Electro-hydraulic Servo Research Articles

Neural network-based finite-time command-filtered adaptive backstepping control of electro-hydraulic servo system with a three-stage valve

This paper aims to improve the tracking control performance of the three-stage valve (TSV) controlled electro-hydraulic servo system (EHSS) with parameter uncertainties and other lumped unknown nonlinearities, including unknown dynamics and disturbances. A more accurate nonlinear model of the TSV-controlled EHSS is established and a neural network-based finite-time command-filtered adaptive backstepping control (NNFCABC) method is proposed for the EHSS. Adaptive control is used to deal with the system parameter uncertainties, and the radial basis function neural network (RBFNN) algorithm is introduced to approximate the lumped unknown nonlinearities. The prediction errors of serial-parallel estimation models (SPEMs) and the tracking errors are utilized together to design adaptive laws to estimate the system parameters and the weights of the RBFNNs. The entire control framework utilizes command-filtered control and backstepping techniques. By applying Levant differentiators as command filters and introducing fractional power terms into the virtual control laws and the SPEMs, the proposed NNFCABC theoretically guarantees the tracking performance of the closed-loop control system with finite-time convergence. Comparative simulations and experiments verify the feasibility and superiority of the proposed control scheme.

A Robust Adaptive Control Strategy for Electro-hydraulic Servo Based on Friction Compensation

Background: The electro-hydraulic servo system has the advantages of high stiffness, fast response speed, high precision and power-to-weight ratio. Objective: In this patent, an adaptive robust control strategy based on friction compensation is proposed for insufficient control accuracy due to a large number of nonlinearities and uncertainties in the system. Methods: In this patent, the mathematical relationship between the physical quantities of the valve-controlled cylinder is analyzed. Then the mathematical model of valve controlled cylinder considering the main nonlinearity and uncertainty of the system is established. The fuzzy proportion-integral-derivative, deterministic robust, and adaptive robust single-cylinder trajectory tracking controllers are designed and the tracking performance of different reference trajectories is analyzed by MATLAB/Simulink software. Results: In this patent, all the three controllers can track the reference trajectories smoothly. Adaptive robust control strategy can make the uncertain parameters of system converge and approach truth value. Conclusion: In this patent, the adaptive robust control strategy has the function of online parameter adjustment. When tracking accuracy is taken as the index, its tracking effect is better than fuzzy proportion-integral-derivative and deterministic robust.

Parameter identification and position control for helical hydraulic rotary actuators based on particle swarm optimization

It is difficult to obtain an accurate mathematical model in electro-hydraulic servo control system, due to the nonlinear factors such as dead zone, saturation, flow coefficient, and friction. Hence, a parameter identification algorithm, combining recursive least squares (RLS) with modified nonlinear particle swarm optimization (NPSO) algorithm, is proposed. On this basis, another improved NPSO algorithm is also put forward, aiming at searching for the optimal proportional–integral (PI) controller gain of the nonlinear hydraulic system while giving comprehensive consideration to the system performance indexes. The system identification experiments and position tracking control are conducted, respectively. As indicated by the comparison with the least squares (LS), RLS, PSO, and RLS–LPSO results, the proposed method shows higher identification and control accuracy.

POSITION CONTROL OF ELECTRO-HYDRAULIC SERVO SYSTEM WITH FRICTION COMPENSATION

This work presents a model-based friction compensation technique and an integral adaptive backstepping controller to improve the position control of the electrohydraulic servo system. The controller design uses a continuous approximation of the LuGre friction model and the Lyapunov theory of nonlinear systems. The friction compensation enhances system performance, and comparison tests are conducted on a hydraulic servo test bench to validate the control strategy's tracking performance under various conditions. KEYWORDS: Electrohydraulic servo systems; Position control; Integral adaptive backstepping controller; LuGre dynamic friction model; Lyapunov theory; Friction compensation.

