+++
title = "A concept of active mount for space applications"
author = ["Thomas Dehaeze"]
draft = false
+++

Tags
: [Active Damping]({{< relref "active_damping" >}})

Reference
: ([Souleille et al. 2018](#orgaa465de))

Author(s)
: Souleille, A., Lampert, T., Lafarga, V., Hellegouarch, S., Rondineau, A., Rodrigues, Gonccalo, & Collette, C.

Year
: 2018

This article discusses the use of Integral Force Feedback with amplified piezoelectric stack actuators.

> In the proposed configuration, it can also be noticed by the softening effect inherent to force control is limited by the metallic suspension.


## Single degree-of-freedom isolator {#single-degree-of-freedom-isolator}

Figure [1](#org024c118) shows a picture of the amplified piezoelectric stack.
The piezoelectric actuator is divided into two parts: one is used as an actuator, and the other one is used as a force sensor.

<a id="org024c118"></a>

{{< figure src="/ox-hugo/souleille18_model_piezo.png" caption="Figure 1: Picture of an APA100M from Cedrat Technologies. Simplified model of a one DoF payload mounted on such isolator" >}}

<div class="table-caption">
  <span class="table-number">Table 1</span>:
  Parameters used for the model of the APA 100M
</div>

|            | Value                 | Meaning                                                        |
|------------|-----------------------|----------------------------------------------------------------|
| \\(m\\)    | \\(1\,[kg]\\)         | Payload mass                                                   |
| \\(k\_e\\) | \\(4.8\,[N/\mu m]\\)  | Stiffness used to adjust the pole of the isolator              |
| \\(k\_1\\) | \\(0.96\,[N/\mu m]\\) | Stiffness of the metallic suspension when the stack is removed |
| \\(k\_a\\) | \\(65\,[N/\mu m]\\)   | Stiffness of the actuator                                      |
| \\(c\_1\\) | \\(10\,[N/(m/s)]\\)   | Added viscous damping                                          |

The dynamic equation of the system is:

\begin{equation}
  m \ddot{x}\_1 = \left( k\_1 + \frac{k\_ek\_a}{k\_e + k\_a} \right) ( w - x\_1) + c\_1 (\dot{w} - \dot{x}\_1) + F + \left( \frac{k\_e}{k\_e + k\_a} \right)f
\end{equation}

The expression of the force measured by the force sensor is:

\begin{equation}
  F\_s = \left( -\frac{k\_e k\_a}{k\_e + k\_a} \right) x\_1 + \left( \frac{k\_e k\_a}{k\_e + k\_a} \right) w + \left( \frac{k\_e}{k\_e + k\_a} \right) f
\end{equation}

and the control force is given by:

\begin{equation}
  f = F\_s G(s) = F\_s \frac{g}{s}
\end{equation}

The effect of the controller are shown in Figure [2](#orge334eeb):

-   the resonance peak is almost critically damped
-   the passive isolation \\(\frac{x\_1}{w}\\) is not degraded at high frequencies
-   the degradation of the compliance \\(\frac{x\_1}{F}\\) induced by feedback is limited at \\(\frac{1}{k\_1}\\)
-   the fraction of the force transmitted to the payload that is measured by the force sensor is reduced at low frequencies

<a id="orge334eeb"></a>

{{< figure src="/ox-hugo/souleille18_tf_iff_result.png" caption="Figure 2: Matrix of transfer functions from input (w, f, F) to output (Fs, x1) in open loop (blue curves) and closed loop (dashed red curves)" >}}

<a id="orgcccf310"></a>

{{< figure src="/ox-hugo/souleille18_root_locus.png" caption="Figure 3: Single DoF system. Comparison between the theoretical (solid curve) and the experimental (crosses) root-locus" >}}


## Flexible payload mounted on three isolators {#flexible-payload-mounted-on-three-isolators}

A heavy payload is mounted on a set of three isolators (Figure [4](#orga53fff7)).
The payload consists of two  masses, connected through flexible blades such that the flexible resonance of the payload in the vertical direction is around 65Hz.

<a id="orga53fff7"></a>

{{< figure src="/ox-hugo/souleille18_setup_flexible_payload.png" caption="Figure 4: Right: picture of the experimental setup. It consists of a flexible payload mounted on a set of three isolators. Left: simplified sketch of the setup, showing only the vertical direction" >}}

As shown in Figure [5](#orge070a1d), both the suspension modes and the flexible modes of the payload can be critically damped.

<a id="orge070a1d"></a>

{{< figure src="/ox-hugo/souleille18_result_damping_transmissibility.png" caption="Figure 5: Transmissibility between the table top \\(w\\) and \\(m\_1\\)" >}}


## Bibliography {#bibliography}

<a id="orgaa465de"></a>Souleille, Adrien, Thibault Lampert, V Lafarga, Sylvain Hellegouarch, Alan Rondineau, Gonçalo Rodrigues, and Christophe Collette. 2018. “A Concept of Active Mount for Space Applications.” _CEAS Space Journal_ 10 (2). Springer:157–65.
