Solving large scale disassembly line balancing problem with uncertainty using reinforcement learning

Due to increasing environmental concerns, manufacturers are forced to take back their products at the end of products’ useful functional life. Manufacturers explore various options including disassembly operations to recover components and subassemblies for reuse, remanufacture, and recycle to extend the life of materials in use and cut down the disposal volume. However, disassembly operations are problematic due to high degree of uncertainty associated with the quality and configuration of product returns. In this research we address the disassembly line balancing problem (DLBP) using a Monte-Carlo based reinforcement learning technique. This reinforcement learning approach is tailored fit to the underlying dynamics of a DLBP. The research results indicate that the reinforcement learning based method is able to perform effectively, even on a complex large scale problem, within a reasonable amount of computational time. The proposed method performed on par or better than the benchmark methods for solving DLBP reported in the literature. Unlike other methods which are usually limited deterministic environments, the reinforcement learning based method is able to operate in deterministic as well as stochastic environments.     

多目标拆卸线平衡问题的Pareto细菌觅食算法*

拆卸线平衡问题的优化涉及多个目标,为克服传统方法在求解多目标拆卸线平衡问题时不能很好处理各子目标间冲突及易于早熟等不足,提出了一种多目标细菌觅食优化算法。算法采用Pareto非劣排序技术对种群进行分级,并结合拥挤距离机制评价同级个体的优劣。为提高算法收敛性能,在趋向性操作结束后引入精英保留策略保留优秀个体,并采用全局信息共享策略引导菌群不断向均匀分布的Pareto最优前沿趋近。通过不同规模算例的对比验证表明了算法的有效性与优越性。     

A Pareto improved artificial fish swarm algorithm for solving a multi-objective fuzzy disassembly line balancing problem

To better reflect the uncertainty existing in the actual disassembly environment, the multi-objective disassembly line balancing problem with fuzzy disassembly times is investigated in this paper. First, a mathematical model of the multi-objective fuzzy disassembly line balancing problem (MFDLBP) is presented, in which task disassembly times are assumed as triangular fuzzy numbers (TFNs). Then a Pareto improved artificial fish swarm algorithm (IAFSA) is proposed to solve the problem. The proposed algorithm is inspired from the food searching behaviors of fish including prey, swarm and follow behaviors. An order crossover operator of the traditional genetic algorithm is employed in the prey stage. The Pareto optimal solutions filter mechanism is adopted to filter non-inferior solutions. The proposed model after the defuzzification is validated by the LINGO solver. And the validity and the superiority of the proposed algorithm are proved by comparing with a kind of hybrid discrete artificial bee colony (HDABC) algorithm using two test problems. Finally, the proposed algorithm is applied to a printer disassembly instance including 55 disassembly tasks, for which the computational results containing 12 non-inferior solutions further confirm the practicality of the proposed Pareto IAFSA in solving the MFDLBP.     

模糊作业时间的拆卸线平衡Pareto多目标优化

针对实际拆卸作业的复杂性,建立了考虑模糊作业时间的多目标拆卸线平衡问题的数学模型,提出了一种基于Pareto解集的多目标遗传模拟退火算法进行求解。改进了模拟退火操作的Metropolis准则,使其能够求解多目标优化问题。采用拥挤距离评价非劣解的优劣,保留了优秀个体,并通过精英选择策略,将非劣解作为遗传操作的个体,引导算法向最优方向收敛。基于25项拆卸任务算例,通过与现有的单目标人工蜂群算法进行对比,验证了所提算法的有效性和优越性。最后将该算法应用于某打印机拆卸线实例中,求得8种可选平衡方案,实现了求解结果的多样性。     

Multi-objective partial disassembly optimization based on sequence feasibility

A sustainable manufacturing system integrates production systems, consumer usage behavior, and End-of-Life (EoL) product value recovery activities. Facilitating multi-objective disassembly planning can be a step toward analyzing the tradeoffs between the environmental impact and profitability of value recovery. In this paper, a Genetic Algorithm (GA) heuristic is developed to optimize partial disassembly sequences based on disassembly operation costs, recovery reprocessing costs, revenues, and environmental impacts. EoL products may not warrant disassembly past a unique disassembly level due to limited recovered component market demand, minimal material recovery value, or minimal functional recovery value. The effectiveness of the proposed GA is first verified and tested using a simple disassembly problem and then applied to the traditional coffee maker disassembly case study. Analyses are disaggregated into multiple disassembly network optimization problems, one for each product subassembly, resulting in a bottom-up approach to EoL product partial disassembly sequence optimization.     

