Modelling and Control of Pneumatic Vane Motors

Abstract

There is a broad area of applications where pneumatic vane motors offer unique advantages: high power-to-weight ratio, indifference to overload and stall, cool operation, indifference to dirty or explosive atmospheres. Typically, they are chosen from manufacturers' diagrams such that the torque needed is provided by the motor at the required speed. If necessary, a nozzle is used to reduce speed. Some guidelines have been published about how to design these motors and how to use them in a position control loop, e.g. for robotic applications. This study derives a mathematical model suited to time-domain simulation of the motor, both in an open-loop or closed-loop system. Using geometrical data and the theory of thermodynamic processes the model of an ideal motor is given. In a second step leakage paths and friction are added to describe the behaviour of real motors. This model is implemented in the modelling language Modelica with the help of the domain library PneuLib and used to estimate values for the conductance of the nozzles or the friction terms. Comparisons between the model and measurements are given, both for open-loop and closed-loop operation.