digital-brain/content/article/ito16_compar_class_high_precis_actuat.md

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title = "Comparison and classification of high-precision actuators based on stiffness influencing vibration isolation"
author = ["Thomas Dehaeze"]
draft = false
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### Backlinks {#backlinks}
- [Actuators]({{< relref "actuators" >}})
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Tags
: [Vibration Isolation]({{< relref "vibration_isolation" >}}), [Actuators]({{< relref "actuators" >}})
Reference
: ([Ito and Schitter 2016](#orga31805f))
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Author(s)
: Ito, S., & Schitter, G.
Year
: 2016
## Classification of high-precision actuators {#classification-of-high-precision-actuators}
<div class="table-caption">
<span class="table-number">Table 1</span>:
Zero/Low and High stiffness actuators
</div>
| **Categories** | **Pros** | **Cons** |
|----------------|---------------------------|-----------------------------|
| Zero stiffness | No vibration transmission | Large and Heavy |
| Low stiffness | High vibration isolation | Typically for low load |
| High Stiffness | High control bandwidth | High vibration transmission |
## Time Delay of Piezoelectric Electronics {#time-delay-of-piezoelectric-electronics}
In this paper, the piezoelectric actuator/electronics adds a time delay which is much higher than the time delay added by the voice coil/electronics.
## Definition of low-stiffness and high-stiffness actuator {#definition-of-low-stiffness-and-high-stiffness-actuator}
- **Low Stiffness** actuator is defined as the ones where the transmissibility stays below 0dB at all frequency
- **High Stiffness** actuator is defined as the ones where the transmissibility goes above 0dB at some frequency
<a id="org0fdae5f"></a>
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{{< figure src="/ox-hugo/ito16_low_high_stiffness_actuators.png" caption="Figure 1: Definition of low-stiffness and high-stiffness actuator" >}}
## Low-Stiffness / High-Stiffness characteristics {#low-stiffness-high-stiffness-characteristics}
- The low stiffness actuators achieve smooth transition from active isolation to passive isolation.
- The high stiffness actuators can have a gap between the passive and active isolation vibration where the vibrations are amplified in a certain frequency band.
## Controller Design {#controller-design}
<a id="org6565e90"></a>
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{{< figure src="/ox-hugo/ito16_transmissibility.png" caption="Figure 2: Obtained transmissibility" >}}
## Discussion {#discussion}
The stiffness requirement for low-stiffness actuators can be rephrased in the frequency domain as: "the cross-over frequency of the sensitivity function of the feedback system must be larger than \\(\sqrt{2} \omega\_r\\) with \\(\omega\_r\\) is the resonant frequency of the uncontrolled system".
In practice, this is difficult to achieve with piezoelectric actuators as their first resonant frequency \\(\omega\_r\\) is **too close to other resonant frequencies to ensure close-loop stability**.
In contrast, the frequency band between the first and the other resonances of Lorentz actuators can be broad by design making them more suitable to construct a low-stiffness actuators.
## Bibliography {#bibliography}
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<a id="orga31805f"></a>Ito, Shingo, and Georg Schitter. 2016. “Comparison and Classification of High-Precision Actuators Based on Stiffness Influencing Vibration Isolation.” _IEEE/ASME Transactions on Mechatronics_ 21 (2):116978. <https://doi.org/10.1109/tmech.2015.2478658>.