Electronic based accuracy enhancement of CNC machine tools

Abstract

The need for better machine tool accuracy is discussed together with the factors which can affect machine tool accuracy. A study is made of the various techniques adopted for the reduction of errors in machine tools. The concept of error compensation is discussed and the different techniques for error compensation are appraised. A critical appraisal is presented of the work undertaken to date in the field of error compensation. Based on this appraisal a criterion is established for a universally applicable error compensation system. The development of a novel, patented microprocessor based machine tool error compensation system which fulfills this criterion is described. This compensation system, which is based on the precalibrated compensation technique, utilizes a unique geometric compensation algorithm. This algorithm allows the compensation system to compensate for the geometric error components of any machine tool configuration up to three axes. The development of this geometric algorithm is presented. The integration of this compensation system to a large moving column milling machine is described. Measurement tests and cutting tests were performed on this milling machine to establish the effectiveness of the compensation system. The results from these experimental tests are presented, and illustrate the significant improvement in machine tool accuracy achieved through error compensation. This is the first attempt at producing a machine tool error compensation system with universal applicability, both in terms of the machine geometric model, and the method of applying the compensation to the machine tool. The error compensation system developed gives the potential for compensating for thermally induced and load induced position errors, and will enable further work in this area to be commercially exploited