Paired-cell Overlapping Loops Of Cards With Authorization Research Articles

Simulation-based optimization of the polca ordering system

Given an increase in consumer demand for product quality, companies need to continually improve their means of production. The use of computational resources assists companies to choose an ordering system that best suits their reality. In this sense, the present study aims to analyze and compare the performance of the Paired-cell Overlapping Loops of Cards with Authorization (POLCA) system, according to pre-established parameters in a real automobile company case, which has a flow-shop production environment. In order to do this, the research has a hypothetical-deductive scientific explanation. Also, the quantitative approach, and the experimental research procedure were employed due to the use of simulation and optimization. The computer simulation was performed using ProModel®. The initial model was optimized, and the results of the two elaborated scenarios were compared. It was verified that the optimized scenario showed improvement in the average total output of the system. The simulation of the optimized model presented an increase in production of approximately 95.29% when compared to the initial scenario. Nevertheless, trade-offs were verified. It is noticeable in the scenario analyzed that to increase the production of axles, the use of intermediate stocks must be increased. Finally, the present research contributes to the academic community since it proposed the study of an ordering system that has a limited number of studies, mainly in Brazil. It also contributes to the business community by encouraging the use of simulation in companies so that a better performance analysis of ordering systems can be performed prior to actual deployment.

Evaluating the effects of inventory stockouts in the performance of production control systems

Studies on the performance of production control systems typically assume that materials are continuously available at stations, thereby neglecting the potential impact of inventory stockouts. Contrarily, this study assesses the performance behavior of two of the most known production control systems, namely POLCA (Paired-cell Overlapping Loops of Cards with Authorization) and WLC (Workload Control) under inventory stockouts, in an assembly-to-order system. For a better understanding of such behavior, Load-Based POLCA (LB-POLCA), i.e. a variant of the POLCA system that takes into account the workload of jobs, is also considered in the study. The study is carried out using discrete event simulation. Results show that stockouts induce loss of system performance, as expected, but the relative performance of the production control systems tested does not change in relation to the situation of continuous availability of materials. Moreover, delivery performance is best using WLC followed first by LB-POLCA and after by POLCA.

Material Flow Control in High‐Variety Make‐to‐Order Shops: Combining COBACABANA and POLCA

Material flow control mechanisms determine: (i) whether an order should be released onto the shop floor; and (ii) whether a station should be authorized to produce. Well‐known approaches include Kanban, Drum‐Buffer‐Rope (DBR), Constant Work‐in‐Process (ConWIP), Paired‐cell Overlapping Loops of Cards with Authorization (POLCA), Workload Control (WLC), and Control of Balance by Card Based Navigation (COBACABANA). The literature typically treats these approaches as competing, meaning studies argue for the superiority of one over another. However, a closer look reveals that existing mechanisms either focus on order release (ConWIP, DBR, WLC, and COBACABANA) or on production authorization (Kanban and POLCA). This study therefore calls for a paradigm shift and argues that the different mechanisms may play complementary rather than competing roles. Using simulation, we assess the performance of COBACABANA and POLCA in a high‐variety make‐to‐order shop, a type of shop arguably in most need of material flow control given the importance of throughput times and delivery time adherence. Results demonstrate that COBACABANA outperforms POLCA, but the simultaneous adoption of both control mechanisms outperforms the use of either one in isolation. More specifically, adding POLCA production authorization to COBACABANA order release enables the superfluous direct load to be further reduced, resulting in shop floor throughput time reductions of between 15% and 26% while further reducing the percentage tardy and mean tardiness by up to 14%. Compared to no material flow control, the new combined mechanism realizes a reduction of almost 50% in the percentage tardy and more than 30% in mean tardiness.

POLCA Control in Two-Stage Production Systems

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.

POLCA: Centralised vs. Decentralised Job Release

POLCA (Paired-cell Overlapping Loops of Cards with Authorization) is a production control system specifically designed for low-volume, high-mix and custom-engineered products. It is a visual control system that manages the flow of jobs though the shop floor by making use of overlapping loops of cards between pairs of successive manufacturing cells. These overlapping loops of cards realize a decentralized decision-making structure for job release. This means that jobs do not await release in a centralized pre-shop pool. Rather jobs are immediately forwarded to a gateway manufacturing cells at their shop arrival, where they wait in release lists for available POLCA cards. However, the Workload Control literature has shown that using a centralized pre-shop pool provides important benefits. Therefore, this paper investigates the impact of centralized job release on POLCA performance. Using simulation, we demonstrate that centralized job release outperforms decentralised release if the right card acquisition rule for job release is used. This has important implications for both research and practice calling for more research on POLCA systems.

Lot splitting under load-limiting order release in high-variety shops: An assessment by simulation

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.

POLC-A: an assessment of POLCA’s authorization element

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. POLCA’s control mechanism is unique since it combines a card-based element (the paired cell overlapping loops of cards) with a higher-level Material Requirements Planning system for release authorization. POLCA has been applied in practice and evaluated in research, but the loops of cards element (POLC) has been adopted without the authorization element (A). In response, we use simulation to evaluate the effect of POLCA’s authorization element. We show that this element has a direct detrimental effect on percentage tardy and mean tardiness performance. While the literature argues that the authorization element should be an integral part of POLCA, our results suggest the opposite. This has important implications for research and practice. Instead of using POLCA with its authorization element, it is preferable to combine POLC—the card-based element—with a shop floor dispatching rule.

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

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.

