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open-hardware transparent polygon scanner

laser scanner which uses transparent instead of reflective polygon

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An open-hardware laser scanner suited for Printed Circuit Board (PCB) manufacturing. The laser scanner uses a transparent prism instead of a reflective polygon with a f-theta lens.

The goal of this project is to develop a PCB machine which can expose a PCB with a track width smaller than 100 micrometers, i.e. 4 mil. The PCB machine will also have a spindle to CNC a PCB board and create through holes. The transparent polygon scanner, which can get a high accuracy and telecentric projection, has been developed. The technology to cut boards with a spindle is under development.

Specifications

The current version of the Hexastorm has the following specifications:

  • wavelength: 405 nm
  • rotation frequency:  up to 21000 RPM, current 2400 RPM
  • line speed: up to 34 meters per min @ 21000 RPM
  • spot size FWHM: circular, 25  micrometers diameter
  • cross scanner error: 40 micrometers  (error orthogonal to scanline)
  • stabilization accuracy scanning direction :  2.2 micrometers (disabling/enabling scanhead)
  • jitter: 35 microns (error parallel to scanline)
  • laser driver frequency: 2.6 MHz
  • maximum scan line length: 24 mm
  • typical scan line length: 8 mm
  • optical power: 500 mW
  • facets: prism has 4 facets

Electronics

  • Beaglebone green
  • Firestarter cape

Status

An image can be uploaded to the scanner and exposed on a substrate.
An exposure result on cyanotype paper is shown below.
Resolution looks to be around 100 microns. Stitching still needs to be fixed, results in white lanes.
The current focus is to add a spindle to the machine.


An exposure goes as follows (for the result see above).


Software
Hexastorm fork of LDGraphy
Optical design
old FPGA code
PCB design

Links
Official website
Failed kickstarter campaign
White paper (on Reprap)

presentation_19419.pdf

elevator pitch

Adobe Portable Document Format - 4.82 MB - 04/30/2019 at 15:52

Preview
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calib_data.zip

calibration data of current scanhead

Zip Archive - 278.28 kB - 01/25/2019 at 18:50

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21measurements.rar

measurements and algorithm used to determine stabilization accuracy, see blog

RAR Archive - 594.17 kB - 01/25/2019 at 14:50

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firestarter2.PDF

bom of firestarter and overview of layout

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

Preview
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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

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  • 1 × Quartz optical window, 2mm thick, 30x30 mm 40 euros, faces 60/40 < 5 arc min, chamfers 0.10 – 0.30mm, edges Polished 60/40, top bottom polished 60/40,
  • 1 × Beaglebone Green 45 euros, kiwi electronics
  • 1 × Heavy Duty Heatsink / Laser Diode Housing for 5.6 mm with Fan 11.93 euro, odic force
  • 1 × BDR-S06J 405nm, 500-600mW Blue-violet Cut-pin Laser Diode 27 euro. odic force
  • 1 × 25 mm focal length, cylinder lens, 12.5 mm x 25 mm 56.50 euro, edmund optics, faces 60/40, MgF2 coated

View all 11 components

  • Populated board

    Hexastorm05/06/2019 at 18:08 0 comments

    Board is populated, next step is testing if it works.

  • Received new boards

    Hexastorm04/30/2019 at 15:32 0 comments

    Boards are in, added logo... hope they work!

  • Finished routing board

    Hexastorm04/18/2019 at 16:54 0 comments

    I finished the routing of the new Firestarter Cape;


    The cape has the following improvements;

    •    PWM control of spindle and fan
    •    added spindle
    •     TMC2130 motors can now be configured via SPI
    •   added third stepper motor for z-axis.
    •  board is now made with Kicad and not Altium.
    • hdmi pins are free, screen can be added


    The current board can be used for 3D printing.  Although, you might want to add a tilt motor, recoat motor and temperature control for your resin.  Some machines use force-feedback,  which is patented.

    The boards still have to go through some final checks, probably you can't run 30A through the board.


    Code can be found here ; firestarter

  • Form 3

    Hexastorm04/02/2019 at 18:48 0 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.

