Hydraulic Positioning System Research Articles

Dynamic Modeling and Simulation of a Discrete Incremental Hydraulic Positioning System Controlled by Binary Valves

This article presents the conceptual design, operation principle, dynamic modeling, and simulation results of a discrete incremental hydraulic positioning system (DIHPS) intended for use in high-precision, heavy-load industrial automation solutions. An original solution for precise incremental step positioning using DIHPS is proposed, comprising an n-step linear double-acting hydraulic actuator (HA) with a double rod, cylinder sleeve with outflow gaps, binary valves (BVs) bleed-off into the tank, and fixed throttle valves (TRVs) at the inlets of the actuator chambers. The discrete incremental shift of the HA is determined by controlling the opening and closing of the individual BVs, and the step shift of the HA piston stops at the opening location of the BV. A dynamic model of incremental step shift for DIHPS is developed, considering the behavior and relationships of its individual elements. A dynamic model of HA with and without a hydropneumatic accumulator (HPA) is presented. HPA has been shown to effectively dampen piston vibrations and pressure peaks at the HA stop position. The design assumptions, dynamic models, and discrete incremental positioning of the DIHPS are verified by simulation tests and assessed with quantitative indicators. Innovative DIHPSs have significant practical potential in the discrete incremental positioning of heavy loads.

Multi-Chamber Actuator Using Digital Pump for Position and Velocity Control Applied in Aircraft

This paper presents a multi-chamber hydraulic actuator controlled by digital pumps and on/off valves, in order to improve the efficiency of hydraulic systems applied in aircraft for flight control. Hydraulic positioning systems are used in many different applications, such as mobile machinery, industry and aerospace. In aircraft, the hydraulic actuators are used at flight control surfaces, cargo doors, steering, landing gear and so one. However, the massive use of resistive control techniques, which throttles the passages of the hydraulic fluid, associated with internal leakage of the hydraulic components, make these systems low energy efficient. In order to improve their energy efficiency, digital hydraulics emerges as a promising solution mainly for mobile applications. In this paper a hydraulic positioning system for aircraft control surfaces using a multi-chamber actuator controlled by on/off valves and a digital pump is proposed. The use of a digital pump with three fixed displacement pumps can provide eight different volumetric displacement outputs. The multi-chamber actuator with four areas can operate in two different modes, normal or regenerative, resulting in six different equivalent areas. The regenerative mode allows the actuator to achieve higher actuation velocity values with smaller pumps. These equivalent areas combined with the different supplied flow rates can deliver 43 different discrete output velocity values for the actuator, in steady-state. For the system dynamic analyses, three mathematical simulation models were developed using MATLAB/Simulink and Hopsan, one for the digital system, and two for the conventional solutions applied in aircraft (Servo Hydraulic Actuators (SHA) and Electro Hydrostatic Actuator (EHA)). The simulation results demonstrate that the digital actuator can achieve, for position control, a maximum position error, in a steady-state, of 0.7 mm. From the energy consumption point of view, the digital circuit consumes 31 times less energy when compared with the SHA and 1.7 when compared to the EHA, resulting in an energy efficiency of 54%.

Hydraulic cylinder position system controlled by piezoelectric high-speed on-off valve

Hydraulic cylinder position system controlled by piezoelectric high-speed on-off valve

Optimization of PID Parameters Utilizing Variable Weight Grey-Taguchi Method and Particle Swarm Optimization

Controller that uses PID parameters requires a good tuning method in order to improve the control system performance. Tuning PID control method is divided into two namely the classical methods and the methods of artificial intelligence. Particle swarm optimization algorithm (PSO) is one of the artificial intelligence methods. Previously, researchers had integrated PSO algorithms in the PID parameter tuning process. This research aims to improve the PSO-PID tuning algorithms by integrating the tuning process with the Variable Weight Grey- Taguchi Design of Experiment (DOE) method. This is done by conducting the DOE on the two PSO optimizing parameters: the particle velocity limit and the weight distribution factor. Computer simulations and physical experiments were conducted by using the proposed PSO- PID with the Variable Weight Grey-Taguchi DOE and the classical Ziegler-Nichols methods. They are implemented on the hydraulic positioning system. Simulation results show that the proposed PSO-PID with the Variable Weight Grey-Taguchi DOE has reduced the rise time by 48.13% and settling time by 48.57% compared to the Ziegler-Nichols method. Furthermore, the physical experiment results also show that the proposed PSO-PID with the Variable Weight Grey-Taguchi DOE tuning method responds better than Ziegler-Nichols tuning. In conclusion, this research has improved the PSO-PID parameter by applying the PSO-PID algorithm together with the Variable Weight Grey-Taguchi DOE method as a tuning method in the hydraulic positioning system.

