Hello everybody, this is tarek…I wanna make a robot arm that will be used in arc welding purpose - a robotic arm that will hold the manual welding torch and manipulate it according to program. I’m gonna do this as my undergraduate project.
The robot arm that I tend to fabricate during my project will use manual arc welding equipment. While some might think that a robotic GMAW torch is nothing more than a manual gun attached to a robot arm, there are significant differences.
Have a look at this Figure1: “the basic arc welding circuit” : lincolnelectric.com/knowledg … ldfund.asp
My goal is simple: my robot arm will hold the electrode holder that is demonstrated in the figure and manipulate the electrode holder in the way sothat the tips squeeze together the two pieces of metal that need to be welded.
Will it be very tough project? How can I make this project easier? What should be the lengths of the links for this purpose? How strong motor/servo will I need for this?
Could you please tell me the required torque and holding force to hold the electrode holder on a robot arm?
What if I consider Lynx 5 robotic arm for welding? I think it has strong arm and stout gripper for precision. But I don’t know about sensors-whether the sensors become useless during welding due to bright light of arc or not. Will it match with that one which I attempt to make for welding? Will it be suitable? Please do reply.
hmmm… so many questions, well as far as sensors go as long as they don’t sense light it should be fine, however u should probably insulate the frame of the bot from the electronics somehow because there are some pretty high currents running through the metal as I am sure u know. as far as servos go I would probably go with 645’s, that should be strong enough for ur purposes.
And my limited knowledge stops there… hope it helps!!!
If you can give us an idea of the weight of the welding impliment that must be lifted by the arm, we can help you out.
Also, if you’ve got a minimum height requirement, we’ll need that, too.
if you didn’t already think of it you might want to fabricate a custom holder for the electrode thingy, the grippe prob wont be enough, hopefully im not repeating wat you just said, id feel even bumber than i do now
I think the link you provide tells a little about the requirements to building this thing - first off 6500 degrees. In short, if your mechanics fail and this thing goes where its not suppose to - cook. Take a look at the industrial robotic tig welders being used today and you will see multi hundred pound devices bolted to floors. I am certainly not trying to disuade you from doing this a project but I admonish you that there are a lot of pieces to this puzzle to make it safe
With that said - I would caution against any hobby servo found on any website (accept maybe - maybe the HSR-5995TG (417 oz. in.) Digital Standard Servo). The longer the arm the more power/torque required. Only you can determine your requirements for your project. If you have heavy requirement your looking at heavy cost.
If your undergraduate project doesnt have to be welding related, try a checkers game with a lynxmotion arm. You can program many different moves. If you get too involved with having to create a welding monstrosity just to make it safe (an unsafe welding project will surely only secure you a C grade in your class) you may run out of time during the semester. If your class focus is on mechanical design - go with a welder. If the class focus is on purely robotics (autonomous or otherwise) look for something that focuses on integration of the various sciences (mechanical, electrical, robotic, programming).
You have to be more specific about the type of welder that you will be using (no one here can tell you the size of the motor and arms required without this info). I love Lynxmotion products and the culture Jim helps to foster - but I have to tell you - there is no way I would used the Lynxmotion 5 robotic arm to hold a TIG welder. However, if I really needed a design that would work for this type of project, I would scale up the design of Jim’s arms (his robotic arms as scale down models and not the wet noodles under his shirt) and attach some big as_ industrial servos.
Hes right. maybe intsead of making a welding arm, you could make it solder instead. The weight of the load would decrease dramatically and would allow you to use less powerful and cheaper servos. Also, the voltage of your tool would be less and would cause less stress on your arm. A lynx arm would be very good for soldering in my opinion (against welding anyway). This would be cheaper and more practical for the lynx arm, but thats just my 2 cents.
Thanks Italian_guy299, cwkoehler, Chunga, NickReiser, Hydrohexapod…thank you all indeed. Actually, I never thought of getting so many response.
NickReiser, the weight of electrode holder would be 400g to 600g and the height of electrode would be 10 inch. So I need additional 5-6 inch height for arm’s movement. The desired movement will be rectangular movement (in X-Y direction).
Have a look at a typical electrode holder: mymall.netbuilder.com.my/pic/wel … erican.jpg
cwkoehler, actually I do not need to make that much strong, gigantic and precise robotic arm welder that are now using in Industires. This is my college project and I need to keep it as simple as possible. Have a look at this robot welder: fronius.com/welding.technolo … cts/robot/
this seems pretty much simplier than those gigantic industrial arms.
