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Form 3

A project log for open-hardware transparent polygon scanner

laser scanner which uses transparent instead of reflective polygon

HexastormHexastorm 04/02/2019 at 18:480 Comments

Formlabs launched the Form 3 . It uses a parabolic mirror and a galvo mirror. The galvo-mirror is used to obtain a constant line speed as they don't use an f-theta lens. The parabolic mirror is used to get the spot into focus over the full scanline.

The galvo mirror can be seen here;

The properties of a parabolic mirror are shown below;

The optical system will produce a better spot quality than their previous galvo design without f-theta lens.

In comparison with the Hexastorm;
Advantages;
  - no cross scan errors / jitter
  -  long scan line
  -  scanhead has to be moved in only one direction, not two
Disadvantages;
  - low scan speed; don't use rotating mirror
  - diffraction limited spotsize is given by 2w0 = 4 lambda / pi * f/d
In the Hexastorm, the focal lengths are very short. It for sure is able to produce a smaller spot size.
  - elliptical correction; seems unlikely that Formlabs is able to circularize the beam.

Form 3 spotsize is 80 micron. For both SLA and SLS a smaller spot size then that does not seem required.  There are systems which use higher resolutions.
A difference with the Form 2 will be that a part will be less smooth. Tracing the outline gives smoother results. Lines imply a discretization in one direction. It can also not employ writing strategies to cure parts. This can be used to mitigate shrinkage. Reflective lenses give errors due to fabrication faults, e.g. some sort of mustage error; the line is not straight.
Reflective optics are  better with high power lasers, e.g. 10 kW lasers. Refractive optics have the problem of thermal lensing. Up to 1 kW you can still use Zinc Sulfide / Zinc Selenide beyond that you want to grab some mirrors (ref DOI: 10.1117/12.2037356 )

Form 3 is 3,499 and begins shipping in June. While the 3L is 9,999 and ship near end of the year.
Their system probably has a safety clearance for lasers of class 3B. This would allow them to ship up to 500 mW. For some reason they only use 250 mW.

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