Abstract:
A robotic library design for a mechanism that picks and places storage cartridges having a robotic shuttle assembly that moves parallel to the storage cartridges, a moveable stage that moves perpendicular to the storage cartridges, and a pair of gripping finger to retain, extract, and deposit the storage cartridges within the library subsystem. The pair of gripping fingers, initially biased in a closed position, are cammed open by the edges of the storage cartridge upon the moveable stage&#39;s approach and close upon engagement with the storage cartridge&#39;s notched recesses. The storage cartridge is moved within the library subsystem and is delivered to its destination when a solenoid activates a mechanical trigger that releases the pair of gripping fingers. The moveable stage completes the storage cartridge&#39;s delivery and resets for its next instruction.

Description:
FIELD OF THE INVENTION 
     The present invention relates to storage library subsystems as commonly used in the computer data storage arts. Specifically, the present invention relates to the management of storage cartridges by the robotic retrieval and delivery of the cartridges from one location to another within a storage library subsystem. More specifically, the present invention relates to a robotic shuttle&#39;s gripping fingers and the associated method by which those fingers grip and release storage cartridges within a storage library subsystem. 
     PROBLEM 
     Storage library subsystems provide large capacity secondary storage to modem computing environments. Such storage library subsystems typically employ robotic control mechanisms to physically manage storage cartridges used by host computer&#39;s system. 
     A plurality of storage cartridges are stored within the storage library subsystem either in a linear, a rectangular or a cylindrical array. Each storage cartridge is in a particular slot in the library subsystem. Each slot is identifiable by its physical position within the library subsystem. 
     The subsystem maintains inventory information to associate a particular cartridge with a particular slot in the subsystem. 
     Responsive to a host computer system request, an appropriate storage cartridge is physically retrieved from its associated slot in the library, moved to an appropriate read/write device for processing, and inserted into that device. Conversely, when the use of the storage cartridge is complete, the cartridge is retrieved by the robotic mechanism from the read/write device, moved adjacent its associated slot according to the inventory maintained by the subsystem, and inserted into the storage slot of the library ready for future use in response to another host computer system request. 
     Over time, computing environments have tended to become smaller and less centralized. Prior storage library subsystems were often costly, complex and bulky. While arguably appropriate for centralized large data processing environments, prior storage library subsystems were inappropriate in the more modem decentralized workgroup environments. In these environments, reduced costs, complexity and size of storage library subsystems are essential features. 
     Related art discloses several data storage options with associated pick and place mechanisms that offer cost, complexity and size reductions. These pick and place mechanisms are notable for their design of a gripping means that is convertible between a retrieval mode, in which the gripping means is capable of engaging and carrying a storage cartridge, and a return mode, in which the gripping means releases the storage cartridge so that the cartridge may be returned to a drive or its storage position. 
     One presently available cartridge retrieval mechanism, described in U.S. Pat. No. 5,450,391, utilizes a carriage that is slidable along a longitudinal base with attached gripping arms that are pivotally mounted on the carriage. These gripping arms are configured such that when they are advanced against a storage cartridge, they will deflect laterally around the corners of the cartridge until they engage the recessed notches of the cartridge. The &#39;391 patent teaches that two setting components control whether the gripping arms are in the engaged position or the relaxed position. These setting controls are likewise controlled by camming members that exist along the extension and retraction path of the slidable carriage and that trigger the setting components by their physical interaction with the carriage. 
     Similarly, U.S. Pat. No. 5,691,859 also utilizes a slidable carriage with pivotally mounted gripper arms useful for picking and placing storage cartridges within a library subsystem. The &#39;859 patent is similar in that two camming members and a gripper-tripping projection located on the magnetic drive&#39;s bezel independent of the slidable carriage dictate the positioning of the gripper arms. Unlike the &#39;391 patent, the &#39;859 patent teaches a method of cartridge picking that allows the arms to avoid contact with the storage cartridge until the moment of actual engagement in which the gripper arms lock into the recessed notches of the cartridge. 
     In both patents, and in other related art disclosures, the gripper arms are naturally biased in an open position. Setting the gripper arms for both the retrieval and the return modes is accomplished by mechanical actuators that exist independent of the slidable stage/gripper arm assembly. What is needed is an inexpensive, simplified, and integrated gripper arm/transport assembly that does not require an independent triggering mechanism to set the gripper arms into position for either cartridge extraction or placement. Especially desirable would be an integrated gripper actuator mechanism that improves upon the related art in picking and placing storage cartridges from a multi-position storage magazine to a tape drive with minimal maintenance and with minimal operator interaction. 
