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In this paper, motivated by considerations of server utilization and energy consumption in cloud computing, we investigate a homogeneous queueing system with a threshold-based workload control sche...

This paper examines the non-linear relationship between a firm’s inventory and sales performance. Specifically, whether there exists an optimal level of inventory that maximizes sales performance i...

This paper deals with improving the lead-time performance of a large crystal manufacturer that uses a state-of-the-art commercial Enterprise Resource Planning system. Since the company encountered ...

This paper calls for a paradigm shift in the production control literature away from assuming due date setting and order release are two independent decision levels. When order release is controlled, jobs do not enter the shop floor directly but are retained in a pre-shop pool and released to meet certain performance targets. This makes the setting of accurate planned release dates - the point at which jobs transition from the pool to the shop floor - a key consideration when setting due dates. We develop a new approach to estimating planned release dates to be embedded in the Workload Control (WLC) concept. Our approach is unique as it anticipates the release decision as part of the due date setting procedure. This makes a second independent release decision superfluous and avoids a major cause of tardiness - deviations between (i) the planned release date used when calculating the delivery time allowance and (ii) the actual, realised release date. Simulation is used to compare the performance of WLC using two decision levels with the new single-level approach where the release decision is anticipated when setting the due date. Performance improvements are shown to be robust to uncertainty in processing time estimates.

Constant Work-in-Process (ConWIP) is a card-based control system that was developed for simple flow shops – a lack of load-balancing capabilities hinders its application to more complex shops. In contrast, load balancing is an integral part of Workload Control, a production planning and control concept developed for high-variety environments. One means of load balancing evident in the Workload Control literature is through the use of a capacity slack-based backlog-sequencing rule. This study therefore investigates the potential of the backlog-sequencing decision to improve load balancing in the context of ConWIP, thereby making it suitable for more complex, high-variety environments. Using simulation, we demonstrate that: (i) the choice of backlog-sequencing rule significantly impacts throughput times and tardiness-related performance measures; and (ii) capacity slack-based sequencing rules achieve significant performance improvements over ‘classical’ ConWIP backlog-sequencing rules. These results significantly extend the applicability of ConWIP. Results from the Workload Control literature however do not directly translate across to ConWIP. The simplified release procedure of ConWIP makes backlog-sequencing based on planned release dates dysfunctional. This negatively impacts the performance of modified capacity slack-based sequencing rules that were recently shown to be the best choice for Workload Control. info:eu-repo/semantics/publishedVersion

To effectively react and meet the current ever growing demand for individualised motor vehicles, built to customer specific requirements, automotive industry has accelerated its transition towards mass-customisation. As a result, the number of new model introductions has drastically increased over the past three decades. To cope with this intensified customisation, the current automotive assembly platforms are designed to assemble a wide range of relatively different models, and are turned into mixed-model assembly lines (MMALs). This implies that the set of tasks to be performed on each workstation is no longer stable but varies highly with the model-mix. As a consequence, the manufacturing complexity increases at the workstations and throughout the whole assembly system. This paper proposes a method to monitor manufacturing complexity at each workstation while the MMAL is being balanced. An entropy-based quantitative measure of complexity, which incorporates the variability of each task duration, is dev...

In the workload control literature, the Load-Oriented Order Release (LOOR) approach has been neglected since its robustness was questioned at the end of the 1990s. This paper revisits LOOR and evaluates whether its performance can be improved in two ways. First, an intermediate pull release mechanism is added to avoid starvation between periodic release events. This mechanism was recently shown to be effective at improving the performance of a state-of-the-art release method known as LUMS COR. Second, an integer linear programming model is used to manage the trade-off between the timing and load balancing functions of order release. The two refinements are assessed using simulations of different shop configurations, which allow us to evaluate robustness. Results demonstrate that the refinements contribute to improving the performance of LOOR such that it can even outperform LUMS COR. Perhaps counter-intuitively, putting more emphasis on load balancing than on the urgency of individual orders is shown to lead to a lower percentage of tardy orders. Overall, the improvements mean that concerns about LOOR’s robustness are no longer valid – it now appears suitable for a wide range of shops found in practice.

