Effect of cycle to cycle task variations in mixed-model assembly lines on workers’ upper body and lower back exertions and recovery time: A simulated assembly study

• Published in: International journal of industrial ergonomics Vol. 61; pp. 88 - 100
• Main Authors: Carrasquillo, Vernnaliz, Armstrong, Thomas J., Hu, S. Jack
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-09-2017; Elsevier BV
• Subjects: Assembly lines; Computer simulation; Conveyor design; Conveyors; Health risks; Indexing conveyors; Mixed-model assembly; Muscle recovery; Musculoskeletal diseases; Posture; Recovery time; Risk analysis; Risk factors; Workers; Conveyor design; Recovery time; Mixed-model assembly; Posture
• ISSN: 0169-8141; 1872-8219
• DOI: 10.1016/j.ergon.2017.05.011

Differences in cycle-to-cycle work content in mixed-model assembly lines (MMAL) may increase exposure to risk factors of work-related musculoskeletal disorders (WMSD). This study investigated the effect of conveyor type and product mix/sequence in MMALs on joint loads and recovery time. An assembly task was simulated using 9 conveyor (continuous moving, synchronous indexing, and asynchronous indexing) and product mix/sequence (single product, 3 products with fixed sequence, and 3 products with random sequence) configurations. Results show the self-paced conveyor resulted in the least frequency of reaching. However, subjects did not use the available time for recovery and worked at a faster pace than in the continuous and synchronous indexing conveyors. In conclusion, an asynchronous indexing conveyor provided workers the flexibility they needed to complete their job correctly without reaching but recovery time was not sufficient.
Cycle-to-cycle task variations in MMAL may increase workers’ risk of developing WMSDs. An asynchronous indexing conveyor, with a minimum work time built in, may allow workers to complete their job with less reaching outside the reach envelope while providing sufficient recovery time.
•Least reaching occurred in the asynchronous indexing assembly lines (99%).•Product sequence did not affect reaching or recovery time.•The most observed recovery time in the synchronous indexing MMAL (2.8%).•A hybrid synchronous/asynchronous indexing conveyor may reduce risk exposure.