Optimal two-degree-of-freedom fuzzy control for locomotion control of a hydraulically actuated hexapod robot

Locomotion control of legged robots is a very challenging task because very accurate foot trajectory tracking control is necessary for stable walking. An electro-hydraulically actuated walking robot has sufficient power to walk on rough terrain and carry a heavier payload. However, electro-hydraulic servo systems suffer from various shortcomings such as a high degree of nonlinearity, uncertainty due to changing hydraulic properties, delay due to oil flow and dead-zone of the proportional electromagnetic control valves. These shortcomings lead to inaccurate analytical system model, therefore, application of classical control techniques result into large tracking error. Fuzzy logic is capable of modeling mathematically complex or ill-defined systems. Therefore, fuzzy logic is becoming popular for synthesis of control systems for complex and nonlinear plants. In this investigation, a two-degree-of-freedom fuzzy controller, consisting of a one-step-ahead fuzzy prefilter in the feed-forward loop and a PI-like fuzzy controller in the feedback loop, has been proposed for foot trajectory tracking control of a hydraulically actuated hexapod robot. The fuzzy prefilter has been designed by a genetic algorithm (GA) based optimization. The prefilter overcomes the flattery delay caused by the hydraulic dead-zone of the electromagnetic proportional control valve and thus helps to achieve better tracking. The feedback fuzzy controller ensures the stability of the overall system in the face of model uncertainty associated with hydraulically actuated robotic mechanisms. Experimental results exhibit that the proposed controller manifests better foot trajectory tracking performance compared to single-degree-of-freedom (SDF) fuzzy controller or optimal classical controller like state feedback LQR controller.     

无人机全电式自主刹车系统滑模极值搜索控制

常规主动刹车系统采用在线辨识跑道特征的算法,但仍需依赖摩擦模型先验知识,难以应对复杂跑道工况.为克服上述问题,提出一种滑模极值搜索控制策略并应用于无人机全电式自主刹车系统.考虑电动作动机构非线性特性,建立系统的状态空间模型并合理简化为严格反馈形式,采用超扭曲算法估计结合系数的梯度,结合反馈线性化控制律得到刹车压力参考值,证明此控制作用下可实现对未知最优滑移率的渐近跟踪.采用反演控制的思想设计无抖振滑模控制器实现对参考刹车压力的跟踪.利用Lyapunov方法获得系统的渐近稳定性条件并分析控制参数对系统的影响.半实物仿真试验结果表明控制策略的有效性.     

High-speed and precision control of a piezoelectric positioner with hysteresis,resonance and disturbance compensation

A novel composite control strategy is developed in this paper to compensate hysteresis, resonance and disturbances in a piezo-actuated nanopositioner. The control objective of the piezoelectric positioner is to achieve high tracking performance in terms of accuracy and speed. For this purpose, a Bouc–Wen model based hysteresis compensator is first applied to mitigate the hysteresis nonlinearity without the complex inverse hysteresis calculation. And then, the linear dynamic of the hysteresis compensated system is identified and inverted to account for the resonance. A model-based inversion feed-forward controller is designed to achieve high speed tracking. Afterwards, a high-gain feedback controller is designed based on a notch filter to handle the modeling inaccuracy and all kinds of disturbances. So, the feed-forward controller can be augmented to the feedback controller to realize high speed and precision tracking. The enhancement of tracking performance is demonstrated through several comparative experiments. The performance of 70 Hz bandwidth and 0.281 μm precision can be achieved, which validated the effectiveness of the proposed composite control scheme.     

Robust design of feedback feed-forward iterative learning control based on 2D system theory for linear uncertain systems

For a class of linear discrete-time uncertain systems, a feedback feed-forward iterative learning control (ILC) scheme is proposed, which is comprised of an iterative learning controller and two current iteration feedback controllers. The iterative learning controller is used to improve the performance along the iteration direction and the feedback controllers are used to improve the performance along the time direction. First of all, the uncertain feedback feed-forward ILC system is presented by an uncertain two-dimensional Roesser model system. Then, two robust control schemes are proposed. One can ensure that the feedback feed-forward ILC system is bounded-input bounded-output stable along time direction, and the other can ensure that the feedback feed-forward ILC system is asymptotically stable along time direction. Both schemes can guarantee the system is robust monotonically convergent along the iteration direction. Third, the robust convergent sufficient conditions are given, which contains a linear matrix inequality (LMI). Moreover, the LMI can be used to determine the gain matrix of the feedback feed-forward iterative learning controller. Finally, the simulation results are presented to demonstrate the effectiveness of the proposed schemes.     

