Patent Publication Number: US-RE37145-E

Title: Apparatus for laser texturing disks

Description:
CROSS-REFERENCE TO A BELATED APPLICATION 
     A co-pending U.S. application, Ser. No. 08/150,525, filed Nov. 10, 1993, now abandoned, entitled “Procedure Employing a Diode-Pumped Laser for Controllably Texturing a Disk Surface,” by Peter M. Baumgart, et al., having a common assignee with the present invention, the disclosure of which is hereby incorporated by reference, describes a process for creating a “distant bump array” surface texture in a magnetic recording disk for reducing stiction, together with the disk so textured. The texturing process uses a tightly focused diode-pumped Nd:YLF or Nd:YVO 4  or other solid-state laser that is pulsed with a 0.3-90 nanosecond pulse train to produce a plurality of distantly-spaced bumps in the disk surface. The bump creation process is highly controllable, permitting repeated creation of a preselected bump profile, such as a smooth dimple or one with a central protrusion useful for low stiction without close spacing or elevated “roughness.” Some bump profiles permit texturing of the data-storage region of the disk surface for low stiction without materially affecting magnetic data storage density. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to apparatus for fabricating a disk, such as a magnetic recording disk used in a computer hardfile, having a surface tenured by exposure to a pulsed laser, and, more particularly, to automated apparatus for moving a number of such disks through a station in which such texturing occurs. 
     2. Background Information 
     Current hardfile drives use a Contact Start-Stop (CSS) system allowing a magnetic head, used to read and write data, to contact the surface of a magnetic disk in a specific CSS region when the disk is stationary. Thus, before the rotation of a spinning disk has stopped, the magnetic head is moved to the CSS region, where the magnetic head settles on the surface of the disk. When the disk again starts to rotate, the magnetic head slides along the disk surface in this region, until the laminar air flow at the disk surface, due to its rotation, fully lifts the magnetic head from the disk surface. 
     After the magnetic head is lifted in this way, it is moved from the CSS region to another region of the disk to read and write data. The CSS region is preferably textured to minimize physical contact between the magnetic head and the disk surface. In this way, the contact stick-slip phenomenon often called “stiction” and other frictional effects are minimized, along with the resulting wear of the magnetic head surface. Outside the CSS region the remainder of the disk surface preferably retains a specular smoothness to permit high-density magnetic data recording. 
     3. Description of the Prior Art 
     U.S. Pat. No. 5,062,021, to Ranjan et al., describes a process in which magnetic recording media are controllably textured, particularly over areas designated for contact with data transducing heads. In conjunction with rigid disk media, the process includes polishing an aluminum nickel-phosphorous substrate to a specular finish, then rotating the disk while directing pulsed laser energy over a limited portion of the radius, thus forming an annular head contact band while leaving the remainder of the surface specular. The band is formed of multiple individual laser spots, each with a center depression surrounded by a substantially circular raised rim. The depth of the depressions and the height of the rims are controlled primarily by laser power and firing pulse duration. The shape of individual laser spots can be altered by varying the laser beam inclination relative to the disk surface. On a larger scale, the frequency of firing the laser, in combination with disk rotational speed controls the pattern or arrangement of laser spots. The smooth, rounded contours of the depressions and surrounding rims, as compared to the acicular character of mechanical textured surfaces, is a primary factor contributing to substantially increased durability of laser textured media. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, there is provided equipment for texturing a disk including a central round hole, a circular periphery, and flat, parallel sides. The apparatus includes a cassette, a lifter, an indexing mechanism, a laser, an optical system, a spindle, and a pick-and-place mechanism. The cassette includes a number of pockets, each of which is open at a first end to allow the insertion of a single such disk. Each pocket also includes a lifter access opening opposite the first end. The lifter is movable through the lifter access opening in a pocket to engage a disk within the pocket. The lifter moves the disk through the first end of the pocket to a first disk transfer point. The indexing mechanism moves the cassette adjacent the lifter, so that the lifter can be moved within each of the pockets. The spindle engages the disk at a second disk transfer point. The pick-and-place mechanism moves the disk from the first disk transfer point to the second disk transfer point. The laser produces a pulsed laser beam. 
     In accordance with another aspect of the invention, there is provided equipment for texturing a number of such disks. The apparatus includes a laser, a beamsplitter, a beam steering mirror, first and second disk-handling stations, and a shuttling mirror assembly. The laser produces a pulsed laser beam, which is divided by the beamsplitter into first and second sub-beams. Beam-steering mirrors direct these sub-beams to travel parallel to one another. Each disk-handling station includes an exposure station in which portions of the opposite sides of the disks are exposed to the sub-beams. The shuttling mirror assembly, which reflects the first and second sub-beams, is movable between a first position, in which the sub-beams are directed to travel toward the exposure station of the first disk-handling station, and a second position, in which the first and second sub-beams are directed to travel toward the exposure station of the second disk-handling station. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an internal portion of a prior-art disk drive unit, including a rotatable magnetic disk having a textured annular region for CSS operation, and a magnetic head; 
     FIGS. 2 and 3 are transverse cross-sectional views of individual textured spots, which form examples of spots which may be made using the apparatus of the present invention, with the spot of FIG. 2, being formed particularly according to the method of U.S. Pat. No. 5,108,781, and with the spot of FIG. 3 being formed particularly according to the method of co-pending U.S. Application Ser. No. 08/150,525. 
     FIG. 4 is an isometric view of a laser disk texturing tool built in accordance with the present invention; 
     FIG. 5 is a cross-sectional plan view of the tool of FIG. 4, taken as indicated by section lines V—V in FIG. 4 to show disk-handling and laser-texturing stations thereof; 
     FIG. 6 is a cross-sectional side elevational view of the tool of FIG. 4, taken as indicated by section lines VI—VI in FIG. 5 to show mechanisms used to handle cassettes holding disks for texturing; 
     FIG. 7 is a cross-sectional rear elevational view of the tool of FIG. 4, taken as indicated by section lines VII—VII in FIG. 5 to show the mechanism used to transfer disks from cassettes within the disk-handling stations to the laser-texturing station and to return the disks to the cassettes; and 
     FIG. 8 is a longitudinal cross-sectional view of an end portion of a spindle, used to move disks through the texturing process in the tool of FIG.  4 . 
