High-bandwidth controller design for dual-stage actuator system in hard disk drives

Large-capacity hard disk drives are important for the development of an information society. The capacities of hard disk drives depend on the positioning accuracy of magnetic heads, which read and write digital data, in disk-positioning control systems. Therefore, it is necessary to improve positioning accuracy to develop hard disk drives with large capacities. Hard disk drives employ dual-stage actuator systems to accurately control the magnetic heads. A dual-stage actuator system consists of a voice coil motor and micro-actuator. In micro-actuators, there is a trade-off between head-positioning accuracy and stroke limitation. In particular, in a conventional controller design, the micro-actuator is required to actuate such that it compensates for low-frequency vibration. To overcome this trade-off, this study proposes a high-bandwidth controller design for the micro-actuator in a dual-stage actuator system. The proposed method can reduce the required stroke of the micro-actuator by increasing the gain of the feedback controller of the voice coil motor at low frequencies. Although the voice coil motor control loop becomes unstable, the micro-actuator stabilizes the entire feedback loop at high frequencies. As a result, the control system improves the positioning accuracy compared to that achieved by conventional control methods, and the required micro-actuator stroke is reduced.

On the Static Pull-In of Tilting Actuation in Electromagnetically Levitating Hybrid Micro-Actuator: Theory and Experiment

This work presents the results of the experimental and theoretical study of the static pull-in of tilting actuation executed by a hybrid levitation micro-actuator (HLMA) based on the combination of inductive levitation and electrostatic actuation. A semi-analytical model to study such a pull-in phenomenon is developed, for the first time, as a result of using the qualitative technique based on the Lagrangian approach to analyze inductive contactless suspensions and a recent progress in the calculation of mutual inductance and force between two circular filaments. The obtained non-linear model, accounting for two degrees of freedom of the actuator, allows us to predict accurately the static pull-in displacement and voltage. The results of modeling were verified experimentally and agree well with measurements.

On the Static Pull-in of Tilting Actuation in Hybrid Levitation Micro-actuator: Theory and Experiment

This work presents the results of the experimental and theoretical study of the static pull-in of tilting actuation executed by a hybrid levitation micro-actuator (HLMA) based on the combination of inductive levitation and electrostatic actuation. A semi-analytical model to study such the pull-in phenomenon is developed, for the first time, as a result of using the qualitative technique based on the Lagrangian approach to analyze inductive contactless suspensions presented in work and a recent progress in the calculation of mutual inductance and force between two circular filaments. The obtained non-linear model, accounting for two degrees of freedom of the actuator, allows us to predict accurately the static pull-in displacement and voltage. The results of modelling were verified experimentally and agree well with measurements.

Periodic oscillations for a graphene-based electrostatic micro actuator

We study the mechanical oscillations for a novel model of a graphene-based electrostatic parallel plates micro actuator introduced by Wei et al.(2017), considering damping effects when a periodic voltage with alternating current is applied. Our analysis starts from recent results about this MEMS model with constant voltage, and provides new insights on the periodic mechanical responses for a variable input voltage. We derive sufficient conditions on the system physical components for which periodic oscillations with constant sign exist together with their stability properties. Specifically, under some conditions, the existence of three periodic solutions is established, one of them is negative and the others are positive in sign. The positive one nearby the origin is asymptotically locally stable, whilst the other two are unstable. Additionally, we prove that no further constant sign periodic solutions can be found. The existence of periodic solutions is approached from direct and reverse order Lower and Upper Solutions Method, and the stability assertions are derived from the Liapounoff-Zukovskii criteria for Hill's equations and the linearization principle. Theoretical results are complemented by numerical simulations and numerical continuation results. Furthermore, these numerical simulations evidence the robustness of the graphene-based MEMS model over the traditional ones.

Data Driven Feedforward Control Design and Input Shaping Techniques for Multi Actuator Drives

The multi actuator drive technology was unveiled by Seagate in December 2017, a breakthrough that can almost double the data performance of the future generation hard disk drives. This technology will equip drives with dual actuators operating on the same pivot point. Each actuator will control half of the drive's arms. Since two actuators operate independently on the same pivot timber, the control forces and torques generated by one actuator can affect the operation of the other actuator. We will have a scenario when one actuator is track seeking and the other actuator is in the track following mode. The track seeking actuator will impart vibration disturbances to the track following actuator. Previously, we presented a single-input single-output (SISO) data driven feedforward control design method [1] to obtain feedforward controllers for the voice coil motor and the micro actuator sequentially. The design was based on multiple frequency response measurements of the actuators. In this paper, firstly, we present a single-input multi-output (SIMO) data driven feedforward control design technique to simultaneously obtain feedforward controllers for the voice coil motor and the micro actuator. This methodology will obtain a common controller for multiple drives. We will compare the performance of this algorithm with the sequential SISO design technique [1]. Secondly, we present an add-on input shaping technique to suppress the residual vibration.