Indexing dithering mechanism and method
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, a second part disposed coaxially of the first part and affixed to the sensing element, a plurality of piezoelectrically driven flexure beams extending radially between the first and second parts for dithering the second part about the dither axis, an arm extending from the second part and a pair of stops on opposite sides of the arm for limiting rotation of the second part between first and second fixed positions, and electrodes on the arm and the stops to which electrostatic holding potentials are applied to hold the second part in the first and second fixed positions during successive data acquisition periods.
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 second part is a hexagonal ring, six arms extend radially from corners of the hexagonal ring, and stops are positioned on opposite sides of each of the arms.
7. The dithering mechanism of claim 1 wherein the dither axis is perpendicular to the input axis.
8. A method of dithering the sensing element of a gyroscope with a mechanism having a first part mounted in a fixed position centered about a dither 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, comprising the steps of: applying a drive signal to the flexure beams to rotate the sensing element toward a first fixed position, applying a first electrostatic holding potential to retain the sensing element in the first fixed position during a first data acquisition period, removing the first electrostatic holding potential at the end of the first data acquisition period, applying another drive signal to the flexure beams to assist the flexure beams in rotating the sensing element back toward a second fixed position, and applying a second electrostatic holding potential to retain the sensing element in the second fixed position during a second data acquisition period.
9. The method of claim 8 wherein the first an second fixed positions are defined by an arm extending from the second part and fixed stops on opposite sides of the arm.
10. The method of claim 9 wherein the electrostatic holding potentials are applied to electrodes mounted on the arm and on the stops.
11. The method of claim 8 wherein the additional drive signal is a voltage pulse.
12. The method of claim 8 wherein the dither axis is perpendicular to an input axis about which rotation is sensed.
13. A method of dithering the sensing element of a gyroscope about a dither axis perpendicular to an input axis about which rotation is monitored, comprising the steps of:
(a) mounting a first part in a fixed position centered about the dither axis;
(b) positioning a second part coaxially of the first part;
(c) connecting the second part to the first part with a plurality of radially extending piezoelectrically excitable flexure beams;
(d) affixing the sensing element to the second part;
(e) applying a drive signal to the flexure beams to rotate the sensing element toward a first fixed position:
(f) applying a first electrostatic holding potential to retain the sensing element in the first fixed position during a first data acquisition period;
(g) removing the first electrostatic holding potential at the end of the first data acquisition period;
(h) applying another drive signal to the flexure beams to assist the flexure beams in rotating the sensing element back toward a second fixed position;
(I) applying a second electrostatic holding potential to retain the sensing element in the second fixed position during a second data acquisition period; and
(j) repeating steps (e)-(i) to swing the sensing element back and forth and hold it in alternate ones of the two fixed positions during successive data acquisition periods.
14. The method of claim 13 wherein the first an second fixed positions are defined by an arm extending from the second part and fixed stops on opposite sides of the arm.
15. The method of claim 14 wherein the electrostatic holding potentials are applied to electrodes mounted on the arm and on the stops.
16. The method of claim 13 wherein the additional drive signal is a voltage pulse.