Angular velocity sensor

Details Angular velocity sensor Angular velocity sensor

2000-02-15

2001-05-29

Moller, Richard A. (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Angular rate using gyroscopic or coriolis effect

Reexamination Certificate

active

06237415

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an angular velocity sensor used in position control or navigation system of a mobile body such as aircraft, automobile, ship, and vehicle, or in a system for preventing shake of camera or video camera, remote control of audio and video appliances, or personal computer, or detection of rotating motion.
BACKGROUND ART
Various forms of angular velocity sensors have been known hitherto, and from the viewpoint that the entire tuning fork is formed of a ceramic piezoelectric element, as prior art, Japanese Laid-open Patent 3-120415 discloses an oscillating gyro integrally forming two rectangular arms, and a base portion for mutually coupling these arms at their lower ends from a piezoelectric material to form the entire shape into a form of a tuning fork, with the base portion polarized in the direction of Y-axis.
This conventional angular velocity sensor is described below by reference to the drawing.
FIG. 32
is a perspective view of a single-shape tuning fork disclosed in Japanese Laid-open Patent 3-120415.
Directions of polarization are orthogonal, with the base portion in the direction of Y-axis and the driving side oscillating arms in the direction of X-axis. Driving electrodes
3
,
4
are partial electrodes of about half of the oscillating arms, and the driving force is {fraction (2/8)} times as seen from the use of the entire four sides.
Besides, by Coriolis force, the oscillating arms
1
,
2
are bent and oscillated in reverse phases in the X-direction, so that a torsional moment about the Y-axis occurs on the base portion
5
. Detecting electrodes
6
,
7
are to detect torsional oscillation of the base portion
5
, and are high in resonance frequency and low in output sensitivity.
Reference numeral
1
is a driving side oscillating arm, and
2
is a monitor oscillating arm for oscillating stably, and the direction of polarization, which is not indicated herein, is supposed to be in the X-direction considering from the function.
In
FIG. 32
, however, the role functions are divided, that is, the oscillating arms
1
,
2
are used for driving, and the base portion
5
for detecting, and although it is only estimation because the mounting or holding method of the base portion
5
is not disclosed, it may be predicted that the oscillation forms are complicated by mixing of (1) oscillating components in the base portion
5
due to driving and oscillation (flexural oscillation in mutually reverse phases in Y-direction), (2) oscillating components in the base portion
5
due to flexural oscillations in mutually reverse phases in X-direction at the time of action of Coriolis force, (3) torsional oscillating components about the Y-axis of the base portion
5
, and (4) disturbance noise components from the holding portions. Accordingly, the separation circuit of these four oscillating components is complicated. Since the oscillation analysis of the base portion of the tuning fork is not elucidated by the mechanical vibration engineering of today, its control seems to be difficult. Therefore, since vibration separation is difficult, it may cause malfunction as the gyro in practical aspect. In particular, it is influenced by disturbance noise transmitted from the holding portion, and it was hard to apply in automobiles, etc.
The torsional oscillation is higher in resonance frequency and smaller in oscillation amplitude as compared with flexural oscillation of cantilever, and is hence low in sensitivity. Therefore, drop of output sensitivity was a cause of temperature drift (fluctuation of detection value due to ambient temperature changes when the input angular velocity is 0).
Moreover, since the driving electrodes
3
,
4
in
FIG. 32
are provided to the leading end in the Y-axis direction of the oscillating arms, according to the vibration theory of tuning fork, 20 to 30% of the leading end functions as floating capacity, not contributing to driving force at all, and only acts to pick up electric noise, and therefore the ratio of detected signal to electric system noise (hereinafter called S/N) was worsened.
SUMMARY OF THE INVENTION
It is hence an object of the invention to isolate and separate the function of driving side tuning fork and detection side tuning fork, without using base portion complicated in the oscillation form, that is, not using the support portion for detection purpose, remove mechanical coupling oscillation of support portion, prevent driving signal from reaching into the detection side, and enhance the drift performance.
To achieve the object, the angular velocity sensor of the invention is characterized by integrally forming a tuning fork in a comb shape with four parallel oscillating arms made of flat ceramic piezoelectric material or crystal material and a common tuning fork support member, defining the X-axis of the three-dimensional system of coordinates in the width direction of the oscillating arms and support member, the Y-axis in the longitudinal direction of the oscillating arms, and the Z-axis in the thickness direction of the entire tuning fork, preliminarily polarizing partially part of the oscillating arms and support member along the Y-axis in the X-direction by an externally applied voltage, using the outer set of two pieces as the driving side tuning fork and the inner set of two pieces as the detection side tuning fork, or using the inner set of two pieces as the driving side tuning fork and the outer set of two pieces as the detection side tuning fork, disposing driving electrodes along the Y-axis on the face, back and side surfaces of part of the driving side oscillating arms and support member of the tuning fork in comb shape, and detection electrodes divided in two sections along the Y-axis on the face and back surfaces in part of the detection side oscillating arms and support member, corresponding to the partial polarization portions, applying an alternating-current signal to the driving electrodes of the driving side tuning fork to generate flexural oscillations in mutually reverse phases in the X-direction (hereinafter called X
D
mode), coupling mechanically the support member to the detection side tuning fork to induce flexural vibrations in mutually reverse phases (hereinafter called X
S
mode), and detecting the electric charge quantity generated by flexural vibrations in mutually reverse phases in the Z-axis direction generated by the Coriolis force based on the rotation angular velocity about the Y-axis applied from outside (hereinafter called Z
S
mode) by the detecting electrode of the detection side tuning fork.
In this constitution, improving the vibration transmission efficiency, improving the detection sensitivity, preventing undue distribution of driving signal, and enhancing the electrical and mechanical S/N ratio, so that a stable constitution of high performance may be obtained.


REFERENCES:
patent: 5824900 (1998-10-01), Konno et al.
patent: 2-129514 (1990-05-01), None
patent: 3-120415 (1991-05-01), None
patent: 5-231870 (1993-09-01), None

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