Servo stiffness optimization of torque motor direct-drive CNC machine tool feed systems
CHEN Yanyu1, FU Meng1, GUAN Liwen1, CHANG Jiahao1, DIAO Lei2, HU Lan2
1. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China; 2. Shanghai Aerospace Equipment Manufacturing General Factory, Shanghai 200245, China
Abstract：The stiffness characteristics of feed systems directly driven by torque motors mainly depend on the servo stiffness. Therefore, the servo stiffness is a key factor affecting the feed system disturbance rejection, dynamics, speed and accuracy. This study analyzes a torque motor direct-drive feed system using a servo stiffness optimization method based on the Routh criterion. The optimization simultaneously sets multiple servo control parameters based on the mutual constraint relationships between the servo control parameters for a stable control system. The analysis uses a complete coupled electromechanical model of the servo feed system based on the direct-drive torque motor model. Then, the influence of the servo system control parameters on the servo stiffness is used to develop a simplified solution method for the system stability Routh criterion inequality and to define the constraint relationships between the system control parameters. The method is verified in Simulink. This research gives a servo control parameter optimization method using the servo stiffness as the optimization objective. The method is then applied to an A-axis direct-drive torque motor feed system in a five-axis computer numerical control (CNC) machine tool to verify the optimization method. The results show that the optimization significantly improves the servo stiffness while maintaining system stability and has little effect on the dynamics of the servo system such as the dynamic tracking accuracy.
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2021, Vol. 61 
