Microactuator

[Rachie5272]

I need an actuator to press a small mechanical button.  It needs about a 2mm displacement, and fairly low force.  Actuation time of about 1 second or less, and a long recovery time is fine.

Does anyone know of a source of microactuators?  I can't find much of anything which is actually small.  Thanks!

[Gyro]

A small solenoid with a push rod would be the simplest solution. How much space around and above the button do you actually have?


E.g. https://uk.rs-online.com/web/p/dc-d-frame-solenoid/3073326/

[splin]

You could make something from 'smart wire' (Nitinol - shape memory alloy or sometimes called muscle wire). See page 2 of:

https://www.rapidonline.com/pdf/87-6118.pdf

That's only one arrangement you could use - for example you could use a straight piece of wire pulling on a small bellcrank which presses the button.

[H.O]

A tiny DC gear motor and an excentric wheel perhaps?

[Berni]

Depends on how much force is required and what sort of timing precision do you want.

For reasonably low forces a solenoid will give very predictable timing and a low duty cycle allows you to even overdrive the coil for more power.

When you need lots of force you will probably want some sort of DC motor with appropriate gearing to give it the oomph. An RC servo motor can put out a lot of force and you get the gearing and control electronics built in. If you need even more force there are also linear actuators that are basically a DC motor on a threaded rod inside, but i don't think you would need that much force for a even the stubbornest of buttons.

[mikeselectricstuff]

A thermal actuator, as commonly used in washing machine door locks might be doable - expansion of a heated wax material confined in  an enclosure causes a small displacement with quite a lot of force. Something like this built in a small tube might work.

[DTJ]

Gyro's solenoid suggestion would be simple and effective. Maybe put some softish urethane rubber on the end of the plunger to make it easier on the switch as well as quieter.

[mathsquid]

My first thought, like the others above, was to use a solenoid.

A small servo could also do the job, and might be preferable since the throw could be adjusted in software.

[Rachie5272]

Nickel titanium wire looks very promising for this.  Where do I get it?  I'm having trouble finding sources, especially ones which have datasheets.  I'm in the US.

[mikeselectricstuff]

Nickel titanium wire looks very promising for this.  Where do I get it?  I'm having trouble finding sources, especially ones which have datasheets.  I'm in the US.

"muscle wire" is the most common term.  Sparkfun sell it

[Rachie5272]

Thanks!  I ordered from sparkfun.

[CM800]

I really would have suggested a simple solinoid, cheap as hell.

Anything else is overcomplication.

Equally, a voice coil would do it.

[Gyro]

Note that 'Muscle wire' needs to be heated to >100'C to shape change. You may need to think about thermal protection if the "mechanical button" has a low melting point actuator. It looks as if the heating current needs to be around 1.5A through the 0.012" wire (0.31 Ohms/inch), or 320mA (datasheet value) through the 0.005" wire (1.9 Ohms/inch).

Interesting looking stuff if you can get the mechanics, terminations (datasheet mention of diameter cycling), and drive circuit right.