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Author Topic: Limit switches acting crazy, crashing  (Read 159 times)

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Limit switches acting crazy, crashing
« on: April 29, 2020, 02:27:44 PM »
In an attempt to dump mechanical limit switches, I installed 3 Hall effect sensors as shown below. When I magnet is passed over the individual sensors its relay indicator lights up and the normally closed relay breaks the circuit to kill the appropriate axis. This works, but...

Each limit switch works so that it stops the travel of that particular axis and requires a reset to continue with its travel.
If you fail to move that axis after resetting it, the other two axes will run passed their stops even though their individual relays are triggered.

This might make it easier to invision what happens:

Scenario 1:

Y hits a limit and stops. I reset it and move it again to make sure it was reset. Then I test X. It hits a stop, I reset it, test to make sure it travels. Ditto for Z.

Secnario 2:

Y hits a limit and stops. I reset it but I DON'T jog it to test for a reset. Then I test X. It passes its magnet, lights up its relay, but continues to travel without setting off an alarm, eventually crashes.

I've tried for a couple of days to figure it out but I'm stumped. Any ideas? I appreciate any help. Diagram attached.
Re: Limit switches acting crazy, crashing
« Reply #1 on: April 30, 2020, 05:48:39 PM »
Hi,
when you say you 'hit a limit switch' are you in fact 'homing or referencing'?

If you are 'homing' then until the homing sequence is complete Mach ignores the limit switches. Once homing is complete
then they are again recognized as limits and behave normally.

From your description it sounds like the machine is ignoring a switch......could this be an explanation?

Craig
My wife left with my best friend...
     and I miss him!
Re: Limit switches acting crazy, crashing
« Reply #2 on: April 30, 2020, 06:23:20 PM »
Thanks for responding. I appreciate it. Been talking with guys at CNCZone.com and we have sort of come to the conclusion that using relays to reverse the hall-effect signal may be the problem. So I'm going to try taking them out of the equation. To answer your question-- I simply jog the Y (for example) past the magnet to cause it to trip an alarm which stops the travel instantly as I was hoping. So that was my test for Y. Then, I test X. When the magnet gets close to the sensor, it lights up the relay indicator light but does not trigger a stop. It will run right past the magnet until I let off the jog key or until it crashes. Same thing happens for the Z test. Now-- if I do the exact same series of tests, but this time, after the Y hits the stop, I reset it and move it any distance at all. Having moved its position somehow allows the X to stop at the sensor just as the Y did. Not a reliable set of circumstances. It's kind of a hard thing to splain on a forum.:-)
Re: Limit switches acting crazy, crashing
« Reply #3 on: May 01, 2020, 10:42:17 AM »
Last night I removed the relay pack and wired it up as shown in the attached pic. It was a total fail. When the Hall effect sensors are triggered (or when they're not) the axes jog as if the sensors weren't even there.

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Re: Limit switches acting crazy, crashing
« Reply #4 on: May 02, 2020, 04:24:16 AM »
You should connect sensors according to the following picture.
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Re: Limit switches acting crazy, crashing
« Reply #5 on: May 02, 2020, 09:26:42 PM »
I'll give it a go. Thanks!
Re: Limit switches acting crazy, crashing
« Reply #6 on: May 03, 2020, 11:12:54 AM »
Per advice from various respondents, I removed the relays altogether and wired it as they recommended. Pics with values attached. As the magnets passed the sensors, the lights in the sensors came on and the voltage changed from 3.75v to 0.08v but no alarms were triggered, like the sensors weren't even there. As far as I could tell, there was nothing happening on the diagnostics screen with or without the sensor activated. The saga continues.

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Re: Limit switches acting crazy, crashing
« Reply #7 on: May 03, 2020, 11:22:04 AM »
You should supply your sensors with 12V
Make no mistake between my personality and my attitude.
My personality is who I am.
My attitude depends on who you are.
Re: Limit switches acting crazy, crashing
« Reply #8 on: May 03, 2020, 11:24:32 AM »
You should supply your sensors with 12V
Will do.
Re: Limit switches acting crazy, crashing
« Reply #9 on: May 03, 2020, 12:34:22 PM »
Instead of 12v I went ahead and used the 36v from my main power supply. Made the sensor lights much brighter of course. But still no trigger action. So far, the closest I've come to success was the 8 relay block. But it does have that one problem mentioned in my original post. And, of course, the primitive mechanical micro switches that I used for several years worked. But they were so crappy looking. I really would like to get this to work. No moving parts, nice clean look.