Precision Positioning of Hard Disk Drives Using Piezoelectric Actuators With Passive Damping

Positioning precision is crucial to today's increasingly high-speed, high-capacity, high-data-density, and miniaturized hard disk drives (HDDs). The demand for higher bandwidth servo systems that can quickly and precisely position the read/write head on a high track density becomes more pressing. The idea of applying dual-stage actuators to track servo systems has been studied. However, the current dual-stage actuator design uses only piezoelectric patches without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. The proposed actuators will improve the existing dual-stage actuators for higher precision and shock resistance, due to the incorporation of passive damping in the design. We aim to develop this hybrid servo system not only to increase the speed of track seeking but also to improve the precision of track following servos in HDDs. New piezoelectrically actuated suspensions with passive damping have been designed and fabricated. In order to evaluate positioning and track following performances for the dual-stage track servo systems, experimental efforts are carried out to investigate the damping abilities and transmissibilities of the microactuators and to implement the synthesized active-passive suspension structure using a composite nonlinear feedback controller.     

压电微执行器在硬盘伺服系统的应用研究

介绍一个硬盘双伺服控制系统的设计和实现。双伺服系统是在硬盘固有的音圈电机上附加了一个压电微执行器,用来执行更快捷、精确的磁头定位。对音圈电机的控制设计采用了一种线性反馈控制技术,结合扰动估计和补偿实现快速、平稳和无静差的设定点跟踪。基于开环逆控制的思想,微执行器环路的控制采用定值比例及滤波器,使得合并的位移输出能更快地跟踪设定点(磁道)。仿真和实验结果证明双伺服控制系统可以实现更快速、精确的磁头定位。     

Two-parameter robust repetitive control with application to a novel dual-stage actuator for noncircular Machining

This work presents a robust repetitive controller design for a novel dual-stage actuator system. The dual-stage actuator, which consists of an electrohydraulic actuator for 25-mm-gross motion and a piezoelectric actuator for 40-/spl mu/m fine motion, is designed for noncircular machining application. The controller is designed through a sequence of two single-input-single-output (SISO) designs by exploiting the triangular structure of the two by two actuator system dynamics. The tracking error from the first stage electrohydraulic actuator is used as reference for the second stage piezoelectric actuator. In this master-slave control arrangement, the overall sensitivity function is the product of two sensitivity functions from each actuator's servo loop. Thus, performance is improved at the frequencies where the sensitivity values are already well less than one. In the real-time control implementation, the effects of finite word length are analyzed and addressed via controller order reduction and realization. In an experiment of tracking an automotive cam profile at the rate of 10 cycles per second (600 rpm), the proposed dual-stage servo system generated tracking error of 4-/spl mu/m peak-to-valley and 0.80-/spl mu/m root-mean-square (RMS) value, showing a substantial improvement over the 16 micron peak-to-valley and 2.64-/spl mu/m RMS errors generated by the electrohydraulic servo system alone.     

空间光通信中精跟踪控制器的设计

精跟踪伺服系统设计是APT的核心技术,决定了通信链路能否建立以及通信系统的性能.针对空间光通信中压电陶瓷驱动FSM偏转具有非线性、时变不确定性和纯滞后等特性,提出变论域自适应模糊PID控制方法.引入变论域思想,并通过对输入变量加入伸缩因子的方式来实现变论域的目的,自适应能力和抗干扰能力明显增强.可有效解决稳定性与准确性的矛盾.实验结果表明:模糊PID控制算法增强了伺服系统鲁棒性,并提高了伺服系统实时性;跟踪精度可达到5μrad,对卫星平台振动和大气湍流引起信标光斑抖动有一定的抑制作用,能够满足空间光通信精跟踪精度的要求.     

Design and control of a rotary dual-stage actuator positioning system

This paper presents the design and control of a rotary dual-stage actuator (DSA) positioning system, which has a flexure-based beam driven by a voice coil motor (VCM) and a piezoelectric (PZT) actuator simultaneously. The design goal is to enable the two actuators complementary to each other for the combined ability of high positioning accuracy and a large tangential displacement range. To achieve a high tracking speed, the flexure beam is designed via finite element method (FEM) analysis to have sufficiently high open-loop bandwidth. System identification and measurements on the DSA prototype are also presented to verify the FEM analysis. Finally, the composite nonlinear control (CNC) method is applied to the DSA system. Experimental results demonstrate that the DSA servo system significantly outperforms the single-stage servo system in both step tracking and disturbance rejection.     

Design and performance of a dual drive system for tip-tilt angular control of a 300 mm diameter mirror

This paper presents the design, manufacture, and implementation of a dual-stage tip-tilt steering mechanism driven by ultra-high strain piezoelectric stacked actuators for coarse and fine motion control. The design of motion control systems often requires a compromise between range and bandwidth response. Consequently, for a given dynamic response, as range increases so too will following errors If advanced information is available, these errors may often be minimized by using feedforward techniques. In recent years, dual-stage systems which incorporate serially connected fine and coarse stages have demonstrated promising results. Related efforts (employing dual-stage methods) have addressed variants on designs using PZT elements, voice coils, or linear motors. The dual-stage uses a fine motion platform (with high frequency response and short range) to actively reduce following errors of the coarse platform which has a lower bandwidth response. This paper presents a dual-stage (also referred to as a multi-coaxial) tip-tilt mechanism with 6 degree of freedom (DOF) comprising two 3 DOF stages connected in series. The ultimate purpose of the mechanism is to position a 300 mm diameter mirror, hence it is referred to as a fast steering mirror. Also described is the nested control algorithm that is used to derive the drive signals for both the fine and coarse platforms. The algorithm provides a method by which the fine platform is actively driven to a commanded offset (usually its mid-range setting) by the coarse platform. Concurrently, the fine platform actively responds to the demand to reduce rapidly changing following errors. Finally, an experimental program is overviewed to assess the closed loop response for the fine, coarse, and dual-stage controllers. In one experiment, a sinusoidal input of amplitude ±300 μrad was employed at 10 Hz. The coarse controller generated a following error up to ±100 μrad at 10 Hz. In contrast, the dual-stage mechanism equipping both the coarse and fine controller reduced the following error to ±5 μrad. Frequency response plots of the closed loop control system are also presented and, with further optimization, indicate potential bandwidth improvements with small following errors and minimal phase lags up to 70 Hz.     

Nonlinear Tracking Control for a Hard Disk Drive Dual-Stage Actuator System

This paper presents a nonlinear tracking control method for a hard disk drive dual-stage actuator (DSA) system that consists of a voice coil motor (VCM) actuator and a piezoelectric (PZT) microactuator. Conventional track seeking controllers for DSA systems were generally designed to enable the VCM actuator to approach the target track without overshoot. However, we observe that this strategy is unable to achieve the minimal settling time when the target tracks are beyond the PZT actuator stroke limit. To further reduce the settling time, we design the VCM actuator controller to yield a closed-loop system with a small damping ratio for a fast rise time and certain allowable overshoot. Then, a composite nonlinear control law is designed for the PZT actuator to reduce the overshoot caused by the VCM actuator as the system output approaches the target track. Experimental results show that the proposed dual-stage servo outperforms the conventional dual-stage servo in short-span seeking and, additionally, achieves better track following accuracy than the VCM only single-stage servo.     

