High Q angular rate sensing gyroscope

Abstract

A structure and arrangement for improving the accuracy and efficiency of an angular rate sensing gyroscope is herein disclosed. Voltage pick-off conductors are applied to an area of the surface of a resonating element of an angular rate sensing gyroscope that is subject to substantially zero stress when the gyroscope is rotationally stationary. Actuator conductors are similarly applied to a resonating element at a location bounded by areas of the resonating element subject to substantially uniform levels of stress when the gyroscope is rotationally stationary. A method for improving the voltage response of a piezoelectric resonating element is also disclosed.

Description

RELATED APPLICATIONS[0001]This applicationNotice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,845,667. The reissue applications are application Ser. No. 13 / 078,538 (the present application), which is a continuation of application Ser. No. 11 / 657,988, filed on Jan. 25, 2007 now U.S. Pat. No. Re. 42,731, both of which are reissue applications of U.S. Pat. No. 6,845,667, which claims priority from Patent Cooperation Treaty application no. PCT / US00 / 25318, filed on Sep. 14, 2000, which is itself a Continuation-in-Part of U.S. patent application Ser. No. 09 / 397,718 filed Sep. 16, 1999 now U.S. Pat. No. 6,272,925. In addition, U.S. patent application Ser. No. 09 / 880,433 filed on 13 Jun. 2001 is a divisional application of U.S. patent application Ser. No. 09 / 397,718.FIELD OF THE INVENTION[0002]The present invention is drawn to an angular rate sensor of the type utilizing an oscillating resonating element. More specifically, the present invention is dr...

AI Technical Summary

Benefits of technology

"The present invention is about improving the accuracy of angular rate sensing gyroscopes by minimizing errors in the angular rate sensed by the gyroscope. This is achieved by developing better pick-off and actuator conductors that are resistant to damage and can sense voltage signals proportional to the rate of stress induced in the resonating element. The actuator conductors are applied to the surface of the resonating element at predetermined locations, which are areas of uniform stress when the gyroscope is rotationally stationary. The pick-off conductors are applied at the nodes of the resonating element, where they sense a net voltage signal of substantially zero when the gyroscope is rotationally stationary. Balancing conductors can also be applied to reduce any net voltage signals sensed by the pick-off conductors. The resonating element can be any of a variety of shapes, such as cylinder, ring, or bar-shaped structures. The invention also includes improvements in the arrangement of the pick-off and actuator conductors to further enhance the accuracy of the gyroscope."

Problems solved by technology

These undesirable bending forces create voltage signals that may degrade the signal to noise ratio of the voltage output of the sensing elements and may indicate falsely that the angular rate sensor is being rotated about its sensitive axis.

Problems with angular rate sensors of the type patented by Varnham include a relatively low Q value, low sensitivity, and low accuracy.

In addition, the application of actuators and pick-offs across a range of stresses, in combination with non-uniform voltage responses in the piezoelectric materials, make it more difficult to force the resonator to oscillate in its desired mode.

Piezoelectric materials are not uniform in their voltage response and therefore it is frequently the case that a pick-off having a large surface area will sense net voltages skewed by an uneven voltage response of the piezoelectric material.

And because the actual voltages sensed by the pick-offs are quite small, voltage signal components due to uneven voltage responses frequently alter the signal to noise ratio of the sensed voltages to an extent that makes it difficult to determine accurately the rate and magnitude of rotation of the gyroscope.

Furthermore, because it is also frequently the case that the voltage response of respective areas of the piezoelectric materials that make up a resonator may vary independently with changes in the ambient temperature of the operating environment of the gyroscope, the noise to signal ratio of the sensed voltages may become further degraded.

A further problem can arise because, in general, piezoelectric materials are made up of many individual crystals that have been sintered together and given a particular polarity by the application of a strong DC voltage.

Where this polarization is performed over a discrete area of the piezoelectric material, such as over the surface of the resonator covered by the conductive patches of the actuators and pick-offs, the polarization of the material at the edges of the discrete area will not be in the desired direction and will therefore generate irregular voltage responses.

In addition, it is not uncommon that the piezoelectric material of the resonator will be subject to irregular stresses or flexure.

The combination of irregular stresses or flexure with uneven edge polarization may cause severe fluctuations in the accuracy and sensitivity of the angular rate sensor and may also lower the Q value of the system.

The small size of the connection wires 23 makes them weak and prone to frequent failure due to applied forces and internal stresses resulting from the ultrasonic wedge bonding processes that are typically used to make such small electrical connections.

In addition, the use of solder or solder-like materials on the resonator at the physical contact between the wire 23 and the resonator tend to interfere with the inducement and maintenance of the desired mode of oscillation, thereby lowering the Q factor of the system.

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