Study On The Control Methods And Dynamic Properties Of Pneumatic Proportional Position System

Pneumatic systems have been widely used in industrial automation fields, such as chemical industry, medicine, textile, micro-electrics and bioengineering, for its advantages of simplicity in structure, anti-pollution, high performance to cost, easy maintenance and anti-jamming. With the development of the pneumatic proportional technology, pneumatic system control is extended from logical control to proportional/servo control area. However, pneumatic systems have some inherent disadvantages as nonlinearity, low stiffness, low damping ratio and low natural frequency, it is difficult to obtain satisfied control performance, and thus its uses in industry area are limited. In this paper, the study on improving the control precision for the pneumatic proportional system is presented. The system friction nonlinear compensation and intelligent control method are developed based on the study of its friction and dynamic characteristics.In this paper, the features and development of pneumatic proportional system are summarized, the buffer positioning technology in pneumatic system is analyzed, also the research and application of intelligent control technology in this domain is expounded. Based on the study on working performance and features of the system, the friction mechanism is developed, the friction is overcome by adding high frequency and low amplitude chatter signals to the system, the fuzzy neural network controller is presented according to its nonlinear, which achieves good precision for the system.Two mathematical modeling methods on pneumatic proportional system are presented. One method is called mechanism modeling, which contains the establishment of nonlinear mathematical model of the system through analyzing the balance of power and pressure - flow characteristics of the cylinder and the proportional direction valve, a more accurate mathematical model is attained according to the system identification in order to provide the basis for further research. The other method is based on the graphical modeling of physical model. Pneumatic proportional system model is established by using the modeling and simulation software AMESim, in this way, the details of the system can be considered at utmost, and more accurate system model can be gained. The graphical modeling is based on the joint simulation platform of AMESim and Matlab / Simulink. The outstanding performance of AMESim is its simulation on fluid mechanism, but MATLAB / Simulink has powerful numerical processing power. The two outstanding professional simulation tools are used together in this study and a perfect complementary effect will be gained. Therefore, all studies in this paper are based on the graphical modeling of physical model.Theoretical analysis on friction compensation based on valve-controlled cylinder system is presented. To overcome the system steady-state error and scrawl under low velocity caused by friction, we usually improve the machining accuracy and lubricating of the moving parts to reduce the system friction. However, in pneumatic proportional system, the nonlinear friction influence on the motion performance can be reduced by improving the mechanical structure of the cylinder, or using new high precision cylinders, but these methods will lead to high cost, the nonlinear friction can not eliminated thoroughly, and the system positioning precision and low-velocity tracking precision can not be improved finally. So that, it is necessary to use adding chatter signal method with friction compensation to overcome the dead area of the pneumatic proportional valve, which improves the sensitivity of the system and reflects the dynamic response characteristics.Based on the non-linearization of the system, intelligent control method on non-linearization of pneumatic system is presented. Fuzzy control and neural network control methods are analyzed and simulated separately. Fuzzy control can follow the fuzzy logic methods of human being and allows the existence of the non-precious numerical type. But the determinations of the fuzzy rules depend on the experience and the expression of operators, therefore, the depth of the understanding of the problem and comprehensive capacity of the operators will directly affect the system performance . Neural network can adapt to the external environment and other factors gradually by the aid of variability of its structures. Besides, it can gain the causal relation between the research objects from less accurate input / output description, then solve the problems.To reduce the dependence on prior knowledge of the control system, and improve the learning ability of the control system to enhance the adaptability to the change of working conditions, the nonlinear of valve-controlled cylinder, time-varying uncertainty, neural network technology or FNN technology can be used to solve these problems. Therefore, FNN control method is presented. By introducing neural network technology on the basis of fuzzy controller, using the learning function of neural network and fuzzy logic, the proportional valve-controlled cylinder system performance and adaptability are improved. The simulation results show that, the fuzzy-neural network controller designed for the system can overcome the outside load disturbance on the system well, and greatly enhance the robustness of the system.Finally, the self-learning function of the fuzzy-neural networks and compensation methods of adding chatter signal to the system are applied to the pneumatic system. The dead area compensation experimental of the proportional valve is presented. On the basis of theoretical analysis for high-order curve, the method which can achieve the tracking trajectory of pneumatic proportional valve-controlled cylinder position control system by using the high-order curve as the ideal curve is put forward. The tracking trajectory control of the pneumatic proportional system is realized according to setting up the control procedures and control interface of a two freedom pneumatic proportional system. the positioning precision of one freedom system is within±0.100mm,and the continuous tracking trajectory control precision of two freedom system is within±0.263mm,it is suitable for replacing some expensive servo system.