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Graham Robinson
03-25-1996, 07:20 PM
A couple of weeks ago I put out a request regarding measuring grasp force. - Thanks to everyone who responded, if anyone has any comments etc. please feel free to e-mail me.
Also thanks to Nicky Fowler (@ Strathclyde University, Glasgow) for demonstrating her 6 DOF grasp force pylon to me.
We'll be contacting various people over the next week or so...

For any one interested in more information about the 'Amadeus' robot hand we're busy constructing our www page at the moment - I'll email the list when its active (I'm aiming for April 1st).

Graham Robinson,
Research Associate,
Department of Mechanical & Chemical Engineering,
Heriot-Watt University
Edinburgh, Scotland.

email: mecgcr@bonaly.hw.ac.uk
phone: +44 (0)131 449 5111 ext 4737
fax: +44 (0)131 451 3129
__________________________________________________ ________________
original message:
Subj: grasping: measuring contact reactions


Dear collegues,
I am part of the Amadeus robotic manipulator project at Heriot-Watt
University, Edinburgh. The project is developing a dextrous three fingered
gripper, which is based upon a flexible continuum structure rather than the more conventional kinematic chain.
At present one of the undergraduate students is doing a project on
identifying when an 'optimum' grasp has been achieved by three fingers. An
obvious answer could be that when force closure has been achieved the resultant reaction of the target object will be a minimum.
Now the question: Has anyone had any experience with measuring finger reaction forces or object reaction forces by either fastening the object to a force plate table or instrumenting the object itself?
We would like to measure the reaction independently of the
instrumentation in the robots finger tips.

__________________________________________________ ________________
summary:
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Your note was interesting to me because a student in a neuro phys
lab I was working in (I was also a student), was working on the
neural response to slip. Motor control of a grasped object is a
difficult feat because it depends on the parameters of the object
and the dynamics. His definition of adequate grip was
"The object does not slip". His goal was FES but similar problems
are put on any control system. I was really impressed with his
abilities, innovations, and results but I cannot remember his
name and don't know how to locate him (although he may be in
Denmark, his home country). He was a student of Andy Hoffer's
(now at Simon Fraser University) and I believe he has published
the work with Andy. Even though this information is not
directly related to your original question I hope it is useful.

Murray Maitland
maitland@acs.ucalgary.ca
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"Now the question: Has anyone had any experience with measuring finger
reaction forces or object reaction forces by either fastening the object to a
force plate table or instrumenting the object itself?"

FYI, Here are some possible sources of information...

Forssberg H, Eliasson AC, Kinoshita H, Johansson RS, Westling G (1991)
Development of human precision grip-1 - basic coordination of force. Exp
Brain Res 85: 451-457
Forssberg H, Kinoshita H, Eliasson AC, Johansson RS, Westling G, Gordon AM
(1992) Development of human precision grip .2. anticipatory control of
isometric forces targeted for objects weight. Exp Brain Res 90: 393-398
Fransson C, Winkel J (1991) Hand strength - the influence of grip span and
grip type. Ergonomics 34: 881-892
Gordon AM, Forssberg H, Johansson RS, Eliasson AC, Westling G (1992)
Development of human precision grip .3. integration of visual size cues
during the programming of isometric forces. Exp Brain Res 90: 399-403
Newell KM, McDonald PV (1994) Information, Coordination Modes, and Control In
a Prehensile Force Task. Human Movement Sciences 13: 375-391
Jensen TR, Radwin RG, J.G. W (1991) A conductive polymer sensor for measuring
external finger forces. J Biomech 24: 851-858
Radwin RG, Masters GP, Lupton FW (1991) A linear force-summing hand
dynamometer independent of point of application. Applied Ergonomics 22:
339-345
Radwin RG, Oh S, Jensen TR, Webster JG (1992) External finger forces in
submaximal five-finger static pinch prehension. Ergonomics 35: 275-288

Vernon McDonald
vmcdonald@sdmail.jsc.nasa.gov
-----

Dr P. Weir at the University of Windsor (Ontario, Canada) looked at
control of prehension in her Ph.D. Thesis. As well I believe she has done
some follow up work since she has been at Windsor. She used a small
dowel with square gripping plates attatched to the top of the dowel
hooked up to a force transducer. This allowed her to look at the forces
associated with the acquiring and release of the dowel along with the
various kinematic measures. The effects of intrinsic object properties
and task requirements were examined.

The only Email address I have for her is : weir1@delta.uwindsor.ca

Tammi Winchester, B.Sc., M.Sc.
twinches@nblab.uwaterloo.ca
-----

I suggest you contact Professor Jim Nightingale in the Engineering
School at the University of Southampton. He successfully built a
fully articulated and instrumented hand some time ago.

