Light Curtain Lock Out

[JankyPLC]

We often run into scenarios where light curtains with muting seem like the go-to solution for entry and exit of product on conveyors into and out of machine cells. These light curtains also end up being a convenient way for operators to enter said machine cell.

A person won't meet muting requirements and will trip out the safety which is good, but I'm curious if any of you have implemented clever -safe- ways of dealing with the fact that once you enter the machine cell, you're no longer blocking the light curtain and someone else can reset and start the machine with you inside the safety zone.

So far I've seen OEMs use a hinged plate that you can swing in front of a couple of the beams of a light curtain and could put a lockout lock through, and one other OEM put a pre-reset button inside the safety zone at the back of the cell so you have to enter to 'look around and verify no one is inside' the area before resetting outside the cell. We've used safet laser scanners and pressure mats in some applications but they don't lend themselves well to many tight machine cell designs.

Any other ideas you all have used or seen?

 

[mk42]

Trapped key interlocks are one solution. I've usually seen them on doors, but I guess something similar could be used to switch a machine into "maintenance mode" and it can't be switched back while person in the cell has the key. Could be paired with a lockout/tagout type system for multiple people if needed.

 

[arpus4KM]

in order to keep people from being in an operating area when they shouldn't be. the light curtains are fine to break an operation. but to keep safety active when someone is in the wrong spot, pressure mats were used for a long time in my experience.

putting pressure mats all over the floor can be an option. or these days area scanners work pretty well without the possibility of being destroyed via dropping items on them. People can and will get into areas they shouldn't be inside of. There is a ton of effort to keep these people out of places they shouldn't be in. But at some point, the only thing you can do is fire people who breaking the rules.

Area scanner for the floor, someone stands on an object in the cell and starts it or has someone else start it.

Light curtain entry, they stand in it and press reset with a stick or pole.

verify no people are inside before starting prompts on screen and tie to security cameras, and the operator just blazes through the buttons and hits start while people are in the cell.

Door lock needs to be closed from the outside, Operator unscrews the key side and inserts it with the door open because hes tired of the sequence of pressing a button to unlock, open, lockout the door latch, enter, fix the problem, exit, unlock the latch, close, reset, restart process... when he can just reach in while its running real quick and just get that part in place.





take your pick for your process, but if area scanners, light curtains, and door lock switches aren't strong enough security, then you've got a people problem that needs to be solved by the bosses.




EDIT:

I probably sound salty, but I've had to deal with through the years of having fully guarded machines with pressure pads that were kicked out of the way, dual hand controls that were physically moved closer so one hand could be used. light curtains that people have actually gone under and reached an arm fully upward into a process to reach something. Guarding that blocked any real access, and operators crawled under a table. Guarding that was screwed in place and operators used their setup tools to remove the guards so they can unjam parts quicker.

Had a rotation table assembly to hold parts for a robot cell that would pick parts from the magazine and place them into another fixture for welding. sometimes they would stick up a little bit too high because they used magnets on the backstops to keep the parts in place, and while the robot was actively picking and plant management was standing next to the operator talking about future improvements, he bends back an 80/20 guard just enough to reach in with his arm and push parts back down so the robot will keep running and he won't need to enter the cell...... He still worked there for years after that.

You name it, I've probably seen it and plenty of processes that weren't even safe in the first place.

 

[roxusa]

All my machines are in a cage that requires removing a key from console and putting it
in a gate to be able to remove the gate key that is there. Breaking a light curtain where product exits or enters requires a supervisor key to reset it. Inside a cage without a key
is instant termination. Period. Once you have seen a few "bodies" mutilated by a machine you understand why.

 

[GaryS]

WOW
First it is never acceptable for any personal to ever walk on any conveyor weather the conveyor is powered or not. Muting a light curtain on a conveyor to allow personal to pass through on the conveyor is the same as disabling it completely. The whole purpose of the light curtain is to prevent personal from entering in an unsafe manor. If personal need to enter the restricted area then provide the appropriate interlocked safety gate it cheaper in the long run than the OSHA fines and paying for personal injuries. When there is an accident.
And keep in mind the company management will always find a way to blame you for safety violations
I have several companies that have very strict rules on this if you walk on any conveyor you will be removed from the building permanently no second chance. That same company recently added policy that no personal will pass through any overhead unless they are in a vehicle with a safety cage again strictly enforced.
We as engineers and programmers must do everything we can to ensure the safety of all personal.
If management wants us to do something that we know is unsafe or could endanger personal have a obligation to refuse and even report you can always get another job you only one shot at life. I myself have left more than one project because of safety problems.
I actually had a company I was looking to work for installed fake E-Buttons. The buttons were mounted and conduit was run but no wires to anything. This came from management and when I asked why they were not wired they said then installed them to meet OSHA code but they could not afford to have the machines stop if somebody actually activated one of them. Needless to say I never went back I want no part of any company they would do that.

