This paper proposes new algorithms for the assembly line balancing problem with hierarchical worker assignment (ALBHW). The ALBHW appears in real industrial contexts, where companies deal with a ...multi-skilled workforce. It considers task execution times that vary depending on the worker type to whom the task is assigned. Qualification levels among workers are ranked hierarchically, where a lower qualified worker costs less but requires larger execution times then a higher qualified one. The aim is to assign workers and tasks to the stations of an assembly line, in such a way that cycle time and precedence constraints are satisfied, and the total cost is minimised. In this paper, we first present a mathematical model and improve it with preprocessing techniques. Then, we propose a constructive heuristic and a variable neighbourhood descent that are useful to solve large instances. Extensive computational experiments on benchmark instances prove the effectiveness of the algorithms.
•Definition of a variant of the assembly line worker integration and balancing problem, which considers an even distribution of workers.•Proposal of a three constructive heuristics.•Computational ...experiments demonstrates that the regularity distribution goal can be easily incorporated without major productivity losses.
The consideration of worker heterogeneity in assembly lines has received a fair amount of attention in the literature in the past decade. Most of this exploration uses as motivation the example of assembly lines in sheltered work centers for the disabled. Only recently has the community started looking at the situation faced in assembly lines in the general industrial park, when in the presence of worker heterogeneity. This step raises a number of questions around the best way to incorporate heterogeneous workers in the line, maximizing their integration while maintaining productivity levels. In this paper we propose the use of Miltenburg’s regularity criterion and cycle time as metrics for integration of workers and productivity, respectively. We then define, model and develop heuristics for a line balancing problem with these two goals. Results obtained through an extensive set of computational experiments indicate that a good planning can obtain trade-off solutions that perform well in both objectives.
•We describe an assembly line problem with worker heterogeneity and uncertainty.•Two mixed-integer formulations and one heuristic method are proposed.•Extensive numerical results show the importance ...of considering uncertainty.•Computational experiments also show that the proposed heuristic is fast and accurate.
Assembly lines are manufacturing systems in which a product is assembled progressively in workstations by different workers or machines, each executing a subset of the needed assembly operations (or tasks). We consider the case in which task execution times are worker-dependent and uncertain, being expressed as intervals of possible values. Our goal is to find an assignment of tasks and workers to a minimal number of stations such that the resulting productivity level respects a desired robust measure. We propose two mixed-integer programming formulations for this problem and explain how these formulations can be adapted to handle the special case in which one must integrate a particular set of workers in the assembly line. We also present a fast construction heuristic that yields high quality solutions in just a fraction of the time needed to solve the problem to optimality. Computational results show the benefits of solving the robust optimization problem instead of its deterministic counterpart.
We propose the Assembly Line Worker Integration and Balancing Problem (ALWIBP), a new assembly line balancing problem arising in lines with conventional and disabled workers. The goal of this problem ...is to maintain high productivity levels by minimizing the number of workstations needed to reach a given output, while integrating in the assembly line a number of disabled workers. Being able to efficiently manage a heterogeneous workforce is especially important in the current social context where companies are urged to integrate workers with different profiles. In this paper we present mathematical models and heuristic methodologies that can help assembly line managers to cope with this additional complexity. We demonstrate by means of a robust benchmark how this integration can be done with losses of productivity that are much lower than expected.
We investigate the problem of balancing assembly lines with heterogeneous workers while considering job rotation schedules. This problem typically occurs in assembly lines in sheltered work centers ...for disabled. We propose a hybrid algorithm that uses a Mixed Integer Programming (MIP) to select appropriate schedules from a pool of heuristically constructed solutions. A local search based on MIP neighborhoods is used as a post-optimization method. Our results show that this approach is fast, flexible and accurate when compared with current available methods.
We propose simple heuristics for the assembly line worker assignment and balancing problem. This problem typically occurs in assembly lines in sheltered work centers for the disabled. Different from ...the well-known simple assembly line balancing problem, the task execution times vary according to the assigned worker. We develop a constructive heuristic framework based on task and worker priority rules defining the order in which the tasks and workers should be assigned to the workstations. We present a number of such rules and compare their performance across three possible uses: as a stand-alone method, as an initial solution generator for meta-heuristics, and as a decoder for a hybrid genetic algorithm. Our results show that the heuristics are fast, they obtain good results as a stand-alone method and are efficient when used as a initial solution generator or as a solution decoder within more elaborate approaches.
We propose simple heuristics for the assembly line worker assignment and balancing problem. This problem typically occurs in assembly lines in sheltered work centers for the disabled. Different from ...the classical simple assembly line balancing problem, the task execution times vary according to the assigned worker. We develop a constructive heuristic framework based on task and worker priority rules defining the order in which the tasks and workers should be assigned to the workstations. We present a number of such rules and compare their performance across three possible uses: as a stand-alone method, as an initial solution generator for meta-heuristics, and as a decoder for a hybrid genetic algorithm. Our results show that the heuristics are fast, they obtain good results as a stand-alone method and are efficient when used as a initial solution generator or as a solution decoder within more elaborate approaches.
We propose the Assembly Line Worker Integration and Balancing Problem (ALWIBP), a new assembly line balancing problem arising in lines with conventional and disabled workers. The goal of this problem ...is to maintain high productivity levels by minimizing the number of workstations needed to reach a given output, while integrating in the assembly line a number of disabled workers. Being able to efficiently manage a heterogeneous workforce is especially important in the current social context where companies are urged to integrate disabled workers. In this paper we present mathematical models and heuristics that can help assembly line managers to cope with this additional complexity; demonstrating by means of a robust benchmark how this integration can be done with losses of productivity that are much lower than expected.
This paper considers the permutation flowshop scheduling problem with blocking in-process with the objective of minimizing the total tardiness of jobs. In this problem there are no buffers between ...successive machines, that is, it is not allowed intermediate queues of jobs waiting in the system for their subsequent operations. To solve the problem, we propose a genetic algorithm that includes strategies like local search, a procedure to control over the diversity of the population and a intensification procedure based on the path relinking technique. The path relinking technique generates new solutions transforming one elite solution to another one of the population. The performance of the proposed genetic algorithm is evaluated comparing with a GRASP metaheuristic with path relinking from the literature. Computational tests show that the genetic algorithm is very efficient and promising.
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