Analysis of the static and dynamic characteristics of the electro-hydraulic pressure servo valve of robot

In this study, we comprehensively investigate the structure and operational principles of the Rotary Direct Drive Electro-Hydraulic Pressure Servo Valve (RDDPV). Our objective is to establish the dynamics equations governing the motor, slide valve, and bias mechanism of the valve. Additionally, we construct a mathematical model for the servo valve controller, while ensuring the linearization of the controller model. Furthermore, we conduct an in-depth analysis of the static characteristics of the valve, including linearity, dead zone, hysteresis loop, and zero drift. Regarding the dynamic characteristics, we establish a dynamic mathematical model for the RDDPV valve. Subsequently, we subject the servo valve to analysis with a focus on frequency response and dynamic response, using the control current as the input and the pressure as the output. To perform these analyses, we employ the software package SIMULINK of MATLAB, facilitating dynamic simulations. Remarkably, the simulation results exhibit the valve's conformity to design requirements, underscoring its suitability for subsequent research and development endeavors. Through our rigorous investigation, we offer essential technical support for the forthcoming stages of the valve's research and development, thereby laying a robust foundation for its further advancement.

Experimental Study of the Mechanical and Acoustic Emission Characteristics of Sandstone by Using High-Temperature Water-Cooling Cycles

In order to study the physical and mechanical properties of sandstone under high-temperature water-cooling cycling conditions, an RMT-150B electrohydraulic servo rock testing system and a DS-5 acoustic emission detection and analysis system were used to conduct uniaxial compression acoustic emission tests on sandstone after high-temperature water-cooling cycles. The deformation, strength, and acoustic emission characteristics of sandstone were analyzed under different temperatures and cycle times. The results show that the high-temperature water-cooling effect caused changes in the physical properties of sandstone. The volumetric expansion rate of the rock samples first decreased, then increased in temperature, and the strength first increased, then decreased, whereas the number of cycles had less of an impact on the physical properties. At 200 °C, with increased cycle number, the elastic modulus increased by 20.1%, and the compressive strength increased from 63.9 MPa to 71.46 MPa. At 300–600 °C, the elastic modulus and compressive strength of sandstone gradually decreased with increases in the temperature and cycle number, with reductions of 6.04%, 7.24%, 28.7%, 35.57%, 17.6%, 18.2%, 20.4%, and 60.5%, respectively. With increased temperature and cycle times, the acoustic emission ringing counts increased, ringing counts and cumulative energy appeared earlier, the rock samples entered elastic deformation earlier, the yield stage length increased, and the samples showed a tendency to transition from brittle to ductile damage.

Sliding-mode control of electro-hydraulic positioning tracking system combining K-observer and nonlinear disturbance observer

High-precision position control of hydraulic systems is of great significance in industrial applications. However, unknown external force disturbance, measurement noise, and other uncertain nonlinearities widely exist in electro-hydraulic servo systems, which severely degrade the system performance. To handle this problem, a sliding-mode controller based on K-observer with nonlinear disturbance observer is proposed for electro-hydraulic position systems in this article. The nonlinear disturbance observer is to estimate and eliminate the time-varying external force disturbance. The sliding-mode controller based on K-observer is to reach low gain observation of states and improve the system performance by reducing the chattering of the sliding-mode algorithm. The proposed controller is proved to be stable by the Lyapunov stability criterion. Comparative experiments support that the controller has high precision and strong robustness.

