Work Variations and Musculoskeletal Stresses in Paced Production Operations

Abstract

This study aimed to test the hypothesis that variations in assembly jobs increase workers’ exposure to risk factors for musculoskeletal disorders. Variations can be caused by different factors such as, materials, material placement, product variety, work flow, etc., and they can require the worker to perform movements not considered in the calculation of the allocated time. Work variations may require workers to work faster and longer to keep up with paced work, which may increase repetition and reduce recovery time. On a moving line, workers may have to reach further to keep up with the work, which requires additional time and results in posture stress. An observational study was conducted in a moving assembly line where food trays were prepared for patients at a large hospital to test the proposed hypothesis. Frequency and quantity of work variations, and the frequency of reaching outside of the reach envelope and recovery time were compared. The variety of materials (along with their location), interarrival of the work object, whether or not the conveyor was moving, and the amount of tasks the worker needed to perform in addition to the main task of placing food on the tray were found to affect recovery time and reach. These factors increased the frequency of reaching outside the reach envelope and reduced the idle time for the station with the largest number and of variations.