A case study in troubleshooting electromechanical software-controlled systems : the InMotion² Robot

Abstract

The InMotion² robot is a clinical version of the MIT-Manus robot, which was developed in the 1990s to help with upper limb rehabilitation of stroke survivors. In 2015, experiments were planned to use the InMotion² robot for studies of human force and motion control. During preparation for the experiments, however, a malfunction was discovered in the robot. A series of systematic tests were carried out to determine what part of the robot was causing the malfunction. It was determined that the magnets on one of the two motors were slipping on the rotor shaft. This slippage caused the malfunctioning motor's torque output to range from 10% to 13% of the other motor's output given the same input signal. The malfunctioning motor was repaired, and the robot was reassembled. Tests were carried out to verify the performance of the robot, and the torque output of the malfunctioning motor was measured to range from 120% to 130% of the other motor's torque output, showing that the malfunction had been fixed.