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'[EE]: open-loop solenoid driving...'
2002\12\06@101156 by Roman Black

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Sorry to take the focus away from global warming and
child aggression, but has anyone done open-loop
solenoid driving, specifically to make a solenoid
move SLOWLY by a simple PWM waveform??

I need to make a solenoid either pull-in or drop-out
(either is ok) but slowly.

Assume a 12v solenoid with a simple spring and about
6mm of travel. The solenoid armature and load have
constant mass, spring tension will remain similar
and friction is within a predictable small range.

Is it feasable to just kill the solenoid current,
wait a time for the armature to travel small distance,
then give a short current pulse to halt armature
movement, then repeat a couple of times? I'm guessing
that a few correctly timed pulses would give an
armature release of maybe 0.5 seconds compared to
the normal release time of <0.1 seconds?
-Roman

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2002\12\06@104125 by Mike Singer

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Roman Black wrote:
> Sorry to take the focus away from global warming and
> child aggression, but has anyone done open-loop
> solenoid driving, specifically to make a solenoid
> move SLOWLY by a simple PWM waveform??

  Add some pneumatic braking as in good old vinyl disks
players to rise pickup arm.

  Mike.

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2002\12\06@152852 by Spehro Pefhany

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At 02:03 AM 12/7/02 +1100, you wrote:
{Quote hidden}

The problem is that the force is a nonlinear function
of the core position. A mechanical dash pot might be
easier. Though your idea is intriguing, I think that
the position would not be predictable enough with
variations in the spring, mass, etc. unless there was
some feedback of core position.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
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2002\12\06@155939 by Bob Axtell

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There are solenoids that have attached hydraulic
pistons to slow the closure and/or opening easily.

Some are used in electric door closing applications

Search the web, you'll find stuff.

--Bob

{Original Message removed}

2002\12\08@044153 by Roman Black

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Mike Singer wrote:
>
> > has anyone done open-loop
> > solenoid driving, specifically to make a solenoid
> > move SLOWLY by a simple PWM waveform??
>
>    Add some pneumatic braking as in good old vinyl disks
> players to rise pickup arm.


Thanks Mike, I have some of these, and some greasy
cog dampers from cassette door openers too. But I
want a PIC solution using a cheap off the shelf
solenoid. :o)
-Roman

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2002\12\08@053036 by Roman Black

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Spehro Pefhany wrote:
{Quote hidden}

Thanks Spehro, i'm hoping to do it on RELEASE of the
armature, where the force is spring tension vs the
constant mass and it should be possible with the
right length pulse to halt the armature travel every
mm or so, with about 6 to 12 pulses. I don't mind that
the pulses will be of different length and need a bit
of tuning.

I really want to avoid the use of expensive solenoids
or mechanical devices as I can get off the shelf
solenoids cheap and prefer to use a PIC to do the
"hard" bit... ;o)
-Roman

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