Abstract:
Aspects of the disclosure relate to optical scanner apparatuses, hard imaging devices, optical scanning methods, and hard imaging scanning methods. In one aspect, an optical scanner apparatus is described. The optical scanner apparatus may include an optical scanning device configured to reflect a received light beam towards a photoconductor, and a beam direction system optically coupled to the optical scanning device. The beam direction system may include a plurality of reflectors, and each reflector may be configured to transmit light of one polarization while reflecting light of another polarization. The reflectors may be individually configured to permit passage of the input light beam and a light beam reflected by the scanning device and to reflect another light beam reflected by the scanning device.

Description:
FIELD OF THE INVENTION 
   Aspects of the invention relate to optical scanner apparatuses, hard imaging devices, optical scanning methods, and hard imaging scanning methods. 
   BACKGROUND OF THE INVENTION 
   High-resolution, high-speed laser scanning exposure systems for electro-photographic printers employing rotating polygonal mirror scanners and multiple beams are known in the art. In such devices, great care is normally required in the optical design of the scan lens to make the scan geometry at a final image plane insensitive to pyramid error (e.g., wobble) in the polygon mirror, and also to eliminate scan bow. Wobble may normally be prevented by bringing the multiple beams to line foci in a direction orthogonal to the scan plane at the polygon face, and then refocusing the beams at the final image plane. This process may require an anamorphic scan lens, which may be considerably more difficult to make, and hence more expensive, than a rotationally symmetric lens. This approach may also have lower performance potential due to the additional operational constraints. 
   Scan bow is a variation along the length of a scan between a plurality of beams in a multi-beam scanner due to the distortion characteristics of a scan lens. If not carefully controlled, the scan lens distortion together with the compound angle effect in a rotating polygon scanner may cause scan lines lying above the middle of the scan lens&#39; field of view to be slightly concave in an upward direction, and scan lines lying below the middle of the scan lens&#39; field of view to be slightly concave in a downward direction. 
   In multi-beam systems configured to write a plurality of scan lines at different vertical locations in a single horizontal swath, the scan bow may cause uppermost and lowermost scan lines to differ in shape, irrespective of placement of the swath in the field of view. When successive swaths are written, the lowermost line from one swath and the uppermost line from the next swath form adjacent lines in the final image. Differences in shape between the swaths may result in visible image defects. Such defects may be made even more visible as defects repeat periodically down a page with each swath. 
   Distortion of scan lens in the direction of scan is typically controlled so that a final scan coordinate is proportional to polygon scan angle θ. Since θ varies linearly in time due to continuous uniform rotation of the polygon, pixel information modulated onto write beam(s) at uniform time intervals may then be written at uniform spatial intervals. A scan lens with this distortion characteristic is commonly called an “fθ” lens. The combination of an fθ lens and a polygon scanner fails to produce straight scan lines away from the scan axis. Since in multi-beam scanning systems, all but one of the scan lines are preferred to be positioned either above or below the scan axis, such a system will exhibit scan bow. 
   In exemplary prior laser scanning systems, anamorphic balancing was used to provide scan bow within acceptable limits. Anamorphic balancing takes advantage of an anamorphic lens having different distortion characteristics in the two directions normal to its optic axis. The distortion experienced by a beam traversing the lens with field components in both directions may be determined by a geometric scan of the lens&#39; two different distortion characteristics operating separately on the beam&#39;s respective field components. 
   Thus, beams scanned exactly along one axis or the other may encounter only the corresponding distortion characteristic. However, beams scanned along any other lines may encounter a composite distortion characteristic depending upon the relative magnitude of the beam&#39;s field components in the two directions. This approach allows compensation of the scan bow due to the distortion along the scan, axis in a narrow region near the scan axis by a large distortion in the orthogonal direction of the opposite sign of the scan bow. 
   Anamorphic balancing places additional demands upon the scan lens and restricts the degrees of freedom that may be used to satisfy other demands, such as increases in the format width and the number of resolvable spots desired of the lens. 
   An alternative approach to scan bow control uses a rotationally symmetric scan lens with an fsinθ distortion characteristic. A scan lens with this distortion exactly compensates for the scan bow characteristic of the rotating polygon mirror, resulting in zero net scan bow for scan lines placed anywhere within the field. However, in such a system, the final scan coordinate may not be proportional to “θ”, and information may have to be modulated onto the beam(s) at non-uniform time intervals in order to be written at uniform spatial intervals. 
