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Gordon Chalmers
12-15-1998, 03:53 AM
To Biomch-l,

I received a number of helpful replies to my request regarding building a
potentiometer based goniometer, and a couple of requests for a copy of the
information that I received. Below is the original posting and a complete
copy of each of the replies. Individual replies are separated by a line of
"%%%..." signs.

***** START OF ORIGINAL POSTING *************
To Biomch-l,

I need a single axis goniometer to report wrist flexion/extension angle
while other measurements are being done on forearm musculature, as a
subject does slow wrist flexion/extension, and the rest of the arm and body
are not moving.

I searched the archives and found most of the previous discussion on
goniometers to be centered around Biometrics (formerly Penny & Giles)
goniometers and a few comments about other possible suppliers. Due to the
limited movements (directions and speeds) I have planned I hope that I can
measure joint position with a less expensive option than those available
commercially. It seems relatively simple to build a goniometer for a
single axis using a high quality rotary potentiometer and a power supply.
Only 2 comments in the archives discussed this possibility. One said it is
easy to build such a goniometer (but that student's e-mail no longer works,
so I can't get details), and one that says he tried, but it didn't work.

If anyone has any suggestions or comments they would be appreciated.
One point I have already come across is whether a transformer based power
supply is constant enough, or if a higher quality power supply (producing
less fluctuation in supply voltage) is needed.

Thanks,
Gordon Chalmers
***** END OF ORIGINAL POSTING *************

RESPONSES:
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X-Sender: hjs1@mail.psu.edu
Date: Tue, 15 Dec 1998 09:27:41 -0500
To: chalmers@cc.wwu.edu (Gordon Chalmers)
From: "H.J. Sommer III"
Subject: Re: goniometers
Mime-Version: 1.0


Over the years we have built several 6-axis Instrumented Spatial
Linkages (ISL) using instrument grade potentiometers that
measure all 6 DOF of position and attitude (3 translations and
3 rotations) with accuracy of 0.4 mm and 0.1 degrees
(Sommer and Miller, 1981, J.Biomechanics 14(2):91-98).
We use the potentiometer shafts as the mechanical elements of
the revolute joints.

For good accuracy, you must use:
1) High quality pots with instrument grade windings and internal
ball bearings to prevent revolute radial and axial compliance;
2) A precision voltage reference that has no ripple or drift;
3) Good electronics that do not cause impedance loading
of the pot output voltage; and,
4) Innovative attachment to the wrist that precludes soft tissue
motion.

We used our first ISL on the wrist and used a plexiglass frame for
attachment (Sommer and Miller, 1980, ASME J.Biomechical Engr.
102(4):311-317.

We currently use Novotechnik 1701 pots (servo size 9 mount, 3 mm shaft,
22.2 mm OD, 5K ohm, $96) from:

Novotechnik U.S.
Attn: Matt Pietro
237 Cedar Hill Street
Marlboro, MA 01752
(508)485-2244
FAX (508)485-2430

We recently built 2 ISL's for Mark Miller and Tony Petrella at Pitt.
We could build you a single axis device but it would probably cost
as much as Penney and Giles.

Best wishes,
Joe Sommer

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X-Sender: Bryan_Buchholz@uml.edu
Date: Mon, 07 Dec 1998 16:23:47 -0500
To: Gordon Chalmers
From: "Bryan Buchholz"
Subject: Re: Building an electronic single axis goniometer, advice
needed.
Mime-Version: 1.0

Gordon-

Look at:

Marras and Schoenmarklin (1993) Wrist motions in industry. Ergonomics 36,
341-351.

They use goniometers built from potentiometers. There is not a lot of
detail (they claim the device is proprietary), but there is probably enough
to get you started.

