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'[Pic]: Counting shaft revolutions'
2002\10\26@083103 by Rod Phillips

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Hello to all,

I'm interested in a device that can be used to count revolutions of a slow
turning shaft, 10 turns/minute,  with 1 or 2 degree resolution.  I will then
use a Pic to read and limit the number of turns and fractional parts of a
turn.  Good resolution is important. Any ideas appreciated.

                                               Rod

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2002\10\26@085421 by Alan Gorham

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You could look at the optical disks and counting modules made by US digital.
They are available for many different shaft diameters and with a range of
count resolutions.

http://www.usdigital.com


Alan



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2002\10\26@120239 by techhead

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A simple, effective way is to strap a magnet or two or three to the
shaft and put a hall effect xsistor where the magnets would sweep by and
count pulses. The more magnets the better the resolution on rotation but
if you are just worried about counting rev's and not about stopping
precisely one magnet will do. The very early add on car cruise controls
used that same method. They tied magnets to the drive shaft. I have an
app where I am doing the same thing and used magnets and a alarm magnet
switch as the sensor. The magnets were pennies apiece and the magnetic
door switch was 99 cents at Radio shack.

{Original Message removed}

2002\10\26@131731 by Alan B. Pearce

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>I'm interested in a device that can be used to count revolutions of a
>slow turning shaft, 10 turns/minute,  with 1 or 2 degree resolution.  I

How accessible, and what diameter is the shaft?

My thinking is you may get away with printing a single line graticule onto a
paper strip with a laser printer, and wrap this round the shaft. Then use a
reflective opto sensor to sense the lines going past. It is about the only
way to "add-on" a fine sensor unless you can add a rotation sensor to the
end of the shaft.

Just a thought after watching what was done to sense the position of a
linear piezo motor by the guys on the Star Tiger project
(http://www.startiger.org/ ). This was exactly how they did it, and it gave
them lines about 0.5mm thick with equal spaces. Good for a quick sensor :)

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2002\10\26@143800 by John Ferrell

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One possibility for increasing the count resolution is to step up the shaft
rate with a couple of gears driving an emitter. IBM has used this
extensively in their big iron printers.

I always read the saw blade ads and count the teeth hoping to find a usable
number greater than 60.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



{Original Message removed}

2002\10\26@155550 by William Chops Westfield

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   I'm interested in a device that can be used to count revolutions of a
   slow turning shaft, 10 turns/minute, with 1 or 2 degree resolution.  I
   will then use a Pic to read and limit the number of turns and
   fractional parts of a turn.  Good resolution is important.

optical encoder?  For a hobbyist project: mouse guts/

BillW

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2002\10\26@165518 by Olin Lathrop

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> I'm interested in a device that can be used to count revolutions of a
slow
> turning shaft, 10 turns/minute,  with 1 or 2 degree resolution.  I will
then
> use a Pic to read and limit the number of turns and fractional parts of
a
> turn.  Good resolution is important. Any ideas appreciated.

Search for "shaft encoders".


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\10\26@180901 by Wagner Lipnharski

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Something really new?
Use a new optical mouse ($15), it can sense the minimum movement of the
shaft rotation and can delivery it to you via RS232...
You need to ensure that no oil or grease will blind the CCD sensor.  The
shaft body should be within milimeters of the mouse.
This solution is cheap and requires no modification or installation of
anything at the shaft, just the mouse.
The CCD captures several images per second and account on image difference
to report the XY movement.

W46NER

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2002\10\28@012655 by Peter L. Peres

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On Sat, 26 Oct 2002, Wagner Lipnharski wrote:

*>Something really new?
*>Use a new optical mouse ($15), it can sense the minimum movement of the
*>shaft rotation and can delivery it to you via RS232...
*>You need to ensure that no oil or grease will blind the CCD sensor.  The
*>shaft body should be within milimeters of the mouse.
*>This solution is cheap and requires no modification or installation of
*>anything at the shaft, just the mouse.
*>The CCD captures several images per second and account on image difference
*>to report the XY movement.

Have you tried this for several tens of rpms ?

Peter

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2002\10\28@041026 by Russell McMahon

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> *>Use a new optical mouse ($15), it can sense the minimum movement of the
> *>shaft rotation and can delivery it to you via RS232...

> Have you tried this for several tens of rpms ?

