Dual Resource Constrained Research Articles

A multi-criteria adaptive control scheme based on neural networks and fuzzy inference for DRC manufacturing systems

Manufacturing systems are uncertain and dynamic systems, hence, they require real-time scheduling to adapt to changing manufacturing conditions. Current real-time scheduling approaches have been devised mainly for machine-only constrained systems, in which the shop capacity is constrained only by machine capacity, rather than for dual resource constrained (DRC) systems, in which the shop capacity is constrained by machine and worker capacity. In particular, there is no study on DRC system scheduling in which the ‘where’ and ‘when’ worker assignment rules, basic features of DRC systems, are altered in real-time (dynamically selected) to respond to new manufacturing conditions. Besides, multi-criteria DRC system scheduling has not yet been addressed extensively. Also, there has been little research on the interactions of dynamically selected job dispatching, worker assignment and job routing rules, which have a significant impact on DRC system performance. This paper proposes a multi-criteria real-time scheduling methodology for DRC systems to address these issues, and investigates these interactions. The methodology employs artificial neural networks as meta-models to reduce computational complexity and a fuzzy inference system to cope with multiple performance criteria. Various simulation experiments demonstrate that the methodology provides satisfactory results for real-time DRC systems scheduling.

Response surface methodology based simulation optimization of a CONWIP controlled dual resource constrained system

We propose an optimal worker flexibility policy for a CONWIP (constant work-in-process) controlled dual resource constrained (DRC) system. A critical issue in DRC systems is the dynamic assignment of workers to the workstations. The proposed worker flexibility policy is designed to evaluate the state of the system at periodic time intervals so that the dynamic assignment of workers to the workstations can be made in an efficient manner. By integrating the response surface methodology (RSM) with simulation, this study provides an approach for optimizing worker transfer decisions. The RSM-based simulation optimization approach adopted in this study provides an effective and robust procedure to determine the optimum level of this decision variable under the given operating conditions.

Performance comparison of virtual cellular manufacturing with functional and cellular layouts in DRC settings

This study investigates the performance of virtual cellular manufacturing (VCM) systems, comparing them with functional layouts (FL) and traditional, physical cellular layout (CL), in a dual-resource-constrained (DRC) system context. VCM systems employ logical cells, retaining the process layouts of job shops. Part family-based scheduling rules are applied to exploit the benefits of group technology while retaining the flexibility and functional synergies of the job shop. Past studies of VCM have been based entirely on single-resource-constrained (SRC) systems, i.e. as purely machine-limited systems, assuming that resources such as labour and tooling do not restrict the output. However, given the fact that labour forms a second major constraining resource, and many of the advantages associated with cellular manufacturing are derived from labour flexibility, it becomes necessary to extend the research to DRC systems. In this study, we assume several levels of labour flexibility in all three systems, in addition to other relevant factors such as lot size, set-up reduction, and labour assignment rules. It is shown that VCM can outperform efficiently operated FL and CL in certain parameter ranges, as preliminary research has shown so far. However, it is shown that CL tends to outperform both VCM and FL in the parameter ranges customarily advocated for CL, namely, low lot sizes, adequate levels of set-up reduction, cross training of workers, and worker mobility within cells.

On the who-rule in Dual Resource Constrained (DRC) manufacturing systems

The who-rule is a labour allocation rule used in labour and machine-limited dual resource constrained (DRC) systems. A who-rule selects one worker out of several workers to be transferred to a work centre. By means of a practical instance, the paper shows that the who-rule plays a role in the daily practice of worker assignment. Previous simulation studies, however, either have not mentioned the who-rule or have treated it as a fixed factor. The present study will explore the need of including the who-rule in simulation studies. It will describe in detail at what decision moments the who-rule needs to be applied in simulation. Further, it will explore the flow time effects of applying different who-rules in several DRC systems where labour flexibility is limited and workers differ with respect to task proficiencies, the number of skills they possess and the loads of work centres for which they are responsible. As with other labour allocation rules, the impact of the who-rule depends on the specific DRC shop modelled. The paper will show that the average labour utilization, and the types and extent of worker differences, determine the impact of the who-rule on shop performance.

Labour flexibility and assignment policies in a job shop having incommensurable objectives

This study evaluates operating policies for offering a near-perfect delivery performance for vital customers in dual resource-constrained (DRC) job shop environments. Prior studies have considered this problem in machine-limited settings, and shown that dispatching rules that help realise a near-perfect delivery performance for vital customers necessarily deteriorate delivery performance for other customers served by the shop. This study extends prior work, and considers additional tools that can be used by managers in DRC shops such as labour flexibility, and assignment rules that incorporate customer-based information to deploy workers to departments containing high-priority jobs. Results show that labour flexibility in conjunction with appropriate decision rules allows for enhanced delivery performance for both vital and normal priority customers. These results hold even under conditions where 80% of the shop's workload is compromised of high-priority orders.

