Charles T. Mosier

Weighted similarity measure heuristics for the group technology machine clustering problem

Heuristique de mesure de similitudes ponderees appliquee au probleme du groupement des machines en cellules dans la technologie de groupe

An experiment investigating the application of clustering procedures and similarity coefficients to the GT machine cell formation problem

This paper reports the development of a number of similarity-based coefficients designed for applying hierarchical cluster analysis to the group technology machine cell formation problem. The paper also discusses an experimental investigation applying these and other well-known similarity coefficients in conjunction with some well-known clustering algorithms. The mixture model experimental approach is used for the investigation. A number of problems were generated via simulation, randomly ‘mixed’ to hide the original cellular structure, and the clustering techniques applied. Extensions of prior research include the development of new similarity coefficients, their comparative evaluation, and the incorporation of the concept of part ‘weighting’ into the cluster analysis, and hence, cell formation

Analysis of group technology scheduling heuristics

The need for increased productivity in small batch manufacturing has recently brought focus to the topics and concepts of group technology. The results of a simulation analysis of the use of three job shop simulation scheduling rules which focus on inducing efficiency in the shop is presented. Two of these rules show significant gains in efficiency and, unexpectedly, they also show significant gains in effectiveness. These rules, in effect, induce the efficiency gains expected with group technology implementation.

A comprehensive analysis of group scheduling heuristics in a job shop cell

This paper describes a broad-based simulation study of the performance of two-stage group scheduling heuristics in a job shop cell. The objective of this study was to examine the direct and interactive effects of a variety of shop factors on the performance of the best, previously reported, group scheduling heuristics. A set of traditional single-stage scheduling heuristics were examined as well. Shop factors considered include: setup to runtime ratio, cell load level and variability of inter-arrival times. An assumption common to group scheduling research which provides for an equal division of the part family into subfamilies is also examined. This is accomplished through the creation of an alternative scenario where the majority of the parts are assigned to one subfamily, i.e. one subfamily dominates the part family population. The effects of set up to runtime ratio and cell load have been examined in previous group scheduling research, but not in conjunction with the inter-arrival time variability fac...

The Effects of Scheduling Rules and Routing Flexibility on the Performance of a Random Flexible Manufacturing System

The increased use of flexible manufacturing systems to efficiently provide customers with diversified products has created a significant set of operational challenges for managers. Many issues concerning procedures and policies for the day-to-day operation of these systems still are unresolved. Previous studies in this area have concentrated on various problems by isolating or simplifying the systems under study. The primary objective of this study is to extend previous research by examining the effects of scheduling rules and routing flexibility on the performance of a constrained, random flexible manufacturing system (FMS). Other experimental factors considered are shop load, shop configuration, and system breakdowns. Within the bounds of this experiment, the results indicate that, in the presence of total routing flexibility, the effects of shop load, system breakdowns, and scheduling rules are significantly dampened. In particular, when total routing flexibility exists, the choice of scheduling rules is not critical. We also show that the behavior of scheduling rules in a more constrained FMS environment (i.e., where system breakdowns occur and material handling capability is limited) is consistent with the findings of previous research conducted under less constrained environments. Finally, results indicate that the shop configuration factor has little or no impact on a systems flow-time performance.

Analysis of automated guided vehicle configurations in flexible manufacturing systems

Automated guided vehicle (AGV) systems complement the operation of flexible manufacturing systems (FMS) by providing integrated automated material handling that capitalizes on the systems flexibility. Previous research considering AGV systems for use in FMS installations has focused on complex control strategies to reduce the congestion problem often encountered in these systems. Recently, attention has been given to tandem system configurations that reduce congestion and simplify system control. The present study uses the simulation methodology to compare the performance of three AGV configurations under a variety of experimental conditions. The results indicate that system size, load/unload time, and machine failure rate factors have significant impacts on the operation of the systems considered. In general, with respect to due date performance, it is recommended to use the traditional configuration in small systems while using the tandem/loop configuration in larger systems. Furthermore, it is shown that the addition of the loop to the tandem configuration mitigates the sensitivity of the tandem configuration to the load/unload time factor as well as significantly improving its performance under high load/unload times. Thus, if tandem configuration is desired to reduce congestion and simplify system control, investments must be made to directly reduce the load/unload times or to construct a loop to avoid the load/unload time penalty.

Scheduling unbalanced cellular manufacturing systems with lot splitting

Recently, a large number of studies have addressed lot splitting as a means to reduce flow times as well as improve due date performance. Furthermore, a number of studies have examined scheduling policies in cellular manufacturing systems. These studies have been conducted under a variety of experimental factors, shop structures and operational assumptions. This study examines scheduling cellular manufacturing systems in the presence of lot splitting. In addition, we utilize various scheduling policies to test formally the underlying principles of the synchronous manufacturing philosophy. This is accomplished by utilizing exhaustive and non-exhaustive scheduling heuristics simultaneously at bottleneck and non-bottleneck workcentres. The results indicate that, under certain conditions, performing additional set-ups before the bottleneck can improve due date performance without an adverse effect on average flow time. Furthermore, we show that incurring additional set-ups after the bottleneck does not improve due date performance and may deteriorate flow time performance. These results conflict with some of the tenets of the synchronous manufacturing philosophy.

