test-bench-vionic/index.org

#+TITLE: Encoder Renishaw Vionic - Test Bench
:DRAWER:
#+LANGUAGE: en
#+EMAIL: dehaeze.thomas@gmail.com
#+AUTHOR: Dehaeze Thomas

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* Introduction                                                        :ignore:

#+begin_note
You can find below the document of:
- [[file:doc/L-9517-9678-05-A_Data_sheet_VIONiC_series_en.pdf][Vionic Encoder]]
- [[file:doc/L-9517-9862-01-C_Data_sheet_RKLC_EN.pdf][Linear Scale]]
#+end_note

We would like to characterize the encoder measurement system.

In particular, we would like to measure:
- Bandwidth/dynamics of the sensor
- Power Spectral Density of the measurement noise
- Linearity/resolution of the sensor

* Encoder Model
The Encoder is characterized by its dynamics $G_m(s)$ from the "true" displacement $y$ to measured displacement $y_m$.
Ideally, this dynamics is constant over a wide frequency band with very small phase drop.

It is also characterized by its measurement noise $n$ that can be described by its Power Spectral Density (PSD).

The model of the encoder is shown in Figure [[fig:encoder-model-schematic]].

#+begin_src latex :file encoder-model-schematic.pdf
  \begin{tikzpicture}
    \node[block] (G) at (0,0){$G_m(s)$};
    \node[addb, left=0.8 of G] (add){};

    \draw[<-] (add.west) -- ++(-1.0, 0) node[above right]{$y$};
    \draw[->] (add.east) -- (G.west);
    \draw[->] (G.east) -- ++(1.0, 0) node[above left]{$y_m$};
    \draw[<-] (add.north) -- ++(0, 0.6) node[below right](n){$n$};

    \begin{scope}[on background layer]
      \node[fit={(add.west|-G.south) (n.north-|G.east)}, inner sep=8pt, draw, dashed, fill=black!20!white] (P) {};
      \node[below left] at (P.north east) {Encoder};
    \end{scope}
  \end{tikzpicture}
#+end_src

#+name: fig:encoder-model-schematic
#+caption: Model of the Encoder
#+RESULTS:
[[file:figs/encoder-model-schematic.png]]

* Test-Bench Description

To measure the noise $n$ of the encoder, one can rigidly fix the head and the ruler together such that no motion should be measured.
Then, the measured signal $y_m$ corresponds to the noise $n$.

In order to measure the linearity, we have to compare the measured displacement with a reference sensor with a known linearity.
An interferometer or capacitive sensor should work.
An actuator should also be there so impose a displacement.

* Measurement procedure

* Measurement Results