Olcay Polat

An iterative genetic algorithm for the assembly line worker assignment and balancing problem of type-II

In this study, we consider the assembly line worker assignment and balancing problem of type-II (ALWABP-2). ALWABP-2 arises when task times differ depending on operator skills and concerns with the assignment of tasks and operators to stations in order to minimize the cycle time. We developed an iterative genetic algorithm (IGA) to solve this problem. In the IGA, three search approaches are adopted in order to obtain search diversity and efficiency: modified bisection search, genetic algorithm and iterated local search. When designing the IGA, all the parameters such as construction heuristics, genetic operators and local search operators are adapted specifically to the ALWABP-2. The performance of the proposed IGA is compared with heuristic and metaheuristic approaches on benchmark problem instances. Experimental results show that the proposed IGA is very effective and robust for a large set of benchmark problems.

A hybrid genetic algorithm for sequence-dependent disassembly line balancing problem

For remanufacturing or recycling companies, a reverse supply chain is of prime importance since it facilitates in recovering parts and materials from end-of-life products. In reverse supply chains, selective separation of desired parts and materials from returned products is achieved by means of disassembly which is a process of systematic separation of an assembly into its components, subassemblies or other groupings. Due to its high productivity and suitability for automation, disassembly line is the most efficient layout for product recovery operations. A disassembly line must be balanced to optimize the use of resources (viz., labor, money and time). In this paper, we consider a sequence-dependent disassembly line balancing problem (SDDLBP) with multiple objectives that requires the assignment of disassembly tasks to a set of ordered disassembly workstations while satisfying the disassembly precedence constraints and optimizing the effectiveness of several measures considering sequence dependent time increments. A hybrid algorithm that combines a genetic algorithm with a variable neighborhood search method (VNSGA) is proposed to solve the SDDLBP. The performance of VNSGA was thoroughly investigated using numerous data instances that have been gathered and adapted from the disassembly and the assembly line balancing literature. Using the data instances, the performance of VNSGA was compared with the best known metaheuristic methods reported in the literature. The tests demonstrated the superiority of the proposed method among all the methods considered.

A perturbation based variable neighborhood search heuristic for solving the Vehicle Routing Problem with Simultaneous Pickup and Delivery with Time Limit

The Vehicle Routing Problem with Simultaneous Pickup and Delivery with Time Limit (VRPSPDTL) is a variant of the basic Vehicle Routing Problem where the vehicles serve delivery as well as pick up operations of the clients under time limit restrictions. The VRPSPDTL determines a set of vehicle routes originating and terminating at a central depot such that the total travel distance is minimized. For this problem, we propose a mixed-integer mathematical optimization model and a perturbation based neighborhood search algorithm combined with the classic savings heuristic, variable neighborhood search and a perturbation mechanism. The numerical results show that the proposed method produces superior solutions for a number of well-known benchmark problems compared to those reported in the literature and reasonably good solutions for the remaining test problems.

A two-phase variable neighbourhood search algorithm for assembly line worker assignment and balancing problem type-II: an industrial case study

The assembly line worker assignment and balancing problem type-II (ALWABP-2) occurs when workers and tasks (where task times depend on workers’ skills) are to be simultaneously assigned to a fixed number of workstations with the goal of minimising the cycle time. In this study, a two-phase variable neighbourhood search (VNS) algorithm is proposed to solve the ALWABP-2 due to the NP-hard nature of this problem. In the first phase of the algorithm, a VNS approach is applied to assign tasks to workstations with the aim of minimising the cycle time while in the second phase, a variable neighbourhood descent method is applied to assign workers to workstations. The performance of the proposed algorithm is tested on well-known benchmark instances. In addition, the proposed algorithm has been used to solve a real case study from a consumer electronics company that manufactures LCD TVs. The results show that the algorithm is superior to the methods reported in the literature in terms of its higher efficiency and robustness. Furthermore, the algorithm is easy to implement and significantly improves the performance of the final assembly line for the investigated LCD TV real case study.

A variable neighbourhood search algorithm for disassembly lines

Purpose – The purpose of this paper is to efficiently solve disassembly line balancing problem (DLBP) and the sequence-dependent disassembly line balancing problem (SDDLBP) which are both known to be NP-complete. Design/methodology/approach – This manuscript utilizes a well-proven metaheuristics solution methodology, namely, variable neighborhood search (VNS), to address the problem. Findings – DLBPs are analyzed using the numerical instances from the literature to show the efficiency of the proposed approach. The proposed algorithm showed superior performance compared to other techniques provided in the literature in terms of robustness to reach better solutions. Practical implications – Since disassembly is the most critical step in end-of-life product treatment, every step toward improving disassembly line balancing brings us closer to cost savings and compelling practicality. Originality/value – This paper is the first adaptation of VNS algorithm for solving DLBP and SDDLBP.

