Abstract:
The present invention is for a vacuum imaging drum with vacuum holes for maintaining a boundary layer in an image processing apparatus ( 10 ). The image processing apparatus ( 10 ) with a vacuum imaging drum ( 300 ) for holding thermal print media ( 32 ) and donor sheet material ( 36 ) in registration on the vacuum imaging drum ( 300 ). A printhead ( 500 ) moves along a line parallel to the longitudinal axis (X) of the vacuum imaging drum ( 300 ) as the vacuum imaging drum ( 300 ) rotates. The printhead ( 500 ) receives information signals and produces radiation which is directed to the donor sheet material ( 36 ) which causes color to transfer from the donor sheet material ( 36 ) to the thermal print media ( 32 ). The vacuum imaging drum ( 300 ) provides vacuum on its surface by means of a first plurality of holes. A second plurality of holes maintains a boundary layer ( 336 ) of air along the drum surface.

Description:
FIELD OF THE INVENTION 
     This invention relates to an image processing apparatus of the lathe bed scanning type and more specifically to using vacuum to maintain a boundary layer of air against the surface of an imaging drum revolving at high speed. 
     BACKGROUND OF THE INVENTION 
     Pre-press color proofing is a procedure used by the printing industry for creating representative images of printed material without the high cost and time required to actually produce printing plates and set up a high-speed, high-volume, printing press to produce a single example of an intended image. These intended images may require several corrections and may need to be reproduced several times to satisfy customers requirements. By utilizing pre-press color proofing time and money can be saved. 
     One such commercially available image processing apparatus, disclosed in commonly assigned U.S. Pat. No. 5,268,708, describes image processing apparatus having half-tone color proofing capabilities. This image processing apparatus is arranged to form an intended image on a sheet of thermal print media by transferring dye from a sheet of dye donor material to the thermal print media by applying a sufficient amount of thermal energy to the dye donor material to form an intended image. This image processing apparatus is comprised of a material supply assembly or carousel; lathe bed scanning subsystem, which includes a lathe bed scanning frame, translation drive, translation stage member, printhead, vacuum imaging drum, thermal print media and dye donor material exit transports. 
     The operation of the image processing apparatus comprises metering a length of the thermal print media, in roll form, from the material assembly or carousel. The thermal print media is cut into sheets, transported to the vacuum imaging drum, registered, wrapped around, and secured onto the vacuum imaging drum. A length of dye donor material, in roll form, is metered out of the material supply assembly or carousel, and cut into sheets. The dye donor material is transported to and wrapped around the vacuum imaging drum, such that it is superposed in the registration with the thermal print media. 
     After the dye donor material is secured to the periphery of the vacuum imaging drum, the scanning subsystem or write engine writes an image on the thermal print media as the thermal print media and the dye donor material on the spinning vacuum imaging drum is rotated past the printhead. The translation drive traverses the printhead and translation stage member axially along the vacuum imaging drum, in coordinated motion with the rotating vacuum imaging drum to produce the intended image on the thermal print media. 
     After the intended image has been written on the thermal print media, the dye donor material is removed from the vacuum imaging drum without disturbing the thermal print media that is beneath it. The dye donor material is transported out of the image processing apparatus by the dye donor material exit transport. Additional sheets of dye donor material are sequentially superposed with the thermal print media on the vacuum imaging drum, and imaged onto the thermal print media as described above until the intended image is completed. The completed image on the thermal print media is unloaded from the vacuum imaging drum and transported to an external holding tray on the image processing apparatus by the receiver sheet material exit transport. 
     The vacuum imaging drum is cylindrical in shape and includes a hollowed-out interior portion. A plurality of holes extending through the drums permit a vacuum to be applied from the interior of the vacuum imaging drum for supporting and maintaining the position of the thermal print media and dye donor material as the vacuum imaging drum rotates. 
     The outer surface of the vacuum imaging drum has an axially extending flat, which covers approximately eight degrees of the vacuum imaging drum circumference. The purpose of the axially extending flat is to assure that the leading and trailing ends of the dye donor material are partially protected from the effect of the air turbulence during the imaging process, since air turbulence has a tendency to lift the leading or trailing edges of the dye donor material. The vacuum imaging drum axially extending flat also ensures that the leading and trailing ends of the dye donor material are recessed from the vacuum imaging drum periphery. This reduces the chance that the dye donor material will contact other parts of the image apparatus, such as the printhead, which may cause a jam and loss of the intended image or worse, catastrophic damage to the image processing apparatus. 