Multi-level heterogeneous worker flexibility in a Dual Resource Constrained (DRC) job-shop

The majority of research on labour flexibility in a DRC job-shop has focused on the situation where all workers are equally trained. In practice, it is likely that workers would not be trained equally and would possess different skills. In this paper, the situation where workers receive different levels of training across the various departments as well as possessing different levels of proficiency at each task is studied. Research results suggest that, even at the same level of shop flexibility, the mixture of cross training can have a significant impact on shop performance. Indeed, results suggest that it is better to have a mix of workers with no flexibility and some workers with very high flexibility rather than all workers with equal flexibility.

Performance evaluation of cellular layouts: Extension to DRC system contexts

This study involves a comparison of the performance of functional layouts (FL) and cellular manufacturing (CM) systems in a dual-resource-constrained (DRC) system context. Past studies of FL and CM have been based mostly on single-resource-constrained (SRC) systems. Recent studies have included labour-related factors, but have assumed high labour flexibility levels, and shown the superiority of CM. In this study we assume more realistic levels of labour flexibility, and factors such as lot size, set-up reduction, labour assignment and transfer rule, and scheduling rules. The parameter range in which CM can outperform efficiently operated FL, in a DRC context, are indicated.

Examination of flexibility acquisition policies in dual resource constrained job shops with simultaneous worker learning and forgetting effects

This study investigates worker training related issues in dual resource constrained (DRC)job shop environments with the simultaneous presence of learning, forgetting (which causes relearning) and worker attrition effects. Learning and forgetting occurs as workers are trained in different departments on the shop floor. A recent survey of job shops based in the US indicates that firms are concerned about the relearning losses that accompany worker transfers, and are using a variety of strategies to reduce the effects of relearning. This study uses the learn-forget-learn (LFL) model to capture different learning and forgetting environments in order to understand whether up-front training can be used to reduce relearning and realize the benefits of worker flexibility. Results show that the existing forgetting rate has a significant impact on inventory and customer service performance. Extensive up-front training helps reduce relearning, however, it does not always help improve performance.

Examination of worker assignment and dispatching rules for managing vital customer priorities in dual resource constrained job shop environments

The focus in this study is on evaluating scheduling policies that may be used to offer a near-perfect delivery performance for vital customers in dual resource constrained (DRC) job shop environments. Prior studies in this area have modeled shops where all orders are considered to be of equal importance, and shown that any reasonable combination of worker assignment and dispatching rules that are sensitive to the shop cost factors modeled works well. However, a recent survey indicates that shops do in fact distinguish among orders on the basis of customer identity, and that certain customers have very rigid delivery guidelines which must be adhered to in order to maintain their ongoing business. The present study models such environments, and shows that the choice of scheduling policies is not inconsequential, especially if the shop aims at providing near-perfect delivery performance to a limited set of customers. In such instances, policies for deploying workers to different departments, as well as dispatching rules that use customer identity based information outperform their counterparts that are not sensitive to orders placed by vital customers. Scope and purpose In today's highly competitive marketplace, an increasing number of firms are being required to provide a high level of delivery performance by their customers. Certain types of vital customers, such as those operating under the JIT manufacturing philosophy, have very rigid delivery guidelines which must be adhered to on a consistent basis in order to retain their business in the long run. Prior studies that have considered this problem from a scheduling perspective have focused only on dispatching rules in machine constrained settings. However, in most real shops, dispatching rules are not the only means available in managing orders from vital customers. Instead, managers rely on flexible workers that can be moved to different departments as the shop load varies. The role of workers, and decision rules that govern worker assignment to different departments has not been considered in the context of managing vital customer priorities. The purpose of this study is to determine the relative importance of worker assignment and dispatching rules in offering a near-perfect delivery performance to vital customers served by the firm.

Modeling simultaneous worker learning and forgetting in dual resource constrained systems

This paper addresses issues related to modeling worker learning and forgetting effects in Dual Resource Constrained (DRC) systems. The learn-forget-learn (LFL) model of Carlson and Rowe (Carlson, J.C., Rowe, A.J., 1976. Industrial Engineering 8, 40–47) is used to critically evaluate several worker training related issues that are associated with the learning and forgetting phenomenon. A numerical analysis is performed on the LFL model within a DRC system to gain insights into the nature of relationships between the extent of worker flexibility, forgetting rates, attrition rates, and flexibility acquisition policies. Results suggest that in the presence of higher attrition and forgetting rates, a worker may not be able to achieve full efficiency in as little as two different departments. Thus acquiring even incremental worker flexibility under such conditions may be infeasible. We also show that managers can use different flexibility acquisition policies designed in this study to reduce relearning losses and consequently improve the system performance.

