Modeling of Hand-arm System for Studying the Dynamic Effects of Impact Generated by Fastening of Shear-type Fasteners

The aim of this study is to model the hand–arm system during fastening operation using shear fasteners. Fastening using powered hand-tool generates considerable dynamic forces caused by the impact delivered to the hand–arm at the end of the operation because of fastener shear-off. The hand–arm is modeled as a rotational single-degree-of-freedom system. The values of the model parameters are obtained by using a parameter extraction algorithm using the characteristic statespace model matrices derived from the measured torque and angular displacement data, which are obtained while installing fasteners on a fixtured experimental setup. The identified parameter values are used to determine the response and the dynamic reaction force generated by the subjects, based on which the dynamic effects of using the power tool on the subject can be quantified. The effect of grip force on the model parameter values is studied. Risk factors such as tooltype and posture are analyzed for their effects using the dynamic reaction force. Strong agreements are seen between the predicted responses using the model and the measured responses. The model parameter values depend upon the grip force and increase with increase in value of grip force. The model parameter values vary between two tools as well as the two postures used in the study. The subjects are able to exert maximum reaction force at the ‘neutral’ posture than any other posture. The pistol-grip tool has larger parameter values than the right-angled tool for all the postures. Relevance to industry This study is useful in selection of tools and workplace designs for assembly shop floors where hand-held power tools are commonly used. It demonstrates a systematic approach in predicting the motion as well as the amount of reaction generated by the operator’s hand–arm for a given torque impulse produced by a fastening tool. The predicted motion and reaction force can be used for further analysis to determine the detrimental effects they may have in causing cumulative trauma disorders or ergonomic injuries.