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'[EE] IBM laptop anti-drop protection.'
2005\03\05@103613 by Russell McMahon

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I see IBM advertising that their Thinkpads have "drop sensing" which
parks the drive when the laptop senses that it has been dropped. May
have had this for years for all I know.

I assume that sensing is done with several accelerometers - an XYZ
cluster would be needed to work in all orientations. When the vector
sum of acceleration falls to near zero it's time to shut down.

They say that head parking time is 500 mS. For a straight clean drop
that's a 1.25m fall :-(. Too far. To get distance down to 600 mm you
need about 350 mS parking.

Has anyone encountered this system yet? Any idea of how it works in
practice and how effective it is? It should really scream when dropped
and before impact to instil user confidence :-).


       RM

2005\03\05@115108 by M. Adam Davis

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Recently someone interfaced to the sensors in an Apple laptop
(slashdot discussion yesterday) and it appears that there are two
gyros and one accelerometer.

The gyros sense rotation of the laptop side to side and front to back
(don't care about spinning the laptop in a circle).  The accelerometer
is in the Z (down) direction as the laptop sits on a table.

I suspect that when a laptop falls the rotation takes more than a few
hundred mS as the unit slides off the surface (hand, table, armrest,
etc).  There should be plenty of time to stop the heads if you sense a
change in angle of more than 10 degrees or so in a short period of
time.

Discussions about it seem to indicate that it's very agressive, and
will park the heads when the user picks the laptop up from a table,
some indicate that if they hit the table next to the laptop hard then
it parks the heads.  They change the sensitivity so they get better
performance since it seems to be parking the heads when they
shouldn't.

But I suspect the roll rate is more easily detected first rather than
0g.  Further, laptop hard drives designed for this should be able to
park their heads significantly faster than 500mS.  All you have to do
is rail the servo with a transister.  The head is tiny and light
enough, and the servo powerful enough (it has to be for fast access
times) that it should be much faster than 1/2 a second.  I imagine you
could test this with an old bad HD by hooking an appropiately
amplified square wave to the servo mechanism and slamming the head
from side to side - increase the frequency until it no longer touches
both limits.  I'd be surprised if it couldn't manage greater than
10Hz.

Might be easier than that, though.  The maximum seek time is the time
it takes to travel from the edge of the platter to the center and
rotate the disk one full revolution.  Average seek time is typically
computed as 1/2 the maximum time.  Most drives are rated for around
10mS for the average seek time (12mS is common).  Parking the head
should not be much longer than twice that.  In most cases, the parking
head time includes spinning down the platters.  For this purpose
parking the head meerely means driving the head to the inner, unused,
tracks and keeping it there in case it falls to the platter during a
hard hit or during spin down.

-Adam

On Sun, 06 Mar 2005 04:36:11 +1300, Russell McMahon
<spam_OUTapptechTakeThisOuTspamparadise.net.nz> wrote:
{Quote hidden}

> -

2005\03\05@121346 by Jack Krause

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I wonder if perhaps ALL computers equipped with relatively modern hard
drives have this 'drop sensor'.

Since the drive platter has mass and is spinning rapidly, any angular change
of the hard drive housing will result in a torque 'bump' reflected back to
the spindle motor. The more rapid the the angular change, the bigger the
'bump'.  If, therefore, one monitored the instantaneous current to the rotor
motor, one could sense a drop of the computer itself.  There is actually an
appreciable torque anomaly generated by radial acceleration.  The effect
from axial acceleration is much less pronounced, but is there nonetheless.
I wonder...

On the other hand, the two-axis accelerometers available today (ADXLxxx et
al) are pretty cheap - probably a buck at OEM quantities.  They are
super-simple to implement, especially for an application like this.  And I
think one could assume that in a drop there'd be enough acceleratio in two
(of the three) axes that 2-axis sensing would be adequate.

Head transit-time from even the outside of the platter to park on a 2.5 inch
drive is well under 100 mS, so it would seem physically possible to park the
drive during a 4 foot fall.  It'd just be a matter of getting the park
instruction to the drive in time.

Bill K.



{Original Message removed}

2005\03\05@141730 by Peter L. Peres

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On Sat, 5 Mar 2005, M. Adam Davis wrote:

> But I suspect the roll rate is more easily detected first rather than
> 0g.  Further, laptop hard drives designed for this should be able to
> park their heads significantly faster than 500mS.  All you have to do
> is rail the servo with a transister.  The head is tiny and light
> enough, and the servo powerful enough (it has to be for fast access
> times) that it should be much faster than 1/2 a second.  I imagine you
> could test this with an old bad HD by hooking an appropiately
> amplified square wave to the servo mechanism and slamming the head
> from side to side - increase the frequency until it no longer touches
> both limits.  I'd be surprised if it couldn't manage greater than
> 10Hz.

A reasonably modern laptop drive does about 30 full head strokes per
second. I measured this (with a dead drive) because I wanted to use the
head servo for other purposes. It moves so fast it's a blur. I measured
with the drive open and spinning and while injecting a sine wave from a
signal generator into the head servo. I increased the frequency until
the (almost full stroke - to avoid the latch - see below) amplitude
started to decrease.

{Quote hidden}

Most laptop drives have a mechanical and/or magnetic latch that catches
the head assembly when it it in the parking position. It retains it
there without power, and is supposed to withstand 20+g shocks while so
parked.

Peter

2005\03\07@034256 by William Chops Westfield

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On Mar 5, 2005, at 8:51 AM, M. Adam Davis wrote:

> Recently someone interfaced to the sensors in an Apple laptop
> (slashdot discussion yesterday)

Discussion of the Apple system here:

http://www.kernelthread.com/software/ams/

BillW

2005\03\07@063303 by Vic Fraenckel

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Go here:
http://www.kionix.com/App-Notes/app-notes.htm

and read this app note
Using the Kionix KXM52-1050 Tri-Axis Accelerometer for Hard Drive Shock
Protection

HTH

Vic Fraenckel
________________________________________________________

Victor Fraenckel - The Windman
victorf ATSIGN windreader DOTcom
KC2GUI

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