Control system for pneumatic actuators

Abstract

A method and apparatus for controlling the state of a pneumatic actuator having a valve that connects the actuator to a supply pressure and a valve that connects the actuator to an exhaust pressure. The method involves closing the supply pressure and exhaust pressure valves, determining the current state of the pneumatic actuator, and then determining the difference between the current state and a desired state. The appropriate pressure valve to be opened and the period to be opened is then calculated based on pre-determined calibration data for the actuator which permits the end state of the actuator to be predicted. The appropriate valve is then opened for the calculated period to adjust the actuator to the desired state. The process is then repeated until the current state of the actuator is the desired state. A controller unit that uses the above method is also disclosed. Equipment incorporating the method and apparatus of the present invention enjoys significantly reduced manufacturing and installation costs. The size of the components and the assembly time for the equipment is also reduced. The design allows for flexibility with regard to various pneumatic actuator types. The system can handle different sources of state feedback such as pressure or position without major changes to hardware. In addition, feedback of the pneumatic actuator state allows for diagnosis of the system with timely scheduling of necessary maintenance. Deterioration of pneumatic actuators is detected and can be compensated for to maintain full operation of the system.