The Use of Mirrors during an Assembly Task: A Study of Ergonomics and Productivity

Assembly jobs often require sustained, awkward neck and/or shoulder postures. It has been shown in previous studies that these postures increase musculoskeletal discomfort and can impact long-term productivity. The aim of this study was to investigate the effects of ergonomic interventions designed to eliminate these awkward postures. Subjects used a cordless screwdriver to drive screws into a pre-tapped aluminum block, simulating a simple assembly task. Four distinct assembly postures were tested: standard industry (in-line screwdriver, work at elbow height, no visual aid), pistol grip (pistol grip screwdriver, work at shoulder height, no visual aid), mirror (in-line screwdriver, work at elbow height, single mirror visual aid) and periscope (in-line screwdriver, work at elbow height, two mirror visual aids). Each was performed for fifteen minutes. Muscular activity, discomfort, postural deviation from neutral, productivity, and operator subjective assessment were recorded to determine the effects of the interventions. Both interventions (mirror and periscope) resulted in lower muscle activity, smaller postural deviations from neutral and lower subjective discomfort levels. Productivity, however, was highest in the standard industry posture followed by the pistol grip (9% lower), the periscope (13% lower) and the mirror posture (23% lower).