Electro-hydrostatic Actuator System Research Articles

Model-Assisted Muti-source Fusion Hypergraph Convolutional Neural Networks for intelligent few-shot fault diagnosis to Electro-Hydrostatic Actuator

Electro-Hydrostatic Actuator (EHA) is a critical electro-hydraulic actuator system widely used in aerospace equipment. To ensure its normal operation, the intelligent fault diagnosis of the EHA system has gained increasing attention. However, the EHA exhibits strong nonlinearity, high structural complexity, and difficulty obtaining fault samples. A Model-Assisted Multi-source Fusion Hypergraph Convolutional Neural Network (MAMF-HGCN) is proposed to address the few-shot intelligent fault diagnosis of EHA. Specifically, the fault data obtained from the hydraulic simulation model is used to establish the relationship among each channel signal. This assists in constructing a hypergraph structure for actual multi-source fault data under limited samples. Each node in the hypergraph employs message transmission to fuse signals from different channels. Subsequently, the hypergraph data are input into the constructed hypergraph convolutional neural network to perform fault classification. Finally, validating the EHA hydraulic system test rig from Nanjing University of Science and Technology illustrates the method’s effectiveness in diagnosing hydraulic system problems under limited fault samples.

Intelligent fault diagnosis for electro-hydrostatic actuator based on multisource information convolutional residual network

The electro-hydrostatic actuator (EHA), known for its advantages such as minimal throttling loss, high efficiency, and a significant volume-to-power ratio, has found extensive application in the fields of aeronautics and astronautics. However, ensuring the safety of aircraft that utilize EHAs requires efficient fault diagnosis due to the demanding operational conditions and prolonged usage. Traditional diagnostic approaches face challenges such as intricate fault modeling, complex multi-channel monitoring data, and a limited number of fault samples within the electro-hydraulic system. To overcome these challenges, we propose an intelligent diagnosis method based on a multi-source information convolutional residual network. Specifically, a multis-cale kernel is implemented to capture features at different scales, enhancing model expressiveness. The efficiency channel attention mechanism dynamically focuses on relevant channel features to improve feature learning ability. The residual network adaptively recalibrates features at each layer to facilitate fault feature learning. Additionally, the activate or not activation function is introduced to selectively activate shallow features, thereby improving the feature representation and generalization capability of the model. Experimental data from the EHA system validates the superiority of the proposed method, demonstrating a significant enhancement in the diagnostic accuracy of EHAs with limited samples.

Study of the Dynamic Properties of the Miniature Electro-Hydrostatic Actuator

The electro-hydrostatic actuator (EHA) is a new type of high-performance servo actuator that originated in the field of aerospace, and it is gradually becoming a common basic component for various types of large equipment. A miniature EHA, mainly composed of a micro two-dimensional (2D) piston pump and a brushless DC motor, is designed in this article by simplifying the system structure. This paper analyzes the structure and working principle of this EHA and establishes the mathematical models of the brushless DC motor, micro two-dimensional pump, and hydraulic cylinder. Field-oriented control (FOC) is used to drive the brushless DC motor, and the models of the controller are established in Simulink. Furthermore, the models of the mechanical and hydraulic systems of the miniature EHA are established in AMESim. In addition to this, a prototype of this miniature EHA was fabricated in this paper and an experimental platform was built for experiments. In the joint simulation environment, the rise time of the EHA system at 6000 r/min is 0.158 s and the frequency response amplitude attenuation to −3 dB has a bandwidth of 20 Hz. On the other hand, the constructed miniature EHA prototype was dynamically characterized to obtain a rise time of 0.242 s at 6000 r/min and a bandwidth of 13 Hz. In this paper, the feasibility of the design scheme of the miniature EHA system is verified, and its excellent dynamic properties are verified with simulation and experiment.

Position control performance analysis of linear actuator in swashplate-controlled electro hydrostatic actuation system

The position control of an energy efficient electrohydraulic actuation system is a decisive characteristic of its performance. In position control applications, a servo valve and/or variable displacement pump are vital to control the position of the linear actuator. In this open-loop control experimental work, the position of a linear actuator having a stroke length of 0.2 m is controlled by a swashplate-controlled electro hydrostatic actuation system. LabVIEW is used to create the control algorithm, and the National Instrument compact-RIO controller is used to control the voltage supply. The National Instruments controller processes sinusoidal and square demand signals at frequencies of 1/16, 1/12, 1/8, and 1/4 Hz. Open-loop control performance is predominantly dependent on the appropriate tuning of the voltage supply. Control performance is evaluated using the parameters integrated absolute error, integrated square error, integrated time absolute error, and integrated time square error. In comparison to square demand, it has been found that sinusoidal demand offers better position control accuracy, and square demand also offers appropriate control accuracy only at lower frequencies (1/16 Hz).

