Slide-rotating collar protecting rotatable shaft

Abstract: A slide-rotating collar integrally mounted on a resin shaft is configured to have a projected portion at one end of the metallic plate and a recessed portion at the other end thereof such that the both ends engageably face each other without aligning in a shaft line direction.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a slide-rotating collar which protects a rotating resin shaft, a developing device using the slide-rotating collar and an image forming apparatus using the developing apparatus, and more particularly to the slide-rotating collar with a simple construction. Discussion of the Background An image forming apparatus, in which an electrostatic latent image is formed on a surface of an image bearing member, is commonly known. The electrostatic latent image is developed into a visible image with toner by a developing device. The visible image is then transferred onto a transfer sheet to obtain a recording image. In the above-described developing device, a conveying screw is used to stir and convey a developer. In recent years, this conveying screw is manufactured of an integrally molded resin to reduce weight and an operational load. The conveying screw includes a rotational shaft. A bearing provided to a non-moving member supports the shaft so that the shaft rotates. The shaft rotates, for example, at high speed of 300rpm. Conventionally, a metallic pipe is inserted and molded with the shaft or the metallic pipe is press-fitted to the resin shaft after the shaft is molded, in order to prevent wear of the resin shaft caused by a friction between the resin shaft and a metallic bearing. Such prior art is known from US-A-5 444 516. However, it is difficult to form a metallic pipe having a thin wall. The thicker the wall of the metallic pipe is, the smaller the diameter of the resin shaft is, resulting in a decrease in mechanical strength of the shaft. A secondary process is required to thin the wall of the metal pipe, resulting in an additional processing cost. A driving load is increased and an apparatus using the resin shaft is increased in size, when a diameter of the shaft is increased. SUMMARY OF THE INVENTION The object of the present invention is to allow an effective shaft protection at low costs. This object is solved by the subject-matter of claims 1, 3, 5, 6, 7 and 10. According to the present invention, a collar is provided for a rotating shaft. This collar protects the rotating shaft by covering it. Preferably, the collar covers the shaft such that a contact between a bearing and the shaft is avoided, i.e. only the collar but not the shaft contacts the bearing. Preferably, the collar is constituted to allow a sliding contact between the collar and the shaft for mounting the collar on the shaft. Herefor, the expression "slide rotating collar" is used. The collar is preferably made of a bent metallic plate. This metallic plate may be for instance a sheet metal, a formed plate (comprising e.g. stamped and/or cut projections or recesses, or a plane plate). The bent shape is preferably such that it covers at least a part of the circumference of the rotating surface of the rotating shaft. Preferably the bent shape is rotationally symmetric (e.g. cylindrically or conically). Preferably the covering is such that it covers a whole circumference of a shaft or most of the circumference of the shaft or at least those sections where the shaft would otherwise contact a bearing. Due to the bending, two ends of the plate which were at opposite ends before the bending, are adjacent to each other. There may be a distance between the two ends which is small in comparison to the circumference of the surface to be covered (e.g. smaller than 10%, preferably smaller than 1% of the circumference) or the adjacent ends may contact each other. The shape of the plate is such that at least a sectional part or a number or plurality of sectional parts of the adjacent ends are inclined (at an arbitrary angle but preferably perpendicular) with respect to the rotational axis of the shaft. This inclination (preferably more than 30°) prevents a deformation of the collar during rotation of the shaft. Preferably, the collar comprises an engaging member (stopper) which allows for an engagement with a mating engaging member provided on the shaft. The engaging members at the collar and at the shaft are preferably constituted such that a relative rotational movement between the shaft and the collar is prevented. Alternatively or additionally, the engaging member allows to fix the position of the collar with respect to the shaft in the direction of the rotational axis. However, it is also possible to provide two different engaging members, one for fixing with respect to the rotational direction and one for fixing with respect to the axial direction. Preferably, the collar is integrally mounted on the shaft in order to avoid relative movements. The shaft is preferably made of a non-metal material, e.g. plastic, e.g. resin. Preferably, the shaft is made of a material which has a hardness which is lower than the hardness of metal. Preferably, the collar is made of a material which has a hardness which is the same or higher then the hardness of metal. Preferably, the collar is made of metal. Preferably, the shaft is moulded. The present invention advantageously provides a novel slide-rotating collar with a simple construction and at a reduced cost. The slide-rotating collar protects a rotating shaft without causing an increased driving load and without resulting in an increased size of an apparatus using a resin shaft. According to an example of the present invention, the slide-rotating collar includes a cylindrically bent metallic plate. One end of the collar engageably faces to the other end of the collar without aligning in a shaft line direction. