Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-03-16
2002-07-09
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06415663
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular velocity sensor for use in technologies, such as navigation systems for automobiles, compensation systems for camera shaking, and robot attitude controlling apparatuses.
2. Description of the Related Art
An angular velocity sensor is generally known which comprises a supporting substrate, a pair of support-fixing portions disposed in the supporting substrate, a first supporting beam connected to the support-fixing portion, a first oscillator supported with the first supporting beam, a second supporting beam connected to the first oscillator, a second oscillator supported with the second supporting beam oscillating in the direction that a Coriolis force is generated, driving means for driving these oscillators in a predetermined direction, and detecting means for detecting the displacement of the second oscillator due to the Coriolis force applied to the second oscillator.
Referring to
FIGS. 9 and 10
, a conventional angular velocity sensor
40
will now be described.
Numeral
31
represents a supporting substrate formed of Pyrex glass and a recess portion
31
a
is disposed in the central portion thereof.
Numeral
32
denotes a frame-shaped supporting body joined to a peripheral portion of the supporting substrate
31
by anodic bonding and the frame-shaped supporting body
32
is formed of silicon in a rectangular shape. In the frame-shaped supporting body
32
, from four portions inside the crosspieces thereof disposed separated in the Y-axis direction from each other, first supporting beams
33
a
,
33
b
,
33
c
, and
33
d
(referred to generically below as first supporting beams
33
) extend respectively in the y-axis direction. In the frame-shaped supporting body
32
, the four portions fixed to the first supporting beams
33
are designated as support-fixing portions
32
a.
End portions of the first supporting beams
33
are joined to outsides of the crosspieces of an oscillator
34
, which is disposed in the inner periphery of the frame-shaped supporting body
32
. The first supporting beams
33
support the oscillator
34
and allow it to oscillate in the x-axis direction. The oscillator
34
is roughly rectangularly frame-shaped and outsides of crosspieces thereof disposed separated in the y-axis direction from each other are joined to four portions of the first supporting beams
33
. In the oscillator
34
, from the four portions inside the crosspieces thereof disposed separated in the X-axis direction from each other, second supporting beams
35
a
,
35
b
,
35
c
, and
35
d
(referred to generically below as second supporting beams
35
) extend respectively in the x-direction, and end portions thereof are respectively joined to the outside surfaces of a second oscillator, a load oscillator
36
, which will be described later. In addition, the first supporting beams
33
and the second supporting beams
35
have an orthogonal relationship and the first supporting beams
33
extend in the Y-axis direction while the second supporting beams
35
extend in the X-axis direction.
The load oscillator
36
, which is formed in a roughly rectangular plane, is disposed in the inner periphery of the oscillator
34
and is supported by the second supporting beams
35
which allow it to oscillate in the Y-axis direction.
Numerals
37
,
37
represent driving portions serving as driving means disposed in the oscillator
34
and the frame shaped supporting body
32
, and separated in the X-direction from each other. The driving portions
37
,
37
are formed of driving electrodes
37
a
and
37
b
respectively disposed in outer surfaces of crosspieces of the oscillator
34
separated in the X-axis direction and driving electrodes
37
c
and
37
d
respectively disposed in inner surfaces of the frame-shaped supporting body
32
, opposing the driving electrodes
37
a
and
37
b.
Numerals
38
,
38
represent detecting portions serving as detecting means disposed in the oscillator
34
and the load oscillator
36
, separated in the Y-direction from each other. The detecting portions
38
,
38
are formed of detecting electrodes
38
a
and
38
b
respectively disposed in inner surfaces of crosspieces of the oscillator
34
separated in the Y-axis direction and detecting electrodes
38
c
and
38
d
respectively disposed in outer surfaces of the load oscillator
36
, opposing the detecting electrodes
38
a
and
38
b.
In addition, the oscillator
34
, the load oscillator
36
, the first supporting beams
33
, and the second supporting beams
35
are integrally formed by working the same silicon base plate as the frame-shaped supporting body
32
.
The conventional angular velocity sensor
40
is formed as described above and the operation thereof will now be described.
The load oscillator
36
and the oscillator
34
oscillate in the X-axis direction by electrostatic forces generated by applying respective ac voltages, which are 180° out of phase with each other and on which respective dc voltages are superimposed, to the driving electrodes
37
a
and
37
c
and the driving electrodes
37
b
and
37
d
. At this time, the oscillating of the load oscillator
36
in the X-axis direction is possible by the deflection of the first supporting beams
33
.
During the oscillation of the load oscillator
36
in such manner, when the angular velocity sensor
40
is rotated by application of an angular velocity “&OHgr;” about the Z-axis passing through the center of the load oscillator
36
, a Coriolis force is generated in the Y-axis direction. Therefore, the load oscillator
36
oscillates also in the Y-axis direction. At this time, the oscillating of the load oscillator
36
in the Y-axis direction is possible by deflection of the second supporting beams
35
.
When the load oscillator
36
oscillates in the Y-axis direction, the electrostatic capacity between the detecting electrodes
38
a
and
38
c
and the electrostatic capacity between the detecting electrodes
38
b
and
38
d
increase and decrease. Accordingly, these varying electrostatic capacities are converted to voltages and differentially amplified, so that a value of the rotational angular velocity “&OHgr;” can be obtained.
However, since in the conventional angular velocity sensor
40
, the supporting substrate
31
formed of Pyrex glass and the frame-shaped supporting body
32
formed of silicon are of a single-piece structure bonded together by anodic bonding, when the ambient temperature is changed, a tensile stress or a compressive stress is generated in the bonded portion due to the difference between respective thermal expansion coefficients.
When the thermal expansion coefficient of the supporting substrate
31
is larger than that of the frame-shaped supporting body
32
, for example, strain is generated so that respective joining portions of the frame-shaped supporting body
32
to the first supporting beams
33
for driving are spread in the outside directions as shown by the arrows “c”. This strain causes tensile forces to be applied in the outside directions in the first supporting beams
33
so as to increase the resonance frequency of driving. In this case, since the resonance frequency of detecting is not changed, the difference between the resonance frequencies of driving and detecting is increased, resulting in reduced detecting sensitivity.
This problem has a large effect especially on an angular velocity sensor designed to be highly sensitive by reducing the difference between the resonance frequencies of driving and detecting. Therefore, the conventional angular velocity sensor
40
has to be designed to increase the difference between the resonance frequencies of driving and detecting in advance for preventing reduction in detecting sensitivity due to the increased difference between the resonance frequencies of driving and detecting. Consequently, it has become a problem that angular velocity sensors having high sensitivity cannot be manufactured.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the pr
Mochida Yoichi
Moriya Kazufumi
Moller Richard A.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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