Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-09-30
2001-10-30
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06308568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular velocity sensor for use in a car navigation system, a camera shaking prevention device, a robot attitude control device, and the like.
2. Description of the Related Art
A conventional angular velocity sensor
40
will be described below with reference to
FIGS. 7 and 8
. Four anchor portions
42
are formed at the four corners of a support substrate
41
made of Pyrex glass. L-shaped beams
43
are connected at one end to the anchor portions
42
and are connected at the other end to the four corners of a vibration weight
44
, respectively. The vibration weight
44
serves as the load mass of the angular velocity sensor
40
, and is allowed by the bending of the beams
43
to freely vibrate in the XY plane.
Comb-shaped movable electrodes
44
a
and
44
b
are formed on end faces (in the X-axis direction) of the vibration weight
44
, and movable electrodes
44
c
and
44
d
shaped like the character are formed on the other end faces (in the Y-axis direction).
Fixed portions
45
a
to
45
d
are formed on the support substrate
41
between the adjoining anchor portions
42
, respectively. A comb-shaped fixed electrode
46
a
formed on the inner side face of the fixed portion
45
a
is meshed with space therebetween with the movable electrode
44
a
to constitute a condenser
47
a
. A comb-shaped fixed electrode
46
b
formed on the inner side face of the fixed portion
45
b
is meshed with space therebetween with the movable electrode
44
b
to constitute a condenser
47
b
. Two F-shaped fixed electrodes
46
c
formed on the inner side face of the fixed portion
45
c
are meshed with space therebetween with the movable electrode
44
c
to constitute a condenser
47
c
. Furthermore, two F-shaped fixed electrodes
46
d
formed on the inner side face of the fixed portion
45
d
are meshed with space therebetween with the movable electrode
44
d
to constitute a condenser
47
d.
A space
41
a
is formed under the beams
43
, the vibration weight
44
, the movable electrodes
44
a
to
44
d
, and the fixed electrodes
46
a
to
46
d
. In the angular velocity sensor
40
, the elements, such as the anchor portions
42
and the vibration weight
44
, excluding the support substrate
41
, are formed by working a silicon substrate. The four anchor portions
42
and the fixed portions
45
a
to
45
d
, which are made of silicon, are joined onto the support substrate
41
of Pyrex glass by anode coupling.
Next, a description will be given of the operation of the angular velocity sensor
40
. Since the angular velocity sensor
40
is operated with the anchor portions
42
connected to ground, the vibration weight
44
and the movable electrodes
44
a
to
44
d
are at ground potential.
The vibration weight
44
is vibrated by electrostatic attractive force in the X-axis direction by applying AC voltages having a phase difference of 180°, which are obtained by superimposing DC voltages, to the condenser
47
a
(between the anchor portion
42
and the fixed portion
45
a
) and the condenser
47
b
(between the anchor portion
42
and the fixed portion
45
b
). When the angular velocity sensor
40
rotates about the Z-axis passing through the center of the vibration weight
44
while the vibration weight
44
is thus vibrating, the vibration weight
44
receives a Coriolis force generated by the rotating force, and also vibrates in the Y-axis direction. The vibration components in the Yaxis direction are detected as capacitance changes by the condensers
47
c
and
47
d
, and these capacitance changes are converted into voltages and are differentially amplified, thereby determining the angular velocity.
In the conventional angular velocity sensor
40
, the four anchor portions
42
made of a silicon material are joined to the four separate corners of the support substrate
41
made of a Pyrex glass material. The vibration weight
44
similarly made of a silicon material is supported integrally with the anchor portions
42
via the four beams
43
.
Therefore, the difference in coefficient of thermal expansion between the support substrate
41
of Pyrex glass and the anchor portions
42
of silicon causes the joint portions therebetween to be warped. Because of this warp, the beams
43
connected to the vibration weight
44
receive compressive stress or tensile stress. The compressive stress and tensile stress become residual stress, which changes the vibration frequency of the vibration weight, and has an adverse effect on sensitivity of detection based on Coriolis force and the temperature characteristics of the mechanical resonant frequency of the vibration weight. For this reason, the detection sensitivity and the mechanical resonant frequency of the angular velocity sensor change substantially due to changes in temperature.
SUMMARY OF THE INVENTION
The present invention can solve the aforementioned problem associated with the conventional art and provides an angular velocity sensor with improved detection sensitivity and temperature characteristics of the mechanical resonant frequency.
The angular velocity sensor comprises a framelike vibrator supported on a support portion via a pair of T-shaped beams, the support portion being disposed in the center of the framelike vibrator and being formed on a support substrate made of a material having a different coefficient of thermal expansion than the support portion. The T-shaped beams include a first beam portion structured and arranged for displacing the framelike vibrator in a first driving direction, and a second beam portion structured and arranged for displacing the framelike vibrator in a second direction orthogonal to the first direction in response to Coriolis force when the support portion is rotated about an axis extending in a third direction orthogonal to the first and second directions.
According to the present invention, even when the fixed support portion and the support substrate are made of different materials and are different in coefficient of thermal expansion, since the framelike vibrator is supported by the single fixed support portion via the beams, tensile stress or compressive stress resulting from the difference in coefficient of thermal expansion is concentrated on the fixed support portion or is reduced, whereby residual stress on the beams decreases. Therefore, it is possible to prevent sensitivity of detection based on Coriolis force and the temperature characteristics of the mechanical resonant frequency of the vibration weight from being deteriorated due to the residual stress.
Furthermore, temperature changes do not have a serious influence on the framelike vibrator because of the action of the pair of T-shaped beams composed of the first beam portion and the second beam portion that are placed orthogonal to each other.
According to another aspect of the present invention, the angular velocity sensor comprises an inner framelike vibrator supported on a fixed support portion via a pair of inner beams and an outer framelike vibrator supported outside the inner framelike vibrator via at least a pair of outer beams. The fixed support portion is disposed in the center of the inner framelike vibrator and is formed on a support substrate made of a material having a different coefficient of thermal expansion in the center of the inner framelike vibrator than the support portion. The inner beams are structured and arranged to displace the inner framelike vibrator and the outer framelike vibrator in a first driving direction and the outer beams are structured and arranged to displace the outer framelike vibrator in a second direction orthogonal to the first direction in response to a Coriolis force when the support portion is rotated about an axis extending in a third direction orthogonal to the first and the second directions.
According to this angular velocity sensor, the action of stress that the fixed support portion receives from the support substrate is similar to that first angular velocity sensor. That is, since th
Moller Richard A.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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