Limit SW to activate pause, not e-stop
- bottleworks
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02 Feb 2015 01:09 #55557
by bottleworks
Limit SW to activate pause, not e-stop was created by bottleworks
Hello.
I am trying to figure out a way for pause or stop to be activated when a limit switch is activated. The standard configuration is for e-stop to be triggered. On one machine, I have a very sensitive Z limit switch which is susceptible to being triggered with certain harmonics. On the other machine, sometimes debris can get into the switch area. Once e-stop is triggered, it turns a 30 second fix into 20 minutes.
Any suggestions would be helpful. Thanks
I am trying to figure out a way for pause or stop to be activated when a limit switch is activated. The standard configuration is for e-stop to be triggered. On one machine, I have a very sensitive Z limit switch which is susceptible to being triggered with certain harmonics. On the other machine, sometimes debris can get into the switch area. Once e-stop is triggered, it turns a 30 second fix into 20 minutes.
Any suggestions would be helpful. Thanks
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02 Feb 2015 02:17 #55559
by andypugh
Replied by andypugh on topic Limit SW to activate pause, not e-stop
What you suggest it possible, but might I suggest that it might be better to fix the switches?
A simple solution is probably to debounce the limit switch inputs with the HAL debounce component. I had to to this with my machine to prevent electrical noise from the VFD triggering the limits.
You can actually afford quite a long debounce time on limit switches, the machine doesn't travel far in 10mS.
www.linuxcnc.org/docs/html/man/man9/debounce.9.html
To pause the program when a limit switch is hit you could use the halui.program.pause pin linked to the limit switch, but you would still get nuisance tripping. So debouncing might still be better.
A simple solution is probably to debounce the limit switch inputs with the HAL debounce component. I had to to this with my machine to prevent electrical noise from the VFD triggering the limits.
You can actually afford quite a long debounce time on limit switches, the machine doesn't travel far in 10mS.
www.linuxcnc.org/docs/html/man/man9/debounce.9.html
To pause the program when a limit switch is hit you could use the halui.program.pause pin linked to the limit switch, but you would still get nuisance tripping. So debouncing might still be better.
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04 Feb 2015 11:19 #55662
by bottleworks
Replied by bottleworks on topic Limit SW to activate pause, not e-stop
It would be nice to repair the hardware, but that would have to be planned out for a year+. There just isn't time right now.
I'll give your suggestions a shot. Thanks
I'll give your suggestions a shot. Thanks
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04 Feb 2015 14:46 #55667
by emcPT
Replied by emcPT on topic Limit SW to activate pause, not e-stop
If you are using 5v for the limit switch voltage you will find a high improvement changing for 24v. 24V and the debounce should be enough for all your needs even in a noisy environment.
Limit switches are for estops, do not change your machine to make a feedhold. Safety first (for you and for the machine).
Limit switches are for estops, do not change your machine to make a feedhold. Safety first (for you and for the machine).
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04 Feb 2015 15:14 #55670
by ArcEye
Replied by ArcEye on topic Limit SW to activate pause, not e-stop
Exactly as emcPT says, increase the voltage at the limit switches.
I had problems with a 'dirty' 200v DC spindle motor on a small mill conversion.
Had intermittent tripping problems on the limits which no amount of grounding of supplies, cables etc. cured.
By simply feeding 12v from a walmart power supply through the limits and using this voltage to activate a small 12v relay which switched the 5v limits signal, I completely cured it, simply and cheaply.
regards
I had problems with a 'dirty' 200v DC spindle motor on a small mill conversion.
Had intermittent tripping problems on the limits which no amount of grounding of supplies, cables etc. cured.
By simply feeding 12v from a walmart power supply through the limits and using this voltage to activate a small 12v relay which switched the 5v limits signal, I completely cured it, simply and cheaply.
regards
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05 Feb 2015 01:05 #55696
by bottleworks
Pausing instead of allowing motors to wind down uncontrolled is by far safer. You will have to explain your logic.
Loss of control is not a safer state.
I believe the switches are on a 12v supply. I think it was changed over from 5v during initial machine troubleshooting. I can add a large cap, but I wouldn't be able to take the machine offline for sometime.
The limits are also home switches, so I wouldn't want a relay in between.
Replied by bottleworks on topic Limit SW to activate pause, not e-stop
Safety first (for you and for the machine).
Pausing instead of allowing motors to wind down uncontrolled is by far safer. You will have to explain your logic.
Loss of control is not a safer state.
I believe the switches are on a 12v supply. I think it was changed over from 5v during initial machine troubleshooting. I can add a large cap, but I wouldn't be able to take the machine offline for sometime.
The limits are also home switches, so I wouldn't want a relay in between.
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05 Feb 2015 02:06 #55699
by andypugh
When we talk about "debouncing" we mean in software.
You can even debounce the signal in software for two different times from the same input, to have fast-response home signals and slower, more robust to noise, limit signals.
Replied by andypugh on topic Limit SW to activate pause, not e-stop
I can add a large cap, but I wouldn't be able to take the machine offline for sometime.
When we talk about "debouncing" we mean in software.
You can even debounce the signal in software for two different times from the same input, to have fast-response home signals and slower, more robust to noise, limit signals.
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05 Feb 2015 02:33 #55701
by emcPT
On situations were the loss of control is an issue, motors have brakes that will avoid unwanted movements. Limit switches should be connected to the control and to a logic more close to motor (for example the drive, taking out the "enable" or similar).
This is safe, not feedhold.
Replied by emcPT on topic Limit SW to activate pause, not e-stop
Safety first (for you and for the machine).
Pausing instead of allowing motors to wind down uncontrolled is by far safer. You will have to explain your logic.
On situations were the loss of control is an issue, motors have brakes that will avoid unwanted movements. Limit switches should be connected to the control and to a logic more close to motor (for example the drive, taking out the "enable" or similar).
This is safe, not feedhold.
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05 Feb 2015 17:25 #55714
by ArcEye
Is it an isolated 12v supply though?
Replied by ArcEye on topic Limit SW to activate pause, not e-stop
I believe the switches are on a 12v supply. I think it was changed over from 5v during initial machine troubleshooting.
Is it an isolated 12v supply though?
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13 Feb 2015 12:44 #55942
by bottleworks
You must work with different motors then I do. NO brakes here. So, as I stated, a controlled stop is safer.
No, the 12V power supply powers MESA board and a couple relays. I could try isolation, however, I wouldn't be able to do that for at least a few months.
Replied by bottleworks on topic Limit SW to activate pause, not e-stop
On situations were the loss of control is an issue, motors have brakes that will avoid unwanted movements.
You must work with different motors then I do. NO brakes here. So, as I stated, a controlled stop is safer.
No, the 12V power supply powers MESA board and a couple relays. I could try isolation, however, I wouldn't be able to do that for at least a few months.
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