Development and Assessment of a Novel Decoupled XY Parallel Micropositioning Platform

This paper presents the development and performance assessment procedures for a new XY parallel micropositioning platform (PMP) aiming at a submicrometer accuracy for microscale manipulation. The uniqueness of the proposed microparallel platform lies in that it possesses an uncomplicated structure as well as actuation isolation and output motion decoupling properties, which facilitates the adoption of two single-input–single-output controllers. Based on the matrix method, the kinetostatics models of the PMP are established and verified by finite-element analysis. Via system identification, a digital lag--lead compensator is designed to compensate for the hysteresis of each piezoelectric actuator. A feedforward control is then implemented to construct a zero phase error tracking controller. Positioning performance of the PMP in terms of resolution, accuracy, repeatability, and contouring performances of 1-D and 2-D motions has been evaluated by several experimental studies. Experimental results not only validate the effectiveness of the designed controller but also show that both positioning and contouring of the PMP can achieve a submicrometer precision within a specified velocity range.      

Performance tuning of robust motion controllers for high-accuracy positioning systems

This paper presents a structural design method of robust motion controllers for high-accuracy positioning systems, which makes it possible to tune the performance of the whole closed-loop system systematically. First, a stabilizing control input is designed based on Lyapunov redesign for the system in the presence of uncertainty and disturbance. And adopting the internal model following control, robust internal-loop compensator (RIC) is proposed. By using the structural characteristics of the RIC, disturbance attenuation properties and the performance of the closed-loop system determined by the variation of controller gains are analyzed. Next, in order to design a robust motion controller for a high performance positioning system, dual RIC structure is proposed and it is shown that if the synthesis of the robust motion control law is performed in the RIC framework, the robust property of RIC can be naturally implanted in the feedback controller. The proposed structural design of robust motion controller provides a systematic approach to the problem of robust stability and performance requirement in the face of uncertainty. Furthermore, by allowing the tradeoffs between robust stability and performance to be quantified in a simple fashion, it can illuminate systematic design procedure of the robust motion controllers. Finally, the proposed method is verified through simulation and the performance is evaluated by experiments using a high-accuracy positioning system.     

High-bandwidth high-accuracy rotary microactuators for magnetichard disk drive tracking servos

Reports on the design, fabrication, and testing of an electrostatic microactuator for a magnetic hard disk drive (HDD) tracking servo. The design requirements for a microactuator are investigated. These include high Z-directional stiffness, low in-plane stiffness, high structural aspect ratio, large output force, high area efficiency, low cost, and mass batch production. An area-efficient rotary microactuator design was devised, and microactuators were successfully fabricated using innovative processing technologies. The microactuator has a structural thickness of 40 μm with a minimum gap/structure width of approximately 2 μm. Its frequency response was measured and it was determined that it can be modeled as a second-order linear system, up to the 26-kHz frequency range. Moreover, the microactuator will enable the design of a servo system that exceeds a 5-kHz servo bandwidth, which is adequate to achieve a track density of more than 25 kilotrack per inch (kTPI). The microactuator/slider assembly was also tested on a spinning disk, with its position controlled by a PID controller using the magnetic position error signal written on the disk. An accuracy of about 0.05 μm was observed when the servo controller was turned on. Continuous-time dual-stage servos were designed and simulated using the μ-synthesis technique. A sequentially designed SISO and a MIMO control design method have been shown to be capable of meeting prescribed uncertainty and performance specifications     

Analysis and experimental comparison of range-based control for dual-stage nanopositioners

In this paper, a novel range-based control algorithm for dual-stage nanopositioners is studied. Dual-stage nanopositioning systems have the powerful ability to achieve high-speed and long-range positioning by coupling a short-range, high-speed actuator with a long-range, low-speed actuator. One of the drawbacks of currently implemented control algorithms is that they tend to determine control allocation to the individual actuators based on the frequency of the desired motion. This can result in reduced positioning resolution and increased energy use, thus motivating this work on a control algorithm that considers range. The range-based algorithm allows the user to allocate control efforts to the individual actuators based on their range capabilities. This paper discusses the analysis, design, and implementation of the range-based control algorithm and highlights its benefits by experimentally comparing it to four other widely used dual-stage positioner control algorithms. Experimental results show that the method effectively splits control effort between the actuators based on range and results in reduced tracking error.     

