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Thread: Over 90 degrees scan?

  1. #1
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    Default Over 90 degrees scan?

    (DT40W for example) If the laser is at a 45 degree angle to the galvo mirror, and the mirror moves 45 degrees up and down (for a total of 90 degrees): at one extreme, the mirror is parallel to the laser and cannot reflect any light. At the other extreme, the beam is reflected back to the source.

    I've probably got it all wrong... but how is >90 degree scanning done?

  2. #2
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    Doesn't answer your question but I've measured 97 degree scan angle on my DT-40W's.
    The amps gain had maxed out...
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  3. #3
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    I think you will find that to scan a beam 90 degrees the mirror and galvo only rotates 45 degrees from one end to the other. If your mirror could rotated 90 degrees, in theory the scan angel would be 180 degrees. As you said this would not work as at one end of the 90 degree rotation the beam would be hitting the edge of the mirror rather than the mirror surface. The beam scan angel in degrees is double that of the rotation degrees of the galvo. Well this is how I see it. Could be wrong.

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  4. #4
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    Yeah, scan angle refers to the full angle covered, not the maximum offset from center. A 90 degree scan angle means the beam can go 45 degrees to the left and 45 degrees to the right of center.

  5. #5
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    Quote Originally Posted by j4cbo View Post
    Yeah, scan angle refers to the full angle covered, not the maximum offset from center. A 90 degree scan angle means the beam can go 45 degrees to the left and 45 degrees to the right of center.
    Yes, and imagine what would happen if you have your galvos set up the usual way?

    Beam comes in at the X galvo at a 45 degree angle (so it would go straight up/forward, hitting the Y galvo at center), so scanning 45 degrees to the right would make the laser come in parallel to the mirror surface -> image is lost.

    Scanning 45 degrees to the other side means the beam will be square to the mirror surface, being reflected straight back where it came from, which is your expensive, nice laser setup -> oops!

    Scanning any further would lose the image as well because the mirror itself would be in the way and the beam would be deflected back onto the projector's base plate.

    The only way I could imagine scanning over 90 degrees would be if either the beam would come in at a different base angle, or the galvo setup would be rotated so the X galvo goes more off center for a 'zero' angle.

  6. #6
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    I have made a drawing once about scanangles, this shows when having scanangles of 90 degree, beamdiameter above 2mm will be clipped with 6mm mirrors

    Click image for larger version. 

Name:	90 degree..jpg 
Views:	37 
Size:	13.5 KB 
ID:	22291

  7. #7
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    Quote Originally Posted by Stoney3K View Post
    Scanning 45 degrees to the other side means the beam will be square to the mirror surface, being reflected straight back where it came from, which is your expensive, nice laser setup -> oops!
    No, scanning 45 degrees to the other side means that the beam will go 45 degrees off from perpendicular. This is not the same as "back where it came from", which would be 90 degrees. See mccarrot's drawing.

    The angle of the *beam* and the angle of the *mirror* are not the same thing.

  8. #8
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    Quote Originally Posted by mccarrot View Post
    I have made a drawing once about scanangles, this shows when having scanangles of 90 degree, beamdiameter above 2mm will be clipped with 6mm mirrors

    Click image for larger version. 

Name:	90 degree..jpg 
Views:	37 
Size:	13.5 KB 
ID:	22291

    So I'm guessing then that if you scan to 90 degrees, the outer edges of the cue will look dimmer due to beam clipping?

  9. #9
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    Quote Originally Posted by White-Light View Post
    So I'm guessing then that if you scan to 90 degrees, the outer edges of the cue will look dimmer due to beam clipping?
    Only if you have those sized mirrors with >2.0mm beam...

    The DT40's have a longer mirror on one axis. So it's not an issue...
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  10. #10
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    To scan 90 the galvo needs to move 45 as Dan pointed out; the biggest problem is the beam scanning past the limits of the Y mirror, hence the DT40W has a very long Y mirror.


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