Alan Walmsley
awalmsley@pooka.otago.ac.nz
-----

I am in my third year of a phd project here at the bioengineering unit
at Strathclyde.

My project involves studying the biomechanics of "normal" and
rheumatoid proximal interphalangeal joints. I have developed a 6 D.O.F
force transducer to measure the force on an individual finger whilst
performing various "everyday" tasks (eg. turning a jar cap, turning a tap
etc). I'm using this transducer in conjunction with our VICON motion
analysis system to determine the external forces and moments on each
finger joint.

Nicky Fowler
n.k.fowler@strath.ac.uk
-----

I am working on a 2-D, flexible, contact force transducer array for
in-vitro studies in the knee. My array will consist of approx. 1500
independent sensors arranged in a cartesian grid with inter-sensor
spacing of less than 1mm. I am beginning the fabrication of the sensor
now and hope to complete the project within a year. I suspect, if
successful, the device will be useful for a number of biomechanics and
robotic applications.

Jack Kotovsky
jjkotovsky@ucdavis.edu
-----

Check out the Hanford Hand home page at:

http://www.cen.uiuc.edu/~jk-smith/hand.html

I'm sure that John Smith or Ken Whiteman can assist you with some of the
research that they have done to date.
Chris Smith
CM_Smith@pnl.gov
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Just a comment on finger closing force determination:

While I was an undergraduate at Brown Univ. during the 80's, a graduate
student developed a project similar to the one which you describe, yet he
used slip to assess proper grip strength. The idea was that the robot
"hand" would increase closing force at tiny increments based on how much a
soft object (with substantial static friction coefficient relative to the
gripping hand) slipped against the the electrostatic surfaces of the "hand".
It was thus a servo method, with amount of sliding friction being the
feedback signal. I thought it was a neat idea.

John H. Lawrence, Ph.D.
jhl@bme1.image.uky.edu
-----

I am a Masters student at the University of Cape Town, South Africa.
For my thesis I am building an artificial hand with Lego blocks. I
have just started my research and have encountered this article (1)
where thy did tests on a hand using methods from Ingvarsson (2).

I don't know if this would be of any help to you but good luck with
the project. I would love to hear of the progress you are making and
or of anything interesting surrounding the subject.

1. Bergman K et al (1992). Functional benefit of an adaptive
myoelectric prosthetic hand compared to a conventional myoelectric
hand. Prosth Orthot Int, 16, 1,32-37

2. Ingvarson B, Karlsson I (1982). Test instructions for the
technical testing of monofunctional myoelectrically-controled
prosthetic hands. Prosth Orthot Int 6, 41-42

Johan Kotze
KOTZE@engfac.uct.ac.za
-----

Roland S. Johansson and his colleagues at Umee University have been studying
the reaction forces at the fingertips during precision gripping in humans
since the early 1980's. Their paradigm inspired a small number of other
investigators (myself included) to study the control of fingertip forces
during dexterous grasp. Johansson's group designed and constructed objects
that were, in effect, multiaxis force transducers. The objects had parallel
sides for placement of the thumb and another digit, respectively. The load
cells independently transduced the force normal to each side, and the
vertical tangential force at each side during tasks like vertical lifting of
the object (for a review see Johansson, R. S., & Cole, K. J. Grasp
stability during manipulative actions. Can. J. Physiol. Pharm., 72, 511-524,
1994). In some objects torques also were transduced, but to my knowledge
the torque data has not been published.

A more complete set of force and torque measures can be obtained with
commercially available miniature 6-axis force/torque transducer systems
(Assurance Technologies, Inc., 503D Highway 70 East, Garner, North Carolina
27529, USA; (919) 772 0115 Ext. 135; FAX 919 772 8259) that can be affixed
to objects or platforms with standard threaded tool adaptors. These
transducers come with a microprocessor controller. Be prepared to spend
about $7000 US per transducer system (including useful options like
temperature compensation and analog output boards). I'm sure there are
other manufacturers for similar devices, but I have personal knowledge only
of the systems from Assurance Technologies, Inc.

Kelly J. Cole, Ph.D.
kjcole@blue.weeg.uiowa.edu
-----

I work for a small company called Novel who research, develop and manufacture
dynamic pressure measuring systems. One of our systems consists of a small mat
that was originally designed to measure the grip of pateints recovering from
hand surgery. It may be that such a system would be suitable for your situation
in that you could fix the mat to the object in order to measure the
pressure/force exerted by the robot on the object. We also produce individual
sensors which may be of use.

If you are interested in receiving any further information on this, please let
me know.

Anna Hayes
100607.2101@compuserve.com
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end of summary.