"Start" Help

[fcflores1]

We currently have a machine in our facility that is started by a single start button. Today I was asked to see if I could eliminate the start button and use the door switch as machine start; is this safe? Currently the operators have to load the machine; closes the door and then press start to initiate auto cycle. Now they want the operator to load the machine; close the door and auto cycle will initiate. Note: This machine is not a press its simple a cutting machine that is protected by door guarding and E-stops. I currently purchased the NFPA 79 Electrical Standard for Industrial Machinery 2007 Edition and I cannot see any reason why not to under “Enabling Control” 9.2.5.7. Thank you,

[PdL]

What is the reason they want the automatic start ? The operators forget to push start ? Or has the plant manager calculated the time savings between closing the door and pushing the start button will result in an overall savings of $100 a month ? Although the machine is not a press, I assume there is a safety risk as there would not be a door if there was no risk. The button assures the operator is standing at the safe side of the door if the start button is pressed (not necessarily but within reason). So even if it was within safety regulations of this particular machine, that doesn't mean it's a good idea. I do not work with machines and E-stops at all but this is just my point of view. No idea about regulations an such.

[jstolaruk]

This is in a grey area with OSHA. Last I looked, they infer that it can be done if the safety portion of the application has been certified by a qualified source but there are no sources that are currently qualified to certify. Personally, I make it a rule that a cycle start has to be initiated by an operator's specific action: a h/w push button or HMI push button. Depending on the machine I may put a seperate push button for resetting the safety relay or use a PLC output that follows the Cycle Start PB. Do a search at the OSHA website for Presence sensing device initiation (PSDI). You'll get references to power presses but if your machine has any movement where a operator could be crushed, pinched, etc, it could be viewed as being in the same category. Edited April 18, 2007 by jstolaruk

[jimtech67]

I would not do this it does not sound safe to me, especially in today's environment of safety first. Too many things can go wrong. A machine (any machine) should only be started when the operator can see that all is safe (This may be over simplifying things but you get the idea) Can the operator activate the door switch accidentally without the door closing? Can the door be closed prematurely when condition are not right? Why were you asked to have the machine start this way? Edited April 18, 2007 by jimtech67

[Sleepy Wombat]

What happens if an operator is inside the machine and some one closes the gate on them NOT knowing that it will automatically start the machine.... This functionality is not normal industry practice and as such how could you defend it in court if something went wrong.... The vast majority of operators / people would assume that a START button would start the machine not the closing of a gate.

[fcflores1]

"What is the reason they want the automatic start ? The operators forget to push start ? Or has the plant manager calculated the time savings between closing the door and pushing the start button will result in an overall savings of $100 a month ?" PDL...you hit the nail on the head; they feel they can save money by doing this. I told them that this was an unsafe practice; but i need facts to back me up. Any help would be appreciated.

[PdL]

I can't give you facts as I don't have the NPFA 97 book, but I would try to convince your boss that even if this solution is allowed according to regulations doesn't imply it is safe practice at the same time. They don't go hand in hand necessarily. Your work is to interpretate these regulations, and translate them into a safe control application, not to literally follow every single rule that is in the book. Perhaps you can find a more clear example in the book of something that is allowed according to that specific regulation but if literally applied to a machine on your plant floor it would in fact be unsafe. If the facts are not there that is where your responsibility comes in.

[Zoran Mihajlovic]

I have similar problem in my old job. Boss tell me to unsafe thing.Becouse he is boss I have to do. But I tell hem thet is unsafe acording to some rule I imagen and ask him to give me writen specifik order to do that. Becouse he consern of perhaps problem if somthing hepend he did't give me writen order , and I didn't turn odd safti switch. Maybe to do same with you boss??

[sparkotronic]

Regs in the UK must be a lot more strict. Over here you could face a custodial sentence for doing something like that if someone got hurt. So I'd say no. It's good practice to have a reset for when the guard/emmergency circuit has been broken. And thats before you press the start button.

[fcflores1]

Thanks for all the help!!! I told them no today it cannot be done safely.

