An ergonomic evaluation of Speed Fastening work rates
MetadataShow full item record
Present day manufacturing assembly relies extensively on a variety of fasteners for the assembly of sub-systems, components and trim. Speed Fastening (SF) is one commonly used non-structural assembly fastening method. The primary limitation of SF is the lack of continuously fed rivets. One path to productivity improvement for SF is the development of a continuously feed tool that would eliminate the non-value added time currently scheduled for reloading in the work cycle. In preparation for the design of a new tool, a proactive ergonomic investigation was carried out to examine differences in muscular effort, upper-body posture, as well as subjective ratings of perceived exertion and discomfort across three different work rates for a simulated SF task conducted in a laboratory setting. The purpose of this investigation was to characterize the ergonomic consequences that an increase in work rate would have on SF operators. Twelve healthy female subjects participated in simulated SF work over four test-sessions. The first test session familiarized subjects with the SF tasks as well as the data collection protocol. Subsequent test days, which were scheduled 24 hours apart, were block randomized to one of three work rates (7, 14 and 21 fasteners/min.) with subjects required to complete 120 minutes of a simulated SF task at both waist and shoulder height using a 50% work to rest duty cycle. The results of this study show significant increases in the amount of muscular activity required to complete the simulated SF, particularly for the 21 fasteners per minute work rate, with increases in peak sEMG amplitudes ranging from 3-12% MVIC. Specifically these increases were most marked in the forearm extensor muscles. In addition, significantly deviated postures were found in upper-limb joint ROM data, particularly when SF work was completed at shoulder height. Overall, based on the increased exposure to risk factors known to be precursors for workplace injury (i.e. repetition and awkward posture), it is inferred that an increase in work rate will put SF operators at an elevated risk of musculoskeletal injury. It is expected that this risk would be even more pronounced for work completed at shoulder height.