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Thread: Scanner Workbench

  1. #1
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    Apr 2006
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    Default Scanner Workbench

    Hi all,

    Since there seems to be some interest in scanner testing, and since I already published a few pictures showing how flatness testing is done, and (lastly) since I told you when I had some time I would post some pictures of my scanner workbench, well, here it is:
    Click image for larger version. 

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    Actually, this is only the main part. There is a power supply (for powering scanners and amps that are not self-powered) and second function generator off to the left, and computer system off to the right (for downloading images from these devices and running Pangolin software).

    On the bench you see a 15MHz function generator (multiple megahertz is absolutely necessary to test a position sensors' ability to reject out-of-band signals, like walkie-talkies and cell phones, etc. Yadda might remember the bad old days of Laser Media amps, where if you key-ed up a walkie talkie anywhere near a laser media scanner amp, it would drive the scanners crazy...), Digital Scope, Dynamic Signal Analyzer, LCR meter and the equipment being tested.

    The scope is a LeCroy four-channel, 8-trace, 8GS/S (yup, 8 billion samples per second single shot, 25 billion samples per second for repetitive signals!!) color scope, with built-in waveform analysis and math. Here you can see the command, position, current, computed velocity (computed by the scope that is) and measured velocity signals.
    Click image for larger version. 

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    The heart of this setup is a Stanford Research SR785 Dynamic Signal Analyzer. You can consider this to be like an X-Ray machine for scanners and servo systems. It can show the gain and phase of any system, including electro-mechanical systems. It can also be used to perform other analysis such as harmonic distortion, interference analysis, vibration analysis, etc. While designing servos, I use it to test each section individually, and then test the entire system as a whole. And when working on scanners, I use it to find mechanical resonances and see how to improve them. In the picture below, you can see about a 12dB resonance peak at 3.17 kHz and the associated phase loss. This particular plant gets pretty nasty after around 6kHz...
    Click image for larger version. 

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    The scanners being used for this test were sort of hand-picked just to illustrate a few things that we have been discussing recently. First, if you take a very close look, you will see the 15-degree set-back. As discussed in another post, this helps reduce the width requirement for the Y mirror. The X mirror still requires full width, but the length is not nearly as long, so the inertias are made to be similar.

    This particular mirror set and scanner system was designed to move a 20mm beam over 40 degrees optical. I put a little "Pangolin" pen there so you can get a size comparison.
    Click image for larger version. 

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    These are Cambridge model 6650 moving coil scanners. Their claim to fame is not speed but accuracy. Short term repeatability of this scanner is in the single digits of micro-radians. It's one of the most accurate scanners in the world!! But since it is a moving coil design, there are long spans of unsupported wires that give the rotor its torque. Because of the long spans of wires, the resonance profile isn't that great when compared to moving magnet scanners which have a completely solid rotor. That's why we see so many resonances starting at around 6kHz. Even if I remove the mirror, there are a lot of resonances that show up... With the current tuning, small signal bandwidth is only on the order of a few hundred hertz. If this were a moving magnet scanner, the small signal bandwidth could easily be 10 times as high, which is the primary reason for the move toward moving magnet scanners.

    Anyway, now you can see the kind of diagnostic equipment that we have at Pangolin. One point in showing you this is to get you thinking. When you go to a hospital, they have all kinds of diagnostic equipment to (hopefully) come up with an accurate diagnosis of your problem, and prescribe a cure. Without the proper equipment, a doctor can only guess at what the problem is... Companies like Cambridge and GS have this kind of equipment so they can do a great job at creating scanners. Companies that don't simply can't... Again, it's my "doctor" analogy. If you can't X-Ray the leg, you can't tell if it is broken or not, or how bad, or figure out how long it will take to heal...

    There are other tools including an LDV where we can see 3D resonances inside of a closed scanner, but that's more complicated to setup and photograph... Also, of course there is the design software to begin with. As I was mentioning in another post, these days the top companies use high-end CAE packages like SolidWorks and Inventor. Even beyond that, we wrote our own software that helps us design scanners. It can tell us the flux density, torque-versus-position profile, torque-constant, radial and axial forces, coil resistance, inductance, etc... When I find a few spare moments, I will load a model and shap a few screen shots. It's all pretty interesting...

