Abstract:
A drawer for use in a dispensing cabinet is comprised of a tray movable between an open position and a closed position. An insert, approximately the length of the tray, is carried by the tray and defines the volume of the drawer. A lockable or sealable lid is carried by the insert. A release mechanism is provided to connect the insert to the tray in a manner that allows the insert to be easily disconnected from the tray. Removal of the insert enables inserts to be swapped so that inserts from which inventory has been depleted can be replaced with stocked inserts. A dispensing cabinet and a method of restocking the cabinet are also disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed to dispensing cabinets and, more particularly, to dispensing cabinets having drawers of the type which are opened and closed under the control of a computer to control access to the contents of the drawer.  
           [0003]    2. Description of the Background  
           [0004]    In large medical facilities, inventories of medical supplies are normally held in centralized storage locations or pharmacies which are often far removed from decentralized storage locations. It is at the decentralized storage locations, e.g. a nurses station, that dispenses for patients are typically performed. To facilitate dispensing of medications and supplies for patients, a variety of dispensing systems have been proposed. For example, several dispensing systems have been proposed which employ a cart or cabinet which is located at the decentralized location.  
           [0005]    Of particular interest to the present invention are dispensing systems which dispense pharmaceuticals and other items which require close monitoring and control. A variety of schemes have been proposed for providing secured access to pharmaceuticals that are held within such dispensing systems, including locking the pharmaceuticals within the carts or by allowing access to only one item at a time, commonly referred to as “single dose” or “unit dose” dispensing.  
           [0006]    One such system is described in U.S. Pat. No. 5,014,875 titled “Medication Dispenser Station.” That system comprises a multiple-drawer cabinet for holding pharmaceuticals, with each drawer containing a covered, multiple-compartment carousel. Access to each drawer and each carousel compartment is controlled to allow access to the contents after a predetermined code or other information has been entered into a controller.  
           [0007]    Another system is described in U.S. Pat. No. 4,847,764 titled “System for Dispensing Drugs in Health Care Institutions.” That dispensing system involves a computer system connected to a number of remote medication dispensers. The computer system includes software for, among other things, controlling access to the medications, identifying potentially dangerous drug interactions, and assisting with inventory control. The remote medication dispensers comprise a number of cabinets, with each cabinet holding a number of unit dose medication packages.  
           [0008]    U.S. Pat. No. 5,927,540 titled “Controlled Dispensing System and Method” discloses apparatus and methods for dispensing articles in a controlled manner. In one embodiment, the invention provides an apparatus comprising a cabinet defining an enclosure. At least one drawer is attached to the cabinet and is configured to slide in and out of the cabinet. The drawer contains an array of compartments. At least one lid is attached to the drawer and is configured to slide forward and backward with respect to the drawer. Each drawer further includes a locking mechanism which may engage the lid at selective locations along the lid. With this arrangement, the locking mechanism may engage the lid to prevent movement of the lid relative to the drawer after a certain compartment has been exposed. Each drawer further includes a distance sensor for detecting the distance traveled by the lid relative to the drawer. A controller is placed in communication with both the locking mechanism and the distance sensor. The controller sends a signal to actuate the locking mechanism after the lid has been moved to expose a desired compartment. In that manner, the lid may be moved to allow access to a compartment containing a desired article or medical supply. The locking mechanism then engages the lid to prevent further movement of the lid, thereby preventing access to additional compartments.  
           [0009]    U.S. Pat. No. 6,109,774 titled “Drawer Operating System” discloses a drawer operating system for allowing graduated access to consecutively spaced bins, partitioned in a drawer, so that access to the bins is controlled. The invention is housed in the rear of each drawer. It tracks the previous activity of the drawer and, when later accessed, allows the drawer to be pulled open to a length that will expose the contents of a bin either not emptied in previous openings or not uncovered in previous openings, retaining the other item-filled bins inside the cabinet and secure from access. In the preferred embodiment, the drawer is driven from its fully-closed position to a slightly-opened position of one inch or so to indicate to the user that this particular drawer may be opened further by merely pulling it outward. When the drawer is later pushed toward its closed position, it is stopped short of full closure and subsequently slowly driven closed into a locked position in the cabinet. This latter feature prevents “slamming” of the drawers into the cabinet and reduces the potential for damage to the contents therein.  
           [0010]    While such systems provide for unit dose dispensing, the need exists for a unit dose dispensing cabinet that provides a means of accessing the medications in the event of a power failure or the need arises to override the computer controlling the cabinet. Additionally, it is desirable for the dispensing cabinet to be refilled or restocked in a convenient manner that reduces the likelihood that a restocking error will occur.  
