WO1992002438A1 - Automated storage and retrieval system - Google Patents

Abstract

An automated storage and retrieval system (10) includes two confrontingly opposed, columnar arrays (12, 14) which define a plurality of vertically spaced tray-receiving recesses (20). A platform (28) is vertically displaceable along and between the arrays and carries an extraction device (46) operable for withdrawing a selected tray (80) from an array recess onto the platform, and for inserting a tray supported on the platform into a vacant recess in either array. The extraction device includes a pair of rods (72, 74) carried on and for movement longitudinally along the platform, toward and away from the opposed arrays, about opposed continuous-loop drive belts (48, 50) which lie in substantially vertical planes. The rods are releasably engageable, through rotation of the drive belts, within handles (98) provided at and extending longitudinally outwardly from the opposite ends of each tray to enable withdrawal and insertion of the selected tray.

Description

AUTOMATED STORAGE AMD RETRIEVAL SYSTEM

FIELD OF THE INVENTION

Tne present invention relates to automated article storage and retrieval systems wherein articles are stored in bins or trays located within and along arrays of such trays. The invention is more particularly directed to such a system wherein the trays, which are vertically spaced within recesses defined alont, a pair of confrontingly opposed columnar arrays separated by an access region within which a platform is vertically displaceable into registration with array-supported trays or tray positions, may be selectively withdrawn from and inserted into the arrays by a novel extraction device carried on the movable platform.

BACKGROUND OF THE INVENTION

Automated storage and retrieval systems for providing high density yet readily accessible storage of articles have long been known. Commonly- owned U.S. Patent No. 4,690,602, for example, discloses a two-dimensional array of storage bins or locations which are extractable for accessing stored articles. To achieve such access a two- dimensionally displaceable platform is movable to selected storage locations thereof and arm-like extractor elements are extendible into the storage location past the front edge of a bin for engagement with the bin sides to withdraw the bin from the array and, similarly, to reinsert the bin into the same or a different storage location. The prior art teaches a variety of arrangements for effecting extraction and return of an array-supported storage bin or tray. Some require highly specialized or complex structural elements and assemblies that are unnecessarily subject to breakdowns or which typically require regular realignment and/or repair. Others operatively grip or grasp or otherwise engage the bins in a fashion that is somewhat less reliable or stable or secure than desired or that does not permit the apparatus to extract bins containing unusually heavy articles. SUMMARY OF THE INVENTION

