Abstract:
A precision partially cylindrical web guide member for use as a backer bar in electrophotographic printers or as a similar web guide in an apparatus with moving webs. In a novel process of the invention, multiple web guide members may be manufactured from arc segments of a tube wherein the finished radial dimensions of the web guide members are formed in a turning process. The bottom surface of the web guide member need not be machined or finished.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to improved precision manufactured web, web guide members made by an improved precision manufacturing process. One embodiment of the improved manufacturing process and improved web guide members is described in relation to precision backer bars for use in electrostatographic printing systems for controlling tension and tolerances of a moving web.  
           [0002]    Rounded web guide members are used frequently during many processes for handling or manufacturing moving webs. Examples include photographic film and paper manufacturing, paper manufacturing, rolled steel and aluminum manufacturing and any number of similar operations. Rounded web guide members are often used in such applications to provide support, tension, and directional control of the moving web. The more precise the requirements for uniform treatment of the web, the more precise the requirements for uniform straightness and curvature of the rounded web guide members.  
           [0003]    One embodiment of an apparatus requiring extreme straightness and length-wise uniformity of web guide members occurs when such web guide members are used as backer bars within imaging-web based electrostatographic printing systems. Backer bars are commonly used in such electrostatographic printing systems to hold flexible electrostatographic imaging members in proper position with proper tension. In order to understand the function and importance of backer bars, a description of printing systems utilizing flexible imaging members follows:  
           [0004]    Flexible electrostatographic imaging members are well known in the art. Typical electrostatographic imaging members include, for example, photoreceptors for electrophotographic imaging systems and electroreceptor such as, ionographic imaging members for electrographic imaging systems. These imaging members generally comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymer matrix material. The “imaging layer” as employed herein is defined as the dielectric imaging layer of an electroreceptor or the photoconductive imaging layer of a photoreceptor. In a photoreceptor, the photoconductive imaging layer may comprise only a single photoconductive layer or a plurality of layers such as, a combination of a charge-generating layer and a charge transport layer.  
           [0005]    Generally, in the art of electrophotography, the process of electrophotographic printing or copying is initiated by exposing an analog or digitally created image of an original document onto a substantially uniformly charged photoreceptive member. Exposing the charged photoreceptive member to a light image discharges a photoconductive surface thereon in areas corresponding to non-image areas in the original document while maintaining the charge in image areas, thereby creating an electrostatic latent image of the original document on the photoreceptive member. This latent image is subsequently developed into a visible image by depositing charged developing material onto the photoreceptive member surface such that the developing material is attracted to the charged image areas on the photoconductive surface. Thereafter, the developing material is transferred from the photoreceptive member to a receiving copy sheet or to some other image support substrate, to create an image, which may be permanently affixed to the image support substrate, thereby providing an electrophotographic reproduction of the original document. In a final step in the process, the photoconductive surface of the photoreceptive member is cleaned with a cleaning device, such as, elastomeric cleaning blade, to remove any residual developing material, which may be remaining on the surface thereof in preparation for successive imaging cycles. Electrostatographic copying and printing processes similar to those described above are well known. Analogous processes exist in other electrostatographic printing applications such as, for example, ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.  
           [0006]    An exemplary use of backer bars in such systems is described in U.S. Pat. No. 5,708,924, issued to Shogren et al. and hereby incorporated herein by reference. The backer bars in Shogren are mounted within a customer replaceable unit that includes a corner and support structure for supporting a photoreceptor belt while it is packaged, shipped and inserted over drive and idler rolls in a machine. The customer replaceable unit prevents a machine operator from having to handle the belt itself and provides protection from extrinsic damage. The system as described includes web guide members for tensioning the photoreceptor belt during use.  
           [0007]    Throughout the electrostatographic imaging process described above, the photoreceptor web must be held in positions within tight tolerances. As shown and described in Shogren, many of these tolerances are maintained by web guide members such as, backer bars. Because of the requirements for tight tolerances, precision manufacturing of prior art backer bars has been an expensive and work intensive process comprising the following prior art processes:  
           [0008]    1) Extruding an aluminum bar conforming to the general profile of the finished backing bar. An extrusion process, however, cannot yield the precision required for the part, particularly in respect to the straightness of the bar along its long dimension.  
