TEST METHOD OF HIGH-SPEED ON-OFF VALVE DYNAMIC CHARACTERISTICS

According to the valve port features of high speed on-off valve and its actions, the valve port can be simplified into an a-type half bridge construction. A method that tests the dynamic characteristics of the high speed on-off valve by the output pressure signal of the a-type half bridge is proposed. Having analyzed the factors related to the dynamic characteristics of an a-type half bridge, a rule for designing the outlet chamber＇s volume is worked out. According to the rule, a test stand is built to test the self-developed high-speed on-off valve. From the test results, it can be seen that with the outlet chamber＇s volume controlled by the rule the rise time of the pressure signals driven by signals with different frequencies changes very little. The test results conform to the simulation results, which nroves the correctness of the method.

Development of High-Speed On-Of Valves and Their Applications

With the widespread application of the computer and microelectronic technology in the industry,digitization becomes the inevitable developing trend of the hydraulic technology.Digitization of the hydraulic components is critical in the digital hydraulic technology.High-speed on-of valves(HSVs)which convert a train of input pulses into the fast and accurate switching between the on and of states belong to widely used basic digital hydraulic elements.In some ways,the characteristics of the HSVs determine the performance of the digital hydraulic systems.This paper discusses the development of HSVs and their applications.First,the HSVs with innovative structures which is classifed into direct drive valves and pilot operated valves are discussed,with the emphasis on their performance.Then,an overview of HSVs with intelligent materials is presented with considering of the switching frequency and fow capacity.Finally,the applications of the HSVs are reviewed,including digital hydraulic components with the integration of the HSVs and digital hydraulic systems controlled by the HSVs.

Research on the Characteristics of Pneumatic PCM Control Valve

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MAGNETIC FIELD ANALYSIS OF ELECTROMAGNETIC VALVE TAKING HYSTERESIS INTO ACCOUNT

Predicting and optimizing of the high-speed solenoid on/off valve behaviorrequires an accurate model of the hysteresis loop of the magnetic material used A ferromagnetichysteresis model and a novel algorithm based on fixed-point technique to optimize theelectromagnetic model are introduced By utilizing a modified vector Preisach model of magnetichysteresis and the global genetic optimization algorithm based on partial mapping cross method, theB-H relation loops are identified accurately.

High-effciency aircraft antiskid brake control algorithm via runway condition identification based on an on-off valve array

The aircraft antiskid braking system is an important hydraulic system for preventing tire bursts and ensuring safe take-off and landing. The brake system adjusts the force applied on the brake discs by controlling the brake pressure. Traditional aircraft antiskid braking systems achieve antiskid performance by controlling the braking pressure with an electrohydraulic servo valve.Because the pilot stage of an electrohydraulic servo valve is easily blocked by carbonized hydraulic oil, the servo valve would become a dangerous weak point for aircraft safety. This paper proposes a new approach that uses an on-off valve array to replace the servo valve for pressure control. Based on this new pressure control component, an efficient antiskid control algorithm that can utilize this discontinuous feature is proposed. Furthermore, the algorithm has the ability to identify the runway circumstances. To overcome the discontinuity in the process of using an on-off valve array, the Filippov framework is introduced. The conditions of convergence of the system are also discussed.The results of the digital simulations and the hardware-in-the-loop(HIL) braking experiments are used to verify the efficiency and stability of the proposed control algorithm. The method also proves that the on-off valve array can replace the servo valve perfectly as a new type of antiskid braking pressure control component.

Design and Dynamic Model of a Frog-inspired Swimming Robot Powered by Pneumatic Muscles

Pneumatic muscles with similar characteristics to biological muscles have been widely used in robots, and thus are promising drivers for frog inspired robots. How- ever, the application and nonlinearity of the pneumatic system limit the advance. On the basis of the swimming mechanism of the frog, a frog-inspired robot based on pneumatic muscles is developed. To realize the indepen- dent tasks by the robot, a pneumatic system with internal chambers, micro air pump, and valves is implemented. The micro pump is used to maintain the pressure difference between the source and exhaust chambers. The pneumatic muscles are controlled by high-speed switch valves which can reduce the robot cost, volume, and mass. A dynamic model of the pneumatic system is established for the sim- ulation to estimate the system, including the chamber, muscle, and pneumatic circuit models. The robot design is verified by the robot swimming experiments and the dynamic model is verified through the experiments and simulations of the pneumatic system. The simulation results are compared to analyze the functions of the source pressure, internal volume of the muscle, and circuit flow rate which is proved the main factor that limits the response of muscle pressure. The proposed research provides the application of the pneumatic muscles in the frog inspired robot and the pneumatic model to study muscle controller.

