I'd like to use a hard disc head positioning servo mech in conjunction with a microcontroller as a servo for a mirror positioner.
Positional feedback is an issue, originally feedback to the headpositioner in a drive is from servo data written to the disc, the control 'knows' where the head is by the data on the disc.
The question is how is the voice coil controlled, using a scope on an old drive you can see there is obviously ac present, so I put a circuit togther that reverses the polarity acrross the coil controlled by a pwm output from a pic, it works but the coil gets to its full movement within a small deviation from 50% symmetry, and its just as good at making sound as it is motion.
I'm assuming that a drive somehow 'holds' the head in a certain position, you can see this when playing with one with the lid off, is the held actually held or does the drive sense a small motion and correct itself.
Yes I know a drive is dead the moment the lid is taken off.
Positional feedback is an issue, originally feedback to the headpositioner in a drive is from servo data written to the disc, the control 'knows' where the head is by the data on the disc.
The question is how is the voice coil controlled, using a scope on an old drive you can see there is obviously ac present, so I put a circuit togther that reverses the polarity acrross the coil controlled by a pwm output from a pic, it works but the coil gets to its full movement within a small deviation from 50% symmetry, and its just as good at making sound as it is motion.
I'm assuming that a drive somehow 'holds' the head in a certain position, you can see this when playing with one with the lid off, is the held actually held or does the drive sense a small motion and correct itself.
Yes I know a drive is dead the moment the lid is taken off.