Design and control of a single-stage dual-actuator system for high-precision manufacturing

This paper proposes a design for the linear state feedback control of the dual-actuator system, which is a dual-input single-output system for the high-precision manufacturing stage. The proposed control prevents saturation or reduces the unnecessary movement of the piezoelectric (PZT) actuator at the transient response by tracking the error between the estimated and actual positions of the coarse-actuator system at each control sample. Also, a new mechanism of the single-stage dual actuator is introduced. The axes of the stepper motor and the PZT actuator are co-axial. The coupling effects between the stepper motor and the PZT actuator are considered. Both the simulation and experiment results show that the proposed algorithm successfully prevents unwanted motions of the PZT actuator at the transient response. The experiment results show that the settling time and overshoot were enhanced by 45.7 and 95.9 %, respectively, for the proposed algorithm when the reference distance was 10 μm, which exceeds the stroke of the PZT actuator.     

Track-following control of a dual-stage hard disk drive using a neuro-control system

This paper describes the track-following control of a dual-stage hard disk drive system using neural-networks. A neural-network approach to on-line learning control, and a real-time implementation for a dual-stage hard disk drive, are presented. The use of the dual-stage actuator in hard disk drive systems has become a means of achieving increased servo actuator bandwidth. The dual-stage actuator presented here uses a voice-coil motor (VCM) as a coarse actuator, and a piezoelectric actuator (PZT) as a fine actuator. The control system consists of a series combination of both a plant with a feedback loop and a neural-network with a feedforward loop. The neural-network functions as the reference input filter, and it organizes a new reference signal to the closed-loop circuit. Numerical and experimental results for the track-following control system of the dual-stage hard disk drive show the validity of the proposed neuro-control system.     

Swing-arm-type PZT dual actuator with fast seeking for optical disk drive

 In this paper, a swing-arm-type dual positioning mechanism using a voice coil motor (VCM) and bimorph PZT actuators is proposed for the possible application to the future optical disc drive actuator. A VCM is used as a coarse motion actuator, and a set of piezoelectric actuators is used for fine motion. The two pairs of PZT actuators are arranged in parallel and are carefully designed to deflect in `S' shape such that tension and compression forces are generated simultaneously and thus the hysteresis is minimized. The static and dynamic analyses are performed and the parameter studies on the key dimensions of the set of PZT actuators are investigated. For fast seeking motion, time optimal control scheme combined with PD algorithm is adopted for the fast seeking motion of VCM. Positive position feedback (PPF) control is used to suppress residual vibration for the PZT actuator beams by activating it at the end of VCM swing motion. The feasibility of the suggested actuator system and the control scheme is demonstrated through simulations and experiments. Received: 5 July 2001/Accepted: 21 December 2001     

A push–pull multi-layered piggyback PZT actuator

 To increase the recording density of hard disk drives (HDDs), we developed a push–pull multi-layered piggyback PZT actuator that enables fine positioning by a dual-stage servo system. This PZT actuator consists of 31-mode push–pull multi-layered PZT strips and a head suspension. It generates a 1.4-μm effective radial head displacement at 5 V. This displacement is twice that of conventional piggyback actuators. The main resonance frequency of the actuator is higher than 9 kHz, its lifetime is longer than five years, and it has a self-latch property. These features mean that the developed actuator can meet all the requirements for implementation in HDD servo systems, including a track density of 100 kTPI (kilo-tracks per inch). The actuator was implemented in two types of HDDs (A-type and B-type), which reduced the repeatable and non-repeatable positioning errors (by 40 to 45% and 28 to 34%, respectively). Received: 25 July 2001/Accepted: 11 December 2001     

Design of a dual stage actuator tape head with high-bandwidth track following capability

As tape recording density increases, high-frequency track following capability of the tape head actuator becomes more important. This paper details the mechanical design and experimental analysis of a dual state actuator tape head. The dual stage actuator design combines a traditional voice coil motor for low frequency track following with a piezoelectric actuator for high-frequency track following. Non-parametric and parametric modeling techniques are used in the analysis of the dual stage actuator. The performance of the dual stage actuator head shows good correlation with the model and will enable improved track following capability for future high-performance tape drives.     

