Fig. 1. 3D vibration measurement system based on monocular vision. (a) Diagram of measurement system; (b) designed composite feature pattern

Fig. 2. Processing steps of composite feature pattern

Fig. 3. Measurement principle of z-axis displacement

Fig. 4. Measurement principle of x-axis and y-axis displacements

Fig. 5. Comparison of z-axis vibration displacement calculated by FFT and SCCM. (a) Amplitude of 15 mm; (b) amplitude of 0.25 mm

Fig. 6. Relationship between image signal-to-noise ratio and displacement standard deviation

Fig. 7. Effect of resolution on measurement performance. (a) x-axis displacement;(b) y-axis displacement; (c) z-axis displacement

Fig. 8. Effect of resolution on actual measurement performance of vision system. (a) x-axis displacement; (b) y-axis displacement; (c) z-axis displacement

Fig. 9. Measurement system

Fig. 10. Actual measurement error curves of measuring system. (a)--(c) Error curves of x-axis, y-axis, and z-axis obtained by barycenter algorithm; (d)--(f) error curves of x-axis, y-axis, and z-axis obtained by Hough transform circle detection algorithm

Fig. 11. Measurement results of 3D vibration of cantilever beam. (a) 3D displacement trajectories measured by barycenter algorithm; (b)--(d) vibration curves of x-axis, y-axis, and z-axis measured by barycenter algorithm; (e)--(g) vibration curves of x-axis, y-axis, and z-axis measured by Hough transform circle detection algorithm

Table 1. Actual measurement errors of barycenter algorithm and Hough transform circle detection algorithm μm