Design and experimental evaluation of a dynamical adaptive backstepping-sliding mode control scheme for positioning of an antagonistically paired pneumatic artificial muscles driven actuating system

Pneumatic artificial muscles (PAMs) are a class of pneumatic drives that have received considerable attention for applications related to bio-inspired robotics. Nevertheless, servo control of PAMs is challenging due to the compressibility and nonlinear flow characteristics of air, hysteresis behaviour as well as uncertainties present. In this paper, positioning of an antagonistically paired PAM with mass flow rate of compressed air regulated by a 5/3-way proportional directional valve and driven by a dynamical adaptive backstepping-sliding mode control (DAB-SMC) scheme is investigated. Implemented for the first time on a PAM-driven actuating system, derivation of this model-based nonlinear control scheme is presented first followed by experimental evaluation. Positioning performance is studied using a sinusoidal trajectory with tracking frequencies of 0.05, 0.1, 0.2 and 0.5 Hz, and a multiple-step polynomial input having step sizes of 0.7°, 1.4°, 2.9° and 5.7°. Over various operating conditions, average root mean square error value of 0.16° and steady-state error value of 0.04° are achieved for position tracking and regulating, respectively. The adaptive LuGre friction observer embedded in the control scheme effectively compensates hysteresis behaviour of the PAMs and helps to improve the performance. The proposed DAB-SMC scheme outperforms the classical SMC scheme by 33% in accuracy. The control scheme has also demonstrated a robust performance towards the uncertainties including loading. In addition, a slight performance compromise in both tracking and regulating tasks was observed, when the 5/3-way proportional valve is replaced by cost-effective 2/2-way pulse width modulation controlled on–off valves.     

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.     

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.     

机器人化悬臂式掘进机液压行走驱动系统建模

为了解决机器人化悬臂式掘进机行走控制问题,在对该掘进机液压行走驱动系统的工作原理分析的基础上,建立了该系统的数学模型。该数学模型悬臂式掘进机行走驱动系统中电液比例方向阀的电压与阀芯位移关系式和流量方程、液压马达的流量与扭矩方程、比例方向阀的阀芯位移与液压马达角速度关系方程以及方向阀的输入电压与液压马达角速度的传递函数。仿真实验结果表明,所建立数学模型与实际基本吻合,为机器人化悬臂式掘进机性能分析和控制系统设计提供了实用的数学模型。     

Design and experimental study of a dynamical adaptive backstepping–sliding mode control scheme for position tracking and regulating of a low‐cost pneumatic cylinder

A dynamical adaptive backstepping–sliding mode control scheme is designed and implemented for the first time, to track and regulate the position of a low‐cost pneumatically driven single‐rod, double‐acting cylinder. The mass flow rate of compressed air into and out of the cylinder is regulated by a 5/3‐way proportional directional control valve. The derivation of the controller, utilizing a design procedure that guarantees stability of the control system, is presented first. Next, experimental evaluation of the controller is conducted with respect to performance and robustness to parametric uncertainties. Experiments employ a sinusoidal reference trajectory with tracking frequencies of 0.05, 0.1, and 0.2 Hz; a multiple‐step polynomial reference trajectory having step sizes of 0.0125, 0.025, 0.05, and 0.1 m; and three external loads of 4.4, 9, and 16 kg operating in two modes (motion assisting and resisting). From over 70 experiments involving various operating conditions, average root mean square of tracking error of 1.73 mm and steady‐state error of 0.71 mm are achieved for the position tracking and regulating, respectively. As compared with the classical sliding mode control scheme alone, the new controller outperforms by more than twofold. The adaptive LuGre‐based friction observer applied in this control scheme significantly assists in compensating the adverse effect of friction with the average of 55% less tracking error. Copyright © 2015 John Wiley & Sons, Ltd.     

Proportional directional valve based automatic steering system for tractors

Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3- position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative (PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods.     

