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Thread: bare bonz laser projector

  1. #21
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    Some things to help you understand:

    A Galvo Scanner... Image from Cambridge Technologies web site. This is a high end device, typically used for laser based machining, not an inexpensive one.
    ~
    The next image is two galvos with mirrors in a scan head, this lets you do X-Y deflection, taken from the Scannermax web site,
    ~
    The third image is conceptually what is going on.
    ~
    The fourth image, is a oscilloscope screen shot of the position feedback signals from a high performance scanner pair, showing you the movement occurring behind a projected image.
    Note the bright spots and some overshoot at the corners, this is a well tuned and accurate scan pair, projecting the standard test pattern at 60KPPS (Image Laser-FX.com, probably taken by L.M. Roberts) . The forth image is the same thing as the eye sees it, with the laser gated on and off as needed. The image is not geometrically corrected, as a test was going on at the time, for something else. The image is about 15 years old, and things are a lot better now. This is a multiple exposure trace of the position signal, its a bit blurry from filming off a scope screen. See where it dwells at the corners? This is the software adding a correction so you see a sharp right angle projected. This is without the "retrace" being blanked. The retrace is the mirrors moving to the next projected position.
    ~
    The fifth image is the same test pattern, but projected by a different system, in Laser, so you can see the difference between what goes on "Behind the scenes" with the mechanical motion, and what actually happens on the screen.
    ~
    The green Ilda Test image is shot on a pair of hand made galvos, by a brilliant technologist who's screen name is Elm Chan, if home made galvos and home made scanner amps can do that, imagine how sharp a good modern system can be.
    ~
    The sixth image is what you would get, in terms of overshoot, if you scanned an image direct from a CSV without correcting for galvo characteristics in software, or without "pulling points".
    ~
    The seventh image with the red bar, shows tangent distortion, which is a curve that occurs naturally any time a mirror on a shaft is used to scan light. This is one of the things we correct for in software. It does not affect the center to outer two thirds of an image much, but it does catch the outer edges at wide angles. Easily corrected for in modern software. Your seeing a raw, uncorrected image there.
    ~
    edits done, I need to get back to work.
    !
    Steve
    Attached Thumbnails Attached Thumbnails Galvo Image.png  

    Cambridge Head1.png  

    506_SMScanner1.jpg  

    Galvo Concept.png  

    GalvoPositionSignal.jpg  

    Galvo 6210_50K_30deg_squarewave_closeup.jpg  

    Elmilda12k20d.jpg  

    TanDist.png  

    ILDATESTpl.jpg  

    Last edited by mixedgas; 05-31-2017 at 11:15.
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  2. #22
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    Quote Originally Posted by chris64 View Post
    I already made a progam that designs this. I input on a spreadsheet the latitude and longitude. It produces all of the x and y cordinates. I have several programs. One on these programs will read this data on a csv or ascii file and will draw it in cad. I'd like to do the same to a laser projector.
    Perfect. This is the information we needed.

    OK, you can still use your software. The key is the final CAD output. *THAT* image can then be used to create the ILDA frame file that the laser projector will display for you.

    Once you have your completed sundial design image loaded into the laser projector software as an ILDA frame, you can display it on the projector. But before you do that, you can tell the projector to display any number of standard test patterns first - these can be used to tweak the geometric correction settings until you get a perfect reference image. At that point you can switch over to your sundial image, and it will be projected on the ground correctly without any distortion.

    Now your gardeners/landscapers can get to work!

    Couple problems I see:

    1) If the image is 6 meters square (more or less), the projector is going to need to be mounted fairly high and/or far away from the work area. Given that positional accuracy is also very important, I'm inclined to suggest something like a scaffold, rather than a simple tripod stand that could rock back and fourth a few cm at the top (causing potentially larger shifts in the image many meters away).

    2) Brightness will be an issue if you're planning on doing this during daylight hours. You will be competing with the sun, and that's hard - even for a laser. This means you will have to use higher power lasers, and that leads to...

