buildlog.net

Has anyone built their own visible pointing/alignment laser?

I had an idea a while back that I thought I would bounce it off the group. I was thinking about putting two very small battery powered laser diodes on my head assembly. They would point from two different angles exactly at the focus point. You would see two dots if the focus length was not right. Move the z until the dots converge to one dot. Then jog the machine XY until the dot is where you want it on the work piece. If you need to move the z to the center of the thickness of the material you would do that last. The weight could probably keep to less than 1/2 oz.

This would accomplish two goals...focus and alignment.

Smart. I like it.

If you ever want to autofocus, you can install something like this device under your gantry arm and have a microcontroller servo loop on your Z axis.

http://mcu-programming.blogspot.com/200 ... ensor.html

I have some of those and some ultra sonic sensors too from some old robotic projects. As I recall, my real world accuracy results were pretty good, but maybe not quite good enough. I think it would work well to get you very close, then just do a quick verify. It would also work well as a limit switch to prevent you from crashing the table into the lens holder (...did that once). With both methods it just gets you to the top of your material. If you cut anything with any thickness, I think you want to focus on the center of the material, which is another manual tweek.

Other options:

If you build your lift with a repeatable motion and lower limit switch, your system can already "know" where it is and you only need to tell it the thickness of the material or where you want the focus.

You can put a swing down linear potentiometer or LVDT on your gantry to measure to the surface - Very accurate.

You can use a line generator mounted to the side of your machine with the projection coming out in a horizontal plane at the focus height. You simply lift your object until you see the line striking the surface. One could imagine two line generators converging to a single line at the focus point also. this is much like your original thought except it uses lines instead of points. People are getting really good with video lately and could certainly make something that can remotely "see" the lines and automatically adjust the depth of the lift.