A neural net-based time-delay compensation scheme and disturbance rejection for pneumatic systems

In practical electro-pneumatic or hydraulic servo mechanism, there is usually an unavoidable operating delay time in the solenoid valves. This may sometimes cause closed-loop instability if the time delay is not treated carefully in the control system designs. Furthermore, pneumatic actuators can offer high performance at low cost, but are often suffered from external disturbances depending on the operating conditions. This paper proposes a non-model-based design approach for pneumatic actuating systems. In the proposed control system, a gain scheduled fuzzy-PID controller ensures tracking performance an adaptable wavelet neuro compensator compensates for time-delay of the control valve, and a disturbance rejecter diminishes influence from load changes. A condition ensuring the closed-loop stability is derived. The proposed design is experimentally verified to show its effectiveness.     

基于滑模观测器的直线伺服系统反馈线性化速度跟踪控制

在许多高速、高精的直线伺服系统中,要求能实现对速度的快速精确跟踪,但其模型的非线性和变量间的耦合给控制带来难度.对高速、高精速度跟踪控制中,电流和速度的变化过程在时间尺度上相对接近,不能简单地采用磁场定向矢量控制方法实现静态解耦,否则电流和速度间的非线性耦合将破坏速度跟踪品质.采用状态反馈线性化方法来实现永磁直线同步电动机(PMLSM)模型的精确线性化和动态解耦.利用非线性坐标变换和非线性反馈将系统解耦成独立的线性电流子系统和速度子系统.通过扩展滑模观测器来实现对所需要的动子速度、加速度和负载扰动的鲁棒观测.并利用李雅普诺夫理论对由反馈线性化和滑模观测器构成的非线性闭环系统的稳定性进行了证明.仿真结果表明该方案使PMLSM伺服系统具有良好的鲁棒速度跟踪性能.     

直驱式巷道超前支架油缸控制方法

考虑到传统的阀控液压系统存在伺服阀容易因受到油液污染而无法正常工作、阀控液压系统效率低、节流损失大、造成能源浪费等问题,研究一种基于伺服电机直驱液压泵的超前支架电液控制方法.伺服电机直驱液压泵系统由于电机的启动和转向过程中存在滞后性,因此使用常规PID算法的控制效果较差,使用模糊PID算法对伺服电机直驱液压泵系统进行控制.使用Matlab/Simulink仿真软件建立本文研究的直驱泵控巷道超前支架控制系统的仿真模型,并建立超前支架的实验样机,使用常规PID与模糊PID算法进行对比研究,研究结果表明:模糊PID算法作用下,伺服电机直驱液压泵的超前支架液压缸位置变化的超调量更低,调整速度更快,能够快速跟踪给定信号曲线,具有较好的鲁棒性.     

电动伺服舵机系统中的迭代学习控制

电动伺服舵机控制系统采用全数字三环控制策略,分别为位置环、速度环和电流环;作为内环的电流环,应具有良好的稳态和动态特性,其输出电流要求快速准确地跟踪给定电流,以保证舵机控制系统高性能位置伺服的要求;在传统的增量式积分分离PI控制算法的基础上,引入-D型迭代学习控制前馈环节,提高了电流跟踪的快速性和跟踪精度,建立了系统的数学模型并在MATLAB上进行了系统仿真;仿真结果表明,引入D型迭代学习控制后,电流环的稳态和动态特性良好,保证了输出电流跟踪的快速性、精确性.     

电液比例位置同步线性自抗扰控制

电液比例位置同步液压系统受到元件安装精度、死区非线性以及系统参数摄动等因素的影响,导致两侧子系统性能不一致进而引起位置不同步.针对这一问题,提出由位置控制器、死区补偿器、同步控制器组成的复合控制方案.首先,建立电液比例位置控制系统数学模型,并分析系统内部参数摄动及比例阀死区特性对同步控制精度造成的影响.在此基础上,设计线性自抗扰同步控制器,实现对系统内外扰动的实时估计与主动补偿,同时为提高液压缸动态性能,减小稳态误差,设计了比例阀死区补偿器.仿真和实验结果表明,自抗扰控制器有效地抑制了内外扰动,提高了位置同步控制精度,而死区补偿器的引入改善了系统动态响应性能,降低了稳态位置同步误差.     

