기어 백래시로 인한 제어성능 저하 개선방안에 관한 연구

Abstract

The aim of this study is to perform robotic motion control that can cope with backlash. Backlash is a typical nonlinear element that causes various problems in system operation. One of the problems is a chattering phenomenon related to stability. Between the drive gear and the driven gear in the reduction gear exist free space due to backlash. Because of the free space, the robot arm can not be fixed in the desired position and oscillates. This results in very unstable results and degrades system performance. Another problem is the time delay phenomenon. Due to the backlash, the gear drive side power can not be transmitted directly to the load side, but after a short time delay, it comes into contact. This means that the system output will appear after a certain period of time, which is why the time delay error occurs. The problems caused by such backlash are solved by designing controllers with different characteristics. First, we introduce a PID control, which is the most common controller, and check how it responds to backlash. Next, Smith predictor is introduced to the existing PID control. Smith predictor is a predictor for time delay compensation. Therefore, It evaluates how well it copes with time delay. Finally, we introduce a Sliding Mode Control to improve the insufficient robustness of the PID control. In this case, we consider the backlash as uncertainty and evaluate the control performance. The robot system introduced in this study is a painting robot, which recognizes a worker's motion pattern. Therefore, it is essential to have tracking performance. However, as described above, various problems arise due to backlash. An appropriate controller of coping with such a problem is designed and compared. The evaluation criterion is judged as the presence of instability factors such as the size of the system error and chattering. Therefore, the effectiveness of each controller is evaluated by applying it to a real robot model based on characteristics of a PID control, a PID and Smith Predictor, and a Sliding Mode Control.