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< title > Encoder Renishaw Vionic - Test Bench< / title >
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< meta name = "author" content = "Dehaeze Thomas" / >
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< h1 class = "title" > Encoder Renishaw Vionic - Test Bench< / h1 >
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< h2 > Table of Contents< / h2 >
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< li > < a href = "#org55157ef" > 1. Encoder Model< / a > < / li >
< li > < a href = "#org8ef40ec" > 2. Test-Bench Description< / a > < / li >
< li > < a href = "#orgce223ed" > 3. Measurement procedure< / a > < / li >
< li > < a href = "#org51852cb" > 4. Measurement Results< / a > < / li >
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< p >
You can find below the document of:
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< li > < a href = "doc/L-9517-9678-05-A_Data_sheet_VIONiC_series_en.pdf" > Vionic Encoder< / a > < / li >
< li > < a href = "doc/L-9517-9862-01-C_Data_sheet_RKLC_EN.pdf" > Linear Scale< / a > < / li >
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We would like to characterize the encoder measurement system.
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In particular, we would like to measure:
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< li > Power Spectral Density of the measurement noise< / li >
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< li > Bandwidth of the sensor< / li >
< li > Linearity of the sensor< / li >
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< p > < img src = "figs/encoder_vionic.png" alt = "encoder_vionic.png" / >
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< p > < span class = "figure-number" > Figure 1: < / span > Picture of the Vionic Encoder< / p >
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< h2 id = "org55157ef" > < span class = "section-number-2" > 1< / span > Encoder Model< / h2 >
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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.
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It is also characterized by its measurement noise \(n\) that can be described by its Power Spectral Density (PSD).
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The model of the encoder is shown in Figure < a href = "#org2d59f14" > 2< / a > .
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< p > < img src = "figs/encoder-model-schematic.png" alt = "encoder-model-schematic.png" / >
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< p > < span class = "figure-number" > Figure 2: < / span > Model of the Encoder< / p >
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< caption class = "t-above" > < span class = "table-number" > Table 1:< / span > Characteristics of the Vionic Encoder< / caption >
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< th scope = "col" class = "org-left" > < b > Characteristics< / b > < / th >
< th scope = "col" class = "org-left" > < b > Manual< / b > < / th >
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< td class = "org-left" > Resolution< / td >
< td class = "org-left" > 2.5nm< / td >
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< td class = "org-left" > Sub-Divisional Error< / td >
< td class = "org-left" > \(< \pm 15\,nm\)< / td >
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< td class = "org-left" > Bandwidth< / td >
< td class = "org-left" > > 50 kHz< / td >
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< div id = "orgb8bf3d5" class = "figure" >
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< p > < img src = "./figs/vionic_expected_noise.png" alt = "vionic_expected_noise.png" / >
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< p > < span class = "figure-number" > Figure 3: < / span > Expected interpolation errors for the Vionic Encoder< / p >
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< h2 id = "org8ef40ec" > < span class = "section-number-2" > 2< / span > Test-Bench Description< / h2 >
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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 \(n\).
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In order to measure the linearity, we have to compare the measured displacement with a reference sensor with a known linearity.
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An interferometer or capacitive sensor should work fine.
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An actuator should also be there so impose a displacement.
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< p >
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One idea is to use the test-bench shown in Figure < a href = "#org1fd5a94" > 4< / a > .
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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).
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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).
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< div id = "org1fd5a94" class = "figure" >
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< p > < img src = "figs/test_bench_encoder_calibration.png" alt = "test_bench_encoder_calibration.png" / >
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< p > < span class = "figure-number" > Figure 4: < / span > Schematic of the test bench< / p >
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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.
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This can be done by clamping the two as done in the mounting strut tool (Figure < a href = "#orgab0ed8d" > 5< / a > ).
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< div id = "orgab0ed8d" class = "figure" >
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< p > < img src = "figs/test_bench_measure_noise.png" alt = "test_bench_measure_noise.png" / >
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< p > < span class = "figure-number" > Figure 5: < / span > Mounting Strut test bench as a clamping method to measure the encoder noise.< / p >
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< h2 id = "orgce223ed" > < span class = "section-number-2" > 3< / span > Measurement procedure< / h2 >
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< h2 id = "org51852cb" > < span class = "section-number-2" > 4< / span > Measurement Results< / h2 >
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< div id = "postamble" class = "status" >
< p class = "author" > Author: Dehaeze Thomas< / p >
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< p class = "date" > Created: 2021-01-04 lun. 11:44< / p >
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