Enhancement of tracking ability in piezoceramic actuators subject to dynamic excitation conditions

An operator representing the inverse dynamics of hysteretic effects inherent to piezoceramic actuators is used to enhance the tracking accuracy of a piezoceramic-driven positioning system when subject to dynamic reference input signals covering a wide frequency range. An open-loop tracking controller and a closed-loop tracking controller are developed based on the new inverse algorithm and are experimentally shown to achieve high-accuracy tracking control.     

Dual-stage HDD head positioning using an H∞ almost disturbance decoupling controller and a tracking differentiator

We adopt in this paper a novel control scheme to achieve fast and accurate head positioning for dual-stage actuated hard disk drive (HDD) servo system with actuator saturation and disturbances. This control scheme consists of a tracking differentiator (TD) to avoid actuator saturation as large as possible and an H_∞ almost disturbance decoupling controller to deal with disturbances and improve the tracking performance. More specifically, the TD aims to provide a smooth reference signal in a feedforward way so as to reduce the system error, and further decrease the control inputs to both the VCM actuator and the micro-actuator such that the saturation problem can be effectively avoided. The H_∞ almost disturbance decoupling controller, when it is applied to control the micro-actuator, is able to almost decouple the disturbance and the controlled output such that satisfactory tracking performance can be achieved. Furthermore, the VCM actuator is controlled by a notch filter in series with a lead compensator so as to stabilize the servo loop. Finally, simulation results in time domain and frequency domain verify the effectiveness of the proposed control scheme.     

MIMO multirate feedforward controller design with selection of input multiplicities and intersample behavior analysis

Inversion-based feedforward control is a basic method of tracking controls. The aim of this paper is to design MIMO multirate feedforward controller that improves continuous-time tracking performance in MIMO LTI systems considering not only on-sample but also intersample behavior. Several types of MIMO multirate feedforward controllers are designed and evaluated in terms of the 2-norm of the control inputs. The approach is compared with a conventional MIMO single-rate feedforward controller in simulations. The approach improves the intersample behavior through the optimal selection of input multiplicities with MIMO multirate system inversion.     

基于迭代学习控制的潜望式激光通信终端系统的动态跟踪设计

为提高潜望式激光通信终端伺服系统的动态跟踪性能,针对基于永磁同步电机的二维伺服转台的控制系统进行了设计。通过采取空间矢量控制方法实现电机的解耦控制,建立控制模型并完成了各控制回路的设计。针对动目标跟踪设计了迭代学习控制方法以提高通信终端的动态跟踪性能,并对控制系统的速度阶跃响应进行测试,分析通信终端系统的低速平稳性。最后,搭建了4.62 km激光通信的动态跟踪实验,利用六自由度转台模拟平台抖动,为动态跟踪验证实验创造外部平台扰动条件。实验结果表明:通信终端系统速度阶跃响应的稳态误差为±0.02 (°)/s,表明伺服系统速度回路具有较快的动态响应特性和较高的稳态精度,在最大加速度为0.219 (°)/s2的正弦波扰动条件,二维伺服转台的动态粗跟踪精度可以达到62 μrad,粗精复合跟踪精度优于2 μrad,验证了通信终端伺服系统的有效性及其动态跟踪性能,为进一步提高终端系统的跟踪精度奠定基础。     

Dual-stage repetitive control with Prandtl–Ishlinskii hysteresis inversion for piezo-based nanopositioning

