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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, 3D printing or detecting eye diseases. The laser scanner uses a transparent prism instead of a reflective polygon. The project challenges the reader with why the concept of transparency is not more used in moving laser beams and business development (open-hardware)

The goal of this project is to develop the electronics and scan head for a PCB machine which can expose a PCB with a track width smaller than 100 micrometers, i.e. 4 mil. The PCB machine also has 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 electronics and software to cut boards with a spindle and expose it with a laser has been developed.
The current goal is to bring the quality of the scanhead to a higher level so it can be sold as minimum viable product.

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  (laser driver, 3x TMC2130 stepper drivers, PWM spindle and fan control)

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 idea is that throughholes are made with a spindle.  There is a project on hackaday where a PCB is cut with an EDM.
At the moment, the goal is develop the scanhead so it can be sold with electronics as MVP.


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


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

Electronics
PCB design

Hardware designs
CAD files

Literature Research
White paper (on Reprap)

Other Links

Official website

Failed kickstarter campaign

Adobe Portable Document Format - 5.57 MB - 06/13/2019 at 07:28

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 ofthe old firestarter and overview of layout. This board is no longer in use.

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

Preview
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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

  • Avoiding patents; a tutorial

    Hexastorm13 hours ago 0 comments

    Incidentally, I claim all patents in the world which use the concept of a galvo scanner or reflective polygon scanner either in claims or the description and do not mention the concept of transparent polygon scanning. I then rewrite this patent but now use the concept of transparent polygon scanning. I then claim I am not under patent as this would have been obvious for a Person Having Ordinary Skill in the Art (PHOSITA) and familiar with my work.

    Example 1: US7892474

    This is an interesting patent it describes something like Continuous 3D printing.

    Wait!  Claim 1 reads  "... comprising the step of Solidifying a photo-polymerizable material by means of mask exposure of a build area or partial build area in a building plane via electromagnetic radiation from a digital light processing/digital micromirror device projection system ...  "

    OMG using transparent prism avoids patent let's reformulate

    "comprising the step of Solidifying a photo-polymerizable material by means of refraction exposure of a build area or partial build area in a building plane via electromagnetic radiation from a transparent polygon scanner device projection system ...  "

    Example 2: US9079355B2

    Impressive, Envsiontec realized they could use a polygon scanner for polymerizing liquids. This is so obvious.. actually there was prior art by Riken in 1997.  OH yes now i see, Envinsiontec realized they could use laser diode. Hmm.. must have been that Yamaza didn't have laser diode at his time because would have been so obvious. Strange country USA but this company has a good legal department... Anywayz let's proceed with the claims...  Let's  have a look at claim 1:

     ."... and deactivatable ultraviolet laser diode and a rotating polygonal mirror "  ...

    OMG using transparent prism avoids patent let's reformulate

    " ... and deactivatable ultraviolet laser diode and a tranparent polygon scanner ..."

    Example 3:  EP3233499B1

    Nice patent, bioprinting...  claim 1... looks pretty rigid... no mention of galvo here
    But wait... these drawings ...... figure 1 and 2... they define as prior art a galvo using the LIFT principle...

    Oh no!!! they do have a nice claim but a description not even close of using  a transparent polygon scanner used to achieve the lift principle for bioprinting.. yep... look at this  nice video , just imagine my transparent polygon scanner sending a light pulse to the disk; exactly that's how I avoid the patent.

  • Glass tubes and laser scanning

    Hexastorm3 days ago 0 comments

    UV Light can be used to disinfect the material flowing in tubes. Infrared laser light can be used to heat specific particles/cells/droplets if the tube is made from glass. Here is a market report on UV disinfection equipment. A company active in UV disinfection is  uvo3. Transparent polygon scanning can be used in vibrometery, which can be used to measure fluid flows in glass tubes using laser doppler velocimetry. Laser galvo scanning interferometry can be used for flow velocity measurements through disturbing interfaces. Likewise a transparent polygon scanner can be used to measure flow in chemical processes.

