Fastening torque control for robotic screw driver under uncertain environment

In automatic screw tightening task, the fastening torque and the angular displacement of the screw have to be closely monitored in order to maintain good product quality. Most automatic screw fastening stations use torque sensors to monitoring the fastening process, and traditional strategy in automatic screw fastening is to limit the maximum value of the fastening toque. However, recent studies show that the relation between the fastening torque and the thread-in depth can be utilized to justify the fastening quality, especially for multi-layered workpiece screw fastening and for self-tapping screws. In order to identify the above-mentioned torque-depth pattern and to control the fastening torque and depth at the same time, we propose a servo control system with a disturbance observer to estimate the applied fastening torque without using a torque sensor to measure the fastening torque.