         SUMMARY OF THE PRESENT INVENTION  
         [0011]    One aspect of the present invention is a drawer for use in a dispensing cabinet. The drawer is comprised of a tray movable between an open position and a closed position. An insert, approximately the length of the tray, is carried by the tray and defines the volume of the drawer. A lockable lid, i.e., mechanically lockable or sealable with an adhesive seal, is carried by the insert. A release mechanism is provided to connect the insert to the tray in a manner that allows the insert to be easily disconnected from the tray. Removal of the insert enables inserts to be swapped so that inserts from which inventory has been depleted can be replaced with stocked inserts. Eliminating the need to transfer inventory from a restocking package to the insert eliminates the possibility of errors occurring from such a transfer.  
           [0012]    Another aspect of the present invention is a dispensing cabinet having unit dose drawers of the type previously described. The dispensing cabinet comprises an input device, an output device and a computer connected to the input and output devices. A cabinet has a plurality of drawers, at least one of the drawers being a unit-dose dispensing drawer capable of dispensing a unit-dose. Each unit-dose dispensing drawer is comprised of a plurality of individual drawers, each individual drawer comprising a tray drivable between an open position and a closed position. An insert is carried by the tray. The insert defines one or more individual compartments each having a lockable lid. The insert is approximately the length of the tray and defines the volume of the drawer. A release mechanism is provided for connecting the insert to the tray. A self locking worm gear driven by a motor is connected to the tray through a clutch to provide a mechanism for driving the tray. During normal operation, the friction provided by the worm gear renders the drawers unmovable unless they are driven by the motor. In the event of a power failure or other problem, the clutch can be used to disengage the tray from the worm gear so that the drawers can be opened and closed.  
           [0013]    Another aspect of the present invention is a method of restocking a unit dose drawer of a dispensing cabinet. The method is comprised of the steps of releasing a first insert that defines the volume of an individual drawer from a tray, connecting a filled insert to the tray from which the first insert has been removed, and unlocking or unsealing the lid of the filled insert. The first insert may then be delivered to a storage location for filling. After filling, the lid is locked and the filled first insert is delivered to a dispensing cabinet.  
           [0014]    The present invention provides a convenient apparatus and method of refilling or restocking a dispensing cabinet in a manner that reduces the possibility of errors. The cabinet can be operated in such a manner that the drawers of the dispensing cabinet may be manually operated in the event of a power failure or problem with the cabinet. Those, and other advantages and benefits, will be apparent from the Description of the Preferred Embodiments herein below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    For the present invention to be easily understood and readily practiced, the present invention will now be described, for purposes of illustration and not limitation, in conjunction with the following figures, wherein:  
         [0016]    [0016]FIG. 1 is a diagram illustrating the relationship between a centralized storage location and a plurality of decentralized storage locations;  
         [0017]    [0017]FIG. 2 is a diagram illustrating a process for distributing items and restocking of items based, at least in part, on records created during distribution;  
         [0018]    [0018]FIG. 3 is one example of hardware located at a decentralized location implementing a closed system for performing dispensing operations;  
         [0019]    [0019]FIG. 4 is one example of hardware located at a decentralized location implementing an open system for performing dispensing operations;  
         [0020]    [0020]FIG. 5 is a diagram illustrating the flow of information between the computers used at various locations within a dispensing/restocking system.  