    3) Safety is a big concern. Anyone who looks back towards the laser projector could potentially be exposed to dangerous levels of light. True, there are ways to make the beam eye-safe (by diverging it, for example), but this also makes the lines on the ground wider, and it might also make them more difficult to see. There are some simple tests you could perform to see how well it will work though... Another alternative would be to have everyone wear protective laser goggles, but those get expensive fast.

    Quote Originally Posted by chris64 View Post
    My sundials are very accurate.<snip>
    This dial was accurate to within under 1 minute.
    However, landscapers are not very accurate. They often make my dial accurate to within 1 hour.
    So your hope is that by projecting a perfect image of the sundial to be constructed, you can increase the accuracy of the landscaper's work, right?

    In that case, the accuracy of the scanners is probably not an issue. Steve's posts above detail some of the limits of scanning technology, but if you only need to be accurate to, say, plus or minus 2 or 3 centimeters over a 6 meter square pattern, then the limits he mentioned won't be a factor for you.

    Adam

  3. #23
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    LaserBoy knows how to read DXF files and can properly render the following drawing ENTITES

    POINT
    LINE
    CIRCLE
    ARC
    ELLIPSE
    POLYLINE
    LWPOLYLINE
    TEXT

    So if you can get to a DXF file that uses these drawing ENTITES you can import that DXF file into LaserBoy and use LaserBoy to optimize the drawing for laser display.

    Also, if you upload an example of the CVS file you get, maybe there is a simple way to edit it so that LB can read it directly as a text table.

    Can you describe the format of your CVS file? Do you know how it works?

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  4. #24
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    My friend in OZ got back to me. I just replied to him with your concept. He knows a few guys in Brisbane who do shows. He'll try to link you up with a appropriate person to help you, or at least get you a demo of a system. This may be as simple as renting the gear from an existing Laserist, who knows.. Once he replies, I'll forward everything. My friend sells gear, so he can help you if you choose to build your own. Importing lasers to OZ can be a pain from Australian Customs , so it helps to know some one who does it. The rest of the gear comes in, no problems.
    ~
    If you can find an old enough PC with a DOS window, I just sent you a email copy of a CSV to ILDA converter that was written for me. The source file needs to be in the same directory as the executable. You'll need to scale your data to a value between +10,000 and -10,000 for the X and Y axis, set the Z value to Zero for a two dimensional ILDA frame. Z in laser is like 3D wireframe CAD, its used to add perspective, setting it to Zero puts your data in the middle of the 3D universe, where it shows up as a two D flat object, which is what you probably want.
    ~
    Format is NNNNNN, XXXXX, YYYYY, ZZZZZ, w XXXXX, YYYYY, ZZZZZ, here N is the total number of points, X is the axis location of a single point and so forth Each triplet of X,Y,Z values denotes a single point in the image. Instructions are included, and you can download an ILDA viewer to see the raw results. Try to stick to groups of 750 to 1000 points maximum.
    ~
    You can then hand that 2D ILDA file to a Laserist for test. They will have to add in the blanking, anchor, corner, and guide points, using their software's optimization function, or by adjusting by hand.
    ~

    Steve
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  5. #25
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    Quote Originally Posted by mixedgas View Post
    If you can find an old enough PC with a DOS window, I just sent you a email copy of a CSV to ILDA converter that was written for me. ~
    If you don't have an old PC, DosBox is a great emulator for running old DOS stuff, and it's free.

    https://sourceforge.net/projects/dosbox/

  6. #26
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    Accuracy is my priority. Viewing the whole image would be nice but it isn't neseccay. I certainly wouldn't trade this luxury at the cost of accuracy. I want the drawing within 3 millimeters. As I look further, I'm sure galvos won't do it.

    I figured out what I'll do. I'll make two tilting mirrors the same as the galvos projector would do. I'll make this myself. I'll make the mirrors tilt via a 50 to 1 worm gear driven by a stepper motor. I'll have to make the software for this. This laser will be VERY slow. (perhaps 4 minutes to view the entire sundial) But like I said, that doesn't matter. I must have it accurate.

