Model parameter estimation for a handheld nutrunner

Sammanfattning: The purpose of this project is to investigate the angled nutrunner, which is a hand held torque tool often used in the industry to tighten bolted joints. The goal is to estimate parameter values for an existing model that can describe the reaction force and the angular displacement of the tool as a function of the torque transferred to the joint. The model is based on a damped mass-spring system with one degree of freedom. The short torque pulse in the tool will induce an oscillating motion of the system. A large amount of data is used that has been collected at an assembly factory. Different tightening conditions tested include tightening strategy (Quick Step and Turbo Tight), joint stiffness (hard and soft joint), tightening pace (5 and 8 tightenings per minute) and target torque. Joint torque, angular acceleration for the tool and, for the Quick Step tightenings, the reaction force is measured. The grey-box model is used in order to estimate the parameters of the model through curve fitting of the data describing the angular displacement. The reaction force on the user is also examined with different methods. The resulting mean values of the model parameters are the mass m = 2.31 kg, the dampening constant m = 103.45 kg/s and the spring stiffness k = 2314.84 N/m. The mean value of the natural frequency of the hand-arm system is f_n = 5.46 Hz. A statistical significance is found for all conditions except the tightening pace.