     FIG. 9 is a cross-sectional plan view of a slider used to move cassettes filled with textured disks from one conveyor to another in the tool of FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a plan view of a portion of a disk drive unit from the prior art for a computing system, including a rotatable magnetic storage disk  10 , together with a magnetic head  12 , which is driven in a generally radial direction relative to the disk  10  by means of a drive arm  13 . This disk  10  is an example of the type of product which can be made using the apparatus of the present invention. When the disk drive unit is in operation, disk  10  is rotated about its central hole  14 , forming a laminar flow of air holding magnetic head  12  slightly away from the adjacent disk surface  16 . Before this rotation is stopped, magnetic head  12  is driven to be adjacent to a textured annular region  18  of the surface of disk  10 . As this disk rotation slows and stops, the frictional and stiction effects occurring between the surface of annular region  18  and the adjacent contacting surface of magnetic head  12  are minimized by the textured nature of the surface of this region  18 . Subsequently, when the rotation of disk  10  is restarted, these effects are again minimized, as the rate of rotation of disk  10  increases until the laminar flow of air near its surface lifts the adjacent surface of magnetic head  12  completely away from the disk surface. Thus, as the rotation of disk  10  is stopped and subsequently restarted, the wear of the surface of magnetic head  12  is minimized. Disk  10  is preferably a double-sided magnetic storage disk, with a second side, opposite the side shown in FIG. 1, having similar features. 
     FIGS. 2 and 3 are transverse cross-sectional views of individual textured spots, which form examples of spots which may be made using the apparatus and method of the present invention. 
     FIG. 2 shows a portion of a disk surface roughened by the prior-art method taught by Ranjan, et al., in U.S. Pat. No. 5,062,021. With this method, a portion of the disk surface to be roughened is exposed to a pulse of laser light. The surface is heated rapidly, so that a part of the surface material is melted and then rapidly cooled, changing the surface topography to include a generally round central depression  24  below the nominal surface plane  26  and a generally round peripheral ridge  28  above this plane  26 . The process described by Ranjan, et al. produces a ring of textured spots of this kind by repeatedly firing a laser as the disk being textured is rotated. The laser is then displaced radially through a pitch distance, and a second ring of textured spots, concentric with the first ring thereof, is produced. This process is repeated until texturing fills the annular region to be textured. The nature of each individual textured spot is determined primarily by the peak energy at which the laser is fired together with the pulse width. The distance between textured spots on the ring is determined by the relationship between the rate at which the laser is fired and the rotational speed at which the disk is turned. 
     FIG. 3 is a transverse cross-sectional profile of a laser textured spot produced using the method of the previously-described co-pending U.S. patent application, Ser. No. 08/150,525. The heights of surface features, compared to their widths, are exaggerated. A central protrusion  30  rises above the depth of the ring depression  32 , preferably to a height somewhat greater than the height of the surrounding peripheral ring  34 . The heights of the protrusion  30  and ring  34  above the nominally level surface  35  before texturing are determined by various laser and disk-material parameters, such as laser fluence, pulse width, spot size, and disk surface composition. 
     FIG. 4 is an isometric view of a laser-texturing tool  37 , built in accordance with the present invention, which is used to apply laser-texturing to disks in a non-stop production mode as long as cassettes filled with disks are loaded and unloaded at a sufficient rate. These cassettes move through a right disk-handling station  38  and a left disk-handling station  39 , with individual disks from these stations  38  and  39  being alternately textured by a single laser assembly in a laser-texturing station  40 . A modular configuration allows the tool  37  to continue running, at a reduced rate of production, even if one of the disk-handling stations  38 ,  39  cannot be used. 
     The laser-texturing tool  37  is a self-contained system, with necessary electrical, electronic, and pneumatic components located in a base section  41  and in a pair of instrumentation cabinets  42 . Various controls and output devices are placed on a slanted control panel  43 . Since the infrared laser used in the texturing process produces invisible, potentially-harmful rays, a laser-texturing station  40  is housed in a light-tight cabinet within the tool  37 , with a safety switch operated by the opening of each access door  44  turning off the laser. Furthermore, these doors  44  can be opened only when the tool is in a maintenance mode. The tool  37  is switched between automatic and maintenance modes by turning a mode switch (not shown) on control panel  43 . Two television cameras (not shown), mounted within the laser-texturing station, allow the process to be viewed on a pair of monitors  45 . 
     The upward-opening doors  46  of disk-handling stations  38  and  39 , providing access for loading and unloading cassettes holding disks, are not interlocked, and may be opened or closed at any time, even during the operation of the texturing process. Within the tool  37 , rays from the laser are blocked from the areas in which these cassettes are loaded and unloaded. 
     FIG. 5 is a horizontal cross-sectional view of laser-texturing tool  37 , taken as indicated by section lines V—V in FIG. 4, to reveal particularly disk-handling stations  38 ,  39  and the laser-texturing station  40 . Left disk-handling station  39  is a mirror image of right disk-handling station  38 . Each disk-handling station  38 ,  39  has an input conveyor  47  carrying cassettes  48  loaded with disks  49  to be textured, rearward, in the direction of arrow  50 . Each cassette  48  has a number of pockets  51  in which disks  49  are loaded in a vertical orientation, and a lower opening  52  allowing the removal of individual disks by lifting from below. While FIG. 5 shows cassettes having only five disks, for clarity, in reality a cassette for this system typically holds 25 disks. 
     FIG. 6 is a cross-sectional side elevational view of the tool of FIG. 4, taken as indicated by cross-section lines VI—VI in FIG. 5, to show the conveyor systems moving cassettes filled with disks into and through the process. The tool operator loads a cassette  48  filled with disks  49  to be textured by opening the access door  46 , which pivots upward along its rear hinge  53 . The cassette  48  is normally loaded onto a raised platform  54 , which, in this position holds the cassette  48  upward, in the direction of arrow  55 , away from input conveyor  47 , allowing this conveyor  47  to move another cassette  56  stored in a queue on the conveyor  47  without simultaneously moving the most-recently loaded cassette  48 . FIG. 6 also shows a cassette indexing conveyor  57 , which moves a cassette  58  in incremental motions above a disk lifter  59 , so that the disk lifter  59  can remove individual disks  49  from the cassette  58  for placement into the laser-texturing process, and so that the disk lifter  59  can subsequently return textured disks to the cassette  58 . FIG. 6 also shows a transfer table conveyor  60 , which is used in the movement of cassettes filled with textured disks from indexing conveyor  57  to an output conveyor  61  (shown in FIG.  5 ). 
