On Tue, 9 Aug 2011, Tobias Gogolin wrote:
> Date: Tue, 9 Aug 2011 10:33:10 -0700
> From: Tobias Gogolin <[email protected]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <[email protected]>
> To: "Enhanced Machine Controller (EMC)" <[email protected]>
> Subject: Re: [Emc-users] Questions about your Stepper kit
>
> I don't like to believe that that is the best 'servo' conversion one could
> make adding a readout, one that would try faster pulses and lock...
> So if I can work with these motors, who can recommend a good high voltage
> power supply and microstepping driver for these?
>
> Nobody has ever implemented a closed loop stepper controller in EMC?
>
> Thanks guys!
There are closed loop stepper systems implemented in EMC by using the stepgen
in velocity mode and feedback from rotary or linear encoders. These are not
fully closed loop in the sense that if the step motor loses position,
re-homing is usually needed.
For full closed loop (no possibility of losing steps), the controller (EMC or
external step drive) must track the step motor rotor position fast enough
that at the highest stepping rates, the control is never more than say 30
electrical degrees delayed, this rate is about 24KHz for a normal 50 pole
stepmotor at 1200 RPM. Running a servo loop at 24 KHz would be pretty tough to
do in EMC.
Note that for decent full close loop, you do not want step/dir drives, but
rather angle/current drives.
Overall by the time you add the encoders and exotic control you are
better off with servo motors (that are more efficient and dont lose torque as
quickly at high speeds)
Peter Wallace
Mesa Electronics
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