RE: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers

Yes, however the principle is still the same.

I have thought more on this and realized that I hadn't seen the forest! ;)

What Alan was saying about the adjacent coil pulling up would solve the
problem I was stating about the semiconductor being reverse biased. Also, I
realized that most drivers have flyback diodes on them that would also solve
that problem.

So sorry for the wasted band width.

-----Original Message-----
From: Ward M. [mailto:wardmerk@...]
Sent: Saturday, August 11, 2001 12:14 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: Tawagawa Seiki steppers


Don't most modern drivers use FETs?

Thanks,

Ward M.

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



#)-----Original Message-----
#)From: Scott M. Thomas [mailto:scott@...]
#)Sent: Friday, August 10, 2001 7:04 PM
#)To: 'CAD_CAM_EDM_DRO@yahoogroups.com'
#)Subject: 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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