Abstract:
Apparatus for precisely positioning one or more of the work stations of a document printer/copier relative to an internal drum, including a first member, attached to either a work station or the internal drum, having two sections, each section having a reference surface forming an angle therebetween, an actuator for changing the included angle between the first reference surface and second reference surface, thus enabling the included angle to be increased or decreased, and a second member having a reference surface that mates with the pair of reference surfaces, associated with the other of the work station or the internal drum, so as to accurately adjust the work station relative to the internal drum dependent upon the included angle of the first reference surface and second reference surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   Reference is made to and priority claimed from U.S. Provisional Application Ser. No. 60/498,564, filed on Aug. 28, 2003, entitled APPARATUS FOR PRECISELY ADJUSTING THE POSITION OF WORK STATIONS IN A DOCUMENT PRINTER/COPIER. 

   FIELD OF THE INVENTION 
   This invention relates to the field of document printing/copying. More particularly, it relates to improvements in apparatus for precisely adjusting the position of various work stations of a document printer/copier, e.g., an electrophotographic printer/copier, relative to a reusable image-recording drum and/or image transfer drum. 
   BACKGROUND OF THE INVENTION 
   In electrophotographic printers and copiers, a toner image is formed on the surface of a photoconductive recording element. This image is commonly transferred, either directly or indirectly, to a receiver member (e.g., a sheet of paper), thereby enabling the recording element to be re-cycled through the image-forming process to make multiple prints/copies. Often, the physical form of the recording element is that of a drum having an outer surface of photoconductive material, either organic or inorganic. As the drum rotates, various work stations positioned about the drum periphery operate collectively to produce the toner image on the drum&#39;s photoconductive surface. These work stations usually comprise (i) a primary charging station for depositing a substantially uniform electrostatic charge on the drum&#39;s photoconductive surface; (ii) an exposure station for imagewise exposing the uniform charge to actinic radiation, thereby selectively dissipating the uniform charge to produce a charge image; and (iii) a development station for applying pigmented thermoplastic particles (toner) to the charge image to render it visible. In addition to these image-processing stations, other work stations, also positioned about the drum periphery, serve to transfer the toner image thus formed to an image-receiving member, e.g., a sheet of paper, or to an intermediate transfer drum from which it may be subsequently transferred to paper or the like, and to remove residual or non-transferred toner from the drum&#39;s photoconductive surface prior to recycling the drum through the image-forming process. When using an intermediate transfer drum, an additional toner-cleaning station is positioned adjacent the intermediate transfer drum, downstream from the second image-transfer station, to remove residual toner particles. 
   As will be appreciated, the consistent production of high quality images requires that certain positional relationships be established and maintained at all times between the above work stations and the photoconductive drum and intermediate transfer drum. For example, the spacing between the drum surface and the corona discharge wire(s) of the primary charging station must be maintained uniform across the drum surface in order to assure a uniform charge distribution across the drum surface. Further, the spacing between the drum surface and a toner-applying magnetic brush (or the like) must be kept within a very tight tolerance to consistently achieve a desired toner image density. The same holds true for spacing between the drum surface and the exposure station, which may be in the form of a solid-state print head or an optical projection system, in order to consistently form a sharply focused image on the drum&#39;s photosensitive surface. In some printer/copiers, such positioning of the work stations relative to the recording drum is maintained by using wheels that contact and rotate on the drum&#39;s outer surface. In other machines, reference rings or other structures are used to maintain the desired spacing. All such approaches require the use of precision parts, and are problematic from the standpoints of contamination and wear. 
   One example of positioning apparatus of the above type is disclosed in U.S. Pat. No. 5,089,846 to H. Tabuchi. In this disclosure, an exposure station in the form of an array of light-emitting diodes is supported for pivotal movement towards and away from a photoconductive drum. The positioning mechanism is mounted on the pivotal support and has an end that is adapted to contact and ride upon the outer edge of the photoconductive drum to thereby establish a desired spacing between the drum surface and the operative surfaces of the LED array. A second support pivotally mounted on the first support is spring biased to urge the first support towards engagement with the drum surface, and a cam surface mounted on the machine frame interacts with the second member to adjust its pivotal position. While intended to provide a simple and inexpensive approach to achieving high positional accuracy between the drum surface and the operative surface of the LED array, this approach is still subject to many of the aforementioned disadvantages, requiring the use of precision parts that eventually wear-out and introduce contamination. 
