Abstract:
The present invention is directed to a data cartridge library system that realizes a reduced cost by reducing the number of certain components, especially expensive components, that are needed to perform certain functions within the library. With respect to certain functions, a reduced cost is realized by using lower precision compenentry in combination with componentry that compensates for lower precision while still providing a reduced component cost with respect to a given function. In one embodiment of the invention, a data cartridge picker is provided that: (1) uses a single electro-mechanical device for the functions of grasping a data cartridge, retracting a grasped cartridge from a drive/storage location, inserting a grasped cartridge into a drive/storage location, and releasing a grasped cartridge once position in a desired location; (2) is capable of compensating for variations in cartridge positioning; (3) has a gripping mechanism that. moves in a sinusiodal manner; and (4) avoids the wear and tear associated with moving fully retracted gripper mechanism that is not holding a data cartridge from a fully retracted position to a position at which a cartridge can be retrieved. Another embodiment provides a elevator mechanism for moving the cartridge picker in which the guiding portion of the mechanism is also part of the portion of the mechanism that moves the cartridge picker.

Description:
This application claims benefit of application Ser. No. 60/045,127 filed Apr. 30, 1997. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to data cartridge library systems that are capable of storing a plurality of data cartridges, such as tape cartridges, in a storage array and selectively moving a data cartridge between the array and a drive that transfers data between a host computer and a recording medium located within a data cartridge device. 
     DESCRIPTION OF THE RELATED ART 
     Data cartridge library systems are primarily used to archive data, i.e. store data that is or may be important to the user of a computer system but not immediately needed by the user. To elaborate, the typical library system receives data from a host computer and stores the data in one or more data cartridges. When the host computer requires some of the data that was previously stored in a data cartridge, a request for the data is sent from the host computer to the library system. In response, the library system locates the data cartridge that contains the data being requested and transmits the data to the host computer. 
     The typical data cartridge library system is comprised of a cartridge holder with a plurality of storage slots that are used for storing a plurality of data cartridges, a player/recorder device for reading data that has been stored on the recording medium located within a data cartridge and/or writing data onto the recording medium, and a transport device for moving data cartridges between the cartridge holder and the player/recorder device. To store data in a data cartridge, the library system initially uses the transport device to load a data cartridge into the player/recorder device. Once the data cartridge has been loaded into the player/recorder device, the drive records or writes data from the host computer onto the recording medium located within the data cartridge. After all of the data has been recorded, the transport device removes the data cartridge from the player/recorder device and places the data cartridge in one of the slots of the cartridge holder. Generally, at some later time, the host computer has a need for the data stored on the data cartridge and issues a request for the data to the library system. In response, the library system identifies the slot of the cartridge holder in which the data cartridge on which the needed data is stored, causes the transport device to move the data cartridge from the slot to the player/recorder device. Once the data cartridge is loaded into the player/recorder, the desired data on the recording medium located within the cartridge is read by the player/recorder and passed on to the host computer. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the need for a low-cost data cartridge library system by reducing the number of certain components, especially expensive components, that are needed to perform certain functions within the library. Cost reduction is also achieved with respect to particular library functions by using less expensive, low-precision componentry in combination with componentry that compensates for the low-precision and still provides a reduced cost relative to high-precision componentry. 
     One embodiment of the invention provides a data cartridge library with a picker assembly that utilizes a single electro-mechanical device to accomplish the following functions: (1) grasping a data cartridge located in either a slot of the data cartridge holder or in the drive; (2) retracting a grasped cartridge a sufficient distance from the holder or the drive so that the cartridge can be moved to another location within the library; (3) inserting a grasped cartridge into a slot of the data cartridge holder or into the drive; and (4) releasing a data cartridge that has been inserted into either a slot of the data cartridge holder or the drive. In contrast, most known data cartridge library systems use two electro-mechanical devices to accomplish the noted functions, one to perform the grasping and releasing function and the other to accomplish the retracting and inserting functions. In one embodiment, a single electro-mechanical device is used to move a cam that contacts a cam follower surface on a grasping portion of the picker, i.e. the portion of the picker that is capable of grasping, retracting, inserting and releasing a data cartridge, in a fashion that accomplishes each of the noted functions. In one embodiment, the cam follower surface includes two distinct cam follower surfaces that are contacted by different portions of the cam. Interaction between the cam with the first cam follower surface causes the grasper to be displaced either towards or away from the data cartridge holder or drive to accomplish the retraction and insertion functions, respectively. The grasping and releasing of a data cartridge is attributable to the interaction between the cam and the second cam follower surface. 
     A further embodiment of the invention provides a data cartridge library with a picker assembly that limits the force applied to the picker assembly during operations involving the drive. For instance, during a retraction operation, variations in the operation of one drive from another drive may result in a data cartridge being positioned closer to the picker by one drive than another drive. A data cartridge that is positioned closer to the picker than anticipated will result in the picker contacting the data cartridge sooner than expected and a force being applied by the data cartridge to the picker that could damage the picker and/or the data cartridge. Similarly, during an insertion operation, the drive may be positioned closer to the picker than anticipated and produce a similar problem. The problems can be addressed by either time consuming and perhaps expensive adjustment of the components and/or by employing high precision design techniques. The present invention reduces the need for such approaches by providing a picker with a force limiter or compensator. In one embodiment, the picker assembly employs a spring between the grasping portion of the picker assembly, i.e. the portion of the picker assembly that is used to grasp, retract, insert and release a data cartridge, and a portion of the picker that contributes to moving the grasper towards and away from the drive to compensate for the noted variations in distance of a cartridge during a retraction operation and factors that may result in an undesirable force being applied to the picker during an insertion operation. The spring permits the grasping portion of the picker assembly to move relative to the portion of the picker assembly that is used to move the grasper when a data cartridge is contacted earlier than anticipated. 