[comeng]

Hope you did it in writing and kept a copy, long and bitter experience has taught me that when a production manager sees a good saving he tends to keep asking different people to do something until someone says yes (generally when the most vociferous no is away on holiday) and usually both him and the person who did it will have bullet proof alibis

[TConnolly]

Is the door there to keep the operator from getting cut or is it also there to protect him from flying material? If there is no risk of material being ejected to the operator (even if the cutter breaks) then why not replace the door with a light curtain and leave the start button there. That would be faster than opening and closing a door.

[gravitar]

In the past, I've been directed to wire up welding/assembly machines that automatically cycle based on the state of the light curtain. They were FAST. The improvement in cycle time is greater than you might imagine. I was a little younger and more naive back then. Now, I think I would pay a little more scrutiny to the safety of cycling a machine that way before committing to build it. If memory serves, I recall reading in an STI light curtain manual that you CANNOT use a light curtain as a safety barrier AND an automatic cycle initiator. There MUST be a way to do this safely, and I think it would be worth the effort in many situations.

[GerryM]

Take a look at 9.2.5.2.1 and 9.3.1 in the NFPA 79. They come close to backing you up on not using the safety device as a machine start. I had the same issue a few years ago, but not with the boss, big difference. I just told them that I can't do it and that was the end of it.

[504bloke]

I think those white coats the managers wear are reinforced with kevlar! Edited April 20, 2007 by 504bloke

[mr_electrician]

Exactly the same situation I was thinking about!!!

[gravitar]

Very good point. I should mention that the ones I built were small tabletop welders that could only be accessed through the light curtain or by a removable back door with a switch on it.

[mconner]

I know this topic should be left to die, but it brought up a lively debate at our site. Our thoughts were, "what happens when the door opens?" If the operation stops, the door switch would then be considered a safety device and should never be used to start an operation. For what its worth from some bored engineers.

[TConnolly]

That is not what I was advocating. Definitely do not use the light curtain as the start device. You wouldn't want the cycle to start if the operator had merely adjusted something. What I was saying was to replace the door with a light curtain and leave the start button there. You can realize huge time savings if the operator doesn't have to swing a door - he removes his hand and presses the start button (sometimes a foot operated switch couple with a light curtain can realize slightly better gains, thats for you to evaluate). But use this approach only if there is no danger from ejected material. That is the purpose of a light curtain, to enable a productivity boost by not having to move a physical barrier when one is not requried except to keep the operator's limb attached to the operator. I once had a manager ask me to replace the safety door on a lathe with a light curatain. I refused. After arguing over it for a while I started to clue in to the fact that the manager actually thought the light curtain was a force field that would protect the operator from cutting chips. I think he felt a little sheepish when I explained that there was no such thing as a force field and he dropped it at that point.

[Sleepy Wombat]

LOL You must of used the force to preform an old Jedi mind trick on him... "The Force can have a strong influence on the weak-minded. You will find it a powerful ally."

[gfunkatoa]

Safety interlock is a safety interlock. No debate possible. Change to a light curtain and add a palm switch for quick activation.

[paulengr]

How about an alternative? When you push the start button, the machine closes and locks the door. There are plenty of mechanical and magnetic latches on the market and it just takes a simply pneumatic cylinder to close the door (with either a pressure edge sensor or else not enough force to break your arm off and with a timeout in case it doesn't close). Then the operator doesn't have to close the door and the start button stays in place. There are lots of examples of this sort of machine...even a simple elevator that closes the doors before changing floors.

[BudMan]

We used to close a counter weighted door. When the door was in the closed position a spring pin held it closed and a few switches detected the door closed. When the machine process was complete a cylinder pulled back on the spring pin and counter weighted door opened (raised). Bud

[Clay B.]

Had a automatic welding booth that used this system. The operator slid the part in then placed their hands on 2 palm switches which in turn closed the door and started the system. The operators had to keep their hands on the palm switches until the door was completely closed and the welding process had started. Door opened automaticaly when the welding cycle was complete. If the door can be mouted where it closes by sliding and not having to swing on hinges this is failry good system. Every automatic door I have seen that uses a swinging system required alot more maintenance.

[Sleepy Wombat]

This thread was complete (dead) a year ago... why bump it again ????? Look at the posting dates...