Motion Analysis And Vibration Measurement Based On Actively Blurred Image Sequence

Vision-based measurements of motion and vibration are widely used in manufacturing, automation and medical field. In several industrial fields such as dynamic behavior testing of electromechanical system and visual servo, the velocity of the motion or the vibrational frequency are usually higher than those in ordinary fields. Therefore, measurements of high-speed motion and high-frequency vibration become important aspects for motion analysis and vibration measurement. This paper is focused on some basic issues in high-speed motion analysis and high-frequency vibration, such as the acquisition and the modeling of actively blurred image sequence, 2D high-speed translational motion analysis, in-plane translational vibration measurement, high-speed rotation and angular vibration measurement and high-speed out-of-plane motion estimation, and so on, for deep research.1. Images tend to be blurred when the motion velocity or the vibrational frequency of the object is large. The so-called motion blur is usually treated as image degradation. But from the"motion-from-blur"mechanism existing in biological vision, we infer that motion blur is an important cue for motion analysis and can be actively used in motion and vibration measurements. Furthermore, according to the theory of active vision, this paper considered that the degree of the motion blur can be controlled by the vision system, and designed an acquisition system of actively blurred image sequence. This image acquisition system can predict and control the exposure time and sampling period according to the degree of motion blur and saturation of previous images. Hence, it can acquire image sequences carrying sufficient motion blur information without image saturation. Considering the characteristics of the image acquisition system, we proposed the general model for the actively blurred image sequence, and analyzed variant models for different motions such as in-plane translation and rotation and out-of-plane motion.2. High-speed translational motion is a simple but very important form among high-speed motion and high-frequency vibration. Block matching, which is widely used in translational motion analysis breaks down when the high velocity causes motion blur in image. According to the"motion-from-blur"and spatio-temporal integration mechanisms existing in biological motion perception, this paper presented a method for estimating 2D high-speed translational motion based on actively blurred images and geometric moments. This approach relies on geometric moments to achieve spatial integration, derives a theorem for the relationship between the geometric moments of the motion blurred image and the translational motion, and extracts the motion blur information of the images to realize motion analysis. The proposed algorithm can calculate the velocity and acceleration of the motion from only 2 successive frames of motion blurred images while existing approaches estimate an accelerated motion from at least 3 images.3. Vibration measurement is very important for testing of mechanical system, especially for the testing of micromechanical system. General techniques employ stroboscopic illumination to"freeze"the vibrating object and acquire unblurred images for vibration measurement. And existing approaches based on motion blurred images only dealt with high-frequency vibration which period was much shorter than the exposure time, and did not mention the low-frequency cases which period was longer than the exposure time (Here note that the low-frequency does not really mean the vibrational frequency is low). This paper laid emphasis on analyzing the difference between the blurred images with low- and high-frequency vibrations and non-vibrational translation, and derived the algorithms for measuring in-plane vibration with low- and high-frequencies, respectively, based on the high-speed non-vibrational translation analysis method mentioned above. This method requires only one motion blurred image and an unblurred image or two successive frames of blurred images to calculate the parameters of the low-frequency vibration as well as the amplitude and direction of the high-frequency vibration. With the existence of high-level noise, we employed data fusion on a short sequence of motion blurred images to improve accuracy. Further, this paper designed a method for controlling the setting of the vision system to improve the adaptability of this algorithm when the frequency was unknown.4. Monoaxial rotation and angular vibration exist in many industrial applications. This paper proposed two algorithms based on motion blurred image sequence and geometric moments for measuring monoaxial rotation and angular vibration, according to the Cartesian coordinate system and polar coordinates, respectively. The one is based on the Cartesian model of the motion blurred image. It derives the theorem for the relationship between the geometric moments of the motion blurred images with Cartesian coordinates and the circular motion, then extracts the motion blur information on the image plane, and calculates the parameters of monoaxial rotation and angular vibration. The other maps the algorithms for measuring translational motion and vibration to the polar plane to realize measurements of the monoaxial rotation and the angular vibration. Compared with existing techniques for measuring monoaxial rotation the angular vibration, the proposed algorithms can measure circular motion with large angular displacement within the exposure time.5. The most widely used techniques for out-of-plane motion measurement are Laser Doppler Velocimetry (LDV), Electronic Speckle Pattern Interferometry (ESPI) and Shearography. They all need additional laser or other light source and interferential path. By analyzing the image blur caused by out-of-plane motion, this paper proposed the motion blurred image model for out-of-plane motion, which was combined with defocus blur and motion blur. We derived the theorem for the relationship between the out-of-plane motion blurred image and the out-of-plane, and then extracted the information of the out-of-plane motion to analyze of the out-of-plane motion. The proposed method can measure the parameters of the out-of-plane motion correctly.