Abstract: A feed system dynamics model is proposed to study the reasons and mechanism that cause the precision lathe dynamic response in the excitation of low frequency servo force. The proposed modeling is based on dynamics theory analysis, from which the influence of low frequency harmonic components of servo force and the mechanical friction characteristics on the dynamic response of the feed system can be described. A classic z axis of lathe tool is taken as an example, lumped-parameter method is used to set up the dynamic model of machine tool and the dynamic equation is derived by Lagrange method. The displacement response of knife tower are measured when the z axis moves at a uniform velocity, and compared with the simulation results to validate the accuracy of the model. The simulation and experimental results show that: ① there are many harmonic components of the servo torque, frequency is far lower than the first order natural frequency (66 Hz)of the feed system, and with the increase of the speed, the frequency components increase; ② the first natural frequency of simulation and experimental results are within 5%, validate the dynamics model; ③ with the test results comparison under the uniform motion velocity, the model can effectively reflect the low frequency harmonic components of servo force on the effect on the dynamic response of the mechanical system, the amplitude variation of about 15%. And also it points out that the low frequency harmonic component of servo force is un-ignorable factor to solve precision displacement response of feeding system movement.

Key words: feed system, low frequency, mechanical friction, modeling, servo force