The present invention provides an automated storage and retrieval system in which articles are storable in outwardly slidable trays that are supported in vertically-stacked relation along a pair of confrontingly-opposed, columnar arrays. A platform carries an extraction device for withdrawing and reinserting trays in the arrays and which is single-dimensionally displaceable vertically along and between the opposed arrays into registration with selected trays or tray-receiving array locations. The extraction device is formed of a pair of continuous loop drive chains spaced from each other widthwise across the platform and lying in substantially vertical planes. The chains carry spanningly therebetween a first and a second rod spaced along and jointly moveable with the chains into releasable engagement within the interior channels of handles that extend longitudinally at or from the tray ends to thereby grasp the tray and enable selected tray withdrawal from and reinsertion into a location in either of the opposed arrays. Other features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein similar reference characters denote similar elements throughout the several views: FIG. 1 is a side view, partly in cross section, of an automated storage and retrieval system constructed in accordance with the present invention; FIG. 2 is an end view, partly in cross section, of the automated storage and retrival system shown in Fig. 1; FIG. 3 is a perspective view, partly broken away and exploded, of a portion of the vertically-displaceable platform and of one of the vertical standards along which the platform rides; FIG. 4 is an elevated perspective view, partly broken away, of a portion of the platform and of one of the arrays including several tray- receiving shelves disposed vertically therealong; FIG. 5 is an elevated perspective view of the major operating components of the platform- carried extraction device of the present invention; and FIGS. 6 to 8 are diagrammatic side views illustrating, for purposes of explanation, the progressive withdrawal of a tray from an array location by operation of the extraction device of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to an automated article storage and retrieval system and, in a currently preferred form of the invention, to a vertically-oriented, optionally self-contained arrangement in which a platform is vertically displaceable along and between a pair of confrontingly opposed or facing arrays or towers or columns in each of which a plurality of vertically- spaced tray locations are defined. The invention is particularly directed to a novel and advantageously- configured extraction device operable for withdrawing any selected tray from its location in one of the arrays, for transporting — in association with a movable platform — the withdrawn tray to a selected vacant tray location in either array and for then inserting the tray into the selected vacant location. With specific reference to the drawings, an overall view of an automated storage and retrieval system constructed in accordance with the invention is shown in Figs. 1 and 2 and there identified by the general reference numeral 10. The system 10 is comprised of first and second vertically-oriented and, if desired, substantially freestanding columnar arrays 12, 14 disposed in opposed or facing relation and spaced apart by a predetermined distance or separatior to delineate an access region 16 therebetween. Each array 12, 14 raay, by way of example, be fabricated as a framework of vertical masts or standards 18 and generally horizontal crossbars 20, the crossbars defining a plurality of tray-receiving locations or recesses or shelves in each array as will hereinafter be described. Top and bottom bracing members 21 may also spanningly connect the opposed arrays 12, 14 for enhanced stability. In a preferred form of the system 10 the absolute and relative vertical positions of the crossbars or shelf members 20 are adjustable for selectively varying the locations of and vertical spacing between all or particular ones of the tray-receiving locations. The system 10 may also be suitably enclosed or enveloped by an outer skin or sheeting 22 so as to limit unintended access to articles stored therewithin and to prevent inadvertent worker injury from moving parts. As is typical in automated storage and retrieval systems, an operator workstation or article delivery area 24 implemented as an enlarged opening in the rear face of one of the arrays — e.g. the first array 12 — and a corresponding vertical separation between appropriately positioned horizontal crossbars or shelf members 20 at the top and bottom of the workstation may also be provided. A keyboard 26 or the like mounted adjacent the workstation 24 enables direct user input to and control of the operation of the system 10. The trays 80 which are receivable in the horizontal crossbar-defining locations or shelves of each array 12, 14 may be fabricated as bins for direct receipt of stored parts or articles — for which purpose the trays may be compartmentalized or otherwise selectively capable of such compartmentalization or segmentation — or as carriers for replaceable or reconfigurable inserts within which such parts or articles are carried as is well known in the art. In the embodiment of the invention herein described, by way of example, each tray 80 comprises a generally rectangular, centrally-open frame within which an article bin is supportedly carryable and made up of unitarily formed or otherwise rigidly attached side members 82 and end members 84 (Fig. 4) . Each of the side and end members 82, 84 is configured, as with an L- shaped cross section, to provide a respective bin- supporting horizontal base 86, 88 and an upstanding respective sidewall 90 or endwall 92. When a tray 80 is disposed within one of the available array locations or recesses, the undersides of its opposed side member bases 86 rest atop the crossbars or shelf members 20 and thereby support the tray within that recess and as the tray is slidably withdrawn or extracted therefrom. Depending longitudinally-outwardly from each endwall 92 of the tray 80 is a ledge 94 and, depending downwardly from the free end of the ledge, is a leg or lip 96. Together, the endwall 92, ledge 94 and lip 96 form, at or proximate each longitudinal end of the tray, a handle-like arrangement including a substantially U-shaped interior channel 98 that is open at its bottom or downwardly-oriented side and which extends along the width of the tray 80. Although the channel 98, ledge 94 and lip 96 are illustrated herein as extending for substantially the entire tray width, those skilled in the art will readily appreciate as this description proceeds that the extent of such widthwise extension is generally a matter of design choice, as is the U-shaped cross-sectional contour of the channel 98 and, too, the exact structure of the tray-carried member(s) by which the channel is defined. Similarly, a