Novel piezoelectric actuator control slider using transverse-mode deformation

This work proposes a novel structure design of active slider with a piezoelectric actuator at the top of the slider body and a soft layer between the substrate and head elements, to efficiently control the flying height of slider. A parametric simulation was performed to obtain an optimize dimension of PZT actuator and the most efficient soft material. Then three types of slider structures were designed and investigated with considering air bearing effects to achieve large actuation efficiency.     

Finite element method analysis and control of micro actuator with piezoelectric element for spinstand

A micro actuator was introduced to achieve highly precise track following with an head gimbals assembly (HGA) for a spinstand tester. The actuator constructed with a piezoelectric element and a stroke amplifying mechanism was designed by using finite element method analysis. According to robust controller using H_∞ control theory was designed so as to guarantee the control performance for two kinds of HGAs. As the experimental results of the step response show, it was found that the settling time and the rise time were about 3.0 ms and about 1.0 ms, respectively.     

Enhancement of PZT embedded swing arm actuator using integrated read/write performance and actuation

The current technological challenges associated with the rotary-type seesaw arm actuator for small-form-factor (SFF) disk drives are the small skew focusing, which causes off-axis aberrations and reduces optical quality. This article develops a novel design for a seesaw arm actuator and suspension assembly that is based on a micro-PZT actuator to position pickup head. Dual-stage actuation relaxes the dynamic requirement on the focusing stroke. The proposed actuator with a tilt-compensation mechanism uses a PZT bender to drive pickup head focusing. This combined system, optical module and dual stage actuator, is effectively self-aligned the optical axis for read/write performance in both experiment and simulation result. Finite element modeling and dynamic measurements reveal significant improvements in the actuator bandwidth with and without micro-PZT actuator compensation.     

Analytical dynamic model for suspension with PZT actuators

Modern hard disk drive uses voice coil motor to move its actuator across spinning disk to access data stored on disk surfaces. To achieve higher area density with narrow tracks, piezoelectric (PZT) ceramics are deployed as secondary actuator in many high capacity drives to increase servo control bandwidth for better positioning accuracy. Piezoelectric secondary stage actuators, often called dual stage actuator or DSA, integrated on suspensions are discussed in this paper. An analytic model is presented to derive a secondary order equation of motion relating suspension dynamics to key suspension and PZT geometric parameters, material properties and voltage applied to PZT. DSA DC gain is then obtained from the equation of motion. By introducing a suspension configuration without PZT installed, the DSA DC gain is then further linked to suspension dynamics parameters. With the equation of motion and DSA DC gain model, design directions for higher stroke and tradeoffs for dynamics and robustness are discussed.     

A new direct Seek Control Design of Optical Disk Drives

This paper is concerned with the seek control of Optical Disk Drives (ODDs). We propose a direct Seek Control Scheme (SCS) that provides fast data access capability and robust stability for high-performance Optical Disk Drives. Although an optical disk drive has a significant advantage of random accessibility, increased rotational speed of a disk and limitations of mechanical structure always make it impossible for the conventional SCS to achieve stable and satisfactory seek performance. The conventional seek control technique utilizes only the coarse actuator without any maneuvering of the fine actuator. In this paper, we analyze the problems that may arise when the conventional SCS is applied to high-speed rotational ODD and propose a new SCS that employs both the coarse and fine actuators. With assistance of the fine actuator, however, the seek control system is designed such that its performance is guaranteed for various disturbances and mechanical limitations. Simulations and experiments show the improvements of the proposed direct SCS implemented on a practical DVD-ROM drive system.     