Bryan

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
From: vxg4@mhg.edu
Date: Mon, 7 Dec 1998 16:47:55 -0500
To: chalmers@cc.wwu.edu
Subject: RE: Building an electronic single axis g
Receipt-Requested-To: vxg4@nrhadmin.mhg.edu
Mime-Version: 1.0
X-Engine: "TFS Engine Release 3.12 Build 101e"
X-MIME-Autoconverted: from quoted-printable to 8bit by titan.cc.wwu.edu id
NAA08962

Dear Gordon Chalmers:

It is relatively simple to built a goniometer. While at the Human
Interface Lab at the Department of Biomedical Engineering at The
University of Akron we built one and it works fine. You need three
things to built the goniometer

1. Precision rotatory potientiometer
2. Two flat arms (simple will be arms of plastic spatula).
3. Power supply.

Attach the arms of the spatula to the rotary end of the potientiometer.
This is done by drilling a hole in each spatula and inserting them
through the rotary arm of the potentiometer. One arm should be fixed on
the potentiometer (should not rotate). Attach it to the bottom portion
of the rotary part that does not rotate. Attach the other flat arm to
the rotary portion of the potentiometer. Moving this arm would change
the resistance and give voltage output..

Supply power to the two end leads of the potentiometer. Get voltage
reading by connecting the voltmeter between the center lead and the
ground lead of the potentiometer.

Let me know if you need further information

With best wishes
Vineet Gupta, Ph.D.

**************************************
Vineet Gupta, Ph.D.
Senior Research Engineer
Rehab. Engineering/ATRC
National Rehabilitation Hospital
102, Irving St, NW
Washington, DC 20010

Phone: (202) 877-1554(Office)
(301) 847-6716(Home)
Fax: (202) 723-0628

e-mail: vxg4@mhg.edu (Office)
seema@sprintmail.com (Home)

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

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Date: Mon, 07 Dec 1998 23:22:54 +0100
From: Patrick Salvia
Organization: ULB
X-Accept-Language: en
MIME-Version: 1.0
To: Gordon Chalmers
Subject: Re: Building an electronic single axis goniometer, advice needed.

Dear Gordon,
I have built six degrees of freedom electrogoniometer for the wrist, knee and
shoulder. The basic to build a goniometer is a rotary potentiometer ( for
example Sakae potentiometer 10 kOhm, endless serie Fcp 12A or FCP 22A, 0.5% of
independence linearity; Special design are available, low cost 100 USD) and a
power supply with a zero volt. Note also the need of an ADC card to collect the
data on the host (PC). Don't forget the cross_talk error but for flexion
extension, error is small.

Patrick Salvia
LAboratory for functional Anatomy
salviap@ulb.ac.be
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X-Sender: petrella@sprite.me.pitt.edu
Date: Mon, 07 Dec 1998 18:00:56 -0500
To: chalmers@cc.wwu.edu
From: "Anthony J. Petrella"
Subject: Single Axis Goniometer
Mime-Version: 1.0

Dr. Chalmers:

I would urge you to contact Dr. H. J. (Joe) Sommer at Penn State in regards
to your inquiry about using a rotary potentiometer as a goniometer:

http://www.personal.psu.edu/faculty/h/j/hjs1/
hjs1@psu.edu

We currently use two instrumented spatial linkages in our laboratory to
measure tibiofemoral and patellofemoral kinematics. These ISL's are rather
simple 6 DOF mechanical linkages with six revolute joints. Each revolute
joint is actually a high quality rotary potentiometer that allows us to
measure the angular orientation of each link relative to its adjacent
segment. Very high quality potentiometers are needed since small errors in
the transformation between adjacent links in the mechanism will lead to a
large overall error in the kinematic measurement of the device. I was not
personally involved in their purchase, but I believe the POT's we use are
made in Germany and marketed by a company in Boston. As I recall, their
cost is not more than $100-$200.

Dr. Sommer built our ISL's for us and he has a great deal of experience
with their use in a variety of biomechanics applications. I'm sure he
could give you more information about the availability of potentiometers
similar to the ones we use and their applicability to your particular need.

Kind regards,

--
----------------------------
Anthony J. Petrella
University of Pittsburgh
petrella@sprite.me.pitt.edu
----------------------------
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X-Sender: molzf31@engem0.eng.uab.edu
Date: Mon, 07 Dec 1998 17:28:15 -0600
To: Gordon Chalmers
From: Fred Molz
Subject: Re: Building an electronic single axis goniometer, advice
needed.
Mime-Version: 1.0

I have built a 3 axis goniometer using commercial pots and a 10V power
supply (high quality). It has been very reliable and I don't think you
will have any trouble making one yourself. I believe I used single turn
500 Ohm Pots (~ $7.50 ea) in an orthogonal arrangement. These pots
provided an output of ~ 0.037V/deg......