modification in which the channel 98 is open upwardly — rather than downwardly — is both contemplated and intended as being within the scope of the invention. A platform, generally designated 28, is adapted for single-dimensional vertical movement along and between the opposed first and second arrays 12, 14 within the access region 16. For this purpose, a lift cable 30 is secured to the platform 28 and is led, as through top and bottom-mounted pulleys 32, 34, to a feed drum 36 about which the lift cable is selectively wound and unwound for respectively raising and lowering the platform. The feed drum is, in turn, rotated by and under the control of an electric, bidirectionally-operable motor 38 located, in the illustrated embodiment, at or proximate the bottom of the first array 12. The drum 36 may also include or carry an encoder (not shown) of any suitable form for use in sensing the rotation of the feed drum and, thereby, determining the resulting anticipated vertical displacement of the platform 28. The platform 28 may be configured in any appropriate manner such, for example, as the generally open frame construction of the presently- disclosed embodiment. The length of the platform — i.e. along the opposed tray-extraction and insertion directions extending between the opposed arrays 12, 14 as indicated by the double-headed arrow 39 in Figs, l and 5 — substantially conforms to the width of the access region 16 and the platform carries, at each of its longitudinal ends, vertically-oriented pairs of guide rollers or castors 40 in continuous engagement with the interior standards 18 that bound the access region 16. More particularly, V-shaped troughs 42 defined in the circumferential faces of the rollers 40 mate with wedge-like surfaces 44 provided on the interior standards 18 (Figs. 3 and 4) along which the guide rollers ride as the platform 28 is vertically displaced and are effective to maintain the engagement of the rollers and vertical standards and prevent unintended horizontal shifting or translation of the platform during, for example, its vertical displacement. The platform frame may be further provided with side- mounted, longitudinally extending tray-support shoulders 45 onto which trays 80 extracted from the arrays 12, 14 are slidably receivable. Also carried on the platform 28 is a tray extraction device 46, the main operating components of which are perhaps best seen in Fig. 5. The extraction device 46 is formed of a pair of continuous loop drive belts or chains 48, 50 or the like disposed proximate or along the opposite sides of and extending for ger.arally the full length of the vertically-displaceable platform. The chains are spaced from each other, across the platform 28, by a distance substantially conforming to the width of the trays 80 and, in the preferred form herein disclosed, by slightly more than the tray width so as to enable supported receipt of a tray, extracted from one of the arrays, on the platform between the opposed chains 48, 50 as will hereinafter become apparent. Each chain is trained about spaced apart first and second rollers or sprocket wheels 52, 54 and lies in a substantially vertical plane with the upper run of the continuous chain loop above and the lower run of the loop below the tray-support shoulders 45. Selectively controlled rotation of the chains 48, 50 about the sprocket wheels 52, 54 is effected by operation of a bidirectional electric motor 56. The motor 56 drives the sprocket wheels 52 through the combination of a first belt or chain linkage 58 and associated intermediate sprocket rollers 60, 62 fixedly secured to a rotatable tie shaft 64, a transfer sprocket roller 66 concentrically rotatable with the roller 60, and second linkages 68 and associated driven sprocket rollers 70 each concentrically rotatable with a respective one of the sprocket wheels 52. Carried on and spanningly between the drive chains 48, 50 are first and second tray engagement rods 72, 74. The elongated rods extend substantially perpendicular to the tray-extraction direction 39 and are suitably configured for releasable engagement with the handles — or more particularly for receipt within the channels 98 — that are defined proximate the longitudinal ends of the trays 80. The rods 72, 74 are, moreover, predeterminately spaced from each other longitudinally along the chains 48, 50 by a distance substantially corresponding to the separation of the channels 98 at opposite ends of each tray. This spacing permits each of the rods 72, 74 to be received and concurrently maintained in a respective one of the channels 98 at the opposite ends of any selected tray 80. Where, as herein disclosed, the tray channels 98 have downwardly-directed openings through which the rods 72, 74 are receivable into the channels, the rod locations illustrated in Fig. 5 — i.e. along the lower runs of the drive chains 48, 50 — correspond to a state or condition in which neither rod 72, 74 is positioned within a tray channel 98 or, put another way, in which no tray 80 is either currently disposed supportedly on the platform 28 or is in the process of being extracted from an array shelf. The platform 28 is additionally provided proximate each of its longitudinal ends — as for example on one of the brackets 100 to which the platform guide rollers 40 are rotatively mounted — with an upper and a lower sensor 102, 104 (Fig. 3) for assuring the achievement and maintenance of proper registration of the platform with a selected tray or with a vacant tray-receiving location in one of the arrays 12, 14. Any suitable sensor may be utilized for this purpose; in the presently disclosed embodiment of the invention, a reflective- type sensor (such as photomicrosensor EE-SY310 of the Omron Tateisi Electronics Co. of Osaka, Japan) is employed for each of the sensors 102, 104. These sensors cooperate with an extension or finger 106 (Fig- 4) that projects outwardly beyond the horizontal standard 18 from one of each pair of the shelf members 20 at its end proximate the access region 16. The finger 106 has a vertical height or size at least equal and preferably closely conforming to the spacing of the upper and lower sensors 102, 104 so that the sensors are capable of simultaneous alignmen" *r opposed adjacency with the surface of the finger. In other words, vertical registration of the platform 28 with a filled or vacant tray-receiving location in one of the columnar arrays 12, 14 is indicated when both sensors 102, 104 simultaneously detect reflective proximity or adjacency with the corresponding shelf member finger 106, and is contraindicated when at least one of the sensors fails to detect such proximity. This arrangement enables — in addition to rapid and accurate determination of tray location registration as the platform is vertically displaced — continued maintenance of registration as a tray is extracted from an array and moved onto the platform, or is inserted into an array recess from the platform; the ability to