Erratum

Lishuang Gong, Baoquan Jin, Hongjuan Zhang, Yan Gao, DongWang and Yu Wang, Anti-disturbance proportional integral attitude control and stabilization of rolling hydraulic position system. Proc IMechE Part I: J Systems and Control Engineering 2017, Vol. 231(2) 117–130. DOI: 10.1177/0959651816687862. SAGE regrets that the ‘Funding’ section of this paper (p. 129) contains errors. The correct funding statement is follows: Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was supported by National Natural Science Foundation of China (grant no. 51375327) and Natural Science Foundation of Shanxi Province (grant no. 201601D102026) and Natural Science Foundation of Shanxi Province (grant no. 2013011023-3).

Anti-disturbance proportional integral attitude control and stabilization of rolling hydraulic position system

Disturbance rejection performance for rolling hydraulic position control system has always been a knotty issue. To guarantee the transient performance and improve disturbance rejection performance of the rolling hydraulic position control system, a compound controller, composed of a feedforward controller part based on proportional integral laws and a compensation part based on disturbance observer, is designed and investigated. In this article, a detailed analysis and design principles of the composite controller are provided. Additionally, stability analysis of the controller is proved using Lyapunov function adapted to the system. Finally, a rigorous analysis of the disturbance rejection performance is given with consideration of both instantaneous disturbances and low-frequency disturbances. For single pulse disturbance, the maximum error is reduced from 3.5% to 0.6%. Furthermore, for more complicated disturbance, sinusoidal disturbance is lower than 50 Hz, disturbance rejection performance decreases with increasing frequency and maximum error is reduced from 5.4% to 1.6%. The test results demonstrate that for single pulse disturbance, the maximum error is reduced from 4.12% to 0.64%. Furthermore, for more complicated disturbance, sinusoidal disturbance is lower than 50 Hz, disturbance rejection performance decreases with increasing frequency and maximum error is reduced from 2.71% to 0.70%. Both simulation and experiment results demonstrate that the proposed method possesses a better disturbance rejection performance than the proportional integral method.

유전 알고리즘을 이용한 유압 위치계의 PID 제어기 동조

유전 알고리즘을 이용한 유압 위치계의 PID 제어기 동조

Proportional Hydraulic Directional Control Valve with Planar Distribution and Differential Control

The paper presents an original solution of hydraulic proportional directional control valve with planar distribution and differential control. The characteristic of the flow section is established and an example of such directional control valve integrated in the structure of a hydraulic positioning system with mechanical feedback is given.

Influence of Internal Leakage in Hydraulic Capsules on Dynamic Behavior of Hydraulic Gap Control System

In hot rolling mills the plastic deformation of the strip is realized at high force and plastic strain speed controlled by electro-hydraulic servo actuators. These hydraulic servo actuators - hydraulic capsules – are capable to adjust the rolling gap at great rolling force dynamically. The dynamic behaviour of the rolling mill’s AGC (automatic gap adjustment) system mainly depends on the correct operation of hydraulic actuators and servo valves. These equipments are great value, planned maintenance is essential for reliable correct operation. The maintenance includes the refurbish of damaged, worn surfaces inside the cylinder and replacement of worn out seals. In the study a laboratory hydraulic positioning system was used to examine the effect of hydraulic actuator internal leakage to dynamic behaviors of the positioning system. Because the laboratory test system is similar to the hydraulic gap adjustment system therefore the laboratory test results can be extended to the rolling mill’s Hydraulic Gap Control system.

Application of Hybrid Fuzzy-PID Control with Coupled Rules in the Hydraulic Positioning System

According to the nonlinearity and time-variation of the positioning control in hydraulic system, a kind of Hybrid Fuzzy-PID Controller with Coupled Rules (HFPIDCR) is proposed. In this control system, the bulk modulus is considered as a variable. The novelty of this controller is to combine the fuzzy logic and PID controllers in a switching condition. Simulation results of the HFPIDCR are compared with the results of traditional PID, Fuzzy Logic Controller (FLC), and Hybrid Fuzzy-PID Controller (HFPID). It is demonstrated that the HFPIDCR has fast response, short adjustment time, high control precision and other advantages, and it can meet the requirements of the positioning control in hydraulic system.