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig. 1A is a perspective view illustrating a slide-rotating collar, a conveying screw, a bearing; Fig. 1B is a schematic drawing illustrating the slide-rotating collar mounted on a shaft of the conveying screw; Fig. 2A is a perspective view illustrating the slide-rotating collar and the shaft of the conveying screw; Fig. 2B is a sectional view illustrating the slide-rotating collar; Fig. 3A is a perspective view illustrating the slide-rotating collar and the shaft of the conveying screw; Fig. 3B a sectional view illustrating the slide-rotating collar; and Fig. 4 is a schematic drawing illustrating an image forming apparatus using a developing device in which a resin shaft and the slide-rotating collar are employed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the present invention may widely be applied to a resin shaft rotating at a high speed. An example of the present invention is a developer conveying screw of a developing unit to be used in an image forming apparatus. Firstly, a developing unit and an image forming apparatus is described below. Then, a rotating shaft and a slide-rotating collar is described. [1] An example of an image forming apparatus. An exemplary construction of an image forming apparatus is now described below. Fig. 4 is a cross section illustrating major components of a digital image forming apparatus. In Fig. 4, an image bearing member 3 includes a drum-shaped rotating substrate and a photoconductive surface layer over the rotating substrate. The surface of the image bearing member 3 is scanned by an optical writing unit. Around the image bearing member 3, a charging roller 5, an optical scanning unit 1, a developing unit 8, a conveying guide 10, and a cleaning unit 157 are disposed in order of a clockwise rotating direction of the image bearing member 3 as indicated by an arrow. The charging roller 5 and the optical scanning unit 1 serve as a charging means and optical writing means, respectively. The developing unit 8 includes a developing roller 15 and conveying screws 6 and 7. The conveying guide 10 guides a sheet-formed medium S on which an image is record. The cleaning unit 157 includes a blade 156 which is in sliding contact with the surface of the image bearing member 3. The optical scanning unit 1 irradiates the surface of the image bearing member 3 (i.e., a position between the charging roller 5 and the developing roller 15) with beam light Lb. The beam light Lb is scanned in a main scanning direction which is parallel with a direction of a rotating shaft of the image bearing member 3. The position where the beam light Lb is irradiated is referred to as an exposed position 158. A transfer roller 4 is arranged beneath the image bearing member 3, which is a transfer means, in contact with the image bearing member 3. This contacting position is refereed to as a transfer position (hereinafter referred to as a nip 159). The transfer roller 4 is rotated by the rotation of the image bearing member 3 in a direction indicated by an arrow. A conveying guide 9 is provided from a sheet feeding unit 160 to a registration roller 17 to guide the conveyed sheet-formed medium S. Further, the conveying guide 10 is arranged from the registration roller 17 toward the nip 159. The conveying guides 9 and 10 include a upper and lower guide, respectively. The sheet-formed medium S loaded in the sheet feeding unit 160 is discharged by a paper feeding roller 164, and is separated into one sheet by a separation mechanism (not shown). The medium S is conveyed to the conveying guide 9, the registration roller 17, the conveying guide 10, the nip 159, and a fixing unit 153. The medium S is then discharged to an exit tray 153. The path through which the sheet-formed medium S is conveyed is indicated in a dotted line in Fig. 4. In this image forming apparatus, an image is formed as described below. The image bearing member 3 starts rotating and a surface of the image bearing member 3 is uniformly charged by the charging roller 5 in the dark while the image bearing member 3 is rotating. The beam light Lb scans the exposed position 158 which eliminates the charge applied to thereof, thereby forming an electrostatic latent image corresponding to an image to be printed. The electrostatic latent image formed on the surface of the image bearing member 3 is moved to the developing unit 8 with the rotation of the image bearing member 3. The electrostatic latent image is then developed into visible toner image by the developing unit 8. The developing roller 15 of the developing unit 8 adheres toner of positive polarity to the electrostatic latent image formed on the surface of the image bearing member 3 to visualize the electrostatic latent image. An image forming system according to an example of the present invention employs a so-called negative-positive development system in which the surface of