Linear Magnetic Resistance

[ornerynorsk]

Hello All! Got one that has me stumped. We are working on a linear (or very slow rotary <100 rpm) magnetic resistance unit that would be used in exercise equipment for the disabled population, wheelchair transfer exercises and such. We chose magnetic because of its smoothness, lack of oil leaks, and controllability. What we need is a relatively inexpensive way to have a variably resistant force that uses little or no electrical current. Toro company apparently bought out a company years ago that was working on something like this, but I have not been able to find out anything about it. If anyone could enlighten me on this subject, and perhaps magnetorheological fluid systems, I would greatly appreciate it. Thanks.

 

[Dynatron]

Dear Sir: Your request is typical in that not enough information is given to permit an informed reply.
I am working with rare-earth magnets for medical devices, and may be helpful, but I would have to see drawings to get a more complete picture of what you're trying to do. There are ways to counter a magnetic field, though none ideal in that they can completely shut off the field.
Sincerely, Don E. Casey CEO Dynatron

 

[ornerynorsk]

Dynatron, thanks for your reply. I have since found some information on what I was looking for, here is a link for anyone else who might be looking for such info.

http://www.rheonetic.com/

 

[howard1954]

Sounds like a hysteresis brake/clutch is what you need. These devices work at any speed above zero. Linear is also no problem. A set of High Coercivity alternating pole permanent magnets (rare earth) on one moving part is positioned near a set of magnets with low coercivity (AlNiCo). As the rare earth magnets magnetize and demagnetize the AlNiCo's the amount of work lost by heat is the area of the hysteresis loop of the AlNiCo's.

see

http://www.magnetictech.com

 

[ornerynorsk]

Thanks Howard.

 

[howard1954]

Looked at the mag-rheo fluids vs hysteresis. Hysteresis requires no outside power source and continuous duty is no problem up to max power dissapation.