Research On Adaptive Control Of Pneumatic Gravity Compensation System

Gravity compensation system can simulate the microgravity environment on the ground and provide technical support for aircrafts before on-orbit flight.Most of the existing gravity compensation methods have the defects of high cost,harsh experimental environment large area and short simulation time.In this study,a gravity compensation device based on static pressure air-floating frictionless cylinder is designed and theoretical and experimental studies are carried out based on it.The device has the advantages of low cost,low requirements on the experimental environment,small area and unlimited simulation time,it can meet the requirements of simulating microgravity environment on the ground.Firstly,the selection of the main components of the pneumatic gravity compensation prototype is carried out and the prototype construction process are analyzed,and the loading implementation of the gravity compensation system is described.Then a second-order pressure differential equation which can roughly reflect the characteristics of the system is established,and the factors affecting the characteristics of the system are analyzed by simulation.Secondly,an improved model free adaptive controller(IMFAC)is designed,which adjusts the pseudo gradient estimation by introducing the pseudo gradient estimation error to accelerate the pseudo gradient identification process to form an advanced control scheme,which makes the pseudo gradient value identification more accurate.The simulation results demonstrate the effectiveness of the IMFAC for the pneumatic gravity compensation system.Finally,the static and dynamic characteristics of the PID controller,traditional model free adaptive controller(MFAC)and IMFAC are analyzed by several groups of experiments.The experimental results show that step response at 0.2MPa steady state error is less than 200Pa under the IMFAC,the average error of sinusoidal tracking(amplitude 0.12MPa,frequency 0.04Hz)is about 1.94 KPa,which phase lag is reduced by 48.5%compared with the PID controller.After the system enters the steady state at 0.3MPa,the pressure error can remain within 300Pa when the pressure of the air source is suddenly reduced,and the static and dynamic gravity compensation of the pneumatic gravity compensation system is realized.