the image bearing member 3 is negatively charged and the toner of positive polarity is used. After the above-described toner image is formed, the paper feeding roller 164 starts conveying the sheet-formed medium S with a predetermined timing. The sheet-formed medium S is conveyed to the registration rollers 17 through a conveying path indicated by a dotted line where the conveyance of the sheet-formed medium S is tentatively stopped. The registration roller 17 then conveys the sheet-formed medium S by adjusting a time. The sheet-formed medium S conveyed from the registration roller 17 is fed to the nip 159. The toner image formed on the surface of the image bearing member 3 is transferred onto the sheet-formed medium S at the nip 159 by an electric field generated by the transfer roller 4. The toner image transferred onto the sheet-formed medium S is fixed by fixing rollers 150 and 151 of the fixing unit 152. The sheet-formed medium S is then discharged to the exit tray. Residual toner remaining on the surface of the image bearing member 3 without being transferred onto the sheet-formed medium S at the nip 159 is conveyed to the cleaning unit 157 with a rotation of the image bearing member 3. The residual toner is removed by the cleaning unit 157. The removed toner is used for the following image forming operations. [2] An example of a developing device. As is described above, the developing unit 8 shown in Fig.4 includes the developing roller 15 and the conveying screws 6 and 7. Shafts of the developing rollers 15 and the conveying screws 6 and 7 along their length are positioned in a direction perpendicular to the surface of the sheet-formed medium S. A toner cartridge 11 is disposed above the conveying screw 7. The conveying screw 7 is located at a position where toner is gradually dropped from the toner cartridge 11 by a dropping means (not shown). Hereinafter, a housing of the developing unit 8 is described with the reference numeral of 12. The housing 12 includes bends and lower portions of the conveying screws 6 and 7 are positioned in the respective bends of the housing 12. A boundary of the two bends is partitioned by a partition 12a. Both end portions of the two bends, which are facing each other, in the direction of the length (i.e., front end and back end portions) are connected with each other. An approximately rectangular conveying path is formed, when it is viewed from the top. Each of the shafts of the conveying screws 6 and 7, which is integral with each screw, is engaged with a gear (not shown) such that the conveying screw 7 rotates in a counterclockwise direction while the conveying screw 6 rotates in a clockwise direction. In Fig. 4, when the conveying screw 6 conveys toner from the front end of the housing 12 toward the back end of thereof, the conveying screw 7 conveys the toner from the back end of the housing 12 toward the front end thereof. With this arrangement, toner is conveyed through the rectangular path while it is stirred. The toner being conveyed by the conveying screw 7 is electrostatically attracted to a magnetic brush formed by a carrier and toner on an outer peripheral surface of the developing roller 15 which includes a magnet inside. The magnetic brush is conveyed to the image bearing member 3 with a rotation of the developing roller 15 to visualize an electrostatic latent image formed on the surface of the image bearing member 3. A rotational speed of the conveying screws 6 and 7 is approximately 300rpm. Because the conveying screws 6 and 7 are approximately identical in both shape and size, description of the present invention will be made assuming that the conveying screw 6 corresponds to a rotating shaft of the present invention. [3] An example of a conveying screw The conveying screw 6 illustrated in Figs. 1A and 1B is an exemplary construction of a rotating shaft according to an example of the present invention. The conveying screw 6 includes a screw 6a, a shaft 6b, and a groove 6c for an E ring. A stopper 6d having a large diameter is provided in a boundary between the screw 6a and the shaft 6b. The screw 6a, the shaft 6b, the groove 6c, and the stopper 6d, which constitute the conveying screw 6, are integrally molded by a resin to save weight and to reduce manufacturing costs by a mass-production. The reference numeral 20 represents a slide-rotating collar which includes a metallic plate bent in a round shape (hereinafter referred to as a collar). An axial length L20 of the collar 20 is at least approximally equal to an axial length L6b of the shaft 6b, said length corresponds to the axial distance between the stopper 6d and the groove 6c. A mild steel having 400N/mm 2 tensile strength and a thickness of between 0.1mm and 0.5mm is used as a material for the collar 20. The material having the above-described thickness may not affect a size of a diameter of the shaft 6b. Basically, the collar 20 is produced by cutting the above-described material into a rectangle which is then pressed into a round shape. The collar 20 is engaged with the shaft 6b. The stopper 6d stops the collar 20 when the collar 20 is engaged with the shaft 6b. A projection 6b1, which is rectangle-shaped in the axial direction of the shaft 6b, is previously formed on a periphery surface of the shaft 6b as a stopper for the collar 20 in order to unite the collar 20 with the shaft 6b. A depression 