     FIG. 1A  illustrates a plan view of a prior art arrangement  100  to overcome the inherent wobble correction defect found in a system of the fsinθ type as described above. Wobble correction defect may be overcome by using arrangement  100  in order to permit a beam of light to double bounce off of a scanning device  102  (e.g., rotating polygon mirror). 
   Continuing to refer to  FIG. 1A , a roof reflector  104  oriented with a roof intersection line in the plane of scan may be used to re-direct a scanned beam to the same polygon face of the scanning device  102  for a second reflection. The double bouncing of a beam of light has the effect of removing any change of angle in the cross-scan direction that may have been imparted to the beam due to polygon pyramid error on the first bounce from the scanning device  102 . 
     FIG. 1B  shows an elevation view of roof reflector  104  of arrangement  100  shown in  FIG. 1A . Disadvantages exist with the arrangement of  FIG. 1A  providing the self-correction action and include utilization of a larger polygon when compared to a polygon used in a single bounce system, and particularly so if the scan angle is large. For example, beam diameter at the input to an fsinθ scan lens required for a scanner desired to cover a 500 mm wide format with a ±30° scan to produce a ˜45 micron spot diameter (FW @ 1/e 2 ) is about 15 mm. For  FIG. 1A , the angle between an incoming beam to the polygon  102  and an outgoing beam to the roof reflector  104  having the minimum polygon facet length was found to be around 50°. An angle of 45° between an incoming beam to the polygon  102  may require the roof reflector  104  to be placed farther away from the polygon  102  to clear the lowermost scanned beam, thus requiring both a larger roof and a larger facet because of the angular spread of the scanned beams. A scan angle of 55° allows a slightly smaller roof to be placed closer to the polygon  102 , but again requires a larger facet because of the more oblique second bounce). The resulting deflection system is shown in  FIG. 2 . 
     FIG. 2  shows a double bounce deflection system  200  using a conventional roof reflector  204 . Polygon  202  may have to be designed to have facets that are 126 mm in width. For example, for a 12-sided polygon, the facet width would correspond to a diameter of 470 mm (&gt;18″). Such a large polygon would be relatively expensive to manufacture, and may be difficult to spin at speeds as high as 16K rpm without serious distortion of the optical figure of the facets. 
     FIG. 3  shows a conventional single-bounce deflection system  300 , using a polygon  302 , for the same beam size and angular scan range illustrated in  FIG. 2 . The deflection system  300 , however, may need a polygon having only six facets, individual facets having a width of only 50 mm, the width corresponding to a polygon diameter of 86.6 mm. This leads to increased cost and complexity, as well as limitations with respect to optical performance (i.e., such a system may not cover as wide a field at a given (high) resolution). 
   SUMMARY OF THE INVENTION 
   At least some embodiments of the invention relate to optical scanner apparatuses, hard imaging devices, optical scanning methods, and hard imaging scanning methods. 
   In one aspect, an optical scanner apparatus is described. The optical scanner apparatus may include an optical scanning device configured to reflect a received light beam towards a photoconductor, and a beam direction system optically coupled to the optical scanning device. The beam direction system may include a plurality of reflectors, and each reflector may be configured to transmit light of one polarization while reflecting light of another polarization. The reflectors may be individually configured to permit passage of one of an input light beam provided by an external source and a light beam reflected by the scanning device and to reflect another light beam reflected by the scanning device. Individual ones of reflectors include a polarization beam splitter coating configured to cause a light beam from the scanning device to be either reflected by the individual one of the reflectors towards another of the reflectors or transmitted through the individual one of the reflectors towards the photoconductor. 
   In another aspect, an optical scanning method is described. The method includes first receiving an input light beam by a scanning device, and first reflecting the input light beam towards a first reflector using the scanning device. The method also includes second receiving a light beam reflected by the scanning device by the first reflector, and first redirecting the light beam received by the first reflector towards a second reflector. The light beam received by the second reflector is redirected towards the scanning device by the second reflector, and the light beam received by the scanning device is reflected towards a photoconductor using the scanning device. The method further includes passing an input light beam through the first reflector before the first receiving, and passing the light beam output from the first reflector through a first optical device. 
