Step/Dir Servo?

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06 Sep 2012 03:47 #23957 by Todd Zuercher
Is there any advantage to having encoder feedback in a system using step/dir servos?

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06 Sep 2012 04:17 #23958 by PCW
Replied by PCW on topic Re:Step/Dir Servo?
One advantage is that you could keep track of the
following error

It could also be used for a dual feedback system
with the step/dir servo+rotary encoder functioning
as a velocity mode drive getting position feedback
from a linear encoder and LinuxCNCs PID loop.

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06 Sep 2012 13:24 #23975 by Todd Zuercher
Replied by Todd Zuercher on topic Re:Step/Dir Servo?
Pardon my ignorance, but could you explain how a step/dir drive can be used as a velocity mode drive? Could that be done without the linear encoder, just the motors rotary one?

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06 Sep 2012 15:42 #23983 by PCW
Replied by PCW on topic Re:Step/Dir Servo?
You set LinuxCNC's stepgen to velocity mode,
now your external step/dir servo is a velocity mode
drive as far as LinuxCNC is concerned.

This like an analog velocity mode servo except that the
velocity command is a step rate and a direction

The fact that the drive is maintaining a position loop can
be ignored as long as you dont exceed its capabilities

I dont know if there is any advantage of velocity mode
if a single encoder is used

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07 Sep 2012 03:02 #23997 by aike
Replied by aike on topic Re:Step/Dir Servo?
I use the same scheme, plus USE_INDEX to make exactly homing.

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