Patent Publication Number: US-6906892-B2

Title: Mechanism and method for positioning data cartridge in disk drive

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to provisional application Ser. No. 60/265,830, filed Jan. 31, 2001, entitled “Cartridge-Loading Mechanism for Data Storage Disk”. 
   This application is also related to application Ser. No. 09/947,151, entitled “Mechanism for Limiting Ejection of Data Cartridge From a Disk Drive”, application Ser. No. 09/946,845, entitled “Data Cartridge Load/Unload Mechanism For Disk Drive”, and application Ser. No. 09/947,313, entitled “Mechanism for Opening a Shutter of a Data Cartridge”, each of which is filed on even date herewith. 
   Each of the above-referenced applications is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a mechanism for loading and unloading a cartridge from a disk drive. 
   2. Description of the Related Art 
   Data storage disks, and in particular optical data storage disks, are widely used for a number of purposes. For example, downloading data via computer networks such as the Internet onto data storage disks is becoming increasingly popular. The downloaded data may include movies, music recordings, books, and other media. There are different types and sizes of data storage disks available for storing and accessing the downloaded information. 
   Data storage disks are often housed in cartridge or cassette to protect the disk from damage. For example, magnetic disks (also referred to as floppy discs) are commonly housed in a cartridge referred to a diskette. Diskettes are inserted into the computer by the user. Typically, a spring is used to exert a force to hold the diskette in a fixed position. Holding the diskette in place using pressure from a spring can be suitable for stationery operation. However, a spring-loaded mechanism has several disadvantages for portable devices. 
   Portable computers and other data reading devices are subject to being bumped, jarred and dropped by the user. These actions can exert transient forces on the body of the computer (or other device) which in turn are transmitted to the cartridge or diskette. These transient forces may compress the spring, allowing the cartridge or diskette to move. Allowing the cartridge or diskette to move can interrupt the transfer of data from the disk to the device and cause operational failure. 
   Accordingly, what is needed is a mechanism to load and unload a data storage cartridge or diskette into a portable disk drive, without use of a spring, such that the cartridge is fixedly held in the correct operational position even when the disk drive is subjected to transient forces. Preferably, the device would be suitable for use in a handheld device such as a portable video camera. Preferably the mechanism would be suitable for loading and unloading a cartridge which contains an optical data storage disk. 
   SUMMARY OF THE INVENTION 
   A disk drive according to this invention comprises a cartridge tray for receiving a cartridge, said cartridge containing a data storage disk, said cartridge comprising an alignment opening; an XY alignment pin for engaging said alignment opening so as to assist in locating said cartridge in X and Y dimensions; a theta datum for engaging an edge of said cartridge; a first mechanism for pressing said cartridge against said alignment pin; and a second mechanism for pressing said edge of said cartridge against said theta datum. The disk drive also comprises at least three Z datums for positioning said cartridge in a Z dimension. 
   The invention also includes a method of positioning a data storage cartridge in a disk drive. The method comprises biasing an alignment feature of said cartridge against an XY alignment pin so as to position said cartridge in X and Y dimensions; biasing said cartridge against a theta datum so as to position said cartridge in a theta rotational dimension; and biasing said cartridge against at least three Z datums so as to position said cartridge in a Z dimension. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the figures designates a like or similar element. 
       FIG. 1  is a perspective view of an optical disk cartridge usable with the load/unload mechanism of this invention, with its shutter closed. 
       FIG. 2  is a perspective view of the cartridge with its shutter open. 
       FIGS. 3A and 3B  are perspective views of the shutter. 
       FIG. 4  is a perspective cross-sectional view of the cartridge. 
       FIG. 5  is a detailed cross-sectional view of part of the structure that holds the shutter on the cartridge. 
       FIG. 6  is a perspective view of one of the housings that form the cartridge. 
       FIG. 7  is a perspective view of the shutter lock mechanism. 
       FIG. 8  is a detailed perspective view of one of the cavities in the cartridge that holds a shutter lock mechanism and a shutter return spring. 
       FIG. 9  is a perspective view of the portions of the shutter that engage the shutter lock mechanism. 
       FIG. 10A  is a top view of one of the cartridge housings partially inserted into the cartridge tray, showing in particular the locations of the shutter return springs. 
       FIG. 10B  is a view of the front portion of the cartridge. 
       FIG. 11  is a detailed perspective view of one of the alignment features in the cartridge. 
       FIG. 12  is a view of the back edge of the cartridge. 
       FIG. 13  is a perspective view of a disk drive in accordance with this invention. 
       FIG. 14  is a perspective view of the inside of the disk drive housing with the internal components removed. 
       FIG. 15  is a tilted or inclined top view of the disk drive housing with the internal components removed. 
       FIG. 16  is a perspective view of the inside of the disk drive housing with some of the internal components present. 
       FIGS. 17 and 18  are exploded views of the cartridge, the cartridge tray and the cam plate. 
       FIG. 19A  is a perspective view of the picker arm from below. 
       FIG. 19B  is a perspective view of the picker arm from above. 
       FIG. 19C  is a view of the end of the picker arm and the shutter when the shutter is in an open position. 
       FIG. 19D  illustrates the reduction of the effective angle between the picker arm and the front edge of the shutter as result of the offset in the picker arm. 
       FIG. 20  is a bottom view of the cartridge tray. 
       FIG. 21  is a perspective view of the cam plate. 
       FIGS. 22 and 23  are perspective views of the disk drive housing with the cam plate and lever arm in place. 
       FIG. 24  is a perspective view of the lever arm. 
       FIG. 25  is a top view of the disk drive housing with the cam plate and lever arm in place. 
       FIG. 26  is a detailed perspective view showing how a cartridge tray pin interacts with the cam plate and one of the tray pin slots. 
       FIG. 27  is a vector diagram showing the force on the cartridge tray pin. 
       FIG. 28  is a cross-sectional view of the disk drive and a cartridge about to be inserted. 
       FIGS. 29 and 30  are perspective views showing the cartridge partially inserted into the cartridge tray. 
       FIGS. 31A and 31B  are cross-sectional views of the disk drive with the cartridge fully inserted. 
       FIG. 32  is a perspective view of the cartridge fully inserted into the cartridge tray and cam plate. 
       FIG. 33A  is a perspective view of the disk drive with several components removed to illustrate several underlying exemplary components. 
