Fastening Torque Control for Robotic Screw Driver under Uncertain Environment

다국어 초록 (Multilingual Abstract)

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.
The paper reports the formulation of the screw tightening process and the disturbance observer. In the formulation, the reaction torque resulted from fastening can be transformed into an equivalent voltage entering with the control voltage. The disturbance observer, which is based on an augmented model with a dynamic model for the fastening torque, and the model of the screw driver system, can estimate the state variables of the screw driver motor and the fastening torque during screw fastening.
The angular displacement of the screw driver is controlled by a state feedback controller, which utilizes the estimated disturbance and states to generate the feedback control input and compensate the reaction torque.
A prototyping screw tightening platform is built to test the proposed method. In the experiments, the control system can accurately control the displacement of the rotating tool bit and rapidly estimate the fastening torque with a very short response time.

목차 (Table of Contents)

• Abstract
• 1. INTRODUCTION
• 2. FORMULATION
• 3. EXPERIMENT VERIFICATION
• 5. CONCLUSIONS
• REFERENCES