A constraint-posting framework for scheduling under complex constraints

Scheduling in many practical industrial domains is complicated by the need to account for diverse and idiosyncratic constraints. Research in temporal reasoning and constraint satisfaction has produced problem solving models that operate with respect to general representational assumptions. These frameworks offer possibilities for developing scheduling technologies that naturally extend to accommodate the peculiarities of various application domains. One critical issue is whether such generality can be obtained without sacrificing scheduling performance. We investigate this issue through application of a previously developed constraint satisfaction problem solving (CSP) model for deadline scheduling to a complicated, multiproduct hoist scheduling problem encountered in printed circuit board (PCB) manufacturing. The goal is to maximize throughput of an automated PCB electroplating facility while ensuring feasibility with respect to process, capacity and material movement constraints. Building from a heuristic procedure generically referred to as PCP (precedence constraint posting), which relies on a temporal constraint graph representation of the problem, we straightforwardly define an extended solution procedure for minimizing makespan. In a series of comparative experiments, our procedure is found to significantly outperform previously published procedures for solving this hoist problem across a broad range of input assumptions