Multi-Objective Optimization of Kinetic Characteristics for the LBPRM-EHSPCS System

As the ‘heart’ of energy vehicles, the lithium-ion battery is in desperate need of precision improvement, green production, and cost reduction. To achieve this goal, the electro-hydraulic servo pump control system (EHSPCS) is applied to the lithium-ion battery pole rolling mill (LBPRM). However, this development can lead to limited dynamic performance and large power loss as a result of the EHSPCS unique volume direct-drive control mode. At present, how to solve this conflict has not been studied and how the EHSPCS component parameters influence the dynamic response, power loss, and economic performance is not clear. In this paper, a multi-objective optimization (MOO) model for the LBPRM-EHSPCS is proposed by comprehensively considering the dynamic, efficiency, and economic characteristics. Firstly, the evaluation model of the dynamic response, power loss, and cost is investigated. Then, the NSGA-II algorithm is introduced to address the Pareto front of the MOO model. Finally, the power loss and dynamic response of the LBPRM-EHSPCS before and after optimization are tested to validate the viability of the raised method. Results indicate that power loss is decreased by as much as 7.2% while steady-state precision is greatly improved after optimization. The proposed framework enhances the performance in lithium-ion battery manufacturing and can be applied to other kinds of hydraulic systems.

Analysis of an Axial-Flux Slotted Limited-Angle Torque Motor with Quasi-Halbach Array for Torque Performance Improvement

Better torque performance and higher reliability have long been the focus of research for slotted limited-angle torque motors (LATMs), which are primarily used to position first-stage valves in electrohydraulic servosystems. This paper presents a high reliability axial-flux slotted LATM with quasi-Halbach array for torque performance improvement including constant torque range (CTR) and output torque. Firstly, the structure with two sets of windings and the operation principle of the proposed slotted LATM is analyzed. Secondly, a brief design procedure is presented, the structure selections of open slot and double-stator single-rotor (DSSR) interior rotor with surface mounted quasi-Halbach permanent magnet (PM) array are illustrated, and the geometric parameters are optimized to obtain the optimal design of the proposed slotted LATM. Then, 3-D finite-element method (FEM) is employed to compare the proposed slotted LATM with the conventional surface mounted PM slotted LATM in terms of cogging torque, no-load back EMF, and output torque, and the results show that the proposed LATM with quasi-Halbach array has a 10% improvement in output torque and a 25% improvement in CTR. Meanwhile, the flux linkages and torque performance of the two sets of windings under various conditions verify good magnetic isolation. Finally, prototypes of two different rotor types are manufactured and a series of experiments are performed to validate the analysis.

Pump-Controlled AGC Micro-Displacement Position Control of Lithium Battery Pole Strip Mill Based on Friction Model

Electrode roll-forming refers to rolling a battery electrode into a preset thickness through the electro-hydraulic servo pump-controlled hydraulic roll gap thickness automatic control system (known to as pump-controlled AGC). Compared with the motor servo system, the friction problem of the electro-hydraulic servo system is more serious and the friction problem of the actuator itself is very prominent. Moreover, low-speed performance is one of its core indicators, the friction phenomenon is the most abundant during the low-speed stage and the impact on the servo system is also the most obvious. Therefore, for high-performance electro-hydraulic servo control, friction compensation is not only unavoidable, but also a very difficult problem. Aiming to influence the friction on the position control of the pump-controlled system of a lithium battery pole strip mill, the rolling mechanism and process procedure under micro-displacement position control based on the friction model were studied and compared from the perspective of considering friction factors, and a friction compensation controller based on the LuGre model was designed. The control precision of a pump-controlled AGC system was improved through combination with an adaptive robust controller. Because of the diversity of unmeasurable states of the system, a dual observer was designed, and the known model of the system was added to the observer. In the final comparative experiment, the steady-state accuracy of the friction adaptive robust compensation controller system based on the LuGre model reached ±0.3 μm, which is superior to the fuzzy IMC compensation and traditional PID control strategies.

