Dual-stage servo systems and vibration compensation in computer hard disk drives

This paper discusses two mechatronic innovations in magnetic hard disk drive servo systems, which may have to be deployed in the near future, in order to sustain the continuing 60% annual increase in storage density of these devices. The first is the use of high bandwidth dual-stage actuator servo systems to improve the precision and track-following capability of the read/write head positioning control system. The second is the instrumentation of disk drive suspensions with vibration sensing strain gages, in order to enhance airflow-induced suspension vibration suppression in hard disk drives.     

Gpc‐Based Self‐Tuning PI Controller for Speed Servo System of PMSLM

In this paper, a generalized predictive control (GPC)‐based two degrees of freedom (2 DOF) proportional integral (PI) controller is proposed for the speed servo system of a permanent magnet synchronous linear motor (PMSLM). In this new approach, based on a dynamic model of a servo system, a simplified and high‐performance GPC supplies a 2 DOF PI controller with suitable control parameters, according to the varied operating conditions. In previous studies, GPC‐based proportional integral derivative (PID) controllers have been designed using a step‐type or ramp‐type reference input. In our work, however, the speed command for PMSLM usually is required to be a trapezium‐type signal because of the limited travel range. Hence, control performance of a speed servo system using a GPC‐based 2 DOF PI controller is enhanced for tracking a trapezium‐type command. The validity and usefulness of the proposed controller are verified through simulation and experiments.     

柔性支撑Stewart平台自适应交互PID隔振控制

为了实现500 m口径球面射电望远镜(five hundred meter aperture spherical radio telescope, FAST)二级精调稳定平台对馈源舱隔振控制的定位和指向精度, 首先提出了基于并联机构学原理的3维机动目标跟踪预测算法, 对柔性支撑Stewart平台的基座运动进行跟踪预测. 进而,在Stewart平台关节空间设计了自适应交互PID控制器, 引入自适应交互算法解决PID参数的实时调整, 以适应柔性支撑Stewart平台的参数变化对不同控制参数的需求. 采用现代机电系统仿真策略, 对柔性支撑Stewart平台隔振系统的动力学与控制问题进行了仿真, 结果表明: 与传统的PID控制器相比, 自适应交互PID控制器大大改善了隔振效果, 完全满足隔振目标的要求.     

Three-degree-of-freedom joint H2/H∞ optima) controllers

The solution is dealt with of the discrete-time LQ stochastic tracking and servo problems for a general system configuration. It is shown that the resultant solution is in the form of a three-degree-of-freedom (3DOF) controller when the vector of the exogenous signal is extended to include accessible disturbances. In particular, it is shown that a separation property between feedback, reference and accessible disturbance feedforward actions, proved for 2DOF optimal LQ stochastic control scheme, also holds true for the general system configuration here considered. Further, this separation property can be suitably extended, when a linear control law is assumed, to the minimax LQ stochastic tracking and servo problems     

Self-sensing actuators with passive damping for adaptive vibration control of hard disk drives

A push–pull piezoelectrically actuated devices have been developed for higher bandwidth servo systems as microactuators for fine and fast positioning, while the voice coil motor functions as a large but coarse seeking. However, the current dual-stage actuator design uses piezoelectric patches only and therefore a dual-stage servo system using enhanced active–passive hybrid micro piezoelectric actuators is proposed to improve the existing dual-stage actuators for higher precision and shock resistance, due to the incorporation of passive damping in the design. In this paper, three different configurations of self-sensing actuators (SSAs) incorporating an adaptive mechanism for vibration control of suspensions in dual-stage hard disk drives (HDDs) are investigated. In the piezo-based SSA configuration, the signal sensed due to mechanical deformation is mixed with the control input signal, which would be corrupted due to the variation of the piezoelectric capacitance when a fixed bridge circuit is used. In this study, a self-tuning adaptive compensation is used to combine with the SSA technique to extract the true sensing signal for the vibration control of suspensions in HDDs. An assembled suspension with piezoelectric microactuators is tested to demonstrate the vibration suppression performance of this adaptive structure under an external shock disturbance such as hammer excitation. The experimental results show that the target vibration modes have been suppressed effectively with using the adaptive positive position feedback controller for the enhanced SSAs with passive damping in HDDs.     

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.     

宽带高精度鲁棒自适应位置跟踪系统研究

设计一宽带高精度鲁棒自适应位置跟踪系统，位置环采用二阶模型参考自适应控制，速度环采用一阶ＭＲＡＣ。采用可编程数字信号处理器ＴＭＳ３２０Ｃ２５作为控制器，实时实现了该系统。     

Improved disturbance rejection with online adaptive pole-zero compensation on a Φ-shaped PZT active suspension

In feedback control systems, the anti-resonant zeros cannot be arbitrarily placed, hence degrading tracking performance as well as input disturbance and noise rejection capabilities due to reduced gain at the frequencies of the zeros. In this paper, an online adaptive inverse control with saturation (OAICS) algorithm is proposed for compensating the minimum phase resonant poles and anti-resonant zeros of a PZT active suspension using measured position error signal. Experimental results on a Φ-shaped PZT active suspension using laser Doppler vibrometer (LDV) shows the proposed OAICS is effective in cancelling the first two dominant minimum phase pole-zero pairs to achieve high servo bandwidth and low sensitivity servo system with small overshoot during set-point tracking.     

