The Research On Some Key Techniques Of Long Stroke Nano-positioning System

With the progress of techniques in fields of IC manufacturing, ultra-precision machining, precision instrument and Biomedical Engineering, etc., requirement of positioning accuracy related to these apparatus is getting higher more and more. Nowadays, nano-positioning technique with long stroke plays an extremely important role in modern science and technology, and for years, it is the focus in precision engineering research. The studying aims of this paper are to develop an experiment system of long stroke nano-positioning stage based on macro-micro (dual) actuators and its calibration system, and then studying some key problems in positioning technique, such as positioning errors modeling, testing and analyzing to inner vibration of positioning system within full working range of the stage, dynamic system modeling on micro-macro positioning system and discussing of its feature.By comprehensive comparing, the structure of long stroke nano-positioning system and its calibration system is determined. Positioning system is consisted of macro stage, which are made of AC servo motor and ball-screw unit, and micro stage, which are made of PZT and flexible hinge respectively. A grating measurement with 10nm resolution is used for position feedback of entire loop of the system. Macro and micro positioning system (stage) are integrated with a PC as host computer and the VB6.0 as software. Single-frequency laser interferometer is used for errors measurement and accuracy evaluation of the positioning system. The system can realize the working parameters as 100mm working range, 10nm positioning resolution and 20mm/s moving velocity.For the study of errors modeling, reasons for producing positioning errors and its features are analyzed completely. Two kinds of errors, i.e. static and dynamic errors are determined according to the characters of time-varying and compensating method of the errors. Interpolation, curve fit and RBF neural network models are used as static errors model, while grey system model GM(1,1) is used as dynamic errors model. Theory analysis and simulation are carried out to these models. By comparing the static models above, it can be concluded that the improved (de-noised) RBF neural network model is an ideal one relatively. As to the strategies of modeling data de-noising in RBF network, the method of two dimensions optimizing to the parameters of radial basis function spread and network training goal is proved to be especially effective. In the dynamic errors modeling, system errors and random errors are treated as a whole in grey system model GM(1,1). The character of dynamic errors is explained in way of energy change by GM(1,1). The model has the merits of little modeling data, little computing time and fast errors compensating speed. So it is an effective method for dynamic errors compensation. For improving the model's precision, the method of using reformed background value is taken. It is proved by simulation and experiment that the model is of higher precision.There are two kinds of vibration affect to positioning accuracy. The first is external environment vibration and another is the inner vibration of positioning system. The later one is studied in this paper. Virtual instrument vibration testing system is developed based on the software of LabVIEW. Testing data for some fixed positions and moving path on working range of macro stage in servo state are analyzed and compared by means of Fourier transform and wavelet transform. Though same conclusions are obtained by two of the studying methods, but wavelet transform can analyze the dynamic features of each position of macro stage, and get more detailed, precise results. The effectiveness of this method is validated by the experiment of PID parameter regulating.For the study of dynamic properties of macro-micro positioning system, the integral dynamic model (macro-micro model) of macro stage and micro stage is established according to series relationship of them. Theoretical Study shows that there is a dynamic coupling between macro stage and micro stage, and step response shows that there is an opposite action on macro-micro positioning system with different system input (macro input and micro input) because of different acting position of the input. So, dynamic parameters of macro and micro stages should be arranged carefully based on particular application. Two kinds of arrangement are applied to dynamic model of the macro-micro stage. With the arrangement, simulating study on dynamic compensation positioning disturbed by white noise and sinusoid signal, continuous compensation positioning to the input of sinusoid signal with low and high frequencies. Simulating study proved the rightness of the macro-micro model, the possibility and practicability of macro-micro positioning. The studying results take great role in the design of macro-micro positioning system.In the end, corresponding experiments are carried out with the dual-actuators positioning system developed in this paper. First of all, the positioning errors in long stroke and micro stroke are calibrated and analyzed carefully. Then the experiments of static and dynamic errors compensating are conducted. At last, macro-micro positioning experiment is achieved and the experiment data are evaluated by international standard of ISO230-2. The correctness and effectiveness of the research in this paper are validated by all of these experiments.