   Other aspects are disclosed herein as is apparent from the following description and figures. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A–1B  show a plan view and an elevation view, respectively, of a conventional optical scanner apparatus. 
       FIG. 2  shows a conventional double-bounce deflection system of an optical scanner apparatus. 
       FIG. 3  shows a conventional single-bounce deflection system of an optical scanner apparatus. 
       FIG. 4  is an isometric view of a hard imaging device in accordance with one embodiment. 
       FIG. 5  is a high-level block diagram of a hard imaging device according to one embodiment. 
       FIG. 6  is a plan view of an optical scanner apparatus according to one embodiment. 
       FIG. 7  is a block diagram of an optical scanner apparatus illustrating double bouncing of a beam of light using an optical scanning device according to one embodiment. 
       FIG. 8  is a plan view of an optical scanner apparatus illustrating a beam direction system according to one embodiment. 
       FIGS. 9A–9B  show elevation views of an optical scanner apparatus illustrating a beam direction system according to various embodiments. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The optical scanner apparatus of the present invention may be capable of covering a scan area having a relatively wide format (e.g., without a need for an anamorphic lens). A double bounce geometry of the optical scanner apparatus according to one embodiment may provide correction of polygon wobble, and also allow use of a smaller and more practical polygon. 
   Referring to  FIG. 4 , an exemplary hard imaging device  400  configured to physically render hard images upon media is shown in accordance with one embodiment. The hard imaging device  400  may be a laser printer. Other configurations to form hard images upon media are possible, and include for example, multi-function peripherals, copiers, facsimile devices, etc. 
     FIG. 5  is an exemplary high-level block diagram of the hard imaging device  400  according to one embodiment. The depicted hard imaging device  400  configured as a laser printer includes a light source  401 , a controller  402 , an optical scanner apparatus  404 , a photoconductor  406 , a charging device  408 , and a developer and fusing assembly  410  configured to form hard images on media  412 . 
   The light source  401  may include a laser or other light source configured to output a light beam that may be scanned by the optical scanner apparatus  404  towards photoconductor  406 , in one embodiment. Light source  401  may emit the light beam comprising data of an image to be formed and outputted by controller  402 . 
   The controller  402  may be configured to control operations of one or more of individual components (e.g.,  401 ,  404 ,  406 ,  408 , and  410 ) of the hard imaging device  400 . Exemplary operations of controller  402  include image data processing operations (e.g., rasterization) of data received from an external source (not shown), internally generated, or otherwise accessed. 
   The optical scanner apparatus  404  may be configured to scan the beam of light (e.g., information) emitted from light source  401  onto photoconductor  406  to form latent images. 
   The photoconductor  406  includes a rotating imaging surface configured to receive information scanned by the optical scanning apparatus  404 . One or more beams of light (e.g., lines of information) may be scanned by optical scanner apparatus  404  onto photoconductor  406 . 
   The charging device  408  may be configured to charge the photoconductor  406  to enable forming of latent images on the photoconductor  406 . In particular, charging device  408  provides a negative charge to the surface of photoconductor  406  and the scanned light beam discharges portions of the charged surface to form latent images in one embodiment. 
   The developer and fusing assembly  410  may be configured to develop latent images formed on photoconductor  406  using a marking agent (e.g., toner), and transfer and fuse the developed image to media  412  (e.g., hard-imaging media such as paper, transparencies, etc.). 
     FIG. 6  is a plan view of an optical scanner apparatus  404  according to one embodiment. The optical scanner apparatus  404  includes an optical scanning device  602  (e.g., rotating polygon mirror having a plurality of facets), a beam direction system  604  (e.g., circulator), input optics  606  (e.g., a collimator system), and output optics  608  (e.g., fsinθ scan lens). The optical scanning device  602  may be alternatively referred to as a rotating reflection device. 
   A light beam from light source  401  ( FIG. 5 ) may be received by input optics  606 . The input optics  606  may be configured to direct the light beam from light source  401  towards beam direction system  604 . In one embodiment, the light beam from source  401  and input optics  606  is configured to pass through the beam direction system  604  prior to being scanned by scanning device  602  towards photoconductor  406 . The scanned light is directed by output optics  608  to photoconductor  406  in the depicted embodiment.  FIG. 6  depicts one fold mirror  613  configured to direct light upwardly from a horizontal direction. Although not shown in  FIG. 6 , one or more additional fold mirrors may be provided to receive light from fold mirror  613  and to redirect the light from the upwardly traveling direction of  FIG. 6  into a perpendicular horizontal direction towards scanning device  602 . Other embodiments are possible for introducing light to scanning device  602 . 
