Limit swtich false trigger

[HakBot]

Hello,

I have a Taig mill powered by a xylotex 3 axis board and turbocnc software. I have setup 6 limit switches according to the xylotex instructions. http://www.xylotex.com/images/xylotexlimits%5B1%5D.jpg

I am currently having a problem with false switch trips when running a gcode program. It usually reports 2-3 false positives per run. The limit switches do work so I believe I have it all setup correctly with a 10k ohm resistor installed. Does anyone have any ideas as to why turbo cnc reports the limit switches as tripped and how I can prevent it? Thanks!

[Bubba]

In a way, I am happy to see someone else have this problem. Maybe between us, we can find a solution.
I also run Turbocnc (V4.01) and at times, have had a similar situation where for unknown reasons, it would trip out and give an indication that a limit had tripped. A check of each of the limits would show that none was near tripping. In my case, I have 5 switches setup on my machine.

Because previous versions of Turbocnc had given the limit that was tripped, I did some tweaking of Turbocnc to put that function back in to tell me WHICH limit tripped.

Well imagine my surprise when I got a fault indicating "A limit switch has tripped"; HUH, that is not possible as it has to tell me which switch has tripped! To date, I cannot explain it and cannot find in the code HOW it can fault out with this message without giving me an indication of which axis has tripped.
I have also discussed this with Dave K and he has no idea either.

In your case, make sure that your lines are not close to power lines where they can pick up extraneous signals or that vibration is causing the problem.

[The Blight]

I have had the same problem for a while now, and this only happens on my 2nd parallel port (PCI card type). Are you running TCNC on a laptop?

[fretsman]

Are your cables shielded? They can pick up stray signals/noise if they're not.

Dave

[HakBot]

I am running on a desktop pc. The parallel port is built into the motherboard.

Hey Bubba, how were you able to get turbocnc to tell you what switch was tripped? What version of turbocnc was this? I am curious to see if it is a different switch or the same on that is always giving the false trigger.

The cable I am using is something I picked up from Mouser. Multi-Conductor Cable SHIELD 4C 24AWG. http://www.mouser.com/Search/Product...ey566-9534-100
Seems like good wire to me.

[Bubba]

I run mine on a desktop (port on the motherboard) and have a solid state drive. There is not other software on this machine. The only add in drivers are for usb to allow use of a thumb drive to transfer files.

[Bubba]

HakBot,
I went into the source code and made some changes (based on MY machine paramaters) and then recompiled it. Whenever I manually trip one of the axis, it give the appropriate message such as "X Limit Tripped".

To do it, I had to violate an admonition from Tony G not to mess with motion.pas, but I did to see if there was a pattern to the problem.

[Stepper Monkey]

Could likely be interference if it isn't actually a software problem. Shielding and proper routing of wiring is key, but a sloppy and fast way to check it is to simply reverse your active high/active low settings so that in the non-tripped state it is constantly high, and tripped it goes low.
Not a great replacement for proper shielding, but it does keep false positives from happening if it is indeed a shielding issue, as if low is the default state interference can make it go high and give a false trip, interference obviously can't happen as easily the other way round and force a pin to go low.

[HakBot]

When you talk of shielding are you talking about shielding from the spindle motor/cnc control power wires or are you referring to the positive line running to the limit switches?

Good idea with the active high/low reversal.

[Bubba]

Stepper Monkey,
With all due respect, HUH! by doing this without a complete wiring change, it will always be in a tripped state. I can't speak for the other guys, but in my case this is an intermittent problem.
I may go a couple of months before a trip may occur. I also note no particular pattern to this happening!

[Clot]

I get fauls tripping too but only on my Z axis. Its driving me mad! I resort to upluginh my Z once its ready to run to ensure that program is not interupted. Blimmin annoying...

[Stepper Monkey]

Bubba - don't know how yours are wired exactly, but it shouldn't need much if any rewiring at all. Number of ways to do it, but basically you can make tripping the switch act to sink an input as readily as bring it high. You can make a resistor in a circuit act to pull-up or pull-down just as easily if that helps any.