TRACKING PHASE LOCKED OSCILLATOR
Original Publication Date: 1980-Aug-01
Included in the Prior Art Database: 2001-Oct-10
A vibrating bar rate gyro contains a bar of a square cross section and length many times larger than its width. It is suspended at its nodes and caused to vibrate at its resonant frequency in a free- free mode in a plane parallel to one of the longitudinal faces. When rotated about its longitudinal axis, a vibration in a plane orthogonal to the driven plane, but at substantially the same frequency, is induced. The magnitude of the induced motion is a measure of the rotation rate. The phase of the induced motion is at 90 degrees to the driven motion. In order for the best sensitivity and accuracy to be obtained, the bar must be driven very accurately at its free resonance frequency, which varies with changes in the environment. The detection of the induced motion, which can be extremely small compared with the driven motion, must be precisely at 90 degrees in phase to the driven motion. The condition of precise oscillation at the free resonant frequency occurs only when the signal from the driven motion sensor (described below) is precisely at 90 degrees to the driving signal applied to the driving transducer, so that the signal suffers a full 360 degrees phase shift through the entire feedback loop.