Off-track vibrations of the read-write heads in hard disk drives

The research presented in this dissertation was aimed at investigating and mitigating off-track vibrations of read-write heads in hard disk drives. It addressed three objectives. The first objective was to study and understand drive dynamics at the system level. The second objective was to determine the optimal orientation of strain sensors on an instrumented suspension to detect suspension vibrations that may contribute significantly to the off-track motion of the read-write head. These strain measurements would provide real-time suspension vibration information that can be employed in control schemes to suppress off-track vibrations. The third objective was to experimentally study and characterize airflow effects in hard drives, and to reach a better understanding of the relationship between airflow and head vibration.; The dynamics of the head stack assembly were studied using finite element modeling and analysis. The approach adopted was to examine the dynamic characteristics of the individual components of the head stack assembly, namely the head gimbal assemblies and the actuator block, and then investigate and understand the dynamic characteristics of the system as a whole in terms of the component dynamics and their coupling. The head stack assembly modes were categorized into two groups: modes that can potentially contribute significantly to off-track vibrations of the read-write heads, and modes that can contribute significantly to flying height-modulation.; Several researchers proposed the use of strain sensors for active vibration control in disk drives. The main idea was to strategically attach strain sensors to measure localized strains at key locations on drive structures, so that the sensors will effectively detect structural vibrations that may result in off-track motion of the heads. The measured strain information can then be used by the servo controller to suppress off-track motion of the heads by using active feedback damping or active feedforward compensation. A prerequisite to implementing such an approach was determining the optimal placement of the strain sensors. In this study, the optimal location and orientation of strain sensors on an instrumented suspension were determined based on the degree of observability of suspension modes that contribute to off-track vibration of the heads.; The final part of this work addressed the characterization of airflow effects in hard disk drives through experimental research of the effects of the actuator arm geometry on the off-track vibrations of the heads and airflow in a modeled drive. (Abstract shortened by UMI.)...