Z-axis angular rate sensor
An oscillatory rate sensor is described for sensing rotation about the “z-axis”. It is tuning-fork in nature with structural linkages and dynamics such that fundamental anti-phase oscillation of two proof masses is accomplished by virtue of the mechanical linkages.
1. A sensor, having orthogonal x-, y-, and z-axes, for detecting a rate of rotation about the z-axis comprising:
a substrate; and
a gross mass, symmetrical with respect to the x-axis, suspended from the substrate by a plurality of interior and exterior anchor points, and comprising:
at least two proof masses, symmetrical with respect to the x-axis and the y-axis;
a driven frame surrounding each proof mass and attached to its proof mass and external anchor points by flexures;
a set of drive banks and a first set of sense banks for each driven frame for oscillating along the x-axis;
a second set of sense banks attached to each proof mass for detecting Coriolis motion along the y-axis;
at least two rotating stiff beams, each centrally mounted to an interior anchor point, oriented in a y-direction at rest, and able to rotate about its anchor point in an xy-plane orthogonal to the z-axis; and
a plurality of inner frame supports, asymmetric with respect to the y-axis, connecting the rotating stiff beams to the frames, and comprising a plurality of non-rotating stiff beams and a plurality of flexures, to allow frame motion predominantly along the x-axis in anti-phase motion only such that Coriolis-induced anti-phase motion of the proof masses along the y-axis results.
2. The sensor of claim 1 , wherein each drive bank and each sensor bank is a capacitive comb.
3. The sensor of claim 2 , wherein the capacitive combs are used to determine the relative positions of the proof masses and the relative positions are used to determine the sensed rate of rotation.
4. The sensor of claim 1 , wherein the rotating stiff beams, the non-rotating stiff beams, and the flexures connecting them form at least one rhombus constrained to collapse.
5. The sensor of claim 1 , wherein the rotating stiff beams comprise two pairs of rotating stiff beams with interior anchor points forming a rectangle in the xy-plane.
6. The sensor of claim 1 , wherein the rotating stiff beams comprise two rotating stiff beams positioned along the same line in the y-axis.
7. The sensor of claim 1 , wherein the rotating stiff beams comprise two sets of at least three rotating stiff beams, each set with anchor points along the same line in the x-axis.
8. The sensor of claim 1 , wherein at least one non-rotating stiff beam includes a gusset to resist bending of the non-rotating stiff beam.
9. The sensor of claim 1 , wherein the sensor is fabricated by a fabrication technique selected from the group consisting of:
a) deep reactive ion etching;
b) surface micromachining; and
c) bulk micromachining.
10. The sensor of claim 1 , wherein the sensor is fabricated using a material selected from the group consisting of:
a) a single crystal silicon wafer;
b) a silicon on insulator wafer;
c) a polysilicon wafer; and
d) an epitaxial wafer.