     Another embodiment of the invention provides a data cartridge library with a picker assembly that includes a grasper, i.e. the portion of the picker assembly that is used to grasp, retract, insert and release a data cartridge, and a device for moving the grasper during insertion and retraction operations such that the velocity of the grasper varies in a substantially sinusoidal manner. The permits the grasper to be moved at a slower velocity when near the data cartridge holder/drive and a faster velocity further from the cartridge holder/drive. In one embodiment, a circular gear with an attached cam that contacts a cam follower surface associated with the grasper is used in the retraction and insertion operations. The gear provides the sinusoidal aspect of the motion. By moving the grasper in a sinusoidal manner, greater force can be applied to a data cartridge during the point in the insertion and retraction operations involving the drive. To elaborate, some drives require that a data cartridge be forcefully inserted into and/or retracted from the drive. The greater force with the slower speed provide reliable insertion/retraction of a data cartridge into/from such drives. In another embodiment, the sinusoidal movement of the grasper is combined with the force limiter. This permits the appropriate amount of force to be applied to a data cartridge during insertion/retraction of a data cartridge with respect to the drive, while also limiting the applied force to prevent damage to the picker assembly and/or the data cartridge. 
     Another embodiment of the invention provides a data cartridge library with picker assembly that can be controlled during insertion and extraction movement to reduce wear on the componentry and thereby reduce maintenance and/or replacement associated costs. Known picker assemblies operate such that the grasper is always returned to the fully retracted position following the insertion of a data cartridge into either the data cartridge holder or the drive. The fully retracted position is the point at which a transport device that is used to move the picker assembly to various locations within the library can move the picker assembly when the picker assembly is grasping a data cartridge. Insertion of a data cartridge that is being held by the grasper commences by moving the grasper towards either the data cartridge holder or drive and continuing with this movement until the data cartridge can be released. Following insertion of the data cartridge, known data cartridge library systems return the picker assembly to the fully retracted position. Subsequently, to retract a data cartridge from either the data cartridge holder or the drive, the known library systems must move the picker assembly from the fully retracted position to a point at which a data cartridge can be grasped. 
     The present invention avoids the need to move the grasper from the fully retracted position when the grasper is not holding a data cartridge to grasp a data cartridge located in either the data cartridge holder or drive. The present invention provides a picker assembly that can be positioned at a point that is closer to one of the data cartridge holder and drive than the fully retracted position when the grasper is not holding a data cartridge. In one embodiment, the picker assembly provides the ability to position the grasper at substantially the extended position at which the grasper grasps or begins to grasp a data cartridge located within the data cartridge holder or drive. Consequently, a subsequent retraction of a data cartridge from either the data cartridge holder or drive merely requires the picker assembly to grasp the cartridge and then retract the cartridge for subsequent positioning elsewhere in the library, thereby avoiding the need to move the picker from the fully retracted position as a preclude to grasping the data cartridge. In another embodiment, the picker assembly employs a grasper with two members for use in grasping opposite sides of a data cartridge that move linearly towards and away from one another in grasping and releasing a data cartridge, respectively. By moving the members in a linear manner, the picker assembly can positioned closer to the cartridge holder/drive than picker assemblies that grasp a data cartridge using members that rotate about a pivot point. In another embodiment, the two members are each L-shaped to further facilitate the positioning of the picker assembly close to the cartridge holder or drive. 
     Yet another embodiment of the invention provides a data cartridge library system that employs a transport mechanism for moving a picker assembly that makes use a guide mechanism which defines at least part of the space in which the picker assembly is constrained to move to also form part of the mechanism that is used to move the picker assembly within the defined space. In one embodiment, the transport assembly includes two opposing surfaces and a drive device for use in moving the picker assembly. A portion of the drive device is operatively attached to the picker assembly and is used to apply force to the opposing surfaces to move the picker assembly to a desired location within the library. Consequently, the opposing surfaces and the portion of the drive device that is attached to the picker act both to: (1) constrain the space within which the picker assembly can move; and (2) cooperate in moving the picker assembly from one location to another within the library. In this embodiment, the opposing surfaces and portion of the drive device associated with the picker assembly constrain movement of the picker assembly in two orthogonal dimensions but not the third orthogonal dimension. As a consequence, it is possible to displace the picker such that the drive device is no longer contact the opposing surfaces. To address this problem, another embodiment uses a second pair of opposing surfaces to constrain the movement of the picker assembly in the third dimension. 
     In one embodiment, the first opposing surface is comprised of a first pair of racks that are substantially parallel to one another and face one direction. The second opposing surface is comprised of a second pair of racks that are substantially parallel to the first pair of racks but face in the opposite direction. Operatively attached to the picker assembly is a gear system that engages the racks and is used in moving the picker assembly within the space defined by the racks. The gear system operates such that the gears that engage the first pair of racks rotate oppositely from the gears that engage the second pair of racks in moving the picker assembly up and down the racks. The gear system and racks cooperate to constrain the space within which the picker assembly can move in two dimensions. A pair of surface that are substantially perpendicular to the directions that the rack face are used to constrain the movement of the picker assembly in the third dimension. 
