Edward D. McDowell

Optimal product layout in an order picking warehouse

Abstract The purpose of this paper is to provide a basis for locating product in an order picking warehouse such that average order picking time will be minimized. A stochastic model is developed to ensure that optimal, rather than just “good,” results are obtained. It is shown that, for a class of order picking warehouse, simple, but general, assignment algorithms may be used to optimally allocate product to locations. The results are then used to explore the effects of average order size and the shape of the inventory curve on order picking efficiency.

Eye Movements in Curve Negotiation

Eye movements and fixations of five drivers were recorded and superimposed on a videotaped recording of the dynamic visual scene as they drove on a two-lane rural road. The results showed that (1) on curved roads, the fixation pattern follows the road geometry, whereas on straight roads, the search behavior is less active, and most of the fixations are close to the focus of expansion. The results indicate that in driving through curves drivers direct foveal fixations to lateral placement cues rather than rely on peripheral vision; (2) the process of curve scanning begins in the approach zone prior to the curve itself, suggesting that perceptually the curve negotiating process precedes the curve by several seconds; (3) the search patterns on right and left curves are not symmetrical; visual excursions to the right on right curves are greater than eye movements to the left on left curves; and (4) fixation duration statistics may be related to accident rates on curves.

Field dependence and driver visual search behavior.

This paper reports on two studies that examined the relationship between field dependence and on-the-road visual search behavior. In the first study, concerned with eye movements in curve negotiation, it was found that field-dependent subjects have a less effective visual search pattern. In the second study, young and aged drivers were compared on several information processing tasks and on their ability to maintain their eyes closed part of the time while driving. Of the various information processing tasks, only field dependence and visual search time correlated significantly with the mean time the drivers needed to maintain their eyes open while driving, Together the two studies indicate that field dependent subjects require more time to process the available visual information and are less effective in their visual search pattern.

An integer programming application to solve sequencer mix problems in printed circuit board production

The production of printed circuit board in the electronics industry requires that the taped components at the insertion machines input be in a predetermined order or sequence. The sequencing operation is performed on a microcomputer-controlled sequencing machine which represents a substantial proportion of both the initial capital and direct costs. The sequencing costs are affected by two sequential decisions: sequencer mix or the size and the number of sequencers required to meet the production requirements, and the processing schedule at each sequencer. An integer programming approach is presented for determining the optimum sequencer mix and is illustrated by means of an industrial case study example.

The Optional Allocation of Inspection Effort in a Class of Nonserial Production Systems

Abstract The allocation of quality control inspection effort (QCIE) within a class of nonserial production systems permitting inspection errors is considered. If the allocation of QCIE is unconstrained, and providing inspected and uninspected items from an operation are aggregated, then, for the cost structure considered, this problem is shown to be equivalent to a nonlinear zero-one integer programming problem. This implies the existence of an optimal inspection policy involving only integer multiples of 100% inspection at each potential location. However, if the allocation of QCIE is constrained or the segregation of inspected and uninspected items is permitted, then the existence of such an optimal policy is no longer assured.

Evaluation of scheduling rules for single- and dual-dock automated storage/retrieval system

Abstract The effect of the number of pick-up delivery stations (or docks or input/output points) is analyzed and compared for three different unit load automated storage and retrieval (AS/R) systems operating under dual command cycle. The AS/R system layouts differ in the number of docks per aisle, and the relationship between the storage and retrieval sources. A simulation model was used to evaluate the systems on three performance criteria—system throughput, mean waiting time and maximum waiting time. The efficiency of the AS/R system can be improved by the introduction of two docks per aisle with the input/output pallets for each dock being independent of each other, the input pallet storage based on closest open location policy, and output pallet withdrawal based on a nearest neighbour policy (or its variant, with a maximum waiting time limit).

Computerized container-ship load planning: a methodology and evaluation

Abstract A heuristic is developed to plan loads for containerized cargo ships. It is designed to serve a port which uses gantry cranes (transtainers) and trucks to handle containers. The model recognizes constraints on ship stability, placing containers in a bay with the proper length, limits on stack height in under-deck bays, limits on stack weight in on-deck bays, refrigerated containers, and the need for support under a container. Provisions are made for the operator to handle overstowage of cargo for different ports and placement of oversize cargo. The model uses minimization of transtainer movement time and minimization of rehandles in the yard as an objective. The heuristic uses strategies for container placement similar to those used in manual load planning. A test of two ships and four voyages at the Port of Portland produced feasible load plans for each voyage. Transtainer movement and rehandling time varied for the four voyages; but on the average, the heuristic reduced a composite material handling measure by 4.8%.

An investigation of the applicability of expert systems to job shop scheduling

Although the job shop scheduling (JSS) problem is of eminent practical importance and has received considerable attention by both industry and academia, because of its complexity, it still remains an enigma. Artificial Intelligence holds the potential for providing solutions to complex problems, such as the JSS problem. However, due to the magnitude of the JSS problem, search techniques are not computationally feasible. Expert Systems, though, have been successfully applied to problems of this type. The development of an expert system, however, implies the availability of an expert. Regrettably, such experts are not readily available in the JSS environment. The approach presented in this paper involves the use of computer simulation models of a job shop to train subjects so that they are capable of effective scheduling, and then extracting the knowledge of these “experts” to develop an expert system.

PREDICTING DRIVER SEEING DISTANCE IN NATURAL RAINFALL

Four field studies were conducted in natural rainfall to develop a model for predicting distances at which drivers are able to see other vehicles in the roadway at various time periods following stoppage of a windshield-wiper stroke. The seeing distance prediction was developed as a function of rain intensity, rain accumulation time, and ambient daylight illumination. Two situations were studied; in the first, drivers seated in a stationary vehicle detected moving vehicles, and in the second, moving drivers detected a stationary vehicle. Useful seeing distance models were developed from the field studies. Seeing distances predicted from the models developed from these earlier studies were compared with seeing distances obtained in a subsequent validation field test. Results indicated that average error in the prediction of seeing distances ranges from 9% to 23%.

A simulation-based production planning support system for printed circuit board fabrication

Abstract A network-based simulation model is described to analyze the circuit board insertion process using surface mount technology. The network simulation model is developed using simulation analysis SIMAN designed for an IBM PC/XT or a compatible system. Among the results of the model are workstation utilizations, size of work-in-process inventories at different locations in the process, throughput times and rates, and production costs. Sensitivity analyses are performed on some of the major factors that can effect the efficiency of the system. The model provides a methodology for evaluating alternative production strategies and offers management a tool to develop efficient production policies, thus minimizing capital and operating costs.