The problem is a Galvo is not a simple device. A small or large jump response time, as used in the marking industry, does not come anywhere near describing what happens in laser show vector graphics. While everybody says "Oh the ILDA Test Pattern doesn't do this..." , most have little idea of what would be involved in presenting a huge 3D vector set of data representing Galvo performance. Performance changes with jump angle, waveform frequency components, and past history of motion. Mirror inertia varies widely with manufacturers, etc.
Point of the matter, the ILDA test pattern provides a nice set of constraints to measure the behavior of an extremely complex beast that can be done by engineers, technicians, and artists, quickly. But the test pattern was not really intended for absolute measurement. Why that is the situation comes up later in this post.
The circle in the square roughly measures the -3dB response frequency for small jumps at a given angle.
Fact of the matter, this has been debated to death, for decades, and not once has anyone ever came up with a better idea for our industry other then the various test patterns. Quantifying Galvo performance is difficult.
How do you read a complex table of jump angle vs frequency vs inertia vs coil resistance vs ma/Per degree vs Back EMF constant vs position sensor constants, vs resonances vs shaft diameter blah blah blah ? The answer is you don't bother with it, as most users simply do not care, and Galvo technology is nearing it's technological limits. How do you test an analog scanner amp with nine variables adjusted by twenty turn potentiometers from model to model vs manufacturer to manufacturer when they often use differing PID loop topologies?
The point of the matter is your facing an infinite data set to display and interpret, let alone compare. The majority of users just don't care to have to try to interpret that, and most do not have the required technical education.
Just because the standards lack "precision engineering documentation" does not represent a major failure in this industry.
While a Galvo manufacturer might have a Dynamic Signal Analyzer at the plant, the great majority of us simply do not have the budget. I have a used one, but I'm a minority and my day job means I need a large variety of instruments, even in the home lab.
I understand where your coming from, but there is very little desire in our industry to bother with this topic. History has shown that the ILDA test pattern and some other patterns used in tuning have provided a reasonable standard for information interchange vis a vis the Galvo's complex mechanical response. That is its job, to insure artwork from XYZ laser corporation can look reasonably good on any properly tuned projector in the world. If you spend some time with actual galvo tuning, scanner amp design, and know your laser show history, you'll find it is actually a pretty good solution to a complex problem.
Laser modulation and beam quality is a separate issue. Beams from overlapping diodes in arrays do not nicely fit the mathematical models and instruments used in laboratory or industrial lasers in terms of mode structure and divergence. Unless your using a OPSL or Ion Laser source, the data can be quite meaningless. Often times no two diode arrays from the same manufacturer are even close to identical. Again, as diode array beam patterns vary wildly with distance and instantaneous intensity, you can end up having to quantify a nearly infinite set of data for each wavelength. I own both CCD based and mechanical scanned beam analyzers. I have found it very difficult to express what I measure with the scientific instruments on show lasers, whereas lab lasers often present simple beams with a good Gaussian fit. Testing at just full power is not a full solution, these sources vary widely. Often the outer portion of the beam is distorted and the inner portion contains most of the power and is quite good quality. How do you define a standard with that condition?
The current ILDA standards let you test a small subsample of the complex data at one easily constrained set of test conditions.
I agree, it is a race to the bottom, these days.
These are nearly the oldest version of the standards available: https://photonlexicon.com/forums/sho...ILDA-STANDARDS
Here is the newest: https://www.ilda.com/technical.htm
Steve
Last edited by mixedgas; 06-23-2023 at 14:02.
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Originally Posted by christo
buffo
), you can always pump Steve Roberts (above) for more information. Steve has been doing the sort of lab testing you've been asking about for a *long* time, mainly because he's been working for university researchers who want to squeeze every ounce of performance out of the equipment. He basically lives and breathes this sort of stuff... He can also recommend test equipment (and parameters) to you, should you ever want to do some of this advanced testing for yourself. 
