hugh email@example.com (Hugh W. Gleaves) wrote:
A solenoid with a 3" throw might be a bit too slam-bam violent. The
actuators will be used to move components on an optical bench. There is
a biological prep with microelectrodes nearby. Impacts and vibrations
could cause problems.
And 3" is a lot for a solenoid. Don't recall ever seeing one with such
a long pull.
Digressing, I recall wondering once (when experimeting with
solenoids), whether there it would be possible to create some waveform
that would pull in a solonoid plunger 'gently' but reliably?
I read in sci.electronics.design that Terry Pinnell <terrypinDELETE@dial
about 'Seeking a simple binary linear actuator', on Fri, 13 Feb 2004:
I just bought an electric nail-gun which has about 50 mm throw. It
failed after about 50 nails; the thyristor has probably died. So now I
have a replacement; I hope this one survives. I didn't have time to try
to repair the original, and the thyristor is *riveted* to the PCB,
without any need for tight contact with a heat sink!
Yes: if there is a return spring. A current ramp pulls the armature in
at a controllable rate. Obtaining the right current waveform is,
however, not straightforward. A starting pulse may be necessary to
overcome 'stiction', and then the inductance increases as the armature
moves into the coil, but it can be done. It's possible, clearly, to use
a position sensor to provide feedback, and then you are into PID
controller territory and you can make the thing do tricks.
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
hugh firstname.lastname@example.org (Hugh W. Gleaves) wrote in message
The problem with solenoids is that there is a trade-off between force
and travel. As mentioned in the other twig of this particular branch
of the thread, the OP wants a three inch (76 mm)travel which is a lot
for a solenoid - I looked into this for the pen drive in a 100mm
pen-recorder some thirty years ago, and the force you could generate
with a simple solenoid was pretty pathetic.
I rather fancied the linear stepping motor approach used in the
Hewlett Packard X-Y recorder of the same period, but for our
application a bit of stainless steel wire and a capstan driven by an
Escap DC motor was a lot cheaper.
Bill Sloman, Nijmegen
Ah I see, the travel is a bit too much for a solenoid, hence the need
to examine all these other options.
Well I wont throw my ideas in, I'm sure there are enough already in
email@example.com (Bill Sloman) wrote in message
On 13 Feb 2004 07:46:35 -0800, hugh firstname.lastname@example.org (Hugh W.
I can't find the site now, but the other day I did a google
search and found a simple servo controller made from a 555 chip
that controlled a servo in two positions. The servo position was
controlled via the value of a resistor. A low resistor held the
servo in one position, and a higher value moved it to another
position. I can't remember if the design flip/floped between two
resistors, or if a second resistor was put in parallel with the
first to get the low resistance value. With a setup like this a
$10 servo could be used to push/pull the device between two
positions in a fairly gentle way. The below links have similar
setups using a 555 chip. I haven't tried using the 555 chips, so
don't know just how well they work controlling servos.
On Sat, 14 Feb 2004 19:05:40 GMT, shb*NO*SPAMemail@example.com (Si
Circuits like those can be found all over, & they're not limited to
just 2 positions. My personal favorite, & quite easy to build, used to
be #4 at the 2nd source above, but I see it's not there anymore for
some reason (found it with a google search for "servo drive, 4" at:
I'm pretty lazy and cheap. Go to an automotive junkyard, pick up a old
automotive heater and A/C case. They are covered with cheap vacuum
acutators to control mode and temperature doors. If you find a unit
with an digital controlled system (in production since the 80's...)
that unit will have a solenoid pack attached to the case. Open the
pack and use the individual solenoid valves to drive individual vacuum
actuators. The solenoids use... you guessed it... 12v dc.
For a vacuum source pick up a cheap venturi device and hook it up to
shop air compressor. For moving things, these HVAC vacuum acuators
are pretty nice... they don't move too fast, are pretty flexible and
if you push against a stop, no big deal. You don't get current draw
issues, etc... they will move a considerable force. I've used them
numerous times in projects (of course, it helps to work at an
automotive company, where you can walk up to the shop floor and get
these parts out of the parts bin...)
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