  • Road ahead

    Hexastorm02/28/2019 at 16:50 0 comments

    I see multiple applications for the Hexastorm. I have explored  a vertical sales model where I cater the specifications of the scanhead to the needs of an industrial customer.  The challenge with this model is that industrial clients require exclusivity and there are still adoption costs.
    This is hard as I also want to use the technology in different markets and have a preference for open-hardware.
    Considering possible beach head markets (SLS, SLA, advanced ceramics, mircro-sla, bioprinting or CLIP-like, i.e. carbon 3D like technology), I have come to the conclusion that the PCB prototyping market has the lowest barrier for entry. 3D printing processes require multiple layers, a customer need which is best served by a fast illumination. This is possible but will drive costs. In addition, it requires some sort of layer application method which is hard to implement in the current setup.
    The current setup is not ideal for PCB prototyping. It is not possible to cut out a board and there are some obvious safety and maturity issues with the current machine.
    As such for a PCB prototype, you would currently need two machines which have to be cross-aligned.
    I plan to address the first issue and will add a spindle to the setup. At the moment, I am thinking about a 775 DC motor with RPMs between 3000 and 9000. They are quite cheap and great for a first test. The software can then be partly copied from Machinekit or Zeller's BeagleG. Personally, I think t-belt will suffice for the x- and y-stage. The scan-head is already fast enough at low stage-speeds for a dual layer PCB.  Besides PCB prototyping, the developed software could also be useful for bio-printing due its ability to parse G-code. The problem with current UV exposure methods in bio-printing is that they typically rely on a non-precise UV light source for resin curing.
    The mechanical design and dimensions have to be determined later.  Bungard sells the following board sizes; 100x160 mm, 210x300 mm and 510x1150 mm. They seem to be industrial standards. I think 210x300 mm should be feasible.
    In the following, I would like to make a remark with respect to Carbon 3D and Nanoscribe. Carbon 3D initially patented Continuous Liquid Interface Processing (CLIP) see patent WO2014126837A2.  The company currently seems to sell it as Digital Light Synthesis (DLS) technology and makes a more general claim; an AM process with oxygen inhibition. Given my current knowledge of its patent portfolio this seems too wide. In the patent it claims that the part moves continuously away. This does not have to be the case.  It would be more likely given a laser-scanner that the part does not move continuously away. You could expose a line multiple times and cannot illuminate a complete cross-section at once. It would circumvent the patent and the resulting parts might still be more flexible and have a higher z-accuracy than classical step-wise produced parts.
    Nanoscribe uses dual photon polymerization with a galvo scanner as can be seen from reference 1. Optically, the advantage of the Hexastorm light module is its telecentric projection. This allows a machine to stitch lanes accurately without a telecenric lens. As such, it could be useful for a dual-photon process. Naturally, this would have to be elaborated further with an optical design.

    Reference;

    1 https://nano.secure.pitt.edu/sites/default/files/Equipment-SOP/Nanoscribe%20user%20guide_0.pdf

  • FPGA code

    Hexastorm02/27/2019 at 22:51 0 comments

    Uploaded my old FPGA code to Github; https://github.com/hstarmans/hexastorm_fpga .
    If you are Hacker enthusiast and think you are capable of controlling laser scanners via FPGA.
    This might give you a start!

  • SLS machine

    Hexastorm02/27/2019 at 21:43 0 comments

    With several industrial parties, I have discussed the possibilities of the Hexastorm in laser sintering, in specific powders.
    Single mode laser diodes are expensive in the IR range. High power laser diodes are typically multi-mode. A possible supplier is Lumics.de . The diodes have a wavelength of  1 micrometer and a power between 3 and 7 W. It's assumed their price is in the order of 1K euro. You can pulse them at 20MHZ so they are suited for laser scanning. A problem is that these fibers are multi-mode lasers so the spot will not be so nice. The fibers have a diameter of 50 and 100 micron for 3 and 7 W respectively. I spoke to an expert and a spot of 100 micron should therefore be feasible as it is a 1 on 1 projection and the numerical aperture is not compressed a lot.
    EOS spends uses a  galvo system and C02 laser and the power is between 40W and 80W. EOS has a minimum feature size of 0.5 mm. Formlabs uses a fiberlaser with a galvo and something like 5-10W power. Hexastorm could provide that with one module.
    To provide a viable commercial alternative for EOS, you can use 25 modules in parallel.
    You would have a power of 75W or 175W. If we assume the price per module is 2K euro the total price would be 50K euro. You would also need a translation axis which is assumed to cost 5K euro.

  • Exposure new scanhead

    Hexastorm01/29/2019 at 21:40 0 comments

    Made an exposure with the improved scanhead today. Results look good, already at 100 microns before optimizing, exposure speed is around 2 mm/s. Still need to fix the stitching error, it result in a white line.

    Image was taken with a Leica DMS 1000. Machine is calibrated, measurements are accurate.

    Full overview of sample shown above, taken with smart phone.

  • Stabilization accuracy

    Hexastorm01/25/2019 at 14:47 0 comments

    Yesterday evening, I measured the stabilization accuracy of the scanhead. I repeated the following;
    enable the scanhead, stabilize it (get it in sync) sent out pixel 3600 and record the image with an exposure time of 50 ms.
    The result; spot is extremely stable. I measure a standard deviation over 21 measurements in the x- and y-direction of [0, 2.2]  micron.  Note that this is expected as the y-axis of the camera was parallel to the scanning direction.  I have added the measurements as rar file, see 21measurements.rar.


