Abstract:
A system for directing robot movement in a storage library is provided, the library comprising at least one horizontal array of storage cells and at least one robot that moves along the horizontal array and can retrieve objects from and place objects into the storage cells. The system comprises a guide rail that runs along the length of the horizontal array and loops around from one end of the horizontal array to the other end. The robot may move along the guide rail in a continuous, unidirectional loop. If multiple robots are added to the library, they can be made to move in the same direction along looping guide rail, thus elimination contention among robot movements. If multiple horizontal arrays are stacked vertically within the library, the looping guide rail allows robots to loop around and return to the same level or move onto a different horizontal level.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to media storage libraries and more specifically to the movement of robotic mechanisms within the library. 
     2. Background of the Invention 
     Typical storage library designs using more than one picker robot have contention problems. For example, when one robot is moving toward a tape reader unit another robot will want to move away from the unit, and their paths must meet somewhere. This is especially likely when two robots are moving in opposite directions on the same guide rail or track. This contention between robots effectively causes performance degradation and makes the control of the robots extremely complex. Special control software is needed to coordinate robot movements in order to avoid contention between robots on the same track. 
     Therefore, it would be desirable to have a method for avoiding robot contention on guide rails, without the need of complex robot coordination and increased software complexity. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for directing robot movement in a storage library, the library comprising at least one horizontal array of storage cells and at least one robot that moves along the horizontal array and can retrieve objects from and place objects into the storage cells. The system comprises a guide rail that runs along the length of the horizontal array and loops around from one end of the horizontal array to the other end. The robot may move along the guide rail in a continuous, unidirectional loop. If multiple robots are added to the library, they can be made to move in the same direction along looping guide rail, thus elimination contention among robot movements. If multiple horizontal arrays are stacked vertically within the library, the looping guide rail allows robots to loop around and return to the same level or move onto a different horizontal level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 depicts an isometric pictorial diagram illustrating a library unit with horizontal storage arrays in accordance with the present invention; 
     FIG. 2 depicts a front isometric view pictorial diagram illustrating the composite library system in accordance with the present invention; 
     FIG. 3 depicts a rear isometric view pictorial diagram illustrating a composite library system in accordance with the present invention; 
     FIG. 4 depicts a top view pictorial diagram illustrating the composite library system in accordance with the present invention; 
     FIG. 5 depicts a cross-section, side view pictorial diagram illustrating a horizontal library unit in accordance with the present invention; 
     FIG. 6 depicts a pictorial diagram illustrating guide track switching mechanisms for each horizontal level in accordance with the present invention; 
     FIG. 7 depicts a pictorial diagram illustrating a Y joint in a track switch in accordance with the present invention; and 
     FIG. 8 depicts an isometric view pictorial diagram illustrating an outer route guide rail mechanism in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an isometric pictorial diagram illustrating a library unit with horizontal storage arrays is depicted in accordance with the present invention. It should be pointed out that FIG. 1, as well as all of the figures discussed below, depicts the library system without side covers, so that the internal components may be viewed. 
     Library unit  100  represents the basic design from which larger horizontal library systems can be built. Media elements (i.e. cartridges) are stored in horizontal array trays, e.g.,  101 , which are arranged in multiple rows. The horizontal arrays are comprised of storage cells arranged horizontally in rows and columns. Media cartridges within the storage cells are retrieved and replaced vertically. 
     Robotic accessors, e.g.,  102 , utilized horizontal guide rails, e.g.,  103 , to move along the array trays  101  in order to access the media elements. The robots  102  use propulsion motors and drive wheels to move along the guide rails  103 . The guide rails  103  may also be used to allow the horizontal array trays  101  to slide in and out of the enclosure of library unit  100 . Alternatively, separate guide rails may be provided to facilitate removal of the storage cell trays  101 . 
     Library unit  100  contains media reader units  104 , power supply units  105 , and a controller  106 . FIG. 1 depicts an open cartridge access port (CAP)  107  and pass-through tray  108 , which are included for each horizontal row in library system  100  and allow media cartridges to be passed between adjacent library units, as explained in detail below. 
     The typical prior art library is configured with vertical cartridge storage walls made up of storage cells arrayed in a vertical plane or curved wall. The storage cells in such a library may be removable to allow access into an enclosure. However, the media storage slots making up a storage wall are seldom deep enough to gain an advantage when removed; i.e. the removal of a wall does not create enough additional space for a human operator to fit through the narrow pathway. 
