Structure Design And Speed Control Research Of Pneumatic Polishing Device

Large free-form surface workpieces are important part of industrial and defense equipments.They are widely used in cutting-edge industries such as ships,aerospace and automobiles,and the quality and precision of them play a vital role in the entire system.The application of mechanical polishing device to the surface polishing can greatly reduce the surface roughness.The rotational stability of polishing device's terminal actuator has an important influence on the processing quality.The thesis mainly focuses on the speed control research of the pneumatic vane motor,which is the terminal actuator of pneumatic polishing device.The main work in this thesis included:(1)In order to meet the requirement of polishing large free-form surfaces,a small and lightweight pneumatic polishing device with a stable polishing force mechanism and a flexible position adjustment mechanism was developed.After that,Establishing a test platform for the rotational speed characteristics research of the pneumatic vane motor.(2)In order to control the speed of pneumatic vane motors,it is considered to use the high speed on-off valve to adjust the pressure and flow of inlet chamber of pneumatic vane motor.By analyzing the structure and working principle of the motor,a periodic and discrete chamber volume model of pneumatic vane motor is established.And then using Fourier series to expanse it to obtain a continuous chamber volume model of vane pneumatic motor.Combining with a kinematics model of vane pneumatic motor and mathematical models of chamber flow and high speed on-off valve orifice flow,we can obtain a mathematical model of valve-controlled pneumatic vane motor speed control system.(3)Considering the actual working conditions of the terminal actuator of pneumatic polishing device,a speed controller based on PID algorithm is designed.For the constant speed and trajectory tracking control test of the pneumatic vane motor,the maximum error in steady state is 29 r/min(control speed is 1000 r/min)and 35 r/min(Sinusoidal frequency is 1/8 Hz).During the test,the external disturbance torque was applied to the shaft end of the pneumatic vane motor.It was found that the valve-controlled pneumatic vane motor system regulated by the PID controller was less resistant to external disturbances.Therefore,the sliding mode control algorithm is introduced and the sliding mode speed controller which is not based on the model is designed.The test shows that the controller is robust to external disturbances and can better cope with the strong nonlinearity of the valve-controlled pneumatic vane motor system.(4)Based on the established mathematical model of the valve-controlled pneumatic vane motor speed control system,a sliding mode speed controller based on model is designed.The constant speed and trajectory tracking control test of the blade air motor was carried out again,and the maximum error in steady state was found to be 20 r/min(control speed is 1000 r/min)and 25 r/min(Sinusoidal frequency is 1/8 Hz).That control algorithm greatly improves the stability and accuracy of the pneumatic vane motor speed control and helps to ensure the processing quality of the polishing device.