Electro-hydraulic Servo Research Articles

Developing the Mathematical Model of the Bipedal Walking Robot Executive Mechanism

The paper considers the accuracy of footstep control in the vicinity of the application object. The methodology of forming a simulation of the executive electro-hydraulic servomechanism is developed. The paper presents control algorithms in the dynamic walking mode. The issues of stabilization of the sensors installed in the soles are investigated. The description of the laboratory model and simulation of the main links of the exoskeleton, approximated to human parameters, allowing to insert the studied algorithms of motion of the executive mechanism into the program of automation of calculations of the links of motion are given. The authors for the first time simulated the bipedal walking robot using modern digital technologies, including the joint use of pneumatic electric drive. This paper proposes an automated control scheme for manipulators controlling immobilized human limbs. Considering the functions of the leg and the phases of movement, the structure scheme is chosen so that the same actuator performs several functions. This construction partially reduces the load on the person, because the drives of the various links due to their gravity can overturn a person. Using the kinematic structure of the model and the method of adaptive control of the manipulator, as well as replacing some movement parts with plastic material, the authors were successful in reducing the total weight by three times compared with foreign analogues, which is important for a sick person.

Analysis of a Novel Automatic Control Approach for the Free Forging Hammer

This paper proposes an electro-hydraulic servo control method and realizes the automatic control and remote control of free forging hammers for the first time. A configuration and control strategy for the program-control free forging hammer are constructed. Based on the configuration, a single-acting differential servo cylinder system is proposed to drive the follow-up spool valve and then control the motion state of the hammerhead. Furthermore, a non-contact measurement method is adopted to detect the real-time position of the hammerhead, and the installation position of the measuring sensor is isolated from the hammer body and foundation, thereby reducing the influence of vibration and impact on the accuracy of the feedback signal and ensuring the successive forming process of the forging hammer. In addition, a blow energy model of the forging hammer processing system is established, and a fuzzy-PID control scheme for the forging hammer is then adopted. Based on the control strategy, the striking accuracy of the proposed automatic forging hammer is significantly improved compared with the traditional forging hammer. Finally, the method is applied to an 8 MN forging hammer, and the results show its better processing performance than traditional hammers in terms of all indices.

RBF Neural Network Sliding Mode Control Method Based on Backstepping for an Electro-hydraulic Actuator

Aiming at the interference problem and the difficulty of model parameter determination caused by the nonlinearity of the valve-controlled hydraulic cylinder position servo system, this study proposes a radial basis function (RBF) neural network sliding mode control strategy based on a backstepping strategy for the electro-hydraulic actuator. First, the non-linear system model of the third-order position electro-hydraulic control servo system is established on the basis of the principle analysis. Second, the model function RBF adaptive law and backstepping control law are designed according to Lyapunov’s stability theorem to solve the problem of external load disturbance and modelling uncertainty, combined with sliding mode control strategy and virtual control law. Finally, simulation and experiment on MATLAB Simulink and semi-physical experimental platform are accomplished to show the effectiveness of the proposed method. Moreover, results show that the designed controller has high tracking accuracy to the given signal.

Fault Prediction of Electro-hydraulic Servo Valve Based on CNN+LSTM Neural Network

Fault Prediction of Electro-hydraulic Servo Valve Based on CNN+LSTM Neural Network

Research on improved active disturbance rejection control of continuous rotary motor electro-hydraulic servo system

In order to meet the precision requirements and tracking performance of the continuous rotary motor electro-hydraulic servo system under unknown strong non-linear and uncertain strong disturbance factors, such as dynamic uncertainty and parameter perturbation, an improved active disturbance rejection control (ADRC) strategy was proposed. The state space model of the fifth order closed-loop system was established based on the principle of valve-controlled hydraulic motor. Then the three parts of ADRC were improved by parameter perturbation and external disturbance; the fast tracking differentiator was introduced into linear and non-linear combinations; the nonlinear state error feedback was proposed using synovial control; the extended state observer was determined by nonlinear compensation. In addition, the grey wolf algorithm was used to set the parameters of the three parts. The simulation and experimental results show that the improved ADRC can realize the system frequency 12 Hz when the tracking accuracy and response speed meet the requirements of double ten indexes, which lay foundation for the motor application.

