Input/Output Module and Overall Temperature Control of Samples

[0001] This application claims priority to U.S. Provisional Patent Application No. 61/381,832, filed on Sep. 10, 2010 entitled “Large Automated Storage and Retrieval System for Storing Biological or Chemical Samples at Ultra-Low or Cryogenic Temperatures”.

[0002] The invention relates to automated storage and retrieval systems for ultra-low temperature or cryogenic freezer systems used primarily to store biological or chemical samples. In particular, the present invention pertains to systems and methods for efficiently inputting and retrieving samples from the freezers without causing significant temperature rise of other samples stored within the system.

[0003] Storage of biological and chemical samples is becoming widespread in the biotechnology and medical industries. To preserve many of these samples, the samples must be stored well below normal freezing temperatures. Generally speaking, a regular freezer operates from about −5° C. to −20° C., an ultra-low temperature freezer operates from about −50° C. to about −130° C. (preferably at about −80° C.), and a cryogenic freezer operates from about −140° C. to about −196° C. (the boiling point of liquid nitrogen). The present invention is directed to a large automated storage and retrieval system containing one or more ultra-low temperature or cryogenic freezer chests operating below about −65° C. The freezers are contained within a refrigerated enclosure, preferably maintained at about −20° C. Most biological samples stored in ultra-low temperature or cryogenic systems are contained in sealed plastic laboratory tubes held in tube storage racks in arrays of for example 48, 96 or 384 tubes. In some cases, the biological samples are stored in sample storage plates such as sealed microtiter or wellplates, rather than stored in sealed tubes held in a rack.

[0004] The inventors have discovered that introducing warm samples into the system, for example when samples arrive from a processing laboratory, can cause temperature rise among other samples stored in the system unless steps are taken to eliminate or mitigate the temperature rise. The present invention is directed primarily to maintaining the thermal integrity of samples during sample introduction into the system.

[0005] As mentioned, the invention pertains to automated storage and retrieval systems for storing sample tube storage racks or plates at an ultra-low or cryogenic temperature. In particular, a system implementing the invention has a refrigerated enclosure maintained at a temperature of approximately −15° C. to −30° C., and one or more freezer chests, normally a bank of multiple freezer chests, located within the refrigerated enclosure. The freezer chests contain compartments that are preferably maintained, under normal operating conditions, at a designated temperature setting at or below −65° C., such as about −80° C. for an ultra-low temperature system. While samples are stored in the freezer chests, a sample input/output module is provided to pass samples through the wall of the refrigerated enclosure so that samples can be robotically transferred within the refrigerated enclosure to the freezers for storage. In accordance with one aspect of the invention, at least one freezer bay or a portion of one freezer bay is defined as an input/output buffer section and is thermally segregated from long-term sample storage sections in the same or other freezer bays. For example, the input/output buffer section can comprise an insulated wall in a single freezer bay thermally segregating the input/output buffer section and the sample storage section. Alternatively, selected nesting tubes in the freezer bay for storing cassettes holding vertical arrays of sample tube storage racks or plates can be separated and thermally isolated from other nesting tubes in the freezer bay by placing insulation in a selected row or column of nesting tubes otherwise intended to hold cassettes. Preferably, samples placed into the system through the sample input/output module are transferred to the input/output buffer section in order to cool the samples to a temperature at or near the designated temperature setting for the freezers (e.g. −80° C.) prior to transferring the samples to a long-term storage location in the same or different freezer chest. Typically, most samples will be fully cooled to the freezer set temperature within no more than five hours. In most cases, it is contemplated that the input/output buffer section will constitute part of one of the freezer bays, and the remaining section of that freezer bay will be used for long-term storage of samples. In that case, it is desirable that the temperature sensor for the refrigeration unit be located within the input/output buffer section of the freezer bay which is normally the section closer to the refrigeration unit. Testing has shown that such a configuration will cause the refrigeration unit to operate more aggressively to prevent temperature rise within the freezer bay that could otherwise affect samples outside of the input/output buffer section.

