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Table of Contents

-
+

You can find below the document of:

@@ -57,13 +57,13 @@ We would like to characterize the encoder measurement system. In particular, we would like to measure:

-
-

1 Encoder Model

+
+

1 Encoder Model

The Encoder is characterized by its dynamics \(G_m(s)\) from the “true” displacement \(y\) to measured displacement \(y_m\). @@ -75,20 +75,62 @@ It is also characterized by its measurement noise \(n\) that can be described by

-The model of the encoder is shown in Figure 1. +The model of the encoder is shown in Figure 1.

-
+

encoder-model-schematic.png

Figure 1: Model of the Encoder

+ + + + + +++ ++ + + + + + + + + + + + + + + + + + + + + + + +
Table 1: Characteristics of the Vionic Encoder
CharacteristicsManual
Resolution2.5nm
Sub-Divisional Error\(< \pm 15\,nm\)
Bandwidth> 50 kHz
+ + + +
+

vionic_expected_noise.png +

+

Figure 2: Expected interpolation errors for the Vionic Encoder

+
-
-

2 Test-Bench Description

+ +
+

2 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. @@ -97,23 +139,55 @@ 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 interferometer or capacitive sensor should work fine. An actuator should also be there so impose a displacement.

+ +

+One idea is to use the test-bench shown in Figure 3. +

+ +

+The APA300ML is used to excite the mass in a broad bandwidth. +The motion is measured at the same time by the Vionic Encoder and by an interferometer (most likely an Attocube). +

+ +

+As the interferometer has a very large bandwidth, we should be able to estimate the bandwidth of the encoder is it is less than the Nyquist frequency (~ 5kHz). +

+ + +
+

test_bench_encoder_calibration.png +

+

Figure 3: Schematic of the test bench

+
+ +

+To measure the noise of the sensor, we can also simply measure the output signal when the relative motion between the encoder and the ruler is null. +This can be done by clamping the two as done in the mounting strut tool (Figure 4). +

+ + +
+

test_bench_measure_noise.png +

+

Figure 4: Mounting Strut test bench as a clamping method to measure the encoder noise.

+
-
-

3 Measurement procedure

+
+

3 Measurement procedure

-
-

4 Measurement Results

+
+

4 Measurement Results

Author: Dehaeze Thomas

-

Created: 2020-12-16 mer. 14:07

+

Created: 2020-12-17 jeu. 14:54

diff --git a/index.org b/index.org index f878e6c..48c3e1a 100644 --- a/index.org +++ b/index.org @@ -51,9 +51,9 @@ You can find below the document of: 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 +- Bandwidth of the sensor +- Linearity of the sensor * Encoder Model The Encoder is characterized by its dynamics $G_m(s)$ from the "true" displacement $y$ to measured displacement $y_m$. @@ -85,15 +85,50 @@ The model of the encoder is shown in Figure [[fig:encoder-model-schematic]]. #+RESULTS: [[file:figs/encoder-model-schematic.png]] + +#+name: tab:vionic_characteristics_manual +#+caption: Characteristics of the Vionic Encoder +#+attr_latex: :environment tabularx :width \linewidth :align lXX +#+attr_latex: :center t :booktabs t :float t +| *Characteristics* | *Manual* | +|----------------------+----------------| +| Resolution | 2.5nm | +| Sub-Divisional Error | $< \pm 15\,nm$ | +| Bandwidth | > 50 kHz | + + +#+name: fig:vionic_expected_noise +#+caption: Expected interpolation errors for the Vionic Encoder +[[file:./figs/vionic_expected_noise.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 interferometer or capacitive sensor should work fine. An actuator should also be there so impose a displacement. +One idea is to use the test-bench shown in Figure [[fig:test_bench_encoder_calibration]]. + +The APA300ML is used to excite the mass in a broad bandwidth. +The motion is measured at the same time by the Vionic Encoder and by an interferometer (most likely an Attocube). + +As the interferometer has a very large bandwidth, we should be able to estimate the bandwidth of the encoder is it is less than the Nyquist frequency (~ 5kHz). + +#+name: fig:test_bench_encoder_calibration +#+caption: Schematic of the test bench +[[file:figs/test_bench_encoder_calibration.png]] + +To measure the noise of the sensor, we can also simply measure the output signal when the relative motion between the encoder and the ruler is null. +This can be done by clamping the two as done in the mounting strut tool (Figure [[fig:test_bench_measure_noise]]). + +#+name: fig:test_bench_measure_noise +#+caption: Mounting Strut test bench as a clamping method to measure the encoder noise. +[[file:figs/test_bench_measure_noise.png]] + * Measurement procedure * Measurement Results