Card-based systems are simple, effective means of controlling production. Yet most systems concentrate on controlling the shop floor. They neglect other planning tasks, like estimating short, feasible due dates during customer enquiry management. A card-based version of the workload control concept for job shops – COBACABANA (COntrol of BAlance by CArd-BAsed Navigation) – was proposed in the literature to overcome this shortcoming. COBACABANA uses cards for due date setting and order release, making it a potentially important solution for small shops with limited resources. But many such firms operate as flow shops rather than job shops. Research demonstrated that COBACABANA’s release mechanism must be adapted if applied to a pure flow shop, but its approach to due date setting has not been evaluated in such an environment. We show COBACABANA has the potential to improve pure flow shop performance, but its due date setting procedure should be adapted compared to job shops. In a flow shop, due date estimation can also be further simplified by considering the load awaiting release to the first (gateway) station only while maintaining most performance benefits. The results are important for all card-based systems that aim to stabilise work-in-process, including kanban and ConWIP (Constant Work-in-Process).

One of the key functions of Workload Control is order release. Jobs are not released immediately onto the shop floor – they are withheld and selectively released to create a mix of jobs that keeps work-in-process within limits and meet due dates. A recent implementation of Workload Control’s release method highlighted an important issue thus far overlooked by research: How to accommodate re-entrant flows, whereby a station is visited multiple times by the same job? We present the first study to compare the performance of Workload Control both with and without re-entrant flows. Simulation results from a job shop model highlight two important aspects: (i) re-entrant flows increase variability in the work arriving at a station, leading to a direct detrimental effect on performance; (ii) re-entrant flows affect the release decision-making process since the load contribution of all visits by a job to a station has to fit within the norm. Both aspects have implications for practice and our interpretation of previous research since: (i) parameters given for work arriving may significantly differ from those realised; (ii) increased workload contributions at release mean that prior simulations may have been unstable, leading to some jobs never being released.

This paper addresses the problem of lot splitting in the context of workload control (WLC). Past studies on WLC assumed that jobs released to the shop floor proceed through the different stages of processing without being split. However, in practice, large jobs are often split into smaller transfer sublots so that they can move more quickly and independently through the production process and allow operations overlapping relating to the same job. This paper assesses the performance of different lot splitting policies for job release and dispatching strategies under lot splitting. A new dispatching rule was designed to specifically take advantage of lot splitting and operations overlapping in the context of WLC. Discrete-event simulation is used to assess system performance in relation to the ability to provide shorter delivery times and on time deliveries. Results highlight the importance of releasing the sublots of the same job together and demonstrate that combining an effective lot splitting policy with an appropriate dispatching rule can enhance the performance of production systems.

The workload control literature highlights the importance of balancing the shop floor workload, but also acknowledges that this can conflict with processing the most urgent orders – hence, there is a trade-off. In practice, shops contain many complexities, e.g. simultaneous batching and sequence-dependent set-up times that may conflict with processing the most urgent orders and require other solutions than workload balancing to avoid capacity losses. This adds to the trade-off dilemma, which traditionally only considers timing and balancing. This paper develops a framework that determines whether to address a complexity through order release or dispatching. It comprises two dimensions: (i) the typical position of a complexity in the routing of an order and (ii) the criticality of the complexity. A case study is presented, which demonstrates the framework’s utility and illustrates the development of specific solutions designed to handle the complexities. Most complexities present in the case require handling at the order release stage. The challenges of handling multiple complexities at this decision level are evaluated. Finally, the implications for managers and future research are outlined.

The environmental impacts of industrial activity are an increasing concern amongst firms and their stakeholders. As a result, companies around the world have been exploring new tools to diminish the adverse impact of their activities on the environment. Eco-efficiency has played an essential role in this scenario, as companies are continuously seeking to produce more while utilizsing fewer resources and minimising adverse effects on the environment. The literature includes several initiatives to improve eco-efficiency and to reduce the environmental impact of manufacturing operations, but the use of production planning and control (PPC) activities to accomplish these goals has rarely been considered. Therefore, to contribute to the assessment of this issue, this paper proposes to integrate environmental concepts and actions as part of the PPC execution; therefore, they could also be applied to minimise environmental impacts, resulting in an increase in the eco-efficiency level of a company. The pr...