Information and scheduling in a dual resource constrained job shop

In today's job shop, computers make information readily available, but there is limited research about which information to use and how to use it controlling a dual resource constrained (DRC) job shop. We develop and test new order review/ release (ORR) job dispatching and labour assignment rules that use different types of information. We compare the performance of a naive ORR rule (i.e., releasing all jobs immediately upon receipt) and other rules in the literature which use little information to a new ORR rule, modified load conversion (MLC), which uses all the available information. Our tests demonstrate that MLC performs better than the other ORR rules we tested. But the new job dispatching and labour assignment rules developed to use different types of information do not significantly improve performance. A sensitivity analysis demonstrates that although the shop performance is sensitive to the cost structure for every policy tested, the new MLC ORR rule performs well over a wide range of cost struc...

Workload smoothing in a bottleneck job shop

Examines the planning and scheduling systems in an integrative framework for a dual resource constrained (DRC) job shop. Models a bottleneck shop environment which represents a common situation in practice. Research on workload smoothing mechanisms which integrate the planning and scheduling systems is sparse. Simulates 13 smoothing rules (utilizing aggregate workload and bottleneck information), three despatching rules and two order review/release rules. The results of this study indicate that workload smoothing by the planning system has a significant effect on the performance of the DRC job shop. Pulling work ahead in valley periods improved the tardy measures of performance, while pushing jobs back in peak periods usually deteriorated shop performance. Suggests that combining a planning system effectively with order review/release can improve mean tardiness, percentage tardy and mean flowtime measures of performance.

Managing worker flexibility and attrition in dual resource constrained job shops

Worker flexibility is an attractive option for enhancing manufacturing performance, since it provides several strategic advantages, and also allows the firm to buffer against uncertainty. In this paper, we investigate issues related to acquiring a flexible work-force in those dual resource constrained (DRC) job-shops that have high learning costs and the presence of worker attrition. Our results show that significant improvement in traditional shop related measures can be attained at even very high attrition rates by incrementally training each worker in one additional department. However, this improvement comes at the expense of productivity losses which shop managers may not be willing to accept. The nature of the tradeoffs that exist in acquiring this incremental worker flexibility are addressed. Two strategies for improving shop performance, based on incrementally training workers or reducing attrition rates, are also recommended for the DRC shop modelled in our study. Conditions under which either of...

Assessing the impact of reducing demand variance through improved planning on the performance of a dual resource constrained job shop

This paper examines the role that both the planning and shop floor control systems play in the operation and performance of a dual resource constrained (DRC) job shop. Using causal analysis, the results show an effective planning system, as it accounts for the largest gain in shop performance. Generating and releasing smoothed schedules (work loads) allows the use of simplified shop floor control procedures such as Order Review/Release (ORR), job dispatching and labour assignment rules without adversely affecting performance. This study uses the results to resolve the current paradox surrounding ORR systems and shows that the ORR rules' performance is strongly dependent on the planning system, and that ORR rules can be considered moderating variables. Further, the study develops a variance control framework that indicates the necessary managerial actions to improve shop performance. This paper demonstrates that the planning system, not the shop floor control system, is the major determinant of shop perfor...

Acquiring and operationalizing worker flexibility in dual resource constrained job shops with worker transfer delays and learning losses

Although several studies within the dual resource constrained (DRC) job shop literature have investigated issues related to worker flexibility, the costs associated with acquiring and operationalizing this flexibility have been addressed in a limited fashion. This study is aimed at understanding whether cross-training workers in DRC job shops in the presence of worker transfer delays, worker learning effects, and worker attrition improves shop performance. Two worker assignment control rules, and two rules to select the department for the transferring worker, are also tested to understand how workers should be assigned to alternate tasks in different departments. Results from our study indicate that cross-training workers in at least two different departments improves shop performance even when large transfer delays are present. Extensive cross-training is shown to increase the associated costs, especially for the centralized transfer rule. Consequently, the decentralized assignment control policy is recommended since it performs well even in the presence of large transfer delays for the cross-trained workers. Consistent with the prior literature, the rules to select the next department for the transferring worker are shown to have negligible impact on the shop performance. Worker utilization level is shown to be the key underlying variable which explains these performance trends and leads to the associated recommendations.

