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open hardware fast high resolution LASER

bringing additive manufacturing to the next level

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An open hardware fast high resolution LASER suited for Printed Circuit Board (PCB) manufacturing or 3D printing. The laser head can be used to write to a substrate. I am working on reading from a substrate.

The goal of this project is to develop a laser head for 3D printing or PCB manufacturing which uses a rotating prism and is easy to assemble.
Cyanotype paper is currently used as it can be developed with water.

Specifications

Specifications are determined by exposure onto a camera without lens and OpenCV. More technical details are available in the whitepaper or the business case pitch.

  • wavelength: 405 nm
  • rotation frequency:  up to 21000 RPM, current 2400 RPM
  • line speed: up to 34 meters per second @ 21000 RPM
  • spot size FWHM: circular, 25 micrometers diameter
  • cross scanner error: 40 micrometers  (error orthogonal to scan line)
  • stabilization accuracy scanning direction:  2.2 micrometers (disabling/enabling scan head)
  • jitter: 35 microns (error parallel to scan line)
  • duty cycle: 47%
  • 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
  • prism dimensions: 30x30x2 mm

Electronics

  • FPGA Ice40HX4K with Icestorm toolchain
  • Firestarter cape  (laser driver, 3x TMC2130 stepper drivers, PWM spindle and fan control)
  • Raspberry 4

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.
I am currently trying to bring the product to production. I also will try to read information from the substrate ( this is actually quite easy).

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

Acknowledgement
Special thanks go to Henner Zeller for his work on LDGraphy. The electronics and software in this project helped me a lot with constructing the laser scanner, see video.
The initial idea of using prism for laser scanning originates from Dr. Jacobus Jamar. This system uses a plurality of laser bundles in a thicker prism under an angle.  TNO, a research institute of the Netherlands, still pursues this idea, in an entity known as Amsystems.
The current gateware relies on Nmigen and some components from Luna. This is the work of white-quark and ktemkin.

Software
Hexastorm fork of LDGraphy
Optical design
old FPGA code

Electronics
PCB design

Hardware designs
CAD files
Cartesian frame was donated by FELIXprinters.

Literature Research
White paper @ Reprap

Other Links
Official website

analysts_presentation.pdf

Pitch intended for analysts who want to get a brief overview of the key markets prism scanning will disrupt.

Adobe Portable Document Format - 781.75 kB - 09/24/2019 at 08:39

Preview
Download

pcb_scanheadfixed.pdf

schema of the pcb for the scanhead

Adobe Portable Document Format - 45.07 kB - 09/23/2019 at 13:51

Preview
Download

bomlist.ods

bill of materials for the photodiode detector

spreadsheet - 13.26 kB - 09/23/2019 at 13:33

Download

scanheadpcb_bom.ods

bill of materials for the scanhead pcb

spreadsheet - 13.04 kB - 09/23/2019 at 13:33

Download

firestarterbase_bom.ods

bill of materials for the cape of the beaglebone

spreadsheet - 14.97 kB - 09/23/2019 at 13:32

Download

View all 8 files

  • 1 × prism, 30x30x2 mm edges parallel to < 1 arc minute 40pcs @ 12 USD per piece @ ebetteroptics
  • 1 × Raspberry pi 3B / 4 at least 35 USD
  • 1 × BPW34-B (photodiode) 7 USD (works also without a blue enhanced photodiode)
  • 1 × Laser diode housing chrome with copper 4.9 USD
  • 1 × BDR-S06J 405nm, 500-600mW Blue-violet Cut-pin Laser Diode 30 USD

View all 12 components

  • holographic imaging

    Hexastorm2 days ago 1 comment

    I started with improving the optical layout of the Hexastorm. Luckily, there is a company from Colombia, cihologramas.com, who made an open-source optical package for optics and also
    provided some instructions on how to integrate this into FreeCAD. You can seen the result below.
    I will explain the whole simulation in a different video.

