Study of the static friction for feed drives of CNC machine tools

Static friction exists in feed drive servomechanisms of CNC machine tools, and it usually affects their motions. Although the existing researches have demonstrated good motion results by applying friction compensation, the simplified characteristics of static friction still limit the motion accuracy for feed drives of CNC machine tools. In this study, the breakaway experiment is performed for obtaining the data values used by the identification processes of static friction. Then, the spectral analysis using the fast Fourier transformation algorithm is applied to analyze the frequency characteristics of the identified static friction. Several experiments and motion tests were carried out on a three-axis CNC milling machine so as to illustrate the feasibility of the developed identification and analysis methods. The experimental results indicate that the friction-compensated motion control system with the friction model obtained by using the developed identification and analysis methods achieves a reduction of 36.94% in the maximum value and achieves a reduction of 40.44% in the root-mean-square value of tracking errors.