[0006] The preferred input/output module is designed to work in connection with the cassette puller described in co-pending U.S. patent application Ser. No. ______, filed on even date herewith, entitled “Cassette Puller”, Attorney Docket No. 5436-00018, and incorporated herein by reference. The input/output module holds multiple cassettes for transferring samples stored in tube storage racks or plates into the refrigerated enclosure from outside of the system and also for transferring samples from inside of the refrigerated enclosure to outside of the system. The most efficient use of the system is with specific input/output cassettes that are preferably configured so that the cassette puller in the above incorporated patent application is able to transfer the input/output cassettes within the refrigerated enclosure to and from the input/output module and to and from the above described input/output buffer section in the freezer. It is also preferred that the cassette puller be able to eject tube storage racks or plates from the input/output cassettes or place sample tube storage racks or plates onto shelves on the input/output cassettes. Preferably, this is done in essentially the same manner that the cassette puller places racks or plates in or ejects racks or plates from a storage cassette used for long-term sample storage in the ultra-low temperature or cryogenic freezers. The preferred configuration for the storage cassette is described in co-pending patent application Ser. No. ______, filed on even date herewith, entitled “Sample Storage Cassette for Ultra-Low or Cryogenic Temperatures”, Attorney Docket No. 5436-00019, and incorporated herein by reference.

[0007] The input/output module includes a manual loading/unloading station that provides a central interface for a user working with the system on an everyday basis. It is desirable that the input/output module be able to accommodate the introduction and removal of a low number of samples, e.g. 20 tubes in a single SBS tube rack or a higher number of samples, e.g. 10,000 tubes in roughly 100 SBS tube racks, as well as bulk introduction and removal of samples. The introduced samples can be warm, for example when arriving from a processing laboratory or alternatively the samples can be cold or ultra-cold such as when arriving on dry ice from a distant laboratory. When introducing ultra-cold samples, the system is desirably operated to minimize temperature rise of the introduced samples during the sample introduction process. On the other hand, when warm samples are introduced to the system, the system is desirably operate to protect the thermal integrity of samples already stored and minimize temperature rise of previously stored samples.

[0008] The preferred input/output module is located within the refrigerated chamber and includes carousel with multiple insulated sleeves that hold input/output cassettes. The exemplary carousel includes eight sleeves for holding eight separate input/output cassettes, although the number of sleeves can be more or less as the application requires. As the carousel is rotated, one of the indexing positions (loading/unloading position) corresponds to a loading/unloading station which is located adjacent an opening through the enclosure wall. At least one door or set of doors covers the opening. Optionally, an air purge system is provided to prevent moisture from encroaching through the input/output module into the refrigerated enclosure when samples are being loaded or unloaded. The door or set of doors is opened to provide access for a user located outside of the refrigerated enclosure to shelves on an input/output cassette located at the loading/unloading position on the carousel. Sample tube storage racks or plates are manually placed by the user on the respective shelves in the input/output cassette to load the system. Once the cassette is filled, the carousel rotates or indexes to the next position allowing the user to fill another input/output cassette if necessary. One of the other carousel indexing positions serves as a designated cassette transfer position and corresponds to the location that the cassette puller removes filled input/output cassettes from the carousel and places empty input/output cassettes into the carousel. The cassette puller transfers filled input/output cassettes to the input/output buffer section in the designated freezer bay as described above. On the other hand, it is preferred that the empty input/output cassettes placed into the insulated sleeves on the carousel be pre-cooled in the input/output buffer section in the designated freezer. In the case that the loaded samples are cold or ultra-cold samples, it is preferred that the carousel rotates 180° from the loading/unloading position to the designated cassette transfer position once the input/output cassette is loaded without stopping at any intermediate indexing positions. The direct 180° rotation to the designated cassette transfer position speeds the transfer of cold or ultra-cold samples to the cassette puller and eventually into the input/output buffer section of the designated freezer bay. Of course, the input/output module can be used to load and unload either warm or cold samples in process sequences other than described above if desired.

