Compensation of thermal errors on a small vertical milling machine

It is well known that thermal distortions are a significant contributor to machine tool inaccuracy. Compensation of thermal errors on CNC machine tools can be an effective solution with some machine tool builders incorporating temperature sensors on the machine at the build stage. Significant research in the field has produced a number of sophisticated techniques for modelling thermal errors ranging from Finite Element Analysis to Neural Networks. In this paper, new development based on a previously published [1] modelling technique is described with emphasis on new measurement methods and compensation implementation methodology. A new Volumetric Compensation System (VCS) has been created to run in a popular modern windows based open architecture controller, namely the Siemens 840D. This enables low cost and efficient implementation of compensation for geometric and thermal errors. This paper will concentrate on the thermal compensation part of the software with results presented for tests similar to those found in the ISO 230-3 standard and cutting trials. The results show accuracy improvements of greater than 70% for position independent and position dependent thermal errors including compensation for environmental fluctuations.