Adaptive reliable guaranteed performance control of uncertain nonlinear systems by using exponent‐dependent barrier Lyapunov function

This paper investigates the issue of adaptive reliable tracking control for a class of uncertain nonlinear parametric strict‐feedback systems under actuator faults. To guarantee better transient performance of adaptive systems especially when actuator faults occur, a novel prescribed performance bounds (PPBs) method based on exponent‐dependent barrier Lyapunov function is developed. Differing from the existing results where the control schemes have introduced the strictly monotone smooth function to achieve constrained error transformation, the proposed PPBs scheme is designed by using the time‐varying barriers to constrain the error trajectories, which accurately characterizes the convergence rates and convergence bounds of errors. Finally, under the framework of backstepping technique and Lyapunov stability theorem, an adaptive reliable controller is designed to ensure that all the closed‐loop signals are semiglobally uniformly ultimately bounded with the tracking errors converging to the specified PPBs. Simulation results demonstrate the effectiveness of the proposed approach.     

Active-head sliders using piezoelectric thin films for flying height control

This paper describes design and fabrication of a MEMS-based active-head slider using a PZT thin film for flying height control in hard disk drives. A piezoelectric cantilever integrated in the air bearing slider is used to adjust the flying height individually. An air bearing surface (ABS) geometry that minimizes the aerodynamic lift force generated beneath the head has been designed based on the molecular gas film lubrication (MGL) theory. The sliders with PZT actuators were fabricated monolithically by silicon micromachining process. Performance of the actuator was tested by using an optical surface profiler. Furthermore, the fabricated slider was mounted on a suspension and the flying height of the slider above a spinning disk has been measured by multiple wavelength interferometry. Change in the head-disk spacing has been successfully confirmed by applying voltage to the actuator.     

Adaptive inverse control for parametric strict feedback systems with unknown failures of hysteretic actuators

An adaptive compensation control scheme is proposed by using backstepping techniques for a class of uncertain nonlinear systems preceded by m hysteretic actuators, which exhibit unknown backlash nonlinearity and possibly experience unknown failures. An estimated smooth inverse of the actuator backlash is utilized in the controller design to compensate for the effects of the backlash and actuator failures. It is shown that the designed controllers can ensure all signals of closed‐loop system bounded for any failure pattern of hysteretic actuators and tracking performance is also maintained. Simulation studies confirm the effectiveness of the proposed controller, especially the improvement of system performances. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance-optimized design of electromagnetic micro-actuator for Probe recording storage device

In this paper the performance-optimized design of an electromagnetic micro-actuator for a Probe data-storage system is described. The Probe recording system considered in this study consists of a MEMS-based recording head array that can translate relative to a Ferroelectric media substrate. The probe device is slated to achieve 1 Tb/in2 recording density and a read/write data rate of 100 Mb/s while operating within a total power budget of 100 mW. Stringent requirements apply to the form-factor and packaging, power consumption, and operating environment making the design of the mechanical architecture and in particular, the actuator a challenging task. A methodology based on an analytical model framework for performance-optimal design of the actuator meeting these constraints is developed and presented.     

A fast settling servo controller for high-density disk drives

During seek operation in disk drives, the recording head is moved toward desired track by seek servo controller and then is settled onto the center of the desired track by settling servo controller. If the head speed at the start of settling servo controller is not slow, it may produce overshoot relative to the center of track and thus extend settling time. The degradation in settling performance will be more severe as the track width becomes smaller for high track density. In this paper we discuss the design of settling servo controller which provides fast settling performance without creating overshoot. It is well known that transient response will be much faster if slow poles are canceled out properly. In order to cancel unwanted poles, we apply a sequence of weighted discrete pulse signals to the system in addition to the state feedback control. For exact pole-zero cancellation, we consider the dynamics of power amplifier used for actuator current regulation and the effects of delay in control action. In addition, we present system parameter identification algorithm for the robustness of our controller to system parameter variation. In order to demonstrate the practical use of our controller, we present experimental results obtained by using a commercially available disk drive.This work was supported by the Nuclear Academic Research Program of the Ministry of Science and Technology in Korea.     

