MATERIAL HANDLING SYSTEM.

Abstract

A system may include a vehicle for delivering items and a plurality of racks with a plurality of storage locations. The racks may be arranged to form one or more aisles. The vehicles are configured to travel horizontally along a path that may extend beneath the racks, parallel to the aisles. Additionally, the vehicles may be operated to turn while positioned beneath one of the racks. The vehicles may pass beneath the racks and traverse one or more aisles to reach a specific column within one of the aisles. The vehicle then moves upward within the column to retrieve an item from a storage location in that column.

Description

MATERIAL HANDLING SYSTEM Cross-reference to related application This application claims priority under 35 USC §119 of U.S. Provisional Patent Application Number 62 / 886,602 filed on August 14, 2019. The full disclosure of U.S. Application Number 62 / 886,602 is incorporated herein by reference. Field of invention The embodiments of the present invention generally relate to automated material and article handling systems that can be used in warehousing, storage and / or distribution environments. Background of the invention Modern material handling systems, such as those used in mail-order warehouses, supply chain distribution centers, and custom-order manufacturing facilities, face significant challenges in responding to requests for inventory items. Initially, companies will typically invest in a level of automation that is at least adequate for current needs. However, as the scale of an inventory management system expands to accommodate a greater quantity and variety of items, so does the cost and complexity of operating it to simultaneously complete packaging, storage, replenishment, and other inventory management tasks for which it is designed. Inefficient use of resources such as space, equipment, and labor in an inventory management facility results in lower throughput, longer response times, and a growing backlog of unfinished tasks. Greater efficiency can often be achieved, for a time, by gradually expanding the capacity of the facility's existing automation infrastructure, particularly when that expansion follows a well-conceived growth plan. However, sooner or later, a point of diminishing returns is reached. That is, achieving additional gains in capacity and / or functionality eventually becomes prohibitively expensive compared to available alternatives, if such gains can even be realized.When that point of diminishing returns is reached, a facility operator may be forced to abandon the pre-existing material handling infrastructure and replace that infrastructure with a completely new automation platform. Brief description of the invention The present invention provides a number of inventive aspects relating to processes of handling and / or storing and retrieving materials. cro tnn / zznz / B / Yii According to one aspect, the present invention provides a method for delivering items to and retrieving items from storage locations. The method may include the step of providing a plurality of storage shelves separated from each other, forming a plurality of aisles. Each storage shelf may include a plurality of columns, and each column may include a plurality of storage locations. The method may also include the step of providing a plurality of delivery vehicles, where each vehicle includes a horizontal drive system that enables the vehicle to be driven along a horizontal surface. The vehicles may also include a vertical guide mechanism that enables the vehicle to be driven vertically and a transfer mechanism that enables the transfer of an item between the vehicle and one of the storage locations.The method may also include the step of driving the first vehicle to the storage racks. Optionally, the method includes the step of driving the first vehicle along a first path under the first rack, where the first rack is adjacent to the first aisle and where the first path extends in a direction parallel to and separate from the first aisle. The method may also include the step of turning the first vehicle while it is under the first rack. Additionally, the method includes the step of driving the vehicle into the first aisle and driving it up the aisle to the first storage location. An item may be transferred between the first vehicle and the first storage location.The first vehicle can then be driven down the aisle until it is on a level surface. It can then be driven through the first aisle and exit from beneath the storage shelves after this initial stage. According to another aspect, a method for delivering items may include a storage rack having a plurality of upright posts forming a first column of the first storage rack and a first vehicle having a first width extending from a first side of the first vehicle to a second side of the first vehicle. The first vehicle may also include a vertical guide projecting outward from the first and second sides, such that the vehicle has a second width corresponding to the distance between the outer edges of the vertical guide, the second width being greater than the first width, and wherein the upright posts of the first column are spaced a distance greater than the first width and less than the second width. According to another aspect, a method for delivering articles may include a plurality of vertical sliding guide segments attached to vertical posts of a first column and the method may include the step of aligning the vertical guide of the first vehicle with the vertical sliding guide segments. According to another aspect, the present invention may provide a method for delivering articles that includes the step of driving a first portion of a vertical vehicle guide through a vertical sliding guide segment and driving a second portion of the vertical drive in operative coupling with the vertical sliding guide segment. According to an additional aspect, a method for delivering items may include the stage of driving a first vehicle along a first path by driving the vehicle along a path separated from the upright posts by a distance greater than half the length of the vehicle. According to another aspect, a method for delivering items may include the stage of driving a first vehicle to a workstation to present an item to an operator after taking the first vehicle out from under the storage shelves. According to another aspect, a method for delivering items may include the stage of driving the first vehicle through the aisle driving the first vehicle under a second of the storage shelves. According to another aspect, a method for delivering items may include the step of rotating a vehicle by turning the vehicle around a vertical axis that extends through the vehicle. Optionally, the vertical axis may extend through the first path. According to an additional aspect, a method for delivering items may include the step of driving a second vehicle under a first shelf along a second path parallel to a first path so that a second vehicle passes the first vehicle as the first vehicle moves along the first path. According to another aspect, a material handling system is provided for delivering items to storage locations and retrieving items from storage locations. The system may include a first storage rack having a plurality of columns, each comprising a plurality of storage locations where the first storage rack is longitudinally elongated, and a second storage rack having a plurality of columns, each comprising a plurality of storage locations where the second storage rack is longitudinally elongated. The first storage rack may be separated from the second storage rack to provide an aisle between the first and second storage racks. Additionally, the system may include a plurality of delivery vehicles.Optionally, each vehicle can have a specific length and width, and each vehicle includes a horizontal drive system that allows the vehicle to be driven along a horizontal surface, a vertical guide that allows the vehicle to be driven vertically, and a transfer mechanism that allows an item to be transferred between vehicles and one of the storage locations. The system can also include a sliding guide positioned in the aisle. Additionally, the vertical guide can be configured to cooperate with the sliding guide and drive the vehicle vertically upward. The system can also include a first horizontal path extending below the first shelf in a direction parallel to the aisle and a second horizontal path extending below the first shelf in a direction parallel to the aisle.Optionally, the horizontal guide is configured to rotate the vehicle beneath the first rack by turning the vehicle around a vertical axis that extends through the vehicle. Additionally, the storage rack may include a plurality of vertical posts, and each of the first and second horizontal tracks may be separated from the vertical posts by a distance greater than half the length of the vehicles. Furthermore, the first horizontal track beneath the first track may be separated from the second horizontal track by a distance greater than the width of the vehicles. According to another aspect, a system for delivering articles may include a vertical guide having a plurality of rotating elements, each of which rotates about a horizontal axis. Additionally, the system may include a horizontal guide comprising a plurality of rotating elements, each of which rotates about a horizontal axis transverse to the axes of rotation of the vertical drive elements. According to another aspect, the present invention can provide a system for delivering articles that includes a plurality of vertical posts forming a first column of a first storage rack and vehicles having a first width extending from a first side of the vehicle to a second side. The vertical guide of the vehicle can project outward from the first and second sides so that the vehicle has a second width corresponding to the distance between the outer edges of the vertical guide, such that the second width is greater than the first width. Optionally, the vertical posts of the first column are spaced a distance greater than the first width and less than the second width. According to another aspect, a system for delivering items may include a sliding guide with drive elements configured to cooperate with a vertical guide such that rotating the vertical guide around a horizontal axis allows the vehicle to be driven upward along the sliding guide. Optionally, the sliding guide includes a lower and an upper section, with the drive elements being more widely spaced in the lower section than in the upper section to provide clearance in the lower section. The system of claim 15, wherein the spaces are configured to facilitate the vertical guide passing through the spaces without coming into contact with the lower section when the vehicle cro Lnn / zznz / B / Yi is driven past the lower section. According to a further aspect, the present invention may provide a method for delivering items to storage locations and retrieving items from storage locations. The method may include the steps of providing a vehicle having a horizontal guide and a vertical guide having a front rotating element adjacent to a front end of the vehicle and a rear rotating element adjacent to a rear end of the vehicle, and providing a first vertical shelf on a first side of a first column. The first vertical shelf may have drive elements configured to cooperate with the front rotating element to drive the vehicle upward.The method may also include the step of providing a second vertical shelf on the second side of the first column, where the second vertical shelf has drive elements configured to cooperate with the rear rotating element to drive the vehicle upwards. The vertical guide and the first and second vertical shelves may be configured so that the vertical shelf prevents the vehicle from moving along a horizontal path when the vertical guide rotates to a misaligned position.Additionally, the method may align the vertical guide, which may include the steps of rotating the front swivel around a horizontal axis substantially parallel to the horizontal path to align the front swivel with the gaps in the first and second vertical shelves, and rotating the rear swivel around a horizontal axis substantially parallel to the horizontal path to align the rear swivel with the gaps in the first and second vertical shelves. After the alignment step, the method may include the step of driving the vehicle along the horizontal path toward the first vertical shelf. The driving step may include driving the vehicle so that