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From: haoxiang on 28 Dec 2009 00:06
Hi all,

I am working on a project on human static standing and i am measuring
the angular body sway of a human when he/she is standing still. I am using
a tri-axis accelerometer
(http://www.sparkfun.com/commerce/product_info.php?products_id=8563) and
obtaining angular displacement estimate based on double integration of
acceleration reading and some least-square estimates. Unfortunately my
experiment duration need to be at least 1 minute and the drift error causes
the estimate to be way off the mark... It doesn't help that i can't exactly
pinpoint my initial acceleration.

Can anyone suggest any method to reduce the error in my measurement? My
prof suggested calibrating the result which another camera system which
simultaneously track position but as time is tight, i would hope to find
solution based solely on accelerometer and parameters i have.... Hope to
hear good news soon

Regards,
Hao Xiang


From: Rune Allnor on 28 Dec 2009 06:02
On 28 Des, 06:06, "haoxiang" <haoxiang1...(a)hotmail.com> wrote:
> Hi all,
>
>   I am working on a project on human static standing and i am measuring
> the angular body sway of a human when he/she is standing still. I am using
> a tri-axis accelerometer
> (http://www.sparkfun.com/commerce/product_info.php?products_id=8563) and
> obtaining angular displacement estimate based on double integration of
> acceleration reading and some least-square estimates. Unfortunately my
> experiment duration need to be at least 1 minute and the drift error causes
> the estimate to be way off the mark... It doesn't help that i can't exactly
> pinpoint my initial acceleration.
>
>   Can anyone suggest any method to reduce the error in my measurement? My
> prof suggested calibrating the result which another camera system which
> simultaneously track position but as time is tight, i would hope to find
> solution based solely on accelerometer and parameters i have.... Hope to
> hear good news soon

Don't expect any fast/simple/easy/convenient solutions...

I would *guess* that part of the problem is that humans
tend to rotate when swaying. So if you fix the sensor
to the human body, the device which is designed to
measure purely translational movements, will also be
subjected to rotations. Which would severely mess up
the data if not accounted for.

And no, I have no idea how to correct for such effects
based on the data you have.

Rune
From: Richard Owlett on 28 Dec 2009 08:52
Rune Allnor wrote:
> On 28 Des, 06:06, "haoxiang" <haoxiang1...(a)hotmail.com> wrote:
>> Hi all,
>>
>> I am working on a project on human static standing and i am measuring
>> the angular body sway of a human when he/she is standing still. I am using
>> a tri-axis accelerometer
>> (http://www.sparkfun.com/commerce/product_info.php?products_id=8563) and
>> obtaining angular displacement estimate based on double integration of
>> acceleration reading and some least-square estimates. Unfortunately my
>> experiment duration need to be at least 1 minute and the drift error causes
>> the estimate to be way off the mark... It doesn't help that i can't exactly
>> pinpoint my initial acceleration.
>>
>> Can anyone suggest any method to reduce the error in my measurement? My
>> prof suggested calibrating the result which another camera system which
>> simultaneously track position but as time is tight, i would hope to find
>> solution based solely on accelerometer and parameters i have.... Hope to
>> hear good news soon
>
> Don't expect any fast/simple/easy/convenient solutions...
>
> I would *guess* that part of the problem is that humans
> tend to rotate when swaying. So if you fix the sensor
> to the human body, the device which is designed to
> measure purely translational movements, will also be
> subjected to rotations. Which would severely mess up
> the data if not accounted for.
>
> And no, I have no idea how to correct for such effects
> based on the data you have.
>
> Rune

I would suggest he run his experiment with an idealized subject -
a pendulum.

A Google search for his accelerometer would also prove
informative (I tried it)

From: haoxiang on 28 Dec 2009 14:39
>
>
>haoxiang wrote:
>
>> I am working on a project on human static standing and i am measuring
>> the angular body sway of a human when he/she is standing still.
>
>What is a purpose of that?

Basically the amount of body sway of a human during static standing has a
correlation to the likelihood of fall. Elderly tend to have larger
magnitude of body sway compare to a young healthy adult.

>
>> I am using
>> a tri-axis accelerometer
>> (http://www.sparkfun.com/commerce/product_info.php?products_id=8563)
and
>> obtaining angular displacement estimate based on double integration of
>> acceleration reading and some least-square estimates. Unfortunately my
>> experiment duration need to be at least 1 minute and the drift error
causes
>> the estimate to be way off the mark... It doesn't help that i can't
exactly
>> pinpoint my initial acceleration.
>>
>> Can anyone suggest any method to reduce the error in my measurement?
My
>> prof suggested calibrating the result which another camera system
which
>> simultaneously track position but as time is tight, i would hope to
find
>> solution based solely on accelerometer and parameters i have.... Hope
to
>> hear good news soon
>
>The accuracy of MEMS accelerometers is inadequate for innertial
>measurements. However, you can measure tilt angle with respect to
>gravitation and figure out the sway from there.
>
>
>Vladimir Vassilevsky
>DSP and Mixed Signal Design Consultant
>http://www.abvolt.com
>

When you figuring out sway based on tilt angle wrt to gravity, could you
elaborate on this further?
From: haoxiang on 28 Dec 2009 14:42
>Vladimir Vassilevsky wrote:
>
>BTW the chip manufacturer has an app note for a related
>application. I'll have to wait to get to a high speed connection
>to download and read it.
>

Hello,

Can you attach the link of this application? I can't seem to find it.
It'll be a great help to me.

Regards,
Hao Xiang
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