maintain registration under such circumstances is particularly advantageous where an extracted tray contains an unusually heavy load which causes even minor stretching of the lift cable 30 (and consequent vertical movement of the platform 28) as a tray 80 is moved onto or off of the platform. The construction and details of a control device or circuitry for effecting dynamic realignment or reregistration of the platform and otherwise operating the lift motor 38 in accordance with, for example, the signals from the sensors 102, 104 is considered to be a matter of design choice to the person of ordinary skill. The process by which the extraction device 46 operatively withdraws trays from, and correspondingly inserts trays into, locations defined in the columnar arrays 12, 14 will now be described. As previously noted, the Fig. 5 position of the rods 72, 74 corresponds to that condition in which no tray is currently supported on the platform 28 and the extraction device is in readiness for withdrawing a tray from a shelf in one of the arrays. The platform is first moved, if necessary, vertically along and between the arrays 12, 14 into registration with a selected tray 80 situated in a recess or location in, for example, the first array 12 by appropriate operation of the lift motor 38; proper vertical registration of the platform with the selected tray is detected by simultaneous reflective coincidence of both the upper sensor 102 and the lower sensor 104 with the shelf-carried finger 106 at the tray position. As seen in Fig. 4, the sprocket wheels 52, 54 are predeterminately located on the platform 28 so that, in this position of registration, the longitudinally outermost edge of each wheel 52, 54 is substantially vertically aligned with tl elongation of the adjacently- disposed (i.e. leading end) tray channel 98. Thus, the innermost longitudinal end of each tray 80 that is properly seated on an opposed pair of shelf members or crossbars 20 projects into the access region by a distance sufficient to vertically align its innermost channel 98 with the longitudinal limit position of each drive chain run or loop 48, 50. The next sequence of events in the withdrawal of the selected tray 80 is illustrated in pertinent part in Figs. 6 through 8. The extraction motor 56 is operated in the appropriate rotational direction or sense to concurrently rotate the chains 48, 50 and jointly carry the rods 72, 74 along the lower chain runs toward the selected tray — i.e. to the right in the drawing Figures. As the first rod 72 reaches its rightward or forwardmost limit position at the second sprocket wheels 54 and is carried by the drive chains 48, 50 about the wheels 54, its direction of movement first shifts from a substantially horizontal to a substantially upwardly-vertical orientation. In so moving vertically upward the first rod 72 enters the channel 98, through its downwardly-directed access opening, and is thereby carried by the drive chains 48, 50 into engagement with the tray handle. The second rod 74, as the first rod moves vertically upward about the sprocket wheels 54, continues its forward or rightward horizontal motion along the lower chain runs. With continued rotation of the drive chains in the same sense, the first rod 72 moves further about the outer circumference of the sprocket wheels 54 and shifts from a substantially vertical to a substantially horizontal direction of movement (Fig. 7) , this time in the opposite or rearward direction — i.e. away from the array 12 bearing the selected tray — along the upper drive chain runs. As the first rod 72 thus moves horizontally away from the array 12 along the upper chain runs, it remains within the front or leading tray channel 98 and pulls the tray 80, through its abutment with the inner side or face of the tray lip 96, slidably along the shelf members 20. The selected tray is thereby withdrawn or extracted from the array shelf (i.e. to the left in Figs. 4 and 7) and onto the support shoulders 45 of the platform 28. During this period of tray extraction, the second rod 74 continues to move horizontally toward the array 12 (from which the selected tray is being extracted) along the lower runs of the drive chains 48, 50. As the selected tray 80 reaches a position of substantially complete withdrawal from support by the array shelf members 20, it attains a position in which the handle channel 98 at the rear or trailing end of the tray becomes vertically aligned with the outward edge of the sprocket wheels 54. This orientation occurs concurrently with the second rod 74 being carried by the drive chains 48, 50 along their lower runs, onto and circu ferentially about the wheels 54, and thus vertically upwardly into the channel 98 at the trailing end of the tray. At this point, therefore, the rods 72, 74 are simultaneously located within the leading and trailing, respectively, channels 98 defined at the opposite longitudinal ends of the selected tray 80. Further continued rotation of the chains 48, 50 in an amount sufficient to carry both rods 72, 74 leftward (in the Figures) along the upper chain runs — to positions immediately above, for example, the lower run positions of the rods shown in Fig. 5 — brings the entirety of the selected tray onto the platform shoulders 45 and clear of the array 11 and its associated structural and functional elements. The rods 72, 74 — while the selected tray is thus supported on the platform 28 — remain within the respective handle channels 98 at the tray ends (Fig. 8) . With the tray thus fully seated on the platform 28, the lift motor 38 may be operated to vertically displace the platform into registration with a vacant tray-receiving location in either of the columnar arrays 12, 14 or with the workstation 24 for enabling user access to the platform-carried tray. Where the tray is to be returned to a vacant recess or slot or shelf in the same array 12 from which it was extracted, operation of the motor 56 to rotate the drive chains 48, 50 in the opposite sense from that by which the selected tray was extracted will effect insertion of the platform-carried tray onto the array shelf. If, on the other hand, it is desired to insert or transfer the tray into the oppositely disposed array 14, the extraction device motor 56 is operated to rotate the chains 48, 50 in the same sense as that used to withdraw the tray from the first array 12. In either event, the joint movements of the rods 72, 74 and their cooperations with the selected tray end-mounted handles to, in effect, push or drive or so insert the tray into an array location or shelf should by now be apparent to those skilled in the art. What should be recognized and appreciated is that the extraction device of the present invention enables ready and reliable withdrawal and insertion of selected trays, from and into either of the confrontingly opposed columnar arrays, without undue structural complexity. While there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

