PLCs and Presses - Safety

I know of a facility that rebuilt a press in-house and put on their own safety system (no drawings of course). From my conversations it appears that they have two hand controls tied into a plc and only inhibit the press start cycle if the light curtain is broken by the operator (lc status signal into the plc). The light curtain does not e-stop the press.

I know that a plc can't be used for safety control and that the light curtain must stop the press if its broken during the press cycle.

My question - how do I prove it to the #%@#& engineer that is not allowed? (press standards references, ANSI, OSHA) I also need to prove that all the press manufacturer DO NOT control safety with a plc (at least a standard plc).

tspisak said:

I know of a facility that rebuilt a press in-house and put on their own safety system (no drawings of course). From my conversations it appears that they have two hand controls tied into a plc and only inhibit the press start cycle if the light curtain is broken by the operator (lc status signal into the plc). The light curtain does not e-stop the press.

I know that a plc can't be used for safety control and that the light curtain must stop the press if its broken during the press cycle.

My question - how do I prove it to the #%@#& engineer that is not allowed? (press standards references, ANSI, OSHA) I also need to prove that all the press manufacturer DO NOT control safety with a plc (at least a standard plc).

Click to expand...

Need a couple minor details such as
1. What kind of press - hydraulic or flywheel type
2. What part of cycle does curtain stop Do you mean that once the press starts actuating the curtain does not stop it ie stop the cylinder if hydro or release teh clutch if flywheel?
3. What happens if you let off the two hand after the press is actuated?
4. What other guarding provisions are there on the machine? IF 100% guarded then in theory you do not need two hand or maybe a curtain such as with fully automated press. Start and can run all by itself all day. Have seen some not many and not big ones.
Dan Bentler

I asked a similar question in this thread:
http://www.plctalk.net/qanda/showthread.php?t=43111
and didn't get much of a response.

I think the rules in the U.S. are generally more lax than other countries. I've read most of the relevant standards and everything seems very vague. I couldn't find any specific mention of using (or not using) PLCs in a safety system. Of course common sense dictates that you shouldn't, but that doesn't stop some people.

The press is hydraulic.

The press single cycles and the operator unloads & loads the press when its open.

No electrical schematics of component list for the two hand controls but I'd guess just standard pushbuttons to PLC inputs

One side hard guarded. Single light curtain with two mirrors for the three open sides. (with 4" blanked out in the middle for a hardware that stuck though the light curtain path)

I would do a search for press controllers. Most of them will have a guide that will give you the ANSI and OSHA numbers.

http://www.pressroomelectronics.com/

The light curtain can be the primary safety control element, but it also has to stop the press unless there is a physical barrier - eg, the light curtain verifies that the operator is clear while a safety interlocked barrier is automatically closed. If the light curtain is the primary safety control element then the two hand start buttons are not required safety controls and can be routed through the PLC. It seems like in this case the light curtain function should be corrected.

What's in ANSI B11.1 Mech Press, B11.2 Hydraulic Press, and B11.16 Metal Powder Press about controllers/ light curtains?

I'm looking for "a plc shall not be used unless it has a xyz safety rating", control reliable, self checking - self monitoring, redundant processors...

I'm looking at the engineering guide for Omrom/STI: OSHA 1910.217 (C)(3)(iii)says that you shall interlock to prevent of stop motion.

tspisak said:

What's in ANSI B11.1 Mech Press, B11.2 Hydraulic Press, and B11.16 Metal Powder Press about controllers/ light curtains?

I'm looking for "a plc shall not be used unless it has a xyz safety rating", control reliable, self checking - self monitoring, redundant processors...

I'm looking at the engineering guide for Omrom/STI: OSHA 1910.217 (C)(3)(iii)says that you shall interlock to prevent of stop motion.

Click to expand...

One major question
Are you just trying to be in compliance with OSHA
OR
are you trying for a well designed machine with good production capabilty, user friendly and assures employee safety.

From 20 year experience in safety and health OSHA is so far behind modern times and is written so poorly it is almost a waste of time. It is good for a dog fight between equipment engineers and the safety guy.

I would look at NFPA standard for machine tools (am I right -- is it NFPA) or the European guidelines. Allen Bradley had a good writeup on machine safety and associated controls at one time.

Dan

Omron(STI) has some good information on light curtains available here.

I have worked on several home made systems. (2) AB 5/05 for the control 1 for aux equipment, robot interfacing. AB still makes Press controls with standard plcs. So the "you have to use a safety plc" doesn't fly yet in the states. OSHA & ANSI are rewriting or have just rewritten their standards. So all the nw standards will be coming out soon.
I have used most of the big guys that make press controls on mechanical presses 17~1100ton and 400~3000 tons on upsetters. Link, Wintress, Pressroomelectronics, Cieco, AB, Helm. The Link is my favorite black box because of all the options. The wintress is much more user friendly, Pressroom electronics was the easiest to get up and running. AB offered the most open and expandable. I just supported the rest so I can't comment on the install.
If you want training the man that own Link used to put on a week long class of What, Why, How of OSHA for mechanical power presses. I highly recommend that class it is free all food and beer is included, you pay for lodging. Well worth the time.
Alaric has already hit it with the light curtains as the Primary safety device. If they are the primary you don't have to have two hand control. You can get by with single point tripping means (foot, single handed control)
So in short a homemade press control can be a good thing or bad depending where you are coming. I like the open controls so you can see the logic and help troubleshoot.

If you have a look at the AB press control it is very close to a safety PLC. Not by make but by functionality.
2 x Micrologix 1500s are used, with all inputs cross monitored.
From my understanding both ML1500s have to agree.
Also I think the software has been certified by your authority responsible for this. Also I am sure the software is unaccessible to the end user.
Regards Alan Case

Check out Rockwells GuardLogix PLC's. Using RSLogix V17, Rockwell has implemented specific safety instructions, that were developped especially for the european market, as we seem to have the most stringent requirements in safety. These safety instructions together with Rockwells safety I/O provide safety, even for press controls, at least for mechanical presses, not yet for hydraulic ones.

Whenever you talk about safety, whether its presses or anything different, never through the term "Standard PLC" into the same bowl.

You could go to this site and download ther safety manual it has all the latest relevant information and regulations you will ever need for machine safety and some good examples its 50 meg www.jokabsafety.com