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Old April 6th, 2021, 02:56 PM   #1
BClark4
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Light curtain as start switch???

Hello all, I am new to this site and I was wondering if anyone here could help me answer a question. We are trying to reduce cycle time on our bottleneck machine and one idea I had was to eliminate the start switch and have the machine start itself once it saw that it had been fully loaded and the operator was clear of the light switch. I am hesitant to make this change because I am unaware if this violates any safety regulations or industry standards. The machine is small and it is "impossible" to interfere with its process without breaking the light curtain so I don't see any immediate issues. Please feel free to chime in with info/ideas/suggestions!
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Old April 6th, 2021, 06:56 PM   #2
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As long as you take every possible scenario of every qualified idiot the HR department can hire.


There are a lot of machines out there with warning or danger signs that they self start automatically. But the use of a light curtain to start might be confusing to some, especially the aforementioned operators, so I would simply use a photoeye or more than one if needed. A light curtain would trip as soon as it was blocked, not wait until the entire field of sensing is blocked, which is what I think the plan for this is.


Just remember the Danger - Self Starting signs
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Old April 6th, 2021, 06:58 PM   #3
alive15
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Probably shouldn't, what if operator mis loads, comes out of light curtain, then operator tries to jump back in and fix part? Machine would start up and operator would be inside again; even though they would break the light curtain and stop machine process, you wouldn't want that to be the norm for the machine.

You may be able to have a safety mat along with the light curtain. So when light curtain clear and safety mat clear and new part loaded, start the machine?

But if you give more details about machine, like what it's doing, that may give us more info. If it's really basic machine, no way to kill or hurt anyone, then you might be able to get away with it? Also, what is your current machine cycle time?

You could definitely do that with a robot (robot sending a cycle start signal after light curtain clear), but way more $$$ probably for what you need?
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Old April 6th, 2021, 08:10 PM   #4
GaryS
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I wouldn't do it setup a palm button where the operator exit's so all he has to do is just tap it when he passes he still makes the call if it is safe
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Old April 6th, 2021, 08:42 PM   #5
James Mcquade
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Welcome to the forum.

Sorry, i don't think what you suggest is allowed.
a safety light curtain cannot be used to start an automatic cycle, it requires human intervention. i got into the same situation years ago, so the rules may have changed. i cannot remember where the code is. maybe nfpa 79. you should also see the manual on the light curtain you are using and contact the distributor and ask questions.
Alive15 and GaryS make very good points.
if i am incorrect, someone please correct me.
james
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Old April 12th, 2021, 08:55 AM   #6
BClark4
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The machine is very basic, it essentially presses a shaft into the inner race of a bearing. there isn't a huge opportunity for any disastrous failure but you are correct that intervention is sometimes required. Our current cycle time is ~30 seconds and we are close to, if not at, our machine limits so we are attempting to remove operations from the machine operator.
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Old April 12th, 2021, 10:01 AM   #7
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For a button, I would recommend the Banner Opto-touch buttons:

https://www.bannerengineering.com/us...m=1&sort=4#all

Probably the easiest and fastest button to operate I have seen.
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Old April 12th, 2021, 10:23 AM   #8
BClark4
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Quote:
Originally Posted by BClark4 View Post
The machine is very basic, it essentially presses a shaft into the inner race of a bearing. there isn't a huge opportunity for any disastrous failure but you are correct that intervention is sometimes required. Our current cycle time is ~30 seconds and we are close to, if not at, our machine limits so we are attempting to remove operations from the machine operator.
Also, the machine is relatively small, the opening that the operators stick their hands in is about 2 feet wide 3 feet tall and 2 feet deep.
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Old April 12th, 2021, 10:28 AM   #9
ndzied1
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One other thought. You mention that your machine is at capacity and the cycle time is around 30 seconds. It seems the most speed gain is to be had by making changes to the machine process to speed it up rather than the 0.5 to 1.0 second you might save by trying to start by clearing the light curtain.

Is this a hydraulic, pneumatic or electric press?

30 seconds seems like a long time for a pressing application on a small machine.
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Old April 12th, 2021, 10:58 AM   #10
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Yes that is what we are looking into, where by clearing the light curtain the machine auto-starts its cycle. we are pressing using servo motors and ball screws. the reason it is 30 seconds is because we are actually checking several parts of our process during the press. after pressing the shaft into the bearing we also have the press do a "pull check" to check for a snapring and a final push to re-seat the shaft
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Old April 12th, 2021, 12:28 PM   #11
jhenson29
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No. You cannot do this. See ANSI B11.19 section 8.3.2.4 or B11.0 section 7.2.3.
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Old April 12th, 2021, 12:32 PM   #12
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I would add that the first OSHA inspector that saw a light curtain being used not as a safety, but a operational control, would have a major issue with it. Possibly even shutting the machine down until it is converted to another sensor(s)

I still suggest a photoeye, or row of them if needed.
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Old April 12th, 2021, 02:48 PM   #13
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If the machine is part of an assembly process, then perhaps divide the machine into two: one machine for pressing and the second machine for error proofing / quality checks. It may sound very time consuming and difficult, but may be the best solution to drastically reduce your cycle time?
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Old April 12th, 2021, 09:27 PM   #14
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I'm with Gary and Norm on this one. Only I would use a different pushbutton of the capacitive type and place it so that the operator can hit it within a tiny fraction of a second after clearing the light curtain. Make it easier on them and faster without the huge potential risk of getting blames for something awful.

If you do one machine like that, and you can measure (perhaps electronically with a PLC timer) the amount of actual time you are losing between the light curtain being cleared and the button being pressed, then you can really quantify exactly how many total hundredths of a second you are losing each day.
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Last edited by OkiePC; April 12th, 2021 at 09:30 PM.
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Old April 12th, 2021, 10:01 PM   #15
James Mcquade
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I like the pushbutton idea.
You still MUST satisfy NFPA 79 - electrical standard for industrial machinery, NFPA 70 - national electric code, light curtain safety standards, AND you MUST have a fail safe to detect if the palm button fails. Press the palm button to start the cycle, release the pushbutton and the N.C. contact energizes a relay. when the press returns home, it makes a limit switch to reset the system for the next cycle. this needs work and i am pressed for time. Osha likes to get you on the fail safe issue. It doesn't matter how simple the system is, you must meet the specs mentioned above.
regards,
james
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