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Chris Kirtley
05-23-1995, 01:25 PM
Dear All,

Steve Hill's enquiry about foot pressure measurement systems prompts me to
deliver this summary to my own enquiry which I'd forgotten to post. Sorry
for the delay. By the way, I reviewed the Parotec system at ISPO Melbourne
a few weeks ago. It's retailing for A$20,000 (about US$15,000 I guess).
That's for three pairs (sizes) of insole. As far as I understand it, the
E-med system is about the same price but only includes one pair of insoles.

Best regards,

Chris

__________________________________________________ ____________________

I have had the opportunity to work with a new system offered by a
German company called the Parotec system. It allows high data
collection rates using a patented hydro-cell technology which allows
accurate measurements from non-planor surfaces (such as in a shoe, or
in a shoe with a brace). I would be happy to talk to you about this
equipment if you think it may meet your needs.

Sincerely,
Jeff Bauer, Ph.D.
Assistant Professor of Biomechanics
University of Florida
jbauer@hhp.ufl.edu

Chris,

to begin with: I am biased towards the EMED system.
We are using the EMED platform for measurements of the
pressure distribution during barefoot walking and
are satisfied with the preformance. The capacitive sensor
principle is adequate for our applications in clinical gait
analysis. Based on the frequency response it might be
inadequate for sports movements with high loading/unlaoding rates.
I have used the Micro-EMED for a study of shoe evaluation and
liked the basic characteristics of the insole. We attached it to
the foot and compared different shoes. The insole
the foot well and stayed in place so that the same position of
the foot on the sensor mat was ensured. The resolution is not
extremely high but usually sufficient for describing the foot
loading pattern. The insoles appear to be very durable.

I have not used the F-scan system but have talked to several people
with experience in pressure distribution measurements. The big
advantage obviously is the high spatial resolution and I also liked
the software that comes with the system. Furthermore, the insole is
described as thin and very flexible. I agree it is thin but due to
the Mylar layer it is only flexible in one direction and does not
adapt well to rounded protrusions. The durability is not very good
and that is the reason why the insoles are fairly cheap. They have
to be replace regularly. The basic problem is the calibration which
the company claims to have solved.
I am not sure how that has been done since the sensor itself seems
to change its properties with every loading cycle. Peter Cavanagh has
written a letter to the Editor of Foot and Ankle (in one of the last
issues) and states that the system apprears to be inappropriate for
repeatible pressure distributioon measurements.

If you have the option to test the systems I would suggest you do your
own repeatability study to find out what suits you best.

I am interested in the upcoming discussion but would like to ask you
to keep this message confidential without publishing to the list.

I hoped this helped. If you have more questions feel free to contact me
directly.

Ciao,

Dieter...

************************************************** **********************
* Dr. Dieter Rosenbaum voice:(0)731 - 502 3492 *
* Abteilung Unfallchirurgische fax: (0)731 - 502 3498 *
* Forschung und Biomechanik email: diro@sirius.medizin.uni-ulm.de *
* Universitaet Ulm *
* Helmholtzstr. 14 *
* 89081 ULM *
* Germany *
************************************************** **********************

Dear Chris

We have an FSCAN system. The major advantage over EMED was insole cost. FSCAN
is US$25 (each or per pair, I can't remember), which can be cut to size, but
only last for perhaps 6 trials. EMED insoles from our local agent were around
AUS$5000 each (one size), and likely to last 6 months from reports we got.

The FSCAN software is very nice. You can get 2D or 3D pressure maps, at up to
about 120 Hz. You can also get the software to calculate force traces, which
bear reasonable resemblance to vertical ground reaction forces (differences
probably due to not measuring forces truly normal to the floor, plus
interface effects ?).

The major concern is with calibration. You can 'calibrate' total pressure to
the known subject body mass applied over one insole (ie stand on one foot);
at the time we bought the system, this was the only option. However, I
understand that there is now a balloon / aluminium sandwich device to
calibrate each force-sensitive resistor element. I believe it costs about
US$5000.

It would be nice if there was a telemetered version available. I understand
that there may be one in the works. Current cable length means that you can't
get too far from your computer.

I had some trouble getting it to work initially. It was very sensitive to non-
100% compatible Microsoft mouse software drivers. Also, the board has to sit
a bit skew in our PC's bus slot for the system to work (but this may be more
of a problem with the PC than the board ??). Get the fastest PC that you can,
to give you the best shot at real-time display and reasonable file loading /
processing times.