20a, corresponding to the projection 6b1, is also previously formed on the collar 20 such that the projection 6b1 engages with the depression 20a. Thus, when the collar 20 is mounted on the shaft 6b, the projection 6b1 is engaged with the depression 20a. The collar 20 then rotates integrally with a rotation of the shaft 6b. A general key mechanism can be used for the projection 6b1. As described above, a slide-rotating collar is configured to rotate integrally with a shaft with a simple configuration. The shaft 6b, on which the collar 20 is mounted, is engaged with a bearing 30 (see Fig. 1A), which is fixed to the housing 12 of the developing unit 8 (see Fig. 4). An E ring is then attached to the groove 6c so that the shaft 6B does not come out of the bearing 30. Therefore, L30, which is an axial length of the bearing 30, is equal to the length of L6b and L20. If both ends of the collar 20 facing each other in a circumferential direction align in a shaft line direction indicated by "0 - 0", each of the ends of the collar 20 may deviate in the axial direction resulting in a deformation of the end portions of the collar 20 when the collar 20 is mounted on the shaft 6b. Thus, a rectangular projected portion is formed at one end of the collar 20 while a rectangular recessed portion is formed at the other end thereof such that the both ends of the collar 20 do not face in line with the line of "0 - 0", as illustrated in Figs. 1A and 1B. The projected portion and the recessed portion will be indicated by the reference numerals of 20c and 20e, respectively. The both ends may be made into a waveshape to face each other. This arrangement prevents a deformation of the collar 20 when the collar 20 is mounted on the shaft 6b, and also decreases a slide resistance because the both ends of the collar 20 do not face by aligning in the shaft line direction but they continuously face in the rotational direction of the collar 20. Parts 20c-1 and 20c-2 of the projection 20c face parts 20e-1 and 20e-2 of the recess 20e, respectively. Those parts are not aligned with the rotational axis but inclined (perpendicularly) thereto in order to prevent the deformation of the collar. In particular, those parts prevent a relative movement of the projection 20c with respect to the recess 20e in axial direction (0-0). Because the collar 20 is produced by bending a metallic plate, it can be sufficiently processed even though the metallic plate is thin. Further, it can be mass-produced. The outer diameter of the shaft 6b with the collar 20 mounted does not become large because the color 20 is thin. Thus, an increase of a driving load caused by using a shaft having a larger diameter is avoided. An apparatus using this resin shaft is also kept downsized. Production cost can be reduced because it can be mass-produced. Further, a durability of the resin shaft increases because the resin shaft is protected by the collar. When a projected portion and a recessed portion is formed at one end and at the other end of the collar 20 such that the both ends of the collar 20 do not face in line with a shaft line, the projected portion 20c and the recessed portion 20e are positioned at an upstream side of a facing line 20f, where the ends of the collar 20 face in a straight line, in the rotating direction 18 of the screw 6. In other words, a top of the projected portion 20c is positioned at an upstream of a bottom of the projected portion 20c in the rotating direction 18 of the screw 6. With this arrangement, curling up of the projected portion 20c and the recessed portion 20e is prevented when the collar 20 rotates because the projected portion 20c and the recessed portion 20e are positioned in a so-called forward direction of the rotation of the collar 20. A slide resistance is also decreased and a smooth rotation of the collar 20 is maintained. [4] An exemplary construction of a stopper for the collar 20. < Example 1 > According to the example illustrated in Figs. 1A and 1B, the projection 6b1 and the depression 20a are provided in the sides of the shaft 6b and the collar 20, respectively. They serve as a stopper by engaging each other, e.g. in a form-fit or interlocking manner According to another example, Figs. 2A and 2B illustrates a projection 40 having a radius between 0.3mm and 0.5mm which is formed toward inside of the collar 20' as a stopper in the side of the collar 20'. A ring-shaped groove 41 is formed on a shaft 6b' in a circumferential direction. A flat portion 42 is formed in the groove 41 as a stopper in the side of the shaft 6b'. The collar 20' is produced in a manner similar to the collar 20 except for the projection 40. A projected portion 20c' and a recessed portion 20e' are formed at one end and at the other end of the collar 20', respectively. According to the example, when the collar 20' is mounted on the shaft 6b', the projection 40 elastically deforms such that it enters into the groove 41 and abuts against the flat portion 42. Thus, a position of the collar 20' in a longer direction of the shaft 6b' is determined by an engagement of the projection 40 with the groove 41. The projection 40 serves as a stopper to stop a rotation of the collar 20' by abutting against the flat portion 42. Therefore, it is not necessary to provide a stopper, such as the stopper 6d in Figs. 1A and 1B to determine a position of the collar 20' in an axial direction. < Example 