           [0009]    2) Machining each bar to enable the bar to be mounted to a grinding fixture and to machine holes at each end required for mounting and positioning of the finished backer bars adjacent to belt  10  within the printing system. The shape of prior art backer bars after machining is shown as bar  100  in FIG. 1. Significantly, although the rounded radius side  111  is the only side in contact with the moving imaging web in the final application, prior art processes require that both the radius surface  111  and at least one other surface be machined to great accuracy. As shown in FIG. 2, the reason is that at least one surface  112  (usually the bottom) other than the radius must be machined precisely in order that the unground raw backer bar be mounted with sufficient precision within a grinding fixture that will shape the final radius surface. If the bottom is not precisely straight, then the top radius surface will not be straight either. Since each backer bar is machined in its “free state”, the costs and difficulty of this precision machining process are very significant.  
           [0010]    3) Mounting each machined bar into a grinding fixture  113 , as shown in FIG. 2. The prior art mounting fixture typically mounts  10  or more backer bars, depending upon the desired top radius.  
           [0011]    4) Cylindrical grinding. Once the machined backer bars are mounted into grinding fixture  113 , fixture  113  is placed in a cylindrical grinding apparatus comprising cylindrical grinding wheel  115  for grinding the top radius  111  of all bars mounted within the fixture to the precise radius curvature required. As noted above, straightness of the bar is largely determined by the straightness of the bottom surface since this bottom surface  112  determines the straightness of the backer bar within mounting fixture  113 . The cylindrical grinding operation yields a precision-straight top surface of uniform radius dimension from the center of the mounting fixture.  
           [0012]    5) Finishing the surface of the backer bars while placed within in the cylindrical grinder apparatus. Such finishing operation may require the additional use of various grades of grinding wheels  115  to achieve the required surface finish.  
           [0013]    6) Anodizing the ground and finished backer bars.  
           [0014]    The above prior art process is time consuming, labor intensive, and requires precision machining on at least two surfaces plus precision grinding. The end result is an expensive process with many opportunities yielding a significant failure rate. It would be advantageous to create precision backer bars having in a process requiring less machining and with higher yields.  
         SUMMARY OF THE INVENTION  
         [0015]    One aspect of the present invention includes a process for manufacturing precision web guide members, comprising: (a) extruding a tube having a tubular body, a length dimension, an outside diameter, and an inside surface, said inside surface having radial cavities extending along the length dimension from the inside surface partially through the tubular body; (b) turning the tube to decrease the outside diameter; and (c) sizing the tube to a desired length.  
           [0016]    Another aspect of the present invention includes a precision partially cylindrical web guide member for guiding a moving web member in an apparatus within which the web is moved, said web guide member comprising: a top surface for contacting the web comprising the outside surface of an arc segment of a cylindrical tube; and a bottom surface comprising the inside surface of the arc segment of the cylindrical tube.  
           [0017]    Yet another aspect of the present invention includes an electrophotographic imaging system, comprising: (a) a partially cylindrical web guide member for guiding a moving web, said web guide member comprising: a top surface for contacting the web comprising the outside surface of an arc segment of a cylindrical tube; and a bottom surface comprising the inside surface of the arc segment of the cylindrical tube; and (b) a fixture for mounting the web guide member within the electrophotographic imaging system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The foregoing and other features of the instant invention will be apparent and easily understood from a further reading of the specification, claims and by reference to the accompanying drawings in which:  
         [0019]    [0019]FIG. 1 is an elevated perspective view of an extruded bar member of the prior art intermediate processes for making web guide members.  
         [0020]    [0020]FIG. 2 is an elevated perspective view of a typical grinding process used to shape and finish web turning bars of the prior art.  
