A proximate-time-optimal-control design and its application to a hard disk drive dual-stage actuator system

We propose a compensator-based strategy for design of a track-seeking and track-following control system for a dual-stage servo actuator in hard disk drives. A well-known decoupling structure is employed to disconnect the control of the primary voice coil motor (VCM) actuator from the loop for a secondary high-bandwidth actuator. The compensator is placed in the secondary loop and suitably combined with a saturation nonlinearity in order to obtain actuator signal boundedness. The design procedure consists of four steps: 1) design of an established nonlinear seek-settle-track following controller for the VCM; 2) design of a linear track following controller for the secondary actuator; 3) observer design; and 4) design of a compensator to retain global stability and to improve performance. The proposed control system improves performance of both long-span seeking (proximate-time-optimal controller) and short-span seeking. In addition, it achieves high-bandwidth track following performance. The experimental results show good track-following performance, and short-span/long-span-seeking performance with fast settling time. The overshoot during track seeking can be made negligible for a suitably tuned VCM-actuator control loop.     

PC-based position error signal generation and servo system for a spinstand

We describe a high-performance servo control system for enhancement of spinstand servo performance. This PC-based system uses a multifunction I/O card for controller output and a high-speed digitizer card capable of sampling the frequency-encoded servo pattern at 500 MS/s. The PC, running under the Linux operating system, uses the Goertzel algorithm decoding scheme to calculate the position error signal (PES) at a 15-kHz update rate for feedback control. The control signal drives a custom-made lead zirconate titanate (PZT) actuator, which moves the suspension and thus the read/write head. A proportional and integral (PI) type servo controller supports a 1.1-kHz servo bandwidth, producing a 21.9% improvement of the positioning accuracy of the spinstand.     

U-type piezoelectric thin-film microactuator for hard disk drives

We have designed, fabricated, and investigated a new dual-stage actuator system based on a thin-film lead-zirconate-titanate (PZT) microactuator and a voice coil motor for positioning a magnetic head in a high-density hard disk drive (HDD). We made the PZT microactuator by using a modified sol-gel technique to deposit PZT thin film and applying reactive ion etching processes to shape the device. We studied the crystalline structure and growth behavior of the piezoelectric films by X-ray diffraction and scanning electron microscopy and found that the PZT material preferably has a composition of Pb(Zr/sub 0.52/Ti/sub 0/.48)O/sub 3/. We also tested and simulated the U-type SUS304 substrate integrated with two single-layer PZT elements in order to investigate the driving mechanics. The device performance is outstanding. With the peak-to-peak head displacement of 1.08 /spl mu/m at the applied voltage of /spl plusmn/20 V and the suspension response frequency higher than 12 kHz, both displacement/voltage sensitivity and resonant frequency are high enough for the device to be used in future high-density HDDs.     

Shock Resistance of a Disk-Drive Assembly Using Piezoelectric Actuators With Passive Damping

Current dual-stage actuator design uses piezoelectric patches only, without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. Because they incorporate passive damping, the proposed actuators will improve the existing dual-stage actuators, giving them higher precision and better shock resistance. We report finite-element analyses of different types of piezoelectric actuators in a disk arm assembly under external shock and vibration. We modeled the viscoelastic damping layers in the hybrid actuators with the Prony series, whose parameters we determined from the dynamic frequency data of a nomograph. In the analyses, a shock impulse (175 g, 1 ms half sine) and a vibration impulse (350 g and 1 ms full sine) are applied at one end of the base, while the other end of the base is fixed. We evaluated and compared the responses of the disk arm assembly with different configurations of the piezoelectric actuators. The simulation results show that the enhanced active-passive hybrid actuator design would reduce the residual in-plane vibration induced during the shock, resist liftoff motion, and reduce the impact damage when the head slaps.     

Modified dual-stage controller for dealing with secondary-stage actuator saturation

This paper proposes a modified decoupled master-slave (DMS) dual-stage control scheme for hard disk drives that offers enhanced stability when the secondary-stage actuator is saturated. A nonlinear secondary-stage actuator model is used instead of a linear model in the controller. This modification allows microactuators with relatively smaller displacement range to be used in the servo system without causing stability problems in the DMS controller. Simulation and experimental results confirm the effectiveness and robustness of the scheme.     

