A switched energy saving position controller for variable-pressure electro-hydraulic servo systems

The electro-hydraulic servo system (EHSS) demonstrates a relatively low level of efficiency compared to other available actuation methods. The objective of this paper is to increase this efficiency by introducing a variable supply pressure into the system and controlling this pressure during the task of position tracking. For this purpose, an EHSS structure with controllable supply pressure is proposed and its dynamic model is derived from the basic laws of physics. A switching control structure is then proposed to control both the supply pressure and the cylinder position at the same time, in a way that reduces the overall energy consumption of the system. The stability of the proposed switching control system is guaranteed by proof, and its performance is verified by experimental testing.     

A compound control strategy combining velocity compensation with ADRC of electro-hydraulic position servo control system

In order to enhance the anti-jamming ability of electro-hydraulic position servo control system at the same time improve the control precision of the system, a compound control strategy that combines velocity compensation with Active Disturbance Rejection Controller (ADRC) is proposed, and the working principle of the compound control strategy is given. ADRC controller is designed, and the extended state observer is used for observing internal parameters uncertainties and external disturbances, so that the disturbances of the system are suppressed effectively. Velocity compensation controller is designed and the compensation model is derived to further improve the positioning accuracy of the system and to achieve the velocity compensation without disturbance. The compound control strategy is verified by the simulation and experiment respectively, and the simulation and experimental results show that the electro-hydraulic position servo control system with ADRC controller can effectively inhibit the external disturbances, the precise positioning control is realized after introducing the velocity compensation controller, and verify that the compound control strategy is effective.     

电液位置伺服系统神经滑模控制仿真

分析了电液位置伺服控制系统的数学模型,提出利用线性化反馈技术构建滑模控制率,并应用神经网络进行参数逼近,实现了自适应神经滑模控制器的设计.仿真结果表明所设计的滑模控制器能进行有效的参数估计,有效的克服系统抖振,取得较为满意的控制品质.     

Sliding mode control with varying boundary layers for an electro-hydraulic position servo system

In this study, a new sliding mode control with varying boundary layers is proposed to improve the tracking performance of a nonlinear electro-hydraulic position servo system, which can be found in many manufacturing devices. The key feature of the proposed control scheme is the use of varying boundary layers instead of fixed boundary layers, which are usually employed in conventional sliding mode control. The validity of the proposed control scheme is verified through practical testing on an experimental electro-hydraulic positioning device. In the cases of step and sinusoidal command inputs, the experimental results strongly suggest that the proposed control scheme is capable of improving the tracking precision without causing any chattering. In addition, the new control scheme seems to be very robust against various set point conditions .     

Real-time tracking control of electro-hydraulic force servo systems using offline feedback control and adaptive control

This paper focuses on an application of an electro-hydraulic force tracking controller combined with an offline designed feedback controller (ODFC) and an online adaptive compensator in order to improve force tracking performance of an electro-hydraulic force servo system (EHFS). A proportional-integral controller has been employed and a parameter-based force closed-loop transfer function of the EHFS is identified by a continuous system identification algorithm. By taking the identified system model as a nominal plant model, an H_∞ offline design method is employed to establish an optimized feedback controller with consideration of the performance, control efforts, and robustness of the EHFS. In order to overcome the disadvantage of the offline designed controller and cope with the varying dynamics of the EHFS, an online adaptive compensator with a normalized least-mean-square algorithm is cascaded to the force closed-loop system of the EHFS compensated by the ODFC. Some comparative experiments are carried out on a real-time EHFS using an xPC rapid prototype technology, and the proposed controller yields a better force tracking performance improvement.     

An optimization-based control strategy for energy efficiency of discrete manufacturing systems

In order to reduce the global energy consumption and avoid highest power peaks during operation of manufacturing systems, an optimization-based controller for selective switching on/off of peripheral devices in a test bench that emulates the energy consumption of a periodic system is proposed. First, energy consumption models for the test-bench devices are obtained based on data and subspace identification methods. Next, a control strategy is designed based on both optimization and receding horizon approach, considering the energy consumption models, operating constraints, and the real processes performed by peripheral devices. Thus, a control policy based on dynamical models of peripheral devices is proposed to reduce the energy consumption of the manufacturing systems without sacrificing the productivity. Afterward, the proposed strategy is validated in the test bench and comparing to a typical rule-based control scheme commonly used for these manufacturing systems. Based on the obtained results, reductions near 7% could be achieved allowing improvements in energy efficiency via minimization of the energy costs related to nominal power purchased.     

电液伺服控制摩托车随机疲劳试验台的研究

分析了摩托车随机疲劳试验台的基本原理与结构特点,并针对其电液伺服系统建立了一种新的疲劳模拟时域控制方法,设计了多级递阶模糊控制器来控制试验台跟踪期望输入信号,以最终实现对电液伺服系统的实时控制.最后在试验台上进行了多种规格摩托车的振动试验,试验结果证明该试验台完全满足摩托车可靠性试验要求,为摩托车零部件及整车疲劳试验提供了新的方法.     

