Anti tie down (again)

I think with the last post concerning ATD I may have misstated or miscontrued what I did.

My machine is not using a PLC, therefore I did use a timer relay with 2 pushbuttons wired in series BUT both buttons have a set of N.O. contacts in series and a set of N.C contacts in series.

The logic behind this is if EITHER button is pushed opening one of the N.C. contacts it initiates the timer ckt. The second button must be pushed within .3 seconds to initiate the cycle.

To put this in ladder logic would be similar to what Rick Densing posted. His way is better I guess because you only need 1 set of contacts.

A QUESTION: When is it considered "needed" to use an ATD.

I know what OSHA (1910.217 pertains to a press) ANSI etc state.

When do you make the call to use an ATD? Is that an engineering call, safety, management or plain old CYA?

I am not asking about rules/regulations. What are the guidelines y'all use to determine when its appropriate is more what I would like to know.

You didnt read what I stated, the timer has 2 connection points. The N.C. contacts of the pushbuttons (reset/start) the timer ckt when either pushbutton is pushed. The other pushbutton must then be pushed within .3 seconds (adjustable) to initiate the cycle. Tie down either button (or just push one and wait too long) and timer should start and it will never allow a cycle initiate. Assuming of course the timer is functioning properly. Yes this is a proper way to do ATD with relay logic involved, there are timers sold for this specific purpose. Onct upon a time this was the only way to do it.

ok I am going crazy, I saw a post here besides mine

The function of the two-hand, anti-tiedown device is to keep the operator's hands out of a dangerous area, particularly in those applications where it is not feasible to use a physical barrier or some other protective device.

The two buttons are physically seperated by enough distance so the operator can't press them both with one hand, leaving his other hand free to get into trouble. They have in inherent timer so that they have to be pressed within a few milliseconds of each other in order to initiate the machine cycle. The operator must maintain the buttons pressed throughout the machine cycle. They must be released and then pressed agian before another machine cycle can be initiated. The obvious applications are machines like presses and shears where the product being operated on has to be fed into the machine, so placing a barrier between the operator's hands and the dangerous area would be impractical.

I have seen exceptions to the requirement for the operator to keep his hands on the buttons. One was a test fixture where the operator had to load a part into the fixture. He then used the ATD device to close a guard around the fixture and initiate a test cycle. Once the test cycle got underway, he could take his hands off the ATD and walk away. However, to open the guard and remove the part at the end of the cycle, he had to use the ATD again.

You ask a darned good question. I have run into this same question at virtually every place I have worked and have come away with my own conclusions but none that appear to be "standard".

I think you "should" use Anti-Tie-Down (ATD) controls in any application where it is possible for a single operator to initiate a potentially hazardous operation where he could be injured by having a hand in the wrong place. Furthermore, the equipment used to create the ATD controls should always meet the ANSI and OSHA guidelines.

So, in a nutshell, the requirement for use of an ATD is really a management call (isn't most everything, really?) with OSHA carrying the big stick. As a Machine Designer and Engineer, your true responsibility is to inform the uniformed of their exposure should unsafe decisions being made and to use your own conscience with regard to their implementation (basically, you can always walk away. After all, if someone gets hurt because it was implemented that way, aren't you also responsible?).

OSHA regulations exist because, historically, management focused on profits over workers' welfare. Unfortunately it is sometimes still difficult get today's managers to break away from this tradition. It is our right and responsibility as workers and designers to make sure we are personally aware of and willing to implement these regulations and stand up against poor management.

I currently work for a company where implementation of these types of regulations is a bit behind schedule. Sometimes I get resistance, event from co-workers, to making some necessary changes. But I persevere. Changes do come. Slowly, but they do.

Steve

rsdoran,
A rule I use is "what could happen if one or both buttons are stuck down"? If this event is not a safety issue then don't bother. If this will cause harm to machinery or people then use it.

"If it don't apply let it fly"

A rule I use is "what could happen if one or both buttons are stuck down"? If this event is not a safety issue then don't bother. If this will cause harm to machinery or people then use it.