the front swivel passes through the gaps in the second vertical shelf.The method may also include the step of continuing to drive the vehicle along the horizontal path to position the front swivel element in operational engagement with the first slide guide and the rear swivel element in operational engagement with the second slide guide. The front and rear swivel elements can then rotate to drive the vehicle upward to a first storage location. Additionally, a first item can be transferred from the first storage location to the vehicle, the vehicle can be driven downward with the item, and the vehicle can be driven with the first item along the horizontal path so that the rear swivel element passes through gaps in the first vertical shelf. According to another aspect, a method of delivering items may include a stage of rotating front and rear swivel elements by synchronously driving the front and rear swivel elements to drive the vehicle vertically upwards while maintaining the vehicle's orientation with respect to the horizon. According to another aspect, a method of delivering items may include a stage of driving a vehicle out from under a sliding guide after driving the vehicle with the first item along a horizontal path. According to another aspect, a delivery method for items may include a step of turning a vehicle onto a path perpendicular to the horizontal path on which the vehicle was traveling. Optionally, the turning step may be performed while the vehicle is under one of the shelves. According to another aspect, a method of delivering articles may include a stage of driving the vehicle along the horizontal path. The driving stage may include the stage of actuating a plurality of horizontal drive elements around a horizontal axis that is substantially perpendicular to the horizontal path. According to an additional aspect, a method of delivering items may include the steps of providing a plurality of storage racks and a plurality of delivery vehicles. The storage racks may be separated from each other, forming a plurality of aisles, and each storage rack may include a plurality of columns, and each column may include a plurality of storage locations. Optionally, each vehicle may include a horizontal drive system that allows the vehicle to be driven along a horizontal surface. Each vehicle may also include a vertical guide that allows the vehicle to be driven vertically. Optionally, a transfer mechanism may allow an item to be transferred between the vehicle and one of the storage locations.The method may also include the step of driving the first vehicle under one or more storage racks along a path that crosses one or more aisles. The step of driving the first vehicle may include driving the first vehicle toward the first column in the first aisle. The first vehicle may be driven vertically upward within the first aisle until it is adjacent to a first storage location. An item may then be transferred from the first storage location to the first vehicle. The first vehicle may then be driven vertically downward within the first aisle and subsequently driven out of the first aisle along a path that extends under at least one storage rack. According to another aspect, a delivery method may include a route that includes a portion passing under one of the shelves and extending parallel to one of the aisles. Optionally, a second vehicle may be driven past the first vehicle under a shelf when the first vehicle is driven along the portion of the route under one of the shelves. cro Lnn / zznz / B / Yi According to another aspect, a method of delivering items may include a stage of turning the vehicle while it is under one of the shelves. The turning stage may include rotating the vehicle to align it with a path perpendicular to the first aisle. Optionally, the turning stage may include rotating the vehicle around a vertical axis that passes through the vehicle. Brief description of the drawings To better understand the features of the present invention mentioned above, a more detailed description of the invention, briefly summarized earlier, can be obtained with reference to its embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only typical embodiments of this invention and should therefore not be considered limiting of its scope, as the invention may admit other equally effective embodiments. Figure 1 is a perspective view of a material handling system; Figure 2 is a perspective view of an automatic guidance of the material handling system illustrated in Figure 1; Figure 3 is a front view of the vehicle illustrated in Figure 2; Figure 4 is a side elevation view of the vehicle illustrated in Figure 2; Figure 5 is a plan view of the vehicle illustrated in Figure 2; Figure 6 is an enlarged fragmentary perspective view of a portion of the shelving of the material handling system illustrated in Figure 1; Figure 7 is a front elevation view of an aisle of a shelving system of the material handling system illustrated in Figure 1; Figure 8 is a side elevation view of the corridor illustrated in Figure 7; Figure 9 is a plan view of the corridor illustrated in Figure 7; Figure 10 is an enlarged fragmentary side elevation view of the corridor illustrated in Figure 13A; Figure 11 is a block diagram representing the subsystems of a plurality of guided vehicles according to one or more modes; and Figure 12 is a schematic block diagram of a controller of the system illustrated in Figure 1. Although the systems and methods described herein are provided as examples for various configurations and illustrative drawings, those skilled in the art will recognize that the systems and methods for performing respective subsets of inventory management tasks using corresponding functional accessory modules are not limited to the configurations or drawings described. It should be understood that the drawings and their detailed descriptions are not intended to limit the configurations to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents, and alternatives that fall within the substance and scope of the systems and methods for performing respective subsets of inventory management tasks using corresponding functional accessory modules as defined by the appended claims.All headings used herein are for organizational purposes only and are not intended to limit the scope of the description or claims. As used herein, the word "may" is used in a permissive sense (i.e., meaning to have the potential to), rather than in a mandatory sense (i.e., meaning to must). Similarly, the words "include," "which includes," and "includes" mean that they include, but are not limited to. Detailed description of modalities Several embodiments of a method and apparatus for performing inventory management tasks in an inventory management system are described. The following detailed description provides numerous specific details to ensure a complete understanding of the claimed subject matter. However, those skilled in the art will understand that the claimed subject matter can be practiced without these specific details. In other cases, methods, apparatus, or systems that would be known to a person skilled in the art have not been described in detail so as not to obscure the claimed subject matter. Some portions of the detailed description that follows are presented in terms of algorithms or symbolic representations of operations on binary digital signals stored within the memory of a specific apparatus or special-purpose computing platform or device. In the context of this particular specification, the term "specific apparatus" or similar may include a general-purpose computer once it is programmed to perform particular functions according to the instructions of the program software. Algorithmic descriptions or symbolic representations are examples of techniques used by signal processing technicians or related arts to convey the substance of their work to other technicians in the field. Here, an algorithm is considered, and is generally regarded as, a self-consistent sequence of operations or similar signal processing that leads to a desired result.In this context, operations or processing involve the physical manipulation of physical quantities. Typically, though not necessarily, such quantities can take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, or otherwise manipulated. It has sometimes been convenient, mainly for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals, or the like. It should be understood, however, that all these terms or similar terms must be associated with appropriate physical quantities and are merely convenient labels. cro Lnn / zznz / B / Yi Unless specifically stated otherwise, as is clear from the following description, it is understood that throughout this specification, descriptions using terms such as processing, computation, calculation, determination, or similar terms refer to actions or processes of a specific apparatus, such as a special-purpose computer or similar special-purpose electronic computing device. In the context of this specification, therefore, a special-purpose computer or similar special-purpose electronic computing device is capable of manipulating or transforming signals, typically represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the special-purpose computer or similar special-purpose electronic computing device. Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to identical or similar parts. Now, with reference to the figures in general and Figure 1 specifically, an apparatus for sorting or retrieving items is generally designated 10. The apparatus 10 includes one or more mechanisms for delivering items and / or retrieving items from one or more locations, such as storage areas located on racks 800 or flow racks 600. The delivery mechanism may include one or more vehicles 100 that transport items. For example, optionally, the vehicles may retrieve items from storage locations 820 on racks 800 and deliver the items to a workstation 500 where an operator can retrieve the item from the vehicle. The vehicle may optionally return to a storage area on the rack to store any remaining items that were not retrieved by the operator. The vehicle may then proceed to another storage area to retrieve the next item.In this way, the system can include a mechanism for continuously storing and retrieving items to and from various storage areas so that the items can be presented to an operator. Optionally, a guide, such as a sliding guide, can be placed next to the rack so that the vehicle can move vertically up the rack to retrieve an item. Optionally, the system can include a mobile rack (700) that is configured to be transported by vehicles. The vehicles can transport the mobile rack to a position adjacent to a storage rack. The vehicle can then move vertically up the rack to transfer items between the vehicle and a storage location on the storage rack. It should be understood that various items and subsets of the overall system can be used alone or in combination with material handling systems that have a different structure or operation than the system illustrated in the figures and described below. cro Lnn / zznz / B / Yi As illustrated in Figures 1 and 7, the material handling system may optionally incorporate one or more storage shelves 800. Each storage shelf may include a plurality of storage locations 820. Optionally, the storage locations may be arranged in one or more vertical columns 810. For example, Figure 1 illustrates a plurality of shelves 800, and each shelf may include a plurality of columns 810, each of which includes a plurality of storage locations. Items handled by the system may be stored directly in the storage locations. Alternatively, items may be stored in bins or containers 55, and the storage locations 820 may be configured to store the containers 55 as shown in Figures 1 and 6-9.Consequently, it should be understood that, unless otherwise stated in the following description, when a storage facility is mentioned, the term "container" is broad enough to include a receptacle for holding one or more items, as well as simply an item that is not necessarily contained in a container. Although the present system is described using containers, it should be understood that any of a variety of storage mechanisms, such as pallets or similar platforms, may be used. Vehicles Figure 2 illustrates details of one of the 100 vehicles shown in Figure 1. As noted earlier, if the system incorporates vehicles, the vehicle structure may vary. Consequently, it should be understood that each of the vehicle features described below are optional features