Stationary Spot Welder help

Sorry if this question isn't entirely PLC related, but I started an internship this summer and was recently given a project to work on for the rest of my internship. The company I work for has several hundred stationary spot welding stations that all use two palm buttons to ensure operator safety. My job is to switch out the palm buttons for foot pedals, but still have the welder be safe in the event that an operator puts their hand in the way. The company used to use foot pedals in the past which greatly improved production time, but were found to be unsafe after several accidents. Now they want to go back to foot pedals. It is my job to make them safe. My boss sent me links to view unitrol-electronics soft touch technology, and entron controls smart detection technology and basically said I am to replicate similar results. (Short videos below if interested)

(http://www.unitrol-electronics.com/soft-touch.html)
(http://www.entroncontrols.com/en/smart-detection.html)

The welding station I am working on has been fitted with an LDT to track the position of the welder. Other than that, the only thing I have are two pressure regulators to raise and lower the welder.

My thoughts were to somehow measure the force between the welding tips and compare that with the position given from the LDT. If a force was detected before the welder was in position for a proper weld, then I would now something was obstructing the welder. But I am not sure how I could detect force between the weld tips due to temperature and current of the weld tips. Other than that, I don't have any real ideas of how to make the welding operation safe. I did notice a different welding machine using a Q4X laser distance sensor at the point of weld. That may be of use...?

If anyone has an ideas on how I can prevent an operators hand from being crushed, please help. Sorry if this matter isn't entirely PLC software related, and if my post isn't the most clear. This is my first time posting and am merely an intern with very little experience outside of the classroom.

Thanks again for any help!

Welcome to the Forum !

Unfortunately, I think you're being given an impossible task:

"Using devices known to be unsafe, and without using specific safety technologies, make a safe machine".

There are truckloads of Federal, international, and State standards that affect safety-related equipment, and you haven't mentioned any of them. Since you're an intern, that's not too surprising and not your fault.

Every machine you design needs to have a risk assessment done. Are you familiar with the methodologies and standards to do one ?

Palm switches with special circuitry called "two hand anti tie-down" are used in this sort of thing specifically because they require the operator to remove both hands from the work area. That might actually be the required technology, depending on which machinery type your particular welders (and their clamping mechanisms) are considered to be.

Your first homework assignment is to find, read, and start to understand OSHA Standard 1910.255.

Also: Unitrol has thought long and hard about a lot of different methods and technologies used to improve safety on resistance welders. Compare some of their ideas to the machines operating in your facility.

http://www.unitrol-electronics.com/assets/docs/tech-papers/Welding Journal Safety Article.pdf

Thanks for responding, I wasn't sure if anyone would. I know of OSHA sure, but am not familiar with any of their standards being an intern and all. I will be sure to check out the standard you mentioned, but I am still curious as to how both of the other companies from my links above managed to have some sort of smart / safe detection. In the videos they stick tubing and pencils in between the weld tips and the machine detects an error and backs off.

My boss did tell me it might not be possible to do what he wants, but he figured it would be a good project for an intern to play around with. Only given the LDT for position, I think it is impossible, but I didn't know if there was some sort of sensor or safety device I could add to achieve my task.

I did talk with one of the weld engineers and told him what I was trying to do and he didn't think it was possible without some modifications. I did find it odd that my boss with over 20 years of experience as a controls engineer didn't know if it was possible but gave it to me, an intern, to figure out.

Anyways thanks for the reply, and I'll be sure to look more into OSHA standards.

Take a look at light curtains. You can program/wire the process to prevent welder movement while curtain is broken. They make all sizes and if installed in a fail safe manner should meet all of your safety requirements.

trentg@felixconstruc said:

Take a look at light curtains. You can program/wire the process to prevent welder movement while curtain is broken. They make all sizes and if installed in a fail safe manner should meet all of your safety requirements.

Click to expand...

That was my first inclination, too. We use a lot of them here. I have them set up to where if the machine is away from you, or moving away, the light curtain has no effect, but if the light curtain is broken the machine will not move toward you, and if it is near you it stops. It works well.

