Spotter-tractor
The Field Robotics Center (FRC) and the Vision and Autonomous Systems Center (VASC) performed an engineering design study for the US Postal Service (USPS) in 1992, in order to develop an automated system for handling mail trailers at the USPS's bulk mail centers (BMC). The goal was to devise an automated method, to improve on the current method which uses human-driven spotter-tractors to move hundreds of these mail trailers within a BMC. The study concluded that the best and most economically feasible approach was to automate the existing spotters and to develop a multi-vehicle operational scenario using novel mechanical approaches, planning/control software, and a new radio- based navigation system to move and dock trailers within the facility. The complete proposed system was split into two high-level areas: the autonomous cargo transporter (ACT) (automated spotter perception and mechanism); and operations (site modifications, human interface, central planner and safety). The ACT mechanism is a modified version of the existing spotter tractor design. Actuators to control steering, braking, propulsion, and air systems would be integrated into the overall design. The critical elements of the mechanism are a low-level controller, on-board computing and telemetry, and air line mating equipment. The controller, computing, and telemetry technologies are mature, while the air line mating equipment would need to be designed and developed. Existing automatic connection designs could be adapted to suit this purpose, and a commercial vendor would iterate the design to reach production quality. In addition to a new spotter, some modifications must be made to the site and operations. The check-in/out station will be expanded to acquire the additional information the ACT system needs. Trailer length and separation distance between the rear spotter tractor wheels and the center of the trailer wheels must be known for vehicle control, path planning, and execution monitoring. A structure would be added to or near the existing check point to house sensors capable of automatically determining this information. This structure would also serve to protect the human operator, who installs the air adaptors on the incoming trailers and removes them from the outbound trailers. The USPS BMCs are well-structured environments for autonomous spotter operations. Critical locations, such as loading docks, check-in/out station, maintenance garage, and fuel pumps are known in advance with a high degree of accuracy. The use of an accurate site positioning system reduces the complexity of automating spotter operations, such that it is technically and economically viable to develop the ACT system with moderate improvements to existing technologies. The FRC has proposed follow-on phases II through IV, which range from demonstrating the automated driving/hitching/docking of an automated spotter/trailer system, to the coordinated operation of several commercially developed automated spotters operating in unison at a BMC under a central planner and controller. The next phase (II) is scheduled to begin in the summer of 1994, and will have FRC and VASC demonstrate automated driving, hitching and the automated air hookup on a retrofitted spotter, by the end of 1994.