汽车操纵稳定性的自适应控制策略研究

针对汽车系统的非线性和参数不确定性,设计了一种“前馈+反馈”自适应神经模糊控制器,通过ESP和AFS的协调控制来提高汽车操纵稳定性.ESP反馈控制器采用模糊控制策略,以横摆角速度和质心侧偏角为控制目标;AFS前馈控制器采用径向基神经网络控制,以反馈控制器的输出作为误差进行学习,从而实现自适应控制.仿真结果表明,上述控制策略是可行和有效的,能显著改善汽车在高速或湿滑路面上的操纵稳定性.     

自调式类神经PID控制器于压电微动平台之追迹控制(英文)

主要针对压电微动平台设计追迹控制器。压电致动器的非线性现象主要是受磁滞现象所影响,首先采用Prandtl-Ishlinskii(PI)模型来描述压电致动器的磁滞现象,利用最小平方算法识别出磁滞模型的权重值,再利用此模型求出其逆模型以前馈控制器来补偿,最后利用自调式类神经PID控制器来消除建模误差。实验验证方面,在PC-based压电控制平台架构下,利用前馈控制器与闭回路结合自调式类神经PID控制器进行定位控制。     

Adaptive feed-forward compensation for hybrid control with acceleration time waveform replication on electro-hydraulic shaking table

This article presents a high fidelity acceleration time waveform replication (TWR) on an electro-hydraulic shaking table (EHST) using the hybrid control combined with an offline feed-forward compensator and an online adaptive inverse control (AIC). This study applies the acceleration and velocity feedback to improve the steady performance of the EHST, and employs the system inverse transfer function (ITF) of the acceleration closed-loop system to extend the frequency bandwidth and a modeling error compensator to improve the dynamic characteristics. Moreover, the investigation utilizes a Zero Phase Error Tracking Controller to improve the accuracy of the designed ITF. The proposed hybrid controller also utilizes an online AIC for a high fidelity TWR after that the dynamic characteristics has been improved by the feedback and feed-forward controllers. Thus, the proposed hybrid control strategy combines the merits of the offline feed-forward compensation and online AIC. Performance analysis and comparison of the experimental results demonstrate that better replication accuracy with the proposed hybrid control can be achieved in experiments on an actual EHST.     

Locomotion Control of a Hydraulically Actuated Hexapod Robot by Robust Adaptive Fuzzy Control with Self-Tuned Adaptation Gain and Dead Zone Fuzzy Pre-compensation

Hydraulically actuated robotic mechanisms are becoming popular for field robotic applications for their compact design and large output power. However, they exhibit nonlinearity, parameter variation and flattery delay in the response. This flattery delay, which often causes poor trajectory tracking performance of the robot, is possibly caused by the dead zone of the proportional electromagnetic control valves and the delay associated with oil flow. In this investigation, we have proposed a trajectory tracking control system for hydraulically actuated robotic mechanism that diminishes the flattery delay in the output response. The proposed controller consists of a robust adaptive fuzzy controller with self-tuned adaptation gain in the feedback loop to cope with the parameter variation and disturbances and a one-step-ahead fuzzy controller in the feed-forward loop for hydraulic dead zone pre-compensation. The adaptation law of the feedback controller has been designed by Lyapunov synthesis method and its adaptation rate is varied by fuzzy self-tuning. The variable adaptation rate helps to improve the tracking performance without sacrificing the stability. The proposed control technique has been applied for locomotion control of a hydraulically actuated hexapod robot under independent joint control framework. For tracking performance of the proposed controller has also been compared with classical PID controller, LQG state feedback controller and static fuzzy controller. The experimental results exhibit a very accurate foot trajectory tracking with very small tracking error with the proposed controller.     