     FIG. 7 is a cross-sectional rear elevational view of the tool of FIG. 4, taken as indicated by section lines VII—VII in FIG. 5 to show the mechanism used to transfer disks from a cassette  58  within the disk-handling station  38  into the laser texturing process and to return textured disks to the cassettes. FIG. 7 also provides a transverse cross-sectional views of cassette indexing conveyor  57  and of output conveyor  61 . 
     The movement of a cassette to the point at which individual disks are removed from the cassette to be carded into the texturing process will now be discussed, with particular reference being made to FIGS. 6 and 7. 
     Thus, referring to FIGS. 5,  6 , and  7 , each conveyor  47 ,  57 ,  60 ,  61  includes a belt  61   a  extending under each side of a cassette  48 ,  56 ,  58  loaded thereon. Each belt  61   a  extends between a pair of end rollers  62  and above a number of idler rollers  63 . At one end of each conveyor  47 ,  57 ,  60 ,  61  the end rollers  62  are driven in either direction by a motor  64 . This system for cassette transport also includes a pair of lateral guides  65 , ensuring that each cassette stays in place atop the conveyors, and cassette detectors  66 ,  66   a,    67 ,  68 ,  69 , which determine when a cassette reaches an adjacent point along a conveyor system. Each cassette detector  66 ,  66   a,    67 ,  68 ,  69  includes a light source  69   a  which is reflected off an adjacent surface of a cassette when such a surface is present, to be detected by a receiver  69   b,  which in turn provides an input to a computing system  70  controlling the operation of the motors  64  and other motors, solenoids, and valves within the laser-texturing tool  37  to effect operation as described herein. 
     When cassette  48  is placed on top of raised platform  54 , its presence is detected by first input cassette detector  66 . Since the input conveyor  47  and the system logic controlling its movement are configured to allow the queuing of cassettes, the subsequent movement of the cassette  48  is determined by whether other cassettes are already present on input conveyor  47  and indexing conveyor  57 . If no cassette is already present on these conveyors  47 ,  57  (i.e., if cassettes  56 ,  58 , and  69   c  are not present), platform  54  is lowered, so that the cassette  48  rests on top of input conveyor  47 , and the conveyors  47 ,  57  are turned on to move cassette  48  rearward, in the direction of arrow  50 . When indexing cassette detector  68  detects the presence of a cassette being moved in this way, input conveyor  47  and indexing conveyor  57  are stopped, leaving the cassette positioned so that the first of its pockets  51  in which diskettes  49  may be placed (i.e. the end pocket farthest in the direction indicated by arrow  50 ) is directly over disk lifter  59 . 
     On the other hand, if a cassette  58  is present on indexing conveyor  57 , and if no other cassette  56 ,  69   c  is present on input conveyor  47 , when cassette  48  is placed on raised platform  54 , this platform  54  is lowered, and conveyor  47  is turned on to move cassette  48  in the direction of arrow  50 . This movement is stopped when the presence of the cassette  48  is detected by second input cassette detector  66   a,  leaving the cassette queued on the input conveyor  47 , in the position in which cassette  69   c  is shown. 
     If a cassette  58  is present on indexing conveyor  57 , and if a single cassette  69   c  is present on input conveyor  47 , when cassette  48  is placed on raised platform  54 , this platform  54  remains raised while input conveyor  47  is turned on to move cassette  69   c  opposite the direction of arrow  50  until this cassette  69   c  is sensed by third cassette sensor  67 . Then, platform  54  is lowered, and input conveyor  47  is turned on to both cassettes  48 ,  69   c  in the direction of arrow  50 . This movement is stopped when cassette  69   c  is detected by second cassette sensor  66   a,  leaving both cassettes  48 ,  69   c  queued on input conveyor  47 . 
     Finally, if all three cassettes  56 ,  69   c,  and  58  are present on conveyors  47 ,  57  when cassette  48  is placed on raised platform  54 , the movement of cassettes does not directly ensue, leaving cassettes  56 ,  69   c  queued on input conveyor  47  and cassette  48  queued on raised platform  54 . 
     When the texturing process has been completed on all of the disks  49  to be textured within the cassette  58  on indexing conveyor  57 , this conveyor  57  and transfer table conveyor  60  are turned on to move the cassette  58  rearward, in the direction of arrow  50 , completely onto the transfer table conveyor  60 . This motion is stopped when the presence of cassette  58  is detected by transfer table cassette detector  69 . If cassette  56  is present on input conveyor  47 , as determined by second input cassette detector  67 , when cassette  58  is transferred from indexing conveyor  57  in this way, this queued cassette  56  is moved by conveyors  47 ,  57  to the point at which its presence is detected by indexing cassette detector  68 . If a second queued cassette  48  is present on raised platform  54  when a first queued cassette  56  is moved from input conveyor  47  to indexing conveyor  57 , platform  54  is lowered, and the first queued cassette  48  is driven by input conveyor  47  until the presence of the cassette  48  is detected by second input cassette detector  67 . 
     The movement of an individual disk from a cassette into the texturing process will now be discussed, with particular reference being made to FIGS. 5 and 7. 
