65 lines
2.3 KiB
Markdown
65 lines
2.3 KiB
Markdown
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title = "A soft 6-axis active vibration isolator"
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author = ["Thomas Dehaeze"]
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draft = false
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Tags
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: [Stewart Platforms]({{< relref "stewart_platforms" >}}), [Vibration Isolation]({{< relref "vibration_isolation" >}})
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Reference
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: ([Spanos, Rahman, and Blackwood 1995](#orgad76892))
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Author(s)
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: Spanos, J., Rahman, Z., & Blackwood, G.
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Year
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: 1995
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**Stewart Platform** (Figure [1](#org6d10ec2)):
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- Voice Coil
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- Flexible joints (cross-blades)
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- Force Sensors
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- Cubic Configuration
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<a id="org6d10ec2"></a>
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{{< figure src="/ox-hugo/spanos95_stewart_platform.png" caption="Figure 1: Stewart Platform" >}}
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Total mass of the paylaod: 30kg
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Center of gravity is 9cm above the geometry center of the mount (cube's center?).
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Limitation of the **Decentralized Force Feedback**:
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- high frequency pole due to internal resonances of the struts
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- low frequency zero due to the rotational stiffness of the flexible joints
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After redesign of the struts:
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- high frequency pole at 4.7kHz
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- low frequency zero at 2.6Hz but non-minimum phase (not explained).
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Small viscous damping material in the cross blade flexures made the zero minimum phase again.
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<a id="orgfef5d56"></a>
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{{< 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" >}}
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The controller used consisted of:
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- second order low pass filter to gain stabilize the plant at high frequencies and provide steep roll-off
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- first order lead filter to provide adequate phase margin at the high frequency crossover
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- first order lag filter to provide adequate phase margin at the low frequency crossover
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- a first order high pass filter to attenuate the excess gain resulting from the low frequency zero
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The results in terms of transmissibility are shown in Figure [3](#orgec62915).
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<a id="orgec62915"></a>
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{{< figure src="/ox-hugo/spanos95_results.png" caption="Figure 3: Experimentally measured Frobenius norm of the 6-axis transmissibility" >}}
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## Bibliography {#bibliography}
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<a id="orgad76892"></a>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>.
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