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TimWilborne

Mechanical Press Two Hand Controls

23 posts in this topic

I was just reading THIS thread and was curious if Chakorules download code HERE would qualify as a legal Mechanical Press two hand control or if anything special was required?

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ABSOLUTELY NOT!!!!!! This code was used in conjuction with a light curtain, and two hand tie down software controlled palm buttons. The light curtain acts as the safety hard wire circuit without buying extra hardware for the two palm buttons. Basically the two palm buttons used in my case were to keep their hands out of the light curtain, the light curtain was the final safety say so to run the machine.... Please read this as reference as well. http://www.mrplc.com/kb/index.php?page=index_v2&id=13&c=12 -

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The press I am thinking about is a physically guarded press. It has palm buttons but not anti-tie down or anti repeat mechanism. I have used the AB two hand controls and safety relays before but it does not incorporate the anti repeat. Just trying to figure out how to add the anti repeat and saw your program.

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Is there a pinch point? Or anyway someone could get their hand chopped off or is it guarded pretty good? I've never seen a press that was guarded mechcanically 100%. How do you take parts in and out of the press with all the guarding?

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It is a cut to length with a motorized drive to push the stock through. You don't actually load the parts. When it hits a hard stop, just press the two palm buttons. But I feel it should still have the anti-tie down and anti-repeat

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ah....in that case, if I did a risk assessment of this machine, it might be ok in this case for software anti-down. So long as the safety of the press could not allow any harm. The safety in this case, is the hard guarding....your not relying on the anti-tie down to keep someone from becoming "lumpy".

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I would rather use a safety relay but I am having trouble with the anti-repeat. Any ideas?

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TW, You can still monitor the two hand buttons and the safety relay with the PLC and let the PLC handle the anti-repeat as long as it does not compromise the operation of the safety relay in any way. You will need to be very through in your analysis. I have used PLCs for anti-tie downs on presses which had both light curtains and safety interlocked guards with non-defeatable safety switches on the guards - but never in cases where there were not other fail safe safety devices. In other words, in places where two hand anti-tie downs weren't required for primary safety but were used for other reasons. Are your machine guards removable in any way? Can the machine be operated without the guards in place? If so then either you need to interlock the shields with non-defeatable safety switches or you have to use a two hand safety relay.

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I assume that its a mechanical press. Either way if you check the OSHA regs, it says that what ever you use for a "safety monitor" should be fail safe, and that pretty much dictates a redundant processor. Besides the anti-tiedowns, there has to be a brake stop monitor as well. Guarding and such is pretty well stated that it has to be interlocked, and cannot be operated with the guards removed, unless you provide a "bar mode" in your monitoring that allows the clutch and brake to release so that the setup operator can manually move the press for set up of shut heights and such, without the motor in operation. This is only for smaller presses, and larger units require blocking anytime the guards are removed. Before investing a lot of effort in design or development of press controls, it might be wise to check out the commercially available units just for liabuility purposes alone, and then install what ever control for feeding that you may need. Beuwolf

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No they will not run without the guards. On ours a foot switch is actually legal, the anti-tiedowns are not really required but I would rather have them not only for safety but also for consistancy between machines where the operators don't need their hands to hold anything.

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You don't mention what platform you are working on, but the new controllogix safety plc I just saw demonstrated might be useful in that your safety monitoring and anti-repeat could all be in the plc.

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There isn't currently a PLC on it, has anyone used any safety PLCs?

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Hi TWControls, Did it before using safety relays in conjunction with a Mitsubishi FX2N PLC. The press was a 600 ton mechanical press with single action ram. I am busy with the quotation of a double action ram. Allen Bradley have plc's that they quote with redundant supplies and cpu's but I have found it to be very expensive!

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I have one CLX being used as a safety shut down, but we only needed a SIL-2 rating. For SIL-3 or SIL-4 we have to go with TRICONEX. Generally speaking a CLX shut down system cost around 20-30k, a Triconex system cost 75-100k. It's true, you get what you pay for, the Triconex system has Triple-redundant everything, they have some models approved for Nuclear applications. http://www.triconex.com/us/eng/default.htm

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I know you have stated in a previous thread that inputs on a redundant system use a 2 out of 3 voting. How do the outputs work? I'm not going to use it on the press. It is legal with the foot switch, I'm just putting the two hand controls on for uniformity. I'm mainly just curious about the safety PLCs at this point since they have been brought up Edited by TWControls

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Depending on the application, you would have redundant outputs, on two separate I/O modules, and redundant final control elements. That way if one card or one device failed, the system is still functional, you also have to monitor the "condition" of the system, so that a device or I/O module failure is detected, and depending on the system, this may or may not generate some type of partial shut down, or just an alarm. AB has a document on how to configure the CLX for safety applications, don't have the number handy, I'll look it up at work on Monday. Out of the box the CLX is not safety rated, but it can be configured for safety applications. You have to only use rated processors, and rated I/O modules, including the rated firmware versions. It can be a challenge the first time you set up a system. We have an in house practice that is used, the logic is written by one person, and reviewed by a second "competent" person. There are also specific system check out procedures and guide lines on frequency of system testing. Many times this safety systems are on for months and months, you have to ensure that when needed, not only the logic works, but the control devices as well.

