Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Timgander on February 12, 2017, 11:00:07 AM
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There's a million hits when I search for this but not a simple answer! I have single inductive proximities on each axis. Told Mach3 to use each signal (each on separate pin) as a combination home, limit+ and limit- trigger. When I 'ref all' machine homes and backs-off in all axes as it should but if I inadvertently jog in the wrong direction the 'limit' switch is re-triggered and all stops...as it should...but then Mach won't let me reset as it 'sees' a limit switch STILL triggered??? I would have thought that it would allow you to manually 'back-off' the limit switch in the opposite direction but until 'reset' is hit (which it won't accept) you can't. I'm sure I have something not set right as each time this happens I have to go into Ports and Pins and disable the X++ and X-- detection just to allow me to move off the limit switch! What am I doing wrong!! This can't be the normal operation of any controller as it ends up in a logical lock-up situation...'Limit switch hit therefore NOTHING moves, reset needed...Oh...you can't reset while a limit switch is STILL hit' therefore solid lock-up??
Tim
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Did you check the box on the Settings Menu "Auto Limits Override" ?
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Hi Kolias..Not yet as I am trying to find a way where Mach allows you to move 'away' from the triggered limit but only stops you from barging any further 'into' the switch.
Tim
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Mach3 is not that smart. Since you're using a single switch, Mach3 has no idea which direction to move.
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Hi Ger,
Thing is there is a switch per axis and if Mach3 moves, say ++ and hits a limit switch then surely it is kids play in software for it to disallow further ++ movement and only allow -- movement??
Tim
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That's not how it works, and since development stopped 5 years ago, it's not going to change.
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:-\ :-\...mmm..OK. Well I've changed a few things, set the soft limits before the physical switch limits, set the auto limits override and ditched having both + and - limits on the same input pin and although it's not perfect it doesn't get into the irreversible lock-up situation that it did before! Does Mach4 address the problem??
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I don't know about Mach4 but once setup and working, limits with soft-limits in Mach3 is pretty bullet proof, I have three machines here all setup the same and all work just fine - I can jog into any soft-limit and it still allows me to jog off ok.
It must be a setting or construction/wiring issue.
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I set my limits in Ports & Pins/Input Signals, at the bottom right of the screen there is a button "Automated Setup of Inputs". Mach3 will do all the work for you
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Hi Guys,
Thanks for the replies but Dave...I can jog into and away from a soft limit like you can... but if I hit a full limit (as opposed to a soft limit) movement stops (correctly) but I can't reset to allow me to manually 'back-off' as the reset says 'no reset while a limit switch is active'.
I set all the pins manually with no issues but there does exist this anomaly in Mach3 that once on a full limit you can do nothing to get off it manually without going back into the program, altering a parameter, coming out the program, moving the axis OFF the limit, going back into the program, returning the parameters to normal and then carrying on! Mach3 is so comprehensive that I had imagined there would be a couple of lines of code that allowed you to jog AWAY from a hit limit switch with a jog button. I'm sure the coder had a reason to not include it...probably safety or something.
I'll live with it ;)
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As Dave mentioned I never had a problem to jog away from a limit. Are your limit switches wired NC or NO?
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Ah, I see - yes i had the same issue and just wound the screw off the stop by hand a few times. Once soft limits are set properly, the issue never occurs again, my soft limits are set 3mm off the hard limits IIRC.
You would think that as Mach knew which way the axis was moving when it hit the limit, it would simply allow movement in the opposite direction, but i Mach is what it is, end of.
What it is, is really a pretty good way of building CNC machinery, there are other options out there now but i have no idea if they are better, the same or worse than Mach3.
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Hi Kolias, my limit switches are inductive proximity, two wire and ground the pin when tripped so they are effectively NO. I know this is not the safest option but the rebuild on this machine has been 'extensive' and expensive and as the sensor limit plates are welded in place (and the sensor adjusts) I decided to run with them. I can jog away from a soft limit as the 'reset' is not flashing but if you hit a hard limit (any of my 3 sensors) then machine stops and you CANNOT move ANY axis while Mach3 is in 'reset' or E-stop. Having the 'auto limit override' solves it to an extent but it would still have been nice to have the software detect which way the limit switch had been hit and know that it will now only allow jogging 'away' from that direction.
Not the end of the world..!
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Not sure what machine this is on but on my bridgeport mill, the hard limits are wired into the safety circuit NOT mach3, if it hits a hard limit it cuts all power to the axis drives so the ONLY way out is the reach for a spanner and screw the axis off by hand.
This was a safety setup decision - it has servo motors and in the event of a runaway drive it would smash the end off the machine in a flash so a very hard limit was thought safest.
The soft limits are the main operation limit system.