Tandem Y Axis - Can't Jog Both at the Same Time

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28 Jan 2023 04:26 #263047 by reynolds087
I set up tandem Y axis for my gantry in PNCConf. I have a mesa 7i96s, and my gantry will be dual motors with auto squaring. I can jog each Y motor individually in gmoccapy by using the 1+ and 1-, or the 2+ and 2-, but I can't jog both sides of the gantry simultaneously. In the mesa card settings, under TB1/TB2, I have 1 set to Y Axis StepGen, and 2 set to Y2 Tandem StepGen. 

Can anyone explain the process of enabling auto squaring and how I can jog the gantry as one axis? I have attached the files that I believe to be relevant, but I am totally new to this, and just taking a shot in the dark. Let me know if you need any more info. Thanks
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28 Jan 2023 04:34 #263048 by PCW
Have you homed the machine? You can only jog joints until the machine is homed

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28 Jan 2023 07:31 #263058 by reynolds087
Thanks, you are right. After clicking the homing buttons for each axis, I can jog the Y motors simultaneously as one axis. Although, homing is behaving differently in LinuxCNC than I am used to in GRBL. It is not seeking the limit switch and then automatically homing. When I click the button, it just sets the current position to home...

How do I get it to use the limit switches to set the home position?

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28 Jan 2023 10:20 #263066 by rodw
Please take the time to read the section n the docs on Hominc Configuration
You have not set HOME_SEQUENCE on your joints and the joint Y axes needs an identical negative value...
ALso review the section there on Immediate Homing which seems you have enabled.

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28 Jan 2023 21:28 #263122 by reynolds087
Thank you. I've updated my files, and it does appear to now attempt to home. However, let's take the z axis, since we can ignore the auto squaring for a moment, when I attempt to home it, I get the following errors:
"joint 3 on limit switch error"
"hit limit in home state 7"

I have updated the following values in the ini file:
HOME = 0
HOME_OFFSET = -1.0
HOME_SEQUENCE = 0
HOME_SEARCH_VEL = 1000
HOME_LATCH_VEL = 25
HOME_FINAL_VEL = 100
HOME_USE_INDEX = NO

Is there anything obvious that I've done wrong?
I have attempted to find the answer in the documentation, but I am not sure. One bit of potentially helpful information, I cannot seem to edit the home switch location, search velocity, search direction, latch velocity, latch direction, final velocity, or use encoder index values from within PNCConf. I had to manually change them in the INI file for some reason because they are all grayed out in PNCConf.
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28 Jan 2023 21:34 #263123 by PCW
An "on limit switch" error typically means you have the limit switch polarity inverted

LinuxCNC expects the limit switch signal in hal to be false unless the limit switch is activated

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28 Jan 2023 22:08 #263125 by reynolds087
I don't think the polarity on my Z limit switch is inverted because I had to invert the polarity of my Y limit switches, and before I did that, I would get an error at startup. I do not see any error at startup now for any of the limit switches. I'm not sure if I made it clear before, but I am sharing the limit and home switch.

I tried adding a line to my ini file "HOME_IGNORE_LIMITS", but that caused it to run right into the mechanical stop when I attempted to home Z. Are the logic for home and limit switches inverted by default? Meaning, should limits be active low and home switches be active high? It's possible that I need to invert the polarity of my home signal if that is the case.

Both the max-z signal and the z-home-sw are showing false in hal meter at startup before I attempt to home.

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28 Jan 2023 22:44 #263128 by reynolds087
I think I found the problem, but I am having a hard time figuring out how to resolve it.

When I jog to the limit switch and observe halmeter, I see that the max-z signal toggles from false to true, but the z-home-sw signal doesn't change. I am not sure how to map both signals to the same pin in the hal file. Can anyone tell me?


I found these lines in the setup home / limit switch signals section:

net z-home-sw  => joint.3.home-sw-in
net z-neg-limit  =>  joint.3.neg-lim-sw-in
net max-z  ==>  joint.3.pos-lim-sw-in

And this entry under external input signals:

# --- MAX-Z ---
net max-z  <=  hm2_7i96s.0.inm.00.input-03

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28 Jan 2023 22:53 #263130 by rodw
You have not connected a homeswitch signal.
Try

net t z-home-sw <=  hm2_7i96s.0.inm.00.input-03

instead of what you have for max z

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28 Jan 2023 23:12 #263133 by reynolds087
Thank you, that helped, I was able to home Z, but now it does not seem to acknowledge the switch as a hard limit. So if I start the machine and do not home first, it will allow me to jog past the switch. Is that just a limitation of shared switches?

Was I supposed to delete this existing line
net max-z <= hm2_7i96s.0.inm.00.input-03

or just add your line below it?

I deleted it and replaced with your line.

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