     Thus, referring to FIGS. 5 and 7, to allow the movement of individual disks  49  through the laser-texturing process, indexing conveyor  57  moves cassette  58  in a number of rearward and forward motions, in and opposite the direction of arrow  50 , sequentially aligning the individual disk pockets  51  of the cassette  58  with a disk lifter  59 . Disk lifter  59  includes a proximity sensing mechanism  70   a,  for determining whether a disk  49  is present in each pocket  51 . This sensing mechanism  70   a  consists of an internal light source aimed at an adjacent edge  70   b  of a disk present in a pocket  51  and an internal sensor detecting light reflected from such an edge  70   b.  The output of sensing mechanism  70   a  provides an additional input to computing system  70 . Thus, cassette  58  is moved to the rear, in the direction of arrow  50 , by indexing conveyor  57 , until proximity sensing mechanism  70   a  indicates the presence of a disk  49  in a particular pocket  51 , passing any empty pockets  51  within the cassette  58 . When a disk is detected by proximity sensing mechanism  70   a,  the rearward movement of cassette  58  is stopped, and the disk lifter  59  moves upward, in the direction of arrow  55 , carrying the disk  49  which is aligned the lifter  59  upward for transfer to a pick-and-place mechanism  71 . 
     Pick-and-place mechanism  71  has an arm  72  rotatable about the axis of a drive shaft  73 , in and opposite the direction of arrow  74 , in 180-degree increments. This rotation is effected by the incremental operation of arm drive motor  75 . At each end of arm  72 , a pair of grippers  77 ,  78  is movable between an open position, in which grippers  77  are shown, and a closed position, in which grippers  78  are shown, by means of a pneumatic actuator  79 . When a pair of grippers  77 ,  78  is in the closed position, a disk placed between the grippers is held by four points around its periphery. When the pair of grippers is opened, a disk held in this way is released. The pick and place mechanism  71  is also moved rearward, in the direction of arrow  50 , into a position in which disks are picked up and released, and forward, in the direction opposite arrow  50 , into a position in which arm  72  is rotated. 
     The upward movement of disk lifter  59  carries a disk  49 , which is to be textured next, upward into the location indicated by phantom line  82 . This motion, which brings the disk  49  into vertical alignment with the open grippers  77  of arm  72 , occurs with pick and place mechanism  71  in its forward position (i.e., moved opposite the direction of arrow  50 ), allowing the upward passage of disk  49  past grippers  77 . At this point, the disk rests within a groove  84  of the lifter  59 . Next, pick and place mechanism  71  moves in the direction of arrow  50  to its rearward position, aligning the open grippers  77  with the edge of disk  49 . Then, grippers  77  are closed, grasping the disk  49 . Disk lifter  59  next descends to disengage from the periphery of disk  49 . Next, pick and place mechanism  71  moves opposite the direction of arrow  50  to its forward position, and the arm  72  rotates 180 degrees in the direction of arrow  74 , placing disk  49  in the position indicated by phantom line  83 , in axial alignment with a spindle  86  of a spindle assembly  88 . Then, pick-and-place mechanism  71  returns in the direction of arrow  50  to its rearward position, placing the disk  49  on the end of spindle  86 . 
     FIG. 8 is a longitudinal cross-sectional view of the end of spindle  86 , which includes a rotationally-driven outer cylinder  89 , in which an internal shaft  90  slides axially, in and opposite the direction of rearward-pointing arrow  50 . A sliding bushing  91  and a piston  92 , and a front end cap  93   94 move axially with internal shaft  90 , while a front bushing  94   93 is held in place within the outer cylinder  89 . A number of curved clamping blocks  95  extend around a truncoconical surface  96  of front bushing  93 , being held inward, against this surface  96 , by an elastomeric “O”-ring  97 . 
     The internal shaft  90  is held in the rearward position shown (i.e. in the direction of arrow  50 ) by means of a compression spring  98  pressing an adjacent surface of the sliding bushing  91 . With internal shaft  90  held rearward in this way, inner face  98   98 a of end cap  94  pushes clamping blocks  95  rearward and outward, along truncoconical surface  96 . This motion of the clamping blocks  95  grasps inner surface  99  of the disk  49 , holding the disk in place against a front face  100  of outer cylinder  89 . The disk  49  is released by applying a force to piston  92  in a forward direction, opposite the direction of arrow  90   50 , to overcome the force exerted by compression spring  98 , so that the internal shaft  90  is moved forward, opposite the direction of arrow  90 . This force may be applied by a number of well known methods, such as through a pneumatically operated push-rod operating on piston  92 . The resulting movement of end cap  94  allows the clamping blocks  95  forward and inward, releasing disk  49  from the spindle  86 . 
     Referring to FIGS. 5,  7 , and  8 , pick-and-place mechanism  71  next moves to the rear, in the direction of arrow  50 , placing the disk  49  to be textured, which is now at the position indicated by phantom line  83  in FIG. 7, on end cap  90   94 of spindle  86 , with inner shaft  90  held in its forward position, so that clamping blocks  95  are retracted inward. Next, inner shaft  90  is moved to its rearward position, so that clamping blocks  95  are moved outward, clamping the disk  49  in place, and the grippers, which have been holding the disk on arm  72 , open, releasing the disk  49 . After disk  49  is placed on spindle  86 , the pick-and-place mechanism  71  moves forward, opposite the direction of arrow  50 , and the spindle drive motor  101  of spindle assembly  88  begins to rotate spindle  86  to bring the disk  49  up to a rotational velocity at which exposure to laser pulses will occur. The spindle assembly  88  also begins to move inward, in the direction of arrow  102 , being driven by a spindle translation motor  104 , carrying the disk  49  into the texturing process. 
     The laser-texturing station  40  will now be discussed, with specific references being made to FIG.  5 . 
     Thus, referring to FIG. 5, within the laser-texturing station  40 , a beam from an infrared pulsed laser  108  is used to produce the desired surface texturing on the disk  49 . As described in the co-pending application referenced above, the laser  108  may be, for example, a Nd:YLF solid state laser, providing an output at a wavelength of 1.047 microns, or Nd:YVO 4  solid state laser, operated with a diode pumping signal, driven from a laser diode  110  through a fiber-optic cable  112 , and pulsed by a Q-switch control  113 . A beam from the laser  108  is directed through an electronic process shutter  114  and a mechanical safety shutter  116 . When the laser-texturing station  40  is operating, a train of laser pulses is emitted from the laser  108 , with the actual texturing process being stated and stopped by opening and closing the electronic process shutter  114 . The safety shutter  116  remains open during the entire texturing process, unless an error condition, such as jam of a disk or cassette, occurs. The detection of such an error condition causes the safety shutter  116  to close, by means of the software running the laser-texturing tool  37 . The laser  108 , electronic process shutter  114 , and safety shutter  116  together form a light-tight assembly, from which even a portion of the laser beam cannot escape when either shutter  114 ,  116  is closed. 