     Although the presently known and utilized image processing apparatus is satisfactory, it is not without drawbacks. The donor and receiver media must be held tightly against the surface of the vacuum imaging drum as the drum rotates at high speeds. Near the surface of the rotating drum, a thin boundary layer condition exists in which the laminar flow of air effectively forms a very thin low-pressure region extending around the cylindrical surface of the drum. This boundary layer acts to provide a consistent low-pressure region on the outside of the film media, which is secured to the drum by vacuum. However, any irregularity in the drum surface, such as the axially extending flat, disturbs the laminar flow. This disturbance creates turbulence, in which the boundary layer separates from the drum surface. As a result, a region of high pressure is created, which can effectively slow drum rotation or lift an edge of the dye donor material, causing fly-off of the dye donor material and consequent damage to the image processing apparatus. 
     As the speed of drum rotation is increased, to increase production speed, this problem is exacerbated. One way to compensate for separation of the boundary layer, is to apply additional vacuum force to hold the leading and trailing edges of the film media against the drum more securely. Increasing the vacuum in the drum, however, requires increased drum thickness, a more heavy duty vacuum pump, and a more powerful drum motor, all of which adds expense. 
     Boundary layer control is an important consideration in design of aircraft. U.S. Pat. No. 4,664,345 (Lurz) for example, describes control of the boundary layer against an aircraft surface. Here, suction is employed to stabilize the boundary layer and prevent separation from a surface. U.S. Pat. No. 5,222,698 (Nelson et al.) also discloses use of suction to control boundary layer attachment and prevent turbulence. U.S. Pat. No. 5,535,967 (Beauchamp et al.) also describes using suction means to control a boundary layer and maintain laminar flow. 
     Boundary layer control along surfaces of rotating devices is not well known. U.S. Pat. No. 5,637,942 (Forni) discloses a method for boundary layer control in electric rotors and similar rotating devices. However, the method disclosed is for containing a boundary layer to effect drag reduction and control of axial air-flow for efficient motor operation. 
     The rotational speed of a vacuum imaging drum is one factor that determines overall throughput of an imaging apparatus. An improvement that allows higher drum speeds would help to increase throughput of the imaging apparatus. It can thus be seen that there is a need for maintaining the boundary layer and minimizing turbulence of surface air for an imaging apparatus that employs a vacuum imaging drum. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide one or more vacuum ports disposed to maintain the boundary layer on a vacuum imaging drum in an imaging apparatus. 
     According to a feature of the present invention an image processing apparatus comprises a vacuum imaging drum for holding thermal print media and dye donor material, in registration on a surface of the vacuum imaging drum. A printhead prints information to the thermal print media as the printhead is moved parallel to a surface of the vacuum imaging drum. The vacuum imaging drum has at least one boundary layer vacuum port located between a leading edge and a trailing edge of the dye donor material to maintain a boundary layer around the vacuum imaging drum as the vacuum imaging drum rotates. 
     An advantage of the present invention is that it adds no components to an existing drum design. A further advantage is that changes to the weight distribution of the drum are negligible. The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view in vertical cross section of an image processing apparatus of the present invention. 
     FIG. 2 is a perspective view of the lathe bed scanning subsystem of the present invention. 
     FIG. 3 is an exploded, perspective view of the vacuum imaging drum of the present invention, showing the placement of additional vacuum ports for boundary layer control. 
     FIG. 4 is a plane view of the vacuum imaging drum surface of the present invention, showing the placement of additional vacuum ports for boundary layer control. 
     FIGS. 5A-5C are plane views of the vacuum imaging drum showing the sequence of placement for the thermal print media and dye donor material. 
