Anti-tie-down buttons

Jimmie_Ohio said:

I have read your post and the replies by others. Here's my question:

If this is for "education", why not have the student research the possibilities him(her)self, learn the details behind OSHA rules and regulations without bias,
REPLY Some good thought. However this guy is a controls engineer not a safety engineer. See my previous comment on adequate.

and then run the various choices by us for additional approvals, feedback, and comments? With our experience, I guarantee all of us will be helpful.
REPLY Well consulting us SHOULD be part of his research.

(I can suggest "Google-ing" the heck out of the web using "OSHA" "anti-tie down controls", "controls safety", etc. as keywords.)
REPLY Another research field to be plowed.

An early reply said to use cheap "regular" pushbuttons, instead of more expensive anti-tie down pushbuttons designed for safety. I totally disagree. If we are to teach the Controls Engineers of Tomorrow what to do, maybe they should learn the minimum industry standards for safety, not "a cheap way to go". Some of these engineers go out in the real world and only know what they saw in school. Therefore, a good (or great) example should be set. Just my opinion...

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REPLY Completely agree -- ASSUMING -- he is not the only one using this gear. If this is a temporary setup to test one "theorem" then the cheap switches (IF 10% of expensive cost) could be used. IF it is permanent setup or there is lots of exposure (ie a training aid etc) then the expensive
-- CORRECT -- "adequately spaced" -- Etc Etc
switches should be used.

Had one or two EE's tell me "well we did not do that at UW".
They learned this is not UW this is Boeing and you either need to do it the right way or go back to UW. One guy really got the message when I refused to sign off the safety portion of the job.

Dan Bentler

rsdoran said:

FYI My link in the above post goes direct to the OSHA standard for power presses and two hand control.

All the OSHA standards are here:
http://www.osha.gov/pls/oshaweb/owasrch.search_form?p_doc_type=STANDARDS&p_toc_level=0&p_keyvalue=

In many cases two-hand control is used as a safety precaution instead of a legal requirement.
REPLY PROPERLY DESIGNED two hand control is one of several ways of complying. Punch presses, brakes are good finger getters and scare the bejeezuz out of me. See below Rons description is pretty good.

The use of standard buttons with a two-hand control relay could be sufficient in a real world application. A risk assessment should be done to determine the proper procedure.
REPLY You bet.


A few years back I rebuilt an L-sealer that used standard buttons and did not require concurrent initiation. I changed the buttons to mushroom head, spaced further apart, and each had an input to the plc. The plc program required concurrent action, each button pressed within .5 seconds. This machine used a sealing arm with hot cut wire that pivoted. I also incorporated a shutdown (arm up/heat off) if the plc did not get a "arm is down signal" within .5 seconds (may have been less in the end). The few modifications I made were not required legally but added to the safety and reliability of the system.

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REPLY I get awful tired of people who ask is this required by OSHA ?? Converseley -- if it is not required we are not doing it??
Well who cares about OSHA I want people to go home at the end of the day with no missing parts.

Dan Bentler

The point I was making is there are few, if any, legal requirements for the use of two-hand control with the exception of power presses.

I am not sure about your sign off procedure but what is the proper procedure...when its not a power press? I take it that means you assumed what was the correct procedure and required it to be done that way.

I stated a risk assessment should be done, this should give provide the information to decide what is needed....but just because it is two-hand control does NOT mean it requires anything more than 2 buttons.

Ron

Not ignoring you but gotta go. Let me think a little before reply -- will do when I get back

Dan Bentler

Jimmie_Ohio said:

An early reply said to use cheap "regular" pushbuttons, instead of more expensive anti-tie down pushbuttons designed for safety. I totally disagree. If we are to teach the Controls Engineers of Tomorrow what to do, maybe they should learn the minimum industry standards for safety, not "a cheap way to go".

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Apparently I need to clairfy something. I did not mean "cheap" as in flimsy. I questioned the widsom of using two 800Z soft touch buttons ($900) verses two 800H/800T buttons ($150) in an educational setting. 800Z soft touch buttons require no activation force, just the presence of the operators hand - they are ideal for highly repetitive operations. On the other hand 800H/800T buttons are high quality mechanical buttons that must be physically depressed. Similar quality Cuter-Hammer brand buttons can be gotten at Automationdirect.com for a little less money.

If the education lab is going to address carpal tunnel syntrome as well, then 800Z buttons might be appropriate - but one student is not going to sit in front of the machine and activate it hundreds of times a day, month after month.

And as I already explained, soft touch buttons do not mean safer buttons.

Its one of these (except green or black-not red):


verses these:

Thanks Alaric for info. I think I'll go with just the anti-tie-down controller. save some $ for the lab. Also, rsdoran good links. very helpful.

Ron - finally getting back to you.

