Modeling And Control Of A Two-dimensional Ultra-precision Positioning Platform Driven By Pneumatic Bellows

Ultra-precision positioning technology refers to the precise positioning of sub-micron or even nanoscale,which is widely used in instrumentation,mechanical and electronic engineering,measurement and control technology,semiconductor manufacturing and other fields.Ultra-precision positioning devices usually use cylinders,voice coil motors,piezoelectric ceramics and hydraulic motors as drivers,but these commonly used components have disadvantages of low precision and high cost.Therefore,finding a new actuator has become the focus of current research.In this paper,the pneumatic bellows are selected as the actuator and a two-dimensional ultra-precision positioning platform is built.The air float mechanism of the working platform is composed of enclosed rectangular air float guide and air float block.The air float guide is used as the supporting part to ensure the stability of the working process of the platform.The bellows produce elastic deformation during the aeration process,and cooperate with the air slider to drive the load movement.The grating ruler is used to collect the displacement signal,preprocess the information,and then transmit it to the core controller MCU.The MCU sends feedback control signal to the electric pressure proportional valve in real time according to the displacement situation,so as to adjust the valve opening area and further control the gas mass flow into the bellow tube cavity.According to the established platform,the corresponding mathematical model is established,and the high-precision control algorithm is designed to ensure the positioning effect of the system.Through simulation,the effectiveness of the control scheme is verified.The first chapter introduces the concept of ultra-precision positioning technology and the development of ultra-precision positioning platform.Scholars at home and abroad have established one-dimensional or multidimensional positioning systems with different driving elements and applied them to different occasions,achieving good positioning results.Through the background investigation,the main work content of this paper is given.The second chapter introduces the design scheme of the ultra-precision positioning platform driven by bellows.The first part is the structural design of the ultra-precision positioning platform,which is a "ten" shape structure built by two "U" bellows.The compressed gas is provided by a small air source,and the pressure can be maintained at0.4Mpa after passing the pressure regulating valve filter.The displacement signal of the system is detected by the grating ruler,and the electrical pressure proportional valve is used to control the gas mass flow into the bellows chamber.Then,the working principle of the platform is explained.Since there is no coupling between the two degrees of freedom,the platform can move independently without affecting each other.In the third section,the hardware components of the platform are introduced in detail.Finally,the LABVIEW upper computer system is introduced,and the upper computer operation interface of the raster ruler encoder is given.The third chapter is the establishment of the model of the ultra-precision positioning platform driven by bellows.Firstly,the nonlinear characteristics of the pneumatic bellows are analyzed and the corresponding model curves are drawn.Hysteresis and creep are two common nonlinear phenomena,which can be regarded as unknown nonlinear functions in actual control.The extended state observer or neural network is used to approximate them.Then,according to Newton’s second law,the dynamic equation of bellows actuator,gas mass flow equation and electric pressure proportional valve are derived one by one.Finally,the mathematical model of the whole system is established according to the above analysis.The fourth chapter is the control algorithm design based on nonlinear extended state observer.Firstly,the ADRC algorithm is introduced,which is divided into two parts: the principle of ADRC algorithm and the concept of extended state observer.Then the nonlinear extended state observer and dynamic plane controller are designed according to the mathematical model of bellow servo system and all signals of the closed-loop system are semi-globally uniformly terminating bounded on the basis of Lyapunov function.The last section is simulation verification and analysis,which are respectively acquisition of output displacement data of bellows actuator and tracking test of reference signal.The fifth chapter is the design of high precision adaptive neural network control scheme.Firstly,the adaptive neural network is introduced and its topology is given.Then the mathematical model of the system is rewritten,and then the neural network state observer and the neural network dynamic plane controller are designed.The stability of the system is proved by selecting the appropriate Lyapunov function.Finally,simulation results show the effectiveness of the proposed algorithm.