     FIG. 7  is an exemplary block diagram of optical scanner apparatus  404  illustrating a configuration having a beam direction system  604  configured to permit passage of both an input light beam  601  from light source  401  and an output light beam  611  scanned by scanning device  602  through the beam direction system  604 . The beam direction system  604  may be configured as an optical circulator in one embodiment. Beam direction system  604  is configured to permit input light beam  601  from light source  401  to pass through the beam direction system  604  to produce a light beam  603 . The scanning device  602  reflects light beam  603  (e.g., first bounce) to produce a light beam  605  which is directed towards the beam direction system  604  for a reflection towards the scanning device  602 . The beam direction system  604  is further configured to reflect light beam  605  received from the scanning device  602  to produce a light beam  607 . The scanning device  602  reflects the light beam  607  (e.g., second bounce) providing and directing light beam  609  towards the beam direction system  604 . The beam direction system  604  is configured to pass light beam  609  as light beam  611  that is scanned onto photoconductor  406 . Further details of reflecting a light beam by the scanning device  602  are described below at  FIG. 9A . 
     FIG. 8  is a plan view of optical scanner apparatus  404  according to one embodiment. As noted above, the optical scanner apparatus  404  includes a beam direction system  604  and a scanning device  602  (e.g., a plurality of facets of an exemplary device  602  comprising a polygon mirror are shown). In one embodiment, the beam direction system  604  is positioned such that one or both the input and output light beams  601 ,  611 , respectively, are permitted to pass through the beam direction system  604 . The output light beam  611  is scanned onto photoconductor  406  by the scanning device  602 . The exemplary configuration of  FIG. 8  including beam direction system  604  passing at least one of the beams  601 ,  611  permits the optical scanner apparatus  404  to have a smaller and more practical scanning device  602  with a compact geometry compared with the configurations of  FIG. 1A  or  FIG. 2 , for example, while still providing relatively wide scan angles. 
     FIGS. 9A–9B  show elevation views of an optical scanner apparatus according to various embodiments. 
   Referring to  FIG. 9A , an exemplary optical scanner apparatus  404  includes a facet of an exemplary scanning device  602  and beam direction system  604 . As noted above, the beam direction system  604  is configured and positioned such that input light beam  601 , and output light beam  611  scanned by the scanning device  602  are permitted to pass through the beam direction system  604 . Although a single input light beam  601  is shown for ease of illustration, a plurality of input light beams (e.g., a fan of light beams) are possible. 
   In one embodiment, beam direction system  604  includes first and second matching prisms  902   a ,  902   b , and a third prism  904 . The first and second matching prisms  902   a ,  902   b  may comprise reflectors such as roof reflectors and third prism  904  may comprise a roof prism in one embodiment. Respective surfaces  903   a ,  903   b  of the first and second prisms  902   a ,  902   b  may be coated with a polarizing beamsplitter coating  907  in order to highly transmit light of a first polarization type (e.g., horizontal polarization light components) while substantially or totally reflecting light having a polarization (e.g., vertical polarization light components) that is opposite to the first polarization type. In one exemplary case, the first and second prisms  902   a ,  902   b  and the roof prism  904  may be attached together (e.g., using glass affixing material) to form a rectangular block  905 . For the exemplary embodiment shown in  FIG. 9A , the polarization beamsplitter coating may be a multi-layer dielectric thin film polarizing beamsplitter coating. Other configurations of prisms  902   a ,  902   b  to permit passage of a first polarization type and reflection of a different second polarization type are possible. 
   The optical scanner apparatus  404  further includes optical devices  906 ,  908  disposed between beam direction system  604  and scanning device  602 . In one exemplary case, optical device  908  may be a compensator, such as an O-plate. One exemplary O-plate is a Liquid Crystal Polymer (LCP) compensator. Compensator  908  may have its axis aligned at an angle of 0 degrees with respect to an entering polarization of light, and optical device  906  may be a quarter waveplate having its axis aligned at an angle of 45 degrees with respect to an entering polarization of light. In one embodiment, device  906  is positioned between device  908  and scanning device  602 . Compensator  908  may be optionally used in optical scanner apparatus  404  in order to prevent loss of desired polarization due to incomplete reflection and transmission at various device interfaces in the optical scanner apparatus  404 . In other embodiments, compensator  908  is omitted, and if desired, the output power of the light source may be increased to account for losses. 
   In the embodiment of  FIG. 9A , light beam  605  scanned by the scanning device  602  towards the beam direction system  604 , and incoming light beam  603  received by the scanning device  602  from the beam direction system  604  are shown to trace distinct optical paths, for ease of illustration. The distinct optical paths result from variations (e.g., pyramid variations) present in the scanning device  602  in one example. 
   However, in the absence of a pyramid error in the scanning device  602 , an optical path of the output light beam  605  scanned by the scanning device  602  towards the beam direction system  604  retraces a path of a corresponding input light beam  603  received by the scanning device  602  from the beam direction system  604 . The reflected light beam is then redirected towards the scanning device  602  using the first and second prisms  902   a ,  902   b  and following an optical path indicated by reference numerals  910 ,  911 . The redirected light beam  911  received by the scanning device  602  is scanned towards the photoconductor  406  ( FIG. 5 ) following optical path  914 . If pyramid error is present, the light beam may be provided at a path illustrated by light beam  611 . 
   In operation, with reference to exemplary optical scanner apparatus  404  having compensator  908 , incoming light beam  601  encounters prism  902   a  and beamsplitter coating (e.g., multi-layer beamsplitter coating) provided on surface  903   a  of prism  902   a . The incoming light beam  601  comprises a polarization in a same direction that the beam splitter coating on surface  903   a  transmits. Therefore, the incoming light beam  601  is highly transmitted and its polarization state is aligned with the polarization of the remainder of rectangular block  905  (e.g., the incoming light beam  601  passes through prism  902   a  and prism  904  without suffering significant losses). Light beam  603  output from rectangular block  905  next encounters compensator  908 . 
   Compensator  908  is configured to rectify any misalignments in a polarization direction of light beam  601 . Compensator  908  may also be used to correct for misalignments (e.g., skew) in s- and p-planes of incidence (e.g., s-plane of incidence corresponding to a perpendicular polarization component of a light beam, and p-plane of incidence corresponding to a parallel polarization component of the light beam) when a reflected beam  605 ,  607  encounters prisms  902   a ,  902   b  at a compound angle of incidence (e.g., near either end of a scan) by causing a rotation in polarization of a skew light beam. 
   When the incidence angle is compound, the s- and p-planes of a reflected light beam  605 ,  607  are rotated due to a purely geometric effect, and reflection characteristics of the multi-layer beamsplitter coating provided on surfaces  903   a ,  903   b  of respective prisms  902   a ,  902   b  are influenced by the s- and p-planes of incidence of the reflected light beam. The compound angle of incidence may cause a portion of the reflected light beam  605 ,  607  desired to be reflected and transmitted at surfaces  903   a ,  903   b  to instead be transmitted and reflected and consequently lost, thereby reducing the efficiency of optical scanner apparatus  404  while also contributing to potential sources of stray light. Accordingly, as mentioned above, compensator  908  may be used in at least some embodiments to correct the misalignments. Compensator  908  may also be used to produce a rotation in polarization direction of a skew light beam (e.g., light beam with misalignments in s- and p-planes of incidence) passing through it in order to compensate for the skew. 
   Light beam  603  after passing through compensator  908  encounters quarter waveplate  906  configured to convert linearly polarized light into circularly polarized light. For example, linearly polarized light of entering light beam  603  is converted to a light beam having circularly polarized light by quarter waveplate  906 . In one example, conversion may include designing a thickness of the quarter waveplate  906  such that the phase difference is ¼ wavelength, and if the angle between electric field vector of an incident linearly polarized light of light beam  603  and a retarder principal plane of the quarter waveplate  906  is 45 degrees, then a light beam output from quarter waveplate  906  is circularly polarized. 
