7i96 Homing Setup

Hello everyone!

I've nearly finished my build of a 24x48" CNC wood router. I'm at the point with only the fiddly bits left before I can start using it. Where I am stuck right now is how I'm supposed to configure the homing switches.

I have homing set on the X and Y axis, but I clearly have it configured wrong. Every time try to home the axis, it moves towards home, trips the limit switch, and then stops with a "joint 1 follow error".

I've read through the documentation here:  Mesa Configuration Wizard (linuxcnc.org)  but I cannot wrap my head around it. 

For the X axis, I have:
Positive Travel Distance - 24.000
Negative Travel Distance - 0.000
Home Position Location - 12.000
Home Switch location - 1.500
Home Search Velocity - 60.00
Home Search Direction - Towards Negative Limit
Home Latch Velocity - 10.000
Home Latch Direction - Opposite
Home Final Velocity - 10.00

I know I'm thinking about this all wrong, but is anyone able to help me understand this?

You would not expect a following error unless the step generator was asked to
make an impossible motion (higher velocity or acceleration requested than
allowed by step generator settings)

Can you post you hal an ini files here as attachments?

I think I attached the right ones.

I don't see anything obvious wrong.

Is it possible you have a wiring issue and you are tripping
an estop with the home switch?

You might try activating all the switches while watching them with halshow
to see if they are working properly

dzawacki wrote:

Hello everyone!

I've nearly finished my build of a 24x48" CNC wood router. I'm at the point with only the fiddly bits left before I can start using it. Where I am stuck right now is how I'm supposed to configure the homing switches.

I have homing set on the X and Y axis, but I clearly have it configured wrong. Every time try to home the axis, it moves towards home, trips the limit switch, and then stops with a "joint 1 follow error".

I've read through the documentation here:  Mesa Configuration Wizard (linuxcnc.org) but I cannot wrap my head around it. 

For the X axis, I have:
Positive Travel Distance - 24.000
Negative Travel Distance - 0.000
Home Position Location - 12.000
Home Switch location - 1.500
Home Search Velocity - 60.00
Home Search Direction - Towards Negative Limit
Home Latch Velocity - 10.000
Home Latch Direction - Opposite
Home Final Velocity - 10.00

I know I'm thinking about this all wrong, but is anyone able to help me understand this?

You have different numbers in the ini file for X ie you have Home Search Vel 60 above and -1 in the ini file

Which one is correct?

In X you have HOME_OFFSET = 1.500000 for a start set that at 0

In Y you have HOME_FINAL_VEL = 0.000000 This need to be a number as it will not move with zero

It is normal to add a HOME_SEQUENCE = number for each axis in the ini file ie HOME_SEQUENCE = 0 would be homed first ie Z first and HOME_SEQUENCE = 1 would be homed second etc.

I can do a test on that.

Can you give an example of how I could have things set up that would cause the e-stop to be triggered by the home switch? If I remember correctly, I have 5 limit switches wired to inputs 0-4. And I have 2 limit switches wired in series to input 5. Both limits and e-stops are utilizing the input common pin on the 7i96.

Thinking about testing, my e-stop isn't being tripped in the UI when I hit any of the limit/home switches but I'll run through halshow just to see if I'm missing something.

Okay, I used halshow to monitor each of the limit switches and the e-stop at once. I triggered each switch and only the associated monitor item was tripped. The e-stop, as expected also only tripped the associated e-stop monitor.

I think I can rule wiring out.

For Clive's questions, I'm only working on the X-axis at the moment and once I get that configured I'll translate that to the Y-axis.

The Home_Search_Vel is marked as -1.000 in the INI but the PNCCONF is showing 60.000. I don't know enough to know if these should match and if it makes a difference. I do know that when I home the axis, it moves at a speed that seems about right.

I swapped the HOME_OFFSET to 0, per the suggestion and saved the config. I opened the machine and homed the x-axis. The machine moved toward the negative limit as expected, hit the limit switch, and stopped. I got a "joint 1 on limit switch error" when this happened.

Maybe I'm thinking about this wrong, but I'd expect the axis to hit the limit switch and then back off on its own so the machine is usable. This would also set the proper coordinates for the machine.
To me, it seems like HOME_IGNORE_LIMITS = YES is being ignored.

For the home sequence, I left it as the default in the UI.

he Home_Search_Vel is marked as -1.000 in the INI but the PNCCONF is showing 60.000. I don't know enough to know if these should match and if it makes a difference. I do know that when I home the axis, it moves at a speed that seems about right.

It's late here. Once you have used Pncconf it is better to hand edit the hal and ini files by hand ie. It IS the hal and ini files that are in the config folder that are used. If you then try and use Pncconf again it will over write them.

Maybe I'm thinking about this wrong, but I'd expect the axis to hit the limit switch and then back off on its own so the machine is usable. This would also set the proper coordinates for the machine.
To me, it seems like HOME_IGNORE_LIMITS = YES is being ignored.

It does not back off a limit switch only a home switch BUT you can have a shared home and limit switch then it will ignore the limit with HOME_IGNORE_LIMITS = YES until it is homed THEN the switch will be treated as a limit

Did you set it up with shared home and limit?

Hope this helps.

I solved my problem. And it was with my wiring. I was reading over the INI homing page (linuxcnc.org/docs/html/config/ini-homing...#_home_ignore_limits) on ignoring limits and it mentioned that:

 LinuxCNC will ignore the limit switch input for this joint while homing. This setting will not ignore limit inputs for other joints.

And that just clicked for me. I had checked that the e-stop wasn't being triggered with halshow, but I hadn't looked closely to confirm that the limit switches were triggering the axis I thought they were. A quick fix to swap the pins in PNCCONF and the axis homed no problem.

It's late here. Once you have used Pncconf it is better to hand edit the hal and ini files by hand ie. It IS the hal and ini files that are in the config folder that are used. If you then try and use Pncconf again it will over write them.

I have to disagree. It can be better/easier/faster to edit the files directly, but PNCCONF has context and explanations that for a novice like myself make it easier to set up a configuration. Running through a config program once does not make me an expert enough to understand the shorthand used in the INI file. 
If I had more experience, I'd probably edit the INI file directly, but for now the UI is a far better choice for me.