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A variety of order release mechanisms have been developed for workload control. In this paper the effectiveness of order release mechanisms in a job shop environment is assessed by studying the influence of single order release dimensions, instead of comparing different mechanisms as a whole. In particular, the paper aims at improving the basis for selecting the workload accounting over time and the workload control strategies, through the understanding of its impact on the overall system performance. The robustness of these order release strategies to environmental perturbations is also assessed through a plan of experiments based on the Taguchi method. Simulation results provide important insights for the implementation of order release mechanisms.
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. Two variants of POLCA have been proposed in the literature to improve POLCA performance: Load Based POLCA and Generic POLCA. In this paper, we combine these two variants into a single production control system and analyse its performance for different backlog-sequencing rules. The results of a simulation study carried out for a make-to-order flow shop, support the strategy of combining these two POLCA variants and show that capacity-slack backlog sequencing based on corrected aggregate load have the potential for improving performance.
A presente comunicação corresponde a uma das fases do trabalho "Estudo e Caracterização dos Postos de Trabalho de Inspecção da Indústria Cerâmica" desenvolvido no âmbito da Campanha Cerâmica do IDICT. O trabalho tem como objectivo a caracterização do ambiente físico dos postos de inspecção, relativamente ao ruído, iluminação e ambiente térmico no subsector da cerâmica estrutural da Beira Interior, identificando situações de potencial melhoria. Os níveis de ruído L(Aeq,T), os valores de iluminância e as temperatura de bolbo húmido (Tnw) e de globo (Tg), para o cálculo do índice WBGT, foram medidos e comparados com os valores recomendados pelas normas. Os valores obtidos encontram-se dentro dos limites estabelecidos, excepção feita à iluminância que se encontra ligeiramente abaixo dos valores recomendados.
A aplicação de um sistema de visão por computador é representada no presente artigo, com o objectivo de automatizar o posto de trabalho de inspecção de produtos cerâmicos, no subsector de pavimentos e revestimentos. O sistema de inspecção apresentado é composto por um sistema de iluminação para garantir luminosidade constante no produto cerâmico a inspeccionar e por um sistema de captura e processamento de imagens a cores. Os algoritmos desenvolvidos para a detecção de defeitos incluem algoritmos de binarização, baseados em análise estatística e morfologia matemática. São apresentados resultados bastante satisfatórios na identificação do defeito grânulo. O sistema realiza ainda o controlo dimensional do mosaico/azulejo, através dos descritores área, largura e comprimento, com uma precisão de décimas de milímetro. O sistema inspecciona de forma automática os defeitos descritos em produtos cerâmicos de padrão uniforme e de uma só cor, tendo sido obtidos resultados bastante satisfatórios para o número de produtos cerâmicos disponibilizados pelas empresas do subsector de pavimentos e revestimentos.
A production and materials flow control mechanism for quick response manufacturing (QRM) is proposed. This is
called generic paired-cell overlapping loops of cards with authorization (GPOLCA). It is an adaptation of the POLCA
mechanism developed as part of the QRM strategy. GPOLCA implements an input–output control order release strategy
based on an inventory of production authorization cards instead of materials. It is best suited for companies that
manufacture large variety of products with variable demand. A description of GPOLCA is made together with a
comparative study of its performance in relation with other mechanisms namely MRP and POLCA. The results show that
GPOLCA attains better performance.
“This is a post-peer-review, pre-copyedit version of an article published in Advances in Intelligent Systems and Computing. The final authenticated version is available online at: 10.1007/978-3-319-77712-2_66 "
“This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Industrial and Production Engineering on 30-05-2018, available online: http://www.tandfonline.com/10.1080/21681015.2018.1479895.”
“This is a post-peer-review, pre-copyedit version of an article published in Lecture Notes in Electrical Engineering. The final authenticated version is available online at: https://doi.org/10.1007/978-3-319-91334-6_58 ”.
Pretende-se com esta comunicação apresentar o trabalho desenvolvido no âmbito da campanha Têxtil do IDICT, onde se realizou um estudo dos postos de trabalho de inspecção de defeitos da Industria Têxtil. O trabalho centrou-se particularmente nos aspectos Ergonómicos dos postos de trabalho: “Metedeira de Fios”, “Revistadeira” e “Inspecção Final”. Cada um dos postos de trabalho foi caracterizado em função dos seguintes aspectos: características gerais; postura e trabalho muscular; percepção, vigilância e destreza; ambiente físico e organização do trabalho. O modelo de actuação usado consistiu na realização de uma série de questões, cuja resposta conduziu à elaboração de um pré-diagnóstico dos postos de trabalho de inspecção. Este pré-diagnóstico constitui, por sua vez, a base para a proposta de um conjunto de recomendações e sugestões ao nível da iluminação, ruído, aspectos ergonómicos do assento e medidas administrativas.
