Optimal job rotation scheduling under productivity and ergonomic risk constraints in assembly lines

Human labor still plays a crucial role in many work contexts. However, increases in production rate usually cause increases in human workloads. In this paper, the Authors propose a mixed integer nonlinear programming model aiming at finding optimal job rotation schedule in work-environments characterized by low load manual tasks with high frequency of repetition. In such a work environment a major risk consists of upper limbs work-related musculoskeletal disorders. Workload risk and acceptability are evaluated by the OCRA index method. Different skilled workers jointly operate on different workstations; workers show different operating times which cause cycle time variability of the assembly line. The model aims at integrating the assignment of work tasks to all classes of workers. Model proposed is applied to an assembly line from the automotive industry. Results obtained revealed the effectiveness of the model as it proved to be an adequate tool to jointly address the increase of manual workstations productivity rates and balancing of human workloads among the workstations, which are consistent with acceptable workloads limits.