The ‘Orchard’ scheduler for manufacturing systems

This paper describes Orchard, which is a heuristic algorithm for scheduling the loading of jobs into a manufacturing system. While Orchard was specifically designed for use at a particular printed circuit board line, it is sufficiently generic to be used at other manufacturing systems as well. In general, such a manufacturing system performs several operations on each job with multiple machines performing each operation. The routing of each job may involve stochastic branching including rework loops, and there may be a need to assign human operators to operations. The Orchard heuristic can be adapted to two different objective functions: weighted mean flow time, and an objective specially formulated for the circuit board line. The present paper describes all aspects of Orchard except its operator assignment module (which is described in another paper) and concludes with results of tests of the algorithm as applied to the circuit board line.