Valve-controlled Asymmetric Cylinder Research Articles

Analysis of Underlapped Symmetrically Ported Valve-Controlled Asymmetric Cylinder Drive

The valve-controlled cylinder drive system is the most common type among hydraulic applications. Nonlinear behaviour in such systems is inevitable when the valve spool is around its null position. We utilised the component linking method to investigate the nonlinearities in a Moog valve-controlled asymmetric cylinder drive system by simulation in Fortran, in which a generalised concept is introduced and validated by comparing to the experimental results. An X factor is proposed in the generalised concept to describe the asymmetric cylinder state, which is a constant when the cylinder is extending or retracting, but numerically calculated when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method. This paper utilises the component linking method to simulate the Moog valve-controlled asymmetric cylinder drive system in Matlab Simulink, and proposes an analytical solution for the X factor when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method.

Design and preliminary evaluation of a lower limb exoskeleton based on hydraulic actuator

PurposeThis paper aims to propose a novel system design and control algorithm of lower limb exoskeleton, which provides walking assistance and load sharing for the wearer.Design/methodology/approachIn this paper, the valve-controlled asymmetrical hydraulic cylinder is selected for driving the hip and knee joint of exoskeleton. Pressure shoe is developed that purpose on detecting changes in plantar force, and a fuzzy recognition algorithm using plantar pressure is proposed. Dynamic model of the exoskeleton is established, and the sliding mode control is developed to implement the position tracking of exoskeleton. A series of prototype experiments including benchtop test, full assistance, partial assistance and loaded walking experiments are set up to verify the tracking performance and power-assisted effect of the proposed exoskeleton.FindingsThe control performance of PID control and sliding mode control are compared. The experimental data shows the tracking trajectories and tracking errors of sliding mode control and demonstrate its good robustness to nonlinearities. sEMG of the gastrocnemius muscle tends to be significantly weakened during assisted walking.Originality/valueIn this paper, a structure that the knee joint and hip joint driven by the valve-controlled asymmetrical cylinder is used to provide walking assistance for the wearer. The sliding mode control is proposed to deal with the nonlinearities during joint rotation and fluids. It shows great robustness and frequency adaptability through experiments under different motion frequencies and assistance modes. The design and control method of exoskeleton is a good attempt, which takes positive impacts on the productivity or quality of the life of wearers.

Position control for a hydraulic loading system using the adaptive backsliding control method

A valve-controlled asymmetric cylinder loading system was taken as the research object in this study. To solve the problems existing in electro-hydraulic servo loading systems, such as low loading accuracy, interference from the external environment, and strong nonlinear, time-variant, and uncertain parameters in position control, a position control strategy for valve-controlled cylinders, based on the adaptive backsliding control method, is proposed. The system was divided into several subsystems, then, the stability of each subsystem was guaranteed by the Lyapunov stability criterion, and the unknown parameters of the system were expressed by known parameters to ensure stability. To conduct experimental verification, a set of valve-controlled asymmetric cylinder loading system hardware-in-a-loop platform is designed based on the xPC Target real-time control kernel in MATLAB, and the application of complex control algorithms is realized in engineering systems. Through experiments and simulations, the effectiveness of the control method is verified. During 2-Hz sinusoidal tracking, the maximum deviation for the adaptive controller was reduced by 47.7% from that for a PID controller, and the phase lag was smaller. The results show that the adaptive backsliding control method is effective, and the research results are of great significance to the high performance control of hydraulic loading system and the engineering application of complex algorithms.

Linear active disturbance rejection control for the electro-hydraulic position servo system.

Valve-controlled asymmetric cylinder is widely used in servo loading system. As a kind of typical electro-hydraulic servo system (EHSS), it inherently has the characteristics such as high order nonlinear, strong coupling, and uncertain, therefore, conventional control strategy is difficult to satisfy the requirements of high-performance control. In this paper, a novel linear active disturbance rejection control (LADRC) method was proposed, in which the internal and external disturbances were actively estimated by the third-order linear extended state observer (LESO) in real-time, and rejected by the control law of proportional integral control (PID) with acceleration feed-forward. The stability of the proposed method was proved, and the influence rules of the LADRC parameters on the control performance were revealed by simulation. Finally, comparative experiments between LADRC and PID control were carried out, results showed that the disturbances can be effectively compensated and the control goals can be successfully achieved with the proposed method.