     Another embodiment of the invention provides a data cartridge library with a face plate extension to the face plate of the drive that facilitates insertion of a data cartridge into a drive, thereby reducing the need for high precision in the componentry and/or design of the library, especially with respect to the picker assembly, transport device for moving the picker assembly, and the positional relationship of the picker assembly, transport device and drive. Generally, a face plate extension positions a data cartridge that is misaligned for insertion into a drive by using ramps to apply aligning forces to the surfaces of the data cartridge as the cartridge is being moved towards the drive. A data cartridge is generally a box-like structure with a top surface, a bottom surface, first side surface, second side surface, front surface and back surface. The front surface is the surface of the data cartridge that initially enters the drive. Known face plate extensions provide ramps for contacting at least one and potentially all of the top, bottom, first side and second side surfaces of a misaligned data cartridge to align the data cartridge for insertion into the drive. One such face plate extension is essentially a rectangularly shaped funnel in which a first pair of oppositely disposed ramps are positioned to contact the sides of the cartridge, and a second pair of oppositely disposed ramps are positioned to contact the top and bottom of the cartridge. 
     The present invention provides a face plate extension that has recognized that certain types of data cartridges have a discontinuity that permits an aligning structure to be realized in which a misaligned data cartridge can be aligned for insertion into the drive by applying an aligning force to one and at most three of the top, bottom, first side and second side surfaces. In one embodiment, the face plate extension provides a ramp structure that applies the necessary aligning forces to one and at most two of the surfaces of a misaligned cartridge. The face plate extension can be used, for example, with a TRAVAN tape cartridge. A TRAVAN tape cartridge has a bottom surface and a top surface with a step discontinuity. The face plate extension provides a first ramp structure for contacting either or both of the top and bottom surface to correct one possible type of misalignment of the data cartridge. A second ramp structure makes use of the discontinuity on the top surface of the cartridge to correct a second type of misalignment. In the case of a TRAVAN tape cartridge, the step in the top surface of the cartridge is utilized to correct a second type of misalignment. In one embodiment, the first ramp structure is located closer to the picker than the second ramp structure. Consequently, the face plate extension operates to sequentially align a misaligned data cartridge, i.e. a first type of misalignment is corrected followed by the correction of a second type of misalignment. 
     The present invention also provides a removable data cartridge holder for use in a data cartridge library that includes an open-sided box-like structure for holding a plurality of data cartridges, a dust cover and an coupling apparatus for attaching the dust cover to the data cartridge library when box-like structure is in use, i.e. mounted in the library with the opening of the box-like cover exposed so that data cartridges can be moved in and out of the box-like structure. When the box-like structure is dismounted from the library, the dust cover can be placed over the opening to protect any data cartridges contained in the box-like structure. In one embodiment, the coupling apparatus operates to attach the dust cover to the box-like structure. In another embodiment, the dust cover possesses a U-shaped cross- section and the coupling apparatus serves to connect the dust cover to the box-like structure such that the box-like structure is nested inside the U-shaped dust cover. A further embodiment of the holder that provides a U-shaped dust cover and the noted nesting feature includes a connecting device for adhering the box-like structure and attached dust cover to a surface within the library. In one embodiment, the connecting device also provides a reference surface that facilitates the desired orientation of the box-like structure within the library housing. 
     The present invention further provides a data cartridge holder that includes a cantilevered retaining member for holding a data cartridge in the holder, thereby inhibiting the accidental displacement or removal of the data cartridge from the holder. The data cartridge holder is a box-like structure with an open side that permits data cartridges to be inserted/removed into/from the holder. The cantilevered retaining member has a fixed end, which is attached to the box-like structure, and a free or floating end that is located further from the opening than the fixed and, in response to the insertion or extraction of a data cartridge, is displaced. To elaborate, during insertion of a data cartridge, the free end of the member is initially displaced to permit the cartridge to be fully inserted into the holder. However, upon complete insertion the free end of member returns to its unflexed or initial position to engage a notch or similar structure associated with the data cartridge and thereby inhibit accidental removal of the cartridge from the holder. In one embodiment, the cantilevered retaining member has a dog-leg shape with a first portion that is located between the point at which the member is attached to the housing and an intermediate point on the member. The portion of the member is disposed at an acute angle to the side wall of the holder and operates as a ramp to aid in positioning a data cartridge during insertion into the holder. The second portion of the member operatively engages the notch or other feature on the cartridge to hold the cartridge in place. In one embodiment, the second portion of the member is substantially parallel to the side wall of the holder. In yet a further embodiment, a second cantilevered retain member is disposed in the holder to engage another notch or other feature associated with a data cartridge. 
