Patent Publication Number: US-6661441-B2

Title: Combined lens, holder, and aperture

Description:
BACKGROUND AND SUMMARY 
     Xerographic printing and reproduction machines, such as that shown schematically in FIG. 1, typically include raster scanners: raster output scanners (ROSs) for printing and raster input scanners (RISs) for image acquisition in reproduction. In raster scanning systems, an imaging light beam scans across a rotating polygon to a movable photoconductive member, recording or writing electrostatic latent images on the member. Generally, a ROS has a laser for generating a collimated beam of monochromatic radiation. The laser beam is modulated in conformance with the image information. The modulated beam is reflected through a lens onto a scanning element, typically a rotating polygon having mirrored facets. Many machines use one ROS for each color being printed, the ROS exposing the photoreceptor to light in a pattern representing an image to be printed, as is known in the art. In multipass machines, a single ROS can write the image for each color. The pattern on the exposed photoreceptor is then used to deposit toner on a substrate, which toner is then fused onto the substrate to produce the final printed image. 
     As an example of the environment in which embodiments can be employed, FIG. 1 schematically illustrates an electrophotographic printing machine  1  that uses raster scanners (RIS  128  and ROS  130 ) and generally employs a photoconductive belt  12 . Preferably, the photoconductive belt  12  is made from a photoconductive material coated on a ground layer, which, in turn, is coated on an anti-curl backing layer. Belt  12  moves in the direction of arrow  18  to advance successive portions sequentially through the various processing stations disposed about the path of movement thereof. Belt  12  is entrained about stripping roller  14 , tensioning roller  15  and drive roller  16 . As roller  16  rotates, it advances belt  12  in the direction of arrow  13 . 
     Initially, a portion of the photoconductive surface passes through charging station A. At charging station A, a corona generating device indicated generally by the reference numeral  122  charges the photoconductive belt  12  to a relatively high, substantially uniform potential. 
     At an exposure station, B, a controller or electronic subsystem (ESS), indicated generally by reference numeral  129 , 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 which is transmitted to a modulated output generator, for example the raster output scanner (ROS), indicated generally by reference numeral  130 . Preferably, ESS  129  is a self-contained, dedicated minicomputer. The image signals transmitted to ESS  129  may originate from a RIS 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  129 , corresponding to the continuous tone image desired to be reproduced by the printing machine, are transmitted to ROS  130 . ROS  130  includes a laser with rotating polygon mirror blocks. The ROS will expose the photoconductive belt to record an electrostatic latent image thereon corresponding to the continuous tone image received from ESS  129 . As an alternative, ROS  130  may employ a linear array of light emitting diodes (LEDs) arranged to illuminate the charged portion of photoconductive belt  12  on a raster-by-raster basis. 
     After the electrostatic latent image has been recorded on photoconductive surface, belt  12  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. 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  144 , dispenses toner particles into developer housing  146  of developer unit  138 . 
     With continued reference to FIG. 1, after the electrostatic latent image is developed, the toner powder image present on belt  12  advances to transfer station D. A print sheet  148  is advanced to the transfer station, D, by a sheet feeding apparatus,  150 . Preferably, sheet feeding apparatus  150  includes a nudger roll  151  which feeds the uppermost sheet of stack  154  to nip  155  formed by feed roll  152  and retard roll  153 . Feed roll  152  rotates to advance the sheet from stack  154  into vertical transport  156 . Vertical transport  156  directs the advancing sheet  148  of support material into the registration transport  120  of the invention herein, described in detail below, past image transfer station D to receive an image from photoreceptor belt  12  in a timed sequence so that the toner powder image formed thereon contacts the advancing sheet  148  at transfer station D. Transfer station D includes a corona generating device  158  which sprays ions onto the back side of sheet  148 . This attracts the toner powder image from photoconductive surface to sheet  148 . The sheet is then detacked from the photoreceptor by corona generating device  159  which sprays oppositely charged ions onto the back side of sheet  148  to assist in removing the sheet from the photoreceptor. After transfer, sheet  148  continues to move in the direction of arrow  60  by way of belt transport  162  which advances sheet  148  to fusing station F. 
     Fusing station F includes a fuser assembly indicated generally by the reference numeral  170  which permanently affixes the transferred toner powder image to the copy sheet. Preferably, fuser assembly  170  includes a heated fuser roller  172  and a pressure roller  174  with the powder image on the copy sheet contacting fuser roller  172 . The pressure roller is cammed 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  172 . 
     The sheet then passes through fuser  170  where the image is permanently fixed or fused to the sheet. After passing through fuser  170 , a gate  180  either allows the sheet to move directly via output  184  to a finisher or stacker, or deflects the sheet into the duplex path  100 , specifically, first into single sheet inverter  182  here. That is, if the sheet is either a simplex sheet, or a completed duplex sheet having both side one and side two images formed thereon, the sheet will be conveyed via gate  180  directly to output  184 . However, if the sheet is being duplexed and is then only printed with a side one image, the gate  180  will be positioned to deflect that sheet into the inverter  182  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  170  for receiving and permanently fixing the side two image to the backside of that duplex sheet, before it exits via exit path  184 . 
     After the print sheet is separated from photoconductive surface of belt  12 , the residual toner/developer and paper fiber particles adhering to photoconductive surface are removed therefrom at cleaning station E. Cleaning station E includes a rotatably mounted fibrous brush in contact with photoconductive surface to disturb and remove paper fibers and a cleaning blade to remove the non-transferred 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 with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof for the next successive imaging cycle. 
     The various machine functions are regulated by controller  129 . 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. 
     To reduce cost in raster scanner optics, many manufacturers have turned to plastic lenses. In addition to lower cost, plastic lenses can easily be manufactured to include their own holders in the part design. This reduces material costs, manufacturing costs, and assembly costs by part count reduction. It also reduces the part weight. However, raster scanners require an aperture to prevent excess light from passing through the lens. Such apertures typically include a piece of sheet metal with a hole of the right shape and size in it. The area surrounding the lens is therefore covered up and no light can go past the lens except the desired light that goes through the hole. The requirement for such an aperture prevents further cost reduction and part number reduction. 
     Additional cost and part number reductions can be achieved by including the aperture in the design of the lens. Since the lens is clear, the material to be used for the part must be clear. Thus, an aperture can be formed by surrounding the lens with one or more refractive surfaces that direct the undesired part of the light beam away from the optical path, which can include another lens or a mirror. The excess light can, for example, be absorbed by the housing of the raster scanner. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a xerographic reproduction machine including a raster input scanner (RIS) and a raster output scanner (ROS). Note that a xerographic reproduction machine incorporates a xerographic printing machine. 
     FIG. 2 is a schematic illustration of a raster output scanner employing an embodiment. 
     FIG. 3 is a schematic elevational of an embodiment. 
     FIG. 4 is a schematic top view of an embodiment. 
     FIG. 5 is a schematic cross sectional view of an embodiment taken along the line  5 — 5  in FIG.  4 . 
     FIG. 6 is a schematic cross sectional view of an embodiment taken along the line  6 — 6  in FIG.  4 . 
     FIG. 7 is a schematic cross sectional view of an embodiment taken perpendicular to line  7 — 7  in FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     For simplicity, embodiments are described in a raster output scanner (ROS), such as that represented by ROS  130  in FIG. 1, in the context of a xerographic printing machine, such as that shown schematically in FIG.  1 . However, those of ordinary skill in the art will understand that embodiments can be applied in other contexts, to other raster scanners, and to other devices requiring an aperture about a lens. Further, while embodiments take advantage of the low cost and easy manipulation of resinous materials, such as plastics, other embodiments can employ glass or other materials refractive of the particular frequencies of electromagnetic radiation the invention would be used to modify. 
