A developing apparatus

Abstract: A developing apparatus includes a rotatable developer carrying member (8) for carrying a developer; an electrode (15) to be supplied with a bias voltage; a coil spring (12), provided in an end portion of the developer carrying member, for electrical connection between the electrode and the developer carrying member.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a developing device usable with an image forming apparatus such as a copying machine or a printer. In an image forming apparatus using an electrophotographic method or an electrostatic recording method, it is known that a developing bias voltage is applied to a developing sleeve to develop an electrostatic image on an image bearing member using force of an electric field. It is also known that in order to apply the bias voltage to a rotating developing sleeve, a leaf spring is urged to a developing sleeve end portion to provide a sliding contact. However, in the case that the rotational speed of the developing sleeve is high, the reliability of energization decreases, and the elasticity of the leaf spring is deteriorated due to long term use, with the result of electric power supply malfunction. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to provide a developing device wherein the developing bias voltage can be applied to the developer carrying member stably for a long term. According to an aspect of the present invention, there is provided a developing apparatus comprising: a rotatable developer carrying member for carrying a developer; an electrode to be supplied with a bias voltage said electrode disposed opposite an end portion of the developer carrying member; a coil spring, provided at an end portion of the developer carrying member, for electrical connection between the electrode and the developer carrying member, wherein a winding direction of said coil spring as seen in a direction from the electrode to the developer carrying member is the same as a rotational direction of the developer carrying member. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an illustration of outer appearance of a process cartridge having a developing device of an embodiment of the present invention. Figure 2 is a sectional view of the process cartridge of Figure 1. Figure 3 is an illustration of a thrust receptor for a developer carrying member in the process cartridge of Figure 1. Figure 4 is an illustration of a thrust receptor of a developer carrying member of a second embodiment of the present invention. Figure 5 is an illustration of thrust receptor for a developer carrying member of a third embodiment of the present invention. Figure 6 is a view illustrating a direction of a thrust force of a sleeve gear. Figure 7 is a front view of a coil spring. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, the embodiments of the present invention will be described. Figure 1 is a perspective view of a process cartridge having a developing device of an embodiment of the present invention as a unit integral with an image bearing member. Figure 2 is a sectional view of the process cartridge of Figure 1, and Figure 3 is a partial enlarged sectional view of the developing device. The process cartridge is a unit detachably mountable to an image forming apparatus, and contains at least an image bearing member and a developing device. It may contain an additional process means. Here, examples of process means include charging means for charging a surface of the image bearing member, cleaning means for removing toner remaining on the surface of the image bearing member. In this example, the process cartridge, as shown in Figure 2, contains the electrophotographic photosensitive drum 1 as the image bearing member, and charging means 2, developing device 3 accommodating developer and cleaning means 4, around the electrophotographic photosensitive drum 1, which are covered by a housing comprising frames 6 and 7, so that it is detachably mountable as a unit relative to the main assembly of the image forming apparatus. The developing device 3 in the process cartridge 5, as shown in Figure 3, includes a developing sleeve 8, as the developer carrying member, of metal such as aluminum or stainless steel, and the developing sleeve 8 enclose a magnet roller 13. The developing sleeve 8 comprises a pipe-like sleeve 8a and a flange 8b. The flange 8b at a driving side is of electroconductive stainless steel, aluminum, electroconductive resin material or the like to permit electric energy supply to the sleeve 8a of aluminum or stainless steel, and is of aluminum in this example since it is good in dimensional accuracy and durable. To one of axial end portions of the developing sleeve 8, a sleeve gear 10 of molded POM (polyacetal), sliding material containing POM, polycarbonate, sliding material containing polycarbonate, Nylon or another resin material, is mounted by an axial snap fit of a claw 17, so as to be rotatable integrally with the developing sleeve 8. The sleeve gear 10 is in meshing engagement with a helical gear (not shown) of the photosensitive drum 1 shown in Figure 2 to rotate the developing sleeve 8 in accordance with the rotation of the photosensitive drum 1. However, the sleeve gear 10 is in the form of a helical gear, and therefore, thrust force is produced in one axial direction so that it is biased to developing device holder 11 side, for example. When the thrust force tending to shift to the developing device holder 11 side is produced to the sleeve gear 10, the end portion of the developing sleeve 8 is urged to the developing device holder 11, since the sleeve gear 10 is mounted by the axial snap fit. Therefore, as shown in Figure 3, at the sliding portions between the developing device holder 11 and the developing sleeve 8, there is provided with a sliding member 9 of molded POM (polyacetal), sliding material containing POM, polycarbonate, sliding material containing polycarbonate, Nylon or another resin material, as a member having high sliding property. The sliding member 9 is integral with developing device holder 11, and is mounted thereto by press-fitting, bonding, screw stop or the like. Therefore, the relative sliding occurs between the developing sleeve 8 and the sliding member 9 by the thrust force. By using a material exhibiting high sliding property relative to the developing sleeve 8, smooth sliding is accomplished with suppressed vibration. By the sliding member 9, the angular position of the magnet roller 13 can be determined. Since the developing sleeve 8 is axially integrally mounted to the sleeve gear 10, the developing sleeve 8 is press-contacted to the sliding member 9 by the thrust force of the sleeve gear 10, so that the position in the axial direction can be maintained constant. Further, since the use is made with snap fit of the claw 17 to mount the sleeve gear 10 to the developing sleeve 8, as described hereinbefore, the cost can be lower than the conventional ones using E shaped stop ring or a parallel pin. The description will be made as to an electric energy supplying structure to developing sleeve 8. A developing bias voltage is supplied from an unshown bias voltage source to a contact plate 15 which is an electrode plate mounted to the developing device holder 11. A coil spring 12 is inserted into the end portion of the flange 8b of the developing sleeve 8. The coil spring 12 is compressed between the sleeve gear 10 and the contact plate 15 and functions to effect electric power supply to the flange 8b from the contact plate 15. As shown in Figure 6, the sleeve gear 10 is a helical gear, and the thrust force produced by rotation of the sleeve gear 10, is toward the holder 11 side, that is, to the coil spring 12 side. Therefore, during rotation of the developing sleeve 8, the coil spring 12 is contacted to the contact plate 15 always at a contact pressure, so that possible contact defect relative to the contact plate 15 can be avoided. Designated by 18 is a driving gear of the photosensitive drum. The coil spring 12 is press-fitted into the flange 8b so that is not easily removed. The inner diameter of the coil spring 12 is preferably 90-99% of the outer diameter of the press-fitting portion of the flange 8b. In order to increase the accuracy of the diameter of the coil spring, the coil spring has a close contact winding end portion, as shown in Figure 7, in this example. The close contact winding preferably has 2-5 windings. The close contact winding portion is provided at least at the press-fitting side end portion of the coil spring, but by providing them at the opposite ends, the assembling operativity is improved. Further, the winding direction as seen in a direction from the holder 11 to the developing sleeve is the same as the rotational direction of the developing sleeve 8. Therefore, when the developing sleeve 8 is rotated, the resultant tightening force of the coil spring 12 is produced to assure the contact with the developing sleeve and to avoid the contact defect between the coil spring and the developing sleeve. The material of the coil spring 12 may be of stainless steel wire, phosphor bronze wire, music wire or anther metal, but phosphor bronze wire is preferable since the sliding noise relative to the contact plate 15 can be reduced. In this example, magnetic toner is used, and therefore, the developer carrying member is a developing sleeve enclosing the magnet roller, but the present invention is applicable to a developing roller not enclosing the magnet roller. Figure 4 shows a device of a second embodiment of the present invention. In this embodiment, the developing device holder 11 is of a member having a high sliding property, for example, molded POM (polyacetal), sliding material containing POM, polycarbonate, sliding material containing polycarbonate, Nylon or the like resin, in place of interposing, between the developing sleeve 8 and the developing device holder 11, a sliding member having high sliding property. In this example device, the sleeve gear 10 is in meshing engagement with a stirring gear 16 shown in Figure 4, which gear is connected with a toner feeding(stirring) member 20 shown in Figure 2 so as the transmit the rotating force of the photosensitive drum 1 to the toner feeding member 20. The stirring gear 16 is in sliding contact with the developing device holder 11, so that by using the high sliding property member, the stirring gear 16 as well as the developing sleeve 8 can rotate smoothly without wearing. Referring to Figure 5, a third embodiment of the present invention will be described. In this embodiment, a high sliding property sliding member 9 is disposed between the developing sleeve 8 and the developing device holder 11, sliding member 9 being of molded POM (polyacetal), sliding material containing POM, polycarbonate, sliding material containing polycarbonate, Nylon or anther resin material. The sliding member 9 is integral with the developing sleeve 8 by press-fitting, bonding, screw stop or the like. Since the relative sliding occurs between the developing device holder 11 and the sliding member 9, smoother sliding is accomplished with further reduced vibration by selecting the material of the developing device holder 11 so as to exhibit high sliding property relative to the sliding member 9. In the embodiment, the developing device is provided in the process cartridge, but the present invention is applicable to a developing device in an image forming apparatus without use of the process cartridge structure. According to the present invention, the developing bias can be supplied assuredly for a long term even if the rotational speed of the developer carrying member is high. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the scope of the following claims.