that may be modified or removed depending on the application. The 100 vehicles can be autonomous systems that include an onboard power source for driving the vehicle. The vehicles can also include a communication system to wirelessly receive and transmit control signals between each vehicle and a control element, such as the 450 central controller. In this way, the vehicle can receive control signals regarding the location to retrieve an item and the location to which the vehicle must deliver the item. The vehicle illustrated in Figure 2 includes a horizontal guide assembly 120 for driving the vehicle 100 in a horizontal direction. The horizontal guide 120 can be configured to drive the vehicle along a sliding guide or along an open horizontal surface, such as a floor. For example, one option for a horizontal guide includes a plurality of rotating elements, such as wheels or rollers. One or more drive mechanisms can be provided to rotate the rotating elements. Additionally, the rotating elements can pivot from side to side to steer the vehicle. Alternatively, as illustrated in Figures 3-5, the vehicle may have a horizontal guide 120 formed by a plurality of rollers 122, 123, 124 that can rotate about a first axis, such as Lnn / zznz / B / Yi, or about a shaft. Additionally, the rollers 122, 123, 124 may be constrained to rotate about a single axis. For example, in the embodiment illustrated in Figures 3-5, the horizontal guide 120 includes a pair of center rollers 124 and first and second sets of outer rollers 122, 123. The first set 122 is positioned forward of the center rollers, while the second set of rollers 123 is positioned rearward of the center rollers 124.The outer rollers 122, 123 may include separate rollers along a horizontal shaft such that each set of outer rollers includes a first roller 122a on one side of the vehicle and a second roller 122b on an opposite side of the vehicle, as shown in Figure 3. Additionally, as shown in Figure 3, each set of outer rollers may include a pair of rollers 122b on each side of the vehicle. As previously stated, the 100 vehicle can have any of a variety of steering mechanisms to control the vehicle's direction of travel. For example, one optional steering mechanism is a zero-turn mechanism that can turn the vehicle without substantially moving it forward. Optionally, the zero-turn mechanism provides a means of turning the vehicle around a vertical axis that extends through the vehicle. The zero-turn mechanism comprises a linkage that allows the wheels or rollers on one side of the vehicle to rotate at a different speed than the wheels or rollers on the opposite side. Optionally, the linkage allows the wheels or rollers on one side of the vehicle to rotate in different directions than the wheels or rollers on the opposite side. By varying the speed and / or direction of rotation of the wheels on one side of the vehicle relative to the speed and / or direction of rotation of the wheels on the opposite side, the zero-turn mechanism changes the direction of travel to steer the vehicle. Optionally, the system may also include one or more guides 880 to guide or align the vehicles in their movement. For example, with reference to Figure 9, the guide 880 may include a channel or groove, and the vehicle may include a corresponding guide element that cooperates with the guide 880 to control the movement of the vehicle 100. An example of a guide element is a follower 126. The follower may be any element configured to engage with or cooperate with the guide 80. In this case, the vehicle 100 includes a center follower 126 that includes a rotating element such as a bearing that rotates about a vertical axis. The center follower 126 engages with the channel in the guide 880 to restrict the horizontal movement of the vehicle. Optionally, the vehicle may also include one or more lateral guide members 127. The lateral guide members 127 may cooperate with an outer surface of the guide 880 to restrict the vehicle's movement. For example, the guides 880 may comprise circular guides having a circumferential surface to guide the vehicle's turning. The vehicle may have a pair of lateral guide members 127 separated from each other by a distance equal to the diameter of the guide's circumferential surface. In this way, the lateral guides 127 engage with the guide's circumferential surface to restrict the vehicle's turning motion. In addition to the horizontal drive mechanism 120, the vehicle may also include a vertical drive system 140 for driving the vehicle 100 vertically within the shelf 20. In particular, as indicated above, the system may include a guide mechanism, such as a sliding guide 840 that is positioned next to the shelf 20. The vertical drive system 140 may be configured to cooperate with the vertical guide mechanism 840 to drive the vehicle 100 vertically. Figures 2-3 illustrate an exemplary vertical guide 140 that includes a plurality of rotating gears 145; however, it should be understood that the vertical guide 140 may include any of several drive mechanisms for driving the vehicle vertically. Referring to Figure 3, the vertical guide may include a driving gear 145 that rotates about a horizontal axis that is transverse to the horizontal axis of rotation of the horizontal drive mechanism 120. In particular, optionally, the vehicle includes a pair of driving gears 145 that are spaced apart from each other such that the teeth of the first gear 145b project outward from a first side of the vehicle and the teeth of the second gear 145d project outward from a second side of the vehicle, as shown in Figure 3. These first and second gears 145b, d may drive synchronously.Additionally, as shown in Figure 2, the vehicle may include two pairs of vertical drive elements that are separated from each other along the length of the vehicle. In particular, optionally, the vehicle includes a first pair of vertical drive elements 145a, c at a first end of the vehicle and a second pair of vertical drive elements 145b, d at a second end of the vehicle. With reference to Figures 1 and 6-7, shelf 20 can be configured so that the sliding guide 40a on one shelf is separated from the sliding guide 40b on a second shelf by a distance corresponding to the space between the first set of vertical drive elements 145a and the second set of drive elements 145b. In this way, the first vertical drive element 145a can cooperate with the first sliding guide 40a to drive the vehicle upwards along the first sliding guide 40a, while the second vertical drive element 145b can cooperate with the second sliding guide 40b to drive the vehicle upwards along the second sliding guide 40b. Optionally, the two vertical drive elements 145a and b are driven synchronously so that the vehicle maintains a horizontal orientation as it transitions from horizontal to vertical movement. As described in U.S. Provisional Patent Application No. 62 / 886,602, CRO Lnn / zznz / B / Yi, the full disclosure of which is incorporated herein by reference, the vertical guide 140 can be optionally configured to maintain a substantially constant width as the vehicle transitions from horizontal to vertical movement. In this way, the vertical guide 140 does not need to extend telescopically outward to transition from horizontal to vertical driving. For example, with reference to Figures 2-3, the forward ascending gears 145b and 145d each have a horizontal pivot axis, and the spacing between the horizontal pivot axis of the drive member 145b and the horizontal pivot axis of the drive member 145d is fixed while the vehicle is moving horizontally and while the vehicle is ascending. The vehicle may also include an optional transfer mechanism to transfer items between the vehicle and a destination, such as a storage location. For example, the transfer mechanism 150 can be operative for transferring an item between a vehicle platform surface and one of the plurality of destination areas 820. As shown in Figure 2, the platform surface is optionally defined by the outer surfaces of a plurality of rollers. The transfer mechanism 150 can be any of a variety of mechanisms for loading items onto the vehicle and for unloading items from the vehicle into one of the storage areas. Additionally, the transfer mechanism 150 can be specifically adapted for a particular application. In the present case, the transfer mechanism 150 comprises one or more movable elements configured to engage an item stored in a storage location and pull the item toward the vehicle. More specifically, in the present case, the vehicle includes one or more movable elements configured to move toward a container in a storage location and releasably engage with the container. After the movable elements engage with the container, each movable element moves away from the storage location, thereby pulling the container toward the vehicle 100. The movable element of the transfer mechanism can be any of a variety of items, such as a bar, rod, or other element configured to engage with an item, for example, a container. For example, with reference to Figures 2-3, the transfer mechanism 150 can include one or more movable pins 152. Additionally, the transfer mechanism can include a drive element for moving the pins 152. For example, optionally, the transfer mechanism 150 includes two drive elements in the form of endless conveyors, such as a drive belt or, as shown, drive chains 154. Optionally, each pin 152 protrudes or extends inward toward the longitudinal centerline of the vehicle. The transfer mechanism is preferably configured to cooperate with one of the containers (Lnn / zznz / E / Yi) to releasably engage the container.For example, in this case, bolts 152 are configured to engage with a groove in the container so that the transfer mechanism can be attached to it. However, it should be recognized that the transfer mechanism may include any of a variety of elements for attaching items to be transferred inside or outside the vehicle. The vehicle includes one or more drive elements for operating the transfer mechanism. Optionally, the vehicle includes one or more motors that drive the transfer mechanism 150. For example, one or more motors of the vehicle's drive mechanism can drive the chains 154 to selectively move the chains and bolts 152 to or from storage locations. As the vehicle approaches a storage location to retrieve a container, the chains can actuate the sliding pins 152 toward the storage location so that the pins are positioned below a groove or notch on the bottom of the container. The vehicle travels a short distance upward until the pins 152 align with the groove or notch in the container. The chain 154 then reverses so that the pins 152 move away from the storage location. Because the pins engage the container within the notch, as the pins move away from the storage location, they pull the container toward a surface on the vehicle. In this way, the transfer mechanism 150 can operate to retrieve items from a storage location.Similarly, to store an item in storage location 820, the chains 154 of the transfer mechanism 150 drive the pins 152 toward the storage location until the item is in place. The vehicle then moves down to disengage the pins from the container, thereby releasing the container. In this case, as shown in Figure 7, two or more containers, such as the 55 containers, can be coupled and uncoupled using coupling connectors. Optionally, the 55 containers can be coupled and uncoupled through a series of lifting and separating movements implemented by the movement of vehicle 100. Optionally, the transfer mechanism 150 can be actuated to pull a forward-facing (main) container onto a surface of the vehicle so that it is fully supported by vehicle 100. If the containers are releasably connected, this pulling movement advances the rear container (i.e., the one immediately behind the main container) into the aisle-facing location.Optionally, the vertical drive mechanism of vehicle 100 can then be operated to drive vehicle 100 vertically to uncouple the main container from the rear containers. Once uncoupling is complete, the Lnn / zznz / B / Yi drive mechanism can be operated again to center the container over vehicle 100. Vehicle 100 may include a separate drive element to operate the transfer mechanism 150. Alternatively, the transfer mechanism may be interconnected with one of the horizontal or drive elements of the vehicle. Specifically, the transfer mechanism may be connected to one of the drive systems so that the drive mechanism is selectively operable between the vehicle drive and the transfer mechanism drive. For example, the