What is claimed is: 1. A storage and retrieval system extraction means, carried on a platform means, for withdrawing a selected tray from a tray location and for inserting a tray carried on said platform means into a tray location, comprising: each said tray having a length and including, at each opposed end along said tray length, handle means engageable by said extraction means for longitudinally withdrawing the tray from a tray location and for longitudinally inserting a tray into a tray location, said handle means including a vertically-oriented opening through which said handle means is engageable by said extraction means; and said extraction means comprising: first and second members concurrently movable along said platform means at a predetermined spaced apart relation to each other toward and away from a tray location, each said member being elongated in a direction 1 substantially perpendicular to said

2 direction of member movement; and

3 drive means operable for

4 concurrently moving said first and second

5 members so that, with said platform means

6 in registration with a selected tray

7 location containing a selected tray, said

8 first member is moved initially toward

9 said selected tray location and vertically

10 into said handle means opening at one end

11 of the selected tray and is then moved

12 away from said selected tray location with

13 said first member in engagement with said

14 one end handle means to thereby

15 longitudinally withdraw the selected tray

16 from the selected tray location onto said

17 platform means until the selected tray is

18 substantially fully withdrawn whereupon

19 said second member is moved vertically

20 into said handle means opening at the

21 opposite end of the selected tray and is

22 then moved away from said selected tray

23 location with said second member in

24 engagement with said opposite end handle

25 means until the selected tray is fully supported on said platform means with both said first and second members engaged with said handle means at said respective one and opposite ends of the tray. 2. A storage and retrieval system extraction means in accordance with claim 1, said extraction means drive means comprising a continuous loop drive belt carrying said first and second members and trained about a pair of spaced apart rotatable pulleys disposed proximate opposite ends of said platform means, and operable means for effecting rotation of said drive belt about said spaced apart pulleys so as to carry said first and second members through said concurrent movements for tray-withdrawing engagement with said handle means at opposite ends of the selected tray. 3. A storage and retrieval system extraction means in accordance with claim 2, wherein said continuous loop drive belt lies in a substantially vertical plane. 4. A storage and retrieval system extraction means in accordance with claim 2, wherein said operable means is operable for bidirectionally driving said continuous loop drive belt and said first and second members carried by said belt. 5. A storage and retrieval system extraction means in accordance with claim 1, wherein each said handle means further comprises an elongated channel extending substantially perpendicular to said tray length and communicating with said opening for enabling access to said channel. 6. A storage and retrieval system extraction means in accordance with claim 5, wherein each of said first and second members comprises an elongated rod engagedly receivable in one of said engageable means channels through said vertically- oriented opening. 7. In a storage and retrieval system including a framework for supporting a plurality of article storage trays in vertically spaced apart relation at plural predetermined permissable tray locations defined in said framework, platform means for relative movement vertically along said framework into registration with selected ones of said tray locations and for supporting and carrying trays withdrawn from and for insertion into tray locations of said framework, and extraction means on said platform means for withdrawing a selected tray from a tray location of said framework and for inserting a tray carried on said platform means into a tray location of said framework, the improvement comprising: each said tray having a length and including, at each opposed end along said tray length, handle means engageable by said extraction mt .ns for longitudinally withdrawing the tray from a permissable tray location of said framework and for longitudinally inserting a tray into a permissable tray location of said framework, said handle means including a vertically-oriented opening through which said handle means is engageable by said extraction means; and said extraction means comprising: first and second members concurrently movable along said platform means at a predetermined spaced apart relation to each other toward and away from said framework, each said member being elongated in a direction substantially perpendicular to said direction of member movement; and drive means operable for concurrently moving said first and second members so that, with said platform means in registration with a framework tray location containing a selected tray, said first member is moved initially toward said framework and vertically into said handle means opening at one end of the selected tray and is then moved away from said framework with said first member in engagement with said one end handle means to thereby longitudinally withdraw the selected tray from the tray location onto said platform means until the selected tray is substantially fully withdrawn whereupon said second member is moved vertically into said handle means opening at the opposite end of the selected tray and is then moved away from said framework with said second member in engagement with said opposite end handle means until the selected tray is fully supported on said platform means with both said first and second members engaged with said handle means at said respective one and opposite ends of the tray. 8. In a storage and retrieval system in accordance with claim 7, said extraction means drive means comprising a continuous loop drive belt carrying said first and second members and trained about a pair of spaced apart rotatable pulleys disposed proximate opposite ends of said platform means, and operable means for effecting rotation of said drive belt about said spaced apart pulleys so as to carry said first and second members through said concurrent movements for tray-withdrawing engagement with said handle means at opposite ends of the selected tray. 9. In a storage and retrieval system in accordance with claim 8, wherein said continuous loop drive belt lies in a substantially vertical plane. 10. In a storage and retrieval system in accordance with claim 8, wherein said operable means is operable for bidirectionally driving said continuous loop drive belt and said first and second members carried by said belt. 11. In a storage and retrieval system in accordance with claim 7, wherein each said handle means further comprises an elongated channel extending substantially perpendicular to said tray length and communicating with said opening for enabling access to said channel. 12. In a storage and retrieval system in accordance with claim 11, wherein each of said first and second members comprises an elongated rod engagedly receivable in one of said engageable means channels through said vertically-oriented opening. 