A minimum time seek controller for a disk drive

A time optimal controller design is proposed for the purpose of steering the read/write head of a magnetic disk drive during a seek manuever. The design includes the development of a switch-on-time (SOT) open loop slew control using a third order model of the voice coil motor. The SOT algorithm employs a look up table of switch times versus angle. A perturbation correction stage is included to tailor the switch times to adjust for variations in the operating characteristic of the disk drive (due, for example to heat buildup, wear, etc.). The design also includes a terminal stage servo control that employs an optimal feedback/feedforward controller which is used to provide precise positioning at the end of the seek maneuver     

Identification and decentralized control of a dual-actuator hard disk drive system

The dual-actuator hard disk drive with two voice coil motor actuators mounted in the diagonal corners of the baseplate allows faster data access with relatively slow spindle speed. However, the mechanical interaction between the actuators tends to affect the head positioning accuracy. In this paper, we use the circle-fit modal testing method to identify the dual-input dual-output frequency response model of the dual-actuator plant. We discuss the decentralized control scheme for the dual-actuator tracking servo. The servo loop decomposition reveals that the interaction induces narrow-band vibrations near the crossover frequency. We propose a phase-lead interaction filter with a slight change to the loop stability to suppress the vibrations. Experimental results on a dual-actuator prototype show that the position error signal 6/spl sigma/ value due to interaction vibrations is reduced by 61% with the interaction filter in combination with the decentralized control scheme.     

高频响应下音圈电机复杂迟滞特性建模与验证

为了实现音圈电机(Voice Coil Motor,VCM)在高频、高速、高加速情况下的精确定位控制,针对引起音圈电机产生振动、系统不稳定等问题的特殊复杂迟滞特性,建立了其复杂迟滞模型。改进了C-S迟滞模型,提出了C-S神经网络混合动态复杂迟滞模型;用音圈电机的两组实测数据验证了模型的有效性。实验结果为：音圈电机工作在低频、低速、低加速时(10Hz)表现出一般的迟滞特性,这时建模的最大误差为4.8μm,是最大输出值的0.48%,表明该方法能够有效的补偿音圈电机一般的迟滞特性;音圈电机工作在高频、高速、高加速时(40Hz)表现出特殊的复杂迟滞特性,其建模的最大误差为6μm,是最大输出值的0.97%。说明该方法能够满足复杂迟滞特性建模的要求。     

Advanced precision linear stage for industrial automation applications

In the area of factory automation, accurate positioning systems are increasingly required in various industries to improve the productivity and to lower the manufacturing cost. In this paper, we present a prototype precision linear stage. It has a positioning accuracy of 1 /spl mu/m and a peak speed above 1 m/s. A permanent magnet DC linear motor has been used in the system as the actuator to eliminate the need for mechanical transmission from the rotary to linear motion. To achieve a fast and accurate closed loop response, we develop a state space predictive controller and a dynamic friction compensation system for the precision stage. The system has been optimally tuned using the genetic algorithm. Some experimental results are presented.     

调谐质量阻尼器用于改善硬盘驱动器读写头动臂的动力特性

通常计算机硬盘中的读写头动臂在3～4kHz的频率范围内有一个准刚性模态，这个准则性模态限制了伺服带宽进而限制了硬盘存储密度的提高。设计了一种调谐阻尼器结构来降低准刚性模态导致的振动，该阻尼器安装在音圈马达的线圈内部，结构简单，不影响动臂移动。所使用的阻尼材料取材于硬盘本身的密封橡胶，也避免了可能的气体污染。实验证明，该阻尼器能够很好地降低动臂在准刚性模态下的振动，因而有利于存储密度的提高。     

新型纳米分辨率位移定位平移台的研制

为克服已有压电驱动器存在的结构及控制系统复杂、定位行程小等缺陷,利用压电陶瓷的逆压电效应设计并制作了一种新型的压电纳米步进驱动器,建立光栅测试系统对这种压电驱动器的动态性能进行了测试.将压电纳米步进驱动器与电磁伺服马达耦合,设计新颖驱动结构,利用微机通过步进运动控制卡统一控制,实现大范围一维纳米分辨率位移定位.系统样机解决了所研制压电纳米步进驱动器双向运动、实用定位等问题.位移定位分辨率为50 nm,定位行程为100mm,纳米分辨率定位最大速度为0.6 mm/s.     

A flexure-based electromagnetic linear actuator

This paper introduces a novel nano-positioning actuator with large displacement and driving force, termed a flexure-based electromagnetic linear actuator (FELA). It mainly comprises an electromagnetic driving scheme and flexure-supporting bearings that provide infinite positioning resolution and highly repeatable motion. In this work, analytical modeling of the proposed electromagnetic scheme and flexure mechanism is presented. Solutions obtained from each model are evaluated by the experimental studies conducted on a FELA prototype. This prototype achieves a stroke of 4?mm with a positioning accuracy of ± 10?nm. With direct force control, it generates various force profiles with a force-current ratio of 60?N?A(-1) and an accuracy of ± 0.3?N. Such capabilities make FELA a promising solution for realizing ultra-high precision layer-over-layer fabrication in the nano-imprinting process.     

Third-order theory and bang-bang control of voice coil actuators

A theory of voice coil motor actuators involving third-order differential terms in displacement that includes the inductance of the motor coil has been developed for bang-bang control time-optimal performance. Universal curves have been obtained using the theory that exhibits relationships between dimensionless quantities. The curves enable designers to choose appropriate actuator performance parameters to meet design objectives. Experimental methods have been described to determine some of the important parameters involved in the theory.     

