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Old September 13th, 2017, 09:06 AM   #1
ashika
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Safety Light Curtains

Hi,

I'm new to the automation industry.

While installing the light curtains what are the main factors to be taken care of? Is there any varying sensitivity for the light curtains depending on the brand we use ?

Also, with the E-stop when it's hit does it mean to stop the machine/de-energize all the units ?
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Old September 13th, 2017, 09:26 AM   #2
jstolaruk
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Light curtains are usually specified by your customer. Location of the light curtains has to be carefully chosen to allow all motion to be de-energized and stopped before anyone can get in the vicinity (light curtain mfg's supply documents on how to calculate this).

All motion (hazardous) has to be stopped and de-energized. Vertical motion will/may require a method to physically lock the motion in position (rod-lock on cylinders, etc).

Customers can be picky and will usually cite an industry standard and have a appending document to it with their own preferences.
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Old September 13th, 2017, 10:00 AM   #3
ashika
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We recently had an accident with one of our crimping machines. When the E-Stop was pressed it din't de-energize the entire system.We had to pull all the air fittings to release the cylinder.

And does the sensitivity of the light curtains vary with brand ?
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Old September 13th, 2017, 10:07 AM   #4
jstolaruk
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Quote:
Originally Posted by ashika View Post
We recently had an accident with one of our crimping machines. When the E-Stop was pressed it din't de-energize the entire system.We had to pull all the air fittings to release the cylinder.

And does the sensitivity of the light curtains vary with brand ?
Yeah, that can be a bad one but there are ways to address it.

When you mean sensitivity, different manufacturer's response time are "faster" than others.

Beam spacing and length are usually part of the selection process. Most offer some type of controller that can be used if the machine doesn't have a way to manage the externally handshaking with the device. I usually don't purchase them because I'm interfacing them with some kind of safety controller or safety PLC.
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Old September 13th, 2017, 10:14 AM   #5
ashika
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Yes. Even we used safety relays to hook up the light curtains.

We had a beam spacing of 40mm. For some reason, unfortunately it happened.

Thank you very much. I appreciate your help.
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Old September 13th, 2017, 11:21 AM   #6
James Mcquade
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no one can answer your question correctly without knowing all the details of your system.

in regards to light curtains.
most light curtains have a spacing between the beams, some have closer beams than others.
Most light curtains allow blanking ( the ability to block part of the light curtain without tripping the light curtain.
when you break the light curtain, all motion should stop. the general rule is if you can put your hand in harms way before the machine stops, you must move the light curtain back more. when the light curtain is cleared, you must reset the light curtain. I cannot say in regards to sensivity, never heard of that before.

in regards to the e-stop.
when an e-stop is pushed, all power to the inputs / outputs must be killed and all machine operations are to stop. this may also require a quick dump exhaust air valve (risk assessment MUST be done - if you dump the air, you may create an even bigger hazard when the air is restored, thus the need for the risk assessment).

In regards to your incident, it all depends on the valve configuration.
are the valves single solenoid spring return, double solenoid open center, double solenoid blocked center, double solenoid with p to a and b, detent valves?

you must look at the valve powering the air cylinder to find out what the nature of the cylinder will be once the valve is energized and you hit the e-stop or loose power. That's the only way that I know of.

for example, a detented valve once energized, will stay in that position until manually reversed or power is applied to the other valve. if the valve was energized and the cylinder was going to the crimp position and you hit the e-stop, the cylinder will continue in that direction until it hits something or the cylinder bottoms out. a quick dump exhaust valve would release the air pressure and stop the cylinder, BUT !!, when the air is reapplied, the cylinder will move in that direction.

that's why I say that you have to look at the valve and determine the nature of its actions.

james

Last edited by James Mcquade; September 13th, 2017 at 11:23 AM. Reason: clearification
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Old September 13th, 2017, 12:20 PM   #7
keshik
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One thing to be careful of is that sometimes just dropping power to something isn't the safest action. For example, a vacuum or magnetic crane. If emergency stopped, you may not want to release/de-energize the vacuum supply or magnet power. This could create a more dangerous situation (falling metal pieces, whatever). Or a motor running at a high speed - under an emergency stop situation you probably want to do a controlled stop as opposed to just letting it freewheel to a stop. You will still need a safety double-check to the controlled stop, but that is something that you determine as part of the risk assessment.

Make sure that you do a risk assessment.
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Old September 14th, 2017, 02:44 AM   #8
bob1371
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Quote:
Originally Posted by ashika View Post
Hi,

I'm new to the automation industry.
Hello,
No disrespect to you and I hope you don't take it as such but after an accident and your trying to design/install a safety system please seek the help of someone who has the experience and knowledge to help you through this. Let them guide you through this and don't be afraid to ask questions.

I'm about 60 miles south of you and just a couple of weeks ago we had a guy at a plant down from us caught in a machine. I knew this gentleman very well and had to attend his funeral this past Friday. Hopefully the accident at your facility wasn't as bad.



Quote:
Originally Posted by ashika View Post
While installing the light curtains what are the main factors to be taken care of? Is there any varying sensitivity for the light curtains depending on the brand we use ?

Also, with the E-stop when it's hit does it mean to stop the machine/de-energize all the units ?
Can't say it enough on this. Have a Risk Assessment done to determine your exact needs here.


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Old September 14th, 2017, 03:32 AM   #9
willxfmr
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Quote:
Originally Posted by ashika View Post
Yes. Even we used safety relays to hook up the light curtains. The use of safety relays would be the industry standard, and required in order to maintain the safety rating of the system.

We had a beam spacing of 40mm. For some reason, unfortunately it happened.

Thank you very much. I appreciate your help.
Just to be sure that we are all talking about the same thing here, what most of think of as a "light curtain" is a 2 piece system that has a transmitter with a line of individual beams that are sent to receiver. They are available in various lengths depending on the application. As James pointed out, light curtains can be setup to ignore certain sections along their length, so it possible that a 3' long light curtain can be set to detect only the middle 12". This may be what you are referring to as "sensitivity". There are also safety scanners that can be set to trip at a set distance from the scanner. These are usually used in situations where fixed fencing that creates fixed entry points is not practical.

This link will give you and idea of the various types of systems available.
http://ab.rockwellautomation.com/Sen...perator-Safety.

This is just my opinion, but I think bob1371 gave you the very best advise there is. While I am a big advocate of "learn as you go, and figure it out yourself". Safety is not the place for that. When literally, life and limb are at risk, you need rock solid expert help.

Keep stopping into the Forum here. There are some seriously smart people here, and they are very generous in the amount of time they will put into helping solve problems. I know I will never be able to thank them enough for all they have taught this knuckle dragging, coffee chugging Bubba.


Bubba
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Old September 18th, 2017, 08:09 AM   #10
ashika
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Thank you very much for all your help.

I figured out that it's very important to find the nature of the valve and it's actions that controls the cylinder to program for the E-stop

Apparently for the light curtains, the spacing between the light beams was more. Finally fixed the issue.
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