       FIGS. 33B and 33C  are top views of the system shown in FIG.  33 A. 
       FIGS. 33A and 33B  are a top views showing the flag and beam arrangement that is used to turn on the cartridge load/unload motor. 
       FIGS. 34A and 34B  are cross-sectional views of the disk drive when the cartridge load/unload motor has just started to lower the cartridge into playing position. 
       FIGS. 35A and 35B  are cross-sectional views of the disk drive when the alignment pin in the disk drive has started to enter the alignment feature on the cartridge. 
       FIGS. 36A and 36B  are cross-sectional views of the disk drive when the cartridge catches are about to release the cartridge. 
       FIGS. 37A and 37B  are cross-sectional views of the disk drive when the alignment feature engages the alignment pin. 
       FIG. 38  is a cross-sectional view of the disk drive when the cartridge has been lowered into the playing position. 
       FIG. 39  is a cross-sectional view of the disk drive when the cartridge has been lifted from the playing position to the point where the alignment feature on the cartridge clears the alignment pin in the disk drive. 
       FIG. 40  is a cross-sectional view of the disk drive when the cartridge has been partially ejected and the eject limiters in the disk drive have engaged the eject limit slot catches on the cartridge. 
       FIG. 41  is a schematic diagram (not drawn to scale) summarizing the movement of the cartridge during the load/unload sequence. 
       FIG. 42  is a perspective view of the cartridge load/unload motor lead screw mechanism. 
       FIGS. 43A-43B  are block diagrams illustrating the transfer function from the output of the cartridge load/unload motor to the cartridge tray. 
       FIG. 43C  is a block diagram illustrating the transfer function from the cartridge tray to the output of the cartridge load/unload motor when the mechanism is back driven. 
   

   DETAILED DESCRIPTION 
   The descriptions herein are of embodiments of a cartridge and mechanism for loading and unloading the cartridge into a disk drive. It should be understood, however, that the load/unload mechanism can be used with cartridges that are different from the cartridge described herein. 
   First the cartridge will be described.  FIG. 1  is a perspective view of a cartridge  10 . Cartridge  10  contains a two-sided optical data storage disk which can be accessed from either side, and cartridge  10  is therefore symmetrical about the plane of the disk. Cartridge is fabricated with similar or identical housings  102 ,  104 , which are bonded together to form an interior cavity to hold the optical disk. Thus, a view from the opposite side of the cartridge would be identical to the view shown in FIG.  1 . 
   Access to the disk (not visible in  FIG. 1 ) is controlled by a shutter  106  which overlies housing  102  and can be displaced to an open position to expose a portion of the optical disk. A similar shutter  107  which fits over housing  104  on the underside of cartridge  10  is only partially visible.  FIG. 2  is view of cartridge  10  with shutter  106  in the open position, thereby exposing an optical disk  108 .  FIGS. 3A and 3B  are views of shutter  106  in isolation, inverted as compared to the position of shutter  106  in  FIGS. 1 and 2 . As indicated, shutter  106  includes a tab  110  which is offset from a main body  109  of shutter  106  and slides in a recess  112  in housing  102 . Tab  110  is maintained in place by a shutter keeper  114 .  FIG. 4  is a cross-sectional view taken at section  4 — 4  in  FIG. 1  which shows the placement of tab  110  in recess  112 .  FIG. 5  is a detailed cross-sectional view of the same structure. As shown in  FIG. 3A , shutter  106  also includes tabs  116  and  118  which fit into a slot between housings  102  and  104  on the front edge of cartridge  10 . Shutter  106  is thus anchored to cartridge  10  by the combined operation of tabs  110 ,  116  and  118 . 
   Shutter  106  also contains an opening  120  which is bounded on one side by a contact edge  122 . As described below, a picker arm makes contact with contact edge  122  to move shutter  106  from the closed to open position. 
   Cartridge  10  also includes mechanisms which (i) lock shutter  106  in its closed position, and (ii) spring-bias shutter  106  towards its closed position when it is in an open position.  FIG. 6  is a view of housing  104  showing cavities  124  and  126  which contain these mechanisms. Cavity  124  contains a shutter lock that controls shutter  107  for housing  104 ; cavity  126  contains a spring that biases shutter  107  toward a closed position. Correspondingly, cavity  124  contains a spring that biases shutter  106 , and cavity  126  contains a shutter lock that controls shutter  106 . 
     FIG. 7  shows a shutter lock  128 , and  FIG. 8  shows shutter lock  128  in position in cavity  124 . A leaf spring portion  130  of shutter lock  128  abuts a wall  132  of cavity  124 , and the spring force from leaf spring portion  130  causes a wedge portion  134  of shutter lock  128  to protrude into opening  120  in shutter  107 .  FIG. 9  is a perspective view of this corner of cartridge  10 , showing wedge portion  134  protruding through opening  120 . As indicated, a locking edge  136  of wedge portion  134  abuts a locking tab  138  of the shutter, thereby holding the shutter in the closed portion. Note that shutter  106  is in the open position in FIG.  9 .  FIG. 10A  is a view of housing  104  that shows how shutter return springs  140  and  142  are positioned in cavities  124  and  126 , respectively. Shutter return spring  142  biases shutter  106  closed, and shutter return spring  140  biases shutter  107  closed.  FIG. 10B  shows another view of the front portion of cartridge  10 . 
   Application Ser. No. 09/730,647, filed Dec. 5, 2000, contains further details on the operation of shutters  106 ,  107 , shutter lock  128  and shutter return springs  140 ,  142  and is incorporated herein by reference in its entirety. 
   Referring again to  FIG. 1 , cartridge  10  also has an alignment feature  143  which, as described below, mates with an alignment pin in the disk drive to assist in positioning the cartridge. A corresponding alignment feature  144 , which is used when cartridge  10  is inverted is also visible.  FIG. 11  is a detailed view of alignment feature  143 , showing an oval portion  146 , where the alignment pin initially enters alignment feature  143 , and a V-shaped portion  148 , against which the alignment pin abuts when cartridge  10  is lowered into its operational position in the disk drive. 