    Anyhow, what is even more interesting is that they also seem to user laser writing to a substrate to  create holograms.
    See the video below

    They report a resolution of  25400 dpi, which is 25.4 (mm)/ 25400 = 1 micron.
    Production speed is 55 cm^2 per hour, i.e. a square sided 7.41 cm.
    These are 74100 lanes with a length of 7.41 cm, which is 1.54 m/s .
    Most likely, they use a galvo scanner. It might be done much faster with a prism as well, but I would have to recheck the whole design. I will outline in the next video, how you can make a design, in the first place.

    Here is one of their holograms;


  • digital holographic microscopy

    Hexastorm05/29/2021 at 11:40 0 comments

    I found a technique, i did not consider earlier.

    Digital holographic microscopy (DHM) is digital holography applied to microscopy.

    I think prisms are suited for this domain. An optical wave is split in two. One part is used to illuminate a sample from the bottom with a plane wave. The other part illuminates the sample at a specific point. The waves interfere and the reflected light is measured by a camera. A prism could be used to to scan this spot. It would require a very fast camera but these do exist.

    It can be used in reverse as well for triggering reactions like polymerization. This requires something like a digital micromirror device, these are typically slower. So that might not be a good fit with current technology.

    There is a very nice old video on holography on YouTube

  • New video

    Hexastorm05/21/2021 at 16:44 0 comments

    I created a new video, where you can see the exposure and the result.

    This makes it much easier to see where the project is at. It is really easy to add measurement, see this excellent video.

    My current aim is at bringing the module to production. I also plan to add confocal. A unique property of laser scanning is that it can read and write at the same time. This is a real advantage compared to other projection techniques like LCD.

  • Gateware working with motion and laser

    Hexastorm05/14/2021 at 16:23 0 comments

    Just a quick update; I am now finally able to make exposures with the new nmigen gateware.

    There are a lot of improvements in the new tool chain with respect to ldgraphy on the beaglebone.
     - Slicing can be done on the Raspberry.
     - Motion can be done with acceleration/jerk profiles
     - Steps per scanline can be altered and is not fixed
     - Whole code base is one language; Python
     - It is much easier to align the optics; 

    the design of the laser head is improved and
    there are algorithms to fix the alignment and calculate; spotsize and cross scan error


    I will make a video for the complete process soon.

  • Ideas & progress

    Hexastorm04/17/2021 at 11:56 0 comments

    I like to keep a record of related ideas I cross over on the web and the involvement of the Netherlands in laser scanning with prisms. 

    Related Ideas

    Various hackers have been active in the field of laser scanning microscopes. There is a project
    on Hackaday (BlueBeam).  A Swiss hacker space, Gaudilabs build one.
    Most are based on components of DVD drives (link to a tear down).
    Loetlabor also did an exceptional write down of DVD-based laser scanning microscopy.
    They even used a FPGA core to control the laser.
    Scanning this literature, I found the following figure;

    It shows how the focus is obtained using a four channel photo-diode. One targeted at 850 can be found here Vishay K857PE.  It could be nice to integrate this concept in the laser head. Possible areas would the current place of the photo-diode. Another option would be to place a beam splitter on the point where the laser is colimated, i.e. after the first aspherical lens and before the first cylinder lens.

    All this thinking about imaging, made me think of another point of improvement.
    Using the camera of an optical mice to record or track the laser beam.
    Optical Mice, have camera's which are 30x30 pixels, e.g. ADNS-9500 S9500. The price is in the order of 3 dollars.  The camera's might be large enough to image the spot formed by the laser.
    At the moment, I use a CMOS camera from Arducam (OV9281) . These are great but much more expensive (in the order of a 100 dollars). Circuit boards are available for this chip.
    Another point of improvement, possible with this chip might be to use it to track the position of the laser head.  A second laser, infrared, would shine on the substrate.  This substrate could be the platform used for printing or the underside of the top of the box that is used to enclose the printer.
    Via speckle the position of the laser head can be actively tracked.
    Finally, MIT made a nice video of the LaserFactory One. I really like the video. It shows, how extrusion and lasers might be combined one day.  Note, MIT doesn't use laser scanning and moves the bundle using a gantry.

