Close
0%
0%

open-hardware transparent polygon scanner

laser scanner which uses transparent instead of reflective polygon

Similar projects worth following
An open-hardware transparent polygon laser diode scanner suited for 3D printing. The laser scanner uses a transparent instead of a reflective polygon.

Hexastorm has build a new type of laser diode scanner; the transparent polygon scanner. Note that this relates to scanning in the broader sense, not the specific form of scanning used to capture 2D and 3D images and shapes. The technology can have a big impact on 3D printing. To clarify, the Hexastorm is put in perspective by comparing it with a Fused Filament Fabrication (FFF) printer. The smallest element of a FFF printer is the nozzle which is a circle with a 300 micrometers diameter. In the latest Hexastorm, this is an elliptical laser spot which is 50 by 60 micrometers. The standard spot speed of a FFF printer is 50-80 millimeters per second. The Hexastorm is able to reach a spot speed of 100 to 467 meters per second. The maximum scan length is 24 mm. The speed of a whole scan line is 16 to 84 mm/s. The outline of the project description is as follows. We start by listing the applications of laser scanners, list the specifications of the Hexastorm, give a brief overview of the technology and outline what source code has been developed

Applications

The market for laser scanners is extremely large as they can be applied on various processes, for example; laser direct imaging of printed circuit boards, 3D printing, self-driving cars, laser printers and microscopes. The current version of the Hexastorm is targeted at hardware developers in the 3D printing market. At a wavelength of 405 nm, possible applications are the fabrication of advanced ceramics or metals via photo-polymers, 3D printing of hydrogels, microfluidic devices, dentures, earmolds and jewelry. Of course, if this wavelength is varied and the laser power is sufficient, a transparent polygon could be used to sinter plastics or melt metals.

Technology

The transparent polygon scanner consists out of a laser diode which is focused directly with an aspherical lens. The bundle refracts through a transparent polygon and is directed to the surface with a 45 degrees first sided mirror. The bundle is deflected by tilting the transparent polygon. The position of the laser bundle is monitored by a photo-diode. A Field Programmable Gate Array (FPGA) is used to ensure the correct timing of and stream data to the laser diode. A detailed explanation, analytical model, review of other exposure technologies and patent analysis has been made available via Reprap.
The technology has four advantages: high optical quality, cost effectiveness, scalable for industrial applications and open hardware.

High optical quality
The transparent polygon scanner projects at 90 degrees of incidence and has a flat field projection, see figure. A numerical and analytical model is available here https://github.com/hexastorm/opticaldesign .
To mitigate in a reflective polygon scanner the simple lens is replaced with a telecentric f-theta lens. In the figure, you can also clearly see that in a transparent polygon scanner the bundle is focused before it hits the transparent prism and must be rotated to translate the bundle.

Cost effectiveness
A high optical quality can be obtained without an expensive f-theta lens.

Scalable
The maximum optical power of laser diodes becomes less as their wavelength becomes shorter. As a result, laser diodes need to be combined to give more power. It is, however, not possible to combine more than two lasers into a single bundle without interference. The electromagnetic field only allows for up to two polarizations. Due to its high optical quality and cost effectiveness, the Hexastorm is very scalable and suited for systems with multiple bundles. An example of such a system is shown here.

Wide range of applications
The current applications we envision; bioprinter, photopolymer printer and device for the creation of microfluidics (see presentation).

Specifications

The current version of the Hexastorm has the following specifications:

  • wavelength: 405 nm
  • rotation frequency: 67-350 Hertz*
  • spot size: elliptical, 50 (short...
Read more »

firestarter2.PDF

bom of firestarter and overview of layout

Adobe Portable Document Format - 912.66 kB - 05/07/2018 at 21:30

Preview
Download

output files.zip

gerber files GBL -> Gerber Bottom Layer GTL -> Gerber Top Layer GTO -> Top Overlay GBO -> Bottom Overlay (empty) GTS -> Top Solder GBS -> Bottom Solder GTP -> Top past GBP -> Bottom Past GKO -> KeepOut Layer DRR is the Drill Layer with APR that is the tool if you wanted to make the cards ... send all the files

