Research On Measurement Method Of Torsion Angle Of Helicopter Rotor Blades Based On Stereo Vision

As an important measurement parameter for helicopter flight safety,the blade torsion angle of helicopter has a great significance for its in-depth study.Due to the high speed motion of the rotor,the measurement of the blade torsion angle is difficult and the accuracy is low.In view of the above problems,this paper adopts binocular stereo vision technology to measure the helicopter blade torsion angle.The main research work and achievements are as follows:(1)Outlines the background and related theoretical knowledge of helicopter blade torsion angle measurement.Firstly,this paper summarizes the research background and measurement methods of the helicopter blade torsion angle.Then,briefly explains the key steps in binocular stereo vision measurement technology,the theoretical basis of camera calibration,stereo matching and three-dimensional information measurement.Finally,introduces the basic principle of the digital speckle correlation method.(2)Proposes a measurement method for helicopter blade torsion angle which based on double-row marking points matching.Firstly,in the camera coordinate system,the binocular stereo vision technology is used to obtain the three-dimensional coordinates of the double row of circular marking points on the blade.Secondly,with the rotor rotates at a low speed,through uses the three-dimensional coordinates of the marking points measured when the blade is in the flat state,the rotor coordinate system is established by calculation.Then,in the rotor coordinate system,when the rotor blade at high speed and low speed rotation,the blade torsion angle is calculated by using the three-dimensional coordinates of the corresponding marking points on the blade.Finally,a rigid blade simulation experiment is carried out to verify the feasibility of the measurement principle and the recognition accuracy of the circular marking points were also studied.On this basis,a helicopter rotor test tower experiment was carried out to further verify the effectiveness of the measurement method based on the matching of double-row circular marking points.(3)Proposes a measurement method for helicopter blade torsion angle which based on digital speckle correlation method.Firstly,the search algorithm in the digital speckle correlation method is studied,and an initial value calculation method based on circular mark matching is proposed,which reduces the times of sub-pixel iterations and improves the matching efficiency.Secondly,uses the digital speckle correlation method to obtain speckles in the region of interest and the three-dimensional coordinates in the camera coordinate system.Then,according to the conversion relationship between the camera coordinate system and the rotor coordinate system,converts the three-dimensional coordinates of speckles of the interest region in the camera coordinate system to the rotor coordinate system.Finally,through the two plane fittings,the normal vector of the plane where the region of interest is located is obtained,and the calculation formula of the helicopter blade torsion angle is deduced.In addition,through the initial value calculation experiment,the effectiveness of the method based on the initial value of circular marking point matching is verified.Through a rigid blade simulation experiment,the effectiveness of the digital speckle correlation measurement method is verified.