Recent research has highlighted the potential impact of pool sequencing on order release performance but it suffered from two shortcomings. First, arguably the best release solution for workload control in practice combines periodic with continuous release. Although the two types of releases serve different functions, recent work assumed the same sequencing rule should be used for both. Here, the use of different sequencing rules for periodic and continuous releases is evaluated. Using a job-shop simulation, we demonstrate that the rule applied during continuous releases has only a negligible impact on performance. Therefore, jobs can be pulled intermediately from the pool by workers using a more straightforward sequencing rule than the one applied for periodic release. Second, it was assumed that all jobs in the pool are sequenced and then a subset is selected for release. But for some load-oriented sequencing rules, the priority value used for sequencing jobs should be updated after each job selection f...

Order release is a key component of the Workload Control concept. Jobs do not enter the shop floor directly – they are retained in a pre-shop pool and released in time to meet due dates while keeping work-in-process within limits or norms. There are two important groups of release methods: continuous methods, for which the workload falling to a specified level can trigger a release at any moment in time; and, periodic release methods, for which releases take place at fixed intervals. Continuous release methods in general have been shown to outperform periodic release methods. Yet, there is incongruence in the results presented in the literature on the relative performance of the various continuous release methods. We use a job shop simulation model to examine the performance of continuous release methods from the literature and find that the contradictory results are explained by the different rules applied to sequence jobs in the pool – a factor neglected in previous work. Finally, a new breed of continuous release methods has recently emerged, but these have not been compared with prior approaches. Therefore, we also examine these methods and show that they significantly improve overall performance, although this is to the detriment of jobs with large processing times.

Purpose: Constant work-in-process (CONWIP) system is one of the most recognised pull systems. New CONWIP systems are constantly derived in research. This study reviews and classifies these new (modified) systems. Methodology: Relevant studies are systematically screened and reviewed. The general breakdown of workload control provides several forms of differentiation to build the scheme. Shared attributes that separate one system from others were used as elements in the classification scheme. The rationale and implication of using these elements are discussed. Findings: In total, 15 modified CONWIP systems are reviewed. Research limitations: Several production planning and control functions are not considered, and these include order entry, protective WIP, product mix, and process characteristics are not considered. Originality: This study contributes to the understanding of CONWIP systems and is the first classification scheme based on the fundamental characteristics of the original system. The exploitati...

Insufficient attention has been paid to behavioural influences on the implementation of the ‘Workload Control’ (WLC) concept – a Production Planning and Control (PPC) approach for small and medium sized Make-To-Order companies – and there is an implicit assumption that managers are rationalistic in their decision-making. This paper analyses the effects of both managerial decision-making behaviour and the size of a company’s order book, affecting the number of decisions that have to be made, on two case study implementations of a WLC system. The Recognition-Primed Decision (RPD) model from the Naturalistic Decision-Making literature is used to unpack the first case where implementation failed. This highlighted a misalignment between how the company’s owner-manager initially made operational decisions and how a rationalistic WLC system functions. But the company is studied over six years, allowing us to show how the owner-manager was forced to transition from the RPD model to a more rationalistic approach t...

Most literature on job shops assumes that an infinite storage space is available on the shop floor. But in practice, storage space is limited or finite. The job shop control problem with finite storage space has received little attention; it is a complex problem for which optimised scheduling may lead to unfeasible and poor quality solutions. The alternative to a scheduling solution is the use of controlled order release. This study uses simulation to assess the performance of four order release control rules. Results indicate that the best results are achieved by the workload control order release WLCOR rule. This rule produces results comparable to the optimum solution identified by analytical modelling in terms of the storage space required to achieve a certain production rate. The advantage of WLCOR is that it does this while simultaneously controlling lead times and the percentage of tardy jobs. Results have significant implications for practice, particularly where space is at a premium.

