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Thread: scanline scanners?

  1. #1
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    Default scanline scanners?

    While I'm not much into this industry of laser projectors, I can't find any non-galvo scanners that can scan like CRT TVs did, but the laser beam and it's baffling why not. I found only one company in Russia who builds their in house scanline scanners and their projectors are very impressive. It's like low resolution video projector but with the brightness of a galvo scanner laser projector. This is why its confusing why nobody sells such scanners, the effect is too good, I'll argue will have more usage than galvo laser scanning for things such as concerts and outdoor advertisement. Sure, for lower resolution than video projectors but as bright as lasers there's LED walls but the installation of such laser projectors would make them a better option than LED walls in many situations and a good competitor to them.
    Any idea why there isnt none? Could even take HDMI as video input with a proper controller. Perhaps a patent troll?


    I wish I could find the site of that russian company I just mentioned but I can't for the life of me remember where I found them and what it was called.
    The only thing remotely similar is Microvision but they make scanline scanners for pico projectors not large outdoor projectors.


    Once more I'd like to mention I think such a scanline scanner would sell like pancakes. And existing laser projector manufacturers would only need to change their designs by swapping the scanner and scanner amps and inputs, they could keep the rest of the optical system.

  2. #2
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    Most likely a better solution for laser driven video projectors would be to use a DLP device rather than a raster scanner.
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  3. #3
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    Zeiss made a a raster scanned laser projector called ADLIP (All Dome Laser Image Projection) for planetariums in the early 2000's. It was expensive, and I think when they brought out the Velvet projectors in 2008 they licensed ADLIP to Jenoptik for simulators, but I'm not sure it was Jenoptik...
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  4. #4
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    DLP won't work for this. Laser powered DLPs already exist and they are as dim as ordinary video projectors because the beam, whether laser, gas lamp or led is covering the whole micromirror array on the DLP chip and picture is generated depending on the angle of each micromirror (there can only be two angles with DLP micromirrors) each few milliseconds. So the brightness of the beam is divided among around a million or more micromirrors. This appears way dimmer than a single very bright thin beam which is scanned instead and you can see its every location because of your persistence of vision. Same reason galvo scanner laser projectors are so much brighter than the brightest DLP projectors.

  5. #5
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    ... search for rotating polygon mirrors (as in laserprinters) and the fail of "laser television" la Sharp and others ...

    Viktor

  6. #6
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    Cool So how does laser TV work anyway?

    VDX hit the nail on the head.

    To emulate VGA video (call it 640x480 at 60fps), you need a horizontal scan speed of 31,400 Hz. That's more than an order of magnitude faster than scanners can handle.

    OK, before we go any further, a disclaimer for those of you who know where I'm going with this: Yes, I acknowledge that because you aren't actually steering an electron beam, you can ignore the wasted scans inherent in a normal VGA signal where the beam has to return to the top or home position. Thus the actual scan speed for the horizontal mirror on a laser TV system can be slightly less than 31.4KHz - especially if you scan from top to bottom, then bottom to top, to maximize your efficiency - but since most people are familiar with the standard video speed examples I'm going to stick with those numbers to simplify things.

    Anyway, that 31,400 Hz scan speed can be attained with a hybrid projector that uses a high-fixed-speed spinning mirror system for the X axis and a conventional galvo for the Y axis. There used to be a couple people doing this. They pretty much all used normal galvos for the Y axis mirror (since the vertical scan speed only needs to be ~ 60 Hz) and the X axis was a multi-faceted polygonal mirror that was rotating *very* fast. How fast, you ask? Well...

    Let's say you want a 10 degree scan angle. That means your spinning mirror needs to have 36 faces. That means each full revolution of the mirror wheel will give you 36 horizontal scans. To get to that 31,400 Hz horizontal scan speed, you're looking at a spindle speed of 52,333 rpm! That's crazy fast for something that is going to be at least 2 or 3 inches in diameter, weighing a couple pounds, with a first-surface mirror on the outer edge (where the G-forces will be highest).

    Hard drive motors top out at around 15,000 RPM. You need something almost 4 times faster, with the same level of spindle speed precision. Oh, and you also need POSITION feedback so you can sync up the color data.

    The problems (then and now) are: controlling spindle RPM to a very precise setpoint at crazy fast speeds, synchronizing the rotation with the laser color data, and controlling/eliminating vibration in the rig. A secondary issue was the poor modulation performance of early solid-state lasers at raster-scan speeds, though with all-direct-diode RGB laser modules and well-designed drivers this should be less of a problem now.

    The fact that it *was* done (by at least a few different operators) and the fact that it's currently *not* being done (by anyone that I'm aware of) should give you a good idea as to just how difficult it was to keep a contraption like this running consistently. And remember, that was for 640x480. Do the math on a 4K projection if you really want a shock!

