RE: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers

I am not arguing that point. If they are connected to directly to ground
you will have braking.

Now, if it is connected to ground through semiconductors which will only
pass current in one direction and they are both set up to sink current to
ground you will have no path for the induced current to take. In other
words: one end of your coil will take on a positive potential which will
flow to ground through the now forward biased semiconductor (saturated NPN
transistor), however, the other end now has a negative potential which will
reverse bias the semiconductor. How can you have braking with no place for
this current to flow?

-----Original Message-----
From: Ward M. [mailto:wardmerk@...]
Sent: Friday, August 10, 2001 10:41 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers


I disagree, if both ends of a coil are connected to ground, there will be a
braking action. Remember, braking is resistance to motion. With zero
applied force and zero RPM, there will be no current in the winding. With
any rotor motion, a current will be induced in the shorted coil, causing a
resistance to motion, i.e. braking.

Thanks,

Ward M.

wardmerk@... <mailto:wardmerk@...>



#)-----Original Message-----
#)From: Scott M. Thomas [mailto:scott@...]
#)Sent: Friday, August 10, 2001 6:29 PM
#)To: 'CAD_CAM_EDM_DRO@yahoogroups.com'
#)Subject: RE: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers
#)
#)
#)I wasn't making any distinction between 2 or 5 phase and I agree that you
#)need to consider the other windings.
#)
#)I also agree that if you short the windings together or to ground that it
#)will cause braking.
#)
#)However, if I connect the coil to ground on both ends with an NPN
#)transistor
#)at each end (and they have sufficient base current to be in saturation) I
#)will not have current flow, therefore no braking. Now if I have
#)enough back
#)EMF (if the RPM is high enough) you would experience one of the adjacent
#)windings losing effectiveness because the current flow would decrease.
#)
#)I am curious what you mean by braking mode on a normal stepper.
#)
#)-----Original Message-----
#)From: Alan King [mailto:alan@...]
#)Sent: Friday, August 10, 2001 9:13 PM
#)To: CAD_CAM_EDM_DRO@yahoogroups.com
#)Subject: Re: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers
#)
#)
#)Hey,
#)
#) If that were the case, then braking mode wouldn't work on a normal
#)stepper either, there isn't anything special about a 5 phase motor for
#)that case. Two ends of a coil switched to ground brakes, just shorting
#)the wires you'll feel it, and it also works with two semiconductors
#)switching to ground. Try it and you'll see, and if what you're thinking
#)were true, braking wouldn't work for a single seperated motor coil on a
#)normal stepper either.
#)
#) Also, on a 5 phase you can *NEVER* (one of the few times you can use
#)that word and be ok!) consider one coil by itself without then taking
#)that info, and apply it back through the other coils. Your end going
#)negative would still not be high impedance, it'd be being pulled up
#)through that other coil that has it's other side connected to +V. But
#)it doesn't get the chance to go negative, braking a coil works even with
#)a seperate coil, so 5 phase or 2 phase doesn't make a difference..
#)
#)
#)
#)"Scott M. Thomas" wrote:
#)>
#)> 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.
#)>
#)
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