Inertial measurement system and method with sensor bias cancellation
View Patent ↗Inertial measurement system and method in which a base is rotated about an input axis in accordance with a rotation to be measured, rotation about the input axis is sensed with one or more angular rate sensors, fixed bias offset is cancelled by dithering the sensors about an axis perpendicular to their sensing axes to vary the orientation of the sensing axes relative to the base in an oscillatory manner, and signals from the sensors are demodulated at the dithering frequency.
1. An inertial measurement method comprising the steps of: rotating a base about an input axis in accordance with a rotation to be measured, sensing rotation about the input axis with an angular rate sensor having a sensing axis, dithering the sensor about an axis perpendicular to the sensing axis to vary the orientation of the sensing axis relative to the base in an oscillatory manner at a modulation frequency, and demodulating signals from the sensor at the modulation frequency.
2. The method of claim 1 wherein the modulation frequency is on the order of a few Hertz to hundreds of Hertz, and the amplitude of the dithering is on the order of several milliradians to several degrees.
3. The method of claim 1 wherein the modulation frequency is on the order of 20–500 Hz, and the amplitude of the dithering is on the order of 2–50 milliradians.
4. The method of claim 1 including the step of demodulating signals from the sensor at twice the modulation frequency.
5. An inertial measurement method comprising the steps of: rotating a base about an input axis in accordance with a rotation to be measured, sensing rotation about the input axis with a pair of angular rate sensors having a sensing axes in a common plane, dithering the sensor about an axis perpendicular to the sensing axes to vary the orientation of the sensing axes relative to the base in an oscillatory manner at a modulation frequency, and demodulating signals from the sensors at the modulation frequency.
6. The method of claim 5 wherein the sensing axes are perpendicular to each other.
7. The method of claim 5 wherein one of the sensing axes is dithered about the input axis.
8. The method of claim 5 wherein the modulation frequency is on the order of a few Hertz to hundreds of Hertz, and the amplitude of the dithering is on the order of several milliradians to several degrees.
9. The method of claim 5 wherein the modulation frequency is on the order of 20–500 Hz, and the amplitude of the dithering is on the order of 2–50 milliradians.
10. An inertial measurement system, comprising a base which rotates about an input axis in accordance with a rotation to be measured, an angular rate sensor carried by the base responsive to rotation about a sensing axis, a modulator for dithering the sensor about an axis perpendicular to the sensing axis to vary the orientation of the sensing axis relative to the base in an oscillatory manner at a modulation frequency, and means for demodulating signals from the sensor at the modulation frequency.
11. The inertial measurement system of claim 1 wherein the modulator is mounted on the base and the sensor is mounted on the modulator.
12. The inertial measurement of claim 1 wherein the modulation frequency is on the order of a few Hertz to hundreds of Hertz, and the amplitude of the dithering is on the order of several milliradians to several degrees.
13. The inertial measurement system of claim 1 wherein the modulation frequency is on the order of 20–500 Hz, and the amplitude of the dithering is on the order of 2–50 milliradians.
14. The inertial measurement system of claim 1 wherein the means for demodulating signals from the sensor also includes means for demodulating signals from the sensor at twice the modulation frequency.
15. An inertial measurement system, comprising a base which rotates about an input axis in accordance with a rotation to be measured, a first angular rate sensor carried by the base responsive to rotation about a first sensing axis, a second angular rate sensor carried by the base responsive to rotation about a second sensing axis which lies in a common plane with the first sensing axis, a modulator for dithering the sensors about an axis perpendicular to the sensing axes to vary the orientation of the sensing axes relative to the base in an oscillatory manner at a modulation frequency, and means for demodulating signals from the sensors at the modulation frequency.
16. The inertial measurement system of claim 15 wherein the modulator is mounted on the base and the sensors are mounted on the modulator.
17. The inertial measurement system of claim 15 wherein the first and second sensing axes are perpendicular to each other.
18. The inertial measurement system of claim 15 wherein one of the sensing axes is dithered about the input axis.
19. The inertial measurement system of claim 15 wherein the modulation frequency is on the order of a few Hertz to hundreds of Hertz, and the amplitude of the dithering is on the order of several milliradians to several degrees.
20. The inertial measurement system of claim 15 wherein the modulation frequency is on the order of 20–500 Hz, and the amplitude of the dithering is on the order of 2–50 milliradians.