         [0021]    [0021]FIG. 6 illustrates a unit dose drawer that may be used in the cabinet or the auxiliary cabinet of FIG. 3;  
         [0022]    [0022]FIG. 7 is an exploded view of one example of the construction of an individual drawer of the type shown in FIG. 6;  
         [0023]    [0023]FIG. 8 illustrates the unit dose drawer in a fully closed position in a cabinet without any other drawers;  
         [0024]    [0024]FIG. 9 illustrates the unit dose drawer in a fully opened condition in a cabinet without any other drawers;  
         [0025]    [0025]FIG. 10 is a flow chart illustrating a dispense operation from a unit dose drawer;  
         [0026]    [0026]FIG. 11 is a perspective view of a drive chassis located at the rear of a unit dose drawer having twelve drawers;  
         [0027]    [0027]FIG. 12 is a cross-section view taken along the lines XI-XI in FIG. 11;  
         [0028]    [0028]FIGS. 13 and 14 illustrate details of portions of FIG. 12;  
         [0029]    [0029]FIG. 15 illustrates the details of the worm drive;  
         [0030]    FIGS.  16 - 20  are electrical schematics of a circuit for receiving drawer identification and distance information as well as certain feedback signals which are used by the circuit to generate certain control signals;  
         [0031]    [0031]FIG. 21 is an electrical schematic of motor sensor interface electronics;  
         [0032]    [0032]FIGS. 22 and 23 are electrical schematics for home sensor electronics;  
         [0033]    [0033]FIG. 24 is an electrical schematic of logic for producing a “Master open/close SNS” signal;  
         [0034]    [0034]FIG. 25 is an electrical schematic of a manual override circuit;  
         [0035]    [0035]FIG. 26 is an electrical schematic of a speed control circuit;  
         [0036]    [0036]FIG. 27 is an electrical schematic of current control circuit and a motor control interface; and  
         [0037]    [0037]FIGS. 28 and 29 are electrical schematics of a drive select circuit and a plurality of relays used to drive a selected motor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    [0038]FIG. 1 is a diagram illustrating the relationship between a centralized storage location  10  and various inventory destinations, including a plurality of decentralized storage locations  12 - 1 ,  12 - 2  through  12 -n, patients  13 , and a remote facility  14 . Each of the decentralized storage locations  12 - 1  through  12 -n is capable of dispensing items stored at the location. The items may include medications, controlled medical supplies, medical supplies or items of a nature consistent with the facility in which the system illustrated in FIG. 1 is located. Items may be dispensed directly from centralized storage location  10  to patients  13 , or from the centralized storage location  10  to a remote facility  14 . Data typically flows from the decentralized storage locations  12 - 1  through  12 -n to the centralized storage location  10 . In response to that data, items are typically moved from the central storage location  10  to the decentralized storage locations  12 - 1  through  12 -n or to the remote facility  14  to restock such locations to either replenish dispensed items or to stock new items. Decentralized locations could include satellite pharmacies, computerized medication cabinets, stationary/mobile medication carts, nurse servers, remote hospital pharmacies, supply closets, supply cabinets, etc. Supplies can be reordered from distributors based on levels of stock in the centralized storage location  10 .  
         [0039]    [0039]FIG. 2 illustrates a process which may begin with a step of dispensing an item at step of  16  from one of the decentralized storage locations  12 - 1  to a patient. A dispensing operation may occur in a variety of ways. In a medical facility, dispenses may be completed from medication orders or they may be completed from inventory lists, to name a few types of dispensing operations. Assuming a medication has been dispensed from decentralized storage location  12 - 1 , the medication may either be administered to a patient or returned as shown by step  18 . Medications may be returned for a variety of reasons such as the patient has checked out, been moved, or the patient&#39;s medication may have been changed. Medications may be returned to the decentralized storage location  12 - 1 . Certain types of medications may simply be replaced in the decentralized storage location  12 - 1  so as to be used in another dispensing operation, or may need to be disposed of.  
         [0040]    The administration of medications occurring at step  18  may be carried out through the use of a hand-held device such as an AcuScan-Rx™ device available from McKesson Automation, Inc., 700 Waterfront Drive, Pittsburgh, Pa. Such devices are wireless devices which communicate with a database to verify the administration of medications to patients. Such communications enable the maintenance of a database of inventory levels as shown by step  20 . The database and associated computer system for maintaining the database of inventory levels may be located at the centralized storage location  10  or may be located remote therefrom. In either event, the computer system necessary for maintaining the database provides information which enables the centralized storage location  10  to perform step  22  of generating a restocking package. The generation of the restocking package may be done completely automatically, manually, or through some combination of manual and automatic processes. The restocking package is used to restock the decentralized storage location  12 - 1 .  
         [0041]    Restocking packages may also be generated at centralized location  10  and delivered to the remote facility  14 . From facility  14  an item may be transferred as shown by step  24 . The transfer may be a dispensing step for a patient or a transfer to another location. Items may also be dispensed directly to the patient from the centralized location  10 .  
         [0042]    [0042]FIG. 3 illustrates one example of hardware which may be located at any of the decentralized locations  12 - 1  through  12 -n. The hardware illustrated in FIG. 3 is comprised of an AcuDose-Rx™ cabinet  26 , having a control computer  32 , and an AcuDose-Rx™ auxiliary cabinet  28 , available from McKesson Automation, Inc. A supply tower  30  is also illustrated. The control computer  32  controls the operation of the cabinet  26 , auxiliary cabinet  28 , and supply tower  30 . The control computer  32  is also in communication with the central database.  