13. A storage and retrieval system, comprising: a first plurality of trays arranged in vertically-stacked relation to define a first column of said trays, each said tray of said first column being individually movable in a substantially horizontal first direction for extracting the tray from said first column; a second plurality of trays arranged in vertically-stacked relation to define a second column of said trays, each said tray of said second column being individually movable in a substantially horizontal second direction opposite said first direction for extracting the tray from said second column; said first and second columns being predeterminately spaced apart in opposed relation and defining an access region between said opposed columns; extraction means operable for releasably engaging a selected one of said trays, withdrawing the selected tray from one of said stacks and inserting the withdrawn tray into one of said stacks; platform means for carrying said extraction means and disposed in said access region for substantially vertical movement along said first and second columns; each said tray having a length oriented along said first and second directions and including, at each opposed end along said tray length, engageable means for releasable engagement with said extraction means, said engageable means comprising a channel extending substantially perpendicular to said tray length and having a vertically-oriented opening through which said extraction means is releasably receivable for engagement with said tray; and said extraction means comprising a pair of members, each said member extending substantially horizontally and being elongated in a direction substantially perpendicular to said first and second directions, and drive means operable for concurrently moving said members in said first and second directions at a predetermined spaced apart relation to each other substantially corresponding to said tray length so that, with said platform disposed adjacent a selected one of said trays in said first column, one of said members is moved by operation of said drive means through said vertically-oriented opening into the channel at the end of the selected tray proximate said access region so as to releasably engage the selected tray and, with continued movement of said members, the selected tray is thereby withdrawn from the first column in said first direction and supportedly onto said platform and the other of said members is moved through said vertically-oriented opening into the channel at the other end of the selected tray when said tray reaches a position of substantially complete withdrawal from said first column and substantially complete support on said platform with each of said members disposed in one of said channels of the selected tray. 14. A storage and retrieval system in accordance with claim 13, wherein said drive means comprises a pair of continuous-loop drive belts, two pairs of spaced apart rotatable pulleys, and operable means for rotating at least one pulley of each said pulley pair, each of said drive belts being trained about one of said spaced apart pulley pairs to define an elongated loop, and said members being carried spanningly between said drive belts so that, as the operable means rotates said pulleys, said drive belts are concurrently driven and carry said members through said movement thereof in said first and second directions. 15. A storage and retrieval system in accordance with claim 14, wherein the elongated loop of each said drive belt lies in a substantially vertical plane. 16. A storage and retrieval system in accordance with claim 14, wherein said operable means comprises an electrically-operable motor. 17. A storage and retrieval system in accordance with claim 14, wherein each said member comprises an elongated rod. 18. A storage and retrieval system in accordance with claim 15, wherein each said member comprises an elongated rod. 19. A storage and retrieval system in accordance with claim 13, wherein each said member comprises an elongated rod. 20. A storage and retrieval system in accordance with claim 13, wherein said first and second columns are spaced apart by at least said tray length. 21. A storage and retrieval system in accordance with claim 14, wherein said members are spaced apart from each other along said drive belts by an amount substantially corresponding to said tray length. 22. A storage and retrieval system in accordance with claim 13, further comprising a plurality of shelf means spaced vertically along each said column for supporting said trays and along which said trays are longitudinally movable as the trays are withdrawn from and inserted into said stacks, each said shelf means defining a permissable tray location vertically along said column, and means for sensing proper registration of said platform with a selected one of said permissable tray locations in one of said columns so as to enable withdrawal of a tray from and insertion of a tray into the selected location. 23. A storage and retrieval system in accordance with claim 22, wherein said sensing means comprises a registration member carried on an end of each said shelf means proximate said access region, and an upper and a lower sensor carried on said platform for detecting coincidence of said sensors with said registration members of said shelf means and thereby indicating registration of said platform with a selected one of said permissable tray locations. 24. A storage and retrieval system in accordance with claim 23, wherein said registration member comprises an outward projection carried on an end of each said shelf means proximate said access region. 25. A method of retrieving a selected storage tray from a selected tray location, said tray having a first engageable means proximate a first longitudinal end of the tray and a second engageable means on a second longitudinal end of the tray opposite said first end, each of said first and second engageable means including a vertically- oriented opening, comprising the steps of: (A) relatively moving, to a position of adjacency, at least one of the selected tray and platform means carrying means for extracting the selected tray from the selected tray location, the extracting means including a first and a second member in a predeterminately spaced apart relation, said first and second members being jointly movable with respect to the platform means toward and away from the selected tray location for engaging said respective first and second engageable means on the selected tray and withdrawing the tray from the selected tray location and onto the platform means, and each of said first and second members being elongated in a direction substantially perpendicular to the directions of member movement; (B) jointly moving the first and second members toward the selected tray location to a position in which the first member is located substantially vertically-adjacent the opening of said first engageable means of the selected tray in the selected tray location; (C) moving the first member substantially vertically through the opening of and into engagement with the first engageable means of the selected tray while the second member is concurrently moved further toward the selected tray location; (D) moving the first member, in continuous engagement with the first engageable means, away from the selected tray location so as to extract the selected tray from the selected tray location and onto the platform while the second member is moved further toward the selected tray location to a position in which the second member is located substantially vertically-adjacent the opening of the second engageable means of the selected tray; and (E) moving the second member substantially vertically through the opening of and into engagement with the second engageable means of the selected tray while the first member, in continued engagement with the first engageable means, is moved further away from the selected tray location so that the first member is disposed in engagement with the first engageable means and the second member is concurrently disposed in engagement with the second engageable means of the selected tray with the selected tray disposed in supported relation on the platform means. 