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. A method for nulling quadrature error in a vibrating gyroscope, having a dither mass and a sensing element vibrating about a dither axis Z and having an output axis Y, the steps of the method comprising:
applying vibration driving forces to vibrate the dithered mass and sensing element, which inherently causes an oscillation about output axis Y that creates quadrature error; and
applying a sinusoidal force to the dithered mass creating movement of the dithered mass about the output axis Y that cancels the quadrature error.
2. The method of claim 1 wherein the sinusoidal force is applied by dc signals.
3. The method of claim 2 wherein the dc signals are a plus or minus voltage applied to top or bottom electrodes adjacent to the dither mass.
4. The method of claim 3 wherein the top or bottom electrodes are the pickoff electrodes for detecting the dither mass motion.
5. The method of claim 1 wherein the applying of a sinusoidal force comprises:
applying a plus or minus dc control voltage to pickoff electrodes adjacent to the dither mass.
6. A method for nulling quadrature error in a vibrating gyroscope having a dither mass within an X-Y plane mounted for rotational movement about a Z axis, and a proof mass mounted within the dither mass for rotational movement about the Y axis of the X-Y plane, the steps of the method comprising:
applying vibration driving signals to the dither mass to vibrate the dither mass and the proof mass at a combined resonant frequency about the Z axis; and
applying a sinusoidal force to the dither mass which reduces the quadrature error.
7. The method of claim 6 wherein the sinusoidal force is applied by dc signals.
8. The method of claim 6 wherein applying the sinusoidal force comprises:
applying a plus or minus dc voltage to electrodes adjacent to the proof mass.
9. The method of claim 6 wherein the dc signals are applied to top or bottom electrodes adjacent to the dither mass at fixed locations.
10. The method of claim 6 wherein the top or bottom electrodes are the pickoff electrodes for detecting the dither mass motion.