MINIMIZING VARIATION OF PRODUCTION-RATES IN JUST-IN-TIME SYSTEMS - A SURVEY

In the past several years, there has been growing interest in scheduli ng problems where jobs are penalized both for being early and for bein g tardy. This notable deviation from previous work, in which finishing early is generally regarded as being at least as desirable as finishi ng on time, is perceived to be the one that well captures the scheduli ng dimension of JIT production systems. A number of excellent surveys on these problems has appeared over the last four years. There is, how ever, another important scheduling objective in JIT production systems which is to minimize variation of rates at which processes supply the ir outputs. These scheduling problems are, for example, of primary con cern in the Toyota JIT system. Thus far, most research efforts in this area have been focused on minimizing variation of the rate at which d ifferent products are being produced on the final, multi-model assembl y line which itself is a supplying process. We shall review the result s of this research, and relate them to the due date based scheduling p roblems. Extensions and open problems will also be reviewed. Schedules that minimize variation of the rate at which different products are b eing produced on the line do not necessarily minimize variation in the line demand for outputs of processes that supply it. Few heuristics f or the problem of minimizing the variation are available and hardly an ything is known on its complexity as wel as exact algorithms to tackle it. We shall review a mathematical programming model of the problem a nd open questions that result from it.