On Wed, 3 Mar 2021, John Dammeyer wrote:
Date: Wed, 3 Mar 2021 23:11:23 -0800
From: John Dammeyer <jo...@autoartisans.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 Joint 2
The comment on the link about Ethernet latency is what interested me.
Again if electrical noise causes retries or delays in the Ethernet
signalling then that could cause this sort of error under heavy load.
John
And this is what the high frequency gains do, FF2 and Dgain, giving a
boost when the velocity changes. All this assumes that the actual power
available is sufficient to achieve what the controller is asked to make
it do. If the available power sags with the initial accell but the speed
being asked is so high the power available cannot catch it up and is
limiting you then following errors creep into long distance moves.
Hi Gene, My AC Servo is run open loop with step/dir. It's not the Servo
Driver that is calling out a following error. It's LinuxCNC that also has no
clue where the motor actually is unless the AC servo asserts a fault output.
And it can't do that because I disconnected it for this test.
I don't know how the Ethernet Communications with the MESA 7i92H works. Page
8 of the user manual says it's UDP which means launch and forget. The sender
has no way of knowing if the message was received although with only two
devices perhaps there's a lower level that does verify that.
In either case Page 31 states there are error counters so if there is a packet
error that is detected after a new motion command is issued; like change
direction for example. Then LinuxCNC might well decide to throw up a
following error.
I will admit that I misread the HAL instructions and had the MAX_ACCELERATION
parameter set to 125% higher. But with Backlash it was supposed to be 200%.
Once I changed that the problem went away. So bad HAL info generates a
following error? Except that never happened without the extra 92 lbs on the
table.
A following error is _expected_ if the stepgen maxaccel parameter is not at
least 2x the joints maxaccel value (or if any stepgen constraint is lower
than what linuxCNC may command it to do) So HAL setup can absolutely cause
following errors.
But if electrical noise from the higher load did cause a damaged UDP packet
then there's the answer. A quick change in direction to handle backlash and a
missing message throws out the timing and results in a following error. John
You can check this by plotting hm2_7i92.packet-error , but if setting the
stepgen maxaccel value stops the following errors it does not seem likely they
are caused by lost packets. Plotting the following error will also give you some
insight into whats going on.
Peter Wallace
Mesa Electronics
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