Finite element analysis of a IBM suspension integrated with a PZT microactuator

This paper presents a piezoelectric-based microactuator concept that could provide an economical and easily integrated option for dual stage actuation used in hard disk drives (HDDs). A simple cantilever beam integrated with the PZT actuator was simulated first in order to testify the driving mechanics of the new design. A modern suspension (IBM Deskstar DTLA-307015) integrated with the developed PZT actuator was then simulated by finite element method (FEM). Theoretical dynamic and electrostatic analyses were performed to investigated the resonant frequency and displacement sensitivity. Good dynamic characteristics were obtained. Further simulation was done based on the optimized structure of the actuator/suspension assembly and results show that >1 μm tip stroke can be obtained while the driving voltage is only 20 V. A 10 V is sufficient to get >1 μm tip stroke if double layer PZT actuator is used.     

Microfabricated Lamb wave device based on PZT sol-gel thin film formechanical transport of solid particles and liquids

The fabrication using silicon micromachining and characterization of an acoustic Lamb wave actuator is presented. The intended use of the device is for mass transport and sensor applications. The device consists of dual interdigitated transducers patterned on a thin-film composite membrane of silicon nitride, platinum, and a sol-gel-derived piezoelectric ceramic (PZT) thin film. The acoustic properties of the device are presented along with preliminary applications to mechanical transport and liquid delivery systems. Improved acoustic signals and improved mass transport are achieved with PZT over present Lamb wave devices utilizing ZnO or AlN as the piezoelectric transducer     

Improving transient performance in tracking control for linear multivariable discrete-time systems with input saturation

In this paper, we present a composite nonlinear feedback (CNF) control technique for linear discrete-time multivariable systems with actuator saturation. The CNF control law serves to improve the transient performance of the closed-loop system by adding an additional nonlinear feedback. The linear feedback can be designed to yield a quick response at the initial stage, then the nonlinear feedback is introduced to smooth out overshoots when the system output approaches the target reference. As such, the resulting closed-loop system typically has very fast transient response and small overshoots. The goal of this work is to complete the theory for general discrete-time systems. The technique is applied to a magnetic-tape-drive servo system design and yields a huge improvement in settling time compared to that of a purely linear controller.     

Design of flexural pivot for use in hard disc drive actuator

A cross leaf flexural pivot is proposed and designed for use in disc drive actuator to replace the currently used ball bearing system. The static and dynamic performances of the proposed design are investigated using finite element analysis. It is shown that flexural pivot can achieve a translatory stiffness comparable to currently used ball bearing. The tilt stiffness is lower than that of ball bearing. The design is prototyped and the life cycling test shows that the prototype can work for more than 3 million life cycles without any failure. Our experimental results show that the single-stage servo loop using the flexural pivot can achieve the performances of open-loop bandwidth of 630 Hz and closed loop bandwidth of 1100 Hz, with phase margin of 60° and gain margin of 6.6 dB. When attaching an actuated suspension to from a dual stage servo loop, we show that the performances as open-loop bandwidth of 1700 Hz with the phase margin of 45° and gain margin of 7 dB.The authors would like to thank Dr. Guoxiao Guo and Dr. Eng Hong Ong at Data Storage Institute, Singapore, for their invaluable input and suggestions.     

NANO TRAJECTORY CONTROL OF MULTILAYER LOW‐VOLTAGE PZT BENDER ACTUATOR SYSTEMS

In this paper, nano trajectory control of the multilayer low‐voltage PZT (lead zirconate titanate) bender actuator system (MLVPZTBAS) is developed. System analyses in of the hysteresis characteristic, frequency response and sinusoidal response, were conducted to evaluate the system features. Because not all of the states of the MLVPZTBAS are directly available, an observer is required to estimate the states. The proposed scheme contains feedback linearization with a sliding‐mode controller and a state observer to estimate the system states of the MLVPZTBAS. The sliding‐mode control possesses an equivalent control and a switching control. To track a trajectory dominant by a specific frequency, a reference model consisting of desired amplitude and phase features is established. The equivalent control using the signals from the observer and the reference model is designed so as to produce the desired control behavior. Due to the existence of modeling and estimation errors, the switching control is then employed to achieve robust performance. Experiments on the MLVPZTBAS were carried out to verify the usefulness of the proposed control.