    Ideally, the glass tube is square to minimize a lensing effect.

    Furthermore, an interesting option would to polymerize particles in the tube, or sintering takes place in the tube.  MIT patented this process in US7709554, but used a DMD projector and not a transparent polygon scanner. In addition, I claim the case the walls of the tube are created Teflon AF. This could for instance done on a micro-fluidic chip.

    The speckle pattern can measured created by shining in the tube. This process can for example be is used in the food industry to measure the water content in cheese or the composition of milk. The laser is pulsed and the time of flight is measured. This allows one to both record the amplitude and time phase spectrum of the material under measurement. The transparent polygon scanner is under an angle so the reflected light does not fully transmit back through the scanner but can be  measured by another device at the same edge of the tube, like a cmos chip.

    The transparent tube is made from teflon AF.

    added this section to give some more prior art.

    I claim the case that gasses are flowing in the tubes

    inkjet section

    There are various ways to create droplets e.g. piezo or using thermal expansion. I imagine that the transparent polygon scanner is used to create droplets. A problem with inkjet is that only fluids of low viscosity can be used. A  solution  is continious flow inkjet. Droplet can then be selected via the electric field. There has been research where droplets were selected with air. I claim a selection mechanism using a transparent polygon scanner. It could be used to detect, the speed and composition of the droplet or evaporate it.  A futher problem is the distance needed to go from a stream of liquid into droplets.  A transparent polygon scanner can be used to speed this up. It could also alter the heat per droplet and detect if the nozzles in an inkjet head are working.

    The hexastorm is used to measure a liquid film on top of fluid,

    Hexastorm is used to create a microfluidic chip with multiple channels. Droplets are ejected from the chip via the LIFT principle and applying thermal expension and the Hexastorm.

    A plurality of bundles used by a transparent polygon scanner are used in an optical tweezer to hold or capture falling particles.

  • 3D Glasses

    Hexastorm4 days ago 0 comments

    In my previous post, I outlined that I think that it might be useful to use a transparent polygon scanner for detecting eye diseases.

    Logically, a transparent polygon scanner can also be used in 3D glasses.  Reflective polygon scanners are used for creating a screen in a laser TV.

    A lot of companies are active in 3D glasses; e.g. Google Glass, Magic Leap, Oculus and Hololens.

    Colors could be created by coupling three lasers of different wavelength in the same bundle. At 50000 RPM and six sides the line rate is in the order of 5000 Hz. If you project a 1000 lines with a 1000 pixels the refresh rate would be 5 Hz., i.e 1 megapixel.

    Let's look into multiple options of solving this;
    Option 1:  Optical transformation
    Project a 1000 lines with 4000 pixels and transform it into 2000 lines at 2000 pixels using optical transformations provided by a combination of lenses, mirrors or surface waves.
    Option 2:  Miniaturization
    Scale down the size of the prism, using possibly transparent conductors (e.g. indium tin oxide ITO). Possibly, put it into a fluid, see Mirada technologies, to reduce the influence of vibrations or place it into a gas with a low drag. Due to the down scaling it will be much easier to balance and spin the prism. The angular momentum drops due to lower mass and radius, which implies lower energies at a fixed RPM. The fastest spinning disk ever made at 600 million RPM is also small. Optionally use two prisms if you want to scan in two directions.  Get hold of a Magic leap Glass and replace Magic Leap core technology; the fiber scanning display with the Transparent Polygon Fiber Scanning Display (TPFSD).  Couple in the light to the eye via WaveOptics as provided by companies like Enhanded World.

    Notes:
    I also challenge someone to make a Digital Prism Device (DPD) instead of a Digital Micro mirror Device (DMD). The DPD would consist out of transparent prisms which can be tilted from e.g. -12 to 12 degrees.
    I also claim the trade mark on Hexa Glass for virtual reality glasses which use a rotating prism to move laser bundles.