Model review and algorithm comparison on multi-objective disassembly line balancing

As the disassembly of end-of-life products is affected by several dynamic and uncertain issues, many mathematical models and solution approaches have been established. However, with more extended objectives, constraints and different methods of disassembly, inconsistent models relating to product representations and types of disassembly lines have become the main barriers for the transfer of research to practise. In this paper, a systematic overview of recent models to summarise the input data, parameters, decision variables, constraints and objectives of disassembly line balancing are presented. After discussing the adaptation and extensibility of these models for different environments, a unified encoding scheme is designed to apply typical multi-objective evolutionary algorithms on this problem with extensive decision variables and seven significant objectives. Algorithm comparison on four typical cases is then carried out based on seven commonly used products to verify the optimisation process for the integrated version of existing models and demonstrate the overall performance of the typical multi-objective evolutionary algorithms on this problem. Experimental results can be a baseline for further algorithm design and practical algorithm selection on these disassembly line balancing scenarios.     

Disassembly line balancing under high variety of end of life states using a joint precedence graph approach

Disassembly is an important aspect of end of life product treatment, as well as having products disassembled in an efficient and responsible manner. Disassembly line balancing is a technique that enables a product to be disassembled as efficiently and economically viable as possible; however, considering all possible end of life (EOL) states of a product makes disassembly line balancing very difficult. The EOL state and the possibility of multiple recovery options of a product can alter both disassembly tasks and task times for the disassembly of the EOL product. This paper shows how generating a joint precedence graph based on the different EOL states of a product is beneficial to achieving an optimal line balance where traditional line balancing approaches are used. We use a simple example of a pen from the literature to show how a joint disassembly precedence graph is created and a laptop example for joint precedence graph generation and balancing. We run multiple scenarios where the EOL conditions have different probabilities and compare results for the case of deterministic task times. We also consider the possibility where some disassembly task times are normally distributed and show how a stochastic joint precedence graph can be created and used in a stochastic line balancing formulation.     

Multi-objective partial parallel disassembly line balancing problem using hybrid group neighbourhood search algorithm

To reduce waste during disassembly production and improve disassembly efficiency, this study investigates a type of partial parallel disassembly line applicable for the simultaneous disassembly of different products. A multi-objective mathematical model for a partial parallel disassembly line balancing problem is built considering four optimisation goals, namely, the minimisation of the cycle time, number of workstations, idle index, and quantity of disassembly resources. In addition, a novel multi-objective hybrid group neighbourhood search algorithm is proposed. First, a certain set of neighbourhood individuals (from the current population of individuals) is generated via neighbourhood search mechanisms based on optimal embedding and exchange operations. Then, a Pareto filtering process is performed on a mixed population composed of the individuals of the current population and all neighbourhoods. Subsequently, the current population individuals are renewed based on the mixed population. To prevent the algorithm from falling into a local optimum and to enhance the algorithm’s global search performance, we conduct a local search strategy based on a simulated annealing operation on the newly generated population individuals. The effectiveness and superiority of the proposed algorithm are proven by solving two complete disassembly line balancing problems at different scales and a partial disassembly line balancing problem, and also by comparison with several algorithms investigated in existing literature. Finally, the proposed model and algorithm are applied to a partial parallel disassembly line designed for the simultaneous disassembly of two types of waste products in a household appliance disassembly enterprise. The results of the partial parallel disassembly line are compared with those of an initial single-product straight disassembly line, and the comparison results show that the solution results of the optimisation goals for the partial parallel disassembly line are more superior than those of the initial single-product straight disassembly line.     

A Pareto-discrete hummingbird algorithm for partial sequence-dependent disassembly line balancing problem considering tool requirements

To reduce the disassembly costs to enterprises and improve the disassembly efficiency of waste products, this study proposed a partial sequence-dependent disassembly line balancing problem (PSD-DLBP) and established a multi-objective mathematical model to simultaneously minimize the number of workstations, total disassembly time, idle balance index and the number of disassembly tools. Then, a Pareto-discrete hummingbird algorithm (PDHA) was proposed to address PSD-DLBP effectively. The PDHA includes two stages: self-searching stage and information-interacting stage. With these two stages, the exploration and exploitation abilities of PDHA can be balanced. Later, the effectiveness and superiority of the PDHA were verified by comparing it with the other four algorithms for two different-scale examples. Finally, the model and PDHA were applied to the optimization of a partial sequence-dependent disassembly line of waste laptops. The optimization results show that the partial disassembly can make the line smoother and the utilization efficiency of workstations higher than full disassembly, and PDHA is superior in solving the PSD-DLBP.     

