Xinghui Huang

Nanoprecision MEMS Capacitive Sensor for Linear and Rotational Positioning

This paper presents a microelectromechanical systems (MEMS) capacitive position sensor for nanopositioning applications in Probe storage systems. The objective of the sensor system design is to develop a high-precision X-Y linear and rotational position sensor with a minimum sensor area and a large range of movements at high speed. To achieve this, first, a simple sensor noise model scalable with a sensor area was developed, in which all the parasitic capacitances are taken into account. Furthermore, a signal-processing solution was developed to compensate for the nonlinearities caused by rotational disturbances and, at the same time, to generate a rotational position signal for active rotation-control purposes. A MEMS capacitive sensor prototype was constructed with the design of a 13-mum pitch, a 300-mum peak-to-peak linear stroke, and a 3.46-mm2 sensor area at a 3-mum gap. The measured sensor noise was 0.2 nm 1sigma, which corresponds to 12 mudeg 1sigma for the fabricated prototype sensor, at 25-kHz bandwidth. Furthermore, the signal linearity was significantly enhanced by the proposed sensor signal processing, with a measured sensor signal nonlinearity of 0.78% for an 80-mum peak-to-peak stroke at 200 Hz. Finally, the capacitive sensor-based dynamic closed-loop X -Y linear and rotational position control of an electromagnetic scanner was successfully demonstrated.

A comparison of multirate robust track-following control synthesis techniques for dual-stage and multisensing servo systems in hard disk drives

This paper presents the design and analysis of multirate robust track-following controllers for a dual-stage servo system with a MEMS microactuator (MA) and an instrumented suspension. Two major categories of controller design methodologies are considered. The first is based on sequential single-input single-output (SISO) design techniques, and includes the sensitivity decoupling (SD) method and the PQ method. High rate inner loop damping control is implemented followed by a low rate outer loop controller. The second category is based on multirate, multi-input multi-output (MIMO) design techniques, including mixed H2/Hinfin, mixed H2/mu and robust H2 synthesis. In this case, a set of controllers are designed all at once by explicitly considering plant uncertainty and hence robust stability. Comparisons are made between these design techniques in terms of nominal H2 performance, robust stability, and robust performance. The advantages and disadvantages of each of these methods are discussed, as well as the guidelines for practical implementation

Robust controller design of a dual-stage disk drive servo system with an instrumented suspension

This paper proposes a robust track-following controller design method for a dual-stage servo system in magnetic hard disk drives (HDDs). The method formulates the problem of minimizing track misregistration (TMR) in the presence of plant uncertainty and variation as a multiobjective optimization problem. Tracking error minimization is naturally formulated as an H/sub 2/ norm minimization problem, while the robust stability issue is addressed by some H/sub /spl infin// norm bounds. This mixed H/sub 2//H/sub /spl infin// control problem can then be formulated as a set of linear matrix inequalities (LMIs) and be efficiently solved through convex optimization algorithms. To enhance the systems tracking performance and stability robustness, the method explicitly takes attenuation of airflow-excited suspension vibration into consideration by an inner loop fast rate damping and compensation controller that utilizes the output of a strain gauge sensor on the suspension surface. Analysis and simulation show that a system designed by this method can achieve good tracking performance while still keeping stability robustness to plant variation and high-frequency spillover.

Multirate track-following control with robust stability for a dual-stage multi-sensing servo system in HDDs

This paper proposes a multirate design method for robust track-following controllers in hard disk drives (HDDs). The HDDs to be considered are dual-stage multi-sensing systems. A track-following problem, which takes into account robust stability, is formulated as a periodic time-varying version of the standard mixed H2/H∞control problem. This problem is solved via the solution of linear matrix inequalities. Simulation results show that multirate controllers can achieve much better track-following performance than single-rate controllers, while achieving the same guaranteed robust stability margin.

A Comparative Study of MEMS Microactuators for Use in a Dual-Stage Servo With an Instrumented Suspension

This paper presents the design and analysis of a dual-stage servo system with an instrumented suspension for use in hard disk drives. The dual-stage system is equipped with a microelectromechanical system microactuator (MA), either rotational or translational, as a secondary actuator. In both cases, the MA has a resonance mode at 2.2 kHz and has virtually no other modes up to 40 kHz. Two design approaches, the sensitivity decoupling design and the multiobjective optimization, are applied to the design of the servo system. With either approach, the translational dual-stage actuator achieves better tracking performance than the rotational one by about 13%, which is achieved mainly by attenuating airflow-excited suspension vibrations. This improvement is significant when the servo systems track misregistration (TMR) budget approaches the level of 5-10 nm. The airflow-excited suspension vibrations then become a significant contribution to the TMR