    Netherlands

    The Netherlands is relocating more assets to laser scanning. Recently, AMSystems got featured by TNO,
    in it's line up of 25 spinoffs.   AMSystems, as far as I know, aims to build a laser scanner with a plurality of laser bundles per prism.  They adapted their European patent.
    Hexastorm no longer falls under the main claim, as it uses a single bundle, which is really good news.

    The Netherlands also supports/is founder of some affiliated startups.
    Keiron Technologies, is basically a laser startup which uses laser scanning in combination with laser induced forward transfer. They are affiliated with TNO.
    Inphocal is using a Bessel beam in laser scanning.  There is also a startup using Bessel beams for communication known as Aircision.
    TNO is also setting up a new startup in STED lithography.

    All these startups, including AMsystems, are related to HighTechXL.  I think it is very possible, one or more will use or are using prism scanning.
    I have looked for patents but so far did not find a lot.

  • FPGA CNC control with nmigen

    Hexastorm04/07/2021 at 16:09 4 comments

    It has been a while, the last months I worked on adding motion control to the FPGA.
    I ended up starting from scratch. I wanted to move from migen to nmigen and structure the FPGA code better.
    A proof of concept is seen in the very rough video below;

    Motors are sampled at 1 MHz. The circuit operates at 50 MHz.  The system can account for; jerk, acceleration and velocity. 

    The software consists out of the following elements;
       * SPI command interface  (receives command and words, copied from Luna)          
       *  Transactionalized FIFO (buffers instruction in sram, copied from luna)
       * SPI parser (basically an extension of SPI command interface, with specifics for my                            
                            project)
       *  Dispatcher; picks up commands from the FIFO buffer and dispatches instructions to                            
                              actual hardware
        * Polynomial integrator: creates pulse train for stepper motors; basically you send the                        
                                               coefficients for the polynomial and the number of ticks in a segment.


    The motor follows the path, coef_0 * t + coef_1 * t^2 + coef_2 * t^3.
    The trajectory of a motor is divided in multiple segments where a segment length is typically 10_000 ticks. If is longer, it is repeated. If it is shorter, this is communicated by setting ticks to lower than 10_000. I looked into using bezier curves for motion control. The main advantage is that they are calculated on the circuit straight from actual positions using de Casteljau Algorithm. My FPGA does not have a hardware multiplier, so I didn't implement it.
    At the moment, I will focus on adding the possibility for controlling the laser and "finally" do more experiments.

    Code is available online, it was quite a lot of work. Especially the boring stuff which "should be easy" took a long time. Thanks go out to Kate Temkin and her work on Luna.

  • Alginment procedure

    Hexastorm01/23/2021 at 14:16 0 comments

    Made a video of the alignment procedure with new updated tool chain. I moved away from the PRU of the Beaglebone to the FPGA and replaced the ueye camera with an arducam. This sounds easy but still took me a year :-).

  • DNA Laser printing & COVID

    Hexastorm01/19/2021 at 16:49 2 comments

    Recently, I was reading upon the character-by-character reconstruction of the BioNTech/Pfizer SARS-CoV-2 Vaccine .
    Most of us, will end up with this in their bloodstream so I thought it was rather interesting. It turns out there was a startup which produced DNA using laser printing . Austen Heinz gives a good presentation of this process below, scroll to time 10.24 min

    The startup Cambrian Genomics was founded by Mr. Heinz in 2014. The startup no longer exists and seems to have faced many difficulties. They did manage to raise over 10 million USD. Austen Heinz committed suicide at the age of 31 on May 24, 2015.
    His patents are still around, see US 10,822,605 B2 which got awarded in November 2020.
    As there are still people funding the patents, there must be people working on it. I looked into the patents for details on the required accuracies. You need optics which provide an accuracy of around 1 micron.  This accuracy could be possible with prisms, if you have a reasonable budget. Process uses laser induced forward transfer or laser catapulting.

