The Lot Scheduling Problem In The Hierarchy Of Decision Models

The Lot Scheduling Problem in the Hierarchy of Decision Models

The economic lot scheduling problem (ELSP) surfaces from competition among products for a scarce resource, usually machine time. When scheduling production of batches in this environment, two issues must be resolved: the size of batches and the start times for production of each batch. Standard approaches to the ELSP focus on scheduling multiple products on a single machine. This thesis addresses three important issues that put the scheduling problem in the context of its physical setting and range of parameters: idle time, the zero switch rule, and stochastic input to a bottleneck machine. In most scheduling heuristics, the reason for idle time is to balance cyclic production patterns. Idle time is also optimal in solutions to problems with high setup costs. We show that the condition for inducing idle time, given zero setup costs, is when one product has dominant holding costs and the remaining products have low machine utilization. A common policy in scheduling is to start production only after the inventory reaches zero. This policy is called the zero switch rule (ZSR) and is regarded as a good scheduling policy. We show that the condition when ZSR is not optimal is when the ZSR solution yields lumpy production patterns for a product with dominant holding costs.

Air University Abstracts of Research Reports

An Integrated Approach in Production Planning and Scheduling

Production Management is a large field concerned with all the aspects related to production, from the very bottom decisions at the machine level, to the top-level strategic decisicns. In this book, we are concerned with production planning and scheduling aspects. Traditional production planning methodologies are based on a now widely ac cepted hierarchical decom?osition into several planning decision levels. The higher in the hierarchy, the more aggregate are the models and the more important are the decisions. In this book, we only consider the last two decision levels in the hierarchy, namely, the mid-term (or tacticaQ planning level and the short-term (or operationaQ scheduling level. In the literature and in practice, the decisions are taken in sequence and in a top-down approach from the highest level in the hierarchy to the bottom level. The decisions taken at some level in the hierarchy are constrained by those already taken at upper levels and in turn, must translate into feasible objectives for the next lower levels in the hierarchy. It is a common sense remark to say that the whole hierarchical decision process is coherent if the interactions between different levels in the hierarchy are taken into account so that a decision taken at some level in the hierarchy translates into a feasible objective for the next decision level in the hierarchy. However, and surpris ingly enough, this crucial consistency issue is rarely investigated and few results are available in the literature.