  • OCT: Transparent polygon scanning in Ophthalmology

    Hexastorm4 days ago 0 comments

    In the following, I would like to outline how transparent polygon scanning can be used to save lives. I again aim to create prior art to extend the freedom of use of transparent polygon scanning. 

    Figure 2 (from Wikipedia).

    Typical optical setup of single point OCT. Scanning the light beam on the sample enables non-invasive cross-sectional imaging up to 3 mm in depth with micrometer resolution

    Optical Coherence Tomography (OCT) is an imaging technique that uses low-coherence light to measure samples based upon the principle of light interference. It is used in the medical industry to detect cancer in tissues and diseases in eyes, e.g. the Cylite of Hewlett Packard. OCT is typically used to obtain information from a sample. In 3D printing it has been used to verify a print. For example, Photoncontrol used Optical Coherence Tomography and Raman spectroscopy to test the quality of bio-printed tissue, see 1. A startup, called Inkbit from MIT, is using it to create samples accurately. They print droplets with an inkjet head and then verify the position of these droplets using among others OCT.
    OCT has also been used to detect the adhesion between layers in a 3D printing process, see Non-destructive testing of layer-to-layer fusion of a 3D print using ultrahigh resolution optical coherence tomography.
    Due to the interest in this area, I decided to elaborate upon how OCT can be used in combination with a transparent polygon scanner. I claim that in figure 2 a transparent polygon scanner is used instead of a galvo scanner. I claim that in the optical path of the Hexastorm a beam splitter is placed after the aspherical lens and before the first cylindrical lens to enable the scanner for optical coherence tomography. I claim the use of a transparent polygon scanner for wavefront measurement in Ophthalmology and Optometry. The vertical measure of an eye ball, generally less than the horizontal, is about 24 mm. The current scan head has a scanline of maximum 24 mm, making it already close to dimensions required for eye ball measurement. I claim that possibly two transparent polygon scanners are used in ophthalmology and optometry, to move the bundle in two directions.
    An OCT enabled transparent polygon scanner might also be useful for 3D printing. Imagine that a small percentage of the bundle is scattered to the reference mirror and most of it used to go to the sample. It will then be possible to sinter powders or polymerize liquids at the sample location. A small portion of the beam will be reflected and refract back to the beam splitter and interfere with the reference beam at the photo-detector.
    This allows one to measure the photo-polymerization or sintering process during printing. I can imagine this is especially useful if the layer height is less than the wavelength. I can also imagine that this is useful during a process akin to Hexaforming (see previous post). A hand held device could be used to check the skin of a patient. An application would be laser surgery, such as eye surgery (Carl Zeiss Meditech) or tattoo removal and laser hair removal.
    The transparent polygon scanner could also be useful in a Raman microscope as galvo's are used by NanoPhoton. In two-photon point-scanning microscopy,temporal focussing can be used to increase the image rate for a transparent polygon scanner similar to a galvo setup. Another option is in vivo imaging with HiLo microscropy but then a transparent polygon scanner.

