Quadrature compensation technique for vibrating gyroscopes
View Patent ↗Quadrature error occurs in vibrating gyroscopes because of manufacturing flaws that permit the sensing element (proof mass) to oscillate about an axis that is not orthogonal to the output axis. This creates an oscillation about the output axis that has a component of the sensing element's vibration acceleration. This output axis oscillation, which is in phase with the driven acceleration of the sensing element, is called quadrature torque since it is ninety degrees out of phase with the angular rate induced acceleration. In order to eliminate this output axis oscillation, the present invention generates sinusoidal forces on the dither mass by applying dc voltages on the dither mass pickoff electrodes. These forces create a counter dither motion about the output axis that cancels the output axis oscillation generated by the non-orthogonal dither axis.
1. An apparatus for nulling quadrature in a vibrating gyroscope having a dither mass and a proof mass, the apparatus comprising:
the dither mass mounted for movement about a dither axis Z;
the proof mass mounted to the dither mass for movement with the dither mass and for movement about an output axis Y, the dither mass movement causing oscillation about output axis Y that creates quadrature error; and
a source of sinusoidal force applied to the dither mass for moving the dither mass in a manner that cancels the quadrature error.
2. The apparatus of claim 1 wherein the source of sinusoidal force comprises dc voltages.
3. The apparatus of claim 2 wherein the dc voltages comprise plus or minus dc voltages, each applied to electrodes close to the dither mass.
4. The method of claim 2 wherein the plus or minus dc voltage is applied to electrodes at the top or bottom sides of the dither mass.
5. An apparatus for compensating for the quadrature error in a vibrating gyroscope, comprising:
a dither mass flexurally mounted within a frame for vibration;
a proof mass mounted to said dither mass by a flexure for oscillating at a predetermined frequency; and
a source of sinusoidal force applied to the dither mass for causing movement that reduces or cancels the quadrature error.
6. The apparatus of claim 5 wherein the source of sinusoidal force comprises plus or minus dc voltages.
7. The apparatus of claim 6 further comprising electrodes adjacent to the dither mass.
8. The apparatus of claim 7 wherein the plus or minus dc voltages are applied to the electrodes.
9. The apparatus of claim 8 wherein the electrodes also create dither mass vibration.