   Referring once again to  FIG. 1 , the back edge of cartridge  10  includes an arc-shaped portion  150 , and shoulders  152 A and  152 B located on either side of arc-shaped portion  150 . As described below, these features interact with the door of the disk drive during the load/unload sequence. Arc-shaped portion  150  includes a raised surface  151 , shown in  FIGS. 2 and 10 , against which the user may press when loading cartridge  10  into disk drive  20 . Along the side edges of cartridge  10  are eject limit slots  154 A and  154 B, respectively, and corresponding eject limit slot catches  156 A and  156 B at the end of eject limit slots  154 A and  154 B.  FIG. 12  is a view of the back edge of cartridge  10 , showing the arc-shaped portion  150 , raised surface  151 , shoulders  152 A,  152 B, and eject limit slots  154 A,  154 B. 
     FIG. 13  is a perspective view of a portable disk drive  20  that can be used to read or write data to or from optical disk  108  in cartridge  10 . As previously stated, however, the principles of this invention are not limited to the specific cartridge described in  FIGS. 1-12  but are applicable to a wide variety of cartridges. 
   Disk drive  20  includes a housing  202  and a cover  204 . A spring-loaded door  206  is positioned at the entrance of the slot into which a cartridge is inserted. Door  206  is hinged at its lower edge, and a spring (not shown) biases door to the closed position shown in FIG.  13 . On the outer surface of door  206  are a pair of cartridge catches  208 A and  208 B and a release cam  210 . These features on door  206  interact with a cartridge as it is inserted into disk drive  20 , as described below. Also shown in  FIG. 13  is a set of axes that will be used in describing the operation of disk drive  20 . The direction from left to right is defined as the positive X direction; the direction from the front to the rear of disk drive  20  is defined as the positive Y direction; and upward is defined as the positive Z direction. Of course, since disk drive  20  is portable, it can be operated while oriented in any direction. 
     FIGS. 14 and 15  show the interior of housing  202  with cover  204  and door  206  removed. Some of the internal components of disk drive  20 , such as the actuator that holds the read/write head, are also omitted. The interior of housing  202  contains a number of datums, i.e., surfaces that are used to properly locate a cartridge for reading and writing. An XY alignment pin  209  and a Y limiter  211  on a backstop  212  help locate the cartridge in the XY plane. Theta datum  214  controls the theta (rotational) position of the cartridge in the XY plane and theta limiter  216  limits the theta rotation of the cartridge in the clockwise direction during the load cycle. 
   As shown in  FIGS. 14 and 15 , there are five datums that locate the cartridge in the Z dimension: an annular surface  218  located at the base of XY alignment pin  209 ; a surface  220  at the base of backstop  212 ; surfaces  222  and  224  at the base of theta datum  214  and theta limiter  216 , respectively; and a surface  226  in the front right area of housing  202 . In this embodiment, Z datums  220  and  222  are relatively close together and function as a single datum. 
   Housing  202  also contains a cavity  228  for mounting a cartridge load/unload motor and lead screw mechanism  229  (shown in  FIG. 33A ) that provides the mechanical power to lower cartridge  10  into operating position. 
     FIG. 16  is another view of the interior of housing  202 , showing the locations of several components that are omitted from  FIGS. 14 and 15 . In particular,  FIG. 16  shows the locations of a spindle motor  230 , which makes contact with an optical disk within cartridge  10 , an actuator arm  232 , which holds an optical pickup unit (OPU)  234  for reading and writing to or from optical disk  108 , a pin  236  about which actuator arm  232  rotates to position OPU  234  over a data track on the disk that is to be written to or read from, a crash stop  238 , which prevents contact between OPU  234  and the surface of the optical disk, and a parking mechanism  240 , which pivots about a pin  242  to “park” actuator arm  232  when OPU  234  is not reading or writing data. 
   When cartridge  10  is introduced to disk drive  20 , it enters a cartridge tray  244 , shown in the exploded view of FIG.  17 . Associated with cartridge tray  244  is a cam plate  252 . These components are shown from a different perspective in the exploded view of FIG.  18 . 
   Mounted in cartridge tray  244  is a picker arm  246 , which rotates about a pin  248  and is biased by a spring  250 . Spring  250  biases picker arm  246  into an extended position wherein picker arm points generally in a direction towards door  206  of disk drive  20 . Picker arm  246  is shown in  FIGS. 19A and 19B . Picker arm  246  includes a protrusion  246 A and a shutter opening surface  246 B, which are shown in detail in FIG.  19 C. 
   A bottom view of cartridge tray  244  is shown in FIG.  20 . As indicated, the bottom of tray  244  is substantially open, thereby allowing OPU  234  to obtain access to optical disk  108 . Cartridge  10  is held in tray  244  by side flanges  254  and  256 , which with the top of tray  244  form opposing channels into which cartridge  10  slides until the front edge of cartridge  10  is enclosed by a flange  258 . Tray  244  has openings at selected positions to allow the X, Y, Z and theta datums in housing  202  (described above) to make contact with cartridge  10  while it is positioned in tray  244 . For example, openings  260  and  262  on the sides of tray  244  allow theta datum  214  and theta limiter  216  to make contact with the side edges of cartridge  10 . Tray pins  264  and  266  project from the sides of tray  244 , and eject limiters  268  and  270  are positioned near the entrance to tray  244 . Eject limiters  268 ,  270  are made of a resilient material such as spring steel and are bent to form protrusions  268 A,  270 A. Pin  248 , about which picker arm  246  (not shown) rotates, is also shown in FIG.  20 . 
   Cam plate  252  is shown in detail in FIG.  21 . If particular note are an aperture  272  and cam slots  274  and  276 , positioned on the side flanges  278  and  280  of cam plate  252 , through which tray pins  264  and  266  extend. When cam plate  252  is mounted in disk drive  20 , main body portion  282  is positioned against the floor of housing  202 , as shown in  FIGS. 22 and 23 . Also shown in  FIGS. 22 and 23  is a lever arm  284  which rotates about a pin  286  in housing  202  (see FIGS.  15  and  16 ). Lever arm  284  is shown in isolation in FIG.  24 . An aperture  288  of lever arm  284  fits over pin  286  of housing  202  (see FIGS.  15  and  16 ). A cam plate pin  290  is inserted through a slot  292  of lever arm  284  and aperture  272  of cam plate  252 . Referring to  FIG. 25 , a pin  328  (shown in  FIG. 42 ) is inserted through slot  295  to form a connection with the cartridge load/unload motor and lead screw mechanism  229  that is mounted in cavity  228 . Thus, as the cartridge load/unload motor drives the lead screw mechanism back and forth between its limits, lever arm  284  rotates clockwise and counterclockwise about pin  286 , and this in turn causes cam plate  252  to slide forward and backward along the Y axis in housing  202 , as cam plate pin  290  slides in slot  292 . This motion is shown by the arrows in  FIGS. 22 and 23 . 
