Conventional parking garages are transforming the landscape to meet the demand for high capacity storage. In urban centers, where space above and below ground is at a premium, the owner of a parking facility is constrained by a fixed footprint and a certain amount of vertical space extending from such footprint. Multi-level garages can only extend so high without becoming an eyesore or unwieldy to navigate. Furthermore, self-park and/or attendant-park locations must account for extra space on either side of a vehicle for human access to and around the vehicles.
In addition, each storage location has an associated amount of overhead that must be accommodated by the facility owner. For example, most facilities usually allow more than adequate space in front of each storage location to allow for typical ingress and egress. Also provided are typical human amenities such as hallways, stairways, elevators, fire escapes, appropriate lighting, and possibly vending machines, bathrooms, office space for onsite personnel, security gates, cameras, alarm systems, and the like. Self park facilities also frequently promote accidental contact between cars due to driver error, and create opportunities for thieves, vandals and other undesirables. Accordingly, for each storage location at a given site, there is an associated amount of extra space necessary to accommodate user access and traffic, as well as an associated amount of additional resources for human amenities, security and the like.
The required level of overhead limits the number of vehicles that can be stored at a site and adds considerably to the cost of operating a parking facility. There is a need, therefore, for an automated storage system that overcomes the need for human-related overhead, that is efficient to construct and operate, and that does not require additional space or property necessary to accommodate sporadic human access.
Existing and established methods of maneuvering an AGV along an in-floor guidance wire use either a single antenna precisely centered on the front of the AGV, or a pair of antennas precisely centered on the front and rear of the AGV relative to the direction of travel. Conventional AGV guidance systems use only the antenna currently leading the AGV, or the “front” antenna based upon the AGV's direction of travel, to follow the in-floor guidance wire. The trailing or “rear” antenna on an AGV equipped with two antennas is inactive until the AGV reverses direction, at which point the rear antenna effectively becomes the “front” antenna and takes over the AGV system guidance responsibilities. The in-floor guidance wire is laid out in a loop connected to, and energized by, a frequency generator, which transmits an alternating current frequency through the guidance wire. Each guidance antenna for the AGV contains two inductor coils, which individually generate an output voltage based upon the coil's proximity to the magnetic field generated by the frequency carrying guidance wire. By balancing the relative strength of the signal output from each of the two inductor coils on the front antenna, and subtracting the strength of the output from one coil from the strength of the output from the other coil, and then adjusting the steering of the AGV to target the point where the “subtractive output” from both coils is equal to zero, the control system of the AGV dynamically adjusts the steering of the AGV to keep the center of the antenna, and therefore the center line of the AGV relative to the direction of travel, approximately centered over the in-floor guidance wire. Often these systems deploy guidance wires in a grid fashion, with one set of wires effectively forming an “X axis” and another forming a “Y axis” to allow AGVs to maneuver in two directions along the wire grid by turning to follow different axis wires and travelling in different directions along the different grid axes. At other times these conventional systems use a gradually curving wire with a fairly large turn radius to allow the AGV to follow a single wire to travel in an alternate direction.
There are three common problems/limitations of existing AGV guidance systems:                1) When the AGV travels to a position where either outer edge of an antenna inductor coil suddenly passes beyond the vertical plane of the in-floor guidance wire, the antenna produces a signal which is the same regardless of which side of the wire the antenna is on. Because the system is unable to positively identify which direction of travel is required to re-acquire the guidance wire, an “off wire” alarm condition usually occurs that stops the AGV and requires human intervention to return the AGV to the guidance wire and reactivate it. Alternately, the AGV can follow a limited search pattern to find the guidance wire, but with the risk of searching too far in the wrong direction and becoming further lost and/or risking a possible collision with objects outside the normal AGV travel lane.        2) The “centered only” travel path greatly limits the ability of AGV systems to efficiently process and transport asymmetrically proportioned items, and with the result that AGV systems are primarily implemented to handle items which have very limited, or at least very predictable, variations in size and shape.        3) The “subtractive output” analysis of the coil signal has some weakness and reliability issues which can cause guidance system problems if there are variations throughout the course of travel in the distance between the antennas and guidance wire or other items which impact the relative strength of the magnetic field generated by the guidance wire signal.        