Vibration Analysis of a Hand-Held Percussion Tool Coupled with the Hand-Arm System
Exposure to hand-transmitted vibration (HTV) arising from hand power tools has long been associated with several disorders of the hand and arm, which are collectively termed as hand-arm vibration syndrome (HAVS). Owing to high prevalence of HAVS among the operators of the power tools, particularly the percussive tools, the desire to develop low vibration tool designs, has been widely recognized. The design of vibration isolators or assessment of vibration performance of tools necessitates development of dynamic model of the tool coupled with that of the hand-arm system (HAS) to account for energy absorption within the HAS.
This dissertation research is aimed at development of dynamic model of a percussive chipping hammer together with a biomechanical model of the hand-arm system. The model could serve as an essential tool for identifying effective vibration attenuation design features. The dynamic model of the tool is formulated considering identifications of various component contact pairs and the air flows between the primary piston and the striker. A tool tip-workpiece contact model is integrated to the tool model to describe the interactions between the tool and an energy dissipator. A biomechanical model of the hand-arm system is implemented to the tool model to develop a coupled hand-tool system, which could be applied to determine the hand vibration responses as a function of the push force. The properties of different impact pairs are identified from the theory of visco-elastic collision between rigid bodies. The validity of the hand-tool model is examined on the basis of available measured data under selected levels of the hand push force. A simple model of an anti-vibration glove is further introduced to study its effectiveness in limiting the vibration exposure.
The simulation results show that the percussive tool model coupled with the biomechanical hand-arm model can yield reasonably good trends in view of the hand-transmitted vibration. The results suggest that the tool vibration transmitted to the hand is more sensitive to variations in push force and the operating speed. Slight increases in the diameter of the upper chamber orifices and the weight of the tool body, together with lower the striker mass, could yield notable reductions in the magnitudes of vibration transmitted to the hand-arm system. The results further show that the anti-vibration gloves yield very minimal vibration attenuation.