Study on the dynamic fracturing characteristics of aggregate-mortar interface under various loading rates using DIC

The dynamics of fracture characteristics at the aggregate-mortar interface under varying loading rates present a significant area of investigation, pivotal for comprehending the response of concrete to dynamic load conditions. In concrete, the interface between the aggregate and the mortar forms a significant region, fundamentally dictating concrete structures' comprehensive strength and durability. This study aims to investigate the interface crack propagation process, including the crack propagation velocity and the propagation direction using Digital Image Correlation (DIC). Three-point bending beams with a single-size aggregate were fabricated. Beams with different initial crack tip-to-aggregate distances, d0 (aggregate position) of 20 mm, 40 mm, and 60 mm, were tested at five different displacement-loading rates (0.012 mm/min, 0.12 mm/min, 1.2 mm/min, 12 mm/min, and 120 mm/min) using an electro-hydraulic servo testing machine. The crack propagation process was documented utilizing a high-speed video camera. The study reveals a direct correlation between loading rates and concrete's mechanical attributes. The results indicate that as loading rates rise, the compressive strength, tensile strength, and modulus of elasticity of concrete notably increase, while the Poisson's ratio decreases. The initial fracture toughness (KIcini) also escalates with increasing the rates, its sensitivity notably influenced by d0. Concurrently, fracture energy increases with the increase of loading rate and the decrease of d0, a trend more evident at high loading rates. The crack initiation load (Pini) for all single-size aggregate concrete beams was higher than that of plain concrete, and Pini decreased as d0 increased. Observations were made on the trajectory of crack formation, further scrutinizing the effects of d0 and the variable loading rate. Notably, the presence of the interface was found to slow the crack propagation velocity, and this ability to inhibit crack propagation decreased as d0 increased. As the loading rate increased, the crack propagation velocity at the mortar matrix and interface also increased. This study also reports additional material properties, such as critical crack length, and interfacial fracture mode.

Direct-Drive Electro-Hydraulic Servo Valve Performance Characteristics Prediction Based on Big Data and Neural Networks.

Direct-drive electro-hydraulic servo valves play a key role in aerospace control systems, and their operational stability and safety reliability are crucial to the safety, stability, and efficiency of the entire control system. Based on the prediction of the performance change of the servo valve and the resulting judgement and prediction of its life, this can effectively avoid serious accidents and economic losses caused by failure due to performance degradation in the work. On the basis of existing research, factors such as opening, oil contamination, and pressure difference are used as prerequisites for the operation of direct-drive electro-hydraulic servo valves. In addition to the current research on pressure gain and leakage, the performance parameters of servo valves, such as overlap, threshold, and symmetry, are also expanded and selected as research objects, combined with pressure design servo valve performance degradation experiments for testing instruments such as flow and position sensors, and data are obtained on changes in various performance parameters. The experimental data are analyzed and a prediction model is built to predict the performance parameters of the servo valve by combining the existing popular neural networks, and the prediction error is calculated to verify the accuracy and validity of the model. The experimental results indicate that as the working time progresses, the degree of erosion and wear on the valve core and valve sleeve of the servo valve increases. Overall, it has been observed that the performance parameters of the servo valve show a slow trend of change under different working conditions, and the rate of change is generally higher under high pollution (level 9) conditions than under other conditions. The prediction results indicate that the predicted values of various performance parameters of the servo valve by the prediction model are lower than 0.2% compared to the experimental test set data. By comparing the two dimensions of the accuracy and prediction trend, this model meets industrial needs and outperforms deep learning algorithm models such as the exponential smoothing algorithm and ARIMA model. The experiments and results of this study provide theoretical support for the life prediction model of servo valves based on neural networks and machine learning in artificial intelligence, and provide a reference for the development of direct-drive electro-hydraulic servo valves in aerospace and other industrial fields for use and failure standards.

Fatigue characteristics of ancient brick masonry under cyclic load

In this study, a low-cycle fatigue test was conducted using an MTS793 electro-hydraulic servo fatigue testing machine and a VIC-3D image acquisition system to explore the effects of different loading frequencies and upper limit stress amplitudes on the fatigue damage characteristics of ancient brick masonry. The test results indicated prominent fatigue damage characteristics and shaping of the ancient brick masonry under cyclic load. The axial deformation development of ancient brick masonry consists of three stages that result in fatigue damage evolution and macroscopic fracture. These stages include a large maximum cyclic stress amplitude, low loading frequency, and a larger hysteresis loopback during the loading and unloading area. The plastic stress variable of each loop increases, and the fatigue life of the specimen decreases with the increase in the sample fatigue damage rate.

