4 research outputs found
Multihoist cyclic scheduling with fixed processing and transfer times
Cataloged from PDF version of article.In this paper, we study the no-wait multihoist cyclic
scheduling problem, in which the processing times in the tanks and
the transfer times between tanks are constant parameters, and develop
a polynomial optimal solution to minimize the production
cycle length.We first analyze the problem with a fixed cycle length
and identify a group of hoist assignment constraints based on the
positions of and the relationships among the part moves in the
cycle.We show that the feasibility of the hoist scheduling problem
with fixed cycle length is consistent with the feasibility of this group
of constraints which can be solved efficiently. We then identify all
of the special values of the cycle length at which the feasibility
property of the problem may change. Finally, the whole problem
is solved optimally by considering the fixed-cycle-length problems
at these special values
An efficient optimal solution to the two-hoist no-wait cyclic scheduling problem
Hoist scheduling is a typical problem in the operation of electroplating systems. The cyclic scheduling policy is widely used in these systems in industry. Research on hoist scheduling has focused on the cyclic problem to minimize the cycle length. Most previous studies consider the single-hoist case. In practice, however, more than one hoist is often used in an electroplating line. This paper addresses the two-hoist, no-wait cyclic scheduling problem, in which the tank-processing times are constants and, upon completion of processing in a tank, the parts have to be moved to the next tank immediately. Based on the analysis of the problem properties, a polynomial algorithm is developed to obtain an optimal schedule. This algorithm first identifies a set of thresholds, which are special values of the cycle length, so that the feasibility property may change only at these thresholds. Feasibility checking is then carried out on each individual threshold in ascending order. The first feasible threshold found will be the optimal cycle length, and the corresponding feasible schedule is an optimal hoist schedule. © 2005 INFORMS