         [0043]    To perform a dispensing operation a user logs onto the control computer  32 . After log-on, patient information and information regarding items to be dispensed is entered. Based on the entered information, various drawers  31  in the cabinet  26  and the auxiliary cabinet  28 , and various doors  33  on the supply tower  30  are unlocked. After the item to be dispensed has been removed, its removal is recorded at the control computer  32 . The user may continue to dispense items for the identified patient, or patient information for another patient may be entered. Entry of information, including log-in, can be performed in a variety of ways with a variety of input devices, e.g., through entry with a keypad, barcode scanning, touch screen, selecting items from a pick list, RF ID, flash memory, magnetic strips, OCR, etc. The reader will understand that the hardware illustrated in FIG. 3 is exemplary and is illustrated for purposes of demonstrating one type of hardware which may be located at the decentralized storage locations  12 - 1  through  12 -n.  
         [0044]    The hardware illustrated in FIG. 3 limits access to the items to be dispensed to those individuals who have properly logged on. Thus, the hardware illustrated in FIG. 3 is referred to as a closed system for performing dispensing operations because a dispensing operation cannot be performed unless the user is identified to, and recognized by, the control computer  32 .  
         [0045]    [0045]FIG. 4 illustrates another example of hardware which may be located at any of the decentralized storage locations  12 - 1  through  12 -n. The hardware is comprised of a first shelving unit  34  and a second shelving unit  36 . An optional interface computer  38  may be provided, which is in communication with the database. If the interface computer is  38  is not provided, a handheld device  40  can be carried into the area to perform the inventory of the shelves. The handheld device  40  is taken back to the centralized storage location  10  where the information is downloaded in any appropriate manner. Alternatively, the hand-held device  40  could be a wireless device communicating over a wireless network link. Alternatively, and as shown in FIG. 4, the hand-held device  40  may be located in the area and have a docking cradle  41  in communication with the interface computer  38 .  
         [0046]    Each of the shelving units  34 ,  36  is comprised of a plurality of bins  42 . Each of the bins carries indicia  44  which may be, for example, a barcode and/or a label identifying the contents of the bin. Additionally, items in the bins may have a bar code, label or other indicia directly on them or on their packaging. The bar code could be scanned, or other methods of inputting the data consistent with the type of indicia used, or push buttons or the like actuated, to perform a dispensing or other type of operation. In addition, the handheld device  40  could be used to generate an ad hoc order through its screen entry in the event that an item is not available to be scanned or otherwise have data pertinent thereto input. The number of shelving units  34 ,  36  and the configuration of the bins  42 , depends upon the number and size of the items to be stocked. Because access to the bins  42  is not restricted, the hardware illustrated in FIG. 4 is referred to as an open system for performing dispensing operations. The reader will understand that the hardware illustrated in FIG. 4 is exemplary and is illustrated for purposes of demonstrating one type of hardware which may be located at the decentralized storage locations  12 - 1  through  12 -n.  
         [0047]    [0047]FIG. 5 illustrates the computers used at various locations within a dispensing/restocking system of the type disclosed herein. As seen in FIG. 5, decentralized storage location  12 - 1  is where control computer  32  (if supplied) is located. Decentralized storage location  12 -n is where interface computer  38  (if supplied) is located. A carousel work station  46  is located at the centralized storage location  10 . The centralized storage location  10  may also have a Robot-x™ support station  48  which is used to control a robot.  
         [0048]    A computer  50 , which may be located at centralized storage location  10  or may be located elsewhere, maintains the database for the system. The computer  50  receives information from the decentralized storage locations  12 - 1  through  12 -n and provides information to the carousel work station  46  and/or the Robot-Rx™ support station  48  to enable restocking packages  52  to be prepared. Additionally, dispenses to patients, distributions to satellite facilities, and the like may occur from centralized location  10 . An interface PC  54  may be provided to enable external systems, such as a PC  56  on which a hospital information system resides, to communicate with the computer  50  on which the database is located. Completing the description of FIG. 5, as has been previously described, restocking packages  52  are prepared at the centralized storage location  10  and delivered to the decentralized storage locations  12 - 1  through  12 -n.  
         [0049]    Returning to FIG. 3, the cabinet  26  available from McKesson Automation, Inc. may be configured with eight (8) drawers and has a maximum capacity of  384  line items. The control computer  32  operates in conjunction with a color touch screen monitor  90  and a full sized keyboard  92 . An integral uninterrupted power supply (not shown) is provided. A scanner port may also be provided to attach a bar code scanner.  
         [0050]    The auxiliary cabinet  28  available from McKesson Automation, Inc. attaches to the main cabinet  26  to expand storage space of narcotic, floor stock and PRN medications. Like the cabinet  26 , the cabinet  28  may be configured with eight (8) drawers and has a maximum capacity of  384  line items.  
