Response of a numerically controlled machine-tool to the modification of its position feedback using real-time solution

Abstract

The dimensional accuracy of machined parts can be influenced by numerous factors, among which inaccuracies in the machine’s structural loop and thermal expansion of components have the biggest impact. Hence, highly accurate machining requires effective error compensation. This motivates the development of a real-time compensation system implemented on a five-axis machine tool. In this study, a physical monitoring device is installed in the feedback loops of the machine’s axial position control circuit, to intercept and modify linear encoder signals. It communicates with a custom software application that processes the data and generates corrected signals according to geometric model based on the rigid body assumption. The numerical controller (NC) is then induced to perform volumetric error correction based on its default programming. The key advantage of this software-based compensation strategy over the use of look-up tables or NC program modification is the total independence from the NC. The same real-time program is also used for the characterization of linear axis controls. This article outlines the behaviour of an NC machine when an axis displacement is generated via the modification of measuring systems feedback. The rate of change of the virtually added movement appears to be more of a limiting factor to the controller than the magnitude. Moreover,