[0009] In another aspect of the invention, the input/output cassette is designed specifically to accommodate manual loading and unloading of samples. In this regard, the shelves on the input/output cassette extend forward beyond the sidewalls in the portion of the cassette in which samples are loaded and unloaded, thereby facilitating convenient access even with gloved fingers. In addition, the distance between the shelves is increased compared to a typical storage cassette. Further, storage cassettes may typically be about six feet tall, and it is desirable that the overall height of the input/output cassette be the same as the storage cassette to enable the cassette puller to effectively retrieve both types of cassettes from the freezer bays. On the other hand, it is not convenient for users to load samples below the height of their thigh or above the height of their shoulder. Therefore, in accordance with this aspect of the invention, the input/output cassettes include a sample storage portion that will typically be about three feet long and stand at a height off the ground to a height range corresponding to a typical user's thigh to shoulder. The sample storage portion of the input/output cassette has a plurality of generally spaced shelves, each for holding sample tube storage racks or plates. The input/output cassettes also include a top plate and a bottom plate. However, an upper portion of the input/output cassette spanning between the sample storage portion and the top plate is not intended to hold sample storage tube racks or plates. Likewise, a lower portion that is not intended to hold sample tube racks or plates spans between the bottom of the sample storage portion and a bottom plate. Desirably, the input/output cassette includes the same or at least compatible top plate and retrieval catch as the storage cassette as well as same or compatible guide legs on the bottom of the cassette so that the overall size and footprint of the input/output cassette is the same as or quite similar to the storage cassettes. This enables the input/output cassettes to be fully compatible with the cassette puller and nesting tubes in the freezer bays.

[0010] Another advantage of the invention is that the storage cassettes for long term storage of the samples can also, in the preferred system, fit into the sleeves in the input/output module, thereby enabling the storage cassettes to be removed from the system for maintenance of the storage cassettes or to substitute storage cassettes in the system with cassettes sized for different storage racks or plates. In the exemplary embodiment, shields cover the top and lower portion of the sleeves, but these sleeves can be made removable to facilitate the transfer of a storage cassette into and out of the system through the input/output module.

[0011] It should also be noted that the storage cassettes in some systems can be shorter than about 6 feet tall, for example about 3½ feet tall. In such a system, the input/output cassette described above does not require an upper portion that is not intended to hold sample storage tube racks or plates, but may very well include a lower portion that is not intended to hold sample tube racks or plates.

[0012] Other features and advantages of the invention may be apparent to those skilled in the art upon reviewing the following drawings and description thereof.

[0027] FIG. 1 illustrates the outside of a refrigerated enclosure 10 maintained at a temperature of approximately −15° C. to −30° C., preferably about −20° C. FIG. 2 shows an automated storage and retrieval system 12 for storing sample tube racks or plates at an ultra-low or cryogenic temperature located within the refrigerated enclosure 10. A sample input/output module 14 is located inside the refrigerated enclosure 10 along its front wall adjacent an opening 16 (FIG. 3) covered by a door 18 or a set of doors. FIGS. 1 and 2 illustrate in phantom that it may desirable for the system to include a second input/output module. In FIGS. 1 and 2, the input/output modules are located along a front wall 20 of the refrigerated enclosure 10, however depending on the application it may desirable to locate the input/output module 14 along a sidewall 22 of the refrigerated enclosure 10, for example in the location of the full length door shown in FIGS. 1 and 2. Multiple horizontal freezer chests 11 are located within the refrigerated enclosure 10 and each storage compartment or freezer bay is maintained at a temperature setting at or below −65° C. under normal operating conditions. Preferably, each freezer chest 11 contains two independently cooled bays. Biological or chemical samples stored in sealed storage tubes held in tube racks or stored in sealed wellplates are stored within the freezer chest 11 for long term storage. In an ultra-low temperature system, the temperature setting within the freezer chest 11 will be maintained at for example −80° C. In a cryogenic system, the temperature within the chest 11 may be maintained at a temperature as low as −196° C. Refrigeration units 13 for the respective freezer chests 11 are located on the exterior of the refrigerated enclosure 10. The size of the refrigerated enclosure 10 as well as the number of freezer chests 11 within the refrigerated enclosure 10 and the requisite refrigeration units 13 can be expanded in order to accommodate the storage needs of the facility.

[0028] The refrigerated enclosure 10 provides a low temperature (−15° C. to −30° C., e.g., −20° C.) work space for the automated storage and retrieval system 12. The automated storage and retrieval system 12 is mounted to a traveling gantry 24 that is driven linearly along horizontal Y-axis rails 26. The gantry 24 moves over and above the top of the freezer chest 11 and also over and above the input/output module 14. The system 12 includes a robotic cassette puller 28 which moves with the gantry 24, thus providing the cassette puller 28 with access to storage cassettes or input/output cassettes stored in the freezers 11 and input/output cassettes residing in the input/output module 14. The invention is not limited to the specific configuration of the cassette puller 28. Nevertheless, it is preferred that the cassette puller be constructed in accordance with the description of co-pending U.S. patent application Ser. No. ______, entitled “Cassette Puller”, Attorney Docket No. 5436-00018, filed on even date herewith and incorporated herein by reference.

