Multi-rate two-degree-of-freedom control for fast and vibration-less seeking of hard disk drives

A novel multi-rate two-degree-of-freedom control algorithm is described that overcomes the residual vibration of the positioning system and attains fast seeking operation. It has three main functions: 1) it generates a target trajectory that minimizes the residual vibration due to the primary resonance of a head positioning actuator; 2) it calculates acceleration feedforward that ensures perfect tracking to a target trajectory at position-sampling points; and 3) it re-calculates the target trajectory for feedback control in order to reduce the modeling error, by taking into account the primary mechanical resonance characteristics and the phase delay caused by the control circuit. Simulations and experiments show that the control algorithm improves the settling performance by reducing the vibrations due to both the primary mechanical resonance and the slow transient response induced by the tracking error to the target trajectory. The one-track seek time of a drive controlled by this algorithm is 15% faster than with the conventional one