Computational approaches to compensating quasistatic errors of three-axis machining centers

This paper, the last in a series of three papers dealing with modeling and compensation of quasistatic machine-tool errors, discusses strategies for introducing compensations for quasistatic errors. It is assumed, based on the work presented in the previous papers in this set, that an adequate and accurate model is available for characterizing the volumetric errors in the work space of a machine due to quasistatic effects. Such models indicate that quasistatic errors result in a nonlinear distortion of the work volume. Consequently, the compensations become position dependent and simple strategies such as using constant offsets will not work. Under the assumption of the availability of an error model, strategies are developed for obtaining compensations when locating the cutting tool at a point in the work space or moving it along a straight line or circular trajectory. The motivation behind this analysis is its use in "preprocessing" NC programs so that compensated NC programs can be developed, based on an updated (current) model of the machine's error, and given to the machine for execution. The strategies developed are tested using experimentally obtained error models for a three-axis machine. The computational tests indicate that a high level of compensation accuracy is possible.