PSDI - Look Ma, No Start Button!

jrexrode · Jun 23, 2011

After failing to successfully argue the point to my handlers that we can safely start a non power press machine cycle using a signal from the light curtain aux relay and some code, I'm curious about how utilized PSDI is among the rest of you guys, and maybe how y'all implement it.

By the way, I'll be adding a photoeye, beaming across the opening of the machine that the light curtain protects, and using the input from the photoeye to start the machine cycle. I'm just replacing the light curtain aux contact with a sensor. I just don't see the need. Or, am I being thick headed?

Lancie1 · Jun 23, 2011

The big question from a safety view, is not CAN you do it, but SHOULD you do it?

Will you modification ALWAYS only start the machine when it was inteneded to be started? Could it be started by an accidental motion?

These type of questions should be answered using the following scenario:
You are in the witness box, being questioned by the attorney of the widow of the former press operator....

Steve Etter · Jun 23, 2011

I'm having a hard time even imagining a situation where allowing a machine to self-initiate a cycle start when it detects an operator has just left an unsafe zone. Is that what you are describing? If not, please help us better understand your application.

Assuming this is the situation, you really need to install some method for the operator to actively initiate cycle-start, not the machine. Two-handed zero-pressure palm buttons come to mind.

Steve

jrexrode · Jun 23, 2011

The machine has an opening, guarded by light curtains, so that the operator can load a stick of extrusion on a fixture. Sensors detect that the extrusion is loaded correctly and of the proper length. The operator backs of the curtain, presses the cycle start button and hydraulic actuated cutters move in on each end of the part to trim the ends. The cutters retract and the operator unloads the part.

The supply voltage for all outputs are fed through 2 force guided control relays in series that are energized independently by the two outputs from the light curtain.

Mainly, by bringing this topic up, I'm seeking clarity for myself on this subject. I've seen articles that promote its use. Light curtain manufacturers provide controllers with that function built in. So, when a light curtain is properly installed on a machine that's not nearly as dangerous as a power press, I'm having a hard time understanding why this couldn't be used. I won't be using the light curtain to initiate a cycle by the way. But I'd like to.

JeffKiper · Jun 23, 2011

It varies by state, and local AHJ. In kentucky we can do that. In indiana we can not do that. I was on a start up in KY when I first witnessed this. Multiple present sensing devices and physical barriers. I don't like it. It can be done doesn't mean it should be done. Single button operation instead of light curtains tripping l.

Lancie1 · Jun 23, 2011

I'm having a hard time understanding why this couldn't be used.

It has to do with liability (who will be blamed) when something goes wrong. As long as the operator swipes his hand, or head, or some other body part, through the light curtain, and MEANT to start the machine, then everybody is fat, dumb, and happy.

What happens if one day he feels a little dizzy (too much fun the night before) and falls into the light curtain and starts a press and it cuts his head off?

dash · Jun 23, 2011

This article is from 2006, but I imagine it is still relevant to your question. According to the article as of printing in 2006, OSHA still had not modified a change it made due to unreliable operation of light curtains PSDI function allowing operators to be hurt or killed between the 50s and 70s (wow had no idea that PSDI was that old) that banned the use of PSDI for presses.

Anyway interesting read. Thanks for asking the question.

http://www.fabricatingandmetalworki...curtains-following-the-psdi-compliance-trail/

Darren

bluebyu · Jun 23, 2011

Read OSHA 1910.217, Mechanical power presses

PSDI is part of the standard and legal to use, BUT;

Part of the standard states that a third party must certify the install. I have not heard of any company that does this, (nor have I looked for one).

Hope this helps

JeffKiper · Jun 23, 2011

Dunn engineering out of California applied for the third party certification to osha. Osha did not grant them the certification.STI bought Dunn and for the most part dismantled them.
The new B11 does allow PSDI but as we all know OSHA trumps ANSI.

ScottTheEngineer · Jun 23, 2011

I had a light curtain fail to detect an operator when he went into a loading station. for whatever reason it simply didn't react to his presence. once he knocked the misplaced part into the holding slots a robot loaded a floorpan into his forehead. fortunately he wasn't too badly injured.
we used a start button and robot zone switches as well as a light curtain. I found one of the robot switches was stuck on (no backcheck on it by the installer) then once the light curtain failed that was it.
I tested the curtain by counting the times I broke it with a broom handle and the times the PLC found it broken and out of 100 breaks it only detected 99.
Don't use a light curtain to start the cycle please; and backcheck your switches.

leitmotif · Jun 24, 2011

jrexrode said:
The machine has an opening, guarded by light curtains, so that the operator can load a stick of extrusion on a fixture. Sensors detect that the extrusion is loaded correctly and of the proper length. The operator backs of the curtain, presses the cycle start button and hydraulic actuated cutters move in on each end of the part to trim the ends. The cutters retract and the operator unloads the part.

The supply voltage for all outputs are fed through 2 force guided control relays in series that are energized independently by the two outputs from the light curtain.

Mainly, by bringing this topic up, I'm seeking clarity for myself on this subject. I've seen articles that promote its use. Light curtain manufacturers provide controllers with that function built in. So, when a light curtain is properly installed on a machine that's not nearly as dangerous as a power press, I'm having a hard time understanding why this couldn't be used. I won't be using the light curtain to initiate a cycle by the way. But I'd like to.

From 20 years field expereince in safety and industrial hygiene and almost maybe more as control electrician I say:
While it may be an interesting concept and something fun to
play with I do not recommend it when it is involving manual feed. If it were fed by another machine I may see the usage but then there is minimal operator involvemend and any failure is just machine damage.

Yes having the operator press two hand control takes a second and sure these seconds add up over a year. For people who really advocate this kind of thing let them guarantee the wages until employee retirement, college education for his her kids -- OUT OF THEIR POCKET

NEVER TRUST INTERLOCKS AND CONTROLS that is why we have lockout tagout. I have replaced too many control switches etc to trust them with my hands.
Dan Bentler

PSDI - Look Ma, No Start Button!

jrexrode

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Lancie1

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Steve Etter

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jrexrode

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Lancie1

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dash

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