26. A method in accordance with claim 25, further comprising, following said step (E) , the step of further moving the first and second members away from the selected tray location to a position in which the selected tray is completely withdrawn from the array and is carried on the platform means with the first member disposed in engagement with the first engageable means and the second member disposed in engagement with the second engageable means. 27. A method in accordance with claim 25, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and-a pair of rotatable pulleys about which the belt is trained, each of said steps (B) , (C) , (D) and (E) further comprising rotating the pulleys so as to drive the belt about the pulleys and thereby cause said movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 28. A method in accordance with claim 25, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which the belt is trained, said steps (B) , (C) , (D) and (E) further comprising rotating the pulleys so as to drive the belt about the pulleys in a single directional sense and thereby cause said movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 29. A method in accordance with claim 25, wherein said step (D) of extracting the selected tray from the selected tray location comprises pulling the selected tray outwardly from the selected tray location through said engagement of the moving first member with the first engageable means of the selected tray. 30. A method in accordance with claim 25, the first and second members extending in substantially parallel relation to each other and said substantially parallel relation being maintained as said first and second members are jointly moved in each of said steps (B) , (C) , (D) and (E) . 31. A method in accordance with claim 25, wherein said step (C) comprises moving the first member vertically-upward through the opening of and int engagement with the first engageable means of the selected tray 32. A method in accordance with claim 25, wherein said step (E) comprises moving the second member vertically-upward through the opening of and into engagement with the second engageable means of the selected tray. 33. A method in accordance with claim 31, wherein said step (E) comprises moving the second member vertically-upward through the opening of and into engagement with the second engageable means of the selected tray. 34. A method of retrieving a selected storage tray from a plurality of trays arranged in vertically-spaced fashion in an array, each tray having a first engageable means proximate a first longitudinal end of the tray at the front surface of the array and a second engageable means on a second longitudinal end of the tray opposite said first end, each of said first and second engageable means including a vertically-oriented opening, comprising the steps of: (A) moving, to a position adjacent the selected tray, platform means carrying means for extracting the selected tray from the array, the extracting means including a first and a second member in a predeterminately spaced apart relation, said first and second members being jointly movable with respect to the platform means toward and away from the array for engaging said respective first and second engageable means on the selected tray and withdrawing the tray from the array and onto the platform means, and each of said first and second members being elongated in a direction substantially perpendicular to the directions of member movement; (B) jointly moving the first and second members toward the array to a position in which the first member is located substantially vertically-adjacent the opening of said first engageable means of the selected tray in the array; (C) moving the first member substantially vertically through the opening of and into engagement with the first engageable means of the selected tray while the second member is concurrently moved further toward the array; (D) moving the first member, in continuous engagement with the first engageable means, away from the array so as to extract the selected tray from the array and onto the platform while the second member is moved further toward the array to a position in which the second member is located substantially vertically-adjacent the opening of the second engageable means of the selected tray; (E) moving the second member substantially vertically through the opening of and into engagement with the second engageable means of the selected tray while the first member, in continued engagement with the first engageable means, is moved further away from the array so that the first member is disposed in engagement with the first engageable means and the second member is concurrently disposed in engagement with the second engageable means of the selected tray; and (F) moving the platform means carrying the extracted selected tray to another desired location. 35. A method in accordance with claim 34, further comprising, between said steps (E) and (F) , the step of further moving the first and second members away from the array to a position in which the selected tray is completely withdrawn from the array and is carried on the platform means with the first member disposed in engagement with the first engageable means and the second member disposed in engagement with the second engageable means. 36. A method in accordance with claim 34, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which t e belt is trained, each of said steps (B) , (C) , (D) and (E) fv ther comprising rotating the pulleys so as to drive the belt about the pulleys and thereby ce ise said movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 37. A method in accordance with claim 34, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which the belt is trained, said steps (B) , (C) , (D) and (E) further comprising rotating the pulleys so as to drive the belt about the pulleys in a single directional sense and thereby cause said movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 38. A method in accordance with claim 34, wherein said step (D) of extracting the selected tray from the array comprises pulling the selected tray outwardly from the array through said engagement of the moving first member with the first engageable means of the selected tray. 39. A method in accordance with claim 34, the first and second members extending in substantially parallel relation to each other and said substantially parallel relation being maintained as said first and second members are jointly moved in each of said steps (B) , (C) , (D) and (E) . 