Development of compact revolute electro-hydrostatic actuator module and evaluation of its backdrivability and internal leakage

Actuators of a robot that physically interacts with objects or human require backdrivability to obtain force controllability, impact resistance and compactness. An electro-hydrostatic actuator (EHA) is a servo pump type hydraulic system that has a potential to satisfy backdrivability. However, the previous mechanical design of a revolute EHA did not achieve compact design compared to the other actuators. The hydraulic pump and vane motor were separately located, which made the size of EHA system larger. To solve this problem, we propose a design methodology of a revolute EHA using a frameless motor. Commercially available frameless motor is suitable for actuating the hydraulic pump. Moreover, the pump can be built in the hollow space of the frameless motor, and this design makes the EHA downsized. We present a prototype design based on the formulation of the output power. Through the experimental validations, we show that developed EHA has higher backdrivability than the comparable harmonic drive, and obtain the knowledges on design factors that are crucial to the EHA with high power-to-weight ratio.

Physics-Informed Machine Learning for Degradation Modeling of an Electro-Hydrostatic Actuator System

Machine learning (ML) methods are becoming popular in prognostics and health management (PHM) of engineering systems due to the recent advances of sensor technology and the prevalent use of artificial neural networks. In practice, mechatronic systems are by nature, prone to degradation/failure due to complex failure mechanisms and other unknown causes. As a result, degradation modeling and prediction of mechatronic systems are quite challenging especially when highly integrative and special operational conditions are considered. To overcome such challenges, artificial neural networks can be employed. This paper proposes the use of a long short-term memory (LSTM)-based multi-input neural network for degradation modeling and prediction of an Electro-Hydrostatic Actuator (EHA) system. The failure mechanisms of the EHA system are explored first, and the obtained physics-of-failure information is utilized in constructing the LSTM neural network to enhance the prediction capability of the model. An actual dataset collected from an EHA test bench is utilized to illustrate the effectiveness of the proposed physics-informed LSTM method for modeling the EHA system's degradation behavior. The result shows that the proposed method provides more accurate life prediction than several benchmark methods for the EHA system.

Double Redundancy Electro-Hydrostatic Actuator Fault Diagnosis Method Based on Progressive Fault Diagnosis Method

The electro-hydrostatic actuator (EHA) is the key component of most electric aircraft, and research on its fault diagnosis technology is of great significance to improve the safety and reliability of aircraft flight. However, traditional fault diagnosis methods only focus on partial failures and cannot completely diagnose the whole EHA system. In this paper, the progressive fault diagnosis method (PFDM) is proposed for overall diagnosis of whole EHA system, which can be divided into four levels for health detection and fault diagnosis of the overall EHA system. PFDM combines fault diagnosis methods based on Kalman filter, threshold, logic, and EHA system analysis model to diagnose the whole EHA system layer by layer. At the same time, in order to ensure the normal operation of the EHA system after fault diagnosis, double redundancy design is creatively carried out for the EHA system to facilitate system reconstruction after fault detection. It can be continuously modified according to different EHA system parameters and measured signals to improve the accuracy of fault diagnosis. The experimental results show that PFDM can accurately locate and identify 22 faults of the double redundancy EHA system by using the accurate EHA system mathematical model. PFDM improves the fault diagnosis response time to 4 ms, greatly improving the safety and reliability of the double redundancy EHA system.

Delay Analysis and the Control of Electro-Hydrostatic Actuators

The electro-hydrostatic actuator (EHA) has a high energy density and a compact structure so it is widely used in all/more electric aircraft. To gain energy-saving capability, the hydraulic lock can be applied in the EHA system, which can overcome the change of load after the position control is complete, reducing the motor’s need to work continuously. Due to the use of a hydraulic lock in the EHA system, there is a more significant position output delay compared with the EHA system. The delay would lead to a dynamic response error. Therefore, an electro-hydrostatic actuator with a bidirectional hydraulic lock (BHL-EHA) model is established that can reflect the position output delay and it can be used to analyze its influence factors. According to the analysis, the factors affecting the delay are pump speed, external load, hydraulic lock cracking pressure, friction load, pump displacement, fluid volume of the system, and effective bulk modulus; thus, an equation that can be used to calculate the delay is proposed. At the same time, the experimental system of the BHL-EHA system is established, and the parameters of the experimental facility are completely consistent with the simulation model. Finally, a delay compensation control method is proposed, and the control time parameter t0 is calculated based on the equation proposed above. The results of the simulation and the experiment show that the method can compensate for the delay caused by the hydraulic lock. Combined with a feedforward control, the method can dismiss the dynamic response error of 0.6 Hz sinusoidal tracking characteristics.

