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Automatic identification of constraints and improvement actions in production systems using multi-objective optimization and post-optimality analysis
University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre. Volvo Car Group. (Production and Automation Engineering)
University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre. (Simulation-Based Optimization)ORCID iD: 0000-0003-0111-1776
University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre. (Production and Automation Engineering)ORCID iD: 0000-0002-9643-6233
2016 (English)In: Journal of manufacturing systems, ISSN 0278-6125, E-ISSN 1878-6642, Vol. 39, p. 24-37Article in journal (Refereed) Published
Abstract [en]

Manufacturing companies are operating in a severely competitive global market, which renders an urgent need for them to explore new methods to enhance the performance of their production systems in order to retain their competitiveness. Regarding the performance of a production system, it is not sufficient simply to detect which operations to improve, but it is imperative to pinpoint the right actions in the right order to avoid sub-optimizations and wastes in time and expense. Therefore, a more accurate and efficient method for supporting system improvement decisions is greatly needed in manufacturing systems management. Based on research in combining simulation-based multi-objective optimization and post-optimality analysis methods for production systems design and analysis, a novel method for the automatic identification of bottlenecks and improvement actions, so-called Simulation-based Constraint Identification (SCI), is proposed in this paper. The essence of the SCI method is the application of simulation-based multi-objective optimization with the conflicting objectives to maximize the throughput and minimize the number of required improvement actions simultaneously. By using post-optimality analysis to process the generated optimization dataset, the exact improvement actions needed to attain a certain level of performance of the production line are automatically put into a rank order. In other words, when compared to other existing approaches in bottleneck detection, the key novelty of combining multi-objective optimization and post-optimality analysis is to make SCI capable of accurately identifying a rank order for the required levels of improvement for a large number of system parameters which impede the performance of the entire system, in a single optimization run. At the same time, since SCI is basically built a top a simulation-based optimization approach, it is capable of handling large-scale, real-world system models with complicated process characteristics. Apart from introducing such a method, this paper provides some detailed validation results from applying SCI both in hypothetical examples that can easily be replicated as well as a complex, real-world industrial improvement project. The promising results compared to other existing bottleneck detection methods have demonstrated that SCI can provide valuable higher-level information to support confident decision-making in production systems improvement.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 39, p. 24-37
Keywords [en]
Multi-objective optimization, Simulation, Production system, SCI
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Technology; Production and Automation Engineering
Identifiers
URN: urn:nbn:se:his:diva-12020DOI: 10.1016/j.jmsy.2016.02.001ISI: 000376694200003Scopus ID: 2-s2.0-84959481904OAI: oai:DiVA.org:his-12020DiVA, id: diva2:910022
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2018-05-31Bibliographically approved
In thesis
1. Automated Bottleneck Analysis of Production Systems: Increasing the applicability of simulation-based multi-objective optimization for bottleneck analysis within industry
Open this publication in new window or tab >>Automated Bottleneck Analysis of Production Systems: Increasing the applicability of simulation-based multi-objective optimization for bottleneck analysis within industry
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Manufacturing companies constantly need to explore new management strategies and new methods to increase the efficiency of their production systems and retain their competitiveness. It is of paramount importance to develop new bottleneck analysis methods that can identify the factors that impede the overall performance of their productionsystems so that the optimal improvement actions can be performed. Many of the bottleneck-related research methods developed in the last two decades are aimed mainly at detecting bottlenecks. Due to their sole reliance on historical data and lackof any predictive capability, they are less useful for evaluating the effect of bottleneck improvements.

There is an urgent need for an efficient and accurate method of pinpointing bottlenecks, identifying the correct improvement actions and the order in which these should be carried out, and evaluating their effects on the overall system performance. SCORE (simulation-based constraint removal) is a novel method that uses simulation based multi-objective optimization to analyze bottlenecks. By innovatively formulating bottleneck analysis as a multi-objective optimization problem and using simulation to evaluate the effects of various combinations of improvements, all attainable, maximum throughput levels of the production system can be sought through a single optimization run. Additionally, post-optimality frequency analysis of the Pareto-optimal solutions can generate a rank order of the attributes of the resources required to achieve the target throughput levels. However, in its original compilation, SCORE has a very high computational cost, especially when the simulation model is complex with a large number of decision variables. Some tedious manual setup of the simulation based optimization is also needed, which restricts its applicability within industry, despite its huge potential. Furthermore, the accuracy of SCORE in terms of convergence in optimization theory and correctness of identifying the optimal improvement actions has not been evaluated scientifically.

Building on previous SCORE research, the aim of this work is to develop an effective method of automated, accurate bottleneck identification and improvement analysis that can be applied in industry.

The contributions of this thesis work include:

(1) implementation of a versatile representation in terms of multiple-choice set variables and a corresponding constraint repair strategy into evolutionary multi-objective optimization algorithms;

(2) introduction of a novel technique that combines variable screening enabled initializationof population and variable-wise genetic operators to support a more efficient search process;

(3) development of an automated setup for SCORE to avoid the tedious manual creation of optimization variables and objectives;

(4) the use of ranking distance metrics to quantify and visualize the convergence and accuracy of the bottleneck ranking generated by SCORE.

