On-line Asynchronous Compensation Methods for static/quasi-static error implemented on CNC machine tools

Abstract

This paper proposes the On-line Asynchronous Compensation Methods (OACM) for static/quasi-static error caused by thermal deformation and machine geometry. The proposed method reduces the complexity of compensation system, which can be implemented on rough interpolation stage or by offset method, depending on the applications. For Position-Dependent Error (PDTE), the rough interpolation compensation is proposed which can deal with volumetric error in an efficient and economical way. Considering the non-uniform error in the whole machining space, the whole error space is divided into subsections along the given tool path, and then combine the subsections as a non-uniform compensation table. Simulation results validate the feasibility of the proposed method based on the rough interpolation data from Non-Uniform Rational B-spline (NURBS) tool path. For Position-Independent Error (PITE), the offset compensation method through CNC-PLC is proposed. Offset compensation method adopts Bayesian Networks to predict error instead of the linear model for thermal compensation inside CNC, but utilizing its interface between CNC and PLC. Machining experiments and successful industry application on Roller Guide Grinding Machine show that this technology can reduce more than 70% of the machining error caused by thermal deformation.