         [0051]    A unit dose dispensing drawer  58  is illustrated in FIG. 6. As the name implies, the unit dose dispensing drawer  58  provides single unit-of-use access to high security medications that are to be stored within either the cabinet  26  or auxiliary cabinet  28 , although access to more than a single unit could be provided if the user so desired. The unit dose dispensing drawer  58  uses one standard drawer space within the cabinets  26 ,  28 . The unit dose dispensing drawer  58  may be provided with twelve (12) individual drawers  60 - 1  through  60 - 12  or in a wider six-drawer version (not shown). Each of the individual drawers  60 - 1  through  60 - 12  is motor-driven so as to provide access to exactly the number of units requested. The construction of the individual drawers  60 - 1  through  60 - 12  is shown in FIG. 7.  
         [0052]    Each of the drawers  60 - 1  through  60 - 12  is comprised, in the presently preferred embodiment, of a drivable tray  62  which moves relative to a slide  61 , an insert  63  and a lid  64 . The drivable tray  62  is connected to a chain, described herein below, so as to be driven between an open position shown in FIG. 7 and a closed position.  
         [0053]    The insert  63  has a tab  65  which mates with a slot  66  in the tray  62 . The insert is approximately the size of the tray  62  such that the insert  62  defines the volume of the drawer  60 - 1 . A pin  67  and spring  68  are inserted through an opening in the side of the tray  62  and retained within insert  63  by a pushbutton  69 . Upon depressing the pushbutton  69 , the spring  68  pushes pin  67  out of its locked position thereby enabling the insert  63  to be removed from the tray  62 . The pin  67 , spring  68 , and pushbutton  69  form a release mechanism. The insert  63  can only be removed from the tray  62  if the tray  62  is driven to its fullest extent. Access to the command to drive the tray  62  to its fullest extent can be password protected so that only administrators and/or pharmacy techs have access.  
         [0054]    The unit dose dispensing drawer of the present invention will also support a feature called “auto ID.” This feature incorporates a chip, switch, or other mechanism for generating, for example, an eight bit signal. The control computer&#39;s  32  software automatically detects the eight bit signal and determines from a table the hardware configuration of any drawer type that is installed in the cabinet. Eight bits enables 256 possible drawer types and configurations using this feature. This feature could also be used on standard drawers used in the cabinets. Additionally, the drawers can be bar-coded to provide data about the drawers.  
         [0055]    The lid  64  is comprised of a plurality of individual lids  70  which are designed to cover individual compartments  71 . The lid  64  is held in place with respect to the insert  63  by a rod  72 . As seen in FIG. 7, the hinge between each individual lid  70  and each individual compartment  71  is along the side of the insert  63 . Accordingly, the individual lid  70  can be fully opened only when the tray  62  is driven so that the individual lid  70  is completely clear of the front portion of the cabinet. The lid  64  can be locked, or can be provided with a tamper-resistant seal, to prevent access when the insert  63  is removed from the tray  62 . That capability can be used to centrally restock the cabinet as inserts  63  are swapped and refilled in the pharmacy or other central storage location. Thus the inserts  63  may provide the function of the restocking packages  52  of FIG. 5.  
         [0056]    The drawer  60 - 1  is completed by a fascia piece  74  and a knob  75 . The end of the tray  62  may have slots and/or tabs which mate with slots and/or tabs at the corresponding end of insert  63 .  
         [0057]    Those of ordinary skill in the art will recognize that other types of inserts  63 , other configurations for providing locked lids, other configurations for releasing the insert from the tray, and other fascia and knob configurations are possible. FIG. 7 is provided only for the purpose of illustrating a presently preferred embodiment. Those of ordinary skill in the art will recognize that many modifications and variations are possible.  
         [0058]    [0058]FIG. 8 illustrates the unit dose drawer  58  of FIG. 6 in a fully closed position in a cabinet  78  without any other drawers. FIG. 9 illustrates the unit dose drawer  58  of FIG. 6 in a fully opened position in the cabinet  78 .  
