Abstract
Linearized analysis is used to design the feedback networks of a high-pressure pneumatic servomechanism in order to meet a performance specification. The effect of torque motor dynamics is pointed out and then digital computation of the complete non-linear equations is used to predict the effect of the following important parameters: saturation, inertia load, stiction and coulomb friction, valve laps and leakage. Others considered briefly are: velocity feedback limiting, position error limiting, the use of a cascade lead network to improve the torque motor response and the effect of different inlet to exhaust port width ratios.
The equations are non-dimensionalized, a load factor α being first defined which is the equivalent of a parameter found to be useful in hydraulic servo design. A saturation ratio is later defined which includes α, and quantifies the ratio of electrical pneumatic gain.
The major part of the results are for step inputs, but the generally poor shape of the response to sinusoidal inputs is examined in some detail. Experiments were conducted to check the validity of the equations, and it is shown that high loop gains can be achieved with adequate stability. It is also shown that the sinewave response can be improved by the correct design of the shaping networks and by a suitable choice of α.
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