     The present invention of the horizontal array structure permits the storage density of a library to reach a new maximum limit, based on robot size, not human size. The horizontal array trays can be packed as closely together as robot height permits, without the need to leave room for a human operator to access components within the enclosure. An access isle can easily be created by removing some of the horizontal arrays, e.g.,  101 , to gain access (illustrated below). 
     Referring to FIG. 2, a front isometric view pictorial diagram illustrating the composite library system is depicted in accordance with the present invention. This composite library is comprised of library unit  100 , depicted in FIG. 1, as well as two larger interconnected units  200  and  210 . Library units  200  and  210  share the same basic horizontal layout as unit  100  but are larger. 
     The view depicted in FIG. 2 illustrates how human operators may access the storage elements and media readers within each of the library enclosures  100 ,  200 , and  210  from the front side. The array tray support structure are designed with linear guide rails, e.g., guide rail  103  in FIG. 1, that allow an array tray to be removed from the library by simply sliding the tray outward (down the end of a guide rails) until the end of the rail is reached, thus allowing the tray to be completely removed from the library structure. Array tray  201  illustrates a tray that is partially withdrawn from library enclosure  200 . Access space  202  illustrates how a service isle may be created when multiple array trays are completely removed from the library enclosure, as explained above. The horizontal configuration allows the design to take advantage of the storage array size to set the width of the pathway created when array packages are removed. For example, by creating a storage array tray of  16  cartridge slots, an isle width of  20  inches can be obtained between support structures for the array trays. 
     In addition to removing single trays, the array tray modules could be hooked together to form a group of trays, such that by pulling an endmost tray, all of the other trays connected to it would slide out to gain full access to all the trays. This process can be performed by an operator or possibly with automated electro-mechanical motors for large systems with many trays, e.g., enclosure  210 . 
     FIG. 2 also depicts the housings for the pass-through mechanisms  220  and  230  that connect the three library enclosures  100 ,  200  and  210 . The operation of these pass-through mechanisms  220  and  230  are discussed in more detail below. 
     Referring to FIG. 3, a rear isometric view pictorial diagram illustrating a composite library system is depicted in accordance with the present invention. As can be seen from this angle, library unit  210  does not contain its own media readers. Cross-enclosure pass-through mechanisms  220  and  230  are able to transfer media cartridges from enclosure  210  to the appropriate media readers in enclosures  100  and  200 . 
     With prior art vertical wall libraries, adding storage walls requires the robot accessors to have a path intersecting at a common “lobby” in front of the media readers, wherein paths intersect in orthogonal directions to reach the common area. These vertical designs require extra guide rails that may have to intersect to get the robots into the shared space in front of a tape reader unit. 
     For horizontal storage, capacity is added without having to join robot spaces in a common “lobby” near the tape reader units. The horizontal configuration of the present invention uses “cross tracks” within the pass-through mechanisms  220  and  230  to move cartridges between expansion units to get the tapes in front of the appropriate media reader. 
     Referring to FIG. 4, a top view pictorial diagram illustrating the composite library system is depicted in accordance with the present invention. FIG. 4 more clearly illustrates the components of the pass-through mechanisms  220  and  230  and cross-track features. 
     The pass-through mechanisms  220  and  230  rely on a cross-cabinet (or across-the-cabinet) guide rail  401 , which can move media cartridges (or robots themselves) against the grain of the normal robot flow. The cross-cabinet guide rail  401  runs through each horizontal row within the library enclosures  100 ,  200 , and  210 . The cross-cabinet guide rail  401  serves as a movement path  1 ) to get media in between adjacent banks of storage cells,  2 ) to provide an easy access method for cartridge entry into the library, and  3 ) to provide a method for movement of cartridges (or robots) between library enclosures. 
     For example, cross-cabinet guide rail  401  allows media cartridges to move between adjacent storage cell banks  402  and  403 . 
     Cartridge access port (CAP)  404  allows easy access for adding or removing media cartridges from enclosure  100 . Additional CAPs  405 ,  406  and  407  are provided on each side of enclosures  100  and  200  to allow motorized pass-through trays, e.g.,  408 , to carry cartridges between enclosures  100 ,  200 , and  210 . Through not pictured in FIG. 4, it should be pointed out that CAPs are placed on all horizontal levels within enclosures  100  and  200 . 
     Another embodiment comprises the movement of the actual robotic accessors between sections of the enclosure, using track joints and sub-rails. This approach is very similar to the pass-through tray method described above, except that robots are used to carry media cartridges between enclosure and reader, rather than pass-through trays. 
