On Sat, 31 Mar 2012, Dave wrote:
> Date: Sat, 31 Mar 2012 14:20:19 -0500
> From: Dave <e...@dc9.tzo.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Trajectory planning and other topics from a,
> EMC(LinuxCNC) newbie (TheNewbie)
>
>My experience with steppers is that once you lose sync with the rotor at
>speed, you have to slow down tremendously to regain sync with the rotor.
>So once you start slipping, you are pretty much done as you have lost
>control of the motor. I don't see how using encoders with steppers
>really helps other than detecting when you have lost control of the motor.
>
>Dave
If you have high res encoders and a high enough loop rate (say 30 -50 KHz) and
a PWM sine/cos drive, you can run step motors as 50 pole 2 phase servos, they
can never lose steps (as the drive phase is always synced to the rotor) and
they have ~0 input power at ~0 load torque. However the driver circuits are
more complicated than 3 phase PMS servo motors (4 1/2 bridges vs 3 1/2
bridges) and you have still have the same torque/vs speed curve as with a
normal step drive so unless you need something the the step motors provide
(low speed torque maybe) step motors make fairly lousy servos
Peter Wallace
Mesa Electronics
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