사역대가 포함된 유압 위치 시스템의 LQG/LTR 제어

A LQG/LTR(linear quadratic Gaussian/loop transfer recovery) controller with an integrator is designed to control the electro-hydraulic positioning system. Without considering the nonlinearity in the dead-zone, computer simulations are performed and show good performances and tracking abilities with the feedback controller based on the linear system model. However, the performance of the closed loop hydraulic positioning system shows big steady-state error in real system because of the dead-zone. In this paper, the feedback controller with a nonlinear compensator is introduced to overcome the dead-zone phenomenon in hydraulic systems. The inverse dead-zone as a nonlinear compensator is used to cancel out the dead-zone phenomenon. Experimental tests are performed to verify the performance of the controller.

Mechatronic Designed Hydraulic Positioning System

The paper presents the hardware structure of an original hydraulic positioning system based on a mechatronic approach. Dedicated control algorithms are also presented.

An Approach to Parameter Identification using Linear Graphs and Improved Particle Swarm Optimization

In this paper, the approach of linear graphs is combined with a modified particle swarm optimization procedure for efficient and effective extraction of parameter values in a model of an engineering system. The approach is applied to the hydraulic positioning system of an industrial fish cutting machine. Both computer simulation and experimentation are used to validate the developed approach. The results show that the combined approach of model parameter identification, as developed in this paper, is able to accurately determine the parameter values in complex engineering models.

Adaptive Nonlinear Optimal Compensation Control for Electro-hydraulic Load Simulator

Directing to the strong position coupling problem of electro-hydraulic load simulator (EHLS), this article presents an adaptive nonlinear optimal compensation control strategy based on two estimated nonlinear parameters, viz. the flow gain coefficient of servo valve and total factors of flow-pressure coefficient. Taking trace error of torque control system to zero as control object, this article designs the adaptive nonlinear optimal compensation control strategy, which regards torque control output of closed-loop controller converging to zero as the control target, to optimize torque tracking performance. Electro-hydraulic load simulator is a typical case of the torque system which is strongly coupled with a hydraulic positioning system. This article firstly builds and analyzes the mathematical models of hydraulic torque and positioning system, then designs an adaptive nonlinear optimal compensation controller, proves the validity of parameters estimation, and shows the comparison data among three control structures with various typical operating conditions, including proportion-integral-derivative (PID) controller only, the velocity synchronizing controller plus PID controller and the proposed adaptive nonlinear optimal compensation controller plus PID controller. Experimental results show that systems' nonlinear parameters are estimated exactly using the proposed method, and the trace accuracy of the torque system is greatly enhanced by adaptive nonlinear optimal compensation control, and the torque servo system capability against sudden disturbance can be greatly improved.

Acoustic radiation force contrast in MRI: Detection of calcifications in tissue‐mimicking phantoms

Mammography is a widely used tool for the screening of breast cancer, and calcifications are a common finding in most mammograms. The location, size, number, morphology, and distribution of calcifications are an important information to differentiate a benign lesion from probably malignant pathologies. Calcifications are not detectable with a standard dynamic contrast enhanced breast MRI. The authors present a novel method for the detection and imaging of calcifications in breast tissue without ionizing radiation or contrast agents. Measurements of localized tissue displacement in phantoms due to applied acoustic radiation force were performed. This displacement was imaged with a displacement sensitive spin-echo MRI sequence. Pieces of eggshell that represent calcifications were embedded in tissue-mimicking agarose phantoms. The sizes of the calcifications were 0.8 x 0.8 x 0.4, 1.5 x 1.5 x 0.4, and 2 x 3 x 0.4 mm3. The calcifications were scanned with ultrasound (U.S.) at 2.5 MHz and intensities up to I(spta) =7.18 W/cm2. The U.S. beam was moved inside the phantom by a computer-controlled three-dimensional hydraulic positioning system. The U.S. beam was scanned over the two smaller calcifications with the displacement sensitivity of the MRI sequence parallel to the U.S. beam path. Grayscale coded maps of the displacement scans are presented. For the 0.8 x 0.8 x 0.4 mm3 calcification, the U.S. intensities were varied. Finite element simulations were performed to verify if the experiments complied with theory. The authors found that the displacement caused by the U.S. is increased at the position of the calcification. The area of increased displacement is at least twice as large as the calcification itself. The simulations show this increase in displacement and area at the position of the calcification. When changing the displacement sensitivity direction to perpendicular to the U.S. beam, a crossed black and white four-leaf clover is visible at the position of the calcification. The U.S. is scattered and reflected by the calcifications. This leads to the increased displacement which is transmitted to the surrounding material because of the elastic coupling between the calcification and the agarose material. Due to the high differences in acoustic impedance and elastic properties between the surrounding tissue and the calcification, even the detection of pieces smaller than the resolution of the MRI scanner is possible. The acoustic radiation force contrast in MR phase-difference images offers a positive signal for calcifications from a smooth background in phantoms. This method offers a possibility of differentiating qualitatively and quantitatively hard calcifications from stiffer inclusions such as tumors.

