Winner, Name that Ware October 2011

The Ware for October 2011 is a galvanometer, taken out of an old chinese-made 2-D laser scanner of the type used in dance clubs. As far as I can tell, this is a hand-built prototype unit from an early production run; there are no distinctive markings on the galvanometer’s case, and to my eye there were indications of prototypey-ness, or pilot production-ness, about the surrounding circuitry.

It was very interesting to read the diverse set of guesses for the ware this month, and the winner is marcan for his useful and informative description of how the ware works. For the benefit of those who were stumped by the ware, here is his explanation:

Since nobody has explained how it works yet, I’ll do so: the infrared LED shines on the vane, which partially blocks the light reaching the two photocells on the left. Depending on the angle of the vane, the amount of light falling on each photocell varies. The feedback loop takes the difference between both cells and uses it as input feedback to a servo loop. The output of the loop drives a single-coil stator (the two solder joints to the bottom right are where the coil is soldered from the other side), which applies torque to a thin permanent magnet rotor that is attached to the vane on one end, and to a small front-surface mirror on the other end. This forms a closed loop system, where the angle of the mirror is directly proportional to the input voltage to the servo controller.

Since the rotor is thin, the mass is concentrated near the axis of rotation, and the rotational inertia is very low. This enables it to vibrate at high frequency, scanning a laser beam to draw an image on a target many times per second. Two galvanometers like this one are used for X-Y control. The amplifier has a bunch of adjustments to optimally tune the analog servo loop (servo gain, HF and LF damping, offset, position scale, etc.) which have to be adjusted for each particular galvanometer.

The full assembly, seen mostly from the other side, looks like this:

While there were others who had guessed the type of the ware correctly before him, the competition is judged not only on timeliness but also by depth of response. Congrats to marcan, email me to claim your prize!

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