Having tested HDD's for many years from the inside out, I have yet to find a servo system more sophisticated , fast and accurate as those use in hard disk drives.
Although the motor can seek to within 10u" accuracy is a rotary voice coil DC motor, the servo feedback is quadrature differential pulses embedded between each track and sector.
The position error signal (PES) from these servo dibits differential amplitude and then differentiated to create velocity and again for acceleration. The HDD servo auto-calibrates magnetic force gain in each directions and compensates the gain error also as a function of temperature with sensing. Each zone may have a different servo profile. The servo control is not simply PID feedback but PID target and PID feedback. This gives the fastest most stable loop. In other words, each servo seek has an acceleration profile, max velocity speed limit and a position error profile to prevent all overshoot in the shortest time. a few milliseconds. Even when we were using 1 Hp linear voice coil motors in 14" HDDs in the early 80's , our best product could seek with a large mass in 50ms avg with embedded servo.
Always start a big project with specs. ( before you start asking for F/V converters, as those are easy with a PLL and position encoder that multiplies frequency of RPM for high bandwidth.
So do me a favour and define your servo in simple point form.
Mass range, max acceleration, max velocity , position error, maximum seek time, power requirements, ambient specs.