On Wed, 21 Jun 2017, Jon Elson wrote:
Date: Wed, 21 Jun 2017 13:22:04 -0500
From: Jon Elson <el...@pico-systems.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] following error only while homing
On 06/21/2017 12:15 PM, Peter C. Wallace wrote:
A step in the FB position from the encoder and an attempt at an impossible
step in the commanded stepgen position...
All the complexities / workrounds of this position step on index could be
avoided if support for encoder counter that can only clear on index was
dropped.
OK, so stepgen also can compute following error. Without encoders, it is
only possible if steps can't be issued fast enough, but with encoders, then
there are other ways to create a following error.
Thanks,
Jon
The stepgen is not computing following error it just cant be driven by a
position command with a stepwise discontinuity and move instantaneously to the
new position.
A PID run velocity mode stepgen (or normal velocity mode servo) can do this
because both its feedback (from the encoder) and the commanded position make
this position step concurrently at index detection so the PID comp just
carries on as if nothing had happened
The PID derivative terms, FF1 and maybe D are patched at index detection so
the step in command and FB doesn't cause a one servo cycle long thump
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Peter Wallace
Mesa Electronics
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