“This is a post-peer-review, pre-copyedit version of an article published in Advances in Intelligent Systems and Computing. The final authenticated version is available online at: https://doi.org/10.1007/978-3-319-56538-5_40"
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.
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.
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.
This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Industrial and Production Engineering on 13/02/2019, available online: https://www.tandfonline.com/doi/full/10.1080/21681015.2019.1576784
This is an Accepted Manuscript of an article published by Taylor & Francis in International Journal of Production Research on 16/01/2018, available online: http://www.tandfonline.com/10.1080/00207543.2018.1425018
Lot splitting is an important approach for shops that compete on short delivery times. Similarly, such shops can benefit from load-limiting order release mechanisms that balance workloads and regulate throughput times. Yet few studies have examined the combined effect of lot splitting and load-limiting order release. We use simulation to assess the combined effect of lot splitting and Paired-cell Overlapping Loops of Cards with Authorization (POLCA), an important load-limiting order release mechanism in the context of time-based competition. The experimental design includes different lot sizes, lot transfer policies, and POLCA quanta, i.e. the limit on the size of jobs represented by a single POLCA card. Lot splitting improves performance if lots can proceed independently as this ensures the quick replenishment of queues at downstream stations. However, we find that enforcing the synchronization of all lots that make up a job at every routing step leads to a deterioration in performance. This extends previous research, which appears to have overemphasized the positive effects of lot splitting. Meanwhile, although POLCA cards were originally used to represent lots, we demonstrate that using cards to represent a certain amount of workload can improve percentage tardy performance. This may also have resonance with other card-based solutions, including kanban.
The rise of Industry 4.0 has highlighted simulation optimisation as a decision-making tool for scheduling complex-manufacturing systems, specifically when resources are expensive and multiple jobs compete for the same resources. In this context, simulation optimisation provides an important mean to predict, evaluate and improve the short-term performance of the manufacturing system.
An important scheduling function is controlled job release; jobs (or orders) are not released immediately to the shop floor, as they arrive to the production system, but release is controlled to stabilize work-in-process, reduce manufacturing lead times and meet customer delivery requirements. While there exists a broad literature on job release, reported release procedures typically use simple rules and greedy heuristics to determine which job to select for release. While this is justified by its simplicity, the advent of Industry 4.0 and its advanced scheduling techniques question its adequateness.
In this study, an integer linear programming model is used to select jobs to be released to the shop floor. While there are some recent studies that use a similar procedure, these studies assume the release decision for a given set of jobs is optimized in discrete time intervals. In contrast, in this study, we analyse the impact of different triggering intervals. Experimental results for a pure flow shop support our contention that simulation optimisation as a decision-making tool for job release is likely to be too important to be overlooked
“This is a pre-print of an article published in Journal of Intelligent Manufacturing. The final authenticated version is available online at Springer http://dx.doi.org/10.1007/s10845-018-1402-2
Maintenance has assumed an increasing importance in the reorganization of the industrial sector. However, there are several companies where a maintenance strategic plan needs to be implemented. This work was developed in an industrial context, in a company of Clutches and Hydraulic Controls. The focus was the implementation of a strategic plan for maintenance. The methodology chosen was Total Productive Maintenance (TPM) and the cells chosen for implementation were CNC Lathes and CNC Machining Centers. The TPM uses some maintenance activities, whose come from preventive maintenance (PM), and focuses on eliminating efficiency losses. The main problems of the cell equipment were analyzed and eliminated. Through the analysis of maintenance manuals and internal know-how, autonomous maintenance (AM) procedures and preventive maintenance plans have been created to be executed following a given timeframe. At the end of the study, the results were clearly positive due to the corrective and preventive maintenance. There was a decrease in breakdowns due to failure by 23% for CNC lathes and by 38% for CNC machining centers, which resulted in an evident increase in machine availability and OEE (Overall Equipment Effectiveness) improved by 5%.