一种基于电磁—空气弹簧的非线性隔振器理论与实验研究

本文提出一种主要由空气弹簧和永磁体所组成的具有准零刚度特性的非线性隔振器.首先,通过分析空气弹簧和磁体的受力特性,建立隔振器力-位移关系和刚度-位移关系,揭示隔振器静态力学特性,并分析隔振器参数对系统刚度的影响规律.然后,采用谐波平衡法计算隔振器力传递率特性.结果表明,通过在适当范围内调节系统阻尼比或激励幅值,所提出的非线性隔振器在隔振频率范围内优于普通空气弹簧隔振器.最后,通过实验验证隔振器的隔振性能.该研究可为小振幅甚至微振动系统的振动隔离提供新的参考.     

分段阻尼隔振系统的动力学特性分析

针对传统线性隔振器在降低共振峰值的同时会牺牲隔振性能的矛盾,设计了一种含分段阻尼的隔振器.首先,采用移动凸轮变阻尼装置,通过凸轮廓线的设计使系统的垂向阻尼系数的受振动位移大小控制并呈现分段线性特征,分析了该装置的阻尼特性.然后将分段阻尼装置应用于隔振器中,建立了含分段阻尼的积极隔振系统模型及其动力学方程,通过能量等效原理求出了分段阻尼系统的等效线性阻尼系数,求解了简谐力激励下系统响应的理论解,并用四阶龙格-库塔法数值仿真验证了理论解的正确性.最后研究了分段阻尼隔振系统的动态特性,分析了主要参数对幅频响应特性与力传递率特性的影响.结果表明,通过合理的参数选择,分段阻尼隔振器可兼顾无阻尼隔振器与线性阻尼隔振器的优点,既能有效降低系统的共振峰值,又能保证高频区域的优秀隔振性能,为新型非线性隔振器的设计提供了理论依据.     

多通道约束下的网络控制系统的最优跟踪性能

本文针对双通道约束下的线性时不变网络控制系统的随机信号跟踪性能极限问题进行了研究.网络通信包含通信噪声和通信带宽两种信道因素.被控系统考虑是非最小相位和不稳定系统,并且系统包含多个不同的非最小相位零点和多个不同的不稳定极点.对上行通道和下行通道都存在通信带宽约束及高斯白噪声影响的情形,从频域角度,通过采用双自由度控制器和尤拉参数化方法,获得了此类网络控制系统的最优可达的跟踪性能.研究结果表明网络控制系统的跟踪性能极限完全由被控对象的结构特征(非最小相位零点、不稳定极点以及被控对象的系统增益),参考输入信号和网络特性(高斯白噪声的统计特征、通信信道带宽)所决定.最后,仿真结果检证了所得结果的正确性.     

基于PMAC卡的FAST馈源位姿主动减振控制系统

基于Stewart平台的馈源位姿主动减振定位机构的控制是五百米口径球面射电天文望远镜(FAST)项目实现的关键.考虑到控制系统对重量、体积和精度的要求,提出了在RTLinux环境下,采用工业计算机上下位机主从控制,配合PMAC运动控制卡对机构进行控制的软硬件控制方案.RTLinux 对中断处理的强实时性及PMAC运动控制卡强大的运动控制功能,保证了控制精度.实验取得了较好的减振控制效果,满足了FAST的指标要求.同时,PMAC运动控制卡提供了开放性的底层伺服环控制算法,这给今后的控制算法研究改进预留了方便的软硬件接口.     

基于神经网络的机电伺服系统非线性控制

针对机电伺服系统精确动力学模型难以获取以及系统状态信息的测量易受噪声影响的问题,设计一种基于指令滤波与神经网络相结合的非线性反步控制算法,该算法能够有效地补偿未建模动态和外部扰动对机电伺服系统的影响.首先,引入指令滤波器来获取已知信号的微分估计并处理噪声;其次,利用神经网络估计未知的系统动态,包括未建模的摩擦和外部干扰;然后,神经网络权值的更新律通过梯度下降算法在线实现,没有离线学习阶段;最后,利用李雅普诺夫函数分析方法证明闭环系统的稳定性.为验证所提出算法的有效性,在机电伺服实验平台上进行大量对比实验,实验结果表明,所提出的算法具有良好的控制效果,对系统不确定性和外部干扰具有良好的鲁棒性.     