         [0021]    [0021]FIG. 3 is a schematic elevational view depicting web guide members of the present invention used as backer bars in a printing system.  
         [0022]    [0022]FIG. 4 is an expanded schematic elevational view of a photoreceptor belt held in tension with the aid of web guide members of the present invention.  
         [0023]    [0023]FIG. 5 is an elevated perspective view of an extruded tube from which web guide members of the present invention are formed.  
         [0024]    [0024]FIG. 6 is an elevational schematic view of a turning process of the present invention used in manufacture of the web guide members of the present invention.  
         [0025]    [0025]FIG. 7 is an elevated perspective view of a turned tube of the present invention after web guide members have been parted.  
         [0026]    [0026]FIG. 8 is a cross-sectional view of an end section of a turned tube of one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teaching additional or alternative details, features, and/or technical background.  
         [0028]    For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements.  
         [0029]    While the present invention will be described hereinafter in connection with a preferred embodiment thereof, it should be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims.  
         [0030]    [0030]FIG. 3 sets forth a more detailed description of on embodiment of an imaging system that utilizes web guide members to guide and position flexible imaging members. In the drawings, like reference numerals have been used through out to identify identical elements. FIG. 3 schematically illustrates an electrophotographic printing machine which generally employs a photoconductive belt  10  mounted on a belt support module  90 . Preferably, the photoconductive belt  10  is made from a photoconductive material coated on a ground layer which, in turn, is coated on an anti-curl backing layer. Belt  10  moves in the direction of arrow  13  to advance successive portions sequentially through the various processing stations disposed about the path of movement thereof. Belt  10  is entrained about stripping belt  14 , drive roll  16 , idler roll  21 , and tensioning steering roll  20 . As roll  16  rotates, it advances belt  10  in the direction of arrow  13 .  
         [0031]    Initially, a portion of the photoconductive belt surface passes through charging station A. At charging station A, a corona generating device indicated generally by the reference numeral  22  charges the photoconductive belt  10  to a relatively high, substantially uniform potential.  
         [0032]    At an exposure station B, a controller or electronic subsystem (ESS), indicated generally be reference numeral  29 , receives the image signals from RIS  28  representing the desired output image and processes these signals to convert them to a continuous tone or greyscale rendition of the image which is transmitted to a modulated output generator, for example the raster output scanner (ROS), indicated generally by reference numeral  30 . Preferably, ESS  29  is a self-contained, dedicated microcomputer. The image signals transmitted to ESS  29  may originate from RIS  28  as described above or from a computer, thereby enabling the electrophotographic printing machine to serve as a remotely located printer for one or more computers. Alternatively, the printer may serve as a dedicated printer for a high-speed 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 . ROS  30  includes a laser with rotating polygon mirror blocks. Preferably a nine-facet polygon is used. The ROS  30  illuminates the charged portion on the surface of photoconductive belt  10  at a resolution of about 300 or more pixels per inch. The ROS will expose the photoconductive belt  10  to record an electrostatic latent image thereon corresponding to the continuous tone image received from ESS  29 . As an alternative, ROS  30  may employ a linear array of light emitting diodes (LEDs) arranged to illuminate the charged portion of photoconductive belt  10  on a raster-by-raster basis.  
         [0033]    After the electrostatic latent image has been recorded on photoconductive surface  12 , belt  10  advances the latent image to a development station C, which includes four developer units containing C-Y-M-K color toners, in the form of liquid or dry particles, is electrostatically attracted to the latent image using commonly known techniques. The latent image attracts toner particles from the carrier granules 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 .  
         [0034]    With continued reference to FIG. 3, 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 vertical transport  56 . Vertical transport  56  directs the advancing sheet  48  of support material into registration transport  57  past image transfer station D to receive an image from photoreceptor belt  10  in a timed sequence so that the toner powder image formed thereon contacts the advancing sheet  48  at transfer station D. Transfer station D includes a corona-generating device  58 , which sprays ions onto the backside 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  by way of belt transport  62 , which advances sheet  48  to fusing station F.  
         [0035]    Fusing station F includes a fuser assembly indicated generally by the reference numeral  70  which permanently affixes the transferred toner power image to the copy sheet. Preferably, fuser assembly  70  includes a heated fuser roller  72  and a pressure roller  74  with the powder image on the copy sheet contacting fuser roller  72 . The pressure roller is crammed against the fuser roller to provide the necessary pressure to fix the toner powder image to the copy sheet. The fuser roll is internally heated by a quartz lamp (not shown). Release agent, stored in a reservoir (not shown), is pumped to a metering roll (not shown). A trim blade (not shown) trims off the excess release agent. The release agent transfers to a donor roll (not shown) and then to the fuser roll  72 .  
         [0036]    The sheet then passes through fuser  70  where the image is permanently fixed or fused to the sheet. After passing through fuser  70 , a gate either allows the sheet to move directly via output  17  to a finisher or stacker, or deflects the sheet into the duplex path  100 , specifically, first into single sheet inverter  82  here. That is, if the second sheet is either a simplex sheet, or a completed duplexed sheet having both side one and side two images formed thereon, the sheet will be conveyed via gate  88  directly to output  17 . However, if the sheet is being duplexed and is then only printed with a side one image, the gate  88  will be positioned to deflect that sheet into the inverter  82  and into the duplex loop path  100 , where that sheet will be inverted and then fed to acceleration nip  102  and belt transports  110 , for recirculation back through transfer station D and fuser  70  for receiving and permanently fixing the side two image to the backside of that duplex sheet, before it exits via exit path  17 .  
         [0037]    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 E. Cleaning station E includes a rotatably mounted fibrous brush in contact with photoconductive surface  12  to disturb and remove paper fibers and a cleaning blade to remove the nontransfered toner particles. The blade may be configured in either a wiper or doctor position depending on the application. 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.  
         [0038]    Controller  29  regulates the various machine functions. The controller is preferably a programmable microprocessor, which controls all of the machine functions hereinbefore described. The controller provides a comparison count of the copy sheets, the number of documents being recirculated, the number of copy sheets selected by the operator, time delays, jam corrections, etc. The control of all of the exemplary systems heretofore described may be accomplished by conventional control switch inputs from the printing machine consoles selected by the operator. Conventional sheet path sensors or switches may be utilized to keep track of the position of the document and the copy sheets.  
         [0039]    More details concerning the function and importance of web guide members such as, backer bars are shown by reference to FIG. 4. In FIG. 4, a photoreceptor belt  10  is shown in a tensioned image receiving position as it is entrained around drive roll  16 , tension steering roll  20 , idler rolls  21 , and stripping roll  14 . Various sized backer bars  23  are stationary and serve to position and guide belt  10 . A controller  29  controls actuation of stepper motor  150  in order to precisely tension photoreceptor belt  10  into a run or image receiving position. Controller  29  has been programmed to apply a predetermined tension standard amount against tension roll  20  and thus against photoreceptor belt  10 . A strain gauge  160  is positioned on housing portion of yoke  170  and measures the tension applied against photoreceptor belt  10 . Stepper motor  150  is actuated by controller  29  to apply tension yoke  170  or relieve tension from the yoke depending on whether tension on photoreceptor belt  10  is to be increased or decreased.  
         [0040]    In operation, a predetermined amount of tension is placed on photoreceptor belt  10  through the actuation of stepper motor  150 . Stepper motor  150  applies tension to photoreceptor belt  10  through pressure on yoke  170 . Strain gauge  160  measures the pressure on photoreceptor belt  10  and signals controller  29  to stop the stepper motor. If the pressure on photoreceptor  10  measured by strain gauge  160  decreases a signal is sent to controller  29  which in turn actuates the stepper motor until strain gauge  160  reaches the predetermined pressure setting.  