Improving the Response of an Electrohydrostatic Actuation (EHA) System Using a High-Pressure Accumulator

This paper proposes an (EHA) system driven in three modes to improve the low reactivity of the existing EHA system. By using a small high-pressure accumulator, servo valve, and mode switching valve, the circuits can be changed so that they are suitable for each mode according to the driving conditions. Each of the three modes consists of the EHA mode, the hybrid mode, and the charging mode, and the EHA mode operates on the same principle as the existing EHA system. The hybrid mode is activated when high-speed position control is performed, and with the help of an add-on servo valve controller, the control volume of the hydraulic cylinder can be stiffened quickly while minimizing the use of high-pressure fluids. The charge mode serves to periodically charge the accumulator under motionless conditions in applications that allow piston holding. Simulations and experiments confirm that the responsiveness of the proposed system is much improved compared to that of the existing EHA system.

Experimental study of position tracking control and pressure variation analysis on electrohydraulic system in open loop

This paper studies on the variable displacement electro-hydrostatic actuation system to control the position of hydraulic actuator with the used of bidirectional swashing variable displacement axial piston pump. The pump control system is more efficient than valve control system. The paper is focused on the experiment of position tracking of a symmetric linear hydraulic actuator in an open loop control, the demand of actuator is sinusoidal with frequencies of 0.10 to 0.25 Hz, amplitude of 0.1 m and offset of demand 0.1 m. The effective pressure force of the actuator depends on the chamber pressure variation of the actuator, the nature of pressure variation measured which played decisive role to control the position of the actuator. In industrial application, the role of the electrohydraulic system with accurate control is quite evident, the present experimental work emphasis to control the hydraulic actuator position.

Optimal Design of Accumulator Parameters for an Electro-Hydrostatic Actuator at Low Speed

The electro-hydrostatic actuator (EHA) is a type of highly integrated, compact, closed pump control drive system composed of a servo motor, a metering pump, a hydraulic cylinder and other components. Compared with the traditional valve control system, the electro-hydrostatic actuator has the advantages of a high power-to-weight ratio, high integration, environmental friendliness, and superior efficiency and energy saving. However, due to the complex mechanical–hydraulic coupling mechanism of the system and the existence of non-linear multi-source disturbances, the dynamic and static performance of the system is limited, particularly the pressure pulsation phenomenon under low-speed conditions, which seriously affects the high precision control requirements of the system. In order to address the low-speed pressure pulsation problem of the electro-hydrostatic actuator, first, the mathematical models of the servo motor, metering pump and hydraulic cylinder are established, and the simulation model of the EHA system is created based on MATLAB/Simulink. Second, from aspects of the servo motor and the quantitative piston pump, the causes of the pressure pulsation under low-speed working conditions are analyzed, and the parameter selection method of the accumulator is proposed to eliminate the pressure pulsation based on ωn and ζ of the EHA system. Finally, the optimal charging pressure of the accumulator is simulated and experimentally analyzed. The simulation and experimental results show that the charging pressure range of the accumulator calculated with this method can effectively improve the pressure pulsation phenomenon of the EHA system under low-speed working conditions, and it plays a positive role in the engineering popularization and application of the EHA system.

Disturbance Observer-Based Chattering-Attenuated Terminal Sliding Mode Control for Nonlinear Systems Subject to Matched and Mismatched Disturbances

This work presents a new disturbance observer-based chattering-attenuated terminal sliding mode control for a class of nonlinear systems in the presence of both mismatched and matched disturbances. A nonlinear disturbance observer is typically employed to accurately estimate mismatched disturbances. In this study, a terminal sliding mode control was designed, based on the disturbance estimation results, to counter the effects of disturbances and ultimately stabilize the target system. The utilization of a chattering-attenuated full-order terminal sliding mode structure satisfactorily resolves both chattering and singularity problems in controller design. It was shown by theoretical analyses that both the disturbance estimation error and the system state converge to the equilibrium point in finite time. Two simulation studies, namely a numerical example and an application to an electro hydrostatic actuator system, were conducted to examine the characteristics and to verify the effectiveness of the proposed algorithm.