   An example of an improved positioning apparatus that is not subject to the aforementioned disadvantages is disclosed in U.S. Pat. No. 6,427,059 to Buch, et. al. Such apparatus includes a pair of drum-support members, each having associated reference surface features adapted to mate with complimentary reference surface features on the individual work stations. The placement of the reference surface features of the drum-support members are factory set to account for any idiosyncrasies (e.g., run-out) of a drum supported by such members. This apparatus does not, however, provide for adjustment of the position of the various work stations relative to photoconductor element at the user site if such adjustment should be determined to be required, for example, by observation of image quality deficiencies and/or the result of prescribed diagnostic procedures. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing discussion, an object of this invention is to provide improved apparatus for precisely positioning one or more of the work stations of a document printer/copier relative to an internal drum, and furthermore, to provide precise adjustment of the position of one or more of such work stations at the user site. According to a preferred embodiment of the invention, apparatus is provided for precisely positioning the work stations of an electrophotographic document printer/copier relative to the outer surface of a rotating drum on which such work stations are required to carry out a process. The apparatus of the invention operates to precisely position an operative component of the work station substantially parallel to and spaced a desired distance from the surface of the rotating drum, and furthermore provides for adjustment of the position of such operative component relative to the rotating drum if such adjustment is required to correct an observed deficiency. The apparatus of the invention includes a first member, attached at a predetermined position with respect to either of the work station or the work piece, the member has first and second relatively movable sections, the first section has a first section surface and the second section has a second section surface at an angle to the first section surface, a second member, attached at a predetermined position with respect to the other of the work station or the work piece, the second member has a reference surface thereon the reference surface being positioned to engage the first section surface and the second section surface to position the work station relative to the work piece; and an actuator for changing the angular position of the first section surface relative to the second section surface, whereby when the reference surface engages the first and second section surfaces, the position of the work piece relative to the work station is accurately adjusted. As the width of the groove in the member attached to the work station is expanded or contracted by advancing or contracting the adjusting screw, the angle between the reference surfaces of the two sections of the member is increased or decreased. As a result, the spacing of the work station operative component from the photoconductive drum is decreased or increased when the reference surface of the drum support member is mated with the pair of grooved member reference surfaces. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and its technical advantageous effects will be better appreciated from the ensuing detailed description of a preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like or functionally similar parts, wherein: 
       FIG. 1A  is an end view of a portion of an exemplary electrophotographic printer embodying drum-support and spacing adjustment members of the prior art; 
       FIG. 1B  is an enlarged view of a detail of the spacing adjustment member portion of the apparatus shown in  FIG. 1A ; 
       FIGS. 2A and 2B  are schematic front views of a portion of an apparatus similar to that shown in  FIG. 1A , respectively in different relative positions of the photoconductor drum and image-transfer drum; 
       FIGS. 3A and 3B  are front isometric views of prior art drum-support members for supporting a photoconductive drum of the type used in the electrophotographic printer of  FIG. 1A ; 
       FIGS. 4A and 4B  are rear isometric views of the drum-support members shown in  FIGS. 3A and 3B , respectively; 
       FIG. 5  is a side elevation view of the spacing adjustment member for adjustment of work station position relative to the drums, according to this invention; 
       FIG. 6  is a view, partially in cross section, of the grooved member in  FIG. 5  taken along the lines  6 — 6  of  FIG. 7 ; 
       FIG. 7  is a front elevation view, in cross section, of the portion of the grooved member with the adjusting screw; and 
       FIG. 8  is similar to  FIG. 6 , but shows an alternate embodiment of the invention in which the adjusting screw in  FIG. 6  is replaced by a cam-shaped member. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings,  FIG. 1A  schematically illustrates a portion of an exemplary electrophotographic printer  10  of the prior art. As shown, printer  10  includes a pair of drum assemblies, DA 1 , DA 2 . Drum assembly DA 1  includes an image-recording drum  12  having a photoconductive outer layer  14  on which toner images are formed in a conventional manner. Drum assembly DA 2  includes an intermediate image-transfer drum  22  having an abhesive (non-stick) surface  25  to which toner images formed on the photoconductive outer surface of image-recording drum  12  are transferred prior to being re-transferred to a receiver sheet (not shown). 
