PID Controller Optimization by GA and Its Performances on the Electro-hydraulic Servo Control System

A proportional integral derivative （PID） controller is designed and attached to electro-hydraulic servo actuator system （EHSAS） to control the angular position of the rotary actuator which control the movable surface of space vehicles. The PID gain parameters are optimized by the genetic algorithm （GA）. The controller is verified on the new state-space model of servo-valves attached to the physical rotary actuator by SIMULINK program. The controller and the state-space model are verified experimentally. Simulation and experimental results verify the effectiveness of the PID controller adaptive by GA to control the angular position of the rotary actuator as compared with the classical PID controller and the compensator controller.

CONTROL STRATEGY FOR ELECTRO-HYDRAULIC POSITION SERVO SYSTEM WITH GENERALIZED PULSE CODE MODULATION

A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation （GPCM）, which is suitable for the area where the work condition is poor and a large flow rate is required. It is difficult to control the GPCM system because the system is discrete. With consideration of the stability and speediness of the GPCM position servo control system, a control strategy is developed through the theoretical and ex-perimental analyses. The control strategy integrates the merits of Bang-Bang control, PID control and fuzzy control. With this hybrid control strategy, the electro hydraulic control system has good per-formances, and the servo control is carried out with GPCM through on-off valves.

Separate Control of High Frequency Electro-hydraulic Vibration Exciter

The working frequency of the conventional electro-hydraulic vibration exciters,which consist of a servo valve and a hydraulic cylinder,is generally restricted within a narrow range due to limited frequency response capability of the servo valve itself.To counteract such restriction,a novel scheme for an electro-hydraulic vibrator,controlled by a two-dimensional valve（2D valve） and a bias valve in parallel,is therefore proposed.The frequency,amplitude and offset are independently controlled by rotary speed,axial sliding of the spool of the 2D valve and axial sliding of the spool of the bias valve.The principle of separate control was presented and the regulation approach of frequency,amplitude and offset was discussed.A mathematical model of the hydraulic power mechanism for the proposed vibration exciter was established to investigate the relationship between the amplitude and the axial sliding of the 2D valve＇ spool,as well as that between the offset and the axial sliding of the bias valve＇s spool at various frequencies.An experimental system was built to validate the theoretical analysis.It is verified that the 2D exciter is capable of working smoothly in a frequency range of 5- 200 Hz.And its frequency,amplitude and offset can be controlled respectively by either closed loop or open loop method.There is a linear relationship between the output amplitude and the spool axial opening of the 2D valve until a point when the flow rate becomes saturate and the amplitude remains constant.The offset displacement of the cylinder＇s piston is linearly proportional to the axial displacement of the spool of the bias valve,when the valve opening is less than 25%.Thereafter,the slop of the offset curve decreases and tends to saturate.The proposed electro-hydraulic vibration controlled by the 2D valve not only facilitates the realization of high-frequency electro-hydraulic vibration,the high-accuracy of vibration can also be achieved by means of independent controls to the frequency,amplitude and offset.

Present Status and Prospect of High-Frequency Electro-hydraulic Vibration Control Technology

Electro-hydraulic vibration equipment(EHVE)is widely used in vibration environment simulation tests,such as vehicles,weapons,ships,aerospace,nuclear industries and seismic waves replication,etc.,due to its large output power,displacement and thrust,as well as good workload adaptation and multi-controllable parameters.Based on the domestic and overseas development of high-frequency EHVE,dividing them into servo-valve controlled vibration equipment and rotary-valve controlled vibration equipment.The research status and progress of high-frequency electro-hydraulic vibration control technology(EHVCT)are discussed,from the perspective of vibration waveform control and vibration controller.The problems of current electro-hydraulic vibration system bandwidth and waveform distortion control,stability control,offset control and complex vibration waveform generation in high-frequency vibration conditions are pointed out.Combining the existing rotary-valve controlled high-frequency electro-hydraulic vibration method,a new twin-valve independently controlled high-frequency electro-hydraulic vibration method is proposed to break through the limitations of current electro-hydraulic vibration technology in terms of system frequency bandwidth and waveform distortion.The new method can realize independent adjustment and control of vibration waveform frequency,amplitude and offset under high-frequency vibration conditions,and provide a new idea for accurate simulation of high-frequency vibration waveform.

Parameter-dependent vibration-attenuation controller design for electro-hydraulic actuated linear structural systems

The problem of robust active vibration control for a class of electro-hydraulic actuated structural systems with time-delay in the control input channel and parameter uncertainties appearing in all the mass, damping and stiffness matrices is investigated in this paper. First, by introducing a linear varying parameter, the nonlinear system is described as a linear parameter varying （LPV） model. Second, based on this LPV model, an LMI-based condition for the system to be asymptotically stabilized is deduced. By solving these LMIs, a parameter-dependent controller is established for the closed- loop system to be stable with a prescribed level of disturbance attenuation. The condition is also extended to the uncertain case. Finally, some numerical simulations demonstrate the satisfying performance of the proposed controller.

Continuous rotary motor electro-hydraulic servo system based on the improved repetitive controller

In order to suppress the periodic interference of the continuous rotary electro-hydraulic servo motor,this paper makes the motor tracking the periodic signals with high accuracy,and improves the influence of friction interference to the performance of continuous rotary electro-hydraulic servo motor.The mathematic model of the electro-hydraulic position servo system of the continuous rotary motor was established,and the compound control method was adopted based on the repetitive control,feed forward and PID to suppress the friction interference.Through the simulation,the result confirms that the compound control method decreases the tracking error of the system,increases the robust performance of the system and improves the performance of the continuous rotary electro-hydraulic servo motor.

Nonlinear Modeling and Identification of the Electro-hydraulic Control System of an Excavator Arm Using BONL Model

Electro-hydraulic control systems are nonlinear in nature and their mathematic models have unknown parameters. Existing research of modeling and identification of the electro-hydraulic control system is mainly based on theoretical state space model, and the parameters identification is hard due to its demand on internal states measurement. Moreover, there are also some hard-to-model nonlinearities in theoretical model, which needs to be overcome. Modeling and identification of the electro-hydraulic control system of an excavator arm based on block-oriented nonlinear（BONL） models is investigated. The nonlinear state space model of the system is built first, and field tests are carried out to reveal the nonlinear characteristics of the system. Based on the physic insight into the system, three BONL models are adopted to describe the highly nonlinear system. The Hammerstein model is composed of a two-segment polynomial nonlinearity followed by a linear dynamic subsystem. The Hammerstein-Wiener（H-W） model is represented by the Hammerstein model in cascade with another single polynomial nonlinearity. A novel Pseudo-Hammerstein-Wiener（P-H-W） model is developed by replacing the single polynomial of the H-W model by a non-smooth backlash function. The key term separation principle is applied to simplify the BONL models into linear-in-parameters struc^tres. Then, a modified recursive least square algorithm（MRLSA） with iterative estimation of internal variables is developed to identify the all the parameters simultaneously. The identification results demonstrate that the BONL models with two-segment polynomial nonlinearities are able to capture the system behavior, and the P-H-W model has the best prediction accuracy. Comparison experiments show that the velocity prediction error of the P-H-W model is reduced by 14%, 30% and 75% to the H-W model, Hammerstein model, and extended auto-regressive （ARX） model, respectively. This research is helpful in controller design, system monitoring and diagnosis.

Angular Position Controller and Its Design Model Verification for the Electro-Hydraulic Servo Control System

The angular position controller is system （EHSAS） to control the output of the rotary applied to electro-hydraulic servo actuator actuator. It works as a compensator based on the frequency response of the EHSAS. Its design model is verified on the state-space model of EHSAS by using simulation program SIMULINK. Real data used to test the system. Simulation results give a good agreement for the controller and also for the state-space model.

FORCE FEEDBACK MODEL OF ELECTRO-HYDRAULIC SERVO TELE-OPERATION ROBOT BASED ON VELOCITY CONTROL

The tele-operation robotic system which consists of an excavator as the construction robot, and two joysticks for operating the robot from a safe place are useful for performing restoration in damaged areas. In order to accomplish a precise task, the operator needs to feel a realistic sense of task force brought about from a feedback force between the fork glove of slave robot and unfamiliar environment. A novel force feedback model is proposed based on velocity control of cylinder to determine environment force acting on fork glove. Namely, the feedback force is formed by the error of displacement of joystick with velocity and driving force of piston, and the gain is calculated by the driving force and threshold of driving force of hydraulic cylinder. Moreover, the variable gain improved algorithm is developed to overcome the defect for grasping soft object. Experimental results for fork glove freedom of robotic system are provided to demonstrate the developed algorithm is available for grasping soft object.

Coordinating optimization-based sliding mode variable structure control for electro-hydraulic servo system

A sliding mode variable structure control （SMVSC） based on a coordinating optimization algorithm has been developed. Steady state error and control switching frequency are used to constitute the system performance indexes in the coordinating optimization, while the tuning rate of boundary layer width （BLW） is employed as the optimization parameter. Based on the mathematical relationship between the BLW and steady-state error, an optimized BLW tuning rate is added to the nonlinear control term of SMVSC. Simulation experiment results applied to the positioning control of an electro-hydraulic servo system show the comprehensive superiority in dynamical and static state performance by using the proposed controller is better than that by using SMVSC without optimized BLW tuning rate. This succeeds in coordinately considering both chattering reduction and high-precision control realization in SMVSC.

Research on Electro Hydraulic Proportional Control for Heavy Vehicle Blend Braking System

A blend braking system of heavy vehicle was proposed.The main control part of the system is the electro hydraulic proportional servo valve.A nonlinear model of brake cylinder controlled by the valve was deduced through the analysis of its control property and system feature.The transfer function of the system was also proposed,and the hydraulic inherent frequency and the PID closed-loop system feature were calculated.The simulated result is consistent with those tested in the bench and on the site with 50 t heavy vehicle.The experimental result shows that the control method has quick response and high precision.

Tri-state Modulation Power Driving of Electro-hydraulic Proportional Amplifier

Switch electro-hydraulic proportional amplifier（PA） widely employs single switch modulation power driving（SSMPD） or reverse discharging power driving（RDPD） at present. SSMPD has slow dynamic response, and can＇t adjust independently the dither signal＇s amplitude and frequency; RDPD accelerates the current decay; consequently, it increases current ripple and power loss. For the purpose of solving the above mentioned problem, the tri-state modulation power driving（TSMPD） scheme was proposed for improving the performance of power driving. Detailedly, the hardware circuit for the tri-state modulation power driving is designed; the tri-state modulation algorithm is realized by digital signal processor（DSP）. The tri-state modulation power driving is investigated by experiments, comparetive experiments among the single switch modulation power driving（SSMPD）, reverse discharging power driving（RDPD）, and the TSMPD are implemented, and the experimental results demonstrate that the linearity error of TSMDP meets the requirement of PA; the current response of TSMSP is the best; the amplitude of ripple current of the TSMPD can be reduced without increasing frequency of PWM, in addition, dither signal amplitude and frequency can be adjusted independently for each other. It is very meaningful to guide the development of high performance proportional amplifier for high frequency response proportional solenoid.

Pseudo Derivative Feedback Control of Electro Hydraulic Speed Servos

The Pseudo-Derivative Feedback (PDF) algorithm is introduced into design of electro-hydraulic speed servos. With limited extra complexity in implementation of controller's electronic circuits, the PDF control enables the electro-hydraulic speed servo to respond to a step command without steady-state error, and also to follow successfully a sinusoidal command at the frequency higher than that the system resulted from traditional design can reach. The numerical example-based comparison in dynamic and static behavior shows also the PDF system is superior to the traditional system in terms of both the capability of handling loads applied to the system and the robustness to ignore variation and uncertainty of the parameters of the hydraulic valve-actuator unit in operation.

Investigation of Semi-Active Hydro-Pneumatic Suspension for a Heavy Vehicle Based on Electro-Hydraulic Proportional Valve

Hydro-pneumatic suspension is widely used in heavy vehicles due to its nonlinear characteristics of stiffness and damping. However, the conventional passive hydro-pneumatic suspension can’t adjust parameters according to the complicated road environment of heavy vehicles to fulfill the requirements of the vehicle ride comfort. In this paper, a semi-active hydro-pneumatic suspension system based on the electro-hydraulic proportional valve control is proposed, and fuzzy control is used as the control strategy to adjust the?damping force of the semi-active hydro-pneumatic suspension. A 1/4?semi-active hydro-pneumatic suspension model is established, which is co-simulated with AMESim and MATLAB/Simulink. The co-simulation results show that the semi-active hydro-pneumatic suspension system can significantly reduce vibration of the vehicle body, and improve the suspension performance comparing with passive hydro-pneumatic suspension.

ROBUST CONTROL OF AN ELECTROHYDRAULIC PROPORTIONAL SPEED CONTROL SYSTEM WITH A SINGLEROD HYDRAULIC ACTUATOR

A robust control algorithm is proposed to focus on the non-linearity and parameters＇ uncertainties of an electro-hydraulic proportional speed control system （EHPSCS） with a single-rod hydraulic actuator. The robust controller proposed does not need to design stable compensator in advance, is simple in design and has large scope of uncertainty applications. The feedback gains of the robust controller proposed are small, so it is easily implemented in engineering applications. Experimental research on the speed control under the different conditions is carried out for an EHPSCS. Experimental results show that the robust controller proposed has better robustness subject to parametric uncertainties, and adaptability of parameters＇ variation of control system itself and plant parameter variation.

Nonlinear control for a class of hydraulic servo system

The dynamics of hydraulic systems are highly nonlinear and the system may be subjected to non-smooth and discontinuous nonlinearities due to directional change of valve opening, friction, etc. Aside from the nonlinear nature of hydraulic dynamics, hydraulic servo systems also have large extent of model uncertainties. To address these challenging issues, a robust state-feedback controller is designed by employing backstepping design technique such that the system output tracks a given signal arbitrarily well, and all signals in the closed-loop system remain bounded. Moreover, a relevant disturbance attenuation inequality is satisfied by the closed-loop signals. Compared with previously proposed robust controllers, this paper's robust controller based on backstepping recursive design method is easier to design, and is more suitable for implementation.

Research on characteristics of integrated type hydraulic transformer's control angle

In order to realize remote control of hydraulic transformers and improve the control precision of the pressure ratio,an integrated type electric hydraulic servo hydraulic transformer is proposed in this paper,a mathematical model is built and simulation of electro-hydraulic servo integrated hydraulic transformer's control angle is carried out,the principle prototype of the transformer is designed and manufactured,and experimental study is carried out on the experimental bench. The experimental results verify the correctness of the mathematical model. The results show that electro hydraulic servo control can improve the accuracy and dynamic response speed of control angle,which provides a reference for the further research of the hydraulic transformers.

基于SimHydraulics的电液伺服系统实物仿真

针对一个采用阀控对称缸的电液伺服系统进行了SimHydraulics实物仿真,根据仿真结果辨识出系统的数学模型,通过与机理建模和Simulink模型仿真的结果相对比进行了验证。总结了综合应用SimHydraulics与Simulink的新仿真方法,该方法使得电液伺服系统的设计和控制方案的选择可以同步进行,提高了系统设计的效率和准确性。

基于阀控缸电液系统的前馈-反馈联合控制策略研究

阀控缸电液系统应用广泛,提高其响应速度、控制精度与可靠性具有重要意义。传统闭环控制基于反馈误差调节,控制简单、稳定性好、易用于复杂系统,但存在时滞与稳定性问题;前馈控制作为一种开环控制方式,具有响应快、无时滞的优点,但控制效果依赖模型精度。针对上述问题,提出一种基于阀控缸电液系统的前馈-反馈联合控制策略,建立其数学模型,运用AMESim软件搭建仿真模型并进行可行性分析,通过实验建立伺服阀流量-压差-电压前馈参数表,最后基于Simulink建立变转速恒压油源实验平台并进行实验验证。仿真及实验结果表明:前馈-反馈联合控制可提高阀控缸电液系统的控制精度和响应性,相较于反馈控制方式跟踪精度提高45%,具有良好的综合控制效果。

Multi-Channel Force Control System for Static Loading

An eight-channel force loading system is presented, which adopts position control system and force control system switching model, small flow servo valve controlled capacious cylinder system scheme, intelligent PID algorithm and distributed load approach. Through the analyses of the equivalent model of valve controlled cylinder force subsystem, a controller based on intelligent PID algorithm is designed, which is not sensitive to the variation of parameters such as environmental stiffness. According to the coupling of multiple load channels, a distributed load approach is employed in the superior monitor computer. Experimental results show that the system designed has high precision and robustness.