RISE-Based Composite Adaptive Control of Electro-Hydrostatic Actuator with Asymptotic Stability

The electro-hydrostatic actuator (EHA), the actuator of electric drive and hydraulic transmission, is competitive since it is small in size, light in weight and high in power density. However, the existence of the velocity loop error of servo motors, unmodeled dynamics and highly nonlinear uncertainties restrict the improvement of the tracking accuracy of the EHA system. In order to achieve high-precision motion control of EHAs, a RISE-based composite adaptive control scheme is proposed in this paper. In the proposed composite adaptive control design, a novel parameter adaptive law is synthesized to compensate for the parametric uncertainties and a robust integral of the sign of error (RISE) feedback is utilized to suppress the adverse effects caused by the lumped disturbances, including the velocity loop error of a servo motor and other unmodeled dynamics. The synthesized parameter adaptive law possesses the advantage of fast convergence, which is beneficial to achieve transient tracking performance improvement. In addition, the proposed controller is more suitable for practical applications since it is chattering free. The closed-loop system stability analysis shows that the proposed control scheme guarantees an excellent asymptotic tracking performance. Finally, comparative simulations are conducted to verify the high-performance nature of the proposed controller.

Performance analysis of an electro-hydrostatic actuator with high-pressure load sensing based on fuzzy PID

Abstract. Electro-hydrostatic actuator (EHA) is an important form of power-by-wire (PBW) technology, which is widely used in aircraft because of the characteristics of small size, high power and light weight. However, the current traditional EHA with fixed pump displacement and variable motor speed (FPVM-EHA) has the problems of high energy consumption and heating of the motor under heavy load. An improved EHA with high-pressure load sensing (HPLS-EHA) is proposed in this paper, which can reduce the pump displacement under heavy load, so as to achieve reducing the torque and heating of the motor, solving the problem of high energy consumption of EHA system and improving the efficiency. The co-simulation model of the FPVM-EHA and the HPLS-EHA was established using the software programs AMESim and MATLAB, and then the simulation results are analysed. The simulation results show that the HPLS-EHA can reduce the torque and heat flow rate of the motor by 23.20 % and 41.02 % under the load of 20.2 MPa, and the fluctuation times and amplitude of output position are also reduced under varying loads at 5 s, but it will slightly reduce the position accuracy of the EHA system. In order to solve this problem, the fuzzy PID control strategy is adopted for the HPLS-EHA. The simulation results show that the position accuracy and response speed of the HPLS-EHA based on fuzzy PID are improved, the output position is improved from 8.93 to 9.25 mm, better than 9.19 mm of the FPVM-EHA, and it also maintains the advantages of low motor torque, heating and output position fluctuation.

A Symmetric Multichamber Hydraulic Cylinder With Variable Piston Area: An Approach to Compact and Efficient Electrohydrostatic Actuation

Abstract This paper presents an approach for designing symmetric (effective cylinder area during extension is the same as that during retraction) multichamber cylinders with discretely variable piston area. The design methodology is presented in a generalizable manner and is demonstrated on an example five-chamber cylinder design. A method for finding symmetric multichamber cylinder configurations from a given cylinder topology is presented, and subsequently, a method for discretely varying the effective piston area is developed, subject to a cylinder symmetry constraint. Furthermore, an algorithm is presented to optimally switch the effective cylinder area of an electrohydrostatic actuation system either to minimize the magnitude of motor torque or to minimize resistive power losses in the system. Additionally, a method for optimizing standard (constant area) hydraulic cylinders to minimize motor torque magnitude or resistive power losses is presented. These methods are then demonstrated on an example electrohydrostatic actuation system via simulation. Results indicate that this multichamber cylinder approach with discretely variable piston area may allow for the design of compact and efficient actuators relative to standard methods.

Active Fault-Tolerant Control Strategy for More Electric Aircraft under Actuation System Failure

The aircraft hydraulic system is very important for the actuation system and its failure has led to a number of catastrophic accidents in the past few years. The reasons for hydraulic loss can be leakage, blockage, and structural damage. Fortunately, the development of more electric aircraft (MEA) provides a new means of solving this difficult problem. This paper designs an active fault tolerant control (AFTC) method for MEA suffering from total hydraulic loss and actuation system failure. Two different kinds of scenarios are considered: leakage/blockage and vertical tail damage. With the application of the dissimilar redundant actuation system (DRAS) in MEA, a switching mechanism can be used to change the hydraulic actuation (HA) system into an electro-hydrostatic actuation (EHA) system when the whole hydraulic system fails. Taking account of the gap between HA and EHA, a degraded model is built. As for vertical tail damage, engine differential thrust control is adopted to help regain lateral-directional stability. The engine thrust dynamics are modeled and the mapping relationship between engine differential thrust and rudder deflection is formulated. Moreover, model reference control (MRC) and linear quadratic regulator (LQR) are used to design the AFTC method. Comparative simulation with the NASA generic transportation model (GTM) is carried out to prove the proposed strategy.

