A friend is trying to get an ele

[Bootstrap]

A friend is trying to get an electromagnet to interact, solenoid style, (push and pull) with a strong rare earth magnet.
The objective is to move a iron spool. Where the coil is wound around a brass tube that spaces the inside of the coil 1/8 inch from the outside surface diameter of the moveable iron spool. The iron spool is attracted to the rare earth magnet and the electro magnet can not induce a magnetic field into the iron spool so as to free it from the rare earth magnet.
Is the 1/8 inch gap between the coil ID and iron spool OD the problem? Maybe a simular gap is needed between the spool and rare earth magnet?
Is the relative strength of the rare earth magnet the problem?
He only gets a weak force change in the iron spool's attachment to the rare earth magnet, but the rare earth magnet does rise in temperature a bit. This happens with PWM, or DC amperage. Why? What possible error/s is/are being made?

 

[hacksaw]

are possible errors that you can imagine are being created

what are you trying to do?

 

[Bootstrap]

The final objective is to find out if he can design his own solenoid with more linear spool travel as current through the coil is varied.

This comes about because the solenoid he has been purchasing has something like 1/8 inch useable semi-linear stroke. He wants up to a 1/4 inch stroke if possible. This is for an application he has been considering, if more solenoid stroke is attainable at low solenoid cost.

At the moment, my questions did not specifically concern his final object, but instead his initial problems. He expected I would have magnetic practice insights, which I did not.

So, I was searching the WEB and happened onto this site. I read the postings and decided this forum could fill the need. Whereupon, I errorred in initially creating a 'Reply' instead of a 'New Thread'. My second attempt was this thread.

This is his first magnetic project. I have not done one either. This is an after working hours project he is doing on his own. So, practical experience is near zero. A learning curve is unfolding. I am semi-retired and enjoy learning from others when I get the chance.

 

[hacksaw]

use a longer coil, winding a new one will be a good exercise...in any event the perm. mag. will only make the situation worse.

 

[frankeng9]

Bootstrap,

Your friend’s objective is to build a proportional, bi-directional solenoid to position something like a valve spool with +/- 0.25 inches of linear stroke – correct? The design of solenoids and solenoid actuators is really as much art as science. From what you have described, it is difficult to imagine a magnetic circuit for a bi-directional, proportional solenoid consisting of a single coil and a single magnet. My first suggestion would be to check out a company like Lisk, Ledex, or Bicron, to see if they have an off-the-shelf catalog item your friend could purchase. I encourage your friend to experiment and learn more about magnetics, but designing a proportional, bi-directional solenoid with linear characteristics is a daunting undertaking for a first-time project. The linearity (stroke position VS current) of a solenoid of this nature will be determined by several factors. Some of these factors are: 1) the mechanical geometry of the pole faces, 2) the linearity of the return spring, 3) the characteristics of leakage flux across the coil from the armature to the housing body, and 4) the hysteresis of the mechanical, electrical, and magnetic components of the entire system (whew!). As a first attempt, I would suggest that your friend eliminate the magnet from the circuit to simplify things. A relatively simple way to get a bi-directional proportional solenoid would be to first develop a proportional, single direction design with a single coil, and then mirror the entire circuit at the base. You would wind up with two coils (one for each direction) and a plunger with the same geometry at both ends. Before embarking on a project of this complexity, I would recommend that your friend get hold of a good textbook on magnetics. One such book is “Electromagnetic Devices” by Herbert C. Roters (John Wiley & Sons, Inc. New York, 1941) (I think the ISBN is 471 73920 0). The book is out of print, but your local library may have it.

 

[IRstuff]

It looks like what you want can only be easily configured as linear position vs time:

http://www.impactdevices.com/solenoids.html

I think that your friend might be better off with a lead screw design, unless he really needs the speed.

TTFN

 

[Bootstrap]

frankeng9,
I was not clear nor should I have indicated a bi-directional solenoid. The need is for a single direction solenoid with 0.25 inches, or more, of semi-linear stroke. Where semi-linear means as linear as possible, but some non-linear characterists is still a useable solenoid. Thanks.

 

[nbucska]

Slow and strong: stepper or servo motor with leadscrew
fast but weaker: Voice coil
short stroke : piezo actuator

<nbucska@pcperipherals.com>