Study On Measurement Technology And Expression Of Twin-screw Compressor Rotor Profile

Twin-screw compressor are widely applied in industrial refrigeration and air-conditioning. Screw rotors are the key parts of twin-screw compressor. The compressor performance is mainly determined by the screw rotor profile. This thesis concentrates on the researches of the twin-screw rotor measurement technology, fitting the measured rotor profile data and model reconstruction.The thesis presents the mathematical model of screw rotor and proposes a measurement method for screw rotor. While measuring the rotor with Coordinate Measuring Machine (CMM), we obtain two-dimensional coordinate data of central point of the measuring ball. After fitting them to a curve, we generate a screw surface with the curve according to the screw spiral, and then offset the surface by the radius of the ball to attain another screw surface which is the measured surface after error compensation. In order to verify the feasibility of this method, the author extracts a curve in a cross-section from the compensated surface and compares it to the curve extracted from the same cross-section from the known CAD prototype of the screw rotor. In the end, theoretical error of the compensation is analyzed by Imageware which is a professional reverse engineering software.To fit screw rotor profile measured data, the author researches fitting method based on Non-uniform Rational B-spline(NURBS). In order to solve the problem that the connections of fitting curves are not smooth enough, we further proposes a method of reverse design of screw profile based on the moving least square(MLS) of the curve fitting. This method greatly improves smoothness of the fitting curve. With the point data of the measured rotor profile as an instance, the method is realized with the MATLAB and compared with the Traditional Least- Square method.The research achieves the measurement and expression of the advanced twin-screw compressor rotor profile, which will be useful in the rotor development, and provides effective measurement technology.