Due to environmental illumination and other factors, actual shearing interference image used to measure the rotation angle contains high-frequency speckle noises. According to the characteristics of shearing interference images, a low-pass filter based on homomorphic filtering principle is selected to filter these images. The desired filtering result can be achieved by adjusting the filter parameters such as the cutoff frequency radius and the order of the filter. The Hilditch thinning algorithm is applied to extract the center of the fringes to calculate the spacing between neighbor fringes. The accuracy of the algorithm is verified by the actual and simulation experiments with the error of fringe spacing detection less than 0.01%.
Advanced low frequency vibration calibration is imperative required as the wide applications of low frequency accelerometers. Low frequency calibration is commonly realized by the Earth’s gravity method or the laser interferometry. However, affected by the limited stroke of the standard vibration shaker, the calibration precision of laser interferometry at very low frequency is usually not ideal. Although the Earth’s gravity method can avoid this low calibration precision at very low frequency, its calibration frequency usually <5 Hz due to the influence of rotator centripetal acceleration. In this paper, the Earth’s gravity method mentioned in ISO 16063-16 is improved by using an effective image feature detection method. This method detects the angel between Earth’s gravity field direction and acceleration sensitivity axis direction to improve the Earth’s gravity static calibration accuracy.
The motion measurement based on machine vision has been more and more widely used in robots, object tracking and other fields. However, the relative motion between camera and object often causes images blurred, which decreases the reliability of detection. To improve the detection accuracy of the motion-blurred images edges, a comprehensive method is proposed. By analyzing the grayscale distribution of the object images in different motion directions, we used different methods to enhance the low frequency sub-band images which were obtained by wavelet transform. The subpixel edge detection method based on cubic spline interpolation was applied to detect the edges of the blurred and enhanced images, respectively. Experimental results show that the proposed method avoids the misdetection of the blurred images edges, and obtains higher edge detection accuracy.
High-acceleration vibrations have a strong effect on parts damage and engine life in the aerospace field. Demand for high-acceleration vibration calibration devices is urgently required. In this paper, a set of resonant high-acceleration calibration system was established. This system generates high-acceleration based on the principle that the resonant beam reaches its natural frequency at the outside frequency to amplify the acceleration amplitude. Experimental results show the system can achieve accurate calibration of sensors at high-acceleration.