Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-05-20
2001-01-09
Kwok, Helen C. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06170330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an angular velocity sensor utilizing a sensor element (vibrator) made of a piezoelectric material and to an angular velocity sensing system utilizing the angular velocity sensor to detect angular velocity, and is used, for example, as an angular velocity sensor in a gyroscope.
2. Description of the Related Art
Mechanical rotor-based gyroscopes have long been used in the inertial navigation systems of aircraft and ships. Although these mechanical rotor-based gyroscopes are excellent in stability and performance, they are not suitable for incorporation in small-scale equipment because of their large size and high cost.
This has led to the recent increasing application of small vibrating gyroscopes of intermediate accuracy. The vibrating gyroscope utilizes an angular velocity sensor which uses a piezoceramic to vibrate a sensor element and a separate piezoceramic provided on the sensor element to detect voltages produced by Coriolis-induced vibrations in proportion to angular velocity.
An angular velocity sensor using a quartz crystal sensor element is taught, for example, by Japanese patent laid-open publication No. 4-504617.
A conventional angular velocity sensor using a quartz crystal will be explained with reference to
FIGS. 12
to
14
.
FIG. 12
is a perspective view of the prior-art angular velocity sensor, and
FIGS. 13 and 14
are sectional views taken along lines B—B and C—C in FIG.
12
.
As shown in these figures, the angular velocity sensor
60
consists mainly of a tuning-fork sensor element
61
having two arms
40
,
41
and a base
42
. The arms
40
,
41
are formed of quartz crystal.
The arm
40
on the left side in the figures is provided with drive electrodes
43
,
44
,
45
,
46
and sensor electrodes
51
,
52
,
53
,
54
. The arm
41
on the right side is provided with drive electrodes
47
,
48
,
49
,
50
and sensor electrodes
55
,
56
,
57
,
58
.
Drive voltages are applied to the drive electrodes
43
-
50
to vibrate the arms
40
and
41
in the plane of the tuning fork (the plane in which the arms vibrate), i.e., in the directions of the arrows −X and X (along the X axis) shown in FIG.
12
. At this time, if the angular velocity sensor
60
is rotated at an angular velocity &ohgr; about the longitudinal axis of the arms
40
,
41
indicated by the arrow Y (the Y axis), Coriolis forces F proportional to the angular velocity &ohgr; are produced in the directions indicated by the arrows −Z and Z (along the Z axis) orthogonal to the X axis. The Coriolis force F is expressed by
F=
2
·M·&ohgr;·V
where M is the mass of the arms and V the vibration velocity.
The Coriolis forces F excite a new vibration in the Z-axis direction of the arms
40
,
41
and the new vibration produces voltages at the sensor electrodes
51
-
58
. The direction and magnitude of the angular velocity &ohgr; produced in the angular velocity sensor
60
can be determined by detecting these voltages by means of a detection circuit.
The symbols + and − in
FIGS. 13 and 14
indicate the polarity of the drive voltages applied to the drive electrodes
43
-
50
and the polarity of the voltages produced at the sensor electrodes
51
-
58
.
In the so-configured prior-art angular velocity sensor, the axis of the rotation whose angular velocity is to be detected must extend in parallel with the longitudinal direction of the two arms of the tuning fork (the Y axis in FIG.
12
). This limits the degree to which the thickness of the angular velocity sensor can be reduced in the direction of this axis of rotation.
Another problem with this angular velocity sensor is the overall complexity of its electrode configuration caused by providing the drive electrodes at an upper portion of the arms
40
,
41
, the sensor electrodes at a lower portion thereof and the means for connection with these electrodes at the base
42
of the tuning-fork sensor element
61
.
Since this arrangement requires vacuum deposition or sputtering steps for forming the sensor electrodes by use of a sensor electrode mask and then forming the drive electrodes by use of a drive electrode mask, it increases the cost of fabrication.
A still further drawback of the so-configured angular velocity sensor is that as a result of mechanical coupling therein a slight leak output voltage is produced at the sensor electrodes solely by the vibration caused by the periodic application of voltage to the drive electrodes, even when no angular velocity is being experienced. Since the phase of this leak output voltage is the same as that of the angular velocity sense voltage, the sense output includes the leak output voltage superimposed on the angular velocity sense voltage.
The angular velocity sensing system utilizing the conventional angular velocity sensor of this type has no means for compensating for this leak output voltage. Since the detection of the angular velocity is therefore made based on changes in the output voltage from the angular velocity sensor including the superimposed leak output voltage, the detection accuracy is markedly degraded.
SUMMARY OF THE INVENTION
One object of this invention is to overcome the foregoing problems by providing an angular velocity sensor which is low in cost and can be made thin in the direction of the axis of the rotation whose angular velocity is to be sensed and to an angular velocity sensing system with high detection accuracy.
In order to achieve this object, the invention provides an angular velocity sensor comprising a tuning-fork sensor element formed of quartz crystal, piezoceramic or other material exhibiting piezoelectricity to have two parallel arms extending integrally from a base and electrodes provided on surfaces of the arms, a free end of each arm being formed with an extension projecting outward in a direction of arm vibration.
The electrodes are preferably provided one each on surfaces of each arm lying in the direction of vibration (X-Y surfaces) and one each on surfaces of each arm lying orthogonal to the X-Y surfaces (Y-Z surfaces).
The arms of the tuning-fork sensor element of the angular velocity sensor are provided at their free ends with the outward projecting extensions. When the tuning-fork sensor element is rotated about an axis orthogonal to the plane of the tuning fork, therefore, the resulting Coriolis forces act on the arms in proportion to the angular velocity of the rotation, thereby producing a bending moments in the arms. The direction and magnitude of the angular velocity can be determined by detecting the voltages produced by the bending moments. The thickness of the angular velocity sensor can therefore be reduced in the direction of the rotational axis.
One embodiment of the angular velocity sensing system according to the invention comprises the aforesaid angular velocity sensor, an oscillation circuit for vibrating the two arms of the tuning-fork sensor element by applying regular periodic drive voltage to the electrodes, two voltage dividers for dividing the output voltages from the electrodes of the respective arms, a differential amplifier for outputting a voltage proportional to the difference between divided voltages input thereto from the voltage dividers, a phase shifter for shifting the phase of the drive voltage produced by the oscillation circuit to the phase of the output of the differential amplifier, a detector for multiplying the output voltage of the differential amplifier and the output voltage of the phase shifter and outputting the product, and a low-pass filter for extracting the DC component from the output of the detector and outputting a signal of a polarity and voltage corresponding to the direction and magnitude of angular velocity experienced by the angular velocity sensor.
Since this angular velocity sensing system cancels the leak output voltage component superimposed on the sense voltage in the angular velocity sensor, it can detect the angular velocity experienced by the angular velocity sensor with high accuracy.
The
Armstrong, Westerman Hattori, McLeland & Naughton
Citizen Watch Co. Ltd.
Kwok Helen C.
LandOfFree
Angular velocity sensor and angular velocity sensing system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Angular velocity sensor and angular velocity sensing system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Angular velocity sensor and angular velocity sensing system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2515171