     SOLUTION 
     The present invention solves the above problems and thereby advances the art by providing a simpler apparatus and corresponding method to retrieve and deliver storage cartridges within a storage library subsystem. Although a tape storage cartridge system is detailed below as the preferred embodiment of the invention, one skilled in the art would recognize that this invention is useful in other storage cartridge systems. The present invention discloses a new robotic shuttle that will pick a tape storage cartridge from a multiple-position storage magazine and place it in a tape drive. In an exemplary embodiment of the present invention, the means to activate and de-activate the gripper arms assembly are located entirely within the motorized stage. The gripper arms are geometrically cammed open by the storage cartridge and fall into the storage cartridge&#39;s notched recesses in combination with the gripper arms&#39; bias springs. The gripper arms are forced open in the cartridge placement phase when an integrated solenoid is activated, forcing a mechanical trigger to trip the lower gripper finger in a camming motion that releases the cartridge. The gripper arms&#39; engaging position is reset when the solenoid deactivates upon the withdrawal of the motorized stage from the placement phase. The simplicity of the library system and the linear drive train upon which the motorized stage travels ensures low initial cost, and ease of maintenance and of use, which addresses the needs of the end user. Previous related art feature more complex apparatus and therefore decrease overall reliability through downtime for repair or adjustment that is too costly to justify. 
     The tape storage cartridge picking and placing apparatus and its associated method are the essential inventions. The robotic shuttle incorporates upper and lower spring-loaded, gripping fingers that are inter-connected by way of a pivot link, attached to the lower gripping finger, and a connecting link, attached to the upper gripping finger, that are themselves inter-connected by a pin. The gripping fingers are mounted to a motorized stage (the Z-stage) that extends from and retracts into the housing of the robotic shuttle (the X-plate) along the Z-axis. The Z-stage is affixed to the X-plate which, in turn, employs a mounted threaded nut to its top panel, that is bi-directionally driven on a worm screw along the X-axis by a motor enabling the robotic shuttle to move cartridges from storage locations to the tape drive and back. 
     In order to pick a tape storage cartridge, the Z-stage extends distally along the positive Z-axis from the X-plate toward the cartridge magazine. As the spring-loaded, gripping fingers contact the stored cartridge, the cartridge&#39;s corners deflect the gripping fingers around the outside of the cartridge in a camming motion against the bias of the springs. The gripping fingers travel around the cartridge&#39;s corners and over the cartridge&#39;s edges until they reach the standard recessed notches on the top and bottom of the cartridge. Due to the complimentary geometry of both the recessed notches and the spring-loaded, gripping fingers, the gripping fingers snap into the cartridge&#39;s recessed notches and securely grasp the cartridge for movement in the opposite direction along the negative Z-axis. When the cartridge is fully extracted from the multipleposition storage magazine and the Z-stage fully retracted into the X-plate, the picked cartridge is ready for a longitudinal move along the X-axis toward the tape drive. 
     To place a tape storage cartridge either in the tape drive or into the multiple-position storage magazine, a push-type solenoid is energized when the Z-stage once again begins to extend along the positive Z-axis. The solenoid is connected to a mechanical trigger, which in this preferred embodiment of the invention, is comprised of a catch-link with a catch-pin affixed to its distal end. The catch link, catch-pin combination is at rest in a down position, but rotates upward into the path of the lower gripping finger when the catch-link is activated by the solenoid. As the Z-stage approaches the storage magazine, and after the cartridge has entered the storage magazine or tape drive, the catch-pin engages the lower gripping finger applying a force that, in combination with the force of the Z-stage&#39;s motion, forces the lower gripping finger and the connected upper gripping finger to release the cartridge&#39;s notched recesses. Those skilled in the art will recognize that there a numerous mechanical trigger designs that are capable of the same function. As the Z-stage gets closer to the end of its Z extension, the gripping fingers open further, enabling them to clear the cartridge&#39;s notched recesses and the cartridge&#39;s upper and lower corners, while the leading edge of the Z-stage pushes the cartridge to its seated position within the storage magazine. At this point, the Z-stage withdraws from the storage magazine and travels back to the X-plate along the negative Z-axis, and the upper and lower spring-loaded, gripping fingers reset, awaiting another X-axis move to pick and place another cartridge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a storage library subsystem showing several tape storage cartridges, a multiple-position storage magazine, a magnetic tape drive, and the preferred robotic shuttle and transport system according to the present invention. 
     FIG. 2 is a partial perspective view of the preferred robotic shuttle&#39;s X-plate with one side panel removed to illustrate the robotic shuttle&#39;s internal components, and in particular, to show the preferred cartridge gripper assembly, including a pair of upper and lower spring-loaded, gripping fingers, their joining linkages, and a push-type solenoid and catch-pin system that are the integral components of the motorized stage&#39;s operation. 
