Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-10-26
2003-07-08
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S001770
Reexamination Certificate
active
06588274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self-diagnosing circuit for a vibrating gyroscope and, more specifically, relates to a self-diagnosing circuit such as that capable of diagnosing a short-circuit failure of a vibrating gyroscope for a vehicle-mounted electrical device to be used in the control of vehicle position requiring high reliability.
2. Description of the Related Art
FIGS. 9A and 9B
respectively show a plan view and a side view of an example of a bimorph vibrator to be used in a vibrating gyroscope. In
FIGS. 9A and 9B
, a bimorph vibrator
1
is formed by two piezoelectric elements having opposite polarization directions attached to each other such that the resulting bimorph vibrator
1
is rectangular in cross-section. If the vibrator
1
vibrates in a flexure vibration mode in a surface-normal direction (the X-axis direction), and is rotated with a certain angular velocity (&OHgr;) about the longitudinal axis direction (the Z-axis direction), a vibration occurs in the flexure vibration mode in a direction normal to the driving surface (the Y-axis direction) by the Coriolis force.
Since the amplitude of the vibration is proportional to the angular velocity, this is utilized in detecting an angular velocity value. The vibrator
1
is provided with detecting electrodes
1
L and
1
R of the left and the right thereof and a full-surface electrode
1
C, and from the detecting electrodes
1
L and
1
R ofthe left and the right of the vibrator
1
, signals L-side output and R-side output are outputted.
FIGS. 10A
to
10
D shows vibration waveforms of the bimorph vibrator shown in
FIG. 9
, and specifically,
FIGS. 10A and 10B
show waveforms when an angular velocity is not applied, for example, a case in which a driving output of 1 V is obtained for a vibration input of 1.5 V.
FIGS. 10C and 10D
show waveforms when the angular velocity is applied, for example, a case in which a Coriolis signal of 2 V is generated.
In the vibrator
1
, if the driving signal CT shown in
FIG. 10A
is applied to the full surface electrode
1
C, the R-side output and L-side output become sine waves of the same phase, as shown in FIG.
10
B. At this time, the vibrator
1
is vibrating in a bending mode in the X-axis direction. However, since the angular velocity about the Z-axis is not applied, the Coriolis force is not generated, and a vibration in the bending mode in the Y-axis direction is not generated. The L-side output and R-side output of the vibrator are generated to vibrate the vibrator
1
in the X-axis direction and, as a result, the same signals are outputted from the R and L outputs.
Then, if an angular velocity &OHgr; is applied about the Z-axis of the vibrator
1
, a force in the −Y direction proportional to the angular velocity &OHgr; and a velocity v
x
in the X-axis is generated. This force is the Coriolis force. By the Coriolis force, the vibrator
1
is bent toward the Y-axis direction, and a bending vibration in the −Y axis direction of the same frequency as the bending vibration in the X-axis direction is generated. Then, in accordance with the bending vibration in the Y-axis direction, Coriolis signals of opposing phases are generated at the R-side and L-side outputs. The Coriolis signals are proportional to the angular velocity, and
FIGS. 10C and 10D
shows a case where a DC angular velocity of a fixed magnitude is applied.
In order to extract a Coriolis signal component from the R-side output and L-side output of the vibrator
1
, driving output components of the same phase included in the R-output and L-output are removed by a differential amplifier. By this, the Coriolis signals obtained in the R-output and L-output in opposite phases are outputted two-fold, unlike the driving output signals. Further, if the R-output and L-output are summed, the Coriolis signals included in the R-output and L-output in opposing phases mutually cancel out, and the driving output signals are outputted two-fold. The output can be used in self-exciting oscillation.
When a dynamic angular velocity (having an AC component) is applied about the Z-axis, a Coriolis signal is generated which has the same AC component as the angular velocity. The Coriolis signal that occurs at the output of the differential amplifier is a sine wave having the bending mode oscillating frequency in the X-axis direction and which is AM-modulated by the AC component of the angular velocity.
FIG. 11A
shows an applied angular velocity, and
FIG. 11B
shows that the sine wave of the oscillating frequency occurring in the differential output becomes an AM-modulated waveform.
Because the vehicle-mounted vibrating gyroscope is related to the basic functional control ofthe vehicle, a failure detecting function or self-diagnosing function is essential. As a means for detecting failure, a structure for monitoring the amplitude or frequency of a vibrator oscillating loop or a structure for monitoring the output amplitude of a differential amplifier in a detecting circuit is employed.
Specifically, for example, Japanese Unexamined patent publication No. 4-215017 discloses a circuit means for simultaneously monitoring an oscillating signal amplitude and a detecting signal (output of the detecting circuit differential amplifier) of a tuning-bar type gyroscope by use of a rectifier circuit, and for detecting a cease of the oscillation or disconnection of a detecting circuit signal wire.
Furthermore, Japanese Unexamined Patent Publication No. 5-264279 discloses a structure for detecting disconnection by monitoring the output amplitude of a detecting circuit differential amplifier, and Japanese Unexamined Patent Publication No. 6-18270 discloses structure for detecting a failure of an oscillating circuit by monitoring a resonant frequency of an oscillating circuit signal.
In such conventional examples, there are described structures of detecting circuits based on technical knowledge intrinsic to the vibrating gyroscope, such as the fact that amplitudes or frequencies of the oscillating loop signals in the normal operation of the gyroscope are constant, or an output amplitude of a detecting circuit is not larger than a fixed value under normal operation.
However, failure modes detectable in the conventional example are only the cessation of oscillation of the gyroscope and the disconnection of a detecting circuit unit to detect short-circuiting of the detecting circuit unit due to, for example, a migration phenomenon of a circuit wiring pattern material inside the gyroscope or the electrode material of the gyroscopic vibrator which can occur in a high temperature and high humidity environment.
SUMMARY OF THE INVENTION
Accordingly, a main object of the present invention is to provide a self-diagnosing circuit for a vibrating gyroscope which has the advantage of failure detection for short-circuiting of the detecting circuit portion.
The self-diagnosing circuit for the vibrating gyroscope for detecting a vibration due to a Coriolis force generated in the Y-axis direction when a vibrator is excited in the X-axis direction and rotated about the Z-axis direction, comprises: differential operating means for calculating a difference between output signals outputted from a plurality of detecting means which is provided on the vibrator to detect the vibration due to a Coriolis force; and an offset signal source for superposing an offset signal on at least one of the signals outputted from said plurality of detecting means such that the signals are offset with different signal levels.
The self-diagnosing circuit for a vibrating gyroscope may further comprises signal detecting means for detecting the presence or absence of a signal component caused by an offset signal included in an output signal of said difference operating means. In addition, means for detecting a failure based on an output voltage and the phase thereof of said difference operating means may be included in the self-diagnosing circuit.
The offset signal source may include either a voltage signal source for
Ebara Kazuhiro
Kumada Akira
Mori Akira
Keating & Bennett LLP
Larkin Daniel S.
Murata Manufacturing Co. Ltd.
Saint-Surin Jacques
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