A soft 6-axis active vibration isolator
Contents
- Tags
- Stewart Platforms, Vibration Isolation
- Reference
- (Spanos {\it et al.}, 1995)
- Author(s)
- Spanos, J., Rahman, Z., & Blackwood, G.
- Year
- 1995
Stewart Platform (Figure 1):
- Voice Coil
- Flexible joints (cross-blades)
- Force Sensors
- Cubic Configuration
Figure 1: Stewart Platform
Total mass of the paylaod: 30kg Center of gravity is 9cm above the geometry center of the mount (cube’s center?).
Limitation of the Decentralized Force Feedback:
- high frequency pole due to internal resonances of the struts
- low frequency zero due to the rotational stiffness of the flexible joints
After redesign of the struts:
- high frequency pole at 4.7kHz
- low frequency zero at 2.6Hz but non-minimum phase (not explained). Small viscous damping material in the cross blade flexures made the zero minimum phase again.
Figure 2: Experimentally measured transfer function from voice coil drive voltage to collocated load cell output voltage
The controller used consisted of:
- second order low pass filter to gain stabilize the plant at high frequencies and provide steep roll-off
- first order lead filter to provide adequate phase margin at the high frequency crossover
- first order lag filter to provide adequate phase margin at the low frequency crossover
- a first order high pass filter to attenuate the excess gain resulting from the low frequency zero
The results in terms of transmissibility are shown in Figure 3.
Figure 3: Experimentally measured Frobenius norm of the 6-axis transmissibility
Bibliography
Spanos, J., Rahman, Z., & Blackwood, G., A soft 6-axis active vibration isolator, In , Proceedings of 1995 American Control Conference - ACC'95 (pp. ) (1995). : . ↩