  7. #27
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    Quote Originally Posted by chris64 View Post
    Accuracy is my priority. Viewing the whole image would be nice but it isn't neseccay. I certainly wouldn't trade this luxury at the cost of accuracy. I want the drawing within 3 millimeters. As I look further, I'm sure galvos won't do it.

    I figured out what I'll do. I'll make two tilting mirrors the same as the galvos projector would do. I'll make this myself. I'll make the mirrors tilt via a 50 to 1 worm gear driven by a stepper motor. I'll have to make the software for this. This laser will be VERY slow. (perhaps 4 minutes to view the entire sundial) But like I said, that doesn't matter. I must have it accurate.
    Don't under estimate the accuracy of laser. The issue I see it is more one of repeatability and for that you'll need very good galvos. If you only want to trace it once slowly, you can do that with galvos. However, the issue of drift might still be there because probably what you're not understanding is a laser line is not a constant line, it is pencil thin beam:




    that is scanned repeatedly back and forth and it's persistence of vision (which Steve mentioned above) that causes you to see a line. However, what's really there is a dot. Everything you see projected with laser is simply a single beam in the form of a dot at the surface end, that's being moved quickly (scanned) to produce lines through persistence of vision.

    Lasers are used for many precision display purposes with geometric conversion, eg someone here practising laser projection mapping at home:



    It's as Steve explained above, the accuracy will depend on the quality of the galvos and more importantly their repeatability so they don't drift over time.

    For that, I'd recommend Pangolin Saturns or failing that some quality Cambridge. I'm going to take a punt and say Saturns are probably your best bet.

    As for using stepper motors and your own mirrors, I think you'll find it difficult to achieve the accuracy. It's stepper motor and mirror combinations that are in the cheap laser projectors, and are bettered by galvos. The distance from laser to surface massively magnifies any error and any small change in mirror angle, literally fractions of a degree, with steppers or galvos can cause visible changes in position. That's going to be your issue and to that end, galvos are far more precise than steppers. If they weren't, we'd all be paying thousands for steppers and hundreds for galvos.

    The other factor you can control is distance from projector to surface, the shorter you keep it, the less pronounced and drift. If you're doing this in a factory, there shouldn't be a large distance and one thing to consider with a permanent installation is don't rule out mounting the projector on the ceiling pointing vertically down - needs less correction and reduces the distance to the surface.
    Last edited by White-Light; 06-01-2017 at 00:59.

  8. #28
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    That's funny, from the bottom of the river valley, at what used to be called Settlers Landing in Cleveland, I could consistently drop a beam into the top spire of Terminal Tower about a mile away, all evening, with no readjustment. That was with stock 6810s driven by 6850s, with the Analog Devices voltage reference chip on the amplifer, and a QM32 for control. EDIT: I just checked, Google maps says 3,900 some feet. (1.2 km)
    `
    Considering used 6250s are going for 250$ a pair, and 6810 pulls from yearly rebuilds of medical x-ray plotters go for around 35-75 USD untested, that's quite a deal, considering a new pair with amps was 1700$ a few years ago. Even a 506 pair by Scannermax, provided he orders the right sensor option, will do what he wants, PROVIDED he uses a good scanner amplifier.
    `
    Galvo pointing accuracy and repeatability is measured in microradians. If you buy the right galvos, not 200$ a pair Chinese clones.
    `
    Steppers, even geared down, have no feedback loop to check their position. You'll get badly burned with steppers. You might get there with DC servo motors with encoders, but the cost of that will exceed the galvo pair.
    ~
    Steve
    Last edited by mixedgas; 06-01-2017 at 07:47.
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  9. #29
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    I'll give you an example from a 62xx family Data Sheet, left data is for the small mirror set, it does a bit better with a larger mirror and frame on the right. Eight micro-radian is around 0.000458 degree.

    Steve

    Scale Drift
    (Maximum)
    50 ppm/°C 15 ppm/°C
    Zero Drift
    (Maximum)
    15 μrad/°C 5 μrad/°C
    Repeatability 8 μrad
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