   Referring back to  FIG. 14 , on either side of housing  202  are X limiters  294  and  296 , which contain tray pin slots  298  and  300 , respectively. Tray pins  264  and  266  extend through cam slots  274  and  276  of cam plate  252 . Tray pin  264  extends into tray pin slot  298 ; tray pine  266  extends into tray pin slot  300 .  FIG. 26  is a detailed view showing tray pin  264 , cam slot  274  and tray pin slot  298 . It will be evident from  FIG. 26  that, as cam plate  252  moves back and forth in housing  202 , as described above, the juxtaposition of cam slots  274 ,  276  and tray pin slots  298 ,  300  causes tray pins  264 ,  266  to move upwards and downwards in tray pin slots  298 ,  300 . The position of tray pin  264  near the top of tray pin slot  298  in  FIG. 26  reflects the condition before a cartridge has been inserted into disk drive  20 . 
   The combined effect of cam slots  274 ,  276  and tray pin slots  298 ,  300  on tray pins  264 ,  266  is further illustrated in  FIG. 27 , which shows that the forces F 1  and F 2  on pins  264 ,  266 . Force F 1  is created by edge  302  of cam slots  274 ,  276  of cam plate  252  when cam plate  252  is moved horizontally to the right. Force F 2  is created by edge  304  of tray pin slots  298 ,  300 . The horizontal component F 2   h  of force F 2  is equal and opposite to the horizontal component F 1   h  of force F 1 , and thus tray pins  264 ,  266  are prevented from moving horizontally. The vertical component F 2   v  of force F 2  is less than the vertical component F 1   v  of force F 1 , and thus tray pins  264 ,  266  are forced to move vertically downward. It will be understood that when cam plate  252  moves in the opposite direction, edge  303  of cam slots  274 ,  276  and edge  305  of tray pin slots  298 ,  300  apply forces to tray pins  264 ,  266 . In this case, the horizontal forces are again canceled, but the vertical forces now are greater in the upward direction. Thus tray pins  264 ,  266  are forced to move upward. 
   In one embodiment, cam slots  274 ,  276  are angled at 38.5 degrees with respect to a main body portion  282  of cam plate  252  and about 51.5 degrees to tray pin slots  298 ,  300 . 
   The load/unload sequence will now be described, with reference to  FIGS. 28-41 . The movement of cartridge  10  during the load/unload sequence is summarized in  FIG. 41 , which indicates that seven stages are involved. 
     FIG. 28  is a cross-sectional view, taken at section  28 - 28  in  FIG. 13 , which shows cartridge  10  just before it is inserted into disk drive  20 .  FIG. 29 , a perspective view of cartridge  10  and cartridge tray  244  taken from the underside of cartridge tray  244 , shows cartridge  10  after it has been partially inserted in disk drive  20  by a user and shows picker arm  246  in its extended position just making contact with wedge portion  134  of shutter lock  128 . The protrusion  246 A of picker arm  246  depresses wedge portion  134  of shutter lock  128 , thereby causing shutter lock  128  to release shutter  106  and shutter opening surface  246 B of picker arm  246  makes contact with contact edge  122  of shutter  106  (see FIGS.  19 A and  19 B).  FIG. 30  shows the condition an instant later, when shutter  106  has partially opened, exposing a portion of optical disk  108 . Through this point, the power to insert cartridge  10  has been provided entirely by the user. Once picker arm  246  starts to open shutter  106 , the further insertion of cartridge  10  is resisted by shutter return spring  140  and picker arm spring  250 . The combined resistance of these two springs is minimal, however, from the standpoint of the user. 
   The angle of picker arm  246  relative to the front edge of shutter  106  as cartridge  10  is inserted should not be too large because otherwise friction between shutter  106  and cartridge housing  102  may be so great as to inhibit or prevent shutter  106  from opening. The opening force applied to shutter  106  by shutter opening surface  246 B must overcome the frictional force between shutter  106  and housing  102 . Therefore, picker arm  246  contains an offset portion  246 C which reduces the effective angle between picker arm  246  and the front edge of shutter  106 .  FIG. 19D  shows the relationship between shutter  106  and picker arm  246  at the point of initial contact. The angle β represents the effective angle between picker arm  246  and front edge  106 E of shutter  106  if there were no offset  246 C and the pivot point of picker arm  246  were located at point  249 . The angle β represents the effective angle between picker arm  246  and front edge  106 E with the pivot point located at pin  248 . As indicated, angle β is smaller than angle α. 
   Moreover, when shutter  106  is fully open, the effective angle between picker arm  246  and front edge  106 E of shutter  106  should be as small as possible. Offset portion  246 C also minimizes this angle. Shutter  106  should be opened to a repeatable position to provide operating clearance to internal components of disk drive  20 . The small angle minimizes the sensitivity of the open position of shutter  106  to small motions of cartridge  10  in the Y dimension, which can be caused by manufacturing tolerances of the parts and by the expected motion of cartridge  10  as it becomes seated against XY alignment pin  209 , as described below. The presence of offset  246 C also provides clearance for cartridge  10  when cartridge  10  is fully inserted in disk drive  20 . 
   Picker arm  246  also includes a guide surface  246 D, shown in  FIGS. 19A-19C , which provides a smooth, rotating interface between picker arm  246  and a surface  141  of shutterl 06  (shown in  FIG. 3B ) and prevents protrusion  246 A from sliding against the interior plastic of cartridge  10 . This guiding action reduces the friction between picker arm  246  and shutter  106 . This reduced friction in turn reduces the force required to insert protrusion  246 A into shutter  106  and provides a smooth “feel” for the insertion. 
   As shown in  FIG. 19C , protrusion  246 A “overhangs” shutter opening surface  246 B, creating a bend or inflection point  246 G at the junction of protrusion  246 A and shutter opening surface  246 B. Inflection point  246 G provides a positive locking force against contact edge  122  of shutter  106  when shutter  106  is in its fully open position (as shown in  FIG. 2 ) and prevents picker arm from becoming disengaged from shutter  106  as a result of shock or vibration. 
