Lab robot conversion to laser cutter

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Re: Lab robot conversion to laser cutter

Postby loopingz » Tue Sep 18, 2012 4:20 pm

That is really good already!
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Re: Lab robot conversion to laser cutter

Postby macona » Sun Oct 28, 2012 6:47 am

I got a new lens for the laser cutter, 18x22mm focal length. I wanted to try something with a smaller spot diameter for higher power density. With the short focal length there was no way to make use of the nozzles I had bought for the other lens I was using (3" FL) so I made a new lens holder/nozzle for it last night.

I found an adapter of some sort lying around. It went from a 25mm thread to a 20mmx.7 internal thread. The 25mm thread was close enought to a 1" c mount where it screwed together just fine, the thread pitches were virtually identical. To back up the lens in the adapter I took some hollow aluminum and made some threaded rings with the 20mm thread in the adapter.

For the nozzle I needed something light. I didnt have any more solid 1" aluminum bar, but I did have some 1" titanium lying around. I cut the 20mm threads on the end (Ti threads very nice) and made a 18.1mm recess for the lens. I drilled down with a #7 drill and finally drilled the final orifice hole with a #60 drill. I opened up the area next to the lens with a 15/32 drill as well. I had just tapered the outside of the nozzle 45 up to about a 1/4" diameter area around the orifice but I was having an issue with the air flow causing the material to pull up against the nozzle, I cant remember what this effect is called, but I see it in plasma cutters a lot. To resolve this I made the outside of the nozzle more round.

After turning I put it on the mill and spot faced a land for the 10-32 gas fitting.

It works pretty well, I do need to space back the lens a but, the focal point is a bit further out than I would like. Nothing an o-ring cant fix.

Image
IMG_3110 by macona, on Flickr

Image
IMG_3112 by macona, on Flickr
Attachments
IMG_3111.jpg
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Re: Lab robot conversion to laser cutter

Postby macona » Sat Apr 20, 2013 6:50 am

I have not messed with the laser cutter now for several months. One of the problems I was having is small movements were not translating well. I think this was a lot to do with the tuning of the servo drives and the "springiness" of the machine between the motors and the linear encoders. This would cause what should be little circles to come out with squarish sides.

The plan was to remove the X and Y motors and replace them and their drives with some brushless motors and drives. I have a small 200W Mitsubishi MR-J2S motor and drive and a Yaskawa 100W Sigma series II drive and motor that would work nice. They have good auto tuning and should eliminate the problem with the motion. The problem with this is I would have to pretty much redesign most of the electrical and mechanical aspects of the machine.

Before I go that far I decided to try sticking encoder directly on the machines to see if that made a difference. I had a 2500 line encoder for the X axis motor in my sensor bin and rounded up a little HEDS encoder for the Y motor. I had to make up some new cables and I had some extra lines from the Y axis head so I was able to wire it in pretty easily. The servo drives require a differential line driver input from the encoders, I found a small board with a line driver IC that I used to convert the single ended output to differential.

The encoders made a heck of a difference. The motors tuned much easier and the circles it makes are actually round now. I still have linear encoder feedback available for use in the future.

I still cant get the tiny Z axis servo to tune right though, every once in a while it starts oscillating for a second or two, if I drop the gain down on the motor it just becomes sluggish. I think it may just be too small for these drives to handle well.
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