    Summarizing; repeatability in scanning direction after disable/enable scanhead is 2.2 micron.

  • Jitter removed

    Hexastorm01/23/2019 at 21:05 0 comments

    I have been able to almost remove the jitter.  I have added a prism to refract the light. Using the prism, I can position my diode closer to the focal point and ensure it is hit in the middle.
    I also realigned the first lens. I used a UV light, bluepoint2, with Norland61 and UVacryl2295 for final fixing. The prism is 7.5x7.8x8 mm. It was still in stock. The single spot is 25x25 micron.
    A spot created by four facets is 48x60 micron. The cross-scan error is 23 micron. The jitter is 35 micron. The facet error was set to 1/3200. In general, the lower the better.
    I still need to measure the lane-to-lane stability if this is done, I will proceed with experiments.
    In the image below a pixel is 4.8 micron. Note that the spot become less sharp at the edges, as predicted by my earlier theoretical calculations.


    The new setup with prism and photodiode.

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Discussions

Gravis wrote 02/03/2019 at 19:16 point

I'm also interested in the possibility of using a motor from a hard disk drive instead of a breaking down a polygon motor.  HDD motors are cheap to buy and (as I understand it,) contain an encoder and have screw holes which makes affixing things easier.

  Are you sure? yes | no

Hexastorm wrote 02/04/2019 at 08:48 point

HDD seem too slow.  They typically spin at 5400 or 7200 RPM.  At the moment, I can go up to 24000 RPM with polygon motor. For some applications, I would like 50000 RPM or 70.000 RPM, like the roadrunner sold by precision laser scanner. Also the motors are not too expensive, they are like 20 euros. I understand 20 euro's can still be a lot but if you look at total costs; you can better pay attention to other components.

  Are you sure? yes | no

Gravis wrote 02/05/2019 at 06:00 point

Oh, I had no idea you were planning on high speed.  Where can you get the motors in the 20 euros range?

  Are you sure? yes | no

Hexastorm wrote 02/06/2019 at 13:40 point

You can find polygon motors at alibaba (https://www.alibaba.com/showroom/polygon-motor-ricoh.html) .  The system is a proof of concept; for desktop PCB prototyping 2400 RPM is fine. If you plan to compete with Kleo https://www.youtube.com/watch?v=7R464iHaTQU . You will need at least 50K RPM.  An option would be to encase the prism and remove the air. This will reduce the drag. You could also fill the encasing with Helium as it has low drag and a high thermal conductivity.  Like the roadrunner the encasing windows would be tilted out of plane to minimize back reflections, see https://precisionlaserscanning.com/2016/03/road-runner-70000-rpm-polygon-scanner-solves-the-noise-problem/

  Are you sure? yes | no

Gravis wrote 02/03/2019 at 15:57 point

My suggestion for this project is to isolate the scanner from the 3 axis robot part so that the scanner could be made into a tool that can be changed out.  I would also ditch using BB's PRU and instead use a dedicated chip (and maybe a RAM buffer) and connect it via CAN bus.

  Are you sure? yes | no

Hexastorm wrote 02/04/2019 at 08:58 point

I intend to isolate the scanner, and design it for specific machines. I like the idea of having a dedicated chip. In the past I used a FPGA (Xula-LX25) with RAM as  bufffer. I can imagine there are even better options. The problem is that developing a dedicated board costs time, money and a lot of experience. Zeller made a very accessible code for the Beaglebone, so I went with that. You are looking at a proof of concept. It's a technology demonstrator. Anyway if you have recommendations; or some example code; feel free to share. 

  Are you sure? yes | no

Gravis wrote 02/05/2019 at 07:48 point

Considering this is a project where accurate timing is vital, I think an XMOS processor (e.g. XS1-L4A) would be a good fit.  Each 100MIPS processing unit is 100% deterministic with fast GPIOs.  I don't know the rate of data throughput you need but it may be easier to just cache to workload on a local FLASH chip than stream it.

  Are you sure? yes | no

Hexastorm wrote 02/05/2019 at 10:53 point

XS1-L4A is nice... but I rather like something with lot of support and examples... probably first gonna optimize the current code and balance my prism.

  Are you sure? yes | no

Gravis wrote 02/05/2019 at 20:37 point

XMOS stuff actually does have lot of support (https://www.xcore.com), examples (https://github.com/xcore/) and even an IDE but I somehow missed the part where you wrote that didn't want to build a custom board.  Sorry about that.  XMOS chips make it easy to glue things together since it's 99% software so it doesn't take too much skill to make a board with them.  Consider enlisting help to make a board as there is a good chance it will alleviate timing related issues.  Good luck! :)

  Are you sure? yes | no

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

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