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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,

Pan
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
NOOOO NEVER EVER IN SOFTWARRE!!!


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

Thanks
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?


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

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
Re: Door Safety interlock?
November 19, 2018 04:16AM
Even cutting power with a relay or anything else is not safe enough- Every spindle has its turn down time - many seconds.
It is a dangerous tool and no pets, kids or not instructed persons are allowed in a room with machines.

That is the simple truth. If you can not ensure this, you should not run/own such machines.
VDX
Re: Door Safety interlock?
November 19, 2018 04:42AM
Quote
Dancer
If you can not ensure this, you should not run/own such machines.

... or count in for lost limbs, pets and childs eye rolling smiley


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Door Safety interlock?
November 19, 2018 05:52AM
I realize this guys, but I still think I would like to add safety features that will at least help prevent such things... A seat belt doesn't prevent 100% deaths in car accidents but if it helps in 99% of cases, shouldn't we have them?
Re: Door Safety interlock?
November 19, 2018 06:40AM
Quote
panterateama
A seat belt doesn't prevent 100% deaths in car accidents but if it helps in 99% of cases, shouldn't we have them?

Some would say no, it breads stupidity and complacency.

If cars didn't have seat belts people would drive slower and take more care...
Re: Door Safety interlock?
November 19, 2018 12:05PM
Quote
Dust
Quote
panterateama
A seat belt doesn't prevent 100% deaths in car accidents but if it helps in 99% of cases, shouldn't we have them?

Some would say no, it breads stupidity and complacency.

If cars didn't have seat belts people would drive slower and take more care...

Even that does not work as the risk is not evident until bad things happen. The best way to make the risk visible is no seat belt for the driver (passengers strapped in) and a big knife sticking out of the steering wheel at the drivers chest.

Mike
Re: Door Safety interlock?
November 19, 2018 12:13PM
For god sakes guys I realize that we have Darwin award nominees everywhere but the fact remains that they don't build cnc machines without interlocks and safety mechanisms anymore because enough people got hurt. I'm just trying to build something safer than it currently is, which let's face it, are not very safe at all. If I want to send one of these into a classroom environment for example, I don't want to risk having things be unsafe so we can weed out the "dumb kids"....

I'm asking for helpful advice, not pointers on how to eliminate the idiots lol
Re: Door Safety interlock?
November 21, 2018 05:03AM
You should never send one of them into a classrom.

You are the builder of this thing, you are responsible for every injury and if anybody gets hurt, you'll be the one who is paying for it.
For classrooms only professional built devices from companies with legal insurance should be used.

But: It is your decission.


hot smiley
*shaking my head for even thinking about something like that*
Re: Door Safety interlock?
November 27, 2018 12:33PM
It was just an example Dancer. I'm looking for help making something safer. I have been in the 3d printing/reprap industry for over 6 years... I know the good bad and ugly of printer design...

I just want to know if anyone has any suggestions for a door interlock system.

I don't know why I'm getting trolling instead of helpful suggestions.
Re: Door Safety interlock?
November 27, 2018 06:37PM
Use RepRapFirmware, connect the door switch to a spare endstop input, and put a M581 command in config.g to command a pause when the door switch is triggered. Have the pause script move the print head to the least accessible back corner of the printer. If you are sufficiently paranoid, turn off all the power too. The pause command will have created a resurrect file on the SD card, so the print can be resumed later, if it remains attached to the bed.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

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 27, 2018 06:49PM
Nice that might work... I'm looking at using the rumba board and it has some spare ends top ports I can use... I'm still thinking of running it through a relay as well to kill power only to the head (heater/laser etc) and trigger this too with a normally closed script should work. Thanks
Re: Door Safety interlock?
December 28, 2018 05:01PM
I would argue that the interlock should work in the opposite way that you want it to in this case. The logic being that you are trying to prevent injury by putting the machine into a safe state.

For a CNC the main safety concern is crushing and cuts. This is relatively easy to prevent as when door opens you simply cut power to all axis (and spindle) and apply breaks to all axis (and spindle). The machine is then in a safe state for interaction as no parts can move to cause injury - they cant move. (Yes I know cutters are still sharp but they are safe to handle etc and shouldn't cause injury)

The primary concern for your health and safety on a printer is burns from the tool head and because a tool and bed retains heat even after power is cut a printer is not put into a safe state simply by cutting power to the drives, bed, and tool. That means the door can be open but the machine is not in a safe state. (that can be misleading to untrained operators and those who are used to CNC machines)

I believe the better option in the case of a printer would be a mechanical lock of some description (the easiest design is probably a solenoid) that when inactive physically locks the door (and fails locked). The controller can then activate and deactivate the interlock when it reads that both tool and bed are at safe handling temperatures (typcially <50C). Secondary door sensors can then be used to ensure that the door is actually shut before the interlock engages and heating starts and to disable motors when the door is open.

The benefits of that system would be that
A: the print cannot be interrupted by someone opening the door (so less scrapped parts from unrecoverable E-Stops).
B: No confusion as to the safety state of the machine - if you can touch it its safe.

In terms of software support, you would typically run safety critical systems on a separate controller (perhaps a PLC or a dedicated safety controller IC) so that in the event of a controller crash the safety systems continue to function as designed.
Re: Door Safety interlock?
January 29, 2019 10:55AM
Thanks ed3D, these are all good suggestions!

I will be running a raspberry pi as the primary computer system in my printer and it will be the one handling the startup, shutdown and safety devices as well as monitoring the environmental input from the rumba board so it will cut the power via relays to the rumba boards outputs. This should eliminate any delays from the software waiting to complete the next command before stopping.

The idea of a door lock is one I am considering for the temp to drop but I will have to figure out a way to trigger the unlock via temperature readings and also need to make a manual release option for when there is a problem with the software or power.

Thanks for the input!
Re: Door Safety interlock?
January 29, 2019 06:37PM
Go simple - thermal switch or resettable thermal fuse that is open over 50C. Solenoid that unlocks when energised. No need for any software then, and locked in a power cut. Just ensure that tools are needed to override the interlock if needed, rather than an override being available with no tools.

Edit: I was thinking this should be on the bed but could be on the hot end too.

Edited 1 time(s). Last edit at 01/29/2019 06:38PM by WesBrooks.
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