Adaptive compensation for position error signal nonlinearity

The magnetoresistive (MR) magnetic head is a poor positioning transducer for a disk file's servo control system because its positioning response is nonlinear with radial displacement. This paper shows how the MR head's poor positioning properties are alleviated by a self-adjusting adaptive algorithm that allows a disk file to linearize its own servo position error signal (PES). The adaptive linearizer uses a nonlinear state estimator whose nonlinearity adjusts to match the nonlinearity of the PES. As the match between the two nonlinearities adaptively improves, the state estimator gives increasingly accurate estimates of the true actuator position     

基于闭环特性的音圈电机驱动快速反射镜控制

建立了音圈电机驱动快速反射镜的控制回路模型,并利用该模型对实际对象的参数进行了辨识。设计调节器时从闭环特性入手,采用了基于理想闭环特性(最佳二阶特性)的逆向设计方法。该方法只需调整两个物理意义明确的控制参数阻尼系数和自然频率,可以得到较好的实际效果,从而提高了调节器设计的简洁性与实用性。经试验与仿真验证,该方法效果明显,扰动抑制带宽能达到采样频率的1/6左右,闭环带宽达到采样频率的1/5。     

Experimental study on control fins of a small flying vehicle using piezo-composite actuators

A camber morphing control fin design and an all-moving control fin design using piezo-composite unimorph actuators are presented in this paper. The control fin of a small flying object is usually actuated using a servo motor system with an electromagnetic motor. Much research has been conducted to solve the structural complexity of servo actuation systems to convert the rotation of a servo motor to a linear actuation motion. To simplify this structural complexity, several types of smart actuators have been developed, such as bimorph or unimorph actuators with piezoelectric material layers and shape memory alloy actuators. In this study, a camber morphing type control fin and an all-moving type control fin actuated using piezo-composite actuators are designed to evaluate their ability to simplify the structural complexity of the gear transmission and electromagnetic servo motor system or hydraulic actuator system. Within the skin of the control fin, a piezo-composite actuator is mounted and the other end inserted in a slot of the control fin. As the piezo-composite actuator is excited by an electric field, the pitch angle of the control fin is changed. Experimental testing for the pitch rotation angle of a control fin in a 450 V electric field showed the deflection angle of the camber morphing control fin was 1.4° and the rotational angle of the all-moving control fin was 5.4°, which is obtained from the rotation angle magnification linkage structural system.     

A Miniature Short Stroke Linear Actuator—Design and Analysis

We report a newly developed miniature short stroke tubular linear permanent-magnet actuator for robotic applications. Compared to a rotary-to-linear mechanism, the linear actuator has the advantages of efficiency, thrust control, and compact size in generating linear motion. We optimized the electromagnetic force of the actuator analytically by selecting appropriate dimensions and then predicted the force produced by the winding currents by the finite-element method under the brushless dc excitation scheme. We analyzed the actuation performance by dynamic modeling of the actuator. We constructed and tested a prototype on a specially designed test bench to verify the design. Finally, we analyzed and measured the end effect on the magnetic force due to the limited length of the stator core and translator.     

音圈电机驱动的双层主动隔振系统设计与仿真

介绍采用音圈电机作为振动主动控制作动器的特点和工作原理,详细分析并建立音圈电机的数学模型,推导其传递函数。并针对双层隔振系统,采用理论建模的方法,建立双层隔振系统的数学模型。以位移传递率最小作为研究分析的目标,设计出一种宽频主动隔振系统,并用音圈电机作为驱动器,最后用Matlab/Simulink进行仿真,仿真结果显示该隔振系统在宽频带内具有良好的隔振性能,有效的提高隔振平台的精度。     

移动硬盘磁头驱动臂的模态分析与脉冲响应

磁头驱动臂组件是硬盘驱动器内重要的机械部件,其冲击载荷下的动态响应是影响硬盘驱动器抗振性能好坏的主要指标。本文以2.5英寸移动硬盘驱动器组件为研究对象,在考虑枢轴轴承刚度影响的基础上,建立了驱动臂组件的三维有限元模型,分析了其各阶振动模态,并讨论了脉冲波形、脉冲幅值、脉冲宽度对磁头驱动臂组件动态响应的影响。     

Application of voice coil motors in active dynamic vibration absorbers

A dynamic vibration absorber reduces the influence of a force whose excitation frequency nearly coincides with the natural frequency of a rotating machine. However, the performance of this type of passive absorber can be affected by changes in the environment. In this paper, we describe a voice coil motor (VCM) that can serve as the actuator in an active dynamic vibration absorber which can be regulated for different conditions. With a VCM, suitable controllers can be designed for periodic excitation force rejection by using the characteristics of the notch filter in combination with the root-locus theorem. We have evaluated the performance of the active vibration absorber by both simulations and experiments.