     The use of horizontal array structure permits the library to grow easily in two dimensions. Expanding a library can be accomplished by growing in the z direction (along the robot guide track) and/or growing sideways in the x direction (side-by-side accumulation of more storage tray rows). The library is limited in the Y direction by the room ceiling height. 
     Referring to FIG. 5, a cross-section, side view pictorial diagram illustrating a horizontal library unit is depicted in accordance with the present invention. FIG. 5 illustrates how Robots, e.g.,  502 , are translated between different horizontal levels within the library. Guide track switches  501  at each level allow the robots  502  to switch between horizontal guide rails, e.g.,  504 , and a vertical guide rail  505 . This enables robots  502  to move between different horizontal levels, as well as move between different media readers/drive  503 , which are stacked vertically along vertical guide rail  505 . 
     Referring to FIG. 6, a pictorial diagram illustrating guide track switching mechanisms for each horizontal level is depicted in accordance with the present invention. The embodiment of the track switch depicted in FIG. 6 uses a “Y” junction  605  wherein a motor or other actuator controls the position of a moving guide rail  606  around a pivot point  607 . This allows the moving guide rail  606  to be aligned with a fixed curve track  603 , thus allowing robot  601  to make the transition from the vertical rail  604  to the horizontal rail  602 . The Y joint is an application of the “turntable joint” (round house) used in railroad examples. The mechanical working of the Y joint are described in more detail below. 
     Referring to FIG. 7, a pictorial diagram illustrating a Y joint in a track switch is depicted in accordance with the present invention. A partial robot structure  700  and robot propulsion motor  701  are illustrated attached to the guide rails. The Y joint  710  is moved by actuator gear  720  (motor not shown). The Y joint  710  has two partial rail sections: a straight section  713  and a curved section  711 / 712 . The curved section of rail is shown in two different positions: disengaged  711 , and engaged  712 . 
     When the Y joint  710  is brought forward by the actuator gear  720 , the curved rail section  711  is disengaged, and the straight section  713  is engaged with the vertical track  730 . In this forward position, the robot  700  will continue to move along the vertical track  730 . 
     When the Y joint  710  is brought backward by the actuator gear  720 , the straight section  713  is disengaged, and the curved section  712  is engaged with the fixed curved rail  740 . In this position, the robot  700  can move onto the horizontal guide rail  750 . 
     Another embodiment of the track switch uses a “passive” Y joint, wherein a spring-loaded moving track section would let a robot pass through it to get on a fixed rail but not come back the other way. The moving section would be fixable to cause the robot to go onto only one of the rail sections of the Y track. This design effectively creates one-way traffic for the robots, because the robots can always be guided forward through the track switch, without returning over the same Y joint in the opposite direction. 
     Referring to FIG. 8, an isometric view pictorial diagram illustrating an outer route guide rail mechanism is depicted in accordance with the present invention. The horizontal library design allows for the addition of guide rail structures  801  that allow any of the robots  804  to move in a loop back to the far end of the structure  800 . For example, robot  804  can use track switch  803  to move from horizontal array  805  to the vertical track  806 . This allows robot  804  to move upward and load (or remove) a media cartridge into one of the media readers  807 . The robot  804  can then loop over the structure  800  by means of the outer route rails  801  and come down on the opposite side. A vertical rail and rack switches, similar to rail  806  and switch  803 , are placed on the opposite end of library  800 , but are not visible due to the angle of the view in FIG.  8 . These other track switches allow robot  804  to move onto any of the horizontal levels in library enclosure  800 . Thus, the outer route rails  801  allow the robot to move in a clockwise direction. This provides a return path for continuous loading of data cartridges toward the tape reader units. 
     To avoid robot contention, the control software can be used to ensure that the robots only move in the clockwise loop described above. If the control software for the system is structured to force the movements of all robots to be in the same direction (i.e. clockwise), the robots can always loop up and around to get to any desired position, thereby achieving a state of operation where no contention occurs between robots on the same track. As explained above, passive, spring-loaded Y joints may also be used to force robots to move in a single direction along the guide rails, thus eliminating the need for additional control software to reduce contention. 
     In addition, opposite directions of movement might be assigned to alternate horizontal levels, thereby allowing robots to use a shorter return loop, rather than having to loop all the way over the library and down the other side. 
     Also shown in FIG. 8 are cross-cabinet tracks  802 , described above. Movement on the cross-cabinet track may also be controlled so that robots only move in one horizontal direction at either end of the library. For example, the robots might be forced to move in a horizontal clockwise path along the horizontal arrays and cross-cabinet tracks, thereby eliminating contention between robots moving between adjacent banks of storage arrays. 
     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.