Experimental Determination of the Open Loop Frequency Response Function of a Hydraulic Servo-Cylinder.

It is known that direct experimental plotting of the frequency response of a servo-mechanism having a zero static error is rather difficult due to the instability of the system when the feedback link is opened. A method is proposed which permits the plot of the open-loop frequency response to be derived from the closed-loop one, which is in turn given by measurements of the closed-loop gain and phase angle. This method is based on the property of the inverse transfer locus which is such that the inverse transfer locus of the open and of the closed loops can be made identical with a suitable translation and similarity of the coordinates. It is then very easy to shift from one plot to the other and therefore from one frequency response to the other one. 10 refs.