digital-brain/content/article/spanos95_soft_activ_vibrat_isolat.md

+++ 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.