Forums

Slowing solenoid action?

Started by Terry Pinnell October 26, 2019
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 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
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.
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.
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 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
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
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.