Click to expand...

tsurber; Could you clarify this a little, please. I have been doing this kinda work for a long time now, and I just don't quite follow your line here.

Steve

I think I got it. What would happen if you pushed both buttons or at the same time both buttons closed to initiate the cycle and stayed there.

Using my timer method (which offers what OSHA calls a no repeat capability) if you were to push both buttons and they stuck then it would cycle once but cant cycle again because power wasnt restored to the timer.

Using the ladder logic Rick posted before applies the same principle I think. Once timer has passed the preset then you can not initiate or restart again if input(s) dont return to false state.

That is what I was looking for...what guidelines (or who should make the call when) to use. I dont work with any (die/punch) presses, quillotine cutters, shears like OSHA refers to in there CRF 29 Part 1910.217
OSHA CRF 29 Part 1910.217

We do have some machines that seal items in plastic that use an air cyclinder to move an arm down that cuts and seals the plastic. The arm has switches on it that are N.O but spring maintained closed, if an object blocks the arm (breaks one of the switches) then it stops the cycle. The heat is only applied when the device is closed (pulse heat) thru a chromium wire to cut/seal. The original schematic for this uses 2 N.O pushbuttons wired in series. We had some minor issues with it and I am doing an upgrade on the machine so attempted to use some "safety style pushbuttons". They failed too often so I went back to old relay/timer type technology until I install a new cabinet with plc. This machine operates and is fed automatically.

We have another machine that works similar but it was designed to manually load. The cutter cuts on close but stays closed to load again. It only has one button to make it cycle and you cant put your arm in at the begining of the cycle because the jaws are closed. People being people though (and we have 1 Engineer and 1 Safety (HR) that do nothing but look at these issues) we were worried about a problem with a miss cycle or mechanical problem leaving the jaws opened. They thought an ATD may be appropriate but the more I look at it the more I think a barrier may be needed to "lockout" I/O when hand/arm is inside. This unit does have a plc, a Series One GE.

I am in a unique situation at my plant. Everyday I or "they" come across issues involving safety. Since alot of these issues are either electrical or electrical devices are used to eliminate the safety issues I am the one that has to implement what is done. That usually means determining what to use. I have no problem with responsibility but I am attempting to use the CYA rule. Make it right so it wont come back and bite me. Above all I dont want to see anyone get hurt in any way.

to RSDORAN,
Spot on.
Sorry about the previous answer to your post, but you appeared to leave out the N/O buttons in your Post.

In Australia the OHSA are very reluctant... (don't wana get sued)
to approve any thing.
They favor RISK ASSESMENT, the blame comes back on your arse.

I have run up with the same mentality in safety issues.
- we ain't had an accident in 40 years that safety device is not nescessary..
- That is the money saving policy of some management.

FOOTNOTE:-
Toyota is fairly good at safety, though there are areas for improvement.
- I left Toyota 7 years ago.

The original Post from - clone93 - was his first PLC program.
He had asked for some assistance.
I know the answers are on this Post, I hope he reads it.

I think youre looking for this, We have a machine almost like you want to do that was a correction press. Were using the pnuematic cylinder(Spring return). In this will never stick their hands in one of the buttons.


-----------] [------------] [-------------]/[----------( out )
PB 1 PB 2 Timer


-----------]/[-------------]/[---------------------------(Timer)
PB 1 PB 2 1 sec

This is just a suggestion, get it if Im wright never mind it if Im wrong.

Sorry Im wrong this is the correct one when I was checked the circuit.


-----------] [-----------] [-----------]/[--------( Out )
PB1
PB2
Timer


-----------] [-----------] [----------------------(Timer)
PB1
PB2


TY

-------] [--------] [----------]/[---------------( OUT )
PB1
PB2
TIMER 0.3 SEC

-------] [---------------------------------------(TIMER)
PB1 „ 
-------] [----

jonjon NEVER EVER stop trying

to post code/ladder here at the beginning put It will look better that way
Do not feel bad..alot of us had to learn that.

dam forgot its code inside [ ] at the beginning and /code inside [] at the end
If you try to show it then it messes with the post.

We all live and learn EVERY DAY