Force-controlled Compensation Scheme for P-Q Valve-controlled Asymmetric Cylinder used on Hydraulic Quadruped Robots

Under the requirement of the force controller of hydraulic quadruped robots, the goal of this work is to accurately track the force commands at the level of the hydraulic drive unit. The main contribution focuses on the development of a force-controlled compensation scheme, which is specifically aimed at the key issues affecting the hydraulic quadrupedal locomotion. With this idea, based on a P-Q valve-controlled asymmetric cylinder, we first establish a mathematical model for the hydraulic drive unit force control system. With the desired force commands, a force feed-forward algorithm is presented to improve the dynamic performance of the system. Meanwhile, we propose a disturbance compensation algorithm to reduce the influence induced by external disturbances due to foot-ground impacts. Afterwards, combining with a variable gain PI controller, a series of experiments are implemented on a force control performance test platform to verify the proposed scheme. The results demonstrate that the force-controlled compensation scheme has the ability to notably improve the force tracking accuracy, reduce the response time and redundant force.

Internal model control of valve‐controlled asymmetric cylinder system based on sectional neural network inverse system

In order to improve the control performance of the valve-controlled asymmetric cylinder system with negative overlap, it is proposed that the complex nonlinear system is transformed into a linear system based on the neural network inverse system. The structure of the inverse system is been constructed by the state model of the system, and optimised by adding state parameter feedback. So the pseudo-linear system is reduced to second order. An improved back-propagation neural network based on a genetic algorithm is used to solve the inverse model. Aiming at the problem of negative overlap of servo valves and laminar and turbulent flow, the sectional inverse system switched by reference speed is established to improve the accuracy of the inverse system model. For pseudo-linear systems, an internal model controller is designed to improve the control performance of the composite system. The proportion–integration–differentiation and the internal model control (IMC) of the sectional inverse system are compared with that of AMESIM and Simulink joint platform. The results show that the system controlled by the IMC of the sectional inverse system has better response performance, eliminates the asymmetric characteristics in extending and retracting motion response and is less affected by load fluctuation.

Modeling and Simulation of Conversion Booster Cylinder Control System

This paper is based on the accelerated fatigue test of aviation hydraulic actuators. For the case where aviation hydraulic actuators transmission medium is different from the testing rig transmission medium, a new type of conversion booster cylinder is designed. This conversion booster cylinder set pressurization, medium conversion, pumping aviation oil as one, and laid the foundation for the pressure pulse fatigue test of aviation hydraulic actuator cylinders. Combined with the principle of valve-controlled asymmetric cylinder, a mathematical model of the control system of the pressurized cylinder was established using the method of parameter weighted averaging to unify the models in both directions. Simulink software is used to simulate the system, and the required time domain and frequency domain performance indexes are obtained. The working condition of confining pressure is simulated and the effectiveness of the design of the conversion booster cylinder is proved.

A compliant control method for robust trot motion of hydraulic actuated quadruped robot

A motion control approach is proposed for hydraulic actuated quadruped robots, aiming to achieve active compliance and robust motion control. The approach is designed with a structure of three layers. Servo valve-controlled asymmetric hydraulic cylinder model is established to obtain the relationship between the desired torque and the control current signal, which is the bottom layer. The middle layer is based on the virtual model of the leg for active compliance. The upper layer considers the torso posture and velocity into planning the foot trajectories based on the spring loaded inverted pendulum model. Trotting gait simulations are conducted based on the proposed framework in the simulation software environment Webots. The motion control approach has been implemented on a robot prototype SCalf-II (SDU calf), where experiments have been conducted including omnidirectional trotting gait, lateral impact recovery and climbing slopes. The experiments demonstrate that the proposed approach can effectively control the hydraulic actuated robots.

Forecast Iterative Learning Control with Forgetting Factor and Its Application in Valve-controlled Asymmetric Cylinder

Valve-controlled asymmetric cylinder belongs to typical nonlinear and time-varying system at elastic load, in order to eliminate oscillation result from traditional PD-type iterative learning control, a kind of forecast iterative learning control with a forgetting factor is designed. The system mathematical model is built, and the performance characteristics of valve-controlled asymmetric cylinder system are analyzed. The fundamental of iterative learning control is introduced, the problems of traditional PD-type algorithm are analyzed; a forgetting factor is added in the iterative learning control to inhibit the oscillation, the control effect by different forgetting factor value is analyzed by simulating, a part of forecast system given is increased to improve the system accuracy, because forgetting factor lower the system performance. Both simulations and experiments show that, in the valve-controlled asymmetric cylinder system, using forecast iterative learning control with a forgetting factor will overcome oscillation well with a forgetting factor, and can improve accuracy by forecast iterative.

A Novel Compound Control Method for Hydraulically Driven Shearer Drum Lifting

In order to adjust shearer drum swiftly and precisely to adapt to the changes of coal seam, a compound control approach based on cerebellar model articulation control and fractional order PID controller was proposed. As the movement precision and response speed of hydraulic system were determined mainly by the control precision of valve-controlled asymmetrical hydraulic cylinder, its working principle and characteristics were analyzed in this paper, with particular focusing on the asymmetry problem. Furthermore, RBF neural network was applied to obtaining reasonable tuning parameters and a control algorithm of proposed controller was designed. Finally, laboratory experiments were developed to verify the validity and effectiveness of proposed compound control method. The testing results, compared with those for other controllers, proved that the proposed compound control method can acquire high movement precision and respond speed in the system of hydraulically driven shearer drum lifting with different control conditions.

Nonlinear Optimal Tracking Control of Valve-Controlled Asymmetrical Cylinder

Considering the complex nonlinearities of valve-controlled asymmetrical cylinder, a more accurate nonlinear state-space model is established. Then, states feedback linearization technique is introduced to linearize the model exactly and the stability of inner subsystem is analysised by zero dynamics method with the specific system parameters. Based on the linearized model, optimal control theory is applied to design a nonlinear optimal tracking controller and confirmatory simulation experiments are carried out. The results reveal that, the controller is reasonable and effective, and shows splendid performance in tracking various inputs with a high level of robustness and strong abilities to keep undisturbed by load varying.

Modeling and Simulating Long-Stroke Valve-Controlled Asymmetrical Cylinder Based on MATLAB/Simulink

Abstract. Based on the redefined flow rate and flow pressure, the forward and backward state equations of long-stroke valve-controlled asymmetrical cylinder system are set up, in which the general mistakes in building up the flow rate equation are avoided. Then the simulation model in MATLAB/Simulink is established. Adopting the conditional-executive subsystem blocks, joint simulation with different models at two directions is realized by taking into account the continuity problems in positioning reversal. The subsystem of introduced equivalent volume function helps to show the effects of piston working position to valve-controlled cylinder system. Furthermore, with this simulation model, dynamic performance analysis of long-stroke valve-controlled asymmetrical cylinder system including some nonlinear factors becomes convenient.

CMAC-based compound control of hydraulically driven 6-DOF parallel manipulator

The movement precision of the hydraulically driven 6-six degrees of freedom (6-DOF) parallel manipulator is determined mainly by the precision of the valve-controlled asymmetrical cylinder (VCAC). Unfortunately, the asymmetrical movement of the VCAC caused by its asymmetrical structure can significantly compromise control precision. Owing to this asymmetry and, more fundamentally, the inherent nonlinearity of hydraulic systems as well as complicated load variations, it is very difficult to achieve ideal control precision with traditional (PID) control. In the present study, the working principle and characteristics of VCAC were analyzed, with particular focus on the asymmetry problem. In order to improve the precision of both VCAC control and 6-DOF parallel manipulator movement, this paper presents a new, cerebellar model articulation control (CMAC)-based control method. Experiments on both the single VCAC system and the parallel manipulator were developed to verify the validity and effectiveness of the new compound control method. The theoretical analysis and testing results, compared with those for the PID control, proved that the proposed CMAC-based control method can acquire high movement precision on the 6-DOF motion simulator while eliminating the need to build a mathematical model or obtain accurate loading conditions.

Modeling Study of Long-Stroke Valve-Controlled Asymmetrical Cylinder

With the consideration of compressibility flow and the redefined load flow and load pressure, the mathematical model of long-stroke valve-controlled asymmetrical cylinder system is presented. The equivalent volume functions, the functions of equivalent volume functions of cylinder's two chambers are introduced, which reflects the influence of piston's positions in its long stroke on the dynamic performance of valve-controlled cylinder. Simulation results show that there exists obvious differences between forward and backward directions of long-stroke valve-controlled asymmetrical cylinder system, and its dynamic performance varies along the whole stroke, where the middle-stroke position may not always be the so-called most dangerous position.