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Thread: Replacing Scanner Mirrors

  1. #21
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    did you color the shaft black?

  2. #22
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    Not the whole shaft as I was paranoid about putting anything under the epoxy, but I used a black Sharpy on the exposed metal. The thing worked! Nothing broke and the scanners are a little quieter, so I bet they may be even better balanced.

    The mirrors are a bit heavier than the originals and so I had to re-tune. The walking the stool technique that Buffo posted before scares me because the two times I tried it the cheep Chinese scanners nearly got away from me. I do not have all the test patterns he recommended and so I used a bastardized mix of the grid, laser media test pattern and the ILDA 12K and so they're tuned, but I bet not very well. Steve sent me a tuning approach that requires a waveform generator and an oscilloscope and this sounds like fun, but I think I'll need a day to dig through this.

  3. #23
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    Eric;

    Will you be bringing this projector to SELEM? If so, I'd be happy to tune them for you then.

    Adam

  4. #24
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    Quote Originally Posted by planters View Post
    Steve sent me a tuning approach that requires a waveform generator and an oscilloscope and this sounds like fun, but I think I'll need a day to dig through this.

    Eric,

    Even if you don't tune with the signal generator, the test point is J4 on the board. Its marked`"+ -" Its worth putting a scope there anyways.

    Its right behind the pots, two plated through holes on a 0.10" spacing. I solder a two pin male header in there or extend that out on wires when I'm tuning.

    The Oscilloscope procedure I sent you results in roughly tuned scanners with excellent damping but just moderate speed. It still needs touched up with the ILDA and Grid Test patterns to ensure images are interchangeable. You can ignore the velocity matching* portion of the procedure, as well. The ILDA and LM patterns take care of the Velo Matching. The scope based procedure does get you tuned from scratch, much, much, faster if you have the gear to do it.

    --------------------------------------------------------------------------------------------------------------------------------------
    * Note for others, it is possible to roughly match amplifier tunings by measuring the response of the Galvo to a low frequency square wave on the Dual Trace Oscilloscope. During this step, you measure the rise time of the Galvo at a given deflection angle. You pick the faster of the two Galvos as the master. You then input the same Square wave to both amplifiers and adjust the slower amp so the Velocity test point scope traces overlap exactly.

    This technique requires considerable thought as to how you set up the amps so they respond at the same deflection angle. With high quality Galvos this is easy and will have been done at the factory, when calibrating the position sensor electronics. It is done by disabling the amplifier output stage and calibrating the position sensor with a laser, a grid on the wall, and a oscilloscope. On Cambridge products the sensor is calibrated to 0.50 Volts per Degree.


    This is one way to tune Galvos to match each other on a marking machine or machine vision system.

    The beauty of the ILDA, Grid, and Laser Media test patterns is they allow you to do this without all the extra lab hardware, and the images will be much more interchangable. If we did not have quality, standardized, test patterns, tuning would depend very much on user skills and a oscilloscope.

    NOTE 2: IT IS STRONGLY RECCOMENDED THE END USER NEVER TOUCHES THE POSITION SENSOR SCALE POTENTIOMETER ONCE THE FACTORY SETS IT. FAILURE TO HEED THIS WARNING MAY RAPIDLY RESULT IN A DAMAGED GALVO.

    Steve
    Attached Thumbnails Attached Thumbnails 605-J4TP.png  

    Last edited by mixedgas; 06-02-2014 at 07:23.
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  5. #25
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    Will you be bringing this projector to SELEM? If so, I'd be happy to tune them for you then.
    If I can make it, I'll bring one or two scanner sets, amps and PSUs. My projectors are too bulky to ship easily, but these can pack up well. It might be interesting to hook up an oscilloscope to the test points Steve recommends and see what happens as it is tuned. After that, I should have more confidence in tuning these myself.

  6. #26
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    I am trying to get quotes from a number of companies to have them fabricate some light weighted, structured scanner mirrors. I am to the point that I need to submit a drawing. The concepts are pretty simple, but I do not have the skill to turn out a CAD type of drawing. Can anyone here that has this skill PM me and I will describe the design and hopefully will then be able to submit something "professional" for their review?

  7. #27
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    Hi Planters,

    Obviously we can help (and maybe more obvious with the screen shots I just sent, before reading this thread).

    By the way, I normally just heat the shaft, for a VERY brief time with the soldering iron. There is normally not much epoxy exposed that can be heated in the first place. Stainless Steel is not that great of a conductor of heat, and so heating the tip of the shaft won't overheat the lube in the bearing or allow heat to travel down into the magnet or shaft-to-magnet joint. Within just a second the epoxy will become soft enough that, by putting "side force" on the tip of the mirror, it will bend sideways. You can then wiggle it out. I've done that a zillion times with all kinds of scanners.

    Then normally I use 5 minute epoxy to re-mount the mirrors. I'd say it isn't a perfect adhesive, and we're still evaluating literally a dozen other candidates right now. But in the words of one of the smartest mechanical engineers I ever met (and inventor of the Counter Rotating Scanner from General Scanning), 5 minute epoxy is not the best solution for anything, but it is a pretty handy solution for many things...

    Bill

  8. #28
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    Thanks Bill,
    I posted this last query before I got your response to my email and so I will give YOU the specifics and see what happens. One improvement that an old epoxy chemist gave some time ago for improving an epoxy- metal bond is to abrade a thin layer of the mixed, but uncured adhesive into the metal prior to applying the bonding layer. This improves the chances of the adhesive contacting fresh un-oxidized metal because the thin layer of adhesive shields the metal from the air.

  9. #29
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    Quote Originally Posted by planters View Post
    This improves the chances of the adhesive contacting fresh un-oxidized metal because the thin layer of adhesive shields the metal from the air.
    Fertile grond for experimentation I am sure!

    Bill

  10. #30
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    I use uv cure acrylic nail gel in some cases

    if it's still relevant, i can help
    Can anyone here that has this skill PM me and I will describe the design

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