     After passing through the shutters  114 ,  116 , the laser beam enters a polarizing beamsplitter  118 , which is oriented so that the portion of the laser beam, if any, having an unwanted p-polarization is directed downwards toward an underlying plate  120 , leaving the portion of the laser beam having a vertical s-polarization to propagate through the remaining optical path. Next, the laser beam passes through a 3X beam expander/collimator  122 , which permits the adjustment of the infrared laser spot size at a lens entrance. From expander collimator  122 , the laser beam is directed by a pair of dielectric-coated steering mirrors  124  to a dichroic beamsplitter  126 . A visible laser beam, for example from a 2-mW laser diode  128 , is also directed toward the beam-splitter  126 , permitting alignment of the optical system by tracing the red laser dot. The infrared beam from laser  108  is made to be coincident with the red beam from laser diode  128  by manipulating the two steering mirrors  124 . About three percent of the laser beam entering beamsplitter  126   126  to a power detector  130 , which provides in-situ monitoring of the laser power. 
     The infrared laser beam leaving the dichroic beamsplitter  126  is directed to a non-polarizing beamsplitter cube  132 , which splits the beam into two beams that are equal in intensity within five percent. These two beams are directed, by means of a pair of steering mirrors  134 , toward opposite sides of the disk being carried through the texturing process by spindle assembly  88 . After reflection off these steering mirrors  134 , the laser beams travel as a pair of parallel beams, separated by a distance of 25 mm, to enter a power control optics block  136 , in which the intensity of the two beams is balanced by controlling the voltage applied to liquid-crystal variable retarders. In this way the intensity of the parallel laser beams leaving the power control optics block  136  is made equal within one percent. 
     In the example of FIG. 5, the parallel laser beams from power control optics block  136  are reflected off a right shuttling mirror  138 , being directed toward a disk carried through the texturing process from the right disk-handling station  38 . Each of these beams passes through a focussing achromatic triplet lens  140 , having a focal length of 25.4 mm, and is reflected toward the surface of the disk being textured by a right-angle prism  142 . Each lens  140  is mounted on a finely adjustable stage, permitting the adjustments needed to center the beam and to achieve optimum focus on each side of the disk. Each prism  142  is slightly tilted, so that a laser beam reflected off the surface of the disk being textured is not transmitted back through the optical path. 
     The movement of a disk through the laser-texturing process, and its subsequent return to the cassette from which it has been taken, will now be discussed, with particular reference being made to FIGS. 5 and 7. 
     Thus, referring to FIGS. 5 and 7, the disk  49  clamped to spindle  86  is first brought up to the rotational speed desired for the texturing process, as the motion of spindle assembly  88  drives the disk  49  inward, in the direction of arrow  102 , to or past the point at which the inner diameter, indicated on FIG. 7 by phantom line  146 , of the surface to be textured is adjacent to the point at which exposure will occur to laser beams reflected from prisms  142 . The actual exposure, which is started by opening electronic process shutter  114 , occurs as the disk  49  is rotated, for example, at a constant speed, by spindle drive motor  101  and as the disk  49  is moved in the outward direction, opposite arrow  102 , for example, at a constant speed, by the spindle translation motor  104 . When the disk  49  passes the point at which the outer diameter, indicated by phantom line  148 , of the surfaces to be textured is adjacent to the point at which exposure occurs to laser beams reflected from prisms  142 , electronic process shutter  114  is closed to terminate the exposure of the surfaces of disk  49  to the laser beam. Thus, an annular space on disk  49  is textured by placing a number of laser-generated texture patterns along a spiral, with the distance between the patterns adjacent along the spiral being determined by the rate at which laser  108  is pulsed, and by the rate of rotation of spindle  86 , while the distance between radially adjacent segments of the spiral is determined by the rates of rotation and translation of spindle  86 . 
     After completion of the texturing process, the rotation of spindle  86  is stopped, or allowed to decelerate, as the spindle assembly  88  continues moving outwardly, opposite arrow  102 , to stop in the position adjacent to grippers  78 , at the inward-extending end of the arm  72 . At this point, the arm  72  is held forward, in the direction opposite arrow  50 , so that the disk  49  can pass behind the grippers  78 , which are held open. When this outward motion of spindle assembly  88  is complete, and when the rotational motion of spindle  86  is fully stopped, the arm  72  is moved rearward, and the grippers are closed to engage the disk  49 . Next, the shaft  90  (shown in FIG. 8) is moved forward so that the clamping blocks  95  (also shown in FIG. 8) are retracted inward, releasing the disk  49  from spindle  86 . Then, the arm  72  is moved forward, opposite the direction of arrow  50 , and arm  72  is rotated 180 degrees about the axis of its drive shaft  73 , opposite the direction of arrow  74 , and the arm  72  is moved rearward, in the direction of arrow  50 , moving the disk  49 , which has most recently been textured, into position above the disk lifter  59 . Next, lifter  59  moves upward, accepting the textured disk in its groove  84 . The grippers on arm  72  holding the textured disk are opened, and the lifter  59  then descends, placing the textured disk  49  in a pocket  51  within the cassette  58 . 
     The preceding discussion has described the movement of a single disk  49  from the cassette  58 , in right disk-handling station  38 , through the texturing process in laser-texturing station  40 , and back into the cassette  58 . In a preferred version of the present invention, two disks are simultaneously moved in opposite directions between the cassette  58  and the spindle  86 , which carries each disk through the texturing process. This type of disk movement will now be described, with particular references being made to FIGS. 5 and 7. 
     Referring to FIGS. 5 and 7, except during the movement of the first and last disks  49  held within an individual cassette  58 , each rotational movement of arm  72  in or opposite the direction of arrow  74  preferably carries one disk  49  from the disk lifter  59  to spindle  86  within grippers  77 , while another disk  49  is simultaneously carried within grippers  78  from the spindle  86  to disk lifter  59 . Sequential rotational movements of arm  72 , which are similar in their movement of disks, occur in opposite rotational directions to avoid the winding of air hoses to actuators  79  and of wires to grippers  77 ,  78 , which would occur if such movements were to continue in one direction. 
