A BELT SUPPORT AND STEERING ROLLER

Abstract: A roller (14) which controls the lateral movement of a belt moving thereover so that the belt moves along a predetermined path includes a shaft (52) having a sleeve (54) mounted thereon. The sleeve is made from a resilient, substantially isotropic material preferably a foam material such as a microcellular urethane having a density of approximately 400 kg/m³, a hardness of about 40 on the Shore 0 scale, and substantially equal radial, axial and circumferential compliance.

Description: This invention relates generally to a roller for supporting a belt arranged to move in a predetermined path and for deterring the lateral movement of the belt from the predetermined path. A roller of this type is frequently employed in an electrophotographic printing machine wherein it is necessary to control the lateral movement of a photoconductive belt. In an electrophotographic printing machine, a photoconductive belt is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive belt is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive belt selectively dissipates the charge thereon in the irradiated area. This records an electrostatic latent image on the photoconductive belt corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive belt, the latent image is developed by bringing a developer mixture into contact therewith. Generally, the developer mixture comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive belt. The toner powder image is then transferred from the photoconductive belt to a copy sheet. Finally, the copy sheet is heated to permanently affix the toner particles thereto in image configuration. It is evident that the location of the latent image recorded on the photoconductive belt must be precisely defined in order to have the various processing stations acting thereon optimize copy quality. To this end, it is critical that the lateral alignment of the photoconductive belt be controlled within prescribed tolerances. Only in this manner will the photoconductive belt move through a predetermined path so that the processing stations disposed thereabout will be located precisely relative to the latent image recorded thereon. When considering control of the lateral movement of the belt, it is well known that if the belt were perfectly constructed and entrained about perfect cylindrical rollers mounted and secured in an exactly parallel relationship with one another, there would be no lateral movement of the belt. In actual practice, however, this is not feasible. Due to the imperfections in the system geometry, the belt velocity vector is not normal to the roller axis of rotation, and the belt will move laterally relative to the roller until reaching a kinematically stable position. Existing methods of controlling belt lateral movement comprise servo systems, crowned rollers and flanged rollers. In any control system, it is necessary to prevent high local stresses which may result in damage to the highly sensitive photoconductive belt. Active systems, such as servo systems employ steering rollers which apply less stress on the belt. However, active systems of this type are generally complex and costly. Passive systems, such as flanged rollers, are less expensive, but generally produce high stresses. Various types of flanged rollers systems have hereinbefore been developed to improve the support and tracking of photoconductive belts. For example, the drive roller may have a pair of flanges secured to opposed ends thereof. If the photoconductive belt moves laterally, and engages one of the flanges, it must be capable of either sliding laterally with respect to the roller system, or locally deforming either itself or the roller system to maintain its position. The edge force required to shift the belt laterally or locally deform itself on the roller system usually greatly exceeds the maximum tolerable edge force. Thus, the belt would start to buckle resulting in failure of the system. Alternatively, the flanges may be mounted on one of the idler rollers rather than the drive roller. Lateral motion is controlled by bending the belt to change the approach angle to the drive roller. A system of this type may develop low edge forces when compared to one having the flanges mounted on the drive roller. However, the primary risk associated with this system is that performance depends significantly on the belt bending in its plane. Although the forces in this type of a system are often reduced, they still appear to be unacceptable in that they generally exceed the belt buckling force. Thus, the side edge of the photoconductive belt eventually buckles reducing the life thereof. US-A-2 925 168 discloses a belt support pulley comprising a rubber sleeve mounted on a shaft for rotation thereof. The sleeve has a plurality of flexible laminations on its outer periphery arranged on both sides of a transverse central plane with the laminations being inclined radially toward the axis of the roller away from the transverse plane. The laminations are formed by means of slits or slots extending angularly or helically around the periphery of the roll surface. US-A- 3 050 178 describes a conveyor belt having a plurality of randomly oriented recesses in the undersurface thereof. A pulley having projections thereon supports the belt such that some of the projections contacting the undersurface of the belt will engage some of the recesses for providing traction to the belt. U5-A-3 219 176 teaches a belt idler comprising a plurality of spaced disks. Each disk is formed with a rigid hub and a flexible portion extending radially outwardly therefrom. The flexible portion of each hub is inclined relative to the axis of the shaft and has a conical configuration. The group of disks assembled on each side of the transverse centerline of the idler have their flexible portions inclined toward the transverse centerline. US-A-3 334 447 describes a pulley having a series of radially outwardly extending flexible ribs arranged circumferentially of the pulley and located in side-by-side spaced relation longitudinally of the pulley. The ribs form a flexible or floating surface which is the operative surface of the pulley engageable by the belt. When the belt attempts to ride sideways into engagement with the pulley flange, these ribs flex laterally while in engagement with the belt. When these ribs become disengaged from the belt (during rotation of the pulley), they resume