[0029] Referring now to FIG. 3, an array of storage cassettes 30 is stored in the bays of the freezer chest 11. The storage cassettes 30 carry samples stored in tube storage racks or plates for the purpose of transporting the racks or plates to a long term storage location and for storing the racks or plates in the long term storage location. It is desirable that the freezer chest 11 contain a nest, preferably an integral array of aluminum nesting tubes, for separating and guiding the placement of the cassettes 30 into the freezer compartments. It is preferred that the storage cassette and nesting configuration within the freezer bay be constructed in accordance with the description of co-pending U.S. patent application Ser. No. ______, entitled “Sample Storage Cassette for Ultra-Low or Cryogenic Temperatures”, Attorney Docket No. 5436-00019, filed on even date herewith and incorporated herein by reference. Each freezer chest 11 includes at least one lid 32 that must be removed in order to access the cassettes 30 within the respective freezer bay. Normally, the freezer chest 11 will have two lids 22 so that removal of one of the lids 22 will provide access to one bay in the freezer and removal of the other lid will provide access to the other bay in the freezer 11. As shown in FIG. 3, a large conduit 34 passes through the wall of 22 of the refrigerated enclosure 10 and provides a passage for refrigerant lines to the freezer chest 11 from the refrigeration unit 13.

[0030] In FIG. 3, the lid is removed from a first bay 35 in the freezer 11. A lid 32 covers a second bay 37 (shown in phantom) in the freezer chest 11. Referring in particular to the first uncovered bay 35, an insulated wall 40 thermally segregates the bay 35 into two sections 36, 38. The thermally segregated section 38 closest to the refrigeration unit 13 is an input/output buffer section 38 and serves the primary purpose of temporarily storing input/output cassettes when samples are loaded into the system. The samples are stored in the input/output buffer section 38 preferably until the samples are ensured to be cooled to the temperature setting for the freezer, i.e. about −80° C. in an ultra-low temperature system. It is expected that holding the samples in the input/output buffer section 38 for a period of five hours will ensure that all samples stored in the input/output buffer section 38 have been appropriately cooled. As will be described in more detail later, in normal operation, only input/output cassettes 44 are stored in the input/output buffer section 38. It is desirable that all samples be transferred to storage cassettes 30 for long term storage.

[0031] Referring briefly to FIG. 2, once the samples in an input/output cassette 44 have been suitably cooled in the input/output buffer section 38 of the freezer 11, the cassette puller 28 removes the input/output cassette 44 and in turn ejects each rack or plate held in the input/output cassette 44. The rack or plate is then processed by the system 12, for example by identifying the samples using a barcode identification station 48 and/or processing the samples held in a tube storage rack in a tube picking mechanism 46. Then the samples are placed onto an open shelf in a storage cassette 30 and the cassette puller 28 places the storage cassette 30 in an appropriate location for long term storage of the sample.

[0032] Referring now to FIGS. 12-14, experiments were run to determine the significance of thermally segregating warm samples placed into a freezer and the effect that the warm samples had on the temperature of samples previously stored and cooled to −80° C. FIG. 13 shows the experimental setup which included a freezer 48 cooled at or near −80° C. and a controller 50. A small nest 52 of aluminum nesting tubes was placed in the freezer 48 and held a cassette 54 that contained an instrumented sample tube in a tube storage rack. A temperature sensor measured the temperature of the sample in the rack over time. Bottles 56 containing two liters total of room temperature water were placed in the freezer 48. FIG. 13 shows insulation 58 located between the bottles 56 of room temperature water and the cassette 54 containing the cold −80° C. samples and temperature sensor. The experiment was also run without the insulation 58 present. Referring to the data shown in FIG. 12, the temperature rise of the previously stored −80° C. samples is substantial when the room temperature water was added to the system and there is not insulation 58. The temperature rise indicates that the −80° C. sample will rise between about 3° C. and 7.5° C. within one hour and that the temperature rise will peak between an hour and two hours. The data in FIG. 12 also indicated that there continues to be significant temperature rise even after the room temperature water bottles 56 were stored in the system for three hours. On the other hand, when the insulation 58 is present and the room temperature water bottles 56 are thermally segregated from the remaining portions of the freezer 48, the detected temperature rise is less than 2° C. The data in FIG. 12 was taken in a system in which the thermostat for the freezer 48 was located on the side of the freezer near the instrumented rack 54 and removed from the room temperature water bottles 56. Even under this scenario the temperature rise in the −80° C. sample as measured in the instrumented rack was minimal when there was insulation. FIG. 14 shows representative data of temperature change in the instrumented rack containing water filled storage tubes at −80° C. when the room temperature water bottles 56 are placed on the side of the insulation 58 in the freezer compartment 48 that the freezer thermostat is located. Under this scenario, the room temperature water bottles 56 drive the temperature in the vicinity of the thermostat upwards causing the refrigerator compressor to run continuously until the water bottles are fully cooled or near fully cooled. The data in FIG. 14 shows that the temperature in the instrumented rack actually drops below its original −80° C. temperature under this scenario. In fact, for the first six hours the temperature of the instrumented rack 54 continued to drop significantly and only recovered after the water in the bottles 56 were sufficiently cold to no longer trigger compressor operation.

