CMM Inspecting Path Planning Of Precision Impeller

The impeller is widely used in centrifugal compressor, centrifugal pump, turbine expansion machine and internal combustion engine supercharger. It is the key part of the mechanical, chemical and other industries. The dimensional accuracy and surface quality of precision impeller machine play a decisive role in its performance,but due to the blade surface is usually free surface, the structure is complex, the digital measurement of the integral impeller blade is the key to ensure the quality of machined surface of blade.CMM(Coordinate Measuring Machine) as a typical representative of the measuring equipment, not only can measure the workpiece with complex shape but also has the advantages of high measuring precision, strong adaptability. The key to achieve efficient, reliable measurement of precision impeller is CMM inspecting path planning. The key technologies of CMM inspecting path planning for the precision impeller are studied in this paper, including: impeller design and 3D digital modeling, CMM high-level inspection planning, CMM low-level inspection path planning, error evaluation of the impeller blade surface and validated by experiments.The design process and 3D digital modeling method of the impeller are researched. The main parts of the impeller size according to the hydraulic parameters of the pump are calculated. The main parts of the impeller are constructed with NURBS curve. The loft method is used to construct the three-dimensional digital model of blade surface. The 3D digital model of the precision impeller lays the foundation for CMM Inspecting path planning of impeller and the error evaluation of impeller surface.The CMM top-level planning of the impeller is researched. Generally, planning for CMM inspection can be divided into two levels. High-level inspection planning seeks to determine how to setup the part on the CMM table, which faces to inspect in each setup, which probes to use, how to orient these probes. A matching arithmetic of the CAD model datum and the CMM inspection datum is investigated.Low-level inspection planning involves selecting a set of specific points to be measured in each surface, accessing measurement points’ accessibility, clustering and sequencing of measurement points, generation of collision-free probe path, and the integration of these tasks into a computer-aided inspection planning system.The inspection paths of impeller surfaces are created with the help of 3D CAD model and the advanced function of surface scan with the analogue probe. An algorithm based on UV parameter to generate an optimum collision-free CMM probe path is proposed. Based on the 3D CAD model and the inspection specification, the number of inspection points, point locations, probing vectors, back-off distance, and the probing sequence is determined.Analysis of the deviation between the impeller and its CAD model is researched through a matching algorithm. The error of the precision blade is gained, and the analyzed results are compared with experimental verification.Through the research on the digital measurement and tolerance evaluation, the error distribution of the precision impeller is obtained. The results of the study can improve the machining accuracy of the impeller. The research method can also be applied to high precision surface in other similar parts, and has certain application value in practical engineering.