Development of a hybrid control system using NURBS interpolator and cross-coupling approach to eliminate contour error : theory and application

Abstract

Over the past decades, advanced motion control systems have received considerable attention in the manufacturing industries. The world of manufacturing has undergone tremendous changes since the introduction of numerical control (NC) for machine tools in the late 1950s. The advent of the computer has created another revolution in manufacturing process and procedure. The quick development of electronic and computer technology has an effect of further pushing NC system to become highly sophisticated. Computer Numerical Control (CNC) technologies have made it possible to manufacture goods faster, improve the product quality, and reduce manufacturing costs. In the past years, advanced motion control systems with multi-axis synchronization together with CNC, have been highly demanded for meeting requirement of high speed and high accuracy. Contour error exists in all multi-axis synchronization systems and CNC machine has no exception. The contour error of a CNC machine is due to four main factors: a) the structure of the machine, b) the way of interpreting the commands generated in CNC systems, c) placement of Acceleration and Deceleration (ACC/DEC) plan, and d) the servo control system. The technology for machine structure attains maturity and the effect of improving the structure of machine is limited. People then focus their attention on the rest of factors. In this study, an improved hybrid control system is proposed. This system composes of NURBS interpolator, ACC/DEC before interpolation plan, and model-free cross-coupling controller. The NURBS interpolator is used to bridge CAD/CAM system and CNC system. The ACC/DEC before interpolation is used to reduce contour error. The cross-coupling controller is used to coordinate axes in the servo control system. Finally, the proposed hybrid control system is verified in an industrial application: CNC engraving machine operation.