Design, fabrication, and control of a high-aspect ratio microactuator for vibration suppression in a hard disk drive

Abstract At bit densities now approaching 1 terabit per square inch, positioning the read-write head in a hard disk drive over data bits will require novel servo configurations and controllers. This paper presents a MEMS microactuator for installation in a dual-stage servo system for a hard disk drive and controller designs that utilize the microactuator to suppress vibration of the servo arm. The microactuator uses high-aspect ratio etching and deep trench isolation to generate high force densities and good mechanical robustness. The microactuator is installed in a hard disk drive and will be used to evaluate controllers designed to suppress airflow-induced vibration. Simulated and experimental results using PQ design methodology are presented.

Robust Control Synthesis Techniques for Multirate and Multisensing Track-Following Servo Systems in Hard Disk Drives

This paper proposes controller design methods, specially for track-following control of the magnetic read/write head in a hard disk drive (HDD). The servo system to be considered is a general dual-stage multisensing system, which encompasses most of the track-following configurations encountered in the HDD industry, including the traditional single-stage system. For the general system, a robust track-following problem is formulated as a time-varying version of the robust H 2 synthesis problem. Both dynamic and real parametric uncertainties, which are typical model uncertainties in track-following control, are taken into account in the formulation. Three optimal robust controller design techniques with different robustness guarantees are applied to solve the synthesis problem. These are mixed H 2 /H ∞ , mixed H 2 /μ, and robust H 2 syntheses. Advantages and disadvantages of each method are presented. Multirate control, which is inherent to control problems in HDDs, is obtained by reducing multirate problems into linear time-invariant ones, for which there are many useful theories and algorithms available. Most of the techniques proposed in this paper heavily rely on efficient numerical tools for solving linear matrix inequalities.

Robust H2 Synthesis for Dual-stage Multi-sensing Track-following Servo Systems in HDDs

This paper presents a robust H2 synthesis technique for designing a track-following servo system for a hard disk drive (HDD) product line. The goal is to design a single robust controller that minimizes the worst case H2 performance of an entire disk drive product line, assuming that dynamic variations in the product line (i.e. variations from one unit to another) are accurately characterized by affine variations in several of the actuators model parameters, such as variations in the resonance frequency or damping ratio of a resonance mode. The advantages and disadvantages of the proposed method are discussed and an illustrative realistic example is presented

Design and analysis of robust track-following controllers for dual-stage servo systems with an instrumented suspension

This paper discusses the design and analysis of two robust track-following controllers for a dual-stage servo system containing a MEMS microactuator and an instrumented suspension in hard disk drives. The first controller is designed using the so-called PQ method, which is a kind of sequential single-input/single-output (SISO) frequency shaping design techniques. Actuation interference is explicitly addressed in this design. The second controller is designed using a multi-objective optimization technique via linear matrix inequalities (LMIs). Stability robustness to plant uncertainty can be explicitly considered by imposing some H/sub /spl infin// norm bounds. In both cases, compensation of airflow-excited suspension vibration is implemented first by using the strain sensor output from the instrumented suspension. Detailed analysis and comparison are carried out on system dynamics, robust stability, robust performance, and implementation complexity.

A comparison of multirate robust track-following control synthesis techniques for dual-stage and multi-sensing servo systems in hard disk drives

This paper presents the system modeling, design, and analysis of multirate robust track-following controllers for a dual-stage servo system with a microelectromechanical systems (MEMS) microactuator (MA) and an instrumented suspension. A generalized model is constructed which includes a nominal plant, disturbances, uncertainties, and multirate sensing and control. Two major categories of controller design methodologies are considered. The first includes synthesis methodologies that are based on single-input single-output (SISO) design techniques, and includes the sensitivity decoupling (SD) and the PQ methods. In this case, a high sampling-rate inner loop damping control is first implemented using the auxiliary sensor signals. Subsequently, a low-rate outer loop controller is designed for the damped plant using either the SD or PQ design methods. The second category of design methodologies includes those based on multirate, multi-input multi-output (MIMO) design techniques, including mixed H/sub 2//H/sub /spl infin//, mixed H/sub 2///spl mu/, and robust H/sub 2/ synthesis. In this case, a set of controllers, which is periodically time-varying due to multirateness, is designed by explicitly considering plant uncertainty and hence robust stability. Comparisons are made between all the design techniques in terms of nominal H/sub 2/ performance, robust stability, and robust performance between these controllers, when the feedback controller is closed around the full order, perturbed plant. The advantages and disadvantages of each of these methods are discussed, as well as guidelines for their practical implementation.