The Three-dimensional Measurement Research Of Aero-engine Blade Based On Surface Structured Light

Aero-engine is known as the "heart" of the aircraft, while blade is a key component of the aviation engines. As the blade must have a precise size, accurate shape, the three-dimensional measurement of the blade is very important. Although there are exist many three-dimensional measurements method at home and abroad, for each method has its own characteristics. But taken measurement accuracy, speed and cost into account, these methods have their own limitations and shortcomings. Finding a high precision, high efficiency and low cost three-dimensional measurement method is bound to become a research hotspot in the field of aero-engine blade. In this paper, the three-dimensional measurement of the blade based on surface structured light is proposed. Since this method based on surface scanning mode, and has advantage of high measurement accuracy, high measurement speed, low measurement cost. It can effectively realize the three-dimensional measurement of the blade.In-depth analysis of theory and method on the three-dimensional measurement of the blade based on surface structured light is done. Select a time encoding method of better phase unwrapping to the complex surface and wide applicability. The resolution and accuracy of the combined coding can improve using the proposed time encoding method. The main research contents are as follows:Firstly, the three-dimensional measurement of the blade is researched using the method combined seven Gray code with the four-step phase shift method. set up the experimental system of the three-dimensional measurement of the blade based on the triangulation method. Calibration the intrinsic and extrinsic parameters of the cameras using the flat checkerboard calibration method. The three-dimensional measurement of the blade using the method combined seven Gray code patterns with the four-step phase shift method, which include grating fringe encoding, image capture, as well as phase unwrapping. The key technology involved in this method are as follows. First, the binarization of the blade Gray code pattern is directly related to whether the blade image can phase unwrapping correctly. Second, the correcting of the period dislocation. Using the image mosaic technology based on sign points and deal with the related software, the three-dimensional model of the blade is got. Secondly, the three-dimensional measurement of the blade is researched using the method combined four coding fringe patterns with the four-step phase shift method. Phase unwrapping is the key of the surface structured light technology. For this, under the premise of assurancing quality, improve the phase unwrapping speed becomes the key question of the three-dimensional measurement of the blade. Gray code design a unique codeword and assign it to each2π phase-change period. Each codeword consists of a sequence of binary structured patterns, and the codewords change from period to period according to the rules of Gray code. In this paper, this is studied and proposed a new phase unwrapping method. Unlike conventional Gray code method, this encoding method combined four coding fringe patterns with the four-step phase shift method, the coding information is embedded into phase to determine fringe order, and obtain the absolute phase of the process. Experiment and simulation is done to the blade under the condition of laboratory environment. As the encoding method is simple, easy to implement, phase unwrapping of the blade can be rapidly realized.The experimental results show that the method can achieve a high precision, high efficiency and low cost three-dimensional measurement of aero-engine blades, and the measurement accuracy reaches0.03mm.