Development of a novel two-stage proportional valve with a pilot digital flow distribution

Pilot two-stage proportional valves are widely used in high-power hydraulic systems. For the purpose of improving the dynamic performance, reliability, and digitization of the traditional proportional valve, a novel two-stage proportional valve with a pilot digital flow distribution is proposed from the viewpoint of the dual nozzle-flapper valve’s working principle. In particular, the dual nozzle-flapper is decoupled by two high-speed on/off valves (HSVs). First, the working principle and mathematical model of the proposed valve are determined. Then, the influences of the control parameters (duty cycle and switching frequency) and structural parameters (fixed orifice’s diameter and main valve’s spring) on the main valve’s motion are analyzed on the basis of theory, simulation, and experiment. In addition, in optimizing the value of the fixed orifice’s diameter, a new design criterion that considers the maximum pressure sensitivity, flow controllability, and flow linearization is proposed to improve the balance between the effective displacement and the displacement fluctuation of the main valve. The new scheme is verified by simulations and experiments. Experimental results of the closed-loop displacement tracking have demonstrated that the delay time of the main valve is always within 3.5 ms under different working conditions, and the tracking error can be significantly reduced using the higher switching frequency. The amplitude–frequency experiments indicate that a −3 dB-frequency of the proposed valve can reach 9.5 Hz in the case of ±50% full scale and 15 Hz in the case of 0%–50% full scale. The values can be further improved by increasing the flow rate of the pilot HSV.

Dynamic performance and control accuracy of a novel proportional valve with a switching technology-controlled pilot stage

Two-stage directional valves usually employ proportional pilot control technology,which has the disadvantages of dead zones,leakage,and the large moving mass of the pilot valve.It is difficult,therefore,to achieve fast-response performance of the main valve.In order to overcome this problem,a switching pilot technology that employs two independent high-speed on/off valves(HSVs)is proposed to replace the traditional pilot proportional valve.Due to the rapid switching characteristics of HSVs,the dead zone of the pilot stage is avoided,and the dynamic response performance of the main valve is improved.The experiments indicate that the switching frequency of the pilot HSVs and supply pressure of the pilot stage have a very large effect on the dynamic performance and control accuracy of the main valve.Increasing the switching frequency of the pilot HSVs is helpful for improving main-valve control accuracy.The larger supply pressure of the pilot stage can achieve a faster dynamic performance of the main valve while causing larger static errors.The results show that the switching pilot technology can clearly improve the static and dynamic performances of the main valve.With the increase of pilot supply pressure,the step rise time is reduced from 21.4 ms to 16.8 ms,and the dynamic performance of the main valve is improved by 21.5%.With the increase of pilot switching frequency,the steady-state error decreases from 24μm to 20μm,and the control accuracy of the main valve is improved by 16.7%.

Pneumatic pressure control based on improved NMPC and its application to aeroengine surge simulation

In the semi-physical simulation of aeroengines,using the pneumatic pressure servo control technology to provide realistic pneumatic excitation to the sensors and electronic controller can improve the confidence of the simulation and reduce the test cost and risk.However,the existing methods could not satisfy the precise simulation of large-amplitude and high-frequency pulsating pressure during aeroengine surge.In this paper,a pneumatic pressure control system with asymmetric groups of the High-Speed on–off Valve(HSV)is designed,and an Improved Nonlinear Model Predictive Control(INMPC)method is proposed.First,the volumetric flow characteristics of HSV are tested and analyzed with Pulse Width Modulation(PWM)signal input.Then,a simplified HSV model with the volume flow characteristic correction is developed.Based on these,an integrated model for the whole system is further established and used as the prediction model in INMPC.To improve the computational speed of the rolling optimization process,the mapping scheme from control signal to PWM duty cycle of HSVs and the objective function with exterior penalty function are designed.Finally,the random step,sinusoidal and real engine surge data are set as the reference pressure in multiple comparative experiments to verify the effectiveness of the pressure tracking system.

Digital switched hydraulics

This paper reviews recent developments in digital switched hydraulics particularly the switched inertance hydraulic systems （SIHSs）. The performance of SIHSs is presented in brief with a discussion of several possible configurations and control strategies. The soft switching technology and high-speed switching valve design techniques are discussed. Challenges and recommendations are given based on the current research achievements.

A novel architecture of electro-hydrostatic actuator with digital distribution

To address the flow imbalance rapidly of the asymmetric Electro-Hydrostatic Actuator(EHA),this paper presents a novel architecture of asymmetric EHA with the Digital Distribution(EHA-DD).It also improves the flow nonlinearity and control accuracy of the pump,especially in the low-speed condition.The digital distribution with two High-Speed on–off Valves(HSVs)not only balances flow instead of the check valves,but also replaces the pump at the low-speed to control output flow by adjusting the PWM signal.The pump and HSVs are the crucial components to control flow output.Firstly,the flow calculation models of the pump and the duty ratio inversed model of the HSV are obtained through experimental tests and the identification method.To get the control input signal for the required flow,the pump speed and PWM duty ratio for the HSVs are inversed to compensate for flow output.Further,a multimode digital flow distribution control method based on pump speed,mainly including the pump-controlled mode for large flow demand and valve-controlled mode for little flow demand,is proposed to control the accurate flow output actively.The step extension experiments based on the flow calculation models are conducted on the EHA-DD prototype under elastic,opposite varying load.The results demonstrate that the EHADD realizes little position error by accurate flow control,and it is also beneficial to improve the service life of the pump.