     The present invention also provides a data cartridge holder that includes an orientation device that inhibits the insertion of improperly oriented data cartridges of the type that include a door which can be rotated about a pivot point to expose the recording media within the cartridge. When a data cartridge of this type is improperly oriented for insertion into the holder, the orient device operates to open door of the cartridge. The opened door subsequently engages a portion of the cartridge holder such that further insertion of the data cartridge is inhibited. It is desirable to insert a data cartridge into the holder in the same orientation as the cartridges are inserted into the drive, i.e. front face first, to simplify the design and operation of the picker assembly. In contrast, if a cartridge is inserted into the data cartridge holder with a different orientation than when the cartridge is inserted into the drive, the picker assembly must provide the ability to reorient the data cartridge between the time the cartridge is removed from the holder and the time the data cartridge is inserted into the drive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exterior perspective view of a preferred embodiment of the tape library system; 
     FIG. 2 is a cutaway, perspective view of the embodiment of the tape library system shown in FIG. 1; 
     FIGS. 3A-3C are perspective views of a Travan tape cartridge that is employed in the tape library system shown in FIG. 1; 
     FIG. 4 is a perspective view of the picker assembly; 
     FIG. 5 is an exploded view of the picker assembly shown in FIG. 4; 
     FIG. 6 illustrates the portions of the elevator assembly that are associated with the picker assembly; 
     FIG. 7 is a free body diagram of the gripper assembly, gripper stepper motor assembly and gripper crank assembly; 
     FIG. 8 illustrates the gripper stepper motor assembly; 
     FIG. 9 illustrates the gripper crank assembly; 
     FIG. 10 illustrates the gripper assembly; 
     FIG. 11 is an exploded view of the gripper assembly; 
     FIG. 12 is a matrix diagram illustrating the relationship of various components in the picker assembly as the gripper crank arm is rotated through its range of motion; 
     FIG. 13 illustrates the tape drive faceplate extension; 
     FIG. 14 illustrates a number of the retaining cells in the tape cartridge holder; 
     FIG. 15 illustrates how the cartridge orientation control rib in one of the retaining cells of the tape cartridge holder prevents a tape cartridge from being inserted into the holder with the incorrect orientation; 
     FIGS. A 1 -A 3  illustrate the face plate extension; 
     FIGS. B 1 -B 5  illustrate the data cartridge holder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIGS. 1 and 2, the primary components associated with the preferred embodiment of the tape library system, hereinafter referred to as library  50 , are described. The library  50  includes a cabinet  52  for housing components of the library and a door  54  that permits user access into the interior of the cabinet  52 . Within the cabinet are located a removable, tape cartridge holder  56  for storing a plurality of tape cartridges, a Travan tape drive  58  that is located behind a drive faceplate extension  60 , and a transport assembly for moving tape cartridges between the holder  56  and the tape drive  58 . The transport assembly includes an elevator assembly  61  that employs a pair of rack gear pairs  64 A,  64 B to move tape cartridges that are held by a picker assembly  62  between the holder  56  and the tape drive  58 . The tape drive  58  is capable of transmitting/receiving data to/from a host computer via a data communication interface (not shown) that is located on the back of the cabinet. While the library  50  is shown as only having one tape drive, it should be appreciated that a slot  66  is available for accommodating another tape drive and face plate assembly. The library  50  can be positioned either vertically, as shown, or horizontally. 
     FIGS. 3A-3C illustrate a Travan tape cartridge  70  suitable for use with the Travan tape drive  58 . The Travan tape cartridge  70  is characterized by a pair of cartridge gripping notches  72 A,  72 B that will be utilized by the picker assembly in moving the cartridge within the library  50 . A pair of cartridge retaining notches  74 A,  74 B are utilized by the Travan tape drive  58  to retain and position the cartridge within the drive. A pair of tapered side surfaces  76 A,  76 B are used to facilitate insertion of the cartridge into a cartridge holder. Also characteristic of the cartridge  70  is a pair of vertical steps  78 A,  78 B in the top surface of the cartridge. The cartridge also includes an access door  80  that protects the tape when closed and exposes the tape for read/write operations when open. As shown in FIG. 3C, the access door  80  pivots to expose the tape when an access door following surface  82  is contacted by a camming surface within the drive. It should be appreciated that the library  50  can be adapted to accommodate data cartridges other than the Travan tape cartridge  70 . The tape cartridge  70  generally has a top side  228 A, bottom side  228 B, first lateral side  228 C, second lateral side  228 D, front side  228 E and back side  228 F. 
     With reference to FIGS. 4 and 5, the picker assembly  62  generally includes a housing that includes a picker housing base  86 , picker top plate  88  and picker bottom plate  90 . Within or attached to the picker housing are components that are used to accomplish one of the two following functions: (1) moving the picker assembly up and down along the rack gear pairs  64 A,  64 B, i.e. components of the elevator assembly  61 ; and (2) extracting/inserting a tape cartridge from/into the cartridge holder  56  or the tape drive  58 , as well as grasping and releasing tape cartridges. 
     With reference to FIG.  6  and continuing reference to FIG. 5, the components associated with moving the picker assembly  62  up and down along the rack gear pairs  64 A,  64 B (which each provide two opposing surfaces) is described. Generally, an elevator stepper motor  94  drives a first elevator gear train  96 A and a second elevator gear train  96 B that are connected to one another by an elevator cross shaft  98  to move the picker assembly  62  up and down along the rack gear pairs  64 A,  64 B. The first and second gear trains  96 A,  96 B respectively interface with the rack gear pairs  64 A,  64 B such that when the elevator stepper motor is activated the picker assembly  62  moves up or down the racks. The position of the picker assembly  62  is known by counting the “steps” needed by the elevator stepper motor  94  relative to a known reference point to position the picker assembly  62  in front of the slots of the tape cartridge holder  56  and the tape drive  58 . An elevator motion detector assembly  100  is used to determine whether or not the elevator stepper motor  94  is moving appropriately in relation to the step count. Failure of the elevator stepper motor  94  to move in response to step commands indicates that the picker assembly  62  has reached an end of its range of motion or has jammed. 
