Transmission of vibration to the wrist and comparison of frequency response function estimators

The purpose of this study was to find the resonance frequencies of the hand, the relations between resonance frequencies and hand-grip force, and between transmission of vibration and hand-grip force, and to compare different frequency response function estimators. The vibration accelaration was measured from the handle and from the wrist in both laboratory and field conditions. The laboratory measurements were made with five research workers as test subjects using five hand-grip forces and three handle vibration levels. Vibration excitation was sinusoidal sweep from 10 to 400 Hz. Field measurements were made from five professional forest workers who were cutting discs from a tree with chain saws manufactured in 1958, 1972 and 1980. Three resonance frequencies were found which increased linearly with increasing hand-grip force. The transmission of vibration to the wrist increased linearly with increasing hand-grip force at frequencies over 100 Hz. Three frequency response function estimators were calculated which seemed to be fairly equal if the coherence function was better than 0·8. The minimum boundary of normalized random error function for frequency response functions was calculated.