Dynamic ergonomic analysis and simulation of fastening operation

Operator performing fastening operation with powered hand-tools at awkward postures is subjected to external forces that may pose a risk of developing ergonomic injuries. For design of safe workplaces and selection of tools it is necessary to identify the probable causes of discomfort by simulating the work conditions and quantifying the risk factors. An ergonomic simulator is developed to simulate the fastening operation and quantify the effects of posture and force in fastening operation. The effect of dynamic forces is analyzed using two approaches. The first approach analyzes the effect of tool vibration while the second analyzes the hand-arm system response to the tool torque by modeling the hand-arm system as a single-degree-of-freedom dynamic system. The hand-arm system model is used to predict the hand-arm displacement and dynamic reaction force. Equivalent static load is calculated to combine the static and dynamic forces in fastening operation. Ergonomic analysis of individual risk factors is conducted and preventive actions are suggested. Tool vibrations were analyzed using the IS0-5349 Standard and quantified as years taken to 10% probability of finger blanching. Strong agreements were observed between the predicted response from the identified hand-arm system model and the measured response with average correlation coefficients of 0.95. Results of the study indicate that the pistol-grip tool had higher vibration and generated higher reaction force than the right-angled tool for all subjects. The reaction force increased with increase in grip force for both tools at all postures. The RULA score utilizing the equivalent static load effectively analyzes load and posture for comparing workplace risk factors --Abstract, page iv