Effect of handle size and hand-handle contact force on the biodynamic response of the hand-arm system under zh-axis vibration

The influences of the handle size and of the hand forces exerted on a vibrating tool handle on the driving-point mechanical impedance (DPMI) response of the human hand-arm system have been investigated through laboratory measurements performed on seven adult male subjects. Measurements were performed with three instrumented cylindrical handles with different diameters (30, 40 and 50 mm) exposed to two different levels of broadband random vibration (2.5 and 5.0 m/s2) along the zh axis, while the variations in the hand forces were realized through nine different combinations of grip (10, 30 and 50 N) and push (25, 50 and 75 N) forces. The static hand-handle contact forces were also evaluated for each combination of grip and push forces, and each handle size through measurements of pressure distribution at the hand-handle interface. The results have shown that the average contact force is a linear combination of the push and grip forces, while the contribution due to grip force is considerably larger than the push force and dependent upon the handle size. The hand-handle coupling force, as defined in ISO/WD-15230, was further evaluated by summing the grip and push forces, which is independent of the handle size. The results have shown that the DPMI magnitude tends to increase with an increase in both the grip and push forces at frequencies above 25 Hz, while the increase in DPMI magnitude was better correlated with the coupling force below 200 Hz. A better correlation with the contact force, however, was attained at frequencies above 200 Hz, suggesting a stronger dependence on the grip force at higher frequencies. The DPMI magnitude response was also found to be influenced by the handle diameter. Increasing the handle size yielded higher peak DPMI magnitude response, specifically under medium to high hand-handle coupling forces (30 N grip and 50 N push; 50 N grip and 75 N push).