SVD‐Based Accurate Identification and Compensation of the Coupling Hysteresis and Creep Dynamics in Piezoelectric Actuators

In this paper, the coupling hysteresis and creep in piezoelectric actuators are identified and compensated for accurate tracking. First, we present the coupling hysteresis and creep model in smart actuators. Next, a complete identification strategy is designed according to the properties of the Preisach model. Then, an approach for parameter updating of the coupling model is provided. With the identified hysteresis and creep, the model‐based inversion compensation is designed. Finally, we apply the model identification and compensation to a piezoelectric stage to demonstrate the effectiveness of the proposed approaches. Significant reduction of the tracking error is achieved with the model‐based inversion feedforward compensator in which the relative errors at 10 Hz and 50 Hz are reduced to 1.85% and 4.53%, respectively. In addition, the model‐based feedforward is augmented with an integral feedback controller. With the composite controller, the relative errors at 10 Hz and 50 Hz are reduced to 0.42% and 3.04%, respectively.     

信号交叉口模糊逻辑自适应控制

针对城市道路交叉口的智能交通信号控制,提出了一种主从式模糊逻辑自适应控制算法,该算法综合考虑了本相位最小绿灯时间结束时刻的路段车辆数和相邻相位的车辆排队长度,以及本相位非关键车流对关键车流的影响,采用两个规则前件进行主模糊控制器的模糊推理,设计了具有更多控制信息的两级模糊控制器。结合已有类似研究成果进行了仿真比较研究,结果表明:该控制算法在减少车辆延误方面有明显改进。     

Self-tuning of quantitative feedback theory for force control of an electro-hydraulic test machine

The aim of this paper is to design and fabricate an electro-hydraulic test machine (EHTM) for conducting performance and stability test of force and/or position control in the bench system and to propose a robust adaptive controller—the self-tuning quantitative feedback theory (STQFT)—in order to improve the force control performance of electro-hydraulic actuators (EHAs). By using the gradient descent method to adjust the QFT parameters, the novel STQFT controller is able to adapt to a wide range of working conditions. Experiments were carried out to evaluate the effectiveness of the proposed control method applied to the EHTM.     

Designing an adaptive type-2 fuzzy logic system load frequency control for a nonlinear time-delay power system

In this paper, a combination of type-2 fuzzy logic system (T2FLS) and a conventional feedback controller (CFC) has been designed for the load frequency control (LFC) of a nonlinear time-delay power system. In this approach, the T2FLS controller which is designed to overcome the uncertainties and nonlinearites of the controlled system is in the feedforward path and the CFC which plays an important role in the transient state is in the feedback path. A Lyapunov–Krasovskii functional has been used to ensure the stability of the system and the parameter adjustment laws for the T2FLS controller are derived using this functional. In this training method, the effect of delay has been considered in tuning the T2FLS controller parameters and thus the performance of the system has been improved. The T2FLS controller is used due to its ability to effectively model uncertainties, which may exist in the rules and data measured by the sensors. To illustrate the effectiveness of the proposed method, a two-area nonlinear time-delay power system has been used and compared with the controller that uses the gradient-descend (GD) algorithm to tune the T2FLS controller parameters.     

Reduced-order observer-based robust synchronisation control of cold rolling mills with measurement delay

To improve the quality of strip thickness, synchronisation control is investigated for cold rolling mills driven by dual-cylinder electro-hydraulic servo systems. Realising synchronised control in hydraulic automatic gauge control (HAGC) systems of cold rolling mills has challenges with not only the inherent nonlinearities of hydraulic servo systems and uncertainties of load variation but also measurement delay of strip thickness. Since all states are not measurable in practice, output feedback robust synchronisation control problem should be addressed for uncertain nonlinear systems with output delay. Thus, a reduced-order observer-based robust synchronous controller is presented by employing Lyapunov functional stability theory. The controller designed by incorporating the integral of the position synchronisation error of two pistons into state variables successfully guarantees asymptotic convergence to zero of both tracking errors and synchronisation error simultaneously regardless of the nonlinearities and uncertainties as well as the measurement delay. Simulation results in a model obtained from a real cold strip rolling mill demonstrate the effectiveness of the approach.     

