Abstract: Because of the changing of the machine tool configuration and the axis coupling forces in multi-axis machine tools motion, the stiffness of the kinematic joints will change nonlinearly, therefore the amount of the inertia matrix, stiffness matrix of the system will vary, resulting in the variation of the dynamic characteristics of the system. A typical three axis gantry-type machine tool is taken as an object of investigation, using the lumped-parameter method to set up the dynamic model of machine tool and derive the dynamic equation. The system matrices with respect to position are established. Based on the dynamic model, the variations of the frequencies and frequency response functions with respect to position parameters are calculated. Modal testing is carried out to validate the accuracy of the model. The simulation and experimental results show that: the dynamic characteristics of the machine tool are greatly affected by axial coupling, the natural frequencies and the reacceptance of the tool cutting point (TCP) are greatly changed when the TCP is moving along x-axis, y-axis or z-axis. Comparing two extreme positions, the maximum changing of natural frequencies is up to 10% and response magnitude up to 2 times.

Key words: axis coupling effects;multi-axis machine tool;variation of the dynamic characteristics;position-dependent