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vfubelgium99
10-11-1998, 05:31 PM
Dear all,

Here is the summary of our request on accelerometers. We would like to
thank all the persons who replied (this helps a lot) and all those who
manifested their interest. This summary includes the following sections:
1. Original request
2. Problems encountered when using accelerometers
3. Summary of replies
4. Suppliers
5. References

Sincerely,

Véronique
************************************************
Veronique Feipel, PhD
Laboratory for Functional Anatomy
University of Brussels (CP 619)
808, route de Lennik
B-1070 Brussels, Belgium
Phone: ++ 32-2-555 6329
Fax: ++ 32-2-555 6378
Email: vfeipel@ulb.ac.be
Homepage: http://homepages.ulb.ac.be/~vfeipel/
************************************************
__________________________________________________ ___
1. ORIGINAL REQUEST

Dear all,

We are interested in purchasing triaxial accelerometers that we would use
for various applications in analyzing joint kinematics and dynamics. Our
applications concern the spine (cervical and lumbar kinematics in vivo),
the wrist and shoulder joint complexes. Moreover we would use them to
validate other instruments, in particular commercial and homemade
electrogoniometers.
Our requests to the biomechanics community are:
1. Has somebody experience with such devices in fields similar to ours that
he would share with us?
2. What kind of accelerometers are used? What are their specifications?
3. What kind of problems are encountered when using accelerometers in
motion analysis (such as inertia,...)?
One of the options would be the 3DM sensor (MicroStrain Inc., Burlington,
VT). Does anyone know about these sensors or has anyone used them? Is this
device valuable?
We thank all of you in advance for your help.
Sincerely,
Veronique Feipel, PhD, Patrick Salvia, Marcel Rooze, MD PhD

__________________________________________________ _______________
2. PROBLEMS ENCOUNTERED

The major problem is that it is difficult (if not impossible) to
distinguish the gravity component of acceleration from the inertial
component. One of the possible solutions is to use two accelerometers on
each segment, placed at different distances from the rotation center and
use the differential signal to derive motion parameters.

There is also a certain amount of drift when sampling over a long period of
time, but this is negligible when short sampling duration is chosen.

Vibration “noise” if existent, can be filtered out (it is usually of higher
frequency than the signal that you want to analyze).

Piezoelectric sensors mostly use a low frequency cut-off, which induces a
loss of slow motion data.

Some accelerometers are very fragile (problems have been encountered with
the Entran and Kistler ones).

__________________________________________________ ____________________
3. SUMMARY OF REPLIES

Rolf Moe-Nilssen (rolf.moe-nilssen@isf.uib.no)
has developed a portable accelerometry system (triaxial, piezoresistant)
for the analysis of the movements of the lumbar spine. He notes that the
gravity component is a limitation.

Ton van den Bogert (bogert@bme.ri.ccf.org)
has used accelerometers from Entran (model EGAX-*-10), which he has found
suitable for human motion applications. They are also very small, but
expensive.

Morris Levy (mlevy@mail.csusb.edu)
uses uniaxial accelerometers from PCB Piezotronics which we found to be of
very high quality. He moreover found that PCB has a good excellent customer
service.

Ruth Mayagoitia (R.Mayagoitia@Sheffield.ac.uk)
has built her own triaxial accelerometer by putting 3 uniaxial
accelerometers (Macrosensors - Eurosensor) on a cube. Their range is +/- 5G
and Ruth found that they work well. The main problem encountered is a small
amount of drift when used over a long period of time. Vibration “noise” can
be filtered out. Ruth also points at McRoberts, who are developing a
triaxial accelerometer, and at a company in Enschede (Gerrit Bulstra or Ed
Droog) that could make triaxial accelerometers.

