Design and Development of a Test Rig for Ergonomic Evaluation of Pistol grip Power Tools

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DC Hand tools are commonly used in manufacturing industries for tightening of fasteners. These hand tools will result in reaction torque on the hand due torque buildup. This results in forceful exertion of the hand operating the hand tools. Repeated stretching of tendons of the wrist during such repetitive tasks results in some of its fibers being torn. This results in inflammation of the tendon leading to tendinitis. Chronic tendon disorders, such as tendinitis, are major causes of lost work and workers' compensation in manufacturing industries. However, the correlation between operational parameters such as operator position, gripping force, tightening algorithm and torque applied to the reaction torque produced is unknown. We propose a combined modelling and experimental approach to study the factors that affect the reaction torque with the aim of minimizing the handle displacement when pistol grip hand tools are used to tighten fasteners in various operating positions. A first order linear model that consists of spring and dashpot will be used to represent the human hand. Twenty experienced hand tool operators will be conducting fastening tasks, in various positions, using instrumented pistol-grip hand tool on a specially made frame. The model parameters such as spring stiffness and damping coefficients will be determined through experiments A custom test rig will be designed and built to simulate the hand-tool interaction. The test rig would have capability to simulate various spring and damping coefficients that are experimentally found. The rig will be used to study the effect of various operational parameters and non-operational parameters such as gender on handle displacement due to reaction torque. The combination of parameters that would minimize the handle displacement in each operational position will then be determined. Using the results of the research, one can determine the parameters that would result in minimal handle displacement for each operational position. This will help the industrial partner to design the task and workplace so that repetitive strain injuries are reduced and safe working habits are followed.