         [0059]    [0059]FIG. 10 is a flow chart illustrating a dispense operation from a unit dose drawer. Assuming that the nurse has properly logged into the cabinet and identified a patient, the dispense operation from the unit dose drawer begins at step  80  in which the nurse indicates the number of units of a medication, previously identified, to be dispensed. At step  82 , the control computer  32  identifies the drawer containing the desired medication and the amount of travel necessary to make the next pocket or pockets containing the medication accessible. At step  84 , signals are sent to a circuit which causes the identified drawer to travel the necessary distance thereby providing access to the necessary pocket or pockets. The nurse then removes the medication from the accessed pockets and provides an indication that the items have been dispensed at step  86 . The control computer  32 , upon receiving an indication that a dispense has occurred, at step  88  sends signals which identify the open drawer and cause the drawer to be driven to its closed position. The foregoing process may be used for one unit-dose of medication where the same medication is in all pockets or can be used for multiple units of the same medication where the same medication is in all pockets. In a situation where multiple units of the same medication are to be dispensed, but different medications are in the drawer pockets, the nurse indicates the number of units to dispense. The drawer then fully extends exposing all of the pockets. The nurse dispenses the desired medications from the fully opened drawer. Such a “matrix mode” of dispensing would be used only in connection with noncontrolled substances.  
         [0060]    The mechanical hardware for driving the trays  62  is illustrated in FIGS. 11 through 15. In FIG. 11, a perspective view of a drive chassis  100  is illustrated. The chassis carries motors  102 - 1  through  102 - 12  which are each used to drive one tray  62 . As seen best in FIG. 15, a shaft  104 - 1  through  104 - 12  of each motor drives an associated worm gear  106 - 1  through  106 - 12 , respectively. As seen best in FIGS. 12 and 15, each side-by-side pair of motors drives one of the upper trays and the lower tray directly beneath it. That is accomplished, in part, by each worm gear  106 - 1  through  106 - 12  mating with and driving a gear  108 - 1  through  108 - 12 . An upper clutch rod  110  carries odd numbered gears  108 - 1 ,  108 - 3 ,  108 - 5 ,  108 - 7 ,  108 - 9 , and  108 - 11  while a lower clutch rod  111  carries even numbered gears  108 - 2 ,  108 - 4 ,  1086 ,  108 - 8 ,  108 - 10 , and  108 - 12 . The upper clutch rod  110  and lower clutch rod  111  are responsive to an override mechanism  113  operated by a user through an override bar  115 . Movement of the override bar  115  to the right in FIG. 11 causes both the upper clutch rod  110  and lower clutch rod  111  to move to the left as seen in FIG. 11. As will now be described, lateral displacement of the upper clutch rod  110  and lower clutch rod  111  disengages the trays from the motors.  
         [0061]    Each of the gears  108 - 1  through  108 - 12  has associated therewith a moveable gear  117 - 1  through  117 - 12 , respectively, seen best in FIGS. 13, 14, and  15 . The moveable gears  117 - 1  through  117 - 12  are free to move along their respective clutch rods  110 ,  111  while at all times being drivable by their associated gear  108 - 1  through  108 - 12 , respectively. That may be accomplished, as seen in FIGS. 13 and 14, by providing gears  108 - 1  through  108 - 12  with a hub  120 - 1  through  120 - 12  having a flattened or shaped exterior circumference which mates with a similarly shaped interior circumference of the moveable gears  117 - 1  through  117 - 12 , respectively.  
         [0062]    Each of the moveable gears  117 - 1  through  117 - 12  has associated therewith a clutch fork  119 - 1  through  119 - 12 , respectively, best seen in FIG. 15. Each of the clutch forks  119 - 1  through  119 - 12  is connected to one of the clutch rods  110 ,  111 . As seen in FIGS. 13 and 14, teeth  122 - 1  through  122 - 12  of moveable gears  117 - 1  through  117 - 12  are adapted to engage teeth  124 - 1  through  124 - 12  of a driven gear  126 - 1  through  126 - 12 , respectively. Each of the driven gears  126 - 1  through  12612  has a set of teeth  128 - 1  through  128 - 12 , respectively, along its outer periphery.  
         [0063]    During normal operation, the clutch rods  110 ,  111  are biased so that the teeth  122 - 1  through  122 - 12  of moveable gears  117 - 1  through  117 - 12  mate with the teeth  124 - 1  through  124 - 12  of driven gear  126 - 1  through  126 - 12 , respectively. When the override bar  115  is moved to the right in FIG. 11, the clutch rods  110  and  111  overcome the bias, normally provided by springs, and therefore move to the left as seen in FIG. 11. Movement to the left of the clutch rods  10 ,  111  causes each of the clutch forks  119 - 1  through  119 - 12  to move to the left pushing with it the moveable gears  117 - 1  through  117 - 12 , respectively. Movement of the moveable gears  117 - 1  through  117 - 12  to the left, causes the teeth  122 - 1  through  122 - 12  of the moveable gears  117 - 1  through  117 - 12  to disengage from the teeth  124 - 1  through  12412  of driven gear  126 - 1  through  126 - 12 , respectively. When that occurs, driven gears  126 - 1  through  126 - 12  are no longer connected via the worm drive to the electric motors  102 - 1  through  102 - 12 .  
