Intelligent dispatching rules for trip-based material handling systems

The literature shows that the manner in which empty devices in a trip-based material handling system are dispatched affects the overall productivity of the handling system. Existing dispatching rules: (1) do not assign a move request until a device deposits a load and becomes empty; (2) with the exception of one rule do not allow an empty device to be reassigned to another move request; (3) do not consider the status and current assignment(s) of other devices before assigning a move request; and (4) may lead to sizable empty travel (also known in industry as ''dead-heading''), which reduces system efficiency. This paper presents two new dispatching rules, modified shortest travel time first (MOD STTF) and bidding-based dynamic dispatching ((BD2)-D-2), which address the above shortcomings and take advantage of information that should be readily available in centrally controlled systems. The latter rule also uses a new concept for device dispatching in that all the devices (empty or otherwise) are allowed to ''bid'' on incoming move requests. Simulation results indicate that, compared to existing rules, both MOD STTF and (BD2)-D-2 improve system performance considerably.