detection of vibrations : experiment with an epilator · epilator signal response uninterrupted...
TRANSCRIPT
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DETECTION OF VIBRATIONS : EXPERIMENT WITH AN EPILATOR
Project : limitations of the e-puck accelerometer to detect earthquakes
supervisor : Bahar Haghighat Valérie Berclaz Karine Sarrasin
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PLAN
Introduction
Principe of an accelerometer
Approach of the project
Experiment
Epilator
Cell phone
Conclusion
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INTRODUCTION
Goal of the project : recognize a vibration of a certain frequency by turning the LED’s on and blinking
Type of vibrations
Shocks : pulsed acceleration
Longer vibration : can be determined by the displacement, the velocity and the acceleration of a given point on a structure
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PRINCIPE OF AN ACCELEROMETER
What is an accelerometer ?
Transform mechanical motion into an electrical signal
Several types used : piezoresistive, piezoelectric, capacitive….
Applications of accelerometer
Aircraft
Digital camera, cell phone
Laptop
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PRINCIPE OF AN ACCELEROMETER
On the e-puck
MMA7260Q : capacitive micromachined accelerometer
Different sensitivities : 1.5g, 2g, 4g, 6g
In our case : 1.5g
Figure 1 : Electrical schema of a capacitive accelerometer
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APPROACH OF THE PROJECT
First try : with a cell phone (Xperia Sony Ericsson) but
Not always the same response (depending on the battery of the phone)
Low amplitudes
Second try : with an epilator
Always the same response
Bigger amplitudes
Tests
With another cell phone
By shaking the e-puck
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EXPERIMENT
Source of vibration : an epilator
Setup
Figure 2 and 3 : experiment’s setup
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EPILATOR
Signal response
Uninterrupted signal
az values : around 800 (due to the gravity)
Figure 4 : signal of the epilator Figure 5 : Fourier transform of the z coordinate
Fourier transform
Contains a lot of frequency
Retained frequency : 26 Hz
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CHOICE OF THE FILTER
Figure 6 : Design of the filter
Figure 7 : Attenuation of the amplitude Figure 8 : Fourier transform of the filtered az
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RANGE OF DETECTION
Method : power spectral density for each direction
where a is the acceleration value and k is the filter order.
Final range :
PSD=∑n=0
n=i∣an∣
2
k
xmin xmax ymin ymax zmin zmax
0 70 40 100 0 20
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VIDEO
Response of the e-puck when it is on the epilator
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CELL PHONE
Smaller range of amplitude and periodic signal
Accelerations in z coordinate are well filtered
Figure 9 : Signal of the cell phone Figure 10 : e-puck on a HTC Wildfire S A510e
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CELL PHONE
Frequency of the cell phone : around 18 Hz
After filtering : reduction of the peak
Figure 11 : Fourier transform of az Figure 12 : Fourier transform of the filtered az
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Conclusion
E-puck detects the desired frequency
Empirical approach : experiments with different devices
Improvements:
Better filtering
Improve efficiency of the threshold
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Thank you for your attention!
Questions?
Good times :