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Walker, Matt
07-29-2004, 12:02 AM
Dear Biomch-L readers,

I appreciate all of the suggestions I received from members on my original
pressure platform question. I received good feedback regarding simultaneous
capture, particularly with the 3D box offered by RSscan. Others suggest
using the VICON Datastation electronic trigger input for data
synchronization. I have spoken with one group who are working on pressure
collection via VICON analog inputs, however I do not believe any such
solution is commercially available as of yet.

I have also spoken with people at the companies themselves regarding various
model specifications, and each have their own advantages depending on your
application. Feel free to contact me if you have any questions. I hope the
information below will also help others.

Best,
Matt Walker
-----------------------------------------------
Matthew R. Walker, MSc
Biomechanical Engineer, Motion Analysis Laboratory
Shriners Hospital for Children, Erie, PA
mrwalker@shrinenet.org


-------------------------------------
ORIGINAL POST:

We would appreciate suggestions on pressure platform (mat) systems,
particularly your experience with Tekscan, Novel, and RSScan models. We
will be looking at walking in children and potentially adults. General pros
and cons of the resistive versus capacitive sensors used in these models
would also be helpful. We are operating a VICON system - has anyone
collected the pressure via analog output (ie. so that collected via
Workstation in sync with all other channels), and then post-processed the
data? Other suggestions for dealing with data synchronization with VICON
and force plates?

Previous biomch-l posts have posed similar questions - I am hoping for any
new developments or additional insight:
http://isb.ri.ccf.org/biomch-l/archives/biomch-l-2001-03/00065.html
http://isb.ri.ccf.org/biomch-l/archives/biomch-l-2001-12/00009.html
http://isb.ri.ccf.org/biomch-l/archives/biomch-l-1997-06/00166.html

-------------------------------------
RESPONSES:

You may want to check out a publication by Hsiao, Guan and Weatherly carried
on Ergonomics, 2002 (vol.45 No. 8, 537-555). The title of the
publication is "Accuracy and precision of two in-shoe pressure measurement
systems".

Jinhua Guan, Ph.D

-------------------------------------

I'm the president of RSscan INTERNATIONAL.
I'm glad that you have interest in pressures analyzing in synchronization
with Vicon.

The RSscan system is working with conductive polymer. The most used system
is the 1m and 2m plate in combination if you want with a force plate (to
have Dynamic calibration frame by frame). By using the 3D box you can
synchronies every other system like EMG, Vicon ......

The new software provide you calculations of the subtalor joint movements,
the forefoot movements and the midfoot naviculaire movements. Frequencies
up to 500Hz.

Jempi Wilssens

-------------------------------------

We have an EMED (SF4, Novel - 50 Hz) platform that we use in combination
with a Vicon system (60 Hz). As far as I know it is not possible to collect
the data from the platform using the analogue capture facility in the
Datastation.

However, using the "first-contact" EMED setting, a trigger signal is
generated with the first contact with the pressure mat. This can be used in
combination with the Vicon post-trigger setting and the external trigger
input in the Datastation to synchronise EMED and Vicon recordings.
(post-trigger uses buffered data to enable captures starting a specified
time before the trigger is received).

Dr. Mark Thompson CEng MIMechE

-------------------------------------

In our biomechanics lab at the Free University of Brussels, we use a 1m
rsscan system on top of a .9m kistler force plate both connected to a Vicon
612 system. The coupling between Vicon and RSscan is established through a
coax cable that connects the J2 connector on the Vicon and the trigger in
connector on the 3d-box. The latter is a special communication box from
RSscan. On one hand it registers the data from the pressure plate and on the
other hand it is able to communicate with different devices. This
connection enables the synchronized measure from all devices. Since
both the 3dbox and de Vicon system register force plate data, we used this
data set to verify the connection. About 2200 trials were used to calculate
the signal correlation between the force signals from the two systems. For
all trials no delays found. If you want to know more, just let me know.

Friso Hagman, MSc. MTD.

-------------------------------------

I'm not really sure how you're going to connect one of these pressure
systems to the analogue input of the Vicon - do they have analogue outputs ?
I seem to remember the Vicon had a electronic trigger input, which you could
use to sysnchronise the data capture for the two systems. You'll need to
talk about that to the engineers from the two companies though.

I'm really writing to offer help, if you need it, with the post-processing
and getting data into the Vicon C3D file via a Pipeline PlugIn - something
like the ASCII Import PlugIn. You can have a look at on my website,
(www.vaquita.co.uk) but I suspect it is too inflexible for you will want.
I'm intending to release a 2nd version which is much more flexible, that
would read say the ASCII output from one of the pressure systems.

Timothy Pitt

-------------------------------------

We have the RSscan system.
It has several advantages
- high spatial resolution
- high temporal resolution
- reasonable price
- available at various sizes, up to 4 m (?)

The main disadvantage is that pressure sensitivity shows a considerable
decline with use. This can in part be compensated by
combination with a force plate under the mat. If this is not possible, a
correction is made on the basis of body weight. In any case,
once or twice a year the resistive mat should be replaced, cost EUR 150,
otherwise low pressures are no more recorded.

In general the RS staff is very supportive, always willing to listen to your
problems and to send you the newest software update.

At Hof




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