    Best regards,

    William Benner

  2. #2
    Join Date
    Jun 2005
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    SoCal
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    Default

    Nice LeCroy. Thanks for the writeup and pictures... using a dynamic signal analyzer is a good idea! Your servo roots are definitely peeking through with your choice of vendors

  3. #3
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    May 2006
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    Thats is cool! EXPENSIVE equipment

    Pangolin FB3 QS/LivePro/SMS2Laser
    Riya MultiBus
    Pangolin LD2000 Pro

  4. #4
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    Oct 2005
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    Melbourne, Australia
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    Wow... those scanners look like they could move a person...
    Now proudly stocking and offering the best deals on laser-wave

    www.lasershowparts.com
    http://stores.ebay.com.au/Lasershow-Parts

  5. #5
    clandestiny's Avatar
    clandestiny is offline Eleventy-Billion Watt Ar/Kr >:)
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    Bill, quit fooling around with stuff you will never use. Donate those scanners to my copper vapor project. Your just the cross benching PR man anyway. Everyone knows Hayden is the brains of the operation.
    Mr allthatwhichis- glad to see you have finally have joined us with your recent
    purchase.
    I was just looking at the un-edited footage of flem. Looks like we had some fun. That little argon held its own with all that atomosphere.
    Last edited by clandestiny; 04-11-2007 at 21:03.
    go big or go home

  6. #6
    Join Date
    Oct 2006
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    Central Florida
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    Talking

    Hey man! I was wondering if you fell off the planet. I agree, when I picked up my intro set I got the feeling that Hayden was the one doing all the work...

    What... little argon? I guess its all about perspective. It was much fun though. When I get a box for my set up we will have to plan FLEM part 2.
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  7. #7
    Join Date
    Jan 2007
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    Florida
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    I was hoping we were going to do a NCLEM or SCLEM
    How about Hilton Head SC?
    (where my mom lives and she keeps complaining that I never visit her)
    (actually she lives in sun-city retirement community-near hilton head)
    Straight up I-95 for you Floridians

  8. #8
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    Charleston, SC
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    Smile

    Clandestiny! Who let you out of your cage? Great to hear from you again... (Been a while pal! I know you've been busy...) And Hey! You better watch it - everyone knows I'm the official "cross-bencher" here. Bill is just a wannabe. (Just kidding Bill; your posts put mine to shame when it comes to completeness.)

    (And if the rest of you are completely lost by now, here's where the whole "cross-bencher" thing got started.)

    Paul's got a point though. Those monster mirrors would be about right for one of his Copper Vapor death-rays. Well - at least as far as the size goes. No telling if the optical coatings could survive >150 watts without slagging.

    Steve-O: I'm glad you brought up the topic of our next meeting. I spoke with my buddy again this afternoon, and he will be meeting with the hotel manager tomorrow. Hopefully by the end of the weekend we will know if everything is a GO for this summer. Right now we're looking at a late-July time frame, and the location will be about an hour north of Charlotte, NC. Details to follow soon. I'm on it.

    We had considered doing another "pre-selem" gathering either in Florida or here in Charleston sometime in May, but I didn't want to steal too much thunder from SELEM this summer. (That, and the first few people I talked to about the idea said that May would be really bad for them.) As of a couple weeks ago, we had sort of abandoned the idea.

    But I'm always up for another gathering... If there's enough interest (read: more than 2 people are up for it), then we can surely set something up in Hilton Head if you'd like. (Hilton Head is about an hour south of Charleston, or roughly 3.5 hours north of Jacksonville, FL) Do you know of a venue we could use in Hilton Head?

    Adam

  9. #9
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    Quote Originally Posted by Buffo View Post
    (Hilton Head is about an hour south of Charleston, or roughly 3.5 hours north of Jacksonville, FL) Do you know of a venue we could use in Hilton Head?

    Sorry Adam, I have to correct your spelling of my home town, its
    Jags!onville


    David

  10. #10
    clandestiny's Avatar
    clandestiny is offline Eleventy-Billion Watt Ar/Kr >:)
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    Bill Brenner was last seen backpacking in the Himalayas. He is probably
    attempting to determine the molecular weight of some scan mirrrors he
    obtained black market from the former U.S.S.R.
    go big or go home

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