40. A method in accordance with claim 34, wherein said step (C) comprises moving the first member vertically-upward through the opening of and into engagement with the first engageable means of the selected tray. 41. A method in accordance with claim 34, wherein said step (E) comprises moving the second member vertically-upward through the opening of and into engagement with the second engageable means of the selected tray. 42. A method in accordance with claim 40, wherein said step (E) comprises moving the second member vertically-upward through the opening of and into engagement with the second engageable means of the selected tray. 43. A method of transferring a selected storage tray from a first plurality of trays arranged in vertically-spaced fashion in a first array to a selected vacant location in a second array of vertically-spaced trays facing the first array, each tray in the first array having a first engageable means proximate a first longitudinal end of the tray at the front surface of the first array and a second engageable means on a second longitudinal end of the tray opposite said first end, each of said first and second engageable means including a vertically-oriented opening, comprising the steps of: (A) moving, to a position adjacent the selected tray, platform means carrying means for extracting the selected tray from the first array, the extracting means including a first and a second member in a predeterminately spaced apart relation, said first and second members being jointly movable with respect to the platform toward and away from the first array for engaging said respective first and second engageable means on the selected tray and withdrawing the tray from the first array and onto the platform means, and each of said first and second members being elongated in a direction substantially perpendicular to the directions of member movement; (B) jointly moving the first and second members toward the first array so as to move the first member to a first limit position in which the first member is located substantially vertically-adjacent the opening of said first engageable means of the selected tray in the first array; (C) moving the first member substantially vertically through the opening of and into engagement with the first engageable means of the selected tray while the second member is concurrently moved further toward the first array; (D) moving the first Tiember, in continuous engagement with the first engageable means, away from the first array so as to extract the selected tray from the first array and onto the platform while the second member is moved further toward the first array to a position in which the second member is located substantially vertically- adjacent the opening of the second engageable means of the selected tray; (E) -moving the second member substantially vertically through the opening of and into engagement with the second engageable means of the selected tray while the first member, in continued engagement with the first engageable means, is moved further away from the first array so that the first member is disposed in engagement with the first engageable means and the second member is concurrently disposed in engagement with the second engageable means of the selected tray; and (F) moving the platform means carrying the extracted selected tray to a position adjacent the vacant location in the second array; (G) jointly moving the first and second members toward the second array so as to move the first member to a second limit position; (H) substantially vertically moving the first member out of engagement with the first engageable means of the extracted selected tray through the vertically-oriented opening of the first engageable means while concurrently further moving the second member toward the second array; (I) further moving the second member, in continued engagement with the second engageable means, toward the second array so as to insert the selected tray into the vacant location in the second array while concurrently moving the first member away from the second array, the second member being thereby moved to the second limit position; and (J) substantially vertically moving the second member out of engagement with the second engageable means of the extracted selected tray through the opening of the second engageable means, while concurrently further moving the first member away from the second array, so as to disengage the second member from the second engageable means and thereby disengage the extraction means from the selected tray. 44. A method in accordance with claim 43, further comprising the step, following said step (J) , of further jointly moving the first and second members away from the second array to thereby prepare the platform means and extraction means for a subsequent tray transfer operation. 45. A method in accordance with claim 43, wherein said step (I) comprises pushing the extracted selected tray from the platform means into the second array through said engagement of the moving second member with the first engageable means of the selected tray. 46. A method in accordance with claim 43, the first and second members extending in substantially parallel relation to each other and said substantially parallel relation being maintained as said first and second members are jointly moved in each of said steps (B) , (C) , (D) , (E), (G), (H), (I) and (J) . 47. A method in accordance with claim 43, wherein said step (C) comprises moving the first member vertically-upward through the opening of and into engagement with the first engageable means of the selected tray. 48. A method in accordance with claim 47, wherein said step (E) comprises moving the second member vertically-upward through the opening of and into engagement with the second engageable means of the selected tray. 49. A method in accordance with claim 43, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which the belt is trained, each of said steps (B) , (C) , (D) , (E) , (G) , (H) , (I) and (J) further comprising rotating the pulleys so as to drive the belt about-the pulleys and thereby cause said joint movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 50. A method in accordance with claim 43, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which the belt is trained, said steps (B) , (C) , (D) and (E) further comprising rotating the pulleys so as to drive the belt about the pulleys in a single directional sense and thereby cause said joint movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 51. A method in accordance with claim 43, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which the belt is trained, said steps (G) , (H) , (I) and (J) further comprising rotating the pulleys so as to drive the belt about the pulleys in a single directional sense and thereby cause said joint movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt. 52. A method in accordance with claim 43, wherein the extracting means further includes a continuous-loop belt to which the first and second members are connected and a pair of rotatable pulleys about which the belt is trained, said steps (B) , (C) , (D) and (E) further comprising rotating the pulleys so as to drive the belt about the pulleys in a first directional sense and thereby cause said joint movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous-loop belt, and said steps (G) , (H) , (I) and (J) further comprising rotating the pulleys so as to drive the belt about the pulleys in a second directional sense and thereby cause said joint movements of the first and second members at said predeterminately spaced apart relation to each other along the continuous- loop belt.