Homing Issue "home switch inactive before backoff"

Hi All,

I have been running PlasmaC for about 2 years now and my X-axis limit switch just randomly started playing up. When I home all axis, the Z homes fine but the X either goes slightly past/before the proximity limit switch and stops, where a "Home Switch Inactive before start of backoff move j=0" error message comes up, or it keeps going past the sensor and crashes into the hard stop. The light on the limit switch still comes on as if it is working. I can open and close PlasmaC about 2-10 times and keep re-homing and eventually it will work.

Does anyone have any ideas? Is it odd that this has randomly started after 2 years of it working fine?

As always, your help and knowledge is very much appreciated.

Thanks, Little_sparky

edit: I am using 12v proximity limit switches, no pull up resistor and no shileded cable. This is what I will be looking into, but wondered if there might be another way to identify/fix the problem.
 

It could be that the sensor appears to be working ( ie it lights up when triggered) but the wire going to it could be broken intermittent.

So check the wiring where it might be flexing.

First, try lowering "home_search_velocity" to at least half of what you have now.

Update:

So I did the above and I think it was a dodgy switch. I have purchased a new inductive proximity sensor, but this time I have a normally closed sensor instead of normally open. I have wired it up and I now need to invert the signal.

I tried to put -not at the end of the 

# - - - HOME - X - - - #
net home-x    <= hm2_7i76e.0.7i76.0.0.input-13-not

in the .Hal file however I now get an error when trying to open PlasmaC. Is there somewhere else I need to put -not? 

what is the best way to edit the base configuration? I tried to use pncconf but I had no luck.

thanks 

little_sparky



 

Also, I have wired the NC sensor exactly the same as the NO sensor, is this correct? Do I just need to invert the signal.

it is a PNP NC Inductive Proximity Limit Switxh

Appending -not is the usual way.

Though the docs:
linuxcnc.org/docs/stable/html/man/man9/h...eral%20Purpose%20I/O
Mention both in-not and in_not. That needs fixing.

I don't have a 7i76 but on my 5i25 the postfix is actually _not, so maybe try that?

Though the smart-serial driver (ie, 7i76 field IO) uses -not:
github.com/LinuxCNC/linuxcnc/blob/master...mot2/sserial.c#L1183

And it _should_ be -not according to the specifications...
linuxcnc.org/docs/2.6/html/hal/canonical-devices.html

But probably too late to make it consistent now.