Toward a universal classification and coding system for assemblies

Abstract A variety of group technology-based classification and coding systems have been developed to handle piece parts. These systems typically characterize parts by geometry or processing requirements, or some combination of the two. However, while there are a few situation specific classification and coding systems that address assemblies, there is no universal paradigm for the design and implementation of such a system. Part of the reason for the lack of such a system is probably due to the inherent difficulty in finding a common basis within the diversity of assemblies from industry to industry. This diversity has necessitated a “reinventing of the wheel” from case to case. In this project, we develop a GT-based classification and coding system designed for assemblies, with specific application to a firm in the pulp and paper making machinery industry. At the same time we attempt to develop a general framework for the design of such specialized coding systems. The framework we propose focuses upon GT-based classification and coding systems from the traditional management information system perspective; that is, the needs of the users, current and future, drive the system logic. We perceive two primary uses of the classification and coding systems. One use is for the direct retrieval of engineering designs and manufacturing plans, thus inducing efficiency within the design and planning functions. Thus, the system must reflect the practices. conventions, and culture of the organization. In most cases, this use of the system is the most immediate, it has the most immediate financial benefits, and in our case, it was the rationale for justifying the expense of the project. The second use of such a coding system is to make information contained within the engineering and manufacturing data bases readily available for operational analysis and management decision making. Examples of this include: analysis investigating cellular restructuring, cost and profit analysis of engineering designs, and evolutionary development of engineering standards by judicious editing of the data bases. The first use implies a strong focus on the user, with considerable time spent determining any cultural phenomena which may impact system use. The second use implies a need for extreme clarity in the categorization inherent in the coding structure. For example, considerable time was spent investigating blueprints to determine the diameter frequency distribution of a particular type of forging. Upon consultation with the firm. we discovered that our categorization roughly matched the categorization implicit in the pattern numbers used by their foundry. After a number ot iterations we determined a categorization of the diameter of this particular forging which reflected the reality of the empirical distribution of diameters and adhered closely with the traditionally used pattern numbering scheme. The result was that this portion of the code structure reflected current firm practice while accurately providing frequency of occurrence data which may in the future be useful to management. The dimensions of assemblies considered in our assembly coding system included: Function . The basic functional requirement satisfied by the assembly. Shape . The intrinsic and observable shape of the assembly. Dimensions(s) . Critical dimensional ranges of the assembly. Facets(s) . The inclusion of specific detailed items which support the primary intrinsic function of the assembly. Feature(s) and detail(s) . The inclusion of items which complement the primary intrinsic function of the assembly. Material(s) . The material specification of the assembly. The final form of our coding and retrieval system was three tiered, including a GT-based coding system for piece parts, a custom GT-based coding system for assemblies, integrated with an existing top-down retrieval system for “large” final assemblies (whole paper-making production systems). The top-down retrieval system was based primarily on function, technology, and customer information. The coding and retrieval of final assemblies is used for all components tied to a unique assembly, while the coding and retrieval of piece parts and subassemblies is used for all components that are not specific to any particular final assembly. Such a system allows for rapid coding and retrieval of all piece parts, subassemblies, and assemblies manufactured by the firm.

The effect of combining simple priority heuristics in flow-dominant shops

SUMMARY Previous scheduling research indicates that no single priority heuristic is effective on all the relevant performance criteria. However, few heuristics have shown to be effective on particular performance criteria. This study examines this issue further by applying various scheduling heuristics at different states of three flow-dominant shops (i.e. entrance, intermediate, and exit workstations), under a variety of experimental conditions. The experimental factors used are shop load, due date tightness, and shop structure. Twenty-eight different combinations of heuristics were investigated. The results indicate that the application of particular priority heuristics at various stages of the production process has a positive impact on the shop performance. By selectively utilizing different scheduling heuristics, it is possible to gain the advantages of each heuristic and at the same time minimize their associated shortcomings. Furthermore, the relative rankings of the heuristic combinations are fair...

A comparison of deadlock avoidance policies in flexible manufacturing systems

Flexible manufacturing systems are prone to deadlock, which may result in costly delays. Deadlock can be defined as a state where there is some blockage in the system that leaves resource requests unanswered forever unless there is outside intervention. We compare the performance of several deadlock avoidance policies in conjunction with scheduling rules as well as gauging the impact of due date tightness on the system performance. Results indicate that the deadlock avoidance policy factor has much more impact on the system performance than the scheduling rule factor. We suggest several deadlock avoidance policies to be used by production managers depending on their desired system performance and shop environment. The results also indicate that production managers should generally utilize the scheduling rule that is easiest to implement in their system.