Characteristics Of Servo Valve Research Articles

Mathematical Modeling and Experimental Characterization of the Piezoelectric Servo Valve System

Abstract The dynamic performance of the hydraulic system depends on the dynamic characteristics of the servo valve. In this article, the control characteristics of the piezoelectric servo valve are studied theoretically and experimentally. The mathematical model of the system is established by considering the influence of the piezoelectric servo valve, the influence of the pipeline, and the interaction between them. The frequency response characteristics of the system and the influence of the pipeline parameters on the control characteristics of the system are discussed. The simulation results are compared with the experimental results to verify the accuracy and efficiency of the piezoelectric servo valve dynamic model established in this article.

Research on the dynamic characteristics of water hydraulic servo valves considering the influence of steady flow force

The International Thermonuclear Experimental Reactor remote-handling (ITER-RH) system powered by water hydraulics is a vision of the future. The 2D servo valve is a new type of servo valve, maybe suitable for the ITER-RH system. It has many advantages, including its fast response and strong anti-pollution ability. However, steady flow force is currently considered to be one factor that impacts the dynamic characteristics of servo valves. In this study, the influence of steady flow force on the dynamic characteristics was analyzed, and the structure was optimized accordingly. A mathematical model of the servo valve was built using theoretical analysis and numerical simulation. Results indicated that the amplitude bandwidth of the 2D water hydraulic servo valve was 169 Hz without considering the steady flow force, and it decreased to 162 Hz when the steady flow force was considered. Furthermore, a newly designed valve sleeve, to compensate for the axial steady flow force, was proposed by changing the angle of the inlet port designed in the valve sleeve to the spool axis. The maximum compensation capacity of the axial steady flow force was 35%, and the best angle of the inclined holes was approximately 120°. The optimized amplitude bandwidth of the 2D servo valve was 167 Hz. The results demonstrate that the optimized valve sleeve improved the dynamic response of the 2D servo valve.

A Nonlinear Model-based Variable Impedance Parameters Control for Position-based Impedance Control System of Hydraulic Drive Unit

In this paper, aimed at the problem of control accuracy when the traditional position-based impedance control is applied in the hydraulic drive unit (HDU) of legged robot, a kind of nonlinear model-based variable impedance parameters controller (MVIPC) is designed. First, the mathematical model of position-based impedance control for HDU is given. Second, the performance of traditional position-based impedance control is tested on the HDU performance test platform under different working conditions, and the experimental results show that the control accuracy of this control method needs to be improved greatly. Thirdly, the control idea of MVIPC is described, and the theoretical derivation is deduced. MVIPC considers the high-order dynamic characteristics of servo valve, pressure-flow nonlinearity of servo valve, oil compressibility and load characteristics. Finally, the control performance of MVIPC is verified on the HDU performance test platform. The experimental results show that MVIPC can significantly improve the performance of traditional position-based impedance control, and have an excellent adaptability under different working conditions. This research can provide an underlying control method of hydraulic systems during the robot locomotion.

Nonlinear mathematical modeling and sensitivity analysis of hydraulic drive unit

The previous sensitivity analysis researches are not accurate enough and also have the limited reference value, because those mathematical models are relatively simple and the change of the load and the initial displacement changes of the piston are ignored, even experiment verification is not conducted. Therefore, in view of deficiencies above, a nonlinear mathematical model is established in this paper, including dynamic characteristics of servo valve, nonlinear characteristics of pressure-flow, initial displacement of servo cylinder piston and friction nonlinearity. The transfer function block diagram is built for the hydraulic drive unit closed loop position control, as well as the state equations. Through deriving the time-varying coefficient items matrix and time-varying free items matrix of sensitivity equations respectively, the expression of sensitivity equations based on the nonlinear mathematical model are obtained. According to structure parameters of hydraulic drive unit, working parameters, fluid transmission characteristics and measured friction-velocity curves, the simulation analysis of hydraulic drive unit is completed on the MATLAB/Simulink simulation platform with the displacement step 2 mm, 5 mm and 10 mm, respectively. The simulation results indicate that the developed nonlinear mathematical model is sufficient by comparing the characteristic curves of experimental step response and simulation step response under different constant load. Then, the sensitivity function time-history curves of seventeen parameters are obtained, basing on each state vector time-history curve of step response characteristic. The maximum value of displacement variation percentage and the sum of displacement variation absolute values in the sampling time are both taken as sensitivity indexes. The sensitivity indexes values above are calculated and shown visually in histograms under different working conditions, and change rules are analyzed. Then the sensitivity indexes values of four measurable parameters, such as supply pressure, proportional gain, initial position of servo cylinder piston and load force, are verified experimentally on test platform of hydraulic drive unit, and the experimental research shows that the sensitivity analysis results obtained through simulation are approximate to the test results. This research indicates each parameter sensitivity characteristics of hydraulic drive unit, the performance-affected main parameters and secondary parameters are got under different working conditions, which will provide the theoretical foundation for the control compensation and structure optimization of hydraulic drive unit.