     Furthermore, a preferred version of the present invention returns each textured disk  49  to the cassette pocket  51  from which it has been taken, leaving the pockets  51  which have been determined to be empty by proximity sensor  70   a  in an empty condition. These conditions are achieved in a preferred version of the present invention, by allowing the simultaneous movement of two disks  49  by the pick and place mechanism  71 , and by using the indexing conveyor  57  to return cassette  58  to the position in which disk lifter  59  accesses the pocket from which a disk  49  was taken before replacing the disk  49  in the cassette  58 . 
     As a disk  49 , which is hereinafter called the “A” disk  49  for convenience, is being taken through the texturing process by spindle  86 , a “B” disk  49 , which is the next disk  49  in the direction opposite arrow  50  past the cassette pocket  51  from which the “A” disk  49  has been taken, is found by movement of the cassette  58  in the direction of arrow  50  past the proximity sensor  70   a.  At this point, the movement of cassette  58  is stopped, and disk lifter  59  moves the “B” disk  49  upward, into the position indicated by phantom line  82 . When the process of texturing the “A” disk  49  is finished, spindle  86  moves the “A” disk  49  into the position indicated by phantom line  83 . When both the “A” and “B” disks  49  have been positioned in this way, pick-and-place mechanism  71  moves to the rear, in the direction of arrow  50 , and both sets of grippers  77 ,  78  are closed to grasp the “A” and “B” disks  49 . Within the spindle  86 , shaft  90  (shown in FIG. 8) is moved to the front, moving clamping blocks  95  inward to disengage the spindle from the “A” disk  49 , and the disk lifter  59  moves downward to disengage from the “B” disk  49 . Next, the pick-and-place mechanism  71  moves forward, opposite the direction of arrow  50 , and the arm rotational drive motor  75  drives aim  72  through a 180-degree angle in the direction of arrow  74 . Now, the positions of the “A” and “B” disks  49  are reversed, with the “A” disk  49  being positioned for movement through the texturing process on spindle  86 , and with the “B” disk  49  being positioned for return to cassette  58 . Next, pick-and-place mechanism  71  moves to the rear, in the direction of arrow  50 , placing the “B” disk  49  on spindle  86 , and aligning the “A” disk  49  with disk lifter  59 . 
     Thus, a first disk transfer point is established at the disk location shown by phantom line  82 , and a second disk transfer point is established at the disk location shown by phantom line  83 , both with pick-and-place mechanism  71  moved to the rear, in the direction of arrow  50 . At the first disk transfer point, a disk  49  is transferred in either direction between pick-and-place mechanism  71  and disk lifter  59 . At the second disk transfer point, a disk  49  is transferred in either direction between pick-and-place mechanism  71  and spindle  86 . 
     In a preferred mode of operation, computing system  70  stores data indicating the pocket  51  within cassette  58  from which each disk is taken. This data is subsequently used to determine how the cassette  58  is moved opposite the direction of arrow  50  to return to the place from which the “A” disk  49  has been taken. When a cassette full of disks to be textured has been loaded into the disk-handling station  38 , the cassette is moved one pocket position in the direction opposite that of arrow  50 , from the position in which the pocket at which “B” disk  49  has been taken is directly above disk lifter  59 , to the position in which the pocket at which “A” disk  49  has been taken is above disk lifter  59 . If the cassette  58  was not full of disks  49  to be textured when it was loaded into disk-handling station  48 , the cassette  58  may have to be moved farther than one pocket position opposite the direction of arrow  50 . In any case, the cassette is moved so that the pocket from which the “A” disk  49  was taken is above disk lifter  59 , using disk position data stored within computing system  70  and moving the cassette using indexing conveyor  57 . This cassette movement can occur as the “A” disk is being moved, by pick-and-place mechanism  71 , into place for reinsertion into the cassette  58 , with the pick-and-place mechanism  71  moved forward, opposite the direction of arrow  50 . 
     Next, disk lifter  59  moves upward, engaging “A” disk  49  within its groove  84 , and the shaft  90  (shown in FIG. 8) is moved rearward, in the direction of arrow  50 , so that clamping blocks  95  are extended outward to hold “B” disk  49  (also shown in FIG. 8) on the spindle  86 . The grippers holding the “A” disk are opened, and disk lifter  59  moves downward, restoring “A” disk  49  into the pocket  51  from which it was taken, and spindle  86  moves inward, in the direction of arrow  102 , while rotationally accelerating the disk to the rotational velocity at which texturing will occur. In this way, preparations are made to texture the next disk  49 , which is, at this time, the “B” disk. 
     The first disk  49  taken from each individual cassette  58  is moved alone from disk lifter  59  to spindle  86 , without the simultaneous movement of another disk  49  in the opposite direction, since there is no other disk available for such movement. Similarly, the last disk  49  taken from each individual cassette  58  is moved alone from spindle  86  to disk lifter  59 , since there is no other disk available for movement in the opposite direction. The determination that the last disk  49  to be textured has been removed from the cassette  58  is made when the last pocket  51  into which disks  49  can be placed is moved past disk lifter  59  without the detection of another disk  49  by proximity sensor  70   a.  Only a single cassette  58  at a time is moved onto indexing conveyor  57 , with all of the disks  49  to be textured within the cassette  58  being removed from the cassette  58 , sent through the texturing process, and returned to the cassette  58  before any of the disks  49  in the next cassette  58  are so processed. 
     FIG. 9 is a cross-sectional plan view of a slider mechanism  149  used to move a transfer table  150  on which cassettes are transferred from indexing conveyor  57  to output conveyor  61 , taken as indicated by section lines IF—IF  IX—IX in FIG.  6 . 