         [0064]    A chain  130 - 1  through  130 - 12  engages the teeth  128 - 1  through  128 - 12  of driven gear  126 - 1  through  126 - 12 , respectively. The other end of the chain may engage an idler gear, one of which  131 - 3  is shown in FIG. 11. Each chain is connected to one of the trays so that the tray moves with the chain. In FIG. 11, chain  130 - 3  is connected to tray  62 - 3 . During normal operation, when any of the motors  102 - 1  through  102 - 12  is energized, its shaft rotates thereby rotating the worm gear  106 - 1  through  106 - 12  and associated gears  108 - 1  through  108 - 12 , which in turn rotates its associated moveable gear  117 - 1  through  117 - 12 , which drives the driven gear  126 - 1  through  126 - 12  causing the chain  130 - 1  through  130 - 12  to move, respectively. Because each tray is attached to its own chain, the position of the tray can be controlled by controlling the amount of rotation of each motor&#39;s shaft  
         [0065]    The worm gear is designed to be self locking. More specifically, when the motor is not energized, the worm gear is designed so that there is sufficient friction to prevent the tray from moving, and hence preventing the drawer from being opened or closed. In the event of a power failure, control computer  32  malfunction, or other event which creates a state in which the drawers cannot be driven by the motors to their open position, the override bar may be used as previously described to disengage the moveable gears from the driven gears. When that occurs, the drawers are no longer connected to the worm gear such that the driven gears  126 - 1  through  126 - 12  are free to rotate thereby allowing each of the drawers to be opened and closed.  
         [0066]    Returning to FIG. 11, each of the motor shafts  104 - 1  through  104 - 12  carries a sensor blade  132 - 1  through  132 - 12 , respectively. The sensor blades  132 - 1  through  132 - 12  each carry two magnets  133 - 1  through  133 - 12  and  134 - 1  through  134 - 12 , respectively. Each of the motors  102 - 1  through  102 - 12  is provided with a Hall effect sensor  136 - 1  through  136 - 12 , respectively. Thus, as the sensor blade  1321  through  132 - 12  rotates its magnets  133 - 1  through  133 - 12 ,  134 - 1  through  134 - 12 , the magnets are brought adjacent to the Hall effect sensor  136 - 1  through  136 - 12 , respectively, such that a 360° rotation of the motor shaft produces two pulses. Those pulses are input to control electronics which will now be described in conjunction with FIGS. 16 through 29.  
         [0067]    Turning first to FIGS. 16, 17 and  18 , two eight bit words are received in the upper left-hand corner of FIG. 16 from the control computer  32 . The first eight bit word  150  represents the distance a drawer is to travel. From the second eight bit word, four bits  152  represent a drawer select signal, a bit  154  is representative of a start transaction, a bit  155  is representative of direction, a bit  156  is representative of a “clear error” signal, and a bit  157  is representative of a “retry” signal. The distance bits  150  are input to a counter  158 . A comparator  160  is responsive to the counter  158 . The comparator  160  is also responsive to a plurality of switches  162  which set a value to which the comparator compares the output of the counter  158 .  
         [0068]    The counter  158  is loaded with the distance information encoded in the bits  150 . The counter  158  then begins counting down from the loaded value. While the counter is counting down, the drawer is being driven at a first, high speed. When the counter reaches the value set by the switches  162 , the comparator  160  produces a signal available at node  164  which is referred to as the “low speed enable” signal. This indicates to a circuit, to be described later, that the drawer has traveled a substantial portion of the distance that it is to travel and the speed should now be reduced for the remainder of the distance to be traveled.  
         [0069]    The drawer select bits  152  are latched in a latch  166  seen in FIG. 16. The drawer select bits  152  are input, via FIG. 18, to a drive select/control circuit described herein below. The drawer select bits  152  are also input, via FIG. 18, to motor sensor select/clock circuit  168 , see FIG. 17, which is used to identify which drawer is to be actuated for purposes of selecting appropriate feedback signals from the actuated drawer.  
         [0070]    [0070]FIG. 19 has in the upper portion thereof a motor enable path  170  which is responsive to a “count complete/enable” signal from FIG. 18 as well as a “delayed start transaction/retry” signal also from FIG. 18. Those two signals are processed as shown in motor enable path  170  to produce a “master motor enable” signal.  
         [0071]    In the middle of FIG. 19, a flip-flop  172  is provided which is responsive to the motor enable path  170  as well as the “delayed start transaction/retry” signal available from FIG. 18. The flip-flop  172  produces the signals “hardware busy” and “command lock out”.  