电液位置伺服系统的三维模糊PID控制

建立了阀控非对称液压缸的动力学模型，其推导过程可以用于任意电液位置伺服系统的数学建模；把模糊控制理论引入了伺服系统，设计了三维模糊PID控制器，基于Matlab／Stimulink软件平台进行了可视化仿真，改善了系统静动态性能和响应速度，为今后多输入一多输出问题的研究提供了可行的思路和方法。     

Novel integrated position measurement unit for stepping motor servo control

Rotor position detection is important for motor servo system design. In general, there are two kinds of methods to obtain the position information in real time, sensor or sensorless methods. The sensor methods use position sensors such as optical encoder. This will greatly increase the cost of the system, and the sensor with high precision is difficult to be installed. On the other hand, the sensorless method can reduce the cost, but the reliability and complexity of the algorithm is still the problems. In this paper, a new low-cost integrated position feedback unit, which is composed of the integrated position sensor, signal processing hardware and software, is described. The sensor is easy to manufacture and has better precision with the help of signal processing circuit and software based on DSP. The sensor can obtain absolute rotating angle using inductance detection method, and it is originally designed and used for a 2-phase hybrid stepping motor position servo system. The integrated sensor and the proper control strategy make the system become a low-cost high-performance position servo system. Even though the feedback unit is originally designed for a 2-phase hybrid stepping motor, the same unit also can be used with other types of motors.     

Coupled-disturbance-observer-based position tracking control for a cascade electro-hydraulic system

The disturbance suppression is one of the most common control problems in electro-hydraulic systems. especially largely an unknown disturbance often obviously degrades the dynamic performance by biasing the desired actuator outputs (e.g., load forces or torques). In order to reject the dynamic disturbances in some multi-degree-of-freedom manipulators driven by electro-hydraulic actuators, this paper proposes a state feedback control of the cascade electro-hydraulic system based on a coupled disturbance observer with backstepping. The coupled disturbance observer is designed to estimate both the independent element and the coupled element of the external loads on each electro-hydraulic actuator. The cascade controller has the ability to compensate for the disturbance estimating, as well as guarantees the system state error convergence to a prescribed steady state level. The effectiveness of the proposed controller for the suppression of largely unknown disturbances has been demonstrated by comparative study, which implies the proposed approach can achieve better dynamic performance on the motion control of Two-Degree-of-Freedom robotic arm.     

Predictive IP controller for robust position control of linear servo system

Position control is a typical application of linear servo system. In this paper, to reduce the system overshoot, an integral plus proportional (IP) controller is used in the position control implementation. To further improve the control performance, a gain-tuning IP controller based on a generalized predictive control (GPC) law is proposed. Firstly, to represent the dynamics of the position loop, a second-order linear model is used and its model parameters are estimated on-line by using a recursive least squares method. Secondly, based on the GPC law, an optimal control sequence is obtained by using receding horizon, then directly supplies the IP controller with the corresponding control parameters in the real operations. Finally, simulation and experimental results are presented to show the efficiency of proposed scheme.     

电液位置伺服系统的计算机辅助设计

利用面向对象编程的思想对电液位置伺服系统CAD软件进行开发.该软件以中文WindowsXP为操作平台,用MicrosoftAccess建立的数据库为基础,以Autodesk公司的AutoCAD2005和MathWorks公司的Matlab7.0为支撑软件,利用VisualBasic6.0开发语言,将系统原理图绘制、参数计算、元件选取、动态仿真集成于一体.使用该软件进行电液位置伺服系统的设计,可获得工程上直接可用的系统原理图.     

Adaptive super-twisting observer for fault reconstruction in electro-hydraulic systems

An adaptive-gain super-twisting sliding mode observer is proposed for fault reconstruction in electro-hydraulic servo systems (EHSS) receiving bounded perturbations with unknown bounds. The objective is to address challenging problems in classic sliding mode observers: chattering effect, conservatism of observer gains, strong condition on the distribution of faults and uncertainties. In this paper, the proposed super-twisting sliding mode observer relaxes the condition on the distribution of uncertainties and faults, and the gain adaptation law leads to eliminate observer gain overestimation and attenuate chattering effects. After using the equivalent output-error-injection feature of sliding mode techniques, a fault reconstruction strategy is proposed. The experimental results are presented, confirming the effectiveness of the proposed adaptive super-twisting observer for precise fault reconstruction in electro-hydraulic servo systems.     

交流电机位置伺服系统的扰动补偿控制

针对交流电机伺服系统在未知负载条件下进行准确位置控制的需求,提出了一种参数化复合控制方案。该方案建立在交流电机磁场定向矢量控制构架的基础上,以转矩电流作为控制信号(电流内环的给定值),以电机转角位置信号作为可量测的系统输出量,设计了基于极点配置的状态反馈与扰动前馈补偿组成的参数化控制律,并利用一个降阶线性扩展状态观测器对电机转速(未量测)和未知负载扰动加以估计。该控制律通过TMS320F28335DSP编程,在一台永磁同步电机伺服系统上进行了实验测试,实验结果验证了伺服系统能在未知负载情况下对各目标位置进行平稳且准确地跟踪。研究结果表明,这种基于扩展状态观测器的复合控制方案可以有效地实现交流伺服系统的高性能位置调节,且对负载幅值和模型参数差异具有较好的鲁棒性。     

工程机械变速系统电液控制技术研究

本文对国外先进的工程机械变速系统电液控制方案进行了分析研究,对电液比例技术进行了探讨,针对国内工程机械传动系统进行了电液控制方案研究,并将电液比例技术应用于工程机械传动系统,采用电液比例控制系统对工程机械变速箱进行电液控制,并对变速箱压力时间离合曲线进行最佳拟合.     

