CORONA DISCHARGE DEVICE

Abstract: A corona discharge device including a shield case (2) having a bottom wall (4) and a pair of walls (8, 12) extending from both sides of the bottom wall and a wire 20) stretched within the shield case. In one embodiment, a guide member (28) for preventing entry of a sheet material into the shield case (2) has a guide arm portion (32) extending across an opening of the shield case, and the free end portion of the guide arm portion is held in resilient press contact with the wall of the shield case. In another embodiment, a guide member (122) for preventing entry of the sheet material into the shield case has one end portion fixed to one wall (108) of the shield case and its other end portion detachably anchored selectively at the one wall (108) and the other wall (110) of the shield case.

Description: This invention relates to a corona discharge device which can be utilized, for example, as a peeling corona discharge device in an electrostatic copying machine. Generally, a peeling corona discharge device is widely utilized in an electrostatic copying machine in order to peel a sheet material such as a copying paper kept in intimate contact with a rotating drum in a transfer zone. The peeling corona discharge device is provided with an electrically conductive shield case and a wire stretched within the shield case, and a corona discharge generated from the wire is applied to the sheet material through an opening in the shield case. The corona discharge device further comprises a guide means provided at the opening of the shield case to prevent entry of the sheet material through it. The guide means is made of, for example, a gut, a plastic film (see, for example, Japanese Laid-Open Utility Model Publication No. 120459/1985), or a plastics member (see, for example, Japanese Laid-Open Utility Model Publication No. 181456/1984). Conventional corona discharge devices, however, have the following problems to be solved in regard to the guide means. When the guide means is formed of a gut, it is troublesome to set it in a stretched state. When the wire is broken, it is troublesome and time-consuming to replace the wire. Cleaning of the wire is also not easy. When the guide means is formed of a plastics film and set between a pair of side walls, the film is likely to become displaced in the event that a relatively thick sheet material acts on it, or in the event of removing a jammed sheet. Cleaning of the wire is not easy, either. When the guide means is formed of a plastics member, deformation (so-called "warping") during moulding causes part of the plastics member to rise at the time of setting it in the shield case. If this rising is large, the sheet material may collide with it, and it fails to guide the sheet. It is a primary object of this invention to provide an improved corona discharge device which permits easy replacement of a wire and its cleaning, and can reliably prevent entry of a sheet material into a shield case. According to the present invention, there is provided a corona discharge device comprising an electrically conductive shield case having a first wall and a pair of opposed second walls which respectively define base and side walls of an elongate cavity which is open at the top, a wire mounted in a stretched state within said cavity and a guide member for preventing entry of a sheet material into said cavity, wherein the guide member has a securing portion adapted to be detachably mounted on one of said second walls and a guide arm portion extending from the securing portion to the other of said second walls across the open mouth of said cavity, the guide arm portion being arranged to be urged into press contact with the upper edge of said other of said second walls of the cavity by means of elastic deformation of the guide member. The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a corona discharger embodying one example of a corona discharge device in accordance with the present invention; Figure 2 is a sectional view taken along line II-II of Figure 1; and Figure 3 is a perspective view showing the corona discharger of Figure 1, with the guide member of the corona discharge device removed from the case. With reference mainly to Figures 1 and 2, the illustrated corona discharger is provided with an electrically conductive case 2 made of a metallic material such as aluminium. The case 2 has a rectangular bottom wall 4 and side walls 6 and 8 extending substantially perpendicularly from both side ends of the bottom wall 4, and an electrically conductive partitioning wall 10 formed of a metallic material is disposed between both side walls 6 and 8. The partitioning wall 10 is substantially L-shaped. Its partitioning portion 12 extends longitudinally of the case 2 in a substantially central part between the side walls 6 and 8, and its securing portion 14 is fixed to the inner surface of the right-hand portion (as viewed in Figure 2) of the bottom wall 4 by welding or otherwise. With this arrangement, a shield case on the right-hand side of Figure 2 comprised of the side wall 6 and the partitioning wall 10 (the partitioning portion 12 and the securing portion 14) functions as a shield case of one corona discharge device. A shield case comprised of the side wall 8, the left-hand portion of the bottom wall 4 in Figure 2, and the partitioning portion 12 of the bottom wall 10 functions as a shield case for the other corona discharge device. The opposed walls 8,12 and part of the bottom wall 4 thus define the side walls and base of a first elongate cavity 3 which is open at the top. Likewise, the opposed walls 6,12 and the part 14 of the partition 12 (over the bottom part 4) define the side walls and base of a second, elongate cavity 5 which is open at the top. With reference mainly to Figures 1 and 3, supporting members 16 (only one of which is shown in Figures 1 to 3) formed