    Granted, I'm simplifying things a bit here. There are ways to split up the image into multiple vertical pieces and use parallel projections to share the load such that you get more than 1 horizontal scan for every face on the polygonal mirror. (Imagine how an interlaced GIF loads and you've got the idea.) Basically you're adding complexity in favor of a lower spindle speed on the spinning mirror of death. And at least one of the systems I read about used either 4 or 5 vertical "slices" to get the spindle speed down to something closer to a hard disc drive motor. (Also, if my memory serves, I think that one ran the vertical at 30 Hz, so only 30 fps, not 60, which helps too...)

    But even with lots of clever ideas like that, every company that worked on this sort of display eventually gave up. One can only assume that the results weren't worth the expense and effort - especially considering the abilities of modern high-power video projectors.

    Adam

  7. #7
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    Very good explanation which makes sense.
    I apologise that I said I believe myself that nobody except one russian company is currently doing this, but that was from my searchers few years ago. Apparently there are companies today that claim to offer such highspeed polygon mirrors or oscillator scanner mirrors.

    Should I give them a try and report back? Or do the claims sound edgy?

    https://precisionlaserscanning.com/polygon-scanners/

    http://www.eopc.com/sc30.html

    These are the only polygon mirror and resonant mirror scanners I found and while the resonant mirror's speed seems only suitable for QVGA (320x240) that's the resolution that russian company used and it looked very good. But the rotation angle is too low.
    But with the polygon mirror scanners there may be some usage for us.

  8. #8
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    Here we go again. I realize I am going to come off like a huge dick right now but everyone here just told you why this is a bad idea. It seems like you're only wanting validation for your project and not genuine info. If I seem like a curmudgeon, it's only because we've had one user who keeps popping in here on multiple accounts and doing the same thing. They ask questions and people answer them with good and honest information and when it doesn't line up with what they're expecting, they try to find different ways to extract the information so that it will line up with their expectations. When it doesn't, they move on to something else and do the same thing. The ambiguity of your project and intended application is suspect.

    Now that I have my rant out of the way, there is something else you need to consider; you're not going to get something for nothing. Scanning a single beam over a given area at the speeds we're talking isn't going to increase the brightness of your projection over a projected (not scanned, conventional projector) image covering the same area. If you want a brighter image, you need a brighter light source. For this particular application, with laser technology where it's currently at, a laser is not the way to go.
    Last edited by absolom7691; 05-24-2018 at 09:13.

  9. #9
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    Quote Originally Posted by piydadorto View Post
    there are companies today that claim to offer such highspeed polygon mirrors or oscillator scanner mirrors.

    Should I give them a try and report back? Or do the claims sound edgy?

    https://precisionlaserscanning.com/polygon-scanners/
    The "Road Runner" polygonal rotating mirror is the one you'd want to work with, if you're going to attempt to re-create the effect. The resonant ones just won't give you enough speed, not to mention their pitifully small scan angle. Even so, the standard 72-facet mirror on the Road Runner will only give you ~ 5 degrees of scan width, so if you want the full 10 degrees as in my example above, you'll need to order a custom mirror with 36 facets. However, their speed specs are impressive (70,000 RPM!) which is encouraging. I honestly had no idea they had commercial polygonal scanners that ran that fast.

    I'm more concerned about the speed consistency though, as they list it at .03% (jitter is the same). So that's an error of around 17 RPM on the low end, and 21 RPM on the high end. You're going to have to compensate for that somehow. Also, they claim 60 arc-seconds for both the facet-to-facet and dynamic tracking specs. (Basically how consistently-flat the faces on the polygonal mirror were made with respect to each other and how well the entire assembly retains it's shape while spinning.) That works out to a variable scan angle error of up to .02 degrees, or 1/500th of your total scan angle, each time the mirror completes 1 revolution. You'll have to decide if you can live with that or not, as I don't know of *any* way to compensate for this short of building a better mirror assembly.

    Also, did you notice the caveat in the datasheet for the Road Runner?
    "a 2.5 inch (64 mm) diameter polygon mirror at 55,000 RPM sounds like a siren as the facet tips travel at over 400 MPH (650KPH). The high noise level makes it impractical to use in some office and medical environments."
    Be sure to keep that in mind as you contemplate things. A "spinning mirror of death" is exactly what you're dealing with here.

    Note that you need to provide your own speed control signal for that model. And your own positional feedback system (need to know where the mirror is to synch it up with the rest of the projector). Then you'll also have to develop custom hardware to use that position feedback to synchronize the X mirror with the Y mirror and the color data. Of course you also need to provide for some fine adjustment of the offset between color and position signals to "tune" things. And finally, you'll need custom software and firmware to create all the frame data to drive everything in the first place. (No commercial laser show software I'm aware of will output the color data at a high enough clock rate to keep up with a scan system like this.)

    There may be some off-the-shelf hardware you can use to get started, especially for the speed control circuit, but before you're finished you will definitely be creating some hardware and software literally from scratch. But yeah, you are on the right track. It's a difficult task, no doubt about it, but if you want to build a laser TV projector, this is where you'd start.

    If you do attempt this, please post pictures of your progress!

    Adam

  10. #10
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    Sorry about that, thank you.

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