Acceleration amplitude-phase regulation for electro-hydraulic servo shaking table based on LMS adaptive filtering algorithm

Electro-hydraulic servo shaking table usually requires good control performance for acceleration replication. The poles of the electro-hydraulic servo shaking table are placed by three-variable control method using pole placement theory. The system frequency band is thus extended and the system stability is also enhanced. The phase delay and amplitude attenuation phenomenon occurs in electro-hydraulic servo shaking table corresponding to an acceleration sinusoidal input. The method for phase delay and amplitude attenuation elimination based on LMS adaptive filtering algorithm is proposed here. The task is accomplished by adjusting the weights using LMS adaptive filtering algorithm when there exits phase delay and amplitude attenuation between the input and its corresponding acceleration response. The reference input is weighted in such a way that it makes the system output track the input efficiently. The weighted input signal is inputted to the control system such that the output phase delay and amplitude attenuation are all cancelled. The above concept is used as a basis for the development of amplitude-phase regulation (APR) algorithm. The method does not need to estimate the system model and has good real-time performance. Experimental results demonstrate the efficiency and validity of the proposed APR control scheme.     

Ｓｔｅｗａｒｔ主动隔振平台的神经网络自适应控制

针对Stewart主动隔振平台,提出一种基于径向基函数(RBF)神经网络的多输入多输出自适应隔振控制方法.考虑外界振动对Stewart主动隔振平台动态特性的影响,建立了隔振平台在工作空间中的动力学模型.推导出RBF神经网络的权值矩阵、高斯基函数中心和宽度的在线自适应调节律,以使神经网络快速逼近系统的非线性动态函数.应用Lyapunov稳定性理论,证明了在扰动力和神经网络逼近误差有界的条件下,闭环控制系统滤波误差和RBF神经网络各调节参数估计误差的一致最终有界.仿真结果表明,该控制方法能有效地抑制不同方向的低频有界振动.     

Optimal tracking performance of MIMO discrete‐time systems with communication constraints

The optimal tracking problem for multiple‐input multiple‐output linear‐time‐invariant discrete‐time systems with communication constraints in the feedback path is studied in this paper. The tracking performance is measured by the energy of the error signal between the output of the plant and the reference signal. The objective is to obtain an optimal tracking performance, attainable by all possible stabilizing compensators. It is shown that the optimal tracking performance consists of two parts, one depends on the nonminimum phase zeros and zero direction of the given plant, as well as the reference input signal direction, and the other depends on the nonminimum phase zeros, unstable poles, and pole direction of the given plant, as well as the bandwidth and additive white Gaussian noise of the communication channel. It is also shown that, if the constraint of the communication channel does not exist, the optimal tracking performance reduces to the existing tracking performance of the control system without communication constraints. A typical example is given to illustrate the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.     

基于降阶扩张状态观测器的重复控制系统设计

针对一类含有非匹配状态相关不确定性和外界干扰的伺服系统,提出一种基于降阶扩张状态观测器的重复控制方法,通过对不确定性和扰动进行实时估计和主动补偿,实现对周期性参考输入信号的高精度跟踪.首先,利用系统可测输出和控制输入信号设计降阶扩张状态观测器,对系统的不可测状态以及包含不确定性和外界干扰的总扰动进行估计;其次,通过选择...     

Computer support for mechatronic control system design

This paper discusses the demands for proper tools for computer aided control system design of mechatronic systems and identifies a number of tasks in this design process. Real mechatronic design, involving input from specialists from varying disciplines, requires that the system can be represented in multiple views. Several tools are already available but there are still substantial shortcomings. The paper gives indications about the developments needed to come to better design tools in the future. A specific example is worked out in more detail, i.e., automated performance assessment of mechatronic motion systems during the conceptual design stage.     

Improvement of dynamic characteristics for optical pickup actuator by magnetic circuit

 As disk rotational speed of optical disk drives (ODD) increases, an optical pickup actuator has a high servo bandwidth for its focusing and tracking control to follow dynamic disturbances by high rotational speed in ODD. However, the servo bandwidth is limited by some vibration modes due to the flexibility of the moving part in the actuator. In this paper, the influence of the driving forces generated by VCM on excitation of flexible modes of the moving part in high frequency range is analyzed. Especially, in order to reduce the first flexible mode affecting the servo bandwidth, it is attempted to modify force distribution on coils. The magnetic simulation is performed by using finite element analysis, and compared with experimental results. Finally, it is shown that flexible mode vibration can be suppressed by proper design of magnetic circuit. Received: 20 June 2002 / Accepted: 29 August 2002     

An Optimal Tracking Performance of MIMO NCS with Quantization and Bandwidth Constraints

This paper presents an optimal tracking performance of multiple‐input multiple‐output (MIMO) networked control systems (NCSs) with quantization and bandwidth constraints. In this study, we simultaneously consider the encoding‐decoding, quantization and bandwidth of communication channel. The optimal tracking performance of NCSs is obtained by spectral factorization technique and partial fraction. The obtained results demonstrate that the optimal tracking performance is influenced by the nonminimum phase zeros and unstable poles as well as their directions for a given plant. In addition, it is shown that characteristics of reference signal, encoding‐decoding, quantization, and bandwidth of communication channel are also closely related to tracking performance. Finally, the efficiency of proposed tracking performance is verified by typical examples.