All these contributions have been demonstrated and evaluated through extensive experiments on scalable benchmark simulation models as well as several large-scale simulation models for real-world improvement projects in the automotive industry.

The promising results have proved that, when augmented with the techniques proposed in this thesis, the SCORE method can offer real benefits to manufacturing companies by optimizing their production systems.

Abstract [sv]

Tillverkningsföretag behöver ständigt utforska nya ledningsstrategier och nya metoder för att påskynda effektiviteten i sina produktionssystem och behålla sin konkurrenskraft. Av yttersta vikt är att utveckla nya flaskhalsanalysmetoder som kan identifierade faktorer som hindrar produktiviteten i produktionssystemen så att optimala förbättringsåtgärderna kan utföras. Många av de flaskhalsrelaterade forskningsmetoder som utvecklats under de senaste två decennierna syftar främst till att upptäcka flaskhalsen. På grund av avsaknaden av förebyggande förmåga är de mindre användbara för att utvärdera effekten av flaskhalsförbättringar.

En effektiv och korrekt metod för identifiering av korrekta förbättringsåtgärder, ordningen de ska utföras i samt dess effekt på produktionssystemets produktivitet är nödvändig. SCORE (simulation-based constraint removal) är en ny metod som möjliggör flaskhalsanalys genom användning av simuleringsbaserad flermålsoptimering. Genom att innovativt formulera flaskhalsanalys till ett flermålsoptimeringsproblem ochanvända simulering för att utvärdera effekterna av olika kombinationer av förbättringar, kan alla uppnåeliga maximala produktivitetsnivåer av produktionssystemet sökas i en enda optimering. Dessutom kan en frekvensanalys på Pareto-optimala lösningar från en sådan optimering generera en rangordning av de systemparameterar som behöver förbättras för att uppnå den önskade produktivitetsnivån. Dessa fördelar med SCORE kan dock endast uppnås med en mycket hög beräkningskostnad, speciellt när simuleringsmodellen är komplex och/eller består av ett stort antal beslutsvariabler. Dessutom innebär formuleringen av det simuleringsbaserade flermålsoptimeringsproblemet mycket manuellt och felbenäget arbete som kan begränsa användbarheten inom industrin, detta trots den enorma potential som metoden erbjuder. Dessutom har noggrannheten i SCORE, när det gäller konvergens i optimeringsteori och korrekthet att identifiera optimala förbättringsåtgärder, inte utvärderats vetenskapligt.

Syftet med denna avhandling är därför att med avstamp i tidigare forskning kring SCORE utveckla en effektiv, automatiserad och korrekt metod för flaskhalsidentifiering och förbättringsanalys som kan tillämpas inom industrin.

Bidrag från detta avhandlingsarbete inkluderar:

(1) implementering av en mångsidig optimeringsvariabel (multiple-choice set variabel) och därtill en reparationsstrategi i evolutionära flermålsoptimeringsalgoritmer(EA);

(2) introducera en ny teknik som baserat på information från en sekventiell screening initialiserar första populationen i en EA samt möjliggör skapandet av variabelvisa genetiska operatorer, båda med syftet att stödja en effektivare sökprocess;

(3) en automatiserad formulering av flermålsoptimeringsproblemet i SCORE för att bespara användarna den stora mängd manuellt och felbenäget arbete med optimeringsvariabler och mål som krävs;

(4) presentera hur upprepad användning av rankningsavstånd (mätetal som visar hur lika/olika två rankningar är varandra) kan användas för att kvantifiera och visualisera konvergens och korrekthet av flaskhalsrankningen genererad av SCORE.

Alla dessa bidrag har demonstrerats och utvärderats genom omfattande experiment på skalbara, benchmark-simuleringsmodeller samt på flera stora simuleringsmodeller som använts i förbättringsprojekt inom fordonsindustrin.

De framgångsrika resultaten har visat att förbättringarna av SCORE-metoden presenterade i detta arbete gör det möjligt för tillverkningsföretag att förvärva verkliga fördelar genom att optimera sina produktionssystem optimalt.

Place, publisher, year, edition, pages
Skövde: University of Skövde, 2018. p. 218
Series
Dissertation Series ; 23(2018)
Keywords
bottleneck analysis, bottleneck identification, bottleneck improvement, multi-objective optimization, simulation
National Category
Production Engineering, Human Work Science and Ergonomics Information Systems
Research subject
Production and Automation Engineering
Identifiers
urn:nbn:se:his:diva-15214 (URN)978-91-984187-6-7 (ISBN)
Public defence
2018-06-08, Portalen, Insikten, Skövde, 13:15 (English)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2018-06-04 Created: 2018-05-31 Last updated: 2018-06-04Bibliographically approved

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Pehrsson, LeifNg, Amos H. C.Bernedixen, Jacob

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