[Emc-users] position pid loop

[Larry Kopas]

hi

I'd like to know how the position control works in emc.  the pid params I
see are only for axis speed control, what I can't understand is how emc
holds the motor at a particlar position and apply opposing force if tried to
rotate.  I was expecting to see pid params for position loop, but cannot
find in any ini file.

tia
Larry
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Re: [Emc-users] position pid loop

[Jeff Epler]

The stepgen HAL module has a tuned feedback loop between the slow
(servo) thread and the fast (base) thread, and it also has
parameters to control the maximum acceleration and velocity.  Whatever
position command you give stepgen, it issues properly-spaced steps that
track that position as closely as possible while respecting the limits
specified by the HAL parameters.

When the position command is emc's axis.X.motor-pos-cmd, stepgen can
reach the requested position every time because emc also includes code
to limit acceleration and velocity to the inifile values.

As you say, the feedback position is simply found by counting the
number of step pulses actually issued.

Jeff

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