Adaptive back-stepping Control of Electro-hydraulic Servo system of Steam Turbine

The parameters such as oil density and bulk elastic modulus of hydraulic oil in steam turbine electro-hydraulic servo system vary with ambient temperature, pressure, and other factors, and there are unmodeled dynamics in the system, so obtaining a satisfactory following effect is a challenging task for the electro-hydraulic servo(EHS) system. According to the principle of force balance and flow continuity, the mathematical model of a bilateral oil intake motor is established in this paper. On this basis, a back-stepping controller is designed, and an adaptive method is used to estimate uncertain parameters and disturbances. The designed control system is simulated and verified, and compared with the RBF control system after parameter optimization. The results show that the controller designed in this paper has good tracking performance and adaptability to uncertain parameters and external load disturbances.

Research on crack evolution law and mechanical analysis of three cracked rock masses subjected to compression load

Rocks containing various types of cracks may undergo microcrack expansion and connection under compressive load, which leads to rock fracture under different loading conditions, posing a significant threat to the stability of underground tunneling. Therefore, studying the mechanical response of rocks with different types of cracks is of great importance for controlling the stability of underground mining projects. In this study, we conducted compression tests on three cracked rock samples with different crack types, using an electro-hydraulic servo universal testing machine. We investigated the effect of crack dip angle on the compressive strength, stress–strain curve, and failure pattern of the three cracked rocks, and examined the fracture morphology of the specimens using an industrial camera and the digital image correlation (DIC) technique. To verify the test results, we constructed a parallel bond model in the discrete element method PFC2D to describe the compression process, and compared the peak strength, damage results, and crack number curves. We also investigated the effect of in-situ stress on the mechanical characteristics of the rock by applying in-situ stress values based on the successful PFC2D model. Our research findings revealed that the weakening effect of cracks parallel to the loading direction on the strength of rock is smaller than that of cracks perpendicular to the loading direction. During the compression process, stress concentration phenomena appear first at the crack tip, and the specimen eventually undergoes tensile splitting-type damage. Furthermore, the compressive strength of the three cracked rock samples tends to increase first and then decrease with the application of in-situ stress. These results provide valuable insights into the behavior of cracked rocks and can be utilized to improve the stability of underground mining projects.

Design and Control of a Linear Rotary Electro-Hydraulic Servo Drive Unit

In this paper, a new solution for an electro-hydraulic servo drive is proposed, which consists of two electro-hydraulic servo drives: one with a hydraulic cylinder and one with a hydraulic rotary motor. In the proposed drive, the linear actuator is attached to a horizontal base and the hydraulic motor is mounted on the actuator piston rod. Thus, the output signal of the drive is the lifting and lowering of the element suspended on the rope. The paper describes the structure, kinematics, dynamics, and control of a novel electro-hydraulic servo drive. A servo valve and a proportional valve are used to control the flow of the hydraulic cylinder and the hydraulic motor. Special attention is paid to the construction of two actuators in one drive unit. The controller is based on the PLC controller. The measuring system uses laser displacement sensors and an encoder. The results of laboratory investigations are discussed in the paper. The proposed drive contains all of the characteristics of a mechatronic device. The main contribution of this study is the proposal of the controller architecture and the algorithm to control the speed and position when lifting or lowering loads.

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.

