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On Tue, Jan 25, 2022 at 6:22 PM Ferenc Éger eegerferenc@gmail.com wrote:
In an optical drive, the analog tracking error signal is fed into the solenoid via an analog feedback loop, keeping the lens over the track. When the solenoid control signal approaches the end of its range in either direction, a comparator senses it and causes the stepper to step one forward or backward (while the movement of the lens caused by the stepping is canceled out by the feedback loop), bringing the solenoid back to the center of its range of movement.
ohh, don't they use some sort of 2D interference pattern for focussing? you get 4 spots and it's easy to measure the intensity of them. something like that, i can't remember where i heard about this, details are fuzzy in my mind.
l.