Workload control (WLC) has been developed as a production planning and control approach for job shop manufacturing. By balancing loads across work centres, WLC anticipates the fact that multiple work centres may become potential bottlenecks in the short term. This approach is generally tested in job shop models that assume equal utilisation levels for all work centres, which will create maximum bottleneck shiftiness. However, job shop practice clearly shows differences in utilisation levels, which means that some work centres can be seen as non-bottlenecks, having protective capacity. This study investigates the effect of different levels of protective capacity on the performance of state-of-the-art WLC release methods. More in detail, it shows how the level of protective capacity interacts with the influence of workload norms at work centres. Despite the fact that WLC has been developed for highly balanced utilisations, results indicate that WLC could also be effective in unbalanced situations. However, ...

This paper proposes a motion estimation algorithm with run-time adaptive workload control. It has optimized performance within limited hardware resources while guaranteeing hard realtime operation. It performs maximum searches within hard realtime constraints, since it determines search steps and workload adaptively. It reduces the hardware size to 1/4~1/400 of conventional algorithms, while its PSNR degradation is only 0.02~0.44 dB. It can be easily applied to most conventional fast algorithms, so it is useful to design realtime encoder chips.

Most studies on the performance of workload control (WLC) order release methods assume products have simple structures. But, in practice, products are often complex and consist of a number of sub-assemblies that flow through a level 1 job shop before converging on several final assembly operations in a level 2 assembly shop. Evaluating the performance of release methods in this context referred to as the two-level multi-stage job shop is an important step towards improving the alignment between WLC theory and practice. We use simulation to assess the performance of four of the best-performing WLC order release methods. Results suggest that WLC order release has the potential to limit work-in-process (WIP) while reducing the percentage of tardy jobs. It is also important to consider when and where release should be controlled. Results suggest that: (1) orders should be considered for release to level 2 when the first sub-assembly is complete, rather than only when all of the sub-assemblies that make up an assembly order are complete at level 1; and, (2) exercising control at level 2 (with or without control at level 1) leads to a greater reduction in the percentage of tardy jobs than control at level 1 only.

Simulation has demonstrated that the workload control (WLC) concept can improve performance in job shops, but positive empirical results are scarce. A key reason for this is that the concept has not been developed to handle a number of practical considerations, including sequence-dependent set-up times. This paper investigates the influence of sequence-dependent set-up times on the performance of a workload-controlled job shop. It introduces new set-up-oriented dispatching rules and assesses the performance impact of controlled order release. Simulation results demonstrate that combining an effective WLC order release rule with an appropriate dispatching rule improves performance over use of a dispatching rule in isolation when set-up times are sequence dependent. The findings improve our understanding of how this key implementation challenge can be overcome. Future research should investigate whether the results hold if set-up time parameters are dynamic and set-up times are not evenly distributed across resources.

Findings from recent implementations of Workload Control (WLC) have called for research to investigate how sequence-dependent set-up times can best be handled within the design of the concept. In response, this study assesses the performance of four of the best-performing release methods from the literature in a job shop with sequence-dependent set-up times by simulation. First, the four methods are compared without considering set-up requirements at release. Second, the methods are refined to consider set-up requirements before being compared against the original methods. A release method that combines continuous and periodic release emerges as the best-performing method. Findings further suggest that considering set-up requirements at release do not have a significant positive effect on performance and may even be counterproductive: conflicting goals between the selection rules employed at release and dispatching may lead to an increase in the percentage of tardy jobs. Future research should consider wh...

Workload control (WLC) is a well established production planning and control concept for make-to-order companies. The main insights into WLC are being gained from stationary simulation studies. Knowledge on its functioning in practice is limited, especially in a dynamic setting. The aim of this paper is to identify and classify the key issues when WLC is being used to control logistical performance in a dynamic setting. For this purpose an empirical research project in a company is carried out, in which both quantitative scanning data and qualitative workshop data are obtained and analysed over one year. Throughput diagrams and order progress diagrams support the analysis of the quantitative data obtained. Various types of dynamics could be discerned, but all implying similar requirements in terms of adaptations to the control concept. Whereas research in stationary settings addresses parameter choices, this study shows that it is issues on timing and magnitude of control adjustments that need to be addressed if WLC is to be used effectively in a dynamic setting. The empirical study shows that if the dynamics are not adequately taken into account, buffers may starve while throughput times become uncontrolled over time, despite the use of WLC.