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I assume with the Controllogix you have to use the diagnostics I/O modules? In other words you can't just just use a 1756-IA16 for example?

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Two hand software control is better than none at all. I would do it as soon as possible, and the anti-repeat? Kinda like key debounce to prevent early operation? Definitely a waste saver. You are talking about an operation that doesn't require two hand control. Make sure the operators don't mind, but it sounds to me like you want to go above and beyond what is required. There is nothing wrong with that. If it's not legal already, make it better right away, and make plans to get it up to code very soon. My rule is never to use a device that the operators will consider a safety device as a PLC input. lThings like ike a light curtain, or a red Mushroom maintained button, safety cable switch etc. Only use safety device in safety circuits. I have some mahcines designed with a light curtain as a PLC input that the operators believe is protecting them, but I have informed them otherwise. It was designed by our corporate engineers that way and meets code because there are three other means of E-Stopping the winder within two feet of it. But I keep seeing operators make tool adjustments and changes without using them because they see the red light on the light curtain and they TRUST it. I am glad my name is nowhere on the drawings. They did this because it ejects a product every 6 seconds. I suggested they use a PLC operated safety relay to bypass the light curtain contacts, but the chief engineer said, "Yeah, I know, but I already have 140 of these machines all over the world." He won't be so casual about it when someone get their arm broke. END RANT. Okie

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OHSA just visited and the ones in question were up to code. Some of the others require two hand controls. I am mainly looking into it for uniformity. Also you know how it goes, if they aren't all the same you will have an operator saying "Well his press doesn't have two hand controls, why do I have to have them." We don't have but a few of these old mechanical presses left and hopefully will be replacing with hydraulic presses, but until then...

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The AB publication for Using CLX in SIL-2 applications can be downloaded here: http://literature.rockwellautomation.com/i...rm001_-en-p.pdf AB equipment approved by TUV for safety applications can be found at the TUV website: http://www.tuv-fs.com/plcrock.htm

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Thanks for the links

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On Safety Rated PLCs. (SIL3 / CAT4 applications) For AB CLX you have to use a companion safety processor (1756-LSP) and safety rated I/O modules (devicenet). I believe these were specificlly designed for the USA motor industry (so our AB rep told me). OK if you are already using a CLX on the machine. Very large safety systems (100s of I/O) Other options are: Omron/SICK (NE1A) - my current favourite programmed in FBD and filling in tag fields (no import/export) Compact and big enough for most machine jobs. Use safety Devicenet modules (Omron, SICK, AB) Can communicate to a standard devicenet master on the same network (ie: coexists) EASLAN /NHP Brick type Programmed by filling in boxes in an electronic sheet and typing tag-names. Very German Network by safe profibus The tell me they are working on bringing this into the 21st centruy Slightly higher cost than Omron Schneider (XPSMC32X) Single block - really is just a bunch of configurable safety relays. 16 or 32 I/Ps 6 SSR, 4 Relay O/P Programmed by a mixture of FBD and tag filling Good and low cost for small machine where you would use more than 3 but less than 8 conventional safety relays. PILZ (3000 series etc) Really just an S5 safety rated Programmed in IL, ladder Very German Can import/export the tag database using excel If I really wanted to waste that much money I would put in an AB. Has its own proprietary bus, very very very poor networking capabilities to other systems. (it's as though they don't want you to use it with any other system) There are others, but I don't believe they are really in the race. They seem to be just reincarnations of smart safety relays. Just my personnel opinions and experience from designing/installing safety systems. Edited by dellae

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I re-automated a press here that had an old modicon running it. No two had controls, no light curtains, pretty much no safeties on it at all. I did kind of a hybrid. I used a GE Fanuc Versamax Micro PLC for part selection and sequence control. For safety I used a Pilz Multi Safety Controller. All of the outputs from the PLC that control Solenoids go into inputs on the multi and ouputs on the multi actually control the solenoids. So if there is an unsafe condition the solenoids will not fire regardless of what the PLC is telling it to do. E-Stops and Light curtains feed into the Pilz as well, along with a raise button, which will abort the sequence and raise the die.

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