Issue getting XYYZ gantry to home (using 7i92t with 7i76u)

Hi All

I have an issue with getting XYYZ gantry to home (using 7i92t with 7i76u)

Home position is at bottom left of the work area.

I am trying to use the second option,  of the four homing sequences,  found in Figure3. Homing Sequences. (stop, back, forward, home)

Order of homing is Z (micro switch), then X (micro switch),  then Y gantry (proximity sensor on both ends of gantry, Y and Y1).

The Z axis homes correctly.

The X axis homes correctly.

The Y gantry axis moves in the correct direction, towards the two proximity sensor stops.
The gantry stops for a spit second, as it find the proximity sensor stops.
The Y motor looks like it tries to begin to do the correct four step process (stop, back, forward, home), and it doesn’t ever crash.
However the Y1 motor side of the gantry, just continues straight forward, and crashes the machine every time, with a hammering sound.

Context:
The two switches, and both proximity sensors, provide +24v to the four inputs on the 7i76u.
in pncconf I had to invert the four inputs, otherwise all four inputs triggered before one began.
In halshow the switches and the proximity sensors all seem fine (to me).

I have negative values on all axis (see attached ini and hal), if I change these to positive, then it homes in the wrong direction.

Any ideas for troubleshooting greatly appreciated

Are you sure the proximity switches are deactivated (red in halshow) when not at home position?

If these were inverted, the "home" move might actually be LinuxCNC backing off what it thinks is
a closed switch.

Hi All

Thank you for your feedback, greatly appreciated
The Y gantry completes the four step process now, well ... very nearly.
I think my problem was here
[AXIS_Y]
[JOINT_1]
has negative values
HOME_SEARCH_VEL = -10.000000
HOME_LATCH_VEL = -5.000000
(and joint 2 had the same negative values).
[JOINT_2]
I changed the signs to both positive
HOME_SEARCH_VEL = 10.000000
HOME_LATCH_VEL = 5.000000
After that change, the Y-axis homed in the four step way.
I don't understand why,  maybe gantry motors that face one another need opposite signs, I have no idea.
I have attached three screen photos with halshow
first - just switched on power supplies, and launched Linuxcnc.
second - after clicked estop, and clicked power.
third - end state after all thee axis homing has completed.
Physically the Y gantry does the correct four step movement.
However, Linuxcnc errors out right at the very end, indicating joint2 on limit switch error.
The  y-is-homed is red , while x-is-homed, y2-is-homed and z-is-homed are all yellow.
These are the cheap 2mm proximity sensors , tommylight said earlier that these are best avoided.
I will buy better quality ones.
If anyone knows why that sign change worked please let me know


 

I think you need to specify a home position that's some distance from the home/limit switch location

linuxcnc.org/docs/html/config/ini-homing.html#_home

Hi PWC  and many other folk. After many months I am having another go. I took the advice from this thread, and installed new proximity sensors, and added home positions. The issue that  now have is that it homes the z axis correctly, homes the X axis correctly. The y axis homes in sync and in tandum (y1 and y2 gantry motors) as seen in the first photo. It completes the four part homing procedure as seen in the second photo. It shows a capital H for X, Y and Z axis and it also shows the correct Home locations. However it also shows an error - exceeded negitive softlimit on joint 2 . So even though it seemed to of homed correctly , it disables the machine, and I can do nothing with it. 

Any suggestions are greatfully received.  

PS: I have tried endless permutations. The current positive and negitive values are the only ones that make the four step process work. The software suggests that I jog the axis off the joint but its part of the gantry pair so wont do it.