In the mixed-production context of make-to-stock (MTS) and make-to-order (MTO), the manufacturing system becomes more complex for comprehensive balance of multiple objectives, including resource utilization, work in process (WIP), on-time delivery and throughput. To deal with this complexity, a dynamic production plannning and control (PPC) model with the hybrid of workload control (WLC) and theory of constraint (TOC) is presented. While the proposed three-tiered hierarchy construction model is relatively similar to WLC model, but the way in which the workloads are controled has changed dramatically. The order acceptance deals with issues of order review and delivery setting in order to balance the overall resource capacity and requirements that is necessary for on-time delivery. The order release deals with issues of release mechanisms and rules in order to control the flow of work to the production floor that is necessary for WIP and resource utilization.And the scheduling deals with issues of bottleneck identicification and task sequencing in order to protect the bottleneck capacity that is necessary for throughput.

Synchronous manufacturing aims at achieving the benefits of intermittent production lines in production situations that operate without lines. Benefits such as short and constant throughput times and predictable capacity loading can be acquired through an appropriate design of the synchronous manufacturing system and its control system. The order release mechanism is an essential part of this control system. It determines the sequence in which orders are released to the shop floor. As orders may differ in the amount and distribution of their capacity requirements over subsequent production stages, total capacity load may vary over time. If the available capacity per period is not flexible, capacity balancing becomes an issue in the order release decision. In practice, heuristics or rules of thumb are used to solve this problem, but their effectiveness is questioned. This paper examines the effectiveness of some new heuristics that are based on insights from assembly system design and work load control, and compare their performance with an optimal solution approach. The approaches are evaluated in a rolling schedule environment, and under different levels of capacity fluctuations and problem sizes. The results show that the performance of the heuristic solutions deteriorates if capacity fluctuations between the stages increase. If we measure both the amount and frequency of shortages over a long period of time in a rolling schedule environment, a quite simple rule that only takes the available capacity during the first stage into account outperforms more intelligent rules.

Synchronous manufacturing aims at achieving the benefits of intermittent production lines in production situations that operate without lines. Benefits such as short and constant throughput times and predictable capacity loading can be acquired through an appropriate design of the synchronous manufacturing system and its control system. The order release mechanism is an essential part of this control system. It determines the sequence in which orders are released to the shop floor. As orders may differ in the amount and distribution of their capacity requirements over subsequent production stages, total capacity load may vary overtime. If the available capacity per period is not flexible, capacity balancing becomes an issue in the order release decision. Human employees that work in such a system should be safeguarded from frequent unbalances in their working pattern. They are empowered and trained to contribute to several stages of production, but their motivation decreases rapidly if their working schedules do not give attention to stability issues. In practice, employees in the cells use heuristics to solve this problem, but the effectiveness of these heuristics is questioned. This article designs heuristics based on insights from assembly system design and workload control. These heuristics can be used by the employees within the synchronous manufacturing system. As an alternative, we design a solution approach that provides the employees with an optimal release sequence. The differences in the design approaches are discussed.

Workload control (WLC) is a production planning and control (PPC) concept designed for complex manufacturing environments, with particular relevance to make-to-order (MTO) companies and small and medium sized enterprises (SMEs). Despite receiving much attention in the literature, few successful implementations have been reported. Moreover, a lack of awareness regarding WLC in industry affects the support it receives from employees within a company and, if implemented, it is sometimes misused or neglected. This article presents a new interactive WLC training and implementation tool developed within a WLC decision support system (DSS) which uses simulation to generate the incoming order stream at the customer enquiry and job entry stages and to mirror the throughput time variability on the shop floor of real-life manufacturing environments. This provides an action-learning package for end-users in order to improve understanding of the concept and generate support prior to implementation. In particular, the tool provides training and decision-making experience in: parameter setting; due date setting; the acceptance/rejection of jobs; scheduling intervention; order release decisions; and capacity management. This article reports on the application of the tool as part of a strategy to implement WLC in a small subcontract MTO company. Among other results, use of the tool: improved understanding of WLC; highlighted gaps between current business processes and those supported by WLC; and led to rethinking the choice of end-user for the DSS.

