Slowing solenoid action?

[Terry Pinnell]

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

 

To do that you have to modulate it based on the desired force, against whatever resistance. I would recommend a motor unless you have another reason for not using one. With a simple solenoid you would probably need positional feedback. Not with a stepper motor.

 

You could do it with a control loop, but you'd need a linear encoder. Your idea of using a rotary model airplane servo gets my vote--all you need is a little metal arm to do the actual pushing.

Cheers

Phil Hobbs

(on the plane to Austin to visit #2 daughter, formerly known as Beautiful Layout Hunchback)

 

On Sat, 26 Oct 2019 17:28:50 +0100, Terry Pinnell
<me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:

On Sat, 26 Oct 2019 15:19:03 +0100, Terry Pinnell
me@somewhere.invalid> wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

A little PWM could help a bit, but most solenoids are very nonlinear
and have a strong positive-feedback snap effect. You'd have to
modulate the PWM just right, to track the armature location open-loop,
but that should be possible.

Thanks all, appreciate the fast feedback.

Floating another idea: start by applying the full 24V, to get it moving, but quickly
reduce it and continue doing so at some fast rate. Say over 100-250 ms. Trial/error
featuring heavily!

Linear ramp-down should improve things. Unfortunately, reversing the
drive to a solenois doesn't reverse the force?

Why not a foam pusher or something?

Not sure about the simplest circuit to crudely test that approach? Presumably power
transistor with the solenoid between its collector and +24V, but what to feed its
base (via Arduino) to rapidly reduce the load voltage?

Declining duty cycle PWM.

Also tentatively considering idea of a small motor spinning a bolt with its threaded
nut doing the push/pull. Or some cheap product that uses a motor to push a rod. I
expect there must be various applications for that, such as opening a skylight or
trapdoor, but not sure about smaller scale.

Or use a stepper motor, smooth and quiet. There are also linear
steppers, which is a stepper motor with a lead screw built in.

I have the servo rotor arm working over the angle required, but not yet done any of
the fiddly work on transferring that to a simple push.

Ebay has some interesting things.

https://tinyurl.com/y3yan2xe


So does Amazon. Search for linear stepper motor maybe.










--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[whit3rd]

On Saturday, October 26, 2019 at 7:19:09 AM UTC-7, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily.

Speed, noise; those are mechanical considerations. So you either want a
linear motor that's quieter, OR you can use a linkage (lever) to alter the
speed/force, and a package to muffle the noise.

Usually, though, one would (for instance) try a solid-state approach for
silence, like bypassing the button contacts with an optoisolator output,
and driving an LED input to activate the circuit.

 

[Terry Pinnell]

jlarkin@highlandsniptechnology.com wrote:

On Sat, 26 Oct 2019 15:19:03 +0100, Terry Pinnell
me@somewhere.invalid> wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

A little PWM could help a bit, but most solenoids are very nonlinear
and have a strong positive-feedback snap effect. You'd have to
modulate the PWM just right, to track the armature location open-loop,
but that should be possible.

Thanks all, appreciate the fast feedback.

Floating another idea: start by applying the full 24V, to get it moving, but quickly
reduce it and continue doing so at some fast rate. Say over 100-250 ms. Trial/error
featuring heavily!

Not sure about the simplest circuit to crudely test that approach? Presumably power
transistor with the solenoid between its collector and +24V, but what to feed its
base (via Arduino) to rapidly reduce the load voltage?

Also tentatively considering idea of a small motor spinning a bolt with its threaded
nut doing the push/pull. Or some cheap product that uses a motor to push a rod. I
expect there must be various applications for that, such as opening a skylight or
trapdoor, but not sure about smaller scale.

I have the servo rotor arm working over the angle required, but not yet done any of
the fiddly work on transferring that to a simple push.

 

[Clive Arthur]

On 26/10/2019 15:19, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

I have tried that, it didn't work at all well, the solenoid snapped over
quickly.

How about a modified loudspeaker? That will move as slow as you like.