their normal radial position so as to again be ready to engage the belt. US-A-3 643 791 discloses a roller for automatically centering the belt. The roller includes a shaft having a rubber sleeve mounted thereon. A circumferential slot is formed in the sleeve at the transverse central plane of the roll. Helical slots are formed in the sleeve. One of the slots has a right hand-lay, the other a left hand-lay. The slots are inclined radially toward the axis of the roll away from the transverse central plane. US-A-3 726 588 describes a steering roller for a belt. The roller has two sealed chambers and an elastomer surface. Fluid pressure is selectively applied to either chamber in response to lateral movement of the belt to tilt the roll surface. This corrects the belt alignment. US-A-3 961 736 describes a self-centering roll comprising a tube having a first rubber sleeve mounted thereon. A seamed rubber sleeve is mounted on the first sleeve. The second rubber sleeve has a central slot and spaced apart slots on each side of the central slots. The slots on each side of the central slot are inclined radially toward the roll axis away from the central slots. US-A-3 980 174 teaches a pair of spaced pulleys supporting an endless belt. Each pulley includes a plurality of spaced grooves which mesh with ribs protruding inwardly from the interior surface of the belt. US-A-4 150 773 describes a deflection roller having a cylindrical sleeve with a plurality of foam rubber or plastic rings secured thereto. US-A-4 221 480 discloses a roller having a plurality of spaced, flexible disks extending outwardly from the exterior surface thereof. A pair of opposed, spaced circular flanges are mounted on either end of the roller. The belt passes between the flanges and is supported by the disks on the roller. A plurality of grooves are formed in the disks extending in a direction substantially parallel to the longitudinal axis of the roller. These grooves decouple portions of each disk from one another. As the belt moves in a lateral direction, it engages the flanges. Relative movement of the belt in the lateral direction, deflects the portion of the disk supporting the belt. The remaining portion of each disk, not in engagement with the belt, remains undeformed. This ensures that the maximum force applied on the edge of the belt never exceeds the buckling force. The polyurethane foam rollers known in prior art printers are normally non-isotropic, of US-A- 4 160 074. In accordance with one aspect of the present invention, there is provided a roller for supporting a belt arranged to move in a predetermined path and for deterring the lateral movement of the belt from the predetermined path. The roller includes a support shaft and a sleeve mounted thereon and arranged to support the belt. The sleeve is made from a substantially isotropic material having substantially equal radial, axial and circumferential compliance. Pursuant to another aspect of the present invention, there is provided an electrophotographic printing machine of the type having an endless photoconductive belt arranged to move in a predetermined path. A roller in accordance with the previous aspect of of the invention supports the photoconductive belt and controls lateral movement thereof from the predetermined path. An embodiment of the present invention will now be described, by way of example with reference to the drawings, in which: Figure 1 is a schematic, elevational view depicting an electrophotographic printing machine incorporating the features of the present invention therein; Figure 2 is a elevational view showing the idler roller employed in the Figure 1 printing machine; and Figure 3 is an elevational view showing the drive roller employed in the Figure 1 printing machine. In the drawings, like reference numerals have been used to identify identical elements. Figure 1 schematically depicts the various components of an illustrative electrophotographic printing machine incorporating the belt support and alignment roller of the present invention. It will become evident from the following discussion that the roller of the present invention is equally well suited for use in a wide variety of devices and is not necessarily limited in its application to the particular embodiment shown herein. For example, the roller of the present invention may be readily employed in magnetic tape systems, motion picture cameras and motion picture projectors, amongst others. Inasmuch as the art of electrophotographic printing is well known, the various processing stations employed in the Figure 1 printing machine will be shown hereinafter schematically and their operation described briefly with reference thereto. As shown in Figure 1, the electrophotographic printing machine employs a belt 10 having a photoconductive surface deposited on a conductive substrate. Preferably, the photoconductive surface is made from a selenium alloy with the conductive substrate made being made from an aluminum alloy. Other suitable photoconductive materials and conductive substrates may be also employed. Belt 10 moves in the direction of arrow 12 to advance successive portions of the photoconductive surface sequentially through the various processing stations disposed about the path of movement thereof. As depicted, belt 10 is entrained about a pair of opposed, spaced rollers 14 and 16. Roller 14 is an idler roller with roller 16 being the drive roller. A flange or edge guide (not shown) is mounted at opposed ends of the rollers. Roller 16 is rotated by a motor coupled thereto by suitable means, such as a drive belt. As roller 16 rotates, belt 10 advances the photoconductive surface in the direction of arrow 12 through the various processing stations disposed about the path of movement thereof. The detailed structure of idler roller 14 and drive roller 16 will be described hereinafter with reference to Figures 2 and 3, respectively. Both rollers 14 and 16 are adapted to deter lateral movement of belt 10, i.e. the movment of belt 10 in a direction substantially normal to the direction of movement in the predetermined path, as indicated by arrow 12. To this end, both roller 14 and roller 16 are made from a resilient, substantially isotropic material. With continued reference to Figure 1, initially, the photoconductive surface passes through charging surface A. At charging station A, a corona generating device 18 charges the photoconductive surface to a relatively