, 11b, 110) is elastically deformable in a stretching direction of the control grid (20). The corona discharging device as set forth in claim 1 or 2, characterized in that the engaging member (11, 11b) is formed integrally with the support member (6, 6b). The corona discharging device as set forth in claim 1 or 2, characterized in that the engaging member (110) is a leaf spring member attached to the support member (60). The corona discharging device as set forth in any of claims 1 to 4, characterized in that the support member (6, 6a, 6b, 60) is a cover member for covering an end of the body (2). The corona discharging device as set forth in any of claims 1 to 5, characterized in that the support member (6, 6a, 6b, 60) includes a height regulating member (13) for regulating the height of the control grid (20). The corona discharging device as set forth in any of claims 1 to 6, characterized in that the lock means (7, 8) is composed of a second engaging member (7) provided on the support member (6, 6b, 60) and a second receiving portion (8) formed in the body (2), and in that the support member (6, 6b, 60) is arranged to be locked to the body (2) by engaging the second engaging member (7) with the second receiving portion (8). A corona discharging device comprising: a shield case (2); end blocks (3, 3a, 3b) formed with openings (5) and provided at both ends of the shield case (2); cover members (6, 6b, 60) detachably mounted on the end blocks (3, 3a, 3b) to cover the openings; a corona wire (4) stretched between the end blocks (3, 3a, 3b); and a control grid (20), formed at its both ends with receiving portions (23), for covering at least a part of the corona wire (4), wherein at least one (11, 11b, 110) of engaging members (11, 11a, 11b, 100) engaging with the receiving portions (23) is provided on one (6, 6b, 60) of the cover members, and at least one of the engaging members (11, 11a, 110) is elastically deformable in a stretching direction of the control grid (20); characterized in that said corona discharging device further comprises lock means (7, 8) for locking a cover member (6, 6b, 60) when being set in the opening of the end block (3, 3b) , wherein said lock means (7, 8) consists of a second engaging member (7) provided on the cover member (6, 6b, 60) and a second receiving portion (8) formed in the end block (3, 3b), arranged to effect locking by abutting an inner end of the cover member (6, 6b, 60) against an inner end of the end block (3, 3b) and by engaging the second engaging member (7) with the second receiving portion (8) while rotating the cover member (6, 6b, 60) with the abutting part thereof serving as a fulcrum. The corona discharging device as set forth in claim 8, characterized in that the engaging member (11, 11b) is formed integrally with the cover member (6, 6b). The corona discharging device as set forth in claim 8, characterized in that the engaging member (110) is a leaf spring member attached to the cover member (60). The corona discharging device as set forth in any of claims 8 to 10, characterized in that the cover member (6, 6a, 6b, 60) includes a height regulating member (13) for regulating the height of the control grid (20).

Inventors: MAESHIMA MASANOBU, MAESHIMA, MASANOBU
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G03G15
IPC codes: G03G15, H01T19