Pressure impact characteristic of vane type continuous rotary motor under different buffer structures

In order to solve the problem of pressure shock on the continuous rotary electro-hydraulic servo motor, the mathematical models of pressure gradient under the structure of pre-compressed chamber and U-shaped groove were established. The optimal structure dimensions of the pre-compressed chamber and the U-shaped groove were determined. The fluid models were established by Solidworks under the four structures of triangular groove, triangular groove with pre-compression chamber, U-shaped groove and U-shaped groove with pre-compression chamber. Simulation analysis of depressurization process of fluid models was performed based on FLUENT. The pressure nephograms of different buffer structures were compared and analyzed, and the pressure change curves and pressure gradient change curves in the process of depressurization were obtained. The results show that the optimal edge length of the pre-compressed chamber of continuous rotary electro-hydraulic servo motor is 20 mm in the process of decompression. The pressure reduction effect is the best when the width of the U-shaped groove is 1.5 mm and the depth is 1.65 mm. The U-shaped groove structure with pre-compression chamber is more conducive to alleviate the pressure shock phenomenon of the motor compared with different combine buffer structures.

Comparative Study on the Mechanical Strength of SAP Internally Cured Concrete

To investigate the relationships between the different mechanical strengths of internally cured concrete with Super Absorbent Polymer (SAP concrete), the uniaxial mechanical properties of SAP concrete with different internal curing water-cement ratios were studied. Various SAP concrete specimens were prepared, and the uniaxial compressive, splitting tensile, as well as four-point bending tests, were carried out using the electro-hydraulic servo testing machine. The cubic compressive strength, splitting tensile strength, and flexural strength of SAP concrete with different internal curing water-cement ratios was obtained. The converting relationships between the internal curing water-cement ratio and different mechanical strengths were analyzed extensively. Based on the conversion formulas of different strength indexes proposed by different national standards and other researchers, the equations among the splitting tensile strength, cubic compressive strength, and flexural strength of SAP concrete were proposed and verified using the experimental data. According to the comparative analysis results, the proposed equations in this study have significant applicability and can be conducted in the practical application of SAP concrete.

Gradient identification method of the model parameters for electrohydraulic servo drive of FESTO learning system

Gradient identification method of the model parameters for electrohydraulic servo drive is considered. The method is adapted to be implemented by an experimental complex consists from FESTO hydraulic learning system and Matlab/Simulink. The implementation of the considered identification algorithm in the Matlab/Simulink package is shown.

Hardware-in-the-loop modeling applied to FESTO hydraulic learning system

The issue of Hardware-in-the-loop modeling in Matlab/Simulink using a physical model of an electrohydraulic servo drive implemented on FESTO learning system is considered. As an example, the synthesis of state components feedback coefficients for the electrohydraulic servo drive control is discussed. The paper provides the block-diagrams for connecting FESTO physical model to Matlab software and algorithms that allow using Matlab for automatic optimization of the controller parameters directly during the operation of the electrohydraulic servo drive physical model. Thus, already at the stage of optimizing the parameters of the controller, its operation as part of a real hydraulic system is studied.

Method for increasing the damping of an electro-hydraulic drive system of anthropomorphic walking robots

Annotation. Due to the fact that anthropomorphic walking robots (AWR) are becoming one of the classes of extreme robotics tools, the task of creating drive systems that simultaneously have high indicators for a set of parameters arises. In particular, the problem arises of preventing the occurrence of self-oscillations in conditions where servo drives with high quality factor experience strong dynamic mutual influence through the actuator. According to the totality of indicators for AWR designed for operation in extreme conditions, electro-hydraulic servo drives are preferable. Features of the dynamics of the ASH actuators and the electro-hydraulic drives used on them force us to look for new ways to correct their dynamic properties. This article presents a method of reducing the propensity of a drive system to generate self-oscillations by correcting hydraulic drives using acceleration feedbacks. It uses an estimate of the relative accelerations of the robot links during movement using the signals from pressure sensors installed in the actuator hydraulic motor. The calculations are made using the equations of dynamics of the AWR actuator, taking into account the temporarily imposed external connections. The method allowed to significantly increase the dynamic accuracy of the drive system of the prototype AWR developed by MSTU N.E. Bauman.

Research on CNC Machining Technology of the Upper Shell of Electro-hydraulic Servo Valve

The CNC machining technology of the upper shell of electro-hydraulic servo valve is complex, and the machining accuracy is required to be high. According to the existing cutting tools and machine tools, the CNC machining process with CNC lathe and 4-axis machining center is designed. First of all, the aluminum alloy blank is roughened and finished on the CNC lathe. After the processing is completed, the two ends of the blank are processed on the CNC lathe, and rough milling, fine milling, drilling and boring processing are carried out with the 4-axis machining center. After the 3D CAD model of the upper shell is constructed, the tool path of rough machining and finish machining is generated by MasterCAM software, and then the G code is generated by the post processor and input to the machining center for machining. The NC machining technology of the upper shell can effectively improve the machining efficiency and accuracy.

