Modular Cross-Coupling Controller for 5-Axis Machine Tools

This paper proposes a modular cross-coupling controller to improve the contouring and tool orientation accuracies in 5-axis CNC machining. The proposed cross-coupling controller is based on real-time estimation of contour and tool orientation errors. In the proposed controller, a 3-diemnsional contour error model and a newly introduced tool orientation error model can provide accurate information respectively on contour and tool orientation errors in real time for an arbitrary machined surface. Both models utilize only interpolator outputs and position and angle feedback from each axis. Therefore, the proposed controller offers a modular structure and can be easily integrated with any type of existing interpolators and servo controllers in a plug and play manner without any additional hardware. The proposed cross-coupling controller coordinates five axes of motion simultaneously, resulting in better performance than the conventional individual axis controllers. The accuracy of the 3-dimensional contour error and new tool orientation error models is compared with that of the existing model. The performance of the proposed cross-coupling controller is also evaluated by computer simulations in comparison with the conventional controller and the existing 5-axis cross-coupling controller.

1. INTRODUCTION

Computer Numerical Control (CNC) has early been applied to control of machine tools and contributed to the automation of machining. Nowadays 5-axis machining realizes high-value added machining of complexand precision products replacing traditional 3-axismachining. A 5-axis machine tool is constituted such that a table or a spindle head has rotary axes of motion and is currently utilized in machining of impellers, turbine blades, propellers, aircraft parts, etc. Itis predicted that the demand in industry for the 5-axis machine tool will continuously increase due to improved productivity and surface finish, despite higher prices than the 3-axis machine tool.