A NOVEL ULTRA-LOW-FREQUENCY MICRO-VIBRATION CALIBRATION METHOD BASED ON VIRTUAL PENDULUM MOTION TRAJECTORIES OF THE STEWART PLATFORM

Micro-acceleration generation during ultra-low-frequency micro-vibration calibration is a sensitive issue. There are issues of traditional pendulum tables being unable to change the pendulum radius and direction to produce micro-accelerations of different magnitudes, and the line shakers having a low signal-to-noise ratio when the vibration amplitude is the same as that of the pendulum tables. Therefore, a novel ultra-low-frequency micro-vibration calibration method is proposed to solve the above issues based on virtual pendulum motion trajectories of the Stewart platform. The micro-accelerations of 10-5 - 5 to 10-3 - 3 m/s2 2 can be generated by the trajectories with the radius of up to 12 m, the displacement amplitudes of up to 11.636 mm and the frequencies between 0.01 and 0.1 Hz. In the virtual pendulum motion, the maximum acceleration can be 2481 times greater than the acceleration of linear motion at the same frequency and displacement amplitude. In a comparison experiment with the current rotating platform, the maximum relative deviation of sensitivity amplitude calibration for pendulum motion around the x- and y-axis based on the Stewart platform are 0.411% and 0.295% respectively. The above results demonstrate the validity and reliability of this kind of method.