[0033] Referring again to FIG. 3, it is contemplated that in most systems the input/output buffer section 38 will constitute only a relatively small portion of one of the freezer bays. The thermally insulated wall 40 can take the form of foam insulation. The location of the thermally insulated wall 40 can be adjusted to enlarge the size of the input/output buffer section 38 if necessary, and in some applications it may even be desirable to designate an entire freezer bay as an input/output buffer section. Note, however, that it would not normally be desirable to provide separate input/output buffer sections in two different freezer bays. In FIG. 3, nesting tubes have been removed to make room for the thermally insulating wall 40. As mentioned, a practical alternative is to leave the complete nest 46 intact as described in the above incorporated patent application entitled “Storage Cassette”, and fill selected nesting tubes with insulation to form a thermally segregating barrier between the input/output buffer section 38 and the long term storage section 36.

[0034] Still referring to FIG. 3, the exemplary input/output module 14 includes eight cassette bays in the form of vertical sleeves 70 which are shown in FIG. 3 to be located in distinct indexing positions labeled with reference numbers 62A-62H. The sleeves 70 are attached to a carousel 60 that is located within an insulated box 64 inside the refrigerated enclosure 10. In the embodiment illustrated in the drawings, cassette sleeve 70 on the carousel 60 in the position labeled 62A is in the loading/unloading position and cassette sleeve 70 in the position labeled 62E is in the designated cassette transfer position. The cassette puller 28 transfers input/output cassettes 44 to and from the input/output module 14 by placing the input/output cassettes 44 or removing the input/output cassettes 44 from the sleeve 70 located at position 62E. The user of the system manually loads or unloads samples into a cassette 44 located in the sleeve 70 located at the loading/unloading position 62A.

[0035] Referring to FIGS. 4 and 5, the insulated box 64 surrounding the input/output module 14 has been removed to show the internal components. FIGS. 4 and 5 show input/output cassettes 44 loaded into vertical sleeves 70 on the carousel 60. In order to place or retrieve a cassette from the input/output module 14, the cassette puller 28 is positioned over port 66E in the top plate 68 of the input/output module 14 which is above the sleeve 70 in the designated cassette transfer position 62E. The top plate 68 of the input/output module 14 includes ports 66C and 66G for the cassette puller 28 that are located over the sleeves 70 positioned at indexing positions 62C and 62G in addition to the port 66E over the sleeve 70 in position 62E. Position 62E is 180° opposite from position 62A corresponding to the loading/unloading station. In most applications, the ports 66E and 66G (corresponding to the 90° and the 270° indexing positions) will be covered. It is desirable that the cassette puller 28 place cassettes 44 into and remove cassettes 44 from a single designated cassette transfer location. The ports 66C and 66G at the 90° and the 270° indexing positions are used in the event that the input/output module 14 is located near the corner of the refrigerated enclosure 10.

