Including rest allowance in mixed-model assembly lines

Ergonomics has a significant impact on productivity and human safety in manual assembly lines. For this reason, several studies in recent years have proposed including ergonomics in assembly lines. However, most works are focused on simple assembly lines, while only a few studies exist for mixed-model assembly lines (MMALs). Thus, in this paper, we propose a new methodological approach to include physical fatigue and rest allowance (RA) as ergonomic parameters in MMAL problems. For the balancing problem, we propose a linear mathematical model that minimises the cycle time by including RA. For the sequencing decision, we develop a heuristic approach that assigns workers to workstations according to the workers’ age and their related maximum physical capacity. Then, we propose a linear sequencing model that minimises the work-overload by also evaluating RA to assign each worker according to her or his features. Finally, to complete the study, we test the mathematical models in a real case application and provide a detailed discussion of the results to highlight the benefits we can achieve with this approach.