On Wed, 21 Jun 2017, Tom Easterday wrote:
Date: Wed, 21 Jun 2017 10:11:01 -0400
From: Tom Easterday <tom-...@bgp.nu>
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
So is that large jump in f-error caused by the difference between
axis.2.joint-pos-cmd and axis.2.joint-pos-fb? There is a small 90 degree
step in pos-cmd that is not mirrored in pos-fb near the end, in line with
the spike of f-error. Is that the cause and why is that there?
Yes, and this is why you cannot do homing to index with a stepgen in position
mode.
When you home to index the encoder position makes a (possibly large on first
home after startup) step change when the index is detected. The commanded position
must make a matching step. With a servo system, this does not cause a major
glitch because the commanded and feedback positions both change at once so
any move in progress just continues, in addition the PID component watches
index-enable so is able to discard the result of the derivative terms (FF1 and
D) so they dont cause a thump.
This does not work with a stepgen in postion mode because the stepgen gets a
step change in position command, that it cannot follow, this causes a large
instantaneous following error when index is detected
You can use step motors with an encoder and homing to index, but you must
setup your hal file differently, running the stepgen in velocity mode and
using a PID component to close the position loop with the feedback from the
encoder
-Tom
On Jun 20, 2017, at 8:54 PM, Tom Easterday <tom-...@bgp.nu> wrote:
Well, it has been homed and is searching for index when it faults with the
following error....but it isn't homed as I have just killed and restarted
Linuxcnc. I then move the Z axis down a little bit and then Home All...
-Tom
On Jun 20, 2017, at 7:54 PM, Peter C. Wallace <p...@mesanet.com> wrote:
This looks like it has been homed before (no large step in encoder position at
index)
Peter Wallace
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