# A soft 6-axis active vibration isolator - My digital brain
Tags Stewart Platforms, Vibration Isolation Reference (Spanos {\it et al.}, 1995) Author(s) Spanos, J., Rahman, Z., &amp; 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&rsquo;s center?). Limitation of the Decentralized Force Feedback:
Author: — Thomas Dehaeze

# A soft 6-axis active vibration isolator

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). : . ↩