Eric Sabelman (sabelman@roses.stanford.edu)
sent a very detailed reply on his experience with micro-machined silicon
piezoresistive accelerometers. Such devices are supplied by IC Sensors,
Silicon Designs, Motorola & SenSym, but none makes a triaxial one (except a
large one by Analog Devices). Eric is testing a capacitative sensor made by
Silicon Designs which gives a pulse-encoded output. The advantage of
piezoresistive sensors detect the steady-state pull of gravity (which is
not detected by piezoelectric sensors) and inertial acceleration due to the
start and stop of motion. Moreover the piezoelectric ones have a
low-frequency cutoff about 10 Hz, causing a loss of slow motion data. Due
to the gravitational component superimposed on the inertial component,
simple integration cannot be used to calculate change in position, but it
provides a continuous vertical reference. Another problem with use of
integration is gravity in the non-sensitive axis direction (1 to 2% error).
Eric uses pattern-matching, peak-detection and Fourier spectrum analytical
methods, rather than double integration, to obtain absolute position. The
sensors can also be used as tilt-meters, by filtering out signals above
about 0.2 Hz (inertial component). High-pass-filtering renders these
accelerometers equivalent to piezoelectric ones, but without need for
charge amplifiers. To compensate for gravity (to integrate only the
inertial component, Eric proposes to use place two accelerometers on the
body segment at different distances from the rotation center, and use the
differential signal to derive angular motion; or to use the integral of the
differences between two samples (if starting from a known motionless
position),which will yield velocity. According to Einstein, there is no way
to distinguish inertial from gravitational acceleration. Eric uses +/-5 G
range IC Sensors devices (in the model 3031 surface mount package). They
are small (.8 x .8 x .4 cm). They are assembled for multi-axis sampling.
Their cost is cheap ($58/channel). Eric stresses the need of regular
recalibration of the sensors. To avoid drifts due to light, he recommends
to paint the sensors in black. The VA Palo Alto Rehabilitation R&D Center
team has developed a self-contained wearable computer/recorder worn on a
belt (that are available for loan until commercial production can be
started). It allows 40 to 180 minutes of data collection, without physical
contact to a computer. Real time data analysis cannot be performed but
sampling can be achieved at 33 - 200 Hertz with 12 channels. Applications
anticipated are diagnostic use (to measure balance; biofeedback (during
therapy); and fall-prevention aid ('balance orthosis').

Peter Veltink (P.H.Veltink@el.utwente.nl)
works with accelerometers for human movement analysis. He thinks that they
have great potential. He is confronted with the problems of measuring
simultaneously actual acceleration (2nd derivative of position) as well as
gravitational acceleration, and of varying sensor orientation which in
general is not known.

Yves Blanc (blanc@cmu.unige.ch)
used piezoelectric Kistler accelerometres (8692C10 for + -10G, 8692C5 for
+-5G; 5134 for the 4 channel charge amplifier) in the evaluation of
abnormal movements and posture of elderly and parkinsonisms. He is
satisfied with these devices over a period of 3 years. He finds the Kistler
devices less fragile than the Entran accelerometers. Yves also advises to
take information on capactive accelerometers used for the car industry that
are very cheap but he has no personal experience with them.

Tom Szonntag (Tszonntag@aol.com) points at two companies for triaxial
accelerometers: SKF and
Wilcoxon Research (see supplier list for addresses).

__________________________________________________ ____________
4. SUPPLIERS (MODELS):

Analog Devices - http://www.analogdevices.com (they seem to be very cheap)
EG&G ICSensors- http://www.egginc.com (3022-005-P)
ENTRAN -http://www.entran.com (EGAX, uniaxial, can be mounted on triaxial
EGCS-3)
Gerrit Bulstra or Ed Droog, A.Droog@el.utwente.nl
Kistler Instrumente AG - http://www.kistler.ch (8692C10, 8692C5)
Macrosensors - http://www.macrosensors.com
(Europe: EuroSensor - 20-24 Kirby Street, London EC1N 8TS, tel: +44 (171)
405 6060, fax: (0171) 405 2040)
McRoberts, bv, NL - info@mcroberts.nl
Motorola - http://mot-sps.com
PCB Piezotronics - http://www.pcb.com (triaxial series: 354B33, 356A07,
356A11)
SenSym - http://www.sensym.com
Silicon Designs - http://www.silicondesigns.com (2412 series or 2430)
SKF Condition monitoring - http://www.skfcm.com
VibraMetrics - http://www.vibrametrics.com (triaxial series: 3000 or 5300)
Wilcoxon Research - http://wilcoxon.com

__________________________________________________ ___________________________
5. REFERENCES

Moe-Nilssen, R: A new method for evaluating motor control in gait under
real-life environmental conditions. Part 1: The instrument. Clin. Biomech.
1998, 13: 320-327

Moe-Nilssen, R: A new method for evaluating motor control in gait under
real-life environmental conditions. Part 2: Gait analysis. Clin. Biomech.
1998, 13: 328-335

Bogert, A.J. van den, L. Read and B.M. Nigg "A method for inverse dynamics
analysis using accelerometry". J. Biomech. 1996, 29: 949-954,

Willemsen A.Th.M., van Alste JA and Boom HBK (1990), Real-time Gait
Assessment Utilizing a New Way of Accelerometry, J. Biomech., 23, pp. 859-863.