Sliding‐mode control of a three‐degrees‐of‐freedom nanopositioner

This paper presents the sliding‐mode control of a three‐degrees‐of‐freedom nanopositioner (Z, θ_x, θ_y). This nanopositioner is actuated by piezoelectric actuators. Capacitive gap sensors are used for position feedback. In order to design the feedback controller, the open‐loop characteristics of this nanopositioner are investigated. Based on the results of the investigation, each pair of piezoelectric actuators and corresponding gap sensors is treated as an independent system and modeled as a first‐order linear model coupled with hysteresis. When the model is identified and the hysteresis nonlinearity is linearized, a linear system model with uncertainty is used to design the controller. When designing the controller, the sliding‐mode disturbance (uncertainty) estimation and compensation scheme is used. The structure of the proposed controller is similar to that of a proportional integral derivative controller. Thus, it can be easily implemented. Experimental results show that 3‐nm tracking resolution can be obtained. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

基于NBPID的回滞系统控制

回滞现象广泛存在于许多领域，其不可积的非线性特性给控制设计带来了困难。提出的NBPID控制器是基于神经网络逆模型前馈控制(N)，加上改进的Bang—Bang控制(B)的PID控制器。首先通过神经网络逆模型的前馈控制来削弱回滞带来的影响，然后在PID控制器的基础上，为了进一步控制误差，加上改进的Bang—Bang控制。通过设计出的NBPID对回滞系统进行控制，仿真结果表明控制方法是有效的。     

电液制动系统液压力控制

电液制动系统(electro-hydraulic brake system,EHB)作为未来制动系统发展的重要方向,已受到广泛关注.本文基于一套自主设计的集成式电液制动系统(integrated electro-hydraulic brake system,I–EHB)系统进行研究,为确保其压力控制动态响应及精度,克服工作中存在的延迟及能量损失,设计了两种液压力控制方法,分别是基于田口方法优化的自适应PID控制和基于滑模变结构的补偿控制,并搭建台架对两种控制方法进行测试.通过对两种控制方法下系统响应的比较分析,发现滑模变结构补偿控制效果较好,系统响应快、稳态误差小、鲁棒性好,尤其在系统常用的低频及中高压阶段控制表现突出,验证了该方法的正确性和有效性,并为进一步探索提出了方向.     

一种机器人轨迹的鲁棒跟踪控制

把基于拉格朗日方程的n关节机器人动力学模型,转化成了一线性状态方程.基于这种线性状态方程,利用李雅普诺夫函数方法分别针对机器人标称模型和有外界不确定性干扰时,设计前馈控制器和反馈控制器,使得机器人的实际运动轨迹在标称模型下,指数收敛于所给定的期望运动轨迹;在有外界不确定性干扰时,它与期望轨迹的误差是终值有界的.并且,针对后者所提出的控制律进行仿真.仿真结果表明,这种连续鲁棒控制律对于机器人系统存在外界不确定性干扰时是十分有效的.     

Event‐triggered fault‐tolerant control and scheduling codesign for nonlinear networked control systems with medium‐access constraint and packet disordering

This paper studies an event‐triggered communication, scheduling, and fault‐tolerant control codesign method for nonlinear networked control systems with medium‐access constraint, delay, and packet disordering using an adaptive approximation method and adaptive technique. By considering nonlinear dynamics and controller reconfiguration, a novel event‐triggering scheme with an adjustable triggering condition and adaptive triggering thresholds is proposed. The stochastic event‐driven actuator scheduling is investigated without the assumption that the controller can access the current modes of the actuators. By considering the Markovian delay and focusing on the transmitter node, a new packet reordering approach is used to cope with packet disordering. This paper proposes an active fault‐tolerant control method, in which the nominal controller is redesigned for the postfault plant by using the fault information provided by an estimator. It is proven that the estimation error of the estimator is uniformly bounded, the reconfigurable controller and event‐trigger ensure the boundedness in probability of the state tracking error before and after the fault occurrence in the presence of medium‐access constraint, delay, and packet disordering while reducing communication load. The effectiveness of the proposed method is demonstrated in the numerical example.     

Output Feedback Control of Surge and Rotating Stall in Axial Compressors

Active control has been widely studied to expand the stable operating range of axial flow compressors in aero‐engines.In this paper, a nonlinear active state feedback controller is proposed first based on bifurcation analysis results of MG model.Then by taking pressure ratio as output parameter, a state observer is designed to estimate the compressor's flow coefficient. An output feedback controller is thus established by combining the observer with the state feedback controller.Finally, digital simulation shows that the proposed output feedback controller not only eliminates the hysteresis loop associated with rotating stall and emergence of surge, but also extends the stable operating range of axial flow compressors effectively.Furthermore, being flexible in using pressure transducer and throttle valve as sensor and actuator respectively, which have been equipped in common engines, the proposed controller has good applicability.