   Briefly, toner images are formed on the photoconductive surface  14  of drum  12  by rotating the drum in the counterclockwise direction (as viewed in  FIG. 1A ) past a series of work stations that sequentially operate on a desired portion of the drum&#39;s photoconductive outer surface. These work stations include a corona charging station  16  that serves to uniformly electrostatically charge the photoconductive surface, a solid-state print head  18  for imagewise exposing the charged photoconductive surface, line-by-line, to actinic radiation, thereby selectively dissipating the uniform charge and leaving behind a latent electrostatic charge image, and a development station  20  for developing the charge image with electroscopic toner particles. The toner image thus formed is then transferred to the outer surface  25  of the intermediate transfer drum  22 , and residual toner on drum  12  is removed by a cleaning station  24 . Upon transferring the toner image on the intermediate transfer drum  22  to an image-receiver sheet, the surface of drum  22  is cleaned by a second cleaning station  26 . 
   Preferably, each work station is mounted for slight movement (e.g., about 5 to 7 mm) towards and away from its respective operative position adjacent the surface  14  of the drum  12  (or surface  25  of the drum  22 ) to provide minimal clearance for installation and replacement of the drum assemblies. During such installation, the drum assemblies are moved substantially parallel to drum&#39;s respective axis of rotation, through an opening in the machine frame. 
   Apparatus is provided for precisely and repeatedly positioning the various work stations of a document printer/copier, of the type described above relative to the outer surfaces of an image-recording drum  12  and/or an intermediate transfer drum  22  to enable, for example, removal, servicing and replacement of the individual work stations and/or drum(s) without altering a desired positional relationship between the work stations and drum(s). Referring additionally to the schematic illustrations of  FIGS. 2A and 2B , such apparatus includes a pair of drum-support members  32 ,  32 ′ and  34 ,  34 ′, each of such members having a centrally located bearing B or the like for rotatably supporting a drum axle  12 A extending outwardly from an end of drum  12 . The drum-support members, in turn, are supported in a predetermined position within the printer frame F, as described in U.S. Pat. No. 6,295,427 to Flick, et. al., and hereby incorporated in its entirety by reference. 
   Each drum-support member  32 ,  32 ′ and  34 ,  34 ′ is provided with a plurality of reference surface features RS 2  which cooperate with complimentary reference surface features RS 1 , carried by the respective work stations, to precisely position the work stations relative to the outer surface of the drum. (Note, the drum-support members  34 ,  34 ′ of drum assembly DA 2  has both types of reference surface features, RS 1  and RS 2 , since DA 2  is both a work station, i.e., an image transfer station that operates on drum  12  to transfer a toner image, and a drum on which processing is effected, i.e., by the cleaning station  26 .) Thus, as the work stations are moved from their respective stand-by or loading positions toward their operative positions, the reference surface features RS 1  of the work stations move into contact with and engage the reference surface features RS 2  on the drum-support members to locate each work station in a desired position relative to the drum surface. 
   The reference surface features RS 1  of most of the work stations take the form of a block  50  (specifically shown in  FIG. 1B ) having a V-groove  52  for receiving a bullet-shaped locator  54  disposed at the distal end of a threaded member  56 . Member  56  is threaded into a threaded hole bored in an outer surface of the drum-support members  32 ,  32 ′, and the height of the locator  54  above its supporting surface (e.g., surface  32 A) is adjustable by rotating and setting a nut  58  threaded on member  56 . 
