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Door Safety interlock?

Posted by panterateama 
Door Safety interlock?
November 02, 2018 01:04PM
Hello all,

I'm working on a printer enclosure that will be tied into the electronics of the printer. I am using RAMPS 1.4 driven by an RPI.

I want to make a switch on the door that will stop the machine from moving unless the door is closed as a safety feature. I plan on using a cnc milling head at some point and for safety, I don't want someone to be able to open the door and stick their fingers in if it is moving. Many CNC machines I have used include a light curtain or doors with switches that prevent the machine from moving and stop the spindle as soon as the door is opened.

I can't seem to find anything in the marlin firmware documentation that would allow this. A sudden stop is a major security need but I don't want to kill the mains power so I don't kill the printer every time I open the door.

The way I would like to wire this is an enstop that would be normally open going to an emergency stop button and then to the pi or the RAMPS. In order for printing to start, the endstop needs to be pressed (By having the door closed) and the emergency stop button in the closed (not activated) position. this would have a closed circuit, telling the pi or RAMPS that the printer is in a safe and ready state. If the door opens, or someone presses the e-stop button, the steppers and the spindle/laser/heaters would all stop immediately WITHOUT stopping the fans, lights and power to the controller itself.

I know there is an M code that tells the machine to STOP but it is software reliant and has to wait for the current command buffer the finish running before stopping, that could mean losing a finger before the machine stops...

Does anyone have anything like this?

The only other idea I have is to run all of the power lines from the steppers, heaters and mill through a set of relays that open if the safety switches open. This option seems rediculously expensive and complicated in terms of wiring...

Let me know what you guys think as I feel this could really help make printing/milling/laser engraving at home much safer.

Thanks Guys,

Re: Door Safety interlock?
November 02, 2018 02:11PM
You can do it with the "Filament Runout" option in Marlin.
Whit this option Marlin control if a pin change and execute an M600 gcode (you can configure some options of this Gcode).
M600 pause the printing and wait until you press the LCD button to continue.
Re: Door Safety interlock?
November 02, 2018 02:22PM
I did think of this too, but I'm wondering if m600 or even triggering m125 to park it would also shut off the heaters/milling head (the milling hear speed would be controlled by the same circuit as the heater on the second extruder controller)
Re: Door Safety interlock?
November 05, 2018 07:40AM

Sorry for shouting out. M600, M125,.... use all moves which are already in buffer - no immediate stop!
If you need a safety feature, it has to stop power to all moving elements (stepper, spindle,...) without any software involved! (As long as it is not security approved)
If you can not sepparate the moving parts electrically, you have to cut power from the controller. (your part will be ruined, but safety does not care about ruined parts)

Edited 2 time(s). Last edit at 11/05/2018 07:42AM by Dancer.
Re: Door Safety interlock?
November 05, 2018 08:12AM
What I'm thinking of doing is creating a relay board. If the emergency stop or either of the doors are triggered, it would cut the power to the spindle/laser emediately by cutting the 12/24v line to them. But it will also send a signal to the controller to run m600/m125 so both will take place. The most u portland thing is to kill the laser and the spinning bit 100% dead immediately. The movement of the steppers I am less worried about doing 1 more pass until 8 find a better solution. Any other ideas to stop the motors without splicing a ton of wires, I'm all ears

Re: Door Safety interlock?
November 07, 2018 07:03PM
I still can't belive that no one has thought of this in terms or ramps or derivative hardware...
Re: Door Safety interlock?
November 08, 2018 03:27AM
Perhaps because RAMPS is a poor choice for CNC milling?

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Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Door Safety interlock?
November 08, 2018 12:39PM
But as a multi axis controller and on/off for a single speed mill it ticks all of the boxes except a hardware safety shutdown. If someone made a good iteration of the ramps base (like Rumba for example) with multi extruder, fans, mosfets etc but also include a hardware shutdown jumper, the world would take notice...
Re: Door Safety interlock?
November 08, 2018 10:43PM
For the controller all you have to do is add a switch to the door, the switch is wired so that when the door is open the switch contact are closed.

This is wired in parallel to the reset switch. The instant the door is open, reset is applied and the controller is held suspended in reset.
This should also turn off mosfets.

Edited 1 time(s). Last edit at 11/09/2018 12:34AM by Dust.
Re: Door Safety interlock?
November 11, 2018 06:27AM
With my last build I made a serious stab at a reliable interlock that mainly focused on the heaters and steppers. This was on a duet, both 0.6 and second generation, specifically an Ethernet model.

Heaters are switched ground, so could be powered by a seperate power supply that I interlocked on the mains side. The duet has the option of powering with a 5V supply for the controller and VIN for steppers and heaters. Looking at a recently aquired ramps 1.4 it looks like this may have a similar split in power supply.

I used two permanently on power supplies. One 5V for the controller and screen and a 12V to power fans and the coils of guided contact safety relays.

Two of the normally open contacts on each of the relays were used to cut the live and neutral mains supply to a third power supply that powered the vin on the duet and the heaters directly. The coils were wired in parrallel through an e-stop button and grounded through the ps-on pin on the duet. What ecer happened the e-stop was near guaranteed to cut the power to the coild, and thus break the mains to the heater/steppers psu. I used used spare contacts on the relays for indicator LEDs and finally added a reset button that initially energises the coils before the relays latch and power themselves, so long as the e-stop button isn't pressed and the controller has grounded the ps-on pin.
Re: Door Safety interlock?
November 11, 2018 06:30AM
Trouble is guided contact relays aren't cheap and the whole interlock system cost more than some cheap machines. It's on my todo lost to see how economically I could make this.

...additional interlock devices should be easy enough to add in between the coils and the e-stop switch. Testing needs to be carried out to ensure all devices in the chain work as expected rather than left alone for momths assuming they'll be fine when needed.

Edited 1 time(s). Last edit at 11/11/2018 06:54AM by WesBrooks.
Re: Door Safety interlock?
November 11, 2018 08:58AM
This all makes sense... Sadly It looks like a relay system would be the most practical in my case. It seems like multiple power supplies would make for much more reliability issues, not to mention needing a much larger containment box. Thanks guys. I'll let you know what I figure out
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