Yong F. Choong

Short-term production scheduling of an automated manufacturing facility

We describe extensions to the on-line hierarchical scheduling scheme for flexible manufacturing systems of Kimemia and Gershwin. Major improvements to all levels of the algorithm are reported, including algorithm simplification, substantial reductions of off-line and on-line computation time, and improvement of performance. Simulation results based on a detailed model of an IBM printed circuit card assembly facility are summarized.

Performance of Hierarchical Production Scheduling Policy

The performance of Kimemia and Gershwins hierarchical scheduling scheme for flexible manufacturing systems, as enhanced by Gershwin, Akella, and Choong, is described. This method calculates times at which to dispatch parts into a system in a way that limits the disruptive effects of such disturbances as machine failures. Simulation results based on a detailed model of an IBM printed circuit card assembly facility are presented. Comparisons are made with other policies and the hierarchical policy is shown to be superior.

A decomposition method for the approximate evaluation of capacitated transfer lines with unreliable machines and random processing times

Abstract This paper presents a decomposition method to evaluate the performance measures of a capacitated transfer line with unreliable machines and random processing times. The decomposition is based on approximating the k - 1-buffer system by k - 1 single-buffer systems. Numerical examples indicate that the approach is accurate as long as the probability that a machine is starved and blocked at the same time is small.

Real-time production scheduling of an automated cardline

In this paper, we describe a flow model of an automated-printed circuit card assembly line at the International Business Machines Corporation (IBM) plant at Tucson, Arizona. We use a simulation based on this model as a test bed to discuss the performance of a hierarchical scheduling policy described in [3]. We compare this with other policies for loading parts into a flexible manufacturing system. We demonstrate that the hierarchical strategy is effective in meeting production requirements (both total volume and balance among part types) while limiting average work-in-process (WIP). This is a consequence of the feedback nature of the policy. Hedging (i.e. building up buffer stock) compensates for machine failures, thus resulting in high production percentages. The work-in-process (WIP) is low, as the policy reduces internal queues by respecting the capacity constraints of the system at every instant.

Dynamic routing in reentrant flexible manufacturing systems

Abstract Consider a flexible manufacturing system (FMS), with several parallel production lines. Each line is statistically balanced. Due to process time and yield variations, some workstations may be temporarily starved of parts during the FMS operation, while others may have too many. The purpose of the dynamic routing algorithm described here is to achieve real-time load balancing in a stochastic processing environment and thus to increase the performance of the system in throughput, workload balance and reduced work-in-process queues. We formulate the problem and develop an optimal stationary policy (for two lines that have a material handling transport between them) based on the input buffer state of each station.

Short term production scheduling of an automated manufacturing facility

We describe extensions to the on-line hierarchical scheduling scheme for flexible manufacturing systems of Kimemia and Gershwin. Major improvements to all levels of the algorithm are reported, including algorithm simplification, substantial reductions of off-line and on-line computation time, and improvement of performance. Simulation results based on a detailed model of an IBM printed circuit card assembly facility are summarized.

A hierarchical scheduling policy applied to printed circuit board assembly

This paper discusses the performance of a new hierarchical production scheduling policy for flexible manufacturing systems. A detailed simulation of an automated printed circuit card assembly line is used as an experimental test bed. This simulation is a model of a line that is currently being installed at the International Business Machines Corporation (IBM) plant at Tucson, Arizona. The hierarchical strategy is effective in meeting production requirements (both total volume and balance among part types) while limiting average work-in-progress. This is a consequence of the nature of the policy whose key elements are a discipline that, at each level of a hierarchy, keeps material flow within capacity, even in the presence of uncertainty, by using feedback.

On dynamic routing in FMS

The purpose of dynamic routing in FMS is to achieve real-time load balancing in a stochastic processing environment and thus to increase the performance of the system, in throughput, workload balance and reduced in-process queues. We formulate and develop a stationary policy based on the input buffer state of each station.