The velocity control of an electro‐hydraulic displacement‐controlled system using adaptive fuzzy controller with self‐tuning fuzzy sliding mode compensation

Hydraulic servo control systems have been used widely in industry. Within the realm of hydraulic control systems, conventional hydraulic valve‐controlled systems have higher response and lower energy efficiency, whereas hydraulic displacement‐controlled servo systems have higher energy efficiency. This paper aims to investigate the velocity control performance of an electro‐hydraulic displacement‐controlled system (EHDCS), where the controlled hydraulic cylinder is altered by a variable displacement axial piston pump to achieve velocity control. For that, a novel adaptive fuzzy controller with self‐tuning fuzzy sliding‐mode compensation (AFC‐STFSMC) is proposed for velocity control in EHDCS. The AFC‐STFSMC approach combining adaptive fuzzy control and the self‐tuning fuzzy sliding‐mode control scheme, has the advantages of the capability of automatically adjusting the fuzzy rules and of reducing the fuzzy rules. The proposed AFC‐STFSMC scheme can design the sliding‐mode controller with no requirement on the system dynamic model, and it can be free of chattering, thereby providing stable tracking control performance and robustness against uncertainties. Moreover, the stability of the proposed scheme via the Lyapunov method is proven. Therefore, the velocity control of EHDCS controlled by AFC‐STFSMC is implemented and verified experimentally in different velocity targets and loading conditions. The experimental results show that the proposed AFC‐STFSMC method can achieve good velocity control performance and robustness in EHDCS with regard to parameter variations and external disturbance. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

含执行机构未知动态的液压伺服系统输出反馈控制

针对含有未知动态(如:执行机构、负载等)液压伺服系统,提出一种基于未知系统动态估计器的输出反馈控制方法.该方法不依赖于函数逼近器和传统反步控制设计,且无需难以测量的系统内部状态.首先,为避免反步控制和系统全部状态,引入等价变换,将含液压执行机构的伺服系统高阶严格反馈模型转化为Brunovsky标准型,进而运用高阶滑模微分器观测转化后的系统未知状态.控制器设计中引入描述收敛速率、最大超调量和稳态误差的性能函数,保证预设控制系统稳态和瞬态控制性能.为补偿系统集总未知动态影响,设计一种仅含一个调节参数并保证指数收敛的未知系统动态估计器.该输出反馈控制器可以实现对系统输出的精确跟踪控制.最后,通过数值仿真结果表明了所提出算法的有效性.     

Networked iterative learning control design for discrete-time systems with stochastic communication delay in input and output channels

This paper develops two kinds of derivative-type networked iterative learning control (NILC) schemes for repetitive discrete-time systems with stochastic communication delay occurred in input and output channels and modelled as 0-1 Bernoulli-type stochastic variable. In the two schemes, the delayed signal of the current control input is replaced by the synchronous input utilised at the previous iteration, whilst for the delayed signal of the system output the one scheme substitutes it by the synchronous predetermined desired trajectory and the other takes it by the synchronous output at the previous operation, respectively. In virtue of the mathematical expectation, the tracking performance is analysed which exhibits that for both the linear time-invariant and nonlinear affine systems the two kinds of NILCs are convergent under the assumptions that the probabilities of communication delays are adequately constrained and the product of the input–output coupling matrices is full-column rank. Last, two illustrative examples are presented to demonstrate the effectiveness and validity of the proposed NILC schemes.     