  • Carbon 3D patent avoidance, a process known as Hexaforming

    Hexastorm5 days ago 0 comments

    Recently, Carbon's 3D valuation exceeded 2.4 billion USD . This provided me with inspiration to again look at its intellectual property and create prior art to facilate circumventions of its patent.
    Carbon has a technique which it denotes as Continuous Liquid Interface Processing (CLIP) . Carbon uses a Digital Micro-mirror Device (DMD) to illuminate a photopolymer through an oxygen-permeable window made of a fluorpolymer such as Teflon AF. Teflon AF can be sourced from Biogeneral . Nasa described how a teflon AF sheet can be made. A supplier of chemicals can be found here .
    The permeation of oxygen through the window creates a persistent liquid interface, nicknamed "dead zone", where photopolymerization is inhibited between the window and the polymerizing part. Oxygen inhibition was an effect that was already shown to play a role by Denkari et al. in 2006 for silicon release coating invented by John Hendrik, see US7052263 (B2) . The "dead zone" in silicone release coating is so small that a peeling is needed to release the part from the transparent window. Hessel Maaldrink sped up the process by adding a force feedback sensor EP2043845B1 . Using Teflon AF and a polyuerethane Tumbleston et al. 2015 where able to extend the "dead zone" to approximately 30 micrometers. As such the part does not have to be peeled of from the optical window during the process and stair stepping is minimized. This allows for the production of flexible parts. Furthermore, the "dead zone" speeds up the viscous flow between two parallel plates, part and window, for the application of a new layer, see WO2014126837A2 , improving the print speed.
    I will now try to create prior art and formulate a work around for the Carbon patent to extend the freedom of application of the transparent polygon scanner marketed as Hexastorm.
    After studying the WO application of CLIP, I noticed that the European patent is different from the US patent. In the European patent EP2956823B1 claim one states ".. irradiating said build region through said optically transparent member to form a solid polymer from said polymerizable liquid while also concurrently advancing carrier away ..".
    As such, I claim irradiating said build region with for example a transparent polygon scanner while not concurrently advancing away the part, but discretely. The part is exposed and moves after a full exposure. Moving during an exposure is also not possible as Hexastorm exposes a line and not a plane.
    DMDs have a pattern/pixel rate of up to 20 kHz. Laser diodes can achieve a refresh rate in the order of 50 MHz. At 50.000 RPM and six sides, a transparent polygon scanner exposes at line rates of 5000 Hz. With a laser diode, the refresh rate is so much higher that it might be possible to alter the polymerization over much smaller distances. Stair stepping would be minimized even though the part is moved discretely.
    If it is not possible, the procedure would still allow for the production of flexible parts.
    The US patent, US 9216546B2, is wider in scope as claim one specifies "A method of forming a three-dimensional object, comprising the steps ...". The formulation using "steps" in US patent differs from "concurrently" in the European patent.
    In the US the process is also under patent if the part is not moved during exposure. Carbon as a result markets its technology as "digital light synthesis technology", although Continuous Liquid Interface Processing (CLIP) seems more accurate in the European union.
    Key in the US patent is that parts are produced upside down and moved away from a build surface which is not air. This is peculiar as the original patent by Hull in 1986 specifies both up and down projection in figure 3 and 4 respectively.
    As such, I claim the use of oxygen-inhibition in down projection, where the top is up, using a transparent polygon scanner. Again, the fast exposure of a laser diode might minimize stair stepping and the "dead zone" will simplify coating. Additionally,...

    Read more »

  • finished height system

    Hexastorm06/21/2019 at 15:32 0 comments

    The proof of concept module was hard to build. I used shims of 100 micrometers and a tweezer to set the height of the laser.  In the next module the build procedure is simplified so it is easier to scale the amount of single bundle transparent polygon scanners in the world from 1 to 10, and make a 10x improvement.
    The procedure is as follows; set height laser, set horizontal position laser by first cylindrical lens, set height diode..  Other components still need to be added an whole system needs testing.

  • disassembled POC head

    Hexastorm06/18/2019 at 21:31 0 comments

    I want  to simplify the fabrication of a scan head. I disassembled the head so I could reuse the components. A colleague advised me to glue the lenses with CAF3 (silicon glue) to the plastic posts. This was good advice, lenses were very easy to take off. I was worried that i had to order the components anew.

    Components are ready for the next iteration.  Some remaining glue can still be seen.

  • Detector bar to allign scanheads

    Hexastorm06/14/2019 at 15:35 4 comments

    As always, I would like to generate some prior art to extend room of operation.  The following concerns the situation that multiple scan heads are used in a single machine. For an example see Kleo which uses 288 bundles by Carl Zeiss.



    If multiple scan heads are used, a challenge is to align these heads. The position of the laser in each head has to be known exactly.
    One way of doing this is by moving a camera under the scan heads and collecting position information per laser. The laser would project directly onto the CCD / CMOS chip and its position would be determined. This is however expensive as it requires an extra stage with camera. The chip has a finite size of for example 5x5 mm and has to be moved.

