Many different types of data storage systems exist and are being used to store data cartridges at known locations and to retrieve desired data cartridges so that data may be written to or read from the data cartridges. Such data storage systems are often referred to as "juke box" data storage systems, particularly if they can accommodate a large number of individual data cartridges.
A typical juke box data storage system may include one or more different types of cartridge receiving devices for holding the various data cartridges. For example, one type of cartridge receiving device may comprise a cartridge storage rack or "magazine" while another type of cartridge receiving device may comprise a cartridge read/write device. The cartridge storage racks or magazines serve to provide storage locations for the data cartridges and are often arranged so that they form one or more vertical stacks, although other configurations are possible. The cartridge read/write device may be located at any convenient location within the data storage system.
The data storage system may also be provided with a moveable cartridge picker assembly or "picker" for transporting the data cartridges between the various cartridge receiving devices, e.g., between the cartridge storage racks and the cartridge read/write devices. A typical cartridge picker assembly or picker may also be provided with a cartridge plunge mechanism or "thumb" assembly for engaging the various data cartridges contained in the cartridge receiving devices and for drawing them into the picker. A picker positioning system associated with the cartridge picker assembly may be used to move the cartridge picker assembly along the various cartridge receiving devices.
Data storage systems of the type described above are usually connected to a host computer system which may be used to access or store data on the data cartridges. For example, if the host computer system issues a request for data contained on a particular data cartridge, a control system associated with the data storage system will actuate the picker positioning system to move the picker assembly along the cartridge storage racks until the picker assembly is positioned adjacent the desired data cartridge. The cartridge plunge mechanism or "thumb" assembly associated with the picker assembly may then remove the data cartridge from the cartridge storage rack and draw it into the picker assembly. The picker positioning system may then be actuated to move the picker assembly to the appropriate cartridge read/write device. Once properly positioned adjacent the cartridge read/write device, the thumb assembly may insert the selected data cartridge into the cartridge read/write device so that the host computer may thereafter read data from or write data to the data cartridge. After the read/write operation is complete, the thumb assembly may be actuated to remove the data cartridge from the cartridge read/write device. The picker assembly may thereafter return the data cartridge to the appropriate location in the cartridge storage rack.
A typical cartridge plunge mechanism or "thumb" assembly is usually slidably mounted to the picker and is provided with a thumb actuator system to move the thumb assembly toward and away from a cartridge access end of the picker. For example, if it is desired to retrieve a data cartridge from a cartridge receiving device, the thumb actuator system moves the thumb assembly toward the cartridge access end of the picker so that the thumb assembly can engage or "grab" the data cartridge. Thereafter, the thumb actuator system may retract the thumb assembly and engaged data cartridge into the picker. If it is desired to load the data cartridge into the cartridge receiving device, then the thumb actuator moves the thumb assembly and data cartridge toward the cartridge access end of the picker, and inserts the data cartridge into the cartridge receiving device.
In order to reliably engage a cartridge, the thumb assembly must be positioned adjacent to the cartridge within precise tolerances. As the thumb assembly is moved toward or away from the cartridge access end of the picker, lateral and vertical movement is limited by the thumb actuator system or by guide rails on each side of the thumb assembly. If the thumb assembly is not correctly positioned adjacent to the cartridge, the thumb assembly will be unable to properly engage or disengage the cartridge.
Currently known mounting systems are not without their problems. In one currently known mounting system, the thumb assembly is mounted to the cartridge picker assembly on a lead screw which drives and positions the thumb assembly. A lead screw is rotatably mounted to the cartridge picker assembly and runs the length of the picker assembly, passing through the thumb assembly and engaging with a gear or teeth on the thumb assembly. Thus, when the lead screw rotates, the thumb assembly is moved toward or away from the cartridge access end of the picker. The lead screw drive system provides generally good positioning accuracy once aligned, but requires the use of expensive machined elements and is difficult to assemble and align. Furthermore, the teeth and threads tend to wear down over time as they turn against each other, reducing the positioning accuracy. In addition, the minimum gaps required for moving parts may exceed the tolerances required for lateral positioning. For example, if the thumb actuator system is a lead-screw drive system, gaps are required between the lead-screw and the teeth in the thumb assembly to prevent binding. These gaps required for the operation of the drive system may allow lateral movement which exceeds the tolerances required for lateral positioning. A lead-screw drive system may also require a secondary guide member, such as a precision-machined rod, which is relatively expensive and may pose assembly and alignment problems.
In addition, positioning errors may accumulate within the picker with each additional part in the guide system. For example, for a lead-screw drive system, the position of the thumb assembly is affected by multiple parts. First, the gap between the lead-screw and the threads in the thumb assembly has a given tolerance. The lead-screw may be held in place by a set of ball bearings which also have a given tolerance. The ball bearings may be held in a casing having a tolerance, which in turn may be attached to the side of the picker which also has a tolerance. Each tolerance adds up, forming a tolerance stack, making it more difficult to maintain the lateral position of the thumb assembly as the tolerance stack deepens.
In another currently known mounting system, the thumb assembly is mounted in the picker with guide rails on each side of the picker. Support members extend from the sides of the thumb assembly to engage in the picker guide rails to guide the thumb assembly as it moves toward and away from the cartridge access end of the picker. A guide rail mounting system provides a less-expensive alternative to a lead-screw, and may eliminate some of the expensive machined parts and may facilitate assembly and alignment. However, a guide rail mounting system is subject to a high tolerance stack and large, molded parts which are easily warped. The guide rails are typically molded into the plastic side panels of the picker, which can warp during manufacture and assembly, and which can flex during operation.
In addition, the drive system of the picker assembly typically mounts to one side, correctly positioning that side of the picker assembly adjacent a cartridge or a cartridge receiving device. However, guide rails are located on both sides of the picker, and there may be several elements between the two sides of the picker. Therefore, the tolerance stack for the guide rail mounting system includes the tolerances for all elements between the correctly positioned first side and the guide rail on the second side. In other words, correct positioning of the thumb assembly in a picker having a guide rail mounting depends upon correct sizing and placement of multiple elements in the picker. The large tolerance stack and the dependence upon easily warped or flexed components leads to an undesirably high rate of incorrect positioning.
Consequently, a need exists for an improved thumb assembly mounting and guide system to control lateral motion. In particular, a need exists for a guide system having a reduced tolerance stack and having more easily controlled tolerances, using relatively inexpensive components.