         [0072]    Finally, in the bottom portion of FIG. 19, a circuit path  174  is provided for producing an “error” signal in response to an “overload detect” signal (indicative of an overcurrent condition) input to the circuit path  174 . In response to the detection of an overcurrent condition, the “error” signal is generated.  
         [0073]    [0073]FIG. 20 illustrates a circuit path  176  for producing a “master low speed enable” signal through the logical combination of the “low speed enable signal” produced by the comparator  160  of FIG. 18 and a “drawer open/closed feedback” signal from FIG. 17.  
         [0074]    [0074]FIG. 21 illustrates motor sensor interface electronics  178 . The motor sensor interface electronics  178  receive the signals produced by the Hall transducers to produce signals MD_ 1  through MD_ 12  MTR SNS signals which are input to the motor sense select/clock circuit  168  shown in FIG. 17. In FIG. 21, the motor sensor interface electronics are shown for four of the drawers.  
         [0075]    [0075]FIG. 22 illustrates home sensor electronics  180  for the upper individual drawers. Each of the trays is provided with an upstanding metal tab or flag ( 95  in FIG. 7). The drive chassis carries sensors, each sensor comprised of one LED  182 - 1 ,  182 - 3 ,  182 - 5 ,  182 - 7 ,  182 - 9 , and  182 - 11  and one corresponding light sensitive transistor  184 - 1 ,  184 - 3 ,  184 - 5 ,  184 - 7 ,  184 - 9 , and  184 - 11  corresponding to the upper trays  62 - 1 ,  62 - 3 ,  62 - 5 ,  62 - 7 ,  62 - 9 , and  62 - 11 , respectively, of which only tray  62 - 3  is shown in FIG. 11. When each tray  62 - 1 ,  62 - 3 ,  62 - 5 ,  62 - 7 ,  62 - 9 , and  62 - 11  is in its closed or home position, the flag carried by that tray blocks the light produced by the LED  182 - 1 ,  182 - 3 ,  182 - 5 ,  182 - 7 ,  182 - 9 , and  182 - 11  from being received by the corresponding light sensitive transistor  184 - 1 ,  184 - 3 ,  184 - 5 ,  184 - 7 ,  184 - 9 , and  18411 , respectively. The signals produced by the sensors  184 - 1  through  184 - 12  are input to the logic shown in FIG. 23 to produce MD_ 1  through MD_ 12  O/C (open/closed) signals and MD_ 1  through MD_ 12  Master O/C signals.  
         [0076]    The MD_ 1  through MD_ 12  O/C signals are input to the logic circuit  188  illustrated in FIG. 24. The logic circuit  188  combines the signals to produce a “Master open/close SNS” signal. The MD_ 1  through MD_ 12  Master O/C signals are input to the motor sensor select/clock circuit  168  illustrated in FIG. 17.  
         [0077]    [0077]FIG. 25 illustrates a manual override circuit  190 . The manual override circuit  190  is responsive to the position of the override bar  115  to produce a signal indicative of a manual override. When a manual override is in effect, a “Manual Override” signal is produced by the manual override circuit  190  illustrated in FIG. 25.  
         [0078]    [0078]FIG. 26 illustrates a pulse width modulated speed control circuit  192  responsive to the MTR-SNS signal produced by the motor sense select/clock circuit  168  of FIG. 17. The speed control circuit produces a “speed enable” signal.  
         [0079]    [0079]FIG. 27 illustrates in the lower portion a motor control interface  194  producing signals input to relays  196 - 1  through  196 - 12  illustrated in FIG. 28. FIG. 27 also illustrates a current control circuit  198 . The current control circuit  198  is responsive to an overcurrent condition, e.g., the drawer has run into an obstacle, jammed, or is otherwise having trouble moving, and produces a “current enable” signal. The current enable signal is used to drive the motors up to a maximum overcurrent condition. The current control circuit  198  may be viewed as a force control. More specifically, sufficient force is generated to overcome system friction and mass, but not enough force to injure anyone should they be in the path of a moving drawer. The control computer  32  may be provided with software for providing an automatic retry and an anti-pitch movement whenever a jam is detected. The relays  196 - 1  through  196 - 12  of FIG. 28 are responsive to signals produced by the logic circuit  200  illustrated in FIG. 29.  
         [0080]    While the present invention has been described in connection with preferred embodiments thereof, those of ordinary skill in the art will recognize that many modifications and variations are possible. The present invention is intended to be limited only by the following claims and not by the foregoing description which is intended to set forth the presently preferred embodiment.