Zip Archive - 258.00 kB - 05/07/2018 at 20:59

Download

basf.pdf

presentation given to various companies on the potential applications of the Hexastorm

Adobe Portable Document Format - 5.37 MB - 11/03/2017 at 12:42

Preview
Download

  • 1 × quartz optical window, 2mm thick, 30x30 mm faces 60/40 < 5 arc min, chamfers 0.10 – 0.30mm, edges Polished 60/40, top bottom polished 60/40, 40 dollars
  • 1 × XULA2-LX25 (FPGA) 119 dollars, xess
  • 1 × Raspberry 3, 16GB SDHC, 1 meter network cable, housing, 2A microusb power, 62 dollars, kiwi electronics
  • 1 × Ricoh Aficio AF-1027/270 polygon mirror motor 20 dollars, ali express
  • 1 × StickIt! v-4 (connector between FPGA and Raspberry 3) 19.95 dollars, xess

View all 10 components

  • prism alignment

    Hexastorm04/26/2018 at 11:27 0 comments

    I recently received a question in my mail on the alignment of the prism. When i made the technical presentation, I did not know how to align the prisms. I have fixed this issue. The prism shown on the project website and photos is not the latest version. I have solved the alignment issues. I have one prism perfectly aligned. Basically what i do is, i take the top of with a Dremel ( a drilling machine). I can then remove the reflective polygon. At the center of the reflective polygon there is an axis. With my Dremel I grind this axis away until i have a small hole at the center of the top plateau of the polygon basis. I put a bit of UV glue in the hole i created and place the prism on top. Then by rotating the prism with respect to a reference point I am able to center it. I then use an UV flash light to fix the prism. Afterwards, I measure how planar the prism is with a displacement meter. The current prism is planar within 5 microns. I spent roughly a 1000 dollars figuring out this procedure. As I had to buy two batches of 10 prisms. In my technical presentation, I outline that I do not know how to do it but actually I now know how to do it. I will provide pictures if I have to do it again.

  • firestarter pcb

    Hexastorm04/25/2018 at 22:34 0 comments

    Hi,

    It has been a while and it is time to give an update. I have decided to drop the FPGA route with the Xula LX25. The Xula LX25 is well documented but produced in low volume and seems to be no longer for sale.
    Luckily, Henner Zeller made a polygon laser scanner, the LDgraphy, with a beagle bone black / green. With the LDgraphy firmware a laser scanner can have a clock speed of 2.7 MHz. This is more than sufficient for a transparent polygon scanner. I looked at Zeller's code and it is actually very accessible. With a couple of minor changes it should be suited for the Hexastorm.
    Finally, I had the luck of finding an electrical engineer, Salvatore Puglisi, who could design me a board. The board is open hardware and has been designed in Altium. I personally prefer Kicad but can't design a board. Result is below see figure 1. Project files are available upon request. I have added the schematics of the board as pdf to the project repository, see firestarter.pdf. I also added the BOM and the gerber files.
    I use a simple voltage divider to detect the signal of the photodiode. This worked with the Xula LX25.
    Zeller uses a Schmitt-Trigger to have a clean signal for the BeagleBone.
    Zeller also didn't mount the laser driver on the cape and made his own laser diode driver.
    I decided to go for the IC-HKB from IC-haus. It is not seen in the picture and needs to be mounted on the board at U2. This will be done in the coming days. I will give an update if I tested the cape successfully.

    Best,

    Rik

    Figure 1:
    Top view of the firestarter cape

  • hello tomorrow

    Hexastorm11/03/2017 at 11:55 0 comments

    Hi,


    It is hard to get funding for this project. I tried Kickstarter but failed. The main problem is that investors don't want to invest as there is no patent and the product is to far out from the market. I have decided to proceed as an open-hardware project and do it for fun. I am looking for supporters. Hopefully one day the project can pay for itself.

    This log is intended to give you an update on the progress

    Best,
    Rik

View all 3 project logs

Enjoy this project?

Share

Discussions

Paul wrote 11/05/2017 at 03:49 point

You've certainly done your homework very thoroughly, and I see that in your application with very small optical cone angles (large focal ratio), the optical aberrations and field curvature appear to be tolerable.  That's great.