     As illustrated in FIG. 2, the typical ROS includes a light source  28 , a collimating lens  32 , and an aperture  34  that eliminates excess light. Such an ROS can be part of a multipass xerographic printing subsystem such as that depicted schematically and designated generally by reference numeral  10 , which can be part of a xerographic printing machine  1  such as that shown in FIG.  1  and described above. The system  10  includes a photoreceptive belt  12  entrained about guide rollers  14  and  16 , at least one of which is driven to advance the belt  12  in a longitudinal direction of processing travel depicted by the arrow  18 . The length of the belt  12  is designed to accept an integral number of spaced image areas I 1 -I n  represented by dashed line rectangles in FIG.  2 . As each of the image areas I 1 -I n  reaches a transverse line of scan, represented at  20 , it is progressively exposed on closely spaced transverse raster lines  22  shown with exaggerated longitudinal spacing on the image area I 1  in FIG.  2 . 
     In FIG. 2, the line  20  is scanned by a raster output scanner so that a modulated laser beam  24  is reflected to the line  20  by successive facets  25  on a rotatable polygon-shaped mirror  26  driven by motor  27  providing suitable feedback signals to control  30 . The beam  24 , illustrated in dotted lines, is emitted by a laser device  28 , such as a laser diode, operated by a laser drive module and power control forming part of a control processor generally designated by the reference numeral  30 . The processor  30  includes other not shown circuit or logic modules such as a scanner drive command circuit, by which operation of motor  27  for rotating the polygon mirror  26  is controlled. A start of scan (SOS) sensor, illustrated at  36 , determines a start of scan reference point and also provides suitable feedback signals to control  30 . 
     In the operation of the system  10 , as thus far described, the control  30  responds to a video signal to expose each raster line  22  to a linear segment of the video signal image. In xerographic color systems, each image area I 1 -I n  must be exposed in the same manner to four successive exposures, one for each of the three basic colors and black. In a multi-pass system such as the system  10 , where only one raster output scanner or head is used, complete exposure of each image area requires four revolutions of the belt  12 . It should also be noted that the present invention is equally applicable to black and white exposure systems. 
     The image areas I 1 -I n  are successively exposed on successive raster lines  22  as each raster line registers with a transverse scan line  20  as a result of longitudinal movement of the belt  12 . The transverse scan line  20  in system  10  is longer than the transverse dimension of the image areas I. Scan line length, in this respect, is determined by the length of each mirror facet  25  and exceeds the length of the raster lines  22 . The length of each raster line is determined by the time during which the laser diode is active to reflect a modulated beam from each facet  25  on the rotating polygon  26  as determined by the laser drive module. Thus, the active portion of each transverse scan line may be shifted in a transverse direction by control of the laser drive module and the transverse position of the exposed raster lines  22 , and image areas I 1 -I n , shifted in relation to the belt  12 . 
     Downstream from the exposure station, a development station (not shown) develops the latent image formed in the preceding image area as described above with relation to the xerographic printing machine shown in FIG.  1 . After the last color exposure, a fully developed color image is then transferred to an output sheet. An Electronic Sub System (ESS) ( such as ESS  129  shown in FIG. 1) contains the circuit and logic modules that respond to input video data signals and other control and timing signals to drive the photoreceptor belt  12  synchronously with the image exposure and to control the rotation of the polygon by the motor. For further details, reference is made to U.S. Pat. Nos. 5,381,165 and 5,208,796 the disclosures of which are incorporated by reference. As illustrated, any suitable marker on the photoconductive surface or belt or any suitable hole, such as T 1 , T 2 , and T 3 , can provide a reference for each projected image on the belt surface. A microprocessor typically controls the laser with two control loops: a Bias control loop, and a Level Control loop. The same microcontroller can also act as the Motor Polygon Assembly (MPA) speed control and all sub-system applications, such as softstart ramping of lasers and diagnostics of laser failures with controlled ROS shutdowns. For additional details of the raster scanner control systems, see, for example, U.S. Pat. No. 6,195,113, the disclosure of which is hereby incorporated by reference. 