Cheers
--
Clive

 

On Sat, 26 Oct 2019 15:19:03 +0100, Terry Pinnell
<me@somewhere.invalid> wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

A little PWM could help a bit, but most solenoids are very nonlinear
and have a strong positive-feedback snap effect. You'd have to
modulate the PWM just right, to track the armature location open-loop,
but that should be possible.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Rick C]

On Saturday, October 26, 2019 at 10:19:09 AM UTC-4, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

What the others are saying is that a solenoid is usually a coil, a plunger and a spring. The plunger is held out of the coil by the spring and pulled in by current through the coil. When the current is applied the plunger starts moving but is accelerated pretty much the whole time it is moving. The result is hits the stop pretty hard. I assume you have it hitting the button at the end of the stroke when activated, so it is moving pretty smartly when it hits the button.

You can put something on the end of the plunger to provide some cushioning and let the plunger hit something else as a stop. So the cushion will hit the button before the plunger stops and the cushion will absorb the impact to the button. Felt pads may do well. The stop can even be somewhat flexible or have it's own cushion to prevent the bang when the plunger is activated.

It just seems like taking the hard route to deal with this electronically. Or are you designing something for a Tesla?

Perhaps the entire idea is overdesigned? They have a single device that would seem to do what you want. It's called a relay, solenoid and switch built into one unit. They generally work well and usually don't make a big noise, rather gentle taps.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Sjouke Burry]

On 26.10.19 16:19, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

Put the moving core in a tightly fitting tube,open at on end.
When the core starts moving, air has to leak in, slowing the core.

 

[Joseph Gwinn]

On Oct 26, 2019, Terry Pinnell wrote
(in article<ihk8re5ncospvblqpgoeiqhh53rji1n5h5@4ax.com&gt:

Is it possible, perhaps using PWM, to slow down the action of a solenoid
while still maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button. The only one I have at present that can do so reliably is a 24V type

that delivers its press too fast and too noisily. Lower voltage types
(already owned or researched on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a
sketch to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although
n
intermediate short spring might allow some tolerance.

What you probably want is what is called "indirect drive", which is that
intermediate short spring, but used in a different way. In short, the
solenoid compresses the spring until a drive ratchet falls into place. When
the solenoid is turned off, the spring then pushes the button. The ratchet is
reset somehow.

This approach is old school:

<https://www.telephonecollectors.info/index.php/browse/bc-switching-
library/automatic-electric/ae-switching-docs/10539-how-to-use-rotary-stepping-
switches-automatic-electric-1964-ocr-r/file>

Joe Gwinn

 

[Klaus Kragelund]

You can do a nice trick:

Use your Arduino to apply the PWM that controls the current in the coil

Then measure the current in the coil, referenced to GND, with an ADC to find the peak to peak ripple

The peak peak current changes amplitude according to the inductance of the coil

Measure this amplitude 100 times per second

The coil inductance is related to the armature position, so now you have a feedback to control the rate of change of the duty cycle of the PWM which is controlled by your ramp

If the armature moves to fast, you will detect a sudden move in inductance change so you can dial down the PWM ramp

You can also just turn the coil on, and monitor the current in the coil. When the armature moves, the back EMF will make a kink in the current so you can reduce the PWM, but that is not closed loop like the previous solution listed above

Cheers

Klaus

 

[Klaus Kragelund]

In the solution, the PWM duty cycle needs to compensate the measured peak peak current

You can measure the dI/dt, that will be a more direct measurement

 

[Jasen Betts]

On 2019-10-26, Terry Pinnell <me@somewhere.invalid> wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

mechanically: attach a dashpot.

PWM or a voltage (or current) ramp into the solenoid could work,
but the response may not be linear, most solenoids have positive
magnetic fedback.

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

a servo or gear-motor with a cam or crank seems the easiest option but
will be less durable than the solenoid.

replace (or parallel) the button with a relay is another option if you
can access the inside of the device.


--
When I tried casting out nines I made a hash of it.

 

[Jasen Betts]

On 2019-10-26, Terry Pinnell <me@somewhere.invalid> wrote:

jlarkin@highlandsniptechnology.com wrote:



Also tentatively considering idea of a small motor spinning a bolt with its threaded
nut doing the push/pull. Or some cheap product that uses a motor to push a rod. I
expect there must be various applications for that, such as opening a skylight or
trapdoor, but not sure about smaller scale.