    Another solution of doing this would be to add a bar from diffuse glass, e.g. opal glass. The light would be scattered in this bar and reach the edges of it. At the edge of this bar there would be a photodiode. The bar could be made of opal glass. One might think that this  bar must be narrow so the position can be detected up to 10 micrometers accurate in one direction. The current photodiode used to calibrate the laser is, however, also not narrow.  You can simply use the rising edge of the signal recorded by the photo-diode used to monitor the diffuse opal bar.
    The stage upon which the scan head is mounted then moves in  orthogonal direction to this bar.
    By turning on the laser and moving it over the bar. The position can be determined exactly in that direction. It might be needed to add a cap-around the bar to minimize stray light. This is also done for the photo-diode  in the scanhead.
    Still, I need two dimensional information. I also need to know the position of the laser diode at the bar.
    To do this I could use multiple photodiodes along edges of the bar. They would all measure a signal if the laser hits the bar. The signals will, however, arrive at different points in time. This allows one to determine the position of the laser along the bar.

  • Designs

    Hexastorm06/05/2019 at 17:11 0 comments

    I have uploaded the current designs of the Hexastorm to hexastorm design.  The project goal has also been slightly altered. The current focus is to develop a scanhead which can be sold for R&D purposes.
    This scanhead in combination with the Firestarter cape and software would then be the MVP. The first target customers are R&D institutes, technical enthusiasts or corporates active in for example the field of 3D printing and PCB manufacturing.
    My current target is entities incorporated as business. The advantage of business customers is that they don't have to pay income tax before the purchase of scanhead and often can deduct value added tax.
    This can easily save you up to 60 percent in price in countries like the Netherlands, as VAT is 21 percent and income tax is around 52 percent. In the Netherlands you also have the change of multiple subsidies like WBSO. Imaging technologies are seen as a "key technology" which makes you applicable for all kinds of grants / collaborations.

  • Tested board

    Hexastorm05/29/2019 at 01:03 0 comments

    Good news! I have been able to test the Firestarter V2 board and most functionality works (still have to test the laser/photodiode but don't expect trouble here). Progress was slow as I had to port the TMC2130 Arduino library to the Beaglebone. You can find the ported library here, it works.
    A challenge was that with multiple SPI devices you have to acknowledge a command by setting and clearing the chip select pin. Although obvious, this took me quite some time as it was done automatically for the default chip select pin and I did not have the right settings which made it a confusing bug.

    I left the laser scanner in the car during day hours. The car became so hot that the PLA became more flexible and the scanhead started to warp. It could be that the laser is still aligned as the plate was reinforced with a metal bar but it doens't look good.
    I started a fork of BeagleG for the Firestarter V2 board.  Making the board ready for BeagleG seems quite easy.  I hope to finish testing soon and will then commit it back to the main branch.

    The Firestarter V2 will then be able to run two firmwares; BeagleG and my Python fork of LDgraphy. This will bring me a lot closer to start making PCBs with a spindle and the Hexastorm :-).

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Discussions

Conny G wrote 05/27/2019 at 12:36 point

What material is the prism made from? How is it manufactured?
Can i make it in my "maker lab"?

  Are you sure? yes | no

Hexastorm wrote 05/29/2019 at 11:39 point

Prism has the following properties; 2 mm thick, 30x30 mm square,  faces 60/40 < 5 arc min, chamfers 0.10 – 0.30mm, edges Polished 60/40, top bottom polished 60/40.  Price is in the order of 40 euro per piece at a minimum order quantity of 10. You will have to discuss details with manufacturers in China over Alibaba. I made the first in a maker styled lab, so yes it can be done.  Note that it will take you significant time. I mean getting the parts with some delay for customs can already set you back at three weeks lead time in Europe. You would then still have to assemble and align the scanner, build a PCB, integrate upon a frame and do some electronics testing. I am currently working at laser scanhead which will be sold to R&D enthusiasts for testing.

  Are you sure? yes | no

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. 

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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.

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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 ..

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