INPUT CONTROL IN JOB SHOPS

Input control plays a critical role in regulating the release of jobs into a production system, and thereby controlling the inventory levels. We model the input control decision as a bicriteria problem that requires the maximization of the sum of job release times subject to minimum total job tardiness. Although the primary objective addresses job completion delays, the secondary objective considers earliness and waiting times. We propose a solution method that decomposes the original problem into a bicriteria problem for the critical jobs and the maximum release time problem for the noncritical jobs. These problems are solved in an iterative manner as the set of critical jobs is repetitively updated until no further improvement takes place. Computational results show the effectiveness of the proposed method as well as the substantial improvement that can be affected in job release times, without adversely affecting the tardiness values, over an approach that considers the single objective of minimizing total tardiness. This result is of interest to an operating manager who is responsible for controlling work-in-process and finished goods inventory related costs in addition to meeting due dates effectively.