     FIG. 3 is a partial perspective view of the preferred robotic shuttle&#39;s X-plate with the preferred cartridge gripper assembly removed to expose a motorized gear drive that allows the Z-stage to travel bi-directionally along the Z-axis. 
     FIG.  4 ( a ) and FIG.  4 ( b )are reverse images of the preferred robotic shuttle&#39;s Z-stage, with FIG.  4 ( a ) particularly illustrating a pair of upper and lower spring-loaded, gripping fingers and their associated linkages, and with FIG.  4 ( b ) particularly illustrating a rack of teeth to generate movement of a Z-stage along the positive and negative Z-axis. Both FIG.  4 ( a ) and  4 ( b ) also show a cylindrical rod which facilitates the Z-stage&#39;s travel. 
     FIG. 5 is a two-dimensional sketch of the preferred cartridge gripper assembly in its natural, spring-loaded, closed position prior to engaging a tape storage cartridge. 
     FIGS.  6 ( a ) through ( d ) are two-dimensional sketches of the preferred gripper assembly&#39;s operational sequence as it engages a tape storage cartridge. 
     FIG.  7 ( a ) and  7 ( b ) are two-dimensional sketches of the preferred gripper assembly&#39;s operational sequence as, upon its approach to a cartridge magazine, the solenoid is energized, thus forcing the catch mechanical trigger to rotate upward to engage the lower spring-loaded, gripping finger. 
     FIGS.  8 ( a ) through  8 ( c ) are two-dimensional sketches of the preferred gripper assembly&#39;s operational sequence as the catch-pin engages the lower spring-loaded, gripping finger, which in combination with the Z-stage&#39;s motion, forces both upper and lower spring-loaded, gripping fingers to disengage from a tape storage cartridge. The sketches further show the leading edge of the Z-stage pushing a tape storage cartridge the remainder of its way into a target drive. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an exemplary form of a preferred embodiment of the robotic shuttle which is the focus of this application, situated within a library storage subsystem. As shown in FIG. 1, a library storage subsystem is comprised generally of a rectangular library frame  10  consisting of a pair of longer walls  12 A,  12 B a pair of shorter walls  14 A,  14 B, and a bottom panel  16  (optional top panel not shown). A magnetic tape drive  20  is mounted to one of the longer walls in the interior of the library frame  12 A, such that a cartridge insertion slot  30  is aligned substantially parallel to a fixed multi-position storage location  40 , which is mounted to the opposite longer wall in the interior of the library frame  12 B on one end, and mounted to an inner wall (not shown) on its other end. A worm screw  50  extends substantially parallel to a magnetic tape drive  20  and to a multi-position storage location  40  and is mounted to the interior of opposing walls of the library frame  12 A,  12 B. A grooved channel  60  likewise extends substantially parallel to a magnetic tape drive  20  and to a multi-position storage location  40  preferably directly beneath a worm screw  50  and is mounted to an interior bottom panel of the library frame  16 . 
     A robotic shuttle assembly (an X-plate)  70  consisting of a top panel  72 , a bottom panel  74 , and a left  76  and a right  78  side panel, which, in combination, frame openings on opposite ends of the X-plate, is attached above to a worm screw  50  by means of a threaded nut  80  attached to a top panel  72 , and attached below to a grooved channel  60  by means of a anti-rotation tab  90  attached to a bottom panel  74 . The X-plate slidably moves the length of a grooved channel  60  across the width of the interior of the library frame  10  by means of the worm screw  50  which is powered by a motor (not shown). A worm screw  50  and a grooved channel  60  define the X-axis along which the X-plate  70  moves in both the positive and the negative direction. Although a worm screw and motor combination is illustrated in the exemplary embodiment, those skilled in the art would recognize that a multitude of linear motion drive mechanisms could be utilized to move the X-plate along the X-axis. 
     FIG. 2 illustrates the interior of the X-plate  70 , and particularly demonstrates the inter-connectiveness between the upper  100  and lower  110  spring-loaded, gripping fingers. The upper gripping finger  100  substantially forms an inverted L-shape with the distal end of the longer leg pivotally attached to the robotic shuttle&#39;s interior plate (a Z-stage)  120  defining a first axis of rotation  122  around the pivot point, the longer leg situated substantially parallel to the leading edge of the Z-stage  120 , the shorter leg extending distally from and substantially perpendicular to the leading edge of the Z-stage  120 , the shorter leg incorporating a triangular aspect  130  with its apex  135  protruding downward along a negative Y-axis. 