     FIGS. 6A and 6B are sectional views along line  6 — 6  of FIG. 5C contrasting boundary layer response with and without the vacuum ports used in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is illustrated an image processing apparatus  10  according to the present invention having an image processor housing  12  which provides a protective cover. A movable, hinged image processor door  14  is attached to the front portion of image processor housing  12  permitting access to two sheet material trays, a lower sheet material tray  50   a  and an upper sheet material tray  50   b , that are positioned in the interior portion of image processor housing  12  for supporting thermal print media  32 , thereon. Only one of sheet material trays will dispense thermal print media  32  to create an intended image thereon; the alternate sheet material tray either holds an alternative type of thermal print media  32  or functions as a back up sheet material tray. In this regard, lower sheet material tray  50   a  includes a lower media lift cam  52   a  for lifting lower sheet material tray  50   a  and ultimately thermal print media  32 , upwardly toward a rotatable, lower media roller  54   a  and towards a second rotatable, upper media roller  54   b  which, when both are rotated, permits thermal print media  32  to be pulled upwardly towards a media guide  56 . Upper sheet material tray  50   b  includes an upper media lift cam  52   b  for lifting upper sheet material tray  50   b  and ultimately thermal print media  32  towards upper media roller  54   b  which directs it towards media guide  56 . 
     Movable media guide  56  directs the thermal print media  32  under a pair of media guide rollers  58  which engages the thermal print media  32  for assisting upper media roller  54   b  in directing it onto a media staging tray  60 . Media guide  56  is attached and hinged to a lathe bed scanning frame  202  (shown in FIG. 2) at one end, and is uninhibited at its other end for permitting multiple positioning media guide  56 . Media guide  56  then rotates its uninhibited end downwardly, as illustrated in the position shown, and the direction of rotation of upper media roller  54   b  is reversed for moving thermal print media  32  resting on media staging tray  60  under a pair of media guide rollers  58 , upwardly through an entrance passageway  204  and around a rotatable vacuum imaging drum  300 . 
     A roll of donor roll material  34  is connected to a media carousel  100  in a lower portion of image processor housing  12 . Four rolls of media are used, but only one is shown for clarity. Each roll media includes a donor roll material  34  of a different color, typically black, yellow, magenta and cyan. These donor roll materials  34  are ultimately cut into donor sheet materials  36  (not shown) and passed to a vacuum imaging drum  300  for forming the medium from which is imbedded therein are passed to the thermal print media  32  resting thereon, which process is described in detail herein below. In this regard, a media drive mechanism  110  is attached to each roll of donor roll material  34 , and includes three media drive rollers  112  through which the donor roll material  34  of interest is metered upwardly into a media knife assembly  120 . After the donor roll material  34  reaches a predetermined position, media drive rollers  112  cease driving donor roll material  34  and two media knife blades  122  positioned at the bottom portion of the media knife assembly  120  cut the donor roll material  34  into donor sheet materials  36 . Lower media roller  54   a  and upper media roller  54   b  along with media guide  56  then pass donor sheet material  36  onto media staging tray  60  and ultimately to vacuum imaging drum  300  and in registration with the thermal print media  32  using the same process as described above for passing thermal print media  32  onto vacuum imaging drum  300 . Donor sheet material  36  now rests atop thermal print media  32  with a narrow space between the two created by microbeads imbedded in the surface of thermal print media  32 . 
     A laser assembly  400  includes a quantity of laser diodes  402  in its interior, laser diode  402  are connected via fiber optic cables  404  to a distribution block  406  and ultimately to a printhead  500 . Printhead  500  directs thermal energy received from laser diodes  402  causing donor sheet material  36  to pass the desired color across the gap to thermal print media  32 . Printhead  500  is attached to a lead screw  250 , shown in FIG. 2, via a lead screw drive nut  254  and a drive coupling (not shown) for permitting movement axially along the longitudinal axis of vacuum imaging drum  300  for transferring the data to create the intended image onto thermal print media  32 . 
     For writing, vacuum imaging drum  300  rotates at a constant velocity, and printhead  500  begins at one end of thermal print media  32  and traverse the entire length of thermal print media  32  for completing the transfer process for the particular donor sheet material  36  (shown in FIG. 5C) resting on thermal print media  32 . After printhead  500  has completed the transfer process, for the particular donor sheet material  36  resting on thermal print media  32  donor sheet material  36  is then removed from vacuum imaging drum  300  and transferred out image processor housing  12  via a skive or donor ejection chute  16 . The donor sheet material  36  eventually comes to rest in a waste bin  18  for removal by the user. The above described process is then repeated for the other three rolls of donor roll materials. 