Research on Power Matching and Energy Optimal Control of Active Load-Sensitive Electro-Hydrostatic Actuator

Electro-hydrostatic actuator (EHA) is an important type of power-by-wire (PBW) which is a highly integrated closed volume control system with the advantages of high reliability, high efficiency and easy maintenance. However, under heavy load conditions, a large amount of heat the EHA motor produces affects the system’s working time and even the system life, which restricts the widespread application of EHA systems. In order to solve the problem of motor heating and the contradiction between high dynamics and high efficiency of the EHA system, a novel active load-sensitive principle and structure of EHA system is proposed based on the load-sensitive principle. The active load-sensitive EHA (ALS-EHA) is a dual control variable system consisting of a motor pump main loop and a load-sensitive loop. As for the latter, the system load pressure is introduced into a special designed and optimized pressure fellow valve (PFV). The valve outlet is connected to the plunger pump swash plate variable mechanism. The EHA pump displacement is actively adjusted by controlling the current input to PFV. The two-degree-of-freedom cooperative control for the output flow of the pump can be implemented by adjusting the motor speed and the pump displacement. An energy optimal robust control law based on fuzzy and disturbance compensation is presented for the control architecture. The simulation results show that the ALS-EHA system based on the control law proposed in this paper can effectively reduce the motor heat while ensuring the dynamic performance of the system.

Effect of Energy Recovery on Efficiency in Electro-Hydrostatic Closed System for Differential Actuator

This paper investigates energy efficiency and dynamic behavior through simulation and experiments of a compact electro-hydrostatic actuator system (EHA) consisting of an electric motor, external gear pump/motors, hydraulic accumulator, and differential cylinder. Tests were performed in a stand-alone crane in order to validate the mathematical model. The influence and importance of a good balance between pump/motors displacement and cylinder areas ratios is discussed. The overall efficiency for the performed motion is also compared considering the capability or not of energy recovery. The results obtained demonstrate the significant gain of efficiency when working in the optimal condition and it is compared to the conventional hydraulic system using proportional valves. The proposed system presents the advantages and disadvantages when utilizing components off-the-shelf taking into account the applicability in mobile and industrial stationary machines.

Improvement of Backdrivability of a Force-Controlled EHA by Introducing Bypass Flow Control

The dynamic response of an electro-hydrostatic actuator (EHA) is limited due to rotational inertia of its servomotor and pump. Thus, when an external disturbance with a high frequency is input to the force-controlled EHA, the pump speed may not be fast enough to attenuate the force control errors. In order to expedite the oil transfer between the cylinder chambers, a bypass valve was employed in this study. The bypass valve connecting both the cylinder chambers can then decompress the high-pressure chamber quickly by bypassing the oil to the low-pressure chamber to compensate for force control errors. To control the bypass flow without affecting the system stability, while the rotational velocity of pump was continuously varied by the force controller, a sliding mode control technique was applied. The sliding mode controller showed satisfactory control performance with respect to stability and robustness, in spite of highly nonlinear properties in the proposed system. Experimentally, where sinusoidal or stepwise velocity disturbance was exerted on the proposed EHA system with the force reference values set at 0 N or 200 N, the force control errors could be reduced markedly, compared to a conventional force-controlled EHA without bypass flow control. The performance improvement was more obvious when the sinusoidal excitation frequency increased from 1 to 3 Hz.

System Reliability Assessment Based on Energy Dissipation: Modeling and Application in Electro-Hydrostatic Actuation System

This paper addresses a new reliability model, based on energy dissipation, considering performance degradation behaviors. Different from the two-state reliability model and traditional reliability model based on failure rate statistics, this paper focuses on the component energy loss due to its fault evolution, such as fatigue, aging and wear, and presents a reliability model based on the component’s energy dissipation, as well as establishing a power dissipation constrained reliability model for degradation-based reliability assessment. As a demonstration, the proposed method is applied to model and evaluate the failure behavior of the electro-hydrostatic actuation system. The results indicate that the proposed method is effective in describing its life-cycle degradation in the energy field, and provides a reliability assessment based on energy dissipation.