Development of a 5-axis CNC milling machine with an open-architecture controller and a real-time NURBS surface interpolator.

摘要

NURBS (Non-Uniform Rational B-Spline) has become the world standard for computer representation and processing of geometric shapes, especially for free form curves and surfaces. Even though advanced commercial CAD systems have made it possible to design parts with NURBS representation, machining these parts on existing machine tools is still complicated, time consuming and prone to errors.; 5-axis CNC machine tools are needed to produce NURBS surfaces with high efficiency and quality. Most commercial 5-axis CNC machine tools are heavy-duty machines with proprietary controllers and linear and circular interpolators (in some cases parabolic interpolators). The drawbacks associated with these CNC machines are: vendor-dictated pricing structures, non-common interfaces, incompatible systems, difficulties in change and expansion, higher integration costs, and re-training needed for trouble shooting and operation. Without general real-time curve and curved-surface interpolators in these machines, traditional off-line interpolation approach has to be used to interpolate NURBS curves and surfaces approximately, which results in contouring errors, machine vibration and jerk, CNC memory shortage, and low machining efficiency.; To overcome these drawbacks, this dissertation developed a 5-axis CNC milling machine test bed with an Open-Architecture Controller and a real-time NURBS surface interpolator.; The developed 5-axis CNC milling machine test bed includes a modified HURCO KMC-3P 3-axis vertical CNC milling machine and an automated tilting rotary table that was a manually operated table originally.; The open-architecture control system consists of a standard AMD K6 PC, a UNIIX-type real-time operating system, QNX (version 4.2), a PCX/DSP-800 motion controller from Motion Engineering, Inc. (MEI), and application interface in C/C++.; The developed real-time NURBS surface interpolator interpolates NURBS curves and surfaces within the CNC machine's controller. The original and high level NURBS representation from a CAD system can be utilized without any approximation. Efficient NURBS algorithms were used. Those eliminate the memory shortage, reduce the contouring errors, and increase the machining efficiency and quality significantly.; The 5-axis CNC control system was setup and tested, the software was implemented, NURBS curves and surfaces were machined, and the results were discussed.