     With respect to movement of picker assembly, it should be noted that the racks gear pairs  64 A,  64 B guide the picker assembly  62 , as well as contribute to the moving of the picker assembly  62  by interacting with the first and second gear trains  96 A,  96 B. With respect to the guiding function, the rack portions of the rack gear pairs  64 A,  64 B cooperate with the first and second gear trains  96 A,  96 B to constrain the movement in two dimensions. Namely, in the illustrated embodiment, the front-to-back dimension and the up-down dimension. To constrain lateral movement of the picker assembly  62 , the rack gear pairs  64 A,  64 B respectively provide surfaces  230 A,  230 B that prevent the picker assembly  62  from being laterally displaced to the point where the first and second gear trains  96 A,  96 B become disengaged from the rack gear pairs  64 A,  64 B. 
     With reference to FIGS. 7-10 and continuing reference to FIG. 5, the components associated with extracting/inserting a tape cartridge from/to the cartridge holder  56  or tape drive  58  and gripping/releasing a tape cartridge are described. Generally, a gripper stepper motor  104  causes a gripper crank assembly  106  that is journaled to the picker bottom plate  90  to rotate. Rotation of the gripper crank assembly  106  causes, in turn, a gripper assembly  108  to either (1) move towards/away from the cartridge holder  56  or tape drive  58  for extraction/insertion operations; or (2) grasp/release a tape cartridge. The position of the gripper assembly  108  is known by counting the “steps” through which the gripper stepper motor  104  has moved relative to a known reference point. A crank position sensor  110  which detects the presence/absence of a crank position edge  112  within the sensor&#39;s field of view is used to determine the state of the gripper during power up. A gripper motion detector  1   14  indicates whether or not the gripper stepper motor  104  is moving appropriately in relation to the step count. Failure of the gripper stepper motor  104  to move in response to step commands indicates that the gripper crank gear  118  has reached an end of its range of motion or has jammed. 
     It should be appreciated that all of the sensor devices previously and hereafter mentioned interface to a computer with in the library that is comprised of a processor, an appropriately programmed memory and one or more output ports for controlling the stepper motors and like devices. 
     The gripper crank assembly  106  is comprised of a gripper crank gear  118  and a slide pin  120  that interfaces with the gripper assembly  108 . The slide pin  120  includes a pin  122  that interacts with a surface of the gripper assembly  108  so as to primarily affect the distance of the gripper assembly  108  from the cartridge holder  56  or tape drive  58 . Also part of the slide pin is cam hold-open  124  arm that primarily interacts with another portion of the gripper assembly  108  to actuate the portion the gripper assembly  108  that is responsible for grasping tape cartridges. The slide pin  120  is biased in the position illustrated in FIG. 9 by a pair of slide pin springs  126 A,  126 B. The slide pin springs  126 A,  126 B do, however, permit the slide pin  120  to move towards the center of the gripper crank gear  118  if a tape cartridge is encountered earlier than expected. This allows the fixed and predetermined path of motion of the gripper assembly  108  to adapt to variations within the library  50  and variations from library to library. The force received by the gripper assembly  108  from the tape cartridge is, in turn, transmitted to the slider pin  120  which accommodates this force by sliding back towards the center of the gripper crank gear  118 . Once the force on the gripper assembly  108  is removed, the slide pin springs  126 A,  126 B operate to return the slide pin  120  to its normal position. 
     With reference to FIGS. 10 and 11, the gripper assembly  108  is comprised of a pusher  130  and first and second gripper jaws  132 A,  132 B, which are slidably mounted on the pusher  130 . The gripper assembly  108  also includes a gripper jaw cam  134  for use in separating first and second jaws  132 A,  132 B from one another so that a tape cartridge can be grasped. The gripper jaw cam  134  operates to open the first and second gripper jaws  132 A,  132 B in opposition to first and second gripper jaw springs  136 A,  136 B. The one end of each of the first and second gripper jaw springs  136 A,  136 B is connected to a gripper jaw and the other end of each of the springs is connected to a gripper standard  138 . The gripper standard  138 , which is a portion of the pusher  130 , also serves as a mount of the gripper jaw cam  134 . 
     Also part of the pusher  130  is a crank pin slot  140  that defines the surface on pusher  130  which engages the pin  122  of the gripper crank assembly  106 . 
     With continuing reference to FIG. 11, the gripper jaw cam  134  includes a hold-open arm  142  that engages the cam hold-open arm  124  of the gripper crank assembly  106 . During a particular point in the rotation of the gripper crank gear  118 , the cam hold-open arm  124  engages the hold-open arm  142  and upon further rotation causes the hold-open arm  142  to remain rotated and necessarily the rest of the gripper jaw cam  134  to remain rotated. 
     With continuing reference to FIG. 11, the gripper jaw cam  134  includes an upper cam surface  144  that contacts the ends of the first and second gripper jaws  132 A,  132 B and upon rotation controls the opening and closing of the first and second gripper jaws  132 A,  132 B in opposition to the first and second gripper jaw springs  136 A,  136 B. Consequently, when the cam hold-open arm  124  causes the hold-open arm  142  to rotate, it also causes the upper cam surface  144  to rotate and thereby control the opening and closing of the first and second gripper jaws  132 A,  132 B. 