In this note, we study the issue of adjusting the workload of an under-utilized server in a queueing system. Using an M/G/1 model with server vacations of two types, we can effectively control the workload level of the server. The server vacations are time periods that the server does not serve the queue. Type 1 vacations represent durations of supplementary non-queue jobs assigned to the server. Type 2 vacations represent the non-productive period for the server such as idle time. With a two threshold policy, we demonstrated that the server's workload can be effectively controlled. A simple procedure for determining the conditionally optimal policy is proposed. Numerical examples are presented to illustrate the use of the procedure.

International audience; Workload Control (WLC) is a leading Production Planning and Control (PPC) concept for manufacturing environments subjected to high levels of uncertainty, such as in the Make-To-Order (MTO) industry. Despite the importance of this concept, few case study applications of WLC have been presented in the literature. This paper takes advantage of a rare opportunity to explore two independent longitudinal empirical WLC projects recently undertaken in Portugal and the United Kingdom. Uniquely, the projects were conducted in parallel and both chose to incorporate the exact same influential WLC methodology in the development of a Decision Support System (DSS), thus providing an ideal platform for cross-case comparison. The paper focuses primarily on theoretical refinements which ultimately had to be made to the WLC methodology applied to the two cases. Reasons for the refinements can be broadly split into two groups: (1) refinements due to the time that has elapsed since the development of the original methodology; and (2) refinements due to company specific characteristics. The paper also reflects upon a number of implementation difficulties common to both case studies, providing insight into how these could be avoided in the future. Finally, eight future research challenges are presented.

This paper stems from an improvement project carried out at a men’s outwear manufacturer, aimed at reducing and stabilising the production lead time (LT). A method has been developed that builds on three well-established operations management theories: Little’s law, the workload control method and the logistic operating curves. In the action research study, by setting the system’s work in process to a level more consistent with its operating curves, the average system LT was reduced by 34% while its coefficient of variation was reduced to one-third. On the grounds of these encouraging results, and given the good fit between empirical results and theoretical expectations, the method is standardised and proposed for general use in the analysis and improvement of manufacturing systems.

This paper deals with Workload Control (WLC), one of the best techniques to control Work In Process (WIP) and to stabilize Lead Time (LT) in job-shop systems. Our focus is on the job release strategy and, specifically, on the selection and dimensioning of suitable norms; a challenging problem, which is often the cause of the little industrial use of WLC. Specifically, our aim is to assess whether or not the use of easy to implement norms, appealing also from an operating point of view, may be enough to boost performance of a productive system. To this aim, a thorough discrete events simulation was made, considering a realistic job-shop environment in different operating conditions. Job release was subjected by WLC, regulated by two consolidated norms (i.e., Shop-Load and Bottleneck-Load) and by a novel one, which leverages on the grouping of jobs into families. Obtained outcomes are highly satisfactory, since good performances, in terms of WIP minimization and Due Dates compliance can be obtained, especially in highly constrained productive environments.

The paper focuses on refining a Workload Control (WLC) concept to improve the applicability of the approach to the shop characteristics found in practice. This is a two-stage process leading to significant conceptual refinements to a key WLC methodology. The first stage focuses on the development of a Decision Support System (DSS) based on a WLC concept designed for Make-To-Order (MTO) companies. Refinements made include changes to the backwards scheduling procedure and the way in which jobs are released onto the shop floor. The second stage focuses on the process of implementation. Using a case study of a MTO company, the paper describes the strategy taken to overcome a number of prerequisites to the successful implementation of a Production Planning and Control (PPC) concept. Issues addressed include grouping machines and determining capacities. This case study adds to the available literature by looking specifically at implementing WLC from the customer enquiry stage, while the case study experience also provides further refinements to the WLC concept.