That's called a jackscrew, and is a recognised technique for building linear
actuators, but most small stuff seems to be levers and cams

as I understand it most (automotive) central locking systems use rack
and pinion actuators instead (but some are pneumatic)

I have the servo rotor arm working over the angle required, but not yet done any of
the fiddly work on transferring that to a simple push.

maybe just put a roller (eg ball bearing) on the end of a short servo arm.

--
When I tried casting out nines I made a hash of it.

 

[dcaster@krl.org]

On Saturday, October 26, 2019 at 10:19:09 AM UTC-4, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

A inducter in series with the current to the solenoid ought to slow things down. It may not be feasible if the inductor is too large. How about a RC circuit feedirg the base of a transistor with solenoid connected to the collector ?

Changing the switch to one easier to press is probably the most reasonable solution.

Dan

 

On Saturday, 26 October 2019 17:28:56 UTC+1, Terry Pinnell wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 26 Oct 2019 15:19:03 +0100, Terry Pinnell
me@somewhere.invalid> wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

A little PWM could help a bit, but most solenoids are very nonlinear
and have a strong positive-feedback snap effect. You'd have to
modulate the PWM just right, to track the armature location open-loop,
but that should be possible.

Thanks all, appreciate the fast feedback.

Floating another idea: start by applying the full 24V, to get it moving, but quickly
reduce it and continue doing so at some fast rate. Say over 100-250 ms. Trial/error
featuring heavily!

I used to do that

Not sure about the simplest circuit to crudely test that approach? Presumably power
transistor with the solenoid between its collector and +24V, but what to feed its
base (via Arduino) to rapidly reduce the load voltage?

simple: drive the solenoid via a resistor to drop the v, and add a lytic cap. When not energised the cap charges to full v, so the solenoid gets an initial kick. With a microprocessor you could deliver 100% duty cycle then reduce it to less, no bulky parts.

Also tentatively considering idea of a small motor spinning a bolt with its threaded
nut doing the push/pull. Or some cheap product that uses a motor to push a rod. I
expect there must be various applications for that, such as opening a skylight or
trapdoor, but not sure about smaller scale.

just bear in mind overshoot could produce destructive forces

I have the servo rotor arm working over the angle required, but not yet done any of
the fiddly work on transferring that to a simple push.

Adding a rubber disc between solenoid armature & switch plus reducing v or duty cycle could both help with noise. Probably not enough. Rubber hardens in time of course, ssome materials like silicone less so.


NT

 

[Jeff Layman]

On 26/10/19 15:19, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

No solenoid.

Motor, gearbox, eccentric cam. Use motor speed and/or gearing to set
operation parameters.

--

Jeff

 

[Jan Panteltje]

On a sunny day (Sun, 27 Oct 2019 08:15:02 +0000) it happened Jeff Layman
<jmlayman@invalid.invalid> wrote in <qp3jm6$bra$1@dont-email.me>:

On 26/10/19 15:19, Terry Pinnell wrote:
Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Terry, East Grinstead, UK

No solenoid.

Motor, gearbox, eccentric cam. Use motor speed and/or gearing to set
operation parameters.

Piece of rubber between solenoid and button?

 

[Martin Brown]

On 26/10/2019 15:19, Terry Pinnell wrote:

Is it possible, perhaps using PWM, to slow down the action of a solenoid while still
maintaining most of its force?

Wouldn't an eccentric cam on a motor be easier.

By way of background, I'm considering a solenoid for pressing a rather firm button.
The only one I have at present that can do so reliably is a 24V type that delivers
its press too fast and too noisily. Lower voltage types (already owned or researched
on ebay or Amazon) seem too weak.

A crude way that might work is a chunky capacitor holding full voltage
at the outset initially to get it moving and a lower sustain current
through a resistor. Trial and error may be necessary.

I'm recently into Arduino and am also considering the alternative of coding a sketch
to do it with a small servo. The downside would be the extra mechanics.

Any other suggestions of applying a firm linear push over 2mm? Reversing it
consistently, ready for the next application, is obviously required. Although an
intermediate short spring might allow some tolerance.

Eccentric cam would be my choice.

--
Regards,
Martin Brown