Neural network control—a case study

Original scientific paper Hydraulic simulators are extremely important in the flight control actuator system’s verification process. Flexible nozzle has a number of specifics, comparing to other flight controls, because the load cannot be described, classically, by the hinge moment. Additionally, classical hydraulic simulator, in which the cylinder simulates the load, is not sufficient for performing a complete simulation of the real load. Building a mechanical pendulum, to which a hydraulic cylinder acts, and that rests on two elastic supports, enables simulation of additional phenomena that exist in flexible nozzle, but not in other control surfaces. Force from impulse that exists in reality, and which is impossible to be generated by standard hydraulic simulator, can be realized through the pendulum. This paper demonstrates that a simulator can be designed through modelling of the elastic load using bond graph, without a precise elaboration of direction of forces in elastic structure, just by observing, on energy level, the input of force in flexible structure over the point in which actuator force acts. Simulator with hydraulic cylinder is convenient to be used when there is a need for considering the risk of self-oscillation of flexible joint and nozzle, i.e. for defining the so-called notch filter. Then, the hydraulic cylinder of load simulator can generate the oscillation, frequency and amplitude that match this dynamic case of flexible nozzle actuator’s load that is being reduced to its piston rod, without a risk of damaging the flexible structure that exists in the construction of a simulator with pendulum.

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Different modeling technologies of hydraulic load simulator for thrust vector control actuator

El trabajo de investigacion que se presenta en esta memoria ha tenido como objetivo avanzar en el conocimiento de guiados lubricados presurizados, tanto hidrostaticos, hidrodinamicos como en regimen hibrido. Se ha trabajado con fluidos convencionales y con fluidos magneticos, lograndose en ambos casos prestaciones mejoradas con respecto a soluciones pasivas convencionales, y una respuesta activa avanzada.En el desarrollo de lubricacion basada aceites minerales convencionales, fluidos Newtonianos, se ha realizado una herramienta de calculo con la que predecir el comportamiento de cojinetes radiales, axiales y guiados lineales; todo ello orientado a su uso durante la fase de diseno de maquinas herramienta. Los modelos se han validado mediante un nuevo banco de ensayos donde analizar los prototipos de cojinetes radiales. El nuevo banco de ensayos ha servido para aislar el comportamiento del cojinete radial a analizar con respecto al resto del sistema, efecto que en los bancos de ensayos clasicos limita su caracterizacion. Para finalizar con las soluciones de lubricacion mediante fluidos convencionales se ha desarrollado una valvula adaptativa en base a diafragmas flexibles; y por otro lado, una solucion de lubricacion autocompensada basada en conductos internos en el propio guiado. Estos desarrollos han sido tanto teoricos, en base a modelos de fluidodinamica, como experimentales, con sendos bancos de ensayos.El siguiente gran bloque de la investigacion presentada en esta memoria se orienta al uso de fluidos magneticos para la obtencion de lubricacion activa. Se ha trabajado con fluidos magnetoreologicos y ferrofluidos, donde tras realizar una actividad de sintesis para adquirir un conocimiento basico sobre su composicion, se ha realizado una caracterizacion experimental en profundidad de dos fluidos comerciales; los dos fluidos que se han utilizado durante la investigacion. Se ha desarrollado un modelo teorico apoyado con su respectivo banco de ensayos para el estudio de cojinetes radiales, tanto hidrodinamicos como hidrostaticos. Para estos ultimos se han desarrollado tambien valvulas magnetoreologicas con las que controlar el caudal de alimentacion. En esta investigacion se ha comprobado la mejora de la linealidad en la lubricacion hidrodinamica, asi como la rigidez infinita con las valvulas magnetoreologicas controladas en lazo cerrado. Finalmente se ha desarrollado una junta de estanqueidad basada en fluidos magneticos, donde los ferrofluidos han demostrado un comportamiento compatible con los requerimientos de cabezales de maquinas herramienta de precision.

Guiados lubricados activos para máquinas herramienta de precisión basados en fluidos magnéticos y válvulas adaptativas

An active preview control strategy is presented to suppress the vibration of hydrostatic guideway under dynamic machining force. A state space model of closed hydrostatic guideway system is built, and the predictability of machining force during cutting process is analyzed. Numerical simulation model of preview compensation control systems is established. The displacements of slide carriage are compared under the condition of no control, optimal control and active preview control. The variations of oil recess pressure are observed when using the two latter control methods. The results show that maximum displacement of slide carriage by using active preview control method reduces 73.3% compared to the optimal control method, and reduces 94.1% compared to the method without any control. Besides, the compliance of the oil recess pressure to machining force is improved by 23%. Finally, an experiment evaluating the displacement of slide carriage and variation of oil recess pressure is carried out and the numerical predictions agree with the experimental results. It is effective to control machining vibration of hydrostatic guideway by using active preview control strategy.

Preview Control of Hydrostatic Guideway for Ultraprecision CNC Machine Tools

Proportional directional control valves (PDCVs) with large flow and high control accuracy in electro-hydraulic servo systems(EHSS) are usually expensive, at the same time, the demand for energy-saving in EHSS is increasing rapidly. In order to solve the cost and achieve energy-saving, an energy-saving position control strategy for EHSS with parallel dual valves is designed. First, the mathematical model of the system is established. Secondly, to obtain a high position tracking performance, the basic controller of the system was designed by back-stepping control method to solve the virtual control law. Then, a control distributor was designed to obtain the smooth switching strategy between different modes. Next, the main approach to energy-saving was to decrease the supply pressure and supply flow as much as possible. A nonlinear set of laws are derived to vary the supply pressure according to the required forces during position tracking, while a servo motor controller was designed for the fixed displacement pump to vary supply flow according to the required flow. Experiment results show that, the cheap parallel dual-parallel PDCVs with common performance can achieve high position tracking performance of EHSS to replace an expensive high performance PDCV, and the effect of energy-saving is obvious.

An Energy-saving Position Control Strategy for Electro-hydraulic Servo System with Parallel Dual Valves

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.

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

The low speed performance is the most important indicators of the continuous rotary electro-hydraulic servo motor. The factors which influence the low speed performance consist of nonlinear characteristics such as structural pulsation, friction and leakage characteristic, oil distributing technique, pressure pulsation, servo valve's distinguish ability and so on. In order to improve the low speed performance, the key technique of servo motor was studied. It is analyzed that velocity pulsation and torque pulsation was eliminated in the structure, the structure of blade and oil distributing plate was optimized for improving leakage and oil distributing characteristic, and friction torque was compensated in order to reducing the pulsation. These results can resolve the basic technique problem of the low speed performance and lay foundation for studying electro-hydraulic servo motor.

Research on the key technique of continuous rotary electro-hydraulic servo motor

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.

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

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.

Control Method of Heavy Hydrostatic Thrust Bearing

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.

Jianying Li

Papers

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

Research on the key technique of continuous rotary electro-hydraulic servo motor

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

Control Method of Heavy Hydrostatic Thrust Bearing

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