The workload control concept is known as a robust shop floor control concept. It is especially suited for the dynamic environment of small- and medium-sized enterprises (SMEs) within the make-to-order sector. Before orders are released to the shop floor, they are collected in an ‘order pool’. To make the release decision, information regarding the actual situation on the shop floor is required. Within SMEs, this information is often incomplete, incorrect or delayed. However, the workload control approaches discussed in the literature assume precise feedback information. The paper discusses the opportunities for information feedback from the shop floor for centralized order release within SMEs and analyses the information requirements of workload control approaches. These approaches are adapted based on more realistic assumptions regarding information supply within SMEs. The different approaches are compared and assessed by a simulation study. Results show that additional investments in more accurate information supply lead to decreasing marginal improvements in overall shop performance. Additionally, they indicate that the choice of the right workload control approach might have important effects on performance.

Studies on controlling the bicycle ergometer workload for middle-aged and elderly people by monitoring their heart rate and surface EMG during exercise have been conducted in the past. In this paper, it is shown that 18 middle-aged and aged subjects studied can be classified into four types in terms of time changes of the indices associated with muscular fatigue, as estimated by tests involving progressively increasing workload. In addition, customization of a workload-control method for middle-aged and aged people who show large individual differences in physical work capacities is discussed on the basis of tests of 8 subjects selected from the above types, conducted five times over 9 months. Specifically, scatter graphs of indices associated with muscular fatigue and heart rates measured during progressively increasing workload tests were divided into three intervals and a membership function was designed for fuzzy workload control for each of these intervals. In addition, fuzzy rules considering subjective indices and anaerobic work thresholds are studied while increasing the workload temporarily. The results show that a workload control method that guarantees safety and a feeling of accomplishment can be developed for exercise in the vicinity of the threshold of anaerobic metabolism. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(9): 56–64, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20116

This paper deals with improving the lead-time performance of a small packaging manufacturer in the Netherlands that had already implemented several facets of Theory of Constraints (TOC) in 1997. Since then, delivery reliability and profits have increased and lead-times reduced substantially. In an attempt to achieve further lead-time improvements in 2001, the firm recently encountered some limitations of its partial TOC implementation. In this paper we focus on the modi. cations of its order acceptance and buffer management system that were necessary in order to obtain the desired lead-time reduction. We describe how Workload Control principles were introduced to improve the buffering approach and planning procedures the firm had been using since 1997. It shows that Workload Control provides effective tools that can be used in combination with the Drum-Buffer-Rope mechanism in order to balance the flow of work to the production floor.

The goal of this paper is to analyze and compare the performances of two Hybrid Production Planning and Control (HPPCs) systems, namely CONWIP and Workload Control. Although several implementations of HPPCs reported excellent results, in fact, many authors have discharged the concept, arguing that these systems can only reduce manufacturing lead times and control WIP to the detriment of production rate, punctuality or service level. The paper starts from a brief review of the literature on HPPCs. Afterwards, the paper uses a common simulation model from the literature to compare two simple and easy-to-implement configurations of CONWIP and Workload Control against the baseline of a classic push system. The results of the simulations lead to important conclusions and suggest interesting improvements of simulation models and future directions of research for better understanding HPPCs.

The present paper is aimed at investigating, through simulation, the behaviour of the POLCA method when a Make-to-Order (MTO) production system is highly unbalanced, in terms of both routings and times. In particular, the study is addressed to verify (i) the effective capability of the POLCA method to improve the uncontrolled system and (ii) the impact of how orders are processed at each workstation, to show that POLCA performance can be further improved in such circumstances by adopting an appropriate selection rule. Germs and Riezebos (2010) proved that POLCA is very effective in reducing the Total Throughput Time (TTT) with respect to the corresponding unconstrained production systems. Owing to this, it appears evident that POLCA represents a valuable and effective Make-to-Order (MTO) production control method. However, they only considered balanced systems, hence some observations must be carefully addressed. In fact, often, in real world applications, the systems to be controlled are designed to process units with very different routings, each with significantly different probability to occur.

