| With the increasing proportion of the noncircular parts in aviation, space navigation, automobiles, machine tools, light industry and some other manufacturing industries, in order to achieve desired performance requirements, the maching precision must be increased.On one hand, micro-feed mechanism which is usually used for high-precision, non-circular cross section cutting can be realized by means of elastic deformation, mechanical profile, low eccentric driving shafts or eccentric cutter arbor. However, these methods can barely be applied widely in reality because of mechanism complexity, difficulties of regulation, low precision, and high cost. While feed mechanism with linear motor or motor satisfies the requirement of machinery high frequency response, long process, and high precision, the design of the control system is too complex, and costs too much. It is also difficult to apply widespeadly in common enterprises. So, the core issue is to develop a tool feed servo mechanism with high frequency response, high resolution, high precision, and long process.On the other hand, the noncircular surface precision machining system, which is driven by Giant Magnetostrictive Actuator(GMA) made up of represented by Terfenol-D of the rare earth-iron giant magnetostrictive material (GMM), has simple and compact structure, high repetition accuracy, no gap, good rigidity, transmission inertia, good job stability and other advantages. It not only can achieve the automatic control of high-precision machining of no phantom, and overcome the shortcomings of traditional hard copying method, but also can overcome the shortcomings of low accuracy by using electromagnetic force-driven lathe tool feed method, and suit the processing of complex line or hard matrix better.However, because of hysteretic nonlinearity of GMM, the design and appliance of GMA are related to an overlap of nonlinear vibration, magneto elasto dynamics, precision machining, automatic control and many other subjects. The problems of micromagnetic machine coupling and the control of non-circular precision machining process synchronous hysteretic compensated, and low precision of control displacement of GMA which is caused by fever, energy consumption, hinder the appliance of GMA seriously. So, the study of GMA micro-feed servo in numerical control turning system becomes very important.In this paper, the model, controlling method, and virtual visualization of expect part and turning result is studied. These are the main work as follows.1. Through the study of the generation of processing data file of complex piston and numerical control turning system, the unified expression of complex surface machining is established by using NURBS curve-fitting method, and the "ladder" problem which existed in the interpolation between two points with the method three spline difference algorithm, is solved. In allusion to the end effect of fitting curve, the method of constructing virtual control point at both ends is proposed, and the fitting accuracy of the curve is improved.2. Based on J-A hysteresis model, according to piezomagnetic theory, considering of the influence of temperature and the geometric nonlinearity of the pre-load spring, the dynamics model of GMA turning system is established. The dynamic characteristics of the GMA turning system is studied in detail by using simulink tool, and the influence of different parameters is studied and compared. Under different parameters, the concept of optimal excitation amplitude, when the displacement of the system output achieve maximum, is proposed.3. Based on the experiment, when GMA is at the linear working area, considering the ideal hysteretic model, according to the Taylor approximation formula, a dynamic model of GMA turning system which only consider the geometric nonlinearity is established. According to the characteristics of the established model and the actual working conditions, the control of the GMA turning system is realized by using the sliding mode variable structure which is based on exact feedback linearization, and the effectiveness of the method for different desired input by simulation is verified.4. When GMA is at the non-linear working area with inverse system, in order to cancel the hysteretic nonlinear of GMA turning system, the control method of a combination of feedforward neural network inverse compensation and adaptive fuzzy sliding mode variable structure control(RDFSC) is studied. PID type sliding surface is designed. The fuzzy control is introduced into the designing of sliding mode variable structure controller to reduce the chattering as well. One hand, there existed the shortcomings of large control fluctuations at the initial stage. On the other hand, because fuzzy rules can automatically update in accordance with the current state of the operation, which make the sytem more intelligent.5. Due to the larger excessive error of RDFSC in the initial stage, the control method of a combination of feedforward neural network inverse compensation and mult-adaptive control(RMDC)is proposd. Let "time" as switch, which determine the stable time of DFSC. Before DFSC reaching the stability, feedback control adopted PID control strategy, at the same time DFSC work in normal, but don’t participate in control. When DFSC achieve stability, DFSC is on work. The simulation results show that RMDC make system has good steady precision and good excessive process.6. In order to eliminate hysteretic and double frequency, based on the model of the equivalent substitution and state feedback, the fuzzy adaptive control method is studied. The validity of the control method is verified by theory and the simulation. This method extends the GMA working interval, which make GMA the more simple and compact.7. Through the secondary development of CAD, Users can perfectly show the cross-sectional contours and the longitudinal contours of the workpiece in an accuracy-setting way. The heads machining moving process is shown simply and clearly. At the same time, the three-dimensional solid model is displaced. The visualization of numerical control machining system can shorten the time of developing new product with low cost and no danger, can predict the error, and examine the effectiveness of the controlling method as well.8. By CAD interface of external development system, using VS2005 as a development platform, the virtual displaying of the processing parts and processing results is realized. The workpiece cross-section profile, longitudinal profile of workpiece in the form of setting precision can be perfect shown through the virtual machining system. Through the choice of different control algorithms,3 d entity model of processing is image displayed. |
PDF Full Text Request