Static Mechanical Properties and Failure Modes of Layered Sandstones in Freeze-thaw Cycles

Because the underground space in the alpine area is often in the freezing and thawing cycle state, as well as the layered rock is widely found in nature and the mechanical properties are complex, the mechanical properties of the lower rock in the freeze-thaw cycle are directly related to the development and utilization of the underground space in the alpine area. Based on the electro-hydraulic servo pressure tester, the static compression test of freeze-thaw damage specimen was carried out to study the strength, deformation, failure mode and anisotropy characteristics of the layered sandstone in freeze-thaw cycle condition. Also, the influence of freezing and thawing action and layered structure on the static mechanical properties and the mechanism of action were analysed. Finally, we obtained the following conclusions: The stress-strain curves of vertical and parallel bedding sandstones under freezing and thawing conditions can be roughly classified into compaction phase, elastic phase, plastic yielding stage and failure stage, and with the increase of freezing and thawing times, the peak stress and elastic modulus of layered sandstone samples decrease gradually; compared with vertical bedding samples, the mechanical parameters of parallel bedding samples deteriorate faster under freeze-thaw cycles; the deterioration of mechanical parameters of parallel layered specimens is faster under the condition of freeze-thaw cycle; the anisotropy index Rc of the intensity increased from 1.07 in 0 freeze-thaw cycle to 1.46 in 40 freeze-thaw cycles, and the intensity anisotropy became more significant as the number of freeze-thaw cycles increased.; when the number of freeze-thaw cycles is less than 10 times, the vertical bedding test specimen breaks the main crack at a certain angle (about 30°), showing shear failure through multiple bedding, while when the number of freeze-thaw cycles increases, the main crack tends to be parallel to the loading direction; parallel bedding samples always exhibit splitting failure along the bedding. The test results can provide theoretical support for the development of special underground space such as alpine and freeze-thaw areas.

Mathematical modeling of autonomous single-stage electro-hydraulic servo drive

Annotation. The study is devoted to mathematical modeling of an autonomous single-stage electro-hydraulic servo drive. Two structural schemes of the drive are considered — simplified and more complex. The drive transient conditions of these two circuits are given.

Model-based detection of soft faults using the smoothed residual for a control system

Soft faults are a very common failure mode in electro hydraulic servo control systems in aero engines, including component characteristic drift, performance degradation and so on. Traditional fault detection approaches for soft faults haveproblems of time delay, inaccuracy and false alarms. In order to solve these problems, a model-based detection approach for soft faults is proposed in this paper. Firstly, a robust, time-saving and reliable modeling method is proposed. This method utilizes a mechanism model and a data-driven correction model to characterize the main features and uncertain features of the practical system, respectively. The data-driven correction model is implemented by a backpropagation neural network, which adopts the input of the actual system and the output of the mechanism model as its training data, and adopts the output of the actual system as its training label. This neural correction model plays an important role in compensating for the deviation between the mechanism model and the practical system. Secondly, a robust fault observer, which is based on the residual between the measurement output of the practical system and the model output of the hybrid mechanism–neural network model, is designed to detect the soft fault. The squared residual is smoothed by a median exponential filter in order to eliminate the disturbances of impulsive interference or noises in measurement. Finally, the detection of soft faults is implemented by comparing the smoothed residual with a presetting threshold. Several simulations have been performed to verify the effectiveness of the proposed method, and the simulation results prove the advancement of the proposed method.

Sliding mode control for electro‐hydraulic proportional directional valve‐controlled position tracking system based on an extended state observer

AbstractA novel method combining the sliding mode control (SMC) and extended state observer (ESO) is proposed for position control of an electro‐hydraulic servo system (EHSS), which is nonlinear in mechanical dynamics. Based on the SMC technique, the corresponding sliding mode controller is designed to guarantee the state variables of the closed‐loop system to converge to the reference state by applying an ESO to estimate external disturbances and the internal dynamics. Also, simulation results are presented to illustrate the effectiveness of the control strategy; synchronously, SMC can achieve better control performance than proportional integral derivative (PID) method in comparison with the PID control approach.

Research on Position / Velocity Synergistic Control of Electro Hydraulic Servo System

Background: In some applications, the requirements of electro-hydraulic servo system are not only precise positioning, but also the speediness capability at which the actuator is operated. Objective: In order to enable the system to achieve rapid start and stop during the work process, reduce the vibration and impact caused by the change of the velocity, at the same time improve the positioning accuracy, and further strengthen the stability and the work efficiency of the system, it is necessary to perform the synergistic control between the position and the velocity of the electrohydraulic servo system. Methods: In order to achieve synergistic control between the position and the velocity, a control method of velocity feed-forward and position feedback is adopted. That is, based on the position control, the speed feed-forward is added to the outer loop as compensation. The position control adopts the PID controller, and the velocity control adopts the adaptive fuzzy neural network controller. At the same time, the position and velocity sensors are used for feedback, and the deviation signals between the position and the velocity obtained by superimposing the feedback are used as the final input of the control object, thereby controlling the whole system. Results: The control effect of the designed position / velocity synergistic controller is verified by simulation and experiment. The results show that the designed controller can effectively reduce the vibration and impact caused by the change of the velocity, and greatly improve the response velocity and the position accuracy of the system. Conclusion: The proposed method provides technical support for multi-objective synergistic control of the electro-hydraulic servo system, completes the requirements of multi-task operation, improves the positioning accuracy and response velocity of the electro-hydraulic servo system, and realizes the synergy between the position and the velocity. In this article, various patents have been discussed.

Failure analysis on unexpected leakage of electro-hydraulic servo valve in digital electric hydraulic control system of 300 MW thermal power plant

Electro hydraulic servo valves, which are used to transform weak electric signals into high power hydraulic energy, are the crucial part of digital electric hydraulic control system. In this paper, inspired by the safety operation of the digital electric hydraulic control system, an unexpected leakage failure of the electro-hydraulic servo valve in the digital electric hydraulic control system of 300 MW thermal power plant was studied in depth. Systematical analysis results finally revealed that this unexpected failure was caused by pitting corrosion induced by chloride ions, which are initiated from improper cleaning agent containing trichloroethane. It reacted with the phenolic compounds came from the degradation of the fire-resistant oil, giving rise to the production of the chloride ions. Passive film on the contacting surface was then destroyed by the chloride ions, leading to the formation of naked areas where the pitting corrosion occurred. After that, the coarse carbides with size exceeding 5 μm in the naked areas were peeled off from the contacting surface under the effect of the pitting corrosion, resulting in the blockage of the servo valve since the maximum allowable clearance between valve spool and valve sleeve was 5 μm. This eventually hindered the movement of the valve spool and caused the unexpected leakage failure. Considering that the failure of the electro-hydraulic servo-valves caused by corrosion is seldom reported before, the achievement of the paper could enhance the understanding of the failed mechanism of the electro hydraulic servo valves under actual service condition.

Research on Electro-hydraulic Servo System of Air Rudder on Model Reference Adaptive Control

An adaptive control system with good following characteristics is designed for the electro-hydraulic servo system which are strongly coupled and seriously nonlinear. The model of position servo system on air rudder is discussed with the uncertain system equivalent to the one with parametric variable double input and single output to establish a Popov-MRAC (Model Reference Adaptive Control) system. The simulation results show that the Popov MRAC system has good following characteristics, precision and robustness.

Mechanical behavior and dynamic damage constitutive model of glass fiber-reinforced Vinyl Ester with different fiber contents.

Glass fiber-reinforced plastics (GFRP) based on polymer materials are widely used in lightweight impac-resistant structure design. In the process of design and development, it is very important to clarify the mechanical behavior under dynamic load to improve the product performance. Therefore, in this paper, Quasi-stati and dynamic compression behaviors of unidirectional continuous glass fiber-reinforced vinyl ester (GF/VE) composites with five kinds of fiber contents in the fiber direction were measured by an electro-hydraulic servo experiment system and a split Hopkinson pressure bar, and damage evolution of the material is analyzed by observing the microstructure of the cross section of the material. Results show that: The content of glass fiber affects the wettability between fiber and matrix, and the failure mechanism of material at high strain rate; Under quasi-static conditions, higher glass fiber content yields greater failure strength; Under dynamic conditions, as glass fiber content increases, toughness decreases, and the peak stress first increases and then decreases. Finally, the nonlinear viscoelastic constitutive model with damage evolution is derived, which can be used to predict the impact resistance of new composite structures in the product development and design stage and reduce the development cycle.

Efficiency of electro-hydraulic servo steering for heavy construction vehicles

The traditional efficiency analysis method of hydraulic system generally neglects the influence of mechanical nonlinearity, which causes great difference between theoretical efficiency optimization and actual application. This will reduce the energy-saving effect. In this paper, the electro-hydraulic servo steering system (EHSSS) of heavy vehicles is taken as the research object. Considering both mechanical nonlinearity and hydraulic nonlinearity of the steering system, this paper establishes the efficiency model of the EHSSS. In order to achieve the efficiency analysis of this nonlinear model, an efficiency analysis method in quasi-steady state condition is proposed. The theoretical analysis is consistent with the experimental results in four different single-side loading conditions, so the validity of the model and method is verified. Then, based on the above model and method, the system efficiency spectrums are obtained in different operating conditions. The efficiency of the EHSSS with strong nonlinearity is not only related to the equivalent load but also the steering angle. The results show that the efficiency is the highest in the maximum equivalent load conditions and at left or right end points. In addition, this paper obtains the efficiency curves of steering system in different speeds, hydraulic parameters and structural parameters. The method presented in this paper takes into account the effect of mechanical nonlinearity on the efficiency, which provides theoretical guidance for further efficiency improvement of electro-hydraulic steering system.