Suchergebnisse

Finger and palmar forces were measured during actual pneumatic nutrunner operation using a strain gauge dynamometer. Eighteen student subjects were assigned to one of three categories based on hand length. Two triggers and four handle spans were presented randomly. Handle span affected maximal and submaximal grip force. Asspan increased from 4 cm to 7 cm, average peak finger force increased 24%, peak palmar force increased 22%, and average finger and palmar tool-holding forces increased 20%. When an extended trigger was used, average peak finger force decreased 9%, peak palmar force decreased 8%, finger tool-holding force decreased 65%, and palmar tool-holding force decreased 48%. Hand size affected grip strength (MVC),grip force, and exertion level (force/MVC). Holding exertion level was maximum for large-handed subjects using a 4-cm handle and for small-handed subjects using a 7-cm handle. Subjective handle span preference increased as hand size increased. A similar experiment was performed using 11 factory workers.

A deterministic mechanical model based on physical tool parameters was used for estimating static and dynamic hand forces from kinematic measurements. We investigated the effects of target torque (25, 40, and 55 Nm) and threaded fastener joint hardness (35-, 150-, 300-, 500-, and 900-ms torque buildup time) on hand force. Estimated hand force was affected by target torque and joint hardness. Peak and average dynamic hand force was least for the hard joint (35-ms buildup) and greatest for the medium hardness joint (150-ms buildup). Tool inertia played the major role in reducing hand reaction force. Estimated hand force decreased when the inertial force component increased. Inertial force decreased by 366% when buildup time increased from 35 to 300 ms. Static modeling overestimated hand force; the error ranged from 10% for a soft joint to 40% for a hard joint. Results from direct hand force measurements using a strain gauge dynamometer showed that the dynamic model overestimated peak hand force by 9%. However, average hand force and force impulse were not significantly overestimated.