    Quote from patent;

    Methods of using emulsion-PCR derived beads by the present assignee have been based on the fact that the bead itself serves as a decent ablation substrate for the approx 1 microJoule nanosecond laser pulse used to induce transfer.
    Beads from 1 to 10 micrometers are easily and specifically ejected by focusing light into their plane.
    Although ejection optics disclosed by the present assignee can target features as small as 600 nm, it is desirable to generate slightly larger, more disperse 1 micron clusters for use with initial prototyping.

  • Freecad Assembly Design

    Hexastorm01/06/2021 at 15:51 0 comments

    I have made an assembly design of the laser scanner in Freecad using the new assembly 4 workbench.

    I am really happy with this workbench. It really helps with the open-hardware concept of the project; without these tools it would not be possible to give other people the ease of use to adapt and add their modifications.  Companies like Prusa Research are open source but not open-hardware as they don't provide access to the assembly drawings. They might do that in the future with these new tools.

  • volumetric 3D printing

    Hexastorm01/06/2021 at 14:19 0 comments

    As described on Hackaday and Sci-hub, a new volumetric printing method has been described which uses two colors.
    A light sheet with a 375 nm laser diode and DLP projection between 450-700 nm.

    The prism scanner can also be used to accomplish this. Basically, you can intersect the projection of the prism scanner with a laser sheet or line.  The prism scanner could operate at 550 nm and the light sheet at 375 nm. It would allow you to solidify resin at the intersection and not at the top of the resin bath.

    Note that if you project a resin bath from above (say from air). The top surface of this resin bath is NOT even. In fact it is wobbly, due to all sorts of surface effects. This would be circumvented by this new technology, as the top of the resin bath is not solidified.  An alternative for this would be to use a process akin to Continuous Liquid Interface Processing (CLIP) (here you also don't solidify the top due to oxygen interaction).
    Back to Xolo, they might infringe patent US10843410B2, there seems to be no patent in Europe... The patents claims something very similar to what Xolo is doing.

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Discussions

Hexastorm wrote 12/30/2019 at 15:53 point

No it wouldn't work.. you need edges polished, not the top and the bottom.
I am not shipping out prism at the moment as they r not balanced yet (working on this). I am also working on a FPGA toolchain, will post an update on my progress here soon.

  Are you sure? yes | no

Ben Wishoshavich wrote 10/27/2019 at 04:56 point

Can you recommend a specific polygon motor module on alibaba? I don't know if there are any differences and I'd like to order one. THanks!

  Are you sure? yes | no

Hexastorm wrote 10/27/2019 at 13:37 point

Yes, you should buy exactly this motor https://nl.aliexpress.com/item/32824649951.html . It uses the NBC3111 chip. I had problems with other motors. Make sure you buy at least 2, although they are quite hard to break.

  Are you sure? yes | no

Ben Wishoshavich wrote 10/23/2019 at 21:59 point

Dude, this is some pretty awesome work. I'd love to help refine some of the manufacturing and board designs, let me know how I can best help

  Are you sure? yes | no

Hexastorm wrote 10/24/2019 at 17:55 point

Thanks! There are two other people who have shown interest. I need at least 10 people to do a run as I have to buy the prisms in bulk. Turn around time would be significant. Producing the prism takes at least a month.
I am fixing the low hanging fruits at the moment. It is hard to help with these as you don't have a laser head. I am building a new one but there is still only one in the world :-).
Things you could look in to;

- a better alignment system for the laser; this uses four screws and is over dimensioned --> see my free cad design files

- a better alignment system for the cylinder lenses; the screw system is not really comfortable --> see my freecad design files

-  how do i put my state machine on an fpga; I have been looking into https://github.com/m-labs/misoc as a replacer for the beaglebone.
This task seems rather complicated but I guess this knowledge could be really help full. The statemachine now runs on pru of the beaglebone and is limited at around 2 MHz.

- how do i balance the prism; i have done some preliminary experiments but still works needs to be done. You could also try to figure this out with a regular polygon motor. Add an imbalance and try to analyze this.