   Still referring to  FIGS. 19A-19C , protrusion  246 A has a angled back wall  246 E which engages locking tab  138  of shutter  106  when shutter  106  is in its fully open position (see FIGS.  8  and  9 ). As a result of this contact, when cartridge  10  is to be removed from disk drive  20 , back wall  246 E provides a positive closing force against shutter  106  and thereby prevents shutter  106  from becoming “stuck” in the fully open position. Once shutter  106  begins to close, shutter return spring  140  takes over. 
   Picker arm  246  also includes a stop surface  246 F which abuts a corresponding stop surface  245  on cartridge tray  244  (see FIGS.  20  and  29 ), thereby holding picker arm  246  in the correct position when disk drive  20  is empty such that protrusion  246 A properly engages shutter lock  128  and shutter  106  when cartridge  10  is inserted into disk drive  20 . The position of picker arm  246  before cartridge  10  is inserted into disk drive  20  is purposely set such that picker arm  246  engages shutter  106  at a surface  139 , in advance of opening  120  of shutter  106  (see FIG.  3 B). As a result, picker arm  246  engages shutter lock  128  and contact edge  122  of shutter  106  with a “sweeping motion”. Positioning stop surface  245  so as to achieve this result adds a margin of error to ensure that picker arm  246  properly engages shutter lock  128  and shutter  106 . 
     FIG. 31A  is a cross-sectional view similar to  FIG. 28  showing cartridge  10  fully inserted into cartridge tray  244 . Picker arm  246  has been rotated against the force of picker arm spring  250  until it is in a retracted position, in this embodiment substantially flat against the back of tray  244 . Shutter  106  (not shown) has been fully opened. Importantly, as shown in the detailed view of  FIG. 31B , cartridge catches  208 A and  208 B on door have engaged shoulders  152 A and  152 B of cartridge  10  (see FIG.  1 ), thereby preventing cartridge  10  from being ejected from disk drive  20  by the forces from picker arm spring  250  and shutter return spring  140 .  FIG. 32  is a perspective view from the bottom showing cartridge  10  fully inserted into cartridge tray  244 . Cam plate  252  is also shown. 
   The insertion of cartridge  10  to the position shown in  FIGS. 31A ,  31 B and  32  is represented as motion # 1  in FIG.  41 . 
   At this point, as shown in  FIGS. 33A-33C , cartridge  10  causes a shield or flag  253  to interrupt a light beam generated by a light-emitting diode (LED)  255 . This, in turn, is detected by a light sensor  257 , which sends a signal that activates cartridge load/unload motor and lead screw mechanism  229 . 
     FIG. 33A  is a perspective view of disk drive  20  with cartridge tray  244  removed.  FIGS. 6B and 6C  are top views of disk drive  20 . In particular,  FIGS. 6A-6C  show flag  253  mounted to housing  202  via a flag spring  261 . The combination of flag  253  and flag spring  261  need not be mounted to housing  202  as shown in  FIGS. 6A-6C . As shown in Application No. 60/265,830, filed Jan. 31, 2001, entitled Cartridge Loading Mechanism for Data Storage Disk, the flag and flag spring may be mounted to the tray. The remaining description will presume that flag  253  and flag spring  261  are mounted to housing  202  as shown in  FIGS. 6A-6C . 
   Flag  253  may be formed from an opaque material. In a preferred embodiment, flag spring  261  is formed from a metal or other flexible material and includes first and second ends. The first end of flag spring  261  may be fixedly connected to housing  202  using, for example, an adhesive or a weld. The second end of flag spring  261  is connected to flag  253 . In one embodiment, flag  253  and flag spring  261  are formed from the same piece of flat metal such that flag  253  is integrally connected to flag spring  261 . As will be more fully described below, flag  253  is movable between beam interruption and beam allowance positions.  FIGS. 6   a  and  6   b  show flag  253  in the beam interruption position, and  FIG. 6   c  shows flag  253  in the beam allowance position. Flag  253  is biased to the beam allowance position by flag spring  261 . 
   LED  255  and a light sensor  257  are mounted to housing  202  via a printed circuit board (not shown). The combination of flag  253 , LED  255  and a light sensor  257  represents one embodiment of a device for detecting the presence of cartridge  10  in disk drive. LED  255 , when active, generates a light beam between LED  255  and light sensor  257 . Light sensor  257 , when active, generates a signal in response to receiving the light beam generated by LED  255  or in response to an interruption of the light beam generated by LED  255 . The remaining description will presume that light sensor  257  generates a signal in response to an interruption of a light beam generated by LED  255 . 
   Flag  253  is movable between the beam-interruption position and the beam allowance position. In the beam-interruption position, as shown in  FIGS. 33A and 33B , flag  253  is positioned between LED  255  and light sensor  257  so that flag  253  interrupts the beam of light received by sensor  257 . In other words, flag  253  shields sensor  257  from receiving light from LED  255  when flag  253  is in the beam-interruption position. In the beam allowance position, as shown in  FIG. 6C , flag  253  is removed from between LED  255  and light sensor  257  so that light sensor  257  may receive the light beam generated by LED  255 . 
   Flag  253  is normally in the beam allowance position and is moved from its beam allowance position to its beam-interruption position when cartridge  10  is fully inserted into cartridge tray  244 . In one embodiment, cartridge  10  directly or indirectly engages and moves flag  253  into its beam-interruption position when cartridge  10  is inserted into tray  244 . Cartridge  10  indirectly engages and moves flag  253  into its beam-interruption position when cartridge  10  is inserted into tray  244 . When cartridge  10  is removed from tray  244 , flag spring  261  returns flag  253  to its beam allowance position shown in FIG.  6 C. 
   When cartridge  10  has been inserted into tray  244 , tray pins  264 ,  266  are near the top of tray pin slots  298 ,  300  (as shown in FIG.  26 ). Cam plate  252  is roughly at the position shown in FIG.  22 . Cartridge load/unload motor and lead screw mechanism  229  moves towards the rear of disk drive  20 . This motion rotates lever arm  284  clockwise and pulls cam plate  252  towards the front of disk drive  20 . As a consequence of the mechanical interaction (described above) between cam slots  274 ,  276 , tray pins  264 ,  266 , and tray pin slots  298 ,  300 , cartridge tray  244  starts to move downward. 
