Measurement of Tightening Torque and Axial Force during Machine Screw Tightening by Servo Controlled Electric Screwdriver using Stepper Motor

Abstract

Machine screws less than M2.0 are increasingly used to assemble small electronic equipment and wearable terminals owing to the thinness and miniaturization of these devices. Defectiveness can easily occur in an assembly and the quality of the assembly is not guaranteed when thread tightening is performed by hand by many workers in a mass production line. Therefore, the automation of screw tightening using robots is advancing. On the other hand, an electric driver, which is controllable with the torque and turning angle by servo controlling a stepping motor has been recently developed. Screw tightening data is managed and quality certification by developing a traceability system is expected. In this paper, an experimental device to measure the fastening torque of the fastening working state of the machine screw and change in the axial force was designed to examine screw tightening conditions for machine screw tightening automation. It was verified that the fastening torque and axial force can be measured simultaneously using this instrumentation system in M2.0 and M1.2 screws.