An evaluation of worker assignment policies in dual resource-constrained job shops with heterogeneous resources and worker transfer delays

Abstract The focus of this study is on investigating worker assignment policies in dual resource constrained (DRC) job shops which include features such as the presence of heterogeneous resources and worker transfer delays between different departments. Previous studies on DRC systems have not modelled a shop which includes these design features simultaneously, although both of them would be present in many actual DRC environments. Several worker assignment policies that can be expected to work well in such environments are proposed and tested. Results indicate that in most DRC shops that have heterogeneous resources and finite transfer delays, decentralized assignments which delay the transfer decisions improve system performance. Additionally, two different task selection rules are shown to be very robust in giving good performance across a wide range of DRC environments modelled in the study.

The Impact of Learning and Labor Attrition on Worker Flexibility in Dual Resource Constrained Job Shops

ABSTRACTThis study investigates the impact of worker learning, worker flexibility, and labor attrition on the system performance of a dual resource constrained (DRC) job‐shop. The effects of learning and labor attrition have not been previously addressed in DRC literature. Results from the study, consistent with previous literature, show that the greatest benefits are achieved when inter‐departmental worker flexibility is incrementally introduced into the system. In addition, the learning environment, which depends on the initial processing time of jobs and the learning rates of workers, is shown to impact the acquisition of flexibility. The study also shows that the impact of labor attrition on system performance under certain shop conditions may be significant.

A Review of the Dual Resource Constrained System Research

Abstract This paper reviews the recent dual resource constrained (DRC)system literature. The DRC system research has gained new significance through the emphasis being placed on cross-training by Just-In-Time (JIT) system advocates. Cross-training is the key to labor flexibility-one of the key issues in the DRC system research. This review covers over twenty-five articles about DRC systems and should be helpful in familiarizing potential DRC system researchers with the field. The DRC system research and results, categorized into design and operating decisions, are summarized and suggestions for future research are provided. A table which summarizes the characteristics of the DRC systems modeled, decision rules examined, statistical analysis methods employed, and the performance criteria used in each study is also provided. An appendix is used to highlight characteristics that are common to many of the models employed in the studies surveyed.

THE TIMING OF LABOR TRANSFERS IN DUAL RESOURCE‐CONSTRAINED SYSTEMS: “PUSH” VS. “PULL” RULES*

ABSTRACTAltough the dual resource‐constrained (DRC) system has been studied, the decision rule used to determine when workers are eligible for transfer largely has been ignored. Some earlier studies examined the impact of this rule [5] [12] [15] but did not include labor‐transfer times in their models. Gunther [6] incorporated labour‐transfer times into his model, but the model involved only one worker and two machines. No previous study has examined decision rules that initiate labor transfers based on labor needs (“pull” rules). Labor transfers always have been initiated based on lack of need (“push” rules).This study examines three “pull” variations of the “When” labor‐assignment decision rule. It compares their performances to the performances of two “push” rules and a comparable machine‐limited system. A nonparametric statistical test, Jonckheere's S statistic, is used to test for significance of the rankings of the rules: a robust parametric multiple‐comparison statistical test, Tukey's B statistic, is used to test the differences.One “pull” and one “push” decision rule provide similar performances and top the rankings consistently. Decision rules for determining when labor should be transferred from one work area to another are valuable aids for managers. This especially is true for the ever‐increasing number of managers operating in organizations that recognize the benefits of a cross‐trained work force. Recently there has been much interest in cross‐training workers, perhaps because one of the mechanisms used in just‐in‐time systems to handle unbalanced work loads is to have cross‐trained workers who can be shifted as demand dictates [8]. If management is to take full advantage of a cross‐trained work force, it need to know when to transfer workers.

JOB‐SHOP VS. HYBRID FLOW‐SHOP ROUTING IN A DUAL RESOURCE CONSTRAINED SYSTEM

ABSTRACTThis paper studies the impact of job routing pattern on the performance of dual resource constrained (DRC) systems. Three markedly different job routing patterns are simulated using a DRC system model that incorporates labor transfer times. The problem is viewed from two perspectives: one portion of the analysis focuses on the relative performances of five different dispatching rules as the routing pattern varies; the other examines the effect of the routing pattern on each rule's individual performance. One generalized conclusion of this study is that routing pattern has no significant impact on the relative effectiveness of various dispatching rules. Consequently, findings from pure job‐shop research studies may be applied to situations where a mixture of job‐shop and flow‐shop routings is present.