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M A Razian
07-03-1997, 08:58 PM
Dear all ;

I would like sincerely to Thank everyone who responded to my
questions. Here a very "compressed summary" of only few early responses
from all the responses that I had, due to short of time I could not
summaries all . But I will defiantly send the summary of the rest
later.
Also any Further questions or suggestions REFERENCE(S) regarding this
research are very welcome and I would appreciated , As I still looking for
answers for my questions. The original questions are:


I am currently working on design and development a tri-axial
transducer (13mm^2 & 3mm thickness) using piezo-electric film.

I think this transducer has many applications, one of which I am
aiming for to measure the step by step in-shoe tri-axial pressure (a
vertical and two shears) instantly. The system will be flexible so that
more then one transducer can be used at the same time under each foot.

I have few questions that I am looking for answers, I will be happy
and grateful if somebody up there that cad help me answering some
of my questions:

1. Are under foot in-shoe Tri-axial measurements (Vertical-Shear)
medically significant? Why? (please explain)

2. What the measurements results expected to show the professional ?

3. I have problems calibrating the shear components of
the transducer with at least 98% accuracy and measuring the
cross-talks. Do you know of any system that can help ?

4. Are there any other applications that a Tri-axial transducer can
be used for (medical or non-medical) ?

Your help will be appreciated.

Thank you
M Razian

University of Kent
Medical Engineering Lab.

************************

SUMMARY:

Dear Razian:
I think such a system is important for a variety of applications, such as
tool design and ergonomics.
the Fscan is only measuring compression and shear will be a unique
capability of your proposed system.

Mohamad Parnianpour


Interesting note because today we will be assessing a patient
that might benefit from your device. She is a nationally
recognized runner with skin problems beneath the metatarsal heads
of her foot. We will be assessing the vertical component
(pressure) in this area but she tells us that she thinks the
shear component is more important. It may be a function of both
variables. The problem restricts her performance even in
relatively short races (10,000 m).

I may be naive (a clinician not an engineer) but don't you calibrate shear in these devices
like you would measure the coefficient of friction.

Murray



In the field of occupational health and safety, the ratio of shear to normal
force at foot-floor contact is useful in understanding the potential for
slips (which can lead to potentially fatal falls from, say, elevations).
Although laboratory studies with high precision force plates are useful in
their own way, they don't capture the real world aspects of the work
environment. I am
excited about your proposed transducer, because it sounds like it might be
able to give a crude estimate of shear and normal forces on the foot.
However, compared to the alternative (how else does one do exposure
assessment for slip potential in real world environments?), and insole
system that could measure shear and compression is potentially very promising.

Richard Hughes, Ph.D.



Hi,

I did a similar study before. If you interested please see the paper "
Li Q.H., Nicol A.C. and Siu S.T.: The study and application of inertia
measurement apparatus to gait. The Proceedings of Sixth International
Conference on Biomedical Engineering. (Singapore) 111-114, 1990."
I hope it will be helpful.

Qinghang Li (M.D. Ph.D)


Dear M. Razian,

>>1. Are under foot in-shoe Tri-axial measurements (Vertical-Shear)
>>medically significant? Why?

SURE !, there are commercial systems (like the EMED system from Novell)
that measure vertical components, to yield the pressure distribution.
Especially in the evaluation of adaptatation within the shoe or
specu\ial shoeware either to compensate for anatomical deformities or
pressure redistribution,(e.g. in diabetic foot care). The addition of
shear force would give important additional information, as it is
expected that also these forces contribute to the ulceration process, or
the development of pressure sores.
>>
>>2. What the measurements results expected to show the professional ?

It should give a distribution over the plantar surface area of the foot.
Thexecact form might need some debate: some combinations of: "total
magnitude, total shear-magnitude, directiion of shear forces, Fz, Fx
and Fy magnitude"

>>3. I have problems calibrating the shear components of
>>the transducer with at least 98% accuracy and measuring the
>>cross-talks. Do you know of any system that can help ?
>
No, sorry I'm not a sensor expert.

>>4. Are there any other applications that a Tri-axial transducer can
>>be used for (medical or non-medical) ?
Medical:
- Measuring the same type of forces in the interface to orthesis and prosthesis.
- Evalulation of chairs and special beds.

With kind regards,

mr. Jaap Harlaar


In response to your questions:

>1. Are under foot in-shoe Tri-axial measurements (Vertical-Shear)
>medically significant? Why? (please explain)

I think they are important, but this has yet to be proved. In almost any
situation where a material breaks down (engineering or biological
structure), one needs to know the nature of ALL of the forces acting on that
structure.

2. What the measurements results expected to show the professional ?
I'm not sure what "professional" refers to-at the moment I think the
measurement of shear and pressure is still in the research phase and
many questions still have to be addressed. The issues are far more
complicated than those related to pressure measurements alone, in
much the same way that 3-D gait analysis is a lot more involved than
2-D gait analysis.

3. I have problems calibrating the shear components of
the transducer with at least 98% accuracy and measuring the
cross-talks. Do you know of any system that can help ?
No. One thing to bear in mind is that a small amount of cross
talk between the vertical channel and either shear channel
becomes a problem when the vertical forces are high and
the shear forces are low.

4. Are there any other applications that a Tri-axial transducer
can be used for (medical or non-medical) ?
Stresses acting between a socket and an amputee patient's
residual limb, stresses on handles of almost any industrial tool,
wheelchair wheels etc etc.

I hope this helps,
Brian Davis


Dear Mr Razian
I think that a sensor like this will be very useful for foot-shoe
characterization purposes. I
1 I think that shear forces are the cause of various dermal disorders
of the foot.
2 If you can measure them in-shoe you may be able to
select the most proper material for the innner of the shoe.
3 The calibrating system I used was very simple and couldn't give
so much accuracy. (Crosstalk is a big problem).
4 For Ergonomics application that study hand-glove interfaces (for
instance).

Arturo Forner


Hi there,
I am a Physiotherapist in Australia who can in part answer only one section
of your posting.
> 1. Are under foot in-shoe Tri-axial measurements (Vertical-Shear)
> medically significant? Why? (please explain)I think so, YES. As the locus of
ground reaction force moves anteriorly
during the stance phase of gait, it also moves on the fromtal plane and the
body compensates using equilibrium in the transverse plane(and others
obviously). To my knowlege this has never been measured, so we don't know
how significant it isbut the results are very deformed feet in some populations.
I can make guesses for you about the primary and secondary causes but
until we start to measure it, see what comes first etc, we will always be
guessing.This is obviously absurd and is a large whole in our knowledge.
It also includes a large slice of out work so I still say it is signigicant.

Michael


Dear Dr. Razian,


1. Are under foot in-shoe Tri-axial measurements (Vertical-Shear)
medically significant? Why?

They would be if they were reliable, for 2 reasons:

a. Skin sores (ulcers),
b. This would enable inverse dynamics modelling of ankle, knee and hip
moments and powers without the need for a force platform (which is
rather messy, requiring a gait lab and the subject to hit the plate)

2. What the measurements results expected to show the professional ?

Mainly creep response, I suspect. You would need to show that the device
remained reliable (repeatable) as it is cyclically loaded - hysteresis
minimal. Linearity would also be nice, but not essential, as you could
always calibrate for this.

Best wishes, and good luck!

Chris
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