     Referring to FIGS. 6 and 9, the transfer table  150  is mounted atop slider mechanism  149 , including a slider  151 , having a pair of cylinders  152 , through which a pair of hollow shafts  153 ,  154  extend. The shafts  153 ,  154  are in turn mounted to extend between end blocks  155 . The slider  151  is slidably mounted on the shafts  153 ,  154  by means of bearing assemblies  156 , which also include air-tight seals preventing the outward flow of air from the ends of cylinders  152 . A central piston  157  is also attached to slide with the slider  151  along each shaft  153 ,  154 . Each piston  157  includes seals separating the cylinder  152 , within which it is attached, into an inward chamber  158  and an outward chamber  159 , each of which is alternately filled with compressed air or exhausted to effect movement of the slider  151 . 
     To move slider  151  inward, in the direction of arrow  102 , compressed air is directed to the inward chambers  158 , from hose  160 , through a hole  161  in shaft  153 . As this occurs, air is exhausted from outward chambers  159 , through a hole  162  in shaft  154 , and through hose  163 . Both inward chambers  158  are connected by an inward transverse hole  164 , and both outward chambers  159  are connected by an outward transverse hole  165 . Thus, as compressed air is directed through hose  160  while hose  163  is exhausted to the atmosphere, the resulting expansion of inward chambers  158 , together with a contraction of outward chambers  159 , moves slider  151  inward, in the direction of arrow  102 , aligning transfer table conveyor  60  with indexing conveyor  57 . 
     Similarly, to move slider  151  outward, opposite the direction of arrow  102 , compressed air is directed to the outward chambers  159 , from hose  163 , through hole  162  in shaft  154 . As this occurs, air is exhausted from inward chambers  158 , through hole  161  in shaft  153 , and through hose  160 . Thus, as compressed air is directed through hose  163  while hose  160  is exhausted to the atmosphere, the resulting expansion of outward chambers  159 , together with a contraction of inward chambers  158 , moves slider  151  outward, opposite the direction of arrow  102 , aligning transfer table conveyor  60  with output conveyor  61 . 
     The movement of a cassette  58  following the return thereto of all disks  49 , having been textured, will now be discussed, with specific references being made to FIGS. 5, and  6 . 
     Thus, referring to FIGS. 5 and 6, when it is determined that the last disk  49  to be textured in a cassette  58  has been processed and returned to the cassette  58 , both intermediate conveyor  57  and transfer table conveyor  60  are turned on to move the cassette  58  rearward, in the direction of arrow  50 , until the cassette  58  is completely on transfer table conveyor  60 , as indicated by the output of transfer table cassette sensor  69 . Upon the indication of sensor  69 , movement of conveyors  57  and  60  is stopped, and a slider mechanism  149  is operated to drive the transfer table  150 , which includes transfer table conveyor  60 , in an outward direction, opposite the direction of arrow  102  along hollow shafts  153 ,  154 . After this motion is stopped with transfer table conveyor  60  in alignment with output conveyor  61 , the conveyors  60 ,  61  are turned on to move cassette  58  to the front, opposite the direction of arrow  50 . If other cassettes are not stored along the output conveyor  61 , this movement is stopped when the cassette has been brought to the front of the conveyor  61 , to the position in which cassette  166  is shown in FIG. 5, as indicated by a first output cassette sensor  168 . At this point, the cassette  166 , with processed disks  49 , is ready for removal from the disk texturing tool  37 . 
     Continuing to refer to FIG. 5, while this condition of readiness is preferably communicated to the system operator through a visible or audible indication, the removal of a cassette  166  with textured disks  49  is not generally required to permit continued operation of the disk texturing tool  37 . Space is provided along output conveyor  61  for the storage of a number of cassettes  166  filled with textured disks  49 . In a first version of this output system, all such cassettes  166  are stored along the surface of output conveyor  61 . In a second version of this output system, the first cassette to reach the front of output conveyor  61  is stored on a raised platform. 
     The operation of the first version of this output system will now be described. In this version, if a cassette  166  is waiting for removal at the front of output conveyor  61  when the processing of disks  49  within another cassette  58  is completed, output conveyor  61  is turned on to move the cassette  166  rearward, in the direction of arrow  50 . This movement is stopped when the presence of cassette  166  is detected by a second output cassette sensor  170 . Then, with transfer table conveyor  60  in alignment with output conveyor  61 , both transfer table conveyor  60  and output conveyor  61  are turned on to move cassettes  166  and  58  together to the front of conveyor  61 , where this motion is stopped as first output cassette sensor  168  detects the presence of cassette  166 . If necessary, this process is repeated several times, until output conveyor  61  is filled with a queue of cassettes holding disks  49  which have completed the texturing process. In each case, the rearward motion of output conveyor  61 , in the direction of arrow  50 , is stopped when the rearmost cassette in the queue reaches second output cassette sensor  170 , and the subsequent forward motion of output conveyor  61  is stopped when the forwardmost cassette in the queue reaches first output cassette sensor  168 . 
     The operation of the second version of this output system will now be described. This version requires an additional cassette lifting platform  172 , which is similar to the platform  54  used with input conveyor  47 , and a third output cassette sensor  174 . With this version, the first cassette  166  to reach the end of output conveyor  61  is raised off the conveyor with lifting platform  172 , to remain in a raised position until it is removed by the tool operator. With a cassette  166  in the raised position, output conveyor  61  is operated in both directions while not affecting the position of the cassette  166 . Thus, when a second cassette, such as cassette  58 , is loaded onto output conveyor  61 , this conveyor  61  is turned on to drive the cassette forward, in the direction opposite arrow  50 . This motion is stopped when the cassette is detected by third output cassette sensor  174 . When the disks in a third cassette are completed, output conveyor  61  is turned on to drive the second cassette rearward. This motion is stopped when the second cassette is detected by second output cassette sensor  170 . Then both transfer table conveyor  60  and output conveyor  61  are turned on to move the second and third cassettes forward, opposite the direction of arrow  50 , until the second cassette is detected by third output cassette sensor  174 . 
     Again, this process is repeated until output conveyor  61  is filled with a queue of cassettes holding disks  49  which have completed the texturing process. In each case, the rearward motion of output conveyor  61 , in the direction of arrow  50 , is stopped when the rearmost cassette in the queue reaches second output cassette sensor  170 , and the subsequent forward motion of output conveyor  61  is stopped when the forwardmost cassette in the queue reaches third output cassette sensor  174 . These movements occur as the first cassette  166  remains on raised platform  172 . 