     FIGS. 3A and 3B  are isometric front views of drum-support members  32  and  32 ′, respectively, and  FIGS. 4A and 4B  are isometric rear views of the same drum-support members, respectively. Member  32  supports a shaft encoder SE through which the rotational speed of drum  12  is controlled. Member  32  further supports bullet-shaped reference features  40  and  41  which together with features  40 ′ and  41 ′ on drum-support member  32 ′, serve to precisely position the operative component of the corona charging station  16 , i.e., the corona discharge wire, substantially parallel to the surface of drum  12 . Similarly, features  43  and  43 ′ (shown in  FIGS. 4A and 4B ) serve to precisely position the operative component of the development station  20 ; features  44  and  44 ′ serve to position the intermediate transfer drum  22 ; features  46  and  46 ′ serve to position an optional pre-clean corona charger (forming part of cleaning station for drum  12 ); and features  48  and  48 ′ serve to position the cleaning brush  24 . Preferably, each of the drum-support members  32 ,  32 ′ further comprises a pair of drum-support legs  60 ,  62 ;  60 ,  62 ′ which, as explained in the aforementioned U.S. Pat. No. 6,295,427, are slidably received in a pair of spaced parallel channels located within the printer frame for supporting the drum assembly in a desired position within the printer. Four clamps C 1 –C 4  serve to retain the bearing B used to rotatably support one of the drum axles A in member  32 , and three additional clamps D 1 –D 3  serve to retain the bearing B′ used to rotatably support the other drum axle in member  32 ′. 
     FIG. 5  is a side elevational view of the spacing adjustment member  70  of the present invention, which enables precise adjustment of the work stations relative to the drum DA 1  (or DA 2 ) at the user site.  FIG. 6  is the same elevational view as  FIG. 5  but in partial cross section so as to more clearly show the regulating groove  72 , of the spacing adjustment member  70 , and to more clearly describe how adjustment with such spacing adjustment member is made.  FIG. 7  is a front elevational cross sectioned view showing the threaded part  76  and tapered end  78  of an adjustment screw  74 . The head of the adjustment screw  74  is seen in  FIG. 5 . Adjustment screw  74  is threaded into wall  80  of the spacing adjustment member  70  and tapered end  78  mates into tapered hole  82  in the regulating groove  72 . Two limit pins  84  and  86 , seen in  FIG. 5 , protrude from wall  80  and limit the rotation of adjusting screw  74  to approximately 180°. Referring again to  FIG. 6 , the regulating groove  72  and flexure groove  73 , cooperate to define two sections  88  and  90  for the spacing adjustment member  70 , each section having a reference surface  92  and  94  respectively. The grooves  72  and  73  enable the sections  88  and  90  to move relative to one another. 
   In  FIG. 6 , reference surfaces  92  and  94  are oriented at an angle α to each other. When the spacing adjustment member  70  is attached to the end of a work station of the document printer/copier described above, reference surfaces  92  and  94  form a V-groove corresponding to the V-groove  52  illustrated in  FIG. 1B , to interface with the appropriate bullet-shaped locator  54  of either drum assembly DA 1  or DA 2 . There, if adjustment screw  74  is turned clockwise, tapered end  78  is advanced into tapered hole  82 , forcing groove  72  to open wider as a result of flexure of section  88  relative to section  90 , thereby decreasing angle α between reference surfaces  92  and  94 . Accordingly when the appropriate bullet-shaped locator  54  nests between the repositioned surfaces  92  and  94 , the spacing between work station and drum will have been increased. Similarly, when adjusting screw  74  is turned counterclockwise, tapered end  78  is retracted from tapered hole  82  enabling sections  88  and  90  to move relative to one another such that angle α increases. Thus, when the locator  54  engages the repositioned surfaces  92  and  94 , the spacing between the work station and drum is decreased. 
