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View Full Version : Reply Summary-Fall Detection & Cheap Accelerometers

Steve Lutes
04-22-1998, 07:55 AM
A big *thank you* to all who responded. Here's a summary or replies so that all
list members can benefit. My original post was

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I'm designing a fall detector. I need the following information

(1) What the level of acceleration when a person falls and
what parts of the body experience what levels?

(2) Source of a *cheap* accelerometer to measure the
acceleration described in (1).
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******Part 1 of Query-Acceleration
Level****************************************

From bkirking@bcm.tmc.edu

Theory:
The answer is 9.81 meters/second squared, if the person does not
contribute to the acceleration caused by gravity by "flailing", which will
obviously be a huge component if you are interested in the acceleration of
the hands. I tend to think that an accelerometer mounted on the thorax
would give you stable results. I would also stay away from the head since
a person could jerk their head to avoid hitting it, unless of course you
are interested in the kinetics and kinematics of the head.

Bryan Kirking
Research Engineer
Department of Orthopedic Surgery
Baylor College of Medicine
Houston, Texas

From Dhendry :
1. g

From: Andrew_Pinder@hsl.gov.uk

The answer to (1) is 'g' the acceleration due to gravity. This is
approximately
9.8 m/s/s, though it varies slightly around the world.

Andrew.Pinder@hsl.gov.uk

From: "R.E.Mayagoitia" :

Dear Steven,
The easiest way to calculate the acceleration and velocity at impact
from a fall is the way presented in problem 7-24 page 197 of
Barney Le Veau's edition (3rd) of Williams' and Lissner's
Biomechanics of Human Motion (W. B. Saunders, 1991). It all comes
down to how high the person falls from, how large the person's
mass is and the length of time of impact. In this problem the center of
mass is considered.The same method can be applied to any body
segment. For this approach you only need high school physics.

Ruth
********************************************
Ruth Mayagoitia
Visiting Professor
R.Mayagoitia@Sheffield.ac.uk

******Part 2 of Query-Cheap Accelerometers************************************ *

From: Gary Kamen
You may be interested in a report I recently published that describes an
inexpensive accelerometer system for measuring balance and postural sway:

Kamen, G. et al. An accelerometry-based system for the assessment of
balance and postural sway. Gerontology. 44:40-45, 1998.

A forthcoming paper will demonstrate its utility in discriminating between
frequent fallers and healthy older adults:

Cho, C.-Y. and G. Kamen. Detecting Balance Deficits in Frequent Fallers
Using Clinical and Quantitative Evaluation Tools. Journal of the American
Geriatrics Society (In Press).
Gary Kamen
Department of Exercise Science
Totman 160A
University of Massachusetts
Amherst, MA 01003
413-545-0784
413-545-2906 (FAX)

From Dhendry :
2. any weight scale

Seriously, what you probably want to know is the acceleration experienced by
different parts of the body in (at the end of) a fall. Those depend on too
many variables. You might get a suitable cheap accelerometer for ~\$100, but
the supporting equipment (amplifiers, recorders, etc) will cost ten times as
much.

From: "Anthony J. Petrella"

Steve:

Check out Analog Devices for accelerometers in the \$15-\$20 range. You may
have to do a little wiring to build a circuit, but the price is right.
They have more expensive devices called evaluation modules that are the
same chip as noted above but they come wired with a signal
conditioning/amplifying circuit all in a little 3/4 x 1/2 inch block for

http://products.analog.com/products_html/list_gen_121.html

Regards,

--
----------------------------
Anthony J. Petrella
University of Pittsburgh
petrella@sprite.me.pitt.edu
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"Geoffrey.Walsh" :

I wonder if you have the elctronics chain ,Maplin, in the US ?

They list a small accelerometer for about 30 pounds I think.

Their Web site is given as
http://www.maplin.co.uk

Email -

Geoffrey.Walsh@ed.ac.uk

http://www.ed.ac.uk/~gwalsh

Phone (0)131.664.3046

64, Liberton Drive,
Edinburgh
EH16 6NW
U.K.