 

[JankyPLC]

Thanks for all the answers everyone. Sorry it took a minute to reply.

I realize the question I asked was somewhat generic looking for different options and you all provided some which all have merit and some we've even used where appropriate. Interlocked gates the preferred entry method. Trapped keys work well with these. We've used area scanners with success as well.

I have one cell in mind that's a head scratcher.

Robot cell with chain conveyors 12" off the floor with walkover plates between the chains. They are spaced close enough together that there's basically no where you can walk within the cell that is not standing on them.

As you can imagine with that much conveyor in such a small space an area scanner wouldn't be able to see much unfortunately.

The light curtain muting requires sensors and production conditions to be activated specifically to prevent people from walking through and appearing as product, so if someone enters the cell it does trip the light curtain and stop the machine safely.

The concern is what happens after. Person is in cell, safety is no longer tripped. Second person comes over and due to the tight nature of the cell and tall products, doesn't see person 1 in the cell. Resets safety and starts system.

I think the suggestion of a trapped key type system next to the light curtain opening is probably the best idea suggested in this instance. It unfortunately relies on operator action, but I'm not sure there's a good way to automatically manage maintaining the inability to reset the cell after passing through a light curtain in this instance.

 

[arpus4KM]

Thanks for all the answers everyone. Sorry it took a minute to reply.

I realize the question I asked was somewhat generic looking for different options and you all provided some which all have merit and some we've even used where appropriate. Interlocked gates the preferred entry method. Trapped keys work well with these. We've used area scanners with success as well.

I have one cell in mind that's a head scratcher.

Robot cell with chain conveyors 12" off the floor with walkover plates between the chains. They are spaced close enough together that there's basically no where you can walk within the cell that is not standing on them.

As you can imagine with that much conveyor in such a small space an area scanner wouldn't be able to see much unfortunately.

The light curtain muting requires sensors and production conditions to be activated specifically to prevent people from walking through and appearing as product, so if someone enters the cell it does trip the light curtain and stop the machine safely.

The concern is what happens after. Person is in cell, safety is no longer tripped. Second person comes over and due to the tight nature of the cell and tall products, doesn't see person 1 in the cell. Resets safety and starts system.

I think the suggestion of a trapped key type system next to the light curtain opening is probably the best idea suggested in this instance. It unfortunately relies on operator action, but I'm not sure there's a good way to automatically manage maintaining the inability to reset the cell after passing through a light curtain in this instance.

can't fit pressure mats on the floors and walkways between conveyors??

 

[GaryS]

Simple
That’s what Lock out / Tag out is for Strictly enforced
If the operator can’t do it replace the operators

 

[Steve Etter]

Simple
That’s what Lock out / Tag out is for Strictly enforced
If the operator can’t do it replace the operators

While appreciate the sentiment, I disagree. Either engineer a solution for the existing equipment that reduces the risk level adequately or replace the equipment. If neither of those is an option, it's time to move on. It is simply irresponsible to rely on "catching" someone in an unsafe act as the solution.

 

[dploof23]

My sales rep was telling me the other day about safety radar scanners. This may be an option for you. Pretty sure Sick and Pilz have them.

 

[Holmux]

In my last project I used Radar scanners to cover the area,
a simple setup where if they enter true the light curtain, they are not able to reset the safety of the cell if there is any movement, within a certain time.

 

[JeffKiper]

I've seen systems do a Category 2 stop on all hazardous operations until the light curtain is broken and cleared.

We have you used 2 light curtains that have to be broken in a certain order without shutting down the system. If they are broken in the wrong order the system shutdown and requires a safety reset.

 

[GaryS]

It sounds like you are trying to bypass lock out tag out policy
Lock out tag out requires that each person must have their own lock out and lock to be in compliance
An alternative may be an RFID ID tag for each employee set to open the guard gate the tag would have to be scanned and the entry logged in order for the guard lock to be reset the same RFID tag would need to be well clear of the entry point. But here again each employee entering would need to have their tag scanned in and out. Compliance must be mandatory and enforced. Without enforcement any system you use will fail.
I did work for a company that had a very strict safety policy. They actually had a policy that you could not walk through an open overhead garage door you had to be in caged vehicle to pass through. You got 1 warning on the 2nd offence you were gone permanently barred from all their plants, no exceptions.
The key to any safety program is compliance and enforcement if you are not willing to enforce the policy then why even have the policy

 

[JeffKiper]

I had a plant manager kick me out of a plant for 1 week because I walked through an overhead door. There was a bunch of union employees and me. I was the example for all of those guys. The plant manager gave me a PO for that week I at my shop. He said "it's worth it just to show them I mean business". I laughed and took his money.

 

[jholm90]

Time to integrate a safety rated thermal camera to see if anyone with a pulse is inside the cell... /s