The arm on my limit switch (mechanical) has a little spring to it. It moves onto a ramp near the limit, and as it rolls up the ramp it eventually trips and stops the axis move, just like it should, and trips an alarm. The problem is when I try to jog off the switch. I clear the alarm and then, because of the spring, the limit switch does not switch immediately on the axis jog move. This immediately registers another alarm which I have to clear, then I get a tiny jog, another alarm, clear alarm, tiny jog, another alarm, clear alarm, tiny jog, another alarm - this goes on quite a while before the switch overcomes its spring hysteresis. Is there a way to override alarms when jogging off a limit switch ? I'm currently handling it by mechanically bending the limit ramp to switch the switch.
Replacing or repositioning the switch so you can jog out of it without retriggering will be your only option
I don't know how your setup is, Jim. My setup is Normally Open (NO) limit switches. Therefore I have a momentary NC switch close by. It has the ground wire, that the limit switches use, run to it and from there to the limit switches. Once I have a limit switch triggered I press this momentary button and jog the axis away from the limit switch. Once the limit switch is cleared everything is back to normal and I release the momentary switch. I am very very carful when I do the jogging away to make sure I jog the correct axis and AWAY from the limit switch.
Not the way it should be. After clearing an alarm you absolutely CAN jog away from the switch. But if the switch retriggers (clears, then closes again) it creates a new alarm. If it does either the way you actuate the switch or the actual switch is flaky and causing retriggers. Hit the switch head on. Ramping is not going to work out.
This entire issue should be solved either by A) increasing the $27 pull-off distance to a not-activating-the-switch distance, or B) setting $130-132 soft limit distances to barely-touching-the-spring-arm numbers so that grbl throws an error before even attempting to go near the limit switches. Hard limits should really only be for extreme scenarios where you've unknowingly lost steps or something and have to avoid machine damage. (But yes, you should be able to jog off an activated switch after a $X or whatever override command.)
Thanks Rob, The situation arose when I was testing the limit switches to be sure they worked. Raised the Z axis until the switch activated, axis stopped movement, and an alarm was generated (all the way it should be so far). Problem arose when I tried to move off the limit switch. Cleared the alarm and attempted to jog the Z axis down. At first movement, the Alarm recurred (I assume because the switch was still activated and did not de-activate after a single Z step). Cleared the alarm, tried to jog, same result. This happened repeatedly getting only one step between alarms. (I finally just reached over and physically moved the limit switch mechanism out of the way to de-activate the switch).
As far as I can tell, the switch is not clearing and resetting (no jitter in the switch). It's just that I have to move the Z axis some small distance before the switch de-activates.
I agree, but what if it is not? Next time I play with my machine I'll confirm that it does but if I recall correctly when I pressed to clear the alarm it immediately triggered the alarm again even before I had a chance to jog away. All I did was move the machine until the limit switch was triggered. Couldn't clear the alarm as I stated above.
I'll look at my setting and see if it helps. I don't remember off hand the settings. It's the default settings that came with GRBL, which I'm not sure are what.
You can do what works for you, but I would not recommend offering your method as the advice to the original poster Are you using a BlackBox and Xtension limits - electrical noise can also cause the retrigger - but open a seperate thread if you need with that
I looked at $27 and it is for 'Homing pull-off, mm'. I'm not using homing. Will it still move off the limit switch? Either one of the two?
Nope. The homing option was for if the OP was having the issue during homing, because they didn't specify when it was during operation that I saw. Otherwise, soft limits are the answer (which... Still requires homing). Jogging should be allowed after clearing an alarm though. Perhaps a direct console G-code input would do better, if it's not letting you, some kind of G91 G0 move that would clear the issue in one shot.
Well, the problem is, when I used Mach3, that the limit switch triggers an alarm and I couldn't do anything before clearing the alarm and I couldn't clear the alarm until the axis moved from the limit switch. You see the problem? I was in a Catch22 situation and if I recall correctly I had the same problem with Control and GRBL which is why I used the momentary switch, as I mentioned a few pagers before, to disconnect the ground wire from ALL the limit switches, clear the alarm and jog the axis away from the limit switch and then let go of the momentary switch. If there is a better way for doing it please let me know and I'll use it.
Grbl DOES allow you to Jog out of a switch, after clearing the alarm. The key thing is the switch should only clear during the move, not retrigger. Use a quality switch with filtering like Xtension Limit Switch Kit and mount it such that coming out of the switch cannot retrigger it (ie head on is best)
I actually do like that idea, it's a good way of thinking around the situation, but... ...The solution is homing. You don't need to use machine coordinates at all in operation, you just need soft limits to protect the machine from itself. You can use whatever switches are already on there. I can't think of a reason not to take the 20 seconds to run a homing cycle every time the machine is turned on. (But quality switches, capacitive filtering, etc etc, as Peter says)
That's the salient point! How do you clear the alarm without moving away from the switch? As long as the switch is pressed the alarm stays and I can't clear it!
You hit In CONTROL, followed by a Jog "away" from the switch If it retriggers during that move, you have a hardware problem to solve (noisy switches,bouncy contacts, emi, too short a debounce value in settings, etc) and nothing else Think about it. If Grbl didn't allow you move out of a triggered limit, and expect you to disconnect switches to do so, "by design" - that would be kinda weird after all right? Surely you'd see everyone mention that as a major shortcoming. Grbl's userbase would be almost non existant
To be honest, I never was active on the Mach3 forum and never looked for a solution for this problem. I just had it, 10 years ago on the PhlatPrinter III, and solved it without much of a search and it worked. In my mind everybody did the same solution as I did and I never gave it a second thought. When I migrated, a few month ago, to GRBL I just took it for granted that that is the solution for this problem here too, again without a second thought or search. You know, why fix it if it works?