   Light beam  603  with circularly polarized light and output from quarter waveplate  906  is first reflected (e.g., first bounce) by the scanning device  602  to produce light beam  605 . After reflection from the scanning device  602 , handedness of the light beam  605  is reversed with respect to light beam  603  (e.g., right circular polarization is converted to left circular polarization, and vice-versa). The light beam  605  now encounters and passes through the quarter waveplate  906 . Upon passing through the quarter waveplate  906 , polarization of the light beam  605  is converted from a circular polarization to a linear polarization that is orthogonal to a polarization state (e.g., polarization vector directed into the page in the illustrated  FIG. 9A ) of the incoming light beam  603 . Such conversion enables light beam  605  passing through the compensator  908  towards the rectangular block  905  to be highly reflected upon encountering surface  903   a  of prism  902   a.    
   Light beam  605  that is highly reflected by surface  903   a  of prism  902   a  is directed towards surface  903   b  of prism  902   b . Since the properties of light beam  605  remain unchanged upon reflection from surface  903   a , the light beam  605  is reflected by surface  903   b  of prism  902   b  towards the scanning device for a second reflection (e.g., second bounce as light beam  607 ). Light beam  607  passes through compensator  908  and quarter wave plate  906  prior to a second reflection (e.g., second bounce) by scanning device  602 . Upon passing through compensator  908 , quarter waveplate  906 , light beam  607  and reflected light beam  609  (e.g., after second bounce from scanning device  602 ) encounter similar actions described above with respect to passing of light beam  601  and reflected light beam  605  (e.g., after first bounce from scanning device  602 ) through compensator  908 , quarter waveplate  906  (e.g., conversion of linear polarization to circular polarization, and reversal of handedness upon second reflection by scanning device  602 ). The compensator  908  imparts a slight rotation to linearly polarized light beam  609  output from quarter waveplate  906  towards the photoconductor  406  ( FIG. 5 ) in order to correct for a compound angle effect at a second encounter with prism  902   b . Upon encountering prism  902   b , light beam  609  may be strongly transmitted since its polarization is rotated to its initial direction (e.g., vertical direction in the illustrated  FIG. 9A ). Light beam  611  is then output from the beam direction system  604  for scanning onto photoconductor  406 . 
   Referring to  FIG. 9B , another exemplary embodiment of optical scanner apparatus is shown wherein like elements are identified with like numerals with a suffix “a” added. In this embodiment, instead of prisms  902   a ,  902   b ,  904 , a beam direction system  604   a  of optical scanner apparatus  404   a  may include a pair of flat glass plates  912   a ,  912   b  having a wire grid type polarizing coating  913 . An exemplary wire grid type polarizing coating  913  may be obtained from Moxtek, Inc., of Orem, Utah. In one exemplary case, the glass plates  912   a ,  912   b  may be oriented at an angle of 90 degrees with respect to one another, and at an angle of 45 degrees with respect to an incoming light beam  601   a . The compensator  908  depicted in  FIG. 9A  is not desirable in the embodiment of  FIG. 9B  as the reflection characteristics of wire grid polarizing coating are not tied to the s- and p-plane directions, but are instead tied to the direction of wires used in the coating. But for the differences identified above, operation of optical scanner apparatus  404   a  having beam direction system  604   a  is substantially similar to the operation of optical scanner apparatus  404  described above at  FIG. 9A . 
   Exemplary advantages of the present invention include providing an optical scanner apparatus capable of covering a wide format (e.g., 500 mm or 700 mm) due to good imaging properties of non-anamorphic scan lens, elimination of a need for an anamorphic lens to correct polygon wobble and scan bow, thereby improving performance of output optics (e.g., scan lens) to achieve a larger number of resolvable spots corresponding to a wider format, and to achieve improved resolution over a wide format compared to conventional approaches. Other advantages include elimination of scan bow, and correction of polygon wobble using double bounce geometry provided by the circulator while maintaining a reasonable polygon size. For example, using a twelve beam laser array source and twelve facet polygon, the optical scanner apparatus of the present invention may achieve a process speed of 1.5 m/sec at a print density of 813 scan lines/inch with a polygon rotation speed of 16 K rpm. If a twenty four beam source is used, rotation speed of the polygon may be halved. 
   The protection sought is not to be limited to the disclosed embodiments, which are given by way of example only, but instead is to be limited only by the scope of the appended claims.