2 > According to another example of the present invention illustrated in Figs. 3A and 3B, a projection 50 is formed as a stopper in the side of a collar 20" by cutting three edges of a rectangular and bending the cut portion of the rectangular toward inside of the collar 20" by a height (h) between 0.3mm and 0.5mm. A groove 51 is formed on a shaft 6b". The groove 51 includes a flat portion 52 which is a stopper in the side of the shaft 6b". The collar 20" is produced in a manner similar to the collar 20 except for the projection 50. A projected portion 20c" and a recessed portion 20e" are formed at one end and at the other end of the collar 20", respectively. According to the example, when the collar 20" is mounted on the shaft 6b", the 12-11 projection 50 elastically deforms such that it enters into the groove 51 and abuts against the flat portion 52. Thus, a position of the collar 20" in the longer direction of the shaft 6b" is determined by an engagement of the projection 50 with the groove 51. The projection 50 serves as a stopper for a rotation of the collar 20" by abutting against the flat portion 52. According to the example, a stopper, such as the stopper 6d in Figs. 1A and 1B to determine a position of the collar 20" in an axial direction, is not required because both ends of the groove 51 in the axial direction serve as a stopper to determine a position of the projection 50. In the example 1, the dome-shaped projection 40 can be processed when stamping a metal plate into the collar 20'. In the example 2, the projection 50 can be processed when stamping a metal plate into the collar 20". In either of these two examples, two functions can be obtained simultaneously when a collar is mounted on a shaft. That is, one function is to stop the collar rotating with respect to the shaft, and the other function is to maintain a position of the collar in an axial direction. Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. This document claims priority and contains subject matter related to Japanese Patent Application No. 2000-191170, filed on June 26, 2000.

Claims: A collar for a rotating shaft, comprising a bent metallic plate which is bent such as to be able to cover at least a part of a surface of the shaft (6) and which is mountable on the rotating shaft such as to rotate together with the rotating shaft, wherein at least a part (20c-1, 20c-2) of one end of the metallic plate and at least a part (20e-1, 20e-2) of another end of the metallic plate, which face each other due to the bending, are inclined or perpendicular with respect to the rotational axis of the shaft. The collar according to claim 1, further comprising a stopper (20a) configured to be engagable with a stopper (6b1) of the shaft to stop a rotation of the slide-rotating collar with respect to the shaft. A shaft arrangement, comprising a rotatable non-metal shaft, wherein the collar recited in claims 1 or 2 is mounted on a portion of the shaft such as to be engagable with a bearing (30) which rotatably supports the shaft via the collar. The shaft arrangement according to claim 3, wherein the collar having a projected portion (20c) at one end and a recessed portion (20e) at the other end is mounted on the shaft such that a top of the projected portion (20c) is positioned at an upstream side of a bottom of the projected portion (20c) in a rotating direction (18) of the shaft. A developing device, comprising a rotatable member configured to stir and convey a developer having a rotatable shaft, wherein the rotatable shaft is the shaft arrangement recited in claims 3 or 4. An image forming apparatus, comprising: an image bearing member configured to form an electrostatic latent image on a surface thereof; a developing device configured to develop the electrostatic latent image into a visible image with a developer; a transfer device configured to transfer the visible image onto a sheet-formed medium to obtain a recording image, wherein the developing device is the developing device recited in claim 5. A method for producing a slide-rotating collar, comprising: bending a metallic plate in an at least partially rotational symmetric shape such that at least a part of one end of the metallic plate engagably or form-fittingly faces to at least a part of the other end of the metallic plate, both ends being at least partially inclined perpendicular to the rotational axis of the shape. The method according to claim 7, further comprising: providing a stopper on a surface of the metallic plate. The method according to claim 7, further comprising: forming a projected portion at one end of the metallic plate and a recessed portion at the other end of the metallic plate such that a top portion of the projected portion is positioned at an upstream side of a bottom of the projected portion in a rotating direction of a shaft. A method for producing a shaft arrangement, comprising the steps of sliding the collar of claims 1 or 2 on a shaft for covering a rotationally symmetric part of the surface of the shaft and engaging the collar with the shaft such as to block or stop a relative rotational movement between the shaft and the collar.

Inventors: ITOH TOSHIYUKI, NAKAHARA TOMOTOSHI, NISHIOKA KEISHI, ITOH, TOSHIYUKI, NAKAHARA, TOMOTOSHI, NISHIOKA, KEISHI
Applicants: RICOH KK, RICOH COMPANY, LTD.
Application year: 2001
Main classification: G03G15
IPC codes: F16C35, G03G15