     After the colors from all four sheets of donor sheet materials  36  have been transferred and donor sheet materials  36  have been removed from vacuum imaging drum  300 , thermal print media  32  is removed from vacuum imaging drum  300  and transported via a transport mechanism  80  to a color binding assembly  180 . A media entrance door  182  of color binding assembly  180  is opened for permitting thermal print media  32  to enter color binding assembly  180 , and shuts once thermal print media  32  comes to rest in color binding assembly  180 . Color binding assembly  180  processes thermal print media  32  for further binding the transferred colors on thermal print media  32  and for sealing the microbeads thereon. After the color binding process has been completed, media exit door  184  is opened and thermal print media  32  with the intended image thereon passes out of color binding assembly  180  and image processor housing  12  and comes to rest against media stop  20 . 
     Referring to FIG. 2, there is illustrated a perspective view of the lathe bed scanning subsystem  200  of image processing apparatus  10 , including vacuum imaging drum  300 , printhead  500  and lead screw  250  assembled in lathe bed scanning frame  202 . Vacuum imaging drum  300  is mounted for rotation about an axis X in lathe bed scanning frame  202 . Printhead  500  is movable with respect to vacuum imaging drum  300 , and is arranged to direct a beam of light to donor sheet material  36  (shown in FIG.  5 C). The beam of light from printhead  500  for each laser diode  402  (not shown in FIG. 2) is modulated individually by modulated electronic signals from image processing apparatus  10 , which are representative of the shape and color of the original image, so that the color on donor sheet material  36  is heated to cause volatilization only in those areas in which its presence is required on thermal print media  32  to reconstruct the shape and color of the original image. 
     Printhead  500  is mounted on a movable translation stage member  220  which, in turn, is supported for low friction slidable movement on translation bearing rods  206  and  208 . Translation bearing rods  206  and  208  are sufficiently rigid so as not to sag or distort as is possible between their mounting points and are arranged as parallel as possible with the axis X of the vacuum imaging drum  300  with the axis of the printhead  500  perpendicular to axis X of the vacuum imaging drum  300 . A front translation bearing rod  208  locates a translation stage member  220  in the vertical and the horizontal directions with respect to axis X of vacuum imaging drum  300 . A rear translation bearing rod  206  locates translation stage member  220  only with respect to rotation of translation stage member  220  about front translation bearing rod  208  so that there is no over-constraint condition of translation stage member  220  which might cause it to bind, chatter, or otherwise impart undesirable vibration or jitters to printhead  500  during the generation of an intended image. 
     Printhead  500  travels in a path along vacuum imaging drum  300 , while being moved at a speed synchronous with vacuum imaging drum  300  rotation and proportional to the width of a writing swath  450  (not shown). The pattern that printhead  500  transfers to the thermal print media  32  along vacuum imaging drum  300 , is a helix. 
     Referring to FIG. 3, there is illustrated an exploded view of vacuum imaging drum  300 . Vacuum imaging drum  300  has a cylindrical shaped vacuum drum housing  302  that has a hollowed-out interior portion  304 , and further includes a plurality of vacuum grooves  332  and vacuum holes  306  which extend through vacuum drum housing  302  for permitting a vacuum to be applied from hollowed-out interior portion  304  of vacuum imaging drum  300  for supporting and maintaining position of thermal print media  32 , and donor sheet material  36 , as vacuum imaging drum  300  rotates. 
     The ends of vacuum imaging drum  300  are closed by a vacuum end plate  308 , and a drive end plate  310 . Drive end plate  310 , is provided with a centrally disposed drive spindle  312  which extends outwardly therefrom. Drive spindle  312  is stepped down to receive a DC drive motor armature  316  (not shown) and mount a drum encoder  344  (also not shown). 