of an insulation material such as a synthetic material are mounted on both end portions of the case 2, more specifically at both its end portions between the side walls 6 and 8. A pair of wires 20 and 22 are stretched between these supporting members 16. As shown in Figures 2 and 3, one wire 20 extends within the cavity 5 between the side wall 6 and the partitioning portion 12 of the partitioning wall 10 longitudinally therealong, and both its end portions are fixed in place to the right-hand portions of the supporting members 16 as viewed in Figure 2. The other wire 22 extends within the cavity 3 between the side wall 8 and the partitioning portion 12 of the partitioning wall 10 longitudinally therealong, and both its end portions are fixed in place to the left-hand portions of the supporting members 16 as viewed in Figure 2. Cover members 24 and 26 are attached to the opposite end portions of the case 2. One cover member 24 extends from the side wall 6 to the side wall 8 at the left-hand end portion of the case 2 in Figures 1 and 3, and covers one supporting member 16. The other cover member 26 extends from the side wall 6 to the side wall 8 at the right-hand end portion of the case 2 in Figures 1 and 3, and covers the other supporting member 16 (not shown). The corona discharger is disposed, for example, in a transfer zone opposite to a rotating drum (not shown) of an electrostatic copying machine. Accordingly, as can be easily seen, one corona discharging device comprising the shield case composed of the side wall 6 and the partitioning wall 10 and one wire 20 functions as a transfer corona discharge device for transferring a toner image formed on the surface of a photosensitive material on the rotating drum to a sheet material such as copying paper, and applies a corona discharge from the wire 20 to the back surface of the sheet material through an upper surface opening defined between the side wall 6 and the partitioning portion 12 of the partitioning wall 10. The other corona discharge device comprising the shield case composed of the side wall 8, the left-hand part of the bottom wall 4 in Figure 2, and the partitioning portion 12 of the partitioning wall 10 and the other wire 22 functions as a peeling corona discharge device for peeling the sheet material in intimate contact with the surface of the photosensitive material on the rotating drum, and applies a corona discharge from the wire 22 to the back surface of the sheet material kept in intimate contact with the rotating drum through an upper surface opening defined between the side wall 8 and the partitioning portion 12 of the partitioning wall 10. The corona discharger is provided with a guide member 28 disposed in relation to the corona discharge device on the left hand side of Figure 2 (i.e., the one which functions as a peeling corona discharge device). The illustrated guide member 28 has a securing portion 30 and a plurality of (6 in the illustrated embodiment) guide arm portions 32 extending from the securing portion 30. In the illustrated embodiment, the securing portion 30 and the guide arm portions 32 are molded from a synthetic resin as a one-piece unit. The securing portion 30 has an outside wall portion 34 and an inner wall portion 36 extending longitudinally in spaced-apart relationship, and a securing depression 38 is defined between the outer wall portion 34 and the inside wall portion 36 (see Figure 2). A plurality of (3 in the illustrated embodiment) rectangular openings 40 are formed in the outside wall portion 34 longitudinally thereof in spaced-apart relationship. On the inside surface of the outside wall portion 34 (specifically, sites between the sites of the openings 40), a plurality of (2 in the illustrated embodiment) nearly hemispherical protrusions 42 are provided integrally in spaced-apart relationship in the longitudinal direction. In providing the openings 40 and/or the protrusions 42, it is possible to project part of the outside wall 34 slightly as in the illustrated embodiment, and form the openings 40 and/or the protrusions 42 in the projecting portion. Alternatively, it is possible to extend the entire outside wall portion 34 further, and form the openings 40 and/or the protrusions 42 in the extended portion. The guide arm portions 32 extend from the securing portion 30 to which they are connected to the right in Figure 2, and to the right top in Figure 3. The guide arm portions 32 are preferably constructed as shown in Figures 1 and 3. Specifically, it is preferred that with the longitudinally central part of the guide member 28 as a standard, the guide arms 32 positioned on one side thereof (the left hand side in Figures 1 and 3) be inclined in a straight line inwardly (to the right in Figures 1 and 3) toward the free end portion, and the guide arm portion 32 positioned on the other side of the standard (the right hand portion in Figures 1 and 3) be inclined in a straight line inwardly (to the left in Figures 1 and 3) toward the free end portion. The free end portion of each guide arm portion 32 is nearly spherical as shown. Correspondingly to the openings 40 formed in the guide member 28, anchoring protrusions 44 are provided on the outside surface of the side wall 8 of the case 2. The anchoring protrusions 44 can be formed in the side wall 8 by, for example, press working. The guide member 28 is detachably mounted as shown in Figures 1 and 2. Specifically, the securing depression 38 defined in the securing portion 30 of the guide member 28 is brought into alignment with the side wall 8 of the case 2, and then the securing portion 30 is depressed downwardly. As a result, the upper end portion of the side wall 8 is inserted between the outside wall portion 34 positioned outwardly and the inside wall portions 36 positioned inwardly, and the guide member 28 is detachably loaded into the case 2. In this loaded state, the anchoring