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Question Physical emergency button

Rede

Member
Hi, I was wondering, is there a way to implement a physical emergency button on the printer? Let me explain better, as you know, the klipper emergency button is present on the screen which stops immediately, but in an emergency you don't have the readiness to go and look for it on the screen, it's better to have an emergency mushroom button. I know that many people connect the emergency mushroom button to the mains power supply but I'm not crazy about the idea, I would prefer to send a signal to the rpi and have it execute the command but it is not m112 because it would go to the queue.
Do you have suggestions?
Thank you.
 
You could set a g-code button on Klipper to do that. However, that's still unsafe because there's always the rare situations where either the Pi and/or the controller board crashes and does not accept commands. For true safety the emergency button should be connected either on mains power, or on the controller board power.
 
thanks, I didn't know this factor of the pi that could not receive the commands. Then I'll do the thing that cuts off the mains power.
 
That's how I have things setup. I have Z-Wave switches controlling all my printers. Because the bigger Vorons draw more power I use high amp rated ones on those. Works quite well if I do need to turn a machine off quickly, even if I'm not in the same room. Otherwise, for a physical switch, could perhaps see about running the power switch to the front of the machine.
 
Honestly if I was that worried I'd just get a mains emergency cut off switch found at any woodworking or metalworking supply house and mount it to the bench the printer is on.
 
Hi, I was wondering, is there a way to implement a physical emergency button on the printer? Let me explain better, as you know, the klipper emergency button is present on the screen which stops immediately, but in an emergency you don't have the readiness to go and look for it on the screen, it's better to have an emergency mushroom button. I know that many people connect the emergency mushroom button to the mains power supply but I'm not crazy about the idea, I would prefer to send a signal to the rpi and have it execute the command but it is not m112 because it would go to the queue.
Do you have suggestions?
Thank you.
I have been active in the open source CNC community for years. CNC tools are a lot like 3D printers except they are bigger, big enough to cause serious injury. It's common to run 6,000 pound milling machines. These people take "emergency Stop" very seriously and a set of best practices has evolved over the years. some of them are

  • The primary rule. The E-Stop is designed to keep the machine alive. When e-stop fails, perhaps a cable is cut or comes loose the machine shall STOP. In short, it MUST fail in a safe way. The last thing you want is for a broken switch to prevent you from shutting the system down.
  • NEVER depend on software for safety. If stopping the machine requires even one line of code or config file to work, it is at high risk of not working because it can be misconfigured in some subtle way

That said, 3D printers are so simple that you might say your e-stop system is the AC mains cord, just pull it from the wall socket and any Voron printer will quickly stop. But this means the cord is always within arm's reach and not plugged in under the workbench and you have thought through how you would shut it if (say) your finger was sucked into a timing belt pulley. Plan ahaed so the cord is always easy to pull.

A better method would be to install one or more E-Stop buttons on the printer. One would be enough but if you want two, wire them in series. These switches when CLOSED power an AC mains rated relay that keeps the printer running. If a switch opens or the wires fall off the switch the relay opens and the printer stops.

To be really safe you could add a thermal fuse to the "loop". It is wired in series with the switch(es). Just design the loop such that if anything fails the loop goes "open circuit".

Why did I call it a "loop". Because you would never want to wire both wires to the switch in parallel. That invites a short. So each wires takes a different route and you have a loop of wire. OK, a Voron v2.4 will not rip your arm off if a long sleeve is caught in the A-belt but it is easy to follow best practice.

The "standard e-stop button is about 40 mm in diameter, red ,and stops the machine when you hit it with your fist. (yes it is sized for your fist, not a fingertip) The button stays down until you twist it to unlock. See photo below, They cost about $8 each for the Chinese kind, or about $80 for American-made kind with all metal machined parts.
1706763893578.png
 
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The definition of "emergency" plays into things here too.

I actually think that for many cases, a *software* e-stop could halt the machine mechanics more quickly than a mains power cut. Case in point, I made a config mistake once, and my v2.4 missed the nozzle probe pin during z-homing, making the most terrible noises as it tried to push the toolhead through the build plate. I flipped the power switch, and then got to sit there listening to it continue to crunch while the capacitors on the 24V power rail bled down enough for it to *actually* stop. A software e-stop would have felt instantaneous in comparison.

However, say we have a MOSFET failure or some logic fault that a watchdog can't resolve... a software e-stop isn't going to keep your mains-powered bed from running away.

A clever solution might be a conceptual 3PST mushroom button - with two legs cutting the mains, and the other a low-voltage signaling for a software shutdown. One action being more responsive but dependent on a certain operational status to be processed, and the other slightly delayed but guaranteeing the ultimate complete removal of power regardless of the fault.
 
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