A real-time error compensation system for a computerized numerical control turning center

A real-time compensation scheme for geometric and thermally-induced errors of a computerized numerical control (CNC) turning center is described. The compensation system predicts these errors using a combination of data taken from various sensors on the machine tool and previously established relationships (transfer functions). The system translates these errors into servo counts and injects them into the control loops of the machine tool controller in real-time. A single-board microcomputer interfaced to the machine tool controller and the sensors is the workhorse of the system. The system control software written in PLM, a high level programming language, is modular, flexible, and easily maintainable. To evaluate the capabilities of the compensation system, a series of cutting tests have been performed, and the results are presented. Along with the elimination of machine warmup periods of 8 to 12 hours, significant geometric accuracy improvements in straightness and squareness have been achieved. An additional accomplishment is a dimensional accuracy improvement of up to 20 times over that of uncompensated workpieces.