Talbot-Moiré Effect Method For Roll Angle Measurement

Angle is one of the basic physical quantities.It has occupied an important position in industrial design,scientific research and production.From the three-dimensional attitudes measurement of space object relative to geodetic coordinate system,to the three-dimensional angular displacement measurement between the different parts of the object,for example,are all the important composition of the angle measurements.Yaw and pitch angle can be detected easily by optical auto collimation method while the roll angle is more difficult to measure since its roll plane normal vector coincides with the incident light propagation direction.In this paper,some basic methods of angular displacement measurement and some commonly used methods of optical non-contact roll angle measurement are introduced analyzed and summarized.The Talbot Moiré effect roll angle measurement methods is focused on to carry out the research work.Transmission grating under monochromatic plane wave irradiation will produce Talbot image in its Talbot distance and then the moire fringes will occur with the reflection grating placed in the same Talbot distance.The orientation angle and width of the Moiré fringes will be changed when the relative angle between reflection grating and transmission grating changes.Based on the analysis of roll angle measurement methods which is on the basic of Talbot Moiré effect,Talbot Moiré effect is calibrated,simulated and analyzed.The scheme of three-dimensional angle measurement system,which based on Talbot effect and photoelectric autocollimator,is determined according to the design requirements.The optical path design of the system is mainly discussed,constructed and adjusted.The image of Moiré fringe is acquired by CCD camera.Though image processing,the angle and width variation of Moiré fringe could be obtained.And then the roll angular displacement could be calculated.Image processing including frequency filter,median filter,threshold segmentation,thinning and line fitting.At last,the influence of three-dimensional angle coupling on the measurement is analyzed.Simulation and experiment results indicated that the object roll angle measurement scheme based on the proposed Moore Talbot effect is feasible and can achieve high measurement accuracy and resolution.Combined with the photoelectric autocollimator,this method can effectively achieve the object space attitude measurement.