Reduction of errors in vibratory gyroscopes by double modulation

Vibratory drive, vibratory output instruments for sensing angular rates, such as tuning forks, potentially offer certain advantages over conventional gyroscopes. The theoretical performance of these devices has not been realized experimentally because of zero-rate errors attributed to mass unbalance, driving force unbalance and other imperfections. By separating the driving and sensing frequencies through a process called double modulation, obtained through an additional rotation or vibration of the basic sensing element, zero-rate errors may be diminished. Theoretical and experimental evidence in support of the double modulation concept is presented. A tuning-fork type of instrument has been used in the initial experiments and a substantial improvement over the performance of the same instrument without double modulation has been realized.