Development and Assessment of a Coupling Force Measurement System Applied to Stationary and Vibrating Tool Handles

Exposure to hand-transmitted vibration (HTV) arising from operating hand-held power tools has been associated with various health consequences. The magnitude of HTV is strongly affected by the hand-handle interface coupling forces, handle geometry and gripping method apart. Assessment of the HTV exposure currently does not incorporate the impact of coupling forces exerted at the hand-handle interface, mostly due to lack of reliable measurement methods for hand-handle interface forces. This dissertation seeks to develop a low cost hand-handle coupling force measurement system and methods for quantifying the hand grip and push forces applied to the tool handles. A hand-handle interface force measurement system was developed using flexible force sensing resistors (FlexiForce). The static properties of the sensors were thoroughly characterized in terms of linearity, hysteresis and repeatability. Moreover, the sensors’ output characteristics were observed by considering the effect of positioning, area and flexibility of the loading medium used to transmit the applied forces. Five different cylindrical and elliptical instrumented handles were subsequently chosen to observe the input-output characteristics of the sensors under stationary and vibrating conditions. The measurements under static and dynamic conditions revealed good linearity and repeatability of the sensors, and affirmed their feasibility for accurate estimations of the hand grip and push forces. The sensors’ outputs also showed strong dependence on the loading medium’s area, position and flexibility as well as the length of the sensor suggesting the need for individual sensor calibration, which was noted as the primary limitation of the system. The effectiveness of the measurement system was further explored through measurements of hand forces on a percussion tool handle and biodynamic responses of the human hand-arm system. The measurement system provided reasonably good estimations of the hand grip and push forces when applied to the percussion tool handle under both stationary as well as vibration conditions. The biodynamic impedance responses measured with six subjects showed trends similar to the reference response. However, a compensation function was necessary and subsequently proposed to account for the limited bandwidth of the sensors