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Dan Ramsey
04-28-1997, 06:37 PM
The following is a summary of my recent query regarding small spherical
reflective markers. I hope this may be of some use for future references in
this matter. Thank you for all your responses to my original inquiry.

>Let me first introduce myself. I am a graduate student investigating
anterior tibial translation in ACL deficient limbs using intra-cortical
pins affixed >with reflective markers.

>In late January, Dipl.-Ing. Gunther Paul posted a question regarding
European distributors of reflective markers. I have obtained his build it
>yourself summary and his e-mail address by referencing the biomch-l
archives in the hopes of obtaining his comprehensive summary. However, I
>have been unable to contact him at the posted address so I have the
unenviable task of having to re-post this question. Sorry about the mail
>clutter.

>Ideally, we require 7-8 mm diameter spherical markers as manually
producing high quality inexpensive markers is not feasible. In our
>experience, gluing 2 reflective hemispheres to obtain a perfect sphere has
been problematic as our infrared motion analysis system (MacReflex)
>identifies these markers as 2 distinct markers and it is unable to
determine the markers centre. Therefore we need a distributor who produces
>small spherical markers rather than hemispheres much like those produced
by Qualisys. Furthermore, these markers must be threaded so as to >be able
to screw them onto our intra-cortical pin fixture. Your replies would be
greatly appreciated and I will post the comprehensive summary.

************************************************** ********************
Mark Miller replied that he purchases wooden and styrofoam spheres from a
local hobby shop (metal should work too). He cuts them in half, and places
retroreflective tape on them. The retroreflective tape can be obtained
from a car detailing company that uses the tape. Anyway, the secret is to
heat the tape during the process which allows us to stretch the tape, thus,
no wrinkles appear on the surface of marker. He used a heat gun similar to
a hair dryer. So far, this method has worked incredibly well. He also
uses the MacReflex system and has had no problems in determining the
marker's center. Although he uses hemispheres and markers of larger sizes,
he believes this process should work favourably with spheres and the
smaller sized markers.

Mark Miller

Mark Miller E-mail: mmiller@emba.uvm.edu
University of Vermont
Mechanical Engineering Phone: (802) 656-4436
119 Votey Building
Burlington, VT 05405 Fax: (802) 656-4441

************************************************** *************
Patrick W. Castagno indicated plastic balls can be covered with reflective
tape and work very well with passive motion analysis systems.
He also posted some vendors addresses which are listed as follows:

1. Techne
3700 Brunswick Pike
Princeton, NJ 08540
609-452-9275

2. McMaster-Carr
310-692-5911

Patrick W. Castagno
Biomechanist - Gait Laboratory
Alfred I. duPont Institute
1600 Rockland Road
Wilmington, DE 19899
302-651-4615
chestnut@udel.edu

************************************************** ***********
Roland Wenzelburger mentioned he uses MacReflex for motion analysis which
is distributed by Qualisys/Sweden
(URL: http://www.qualisys.com/MacRef.html). Qualisys provides 10, 20 and 30
mm spherical markers but plan to produce also smaller ones. The sales-agent
for Germany ist Mr. Eggers (Email j.eggers@cl-hh.comlink.de) who can give
further information.

* Dr. Roland Wenzelburger *
* Klinik für Neurologie der CAU - Niemannweg 147 *
* D - 24105 Kiel - Tel. 49-431-597-2681 *
* Homepage: http://www.uni-kiel.de:8080/neurologie/ *
* Mail: r.wenzelburger@neurologie.uni-kiel.de *

************************************************** ***********
Fabio Rotelli can provide 10mm and 15mm-diameter spherical reflective
markers for gait analysis to be used in conjunction with the ELITEplus
Motion Analyser. The markers feature a special 'hole' in which an
appropriate pin, mounted on a circular base, can be inserted to facilitate
the fixing on the skin. The full kit (markers, pin, base, double-sided
adhesive tape) as well as only the markers can be provided. Additionally,
semispherical markers of various sizes (3mm, 6mm, 10mm and 15mm diameter)
have been successfully used to create a spherical marker. Flat markers,
1mm diameter, are also available.

Fabio Rotelli, B Sc Eng
Product Line Specialist
B|T|S Bioengineering Technology & Systems S.r.l.
Via C. Colombo 1/A
20094 Corsico (MI) ITALY
Phone : +39-2-45875.1
Fax : +39-2-45867074
e-mail : fabio.rotelli@bts.it
URL : http://www.bts.it/bts

************************************************** **************
Melinda Whetstone states Oxford Metrics manufactures spherical markers of
several sizes to be used with used with the VICON system. She provided me
the following contacts:
Pete Meddings or Geoff Shaw at the following address

Oxford Metrics Ltd
14, Minns Estate
West Way
Oxford OX2 0JB
Telephone +44 1865 261800
Fax +44 1865 240527

The following address is for the VICON distributor in the Netherlands and
Germany.
Biometrics Europe
Printerweg 11
3821 AP Amersfoort
phone: (31) 33 4565558
fax: (31) 33 4550605
biomeuro@pi.net

Melinda Whetstone
mrw@metricsnet.com
Oxford Metrics, Inc.
Phone: (504) 928-0616
Fax: (504) 928-0261

************************************************** *************
Georges Roudanez can provide markers of any size. Prices are relative to
the size - for example, a one inch diameter marker sells for $6.00 US each.

