So I’ve built myself an enclosure for my A350, and while it’s not the most elegant you’ll find here, it has most of the necessary: strip lights, extractor fan, OD3+ window in the top for checking on the laser (can’t see the laser from there anyway). And I felt it was pretty good, until today, when I accidentally opened the door while the laser was on.
Oops.
My question is to anyone who has designed their own enclosure - do you have any suggestions for how to install safety laser interlocks on the doors?
One option might be to put a window actually into the door, to make it harder to approach the machine without seeing if it’s on - didn’t think of that when I was designing it! But we have kids, and an interlock switch is really the only fully safe option. An interlock on the mains cable would cause the printer to switch off every time I opened the door, which is no good. I could put some sort of actuated lock which would prevent the door opening until the head was in the home position… that’s the best I’ve come up with so far.
Any thoughts? Has anyone else had a go at this? I understand it’s not possible to interface with the snapmaker’s own enclosure interlock system, is that right?
Most extreme version i can think of right now, padlock that prevents the doors from opening.
Next option, Camera and a small screen on the outside to check whats going on.
The toolhead itself nor the controller expose pins to hoockup a light that is lit when the laser is on (quite the strobo effect possibly). If you have an enclosure aswell, take the print and the hall sensors and mount them?
I guess I could make up a circuit with a LDR pointing at the workbed, connected to a servo-controlled latch. I’d have to put some sort of time delay on it to ensure it didn’t unlock the doors whenever the head was moving between laser paths, I guess.
I think something based on the head being in the home position seems like the best option right now.
As much I as I enjoy to over-engineer things, personally I would go for the more low tech solution of a padlock if you want to keep your children and/or pets out. Or the type of latch you need two hands for to open it.
What will you do if the thing you’re lasering catches on fire and you need quick access to extinguish it? At that point you don’t want to be depending on motors to open up the lock. I like that you have the little window on top to have a quick peek to see if the job is finished or not. So just creating the habit of hanging a warning sign on the know “Laser in progress, watch out” might already be enough. (but that won’t stop children of course).
Or change the position of the touch screen so that you hang it on the knob of the door and have to take it off to open the door. As such you’ll be forced to look at it before you do open the door.
If you do want to automate, using a limit switch that you mount in such a way that it gets pushed when the machine reaches the home position might be easier and more reliable than a light dependent resistor.
You’ve got three problems here. If you identify them as separate, it’ll be easier to think about. You will end up with a combination solution, but that will fall out of your design process.
If the door is opened when a laser operation is in progress, you want the laser to turn off.
While a laser operation is in progress, you want opening the door to always be deliberate and conscious.
While a laser is in operation, there should be a visual indication that it is.
Common to both these problems is the question “when is the laser in operation?” In an ideal world, you would easily get a signal out of the machine. The Snapmaker lives very far from that ideal world. As an alternative, you the user can designate when the laser is in operation by some physical action. That operation should engage a sensor whose electrical signal substitutes for a fully automatic one from the machine. This action could be as simple as a push-button labelled “start laser operation”. You could also put a contact switch on a lock hasp, or a switch on a bracket to detect a bar across the door, or whatever.
Problem 1 is safety. You should implement an interlock switch on the door regardless. It only needs to kill power when an operation is in progress. Even if you’re locking the door, you should have an interlock in case the lock mechanism fails.
Problem 2 is about creating a pause in an operator’s mind. The first thing they touch to open the door should not be the handle on the door. You can use a magnetic or solenoid latch on the door and a push-button labelled “stop laser operation”. You could use a pin with an attached flag that needs to be pulled. If you bar the door, you have to remove the bar.
Problem 3 is about user interface. I’d recommend the most blatant, a backlit studio sign that says “laser in operation”. A simple indicator light could work. A bar across the door is its own indicator. The flag on an interlock pin is an indicator.
Since you’ve got kids, I’d recommend a bar across the door. It doesn’t require any abstract explanation about what it does. It’s easy to explain the rule “Don’t move the bar. If you want to see, ask.”
Thanks all, really great suggestions. @brvdboss:
On the subject of fire, I have a little “exploding ball” fire extinguisher in the enclosure, mostly to allow unattended operation… so if there was a fire then I would close the doors and wait for that to go off (and make a mess of the machine, probably) rather than dive in and run the risk of it exploding in my face. But I take your point - a physical lock should be overridable by grownups. Given the height of the enclosure I think that is doable by putting something near the top, out of the reach of grasping little hands.
(Btw, the kids are 3 and 5 and not inclined to listen to Daddy, especially the 3 year old. The saving grace is that the route to the machine is an obstacle course of daddy’s junk, and you have to go past daddy’s desk)
also, I’ve been doing a lot of laser cutting from the PC (much quicker when you’ve got a repetitive run of jobs that you can just create a fixture and press the go button) - this means the touchscreen is not so useful as a status indicator.
@eh9 Your scenarios are correct. You correctly identify an important point, which is that you want the laser to turn off, not necessarily the machine. That has a corollary in that, while it’s okay for the mains supply to be turned off in an emergency, you don’t want to interrupt the power to the machine when opening the doors normally.
I like your pin lock idea - that would be easy to implement, and can be placed out of reach of little hands. It might even save me from doing something stupid, although when you’re cutting the twentieth bit of cardboard you are basically on autopilot. Where I’ve tripped up so far is in thinking that (because I can’t hear the machine moving over the racket of the power supply) the laser is finished, when it isn’t.
I guess I could route an interlock to the power supply through a microswitch so that it would only operate when the machine wasn’t in home position… but that seems very complicated and likely to go wrong, and electrics are not my field. I’m reluctant to mess around with 240V if I can avoid it.
You’ve pointed out a deficiency in my analysis. I was concerned about how a user might manually indicate that the machine went into operation, but not how they would take the machine out of operation or know that the machine was not in operation.
As far as detection goes, “X axis at home position” seems like a reasonably proxy for “machine not in operation”, even better if you were to use “all three axes at home position”. It might be possible for the controller to send such a notification, perhaps by itself, perhaps by some postfix added to the G-code.
You’ve also pointed out a different practical part of the problem: How does the operator find out when the machine is out of operation? I’ve considered getting stack lights for this purpose. This article is the source of the image; should give an indication about why they’re even more expensive than you expect. Industrial-looking but far from industrial-quality ones are also on market; they’re much cheaper, both in cost and quality.
In the present application, I’d use a stack of two lights. A red light indicates “process in operation”. A blue light indicates “process complete”.
You could also interlock the power to the laser head. This would require making custom cables to connect the controller to the interlock and the interlock to the laser head. If you don’t want to do electronics, this would be a no-go, since it’s harder to get right than a mains interlock.
A mains interlock is pretty basic for electronics and makes a good beginniner’s project. It has an additional benefit that you can easily integrate an emergency shutdown switch into the interlock. 12 V and 24 V (either AC or DC) signals are pretty common for low voltage signalling in an industrial context, so you’re not running mains voltage through a sensor switch. Easiest would be to use a 24 VAC transformer (readily available for doorbells), a DPDT relay with a 24 VAC coil, an ON pushbutton, and OFF pushbutton. This can all be wired up as an SR flip-flop (set-reset latch). One set of relay contacts controls the mains; the other set of contacts controls the relay coil. On this foundation you can integrate everything else discussed here.