Hydrohexapod, would you please tell me details(cost, power, etc) about servo 645’s?
Italian_guy299, yes i’m really thinking of brazing or soldering instead…but it might not be as simple as you thought…I agree brazing/soldering is cheaper, lighter, and requires less precision pathfinding…but there r alot of things to do in soldering…welding might be easier in terms of number of processes required.
yes, you are right. And now that I see these other images of welding arms, your project does seem more simple and actually practical. Have fun with your project!!
o yea, just in case anyone else is confused about the grams like i was , thats 14-21 ounces, if you want the exact ounces they are 14.1096 to 21.1644 ounces
o yea, i agree with you on the soldering being more comlicated, because you also need to find a way to feed the solder to the iron
I’d recommend going with 5995TG or 5645’s.
Those are both digital servos.
As long as you give them power, they’ll hold whatever position they were last told to.
645’s, 855BB, etc are analog servos.
If you have a communication error for whatever reason (severed wire, overdrawn/overheated control board, microcontroller bug, bad luck, the list goes on) between the servo and the controller for more than 20ms or so, you’ll be in big trouble.
Analog servos only hold their position when continuously told to (like a few siblings of mine ).
I’d recommend slapping a nice big servo gear reduction (ServoCity.com) on either the 5995 or the 5645, as well.
Stick a 5:1 on a 5645 and you’ve (theoretically) got a slow (which probably would only help) servo with a torque of around 800 oz-in.
With that, you should have no problem building a small arm capable of lifting a pound.
I’d definitely recommend putting only what is absolutely needed on the bot itself (unlike the robot shown in that picture).
As Chris said, be sure that you have multiple stop-gaps set in place to keep your pretty little bot from welding itself to the floor.
I don’t think that there’s any other feesable way to go than IK for this, which will be one way to keep your welder where it’s supposed to be.
I’d recommend limit switches at each joint.
You can either directly link them to shutting off the welder power or have a micro monitor them and decide what to do.
You’ll probably want a remote shutdown for the welder, as well as an onboard one controlled by the bot itself (relays work well in both cases).
I’m thinking that you’ll want to use encoders of some sort, as well, since you’ll be carrying a large load on gear-reduced servos, which will distort the already-iffy precision of a normal hobby servo down to an accuracy that’s probably worthless for welding.
If you go with encoders, you’ll be able to tell where your servos actually are, instead of where they think they are.
I agree. As I mentioned to another servo questioner (although I am not an expert in this field), encoder disks should be used. This will give you an acurate degree of your positioning so you should be able to weld more precisely.
you can buy them here at robotshop (canadian prices).
Do you have previous welding experience? If not, then you probably need to do some welding to understand what will be involved with just that part of your project. How much $$$ do you plan to spend on your project? The welding arm shown in your link looks like it is using a wire feed MIG welder. This type of equipment is heavy and probably beyond the capability of typical hobby types of servos to move around. You would probably need larger geared motors to do the actual movement of the equipment.
I believe that his arm is going to be stationary.
So, he can probably get away with leaving the power box on the floor next to it.
A warning:
If you do chose to go with a wirefeed welder, you’ll probably want to buy/make something that can fix/prevent a kink in the feeder.
I’ve got a pretty decent welder, and it still kinks rather frequently.
This means having to open the side of the power box, cut the wire downstream of the feeder, pull the kinked excess out through the tip of the torch (which means 10 feet of wasted wire), manually thread the fresh wire into the feeder, and then turn on the feeder and pray that it manages to push the wire back through the hose and out the torch tip without again kinking.
If you can manage to use a spot welder/TIG, it’ll save you that hassle (although, it’ll incur more safety hazards).
One more thing…
I just realized that you’re going to have big problems with the intense light thrown off when welding.
I’m not sure if TIG is as bad as arc is, but I’m willing to bet that it’ll mess up your sensors, at the very least.
So, if you’re going to use encoders, be sure to completely shield them.
It probably wouldn’t hurt to keep all servos and electronics shielded as well.
Oh, and you might want to use a metal tubing to cover your wires (www.cableorganizers.com).
As I’ve before been told, the TTL PWM that needs to be sent to the servos is pretty fragile.
Encasing them in a metal will prevent external signal disruption quite nicely.
(Check out “Electric Fields” and “Electrostatic Shielding” in a Physics textbook if you want to find out why.)
, thats 14-21 ounces, if you want the exact ounces they are 14.1096 to 21.1644 ounces
).