Nonlinear robust dual-loop control for electro-hydraulic load simulator

This paper investigates on the high performance torque control of electro-hydraulic load simulator (EHLS). In order to suppress actuator׳s motion disturbance, a nonlinear robust dual-loop control scheme is developed, which consists of a open-loop nonlinear velocity feed-forward compensator and a closed-loop nonlinear deterministic robust torque controller. The main function of the open-loop compensator is to decouple actuator׳s active motion disturbance, whereas the torque loop controller aims at guaranteeing the dynamics performance of tracking torque reference. Besides actuator׳s motion disturbance, both the nonlinearity characteristics and friction problem of the EHLS system are taken into consideration in this paper. The effectiveness of the developed method are verified through comparative co-simulations and experiments.     

Multi-loop nonlinear control design for performance improvement of LTI systems

This paper puts forward a multi-loop nonlinear control (MLNC) strategy to overcome the limited performance of LTI controllers due to the so-called “waterbed” effect. According to “Bode's sensitivity integral”, increasing the bandwidth or additional integral gain of LTI controller to improve the low-frequency disturbance attenuation irrefutably increases the sensitivity to high-frequency disturbances or measurement noise. Hence, it is impossible to attain the best of both worlds in the case of linear controllers. Therefore, with an aim to improve the transient and steady state performance of linear controllers, in this paper, a nonlinear control framework using circle criterion method and saturation nonlinearity, which adjusts the integral gain based on the error threshold, is discussed. The global asymptotic stability (GAS) of the MLNC strategy is theoretically proved using LaSalle's invariance principle and experimentally validated using measured frequency response function (FRF). Moreover, the performance of the MLNC strategy is compared with that of the multi-loop linear control (MLLC) strategy on a benchmark magnetic levitation system for tracking application. The cumulative power spectral density (CPSD) of tracking error, which is used as the performance index to assess the overall closed loop performance, accentuates that MLNC can yield better steady state and transient performance compared to MLLC scheme.     

Characterization and quenching of friction-induced limit cycles of electro-hydraulic servovalve control systems with transport delay

This paper develops a systematic and straightforward methodology to characterize and quench the friction-induced limit cycle conditions in electro-hydraulic servovalve control systems with transport delay in the transmission line. The nonlinear friction characteristic is linearized by using its corresponding describing function. The delay time in the transmission line, which could accelerate the generation of limit cycles is particularly considered. The stability equation method together with parameter plane method provides a useful tool for the establishment of necessary conditions to sustain a limit cycle directly in the constructed controller coefficient plane. Also, the stable region, the unstable region, and the limit cycle region are identified in the parameter plane. The parameter plane characterizes a clear relationship between limit cycle amplitude, frequency, transport delay, and the controller coefficients to be designed. The stability of the predicted limit cycle is checked by plotting stability curves. The stability of the system is examined when the viscous gain changes with respect to the temperature of the working fluid. A feasible stable region is characterized in the parameter plane to allow a flexible choice of controller gains. The robust prevention of limit cycle is achieved by selecting controller gains from the asymptotic stability region. The predicted results are verified by simulations. It is seen that the friction-induced limit cycles can be effectively predicted, removed, and quenched via the design of the compensator even in the case of viscous gain and delay time variations unconditionally.     

Modal space three-state feedback control for electro-hydraulic servo plane redundant driving mechanism with eccentric load decoupling

The shaking table based on electro-hydraulic servo parallel mechanism has the advantage of strong carrying capacity. However, the strong coupling caused by the eccentric load not only affects the degree of freedom space control precision, but also brings trouble to the system control. A novel decoupling control strategy is proposed, which is based on modal space to solve the coupling problem for parallel mechanism with eccentric load. The phenomenon of strong dynamic coupling among degree of freedom space is described by experiments, and its influence on control design is discussed. Considering the particularity of plane motion, the dynamic model is built by Lagrangian method to avoid complex calculations. The dynamic equations of the coupling physical space are transformed into the dynamic equations of the decoupling modal space by using the weighted orthogonality of the modal main mode with respect to mass matrix and stiffness matrix. In the modal space, the adjustments of the modal channels are independent of each other. Moreover, the paper discusses identical closed-loop dynamic characteristics of modal channels, which will realize decoupling for degree of freedom space, thus a modal space three-state feedback control is proposed to expand the frequency bandwidth of each modal channel for ensuring their near-identical responses in a larger frequency range. Experimental results show that the concept of modal space three-state feedback control proposed in this paper can effectively reduce the strong coupling problem of degree of freedom space channels, which verify the effectiveness of the proposed model space state feedback control strategy for improving the control performance of the electro-hydraulic servo plane redundant driving mechanism.