Development and Experimental Study of Dynamic Characteristics for Servo Valve Torque Motor

Torque motor is the electrical - mechanical converter of servo valve, is the bridge connecting electrical devices and hydraulic devices, is one of the key elements of electro-hydraulic servo valve. The main object of study of this paper is moving iron permanent magnet torque motor. The dynamic characteristics of torque motor are the key parameter to measure the overall performance. At present, the research of most of manufacturers emphasize on the test of integral valve servo valve. Torque motor is also designed to mimic the structure and size of foreign-based valve, lacking of system understanding for characteristics of servo valve. Early in the design, people cannot effectively control the overall performance of the torque motor products. There is large performance difference with a larger group of torque motor, producing serious waste. This paper describes the principle of dynamic characteristics test, establishes a test system of dynamic characteristics for torque motor, accurately obtain nature frequency and bandwidth of torque motor on the test bench which we have established before.

Application of the Jerk Feedback on the Shaking Table

For the shaking table system, the 90o phase shift frequency of the servo valve system is close to the oil column resonance frequency, the bandwidth under the influence of servo valve features was so narrow that it cannot meet requirements. Multi-variable control is presented in this paper by introducing the jerk feedback on the basis of the three-variable control. The theoretical derivation and the system simulation show that: the jerk feedback can reduce the oil column resonance frequency, and decrease the influence of the system performance caused by the servo valve characteristics.

Simulation on Static and Dynamic Characteristics of Servovalve

In this paper, we build a simulation model of the two stage flapper-nozzle electro hydraulic servovalve with the hydraulic component design libraries and the AMESet secondary development of modeling in AMESim simulation environment. By adjusting the parameters of the model, the performance of the servovalve were analyzed. At the same time, we can get the characteristic curve of the servovalve. These characteristic curves can describe the static and dynamic characteristics of the valve which can greatly guide for the study of the servovalve.

Harmonic distortion reduction on seismic vibrators

To improve seismic resolution using vibroseis, vibrators must output the ground-force energy with minimum harmonic distortion. Four main sources within the vibrator system cause the ground force to suffer severe harmonic distortion: the nonlinear servo-valve flow-pressure character-istics, the servo-valve characteristics near null, the fluctuations in the hydraulic pressure, and the nonlinear contact-stiffness between the baseplate and the ground. Modeling was undertaken to investigate and quantify harmonic distortion from each source. As a result, three modifications have been made to reduce the harmonic distortion of the ground force:

Design of a P-wave seismic vibrator with advanced performance

ABSTRACT For optimal seismic imaging, the vibroseis method requires the vibrator to generate synchronous, repeatable sweeps over a broad frequency range and output the ground-force energy with minimum harmonic distortion. This requires re-evaluating each element of the vibrator system to ensure that it contributes to the success of the method. Key factors that cause the vibrator to suffer from severe harmonic distortion are fluctuations in the hydraulic power supply pressure, flexing of the baseplate, coupling or loading between the baseplate and the ground, nonlinear servo-valve flow-pressure characteristics, and servo-valve characteristics near null. This paper examines these factors and describes the design of a new P-wave vibrator by ION (previously I-O) to improve seismic resolution. Experimental results demonstrate that the newly designed vibrator dramatically reduces harmonic distortion in the ground-force signal under various coupling conditions, particularly on hard and uneven ground. With the high-frequency controller and Pelton DR valve, a broad-band sweep frequency is achieved. Cavitations in the supply pressure, a long-standing problem in vibrator mechanics, are almost completely eliminated.

Precise Position Control of Pneumatic Servo System Considered Dynamic Characteristics of Servo Valve

Precise positioning system is required in the fields of semi-conductor manufacturing process. A pneumatic servo table system is one of a precise positioning system. The features of the table are little friction force and little heat generation. Generally, the controller of this system is designed by neglecting the characteristics of servo valves. However, in high frequency band, the response of this system becomes unstable because of the characteristics of the valves. In this paper, we demonstrate that by considering the characteristics of servo valves, the position control of a pneumatic servo table could be improved. First, the dynamic characteristics of servo valves were examined. It became clear that the characteristics could be described as a second-order system. Then, the servo table system was designed as a fifth-order system. It became clear that the position accuracy of this system were greatly improved.