         [0041]    A sensor  180  is positioned on shaft  181  of drive roll  16  and monitors the rotation of the shaft. When photoreceptor belt  10  runs it experiences changes in drag of the belt on backer bars  23 . If the drag of the belt on the backer bars becomes too large, drive roll  16  does not have enough friction to drive the belt creating a machine failure. The drag of photoreceptor belt  10  is monitored by sensor  180 , and when it exceeds a safe limit, a signal from sensor  180  is sent to the controller which in turn actuates stepper motor  150  to slightly raise the tension on the belt which will develop enough drive friction to allow the printer to continue to run. In order to maintain belt  10  precisely in its intended track, steering roll  20  is positioned by a conventional stepping motor driving a rack and pinion through gate (not shown). This ability to steer belt  10  is indicated by the dotted lines showing variable positions of steering roll  20 .  
         [0042]    Throughout the above description, it should be clear that tolerances surrounding flexible belt  10  are maintained only if backer bars are shaped, positioned, and aligned extremely precisely. This precision is especially required for those backer bars that position belt  10  as it moves proximately to development station C. A description of the precision in this region is set forth in U.S. Pat. No. 5,491,538, hereby incorporated herein entirely by reference. In summary, web guide members such as, backer bars are one of three critical components controlling the tolerances in development station C since they control ⅓ of the variability in the development gap between the apparatus that donates toner and belt  10  that receives the toner. Quality imaging onto belt  10  requires that the entire development gap be enveloped within a cloud of toner emanating from the rolls or other apparatus that donate toner. Any non-uniformity in donor rolls (or other donating surfaces), belt  10 , and web guide members  23  creates variability in the development zone within development station C. Even minor variations in the thickness of belt  10  across its width may substantially affect the consistency of toner transfer and, therefore, image quality. Accordingly, each web guide member  23  within the development zone of development station C must be extremely straight, smooth, aligned, and positioned correctly.  
         [0043]    One embodiment of the novel process of manufacturing web guide members of the present invention involves the following intermediate processes: extruding a tube; turning the tube; parting the tube in arc segments; finishing; machining; and anodizing. Each parted arc segment becomes a web guide member  23 . One embodiment of the novel processes of the present invention will now be further described below.  
         [0044]    Extruding. FIG. 5 shows an elevated perspective view of a portion of one embodiment of an aluminum alloy tube extruded using one embodiment of processes of the present invention. As shown in FIG. 5, the extrusion is in the shape of a round tube  120  with a series of internal spoke-like radial cavities labeled  121 . Each radial cavity  121  is aligned along a radius of the cross-sectional profile. Any number of radial cavities  121  is possible depending upon the size of the tube and the number of web guide members expected to by yielded.  114  radial cavities are a common embodiment. Usually, each of the radial cavities is equidistantly spaced apart. As shown in relation to FIGS. 6 and 7, each radial cavity  121  forms the divide between arc segments of tube  120 . Also, future machining may be aided if at least some spokes align along a diameter line bisecting tube  120 . In one embodiment, radial cavities  121  are formed during extrusion a radial distance from the center of tube  120  that exceeds the outside diameter of tube  120  once it is turned in the turning process described below.  
         [0045]    Machining/Drilling/Tapping. In alternative embodiments, tube  120  may be milled to final length prior to turning or may remain at an unfinished length. In the embodiment in which radial cavities  121  extend through the eventual outside diameter of tube  120 , then a series of holes  124  are drilled and tapped into the ends of tube  120 . These holes are for mounting tube  120  to faceplate fixtures as shown in FIG. 7. Such drilling and tapping may also occur even if radial cavities  121  do not extend beyond the eventual outside diameter, especially if a faceplate such as shown in FIG. 7 is used during turning.  
         [0046]    Turning. FIG. 6 is an elevated schematic view of a turning process in which extruded tube  120  is turned in a suitable lathe (represented schematically by tool  130 ) to the desired size. For web guide members with a radius of 100.00 mm, the tube is turned to an outside diameter of 200.00 mm. A tube of this radius suffices for approximately  14  web guide members when finished. In the embodiment in which radial cavities  121  exceed the outside diameter of turned tube  120 , it is anticipated that each radial cavity  121  may have a radius length  101  mm. When tube  120  is turned to a diameter of 200.00 mm, radial cavities  121  become exposed, thereby parting each of the arc segments  123  into shaped parts that can be finished into guide member bars  23 .  
