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.     

Position control of high performance hydrostatic actuation system using a simple adaptive control (SAC) method

This paper deals with the issue of position tracking control of a high performance hydrostatic actuation system using simple adaptive control. For energy-efficiency and savings, a speed-controlled fixed displacement pump is utilized to drive a symmetrical linear actuator instead of a directional control servo valve. The whole control system is composed of a pair of interconnected subsystems, that is, a feedback control system and a feedforward control system to enhance the tracking performance. The experiment using the proposed control scheme has been performed and a significant reduction in position tracking error is achieved compared to a conventional PID 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.     

超磁致伸缩伺服阀用伺服放大器的设计及分析

为驱动超磁致伸缩伺服阀,结合超磁致伸缩执行器驱动电源与伺服阀用伺服放大器的性能要求设计了超磁致伸缩伺服阀用伺服放大器,并建立了其电路模型,仿真分析了功率运算放大器的开环增益对其输出性能的影响.仿真结果表明,在功率运算放大器开环增益大于80 dB时,电路特性可满足设计要求.在驱动负载为额定值时,测试结果表明,样机的输出电流线性度为3％;输出电流2A时,其阶跃响应的调节时间小于0.5 ms,幅频宽可达2 kHz;在驱动频率小于1 kHz时,输出电流失真小且无相位滞后.     

Characteristics of AlGaAs Fabry-Perot cavity type laser amplifiers

Signal gain, saturation power, and noise bandwidth, which are important parameters determining preamplifier and linear repeater system performance [1], were measured for an AlGaAs Fabry-Perot cavity type laser amplifier. The unsaturated signal gain increases with the pumping level and a maximum signal gain as high as 27 dB is obtained near oscillation threshold. The saturation output power, at which the signal gain is decreased from the unsaturated value by 3 dB, is -6 to -8 dBm. The beat noise powers between signal and spontaneous emission components were measured. The error rate characteristics of an AlGaAs laser preamplifier and Si photodiode scheme were studied at a data rate of 100 Mbits/s. The experimental results on noise powers and error rate performance are in reasonable agreement with the theoretical analysis given in an accompanying paper [1].     

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.     

Robust Smooth-Trajectory Control of Nonlinear Servo Systems Based on Neural Networks

The electromagnetic torque introduces ripples into the electromechanical motion system due to nonlinearities, such as uncertain changes of magnet field, load, and friction, which generate speed oscillations and deteriorate the tracking performance of servo system. Furthermore, the minimum time response and smooth trajectory tracking are cruces in servo control. In this paper, an available method is proposed to solve them by using neural networks (NNs) and a nonlinear smooth trajectory filter (STF) for the robust smoothing feedforward control of a class of general nonlinear systems. First, the online weight-tuning scheme based on Lyapunov function can guarantee the boundedness of tracking error by good performance of NNs modeling nonlinear functions. Second, a feedforward controller based on the output of nonlinear STF is designed to guarantee minimum time response and smooth trajectory tracking. Finally, as a example, the motion system can be equivalent to the two-order system under the linear closed-loop current control in view of the (d,q) mathematic model for PM synchronous motor, so that this robust smoothing control method using neutral networks can be applied into position servo control. Moreover, the validity and effectiveness of this control method are verified through simulations and experiments     

Background interstage gain calibration technique for pipelined ADCs

A background self-calibration technique is proposed that can correct both linear and nonlinear errors in the interstage amplifiers of pipeline and algorithmic analog-to-digital converters (ADCs). Stage redundancy in a pipeline architecture is exploited to measure gain errors that are corrected using digital post-processing. The proposed technique allows faster convergence and has less dependence on input signal statistics than a similar technique described by Murmann and Boser. Simulation results are presented for a 12-bit pipelined ADC architecture, similar to that described by Murmann and Boser, using nonideal interstage residue amplifiers. With calibration, the simulations show a signal-to-noise-and-distortion-ratio performance of 72 dB and a spurious-free dynamic range performance of 112 dB, with calibration tracking time constants of approximately 8/spl times/10/sup 5/ sample periods, which is over ten times faster than that reported by Murmann and Boser at a similar performance level.     