- the slicer or interpolater can only be run on a computer, as it overflows the ram of the beaglebone https://github.com/hstarmans/ldgraphy/blob/master/interpolator/interpolator.py . Remove this problem, optimize the code.

In the mean time, I am cleaning up the code, building a second head and still have to do more experiments.
I am also waiting for news on the hackaday prize. That's also why I have been quiet on the blog.

  Are you sure? yes | no

Ben Wishoshavich wrote 10/24/2019 at 22:57 point

I'm wondering if there isn't a BLDC motor that could be substituted for the polygon motor, hopefully something that is more available. And then I'd need an encoder. I'll take a look at this, although I suspect going greater than 20k rpm requries air bearings and a custom design.

The rectangular prism does seem to be a challenge. I'll let you worry about that. Out of curiosity, do you know how much it'd cost for a custom order?

An FPGA should be able to handle the state machine. I'm working on the FPGA that's in the Hackaday Superconference badge, and it's got an open toolchain. It might be overkill though. The ICE40 may be better(and cheaper). I might be in the minority in that I'm not sure this is a huge priority, as your electronics are pretty cheap. It's probably a pretty significant time sync to rewrite the assembly for the PRUs into a state machine. I'd probably focus on a command and control system to interact with GCODE or something else.

 I could jump into the MCAD, but I only know Solidworks. I suspect someone else might be better suited for that.
At work, we have specifications for balancing motors for EVs. The most relevant standard is ISO1940. Let me know if that's useful for you. Usually a balancing machine is used to detect vibrations while the part is rotated. They're pretty rare and fairly expensive though. They do make some simple ones for balancing quadcopter props you could look into. Usually you have to add or remove material in a specific spot to make it work.

I already have some of the parts you've used. Perhaps it won't be as hard to duplicate some version of this as I expect.(expect for that lens).

  Are you sure? yes | no

Hexastorm wrote 10/25/2019 at 17:13 point

-  i wouldn't substitute the motors; they have been used in this application for years by a large industry. Rotating polygon mirrors are produced in the tens of thousands. Motors can handle up to 21000 RPM.  This is more than what is needed at the moment, 2400 RPM, as the beaglebone can't go faster.
- custom order is around 500-600$ and MOQ is 10. for the prisms
- Henner zeller wrote a GCODE parser for the beaglebone called beagleg; my idea is that this used and you simply flip the machine between gcode mode and laser writing mode
- never heard of this standard good tip
- all parts are easy to obtain including lenses, motor etc; the only challenge is the prism and time. You will need time :-)

  Are you sure? yes | no

rajhlinux wrote 01/01/2021 at 08:17 point

well you can count me in, i'm interested with this project

  Are you sure? yes | no

Robert Mateja wrote 07/31/2019 at 11:48 point

Congratulations on winning Hackaday Prize 2019!  (at least in my opinion)

  Are you sure? yes | no

Hexastorm wrote 08/01/2019 at 09:30 point

Robert, thank you for supporting me! Winning the prize would be amazing.  My current target is to get other people to try out the technology, I am really trying to make it more accessible. I hope I can show an improved prototype of the scan head soon.

  Are you sure? yes | no

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.   You will have to discuss details with manufacturers in China over Alibaba. I made the first in a maker styled lab, a description of the process is in this log https://hackaday.io/project/21933-open-hardware-fast-high-resolution-laser/log/167433-how-to-be-transparent

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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

rajhlinux wrote 01/03/2021 at 13:24 point

This is a good idea, but honestly I think the best thing is to focus on getting the precision as perfect as possible. There's no consumer grade PCB maker device that can give traces/spaces resolution down to 0.01mm. It's crazy we are still using tonner transfer and UV exposure. I'm planning to build a CNC gantry made from granite, magnetic actuators and air bearings to get the most accurate, friction free, repeatable long term PCB manufacturing with >0.7 traces and spaces. But yes, would be nice down the road to have the scanner head removed for another tool... but for now precision is priority. Precision & Resolution is the reason why this project brings my interest and everyone here.

  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. 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 for the current spot size and line length.

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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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