Light Curtain Machine Reset?
- Thread starter R_C
- Start date
That depends.
What kind of machine is it?
What type of hazard is there with the machine?
Is this a safety system?
Would an auto start pose a to be a hazard?
How is it programmed now?
Who programmed it?
Can you program it either way?
Then ask "May I"?
What kind of machine is it?
What type of hazard is there with the machine?
Is this a safety system?
Would an auto start pose a to be a hazard?
How is it programmed now?
Who programmed it?
Can you program it either way?
Then ask "May I"?
R_C
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No, if the light curtain is broken anytime during an automatic cycle the machine will stop. It is muted at the end of the cycle for part removal.
The machine is a small pneumatic press, in the design stage.
Good thing it is in the design stage. Are you using redundant fail safe valves?
here is what I have going on at one of my customers.
Well who's life the bean counter or the guy on the plant floor? I quoted a change to a machine Oct. 2010. "That was too expensive" is what the bean counter said. It was only $15~20K. Cheap compared to having a hand smashed off or into two pieces. Does anyone what to bet if the lost time wages and the lay suit is costing them over the $15~20K?
So know I have a issue that the CEO and CFO don't want to hear about the "I brought this to your attention". I left the meeting today with a question as I shook hands with everybody. The question was "What is your child's, wife's, etc. hand worth? Do you want them working on this machine after you cut the budget and didn't see that the safety cost could be justified?"
here is what I have going on at one of my customers.
Well who's life the bean counter or the guy on the plant floor? I quoted a change to a machine Oct. 2010. "That was too expensive" is what the bean counter said. It was only $15~20K. Cheap compared to having a hand smashed off or into two pieces. Does anyone what to bet if the lost time wages and the lay suit is costing them over the $15~20K?
So know I have a issue that the CEO and CFO don't want to hear about the "I brought this to your attention". I left the meeting today with a question as I shook hands with everybody. The question was "What is your child's, wife's, etc. hand worth? Do you want them working on this machine after you cut the budget and didn't see that the safety cost could be justified?"
R_C
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No, we will be using redundant safety relays but not redundant safety valves.
Is this a new OSHA requirement?
ANSI B11.2 The new revision is Hydraulic and Pneumatic power presses. If you look at the OSHA listing they refer to the 1995 version of ANSI. You will be shocked at how many equipment builders are just doing single channel pneumatic circuits. They use redundant electrical power but not on the motion side.
There was a single valve failure that trapped a guys hand.
There was a single valve failure that trapped a guys hand.
R_C
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Thanks!
Now back to my original question can a light curtain be used in this manner?
It all depends on the design of the control circuit. Will the machine re-initiate motion once the light curtains are reset? When you did your risk assessment what level are you designing to?
Some machines I would say yes you can auto reset other no. It is all machine and designed usage dependent.
Some machines I would say yes you can auto reset other no. It is all machine and designed usage dependent.
dmargineau
Lifetime Supporting Member
Yes, if it is not an EStop condition.
Most of the major brand safety relays could be configured(wired up) as Auto Reset.
The site/equipment Risk Assessment Safety Survey would determine if the safety curtain is or it is not an EStop circuit component.
If the light curtain is an EStop device, then the reset will have to be performed via hard wired push button.
Most of the major brand safety relays could be configured(wired up) as Auto Reset.
The site/equipment Risk Assessment Safety Survey would determine if the safety curtain is or it is not an EStop circuit component.
If the light curtain is an EStop device, then the reset will have to be performed via hard wired push button.
Never thought of it like that.
DamianInRochester
Lifetime Supporting Member
Another aspect is, even if it is "legal" does that still really mean you should. I have a bias against machines auto resetting when clearing a light curtain. Espcially when that reset re-iniates another cycle. I know it is accepted, i know it is done often, I just don't like it.
Steve Etter
Lifetime Supporting Member + Moderator
If, as you say, your design has the machine stopping during the automatic cycle any time the light curtain is broken, I'm curious. What conditions are you seeing where it might make sense to want the light curtain to reset automatically? Wouldn't you need to initiate a manual reset anyway? If so, where is the advantage?
Steve
Steve
My 2c....
A light curtain is just a switch that says something has broken it's barrier.
It is incumbent upon the machine designer/manufacturer to decide if that "switch" should be considered as a protective device (e-stop), or as a permissive device.
And it's not simple - it could be both, at different parts of the machine cycle.
Most times i've seen light curtains in a system they are "protective" (i.e. e-stop), and muting is used when it is "safe" to break the curtain. After the muting is released, the "protective" response is re-established.
And sometimes a curtain instigates a "safe response" in the area guarded, in which case it is not considered a true "safety device" at all.
Too many variables to give sound judgement on, but in my opinion a curtain should always be manually reset - it's an extra layer of confidence that the operator is not the wrong side of the curtain.
A light curtain is just a switch that says something has broken it's barrier.
It is incumbent upon the machine designer/manufacturer to decide if that "switch" should be considered as a protective device (e-stop), or as a permissive device.
And it's not simple - it could be both, at different parts of the machine cycle.
Most times i've seen light curtains in a system they are "protective" (i.e. e-stop), and muting is used when it is "safe" to break the curtain. After the muting is released, the "protective" response is re-established.
And sometimes a curtain instigates a "safe response" in the area guarded, in which case it is not considered a true "safety device" at all.
Too many variables to give sound judgement on, but in my opinion a curtain should always be manually reset - it's an extra layer of confidence that the operator is not the wrong side of the curtain.
R_C
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I agree that if the light curtain is broken during an auto cycle a manual reset should be required. But, I have a customer who wants the machine to auto reset after the light curtain has been cleared.
I wasn’t sure if OSHA set standard guidelines on resetting a light curtain. After all the replies from you guys it looks like OSHA doesn’t spell it out exactly.
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