Collaborative optimization of robotic disassembly sequence planning and robotic disassembly line balancing problem using improved discrete Bees algorithm in remanufacturing✰

Remanufacturing helps to reduce manufacturing cost and environmental pollution by reusing end-of-life products. Disassembly is an inevitable process of remanufacturing and it is always finished by manual labor which is high cost and low efficiency while robotic disassembly helps to cover these shortages. Before the execution of disassembly, well-designed disassembly sequence and disassembly line balancing solution help to improve disassembly efficiency. However, most of the research used for disassembly sequence planning and disassembly line balancing problem is only applicable to manual disassembly. Also, disassembly sequence planning and disassembly line balancing problem are separately studied. In this paper, an improved discrete Bees algorithm is developed to solve the collaborative optimization of robotic disassembly sequence planning and robotic disassembly line balancing problem. Robotic workstation assignment method is used to generate robotic disassembly line solutions based on feasible disassembly solutions obtained by the space interference matrices. Optimization objectives of the collaborative optimization problem are described, and the analytic network process is used to assign suitable weights to different indicators. With the help of variable neighborhood search, an improved discrete Bees algorithm is developed to find the optimal solution. Finally, based on a gear pump and a camera, case studies are used to verify the effectiveness of the proposed method. The results under different cycle time of robotic disassembly line are analyzed. Under the best cycle time, the performance of the improved discrete Bees algorithm under different populations and iterations are analyzed and compared with the other three optimization algorithms. The results under different assessment methods and scenarios are also analyzed.     

一种混合人工蜂群算法求解顺序相依拆卸线平衡问题

拆卸线平衡问题直接影响回收再制造成本.为此,构建了最小工作站开启数量、最短总拆卸时间、均衡工作站空闲时间、尽早拆卸有危害和高需求零部件的多目标顺序相依拆卸线平衡问题优化模型,提出一种混合人工蜂群算法.所提出算法在观察蜂跟随阶段采用分阶段选择评价法,以便更好地区分蜜源;在侦查蜂开采阶段构建基于全局学习的搜索机制,以提高开采能力.蜜蜂寻优过程中设计了简化变邻域搜索策略,提高了寻优效率.对比实验结果验证了模型的有效性和算法的优越性.     

A simulated annealing algorithm for multi-manned assembly line balancing problem

Assembly line balancing problems with multi-manned workstations usually occur in plants producing high volume products (e.g. automotive industry) in which the size of the product is reasonably large to utilize the multi-manned assembly line configuration. In these kinds of assembly lines, usually there are multi-manned workstations where a group of workers simultaneously performs different operations on the same individual product. However, owing to the high computational complexity, it is quite difficult to achieve an optimal solution to the balancing problem of multi-manned assembly lines with traditional optimization approaches. In this study, a simulated annealing heuristic is proposed for solving assembly line balancing problems with multi-manned workstations. The line efficiency, line length and the smoothness index are considered as the performance criteria. The proposed algorithm is illustrated with a numerical example problem, and its performance is tested on a set of test problems taken from literature. The performance of the proposed algorithm is compared to the existing approaches. Results show that the proposed algorithm performs well.     

最大化个人偏好的多目标优化进化算法

针对多目标优化过程中如何将个人偏好信息融入寻优搜索过程的问题,本文提出一种最大化个人偏好 以确定搜索方向的多目标优化进化算法．该算法首先采用权重和法将多目标问题转换为单目标问题,再利用遗传算 法进行全局搜索,在满足个人偏好约束条件下,每一代进化结束后通过解约束优化问题获得能够使种群综合适应度 具有最大方差的权重组合,从而最大化个人偏好以选择综合最优的个体进行遗传操作．按照不同个人偏好应用于传 动系统进行控制器设计,仿真结果表明该算法能够获得满足个人偏好约束条件下的全局最优解．     

Mixed-model assembly line balancing using a multi-objective ant colony optimization approach

Mixed-model assembly lines are production systems at which two or more models are assembled sequentially at the same line. For optimal productivity and efficiency, during the design of these lines, the work to be done at stations must be well balanced satisfying the constraints such as time, space and location. This paper deals with the mixed-model assembly line balancing problem (MALBP). The most common objective for this problem is to minimize the number of stations for a given cycle time. However, the problem of capacity utilization and the discrepancies among station times due to operation time variations are of design concerns together with the number of stations, the line efficiency and the smooth production. A multi-objective ant colony optimization (MOACO) algorithm is proposed here to solve this problem. To prove the efficiency of the proposed algorithm, a number of test problems are solved. The results show that the MOACO algorithm is an efficient and effective algorithm which gives better results than other methods compared.     