protrusions 44 provided in the side wall 8 are positioned in the corresponding openings 40 formed in the securing portion 30 to restrain vertical and longitudinal movements of the guide member 28 with respect to the side wall 8 and prevent detachment of the guide member 28 from the side wall 8, as shown in Figure 1. Furthermore, in this loaded state, each of the guide arm portions 32 extends across the upper surface opening from one side wall of the shield case in the corona discharge device functioning as the peeling corona discharge device (i.e., the side wall 8 of the case 2) to the other side wall (i.e., the partitioning portion 12 of the partitioning wall 10), and its free end portion slightly projects toward the side wall 6 beyond the partitioning portion 12. Accordingly, the sheet material peeled from the rotating drum (not shown) is conveyed downstream while being guided by the guide arm portions 32 and its entry into the peeling corona discharge device is accurately hampered, as shown in Figures 1 and 2. Moreover, in the above loaded state, the protrusions 42 provided in the outside wall portion 34 of the securing portion 30 act on the side wall 8 of the case 2, as shown in Figure 2. Hence, the inside portion 36 of the securing portion 30 is kept in press contact with the inside surface of the side wall 8 and the outside wall portion 34 is elastically deformed slightly to the left in Figure 2. The elastic deformation of the securing portion 30 biases the guide arm portions 32 clockwise in Figure 2 with the base portion as a fulcrum. Accordingly, the free end portions of the guide arm portions 32 are kept in press contact with the upper edge of the partitioning portion 12 by their own elastic deformation, and substantially no space is formed between the lower edges of the guide arm portions 32 and the upper edge of the partitioning portion. Consequently, entry of the sheet material between the partitioning portion 12 of the partitioning wall 10 and the guide member 28 can be accurately prevented. Furthermore, the elastic deformation of the guide member 28 can effectively compensate for any "warping" of the guide member which occurred during moulding, and the guide arm portions 32 are not partly raised. To detach the guide member 28 from the side wall 8 of the case 2, the guide member 28 is relatively strongly pushed up in Figure 2 with respect to the case 2. This causes disengagement between the openings 40 formed in the securing portion 30 and the anchoring protrusions 44 formed in the side wall 8, and the guide member 28 is detached from the side wall 8 as is required. Accordingly, in the above corona discharger, the guide member 28 can be easily loaded into, and detached, from the side wall 8. In this regard, the wire 22 can be cleaned and replaced easily. In the illustrated embodiment, the protrusions 42 for elastically deforming the guide member 28 are provided on the securing portion 30 of the guide member 28 (more specifically, in the inside surface of the outside wall portion 34). If desired, protrusions for elastically deforming the guide member 28 may be provided on the outside surface of the side wall 8. The above embodiment has been described with reference to a corona discharger consisting of two corona discharge devices. This is not limitative, and the invention applies equally to a corona discharger consisting of a single corona discharge device.

Claims: A corona discharge device comprising an electrically conductive shield case (2) having a first wall (4) and a pair of opposed second walls (8,12) which respectively define base and side walls of an elongate cavity (3) which is open at the top, a wire (22) mounted in a stretched state within said cavity (3) and a guide member (28) for preventing entry of a sheet material into said cavity (3), characterised in that the guide member (28) has a securing portion (30) adapted to be detachably mounted on one (8) of said second walls and a guide arm portion (32) extending from the securing portion (30) to the other (12) of said second walls across the top opening of said cavity, the guide arm portion (32) being arranged to be urged into press contact with the upper edge of said other of said second walls (12) of the cavity (3) by means of elastic deformation of the guide member. A corona discharge device as claimed in claim 1, in which the securing portion (30) of the guide member (28) contains a protrusion (42) so that when the securing portion (30) is detachably mounted on said one (8) of the second walls, the guide member is slightly deformed elastically. A corona discharge device as claimed in claim 2, in which the securing portion (30) of the guide member (28) has an inside wall portion (36) adapted to be positioned inwardly of said one wall (8) and an outside wall portion (34) adapted to be positioned outwardly of said one wall (8), said protrusion (42) being located on the inside surface of the outside wall portion (34) so as to urge said outside wall portion (34) of the securing portion (30) away from said one wall (8) of the shield case (2) whereby to cause said elastic deformation of the guide member. A corona discharge device as claimed in claim 1, in which the securing portion (30) of the guide member (28) has an inside wall portion (36) adapted to be positioned inwardly of said one wall (8) and an outside wall portion (34) adapted to be positioned outwardly of said one wall (8) and in which the outside surface of the wall (8) of the shield case (2) carries a protrusion (42) which engages the inside surface of said outside wall portion (34) so as to urge said outside wall portion (34) away from said wall (8) whereby to cause said elastic deformation of the guide member.

Inventors: KAMEDA, KIYOSHIGE, KANO, ATSUSHI, TANIGUCHI, MASAMI
Applicants: MITA INDUSTRIAL CO. LTD.
Application year: 1988
Main classification: H01T19
IPC codes: G03G15, H01T19