Tracking control of electro-hydraulic servo multi-closed-chain mechanisms with the use of an approximate nonlinear internal model

This paper studied the trajectory-tracking problem of a hydraulic servo multi-closed-chain mechanism. The nonaffine nonlinear characteristic of the electro-hydraulic actuator and its time-varying uncertainty load resulting from the multi-closed-chain mechanism was taken into consideration in the proposed novel nonlinear control algorithm, that is, the approximate internal model control (AIMC) integrated with a position feedback control in cascade control design. This algorithm improves the trajectory-tracking performance of the hydraulic servomechanism (HSM). To reduce the difficulty in directly utilizing the AIMC for the HSM position trajectory, the complex electro-hydraulic mechanical system was divided into two subsystems: nonaffine nonlinear, and linear. The AIMC controller was designed for the nonaffine nonlinear subsystem to realize velocity trajectory tracking control, whereas a position feedback control was derived for the linear subsystem. The position trajectory tracking control was achieved by congruently combining the AIMC, and the position feedback control based on a recursive design idea. In addition, a complete state-space mathematical model for the HSM was developed and illustrated through simulations and experiments. Based on the proposed approach and the AIMC, the desired position and velocity trajectory tracking was examined on a hydraulic forging manipulator. The stability of the proposed method was analytically derived. Results of the simulations and experiments performed with the hydraulic manipulator demonstrated the effectiveness of the proposed approach.     

基于PC的开放式数控系统关键技术研究

主要研究了基于PC的开放式数控系统功能实现的方案与关键技术。在分析了开放式数控系统应用现状并阐述了PC数控系统结构及开放式数控系统构成的基础上,完成了低成本、可重构的开放式数控系统的设计及系统开放式软硬件体系的建立,系统控制器通过编程完成对输入、输出量的规划过程,通过PID控制伺服电机的输出,从而实现对伺服电机轨迹输出的优化控制目标,实现交互控制机制的开发,该模块化可重构系统在降低系统成本的同时显著提高了使用性能,具备较高的实际应用价值。     

一种模糊学习控制方法及其在多指手爪位置伺服系统中的应用

本文针对重复抓取与操作的多指手爪，提出了一种模糊学习控制方法，该方法利用先前的控制误差，逐步地修正不完善的控制规则，使系统的实际输出收敛于给定的轨迹，本文还给出了这种方法的收敛性条件，并应用于多指手爪的位置伺服系统中，改善控制性能，达到了预期的控制效果。     

基于位置控制和均衡分配输出模式的轧机HGC控制系统

位置控制和均衡分配输出控制思想根据轧机HGC位置的实际值与给定值形成一个负反馈,通过比例控制器计算出轧机HGC伺服阀的开口度输出,并将输出分解成主调节量和辅调节量两个分量,由伺服模式控制字选择伺服阀输出其中一个分量,两个伺服阀相互协调以达到均衡分配输出,更好地有效利用伺服阀并保证生产精度的要求。     

基于DSP的液压伺服系统H∞控制研究

以高速开关阀控液压缸的液压伺服系统为基础,分析和建立了复杂的非线性液压伺服系统数学模型,采用TMS320LF2407A DSP芯片为主处理器,提出了一种智能鲁棒H∞控制方法。仿真结果表明,该控制策略与常规的PID控制比较,能很好地跟踪期望输出,响应速度更快,过渡时间更短,基本上能实现系统的无差控制。     

A modified direct adaptive robust motion trajectory tracking controller of a pneumatic system

In this study, we developed and tested a high-precision motion trajectory tracking controller of a pneumatic cylinder driven by four costless on/off solenoid valves rather than by a proportional directional control valve. The relationship between the pulse width modulation （PWM） of a signal＇s duty cycle and control law was determined experimentally, and a mathematical model of the whole system established. Owing to unknown disturbances and unmodeled dynamics, there are considerable uncertain nonlinearities and parametric uncertainties in this pneumatic system. A modified direct adaptive robust controller （DARC） was constructed to cope with these issues. The controller employs a gradient type adaptation law based on discontinuous projection mapping to guarantee that estimated unknown model parameters stay within a known bounded region, and uses a deterministic robust control strategy to weaken the effects of unmodeled dynamics, disturbances, and parameter estimation errors. By using discontinuous projection mapping, the parameter adaptation law and the robust control law can be synthesized separately. A recursive backstepping technology is applied to account for unmatched model uncertainties. Kalman filters were designed sepa- rately to estimate the motion states and the derivative of the intermediate control law in synthesizing the deterministic robust control law. Experimental results illustrate the effectiveness of the proposed controller.