     At the joinder of the longer leg and the shorter leg, the upper gripping finger  100  is pivotally linked to the distal end of the connecting link  140  defining a second axis of rotation  124  around the pivot point. The connecting link  140  is substantially rectangular in shape with its distal end connected by pin  145  to the proximal end of a shorter, pivot link  150  forming an angle of rotation α and a third axis of rotation  126 . The pivot link  150  is mounted preferably at its mid-point to the Z-stage  120  by a stand-off  155  and is engaged at its proximal end with a slidable catch-pin  160  that is part of the lower spring-loaded, gripping finger  110 . 
     The lower spring-loaded, gripping finger  110  substantially forms an inverted S-shape with the slidable catch-pin  160  of its proximal end connected to the pivot link  150 . The lower gripping finger  110  is pivotally mounted to the Z-stage  120  by a pin which defines a fourth axis of rotation  128 . The upper hook of the S-shaped bottom gripping finger  110  incorporates a triangular aspect  170  with its apex  175  protruding upward along a positive Y-axis substantially directly below the upper gripping finger&#39;s protruding triangular aspect  130 . At the base of the lower hook of the S-shaped lower gripping finger  110  is a concave protrusion  180  curved outward along the positive Z-axis from the robotic shuttle&#39;s Z-stage with enough curvature to accommodate an independent catch pin  190 . 
     The independent catch-pin  190  is preferably cylindrical and is attached to the distal end of a catch-link  195 . The catch-link  195  is substantially rectangular and is mounted to the interior side of the X-plate  70 . A bracket  198  is mounted substantially perpendicular between the left and the right side panels of the X-plate  70 . On the proximal side of the bracket  198 , a solenoid  200  is mounted, that upon activation, forces the catch-link  195  and catch-pin  190  combination to rotate upward and into the path of the lower gripping finger&#39;s concave protrusion  180 . Although a solenoid  200  is illustrated in this exemplary embodiment of the robotic shuttle, those skilled in the art would recognize that a multitude of actuators could be utilized to trigger the generation of the necessary linear motion of the catch-link  195  and catch-pin  190  combination. The engagement with the catch-pin  190  opposes the lower gripping finger&#39;s natural spring bias and forces the lower gripping finger  110  downward along the negative Y-axis. This force, transferred through the pivot link  150  and connecting link  140  combination, in combination with the force generated by the Z-stage&#39;s  120  motion, simultaneously forces the upper gripping finger  100  upward along a positive Y-axis, thus releasing both gripping fingers&#39; hold on the cartridge. 
     FIG. 3 shows an interior view of the X-plate  70  with the Z-stage  120  removed. In this exemplary embodiment of the robotic shuttle, a motor  210  is mounted to the interior side of the X-plate  70  by a bracket  220 . The motor  210  engages a worm gear  230 , that when rotated, turns a pinion gear  240 , thus generating motion for the robotic shuttle along the Z-axis. The pinion gear  240  is likewise mounted to the interior side of the X-plate  70 . Although a motor-driven pinion gear drive is illustrated in this embodiment of the robotic shuttle, those skilled in the art would recognize that a multitude of assemblies could be utilized to generate Z-axis motion for the robotic shuttle. 
     In FIG. 4B, a rack  250  with teeth is mounted to the Z-stage  120 . When the pinion gear is turned, it engages the rack&#39;s teeth, thus moving the motorized Z-stage bi-directionally along the Z-axis. In FIGS. 4A and 4B, a right eye bracket sleeve  260  and a left eye bracket sleeve  270  are shown with a substantially cylindrical rod  280  passing through both. In the preferred embodiment of the invention, a bearing is disposed within each eye bracket sleeve that facilitates the bi-directional movement of the cylinder as it passes through each eye bracket sleeve. Those skilled in the art would recognize that other embodiments exist that facilitate the movement of a cylindrical rod through a set of eye bracket sleeves. As the motor  210  turns the pinion gear  240  and the rack&#39;s  250  teeth are engaged, the rod  280  guides the Z-stage  120  back and forth along the Z-axis. 