Identification and Real-Time Control of an Electrohydraulic Servo System Based on Nonlinear Backstepping

This paper studies the identification and the real-time control of an electrohydraulic servo system. The control strategy is based on the nonlinear backstepping approach. Emphasis is essentially on the tuning parameters effect and on how it influences the dynamic behavior of the errors. While the backstepping control ensures the global asymptotic stability of the system, the tuning parameters of the controller, nonetheless, do greatly affect the saturation and chattering in the control signal, and consequently, the dynamic errors. In fact, electrohydraulic systems are known to be highly nonlinear and non-differentiable due to many factors, such as leakage, friction, and especially, the fluid flow expression through the servo valve. These nonlinear terms appear in the closed loop dynamic errors. Their values are so large that in the presence of a poor design, they can easily overwhelm the effect of the controller parameters. Backstepping is used here because it is a powerful and robust nonlinear strategy. The experimental results are compared to those obtained with a real-time proportional-integral-derivative (PID) controller, to prove that classic linear controllers fail to achieve a good tracking of the desired output, especially, when the hydraulic actuator operates at the maximum load. Before going through the controller design, the system parameters are identified. Despite the nonlinearity of the system, identification is based on the recursive least squares method. This is done by rewriting the mathematical model of the system in a linear in parameters (LP) form. Finally, the experimental results will show the effectiveness of the proposed approach in terms of guaranteed stability and zero tracking error     

On stability and performance of disturbance observer-based-dynamic load torque compensator for assistive exoskeleton: A hybrid approach

A disturbance observer-based-dynamic load-torque compensator for current-controlled DC-drives, as joint actuator of assistive exoskeletons, has been recently proposed. It has been shown that this compensator can effectively linearize and decouple the coupled nonlinear dynamics of the human-exoskeleton system, by more effectively compensating the associated nonlinear load-torques of the exoskeleton at the joint level. In this paper, a detailed analysis of the current controlled DC drive-servo system using the said compensator, with respect to performance and stability is presented, highlighting the key factors and considerations affecting both the stability and performance of the compensated servo system. It is shown both theoretically and through simulation results that the stability of the compensated servo system is compromised as performance is increased and vice-versa. Based on the saturation state of the servo system, a new hybrid switching control strategy is then proposed to select stability or performance-based compensator and controller optimally. The strategy is then experimentally verified both at the joint and task space level by using the developed four active-degree of freedom exoskeleton test rig.     

Propagation of short pulses in an active nonlinear two-core optical fiber

The switching dynamics of short pulses in an active nonlinear two-core fiber coupler is investigated theoretically. The analysis takes into account the effects of coupling-coefficient dispersion, gain bandwidth, and gain saturation. In particular, we demonstrate that the pulse breakup effect due to coupling-coefficient dispersion can be suppressed by limiting the bandwidth of the linear gain, whether gain saturation is considered or not.     

Turbo coding applied to pragmatic trellis-coded modulation

This letter reports the application of the powerful turbo coding technique combined with the bandwidth efficient method known as trellis-coded modulation (TCM). Implemented as a simple modification of pragmatic TCM, our turbo-coded pragmatic TCM system achieved coding gains of 1-2 dB in simulations relative to pragmatic TCM. These gains were achieved with comparable complexity but greater delay than with pragmatic TCM. A table of delay as a function of interleaver length and data rate is provided as a preliminary analysis of the trade-off between the benefits of large coding gain and the costs of increased delay     

Dual-band UWB bandpass filter with triangular DB-DGS for WLAN applications in DSRC band

A dual-band Ultra-wideband (UWB) bandpass microstrip filter with triangular dumbbell shaped defected ground structure (DB-DGS) for wireless local area network applications in DSRC band is proposed in this article. The proposed dual-band filter has center frequencies at 2.67 GHz and 4.68 GHz, return loss obtained is −33.40 dB and −16.55 dB respectively, wide bandwidth of 1.21 GHz (26%), pass band between 2.14 GHz and 6.44 GHz and high gain of 10.30 dB which makes it suitable for modern applications in dedicated short range communication operating in 5.8 GHz band. To further validate the design concept, a microstrip UWB filter is designed, fabricated and tested. Comparison is made among circular, square and triangular dumbbell shaped DGS on the basis of scattering parameters and bandwidth, in which triangular shaped DB-DGS outperforms the other two. Further, parametric analysis of triangular DB-DGS has been performed and comparison is made with filters of similar nature. Experimental results are in good agreement with simulations. The fabricated filter is compact in size, has low insertion loss, exhibits high selectivity and demonstrates excellent out of-band performance.     