Using an optical mouse in this way is such a good idea that I feel I have to
test it.
Using a mechanical mouse and moving it all the way up the mouse pad, lifting
it, taking it to the bottom :"in the air" and repeating 30 times, then
moving it downwards, instantly produced a correct downwards response. ie the
mouse electronics did not "get lost". This was what I would have expected as
the mouse only has to send delta position information BUT there is no
accounting for the stupidities that can creep into software design.

Hopefully this applies to optical mice as well.

Sudden recollection - my son is using an optical mouse - quick trip to his
PC reveals that it also allows multiple passes in one direction without
losing track. Don't know how accurate it is over substantial distance. May
yet fail over a very long distance but it seems OK.


       Russell McMahon

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2002\10\28@050043 by Siiskonen, Pekka

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> -----Original Message-----
> From: Russell McMahon [apptechspamKILLspamPARADISE.NET.NZ]
> > *>Use a new optical mouse ($15), it can sense the minimum
> movement of the
> > *>shaft rotation and can delivery it to you via RS232...
>

Just crossed my mind: is the "ballistic" property of a mouse built into the
mouse hardware or is it a operating system's property (moving the mouse
faster gets you further although the actual distance the mouse moved is the
same!). If it is related to mouse hardware then rapid acceleration may spoil
the counting....

Pekka Siiskonen

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2002\10\28@054854 by lexandre_Guimar=E3es?=

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Hi,

> Just crossed my mind: is the "ballistic" property of a mouse built into
the
> mouse hardware or is it a operating system's property (moving the mouse
> faster gets you further although the actual distance the mouse moved is
the
> same!). If it is related to mouse hardware then rapid acceleration may
spoil
> the counting....


   It is done in the mouse driver, not the firmware.

Best regards,
Alexandre Guimaraes

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2002\10\28@122039 by Peter L. Peres
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On Mon, 28 Oct 2002, Russell McMahon wrote:

*>> *>Use a new optical mouse ($15), it can sense the minimum movement of the
*>> *>shaft rotation and can delivery it to you via RS232...
*>
*>> Have you tried this for several tens of rpms ?
*>
*>Using an optical mouse in this way is such a good idea that I feel I have to
*>test it.

YES BUT WHAT ABOUT THE SPEED. Shafts are known to move slightly faster
than people's hands. Also what is the creep of this method. I am SURE that
it creeps. The measuring method has no fixed datums. I am eager to hear
otherwise.

Peter

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2002\10\28@123955 by Alan B. Pearce

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>YES BUT WHAT ABOUT THE SPEED. Shafts are known to move slightly
>faster than people's hands.

Well the original request was for a reasonably slow ratation rate.

>Also what is the creep of this method. I am SURE that
>it creeps. The measuring method has no fixed datums.

This may be a problem. I guess it depends on if you want to know the
rotation speed, or the equivalent linear distance the periphery of the shaft
has travelled. IIRC the original request was to know how far the shaft had
rotated to an accuracy of better then 2 degrees. Now to do this a knowledge
of the circumference and an index pulse from a suitable sensor should be
enough to use an optical mouse for this purpose. An initial calibration to
get mickeys/revolution would be needed, but once you have that then the rest
would be easy.

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2002\10\28@131120 by Peter L. Peres

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On Mon, 28 Oct 2002, Alan B. Pearce wrote:

*>>Also what is the creep of this method. I am SURE that
*>>it creeps. The measuring method has no fixed datums.
*>
*>This may be a problem. I guess it depends on if you want to know the
*>rotation speed, or the equivalent linear distance the periphery of the shaft
*>has travelled. IIRC the original request was to know how far the shaft had
*>rotated to an accuracy of better then 2 degrees. Now to do this a knowledge
*>of the circumference and an index pulse from a suitable sensor should be
*>enough to use an optical mouse for this purpose. An initial calibration to
*>get mickeys/revolution would be needed, but once you have that then the rest
*>would be easy.

Whenever I see such a spec I think for five seconds and then I say, ha, 2
degrees are 2/360 = 0.55%, and you want to resolve twise as good in the
sensor to be able to claim 2 degrees, or 0.25%. A $5 mouse is perhaps good
to 5% due to mechanics and slotted disc resolution (not to mention edge
detection accuracy), so it's twenty times too bad for that imho. I am not
saying it can't be done. I'm saying it can't be done in 5 minutes ;-).

Peter

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