     With reference to FIG. 12, the operation of the picker assembly  62  in grasping and extracting/retracting a tape cartridge from either the cartridge holder  56  or the tape drive  58  to a point at which the elevator assembly  61  can move the tape cartridge to another location in the library is described. Initially, the picker assembly  62  must be positioned in front of a cell in the cartridge holder  56  or the tape drive  58 . Such positioning is accomplished with the orientation of elements of the picker assembly  62  illustrated in the sub-drawings  1  A - 4 A of FIG.  12 . (A point of reference for all of the sub-drawings in FIG. 12 is an axis of rotation  166  for the gripper crank gear  118 ). Notably, with this orientation of the picker assembly elements, the picker assembly  62  can be positioned by the elevator assembly  61  in front of any cell in the cartridge holder  56  or in front of the tape drive  58  with the first and second gripper jaws  136 A,  136 B positioned very close to the gripper notches  72 A,  72 B of the tape cartridge. As a consequence, the picker assembly  62  avoids the wear and tear that is associated with picker mechanisms where a full extension of the picker mechanism is required after the picker mechanism has been appropriately positioned. To elaborate, when the picker assembly  62  is not grasping a data cartridge (for example, after the insertion of a data cartridge into the holder  56  or the drive  58 ), the picker assembly  62  and particularly the gripper assembly  108  is capable of being positioned close to the holder  56  or the drive  58  rather than being positioned at the fully retracted position. The fully retracted position is the point at which the elevator assembly  61  can move the picker assembly  62  to desired locations within the library  50  when the gripper assembly  108  is holding a data cartridge. By providing the ability to position the gripper assembly  108  close to the holder  56  or drive  58  when the gripper assembly  108  is not holding a tape cartridge, the wear and tear associated with moving the gripper assembly  108  to retract a data cartridge is avoided, thereby reducing wear and tear on the system. Moreover, the speed of operation is improved. 
     In sub-drawing  1 A, the gripper crank gear  118  has been fully rotated in the clockwise direction. With the gripper crank gear  118  in this position, the pin  122  is positioned at the right end of the crank pin slot  140  ( 2 A); the cam hold-open arm  124  is contacting the hold-open arm  142  ( 3 A); and the upper cam surface  144  is bearing against the ends of the first and second gripper jaws  132 A,  132 B (in opposition to the first and second gripper jaw springs  136 A,  136 B) such that the jaws are both laterally spaced and somewhat retracted from the gripper notches  72 A,  72 B of the cartridge ( 4 A). Again, with this orientation of picker assembly components, the picker assembly  62  can be positioned anywhere within the range of motion defined for the elevator components of the library  50 . 
     In sub-drawing  11 B, the gripper crank gear  118  has been rotated in a counter-clockwise direction so as to position the first and second gripper jaws  132 A,  132 B for gripping the tape cartridge. With the gripper crank gear  118  in this position, the pin  122  has now moved down and left in the crank pin slot  140  such that it is positioned at the end of a straight portion of the slot and at the beginning of an arcuate portion of the slot ( 2 B). Further, the cam hold-open arm  124  is still in contact with the hold-open arm  142  ( 3 B). As a consequence, the upper cam surface  144  is still contacting the ends of the first and second gripper jaws  132 A,  132 B such that the jaws are laterally spaced from the gripper notches  72 A,  72 B of the tape cartridge ( 4 B). However, due to the interaction between the pin  122  with the crank pin slot  140 , the first and second gripper jaws  132 A,  132 B are now positioned for grasping the tape cartridge ( 4 B). 
     In sub-drawing  1 C, the gripper crank gear  118  has been further rotated in the counter-clockwise direction so as to cause the first and second gripper jaws  132 A,  132 B to grasp the tape cartridge. With the gripper crank gear  118  in this position, it should be appreciated that the pin  122  has now moved over the arcuate section of the crank pin slot  140  ( 2 C). The arcuate section of the crank pin slot  140  has a radius measured from the axis  166  that is substantially equal to the radius from the axis  166  to the pin  122 . As a consequence, when the pin  122  is moved along this section of the crank pin slot  140 , the position of the pusher  130  is substantially unaffected, thereby maintaining the position of the first and second gripper jaws  132 A,  132 B SO that the tape cartridge can be grasped. During the further counter clockwise rotation of the gripper crank gear  118 , the cam hold-open arm  124  has begun to disengage from the hold-open arm  142 , thereby permitting the hold-open arm  142  to rotate in a clockwise direction ( 3 C). Due to the rotation of the hold-open arm  142 , the upper cam surface  144  has also rotated in a clockwise direction, thereby permitting the first and second gripper jaw springs  136 A,  136 B to pull the first and second gripper jaws  132 A,  132 B together and thereby grasp the tape cartridge ( 4 C). It should also be appreciated that the cam hold-open arm  124  contacts a safety arm  168  that forces the hold-open arm  142  to rotate if, for some reason, the first and second gripper jaw springs  136 A,  136 B are unable to force the required rotation of the hold-open arm  142  ( 3 C). 
     In sub-drawing  1 D, the gripper crank gear  118  has been further rotated in the counter- clockwise direction so as to begin to retract the pusher and the tape cartridge back into the picker housing. During the further rotation of the gripper crank gear  118 , the pin  122  has moved from the end of the arcuate section of the crank pin slot  140  to the left end of the crank pin slot  140  ( 2 D); the cam hold-open arm has entirely disengaged from the hold-open arm  142  ( 3 D); and the pusher  130  has begun to retract into the picker housing ( 4 D). 
