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Publications

On the backlog-sequencing decision for extending the applicability of ConWIP to high-variety contexts: an assessment by simulation

Publication . Thürer, Matthias; Fernandes, Nuno O.; Stevenson, Mark; Qu, Ting

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.

2017Journal article

Open access

Improving performance in POLCA controlled high variety shops: an assessment by simulation

Publication . Thürer, Matthias; Fernandes, Nuno O.; Silva, Sílvio do Carmo; Stevenson, Mark

POLCA (i.e. Paired-cell Overlapping Loops of Cards with Authorization) is a card-based production control approach developed to support the adoption of Quick Response Manufacturing. The approach has received significant research attention but has remained largely unchanged since its introduction in the late 1990s. The main improvements have occurred in the context of an electronic POLCA system, but such developments undermine the simplicity of the original card-based concept. We ask: is there any refinement possible to enhance the performance of POLCA without jeopardizing its simplicity? By analyzing POLCA, two possible refinements are identified: (i) the choice of rule to support both the card allocation and dispatching decisions; and (ii) the use of a starvation avoidance mechanism to overcome premature station idleness, as reported in the context of load limiting order release. Using simulation, we demonstrate that performance gains can be obtained by using different rules for card allocation and dispatching other than the earliest release date rule typically applied in POLCA for both decisions. Further, results demonstrate performance improvements for all combinations of card allocation and dispatching rules considered via the addition of a simple starvation avoidance mechanism. Both refinements significantly enhance POLCA performance, potentially furthering its application in practice.

2017Journal article

Open access

Improving workload control order release: incorporating a starvation avoidance trigger into continuous release

Publication . Fernandes, Nuno O.; Thürer, Matthias; Silva, Cristóvão; Silva, Sílvio do Carmo

Order release is a key component of Workload Control - a production planning and control system that aims at balancing workloads across workstations, while ensuring the timely release of jobs (or orders) to the shop floor in order to meet due dates. Several release methods have been proposed and evaluated in the WLC literature. A major criterion to distinguish between release methods is whether they take the release decision at periodic time intervals or continuously. This paper aims at improving WLC order release by incorporating a starvation avoidance trigger into continuous release. Using simulation, we demonstrate that significant performance improvements in terms of mean tardiness and standard deviation of lateness can be obtained. These results are expected to have important implications for industrial practice and for future research on WLC.

2016Journal article

Open access

Iterative optimization-based simulation: a decision support tool for job release

Publication . Fernandes, Nuno O.; Dehghanimohammadabadi, M.; Silva, Sílvio do Carmo

Job release is an essential scheduling function and a core part of every production planning and control system. Essentially, job release has to do with the timing and the jobs to release on to the shop floor, in such way that, a balanced and restricted workload is achieved. In this paper, an Iterative Optimization-based Simulation (IOS) decision support tool is proposed for job release. This is in line with Industry 4.0 paradigm, allowing the autonomous selection of jobs based on the current shop floor situation. This decision support tool is implemented using SIMIO as a simulation manager, MATLAB as an optimization manager and MySQL as a database manager.

2018Book part

Restricted access

Load-Based POLCA: an assessment of the load accounting approach

Publication . Fernandes, Nuno O.; Thürer, M.; Stevenson, M.; Silva, Sílvio do Carmo

POLCA (i.e. Paired-cell Overlapping Loops of Cards with Authorization) is a card-based decision support system for production control developed to support the adoption of Quick Response Manufacturing. In POLCA, the flow of jobs through the production system is controlled through a combination of release authorisations and production control cards - POLCA cards. In this paper, we discuss a load-based version of the POLCA system (LB-POLCA), which draws on recent insights from the Workload Control literature. In this context, a question arises: what is the load (e.g. in hours) that a POLCA card should represent? Using simulation, we demonstrate that insights from the Workload Control literature cannot be straight transferred to the POLCA system. Results further demonstrate that significant performance improvements for all card acquisition rules considered in this study can be realized when the POLCA card represents the operation time the job imposes to the second station of the pair.

2017Book part

Restricted access