Servo-Performance Parameters of the NASA Deep Space Network Antennas

The performance of an antenna control system is evaluated using performance parameters such as settling time, bandwidth, steady-state error in rate offsets, and antenna root-mean-square servo error while tracking in wind gusts. The performance parameters are measured in the field, or obtained through analysis and simulations. Limited access time to antennas, incomplete test equipment, limited test/analysis time, and partial models do not allow determination of all the parameters. However, field practice and analytical results indicate correlations among them; hence, even incomplete knowledge of the performance parameters would allow for estimation of the missing parameters. This paper investigates the relationships of the antenna performance parameters as a function of controller gains. It also establishes the interrelationships among the parameters. It does this for an idealized (or rigid) antenna, and extends the relationships to the NASA Deep Space Network antennas (flexible structures with dish sizes of 34 or 70 meters). The results obtained should simplify antenna testing, and allow for better performance evaluation from limited data.     

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.     

Performance enhancement of a compact wideband patch antenna array using EBG structures

In this paper, a compact wideband linear microstrip phased array antenna (MPAA) is proposed. To reduce the size of MPAA, a compact wideband aperture coupled microstrip patch antenna (MPA) is utilized as array element. Size reduction of the array element is performed through incorporating an interdigital capacitor (IDC) in the patch and a metamaterial (MTM) unit cell close to slot in the ground plane of the antenna. By cutting two vertical slits from the slot, further compacting of the slot in the ground plane of array element is obtained. By this technique dimensions of the patch and slot are reduced by 12.9% and 12.2%, respectively. Furthermore, dimensions of the MPAA are reduced through decreasing the spacing between array elements causing the antenna performance degradation. To overcome this shortage and improve the radiation characteristics of the proposed MPAA, an electromagnetic bandgap structure (EBG) is utilized. The effect of implementing EBG cells on the reflection coefficient of the elements in the MPAA during beam scanning is studied in details. The maximum measured gain, bandwidth and cross-polarization level of the fabricated MPAA are 13.3 dBi, 24.4% and −40 dB, respectively making it a good candidate for monopulse tracking radar applications. The measurement results confirm the simulation results.     

Parameter identification and position control for helical hydraulic rotary actuators based on particle swarm optimization

It is difficult to obtain an accurate mathematical model in electro-hydraulic servo control system, due to the nonlinear factors such as dead zone, saturation, flow coefficient, and friction. Hence, a parameter identification algorithm, combining recursive least squares (RLS) with modified nonlinear particle swarm optimization (NPSO) algorithm, is proposed. On this basis, another improved NPSO algorithm is also put forward, aiming at searching for the optimal proportional–integral (PI) controller gain of the nonlinear hydraulic system while giving comprehensive consideration to the system performance indexes. The system identification experiments and position tracking control are conducted, respectively. As indicated by the comparison with the least squares (LS), RLS, PSO, and RLS–LPSO results, the proposed method shows higher identification and control accuracy.     

目标跟踪性能的仿真研究

系统目标的跟踪性能,一般要通过实际跟踪才能得到检验,如何定量地检验系统的目标跟踪性能是否满足系统指标一直是困扰使用者的难题。结合船载雷达的特点,通过MATLAB仿真软件对伺服系统位置回路带宽与系统跟踪性能之间的定性、定量关系进行描述,为检验系统适应不同特性目标的能力提供可靠的测试依据。     

Design and Simulation of an Ultra-Broadband Ku-BandGyro-TWT for Radar Applications

In this paper, the design of an ultra-broadband Ku-band gyro-TWT amplifier is presented in detail. The preliminary parameters of the interaction structure derived from the dispersion relationship and the linear theory of the gyro-TWT with distributed wall losses is optimized by the self-consistent nonlinear code. The performance of the designed gyro-TWT is simulated by the nonlinear code. The simulation results show that the gain and the bandwidth of the designed Ku-band gyro-TWT is about 36.5 dB and 2.1 GHz with 3 dB bandwidth (about 12.7%) respectively at the input power 19.0 W.     

具有高稳定性的超高增益回旋行波管放大器

该文结合线性理论和自洽非线性理论对Ka波段TE11模超高增益回旋行波管放大器的稳定性进行了研究。 研究揭示了回旋行波管中前向波绝对不稳定性和返向波振荡之间的区别,以及分布损耗技术对这两种自激振荡的抑制作用,并首次提出通过渐变磁场技术来提高系统的稳定性。基于该分析方法设计的Ka波段超高增益回旋行波管,采用电压100 kV,电流7 A,速度零散5％的电子注,获得了-1 dB的饱和功率带宽约5 GHz,最高增益约80 dB。