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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