Research On Visual Measurement Method Of Vertical Displacement Of Coaxial Rotor Tip

The rotor is one of the core components of the helicopter power system.The measurement of the vertical displacement of the rotor blade tip guides the test direction of the rotor and guarantees the safety of the test.Because rotors are often in a highspeed motion state,traditional methods are difficult to measure dynamically or have low precision.Many existing methods cannot be used to measure a coaxial dual rotor because the upper and lower rotors obstruct each other.In this paper,high-speed moving image preprocessing and monocular vision measurement technology are used to deeply develop the visual measurement method of the vertical displacement of the coaxial dual rotor blade tip.The main research work and achievements are as follows:(1)A comprehensive and detailed analysis of the background knowledge of visual measurement was conducted.Based on this,the research work included two parts: highspeed image preprocessing and vertical tip displacement measurement.(2)A pre-processing method for removing noise and motion blurring in high-speed tip images is proposed.Firstly,the types of noise in the image are analyzed.The best noise reduction method is obtained through various contrast experiments.The best noise reduction method is verified according to subjective and objective criteria.Secondly,the tip region in image is restored by a deblurring method which includes the process of salient edge selection and texture detail restoration.Thirdly,the ROI(Region of Interest)containing the tip is located to reduce the interference of the background in the tip region based on the analysis results of the grayscale histogram of the tip image and the motion law of the tip,and the ROI is splited by using the OTSU method.Finally,the largest connected domain(the tip region)is selected by using the connected-domain scanning method.The validity of the above methods are verified by the denoising,deblurring and paddle region segmentation experiments in the moving images taken by the rotor at high speed.(3)A method for measuring the vertical displacement of a high-speed rotor blade tip is proposed.Firstly,the minimum circumcircle method is used to locate the section of the tip,and the key points are automatically located according to the geometric characteristics of the blade tip.Secondly,the rotor blade number can be identified automatically and rapidly by binary coding the number of each blade.Thirdly,two monocular vision measurement calibration methods are designed and implemented.One of the methods is a standard block calibration method with a small system error,and the other is a checkerboard calibration method with a smaller accidental error.Finally,the vertical displacement of the same blade with different experimental parameters and the vertical displacement of the upper and lower rotors can be calculated by pixel distance between the key points of the blade and visual calibration results.(4)A visual measurement system for the vertical displacement of the blade tip is built and a large number of actual experiments are conducted.The visual measurement system consists of hardware and software.The development of hardware includes the selection,connection and debugging.The software involves algorithms and interfaces.The vision measurement system has been applied to the actual environment and has achieved good experimental results.