P.H. Veltink, H.B.J. Bussmann, W. de Vries, W.L.J. Martens, R.C. van
Lummel, Detection of Static and Dynamic Activities using Uni-axial
Accelerometers, IEEE Trans. Rehab. Eng., vol. 4, 1996, pp. 375-385.

P.H. Veltink and H.M. Franken, Detection of Knee Unlock during Stance by
Accelerometry, IEEE Trans. Rehab. Eng., vol. 4, 1996, pp. 395-402.

J.B.J. Bussmann, P.H. Veltink, F. Koelma, R.C. van Lummel, H.J. Stam,
Ambulatory Monitoring of Mobility-Related Activities: the Initial Phase of
the Development of an Activity Monitor, Eur. J. Phys. Med. Rehabil, vol. 5,
1995, pp. 2-7.

J.C. Lötters, W. Olthuis, P.H. Veltink, P. Bergveld, On the Design of a
Triaxial Accelerometer, Journal of Micromechanics and Microengineering,
vol. 5, 1995, pp. 128-131.

J.C. Lötters, W. Olthuis, P.H. Veltink, P. Bergveld, Polydimethylsiloxane
as an elastic material applied in a Capacitive Accelerometer, Journal of
Micromechanics and Microengineering, vol. 6, 1996, pp. 52-54.

J.C. Lötters, J. Schipper, P.H. Veltink, W. Olthuis and P. Bergveld,
Procedure for in-use calibration of triaxial accelerometers in medical
applications, Sensors and Actuators A, vol. 68, 1998, pp. 221-228.

A. Nene, R.E. Mayagoitia, P.H. Veltink, Assessment of Rectus Femoris
Function during Initial Swing Phase, Gait and Posture, conditionally accepted.

H.B.J .Bussmann, P.J. Revekamp, P.H. Veltink, W.L.J. Martens, H.J. Stam,
Validity and reliability of measurements obtained with an "Activity
Monitor" in persons with and without a transtibial amputation, Physical
Therapy, in press, (to appear in September 1998).

P.H. Veltink, H.B.K. Boom, 3D Movement Analysis using Accelerometry -
Theoretical Concepts, in: A. Pedotti, M. Ferrarin, J. Quintern and R.
Riener (eds.), Neuroprosthetics - from Basic Research to Clinical
Applications, Biomedical and health Research Program (BIOMED) of the
European Union, Concerted Action: Restoration of Muscle Activity through
FES and Associated Technology (RAFT), Springer Verlag (ISBN 3-540-61084-7),
1996, pp.317-326

P.H. Veltink, T. Sinkjær, C.T.M. Baten, P. Bergveld, J. van der Spek, M.
Haugland, Artificial and Natural Sensors in FES-assisted Human Movement
Control, Proceedings of the 20th Annual International Conf. of the IEEE
Eng. in Med. & Biol. Soc, Hong Kong, 29 October - 1 November 1998, accepted.

C.T.M. Baten, P. Oosterhoff, I. Kingma, P.H. Veltink, H.J. Hermens,
Inertial Sensing in ambulatory load estimation, Proceedings of the IEEE
Eng. in Med. & Biol. Soc., 18th Annual Int. Conf., Amsterdam, October 31 -
November 3 1996, 2pp.

P.H. Veltink, D.M. Nieuwland, J. Harlaar, C.T.M. Baten, Inertial Sensing in
a Hand Held Dynamometer, Proceedings of the IEEE Eng. in Med. & Biol. Soc.,
18th Annual Int. Conf., Amsterdam, October 31 - November 3 1996, 2pp.


************************************************
Veronique Feipel, PhD
Laboratory for Functional Anatomy
University of Brussels (CP 619)
808, route de Lennik
B-1070 Brussels, Belgium
Phone: ++ 32-2-555 6329
Fax: ++ 32-2-555 6378
Email: vfeipel@ulb.ac.be
Homepage: http://homepages.ulb.ac.be/~vfeipel/
************************************************

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