Understanding hysteresis brakes
Understanding hysteresis brakes
(OP)
I've enclosed a cut-away of a hysteresis brake. I think I understand how it works:
1) When the poles align a strong flux density flows and drives the cup into saturation.
2) The flux goes low when the alignment of the poles is minimal.
If that's true, then I believe you are working only in the first quadrant of the hysteresis loop, i.e. there is no flux (or H) reversal (assuming a DC coil), correct? Also, you would want a wide hysteresis loop for the cup, correct? If I wanted to operate at high rotational speeds I would probably be limited to steels for the cup material, correct?
1) When the poles align a strong flux density flows and drives the cup into saturation.
2) The flux goes low when the alignment of the poles is minimal.
If that's true, then I believe you are working only in the first quadrant of the hysteresis loop, i.e. there is no flux (or H) reversal (assuming a DC coil), correct? Also, you would want a wide hysteresis loop for the cup, correct? If I wanted to operate at high rotational speeds I would probably be limited to steels for the cup material, correct?





RE: Understanding hysteresis brakes
For a specific local point in the cup, there is an alignment issue, this point "see" a stronger field and a weaker field alternatively as it rotates.
It is not true that the wider the loop, the better the performance. Wide loop only means the material is hard to reverse. In your design, there is not even a reversal. I feel even a soft magnetic material works for the rotor.
RE: Understanding hysteresis brakes
I'm struggling a bit with seeing how there is much movement on the loop when the cup rotates and the poles align and then don't align. Even at max-unalignment there will still be H and B passing through the cup.
I'm dissecting a unit I bought off Ebay and I'm going to look at the gaps and poles and amp-turns and then model it with my (not-very-powerful) 2d magnetics software. Hopefully I'll gain more insight in to how B and H varies in the cup.
RE: Understanding hysteresis brakes
Braking torque is created by forcing like poles of the rotor (induced pole) & stator together, and opposite poles apart (rotor's original poles).
the wider the loop of rotor, the more difficult to create an induce pole, and so the material should not be too magnetically hard, or not too soft.
If the cup is soft material, say carbon steel, the attracting force between rotor and stator should create a baking torque. However, this simple mode might not work as well as using hysteresis material.
RE: Understanding hysteresis brakes
RE: Understanding hysteresis brakes
http://machinedesign.com/mechanical-drives/electro...
http://www.designworldonline.com/the-development-o...
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Understanding hysteresis brakes
The sample I have is designed for a DC input voltage but I'm going to try an AC voltage and see how it acts. If my understanding is correct then I would think the AC excitation would be able to absorb quite a bit more energy per revolution of the cup.
We also have a dyno for testing our motors that uses a larger hysteresis brake. For that I have removed the cogging by ramping down the current and spinning the rotor. The cogging will happen if I suddenly stop rotation while the coil current is high.
RE: Understanding hysteresis brakes
RE: Understanding hysteresis brakes
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers