Analysis of the critical Stick-slip velocity of CNC machine tool combining friction parameters identification and dynamic model

Stick-slip is a negative phenomenon caused by friction in servo feed systems, which is particularly prominent in low-speed and heavy-load conditions. At present, most research on the critical Stick-slip velocity ignores higher-order terms of the equivalent damping ratio; the calculation accuracy is greatly reduced when the system has a large equivalent damping ratio. To solve it, firstly, an improved Stribeck model based on the least squares genetic algorithm is proposed for friction identification; meanwhile, the identification of shape parameters of the traditional Stribeck model is extended instead of empirical values. Then, an improved method of the critical Stick-slip velocity based on the dynamic model is constructed, and the influence of the higher-order term of the equivalent damping ratio on the critical velocity identification accuracy is analyzed. Finally, this method is verified by the computerized numerical control end-face cylindrical grinder with a hard guideway. The friction force identification error of the proposed method is reduced by 10% compared with the traditional method, and the error of the critical Stick-slip velocity by retaining the higher-order term is reduced by 37% compared with the critical Stick-slip velocity by ignoring the higher-order term.