If you want your goniometer more precise go with precision pots and a high
quality power supply (as you mentioned)

Note: You will probably want to incorporate a gimble and slider to allow
for the other degrees of freedom you will not be measuring. This design
will keep the goniometer from binding...... Good Luck!

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
From: "A.L.HOF"
Organization: faculty of medical sciences (RuG)
To: chalmers@cc.wwu.edu
Date: Tue, 8 Dec 1998 08:58:16 GMT+0100
MIME-Version: 1.0
Subject: Re: Building an electronic single axis goniometer, advice neede
Reply-to: a.l.hof@med.rug.nl
Priority: normal

Dear Gordon,
Yes, I think it is possible to build such a goniometer, but you will
probably need assistance of a good mechanic.
- Use a transducer quality potentiometer (I can provide
manufacturers if you need that.)
- Two possibilities a) mount the potmeter such that its shaft
coincides with the axis of rotation (if such a fixed axis exists!),
or b) have a sliding mechanism made, that allows for non-coaxial
axes.
- Use a high quality stabilized power supply. These are not that
expensive. If you do A/D conversion, most A/D card have their own
stabilized power output.

Succes,
Best wishes,
At Hof
Department of Medical Physiology
University of Groningen
Bloemsingel 10
NL-9712 KZ GRONINGEN
THE NETHERLANDS |-----|-====-|--|
|\
Tel: (31) 50 3632645
Fax: (31) 50 3632751
e-mail: a.l.hof@med.rug.nl
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
From: "A.D.Pandyan"
Organization: CREST
To: Gordon Chalmers
Date: Tue, 8 Dec 1998 09:29:06 +0000
MIME-Version: 1.0
Subject: Re: Building an electronic single axis goniometer, advice needed
Reply-to: A.D.Pandyan@ncl.ac.uk
X-Confirm-Reading-To: A.D.Pandyan@ncl.ac.uk
X-pmrqc: 1
Priority: normal

What position will you be taking measurements under - We made a
custom built device during my previous study - Details of the device
a re in Pandyan et al (1997) - Clin Rehab; 11 123 - 130. If you think
the system is relevant let meknow and I can probably help out.
Kind regards
David
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Date: Tue, 08 Dec 1998 14:03:22 +0100
From: Stefan Fiedler
Reply-To: stefan.fiedler@medizin.uni-ulm.de
Organization: University of Ulm
MIME-Version: 1.0
To: chalmers@cc.wwu.edu
Subject: potentiometer-based goniometer

Dear Gordon Chalmers,
we use in our institute an potentiometer-based goniometer (six degrees
of freedom), developed by Dr. Wilke.
This goniometer is basically built up by high precision potentiometers
developed and distributed by the company

novotechnik
Horbstr 12
D-73760 Ostfildern
(Postfach:4220
D-73745 Ostfildern)

Telefon:(0711) 44 89-0
Telefax:(0711) 44 89-118

The voltages of 6 potentiometers are sampled by a 12 bit A/D-board and
calculated in 3 translations and 3 rotations by self-developed
software.
Of cause you should take care for stabilized power-supply, but there
are numerous integrated voltage stabilizers available.
Another way to detect rotation offer optical angle-detektors.
They offer a 0.5 degree solution, maybe even more now.
If this solution is enough for your purpose you may contact the swedish
enterprise Linde & Leiner or their distributors

Yours
Stefan Fiedler
--
_________________________________________________

Stefan Fiedler Dipl.-Ing. (FH)
Universtitätsklinikum Ulm
Abt. Unfallchirurgische Forschung u. Biomechanik

Tel: ++49-731/50-22908
Fax: ++49-731/50-23498

mail: stefan.fiedler@medizin.uni-ulm.de
_________________________________________________
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Date: Tue, 08 Dec 1998 09:50:40 -0500
From: Jeff Ives
Subject: Re: electronic single axis goniometer
To: Gordon Chalmers
Reply-to: jives@ithaca.edu
Organization: Ithaca College
MIME-version: 1.0

