On Mon, 19 Jun 2017, tom-...@bgp.nu wrote:
Date: Mon, 19 Jun 2017 22:51:59 -0400 From: 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: [Emc-users] following
error only while homing
Why would I get a following error only while homing (latest Linuxcnc 2.7.9)?
I recently added home switches to my machine. My machine has encoders on
the steppers on each of the 3 axes so I want to use the index pulse for
home. I set up the homing sequence each axis and when I do "Home All" I get
a following error on my Z axis (first one to home). I played with all the
settings and can??t get it to complete unless I set ferror and min_ferror
very high Also, once there is a following error I can only clear it by
exiting Linuxcnc and restarting it. If I just turn it back on, it
immediately faults again with the same following error. If I don??t home,
after restarting Linuxcnc, I can run the Z axis (and X and Y) all day at any
speed without a following error.
I have tried setting the ferror and min_ferror settings to various reasonable
values but it didn??t work. Before adding the switches I had error=0.001 and
min_ferror=0.0005 and never had a following error appear. I set ferror to 2
and min_ferror to 1 (I think those were the values) and it worked but then got
the following error on the Y axis (the second axis homed). The values for
ferror and min_ferror that ??worked?? seem completely unreasonable given I am
not even moving anywhere near my max velocity during homing.
I have tried changing the sign on the HOME_LATCH_VEL to make it search for
index in the other direction but the same thing happens. Below are my
(current) machine hal and ini.
-Tom
I suspect this cannot work the way you have this setup because of the
instantaneous jump in encoder (feedback) position at index (and
cooresponding jump in commanded position) cannot be followed by the
stepgen in position mode. It only happens once because index will not
cause a feedback position jump a second time since its already at 0
One way to make this work is do as others have siggested and run the stepgen
in velocity mode and run a standard servo velocity PID loop
This has the advantage the you are actually using the encoder feedback
for control rather than just monitoring following error
Peter Wallace
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