Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Daniel Peixoto on May 06, 2008, 12:53:17 PM
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I put 4 limit switch (X++, X--, Y++ and Y--) on my CNC router, but for example: If X++ is triggered the RESET button starts to blink and I can't move to X- for moving off the limit switch?
I read the past posts and someone told to turn on the Limit override, but this is not good because when LIMIT OVERRIDE is on the X axis move + and - destroying the limit switch. ( If X++ limit switch is trigger the X axis cannot move to X++)
Is there a way to move off the limit switch without turn on the LIMIT OVERRIDE? ???
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Hi, Daniel
Selecting Limit Override is just to move off the Limit Switch then you turn it back Off.
Thanks , Chip
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If you select the Settings Page and tick Auto Limit Override - this will allow you to back off the switch.
Without being pedantic, you shouldn't make a habit of hitting them - you can set your soft limits to avoid it. The limits are there as a last resort.
Yes - you are right - if you turn off the limits - your switches get wiped out, which happened to me a time or two. My limit switches are now laser beams shining on detectors - which avoids the crunch.
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I don't think software limits are trustable, because its easy to zero the axis in the middle of the movement then the machine will hit limit switch because the software limit will never reach.
There's a error in MACH 3, as I told before if X++ switch is reached the machine should not move more to X+ (This happen when tick Auto limit Override)
For me MACH3 deals with limit switch like an emergency stop (This is wrong), and I'm a idiot to use 4 pins for limit switch (it's better to tied the 4 limit switchs on only one parallel pin, thats because the MACH3 will stop the machine, and he doesn't have the capacibility to know what movement (+ or -) triggered the Limit switch.
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Is there a way to move off the limit switch without turn on the LIMIT OVERRIDE?
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Daniel,
Softlimits are tied to machine coordinates so they will stop an axis from hitting a physical limit no matter where you have your offset zero position.
Basically, yes you have wasted your pins by using seperate inputs for each axis, a limit switch is an emergency stop, it is to prevent damage to your machine and the softlimits are there to be used as you are thinking the hardlimits should be set up.
Hood
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Hi, Daniel
Limit switches are Limit's, Last Line of Defense, An "E-Stop Situation".
It Requires "Further Action" By Selecting "Limit Override" and Joging off the switch in the proper Direction By the "Operator".
Many Machines work this way, Requiring "Further Action".
As Hood Stater,
Set up your Soft Limits, It is what your describing/looking for.
After you home Mach, It moves Just off the SW and it revert's/changes to a limit SW.
DRO's zero ("Current Position" & "Machine Coord" to 0,0,0).
Soft-Limits work, At/Just inside your Limits, In "Machine Coord" and will slow down your feed-rate and stop just before your Limit switches would Trip.
You can Jog and Zero your to a "New" Current Position and the Soft limits remain just inside your Machine Limit Switch's,
See Pictures Below:
Dashed Lines are Soft-Limit's 0,0 X100" by Y50" Table, Part is at 0,0 Current Position.
If you hit a soft-limit you can Jog off it but not Jog further into the switch.
If you don't trust Soft-Limit's the "Limit" sw's are there to Save you.
Mach provides a way to setup Limits & home swithces using the Same Switch's with 1 Input Pin. You wire all the switches "NC" Normally Closed and in series with one another.
Mach now's which axis is moving during Homeing and only looks for a switch to open,
As the Operator you should be able to See what's going ON.
Why trust any cnc Machine , Hand Crank it!!
Think About It, Chip
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In Mach 2, I could simple hold the Reset button down with the mouse while hitting a jog key (arrow key) to jog off of the limit switch. Is this no longer the case in Mach 3?
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If you go to the settings page you can choose to have Auto Limit Override, what this does is if you hit a limit you can then reset Mach and then jog away from it. The Jog will be at a lower rate than normal, this is so you have time to react if you accidentally jog the wrong way. Once you release the jog key the next time you press it you will have full jog speed again.
Hood
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One other option. Many of the homebuilt machines have easy access to the axis screw, pulley, belt or motor coupling. And of course many don't. But for those that do, when a limit is hit all goes dead and it's sometimes easiest to just turn the screw and move the axis off of the switch. On my lathe, it's quicker than the "clicking" and requires less than 1/2 turn. Then reset, re-reference and roll on.
That was in the early days....I've now learned not to hit them. Softlimits are there to protect them.
RC
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RC if you use the Auto Override you dont have to clcik anything apart from the reset.
Hood
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First,click settings page, then click override, then keyboard jog off, then click override off, then click reset. or just turn the screw..
Or are you talking about leaving the override on ? Or...as usual, am I missing something
RC
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Yes if you use the Auto Limit Override it just needs a reset from any page you are on then you can jog off. You are thinking of the manual Limit Override. For that you need to go to the settings page and press it then the reset then jog.
Hood
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Ahh..yes. I see what you mean. I had the habit of turning it off every time after clearing the switch, maybe so no one else could just reset and crunch the switch by jogging the wrong direction from inexperience. Some operators dont need that option.
What is the purpose of having the option to leave it on or off ?
Thanks Hood
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There are 2 different Override switches, one manual and the other Auto. If you have the Auto on then you can just press the Reset and Jog off a limit, no need to go to settings page.
If you dont have the Auto set then you have to go to the settings page and press the manual override, you can then reset and jog off. In both cases as soon as the limit is closed again the limit switches become ready for your next attempt at machine destruction :D.
Some people may prefer to go to the settings page and use the manual option, could be for reasons like you suggested but I prefer to just have the Auto limit on, saves hassles of changing pages etc.