high, substantially uniform potential. Next, the charged portion of the photoconductive surface is advanced through imaging station B. At imaging station B, an original document is positioned face down upon a transparent platen 20. Imaging of the document on platen 20 is achieved by an exposure system which includes a lamp 22, mirrors 24 and a moving lens 26. The exposure system is a moving optical system wherein the lamps, mirrors and lens move across the original document illuminating incremental widths thereof. In this way, an incremental width light image is formed. The light image is projected onto the charged portion of the photoconductive surface. The charged photoconductive surface is discharged selectively by the light image to record an electrostatic latent image of the original document thereon. Thereafter, belt 10 advances the electrostatic latent image recorded on the photoconductive surface to development station C. With continued reference to Figure 1, at development station C, a magnetic brush developer roller 28 advances developer material into contact with the electrostatic latent image. The latent image attracts toner particles from the carrier granules of the developer material to form a toner powder image on the photoconductive surface of belt 10. Belt 10 then advances the toner powder image to transfer station D. Successive copy sheets are advanced from stack 32 by sheet feeder 34. Sheet feeder 34 advances the uppermost sheet from stack 32 into chute 36. Forwarding rollers 38 and 40 continue to advance the sheet to transfer station D. At transfer station D, a corona generating device sprays ions onto the backside of the copy sheet positioned thereat. This attracts the toner powder image from the photoconductive surface of belt 10 to the copy sheet. After transfer of the toner powder image to the copy sheet, the copy sheet advances through fusing station E. Fusing station E includes a heated fuser roller 42 and a back-up roller 44 with the toner powder image on the sheet contacting fuser roller 42. In this manner, the powder image is permanently affixed to the copy sheet. After fusing, the copy sheet is advanced by forwarding rollers 46 through chutes 48 to the copy sheet tray 50. After the sheet is received in copy sheet tray 50, it may be removed therefrom by the machine operator. It is believed that the foregoing description is sufficient for purposes of the present application to illustrate the general operation of an electrophotographic printing machine incorporating the belt support rollers of the present invention therein. Referring now to the specific subject matter of the present invention, Figure 2 depicts idler roller 14 in greater detail. As shown thereat, idler roller 14 includes a substantially rigid shaft 52 having a resilient, substantially isotropic sleeve 54 secured thereon. Sleeve 54 is made from microcellular urethane having a density of 400 kg/m³ (25 pounds per cubic foot) and a hardness of 40 on the Shore 0 scale. The microcellular urethane foam used to form sleeve 54 has substantially equal radial, circumferential and axial compliance. Thus, the urethane is isotropic. Urethane of this type is made by the Rogers Corporation of Willimantic, Connecticut, USA, under the tradename ENDUR-C100. Turning now to Figure 3, there is shown drive roller 16 in greater detail. As depicted thereat, drive roller 16 includes a substantially rigid shaft 56 having a resilient, substantially isotropic sleeve 58 mounted thereon. End 60 of shaft 56 is adapted to have a pulley mounted thereon. A belt is entrained about the pulley and coupled to a drive motor (not shown) which rotates roller 16 so as to advance photoconductive belt 10 in the direction of arrow 12. Sleeve 58 is also made from microcellular urethane foam having a density of 400 kg/m³ (25 pounds per cubic foot) and a hardness of 40 on the Shore 0 scale. The microcellular urethane has substantially equal radial, circumferential and axial compliance so as to be substantially isotropic. A suitable microcellular uthethane foam is made by the Rogers Corporation of Willimantic, Connecticut, USA, under the tradename ENDUR-C100. Flange or edge guides (not shown) are mounted on opposed ends of the shaft of either the idler roller or drive roller to engage the side edge of the belt as it moves laterally. An idler roller 14 and a drive roller 16 of the type heretofore described have been employed in an electrophotographic printing machine of the type shown in the Figure 1, and have maintained photoconductive belt 10 in the desired path of travel, i.e. exhibiting excellent tracking properties, for more than 100,000 cycles of revolutions of belt 10. An idler roller and a drive roller made from microcellular urethane are inexpensive and provide a simple, effective solution to maintaining a photoconductive belt in the desired path of travel preventing lateral movement thereof. Thus, by employing an idler roller and a drive roller which are made from a resilient, substantially isotropic material, the photoconductive belt is maintained in the predetermined path of travel with tracking errors, minimized, and the force applied to the belt side edges by the edge guides maintained beneath the buckling force thereof. While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.

Claims: A roller for supporting a belt arranged to move in a predetermined path and for deterring the lateral movement of the belt from the predetermined path, including: a support shaft (52); and a resilient sleeve (54) mounted on said shaft and arranged to support the belt thereon, characterized in that said sleeve is made from a substantially isotropic material having substantially equal radial, axial and circumferential compliance. A roller according to claim 1, wherein said sleeve is made from a foam material. A roller according to claim 2, wherein said foam material is a microcellular urethane. A roller according to claim 3, wherein said urethane material has a density of about 400 kg/m³ (25 pounds per cubic foot) and a hardness of about 40 on the Shore 0 scale. An electrophotographic printing machine of the type having an endless photoconductive belt (10) arranged to move in a predetermined path, and a roller (14) for supporting the belt according to any of the preceding claims.

Inventors: LANGENHEIM, RICHARD H.
Applicants: XEROX CORPORATION
Application year: 1986
Main classification: G03G15
IPC codes: B65H5, B65H27, G03G21, B65G39, G03G15