The positioning performance of piezo-based nanopositioning systems is limited by dynamic and hysteresis effects in the piezoactuator. Herein, a high-performance, dual-stage repetitive controller (dual-RC) with a feedforward hysteresis compensator is proposed for tracking periodic trajectories, such as the scanning-type motion, in nanopositioning systems. Firstly, a discrete-time dual-RC is created by cascading a conventional RC with an odd-harmonic RC. The favorable gain characteristics of the dual-RC coincide with the odd harmonics of the scanning-type periodic reference trajectory, thus offering good robustness and low tracking error. Secondly, a new inverse-hysteresis compensator is developed based on the Prandtl–Ishlinskii hysteresis model. The structure of the inverse model mimics the structure of the forward model, where the parameters of the inverse model can be easily identified from measured input–output data. Finally, the controllers are applied to a custom-designed high-speed nanopositioner, and simulations and experimental results are provided to illustrate the performance improvement of the proposed control scheme compared to industry-standard PID control and conventional RC. High-speed positioning results (tracking of triangle scan trajectories) at rates of 1 kHz, 1.5 kHz, and 2 kHz are shown. Compared to a conventional RC, the tracking error of the dual-RC is 48% lower at 1 kHz and 33% lower at 2 kHz scanning frequency. It is also shown that by compensating for hysteresis, the performance of the RC system designed based on the linear dynamics can be enhanced.     

Active tape steering control system

Lateral tape motion (LTM) in tape drives hinders accurate servo head positioning and can cause damage to the tape. It is one of the major obstacles to developing high density, high performance tape drives. This paper presents the development an active tape steering system to reduce LTM. The paper also shows the use of Robust Bode (RBode) plot, a relatively new technique for designing robust controllers. The RBode plot translates a robust performance criterion into allowable and forbidden regions on the open-loop Bode plot of a compensated SISO system. With the RBode plot robust controllers can be directly synthesized with classical loop shaping.     

Precision tracking control of a biaxial piezo stage using repetitive control and double-feedforward compensation

This article presents precision tracking control of an XY piezo stage using repetitive control and double-feedforward compensation. The XY piezo stage is composed of two piezoelectric actuators within a leaf spring mechanism. The study applies two feedback controllers, a Proportional-Integral-Derivative controller and a repetitive controller, to achieve precision trajectory tracking and evaluate performance against benchmarks. Moreover, the investigation applies a double-feedforward compensation approach that integrates a Zero-Phase-Error-Tracking-Controller and an adaptive plant inversion compensator adapted by a Least-Mean-Square algorithm, based on an inverse Prandtl-Ishlinskii model, to improve tracking control performance further. Performance analysis and comparison of the experimental results demonstrate that the proposed control structure improves dynamic tracking accuracy of the XY piezo stage.     

Integral sliding mode control with a disturbance observer for next-generation servo track writing

In this paper, we propose a new control scheme that provides position and velocity profile tracking control for next-generation servo track writing (STW). Whereas conventional servo track writers require controllers that perform fast positioning control with fast track seeking and regulation, spiral servo track writers require accurate position and velocity profile tracking control to achieve high quality servo patterns on the media disk. Because STW timing eventually renders geometrically accurate servo patterns, both position and velocity error signals should be regulated within small bounds in a constant velocity region. Regulation via an integral sliding mode controller (SMC) is known to provide good tracking performance; however, use of a high switching gain is inappropriate for an actuator with resonance modes. In this paper, we therefore apply integral sliding mode control with a disturbance observer to STW. The relationship between eigenvalues and control gains is mathematically analyzed to improve dynamic tracking response. To verify the utility of the proposed position and velocity profile tracking control, we perform a comparative study between the proposed and conventional control methods and experimentally validate the performance of the proposed method.     

光电跟踪转台伺服控制策略研究

针对高性能光电跟踪转台负载重、摩擦大、跟踪精度要求高等特点,提出了基于复合控制的伺服控制策略,速度环路设计了带有扰动观测器的线性二次最优反馈控制器,并在前向通道增加了零相位误差跟踪控制器(ZPETC),提高速度环的跟踪性能,位置环采用非线性PID反馈控制方式降低超调,提高稳态精度;将低速率的位置给定信息分别进行插值细分和滤波,通过高增益微分器和卡尔曼预测滤波,对转台速度和加速度进行预测和估计,进行前馈实现复合控制,实践证明,这种策略可以有效提高大加速度下的跟踪精度。