Georges Roudanez, VP
georges@viconsys.com

************************************************** *************
Bruce Etnyre recently searched the Biomech-L archives for replies to the
question of "do it yourself" reflective markers to find out about adhesives
for applying them. He suggested I try search the Biomch-l archives again as
several suggestions about making inexpensive reflective markers were
posted. His basic procedure for making the markers includes purchasing
wooden spheres (some people suggested styrofoam or ping-pong balls). You
then cover the spheres with a dozen or so small strips of reflective tape
(as I recall everyone referred to the 3M company as the best source for the
tape). For threading, the wooden spheres would probably suit you best as
you could easily drill a small hole in them and they would self thread.
The wooden spheres (and styrofoam) come in many different sizes and can be
purchased at any crafts store. We use 1-1/2 to 2 cm diameter spheres
mounted (glued) on flat wooden circles (also purchased at a crafts store)
in our total body analysis of a sit-to-stand motion, which are then
attatched to the subject with double sided adhesive electrode washers.
>From my experience (and my students) the markers are often too small and
the autodigitizing (we use the Ariel system) cannot find the marker which
requires the much slower method of manually digitizing. After digitizing
two camera views of over 100 subjects with 14-16 markers each, I would
recommend larger markers. I have not tried the ping pong ball method, but
I think that size would be better. As you said the digitizer calculates
the center of the marker area so the increased size should not reduce
accuracy.

Purchased from a motion analysis company the markers are rather expensive.
They cost about $10 US each, as I recall. We made ours for less than 1/10
that cost. Let me know if you need any further information on making the
markers.

Bruce Etnyre, Ph.D., P.T. _/_/_/_/ _/_/_/_/ _/_/_/ _/_/_/_/ _/ _/
Human Performance and _/ _/ _/ _/ _/ _/ _/ _/
Health Sciences Dept. _/ _/ _/ _/ _/ _/ _/
Rice University _/_/_/_/_/ _/ _/ _/_/_/ _/ _/
6100 Main MS 545 _/ _/ _/ _/ _/ _/ _/
Houston, Texas 77005 _/ _/ _/ _/ _/ _/ _/
USA _/ _/ _/ _/ _/ _/ _/ _/
etnyre@rice.edu _/ _/ _/_/_/_/ _/_/_/ _/_/_/_/ _/_/ _/
(713)527-4058
FAX: (713)285-5329

************************************************** *********
As I mentioned in my initial inquiry, I had searched the archives and
found the posting of manufacturing inexpensive reflective markers. Due to
the small sizes I require, I suspect that making such a precise high
quality marker is not feasible prompting my original inquiry. However, I
will repost the summary regaring inexpensive methods of making these for
those of you how may be interested. The original summary was posted by
Dipl.-Ing. Gunther Paul
Ergonomics
TH Darmstadt
paul@hrz1.hrz.th-darmstadt.de

I received 3 different types of advice:

1. Build them myself - see answers below
2. Buy them from producers like Ariel Dynamics, BTS, Qualysis....
3. I received adresses of users for further information

########################
Wir verwenden Reflexfolien der Firma 3M (Niederlassung Wien). Fuer 3D
Marker verwenden wir Styroporkugeln, auf die wir die Reflexfolie in
Streifen aufkleben.

Mit freundlichem Gruss
Dipl. Ing. Dr. Christian Peham

########################
We have a PRIMAS system from Delft and produce the markers ourselves. I
would suggest you to do the same, as you can make the best solution.
We got a sheet of Scotch 7610 retroreflective material from the
manufacturer which has an adhesive cover on the back side. We
made stripes and attached them on the surface of spheres. For big markers
we used ping-pong balls and for small markers different size beads.
Finally, the covered markers were sewed or glued to elastic rubber which
can be fastened to the required anatomical landmark point easily.
I saw some ready - made (and very expensive) markers which seemed to have
been fabricated with much less care.

With best regards,
Akos

###############################
I saw your request for companies selling markers on BIOMCH-L. They are
considerably more expensive to buy than to make yourself. This question
came up some time ago, I believe on this list. You may be able to find the
replies from the archives. Basically all you need is small wooden spheres
and wooden disks (you can find in any craft shop) some reflective tape (the
3M corporation sells rolls of it) and a little glue. Glue the sphere onto
the disk, cut small strips of the reflective tape (about 1/2 cm wide) and
apply them on the sphere until it is covered. Use double sided adhesive
electrode washers to attach the disk to the subject.

Good luck!
BE

##################################
3M do just about anything you could want. Alternatively, cheap is the local
fabric shop who sells reflective tape for sewing into high visibility
jackets (eg. police/road workers).

Good Luck
Tim Lawes

######################################
If you want cheap markers, you can build them yourself from 3M reflective
tape and a styrofoam ball. This is definiitely the cheapest, and is the
way some companies make them.

Neil
#######################################

************************************
Dan Ramsey

Motoriklab, plan -1
Barndivisionen
S:t Göransgatan 141
112 81 Stockholm
Sweden
Tel: +46 (0)8 672 47 04
Fax: +46 (0)8 672 49 15
Email: Dan.Ramsey@kbh.ki.se
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