Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-01-12
2001-05-01
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06223597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an angular rate sensor which may be employed in an attitude control system for automotive vehicles, a hand-shake compensating system for video cameras, or a gyroscope of a navigation system for moving objects and a method of improving output characteristics of an angular rate sensor.
2. Background of Related Art
Japanese Patent First Publication Nos. 8-210860, 8-152328, and 6-241815 teach conventional angular rate sensors which include an oscillator mounted on a base through a supporter. The oscillator is vibrated by the Coriolis force produced by the angular rate acting thereon during excitation, which is monitored to determine the angular rate.
Such angular rate sensors, as will be discussed later in detail, encounter several problems leading to errors of sensor outputs which will result in lack of reliability and confidence of sensor operations.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide an angular rate sensor designed to measure an angular rate acting on a moving object with high accuracy.
It is a further object of the invention to provide a method of adjusting a physical structure of an angular rate sensor to improve an output characteristic thereof.
According to one aspect of the present invention, there is provided a method of adjusting an oscillation characteristic of an oscillator of an angular rate sensor, the oscillator having a given length and being shaped to have a plurality of longitudinal edges, the oscillator being excited by input of an excitation signal to oscillate in a first direction perpendicular to the length of the oscillator and, when the angular rate sensor undergoes an angular rate during excitation of the oscillator, oscillating in a second direction perpendicular to the length of the oscillator to provide an output indicative of the angular rate, which comprises the steps of: (a) applying to the oscillator an ac voltage having a resonant frequency, at which the oscillator resonates in the first direction, to oscillate the oscillator; (b) monitoring an output signal of the oscillator during oscillation of the oscillator by application of the ac voltage; and (c) adjusting the oscillation characteristic of the oscillator so as to decrease an amplitude of the monitored output signal of the oscillator to minimize undesired oscillations of the oscillator in the second direction when excited by the input of the excitation signal.
In the preferred mode of the invention, the adjusting step removes a portion of the oscillator to adjust the oscillation characteristic of the oscillator. The removed portion of the oscillator may be one of the longitudinal edges of the oscillator.
The oscillator is a fork oscillator including a pair of arms and a connecting portion connecting ends of the arms. The adjusting step removes a portion of at least one of longitudinal edges of the arms to adjust the oscillation characteristic of the oscillator.
The adjusting step may remove at least one of an longitudinal edge portion of one of the arms leading to the connecting portion, an edge portion of the connecting portion extending in a lengthwise direction of the arms, and a portion of the longitudinal edges of the oscillator extending over a connection between one of the arms and the connecting portion.
The oscillator may alternatively include a single oscillating portion made of a polygonal rod member whose end is fixed on the angular rate sensor. The adjusting step may remove a portion of the oscillating portion leading to the fixed end or alternatively remove a central portion of a longitudinal edge of the oscillating portion to adjust the oscillation characteristic of the oscillator.
The adjusting step may machine a portion of the oscillator in a lengthwise direction or alternatively in a depthwise direction to adjust the oscillation characteristic of the oscillator.
The oscillator is made of a piezoelectric element.
According to the second aspect of the invention, there is provided a method of adjusting an output characteristic of an angular rate sensor which includes a first oscillator having a given length, shaped to have a plurality of longitudinal edges, excitation means responsive to input of an excitation signal for exciting the first oscillator to oscillate in an excitation-axis direction perpendicular to a longitudinal center line of the first oscillator, and a second oscillator having a given length, shaped to have a plurality of longitudinal edges having pickup means for picking up oscillations of the second oscillator in a pickup-axis direction perpendicular to a longitudinal center line of the second oscillator, which comprises the steps of: (a) applying an ac voltage having a resonant frequency, at which the first oscillator resonates in the excitation-axis direction, to the excitation means to oscillate the oscillating portion of the first oscillator; (b) monitoring an output of the pickup means during oscillation of the first oscillator by application of the ac voltage; and (c) adjusting oscillation characteristics of the first and second oscillators so as to decrease an amplitude of the monitored output of the pickup means to minimize undesired oscillations of the second oscillator in the pickup-axis direction produced during oscillation of the first oscillator by the excitation means.
In the preferred mode of the invention, the adjusting step removes portions of the first and second oscillators to adjust the oscillation characteristics of the first and second oscillators. Each of the removed portions of the first and second oscillators may be one of the longitudinal edges of corresponding one of the first and second oscillators.
Each of the first and second oscillator may be a fork oscillator including a pair of arms and a connecting portion connecting ends of the arms. In this case, the adjusting step removes a portion of at one of longitudinal edges of the arms of each of the first and second oscillators to adjust the oscillation characteristic of the oscillator.
The adjusting step may remove at least one of an longitudinal edge portion of one of the arms leading to the connecting portion of each of the first and second oscillators, an edge portion of the connecting portion extending in a lengthwise direction of the arms of each of the first and second oscillators, and a portion of the longitudinal edges extending over a connection between one of the arms and the connecting portion of each of the first and second oscillators.
According to the third aspect of the invention, there is provided an angular rate sensor for determining an angular rate of rotation when the angular rate sensor experiences the rotation about a given axis, which comprises: (a) an oscillator made of a piezoelectric element including at least one pair of arms and a connecting portion connecting ends of the arms; ()) a drive electrode formed on an outer wall of the oscillator, the drive electrode being responsive to input of an excitation signal to oscillate the arms of the oscillator in a first direction perpendicular to length of the oscillator; (c) a pickup electrode formed on the outer wall of the oscillator, the pickup electrode electrically picking up oscillations of the arms in a second direction different form the first direction which indicate the angular rate acting on the angular rate sensor; and (d) an uneven portion formed on a portion of the oscillator near a connection of the connecting portion and the arms for adjusting an oscillation characteristic of the oscillator.
In the preferred mode of the invention, the uneven portion occupies a length of at least one of the arms which extends from the connection and which corresponds to 170% or less of a dimension of the connecting portion in a lengthwise direction of the one of the arms, a portion of the connecting portion ranging from the connection to 70% or less of a dimens
Denso Corporation
Moller Richard A.
Pillsbury & Winthrop LLP
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