   As can be seen in  FIG. 34A , when cartridge  10  has been fully inserted into cartridge tray  244 , a front edge  304  of cartridge  10  is positioned directly over backstop  212  in housing  202 . (Backstop  212  is shown in  FIGS. 14 and 15 .)  FIGS. 34A and 34B  show the position when the lowering of cartridge  10  has just begun. As indicated, front edge  304  has contacted the top surface of backstop  212 , while cartridge  10  as a whole is still substantially horizontal. With the slight lowering of cartridge  10 , door  206  has opened slightly further (as compared to its position in FIGS.  31 A and  31 B), and the continued contact between release cam  210  on door  206  and the surface of cartridge  10  has started to release cartridge  10  from cartridge catches  208 A,  208 B. 
     FIGS. 35A and 35B  show the situation an instant later. Front edge  304  has come into contact with the top of backstop  212 , and cartridge  10  is slightly tilted in a direction away from front edge  304 . XY alignment pin  209  has started to enter the mouth of alignment feature  143 . Alignment pin  209  is shown in  FIGS. 14-16 , and alignment feature  143  is shown in  FIGS. 1 and 11 . 
   In  FIGS. 36A and 36B , the tilting of cartridge  10  has continued, and as shown in  FIG. 36A  XY alignment pin  209  has further entered the oval portion  146  of alignment feature  143 . Importantly, the continued lowering of the back edge of cartridge  10  against release cam  210  on door  206  has caused cartridge catches  208 A and  208 B almost to release cartridge  10 . 
   The motion of cartridge  10  from the time cartridge  10  has been fully inserted into cartridge tray  244  until cartridge catches  208 A and  208 B release cartridge  10  is represented as motion # 2  in FIG.  41 . 
   In  FIGS. 37A and 37B , cartridge catches  208 A and  208 B have released cartridge  10 . With cartridge  10  released, spring-loaded picker arm  246  tries to eject cartridge  10  from disk drive  20 . Since XY alignment pin  209  has entered alignment feature  143 , however, cartridge  10  is not ejected. Instead, the motion of cartridge  10  towards door  206  causes XY alignment pin  209  to become lodged against V-shaped portion  148  of alignment feature  143  (see FIG.  11 ), fixing the position of cartridge  10  in the X and Y dimensions. At the same time, the motion of cartridge  10  towards door  206  causes the front edge  304  to clear backstop  212 . The end result is that cartridge  10  falls between V-shaped portion  148  of alignment feature  143  and the Y limiter  211 . 
   The motion of cartridge  10  from the time cartridge catches  208 A and  208 B release cartridge  10  until XY alignment pin  209  becomes lodged against V-shaped portion  148  of alignment feature  143  is represented as motion # 3  in FIG.  41 . 
   After XY alignment pin  209  becomes lodged against V-shaped portion  148  of alignment feature  143 , cartridge tray  244  begins to move downward. Cartridge tray  244  and cartridge  10  are guided into position by theta datum  214 , theta limiter  216 , Y limiter  211 , and X limiters  294  and  296 . Theta datum  214 , theta limiter  216 , Y limiter  211  contact cartridge  10  itself through openings in cartridge tray  244 , and X limiters  294  and  296  contact the sides of cam plate  252 . 
   This process continues until the lower surface of cartridge  10  comes into contact with Z datums  218 ,  220 ,  222 ,  224  and  226 . As indicated above, datums  220  and  222  function as a single datum. Cartridge  10  flexes as necessary to insure contact with each of Z datums  218 ,  220 / 222 ,  224  and  226 . In this position, optical disk  108  is properly seated on spindle motor  230  such that optical disk  108  may rotate freely without contacting the cartridge housings  102  and  104 . This is the playing position for cartridge  10 . This condition is shown in FIG.  38 . At this point, in one embodiment the cartridge load/unload motor stalls and thereby maintains a force between cartridge tray  244 , through cartridge  10  to housing  202  at Z datums  218 ,  220 / 222 ,  224  and  226 . The nature of the system including the lead screw, lever arm  284  and cam slots  274 ,  276  is such that cam plate  252  cannot be back driven, and a clamping load is maintained through cartridge  10  against Z datums  218 ,  220 / 222 ,  224  and  226 . In another embodiment, the operation of the cartridge load/unload motor is timed such that the motor turns off after cartridge  10  is clamped against the surfaces of Z datums  218 ,  220 / 222 ,  224  and  226 . In either embodiment, spindle motor  230  then begins to rotate, allowing data to be read from or written to optical disk  108 . 
   When cartridge  10  is seated on Z datums  218 ,  220 / 222 ,  224  and  226 , the V-shaped portion  148  of alignment feature  143  is pressed against XY alignment pin  209  by the combined action of picker arm  246  and picker arm spring  250 , thereby defining the position of cartridge  10  in the X and Y dimensions. An edge of cartridge  10  is pressed against theta datum  214  by the force of one of shutter return springs  140  and  142 , thereby defining the position of cartridge  10  in the theta dimension. 
   The motion of cartridge  10  from the time XY alignment pin  209  becomes lodged against V-shaped portion  148  of alignment feature  143  until cartridge  10  is clamped against Z datums  218 ,  220 / 222 ,  224  and  226  is represented as motion # 4  in FIG.  41 . 
   When cartridge  10  is in the playing position, it is located as follows precisely in the correct location for reading and writing data to and reading data from optical disk  108 . During the load process, cartridge  10  becomes located properly against datums in the X, Y, Z and theta dimensions. Cartridge  10  is located at alignment feature  143  in the X and Y dimensions by the biasing action of picker arm spring  250  to force V-shaped portion  148  of alignment feature  143  against XY alignment pin  209 . Cartridge  10  is located in the theta dimension by the biasing action of shutter return spring  140  to force cartridge housing  102  against theta datum  214 . Thus, cartridge  10  is located in the X, Y and theta dimensions by XY alignment pin  209  and theta datum  214 , respectively. Cartridge  10  is located at the lower surface of housing  102  by the clamping action of cartridge tray  244 , which is driven by cam plate  252 , lever arm  284  and lead screw (not shown) against Z datums  218 ,  220 / 222 ,  224  and  226 . Cartridge  10  is thus located in the X, Y, theta and Z dimensions, fully constraining its position. Cartridge  10  is prevented from moving during shock and vibration by a combination of forces. Shutter return spring  140  maintains a bias force against theta datum  214 . Picker arm spring  250  maintains a bias force against XY alignment pin  209 . In addition, the Z clamping force generated by the lead screw, lever arm  284  and cam plate  252  causes friction between cartridge  10  and the housing  202  which prevents movement except at high shock. Further limitation to misalignment in the X, Y and theta dimensions is provided by limiters. Theta limiter surface  216  limits theta rotation of the cartridge  10  in the clockwise direction. Y limiter  211  limits y movement of the cartridge in the positive y direction. The position of limit surfaces  216  and  211  act to prevent cartridge motion of sufficient magnitude to cause optical disk  108  to contact cartridge housings  102  and  104  during operation. 
