2.3 KiB
+++ title = "A soft 6-axis active vibration isolator" author = ["Thomas Dehaeze"] draft = false +++
- Tags
- [Stewart Platforms]({{< relref "stewart_platforms" >}}), [Vibration Isolation]({{< relref "vibration_isolation" >}})
- Reference
- (Spanos, Rahman, and Blackwood 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 src="/ox-hugo/spanos95_stewart_platform.png" caption="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 src="/ox-hugo/spanos95_iff_plant.png" caption="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 src="/ox-hugo/spanos95_results.png" caption="Figure 3: Experimentally measured Frobenius norm of the 6-axis transmissibility" >}}
Bibliography
Spanos, J., Z. Rahman, and G. Blackwood. 1995. “A Soft 6-Axis Active Vibration Isolator.” In Proceedings of 1995 American Control Conference - ACC’95, nil. https://doi.org/10.1109/acc.1995.529280.