Alternative focus improvement

[connyg]

Hi Henner,

I have been following your LDGraphy project for about a year, have you done more work on that?
Last thing you were experimenting with was the cone mirror to improve the focus and achieve a higher resolution.

In a discussion about galvo & fiber laser arrangements a guy recently had an interesting idea:
Instead of using a f-theta lens he thought about lasering zones and move the z-axis for the focus.

That could be an idea for LDGraphy, too.
It could have two modes, one for "regular resolution" (6 mil) that would do a PCB in one pass on one z-level.
And a second mode, "high resolution" that would expose the PCB in multiple stripes for different z-focus zones and have some mechanic to move the focus by a few mm.
Softwarewise you would only "black out" certain areas of a line, on basis of the zone calculation.
There could be a zone for each mm of focus.

If I am calculating correctly if you have 250mm distance diode-focus point and an angle of 25 degrees for the laser, the focus deviation is some 6mm.
Possibly 2mm for one zone is already providing enough improvement, then there would be 3 zones = 3 passes. For 1mm there would be 5 or 6 passes.

There could be different solutions to move the focus:

• move the laser unit (rail and lead screw)
• move the small mirror in front of the laser unit (rail/lead screw)
• rotate the lens with belt/gear

For the lens it needs fixing of the wobbly gear (maybe external mount on rail?), moving the small mirror changes the z arrangement of laser, mirror, facet mirror, moving the laser unit seems quite doable.

What do you think?

Kind regards,
Conny

[hstarmans]

Hey Conny,

I have looked into another solution with a transparent where an f-theta lens is not needed, see hexastorm. Resolutions down to 20 micrometers can be reached. In general, it is possible to do what you suggest. The process will take longer and will likely require an extra actuator.
The key question is; will there be a business case!? This is much harder.

Best,
Rik

[connyg]

Hi Rik,

looked at the hexastorm pages and it's quite an interesting idea to simply use optical refraction through two parallel edges.

There's two key questions left for me:

1. Can I manufacture the transparent polygon with maker tools? What material is it from, how did you make it?

2. Am I understanding correctly that for exposing a 100mm wide PCB I need a transparent polygon that has an edge length (if it's a quadron) of about that size? In your demo device there is a quadron of about 3-4cm edge length and you state the scan length is 24mm maximum. Then I'd need a quadron that's larger than 100mm?
   Of course I could scan a PCB in 4 lanes, but then it (or the laser unit) needs to move in X direction to allow for the lanes and the setup is more complex plus the exposure process takes 4x again.

As these quadrons are not available to buy or not trivial to manufacture "at home" (I assume it requires optical quality of the edge and optical precision in alignment of at least two edges) it seems that's not a "maker" solutions in the end.

Regarding business case: I am looking at this from a maker / hobbyist point of view, I am not interested in a business case. But in a cool & working solution that I can manufacture on my own, without buying expensive components like F-Theta lenses...
Of course such device could be sold, even in masses, if it had a price tag of a "few hundred" dollars, let's say 200-300.

[hstarmans]

1. No, you can't manufacture them with maker tools. I had them custom made in China,
   square prisms i.e. 4 sides a = 30mm x 30 mm, thickness = 2mm, Faces 60/40 < 5 arc min, Chamfers 0.10 – 0.30mm, Edges Polished 60/40. The material is quartz and the price is 55 dollar a piece, with a Minimum Order Quantity (MOQ) of 10 so 550 dollars.

2. You understand this correctly. There are two options; a large prism or multiple scans. The large prism is physically not feasible as you can't spin a polygon off this size on commercially available polygon motors.

It's good to hear you are doing this for fun and not the money. In the end, and I have seen many projects, I would advice you to look for a project where you can also break even and make a little money. Or a project which has some other benefits, being good for your career or for the environment / mankind. It will be hard to sustain them otherwise.
There is a need for laser scanner in microfluidics, bioprinting and photo-polymerization. The first customers will most likely be Industry and R&D institutes. Although it is admirable to make something for the masses. Making money from a 200-300 dollar product is really hard. The prusa i3 costs something like 919 euro. Most vendors in this market, like ultimaker, moved to small business and have a starting price around 2000-3000 euro.

[connyg]

Ok, so "unfortunately" both assumptions were correct :-)
Well, I have a nice "day job" that gives me enough, no need to earn money with my hobby/spare time stuff - 3D printing (including modding the printers), electronics and laser cutting/engraving (including modding the laser cutter).
I am doing those things just for personal challenge, to see what can be done and to try / learn new things.
Of course it is hard to make money of a mass market product in that segment and I don't feel like engaging in that segment. :-)

[hstarmans]

Working version of the transparent scanner is shown here; https://youtu.be/SofTXG5s_MA .