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Velocity and Location Information from Onboard Vibration Measurements of Rail Vehicles
Oliver Heirich, Alexander Steingass, Andreas Lehner, Thomas Strang
> Oliver Heirich > 2013 www.DLR.de • Chart 1
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Vehicle Vibrations
- Vehicle vibrations: oscillatory motion of many different frequencies
- Often undesired effect of a moving vehicle: “NVH engineering” in vehicle design
- Desired vibrations - Feedback control - Mechanical fault diagnostics - Engine speed estimation - Terrain classification based on wheel vibrations (Robotics) - Vehicle speed measurement by driving over a street bumper
We propose: Using vibration information for velocity and location computation
www.DLR.de • Chart 2 > Oliver Heirich > 2013
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Measurement setup on over-head rack
www.DLR.de • Chart 3 > Oliver Heirich > 2013
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Data recording experiment
www.DLR.de • Chart 4 > Oliver Heirich > 2013
IMU GPS
Munich Lenggries
5 km
Lenggries
Munich
Spectrogram of Z acceleration
Train Speed (GPS)
Holzkirchen
Osterhofen Alps
2x 2x
4x 5x
3x
2x
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Spectrogram: speed over Z-Acceleration (f) - data sequences of 1024 samples: 10,24s at 100Hz - power spectral density (PSD) of each sequence - sorted into speed bins by mean GNSS speed of sequence - 150 bins of 1km/h width, multiple PSDs in one bin are averaged
www.DLR.de • Chart 5 > Oliver Heirich > 2013
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Vehicle vibration model
www.DLR.de • Chart 6 > Oliver Heirich > 2013
train datasheet: D=4.7 m dnew=0.84 m dEOL=0.78 m
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Application: speed measurement
www.DLR.de • Chart 7 > Oliver Heirich > 2013
hypothesis:
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Speed measurement processing
1. Sequence of data (e.g. 100 samples)
2. Multi-Notch filter: removal of from speed independent vibrations (horizontal lines)
3. 150 defined speed hypotheses from 0 to 150 km/h (1 km/h width):
4. Computation of multiple band pass filters for each speed hypothesis
5. Compute signal energy of every speed hypothesis:
6. Search the maximum
www.DLR.de • Chart 8 > Oliver Heirich > 2013
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Speed measurement results
www.DLR.de • Chart 9 > Oliver Heirich > 2013
true speed (GPS): 101 km/h
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Wheel radius measurement - Now: speed is known (odometer / GPS) - Application: Monitoring the wheels - Train’s datasheet: 0.78 m for used wheels, 0.84m for new wheels
- first harmonic f1 at 150km/h: new wheel 15.8Hz, end-of-life wheel: 17.0 Hz
- Here: “snapshot in time”
www.DLR.de • Chart 10 > Oliver Heirich > 2013
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Application: Localization
- Signal preprocessing - transformation from time to spatial samples (known speed) by interpolation:
- Matched filter: 2 Dirac-Delta functions with distance of wheelbase D (4.7m)
- Removing the phase information (better S/N): computing the signal envelope:
www.DLR.de • Chart 11 > Oliver Heirich > 2013
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Localization Processing 1. Prior track map recording:
2. Correlation of hypothetical signal (from map) and measured signal:
3. Localization computation - Track: search for the hypothesis with the highest correlation
- Track position: peak position
www.DLR.de • Chart 12 > Oliver Heirich > 2013
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Localization results
www.DLR.de • Chart 13 > Oliver Heirich > 2013
wrong hypothesis
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Localization results
www.DLR.de • Chart 14 > Oliver Heirich > 2013
Snapshot in time, no prior knowledge of past position !
wrong hypothesis correct hypothesis
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Localization results
www.DLR.de • Chart 15 > Oliver Heirich > 2013
Snapshot in time, no prior knowledge of past position !
wrong hypothesis correct hypothesis Zoom
GPS reference
estimated location
13m
speed: 27 m/s
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Key benefits
- independency from other measurements (e.g. GNSS, low frequent IMU, Camera)
- absolute vehicle speed and localization for track-selective localization
- augment strapdown navigation approaches, IMU bias observation
- add-on to navigation systems: no additional hardware required, low cost approach
- low installation complexity & high installation flexibility
www.DLR.de • Chart 16 > Oliver Heirich > 2013
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Approach of vibration navigation
- Approach by accident - over-head rack measurements - first approach: snap-shot speed/location estimation
- Future: Measurement improvements - enhanced pre-filter - optimized sensor placing - higher sampling frequency
- Future: Algorithmic improvements (FUSION’14+): - Advanced algorithms for speed estimation - Tracking of the speed hypothesis and position - Multisensory fusion (GPS, IMU, Vibration method)
www.DLR.de • Chart 17 > Oliver Heirich > 2013
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Summary and conclusions
- Vertical mounted acceleration sensor shows horizontal speed dependency in frequency domain
- We presented an approach and a proof of concept for: - absolute speed computation - wheel size monitoring - absolute, track selective location computation
- Matched filter (wheelbase) is the key for using vibrations for localization
- It was possible to compute speed and location from a over-head rack
mounted sensor
www.DLR.de • Chart 18 > Oliver Heirich > 2013
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Velocity and Location Information from Onboard Vibration Measurements of Rail Vehicles
Oliver Heirich, Alexander Steingass, Andreas Lehner, Thomas Strang
> Oliver Heirich > 2013 www.DLR.de • Chart 19
„One man‘s noise is another man‘s data“, B. Parkinson (GPS chief architect)