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 prod uctivity of the handling system. Existing dispatching rules: (1) do no t assign a move request until a device deposits a load and becomes emp ty; (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 re quest; and (4) may lead to sizable empty travel (also known in industr y as ''dead-heading''), which reduces system efficiency. This paper pr esents two new dispatching rules, modified shortest travel time first (MOD STTF) and bidding-based dynamic dispatching ((BD2)-D-2), which ad dress the above shortcomings and take advantage of information that sh ould be readily available in centrally controlled systems. The latter rule also uses a new concept for device dispatching in that all the de vices (empty or otherwise) are allowed to ''bid'' on incoming move req uests. Simulation results indicate that, compared to existing rules, b oth MOD STTF and (BD2)-D-2 improve system performance considerably.