light curtain muting photo eyes getting bumped

[unsaint32]

We have a muting light curtain setup like the picture I am attaching here. However, a pallet sometimes hits the photo eyes (MS1 & MS2 in the picture) and they get out of alignment. If one misaligns, next pallet going through the light curtain shuts the system power. Then I know the muting did not work and I can fix it. Here is the problem... if both of them misalign, it's same as the muting condition, so next pallet going through the light curtain does not shut down the machines. At the same time, anybody can walk through the light curtain and nothing shuts down. The muting relay is Sick UE410-MU. I am requesting to install two pilot lights to indicate the photo eyes misalignment. But is there a better solution?

 

[g.mccormick]

Can you guard the muting curtains so that the pallets can't knock them around?

 

[Steve Bailey]

Does your light curtain not have a time limit on muting? If you remain in the muted condition for longer than the duration of the timer, the light curtain reverts to the unmuted state and the next pallet will trip it.

 

[unsaint32]

Can you guard the muting curtains so that the pallets can't knock them around?

Yes that is another thing we are going to implement. But one thing I didn't mention is that, even when the pallet doesn't bump the sensors, sometimes, when we have conveyor issues, the operators go and pull the pallets by hand and they had bumped the sensors out of alignment. So, after installing the guard, we will need additional protection.

 

[unsaint32]

Does your light curtain not have a time limit on muting? If you remain in the muted condition for longer than the duration of the timer, the light curtain reverts to the unmuted state and the next pallet will trip it.

I don't know if it does or not. But we cannot have that time limit anyway because we have to allow the pallets to be stopped right at the light curtain for a while because where we have this setup happens to be where the pallets get picked up by the forklifts. Sometimes, two or three pallets stopped there waiting to be picked up.

 

[GaryS]

I have looked at you drawing and it’s no wonder you are having trouble
This may help
I have done a few light curtains over the years and I only use 1 mutt eye, the location is always as close to the curtain as possible with the beam running parallel to the curtain.
The mounting of all the components should be in a way that they can’t be hit or damaged by the skids

Programming wise I monitor both the curtain and mute eyes as to if they are blocked or clear
Both have fault timers if they stay blocked to long as fault is set. Shutting everything down conveyor machine anything that could cause injury.
The curtain should only be muted with the conveyor running and the mute eye detecting a skid. Both condition true, this would indicate that a skid is on the conveyor and about to enter the curtain. When the skid enters the curtain zone it is muted and will remain muted until the curtain is blocked and cleared again meaning the skid has passed completely through the curtain. Any gap at all will reset the mute and curtain will trip shutting down in a safe mode. If the mute eye I still blocked after the skid passé through the curtain.
As pass through is indicated by first the mute eye blocked and the curtain is muted. The curtain is blocked and then finely the curtain is cleared. All 3 action happen in a predefined time.
Once the skid passes through the curtain it is reset to safe protection mode.
This way the only time that a person could pass through is while a skid is on the conveyor and blocking the curtain.
Anytime the curtain trips due to an unmuted entry the curtain should trip off in a safe mode and require that it be manually reset from a safe location that has visibility of the equipment and area that is protected. Or even better require supervisory level personnel to reset the fault
They are really fairly simple to setup you need to think about it.

 

[unsaint32]

beam running parallel to the curtain.

Are you saying the crossing-beam setup does not work? The drawing is from an Allen Bradley site.

Both have fault timers if they stay blocked to long as fault is set.

As I said to Steve Bailey, we have to allow the pallet to stay blocking the light curtain indefinitely due to frequent backing up before the pallets are picked up by a forklift. That is why our light curtain has to be able to be muted regardless of the conveyor status.

I agree with everything else you said.

 

[Steve Bailey]

You seem to be of the opinion that pallets blocking access to the area protected by the light curtain is as effective a safety barrier as the light curtain itself.

 

[GaryS]

I see no reason for the crossed beams that I see they will leave a lot of dead area that is unprotected. use the curtain itself as the exit eye when it's clear the pallet is through
if you are blocking the either the curtain or the mute eye for a long time then you have a curtain placement problem. You can use the mute eye to control the conveyor to force a gap between the pallets if needed. I would have to see more details on this.
you will need to control the conveyor. have a speed difference between the conveyors will generate a gap between the pallets

 

[GaryS]

Steve unfortunately anytime you mute a light curtain you create an unprotected zone and it I possible for personal to enter while it's muted. that's why you need to keep the muted area as small as possible and for as short a time as possible and you should never allow the curtain to be blocked by a pallet that I not moving. if it's setup right it' almost imposable to even reach through even while the pallet is in the zone

 

[Steve Bailey]

GaryS, I think you misunderstood my comment. Unsaint32 may think the pallets are an effective barrier, but I don't. As currently configured, I think the setup is an accident waiting to happen.

 

[GaryS]

Steve I agree that the current setup is an accident waiting to happen
and I wouldn't except it that way but it' not my call.
that's why you never block the curtain for an indefinite time and that's why you need to maintain a gap between pallets. the new system actually measure the product and adjust the curtain to keep the gaps as small as possible. depending on the distances you can have a wider gap. A hand reaching in bur you should be setup not to allow a person to pass through

 

[JRoss]

Gary, I'm not sure I follow your muting method. It seems to me that it would allow a human to get through the light curtain. The crossed sensor muting method is fairly common, and protects against a human causing muting because it's impossible for a single person to break both eyes. You also have redundancy. The position of the sensors can be adjusted so that the pallets break them as close the the curtain as you want.

I think the problem here is that the sensors are NC, so when they are misaligned they give a signal to the muting system. If the muting system can have the input logic reversed, change the sensors to NO operation so that when they are misaligned they don't fool the muting system.

 

[GaryS]

the only way anybody could pass through would be to clime over the pallet while it I in the curtain. there is only about 1 in of room between the mute and the curtain and then about the same after the pallet leaves the curtain. they could go in the sides but if they are place correctly then there is just no enough room for that. and with the new variable height curtains even the height above the pallet would only be about 2 to 3 inches. It would have to be a deliberate safety violation and if any personal did that they should be fired on the spot

 

[GaryS]

also the way you describe if an eye was misaligned or stays blocked with no pallet the curtain would stay muted with nothing to block the conveyor that's why the timers
impossible to tie the blocked so they would fault the system shut it down fail safe mode
I have done it this way for many years and have jet seen anybody slip through
in fact I have had request to open things a little to allow a hand to pass through if needed. when that is done I limit the reach of the operator so they can't get into trouble