     In sub-drawing  1 E, the gripper crank gear  118  has been further rotated in the counter-clockwise direction so as to fully retract the pusher and the tape cartridge back into the picker housing. During the further rotation of the gripper crank gear  118 , the pin  122  has moved from the left end of the crank pin slot  140  back toward the arcuate section of the slot ( 2 E); and the pusher  130  and tape cartridge have been entirely retracted into the picker housing ( 4 E). At this point, the picker assembly  62  can be moved to a new location (a cell of the cartridge holder  56  or the tape drive  58 ) and the tape cartridge inserted and released by reversing the noted sequence of operations. 
     It should also be appreciated at this point that, other than the gripper stepper motor  104 , no other electro-mechanical device is utilized in the gripping, retracting, inserting and releasing operations. 
     It should also be appreciated that the circular movement of the gripper crank gear  118  and the interaction of the pin  122  with the pusher  130 , which is constrained to move linearly by a rail structure  212  (FIG.  5 ), the gripper assembly  108  moves in a sinusoidal manner. More specifically, the velocity of the gripper assembly  108  during insertion and retraction is described by a substantially sinusoidal curve, i.e. a plot of the velocity of the gripper assembly during insertion and retraction substantially follows a sinusoidal curve. Moreover, the relationship of the noted elements has been chosen so that when the gripper assembly  108  is near either the holder  56  or drive  58 , the velocity of the gripper assembly  108  is at or near a low velocity point on a sinusoidal velocity curve. Relatedly, when the gripper assembly  108  is further from the holder  56  or drive  58 , the velocity of the gripper assembly is at a higher velocity point on the sinusoidal velocity curve. another aspect of this sinusoidal operation is that the force applied by the gripper assembly  108  to a data cartridge is greater near the holder  56  or drive  58  and lower further from the holder  56  or drive  58 . This is particularly important when a drive is used that requires a forced insertion/extraction of a data cartridge. In such cases, the operation of the slide pin  120  as a safety is further appreciated. 
     With reference to FIG. 13, the drive faceplate extension  60  is comprised of an opening  148  with a width  150  that is only slightly larger than the width of the Travan tape cartridge illustrated in FIGS. 3A-3C. By keeping the drive faceplate extension  60  narrow, it is possible to maintain the overall width of the library at approximately 8.6″, thereby facilitating rack mounting of the library  50  in a greater number of racks. The drive faceplate extension  60  includes first and second pairs of vertical guides  152 A,  152 B for vertically positioning the Travan tape cartridge  70  for the tape drive  58 . First and second step guide ramps  154 A,  154 B for engaging the first and second vertical steps  78 A,  78 B of the Travan cartridge  70  and thereby horizontally positioning the cartridge for the tape drive  58 . In operation, the first and second pairs of vertical guides  152 A,  152 B initially engage the cartridge  70  as it is being inserted into the tape drive  58  by the picker assembly  62  and vertically position the cartridge. As the cartridge  70  is inserted further into the tape drive  58  by the picker assembly  62 , the first and second step guide ramps  154 A,  154 B engage the first and second vertical steps  78 A,  78 B on cartridge  70  and horizontally position the cartridge for the tape drive  58 . 
     With reference to FIGS. A 1 -A 2  and continuing reference to FIG. 13, the face plate extension  60  includes a recess  216  for receiving the face plate  218  of the drive (FIG. A 3 ). Located within the recess  216  are a plurality of crush pins  220  that facilitate a tight fit of the face plate extension  60  over the face plate  218  of the drive  58  and at the same time avoiding the need to manufacture the recess  216  to a high tolerance. The face plate extension  60  also includes clasps  222 A- 222 D that are used to operatively attach the face plate extension  60  to the drive  58 . More specifically, the clasps engage notches that are associated with a frame  224  that is, in turn, attached to the drive  58 . The face plate extension  60  also includes an orientation device that is used to position the extension  60  as well as the drive  58  within the library while allowing for variations. The orientation device includes a pair of holes  226 A,  226 B that engage a pair of pins (one of which is illustrated in FIG. A 2 ) associated with the mounting surface  194  within the library. One of the holes is oblong to compensate for manufacturing variations while at the same time cooperating with the other hole, which is round, to fix the position of the drive  58  and extension  60  in two dimensions. 
     With reference to FIGS. B 1 -B 5 , the tape cartridge holder  56  is comprised of an open-sided box-like structure  172  that is capable of holding a plurality of tape cartridges and a dust cover  174  for covering the open side of the tape cartridge holder  56  when the holder has, for example, been removed from the cabinet  52 . The cartridge holder  56  includes a coupling structure  176  for attaching the dust cover  174  to the open-sided box-like structure. The coupling structure  176  operates to attach the dust cover  174  to the box-like structure both when the holder is not in use and when the holder  56  is in use, i.e. mounted within the cabinet  52 . The coupling structure  176  includes a pair of arrow-shaped structures  178 A,  178 B that are attached to the ends of the box-like structure and a pair of slots  180 A,  180 B that are associated with the dust cover  174 . In operation, the pair of arrow-shaped structures  178 A,  178 B pass through the pair slots  180 A,  180 B to attach the dust cover  174  to the box-like structure  172 . 
     With reference to FIG. B 3 , the depth of the box-like structure  172  leaves the gripping notches  72 A,  72 B of the cartridge  70  exposed to facilitate grasping by the picker assembly. 