   The datums are shown in one or more of  FIGS. 14-16  and  22 . Openings are provided at appropriate locations on cartridge tray  244  and cam plate  252  to ensure that theta datum  214 , theta limiter  216  and Y limiter  211  are able to contact the corresponding surfaces of cartridge  10 . For example theta datum  214  and theta limiter  216  contact cartridge  10  through openings  260  and  262 , shown in  FIGS. 20 and 32 . As can be seen in  FIGS. 29 ,  30  and  32 , the surfaces of cartridge  10  which contact Z datums  218 ,  220 / 222 ,  224  and  226  are exposed through open areas of cartridge tray  244 . X limiters  294  and  296  do not contact the cartridge itself but instead contact the surface of cam plate  252 . 
   In some embodiments there may be only three Z datums, in which case the cartridge need not be flexible to be fully seated on the Z datums. In other embodiments there may be five or more Z datums. 
   Thus the position of cartridge  10  is defined kinematically by six points: two points of contact between XY alignment pin  209  and the V-shaped portion  148  of alignment feature  143 ; one point of contain between cartridge  10  and theta datum  214 , and three points of contact between cartridge  10  and the Z datums. 
   After data has been read from or written to optical disk  108 , a signal is transmitted to the cartridge load/unload motor-lead screw arrangement causing the motor to begin rotating in the reverse direction. This causes lever arm  284  to rotate in a counterclockwise direction, moving cam plate  252  towards the rear of disk drive  20 . As is apparent from  FIG. 22 , for example, as cam plate  252  moves towards the rear of disk drive  20 , cam slots  274 ,  276  force tray pins  264 ,  266  (and cartridge tray  244 ) upward in tray pin slots  298 ,  300 . This motion continues until alignment feature  143  clears XY alignment pin  209 . 
   The motion of cartridge  10  from the time cartridge  10  begins to rise from Z datums  218 ,  220 / 222 ,  224  and  226  until alignment feature  143  clears XY alignment pin  209  is represented as motion # 5  in FIG.  41 . 
   The condition when alignment feature  143  has cleared XY alignment pin  209  is shown in FIG.  39 . As indicated, cartridge catches  208 A and  208 B are pressed against the flat bottom surface of cartridge  10  and do not operate to restrain cartridge  10 . Therefore, with nothing restraining cartridge  10  in disk drive  20 , the force of spring-loaded picker arm  246  takes over, beginning to eject cartridge  10  from drive  20 . 
   As picker arm  246  continues to push cartridge  10  out of drive  20 , protrusions  268 A,  270 A of eject limiters  268 ,  270  (shown in  FIG. 20 ) slide along eject limit slots  154 A,  154 B, respectively, (shown in  FIG. 1 ) until protrusions  268 A,  270 A come into contact with eject limit slot catches  156 A,  156 B at the respective ends of eject limit slots  154 A,  154 B. At this point picker arm  246  does not provide enough force to overcome the resistance of eject limit slot catches  156 A,  156 B and the ejection of cartridge  10  from disk drive  20  is suspended. Thus eject limiters  268 ,  270  operate to prevent cartridge  10  from being ejected from drive  20  onto, for example, the floor, where cartridge  10  could be damaged. The position of cartridge  10  at this point is shown in  FIGS. 10 and 40 . 
   The motion of cartridge  10  from the time alignment feature  143  has cleared XY alignment pin  209  until protrusions  268 A,  270 A come into contact with eject limit slot catches  156 A,  156 B is represented as motion # 6  in FIG.  41 . 
   At this point the back of cartridge  10  protrudes from disk drive  20 , and the user is free to remove cartridge  10  entirely from disk drive  20 . The force applied by the user easily overcomes the spring force of eject limiters  268 ,  270  and causes eject limiters  268 ,  270  to ride over eject limit slot catches  156 A,  156 B. This motion of cartridge  10  is represented as motion # 7  in FIG.  41 . 
   As is evident from  FIGS. 14 ,  16  and  20 - 23 , the loading/unloading of cartridge  10  is largely governed by the action of the pair of tray pins  264 ,  266  in tray pin slots  298 ,  300  and cam slots  274 ,  276 . The use of two tray pins has several advantages over the use of three or more tray pins. First, with two tray pins cartridge tray  244  is free to rotate to some extent about the X axis (see, for example, FIG.  29 ). This allows the tilting of cartridge tray  244 , as shown in  FIGS. 35A and 36A , and thereby assists in the positioning of cartridge  10  against XY alignment pin  209 . This type of action is difficult if not impossible to achieve if more than two tray pins are used. In addition, the positioning of the two tray pins  264 ,  266  in the Y-direction on cartridge tray  244  can be adjusted to obtain a desired distribution of the clamping force against Z datums  218 ,  220 / 222 ,  224  and  226 , respectively, when the cartridge is fully loaded. For example, moving the tray pins  264 ,  266  in the direction away from the front edge  304  of cartridge  10  (and towards door  206 ) causes a greater portion of the clamping force to be applied against Z datums  218  and  226  (see FIG.  15 ). 
   Moreover, using two tray pins establishes a unique, definitive clamping line that determines the forces against the Z datums. If three or more tray pins are provided, depending on manufacturing tolerances the lines between different pairs of the tray pins could form the operative clamping line for a given cartridge and thus the clamping force against the Z datums is less predictable than if two tray pins are used. 
