An idler roll assembly

Abstract: An idler assembly (200) that is both self-centering and self-aligning with a drive roll (204). The idler assembly consists of a pair of rolls (202) coaxially connected by a shaft (203), the shaft being rotatably supported in a housing (206). The housing is resiliently retained by a removable resilient spring member (208) to a fixed frame member (220) which allows the axis of rotation (250) of the pair of idler rolls and housing to pivot in more than one plane (252,254) simultaneously. This pivoting causes the axis of rotation of the idler rolls to align parallel and in contact with the drive roll. The spring member also provides an even loading of the normal force across the width of the drive nip. As a result of the alignment and even loading, skewing of a sheet is prevented as it is driven through the nip formed by the drive roll and the pair of idler rolls. The removable resilient spring member also allows for easy replaceability of the idler assembly. The housing is easily replaced between tabs (210,212) formed in the fixed frame member of a machine and opposite ends of the spring member reconnected to the tabs, thereby resiliently mounting the idler assembly in the frame member.

Description: This invention relates generally to an idler roll assembly. In typical printing machines, a paper path, using drive rolls and idler rolls, directs the copy receiving substrates throughout the machine. Similar drive and idler rolls are used to handle original documents in automatic document handlers for imaging original documents. Two common configurations of idler roll assemblies are often used. The first has one, two or more idler rolls with internally mounted bearings rotating independently on a stationary shaft. The shaft can be either center or end loaded. In the second configuration the rolls are press fit or molded to a rotating shaft, the shaft is loaded at both ends requiring two bearing surfaces. These configurations present two problems. In the first configuration, independent roll rotation allows the individual idler roll to follow the individual drive roll speeds. If the drive roll speeds are not exactly the same, due to slight differences in roll radii and/or uneven loading, a piece of paper driven at two different speeds will rotate, skewing the sheet as it travels through the nip. The second problem is caused by dual loading points. Any variation in spring force will apply uneven loading, compressing the drive roll elastomer to different radii with respect to the second roll on the same shaft and the end result again is different drive roll velocities skewing the sheet as it travels through the nip. DE-A-3,942,272 describes an idler roll assembly comprising an idler member, a drive member and retaining means including a peripherally located resilient retaining member mounted for urging said idler member into contact with the drive member. US-A-5,269,509 describes a cut sheet registration guide having at least two idler rolls biased into contact with a feed roll, the idler rolls being pivotally mounted on a bar which is itself pivotally mounted with respect to the axis of the feed roll. US-A-4,997,179 discloses a sheet feeder having a drive roller in contact with an idler roll retained by a leaf spring to provide a normal force to a sheet. JP-A-3293242 illustrates a system for evening out the pressure distribution between a capstan roller and hollow pinch rollers by applying pushing loads against the bearings of the pinch rollers using compression springs. An object of the invention is to provide an improved self-aligning, low jam rate idler assembly for use in transporting cut sheets in an electrophotographic printing machine. A further object is to provide a low cost idler roll that is self-centering and applies an equal load to the sheets to minimize sheet skewing. It is a further object to have an idler roll that can maintain a constant normal force against a drive roll even if the drive roll has variations, so that more precise paper control is provided with less skew. In accordance with one aspect of the present invention, there is provided an idler roll assembly for applying a normal force to a sheet being advanced by a drive member, comprising: an idler member having a longitudinal axis of rotation, rotatably mounted in contact with the drive member to define a nip therebetween through which the sheet advances, and retaining means for maintaining contact between the idler member and the drive member, wherein said retaining means includes a single, centrally located resilient retaining member mounted for urging said idler member in contact with the drive member, and for permitting said idler member to pivot simultaneously in a plurality of planes about a preselected point on the longitudinal axis of rotation, so that alignment of the idler member with the drive member is maintained. The invention will be described by way of example with reference to the accompanying drawings, in which like reference numerals refer to like elements and wherein: Figure 1 is a perspective view of the idler roll assembly of the present invention; Figure 2 is a side elevational view of the idler roll assembly illustrating the cooperation between a drive roll and the idler roll assembly of the present invention; Figure 3 is a partial sectional plan view of the idler roll assembly; Figure 4 is a graphical illustration of the range of motion of the axis of rotation of the idler roll assembly of the present invention; and Figure 5 is a schematic elevational view of a typical electrophotographic printing machine utilizing the idler roll assembly shown in Figure 1. Figure 5 schematically illustrates an electrophotographic printing machine utilizing an idler roll assembly (200) of the present invention. The printing machine generally employs a belt 10 having a photoconductive surface 12 deposited on a conductive ground layer 14. Belt 10 moves in the direction of arrow 16 to advance successive portions of photoconductive surface 12 sequentially through the various processing stations disposed about the path of movement thereof. Initially, a portion of belt 10 passes through charging station A, having a corona generating device 26 which charges the photoconductive surface 12, to a relatively high, substantially uniform potential. After photoconductive surface 12 of belt 10 is charged, the charged portion thereof is advanced through exposure station B, where a controller or electronic subsystem (ESS) 29 receives the image signals representing the desired output image and processes these signals to convert them to a continuous tone or greyscale rendition of the image. The processed image signals are transmitted to a modulated output generator, for example, the raster output scanner (ROS) 30. Preferably, ESS 29 is a self-contained, dedicated minicomputer. The image signals transmitted to ESS 29 may originate from a raster input scanner (RIS) 28, which scans an original document positioned thereon by a document handler 27, or from a computer. The signals from ESS 29, corresponding to the continuous tone image desired to be reproduced by the printing machine, are transmitted to ROS 30. As an alternative, ROS 30 may employ a linear array of light emitting diodes (LEDs) arranged to illuminate the charged portion of photoconductive belt 20 on a raster-by-raster basis. After the electrostatic latent image has been recorded on photoconductive surface 12, belt 10 advances the latent image to a development station, C, where toner, in the form of liquid or dry particles, is electrostatically attracted to the latent image using commonly known techniques and forming a toner powder image thereon. As successive electrostatic latent images are developed, toner particles are depleted from the developer material. A toner particle dispenser, indicated generally by the reference numeral 44, dispenses toner particles into developer housing 46 of developer unit 38. After the electrostatic latent image is developed, the toner powder image present on belt 10 advances to transfer station D. A print sheet 48 is advanced to the transfer station, D, by a sheet feeding apparatus, 50. Preferably, sheet feeding apparatus 50 includes a feed roll 52 contacting the uppermost sheet of stack 54. Feed roll 52 rotates to advance the uppermost sheet from stack 54 to the idler roll assembly 200 of the present invention which forwards the sheet into chute 56. Chute 56 directs the advancing sheet into contact with photoconductive surface 12 of belt 10 in a timed sequence so that the toner powder image formed thereon contacts the advancing sheet at transfer station D. Transfer station D includes a corona generating device 58 which sprays ions onto the back side of sheet 48. This attracts the toner powder image from photoconductive surface 12 to sheet 48. After transfer, sheet 48 continues to move in the direction of arrow 60 onto a conveyor (not shown) which advances sheet 48 to fusing station E. The fusing station E, includes a fuser assembly 62, which permanently affixes the transferred powder image to sheet 48. Fuser assembly 62 includes a heated fuser roller 64 and a back-up roller 66. Sheet 48 passes between fuser roller 64 and back-up roller 66 with the toner powder image contacting fuser roller 64, permanently affixing the toner powder image to sheet 48. After fusing, sheet 48 advances through chute 68 again through one or more idler roll assemblies 200 of the present invention to catch tray 72 for subsequent removal from the printing machine by the operator. After the print sheet is separated from photoconductive surface 12 of belt 10, the residual toner/developer and paper fiber particles adhering to photoconductive surface 12 are removed therefrom at cleaning station F, which includes a rotatably mounted fibrous brush in contact with photoconductive surface 12 to remove the nontransferred toner particles. Subsequent to cleaning, a discharge lamp (not shown) floods photoconductive surface 12 with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof for the next successive imaging cycle. In Figure 1, there is illustrated a perspective view of the idler assembly 200 of the present invention. The idler assembly is shown mounted in circumferential contact with drive rolls 204. The idler assembly 200 comprises a pair of coaxially aligned rolls 202, each roll having an end confronting and adjacent to each other and supported by a housing 206 located between the rolls 202. A resilient mounting member, illustrated in the form of a spring 208, is used to secure the housing 206 to the machine frame 220. Figure 2 is a side elevational view of the idler assembly 200 shown with the idler rolls 202 extending through an opening, in the machine frame and in contact with the drive roll 204. The housing 206, which contains a bearing 218 (Figure 3) for the idler shaft 203 (Figure 3), has a baffle 214 built into it, so that the leading edge of a sheet (not shown) is guided into the nip formed between the idler rolls 202 and the drive roll 204. The drive roll 204 is coated with an elastomer coating 205, such as silicone rubber, which provides good frictional contact with the sheets being fed and is impervious to commonly used silicone release agents. The housing 206 is prevented from rotating with the idler rolls 202 by way of an abutment 216 which fits against a tab 210 on the machine frame 220 and also by the baffles 214 fitting into the machine frame. The retaining spring 208 is connected to tabs 210 and 212 to retain the idler assembly in position. The opening in the frame 220 is slightly larger than the idler assembly to allow the assembly 200 to move to obtain alignment with the drive rolls 204. As a result of the center location of the spring 208, the idler assembly 200 is free to move in more than one plane simultaneously, so as to align and remain in aligned contact with the drive rolls 204. The spring 208 and the housing 206 create a pivot point about which the idler assembly 200 is free to pivot. The pivot point is located at approximately the center point of housing 206, between the pair of rolls 202, and on the axis of rotation 250 of the pair of rolls. As shown in Figure 4, this allows the idler assembly 200 to pivot in both a plane 252 essentially parallel to the plane of a sheet passing through the nip as well as in a plane 254 essentially perpendicular to the first plane 252. The resultant of each of these pivoting motions, shown in Fig. 4, is described below. It is possible to locate the pivot point at a location other than the approximate center of the axis of rotation between the pair of idler rolls, depending upon the particular application. As a result of the pivoting motion, the axes of rotation of the idler roll assembly 200 and the drive roll 204 remain parallel. This prevents a side force from being exerted on a sheet which will cause sheet skew. Further, as a result of the idler rolls 202 being connected by shaft 203, the idler rolls 202 rotate at the same speed and prevent sheet skew as a result of a differential drive speed. Figure 4 illustrates the range of motion that is possible for the axis of rotation 250 of the idler assembly 200 as a result of the resilient central mounting. The axis of rotation is movable in both planes 252 and 254 simultaneously. The range of motion of the axis of rotation is essentially bounded by the conical areas shown as 260 and 262 in Figure 4. Arrows 258 and 256 illustrate the motion directions of the axis of rotation, the combined resultant of which forms the conical sections 260, 262. As the idler assembly 200 is retained by a single, centrally located resilient member 208, there is not a problem of uneven loading as can be caused when multiple spring mounts are used. The central mount causes the idler assembly 200 to pivot in any direction necessary to align with the drive rolls 204. This pivot action also causes the nip normal force applied to the drive nip to equalize for each roll 202 as a result of the single spring mounting scheme. The idler assembly, as shown, is adaptable to various locations throughout a printing machine. It may be used in a flat paper path, a curved paper path, or it may be used in any one of a variety of document handling and finishing devices to provide a nip normal force without inducing sheet skew. Because of this versatility, the same idler design can be located in several locations, thereby reducing the spare part inventory required for a particular machine or machines. The simplicity of the mounting device also allows for user replacement without the need for factory service calls. The above embodiment describes a single idler member, in the form of idler rolls 202, mounted for rotation with the drive roll 204. It will be appreciated that in alternative embodiments a further idler roller may be mounted for rotation with the idler rolls 202, the spring 208 urging the further idler roll into contact with the idler rolls 202 thereby urging those rolls 202 into contact with the drive roll 204.

Claims: An idler roll assembly (200) for applying a normal force to a sheet being advanced by a drive member (204), comprising: an idler member (202) having a longitudinal axis of rotation, rotatably mounted in contact with the drive member (204) to define a nip therebetween through which the sheet advances, and retaining means for maintaining contact between the idler member and the drive member, characterised in that: said retaining means includes a single, centrally located resilient retaining member (208) mounted for urging said idler member in contact with the drive member, and for permiting said idler member to pivot simultaneously in a plurality of planes (252,254) about a preselected point on the longitudinal axis of rotation (250), so that alignment of the idler member with the drive member is maintained. The idler roll assembly as claimed in claim 1, wherein said resilient retaining member (208) comprises a spring. The idler roll assembly as claimed in claim 1 or 2, wherein said idler member (202) comprises a pair of rolls (202), each one of said rolls coaxially connected to opposite ends of a shaft (203); and a housing (206), located on said shaft, being provided for rotatably supporting said shaft. The idler roll assembly as claimed in claim 3, wherein said resilient retaining member resiliently fastens said housing to a fixed frame member (220), so that the housing retains said pair of rolls (202) in contact with the drive member. The idler roll assembly as claimed in claim 4, wherein said housing (206) comprises a bearing member (218) for rotatably supporting said shaft (203) in said housing. An idler roll assembly as claimed in any one of claims 1 to 5, wherein a further idler roller is mounted for rotating with said idler member (202), said resilient retaining member (208) urging said further idler roller into contact with said idler member thereby urging said idler member into contact with the drive member (204). An electrophotographic printing machine having a paper path in which sheets are advanced by a drive member (204) while having a normal force applied thereto, characterised by an idler roll assembly (200) as claimed in any of the preceding claims for applying said normal force.

Inventors: DICESARE CESIDIO J, GRAMLICH JOHN D, KELLOGG THEODORE J, PLAIN MARGARET C, RUBSCHA ROBERT F, DICESARE, CESIDIO J., GRAMLICH, JOHN D., KELLOGG, THEODORE J., PLAIN, MARGARET C., RUBSCHA, ROBERT F.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: B65H5
IPC codes: B65H5, G03G15