Gordon,
I built a simple goniometer with a precision linear pot for use in a
pilot study of
ankle dorsi-plantar flexion. The elgon worked well, but not for the
application--
it was too cumbersome and was hard to securely affix over the malleolus.
It
moved around too much during ankle movements so those data are useless.
I tried
a couple of different pots from Mouser Electronics (800-346-6873); their
1/2"
single turn precision wirewound (20K Ohms, 1% linearity, $31.00) and the

7/8" single turn conductive plastic pot with no mechanical stops (50K
Ohms,
2% linearity, $14.82--prices from 1995). I used the 5 VDC output from my

A/D board to run the device. Securing the metal arms to the pot was
somewhat
easy (but harder than expected). I would suggest affixing the elgon in
some
manner to a wrist sleeve (e.g., a carpal tunnel wrist support device
that has
the plastic stays removed) that would help to keep the device positioned

properly.
Hope this helps,
Jeff
--
Jeffrey C. Ives, Ph.D.
Department of Exercise & Sport Sciences Phone: 607-274-1751
Ithaca College Fax:
607-274-1943
Ithaca, NY 14850 USA Email:
jives@ithaca.edu

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
From: "PMUSERS"
Organization: Indiana State University
To: chalmers@cc.wwu.edu
Date: Tue, 8 Dec 1998 10:09:25 -0500
Subject: Re: Building an electronic single axis goniometer, advice neede
Priority: normal
Mime-Version: 1.0

Dear Gordon,
I build a single plane electrogoniometer similar to the one shown in
first chapter of Luttgens & Hamilton's text entitled
"Kinesiology-Scientific Basis of Human Movement" which was originally
presented by M. Adrian.
It consists of 2 aluminium flat rods that have about a 3/4 inch
offset on the potentiometer end in order to place the potentiometer
next to the joint and then be able to attach the shafts of the ELGON
with velcro or tape, a 180 degree rotary potentiometer that has
linear resistance changes throughout the ranges, shielded cable, and I
used a 5 pin biopotential connector. The unit is connected to a
Beckman(Sensormedics) dynograph recorder. One pin provides a tuneable
0 to 10 volts power source and then we sized the resistance to
provide a 0 to 5 volt output to the chart coupler. If you choose not
to use the power source from the recorder then I used a lithium
battery to provide similar excitation. If you have an analog to
digital convertor for a computer collection, the coupler would
probably be a BNC connector and you will have to check the ranges of
the A/D board.
Also, check with your technology/electronics department, because
senior students are always looking for projects for their culminating
experience. They may be able to build it for you or at least you
could pay them. My ELGON cost about $30 to build, Layfayette has one
for about $400.
Good Luck.
Al Finch
Physical Education
Indiana State University
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Date: Tue, 8 Dec 1998 11:26:25 -0800 (PST)
From: Martha Jack
To: Gordon Chalmers
Subject: Re: Building an electronic single axis goniometer, advice needed.
MIME-Version: 1.0

Gordon,
When at WSU I used to build goniometers for the equine studies and some
I did on the forearm. Use a 10K potentiometer with the center of the axis
at the approximate center of the ROM for the joint and movement in
question. Make the arms of the goniometer out of flexible PVC and the
approximate length of the bones on either side of the joint axis. Place
the leds of the soldered wires along the arms with a lot of wire loop with
electrical tape. Connect the wires to a preamplifer and then the amplifer
to a physiograph or some recording device - ink, light, electronic,
oscilloscope, etc. For the radial-ulnar joint to measure
pronation/supination: place the potentiometer center on a rod which
swivels in a circle freely. Think of what the head of the radius looks
like and then try to emulate that motion on the ulna in constructing the
goniometer.
If you have any questions about this, just E-mail me.
__________________________________________________ ____________________
Martha Jack, Ph.D. :) E-mail: mjack@beta.tricity.wsu.edu
Biomechanical Engineer :) Voice: (509) 943-0043
___o P.O. Box 776 :) FAX: (509) 943-4642 ___o
_ \