Load‐limited order release in job shop scheduling systems

Abstract

This report examines the practice of using work load limits to control the release of orders to a job shop. Load limits function in the following general way. Whenever the inventory of work at a work center exceeds some critical value (its “load limit”), further release of orders which are routed to that work center are blocked from entering the shop. After the inventory is “worked off,” release of work to the shop gateways is again permitted. Load‐limited order release is intuitively appealing because it appears to be a method for reducing system inventory and flow times. The practice of load limiting order release is becoming popularized by some of the recent production planning software products now on the market. A notable example is OPT. In this report, analytical results for an M/M/1 queueing model, along with existing simulation studies of multi‐machine job shops are interpreted to form a theory about the effects of using load limits.The major finding here is the proposition that system flow time, inventory, and order tardiness all deteriorate to the extent that load limits introduce idle time into the schedule. Based on the arguments presented here, a very cautious approach toward the use of input control schemes for anywhere but gateway work centers would be advised. The conclusions drawn here are to a great extent arrived at by interpreting the research results of others, so there is a clear need for further research which tests these assertions in a more direct and controlled way.

Deconstructing bottleneck shiftiness: the impact of bottleneck position on order release control in pure flow shops

“…This means that the further downstream the bottleneck is positioned, the more jobs should be allowed to be on their way to the bottleneck (and still at upstream stations). This means that DBR's limit needs to be continuously adjusted to obtain stable performance, avoiding both a loss of control, leading to congestion, and control that is too tight, resulting in premature station idleness (Kanet, 1988). Meanwhile, SA COR accounts for the interdependency between the limit and the bottleneck position by using the corrected aggregate load to automatically allow more work to be on its way to a station the further downstream a station is located.…”

On the integration of due date setting and order release control

“…The continuous trigger avoids premature station idleness (see, e.g. Kanet, 1988;Land & Gaalman, 1998). When the continuous workload trigger releases a job, its workload contribution to a station is calculated using the same corrected aggregate load approach as used for the periodic release time element of LUMS COR.…”

Integrating material coordination and capacity load smoothing in multi-product multi-phase production systems

“…This relationship between capacity load and throughput time has been studied by Bertrand 1981Bertrand 8 , 1983 b , Baker 1984, Kanet 1988, Bechte 1982, Karmarkar 1987, and Wein and Chevalier 1992 On the one hand, this research has resulted in procedures to generate workload dependent work order due dates which largely improve the due date performance as compared to the performance of their workload independent counterparts (i.e. Ellon andChowdhuny 1976, Bertrand 1983 8 , Baker and Bertrand 1981).…”