A Muscle like electric linear actuator

[Chrisc]

Hi everybody. I was recently thinking about artificial muscles and why some electromagnetic based system couldn't be used. Admittedly my understanding is not as rock solid as I would like, but as I understand it the main inefficiency of a solenoid comes from the air gap within the core, that the armature moves to fill. I was curious to whether a soft foam impregnated with a powdered ferromagnetic substance with a high permeability could be placed within this region. The foam acts as a spring whilst the powdered ferromagnet acts as core.
Is there some aspect to this that I'm missing?
Also why aren't electromagnets used in a stack, when trying to create large stroke? Is it somehow really inefficient, harder to produce, or just not really suitable for the majority of systems that need a linear actuator?
Thanks for any advice.

Oh also a slight plug. I'm nearly at the end of developing a robot hand structure that I plan to sell through shapeways. It's just the structure of the hand, as I know most of my target market are skilled in motors and electronics, and so will add their own. Also it would set a standard for people to tinker with and talk about with each other, like the Arduino for example. The shop on shapeways is called Anthromod, and I have a website at Anthromod.com

[Soeren]

Hi,

I was curious to whether a soft foam impregnated with a powdered ferromagnetic substance with a high permeability could be placed within this region. The foam acts as a spring whilst the powdered ferromagnet acts as core.
Is there some aspect to this that I'm missing?

Look up "ferro fluid", as used in some loudspeakers. With a (complicated) valve system, this would help, but a sponge that needs to be compressable won't hold much ferro, so aren't worth the bother.
Still... Solenoids goes clonck, muscles contracts and relax in a quite different fashion, mostly following the biological (S-shaped) curve.

Also why aren't electromagnets used in a stack, when trying to create large stroke? Is it somehow really inefficient, harder to produce, or just not really suitable for the majority of systems that need a linear actuator?

They are used in stacks in some places, coil guns are probably an example that you have heard of. But this is due to the need for timed actuation - if you need it all at the same time, what would you think you'd gain by stacking  several short ones, rather than a single of equivalent length?

Oh also a slight plug.

How can you produce/sell something that you do not fully understand?

[Chrisc]

Hi Soeren

Thanks for the reply but I've already looked up ferrofluid. In fact there was a patent where ferrofluid was encapsulated within a polyurethane foam, although for an entirely different purpose. Unfortunately the closest I could find to some sort of 'ferrofoam' would be magnetorheological foam, which isn't the property I'm looking for. Also one would need to 'run the numbers' to see exactly how much ferromagnetic material could be held within a foam. Probably something that would need a lot of fine tuning to get it right, supposing there is any advantage.

I'd have thought that by stacking you could can achieve a longer movement, with less wasted power since each region is closer, and the magnetic field falls off faster than a linear relationship... Anyway that's why I'm asking, to make sure my understanding isn't way off base.

"How can you produce/sell something that you do not fully understand?" - Ouch... Although the above idea wasn't what I was plugging. Besides I'm still relatively young and still have the chance to learn anything should I put energy into learning to do so.   

[Soeren]

Hi,

I'd have thought that by stacking you could can achieve a longer movement, with less wasted power since each region is closer, and the magnetic field falls off faster than a linear relationship...

Assuming the same total length, whether achieved by stacking or one long coil.
If stacked coils are used, the plunger will only be within reach of the first coil initially and when it pulls in, brings the plunger within reach of the next in line (which will have to battle the magnetic drag of the fist coil) and so on until the last one. Only one coil at a time will do work, while those coil already "filled" will only drag.
One long coil will pull with the full power from the start and since it's longer, it will have much more power.

I'm still relatively young and still have the chance to learn anything should I put energy into learning to do so.   

What has learning got to do with age?
Unless you get dementia, Alzheimers or similar, you'll be able to learn anything (within reason of course) - I learn new stuff and enhances on already learned stuff regularly and I'm a few hours past my teens

[Chrisc]

"Assuming the same total length, whether achieved by stacking or one long coil."
Ahh well that's not what I meant.
I was thinking more along the lines of this http://www.google.com/patents/US5030936 or this http://www.google.com/patents/US3486147
Someone clearly went to the bother of patenting it, but it doesn't look like anything ever came from it.

[Soeren]

Hi,

Not all patents are realistic or even usable - just unique in some way.
I only looked at the drawings, but it resembles the principles in linear motors, which are in turn quite similar to brushless motors and steppers, only linear instead of round. If you imagine a brushless motor, cut along a radius and hammered flat, you are close.

When it comes to simulating muscles, air muscles and NiTiNol wire behave much more realistic.