Nonlinear Adaptive Back-Stepping Optimization Control of the Hydraulic Active Suspension Actuator

The displacement tracking performance of the electro-hydraulic servo actuator is critical for hydraulic active suspension control. To tackle the problem of slow time-varying parameters in the existing actuator dynamics model, a nonlinear adaptive back-stepping control (ABC) approach is adopted. Simultaneously, the parameters of the nonlinear ABC are difficult to configure, resulting in a poor control effect. An enhanced particle swarm optimization (PSO) approach integrating crazy particles (CP) and time-varying acceleration coefficients (TVAC) is suggested to optimize the controller settings. Furthermore, in order to obtain satisfactory dynamic characteristics of the transition process, the absolute value of the error time integral performance index is used as the minimum performance index function of parameter selection, and the square term of the control input is added to the performance index function to prevent excessive controller energy. Finally, it can be observed from the simulation results of the highest value emax of the displacement tracking error, the average value eμ of error, and the standard deviation eσ of error that the performance of the ABC parameters optimized by PSO+CP+ATVC is superior to the manually given ABC parameters. Therefore, this control method significantly improves the stability and speed of the control system. It provides a new research idea for the parameter optimization of controllers.

Electrohydraulic Servo Shaker Control Based on the Single Layer Flexible Structure Load

As a kind of equipment commonly applied in laboratory vibration test simulation, the shaker has been widely used in many important fields of scientific research on experimental engineering vibration. It is employed for the numerical simulation of seismic activities of large buildings to quickly and quantitatively detect and calculate building components related to different building forces, analyze and study various changes of on-site structural forms and the influence mechanism of common earthquake damages or deformations with the actual existence of large-scale seismic activities, as well as to test the antiseismic strengthening structure of buildings to reduce the impact of destructive earthquakes on buildings losses. In general, the load of the shaker is regarded as a rigid structure. But in terms of the load of an electrohydraulic servo shaker with a flexible structure, the system control tends to be nonlinear accompanied by the output signals distorted. In order to achieve the goal of improving the waveform accuracy of shaking tables, it is necessary to combine the corresponding control algorithm strategy. Hence, in compliance with the working principles and functions of shaking table systems, the reasons for the coupling between flexible structure loads and shaking tables are carefully analyzed in this paper. Meanwhile, a control strategy based on the Luenberger observer control method is proposed to effectively realize the coupling suppression within the system and make the output signals of the shaking table reach the required accuracy. Finally, by comparing the frequency characteristic curves of the system before and after the introduction of the Luenberger observer, as well as the output and input analog signals, it can be seen that the Luenberger observer can effectively suppress the impact of oscillations within the system and reproduce the accuracy of the input signals.

Method of individual selection of parts for selective assembly of electrohydraulic servo drives

A method for selecting parts and assembly units (hereinafter briefly referred to as parts) in sets for assembling a batch of electrohydraulic servo drives is presented, based on the measured (individual) mechanical and hydraulic characteristics of the parts. The preparatory stage is described: construction of a mathematical model of the product, determination of the parameters of parts and adjustments that have the greatest impact on the parameters of end products, formation of a system for assessing the quality of products in the batch, mathematical formulation of the task of selecting parts. The task of selecting parts is formulated as the assignment problem in the maximin formulation. A deterministic algorithm for solving the problem is presented, based on the branch and bound method and taking into account the fact that adjustments are made during the assembly of drives. A significant reduction in the number of steps (iterations) when searching for the optimal distribution of parts across assembly sets achieved due to the chosen mathematical formulation of the task, as well as due to the chosen strategy of selecting parts in the next assembly set. We suggest that an assembly set should include, first of all, the most troublesome parts the parameters of which do not allow obtaining a set, the projected quality indicator of which will be higher than the established value. At the same time, the negative impact of these parts on the product parameters is compensated by combining them with other parts in one assembly set. The results of mathematical modeling of assembling 992 drives with random formation of assembly sets and with individual selection of parts are presented. Modeling shows that as a result of implementing individual selection of parts in accordance with the described method, a significant reduction in the spread of parameters of end products within batches can be expected, as well as improvements in functional performance of the products. The presented method of individual selection of parts can be used in the assembly of various products.