Evaluation of ergonomic interventions for bucking bars in aircraft manufacturing
Steel bucking bars used in sheet metal assembly tasks lack application of ergonomic principles. Four bucking bar interventions were evaluated and compared to a steel bucking bar. The interventions included a tungsten bucking bar, Viscolas® rubber wrap adhered to a steel bucking bar, a steel bar paired with an anti-vibration glove, and a steel bar with a detachable handle. All interventions and the steel bar were evaluated for vibration transmitted to the hand and elbow, relative muscle activity of the flexor and extensor muscle groups of the forearms, and usability. Vibration data collected at the hand revealed that the steel bucking bar transmitted the most vibration and the tungsten bucking bar transmitted the least. Transmission of vibration to the hand using the detachable handle was comparable to the tungsten bucking bar. All bucking bar interventions failed to meet the ANSI S2.70 standard for vibration exposure at the hand. Vibration measured at the elbow revealed that the tungsten bucking bar and the handle transmitted the least amount of vibration while the steel bucking bar and the steel bar with the Viscolas® wrap transmitted the most vibration to the elbow. The anti-vibration glove transmitted more vibration than the tungsten bar and the handle, but overall, less vibration was transmitted using the anti-vibration glove than the steel bar at both the hand and elbow. Electromyography (EMG) was used to measure relative muscle activity of the flexor and extensor muscle groups. There were no significant differences between any of the interventions or the steel bar for the extensor muscle group. However, the handle produced the least amount of relative forearm flexor muscle activity. In terms of usability, participants perceived less exertion using the tungsten bucking bar and were more likely to recommend the tungsten bucking bars to others. Half of the participants ranked the tungsten bucking bar as their first choice of all the interventions tested. The handle and the wrap were also considered usable by most participants. Participants perceived the most exertion using the steel bucking bar and were less likely to recommend it to others. Vibration, EMG, and usability measures were also analyzed for differences between asymptomatic and symptomatic participants. Relative flexor muscle activity was found to be significantly different between the two groups. Symptomatic participants required less flexor muscle activity to grip the handle during the bucking task comparable to muscle activity levels in asymptomatic participants. The anti-vibration glove produced the highest mean flexor muscle activity in symptomatic participants. Conversely, the glove produced the lowest mean flexor muscle activity in asymptomatic participants. In conclusion, the steel bucking bar transmitted more vibration to the hand and elbow and was not considered usable in terms of preference and perceived exertion. The tungsten bucking bar decreased vibration transmission to the hand and elbow without increased relative grip muscle activity. Decreased flexor muscle activity was observed for the handle and was especially pronounced in symptomatic participants. In general, the anti-vibration glove and Viscolas® wrap did transmit less vibration than the steel bucking bar alone. However, these types of interventions may be better suited for damping high frequency, low impact vibration.
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