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Thread: Maximizing Scanner Speed

  1. #11
    Join Date
    Oct 2016
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    Quote Originally Posted by mixedgas View Post
    Please note that there is a small angle step time and a large angle step time for any given Galvo-Amp-Mirror combination. It is not as simple as just "bandwidth".

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    You can tune the existing scanners for a very high speed at a very small angle. You do this by monitoring the position sensor and galvo current on scope while driving with a square wave generator, then a specially designed ramp waveform, and re-tuning. However it involves understanding PID theory. You basically have Low Frequency Damping, High Frequency Damping, Integration, Servo Gain, to tune. Most beginners are better off ordering a set of Scannermax, tuned for your use, then doing it yourself. This is because the controls all interact.
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    However it is possible to retune what you have, however a beginner is likely to fry the analog amplifier the first time he tries this.
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    For very fast speed, you need modified waveforms that are somewhat out of the scope of a laser show forum. You also need to ignore the ILDA test pattern, which is optimized for vector imaging, not raster scanning. You can then optimize your optics train for expanding angle vs. spot size vs. linearity. The Laser Media test pattern and Grid test patterns are actually somewhat applicable for marking, as is the "Circle in the Square" portion of the ILDA pattern.
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    You will note that Mr. Smith is giving you both KHz (Sine Wave) and ILDA numbers. This is part, but NOT ALL, of the picture when scanning. Scan speed is angle dependent. Small jumps or ramps can be amazingly fast, but the Galvo will slow down in a non-linear manor as angle increases. A good first order impression of a galvo is" "A DC Coupled Low Pass Filter with interesting Non-Linearities and Resonances"
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    There are peer reviewed papers and corporate white papers out there on how to optimize scan speed for bidirectional rastor imaging, which seems is what you want to do.
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    Part but NOT ALL of the Square Wave initial tuning procedure is hosted here for me by a friend of Lasers. Ignore setting the scale factor, that has been done at the factory for your Existing Galvos. This gives you an idea of how an "industrial" tuning procedure starts. It is by no means complete, and the part numbers in this document DO NOT DIRECTLY correspond to your existing scanner amp, even though it is copy of what is mentioned here. This is an excerpt of three different documents, and we've had it up for about ten years, so it is outdated. Part of the procedure for an older laser show technology is included, so ignore that.

    http://www.skywise711.com/lasers/scanner/scanner.html
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    As you develop this application you will invariably develop your own test pattern(s) as well.
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    RANT MODE:
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    The ILDA test pattern is not intentionally misleading, it is a old test devised by a group of very serious, highly qualified, Engineers and Technological Artists to allow information interchange in a specific application. The people who call it misleading have never learned enough about Galvo Mechanics and Electrical Engineering to understand what they are talking about in the first place. You need a bit of Calculus and time domain Electrical Engineering to understand the equation of state for a Galvo, and most of the complainers don't have that. So it is easy to "Dog" on the ILDA test pattern, but NONE of the complainers have EVER posted a successful alternative.
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    END RANT MODE
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    If you have a bit of time, Bill Benner's book (as mentioned) is very much worth reading for a Galvo Scanning beginner. It will let you visualize the tradeoffs between mirror sizes and scan angles. As mirror sizes increase, a given galvo slows down.
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    Either the velocity or position sensor feedback test point is brought out on most "Clone" scanner amps, and you can learn much by hooking an oscilloscope there. Then inject a small square wave and look at the overshoot, undershoot, and ringing. Keep the square wave at low amplitude, as most of the clones save money by removing the protection circuitry that prevents you from overheating the galvo. Note as you expand the angle, the time required to compete a given "jump" grows larger. If your really good with electronics, you can then find the 0.1 Ohm current sensing resistor on the board and see how the amplifier waveforms change using the oscilloscope. Look at the settling time on the leading edge as well.
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    Steve
    Do you have any info on how to go about accurately determining the linear scan speed (perhaps in real time) of my galvos?

    Also any further resources on tuning (especially for high speed) would be much appreciated.

    Thanks,
    Last edited by scoobydoo; 11-26-2016 at 15:15.

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