Influence of Control Valve Delay and Dead Zone on the Stability of a Simple Hydraulic Positioning System

This paper deals with the PI control of a highly simplified dynamic model of a hydraulic cylinder. It is assumed that the hydraulic fluid is incompressible and that the pump provides constant flow rates, which results in the possibility of velocity control. Two types of anomalies are taken into account: (a) the time delay due to the controller computations and the internal pressure dynamics and (b) the dead zone of the controller valve. This results in a nonlinear system are described by a piecewise linear discontinuous map. Nonlinear behavior of the system is explored and the practically globally stable parameter domains are identified.

Gaussian process approach for modelling of nonlinear systems

Parametric modelling principals such as neural networks, fuzzy models and multiple model techniques have been proposed for modelling of nonlinear systems. Research effort has focused on issues such as the selection of the structure, constructive learning techniques, computational issues, the curse of dimensionality, off-equilibrium behaviour, etc. To reduce these problems, the use of non-parametrical modelling approaches have been proposed. This paper introduces the Gaussian process (GP) prior approach for the modelling of nonlinear dynamic systems. The relationship between the GP model and the radial basis function neural network is explained. Issues such as selection of the dimension of the input space and the computation load are also discussed. The GP modelling technique is demonstrated on an example of the nonlinear hydraulic positioning system.

Discrete-time H<SUB align=right>2-optimal output tracking control for an experimental hydraulic positioning control system

This paper explores the application of discrete-time H2-optimal output tracking control for a hydraulic positioning control system (HPCS). By minimising the H2-norm of the system, the discrete-time H2-optimal control both stabilises the plant and minimises the root-mean-square of the servo position error simultaneously. To facilitate computation of the H2-optimal controller, linear matrix inequalities (LMIs) technique is applied. Computer simulations illustrate the design procedure and the effectiveness of the proposed method. Experimental tests on a real hydraulic positioning system for a tracking application are also conducted and the results show that the method is suitable for practical applications.

Compensation for transmission delays in an ethernet-based control network using variable-horizon predictive control

Distributed control networks encounter nondeterministic delays in data communication between sensors, actuators, and controllers, including direct-feedback control and higher level supervisor control. This paper presents a novel strategy, which extends the Generalized Predictive Control (GPC) algorithm to compensate for these data-transmission delays. Communication lines between sensors to controller and controller to actuators are considered. The present strategy incorporates a minimum-effort estimator to estimate missing or delayed sensor data and a variable-horizon adaptive GPC controller to predict the required future control efforts to drive the plant to track a desired reference trajectory. Action buffers are introduced at the actuators to sequence the future control efforts. A parallel objective of this paper is to investigate the suitability of the Ethernet network, which is cost-effective and widely deployed for implementing networked control systems. An Ethernet-based client-server control architecture is developed. The developed scheme is implemented on the dual-axis hydraulic position system of an industrial fish-processing machine.

Deadzone compensation based on constrained RBF neural network

In this paper, a modified adaptive neural network for the compensation of deadzone is described, and simulated on a hydraulic positioning system, in which the dynamic model is separated into a series of connection of a nonlinear (deadzone) subsystem and a linear plant. The proposed approach uses two neural networks. One is the radial basis function (RBF) neural network, which is used for identifying parameters of deadzone. Based on the penalty function used in optimization theory, a multi-objective cost function with constraint is adopted to provide the best deadzone approximation. The result is used to train the other neural network for the inverse compensation of deadzone. The RBF neural network also generates the parameters of the linear plant for the design of an adaptive controller. A convergence analysis for the network training process is also presented.