     In FIGS. 5 through 8C, the sequential operation of the picking and placing of a tape storage cartridge are illustrated in detail. Although a tape storage cartridge is illustrated in the exemplary embodiment, those skilled in the art would recognized that other storage cartridge media could be utilize as well. In FIG. 5, the Z-stage  120  is in its natural position as is noted by the upper and lower spring-loaded, gripping fingers  100 ,  110  exhibiting the closed bias of their respective springs, i.e., the upper gripping finger&#39;s triangular protrusion  130  and the lower gripping finger&#39;s triangular protrusion  170  are aligned at their shortest distance of separation substantially along the Y-axis. This natural closed position is also characterized by a maximum angle of rotation a between the connecting link  140  and the pivot link  150 . A tape storage cartridge  300  is also shown with a proximal edge  314 , an upper corner  302  and a lower corner  304  at the top and bottom of the proximal edge  314  respectively, an upper edge  306  and a lower edge  308  substantially perpendicular to the proximal edge  314 , and an upper notched recess  310  and a lower notched recess  312  inset from the upper edge  306  and the lower edge  308  respectively. 
     In FIGS. 6A through 6D, the Z-plate  120  is traveling toward a tape storage cartridge  300  along the Z-axis. As the apex  135  of the upper gripping finger&#39;s triangular protrusion  130  and the apex  175  of the lower finger&#39;s triangular protrusion  170  come into initial contact with the cartridge  300 , the dynamic force of the Z-stage  120  and the static force of the cartridge&#39;s upper and lower corners  302 ,  304 , overcome the gripping fingers&#39; spring bias, camming the respective apexes  135 ,  175  of the respective triangular protrusions  130 ,  170  around the cartridge&#39;s upper and lower corners  302 ,  304  and off their Y-axis alignment at an angle β. The angle β increases as the robotic shuttle&#39;s Z-plate  120  continues its positive Z-axis travel and the gripping fingers are forced to travel along the tape storage cartridge&#39;s upper and lower edges  306 ,  308 , thus increasing the angular profile β from the Y axis. When the apexes  135 ,  175  of the gripping fingers&#39; triangular protrusions  130 ,  170  reach the cartridge&#39;s upper and lower notched recesses  310 ,  312 , the triangular protrustions seat within the cartridge&#39;s notched recesses snugly via the force of the bias springs. The bias springs do not provide a clamping force on the cartridge for extraction. 
     Upon retraction of the Z-stage  120  along the negative Z-axis with the tape storage  106  cartridge  300  securely grasped by the upper and lower gripping fingers  100 ,  110 , the X-plate  70  makes an X-axis move by means of its attached threaded nut  80  and the worm screw  50  plus its anti-rotation tab  90  and the grooved channel  60 . The geometry of the gripping fingers, the pivot point of the gripping fingers, and the cartridge recesses provide a linear clamping force on the cartridge for extraction. As the linear force increases, the clamping force increases proportionately. Again, those skilled in the art will recognize that there are additional assemblies that can generate similar motion for the robotic shuttle along the X-axis. When the X-plate  70  arrives at the destination cartridge magazine  40  or the tape drive  30 , the Z-stage  120  begins travel along the positive Z-axis with the tape storage cartridge  300  still held by the upper and lower spring-loaded, gripping fingers  100 ,  110 . At a pre-programmed distance from the cartridge magazine  40  or tape drive  30 , the solenoid  200  is instructed to activate as shown in FIG.  7 B. Upon activation, the mechanical trigger, comprised of the connected catch-link  195  and catch-pin  190 , is rotated upward into the path of the oncoming lower gripping finger&#39;s concave protrusion  180  as shown in FIG.  8 A. 
     Before the tape storage cartridge  300  is fully seated within the cartridge magazine  40  or the tape drive  30 , the catch-pin  190  engages the concave protrusion  180 . The opposing dynamic force of the Z-stage  120  moving along the positive Z-axis and the camming force that the catch-pin  190  exerts upon the concave protrusion  180  causes the lower gripping finger&#39;s triangular protrusion  170  to begin to release the tape storage cartridge&#39;s lower notched recess  312 . As this occurs, the pivot link  150  and the connecting link  140  rotate thus forcing the upper gripping finger&#39;s triangular protrusion  130  to simultaneously release the tape storage cartridge&#39;s upper notched recess  310 . The angle of rotation a gradually decreases as the upper and lower spring-loaded, gripping fingers  100 ,  110  are forced further away from the cartridge  300 . The leading edge of the Z-stage  120  retains contact with the cartridge&#39;s proximal edge  314 . The dynamic force of the Z-stage&#39;s  120  continued positive Z-axis motion causes the cartridge  300  to be pushed into its final seating within the cartridge magazine  40  or the tape drive  30 . 
     Upon completion, the Z-stage  120  begins to withdraw along the negative Z-axis toward the X-plate  70 . As this motion occurs, the solenoid  200  deactivates, thus allowing the catch-pin  190  to disengage from the lower gripping finger&#39;s concave protrusion  180 . This allows the natural spring bias to reset the gripping fingers for the next pick and place instruction.