Guihua Han

Model Identification and Control of Electro-hydraulic Position Servo System

In view of introduction of the composition and working principle of the electro-hydraulic position servo control system, the mathematical model of the system was built. In order to acquire more accuracy system mathematical model, System model identification and verification of electro-hydraulic position servo system were carried out based on hardware-in-the-loop simulation environment of Real-time Workshop (RTW) and system identification toolbox in MATLAB. A hybrid controller composed of a proportional controller, a fuzzy controller and a classical PID controller, for which the parameters of the PID controller can be adjusted online by using the fuzzy control rule, The zero position of fuzzy domain was regarded as the switching threshold, and stable switching is implemented between the proportional control and the proportion-fuzzy PID control. The simulation results show that the steady-state error of system is eliminated, the rapidity is enhanced by the hybrid control strategy, Moreover, and its ability of adapting to system parameter variation is superior to the other controllers.

Study of the Electro-hydraulic Load Simulator Based on Flow-Press Servo Valve and Flow Servo Valve Parallel Control

The superfluous force seriously affects the dynamic load precision of the electro-hydraulic load simulator. Aiming at this question, the work principle of the electro-hydraulic load simulator was analyzed, and the bond graph models of the flow servo valve, hydraulic cylinder and load were established. These models sufficiently contain the higher-order nonlinear dynamic character of the electro-hydraulic servo valve and describe the time variant character of the liquid capacitance of two cavities in hydraulic cylinder. Then the bond graph model of the electro-hydraulic load simulator system was established by combining the above bond graph models. In order to study the performance of the electro-hydraulic load simulator parallel controlled by the flow-press servo valve and the flow servo valve, and to study the effect of eliminating the superfluous force by this parallel control way, the structure and the working principle of the flow-press servo valve was analyzed, and the bond graph model of the electro-hydraulic load simulator parallel controlled by the flow-press servo valve and the flow servo valve was established. The simulation and experimentation study shows that the double servo valves parallel control method is very efficient to eliminate the superfluous force of the electro-hydraulic load simulator and is very obvious to improve the system performance of dynamic load. The study of simulation and experimentation also prove that the bond graph models are correct.

Hardware-in-the-loop simulation of electro-hydraulic pressure servo system

In order to improve the rigidity performance of the hydrostatic thrust bearing, an electro-hydraulic pressure servo system is proposed to adjust oil film pressure in real-time. A rapid prototyping method is adopted to identify the model of the pressure servo system. A non-linear hybrid controller is applied, which is composed of a classical PID controller and a fuzzy controller based on self-adjusting modifying factor and a fuzzy switching mode is employed to reject undesirable disturbances caused by the switchover between the two control methods. The identification model of the practical system and the feasibility of the control scheme are validated by hardware-in-the-loop simulation experiments. The experiments results show that the hybrid PID controller exhibits high bearing rigidity (the maximum overshoot is 0.07, while PID is 0.2), improves stability and rapidity when load changes. Further, the control performance can be enhanced through matching the load rigidity and mass reasonably; and it is feasible to apply electro-hydraulic pressure servo system to hydrostatic thrust bearing.

Hardware-in-the-loop simulation on controllable hydrostatic thrust bearing

In the hydrostatic thrust bearing with open-loop quantity oil supply system for the heavy NC machine tool, the time-variable oil viscosity and the loads will cause the lubricant film thickness deviating from the optimum value, which reduce the bearing film rigidity and affect the machine tool precision. This paper proposed a controllable hydrostatic thrust bearing, which combined the constant flow chambers and the controllable flow chambers. The chamber flow can be adjusted automatically according to the load, the cutting force, and the thermal results of thrust bearing. The controllable chamber flow was adjusted by the electro-hydraulic servo variable mechanism. The oil film thickness error was measured in real time to maintain the most optimum film thickness. The models of controllable chamber flow and servo variable mechanism were established, and the model identification experiments for servo variable mechanism were carried on. The hardware-in-loop simulation results show that the controllable bearings assure the stability and rapidity of system, compensate effectively the effect of load parameter on oil film thickness, and improve the position tracking performance, and validate the creditability of the identification model.

