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Author Topic: Moving off Limit switch  (Read 46537 times)

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Re: Moving off Limit switch
« Reply #20 on: June 10, 2009, 02:36:23 PM »
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

Offline Hood

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Re: Moving off Limit switch
« Reply #21 on: June 10, 2009, 02:44:34 PM »
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
Re: Moving off Limit switch
« Reply #22 on: June 10, 2009, 03:03:02 PM »
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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Re: Moving off Limit switch
« Reply #23 on: June 10, 2009, 03:09:42 PM »
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
Re: Moving off Limit switch
« Reply #24 on: June 10, 2009, 04:46:26 PM »
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  

Offline Hood

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Re: Moving off Limit switch
« Reply #25 on: June 10, 2009, 05:08:46 PM »
Have you got the limits shielded?
Hood
Re: Moving off Limit switch
« Reply #26 on: June 10, 2009, 05:17:33 PM »
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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Re: Moving off Limit switch
« Reply #27 on: June 10, 2009, 05:20:00 PM »
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

Offline simpson36

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Re: Moving off Limit switch
« Reply #28 on: June 11, 2009, 06:44:20 AM »
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.
« Last Edit: June 11, 2009, 06:46:30 AM by simpson36 »
Re: Moving off Limit switch
« Reply #29 on: June 14, 2009, 07:21:32 PM »
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