拆卸线平衡问题的改进细菌觅食优化算法

拆卸是产品回收过程中最重要的环节,拆卸过程高效与否直接影响产品的回收效率。为克服传统算法求解拆卸线平衡问题时性能不稳定的缺陷,在构建基于工作站利用率、负荷均衡,尽早拆卸有危害、高需求的零件,最小化拆卸成本等方面的拆卸线平衡问题多目标优化模型的基础上,提出一种改进的细菌觅食优化算法对问题求解。通过改进细菌的移动规则扩大搜索空间,引入全局信息共享策略增强算法收敛性能,定义了一种自适应驱散概率防止驱散操作中解的退化。在对不同规模算例的对比分析中,验证了该算法的有效性。     

Software prototype for solving multi-objective machining optimization problems: Application in non-conventional machining processes

For an effective and efficient application of machining processes it is often necessary to consider more than one machining performance characteristics for the selection of optimal machining parameters. This implies the need to formulate and solve multi-objective optimization problems. In recent years, there has been an increasing trend of using meta-heuristic algorithms for solving multi-objective machining optimization problems. Although having the ability to efficiently handle highly non-linear, multi-dimensional and multi-modal optimization problems, meta-heuristic algorithms are plagued by numerous limitations as a consequence of their stochastic nature. To overcome some of these limitations in the machining optimization domain, a software prototype for solving multi-objective machining optimization problems was developed. The core of the developed software prototype is an algorithm based on exhaustive iterative search which guarantees the optimality of a determined solution in a given discrete search space. This approach is justified by a continual increase in computing power and memory size in recent years. To analyze the developed software prototype applicability and performance, four case studies dealing with multi-objective optimization problems of non-conventional machining processes were considered. Case studies are selected to cover different formulations of multi-objective optimization problems: optimization of one objective function while all the other are converted into constraints, optimization of a utility function which combines all objective functions and determination of a set of Pareto optimal solutions. In each case study optimization solutions that had been determined by past researchers using meta-heuristic algorithms were improved by using the developed software prototype.     

An effective hybrid particle swarm optimization algorithm for multi-objective flexible job-shop scheduling problem

Flexible job-shop scheduling problem (FJSP) is an extension of the classical job-shop scheduling problem. Although the traditional optimization algorithms could obtain preferable results in solving the mono-objective FJSP. However, they are very difficult to solve multi-objective FJSP very well. In this paper, a particle swarm optimization (PSO) algorithm and a tabu search (TS) algorithm are combined to solve the multi-objective FJSP with several conflicting and incommensurable objectives. PSO which integrates local search and global search scheme possesses high search efficiency. And, TS is a meta-heuristic which is designed for finding a near optimal solution of combinatorial optimization problems. Through reasonably hybridizing the two optimization algorithms, an effective hybrid approach for the multi-objective FJSP has been proposed. The computational results have proved that the proposed hybrid algorithm is an efficient and effective approach to solve the multi-objective FJSP, especially for the problems on a large scale.     

A multi-objective scatter search for a mixed-model assembly line sequencing problem

A mixed-model assembly line (MMAL) is a type of production line where a variety of product models similar to product characteristics are assembled. There is a set of criteria on which to judge sequences of product models in terms of the effective utilization of this line. In this paper, we consider three objectives, simultaneously: minimizing total utility work, total production rate variation, and total setup cost. A multi-objective sequencing problem and its mathematical formulation are described. Since this type of problem is NP-hard, a new multi-objective scatter search (MOSS) is designed for searching locally Pareto-optimal frontier for the problem. To validate the performance of the proposed algorithm, in terms of solution quality and diversity level, various test problems are made and the reliability of the proposed algorithm, based on some comparison metrics, is compared with three prominent multi-objective genetic algorithms, i.e. PS-NC GA, NSGA-II, and SPEA-II. The computational results show that the proposed MOSS outperforms the existing genetic algorithms, especially for the large-sized problems.     

基于病毒进化遗传算法的复杂产品设计任务规划

为提高复杂决策环境下产品设计任务规划的科学性,针对设计项目中资源以知识型员工为主的特点,综合考虑项目时间最短、完成质量最高及设计人员负载均衡等问题建立多目标优化的数学模型.在此基础上,为提高横向搜索能力以获得多样性解,提出了基于病毒进化机制的求解算法,其中引入多种群思想以使算法适用于多目标问题,并采用非支配排序保证算法全局搜索能力.最后通过仿真分析对文中算法进行了验证.     

A genetic algorithm-based solution methodology for modular design

Combinatorial optimization problems usually have a finite number of feasible solutions. However, the process of solving these types of problems can be a very long and tedious task. Moreover, the cost and time for getting accurate and acceptable results is usually quite large. As the complexity and size of these problems grow, the current methods for solving problems such as the scheduling problem or the classification problem have become obsolete, and the need for an efficient method that will ensure good solutions for these complicated problems has increased. This paper presents a genetic algorithm (GA)-based method used in the solution of a set of combinatorial optimization problems. A definition of a combinatorial optimization problem is first given. The definition is followed by an introduction to genetic algorithms and an explanation of their role in solving combinatorial optimization problems such as the traveling salesman problem. A heuristic GA is then developed and used as a tool for solving various combinatorial optimization problems such as the modular design problem. A modularity case study is used to test and measure the performance of the developed algorithm.