Research On Pneumatic Rotation Position Servo Control Technology

Pneumatic technology has been widely used in industrial automation area because of its unique advantages. The actual requirements and technical impetus motivate the development of the pneumatic servo technology. However, due to its strong nonlinearities, it is difficult for a pneumatic servo system to achieve higher control precision. So far, most of the research work reported has been focused on the position control of the linear cylinder, and fewer researches on the position control of the rotary actuator were reported. In the fields of industrial automation and robot, there is a wide requirement for rotation position servo control. Therefore, it is of practical value to conduct study on the pneumatic rotation position servo control.Pneumatic rotary actuator is an actuating device of rotation motion used widely in pneumatic systems. However, its smaller stroke and larger friction torque make it more difficult to implement angular position servo control of high performance. At present, the positioning precision couldn't meet the practical requirement. In this paper, a pneumatic rotary actuator position servo system with proportional flow valves as the control devices is studied. The study is conducted in the following aspects: compensation method of the nonlinear characteristics, method of establishing linear model, control strategy and so on.System characteristics are investigated thoroughly through theoretical analysis and experiments. The influence of the nonlinear friction and the operating parameters, including positions of the operating points, magnitude of the payloads and the initial pressures in the two chambers, is studied first. Then, some particular phenomena such as stick-slip oscillation and displacement fluctuation around the desired position are analyzed.Corresponding to the nonlinear property of the proportional flow valve and the displacement fluctuation phenomenon of the system, two auxiliary control approaches are proposed. One is the compensation method of the valves' nonlinear property, and the other is the composite control scheme integrating position control mode with pressure difference auxiliary control mode. Using the nonlinear compensation method, the system characteristics can be improved and the control of the system can be facilitated. With the composite control scheme, the displacement fluctuation phenomenon can be avoided effectively and the positioning accuracy can be improved.To minimize the influence of the nonlinear friction torque, a method of establishing linearized mathematic model that can reveal the system behaviors more precisely is...