The point I was making is there are few, if any, legal requirements for the use of two-hand control with the exception of power presses.
REPLY Those are all that come to mind to me also.


I am not sure about your sign off procedure but what is the proper procedure...when its not a power press? I take it that means you assumed what was the correct procedure and required it to be done that way.
REPLY See below

I stated a risk assessment should be done, this should give provide the information to decide what is needed....but just because it is two-hand control does NOT mean it requires anything more than 2 buttons.
REPLY let me try to answer both paragraphs since they seem to be closely related.
1. We did the risk evaluation of the the machine looking at what it did, operator proximity to point of operation, the hazard and risk of accident.
2. We then decided how to safeguard the machine - lite curtain, two hand control etc etc
3. We used the appropriate safeguards needed for that operation and did not "throw on extras" just because we could or it looked neat - at least in the vast majority.

Dan Bentler

[/QUOTE]

i recall 12" as minimum distance between buttons

also if they are in same plane, they must be guarded.
this is not nececary if they are say on oposite sides of the
enclosure for example 9left and right).

Could someone please briefly explain

1) anti-tie down switch

2} anti-tie down controller


I am getting from the thread it is the same as two-hand control?
I don't do power press controls and haven't run across it yet.
Thanks,
Brian.

On some machinery where the operator could have his hands or body in the machine when started 2 hand control is used to lower the risk.

It depends on the level of risk how this is done. In the US OSHA has guidelines (poorly defined in some aspects) to require the use of 2 hand control with anti-tie down (cant tie down 1 button and just operate with the other) and in some cases anti-repeat. The anti-tie down requires each button to be pressed "concurrently", basically within a second or so.

Some buttons are designed to incorporate the anti-tie down feature. There are also modules that can be used with standard mechanical pushbuttons that provide the anti-tie down features.

I have dealt with a variety of applications that needed 2 hand control with anti-tie down. An example is a sealer something like this: http://www.latter.com/ModLseal.htm

rsdoran said:

The anti-tie down requires each button to be pressed "concurrently", basically within a second or so.[/url]

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I think the 'standard' is 1/2 second, though it probably should be raised to a full second. You'd think 1/2 second would be more than sufficient, but I'm amazed at the number of people that seem to lack the ability to press two buttons within that time frame. I see operators struggle with 2-hand controls, trying over and over again until they happen to 'get lucky'...



-Eric

I am not sure I have seen a "standard" except where distance and time issues are involved on power presses. I just threw the 1 second out as a basic guide, I meant to say or less. I doubt I would ever allow the time to be higher than 1 second.

FYI: I never use 2 hand control without the anti-tie down feature. It defeats the purpose, in my opinion, if you dont. I am not aware of any guidelines, regulations or standards, besides OSHA's power press, that directly addresses this issue. In my earlier posts I was just mentioning this point....it was never to imply that I would not attempt to address any safety aspects.

Using that point I have used the mushroom head style pushbuttons shown in Alarics post with a PLC providing the anti-tie down (and anti-repeat when needed) to the machine. In my cases the safety risks did not involve death or dismemberment so it did not require special modules or safety devices, just a requirement there hands/arms were not in the machine when initiated which the anti-tie down offered.

It depends on the situation what is necessary and in many cases that may be debated because of other issues. Its like many issues in this field, there are no real standards so its open to interpretation....and in some cases how much money is to be spent.

I see, an anti-tie down switch is an impossibility as any switch can be rigged to be held on. In my workplace you can see some ingenius use of welding rods. So ant-tie down logic would only allow a start if the two switches had positive transitions, within a short time and stayed on. Too quick to rig. Makes sense, thanks.
Brian

EN 574 recommends 550mm minimum spacing

Hi All,

This is a very old thread now, but it comes up near the top of a Google search, so I'm going to post here anyway.

I have attached a page out of the manual for a two-hand control module made by Banner Engineering (Part number: AT-FM-10K). Banner does a good job of rounding up information you need, so their manuals can be a great resource. If you want the rest of the manual you should be able to get it from their web site. The page I attached is from their publication 64137.

Here in the United States, we often use the European safety standards just because they are willing to commit to actual numbers, circuit designs, etc. Like everyone posted up above, we leave it pretty vague on our side of the pond.

Banner says that over in Europe they have a standard called "EN 574 Two-Hand Control Devices – Functional Aspects – Principles for Design".

Based on EN 574, the minimum spacing for the buttons is 550mm. They also say you can go less than that if you do things like put the buttons on opposite ends of a wiring trough, or guard them somehow.

I don't believe EN 574 has the force of law in the US. It's more of a serving suggestion for us. Still, people say that the OSHA inspectors generally accept the EU standards, so it's not a bad idea to follow them.

If you go looking for your own copy of EN 574, you will discover that you have to buy it. Big problem these days, all our safety codes are behind pay walls.

Good luck!