     Vacuum spindle  318  is provided with a central vacuum opening  320  that aligns with and accepts a vacuum fitting  222  (not shown). Vacuum fitting  222  is connected to a high-volume vacuum blower  224  (not shown) which is capable of producing 50-60 inches of water (93.5-112.2 mm of mercury) at an air flow volume of 60-70 cfm (28.368-33.096 liters per second). This provides the vacuum imaging drum  300  for supporting the various internal vacuum levels of vacuum imaging drum  300  required during the loading, scanning and unloading of thermal print media  32  and donor sheet materials  36  (shown in FIG. 5C) to create the intended image. With no media loaded on vacuum imaging drum  300 , the internal vacuum level of vacuum imaging drum  300  is approximately 10-15 inches of water (18.7-28.05 mm mercury). With just thermal print media  32  loaded on vacuum imaging drum  300  the internal vacuum level of vacuum imaging drum  300  is approximately 20-25 inches of water (37.4-46.75 mm of mercury). This level is required such that when a donor sheet material  36  is removed, thermal print media  32  does not move. Otherwise, color to color registration would be adversely affected. With both thermal print media  32  and donor sheet material  36  completely loaded on vacuum imaging drum  300  the internal vacuum level of vacuum imaging drum  300  is approximately 50-60 inches of water (93.5-112.2 mm of mercury) in this configuration. 
     The outer surface of vacuum imaging drum  300  is provided with an axially extending flat  322  shown in FIGS.  4  and  5 A-C, which extends approximately 8 degrees of the vacuum imaging drum  300  circumference. Vacuum imaging drum  300  is also provided with donor support rings  324  which form a circumferential recess  326  which extends from one side of axially extending flat  322  circumferentially around vacuum imaging drum  300  to the other side of axially extending flat  322 , and from approximately one inch (24.4 mm) from one end of vacuum imaging drum  300  to approximately one inch (25.4 mm) from the other end of vacuum imaging drum  300 . 
     Thermal print media  32 , when mounted on the vacuum imaging drum, is seated within circumferential recess  326 . To accommodate media sheet sizes, donor support rings  324  have a thickness substantially equal to thermal print media  32  thickness seated therebetween, which is approximately 0.004 inches (0.102 mm) in thickness. The purpose of circumferential recess  326  on vacuum imaging drum  300  surface is to eliminate any creases in donor sheet material  36 , as the sheet is drawn down over thermal print media  32  during the loading of donor sheet material  36 . This ensures that no folds or creases will be generated in donor sheet material  36  which could extend into the image area and adversely affect the intended image. Circumferential recess  326  also substantially eliminates the entrapment of air along the edge of thermal print media  32 , where it is difficult for vacuum holes  306  in vacuum imaging drum  300  to assure the removal of the entrapped air. Any residual air between thermal print media  32  and donor sheet material  36 , can also adversely affect the intended image. 
     Formed in the donor support rings  324  along the edges of axially extending flat  322  are media contours  328 . Axially extending flat  322  and media contours  328  are somewhat the same, they assure that the leading and trailing ends of donor sheet material  36  are somewhat protected from the effect of increased air turbulence during the relatively high speed rotation that vacuum imaging drum  300  undergoes during the image scanning process. Thus increased air turbulence will have less tendency to lift or separate the leading or trailing edges of donor sheet material  36  from vacuum imaging drum  300 . In addition, axially extending flat  322  and media contours  328  ensure that the leading and trailing ends of donor sheet material  36  are recessed from the periphery of vacuum imaging drum  300 . This reduces the chance that donor sheet material  36  can come in contact with other parts of image processing apparatus  10 , such as printhead  500 . Inadvertent contact could cause a media jam within the image processing apparatus, resulting in the possible loss of the intended image or, at worst, catastrophic damage to image processing apparatus  10  possibly damaging printhead  500 . 
     Media contours  328  support the corners of donor sheet material  36  preventing flutes or air under the corners of donor sheet material  36 . This helps to allow full contact with the surface of vacuum imaging drum  300  and minimize the tendency of the media to lift or separate from vacuum imaging drum  300  when rotating at high speeds. 
     FIG. 5A illustrates a plane view of the surface of vacuum imaging drum  300 , prior to loading a sheet of media. FIG. 5B shows vacuum imaging drum  300  after loading a single sheet of thermal media  32 . FIG. 5C shows vacuum imaging drum  300  after loading a sheet of donor sheet material  36  on top of the sheet of thermal media  32 . 
     Boundary layer vacuum ports  334 , shown in FIGS. 3,  4 , and  5 A-C, are centered within the width of axially extending flat  322 . As FIG. 5C shows, boundary layer vacuum ports  334  are not covered by thermal media  32  or donor sheet material  36 . This arrangement allows boundary layer vacuum ports  334  to provide suction (indicated by arrow A in FIG. 6A) that thins a boundary layer  336  of air (indicated with a dashed line) along the surface of vacuum imaging drum  300 . FIG. 6B shows detachment of boundary layer  336  which occur over axially extending flat  322  at high rotational speeds if boundary layer vacuum ports  334  are not provided. 