One question: You say that previous scan techniques require a large (and therefore expensive, you argue) f-theta lens, which must have one dimension at least as wide as the scan line.  In your approach, your polygons must be larger than the scan line length, but in *two* dimensions, making the volume of your optical element much larger.  Since either shape would use identical materials and fabrication processes in volume production (i.e. injection molding), one would naively expect the smaller element (the f-theta lens) to be cheaper.   How is this line of reasoning flawed?

  Are you sure? yes | no

Hexastorm wrote 11/05/2017 at 10:51 point

A telecentric f-theta lens requires one dimension at least as wide as the scan line. A non-telecentric f-theta lens does not require that.  In my approach, the polygon must have one dimension longer than the scan line. The second dimension is 2 mm. An f-theta lens consists out of multiple lens elements, e.g. a 3 element f-theta lens. These elements have curved surfaces. The prism consists out of a single element with a flat surface. The prisms now costs 40 euro's per piece with a minimum batch size of 10. They are not injection molded. You can't make the f-theta lens out of plastic, so you would have to injection mold quartz. I am unfamiliar with the prizes for that. Besides most likely a higher price and the fact you have to use multiple elements, you also need to worry about patents. Envisiontec patented the usage of reflective polygons; US 9079355 B2 . Finally, you need a thick reflective polygon as thick polygons can deflect collimated bundles with a large diameter and these can be focused to smaller spots.  A transparent prism uses a focused bundle and therefore typically can be thinner, which keeps the price of the bearing lower.

  Are you sure? yes | no

Paul wrote 11/05/2017 at 15:55 point

You have clearly thought about this a great deal, and have your arguments worked out well.

I wasn't considering that you might be requiring quartz.  I would have guessed even BK7 would be overkill for this application.

I mention injection molding because I look around my offices and see several laser printers.  Each of them contain a laser scanning unit with a rotating (reflective) polygon and a f-theta lens arrangement, with the final element being very large (>200 mm long).  All the optical elements of the ones I have inspected appear to be injection-molded PMMA or similar plastic.  The entire laser scanning unit must cost considerably less than $50, given the prices of the printers (all less than $200, two less than $70).  Granted, these are produced in huge volumes, but they serve as existence proof that these scanning systems with large optical elements are not intrinsically costly.

  Are you sure? yes | no

Hexastorm wrote 11/05/2017 at 16:52 point

PMMA absorbs light at 405 nm. The laser printers at your office use 800 nm and low power lasers. I use 405 nm and high power lasers. So yes; there is concrete proof that PMMA injection molded systems are not intrinsically costly. There is no proof that quartz systems are not intrinsically costly.  It's unclear what the prices of these systems would be .

  Are you sure? yes | no

Paul wrote 11/03/2017 at 13:21 point

A good variation on the usual way.  I build a few instruments based on this and similar methods between 1985-1989.  A couple of important notes:  

1. The scanned field is NOT flat: The optical distance to the target plane *increases* as the polygon rotates away from normal.  Not only is it geometrically longer, some of the increased  path length is in the high-index polygon too, increasing the path length even more.  The result is a curved focal or scan plane.  One of my instruments actually depended on this: a rotating polygon was used to tune the optical path length inside an optical resonator cavity, to adjust a tunable laser that was phase-locked to that cavity. 

2. You get some significant spherical aberration when you focus through a thick window like that, for similar reasons: the light rays at the periphery of the optical cone take a longer path to the target plane than rays going through the middle of the cone, with the result that they focus at a different depth.  For a laser at f/50 (or whatever it is), this probably isn't significant, but in an imaging system at f/2, it seriously degrades focus. 

  Are you sure? yes | no

Hexastorm wrote 11/04/2017 at 22:09 point

Paul, thank you for your reply!
A transparent polygon scanner with a single laser bundle was first patented by Lindberg in 1962.  The scan field is not flat and you can get some significant optical aberrations. A full numerical model is available here https://github.com/hexastorm/opticaldesign . A description of this model is available in the technical presentation. The result shows that in practice the scan field is flat and the optical aberrations are not significant.

  Are you sure? yes | no

Hexastorm wrote 11/03/2017 at 11:58 point

Well this is the first comment! If Hackers are interested in transparent polygon scanning let me know :P ..

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates