Need way to detect laser

Sounds like a good transimpedance application using a photodiode. Perhaps a comparator if it is needed to ensure a proper trigger level.

I was afraid my description was confusing. I have the seam of the 8 ft tank but also the automatic welder travel arm which is pivoting as the tank travels eastand west to where it is aligned. As the tank travels and the welder arm rotates there is one point where the arm travel and the tank seam are aligned. once aligned the tank is stationary while the rotating arm is locked down. Now the arm can move in a linear motion while welding. But if all arn't aligned it won,t be welding the seam and I'm in trouble. Clear as mud right? I had thought to put laser on the rotating arm aligned with its linear motion, something at front of tank to block laser but with a small hole. then at rear of tank a detector. That is where I got the point description. I'l try getting pictures and posting them. Ken

Ken,

I can't quite visualize your setup. But, could you use a rotating-mirror laser unit, attached to the welding unit, that would make a line that is always in line with your welder's linear motion plane, and then just make sure that the laser line is on the seam before welding? The rotating-mirror laser units are commonly available.

Or, are you trying to automate the process? If so, maybe something at the following site might be helpful:

You might also want to ask in one of the "amateur telescope makers" (aka ATM) groups. They are extremely good at using lasers to align their telescopes' cylinders with their optics, and might come up with some good ideas about your problem.

Good luck!

Tom Gootee

WIll have to check and see what a "rotating-mirror laser unit" is. I can't automate it with the money restricions I have. Also the welders travel arm is going to have to be pivoted manually even if I can get a DC motor to move the tanks which I am sure we will do once the boss realized how his idea of moving it with a pry bar is going to take two people and be too time consuming. I will try and post pictures tommorrow. I know its very hard to understand without a picture. Ken

The rotating-mirror laser units are basically just a small laser (imagine one of those "laser pointer" keychain things) and a rotating mirror. The mirror is at a 45-deg angle to the beam. Its axis of rotation is coincident with the beam. So, it reflects the beam to be perpendicular to its original direction. And since the mirror is spinning, the beam sweeps continuously through a plane.

They are used as aids for all kinds of simple alignment jobs, in fields such as construction, painting, etc. For example, if you set one up inside a room, with the beam horizontally oriented, you'd see a line on the walls, going all the way around the room. You could also install a cover with whatever size opening you needed, so only a portion of the

At close range, even a cheap one (or a home-made one) might be "good enough".

- Tom Gootee

geocities.com/clannorm/subarc

I got some pictures which should be much better than my explanation

Not sure if this would suit you, but if you have a number of these tanks to weld it would be easier to build a cradle for the tank (secures the tank side to side) and have the cradle on wheels and straddling a length of old railway line. If the bottom of the cradle has rollers then you can easily rotate it to put the seam under the welder arm

Little bit of work to set up, but from then on no sweat - and cheap as chips to build

David - who likes to do things the simple way when possible

" snipped-for-privacy@yahoo.com" wrote:

I must be missing something. Why do you need a laser to do this? Can't you just drop the welding head down and use it to align the welder gantry to the tank seam?Also, isn't this pretty much a one time setup to get the welder gantry aligned to the rollers that will support the tank while you weld it?

I don't need a laser to do this. I thought it would be easier than what I have now. It also takes about 10-15 minutes with one person doing it. Its not a one time setup since we have different diameter tanks and have to move the rollers for each size. Also the seams aren't perfectly square so they vary one to the next even on the same diameter. I did three today and they all varied. Hopefully with a laser I can get it done in a minute. Ken