The pneumatic actuator and valve system is used extensively in a wide variety of applications and yet it has received little attention in comparison with that given to the similar oil hydraulic system. Several analysies have been attempted using linearisation techniques but this is of little use in the majority of open-loop systems where variables change over a wide range. The full non-linear equations are developed for the pneumatic actuator and valve system taking into account the fact that real control valves do not behave as ideal nozzles. The equations are programmed for a digital computer using two specialised continuous system simulation languages. Extensions to the theory are presented which permit the development of the model for simulation of a pneumatic rotary actuator and actuator cushioning. Experimental work has been carried out to determine the dynamic characteristics of a real system and measurements have been made of seal friction in the actuator. Seal friction is shown to be a very important factor in determining the dynamic characteristics and empirical equations are developed which are used to simulate this. Extensive results are presented which have been obtained from the computer simulations and comparisons of experimental and simulated results show that the accuracy of the simulation is good but depends to a large extent on the simulation of the friction. The work on seal fraction is developed with the use of a PDP8/E digital computer which has been used for on-line data acquisition and processing. A range of test results obtained with this computer is presented and the results are correlated using a least squares curve fitting technique.
|Date of Award||1974|