A few weeks ago I placed the following inquiry on the list:

>Does anyone know of a relatively low-cost commercially available force platform
>(US $1000 or less) that measures only the force normal to the platform? In >addition, I would like to know if there are commercially available platforms >which simply measure contact and non-contact times (for example in repeated >vertical jumps). I would like to use them for teaching undergraduate >students. Thanks in advance for any information that you might have. > Since that time I have received several responses, which I summarize here. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - From: Francisco Valero >Hi, My name id Francisco Valero ahd I am doing a PhD in Mechanica >Engineering at Stanford. As a sophomore, I designed and built a force >plate for jumping experiments. It was a uniaxial plate that cost >about 200 Dlls to build. I can send you the description of it if you >are interested. It takes about a week to build, and It has a resonant >frequency of 300 Hz. >Do let me know If you found something commercially available. > >Good Luck > >-Francisco Valero - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - From: Didier Geiger >In response to your recent posting, >you can contact by mail : > >Dr Francois PELISSE >CERAVAL >rue du Parc >94460 VALENTON (FRANCE) > >This man has a great experience on low cost force >plates and associated software. >Unfortunately, I am not quite sure that he has devloped an >overseas commercial activity (from French part of the sea !) > >Sincerely, >Didier GEIGER. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - From: Tom Cahalan >Dear Dr. Hinrichs: > >I recently performed some basic studies using a prototype two plate system >from Kistler. The system included a small PC, software, and a segmented >walkway. The plates recorded only the vertical component of the ground >reaction force. The system did not appear to have enought range to be able >to assess jumping (we tried, but I didn't trust the data, the top end was >about 2 kN). The system is not yet being marketed, but you might contact >Dave Schieb, 25 John Glenn Drive, Amherst, NY 14228-2171, phone 800-745-7484, >FAX 716-691-5226. In my experience, Dave has been easy to work with, and has >been very helpful regarding product information. > >Another idea that you might consider is to present your problem to the >mechanical engineers at your school. This might be a good undergrad project. >Take four load cells and place them into a plate, develop some simple >software to work on a MAC or PC and away you go. Who knows, maybe that >student will go on to challenge Kistler, AMTI, and Necip Berme. > >Good luck. >Tom Cahalan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - From: James R Harvey >Rick: >Interlink is a company making "Force Sense Resistors" that might be an >inexpensive way to implement what you want. The devices physically look >like a photocell, i.e., little fingers laid out evenly in an array. They >are flat and can be covered with a rubber material to show not only force >but, in some cases, the x-y coordinates of the point of contact. > >Interlink Electronics >Corporate Office >1110 Mark Avenue >Carpinteria, CA 93013-2918 >805/684-2100, FAX 805/684-8282 > >Our contact is Tom Brassil, Director Of Sales. You will be better off, I >think, to contact the corporate office above rather than Tom's address >below: > >Tom Brassil >Phone/Fax 510/672/3342 > >Please let me know if this stuff works out. We are looking at it for a >collision detector on an x-ray system. If you have any technical questions >and want answers "without a sales pitch", give me a call or email. > >Regards, >Jim Harvey >VP, Engineering >OEC-Diasonics >Salt Lake CIty, UT >801/536-4526 > - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - From: Paul J Guy >Rick: > > I know of no really cheap force platforms with an electrical output >unless you try the type that consist of two films with a carbon (?) >sandwitch bewteen them, these are cheap, but not very accurate. They >are also dependent on the surface area of the applied force. >The only other cheapy way to go, is if you can find someone who can >make up strain gauges (a lot of universities may have someone in civil >or mechanical engineering) to make up a four post plate. One of the >nice features of this type, is that it can give you a measure of >"centre of applied pressure". If you include the cost of electronics, >I doubt if you can keep the costs much below several thousand (including >labour). > For contact to floor measurement, I suggest a "tapeswitch" which >will sense foot contact. These are available in many sizes and configurations >from Tapeswitch of America. I don't have the adress handy at the moment, >but it should be available from any industrial directory. We use a >version of these, about an inch in diameter, taped to the subject's foot, >to sense heel, ball, toe contact during walking. This is used for >timing, in the processing and averaging of linear envelope EMG. > > Paul - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - From: Peter Vint >About the "time of contact" things: At the [USOC] training center, we used >"timing mats" which were really just pressure sensitive switches. I'm sure >they were relatively inexpensive, and could be set up to determine "time of >contact" or "time in air". I can also call about those if you want. > >.... > >I called the USOTC and obtained some information about the timing mat systems >we discussed yesterday. Depending on the system, prices range from$55 (mats
>alone) to $1400 (mats/lights/switches/controls/etc...). Here are two companies >which distribute such devices: > > Dekan Timing Devices Inc. > West Chicago, IL > (312) 231-7740 (area code may have changed to 708) > switch mats: 14" X 23" > Price range (as of 6/1/86):$55 - $1400 > > Lafayette Instrument Co. > West Lafayette, IN > (800) 428-7545 > Switch mats: 17" X 23" (Stock #63515 --> may not be up to date) > Price estimate:$69 (I don't know what date that price was quoted)

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Finally:

The following information did not come from BIOMCH-L directly, but from Jim
Hay at the University of Iowa in the form of a FAX. This refers to a
commercially available device: (My questions in parenthesis...)

It is called the IMPAX 420 and is a portable force (or pressure?) mat attached
to a small microprocessor which when used with vertical jumping gives a
digital readout of "total force" generated in the jump (impulse?),
"coupling time" (time of takeoff?), "vertical leap height", "mechanical work",
etc. The literature also says it can tell if the jump is a squat jump or a
countermovement jump. Thus it must be detecting an "unweighting" phase from
the vertical force curve. It costs \$495 and can be ordered from:

Novel Products, Inc.
P.O. Box 408,
Rockton, IL 61072-0408
Phone: 800-323-5143.

I have not contacted this company yet, but am very intriqued by this
device as a teaching tool. It would be even more useful if it gave an analog
force output, but I do not think it does. If I get any more information on
this device, I pass it along to interested parties.

--Rick

Richard N. Hinrichs, Ph.D.
Dept. of Exercise Science
Arizona State University
Tempe, AZ 85287-0404 USA

email (alias): Hinrichs@ESPE1.LA.ASU.EDU