transfer mechanism can be optionally connected to one of the horizontal guide systems via a selectable connection, such that in one orientation the drive mechanism drives the vehicle horizontally, and in the other orientation the drive mechanism drives the transfer mechanism. The optional clutch mechanism can be selectively engaged and disengaged to initiate and terminate power transmission, respectively, from the horizontal drive system motors to the transfer mechanism, allowing the second guide system to be operated independently of the transfer mechanism. In this configuration, the clutch mechanism can be configured as two clutch subassemblies positioned symmetrically with respect to a longitudinal centerline of the vehicle. Vehicle 100 can be semi-autonomous or, alternatively, fully autonomous. In the latter case, a multitude of contactless systems have been proposed to continuously determine the actual position of an automated guided vehicle in absolute coordinates and reset the navigation parameters (i.e., X, Y, and heading) to cancel accumulated errors, thereby re-referencing the vehicle. Any of these can be used in the position referencing application for automated guided vehicles in an inventory management system consistent with the modalities of this disclosure. Such referencing systems can be ultrasonic, RF, or optical, with ultrasonic and optical systems being particularly suitable for indoor scenarios. Of these two categories, optical systems are generally more accurate and are therefore more widely used in commercial practice. Exemplary position detection systems utilize a scanning mechanism that works in conjunction with fixed location references strategically placed at predefined inspection sites. Such scanning mechanisms may include scanning detectors with fixed active beacon emitters, scanning emitters / detectors with passive retroreflective targets, scanning emitters / detectors with active transponder targets, and rotating emitters with fixed detector targets. In one or more illustrative modes consistent with this disclosure, the CRO Lnn / zznz / B / Yi vehicles may optionally rely on a scanning laser triangulation scheme (SLTS) to provide position updates to an onboard dead reckoning navigation system. A laser emitter rotating, for example, at two rpm illuminates passive retroreflective barcode targets affixed to walls or support columns at known locations on the order of fifteen meters from the vehicle. The barcodes are used to positively identify the reference target and eliminate ambiguities due to false returns from other reflective surfaces within the operating area. An onboard computer in each vehicle calculates the XY position updates through simple triangulation to cancel accumulated dead reckoning errors. Alternatively, each vehicle can optionally use retroreflective targets, distributed throughout the operational area, in a way that allows each vehicle to determine both the range and angular orientation. For example, a servo-controlled rotating mirror on the vehicle can optionally shift a near-infrared laser beam across a 90-degree horizontal arc at, say, a refresh rate of 20 Hz. When the beam sweeps across a target of known dimensions, the detector detects a return signal of finite duration. When the retroreflective targets are all the same size, the signal generated by a nearby target will be longer than that of a distant one. Angle measurement begins when the scanner starts its right-to-left sweep, where the detection of the reflected signal ends the timing sequence. Another position referencing technique that can be employed on the vehicle is a laser-based scanning beacon system that calculates the vehicle's position and heading using cooperative electronic transponders with passive reflectors. Such a scanning mechanism includes a rotating mirror attached, for example, at a 45-degree angle to the vertical axis of an incremental optical encoder. To improve azimuthal accuracy, a timer optionally interpolates between encoder counts. The fan-shaped beam diverges vertically at, for example, a scattering angle of four degrees to ensure detection of long-range targets while traversing irregular floor surfaces. Each target has a unique code, and many (for example, 32) targets can be processed in a single scan, with the vehicle's XY position calculated every 100 milliseconds. In one or more modes, each vehicle can maintain an internally stored map of its own position within a facility. Additionally, each vehicle provides signals to the central controller, which may include data such as position, speed, angular orientation on the plane of travel, and a selected travel path, to other vehicles within the facility. The vehicle may also include a receiver to receive such data regarding other vehicles. The vehicle can receive this data regarding another vehicle (e.g., coordinates Lnn / zznz / B / Yi) directly from other vehicles or from a central controller. Using the vehicle data, each vehicle can maintain a dynamically updated map reflecting the position of all vehicles within the specific zones of an inventory management facility to which that vehicle has been assigned.When dynamically updated position data is available locally on each vehicle, a central controller 450 can assign a task to a vehicle, including path segments taken by a vehicle to reach the locations where the elements of the assigned task are to be performed, which can be selected by the vehicle. Each vehicle can include a processor configured to execute the stages of a navigation process stored in memory, which causes the vehicle to follow the shortest path from its current location to a destination where the next subtasks of an assigned task will be performed. In such modes, the central controller 450 does not need to be configured to perform traffic control and collision avoidance functions (unless a backup control scheme is desired). Instead, the central controller 450 can be configured to transmit instruction-representative signals that identify the next tasks to be assigned to each vehicle and specify the various locations within the facility where those tasks will be performed.Vehicles, on the other hand, can be configured to transmit signals to the controller that are representative of task assignment acknowledgments, position updates, status updates (e.g., subtask completed or in progress, current power status, etc.) and other information that the controller may need to assess the relative ability of the vehicles to perform pending assignment tasks. In a fully autonomous scheme according to one or more modalities, each vehicle may alternatively use a local processor to determine speed and direction of movement from detected cues placed on an underlying support surface in one or more zones of an inventory management facility, to exchange that position data with other vehicles within the facility, and to maintain a dynamically updated local map to achieve a form of decentralized traffic control similar to that described above using other position detection processes. In semi-autonomous vehicle configurations, also known as automated guided vehicles (AGVs), a central controller, such as the 450 controller, provides necessary traffic control functions, for example, to prevent collisions between vehicles and / or with any potential obstructions to vehicle movement that may be present in one or more zones of a facility to which a subset of vehicles is assigned. In such configurations, the 450 controller receives current position and support data in the form of update signals transmitted from the 100 vehicles. The received position and heading data are compared with the Lnn / zznz / B / Yi estimates that the controller has derived from previous speed and heading instructions transmitted by the controller to the vehicle.Based on the comparison, the 450 controller can determine the corrections to one or more of the speed and direction of one or more vehicles that are needed to avoid a collision and, if so, transmit those instructions to the vehicles. In one or more semi-autonomous modes, each vehicle 100 can include a reader for reading clues placed on a surface over which the vehicle travels and / or in positions within access columns aligned with the series of storage areas 820 (see Figure 1). In some modes, each clue in a first group of clues corresponds to a unique location, forming a grid of locations. These locations can be stored in a data table in memory accessible to a vehicle processor, the central controller 450, or both. Following a path designed to intersect with a particular sequence of these clues, each vehicle can transmit a clue identifier as it passes over it and confirm this to the controller 450, thereby achieving semi-autonomous vehicle guidance through instructions transmitted from the controller to the vehicle.Based on this information and other data reported by each vehicle, the 450 controller can confirm the speed, direction, and trajectory of each vehicle. In one or more modes, the 450 controller uses directional and speed data to enforce collision avoidance policies, to assign inventory management tasks according to the location and energy reserve status of each vehicle, and, for safety purposes, to maintain a safe distance from any authorized personnel in the area. Additional indicators can be affixed, either within the access columns or on the storage containers themselves, in positions adjacent to each storage location. Each indicator can include a unique barcode, and the reader on each vehicle 100 can scan the area around the storage location where an item is to be delivered or retrieved. The data held by the central processor 450 regarding the path a vehicle 100 should follow, and the data regarding the distance the vehicle has traveled based on the drive motor's rotation, may be sufficient to determine whether the vehicle 100 is positioned in the appropriate storage location within the storage areas.However, the evidence adjacent to the storage areas allows for redundant verification of the vehicle's location before unloading or receiving an item at the appropriate storage location. Therefore, the scanner can function to scan and read information related to the storage location where the vehicle stops. If the scanned data indicates that the storage location is the correct one, then the vehicle unloads its item at that location. Similarly, the vehicle can have a second reader to scan evidence adjacent to the rear edge of the vehicle.The second reader can be used in cro Lnn / zznz / B / Yi applications where the system is configured to use a first set of storage locations along the front side of an access column and a second set of storage locations along the rear side of an access column, as shown in Figure 1. In some configurations, the functionality for autonomous or semi-autonomous guidance of the 100 vehicles can be integrated into one or more functional accessories. This process can be beneficial when precise position detection is required in some areas within an inventory management facility, while a less precise position detection process may be acceptable in other areas. For example, in configurations such as the one depicted in Figure 1, the 700 functional accessories are represented as performing a support function to maintain the necessary supply of items for operators at a workstation. In the description above, the vehicles have a vertical guide 140 that is sized and positioned to interact with the sliding guides located adjacent to the storage areas 820 of the racks 800, as described below. The drive gears effect the raising or lowering of a vehicle, depending on the direction of rotation of the motor 230. In addition, functional accessories may incorporate sliding guides that cooperate with the vertical guide to allow a vehicle to raise and lower a functional accessory with which it is associated. In some configurations, each vehicle's processor controls its operation in response to signals received from the central processor 450. Additionally, the vehicle includes a wireless transceiver so that it can continuously communicate with the central processor as it travels along the guideway. Alternatively, in some applications, it may be desirable to incorporate multiple sensors or indicators along the paths the vehicles may traverse. The vehicle may include a reader to detect the signals from the sensors and / or indicators, as well as a central processor to control the vehicle's operation in response to these sensors or indicators. As shown in Figure 1, a material handling system 10 can include several different stations or areas. For