POLCA (Paired-cell Overlapping Loops of Cards with Authorization) is a decision support system for material flow control under Quick Response Manufacturing. It operates in the context of low-volume, high-mix, and cellular manufacturing. While there is an increasing literature on POLCA performance, current studies usually assume full availability of components (or parts) at assembly stations, neglecting parts manufacturing and feeding. Therefore, this study uses simulation to assess POLCA performance in a two-stage production system, where at the first stage parts are manufactured and at the second, they are assembled into end-products. The study demonstrates that using POLCA to control both production stages, manufacturing and assembly, significantly outperforms the use of POLCA at the assembly stage only, leading to important reductions of the total throughput time of orders and on the percentage of tardy orders. Statistical analysis of our results was conducted using ANOVA.
Manual operations in manufacturing companies are still a common practice. This often results in high costs, high cycle times and therefore in lower productivity, particularly for companies operating in western countries. This is why many manufacturing companies relocated their production facilities in low age countries. This study was developed at a leading Portuguese material construction manufacturing company. The objective was to improve the packaging and labeling processes, that were identified as main bottlenecks in the factory. Lean was used to streamline these processes before being automated. This allowed for annual savings of 12432 €, with human operators being reallocated to other departments where they are more useful. Furthermore, cycle times were reduced by 42,9%, non-value-added activities were minimized, and operations with potentially high ergonomic risks were eliminated. In addition, a reduction of 84,3% in lithographed packaging was achieved, with a cost reduction of around 36 000 €/year, which is expected to continue in the forthcoming years.
This project was carried out at a company in the electric mobility sector, which manufactures chargers for electric vehicles, specifically in the wiring section. The main objective of the developed work was to improve the production processes in order to enhance responsiveness to the growing demand. After analyzing the processes in the section, the objectives were outlined to enable the improvement of some practices in the production department, such as the ones related to the organization of the raw material supermarket, as well as the calculation of the wiring consumption by chargers, and the implementation of a production control system. After the improvement actions were implemented, it was possible to observe a 14,9% reduction in the changeover process of the cable cutting process; weekly wiring consumptions were estimated, and procedures were defined to generate orders of raw material and supply to the workstation, which led to the elimination of stock shortages. In addition, worker autonomy increased and production downtime was reduced.
Production environments are becoming more complex and dynamics. This is influenced by external factors related with products’ characteristics and costumers’ requirements and internal factors related with processing times variability, machine failures, setup times, between others. To face this increasing complexity and dynamics, it is crucial to have effective production control methods, considering Interoperability Enablers for Cyber-Physical Systems. However, production control methods most in used today, are focused on centralised decision-making and planning, and considered inadequate to deal with the increasing dynamics of these systems. Autonomous Production Control (APC) may be an adequate alternative to face this complexity, allowing flexible and rapid reaction to possible disturbances that may occur in the production system. However, as APC is the relatively new concept, there are no existing surveys. Therefore, we review and discuss the literature on APC methods to bring more attention to this promising topic of research, highlighting future research directions.
An important scheduling function of manufacturing systems is controlled order release. While there exists a broad literature on order release, reported release procedures typically use simple sequencing rules and greedy heuristics to determine which jobs to select for release. While this is appealing due to its simplicity, its adequateness has recently been questioned. In response, this study uses an integer linear programming model to select orders for release to the shop floor. Using simulation, we show that optimisation has the potential to improve performance compared to ‘classical’ release based on pool sequencing rules. However, in order to also outperform more powerful pool sequencing rules, load balancing and timing must be considered at release. Existing optimisation-based release methods emphasise load balancing in periods when jobs are on time. In line with recent advances in Workload Control theory, we show that a better percentage tardy performance can be achieved by only emphasising load balancing when many jobs are urgent. However, counterintuitively, emphasising urgency in underload periods leads to higher mean tardiness. Compared to previous literature we further highlight that continuous optimisation-based release outperforms periodic optimisation-based release. This has important implications on how optimised-based release should be designed.
Production control in make-to-order must address the companies’ need for short delivery times and on-time deliveries. Several production control systems may be used to meet these needs. This paper presents a simulation study to evaluate the delivery performance of the TKS, GKS and POLCA production control systems, in the context of a make-to-order flexible flow shop. Since TKS is used for make-to-stock manufacturing, an adaptation of it is made to use in make-to-order. Results of a simulation study show that the adapted TKS outperforms POLCA, but performs worse than GKS. The study is a contribution for the alignment of production control theory to the industrial practice.
