Dithering mechanism for eliminating zero-rate bias in a gyroscope
View Patent ↗Dithering mechanism and method for eliminating the effects of zero-rate bias in a rate sensor or gyroscope. Both continuously moving and indexing embodiments are disclosed. The mechanism includes a first part mounted in a fixed position centered about a dither axis perpendicular to the input axis of the gyroscope, a second part disposed coaxially of the first part and affixed to the sensing element of the gyroscope, and a plurality of piezoelectrically driven quartz flexure beams extending radially between the first and second parts for dithering the second part about the dither axis. In some embodiments, the dithering mechanism is formed separately from and affixed to the sensing element of the gyroscope, and in others it is formed integrally with the sensing element. In the indexing embodiments, radial arms and fixed stops limit movement of the mechanism between two fixed positions, and drive signals and holding potentials are applied alternately to dither the mechanism between the two positions and to hold it alternately in those positions during successive data acquisition periods.
1. A dithering mechanism for a gyroscope having a sensing element for monitoring rotation about an input axis, comprising: a first part mounted in a fixed position centered about a dither axis perpendicular to the input axis, a second part disposed coaxially of the first part and affixed to the sensing element, and a plurality of piezoelectrically driven flexure beams extending radially between the first and second parts for dithering the second part about the dither axis.
2. The dithering mechanism of claim 1 wherein the first part, the second part and the flexure beams are formed as a unitary structure of crystalline quartz.
3. The dithering mechanism of claim 2 wherein at least one of the flexure beams is aligned along a crystallographic axis of the quartz.
4. The dithering mechanism of claim 1 wherein the first part is disposed coaxially within the second part.
5. The dithering mechanism of claim 1 wherein the first part is a hexagonal post, the second part is a hexagonal ring, and six flexure beams extend between the post and the ring.
6. The dithering mechanism of claim 1 wherein the sensing element is fabricated of quartz, and the second part is an integral part of the sensing element.
7. The dithering mechanism of claim 1 wherein the flexure beams are fabricated of a material selected from the group consisting of quartz, other piezoelectric crystals, piezoelectric ceramics, and thin-film piezoelectric coatings.
8. The dithering mechanism of claim 1 including a balancing element which is similar to and stacked congruently with the sensing element, with the first part also extending through an opening in the balancing element, and piezoelectrically driven flexure beams extending between the first part and the balancing element for dithering the balancing element about the dither axis in an anti-phase manner relative to the sensing element.
9. The dithering mechanism of claim 8 wherein the balancing element is also a sensing element.
10. A dithering mechanism for a gyroscope having a sensing element with elongated tines extending from a central body in a direction parallel to an input axis, comprising: a post disposed within in an opening in the central body, and a plurality of piezoelectrically driven flexure beams extending radially between the post and the body for dithering the sensing element about a dither axis perpendicular to the input axis.
11. The dithering mechanism of claim 10 wherein the sensing element, the post and the flexure beams are formed as a unitary structure of crystalline quartz.
12. The dithering mechanism of claim 11 wherein at least one of the flexure beams is aligned along a crystallographic axis of the quartz.
13. The dithering mechanism of claim 10 wherein the post and the opening in the body are hexagonal, and six flexure beams extend between the post and the body.
14. The dithering mechanism of claim 10 wherein the flexure beams are fabricated of a material selected from the group consisting of quartz, other piezoelectric crystals, piezoelectric ceramics, and thin-film piezoelectric coatings.
15. The dithering mechanism of claim 10 including a balancing element which is similar to and stacked congruently with the sensing element, with the post also extending through an opening in the balancing element, and piezoelectrically driven flexure beams extending between the post and the balancing element for dithering the balancing element about the dither axis in an anti-phase manner relative to the sensing element.
16. The dithering mechanism of claim 15 wherein the balancing element is also a sensing element.
17. The dithering mechanism of claim 10 including an encoder scale on the sensing element for monitoring the angular position of the input axis about the dither axis.
18. A dithering mechanism for a gyroscope having a sensing element with elongated tines extending from a central body in a direction parallel to an input axis, comprising: a balancing element which is similar to and stacked congruently with the sensing element, a mounting post extending through aligned openings in the central body and in the balancing element, and first and second sets of piezoelectrically driven flexure beams extending radially between the mounting post and respective ones of the body and the balancing element for dithering the sensing element and the balancing element in an anti-phase manner about a dither axis perpendicular to the input axis.
19. The dithering mechanism of claim 18 wherein the sensing element, the balancing element, the post and the flexure beams are formed as a unitary structure of crystalline quartz.
20. The dithering mechanism of claim 19 wherein at least one of the flexure beams is aligned along a crystallographic axis of the quartz.
21. The dithering mechanism of claim 20 wherein the openings and the post are hexagonal in shape, and there are six flexure beams in each of the first and second sets.
22. The dithering mechanism of claim 18 wherein the flexure beams are fabricated of a material selected from the group consisting of quartz, other piezoelectric crystals, piezoelectric ceramics, and thin-film piezoelectric coatings.