Research On The Forming Method And Control Technology Of Elliptical Track

Based on the movement forming methods for elliptical inner surface, this paper focuses on carrying out control technology research on elliptical shaft center orbit. The paper builds the hydraulic control system based on new type hydrostatic bearing and servo throttle valve. It also researches the kinetic property and controlling characteristics of new type bearing-rotor system and new type servo throttle valve systems. Control technology and methods of elliptical shaft center orbit are studied. This study lays a theoretical foundation for realization of new machining methods for elliptical inner surface.The basic theoretical studies are made on movement forming methods for elliptical inner surface, and the implementation scheme and forming principle are clarified in detail. Necessary and sufficient conditions for forming elliptic tool nose orbit, under the condition that multiple shaft center orbits and the tool nose’s rotation orbit take synchronous forward synthesis and synchronous backward synthesis, are studied. The influence of initial phase angle of the tool nose on the formation of elliptic tool nose orbit has also been investigated. Characteristics and control equations of elliptic tool nose orbit under the conditions of multiple shaft center orbits and different initial phase angles of the tool nose are given.In order to meet the space requirement of elliptical shaft center orbit, the hydrostatic bearing whose inner face is an elliptic cylindrical surface is studied. The paper provides the fundamental equations(such as Reynolds equation and flow continuity equation) and their computing methods. The concept of dynamic pressure ratio is put forward to measure the hydrodynamic effect on bearing land, and the dynamic pressure ratio is computed when shaft center orbit is a small elliptical track in the new type hydrostatic bearing. Using partial derivative method, the paper studies the impacts of radius clearance and ovality on new hydrostatic bearing’s static and dynamic performance parameters.The hydraulic control system is built based on special structure of the new nest-pocket bearing and servo throttle valve. A new-type servo throttle is designed based on piezoelectric ceramics, which can make up the disadvantage of low frequency response for ordinary electro-hydraulic servo valve. The flow formula of new servo throttle is obtained using simulation and fitting process. Output displacement of piezoelectric ceramics is predicted utilizing BP neural network(based on bayesian regular algorithms). The pressure value on bearing land is linearly assigned, and recess pressure computational formula of hydrostatic recess and control recess are obtained through combining flow equilibrium equation and Gaussian-Legendre integral formula. The quantitative relationship between expected shaft movement orbit and the control voltage of new type servo throttle is studied.The model of elliptical shaft center revolution orbit is built based on the optimal control theory. The bearing-rotor system kinetic model is built, and position coordinates of shaft center are taken as optimized state variable, external force(here, it is bearing force) taken as control variable, deviation between optimized shaft center coordinates and expected shaft center coordinates taken as performance index. With the solution of legendre zeros and approximation of state variable and control variable, the optimal control problem is transformed into general nonlinear programming problem using pseudo-spectral method, and at last, optimum control parameters of shaft center orbit are obtained using sequence quadratic programming method. The simulation results indicate that difference between optimized shaft center coordinates and expected shaft center coordinates is very small, and the Gaussian pseudo-spectral method has a advantage of high precision and can be used in optimum controlling of shaft center movement orbit.The open-loop control simulation is made on the shaft center movement orbit. Using the quantitative relationship between expected shaft movement orbit and control voltage of new type servo throttle valve, the open-loop control simulation orbit is obtain. The shaft center’s kinetic parameters are calculated when the shaft center’s coordinate is in the expected small ellipse orbit, and active control parameters for throttle valve in hydraulic control system are also solved. Then using the active control parameters, the open-loop control simulation orbits of shaft center are obtained with Euler’s method iteration. The open loop control orbits are got when the shaft center orbits are different ovality ellipses, and the open loop control simulation of shaft center is also made when there is the transient disturbance force. The simulation results indicate that open-loop control method can control the shaft center and realize different ovality elliptical shaft center orbits, and keeps good robustness when the system is disturbed.Dynamics modeling is taken on piezoelectric servo valve and the whole system seperately. The system transferring function is obtained, and feedforward decoupling is taken. Based on periodical characteristic of expected orbit of shaft center, the repetition control algorithm is used as closed-loop control method. Under the simulink environment of MATLAB, the whole system is modeled, and the closed-loop control simulation of the system is made using designed repetition controller. Simulation results show repetitive control algorithm has high validity on controlling shaft center to track expected orbit.