A novel disturbance observer design for magnetic hard drive servo system with a rotary actuator

This paper presents a novel disturbance observer design for the magnetic hard drive servo systems with rotary actuators to improve the access time. One of the major drawbacks of the conventional disturbance observer design is that the disturbance rejection rate is increased at the cost of increased amplification on high frequency system noise, and consequently, system stability. To improve the disturbance compensation capability without affecting the system stability, a novel disturbance observer design is proposed in this paper. The idea is to replace the constant controller gain in the conventional disturbance observer with a first order filter. Compared with the conventional disturbance observer design, the proposed disturbance observer is shown to decrease the settling time by 40% and increase high frequency measurement noise attenuation by 10 db, respectively. The proposed design has been implemented on a test stand with a 3.5" hard drive. Both simulation and experimental results have validated the claim