Compensation algorithms for the real-time correction of time and spatial errors in a vertical machining centre

This paper describes research into a machine tool error compensation system for universal application. Based on an indirect identification precalibrat ed technique, it utilizes a unique algorithm, which allows the compensation system to compensate for the geometric error components of any normal orth ogonal machine tool configuration. The movement and position of the machine tool axes can affect individual ma chine tool axis error components (such as yaw, pitch, roll and straightness ). The level of this axis coupling is dependent on the machine tool configu ration and the rigidity of the machine tool structure. Also, thermal effect s can affect the machine tool axis error components. The kinematic (rigid body) model will be modified to allow for the non-rigi d effects, and a novel technique for reducing workpiece errors caused by th e thermal distortion of a computer numerical control (CNC) machine tool is introduced. This new approach to thermal error reduction is based on an ind irect measurement technique where temperature/distortion relationships are developed by splitting the problem into two parts, a thermal model and a di stortion model. Thermal imaging has been used extensively, and research int o its usefulness for developing models has been under investigation. The us e of separate thermal and distortion models allows analytical techniques, s uch as finite element analysis, to be used to verify performance. Novel techniques for the fast, accurate and detailed geometric calibration of CNC machine tools were also investigated. Although the wide availability of modern metrology equipment has provided the means for accurate measurem ent of machine errors, geometric calibration of machine tools is a time con suming, labour intensive and therefore costly process. The methodology and validation of the universal rigid body compensation mod el with its machine-specific non-rigid body and thermal effects suitably in tegrated have been demonstrated. Other elements such as calibration methodo logy, dynamic measurement, non-rigid effects/compensation and thermal disto rtion models will be the subject of further papers leading to the overall o bjective.