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 (xcexa9) 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 1L and 1R of the left and the right thereof and a full-surface electrode 1C, and from the detecting electrodes 1L and 1R ofthe left and the right of the vibrator 1, signals L-side output and R-side output are outputted.
FIGS. 10A to 10D 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 1C, the R-side output and L-side output become sine waves of the same phase, as shown in FIG. 10B. 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 xcexa9 is applied about the Z-axis of the vibrator 1, a force in the xe2x88x92Y direction proportional to the angular velocity xcexa9 and a velocity vx 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 xe2x88x92Y 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.
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 outputting an offset voltage as an offset signal or a current signal source for outputting an offset current as an offset signal.
As described above, according to the present invention, by superposing an offset signal on at least one of the signals outputted after detecting a vibration due to the Coriolis force of a vibrator, and by detecting the presence or absence of a signal component caused by the offset signal included in the outputted signals ofthe difference operating means for calculating the difference of the detecting outputs, it becomes possible to detect short-circuiting between detecting electrodes, or short-circuiting between a detecting electrode and a grounded potential, or a source voltage and a circuit reference potential, which has been difficult to detect so far. Thus, a vibrating gyroscope having higher self-diagnosing ability and reliability than previously can be realized.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.