Structural analysis and optimization on crossbeam of heavy NC gantry moving boring & milling machine

In order to improve the work precision, the finite element models of crossbeam of heavy NC gantry moving boring & milling machine were established, and static/dynamic characteristics were analyzed. The crossbeam itself stiffness and the tip displacement converted by beam deformation under the largest cutting force and gravity load were calculated. According to the results of calculation and analysis, optimal structures of the crossbeam were designed, in which structure form and size were modified. And optimal structure was obtained by calculation crossbeam itself stiffness and crossbeam distortion of three schemes Kl, K2 and K3. The dynamic analysis results of the crossbeam show that the optimized structure improves the machine design accuracy and that can be a good reference for designing all kinds of machine tools.

Design of Intelligent Washout Filtering Algorithm for Water and Land Tank Motion Simulation

Aiming at the matter of incompatible problem between workspace limiting and motion simulation fidelity, based on BP neural network theory, a kind of intelligent washout filter algorithm was designed, and simulation research was done combining water and land tank typical motion conditon of working. Research results showed that intelligent washout filtering algorithm improved the simulator workspace using efficiency and motion simulation reality greatly comparing with classical washout filtering algorithm. A kind of efficient method was presented for realized motion simulation of high fidelity within simulator limited workspace, and have reference significance for other kinds of motion simulator implementing simulaiton of high fidelity.

Control Method of Heavy Hydrostatic Thrust Bearing

A hybrid fuzzy control scheme was applied to improve the rigidity of hydrostatic thrust bearing. The bearing oil film control was realized by coupling oil film thickness of four controllable chambers. The chamber flow can be regulated by electro hydraulic servo valve-control variable pump according to the surface roughness, load, cutting force, and thermal effects of worktable. The nonlinear hybrid controller developed was composed of a classical PID controller and a fuzzy controller based on self-adjusting modifying factor, and feed-forward compensation was added. A fuzzy switching mode was employed to avoid the undesirable disturbances caused by the switchover between the two control methods. By simulations and experiments on an electro-hydraulic servo test bench the feasibility of the control scheme was validated by comparison with a PID and a conventional fuzzy control. The research results show that the hybrid fuzzy controller exhibit good dynamic and steady quality, eliminate oil film lubrication failure and be broadly applied in high precision heavy machine tool.

Study of electro-hydraulic force servo control system based on fuzzy control

Because there is flexible load in electro-hydraulic force servo control system, and there is second-order differential section whose oscillation frequency is low in the numerator of the transfer function, the frequency range of the electro-hydraulic force servo control system is influenced badly and the system may oscillate easily even is instability. Aiming at this characteristic of electro-hydraulic force servo control system and the characteristic of the system whose open loop gain is small; the fuzzy control theory is applied to electro-hydraulic force servo control system this typical nonlinear system in order to improve the performance of the system. The models of the system with the fuzzy control theory and without it are built and the simulation and experiment study is done. Comparing the control result of the controller with the fuzzy control theory to the control result of the controller with the traditional PID, and from the results of simulation and experiment, we can find that the controller with the fuzzy control theory can not only increase the frequency range of system, but also improve the precision of system, and the controller can quicken the response ability of the system obviously.

Stiffness simulation analysis of rubber bush mountings

The finite element model of rubber bush mountings based on ANSYS is built up. And the value of the reduced radial stiffness is obtained directly by solving the model. The analysis of the experimental data, the theoretical calculation data and the simulation data indicates that the simulation model of the rubber bush which has been established is correct. Based on the simulation model, which has been parameterized, the radial stiffness characteristics of rubber bush are studied by analyzing the influence of the axial length and the Poissons ratio on the reduced radial stiffness. It is shown that the influence of the axial length on the reduced radial stiffness of short rubber bush is great and the influence of the Poissons ratio on the reduced radial stiffness of long rubber bush is great.

Model Identification and Control Method Study on Electro-Hydraulic Pressure Servo System

Mathematic model of electro-hydraulic pressure servo test bench was obtained based on xPC technique. In order to improve the tracking performance of the pressure servo system a new nonlinear hybrid controller was developed according to the mathematic model, which composed of a classical PID controller and a fuzzy controller based on self-adjusting modifying factor. And interpolation method was used in the modifying factor fuzzy number model; a fuzzy switching mode was employed to avoid the undesirable disturbances caused by the switchover between the two control methods. The hardware-in-the-loop simulation results show that the problems of steady-state error for fuzzy control and rapidity for PID control are solved, and the comprehensive performance of electrohydraulic pressure servo is enhanced when load rigidity and mass changed.