The use of mirrors during an assembly task: a study of ergonomics and productivity

Industrial assembly tasks often require awkward, sustained neck and/or shou lder postures that can lead to increased musculoskeletal discomfort and red uced productivity. The aim of this study was to investigate the effects of mirror and periscope visual aids as ergonomic interventions designed to eli minate awkward postures of the cervicobrachial region during assembly tasks . Participants simulated a simple assembly task by using a cordless screwdr iver to drive screws into a pre-tapped aluminium block. Trials of 15 min we re run for each of four distinct assembly workstation configurations: indus try standard (in-line screwdriver, work at elbow height, no visual aid); pi stol grip (pistol grip screwdriver, work at shoulder height, no visual aid) ; mirror (in-line screwdriver, work at elbow height, single mirror visual a id); and periscope (in-line screwdriver, work at elbow height, two-mirror v isual aid system). Muscular activity, discomfort, body posture, productivit y and operator subjective assessment were recorded to determine the effects of the visual aid interventions. The results show that when comparing the interventions to the industry standard condition, there was a 45% reduction in average cervical erector spinae activity, a 90% reduction in average ne ck flexion angle and a 72% reduction in neck discomfort with the interventi ons. When comparing these interventions to the pistol grip condition there was an 80% reduction in activity of the dominant side deltoid, a 92% reduct ion in shoulder flexion angle and an 81% decrease in shoulder discomfort wi th the interventions. Productivity was greatest in the industry standard co nfiguration followed by the pistol grip (9% lower), the periscope (13% lowe r) and the mirror (23% lower) configurations. A follow-up study that compar ed the productivity of the periscope configuration with that of the industr y standard configuration showed that within a 4-h work period this producti vity differential decreased by over 33%.