     The size and number of boundary layer vacuum ports  334  are determined to suit the specific application. In the preferred embodiment, four boundary layer vacuum ports  334  are provided, each having a radius of 0.34 mm. No vacuum force in addition to that described above is provided. Even one boundary layer vacuum port, however, would decrease separation of the boundary layer if more than one boundary layer vacuum port is used in the preferred embodiment the vacuum layer boundary ports are at equally spaced intervals. For example, if two boundary layer vacuum ports are used, the distance between each end of the axially extending flat and the boundary port and the distance between boundary layer vacuum ports are equal. The use of boundary layer vacuum ports as described in the present invention allows for faster rotation of the vacuum imaging drum, which results in faster processing of intended images. This allows for more efficient utilization of equipment and quicker response time to customers needs. An additional benefit of the present invention is that there is a decreased possibility of the dye donor material lifting off the vacuum imaging drum and causing damage to the printhead and other components. 
     The invention has been described with reference to the preferred embodiment thereof. However, it will be appreciated and understood that variations and modifications can be effected within the scope of the invention as described herein above and as defined in the appended claims by a person of ordinary skill in the art without departing from the scope of the invention. For example, the specific arrangement or number of boundary layer vacuum ports  334  in the drum surface may be different from that represented in FIGS. 3,  4 , and  5 A-C. This invention could also be employed with a vacuum imaging drum that does not use an axially extending flat, but has some other surface obtrusion that could cause boundary layer separation. In addition, precise placement, number, and sizing of boundary layer vacuum ports  334  depend on the size of the surface irregularity and rotational speed of the drum. Although not described in detail it would be obvious to one skilled in the art that this invention could be used in other applications, including single sheet vacuum imaging drums, and other apparatus where it is desirable to hold a sheet of media on a rotating vacuum imaging drum. 
     PARTS LIST 
       10 . Image processing apparatus 
       12 . Image processor housing 
       14 . Image processor door 
       16 . Donor ejection chute 
       18 . Waste bin 
       20 . Media stop 
       32 . Thermal print media 
       34 . Donor roll material 
       36 . Donor sheet material 
       50   a . Lower sheet material tray 
       50   b . Upper sheet material tray 
       52 . Media lift cams 
       52   a . Lower media lift cam 
       52   b . Upper media lift cam 
       54 . Media rollers 
       54   a . Lower media roller 
       54   b . Upper media roller 
       56 . Media guide 
       58 . Media guide rollers 
       60 . Media staging tray 
       80 . Transport mechanism 
       100 . Media carousel 
       110 . Media drive mechanism 
       112 . Media drive rollers 
       120 . Media knife assembly 
       122 . Media knife blades 
       180 . Color binding assembly 
       182 . Media entrance door 
       184 . Media exit door 
       200 . Lathe bed scanning subsystem 
       202 . Lathe bed scanning frame 
       204 . Entrance passageway 
       206 . Rear translation bearing rod 
       208 . Front translation bearing rod 
       220 . Translation stage member 
       222 . Vacuum fitting 
       224 . Vacuum blower 
       250 . Lead screw 
       254 . Lead screw drive nut 
       300 . Vacuum imaging drum 
       301 . Axis of rotation 
       302 . Vacuum drum housing 
       304 . Hollowed out interior portion 
       306 . Vacuum hole 
       308 . Vacuum end plate 
       310 . Drive end plate 
       312 . Drive spindle 
       314 . Support bearing 
       316 . DC drive motor armature 
       318 . Vacuum spindle 
       320 . Central vacuum opening 
       322 . Axially extending flat 
       324 . Donor support ring 
       326 . Circumferential recess 
       328 . Media contours 
       332 . Vacuum grooves 
       334 . Boundary layer vacuum port 
       336 . Boundary layer 
       344 . Drum encoder 
       400 . Laser assembly 
       402 . Lasers diode 
       404 . Fiber optic cables 
       406 . Distribution block 
       450 . Writing swath 
       452 . Pixel to pixel distance 
       500 . Printhead