[0036] The preferred methods of loading samples into the system using the input/output module 14 is now discussed in connection with FIGS. 6A and 6B. FIG. 6A describes the procedure that will typically be used when loading a large number of warm samples into the system. FIG. 6A shows input/output cassettes 44 being located in each of the insulated sleeves 70 on the carousel 60; however the cassettes in positions 62F, 62G and 62H are empty. As a first step, an empty input/output cassette 44 is placed in the sleeve 70 located at position 62E corresponding to the designated cassette transfer location. (FIG. 6A shows a loaded cassette 44 at position 62E which corresponds to a subsequent step in the process.) The input/output cassette 44 is preferably pre-cooled to −80° C. in the input/output buffer section 38 of freezer bay 35 prior to loading the empty cassette 44 into the sleeve 70 at position 62E. The carousel 60 is then rotated to present the input/output cassette 44 to the loading/unloading station at position 62A. When warm samples are being loaded, and especially a large number of warm samples, it is normally be sufficient to index the carousel 60 one position at a time to introduce the next empty cassette 44 to the loading/unloading position 62A. Once an empty cassette is presented at the loading/unloading position 62A, the system doors 18 are opened. FIG. 6A shows an internal door 74 which is optional. If present, the internal door 74 is opened as well to provide the user access to the empty input/output cassette 44 on the carousel 60 at the loading/unloading position 62A. Optionally, the system can provide an air purge, when the doors 18 are opened, to prevent or mitigate moisture from encroaching from outside of the refrigerated enclosure 10 into the input/output module 14 and eventually inside of the enclosure 10. With the doors open, the user manually loads tube storage racks 72 or plates into shelves on the input/output cassette 44 at the loading/unloading station 62A. FIG. 6A shows the rack 72 loaded into the input/output cassette 44 at the loading/unloading position 62A. The doors 18 are then closed and the carousel 60 is indexed to present the next sleeve 70 to the loading/unloading position 62A. The above steps are repeated as necessary to accommodate all of the samples that need to be loaded into the system. When the carousel 60 rotates so that a loaded input/output cassette 44 is presented at the designated cassette transfer position 62E, the cassette puller 28 lifts the loaded input/output cassette 44 and transfers it to the input/output buffer section 38 in the freezer bay, see FIG. 3. Normally, the loading and unloading of tube storage racks and/or plates at the loading/unloading position 62A is accomplished by placing individual racks or plates on individual shelves. In some applications, however, it may be desirable to modify the input/output cassette 44 to include a removable module of multiple shelves which can be preloaded with tube storage racks or plates prior to loading the samples into the input/output cassette when it is located at the loading/unloading station 62A.

[0037] FIG. 6B illustrates the preferred method of loading cold or ultra-cold samples into the system. In this method, it is only necessary to include input/output cassettes 44 in two sleeves 70 preferably disposed 180° from each other in the loading/unloading position 62A and in the designated cassette transfer position 62E. Again, it is desired that the input/output cassettes 44 be pre-cooled in the input/output buffer section 38 prior to loading the empty cassettes 44 into the respective sleeve 70 in the input/output module 14. Once the empty, pre-cooled input/output cassette 44 is placed into the appropriate carousel sleeve 70, the carousel rotates 180° to present the empty, pre-cooled cassette 44 at the loading/unloading position 62A. The doors 18 (and optional door 74) are opened and the user loads cold or ultra-cold sample tube storage racks 72 or plates into the input/output cassette 44 at loading/unloading position 62A. Once the cassette is loaded, the doors are closed and the carousel is rotated 180°. Prior to the 180° rotation, however, another empty, pre-cooled cassette 44 is loaded into the sleeve 70 at the designated cassette transfer position 62E. The 180° rotation therefore simultaneously positions a loaded cassette 44 at the designated cassette transfer location 62E which is ready for removal by the cassette puller 28 to the input/output buffer section 38 and positions an empty, pre-cooled cassette 44 at the loading/unloading position 62A. This procedure is repeated as necessary to accommodate all of the cold or ultra-cold samples that need to be loaded into the system.

[0038] Referring to now FIG. 7, the carousel 60 includes a carousel frame 76 that is mounted on a turntable 78. The vertical sleeves 70 are attached to the carousel frame 76. A central pedestal 80 is attached to the floor 82 of the input/output module 14. The carousel motor 84 is mounted to the pedestal 80 and drives a universal joint 86 connected to the turntable 78 to rotate the carousel frame 76 and sleeve 70. A homing sensor 88 is mounted to the pedestal 80 and detects the position of the carousel 60, particularly when it is necessary to determine the home position of the carousel 60. FIG. 7 shows input/output cassettes 44 located in two of the insulated sleeves 70 attached to the carousel frame 76. FIG. 7 also illustrates a rack 72 in phantom being loaded into the cassette 44 located near the opening 90 in the front wall of the refrigerated enclosure 10. FIG. 8 is a sectional view taken along line 8-8 in FIG. 7 and illustrates a rack 72 loaded onto a cassette shelf 44 contained within the insulated sleeve 70. It also shows the cross section of a mounting bracket 91 used to mount the illustrated insulated sleeve 70 to the carousel frame 76.