Workload control (WLC) systems can be seen as a natural extension of input-output control systems which allow both the control of jobs into the shop and the control of capacity which affects the flow of finished goods out of the shop. In previous research, it has been shown that WLC can help to reduce manufacturing lead times, even if the total workload processed by the shop in a given time period is maintained at a constant rate. However, the relative contributions of the input control mechanisms versus the output control mechanisms have not been clearly determined. This paper seeks to explore this which affects the flow of finished goods out of the shop. In previous research, it has been shown that WLC can help to reduce manufacturing lead times, even if the total workload processed by the shop in a given time period is maintained at a constant rate. However, the relative contributions of the input control mechanisms versus the output control mechanisms have not been clearly determined. This paper seeks...

This study compares input control based on aggregate shop loads with that based on bottleneck resource loads. Two appropriate release mechanisms are developed and compared in flow and job shops tha...

The state-of-the-art in published research on workload control as applied to the semiconductor industry is described. The focus is on examining the concepts behind workload control heuristics and evaluating their effectiveness, overhead requirements, and implementability. Individual sections provide an overview of the distinctive elements in a semiconductor manufacturing environment, general dispatching and order release methods, workload control strategies developed for semiconductor manufacturing, and future directions.

The diversity of requirements and the frequency of change in the market can only be competed with dynamicity and responsiveness in both production and planning systems. In this sense, working principles of a novel workload control method, called continuous precise workload control are presented in this paper. The implementation of the method is based on a multi-agent based architecture. The presented approach generates dynamic non periodic release decisions exploiting real time shop floor information. The performance of the system and correlation of norm value against the assessment range are investigated through an experimented test case.

An agent based workload control method is developed.Distinguishing characteristics are highlighted.Release decisions are taken on a continuous time basis with precise load graphs.Successful regulation of workload is achieved. The variability in the market conditions is growing in terms of its frequency of change and range of diversity. In response to this new industrial panorama, research on production systems is aiming to achieve highly reconfigurable shop floors. Frequent changes in such systems require also frequent re-planning with updated information. In this regard the Continuous Precise Workload Control method, is a recent approach aiming at precise control of workload in shop floor with the use of direct load graphs. Supported by a multi-agent platform, it generates dynamic non-periodic release decisions exploiting real time shop floor information. The study in this paper is two folded; (1) the presented workload approach is defined in terms of eight dimensions of the workload control concept in order to highlight its distinctive characteristics and (2) the impact of idleness penalty factor is analyzed by an experiment design in order to investigate its effect on the job release decision. The results show that the idleness penalty factor decreases the idleness of the resources up to a point where the adverse effect is initiated.

In many job shop environments production orders arrive continuously at the production system over time. If an 'order review and release'(ORR) technique is applied, the arrival itself does not necessarily involve the release of a job to the shop floor; in fact, the ORR activities determine which jobs have to be selectively dispatched to theshop floor and when job releaseis to takeplace, so as to improve job shop management and performances. This paper introduces a review and a classification framework of the main research work carried out to date. We have considered eight main dimensions that describe the fundamental principles, characteristics and logic of existing order review and release techniques. The classification of selected models from the specialised literature by means of the proposed framework provides a better understanding for the practitioners and, on the other hand, aims to indicate to researchers the most promising research paths.

We review mechanisms which control the flow or material into and within a manufacturing line. These material flow control (MFC) mechanisms address the problem of when to release material into a manufacturing line and when workcentres should be authorized to produce. The MFC mechanisms reviewed include: Kanban, CONWIP, workload regulating, starvation avoidance, BORA, maximum load limit, MRP, the base stock system, workload control, and production authorization cards.

The paper describes the principles of load-oriented manufacturing control as a new solution for job shops and its successful implementation in a pump-manufacturing factory. The idea of load-oriented manufacturing control is to limit and balance work-in-process inventory on a level as low as possible in order to accomplish a high work-centre utilization as well as a rapid and in-time flow of orders. As the new system keeps actual lead times on a planned level in a self-regulating way, it allows reliable due-date scheduling. Furthermore it points out the bottlenecks and performs applicable mid-term and short-term capacity planning.