The Research On Pneumatic Gravity Compensation And Vertical Movement Control Of Air Bearing Testbed

Nowadays astronautical technology is developing with a dramatic speed, andspacecrafts are designed to be more versatile and complicated. Air bearingsimulation test system is an important way to test spacecrafts in the ground beforelaunching them. This paper studies on vertical gravity compensation mechanism andmotion control method of Z direction, and it’s an important part of air bearingsimulation test system with six degrees of freedom.Firstly the principle of compensation of vertical gravity by air pressure andmotion control of vertical direction is discussed in this paper. Combined with therelevant contents of the gas thermodynamic, the driving model of gravitycompensation device is established. Then according to the model with someunknown parameters to identify, this paper proposes a method based on neuralnetwork to get the concrete number. Some important parameters of motion systemare also calculated to meet the demand of design.Secondly two different stages of pressure regulation are studied in this paper,namely compensation of static gravity and lock of a specific pressure. By combiningcoarse and fine adjustment, static gravity can be well compensated and the load canget the set position,which can be confirmed by simulation. At the stage of pressurelock, a method based on improved Smith predictive controller is proposed to keepthe air pressure exactly equal to the gravity of load. Compared with the commonPID regulation, this method is confirmed working well in conquering the effect ofdelay part by simulation. This paper comes up with a design using sensitivity indexas performance of system’s robust, and the robust performance under differentsensitivity is compared by simulation.Thirdly vertical movement control schemes are discussed in this paper. As theactuator is nozzle,of which output can only be discrete, thus constant input ismodulated into discrete output pulse series by PWPF(pulse width and frequencymodulation). Displacement control is divided into long distance control which usesoptimal time control and high precision control. As the load quality decreases in jetprocess, the MIT scheme is adopted in the vertical displacement of the adaptivecontrol combined with repetitive compensation control, and the simulation showsthis scheme is feasible.Finally, hardware and software of the system are designed in this paper. Sensors,signal processing card,embedded computer and wireless modules are used to construct the system. Some software work are also done as follow to run the system:the real time platform, two different kinds of RTX driver, different classes designedand described by UML, multithread scheme which is used to promote the controlprogram, and user interface developed by C++Builder. In the end the function of airpressure regulation is tested in the system.