     The light beam  24  is reflected from a facet  25  and thereafter focused to a “spot” on the photosensitive member using optics  40 . The rotation of the polygon  26  causes the spot to scan across the photoconductive member  12  in a fast scan (i.e., line scan) direction. Meanwhile, the photoconductive member  12  is advanced relatively more slowly than the rate of the fast scan in a slow scan (process) direction indicated by arrow  18  which is orthogonal to the fast scan direction, which is parallel to the axis Y-Y. In this way, the beam  24  scans the recording medium  12  in a raster scanning pattern. The light beam  24  is intensity-modulated in accordance with an input image serial data stream at a rate such that individual picture elements (“pixels”) of the image represented by the data stream are exposed on the photosensitive medium to form the latent image, which is then transferred to an appropriate image receiving medium such as paper. 
     Before the light reaches the rotating polygon  26 , it passes through the collimating lens  32 , which conditions the modulated laser beam  24  to ensure proper spot formation on the belt  12 . After the beam  24  passes through the lens  32 , it is further conditioned by passing through an aperture  34 . The aperture  34  blocks and/or diverts excess light that would hamper proper spot formation on the belt  12 . The aperture  34  can be a refractive aperture that diverts excess light away from the path of the beam  24 , a reflective aperture that reflects the light away from the path, or an absorptive aperture that simply absorbs the excess light. Once through the aperture  34 , the beam  24  proceeds to the polygon  26  as described above. It can be said that the lens  32  and aperture  34  are in “photonic communication” with the light source  28 , and that the lens  32 , aperture  34 , polygon  26 , optics  40 , and even the belt  12  lie on an optical path of the ROS. Further, the photonic communication between the light source  28  and the various elements on the optical path is selective inasmuch as the beam  24  will disappear when the light source  28  is turned off. 
     With particular reference to FIGS. 3-7, embodiments can be incorporated into an ROS such as that shown in FIG.  3 . The ROS includes a light source  28 , a rotating polygonal mirror  26 , and a light-conditioning member  35  interposed between the light source  28  and the mirror  26 . The light conditioning member  35  includes a lens  32  and an aperture  34  combined into the single member  35 . The lens  32  can, for example, collimate the light emitted by the light source  28  as in the prior art ROS. In addition, the aperture  35  can remove excess light from the optical path of the scanner. 
     With particular reference to FIGS. 3-7, embodiments can be incorporated into an ROS such as that shown in FIG.  3 . The ROS includes a light source  28 , a rotating polygonal mirror  26 , and a light-conditioning member  35  interposed between the light source  28  and the mirror  26 . The light conditioning member  35  includes a lens  32  and an aperture  34  combined into the single member  35 . The lens  32  can, for example, collimate the light emitted by the light source  28  as in the prior art ROS. In addition, the aperture  34  and/or member  35  can remove excess light from the optical path of the scanner. 
     In embodiments, the member  35  can include portions  34   a-d , such as facets, that divert light away from the optical path of the ROS, as by refraction or reflection, to form the aperture  34  for and around the lens  32 . Whether by refraction or reflection, the light diverted by the aperture  34  can be directed at and absorbed by a housing of the ROS. 
     Embodiments employ refractive portions  34   a-d  of a refractive version of the member  35  that refract light away from the optical/beam path. In such instances, outer surfaces of the refractive portions  34   a-d  should be angled relative to the optical path taking into account the indices of refraction of air and of the refractive material used in the refractive body. Other embodiments employ reflective surfaces of the portions  34   a-d  that reflect light away from the optical path. In such instances, outer surfaces of the refractive version of the member  35  are polished or coated to be reflective and are angled to reflect light away from the optical path. Additionally, the portions  34   a-d  can be coated with a material that will absorb the excess light from the beam  24 . 
     While embodiments have been described in the context of the frequencies of light used in xerographic printing machines, it is conceivable that embodiments could employ a refractive body that could accommodate other frequencies of light. For example, a refractive body made from fused silica could serve as a lens and aperture for ultraviolet radiation. 
     Other modifications of the present invention may occur to those skilled in the art subsequent to a review of the present application, and these modifications, including equivalents thereof, are intended to be included within the scope of the present invention.