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.
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.
Phase response is an essential parameter of vibration sensors in primary vibration calibration, heterodyne interferometer was usually used to obtain this parameter. To reduce sampling rate of heterodyne interferometer signal and sampling number, analog mixer and lowpass filter are used to down-convert the interferometer signal. However, the using of analog devices will introduce additional phase delay for the measurement of the phase response, it leads to the measurement by the calibration is unreliable. A novel correction of phase delay method was proposed to precisely measure the phase response of the vibration sensors. Experiment results show the performance of the proposed correction method.
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