     At any point, if the cassette  166  on platform  172  is removed by the tool operator with one or more cassettes remaining on output conveyor  61 , the conveyor  61  is turned on to drive the next cassette to the end of the conveyor  61 , as detected by first output cassette sensor  168 . The platform  172  is again raised to lift this cassette off output conveyor  61 . 
     The methods described above for handling cassettes provide the particular advantage of not operating any conveyor system  47 ,  57 ,  60 ,  61  in sliding contact with a cassette. The generation of wear particles from relative motion between conveyor systems and cassettes is therefore avoided. Such wear particles could otherwise contaminate the manufacturing process of which this texturing is a part. Furthermore, the useful life of conveyor belts and cassettes is increased, with cassettes and conveyor belts being likely to last as long as various other moving parts of the disk texturing tool  37 . 
     The configuration of output conveyor  61  extending alongside input conveyor  47  provides the advantage of bringing output cassettes, holding disks which have gone through the texturing process, back to a place adjacent to the place where input cassettes are loaded. This facilitates servicing the tool  37  by personnel who must both load and unload cassettes. Furthermore, additional space for queuing cassettes along the conveyors is gained without having to increase the length of the tool  37  along the conveyors. 
     The preceding discussion of the movement of cassettes and disks has focussed on such movement within right disk-handling station  38  of the laser-texturing tool  37 . Thus, the various movements of disks and cassettes described above are used alone if the left disk-handling station  39  is not available. For example, the left disk-handling station may not be available due to a technical problem, or simply because cassettes have not been loaded into it. Furthermore, an embodiment of the present invention has only a single disk-handling tool, which is operated is described in detail above. Nevertheless, in the preferred method of operation of the preferred embodiment of the present invention, which will now be described with particular reference being made to FIG. 5, both right disk-handling station  38  and left disk-handling station  39  are used in an alternating fashion to present disks to be textured within laser-texturing station  40 . 
     Thus, referring to FIG. 5, in a preferred version of the present invention, the operation of left disk-handling station  39  is generally the same as operation of right disk-handling station  38 , with various elements of the apparatus within the left disk-handling station  39  being mirror image configurations of corresponding elements within the right disk-handling station  38 . The preceding discussion of operations within right disk-handling station  38  is equally applicable to operations within left disk-handling station  39 , with rearward motions, in the direction of arrow  50 , remaining the same, and with inward motions, in the direction of arrow  102  continuing to be directed toward the center of the laser texturing tool  37 , in the direction of arrow  166 , within left disk-handling station  39 . Similarly, forward motions, opposite the direction of arrow  50  are in the same direction in both left and right disk-handling stations  38 ,  39 , while outward motions in left disk-handling station  39  are opposite the direction of arrow  166 . 
     Within disk-texturing station  40 , right shuttling mirror  138  is mounted on a mirror slide  176 , together with a left shuttling mirror  178 . Mirror slide  176  is operated pneumatically, sliding on a pair of shafts  180 , using a mechanism operating generally as described above in reference to FIG.  9 . With mirror slide  176  in its leftward position, moved in the direction of arrow  181  as shown in FIG. 5, the laser beams passing through power control optics block  136 , having been derived from the output of infrared laser  108 , are directed to disk  49 , clamped on spindle  86  of right disk-handling station  39 , as previously described. Mirror slide  176  is alternately moved into a rightward position, so that the laser beams passing through power control optics block  136  reflect off left shuttling mirror  178 , being directed to a disk  182  held by spindle  184  of left disk-handling station  39 . In this way, the laser beams employed in the disk texturing process are directed to either disks within the right disk-handling station  38  or left disk-handling station  39  simply by moving mirror slider  176 . 
     While the above discussion describes the use of a sliding mechanism having two mirrors to direct the laser beams between the two disk-handling stations  38 ,  39 , a single pivoting mirror could alternately be used for this purpose. 
     The operation of right disk-handling station  38 , which has been described in some detail above, may be considered to consist basically of disk-movement cycles alternating with texturing cycles, wherein each disk movement cycle consists of the movement of one or two disks by pick-and-place mechanism  71 , and wherein each texturing cycle consists of the movement of a single disk on the spindle  86 . Whenever sufficient disks are available for texturing to allow the disk texturing tool  37  to operate at full capacity, each disk-movement cycle of right disk-handling station  38  occurs simultaneously with a texturing cycle of left disk-handling station  39 , and each disk-movement cycle of left disk-handling station  39  occurs simultaneously with a texturing cycle of right disk-handling station  38 . In this way, the use of the texturing process available through operation of infrared laser  108  is maximized, along with the overall process speed of the laser texturing tool  37 . However, when disks to be textured are not available from one of the disk-handling stations  38 ,  39 , the other disk handling station can continue to run at its full speed. 
     Referring to FIGS. 5-7, a preferred version of the present invention includes a bar code scanner  186  for reading bar code labels (not shown) placed on a side of a cassette  48 , which is put on platform  54 . To use this feature, the computing unit  70  executes a program relating bar codes read by scanner  186 . Data gathered by reading bar code labels may be stored and used by an inventory control system to keep track of work in process. 
     The present invention provides advantages of optimized productivity and flexibility. In a preferred mode of operation, both disk-handling stations  38 ,  39  are simultaneously used as described above, maximizing the rate of production for the laser texturing tool  37 . The use of laser  108  is optimized, with various disk-handling processes in each disk-handling station  38 ,  39  occurring while a disk  49 ,  172  in the other disk-handling station is being exposed to the laser. The use of separate disk-handling stations also provides flexibility; if either of the disk-handling stations  38 ,  39  is disabled, production can continue at a reduced rate using the other disk-handling station. A single disk-handling station  38 ,  39  can also be used, if desired, when untextured disks sufficient for the use of both stations are not available for the process. 
     While the invention has been described in its preferred form or embodiment with some degree of particularity, it is understood that this description has been given only by way of example and that numerous changes in the details of construction, fabrication and use, including the combination and arrangement of parts, may be made without departing from the spirit and scope of the invention. For example, the pneumatic sliders described in reference to FIG. 9 may be replaced by a number of well-known methods for achieving and controlling movement, such as electric motors driving leadscrews.