CONWIP versus POLCA: A comparative analysis in a high-mix, low-volume (HMLV) manufacturing environment

Purpose: Few studies comparing manufacturing control systems as they relate to high-mix, low-volume applications have been reported. This paper compares two strategies, constant work in process (CONWIP) and Paired-cell Overlapping Loops of Cards with Authorization (POLCA), for controlling work in process (WIP) in such a manufacturing environment. Characteristics of each control method are explained in regards to lead time impact and thus, why one may be advantageous over the other.Design/methodology/approach: An industrial system in the Photonics industry is studied. Discrete event simulation is used as the primary tool to compare performance of CONWIP and POLCA controls for the same WIP level with respect to lead time. Model verification and validation are accomplished by comparing historic data to simulation generated data including utilizations. Both deterministic and Poisson distributed order arrivals are considered. Findings: For the system considered in this case study, including order arrival patterns, a POLCA control can outperform a CONWIP parameter in terms of average lead time for a given level of WIP. At higher levels of WIP, the performance of POLCA and CONWIP is equivalent. Practical Implications: The POLCA control helps limit WIP in specific áreas of the system where the CONWIP control only limits the overall WIP in the system. Thus, POLCA can generate acceptably low lead times at lower levels of WIP for conditions equivalent to the HMLV manufacturing systems studied.Originality/value: The study compliments and extends previous studies of CONWIP and POLCA performance to a HMLV manufacturing environment. It demonstrates the utility of discrete event simulation in that regard. It shows that proper inventory controls in bottleneck áreas of a system can reduce average lead time.

Sistema POLCA: revisão, classificação e análise da literatura

Este trabalho apresenta uma revisão bibliográfica (20 artigos) sobre o sistema de coordenação de ordem (SCO) denominado Paired-cell Overlapping Loops of Cards with Authorization (POLCA). A partir de tal revisão, propôs-se um sistema de classificação do sistema POLCA baseado em quatro categorias: sistema POLCA considerado (original/modificado); objetivo principal da pesquisa; fonte da publicação; e metodologia de pesquisa empregada. Uma vez classificada e estruturada, a revisão bibliográfica serviu de base para uma análise do tema. A literatura pesquisada mostrou a existência de algumas lacunas que merecem ser exploradas em pesquisas futuras, são elas: proposta de novas melhorias no sistema POLCA original, ou mesmo a hibridização de tal sistema com outro SCO; comparação, via simulação ou teoria de filas, do sistema POLCA com outros SCOs utilizados em ambientes de alta variedade de produtos; mostrar a aplicação do sistema POLCA na prática. Além disso, referente à prática, principalmente brasileira, tem-se que o sistema POLCA ainda é pouco conhecido em território nacional. Devido a esse fato, muitas oportunidades existem para os gerentes de Planejamento e Controle da Produção na prática, uma vez que internacionalmente tal sistema vem mostrando excelentes resultados em termos de redução de lead time.

Optimization of POLCA-controlled production systems with a simulation-driven genetic algorithm

The present work is meant to show the effective capability of optimizing an unbalanced Paired-Cell Overlapping Loops of Cards with Authorization (POLCA)-controlled production system by means of a heuristic algorithm. This objective is suggested by the fact that one of the most significant issues when using card-driven production control systems is represented by the optimized setting of the large number of cards within the control loops. This is particularly true in the case of unbalanced systems, where the number of cards may vary significantly among the different loops. Little law is usually adopted in literature to infer this number from historical data, but the obtained number is usually far from the optimum. Indeed, in real-world applications, the systems to be controlled are designed to process units with very different routings, each with different probability to occur. In all these situations, they result particularly difficult to set correctly. To this aim, in the present work a Genetic Algorithm is used. The objective is that of finding the correct number of cards and to reduce the overall Total Throughput Time and the average Work In Process. The proposed approach may provide a valid support tool to overcome these limitations, making the most of POLCA capabilities in many manufacturing configurations.

Load-Based POLCA: An Integrated Material Control System for Multiproduct, Multimachine Job Shops

This article proposes a supporting framework for the implementation of the material control system POLCA (paired-cell overlapping loops of cards with authorization). The POLCA system is particularly appropriate for environments that involve highly variable demand and large product variety, which force small batch (or even one-of-a-kind) production. We propose a load-based version of the POLCA control system (LB-POLCA), which determines the POLCA parameters (release authorizations, allowed workloads in the loops) according to an advanced resources planning (ARP) system that adequately captures the stochastic behavior of the production system and enables fine-tuning and high-level optimization of the manufacturing lot sizes. We also discuss the implementation of an electronic LB-POLCA system in a metal shop of Spicer Off-Highway Products Division, a subsidiary of the Dana Corporation.

A review of production planning and control: the applicability of key concepts to the make-to-order industry

The paper reviews ‘classic approaches’ to Production Planning and Control (PPC) such as Kanban, Manufacturing Resource Planning (MRP II) and Theory of Constrains (TOC), and elaborates upon the emergence of techniques such as Workload Control (WLC), Constant Work In Process (CONWIP), Paired cell Overlapping Loops of Cards with Authorization (POLCA) and web- or e-based Supply Chain Management (SCM) solutions. A critical assessment of the approaches from the point of view of various sectors of the Make-To-Order (MTO) Industry is presented. The paper considers factors such as the importance of the customer enquiry stage, company size, degree of customization and shop floor configuration and shows them to play a large role in the applicability of planning and control concepts. The paper heightens the awareness of researchers and practitioners to the PPC options, aids managerial system selection decision-making, and highlights the importance of a clear implementation strategy. WLC emerges as the most effective Job Shop solution; whilst for other configurations there are several alternatives depending on individual company characteristics and objectives. The paper outlines key areas for future research, including the need for empirical research into the use of Workload Control in small and medium sized MTO companies.