Another option of course would be to set up a physical switch on your control panel and use that as a limit override.
Hood
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There IS one advantage by clearing the limit manually, IF it's convenient at the machine. Some even have dual output motor shafts with a hand wheel... and a gantry with a belt or rack and pinion without a brake may just require a nudge. There's no way to inadvertently crunch the switch. Overrides are not on making it impossible to jog through the switch.
As you say though, a clear understanding of how it is intended to work is definitely the best defense. But if all was clear...we shouldn't be on the dang switch. ;)
I've never had the pleasure of crunching a switch.....luckily, my switch mounting bracket yielded. :D
But only once.
RC
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I have turned on autooveride. I hit the limit switch and the system goes on emergency stop. I hit reset but emergency mode keeps flashing and I cannot jog away from the switch. what am i missing. ????
the only way to move away from the switch is to disable it...
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Please attach your xml and I will see if there are any problems in it.
Hood
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Here is my XML code
I had hard time finding how to attach files....
John
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I have just tried your xml and it works fine here, what I would suggest is you load the standard screenset and test, it could be a problem with the screenset you are using.
Hood
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Hood
thanks for checking the xml me. I tried with the standard screen with no success.
The reset button does not clear after I pressed it and the alarm state remains. I cannot walk away from the switch unless I disable the switch from the inputs configuration.
It is so frustrating not to be able to duplicate what everyone else is getting.
John
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The only thing I can think of then is the switch is constanly bouncing and thus Mach is seeing repeated hits of it and wont allow the reset. Try setting a 2000 debounce interval and see if that helps any, if it does then it might be worthwhile looking for better switches.
Hood
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Hood
Just to make things clear. the RESET button is the big GUI button on the Mach screen. I dont have a physical reset button. did I get this right?
I do have a debounce of 400 on all my inputs so it is not a debounce problem.
John.
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Yes thats the Reset I am meaning, you should be able to press it after you have hit a limit and then jog off the limit.
You actually have a Debounce Interval of 1000 set, still worth trying higher to see if you can find the cause of the problem, I cant recall anyone else with this problem so it is a strange one indeed.
I am presuming you are just using the parallel port and not any external motion controller such as Gallil?
Hood
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Hood
You were right. I have a very noisy input and after I reset something triggers it again.
thats why I could not see the reset taking hold!
I use a a parallel port breakout board (C-10 from CNC4PC). I have set it active low. when the switch the 5v input is cutoff and the input is hanging unconnected. I suppose it picks up the occasional noise that trigers it.
my challenge is to get the input to stay low, when I cut off the 5v signal to it.
John
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Have you got the limits shielded?
Hood
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the wires are shielded but are not configured as twisted pairs. Three pairs of wires carry all 6 limits switches inputs with one common 5 volt wire going to all swithes.
I never thought that steady signals can such a source of noise frustration.
John
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Shouldnt need twisted pairs as long as the shielding is grounded properly at a single point. One thing you may want to try is putting them on another input on the BOB if you have one spare.
Hood
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Two things you can do to clear erratic limit switch behavior are:
1) increase the voltage of the limit switches to 12v or 24v which will also scale the immunity.
2) replace the mechanical switches with photointerruptors which are not effected by the machines vibrations.
FWIW, my initial problems with limit switches triggering e-stops was swarf getting between the switch contacts and the grounded machine parts. Putting heat shrink eliminated most of the false stops, but still tiny pices could get in there. I eventually covered the contacts with 'liquid electrical tape' and that finally sealed them up. You might check that also.
I now have two of my 4 axis to photointerruptors and they are dead on accurate in homing and so far have not triggered any false e-stops. I'll convert the other two axis when I get time.
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I ran new shielded wires and the problem went away. The old wiring was twisted pairs without shielding!!!.
on the suggestion to increase the voltage to 12V or 24V I am afraid that will likely burn the TTL inputs of the card.
I still get an estop spurious trigger. Is the estop switch also debounced in Mach?
John
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Yes, you definately cannot directly connect 12V or 24V to your BOB!
You need a transitor inteface. The 12v or 24v triggers the transistor which then directs the BOBs own 5v back to the limit switch pin on the BOB. Simple, but neccessary.
If the estop is being triggered by the limit switches, then yes, you can indrease the debounce, but if you are still having that problem then it didn't go away.
There may be other things that debounce applies to but one more experienced than I would need to chime in on that.
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Hi everyone!
I have the same question as was in the first post of this topic: Is it possible to move off a limit switch without turn on the LIMIT OVERRIDE?
I came up with this problem again, because I don't understand if Mach3 knows that the X++ limit switch is triggered than why doesn't let you to move off the switch in X- direction???
(Limit override is not good because it let you to move in X+ direction as well, so you can easily break the limit switch.)
All in all the feature i would like to have:
If limit switch X++ is triggered, after pressing the RESET button I can move the axis in X- direction (only, and not in X+).
If limit switch X-- is triggered, after pressing the RESET button I can move the axis in X+ direction (only, and not in X-).
Is there a way to implement this feature? Maybe in brain editor?
Thanks for your help in advance!
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COUPLE OF QUESTIONS:
1.where within the Mach 3 file system can I locate and review the Default G Codes as they appear in the upper right of the menu screen?
2. have there been any updates to the Mach3 software in the last three to 5 months?
3.how can I manually edit Machine Coord under the Diagnostis menu/screen and
4. under the Offsets menu/screen how can I manually edit the Part offsets?
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HIYA HHR, you really need to start your own new thread for these questions(;-) Not many people will notice you hidden at the end of this one.
Just a thought,(;-) TP
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ok
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i'd still like to know the answer to perla's question...