RE: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers

If you think about it, with 4 coils powered you really don't have one in
brake mode. Even though both ends of the coils are at the same potential
(either + or -) the semiconductors on either end can only pass current in
one direction, therefore which ever direction the back EMF generated on that
coil was flowing, one end would be always be in a high impedance state so no
braking would occur.

-----Original Message-----
From: Alan King [mailto:alan@...]
Sent: Wednesday, August 01, 2001 4:10 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers


"Scott M. Thomas" wrote:

>
> There must be some variation on this theme between manufacturers (or just
> plain preference) because my interpretation of Sanyo-Denki's excitation
> sequence shows three adjacent coils energized with one of the five
> connections floating.
>
> Here is the link:
> http://www.sanyo-denki.com/Servo/60mm.pdf
>
> I agree with everything that has been said and I see how this can work,

but

> I wonder if there is a significant advantage to having 3 or 4 windings
> energized.
>
> Any thoughts welcomed.
>

Ah, but actually all five windings are powered in this arrangement.
Red is indeed floating, but take a look at say step 1, and black is
minus and orange is plus. So red is at approx 1/2 between - and +, and
approx 1/2 power in black to red coil and also orange to red coil. So
basically 3 + 2*(1/2) for a total of 4 coils powered, pretty much the
same as 4 fully powered coils with the other in brake. And since you
don't get something for nothing in either direction (in other words
things tend to even out) I would imagine that 4 fully powered coils with
one in brake is almost exactly equal to 3 fully powered coils with 2
half powered coils, that probably are about the same as two half braked
coils at the same time. Maybe a constant difference in deflection due
to the 1/2 powered coils way being centered between the coils while the
power/brake way will be pulled toward the powered coil and only braked
by the other, but in general I bet they'll be extrememly close in other
characteristics.
It really only takes 2 phases to get motion, 3 gets smoother motion,
and 5 smoother still. But with all the extra in 5, you can come up with
different patterns to run the coils, but they always tend to even out.
Any set of patterns that gets you around in 5 steps with an even pattern
ends up being the same as any other pattern that does the same. And
they all come back to the two basic modes, joined coils with 4 powered
with one in brake, or split coils with all 5 powered.

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