example, the system 10 may include a large number of storage locations placed on numerous racks 800. The racks may hold thousands or tens of thousands of storage locations 820. Standalone storage Referring again to Figures 1 and 6, the system may include a plurality of 800 shelves, which may optionally be arranged to form rows or 850 aisles. For example, a first 800a shelf may be separated from a second 820b shelf so that an 850a aisle is formed between the two shelves. In particular, the first 820a shelf may be substantially parallel to the second shelf to form an aisle of substantially uniform width. Additionally, the system may include a plurality of shelves forming a plurality of 850 aisles. Although the 850 aisles are illustrated in Figure 6 as parallel, it should be understood that if the system incorporates a plurality of 800 shelves, the shelves may be arranged in a variety of configurations, and if the system includes a plurality of 850 aisles, the aisles need not be parallel. One of the inventory management tasks assigned to a vehicle 100 might be to retrieve items from storage locations 800. This task can be viewed as a series of subtasks, including leaving the vehicle's current or initial location, traversing a path the vehicle takes from the initial location to an intermediate destination adjacent to an entry point into the series of storage locations, and, at the intermediate destination, aligning the vehicle 100 with the entry point. As a further subtask of the retrieval task, the aligned vehicle enters the series and maintains its alignment until it reaches the column within which the vehicle is positioned. It is then moved up, according to another subtask, until it reaches a target—one of the storage areas 820.As additional subtasks of the retrieval process, a vehicle transfer mechanism is operated to retrieve an item, lower it within the column until it rests on a support surface, and then exit the storage location series. As the final subtask of the retrieval operation, vehicle 100 advances along a path to an exit station 500, where an operator can retrieve the item from the vehicle. Optionally, the system includes an automated element for storing and retrieving containers from storage locations. One such automated element is an autonomous vehicle. For example, as described below, the automated element may include a plurality of autonomous vehicles 100. Additionally, the automated vehicles 100 may be configured to transport containers 55 to workstations 500. At workstation 500, one or more items may be removed from a container into one of the vehicles 100. In one mode, a human operator may remove an item from the vehicle. However, it should be understood that an automated mechanism may also remove the item from the vehicle. Consequently, it should be understood that the operator handling items at workstations 500 may be a human operator, an automated mechanism, or a combination of both. System 10 and / or various system components can be controlled by a central controller, such as a microcomputer. The central computer can receive signals from various elements, such as sensors, and control various aspects of the system based on the signals received from the different components. The central controller can also store data about the location of various items to be retrieved from the system. Additionally, the central controller can include data about the identification of the items to be retrieved, such as the quantity of items to fulfill customer orders, as well as the quantity of those items. In this way, the central controller can control and coordinate the operation of various elements to schedule the retrieval and processing of a variety of items from storage locations. Figure 6 is a plan view depicting a portion of an inventory management system 800, which may form part of the system shown in Figure 1 and uses autonomous vehicles 100 to transfer containers 55 of inventory items back and forth between a picking area and a vertical series of storage locations 820. The system may incorporate a plurality of vehicles 100 and the series of storage locations 820 as elements of an automated storage and retrieval system (AS / RS). The vehicles 100 may be configured in the same manner as the vehicles 100 described above. However, it should be understood that the vehicles may be modified for different tasks within the system if desired. In any case, and now returning to Figures 1 and 6-10, a system for storing and retrieving items within a series of storage locations 820 will now be described in detail. Returning first to Figures 1 and 6, a plurality of automated guided vehicles 100a to 100f operating within or around a racking structure 800 are depicted. As in the modalities described above, the vehicles perform various item replenishment and / or retrieval tasks, and in this case, some of those tasks involve retrieving bins or returning containers to storage locations 820. As described above, the system may include a plurality of shelves that are spaced apart to form one or more aisles 850. Optionally, a shelf 840 may be placed along one or more of the shelves. For example, the sliding guide may be permanently attached to the shelves 800. Additionally, the sliding guide may be configured to guide vehicles vertically so that the vehicles can be transported up and down the column to the storage locations within the column. Furthermore, it may be desirable to place a first sliding guide along a shelf on one side of the aisle, such as along shelf 800a, and a second sliding guide along a shelf on the opposite side of the aisle, such as along shelf 800b.The 100 vehicles can be configured so that the vehicle travels down aisle 850a with one side of the vehicle moving vertically along a slide guide on shelf 800a while simultaneously a second side of the vehicle moves vertically along a slide guide on shelf 800b. Each column may consist of a plurality of vertical posts 815. The posts may be positioned so that a plurality of vertical posts are aligned in a parallel relationship on one side of the column and a plurality of posts may be positioned parallel to the posts on the first side on a second side of the column, opposite the posts on the first side, as shown in Figures 7-10. As shown in Figure 7, the posts 815 on each side may be interconnected by a plurality of horizontal members 817 that extend the full depth of the column. The horizontal members 817 may be separate elements that solely provide structural support for the column. Alternatively, the horizontal members may also support items stored in the storage locations 820. For example, the horizontal supports may be flat elements that form shelves, so that the shelves form storage locations. However, it should be understood that the horizontal supports may be any of a variety of configurations. For example, in the embodiment illustrated in Figure 8, the horizontal members are L-shaped supports 817 that form elongated horizontal projections to support the edges of the containers 55 along the depth of the storage location. The horizontal supports may be spaced apart up to the height of the vertical legs 815 to form a column of vertically spaced storage locations 820. The column 810 of rack 800 has a depth that, from the perspective of Figure 7, is similar to the length of the horizontal support 817. The column 810 has a depth that is similar to the length of a 55 or larger container. For example, the column may be deep enough to accommodate at least one container. However, the container may overhang the aisle 850, so the column may be slightly less than the length of a container. Alternatively, the column may be deep enough to accommodate a plurality of containers placed end-to-end as shown in Figure 7. In the example illustrated in Figure 7, the racks are deep enough so that each storage location 820 can accommodate three 55 containers aligned end-to-end, where each container is approximately similar to the length of the 100 vehicles. As described above, the vehicle has a length and a width. As shown in Figure 5, the vehicle optionally has a length L that is significantly greater than its width W2. Referring to Figures 6 to 10, the 800 shelf is configured so that each 810 column has a width that is significantly less than its depth. Specifically, the width of each column is similar to the width of the vehicle, and the column depth is substantially greater than the vehicle's length. Optionally, the column has a depth greater than twice the vehicle's width, as shown in Figures 7 and 10. Additionally, the column depth can optionally be greater than the vehicle's length. Figure 7 illustrates a plurality of vehicles in different orientations with respect to the shelves 800 and the storage locations 820. For example, a first vehicle 100a is oriented for horizontal movement along path 860c, transverse to the length of aisle 850. A second vehicle 100b is oriented for horizontal movement under the shelf 860b along path 860b, which is parallel to the length of aisle 850. Additionally, a third vehicle 100c is positioned within aisle 850 to climb the vertical shelves along the shelves 800 on either side of the aisle. A fourth vehicle 100d is also positioned within the aisle and has climbed up the slide guide 840a, b to a storage location 820 in an upper portion of column 810.Finally, a fifth 100 vehicle is positioned below shelf 800 and is oriented in a position intermediate between the orientation of vehicle 100a and the orientation of vehicle 100b. Specifically, the shelves can be configured to facilitate horizontal rotation of the vehicles beneath them. The fifth 100 vehicle illustrates the vehicle in the process of rotating beneath the shelf from a first trajectory to a second trajectory. As mentioned previously, the 800 structure is sized and positioned so that vehicles can enter and exit from various locations beneath the storage locations, allowing flexibility in the installation of picking and / or replenishment stations. If the system uses one or more vehicles and one or more racks, the racks can be configured to allow vehicles to travel beneath the 800 racks and to move through or along one or more aisles that can be incorporated into the system. For example, with reference to Figure 6, vehicles can follow a path that moves along one or more path segments that can be parallel or perpendicular to the aisle. One such path is designated as path 860a. Path 860a is within and parallel to the length of aisle 850a.A second path is designated path 860b, which is parallel to the length of aisle 850a but separate from the aisle. Specifically, path 860b is located below rack 800b. Rack 800b can be configured to provide space for vehicle movement below the lowest storage location 820 so that the vehicle can travel under rack 800b along path 860b, which is parallel to the length of the aisle. A third path is designated 860c, which is transverse to 860a and 860b. As shown in Figure 6, path 860c is parallel to the depth of column 810. With reference to Figures 7 and 9, the rack is optionally configured so that the rack columns have sufficient depth to provide multiple paths under each column that are substantially parallel to the length of aisle 850. Specifically, as shown in Figure 7, the 815 posts adjacent to aisle 850 can be separated from the 815 posts away from the aisle to form an opening that is wider than twice the width of the vehicle. Figure 9 illustrates vehicle 100b moving along path 860, which is parallel to the aisle, and vehicle 100c moving along path 860', which is parallel to path 860. Preferably, path 860' has a centerline that is separated from the posts 815 adjacent to the aisle by more than half the length L of vehicle 100 (see Figure 5). Similarly, path 860 preferably has a centerline that is separated from the posts on the trailing edge of the column farthest from the aisle 850 by a distance greater than half the length of the vehicle. Optionally, the paths 860, 860' under the rack, which are parallel to the aisle, can be separated to provide a space that allows a first vehicle traveling along path 860 to pass a second vehicle positioned along path 860', such as a vehicle traveling in the opposite direction along path 860'. For example, path 860 can be separated from path 860' by a distance greater than the width W2 of vehicle 100 (see Figure 5). Additionally, as described above, the vehicles can change direction by rotating around a vertical pivot axis that passes through the vehicle. In particular, the pivot axis can pass through the center of the vehicle. The columns 810 are preferably deep enough to allow the vehicle to rotate around the pivot axis while positioned on the column below the rack. Specifically, each of the paths 860, 860' is preferably separated from the posts 815 by a distance greater than the distance from the pivot axis to each of the vehicle's corners. When the vehicle turns under the 800 shelf, it can rotate to any of a variety of angles. Optionally, the vehicle can turn in 90-degree increments. Specifically, optionally, the vehicle turns 90 degrees or 270 degrees after exiting the aisle, so that it travels parallel to the aisle under the shelf after moving up the aisle guide rail. Figure 8 is a side elevation view depicting the racking structure 800, which includes a plurality of columns 810a-810f populated within a series of bins or containers, including containers Ta, Tb, Tc, and Td. A plurality of vehicles are operating to perform various item replenishment and / or item retrieval tasks as part of the inventory management system. Vehicle 100a is shown having entered the leftmost drive column 810a. In this respect, and now with reference to Figure 9, it will be seen that the structure 800 can incorporate a series of parallel guide rails, such as rails R1 and R2, which define a space gG between them. The space is dimensioned and positioned to receive the corresponding alignment structures on the vehicles to allow the vehicles to enter, exit, and reorient themselves without damaging each other or the racking structure, as described later. Optionally, the system may also include one or more guides 880 to guide or align the vehicles in their movement. For example, with reference to Figure 10, the guide 880 may include a channel or slot, and the vehicle may include a corresponding guide element 127 that cooperates with the guide 880 to control the movement of the vehicle 100. An example of a guide element is a follower 127. The follower may be any element configured to engage or cooperate with the guide 880. In this case, the vehicle 100 includes a center follower 126 that includes a rotating element, such as a bearing, that rotates about a vertical axis. Optionally, the follower 126 includes a shaft so that the follower protrudes from a surface of the vehicle, such as downward from a lower surface of the vehicle. The center follower 126 engages the channel in the guide 880 to restrict the horizontal movement of the vehicle. Optionally, the vehicle may also include one or more lateral guide members 127. The lateral guide members 127 may cooperate with an outer surface of the guide 880 to restrict the vehicle's movement. For example, the guides 880 may comprise circular guides having a circumferential surface to guide the vehicle's turning. The vehicle may have a pair of lateral guide members 127 separated from each other by a distance equal to the diameter of the guide's circumferential surface. In this way, the lateral guides 127 engage with the guide's circumferential surface to restrict the vehicle's turning motion. Referring to Figure 8, guide 880 optionally includes a plurality of intersecting guides. For example, guide 880 may include a first guide rail 882 in the form of a slot or channel having walls separated by a distance substantially similar to the width of the vehicle's center follower 126. The first guide rail 882 may be oriented so that it extends parallel to route 860. Additionally, guide rail 880 may have a second guide rail 884 in the form of a slot or channel with walls separated by a distance substantially similar to the width of the vehicle 100 follower 126. The second guide rail 884 may be oriented so that it extends transversely to route 860. In the present case, guide rail 884 extends substantially perpendicular to route 860. In this manner, the first and second guide rails 882, 884 of guide rail 880 extend in a linear direction that is preferably parallel or perpendicular to aisle 850. The guide 880 may optionally include a non-linear guide rail. For example, the perimeter of the guide may form a non-linear guide surface identified as 886 in Figure 9. Specifically, the guide may have a substantially circular profile that forms a circumferential support surface. The diameter of the circular profile may correspond to the distance between the side guides 127 of the vehicle 100 (see Figure 3). The guide rails of guide 880 can optionally cross to facilitate changing the vehicle's direction of travel. For example, guide rail 882 can cross with guide rail 884 to allow the vehicle to change direction from parallel to the aisle to perpendicular to the aisle, or vice versa. Guide rails 882 and 884 can also cross at a central point of the guide. In this way, the guide can facilitate turning the vehicle around a vertical axis, allowing it to rotate from one direction of travel along guide rail 882 to a second direction of travel along guide rail 884. The guide 880 can guide the vehicle 100 to change direction as follows. The vehicle can move along a linear path with the central follower 884 coupled to the guide rail 882 or 884 to prevent lateral movement away from the linear path. The vehicle moves horizontally along the linear path until the central follower is positioned at the center point of the guide with the vehicle's side guides 127 coupled to the circumferential guide rail 886. The vehicle 100 then rotates about a vertical axis to change its direction of travel. For example, the drive wheel 124 on one side of the vehicle can rotate in a first direction while the drive wheel 124 on the opposite side of the vehicle rotates in a second direction, which is the reverse of the first, to perform a zero-radius turn.While the drive wheels 124 rotate the vehicle around the pivot axis, the side guides 127 prevent the vehicle from moving laterally out of the pivot path. Optionally, the 880 guides are aligned with the columns to facilitate turning the vehicle inside the column while aligning the vehicle width with the opening between the 815 posts at the front of the column (adjacent to aisle 850) or at the rear of the column (away from aisle 850). Optionally, as shown in Figure 9, the system may include a floor-mounted lateral alignment system 890 consisting of a pair of plate members separated by a gap gG. In this case, the gap defined by the alignment system 890 is oriented with those defined by the alignment system 895 to allow a vehicle to quickly and easily traverse the entire width of the structure while maintaining a generally constant angular orientation within the drive columns DI for D6. As described above, a plurality of guide elements, such as sliding guide elements 840, can be attached to the rack 800 to guide vehicles into alignment with above-floor storage locations. For example, the sliding guide 840 can comprise a plurality of vertical sections. Specifically, a vertical rack section can be attached to each post within the aisle 850. Referring to Figure 10, the vertical rack section can be profiled to engage the vehicle's vertical drive system 140. For example, the sliding guide can include a plurality of teeth forming a rack that extends to the height of the post 815. As shown in Figure 10, the sliding guide 840 can cross the aisle such that a first sliding guide extends vertically upward along a first side of the column and a second sliding guide extends upward along a second side of the column. For example, the column DI and vehicle 10 are illustrated in Figure 10. The column DI includes two separate vertical posts 815 that form an opening of width W1. Specifically, the first post has a first vertical edge E1 and a second vertical edge E2; and the second post has a first vertical edge E3 and a second vertical edge E4. The distance between the vertical edges E2 and E3 is greater than the width W1 of the vehicle (see Figure 5). Optionally, the distance between the vertical edges E2 and E3 is less than the width W2 of the vehicle (see Figure 5).In this way, the width of the column can be less than the distance between the outer tips of the gears of the vertical guide 140 of the vehicle 100. Consequently, most of the column can be narrower than the width of the vehicle at its widest point. Optionally, the 840 slide guide can be configured so that a first edge of the slide guide projects into a first column to provide a guide surface for the first column, and a second edge of the slide guide projects into a second column to provide a guide surface for an adjacent column. For example, the 840 slide guide can provide a first set of teeth projecting into column D1 and a second set of teeth projecting into column D2. Additionally, the vertical posts 815 can be optionally configured to provide a stop to prevent lateral displacement of the vehicle as it ascends the sliding guide 840. For example, with reference to Figure 10, post 815 overlaps the teeth of the sliding guide 840 such that edge E3 of post 815 extends beyond the base of the sliding guide teeth and preferably towards the ridges of the sliding guide. In this way, the teeth of the vertical guide 140 engage with the sliding guide while the post prevents the vertical guide from moving laterally parallel to the column depth. The vertical guide 140 of vehicle 100 can be configured so that the vertical drive gears 145 can be moved inwards to reduce the distance between them. In this way, the drive gears can be moved inwards to provide clearance between the sliding guides 840 and the vertical drive gears as the vehicle moves towards the column. Alternatively, as described above, the vertical drive gears can be mounted on shafts so that the axis of rotation of each vertical gear is substantially parallel to the horizontal direction of travel. Additionally, the axes of rotation of the vertical drive gears can be substantially fixed so that the lateral distance between each pair of vertical drive gears is substantially fixed.To enter the column, the teeth of the vertical drive gears align with the teeth of the 840 slide guide so that the teeth of the vertical drive gears pass through the teeth of the Lnn / zznz / B / Yi slide guide. Referring to Figure 10, the sliding guide 840 and the vertical drive gear 145 can be aligned so that the vertical drive gears do not collide with or contact the sliding guide when the vertical gear moves relative to the sliding guide. For example, the spacing between the teeth of the sliding guide 840 provides sufficient clearance for the teeth of the vertical drive gear 145 to pass between the spacings between the teeth of the sliding guide 840 when the vertical drive gear moves horizontally along a line parallel to the axis of rotation of the vertical drive gear 145. More specifically, the vertical drive gear and the sliding guide can be configured and positioned so that the addition circle of the vertical drive gear 145 overlaps with the additional line of teeth on the sliding guide 840.While the drive gear's addition circle overlaps the slide guide's addition line, the gear teeth are configured and oriented so that the vertical drive gear passes through the spaces between the teeth in the 840 slide guide. Again, with reference to Figure 10, the vertical drive gear 145 and the sliding guide 840 can optionally be configured and oriented to increase the clearance for the vertical drive gear to pass through the sliding guide when the vehicle drives the opening between the vertical posts 815 that form the column width (i.e., when the vertical drive gear is translated so that its axis of rotation is in a horizontal direction perpendicular to the aisle). For example, the sliding guide 840 can have an upper portion and a lower portion 842. The upper portion can have a tooth pitch and configuration to engage with the teeth of the vertical drive gear 145.The lower portion 842 may have a tooth pitch that is substantially similar to the tooth pitch of the upper section, but the tooth profile of the lower section may be substantially different from that of the upper section. For example, the teeth of the lower section may be substantially narrower than the teeth of the upper section. For example, the teeth may be at least 10% narrower and preferably at least 20% narrower. Optionally or additionally, the teeth of the lower section 842 may have a tooth root height that is substantially greater than the tooth root height of the upper section. For example, the tooth root height of the lower section may be greater than that of the upper section so that the root of the teeth extends inward away from the driving gears a greater distance than the root of the teeth of the upper section.For example, the tooth foot height of the teeth in the lower section can be 10% greater and