A parallel variable neighborhood search for the vehicle routing problem with divisible deliveries and pickups

The vehicle routing problem with divisible delivery and pickup is considered.A parallel approach based on variable neighborhood search is proposed.A number of well-known benchmark problems are solved and compared.Proposed parallel approach outperforms the existing methods.New best solutions for 179 of 220 benchmark instances are found. A well-known variant of the vehicle routing problem involves backhauls, where vehicles deliver goods from a depot to linehaul customers and pick up goods from backhaul customers to the depot. The vehicle routing problem with divisible deliveries and pickups (VRPDDP) allows vehicles to visit each client once or twice for deliveries or pickups. In this study, a very efficient parallel approach based on variable neighborhood search (VNS) is proposed to solve VRPDDP. In this approach, asynchronous cooperation with a centralized information exchange strategy is used for parallelization of the VNS approach, called cooperative VNS (CVNS). All available problem sets of VRPDDP have been successfully solved with the CVNS, and the best solutions available in the literature have been significantly improved.

Performance evaluation of waste electrical and electronic equipment disassembly layout configurations using simulation

Recycling of waste electrical and electronic equipment (WEEE) is crucially important since it handles hazardous waste according to ever tightening laws and regulations and it adds benefits to economy and sustainable environment. Disassembly is one of the most important processes performed during the recovery of WEEE. The overall goal of disassembly is to maximize the retrieval of various metals and plastics contained in WEEE in order to reduce their negative effects on human health and environmental sustainability and to increase economic gains. This study aims to evaluate alternative layout configurations for WEEE disassembly systems (WDS). In this context, various configurations were compared in terms of pre-defined performance criteria, such as the total number of disassembled WEEE and the total revenue from sales, using simulation models. The results of this study show that the performance of a WDS was significantly affected by output transfer systems along with the specialization of operators on certain types of WEEE.

Physical Workload Assessment of Furniture Industry Workers by Using Owas Method

Received: April 30, 2018 Revised: June 04, 2018 Accepted: June 11, 2018 Abstract: Object: Improper workplace design is one of the significant reasons for occupational accidents and injuries in labor-intensive production sites. Inadequate and incomplete working environments ignoring ergonomic factors at the planning level create persistent psychical disorders, increase mistakes and accident rates and decrease work productivity. Enhancement of the compliance between worker and task is a crucial step for improving productivity.

A Mathematical Model For Assembly Line Balancing Problem Type 2 Under Ergonomic Workload Constraint

Method: Because of the heavy physical workloads along with monotonous body postures, the workers are dealing with low performance and Work-related Musculoskeletal Disorders (WMSDs). WMSDs result in high compensation costs for companies and totally decrease the life quality of the workers. In order to improve the efficiency of assembly lines, the companies should not only consider cycle time and precedence constraints, but also physical workloads of the stations. This paper addresses Assembly Line Balancing Problem (ALBP) Type 2 where the number of workstation lines is known. The main objective is balancing the cycle time and physical workload of the stations simultaneously. Rapid Entire Body Assessment (REBA) method from the literature is proposed to determine workload of operations.

MOBİLYA SEKTÖRÜ ÇALIŞANLARINDA FİZİKSEL ZORLANMANIN BELİRLENMESİ

Mobilya sektoru emek yogun ve isin genellikle elle yapildigi sektorlerden biridir. Uretimin elle yapilmasi fiziksel is talebini artirdigi gibi kas-iskelet sistemi rahatsizliklarini ve riskleri de beraberinde getirmektedir. Zira mobilya uretimi kas-iskelet rahatsizliklarinin en yogun oldugu, bel, sirt ve omuz sorunlarinin en cok yasandigi sektorlerden biridir. Son yillarda bu sorunlar giderek artmakta, ozellikle depolama, uretim ve dagitim asamalarinda bedensel zorlanma ve sakatlanmalar daha fazla olmaktadir. Bu sakatlanmalara neden olan sayisiz risk faktoru vardir. Bu risk faktorleri biyomekanik, psikososyal ve bireysel olarak siniflandirilmaktadir. Calisma kosullari ve calisma biciminin neden oldugu biyomekanik risk faktorleri mobilya sektorunde cok sik gerceklesen egilme, bukulme, kaldirma, itme-cekme, agir fiziksel is, tekrarli is, postur-durus ve vibrasyondan kaynaklanmaktadir. Bu riskleri azaltmada en onemli yaklasim agir calismalarda fiziksel is ihtiyacini azaltmaktir. Bu calisma ulkemizde farkli illerde mobilya uretimi yapan 5 isletmede calisanlarin is ve is ortami kaynakli fiziksel zorlanmalarini belirlemek amaciyla yapilmistir. Bu amacla bir kontrol listesi hazirlanmis, masifleme, levha isleme, zimparalama, montaj, vernik-boya ve paketleme birimlerinde calisan 239 bireyin calisma ortami ve kosullarini degerlendirmesi istenmistir. Degerlendirme elle calisma, fiziksel enerji tuketimi, kas-iskelet sistemi kullanimi, iste kullanilan arac ve gerecler, calisma istasyonu ve is kolaylastirmaya iliskin 60 soruyu icermektedir. Arastirma sonucunda is ve ortam kosullarinin bireyde zorlanmayi artirdigi (p<0.05) ve is memnuniyetini azalttigi (p<0.001) belirlenmistir. Calisma ortami ile isten memnuniyet arasinda da yuksek korelasyon (r=-.436, p<0.001) soz konusudur. Arastirma sonuclarinin bireyin calisma yasami kalitesini artirmada, saglik ve is verimini iyilestirmede yararli olmasi beklenmektedir.