     As a consequence, the dust cover  174  has a U-shaped cross-section. Further, the dust cover  174  is of slightly greater length and width than the box-like structure. These greater dimensions permit the dust cover  174  to “nest” the box-like structure  172  when the box-like structure is mounted within the cabinet  52 , as shown in FIG. B 4 . To facilitate this nesting capability the pair of arrow-shaped structures  178 A,  178  B are located on the side of the box-like structure at a point that is approximately mid-way between the bottom of the box-like structure  172  and the upper-most surface of a data cartridge that is housed in the holder  56 . 
     With continuing reference to FIGS. B 1 -B 5 , the removable tape cartridge holder  56  also includes a connector structure for facilitating attachment of the holder  56  within the cabinet  52  of the library  50 . The connector structure includes a pair of hooks  184 A,  184 B that cooperate with a pair of latches  186 A,  186 B (FIG. 2) located adjacent to a mounting hole  188  (FIG. 2) that receives the box-like structure  172  and any attached dust cover  174 . The pair of hooks  184 A,  184 B are attached to the side of the box-like structure  172  but spaced sufficiently away from the side of box-like structure  172  so as not to interfere with the nesting of the box-like structure  172  within the dust cover  174 . 
     The connector structure also provides a reference structure that facilitates proper orientation of the holder when mounted in the cabinet  54 . With continuing reference to FIGS. B 1 -B 5 , the flat undersides of mounting bosses  192 A- 192 D define a reference plane that contacts the flat mounting surface  194  (FIG. 2) adjacent to the hole  188  that receives the holder  56  within the cabinet  52  when the holder  56  is properly oriented in one dimension. Further, bosses  192 C,  192 D respectively include holes  196 A,  196 B that receive mounting pins  198 A,  198 B (FIG. 2) that are associated with the mounting surface  194  to properly orient the holder in the other two dimensions. Because the holder is symmetrical about its longitudinal axis, the mounting pins  198 A,  198 B and the holes  196 A,  196 B also insure that the holder  56  is oriented so that cartridges are stored in the holder  56  with an orientation that facilitates the transfer of cartridges between the holder  56  and the drive  58 . 
     With reference to FIGS. 14 and 15, the tape cartridge holder  56  is comprised of a number of cells  158 . Associated with each cell of the tape cartridge holder  56  are structures for retaining the Travan cartridge  70  and for preventing the Travan cartridge  70  from being inserted with the incorrect orientation for the picker assembly  62  and the tape drive  58 . If the cartridge holder  56  permitted a tape cartridge to be inserted with the incorrect orientation, operation of the picker assembly  62  and tape drive  58  could be adversely affected. 
     For retaining a tape cartridge, each cell has a first and second flexible cartridge retention clips  160 A,  160 B that respectively engage the retaining notches  74 A,  74 B of the Travan cartridge  70 . The picker assembly  62  is capable of applying enough force to overcome the bias of the first and second flexible cartridge retention clips  160 A,  160 B for purposes of inserting a cartridge into and removing a cartridge from the cartridge holder  56 . The retaining clips  160 A,  160 B respectively have fixed ends  202 A,  202 B that are attached to the interior side of the box-like structure  172  and free ends  204 A,  204 B that are located closer to the bottom of the box-like structure  172  than the fixed ends and are free to flex in response to the insertion/retraction of a data cartridge. The free ends  204 A,  204 B respectively include detents  206 A,  206 B that engage the retaining notches  74 A,  74 B of the data cartridge. The detents  206 A,  206 B are sloped to facilitate the engagement of the detents  206 A,  206 B to the notches  74 A,  74 B and the subsequent disengagement therefrom. The retaining clips  160 A,  160 B are dog-leg shaped with upper portions  207 A,  207 B and lower portions  208 A,  208 B. The upper portions  207 A,  207 B are disposed at an acute angle. to the side of the holder  56  to facilitate insertion of a tape cartridge into the holder. In addition, the upper portions  207 A,  207 B provide contact surfaces during the insertion of a data cartridge that facilitate the displacement of the lower portions  208 A,  208 B and thereby facilitate the insertion of the data cartridge. 
     For preventing a tape cartridge from being inserted with the incorrect orientation, each cell includes a cartridge orientation control rib  162 . With reference to FIG. 15, if a tape cartridge is inserted with one type of incorrect orientation, the control rib  162  operates to open the access door  80  of the tape cartridge  70  and prevent insertion of the cartridge into the cell. To elaborate, when the access door  80  is opened, a portion of the door engages the box-like structure  172  to inhibit further insertion of the cartridge into the cell. Generally, this improper insertion of a tape cartridge  70  into the cartridge holder  56  occurs when a person rather than the picker is loading tape cartridges into the holder prior to placing the holder in the cabinet  52 . While the rib  162  is illustrated in FIG. 15 as preventing insertion when the cartridge is inserted front side  228 E first (which is correct) but backwards, the rib  162  also prevents insertion when the back side  228 F is inserted first. In this case, the rib  162  contacts the cartridge housing in a manner that interferes with the insertion. 
     The foregoing description of the invention has been presented for the purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge in the relevant art are within the scope of the present invention. The preferred embodiment described hereinabove is further intended to explain the best mode known of practicing the invention and to enable others skilled in the art to utilize the invention in various embodiments and with the various modifications required by their particular applications or uses of the invention. It is intended that the appended claims be construed to include alternate embodiments to the extend permitted by the prior art.