[0039] Referring to FIGS. 9-11, the exemplary input/output cassette 44, as mentioned, is preferably designed to have the same height as the storage cassettes 30 used for long term storage in the system. However, as mentioned, the input/output cassettes 44 are configured for loading and unloading samples only over a portion of their height which is convenient for loading and unloading by the normal user of the system. In particular, the input/output cassette 44 includes a sample storage portion 92 as well as an upper portion 94 and a lower portion 96 which are not intended to hold sample tube storage racks or plates. The cassette 44 also includes a top plate 98 and a bottom plate 100. The upper portion 94 spans between the top end of the storage sample portion 92 and the top plate 98, whereas the lower portion 96 spans between the lower end of the sample storage portion 92 and the bottom plate 100. The top portion 94 as well as the top plate 98 is preferably constructed in a manner similar or identical to the corresponding structure in a storage cassette 30, such as described in the above incorporated patent application entitled “Storage Cassette.” Likewise, the bottom end of the input/output cassette 44 including the lower portion 96 and tapered feet 102 are preferably constructed in a manner similar or identical to the corresponding portion of the storage cassette described in the above incorporated patent application entitled “Storage Cassette.” The vertical sleeves 70 into which the input/output cassettes 44 are placed on the input/output module 14 preferably have insulated walls 104 on three sides, and also desirably includes shields 106, 108 corresponding to the location of the upper portion 94 and lower portion 96 of the input/output cassette 44. The shields 106, 108 help to prevent convective heat transfer. Note that the top 68 (FIG. 5) of the input/output module 14 covers the top of the sleeve 70 unless the sleeve 70 is located at the designated cassette transfer station (position 62E in FIGS. 6A and 6B). As can be seen in FIG. 10, the compartments in the sample storage portion 92 of the input/output cassette 44 are slightly taller than the height that the compartments would normally be in a storage cassette 30. In addition, the compartment shelves 112 in the sample storage section 92 extend a forward beyond the sidewall 110 which facilitates accessibility with gloved fingers.

[0040] It is desirable that the shields 106, 108 on the vertical sleeves 70 in the input/output module 14 be removable by a user outside of the system so that a full cassette 44, 30 in the sleeve 70 can be removed from or placed into the system. By removing the shields 106, 108 both input/output cassettes 44 and storage cassettes 30 can be removed from or placed into the system which can be particularly beneficial for maintenance. Further, it is convenient way to replace a storage cassette 30 with one having different shelf spacing. It is likely that users will find it convenient to load or unload full input/output cassettes 44 into a sleeve 70 (with the shields 106, 108 removed or nonexistent) under normal operation of the system, although it is possible.

[0041] Referring in particular to FIG. 11, the shelves 112 are preferably closed shelves to help prevent convective air flow through the input/output cassette 44. The shelves 112 desirably include lips 114 on the front edge to help prevent racks or plates from sliding off of the shelf 112 when the cassette 44 is moved. In addition, the front edge of the shelf 112 includes an indentation 116 that provides clearance for lifting fingers on the ejector mechanism for the cassette puller 28. This indentation 116 allows for an optical sensor to detect whether any racks have been loaded into the cassette 44 or whether all racks have been unloaded from the cassette 44. The shelves 112 are preferably made of aluminum and form part of a plate that also includes a reference positioning stop 118. The reference positioning stop 118 is used by the cassette puller 28 to mechanically reference the respective shelf 112 at the appropriate height in the cassette puller 28 for ejection of a rack or plate from the shelf 112 or for placement of a rack or plate onto the shelf 112 as described in connection with the above incorporated patent application entitled “Cassette Puller.” It also provides mechanical means for the cassette puller 28 to lock the input/output cassette 44 in place in the cassette puller 28 when transferring the input/output cassette 44 from or to the input/output module 14 or otherwise. FIG. 11 illustrates the assembly of the input/output cassette 44 and in particular that the shelves 112 and the sample storage portion 92 are connected together with wires and are held in the appropriate vertical location via openings 120 in the plastic sidewall 110. FIG. 11 also shows that the sample storage portion 92 is attached to the upper and the lower portions 94, 96 by connecting the wires with brackets to the upper and lower 94, 96 portions respectively.

[0042] In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.