   In an alternative embodiment of the adjustment apparatus embodied in the spacing adjustment member  70  described above (and illustrated in  FIGS. 5–7 ), a cam-shaped member  98  may be used to selectively expand or contract the regulating groove  72 , instead of adjustment screw  74 , with threaded part  76  and tapered end  78 . This alternative embodiment is illustrated in  FIG. 8 . In this alternative embodiment, a screw-like member  96 , with a distal cam-shaped end  98  replaces adjustment screw  74 . The cam-shaped end  98  is located within an expanded section  100  of the regulating groove  72 , such that groove  72  is selectively expanded or contracted by action of the cam-shaped end  98  on the walls of the expanded section  100  as screw-like member  96  is rotatably turned. The head of screw-like member  96  in this embodiment is identical to the head of adjustment screw  74  in the previous embodiment illustrated in  FIGS. 5–7 , so  FIG. 5  applies to this alternative embodiment also. However, for this alternative embodiment, the cross-section view corresponding to  FIG. 6  is shown in  FIG. 8  in which is shown the cam-shaped end  98  of screw-like member  96  located in the expanded section  100  of groove  72 . 
   In one exemplary embodiment, the adjustment apparatus embodied in the spacing adjustment member  70  described above and illustrated in  FIGS. 5–7  (or  FIG. 8 ), is used to adjust the spacing between the operative component of developer station  20 , namely a magnetic brush roller, and image-recording drum  12  in the electrophotographic printer  10  illustrated in  FIG. 1A . With the spacing adjustment member  70  attached to the housing of development station  20 , such spacing is initially set with the adjustment screw  74  positioned, for example, substantially midway between the two limit pins  84  and  86  (as is shown in  FIG. 5 ). A test print is then produced by the electrophotographic printer  10  and the density of the toner image on the test print is measured with an optical densitometer, and compared to a predetermined target density. If the measured toner density on the test print is less than the target density, such an error is an indication that the spacing between the operative component of developer station  20 , namely a magnetic brush roller, and image-recording drum  12  is too large. The adjustment screw  74  is then turned counter-clockwise to decrease the spacing between the magnetic brush roller and the image-recording drum  12  as described above. If the measured toner density on the test print is greater than the target density, such an error is an indication that the spacing between the operative component of developer station  20 , namely a magnetic brush roller, and the image-recording drum  12  is too small. The adjustment screw  74  is then turned clockwise to increase the spacing between the magnetic brush roller and the image-recording drum  12  as described above. This test printing process is iterated until the toner density on the test print is on target. 
   In another exemplary embodiment, the adjustment apparatus described above is used to adjust the spacing between the corona charging station  16  and the image-recording drum  12  in the electrophotographic printer  10  illustrated in  FIG. 1A . It is well known to include an electrostatic voltmeter (not shown in  FIG. 1A ) in electrophotographic printers of the type illustrated in  FIG. 1A  to measure the electrostatic surface potential created by the electrostatic charge deposited by corona charging station onto photoconductive surface  14  of image-recording drum  12 . With spacing adjustment member  70  attached to the housing of corona charging station  16 , the surface potential created on photoconductive surface  14  by corona charging station  16 , is measured with the electrostatic voltmeter while producing a test print. The measured surface potential is compared to a predetermined target surface potential. If the measured surface potential is less than the target surface potential, such an error is an indication that the spacing between the operative component of corona charging station  16 , namely the high voltage corona wires, and image-recording drum  12  is too large. The adjustment screw  74  is then turned counter-clockwise to decrease the spacing between the high voltage wires and the image-recording drum  12 . If the measured surface potential is greater than the target surface potential, such an error is an indication that the spacing between the operative component of corona charging station  16 , namely the high voltage corona wires, and the image-recording drum  12  is too small. The adjustment screw  74  is then turned clockwise to increase the spacing between the high voltage corona wires and the image-recording drum  12 . This test printing process is iterated until the measured surface potential is on target. 
   It should be clear that the above described apparatus can also be used with the other work stations of electrophotographic printer  10 , namely print head  18 , image-transfer drum  22 , and cleaning stations  24  and  26 . 
   While the invention has been described with reference to exemplary embodiments, it will be appreciated that variations can be made without departing from the spirit of the invention, and such variations are intended to fall within the scope of the appended claims.