A bi-objective optimization model for work activity scheduling of workers exposed to ergonomic risk

Repetitive work as handling of low loads at high frequency commonly leads to deteriorated posture and movement co-ordination. Such behaviors are the main cause of occupational diseases as the so-called musculoskeletal disorders (MSDs). The appearance of such occupational diseases exposes the workers to hazardous situations, furthermore, work-related MSDs increase the risk of errors and frequently result in reduced productivity and quality. The features of the task, the characteristics and expertise of the workers and the work organization are the main risk factors in repetitive work. Additional factors include the work conditions as noise, illumination, climate and vibration. The legislation in force suggests avoiding hazardous manual handling tasks wherever possible. When repetitive handling is unavoidable, the corrective procedure includes the ergonomic design of the tools and workplace dimensions, as well as the systematic variation of activities to equalize the load situation. This paper presents an integer linear programming model to seek the optimal activity scheduling for workers exposed to the ergonomic risk of repetitive work. The aim is to define the scheduling of the work activities for each worker from a bi-objective perspective. Two different functions are introduced: the first charges the workers with the activities that better fit their competencies and characteristics, while the latter tackles the ergonomic risk of the repetitive activities by varying the intensity of movements throughout the shift. Finally, the proposed model includes the ergonomic risk assessment to ensure the ergonomic safety of each worker. A case study, based on a bi-objective analysis, is discussed to show the benefits coming from the application of the proposed model and to evaluate the impact of the ergonomic issues on the overall efficiency of the work system. The key results outline the effectiveness of the proposed method revealing that the ergonomic based approach leads to minimal decreasing in the overall efficiency of the work system. Furthermore, the proposed model is applicable to several contexts where workers are asked to perform repetitive tasks with low loads at high frequency.