An electronic tachometer for disk file motion control

An electronic tachometer system used as a velocity transducer for the track-accessing control system of a disk file is described. Rather than employing a conventional moving magnet and fixed-coil velocity transducer, this electronic tachometer combines information from the servo head position signal and from the actuator motor current to generate an accurate measurement of actuator velocity. Transducer bandwidths of several kilohertz, together with good calibration accuracy and linearity, are obtained over the 100:1 dynamic range of 0.013 to 1.3 meters per second.