Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Utility Patent
1998-11-18
2001-01-02
Moller, Richard A. (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
C073S504120
Utility Patent
active
06167744
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an angular velocity sensor which can be employed in various control systems, such as a vehicle motion/behavior control system as well as a navigation system, or in a video camera for compensating the operator's hand movements, and more particularly to an angular velocity sensor which detects an angular velocity using a piezoelectric vibrator.
Unexamined Japanese Patent Application No. 7-181042, published in 1995, discloses a conventional angular velocity sensor which comprises a tuning fork vibrator, a drive circuit means for vibrating this vibrator, and an angular velocity sending means for detecting a vibratory movement caused in a direction normal to an oscillating direction of the vibrator, thereby obtaining an angular velocity of the vibrator entered about a predetermined axis.
Furthermore, a diagnosis circuit is provided to detect a failure in the system. A charge amplifier generates an output signal representing a sensed angular velocity. A band pass filter (BPF) is connected to the output terminal of this charge amplifier. A differential amplifier compares the output of the charge amplifier with the output of the BPF. When the obtained differential output is larger than a predetermined reference value, it is judged that the breakdown (such as, exfoliation of a piezoelectric element attached on a piezoelectric body) occurs in the sensor.
However, according to this diagnosis circuit, the differential amplifier produces no differential output signal when a sensing wire is broken, because both the charge amplifier and the BPF produce no output signal (0V). In other words, the diagnosis circuit of this conventional angular velocity sensor cannot detect the breaking of sensor wires.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an angular velocity sensor including a diagnosis system capable of detecting the breakdown of the sensor including the breaking of sensor wires.
Another aspect of the present invention is to provide an angular velocity sensor having an electrode arrangement capable of reducing the error in the detection of the angular velocity.
In order to accomplish the above-described and other related objects, the present invention provides an angular velocity sensor comprising a vibrator, drive electrode means provided on the vibrator for driving the vibrator, and angular velocity sensing electrode means provided on the vibrator for generating a sensing signal representing an angular velocity entered to the vibrator. A drive circuit supplies a drive signal to the drive electrode means to vibrate the vibrator. An angular velocity detecting circuit detects a vibratory movement caused in a direction normal to an oscillating direction of the vibrator based on the sensing signal of the angular velocity sensing electrode means, thereby obtaining an angular velocity of the vibrator appearing about a predetermined axis. A signal input circuit supplies a diagnostic signal to the vibrator via diagnostic signal input electrode means provided on the vibrator. A diagnosis means diagnoses the angular velocity sensor based on a signal responsive to the diagnostic signal which is obtained from at least one of the drive electrode means and the angular velocity sensing electrode means.
The drive circuit may supply the drive signal having a predetermined frequency to the drive electrode means to vibrate the vibrator. In this case, the signal input circuit supplies the diagnostic signal having a frequency different from the predetermined frequency of the drive signal.
Preferably, in response to the diagnostic signal, the vibrator oscillates in a direction normal to the oscillating direction of the vibrator.
Preferably, the diagnosis means comprises sync detecting means for sync detecting the signal responsive to the diagnostic signal by using a signal in phase with the diagnostic signal.
Preferably, the diagnosis means detects a changed direct current component of the signal responsive to the diagnostic signal.
Preferably, the signal input circuit generates the diagnostic signal by modifying an internal signal used in the drive circuit. The drive circuit controls an oscillation amplitude of the vibrator by using a feedback signal reflecting the oscillation of the vibrator. Thus, the signal input circuit uses the feedback signal as the internal signal for generating the diagnostic signal. Preferably, frequency conversion means is provided for multiplying an even number with a frequency of the feedback signal to generate the diagnostic signal.
The signal input circuit may comprise a band-pass filter for filtering the internal signal to be modified into the diagnostic signal. The signal input circuit may comprise a DC voltage changing means for changing a DC voltage of the internal signal to be modified into the diagnostic signal.
Alternatively, it is preferable that the signal input circuit intermittently supplies the diagnostic signal based on an external signal supplied from an appropriate signal generating device.
Preferably, a frequency of the diagnostic signal is the same as that of the drive signal supplied to the vibrator.
Preferably, the signal supply circuit comprises amplitude changing means for changing an amplitude of the diagnostic signal.
According to another aspect of the present invention, the vibrator has a piezoelectric body and a reference potential electrode means is provided for giving an electrode region maintained at a predetermined reference potential between the diagnostic signal input electrode means and the angular velocity sensing electrode means.
Preferably, the reference potential electrode means and the diagnostic signal input electrode means are interposed between the drive electrode means and the angular velocity sensing electrode means.
The vibrator may have at least one arm bar having a front face and opposed side faces, so that the angular velocity sensing electrode means is formed on one side face while the diagnostic signal input electrode means is formed on the front face closely to the other side face.
Preferably, an area of the diagnostic signal input electrode means is in the range from 1.5 mm
2
to 2.5 mm
2
. The reference potential electrode means is formed on the front face of the arm bar, and the diagnostic signal input electrode means is spaced from the reference potential electrode means with a gap in the range from 0.4 mm to 0.6 mm.
REFERENCES:
patent: 3697766 (1972-10-01), Ganter et al.
patent: 5388458 (1995-02-01), Weinberg et al.
patent: 5408876 (1995-04-01), Macy
patent: 5426970 (1995-06-01), Florida et al.
patent: 5719460 (1998-02-01), Watarai et al.
patent: 7-181042 (1995-07-01), None
Akimoto Katsuhide
Kato Kenji
Miura Kazuhiko
Watarai Takehiro
Denso Corporation
Moller Richard A.
Pillsbury Madison & Sutro LLP
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