preferably 20% greater. Additionally, the lower section 842 may optionally have a tapered pitch line so that the spacing between adjacent teeth gradually decreases as the teeth ascend the height of the lower section. In other words, the spacing 845 between adjacent teeth at the bottom of the lower section is maximum, and the spacing between adjacent teeth at the top of the lower section is minimum, with the spacing gradually decreasing from maximum to minimum. Optionally, the 815 posts can have a variable width to facilitate the passage of the vertical guide through the opening between the 815 posts. For example, as described above, the 815 posts can have a first width so that the E3 edge of the post extends beyond the base of the sliding guide teeth. Additionally, the lower 816a, b portion of the 815 post can be narrower than the upper portion. Specifically, the post can be narrower so that the edge of the post ends below the base of the tooth. In this way, the lower portion of the post is narrower than the upper portion. Similarly, the distance between the lower 816a and lower 816b posts is greater than the distance between the E2 edge and the E3 edge. Additionally, the column opening between the lower 816a and 816b portions is greater than the maximum W2 width of the vehicle. Configured as described above, the 140 vertical guide can optionally be set up to pass through openings in the sliding guide so that the vertical guide is aligned with the sliding guide. After the vertical guide is aligned with the sliding guide, it is positioned to cooperate with the sliding guide to raise and / or lift the sliding guide as described above. As previously stated, a central controller 450 can provide control signals to control the vehicles 100. For example, the central controller can control the operation of a vehicle to follow a path through the rack to retrieve a container 55 from a storage location 820 in one of the columns 810 on the rack 800. The vehicle can follow a path along the floor to align the width of the vehicle with a path that extends through an opening between two vertical posts 815 of the rack 800. The vehicle can travel along the path that passes through a plurality of columns on the rack.Optionally, the central controller can provide signals to control a second vehicle so that the second vehicle travels along a second path parallel to the first path and under the same shelf as the first vehicle so that the second vehicle passes the first vehicle under the shelf. After the vehicle passes through a plurality of columns beneath the rack, it reaches the column on the rack where the selected storage location is situated. The central controller provides signals to halt the vehicle's movement along the path. The central controller then provides signals to rotate the vehicle beneath the rack to align it with an opening in the column. After rotating, the vehicle moves along a path parallel to the depth of the column so that it passes through the column opening and into the aisle. Optionally, the stage of moving the vehicle into the aisle includes the stage of aligning a vertical drive element with gaps in the column opening. Once in the aisle, the vehicle is driven vertically upward until it aligns with the desired storage location.The vehicle activates a transfer mechanism to move an item from its storage location into the vehicle. Optionally, the storage location may include an item at its leading edge, separating the vehicle from the desired item. The vehicle then transfers the item at the leading edge to the vehicle, which in turn pulls the desired item to the leading edge of the storage location. The vehicle then drives vertically to a storage location with an open slot to receive an item. The vehicle then transfers the item into the open slot. Finally, the vehicle moves vertically to the storage location containing the desired item and activates the transfer mechanism to move the desired item into the vehicle.After retrieving the desired item, the vehicle engages the vertical drive mechanism to lower the column until the vehicle engages a horizontal guide surface, such as the floor. The vehicle's horizontal guide then engages to drive it through the opening in the column in a direction perpendicular to the aisle. After driving out of the aisle, the vehicle continues driving horizontally to exit shelf 800. For example, the vehicle may continue along a path perpendicular to aisle 850, passing under one or more additional shelves 800 and across one or more additional aisles 850. Following such a path, the vehicle's trajectory is controlled so that the vehicle's width is aligned with the opening in each column it passes through.Alternatively, the vehicle rotates around a vertical axis to align it with a path parallel to the aisle while remaining under the rack. The vehicle then passes under one or more columns of the 800 rack until it exits from beneath the rack. After the vehicle leaves rack 800, the central controller 450 can control the vehicle to direct it to one of a plurality of workstations 500. At the workstation, the vehicle presents itself to an operator to retrieve one or more items. The central controller can then control the vehicle to direct it along a path to store the item it is carrying in an open storage location on the rack and retrieve a subsequent item from a different storage location. In this way, the central controller provides control signals to a plurality of vehicles to direct them along a plurality of paths to retrieve a plurality of items from storage locations Lnn / zznz / E / Yi and deliver items to workstation 500. Control process Figure 11 is a block diagram representing the subsystems of a plurality of guided vehicles 100-1 to 100-n, according to one or more modes. Each vehicle, such as vehicle 100-1, may comprise a central processing unit (CPU) 103, memory 105, and communication interfaces. In some modes, the communication interfaces comprise one or more wireless transceivers compliant with the corresponding wireless transmission protocols, such as IEEE 802.11, and a vehicle's interfaces are used to communicate with other vehicles, as in a peer-to-peer topology, or with a central controller. In the latter case, vehicles 100-1 to 100-n may include position sensors 280 and object sensors 282 and use the interfaces to communicate sensed information with a master controller, such as the central controller 450.Position sensors, in one or more modalities, include integrated image sensors to determine when the vehicle has passed over a fiduciary mark placed on an underlying support surface. Alternatively, however, 100-1 to 100-n vehicles may use signal triangulation and / or any other conventional technique to determine their respective locations relative to each other or allow the controller to do so. Each 100-1 vehicle includes a power supply 288, which may be, for example, a rechargeable power supply comprising ultracapacitors, one or more batteries, or a combination thereof. In one or more embodiments, the power supply drives a first motor 230 of the first drive mechanism. The first drive mechanism may further include gears driven by the first motor and used, for example, to drive the vehicle vertically. In the present case, the power supply 288 also supplies power to a second drive mechanism, which includes a second motor 250a and, optionally, a third motor 250b. The 286 CPU may comprise one or more commercially available microprocessors or microcontrollers that facilitate data processing and storage. Various supporting circuitry facilitates the operation of the 286 CPU and includes one or more clock circuits, power supplies, cache, input / output circuitry, and the like. The 287 memory comprises at least one of the following: read-only memory (ROM), random-access memory (RAM), disk drive storage, optical storage, removable storage, and / or the like. Figure 12 is a schematic block diagram of a 450 controller that can respond to instructions received from a 1440 warehouse automation system (WMS) to coordinate the allocation and execution of inventory management task activities by a plurality of vehicles and subassemblies (e.g., mobile slide guide 700 or flow rack 600), such as those allocated to AGV task groups 902-1, 904-1, 906-1, and 908-1. The controller 450 comprises a central processing unit (CPU) 951, supporting circuitry 955, a memory 952, user interface components 954 (which may include, for example, a touch-sensitive display or a separate keyboard), and communication interfaces 953. In some embodiments, the server 450 comprises one or more wireless transceivers that comply with the corresponding wireless transmission protocols, such as IEEE 802.11. The CPU 951 may comprise one or more commercially available microprocessors or microcontrollers that facilitate data processing and storage. The various support circuits 955 facilitate the operation of the CPU 951 and include one or more clock circuits, power supplies, cache, input / output circuits, and the like. The memory 952 comprises at least one of the following: read-only memory (ROM), random-access memory (RAM), disk drive storage, optical storage, removable storage, and / or the like. In some embodiments, the memory 952 comprises an operating system 956 and one or more inventory management applications. In some embodiments, the inventory management applications include a task agent management module 960, an AGV traffic management module 970, a status / event monitoring module 980, and a data repository 990. In one or more modes, the task agent manager 960 is configured with an inventory management task processor 961, a dynamic inventory allocation analyzer 962, a subtask sequence identifier 963, a task priority manager 964, an event notification detector 965, a state transition detector 966, and an AGV selector 967. The inventory management task processor 961, through the execution of instructions by CPU 951, processes inventory management task requests received from WMS 940. In some configurations, AGV traffic management is performed by a traffic management module 470 of the controller 450. In such cases, the controller collects vehicle position, speed, and direction data at regular intervals. The position data is analyzed, and the path segment selector 474 selects paths for each vehicle during the next control interval to ensure no collisions occur with other vehicles, personnel, or fixed structures. Updated instructions corresponding to the path selections, including heading and direction, are transmitted by the controller back to the vehicles. In other configurations, however, the vehicles do not rely on the controller for relative positioning instructions, but only for task and destination assignments, with the vehicles instead relying on internal data collection and spatial analysis capabilities. To facilitate the aforementioned operations, the 450 controller in Figure 12 includes a data repository that reflects an up-to-date location of all inventory items for which the WMS has assigned management and allocation responsibility, as well as a map of vehicle locations within the facility. Furthermore, to facilitate the scheduling of preventive maintenance procedures, usage statistics are collected for all AGVs with moving parts so that, at regular intervals, these parts can be inspected, lubricated, and / or replaced. The order of the methods described herein may be changed, and various elements may be added, reordered, combined, omitted, modified, etc. All examples described herein are presented in a non-limiting manner. Various modifications and changes may be made, as would be obvious to a person skilled in the art who benefits from this disclosure. Implementations according to the modalities have been described in the context of particular modalities. These modalities are intended to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, several instances of the components described herein may be provided as a single instance. The boundaries between various components, operations, and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations.Other functional assignments are foreseen and may fall within the scope of the following claims. Finally, the structures and functionality presented as discrete components in the example configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the modalities defined in the following claims. Accordingly, although the foregoing refers to embodiments of the present invention, additional embodiments of the invention may be devised without departing from its basic scope, and the scope thereof is determined by the following claims.

