Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-02-15
2002-05-21
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06389897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a vibratory gyroscope and a method for manufacturing the same.
2. Related Arts
It has been studied to mount a vibratory gyroscope in a car body for controlling its orientation. In such application, the vibratory gyroscope is mounted in a housing, which is then attached on a chassis of the car body. External vibration is inevitably transmitted through the chassis to the gyroscope, possibly causing a malfunction or vibration noise. It is necessary to minimize the noise caused by the external vibration.
Japanese patent application publication “Kokai” 269228/1997 discloses, in a gyroscope using a tuning-fork type vibrator comprising a base and a tuning-fork, a method for reducing the cross-talk noise induced by external vibration. In the column (0002), this publication discloses a method to reduce the vibration noise by adjusting the length of the base within a certain range. J. Yukawa et al. “Angular Rate Sensor for Dynamic Chassis Control” (Sensors and Actuators) 980269, pages 49 to 54, 1998 discloses a method for reducing vibration noise in a vibratory gyroscope comprising a metal vibrator and poly-crystalline piezoelectric elements to drive the vibrator. They reduced vibration noise, due to the beat of the vibrator, by increasing the detuned frequency to a value suitably larger than the cut-off frequency of a low pass filter. The detuned frequency is the difference of resonance frequencies of driving and detection modes of the vibrator. The detuned frequency disclosed is as large as 600 Hz.
SUMMARY OF THE INVENTION
The present inventors have researched to reduce the influence of external vibration on vibratory gyroscopes using a vibrator, and subsequently found that, when external vibration of the same frequency as the detuned frequency is transmitted to the vibrator, relatively large noise is induced in the signal output from the vibrator. Vibration transmitted through a car chassis to a vibratory gyroscope usually includes various frequency components, and the frequency component of the detuned frequency causes the above noise. Therefore, it is necessary to reduce such “vibration noise” induced by an external vibration including the frequency component of the detuned frequency.
The present invention aims to reduce “vibration noise” which is included in the output of a vibrator used in vibratory gyroscopes for detecting the turning angular rate, when the gyroscopes are subjected to external vibrations including the frequency component of the detuned frequency of the vibrator.
One aspect of the present invention provides a vibratory gyroscope for detecting a turning angular rate;
wherein the gyroscope comprises a vibrator made out of a piezoelectric material, the vibrator has a driving vibration mode in which the vibrator is electrically excited and another detection vibration mode for detecting Coriolis vibration occurring in the vibrator when the vibrator is rotated around a detection axis at a turning angular rate, and the vibrator has a surface including a region where stress induced in the vibrator in the detection vibration mode is in a range of a local maximum, the gyroscope further comprising a damper for reducing vibration sensitivity to external vibrations applied externally on the vibrator, the damper being made of a polymer and provided on at least said region.
In this embodiment, the vibrator has a region which does not substantially vibrate in the driving vibration mode and substantially vibrates in the detection vibration mode and a detecting electrode provided on the region. In the driving vibration mode, the amplitude of vibration in the region may preferably be not more than 0.01 of the maximum amplitude of vibration in the vibrator.
Another aspect of the present invention also provides a vibratory gyroscope for detecting a turning angular rate;
the gyroscope comprising a vibrator made of a piezoelectric material, the vibrator comprising one or more driving parts for electrically exciting a driving-mode vibration in the vibrator, one or more detecting parts provided separately from the driving part for detecting a Coriolis vibration occurring in the vibrator when the vibrator is rotated, and a damper for reducing vibration sensitivity to external vibrations applied externally on the vibrator, the damper being made of a polymer and is provided on a surface of the detecting part. Preferably, the damper is not provided on the driving part.
The “driving part” is defined as a part on which a driving means such as a driving electrode is provided. The “detection part” is defined as a part on which a detection means such as a detection electrode is provided. In this aspect, the detection part does not substantially vibrate in the driving vibration mode. Alternatively, in the driving vibration mode, the amplitude in detection part may preferably be not more than 0.01 of the maximum amplitude of vibration in the vibrator.
The present invention also provides a method for manufacturing a vibratory gyroscope for detecting a turning angular rate, the gyroscope comprising a vibrator which has a driving vibration mode for electrically vibrating the vibrator and has a detection vibration mode for detecting Coriolis vibration occurring in the vibrator due to the rotation of the vibrator, the method comprising the steps of;
computing each ratio of each stress at each point of the vibrator to a maximum stress in the whole vibrator by means of a characteristic mode analysis by the finite element method, for the case of the detection vibration mode, determining a region where the ratio is in a range of a local maximum, and providing a damper made of a polymer on the region.
The present inventor succeeded to substantially reduce the above vibration noise included in signal output from a vibrator having a detecting arm, when external vibration including the frequency component of the detuned frequency is transmitted to the vibrator, by providing a damper made of a polymer on the detecting arm.
When the vibrator has a detecting part or parts and a base part, the damper may be provided on either of its main faces and side faces, or on both the main faces, or on either of the main faces and on the side faces, or on both the main faces and on both the side faces. When the detecting part has an elongated shape, and has a root portion extending onto the base part, the damper may preferably be provided in a position which distance from the root is within a half of the length of the detecting part. The damper provided on or near the end portion of the detection part may increase the temperature drift of the gyroscope.
In the above publication “Sensors and Actuators”, the authors tried to reduce the vibration noise detected from the gyroscope due to the beat, by increasing the detuned frequency sufficiently larger than the cut off frequency of the low pass filter installed in the gyroscope. However, such method described in the publication does not reduce the induction of the vibration noise in the vibrator due to an external vibration, but reduces such vibration noise component by means of an electric filter. Because the method increases the detuned frequency, the sensitivity of the gyroscope and its signal
oise ratio decrease in an inversely proportional manner to the detuned frequency.
When a damper is provided on the surface of a vibrator, the damper may preferably be provided on a region where stress induced in the vibrator in the detection vibration mode is in a range of a local maximum oh the surface of the vibrator. Such a region includes and is not necessarily identical with the region where stress induced in the vibrator is in a range of the maximum, which does not necessarily mean local maximum. However, assuming a maximum stress in the vibrator in the detection vibration mode as 1.0, the damper may preferably be provided on a region where its minimum stress is not less than 0.01 and its maximum stress is not less than 0.7, more preferably not less than 0.8.
The damper may preferably be provided, on
Kikuchi Takayuki
Tani Makoto
Burr & Brown
Chapman John E.
NGK Insulators Ltd.
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