Essentially B drops above and below the gap. Even within the gap (between the front and back of the top plate) B will not be constant and will peak at about the center of the top plate.
Bl is essentially an integration over an interval equal to the coil length. This makes sense because the windings are equally spaced, so the coil just sees an average of the B covered by its instantaneous position.
Since the B field is non flat within the gap and falls rapidly outside the gap, Bl will always peak at more or less the centered position and fall off to either side.
On the other hand, if you design a short coil, long gap motor you will find that the B in the gap tends to be more constant and the Bl vs. X is quite a bit more constant. It does fall off very quickly when you get to the edge of the gap, though.
David
Oké I get it. So the roll off on the edge is very important to maintain linearity.
Why do most manufacturers use straight polepieces like in the example? This is not good for lineairity (low roll off on the edge)
Would this not to be better? (don't look at the double gap)
With a higher roll off.
thx,
Why do most manufacturers use straight polepieces like in the example? This is not good for lineairity (low roll off on the edge)
Would this not to be better? (don't look at the double gap)
With a higher roll off.
thx,
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