I did initially think about using light curtains, but from my understanding, they wanted to use the foot pedal so the operator could hold the piece being welded. I think the operator's hands would be close to the actual weld and would trip the light curtain in normal operation. I could be wrong, but I will look more into using light curtains.

I'm sure there is something available that will do that. This isn't applicable to your situation, but if they can do this...http://www.sawstop.com/

You might want to give detect-a-finger a look.

It sound to me like that is going backwards in regards to safety... provide pedal so hands are free to put into machine, by design?!

This is probably the point that I would look at what the buy back rate is for automation. Depending on your operation, 3 people minimum required for 24hr shift per machine (I know there are 12 hr shifts but when you figure in vacations, sick days and such it is 3 people). Wages, benefits, time off, sick time, slow days, employee appreciation days, lunches... all this stuff adds up QUICK. Once you have the true cost to produce a part call FANUC and start exploring options. Most factories (at least the ones I have dealt with) want a 3 year buy back on a process. The though is that process and product evolve every 5 years (not to mention CEO's average tenure is 4-5 years... and they want to hit bonus marks).

Not keen on robots, build a station that holds part and one operator to load all stations. This usually costs more than off the shelf (engineering time, testing....) but in the long run (and often short term) this saves money, time and other jobs. Now that your company is considering re-introducing hands to a dangerous process one hurt employee can cost more than a fleet of robots or custom stations.

Consider this as a learning experience in safety requirements. I hope that's why your boss assigned you to this project. Before you do any investigating into hardware or consider any potential solutions, do a thorough study of the applicable safety standards. Start by talking to your company's safety person.
If you get a lot of flak after raising the issue of safety standards, then don't even consider this company for permanent employment after your internship is over.

If you use light curtains, then the piece of metal would need to be flat and be specific for blanking like a punch press decoiler. Anything bigger than that would not be allowed because you can get your hands in the way.

Since you have already had several accidents, You MUST learn the safety rules first and know them very well and be able to defend the rules.
Don't rush or be pressured into doing something that will get someone injured
and then become the scapegoat.

james

Thanks for the saw and detect a finger ideas, food for thought at least.

The idea behind reintroducing the foot pedals is to cut down on production time. My boss said with the current palm button setup, a part needing a dozen welds or so, welding nuts and whatnot to a piece may take 20 minutes or so, compared to when the company used to use foot pedals. He told me the same part used to take 5 minutes in the hands of a skilled operator. My boss realizes the foot pedals were unsafe from accidents the company had in the past, but if I could find a way to make them safe, such as in the links from my original post, it could really save the company a lot of money. Other companies / suppliers have made their spot welders safe, such as in the videos, they stick a pencil in between the weld tips and it does not get crushed. So the ability is out there, I'm just not sure if I can retrofit our machines to make them behave in a similar manner, and neither is my boss. He started off by telling me, "This might not be possible, but what I want you to do is..."

As far as safety is concerned, I have learned a lot in general over the last month. (You can only learn so much in a classroom.) The company does seem to be willing to work with me on things, but there is a lot I'm left with to figure out on my own. Everyone seems to be friendly, and the company does pay fairly well, so with any luck, I'd like to make some progress in improving the machines and hopefully get a job offer.

James Mcquade said:

Since you have already had several accidents, You MUST learn the safety rules first and know them very well and be able to defend the rules.
Don't rush or be pressured into doing something that will get someone injured
and then become the scapegoat.

james

Click to expand...

I did think of that when I was assigned the project. I don't want to be the intern who comes up with an idea that ends up getting someone hurt. Especially since I am fairly inexperienced. I'm sure my boss would test and look though any work I do though, before ok'ing it to go into our other facilities.

Hodor said:

I'm sure my boss would test and look though any work I do though, before ok'ing it to go into our other facilities.

Click to expand...

I would be veerrryyy careful making that assumption.

If all welds are coplanar, a clamping jig mounted on an X-Y table could be much faster/more accurate than the operators' manipulation of parts around weld electrodes.
Maybe a rotating index table for parts requiring concentric welds.