Claims

1. A method for delivering items to storage locations and retrieving items from storage locations, comprising the steps of: providing a plurality of storage racks separated from each other forming a plurality of aisles, wherein each storage rack comprises a plurality of columns and each column comprises a plurality of storage locations; providing a plurality of delivery vehicles, wherein each vehicle comprises a horizontal drive system enabling the vehicle to be driven along a horizontal surface, a vertical drive system enabling the vehicle to be driven vertically, and a transfer mechanism enabling the transfer of an item between the vehicle and one of the storage locations; driving the first of the vehicles to the storage racks;Drive the first vehicle along a first path under the first shelf, where the first shelf is adjacent to the first aisle and where the first path extends in a direction parallel to and separate from the first aisle; turn the first vehicle while it is under the first shelf; drive the vehicle into the first aisle; drive the first vehicle up the aisle to the first storage location; transfer an item between the first vehicle and the first storage location; drive the first vehicle down the aisle until the vehicle is on a horizontal surface; drive the first vehicle through the first aisle after the step of driving the first vehicle down;and drive the vehicle out from under the storage shelves after the stage of driving the first vehicle through the first aisle.; 2. The method according to claim 1, wherein a plurality of vertical posts form a first column of the first storage rack, and wherein the first vehicle has a first width extending from a first side of the first vehicle to a second side of the first vehicle, and wherein the vertical guide of the first vehicle projects outward from the first and second sides so that the vehicle has a second width corresponding to the distance between the outer edges of the vertical guide, such that the second width is greater than the first width, and wherein the vertical posts of the first column are separated by a distance greater than the first width and less than the second width.

3. The method according to claim 1, wherein a plurality of vertical sliding guide segments are attached to the vertical posts of the first column and wherein the step of driving the first vehicle into the first aisle comprises aligning the vertical guide of the first vehicle with the vertical sliding guide segments.

4. The method according to claim 3, wherein the step of driving the first vehicle into the aisle comprises driving a first portion of the vertical guide through the vertical sliding guide segment and driving a second portion of the vertical guide in operational coupling with the vertical sliding guide segment.

5. The method according to claim 1, wherein the first storage rack is formed by a plurality of vertical posts and the first vehicle has a length and a width, the length being greater than the width, and wherein the step of driving the first vehicle along the first path comprises driving the vehicle along a path separated from the vertical posts by a distance greater than half the length of the vehicle.

6. The method according to claim 1 comprising the step of driving the first vehicle to a workstation to present an item to an operator after the step of driving the first vehicle out from under the storage shelves.

7. The method according to claim 1, wherein the step of driving the first vehicle through the aisle comprises driving the first vehicle out from under a second storage rack.

8. The method according to claim 1, wherein the turning step comprises turning the first vehicle about a vertical axis extending through the first vehicle.

9. The method according to claim 8, wherein the vertical axis extends through the first path.

10. The method according to claims 1-9 comprising the step of driving a second vehicle under the first shelf along a second path parallel to the first path so that the second vehicle passes the first vehicle as the first vehicle travels along the first path 11. A material handling system for delivering items to storage locations and retrieving items from storage locations, comprising: a first storage rack having a plurality of columns, each comprising a plurality of storage locations wherein the first storage rack is longitudinally elongated; a second storage rack having a plurality of columns, each comprising a plurality of storage locations wherein the second storage rack is longitudinally elongated, wherein the first storage rack is separated from the first storage rack to provide an aisle between the first and second storage racks;a plurality of delivery vehicles wherein each vehicle has a length and a width and each vehicle comprises: a horizontal drive system enabling the vehicle to be driven along a horizontal surface; a vertical guide enabling the vehicle to be driven vertically; and a transfer mechanism enabling the transfer of an item between the vehicle and one of the storage locations; a sliding guide positioned in the aisle wherein the vertical guide is configured to cooperate with the sliding guide to drive the vehicle vertically upwards; a first horizontal path extending under the first shelf in a direction parallel to the aisle; a second horizontal path extending under the first shelf in a direction parallel to the aisle;wherein the horizontal guide is configured to rotate the vehicle beneath the first rack by turning the vehicle around a vertical axis extending through the vehicle; wherein the storage rack comprises a plurality of vertical posts and the first and second horizontal tracks are each separated from the vertical posts by a distance greater than half the length of the vehicles; wherein the first horizontal track beneath the track is separated from the first horizontal track by a distance greater than the width of the vehicles.

12. The system according to claim 11, wherein the vertical guide comprises a plurality of rotating elements, each of which rotates about a horizontal axis, and wherein the horizontal guide comprises a plurality of rotating elements, each of which rotates about a horizontal axis transverse to the rotation axes of the vertical drive elements.

13. The system according to claim 12, wherein the plurality of vertical posts forms a first column of the first storage rack and wherein the vehicles have a first width extending from a first side of the vehicle to a second side of the vehicle and wherein the vertical guide of the vehicle projects outwards from the first side and the second side such that the vehicle has a second width corresponding to the distance between the outer edges of the vertical guide so that the second width is greater than the first width and wherein the vertical posts of the first column are separated by a distance greater than the first width and less than the second width.

14. The system according to claim 11, wherein the sliding guide comprises drive elements configured to cooperate with the vertical guide so that rotating the vertical guide about a horizontal axis allows the vehicle to be driven upwards along the sliding guide.

15. The system according to claim 14, wherein the sliding guide comprises a lower section and an upper section, wherein the drive elements are more widely spaced in the lower section than in the upper section to provide spaces in the lower section.

16. The system according to claim 15, wherein the spaces are configured to facilitate the vertical guide passing through the spaces without coming into contact with the lower section when the vehicle is driven past the lower section.

17. A method for delivering items to storage locations and retrieving items from storage locations, comprising the steps of: providing a vehicle having a horizontal guide and a vertical guide comprising a front rotating element adjacent to a front end of the vehicle and a rear rotating element adjacent to a rear end of the vehicle; providing a first vertical shelf on a first side of a first column wherein the first vertical shelf has drive elements configured to cooperate with the front rotating element to drive the vehicle upwards;providing a second vertical shelf on the second side of the first column wherein the second vertical shelf has drive elements configured to cooperate with the rear rotating element to drive the vehicle upwards, wherein the vertical guide and the first and second vertical shelves are configured such that the vertical shelf prevents the vehicle from moving along a horizontal path when the vertical guide is rotated to a misalignment position; aligning the vertical guide, wherein the alignment step comprises the steps of: rotating the front rotating element about a horizontal axis substantially parallel to the horizontal path to align the front rotating element with gaps in the first and second vertical shelves;and rotating the rear swivel about a horizontal axis substantially parallel to the horizontal path to align the rear swivel with spaces in the first and second vertical shelves; after the alignment step, driving the vehicle along the horizontal path towards the first vertical shelf, wherein the driving step comprises driving the vehicle so that the front swivel passes through the spaces in the second vertical shelf; continuing to drive the vehicle along the horizontal path to place the front swivel in operational engagement with the first slide guide and the rear swivel in operational engagement with the second slide guide; rotating the front and rear swivels to drive the vehicle upwards towards a first storage location;transfer a first item from the first storage location to the vehicle; drive the vehicle down with the first item; drive the vehicle with the first item along the horizontal path so that the rear rotating element passes through gaps in the first vertical shelf.

18. The method according to claim 17, wherein the step of rotating the front and rear rotating elements comprises synchronously driving the front and rear rotating elements to drive the vehicle vertically upwards while maintaining the orientation of the vehicle with respect to the horizon.

19. The method according to claim 17 or 18 comprising the step of driving the vehicle out from under the sliding guide after the step of driving the vehicle with the first article along a horizontal path.

20. The method according to any of claims 17-10 comprising the step of turning the vehicle onto a path perpendicular to the horizontal path while the vehicle is under one of the shelves.

21. The method according to any of claims 17-20 comprising the step of driving the vehicle with the first article to a workstation to present the first article to an operator.

22. The method according to any of claims 17-21, wherein the step of driving the vehicle along the horizontal path comprises actuating a plurality of horizontal drive elements about a horizontal axis that is substantially perpendicular to the horizontal path.

23. A method for delivering items to storage locations and retrieving items from storage locations, comprising the steps of: providing a plurality of storage racks separated from each other forming a plurality of aisles, wherein each storage rack comprises a plurality of columns and each column comprises a plurality of storage locations; providing a plurality of delivery vehicles wherein each vehicle comprises a horizontal drive system enabling the vehicle to be driven along a horizontal surface, a vertical guide enabling the vehicle to be driven vertically, and a transfer mechanism enabling the transfer of an item between the vehicle and one of the storage locations;driving a first vehicle under one or more storage racks along a path that crosses one or more aisles, wherein the step of driving the first vehicle includes driving the first vehicle toward a first column in a first aisle; driving the first vehicle vertically upward within the first aisle until the first vehicle is adjacent to a first storage location; transferring an item from the first storage location to the first vehicle; driving the first vehicle vertically downward within the first aisle; driving the vehicle out of the first aisle through a path that extends under at least one of the storage racks.

24. The method according to claim 23, wherein the path includes a portion that passes under one of the shelves and extends parallel to one of the aisles.

25. The method according to claim 24 comprising the step of driving a second vehicle past the first vehicle under a shelf while the first vehicle is driven along the portion of the path under one of the shelves.

26. The method according to any of claims 23-25 ​​comprising the step of turning the vehicle while the vehicle is under one of the shelves, wherein the turning step comprises turning the vehicle to align the vehicle with a path perpendicular to the first aisle.

27. The method according to claim 26, wherein the step of turning the vehicle comprises turning the vehicle about a vertical axis passing through the vehicle.

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