[Emc-users] Homing To Index Following Error

[Todd Zuercher]

I gave Master a try using only 4 joints for my XYZW machine, and that did not make any difference.
I still get a following error on the W (joint3) every first try. (unless the W is parked against the limit switch at machine turn on.)

I don't understand why it always seems to work right for the Z axis, but never for the W. When I scope the homing of the Z the plots look the same, except for the obvious spike of following error on the W, and the time between when the index-enable changes and the step in the position feedback. The Z shows they happen together in halscope, and W seems to be separated by a couple of base-thread cycles.

Is that the source of the problem? And what if anything can I do about it?

[andy pugh]

Post by Todd Zuercher
I still get a following error on the W (joint3) every first try.

Is W a second spindle axis?

I wonder if you are the only one actually homing a W-axis?

[Peter C. Wallace]

Date: Mon, 26 Jun 2017 12:11:51 -0400 (EDT)
Reply-To: "Enhanced Machine Controller (EMC)"
Subject: [Emc-users] Homing To Index Following Error
I gave Master a try using only 4 joints for my XYZW machine, and that did not make any difference.
I still get a following error on the W (joint3) every first try. (unless the W is parked against the limit switch at machine turn on.)
I don't understand why it always seems to work right for the Z axis, but never for the W. When I scope the homing of the Z the plots look the same, except for the obvious spike of following error on the W, and the time between when the index-enable changes and the step in the position feedback. The Z shows they happen together in halscope, and W seems to be separated by a couple of base-thread cycles.
Is that the source of the problem? And what if anything can I do about it?
--

Pretty sure the mix of base thread and servo thread cycles is what causes
the problem, homimg to index requires a precise function ordering and I
dont think you can have the correct function ordering when you have the base
thread accesing hardware.

I suspect the easiset solution is to choose a fast enought host CPU that
is capable of running a 4 KHz or so servo thread

========================================
Todd Zuercher
========================================

Peter Wallace
Mesa Electronics

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