Thermal error compensation in high-speed CNC machine feed drives

The CNC machine tool feed axesdrives includecomplex transmission mechanisms having mechanical and thermal errors, which adversely affect the geometrical accuracy. Proper axes drive configurations haveto be designed along with advanced control systems to compensate for various errors. For achieving a precise axis control, accurate measuring systems are required along with advanced position sensors (scales and encoders)and laser interferometers A complete check on a machine tool is made for kinematic errors which include linear positional errors, repeatability, reverse errors, pitch. The Renishaw laser diagnostic equipment, model ML10 is used for dynamic measurements of slides that reveal drive errors and stick-slip motion. The laser calibration is carried as per JIS B-6330 in effecting immediate mechanical adjustments on the machine and software compensation in the control system. For the feed sub-assemblies to have a high degree of positional accuracy and repeatability at high-speed machining, thermal error compensation has to be done. Heat generation takes place at ball screw, bearings, and guideways, causing non-uniformtemperature distribution and causes thermal deformation. The sub-assembly involves the feed motor, recirculating ball-screw, bearing assembly, and coupling mounted to slides (x and z) of the lathe machines. The ambient temperature variation, the impact of viscous friction, and the influence of cutting load affect the positional and machining accuracy. In the present work, the thermal deformations in the feed motor assembly are calculated theoretically usinga heat transfer approach and are validated experimentally using laser-interferometer calibration. Also, a statistical analysis is presented for the Z-axis feed drive, and the results are in agreement with the laser-interferometry experiments.