Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-05-01
2002-12-17
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06494094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular rate sensor used for controlling the motion of a vehicle and an aircraft.
2. Description of Related Art
FIG. 19
is a top view showing a conventional angular rate sensor disclosed in U.S. Pat. No. 5,408,877.
FIG. 20
is a sectional view along the line XX—XX of FIG.
19
. In these figures, the reference numeral
101
designates an inertial mass;
102
designates a drive gimbal frame on which the inertial mass is mounted;
103
designates a detection gimbal frame surrounding the drive gimbal frame
102
;
104
designates a first torsion beam connecting the drive gimbal frame
102
with the detection gimbal frame
103
to rotatably support the drive gimbal frame
102
at two opposed positions;
105
designates a second torsion beam rotatably supporting the detection gimbal frame
103
at two opposed positions;
106
designates a drive electrode disposed below the drive gimbal frame
102
apart from the frame
102
by a certain gap;
107
designates a detection electrode disposed above the detection gimbal frame
103
; and
108
designates a silicon substrate supporting the second torsion beam
105
and the drive electrodes
106
.
The torsion axes of the first torsion beams
104
are parallel to the Y axis, while the torsion axes of the second torsion beams
105
are parallel to the X axis. The torsion axes of the first torsion beams
104
are perpendicular to the torsion axes of the second torsion beams
105
.
The drive electrodes
106
are parallel to the torsion axes of the first torsion beams
104
. These two electrodes
106
are symmetrically placed about the line extended from the torsion axes of the first torsion beams
104
viewed from the direction of the Z axis.
The detection electrodes
107
parallel to the torsion axes of the second torsion beam
105
are symmetrically placed about the line extended from the torsion axes of the second torsion beams
105
viewed from the direction of the Z axis.
Next, the operation of the conventional angular rate sensor will be described.
On applying alternating voltages with mutual phase-difference of 180 degrees to the two drive electrodes
106
, an electrostatic attractive force induced between the drive gimbal frame
102
and one of the drive electrodes
106
leads to torsion of the first torsion beams
104
, causing a rotational oscillation of the drive gimbal frame
102
(reference oscillation) about the torsion axes of the first torsion beams
104
which function as a rotational axis. As a result, the mass center of the inertial mass
101
oscillates in a simple harmonic motion in the direction parallel to the X axis.
In this state, the rotation of the entire angular rate sensor about the Z axis generates the Coriolis force represented by the following equation (1) acting on the center of the inertial mass
101
in the direction parallel to the Y axis. The second torsion beams
105
are then distorted and the detection gimbal frame
103
rotationally oscillates about the torsion axes of the second torsion beams
105
as a rotational axis.
F=
2
VM&OHgr;
(1)
wherein V represents a rate of the inertial mass
101
in the direction parallel to the X axis, M represents an inertial mass and &OHgr; represents a rotational angular rate about the Z axis.
The displacement amplitude of the rotational oscillation of the detection gimbal frame
103
is proportional to the maximum absolute value of the Coriolis force F which is proportional to the angular rate &OHgr;. Further, as the detection gimbal frame
103
rotationally oscillates, the electrostatic capacity between the detection gimbal frame
103
and the detection electrode
107
changes. This change in electrostatic capacity is converted into a voltage to obtain a sensor output proportional to the angular rate &OHgr;.
As stated above, in the conventional angular rate sensor the electrostatic attractive force generated between the drive gimbal frame
102
and the drive electrodes
106
is used for inducing reference oscillation. The electrostatic attractive force is inversely proportional to the square of the distance between the drive gimbal frame
102
and the drive electrodes
106
. Thus, once the first torsion beams
104
are greatly distorted, the rotational angle of the drive gimbal frame
102
increases and the distance between the drive gimbal frame
102
and one of the drive electrodes
106
decreases. As a result, an electrostatic attractive force exceeds the restoring force of the first torsion beams
104
, causing the Pulled-in phenomenon where the drive gimbal frame
102
is attached to one of the drive electrodes
106
. Consequently, the displacement amplitude of the rotational oscillation of the drive gimbal frame
102
is limited such that the distance between the drive gimbal frame
102
and the drive electrodes
106
is not more than one third of the gap therebetween for a stable rotational oscillation of the drive gimbal frame
102
.
Since the conventional angular rate sensor is constructed as above, the displacement amplitude of the rotational oscillation of the drive gimbal frame
102
is limited for avoiding the Pulled-in phenomenon. As a result, a rate V of the mass center of the inertial mass
101
in the direction parallel to the X axis is limited and the Coriolis force F is thus limited. In other words, there exists a problem that the displacement amplitude of the rotational oscillation of the drive gimbal frame
102
is limited, and hence the sensitivity of the angular rate sensor is limited.
Alternatively, in a case that an angular rate sensor of high sensitivity is designed under the condition that the distance between the drive gimbal frame
102
and the drive electrodes
106
is not more than one third of the gap therebetween, a large gap is required for a large displacement amplitude of the rotational oscillation of the drive gimbal frame
102
. However, in this case, since a large electrostatic attractive force is required, larger driving voltages should be applied to the drive electrodes
106
and the facing areas between the drive gimbal frame
102
and the drive electrodes
106
should be larger. This design is impractical.
In addition, there is another problem that the conventional angular rate sensor can detect only a rotational angular rate about one axis.
SUMMARY OF THE INVENTION
The present invention is implemented to solve the above problems. An object of the present invention is to provide an angular rate sensor of high sensitivity with a drive frame and a frame to be driven (hereinafter referred to as driven frame) separately provided, in which the driven frame is not directly but indirectly driven through the drive frame.
Another object of the present invention is to provide an angular rate sensor capable of detecting rotational angular rates about a plurality of axes.
According to a first aspect of the present invention, there is provided an angular rate sensor comprising: an inertial mass; a driven frame surrounding the inertial mass; inertial mass torsion beams connecting the inertial mass with the driven frame to rotatably support the inertial mass at two opposed positions; driven frame torsion beams rotatably supporting the driven frame at two opposed positions; a drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams; driving force generation means for giving a driving force to cause a bending oscillation of the drive frame in an out-of-plane direction; link beams connecting the driven frame with the drive frame; and detection means for detecting a displacement amplitude of a rotational oscillation of the inertial mass.
According to a second aspect of the present invention, there is provided an angular rate sensor comprising: an inertial mass; a driven frame surrounding the inertial mass; inertial mass torsion beams connecting the inertial mass with the driven frame to rotatably support the inertial mass at two opposed positions;
Fujita Hiroyuki
Konno Nobuaki
Tsugai Masahiro
Kwok Helen
Mitsubishi Denki & Kabushiki Kaisha
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