An evaluation of vibration and other effects on the accuracy of grip and push force recall

Abstract

Operators of vibratory hand tools can be at risk of developing health problems associated with repeated forceful actions and exposure to intense hand-transmitted vibration. To better assess health risks, comprehensive risk evaluations of these tasks must include quantitative assessments of hand-tool coupling forces. Researchers have used instrumentation for such measurements; but those techniques may be ill-suited for certain field environments. Psychophysical force-recall techniques have been proposed as alternatives to handle instrumentation. This study comprised two experiments that examined the effects of vibration and other factors upon force-recall accuracy and reliability. In each experiment, participants applied specific grip and push forces to an instrumented handle mounted on a shaker system. Participants were exposed to sinusoidal vibration at frequencies that ranged from 0 Hz to 250 Hz. Three levels of applied force (grip = 30±15 N; push = 50±25 N) and two levels of vibration magnitude were examined. During the vibration exposure period, participants were provided with visual feedback while they attempted to "memorize" their applied grip and push forces. Following vibration exposure and a rest period, participants tried to duplicate the hand forces without visual feedback. Vibration frequencies, magnitudes, and hand force levels were randomized from trial to trial. To evaluate test-retest reliability, the test was repeated on a later day with each participant. Participants overestimated grip and push forces. Depending on exposure conditions, error means ranged from 2 N to 10 N. The ANOVA revealed that force-recall errors for exposures between 31.5 Hz and 63 Hz were significantly higher than those at other vibration frequencies (p < 0.05). Errors were greater when participants were exposed to the higher vibration magnitude (mean = 9.1 N, 95% C.I. = 8.1-10.2 N) when compared with the lower vibration magnitude (mean = 4.9 N, 95% C.I. = 4.0-5.7 N) (p < 0.05). The average error for females (4.9 N, 95% C.I. = 3.9-5.9 N) was significantly less than that for males (8.3 N, 95% C.I. = 7.5-9.1 N) (p < 0.05). The effects of force level were mixed. This method demonstrated strong testretest reliability as correlations for all but one participant were found to be significant (0.45 < r < 0.95, p < 0.01). Overall, recalled force errors were relatively small over the range of operationally-relevant hand-handle coupling forces and vibration exposure conditions. This force-recall technique shows promise as an alternative to expensive and fragile force-sensing instrumentation. iii This dissertation is dedicated to my wife, Sherry Vincent McDowell. Without her love, unconditional support, and never-ending patience, this work would have never been completed. I would like to express my sincere gratitude to my advisor, Dr. Steven Wiker for setting a high bar and providing the necessary support to facilitate my success in this incredible learning experience. Dr. Wiker has never hesitated to share his time, knowledge, and guid...