Claims: A developing apparatus comprising: a rotatable developer carrying member (8) for carrying a developer; an electrode (15) to be supplied with a bias voltage said electrode disposed opposite an end portion of the developer carrying member (8); a coil spring (12), provided at an end portion of the developer carrying member (8), for electrical connection between the electrode (15) and the developer carrying member (8), wherein a winding direction of said coil spring (12) as seen in a direction from the electrode (15) to the developer carrying member (8) is the same as a rotational direction of the developer carrying member. An apparatus according to claim 1, wherein the coil spring (12) is press-fitted onto the developer carrying member. An apparatus according to claim 2, wherein the coil spring (12) has an inner diameter which is 90-99% of an outer diameter of the developer carrying member end portion onto which said coil spring (12) is press-fitted. An apparatus according to claim 1, wherein said coil spring (12) has 2-5 windings of close contact winding portion at each of opposite ends thereof. An apparatus according to claim 1, further comprising a driving gear (10) for driving the developer carrying member, wherein the coil spring (12) is compressed between the driving gear (10) and the electrode (15). An apparatus according to claim 5, wherein the driving gear (10) is a helical gear which produces thrust force toward the coil spring (12) by rotation of the driving gear. An apparatus according to claim 1, wherein the coil spring (12) is of phosphor bronze. An apparatus according to claim 1, wherein said apparatus is contained, together with an image bearing member (1), in a process cartridge as a unit, which is detachably mountable relative to an image forming apparatus.

Inventors: MIYABE SHIGEO, YOKOMORI KANJI, MIYABE, SHIGEO, YOKOMORI, KANJI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1996
Main classification: G03G15
IPC codes: G03G21, G03G15