Modeling of Direct-Drive Servovalve which Has Giant Magnetrostrictive Material and Spool Position Control by Gain Scheduling

Because of the reasons of favorable features such as high driving force, fast response, fine environmental durability and big distortion about 10 times more than that of PZT, GMM (Giant Magnetrostrictive Material) is suitable for the actuation structure of servovalve. But, GMM distortion depends on the magnitude of coil current and the output-gain declines according to decreasing current magnitude. Then, the dead-zone appears in small current range. One of the important characteristics of servovalve is the fine tracking performance to the reference signal. So far, we attempted to apply linear controllers, such as PI or H∞controller. However GMM tracking performance is inferior to the traditional driving device for reference signal around null area, and this flaw remains as an important matter.In this paper, adopting LPV (Linear Parameter-Varying) system modeling in which we regard the magnitude of input signal as a scheduling parameter, we design a gain scheduling controller and attempt to solve the problem that is caused by the nonlinearities mentioned above. Since it is hard to implement the controller which uses the information on the varying rate of scheduling parameters, we propose a new approach for output-feedback controller design. First, we describe the plant modeling as an LPV system, then present an outline of the controller design synthesis without any information on the varying rate of scheduling parameter and the design process. Lastly, we show the usefulness of the proposed controller by experimental results.

The Effect of Nonlinear Characteristics on Pneumatic Servo Systems

Pneumatic servo systems are used on fatigue machines and robots. Although, those systems have nonlinear elements which make the motion control difficult On the sinusoidal movements, the non-linearity of the servo valves, especially the lap conditionof the valves, is considered to cause a bad effect on the position control. We have already proposed a new method to measure thestatic characteristics of servo valves including the lap condition using an is othermal chamber. In this paper, firstly the lap condition of a servo valve is measured by the proposed method. Secondly, the effect of the lap condition of the servo valve during sinusoidal position control on a pneumatic cylinder is investigated. Finally, we compensate the effect of the lap condition of the valve using repetitive control.

Dynamic Characteristics of Roll Push-Up Cylinder Based on Direct-Operated Servo Valve.

Force-motor direct-operated servo valves are increasingly used to improve the thickness control accuracy of hydraulic screw-down systems in rolling mills. The authors have proposed to use expandable, compressible metal springs instead of conventional rubber springs to position the spool in a servo valve, and a unique method to damp it with eddy current. The experiment on commercially operated mills has proven that the metal-spring valve exhibits excellent system response compared to the rubber-spring valve, though the independent response of the former is lower than the latter. Furthermore, a simulation study of dynamic characteristics of servo valves to control the roll push-up cylinder under an intended load was conducted using mathematical models in quadratic form considering complex or viscous damping. The result generally agreed with that of experiment and clarified that damping characteristics of the valve and the spring constant of the spool-supporting spring have significant influence on frequency response of the roll push-up cylinder.

静圧支持回転軸系の回転振れ自動補正機構 たて型高精密回転テーブルの試作

A highly precise vertical turntable provided with hydrostatic bearings and radial runout error compensator has been developped. The compensator has two functions of a closed loop differential hydrostatic actuator for positioning a spindle to a nanometer accuracy and a datum roundness error measuring instrument with multiple position sensors. By separating the datum error from the runout error readings, the compensator can overcome the limitation of geometrical datum accu racy. Design philosophy of the turntable spindle system is as follows : (1) Isolation of disturbance sources within the system. (2) Design procedure of bearing pads taking into consideration of the performance of servd valve. (3) Introduction of microprocessor for separating the datum error in rounout error measurment from the runout error readings. Several test results are concluded as follows : (1) The bearing pad dimensions are determined in connecting with servo valve characteristics. (2) The positioning resolution is at least 1 nm and the bandwidth is 250 Hz. (3) Two point roundness measurement method has proved that the compensation accuracy is ± 4.5nm (3 σ). However, correcting the datum error in accordance with the measurement principle, compensation accuracy improved to 6.1nm (2LSB, 5rpm) or 9.15nm (3LSB, 30rpm) in peak to valley.

Design of Hydraulic Servovalve for Maximum Pressure Sensitivity

The performance of a hydraulic servomechanism depends largely upon the servovalve characteristics which in turn are determined by various physical parameters such as spool land width, radial clearance etc... The work described in this paper is concerned with the design of hydraulic spool valve for a maximum pressure sensitivity in a no load flow application. It has been demonstrated that this condition is achieved by having an underlap equal to the radial clearance. The results are experimentally verified and the effects of rounded corners of metering lands on the pressure sensitivity curves are discussed.

Simulation based design of hydraulic servo-controlled apparatus for damping measurement

An apparatus for the measurement of damping properties of materials under biaxial stress conditions utilizes three electro- hydraulic servo-systems to apply fluctuating internal, external, and axial pressures to a hollow cylindrical specimen. The ar rangement imposes difficulties with respect to specimen loading, system interactions, stability and control. An analog simulation was conducted as a direct step in the design procedure in order to prove the feasibility of the apparatus, to provide guidance in the choice of design parameters, and to investigate system operating conditions and procedures. The simulation and its use with respect to both design and opera tion of the apparatus are described. In the simulation, account is taken of servo-valve characteristics, fluid leakage paths, specimen deflection, chamber volumes, and fluid compressibil ity. The (successful) performance of the apparatus as built is also described, and the similarity of simulated and actual behaviour is apparent.

The effects of radial clearance, rounded corners, and underlap on servovalve characteristics

The effects of radial clearance, rounded corners, and underlap on servovalve characteristics