Cheers

Tim Wrigley

Centre for Rehabilitation, Exercise and Sport Science (CRESS)
Victoria University of Technology
City Campus
300 Flinders Street ph: +61 3 248 1119
P.O. Box 14428 MMC fax: +61 3 248 1110
Melbourne 3000 email: timw@dingo.vut.edu.au
Victoria, Australia

My name is Jim Woodburn and I teach in the Department of Podiatry at the
University of Huddersfield. I use the F-Scan system here and have done some
recent work on the output/input characteristics, durability and calibration
of the system. This work is just finished and I'm in the process of writing
a report. I will have some major findings available by Friday 30th March if
you are still intrested.

Best Wishes

Jim Woodburn

Dear colleague,
I have to appologize since I deleted your message accidentially and
now just got your email address from somebody else; consequently I
don't know your name....but I do know the issue:

The decision about choosing a pressure distribution system is not a
esay one as long you don't know, what exacrtly you are going to do
with it. As soon as you know that, it's an easy choice: First you
have to decide if you want a system, which covers the whole area
of the foot (pressure distribution) or if you can live with a
multiple sensor system (local pressure measurements). If you choose
the later possibility, the PAROTEC or the HALM system are the systems
you have to look at. If you want a "real" pressure distribution
system, the F-SCAN and MIKRO-EMED (or PEDAR) systems are the
ones to look at. Next choice: if you want a qualitative, low-cost
measurement system, which covers all sizes and is easy to use -- take
the FSCAN. If you want a system, which produces results which are
reproducable and quantitative, take the MIKRO-EMED (better the
PEDAR).
A good test for a pressure distribution system is always that you ask
the people for your weight when you wear one and -- don't take any
excuses!!

If you have any further questions, feel free to contact me.

Michael

Michael M. Morlock PhD.
AB Biomechanics
TU Hamburg Harburg
Denickestrasse 15
21073 Hamburg
Germany
tel: +49-40-7718-3175
fax: +49-40-7718-2579

Chris,

I've been working with the Novel Pedar system for quite a while. It has
performed very well for our applications in gait analysis. One of the
advantages of this system is that you are able to calibrate each sensor
in the insole matrix. So now you get a calibration curve for each
sensor throughout the measurement range. Pressure values can be
verified after calibrating by placing the sensor matrix back in the
calibration device, loading them and measuring online. Thus, values for
force are very close to body weight when standing on the sensor matrix.
In some of our research, we found excellent reliability (repeatability)
when walking at a constant rate. Regarding the Fscan, current research
has shown poorer results in bench and dynamic testing. Some references for
you on the systems:

Xia, B., Garbalosa, J.C., & Cavanaugh, P.R. (1994).
Error analysis of two systems to measure in-shoe pressures. Proceedings
of the American Society of Biomechanics. Ohio State University.
Cavanaugh, P.R. (1995). Letter to the Editor. Foot & Ankle.

Apparently, when using a conductive ink sensor (such as in the Fscan) the
ink begins to smear with repeated loadings. As a result, when the
properties of the sensors change so do the values. Also, the change
appears to be non linear making "correction" difficult. Thus, a
quantitative comparision of changes in pressure values due to shoe or
orthotic intervention are difficult if not impossible.

If you have any further questions, please do not hesitate to contact me.

Sincerely,

Tom Kernozek, Ph.D.
University of Minnesota
e-mail: kerno001@maroon.tc.umn.edu

Dr. Kirtley,

If possible, try to get a hold of an abstract from the 1994 American Society
of Biomechanics Meeting from Peter Cavanaugh's group at Penn State. The
abstract described some direct EMED to F-Scan comparisons. The EMED data
may have been from a PEDAR system; however, the sensor technology is the
same as for the Micro-EMED. In general, I believe that they found the
repeatability of the EMED measurements to be substantially better. I expect
that I could probably FAX you a copy if you do not know of anyone locally who
would have a copy.

Peter M. Quesada, Ph.D.
Ohio State University


__________________________________________________ __________________
Dr. Chris Kirtley MB ChB, PhD c.kirtley@info.curtin.edu.au
^
Lecturer, Bio-engineering --_ / \
/ \
School of Physiotherapy, Perth #_.---._/
Curtin University of Technology, V
GPO Box U1987,
Perth 6001, Tel +61 9 351 3649
Western Australia. Fax +61 9 351 3636
__________________________________________________ __________________