     FIG. 42  shows cartridge load/unload motor and lead screw mechanism  229 , which includes a cartridge load/unload motor  320  and a lead screw mechanism  322 . Lead screw mechanism  322  includes a lead screw  324  and a nut  326 . A pin  328 , attached to nut  326 , fits through slot  295  of lever arm  284 . Cartridge load/unload motor  320  is a DC motor which can be run in either of two directions, depending on the polarity of the current supplied to the motor leads. An output shaft  336  of motor  320  drives a gear train comprising an input gear  334 , second stage gears  332 A and  332 B (which share a common shaft), and an output gear  330 . Input gear  334  meshes with gear  332 A, and gear  332 B meshes with output gear  330 . Output gear  330  is mounted on a shaft which drives a lead screw  324 . Thus pin  328  is the output point of cartridge load/unload motor and lead screw mechanism  229  and drives lever arm  284 , which drives cam plate  252 . Cam plate  252  in turn drives tray pins  264 ,  266  via cam slots  274 ,  276 . Tray pins  264 ,  266  are attached to cartridge tray  244 . The force on tray pins  264 ,  266  is transferred to cartridge  10  via cartridge tray  244  and represents the clamping force that holds cartridge  10  against the Z datums in the playing position. The net effect of this entire mechanism is to convert a torque at input gear  334  of cartridge load/unload motor and lead screw mechanism  229  into a linear clamping force applied to cartridge  10 . The nature of the mechanism is to amplify the force through the various stages of the linkage. 
   Chapter 5 of M. F. Spotts,  Design of Machine Elements , 4 th  ed., Prentice-Hall (1971), incorporated herein by reference, describes the usage and design of power screws. Lead screw mechanism  322  is a specific embodiment of one such power screw. The equation relating the force provided by the nut to the torque applied to the lead screw is as follows: 
       T   =       r   t     ⁢     W   ⁢     (           cos   ⁢           ⁢     θ   n     ⁢   tan   ⁢           ⁢   α     -     μ   1           cos   ⁢           ⁢     θ   n       +       μ   1     ⁢   tan   ⁢           ⁢   α         +         r   c       r   t       ⁢     μ   2         )             
 
where T is torque applied to the lead screw (N mm), r t  is the pitch radius of the lead screw (mm), W is the force provided by the nut (N), θ n  is one-half the included thread angle of the lead screw (deg), α is thread helix angle (deg), μ 1  is the coefficient of friction between the lead screw and the nut, r c  is the radius of the lead screw&#39;s thrust bearing (mm), and μ 2  is the coefficient of friction between the lead screw and the thrust bearing.
 
   One of the specific design objectives and advantages of the mechanical linkage between gear  334  and cartridge tray  244  is that it cannot be “driven backwards”. In other words, a force on the cartridge, created for example by a shock event, is not be able to cause cartridge tray  244  or gear  334  to move. The mechanism cannot be driven backwards from its output end (the cartridge). 
   The gain of the mechanism when driven in reverse is essentially the inverse of the gain of the mechanism when driven in the forward direction. Thus the gain is actually a force reducer when driven in reverse. In addition, the embodiment of the lead screw or power screw element of the load/eject module is specifically designed to prevent back driving. Spotts, supra, refers to this as “overhauling”, where the force input at the nut will drive the lead screw. With careful selection of the design parameters listed above, back driving of the lead screw is impossible. As indicated in Spotts, the equation relating force and torque for the “overhauling” screw is: 
       T   =       r   t     ⁢     W   ⁢     (           cos   ⁢           ⁢     θ   n     ⁢   sin   ⁢           ⁢   α     -     μ   1           cos   ⁢           ⁢     θ   n       -       μ   1     ⁢   tan   ⁢           ⁢   α         +         r   c       r   t       ⁢     μ   2         )             
 
   When the term in parenthesis goes to zero, the transition between a geometry that can be back driven and one that cannot be back driven is reached. 
   The thread helix angle (α) is the variable of interest. The following values are assumed for the other parameters: r t =0.75 mm, θ n =approximately zero, μ 1 =0.2, r c =0.2 mm, μ 2 =0.2. 
   Solving for the helix angle α yields a value of approximately 14 degrees. In other words, a helix angle of less than 14 degrees will result in a lead screw that will not turn when force is applied to the nut. A helix angle greater than 14 degrees would allow the nut to force the lead screw to turn. 
   As the helix angle is increased, the force required to turn the screw becomes less (i.e., back-driving becomes easier). The helix angle for this embodiment has been selected to be approximately 4 degrees, safely on the side of the critical angle to prevent back-driving. Once the condition of no back-driving is satisfied, the helix angle is optimized to increase force output at the nut for a given torque input on the lead screw, as well as to define the speed that the nut moves as a function of the lead screw speed. 
   The mechanical linkage between gear  334  and cartridge tray  244  can be represented by a block diagram transfer function as shown in  FIGS. 43A-43C . Each block in  43 A represents a mechanical element of the linkage between gear  334  and cartridge tray  244 . The gear train coefficient (Kg) has a value of approximately 6.25 and is a unit-less factor, since the input and output of this stage are both torques. The lead screw coefficient (Ks) has a value of 15.28 and units of mm−1, since the input is a torque and the output is a force. The lever arm coefficient (K L ) is 1.905 and is unit-less, since the input and output are both forces. The cam plate coefficient (K Cam) has a value of 1.42 resulting from the 35 degree cam slot angle and is unit-less, since the input and output are both forces. The block diagram of  FIG. 43A  can be represented by an equivalent block diagram as in  FIG. 43B , where the coefficients Kg, Ks, K L  and K Cam have been combined by multiplication and the resulting coefficient K is about 258 mm −1 .  FIG. 43C  represents the mechanism of  FIG. 43B  when the mechanism is inverted or “driven backwards”. The resulting gain of the system when driven backwards (K bd ) is 0.0038 (mm), significantly less than one, meaning the force is reduced through the mechanism. Even in a system where the helix angle is greater than the critical “overhauling” angle, the reduction of force through the mechanism acts to prevent back driving. 
   An advantage of this load mechanism over prior art is that this mechanism does not utilize a spring to hold the cartridge against the location datums. Rather, it uses a system comprising cams, levers, lead screws and gears to provide both translation of the cartridge (loading) and constraint of the cartridge (not back driveable). 
   While particular embodiments of the present invention have been shown and described, it will be recognized by those skilled in the art that, based upon the teachings herein, further changes and modifications may be made without departing from this invention and its broader aspects, and thus, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention.