Liz K. Rincón Ardila and João M. Rosario
Dynamic Model, CNC, Friction, Nonlinear Model
One of the biggest problems with CNC (Computer Numerical Control) machines tool is to achieve high operational efficiency with high accuracy. The machine dynamic is affected by external disturbance and friction effects decreasing precision and robustness when the machine is handled at high speeds. This paper develops a CNC Machine Tool analysis based in the dynamic model with the influence of cutting force disturbance and nonlinear friction. The dynamic analysis aims at improving the performance in the control structure. For this purpose, this study focuses on nonlinear models for friction forces and external disturbances, taking into account Coulomb and Viscous nonlinear friction parameters, and the cutting force as the disturbance input. The dynamic model is simulated within position and velocity control loops, using the classical PI (proportional and integral) controllers, varying each parameter within the machine operation range. This study uses: contour error, control loop position error and stability, in order to estimate the influence of these variables on CNC machine precision and stability. Analysis and simulation results presented in this article show that Viscous friction has greater influence on the system dynamics than with Coulomb friction and Cutting force, in terms of response time, critical gain for stability and control loops error.
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