Proceedings of the 8th IIAE International Conference on Industrial Application Engineering 2020 © 2020 The Institute of Industrial Applications Engineers, Japan. Tuning of Servo Control Gains for Five-Axis CNC Machine Tools Considering Circularity of Inclined Circular Motions in Workspace Diego Hidalgo a , Syh-Shiuh Yeh b,* a Dept. Mechanical and Automation Engineering, NTUT, Taipei 10608, Taiwan, R.O.C. b Dept. Mechanical Engineering, NTUT, Taipei 10608, Taiwan, R.O.C. *Corresponding Author: ssyeh@ntut.edu.tw Abstract To improve both production quality and capacity, CNC machine tools must have high-accuracy and high-speed machining abilities regarding manufacture of mechanical parts. However, CNC machine tool operators experience difficulty in handling the complicated settings of control parameters, which are usually enabled in advanced servomotor drivers. Therefore, a tuning method is developed in this study to determine the best-fitting control gains for a five-axis CNC machine tool using the measurement data acquired during tests of inclined circular motions in the workspace. Rates of improvement higher than 80% were achieved after using the proposed method to tune the control gains of each motion axis. Keywords: control gains, circular motions, five-axis machine tools. 1. Introduction There is an increasing need to manufacture complex mechanical parts, which requires high levels of precision. Five-axis CNC machine tools with three linear and two rotary axes are rapidly becoming a popular solution for this issue. Generally, five-axis CNC machine tools are equipped with drivers for each motor. These drivers’ actions usually depend upon the configuration of several parameters which contain information about the stiffness of the machine, input commands, and control gains for the velocity and position of the servomotors. Despite the availability of tuning guides for different applications, tuning control gains in a five-axis CNC machine tool to enhance its motion performance is still a highly difficult task. Although there are many approaches to analyze and evaluate a five-axis CNC machine tool’s motion performance [1] , a lot of time and resources are usually expended in performing the tests for tuning servo control gains of these tools. A tuning method is therefore developed in this study considering the circularity of the inclined circular motions in the workspace of a five-axis CNC machine tool. In recent years, many studies have focused not only on understanding the influence of motion errors on geometric imperfections when using five-axis CNC machine tools, but also on how to enhance the motion accuracy. Lin et al. [2] developed a virtual machine tool simulation system that considers the servo dynamics of feed drive systems and the tool center point interpolation algorithm of a five-axis machine tool. Geometric errors and component locations were also considered in the developed simulation system; thus, possible error sources during the operations of a real five-axis machine tool could be identified. Because vibration suppression is critical for achieving high-speed and high-precision machining results, Tsai et al. [3] built a detailed dynamic model to represent the dynamics of a feed drive system with closed-loop servo control. Then, an input shaping method with zero vibration was developed to suppress the vibrations of the feed drive system. Zhang and Wu [4] developed an identification method to precisely identify the model of a multi-axis servo drive system using a support vector machine, with the structure parameters optimized by an immune particle swarm optimization algorithm. Hong et al. [5] showed that there are position-independent and position-dependent errors; however, finding these errors is challenging and could be cumbersome, as some of the errors are dependent on others. If these errors are not identified correctly, the precision and accuracy of the machine tool could be further reduced. Lei et al. [6] presented total ball bar dynamic tests, which could be used to inspect and improve dynamic errors of five-axis CNC machine tools, particularly the errors resulting from the gain mismatch. Tsutsumi et al. [7] showed that there are major differences in the clockwise and counterclockwise directions when the tool center path is tracing a circle equivalent to cone-frustum cutting. A significant improvement in roundness cannot be expected because of mechanism errors such as the backlash and pitch errors of the axes of rotation, which cannot be corrected even if the geometric deviations are corrected. Sato et al. [8] showed that tool vibration, vibration of the mechanical structure, the motion error of the feed drive systems, and other factors influence the machined surface. Kato et al. [9] defined a sensitivity coefficient of measurement which is the ratio of the measurement value to the actual error. Moreover, this DOI: 10.12792/iciae2020.036 182