         [0047]    Finishing. FIG. 7 shows turned tube  120  with parted web guide members  123  still mounted in mounting fixture  125  after being turned in lathe  130 . While is still mounted within the turning lathe  130 , the outside surface of web guide members  123  are smoothed and finished using standard turning tools such as, steel and carbide inserts or a grinding process using wheels.  
         [0048]    Machining. In the embodiment described above in which parting occurs during the turning process, no further machining may be necessary if the end faces of tube  120  had been milled to length and holes  124  were in correct number and position on each arc segment  123  to be used when finally mounting web guide members  123  in final position within the imaging apparatus as shown in FIG. 3. Alternatively, the end faces of guide members  123  are milled to length after turning, and new holds are drilled and tapped in proper position and number for final guide member bars  123 .  
         [0049]    In an alternative embodiment, radial cavities  121  do not extend through tube  120  to the outside diameter to which tube  120  will eventually be turned. In this embodiment, tube  120  remains intact during and after the turning process. Milling to proper length may occur before or after the turning process, and drilling and tapping holes  124  may similarly occur before or after the turning process. Whichever sequence is followed, turned tube  120  is mounted in fixture similar to faceplate fixture  125  and is mounted in a horizontal mill using the faceplates to hold the assembly. Once mounted in the mill, the separate web guide members  23  within the extrusion  120  are parted through a routing operation. As shown in FIG. 8, routing cuts  126  in this embodiment are aligned with radial cavities  121 .  
         [0050]    Anodizing. Once parted, the separated web guide members are completed by a standard anodizing process. Other coating methods and materials can also be used as needed. An example would be deposition coat of diamond like materials.  
         [0051]    As described above, a number of important advantages result from the described embodiment of the present invention. First, the opportunity for error in the straightness of web guide members  123  is reduced essentially by  50  percent. This is because in prior art processes, as explained above, the longitudinal straightness of top radius surface  111  is determined by the straightness of the bottom surface, since this bottom surface determines the straightness of the web guide member within the cylindrical grinding mounting fixture. In contrast, only the top radius surface  111  of web guide members of the present invention need to be machined, and these are machined using a precision turning process rather than cylindrical grinding. Longitudinal straightness, therefore, is affected by precision machining of only one surface rather than two. It should be noted that whether web guide members  123  are made by the prior art process or the process of the present invention, the bottom surface is not essential to alignment of the web guide member within the electrophotographic printer or other web control device. Such mounting within the final apparatus is accomplished using fixtures attached to web guide members  123 , typically using drilled and tapped holes  124 . In doing so, the straightness or roughness of the bottom surface does not matter. Indeed, the bottom surface  112  of web guide members  123  of the present invention may remain round in conformance with the inside diameter of the original tube extrusion.  
         [0052]    A second advantage of the web guide members and processes of the present invention is a significantly lower cost of producing web guide members  123 . Specifically, the precision machining process of the prior art requires at least two surfaces to be precision machined along their full length in a linear milling process. Worse, such machining manufactures essentially one web guide member at a time. In contrast, one embodiment of the process of the present invention allows the top radius surface of many web guide members to be shaped, sized and finished using a simple turning process and length machining process. Instead of manufacture of one web guide member at a time and each web guide member requiring two precision machining processes, the present invention enables four, fourteen or more web guide members to be turned and finished at the same time. The top radius surface is the only surface requiring a precision surface, and the turning operation provides at least as much accuracy as a single linear machining process used in the prior art.  
         [0053]    It should now be apparent that an improved web guide member and an improved process for making the same has been disclosed that lowers the cost and increases the precision required of web guide members used in web transport systems requiring precise tolerances. Such web systems are exemplified by electrophotographic imaging systems of the type described above.  
         [0054]    While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.