Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-10-19
2002-10-22
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06467347
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular velocity detection circuit in a vibrating gyroscope, for example, an angular velocity detection circuit in a vibrating gyroscope for detecting an angular velocity based on an oscillation output of a vibrating gyroscope including a bimorph vibrator for use in correction of camera-shake, a navigation system, and so forth, and to a method of detecting angular velocity.
2. Description of the Related Art
FIG. 11
is a schematic perspective view showing an example of a conventional bimorph vibrator for use in a vibrating gyroscope. In
FIG. 11
, the bimorph vibrator
1
is formed by two piezoelectric element sheets having polarization directions which are opposite to each other (as shown by the oppositely facing arrows), and which are bonded to each such that the vibrator
1
has a rectangular cross-section. When the vibrator
1
vibrates in the longitudinal mode, i.e., vibrates in the X-axis direction, and the vibrator is rotated at an angle (&OHgr;) about the Z-axis direction, vibration is generated in the transverse vibrating mode, i.e., in the vertical Y-axis direction, due to the Coriolis force.
The amplitude of this vibration is proportional to the angular velocity. Thus, the angular velocity can be detected by utilizing the proportional relation. The vibrator
1
is provided with right and left electrodes
1
R and
1
L, respectively, and a common electrode (not shown). A differential output signal of a left signal and a right signal is output from the right and left electrodes
1
L and
1
R, respectively. For the above described vibrator
1
, it is necessary to adjust the balance, the null voltage (also called an offset voltage or a neutral point voltage), the sensitivity, and so forth, individually.
FIG. 12
is a block diagram of an angular velocity detection circuit for producing an output from the vibrator
1
shown in FIG.
11
. In
FIG. 12
, the differential output signal from the vibrator
1
is amplified in a differential amplification circuit
21
. The amplified waveform is detected in a synchronous detection circuit
22
and smoothed in a smoothing circuit
23
. The produced DC voltage is DC amplified in a DC amplifier
24
. When the signal is amplified in the DC amplifier
24
, the null voltage is also DC amplified. Accordingly, the DC component is cut off in a DC cut circuit
25
comprising, e.g., a filter. The signal is further amplified in an amplification circuit
26
to be output as an analog signal. Then, the analog signal is converted to a digital signal in an A/D converter
27
. Thereafter, the angular velocity detection signal is supplied to a microcomputer
28
, so that camera-vibrating shake is suppressed, or control for navigation is carried out.
Generally, a conventional gyroscope chip includes the vibrator
1
through the amplifier
26
. As a result, the conventional vibrating gyroscope chip tends to become large in size. In addition, it is necessary for an apparatus installed with a vibrating gyroscope to employ an A/D converter. There is a great demand for a vibrating gyroscope which can output a digital signal corresponding to a detected angular velocity, thereby enabling cost reduction of the vibrating gyroscope, as well as cost reduction of the entire the apparatus installed within the vibrating gyroscope.
The conventional gyroscopes have additional drawbacks. Specifically, when a signal component is amplified in the DC amplifier
24
in the angular velocity detection circuit shown in
FIG. 12
, the null voltage is also amplified. If the gain of the DC amplifier is high, the fluctuation of the null voltage in response to the change in temperature become so large to affect the detection of a signal representing the angular velocity. For this reason, the gain of the DC amplifier
24
cannot too large.
Furthermore, the null voltage cannot become 0V due to the unbalance between the right signal and the left signal. As a result, the gain of the DC amplifier
24
has to be so small that the null voltage does not saturate at power voltage or the ground potential, regardless of the fluctuation of the null voltage.
In addition, if a high pass filter for passing a signal having a frequency of at least 0.1 Hz is formed to cut the DC component in the DC cut circuit
25
, it is necessary to provide a combination of a 20 &mgr;F large capacitance capacitor and a 1 M&OHgr; resistor for the high pass filter. Thus, a large-sized apparatus is required.
Furthermore, in the circuit shown in
FIG. 12
, the output signal is output from the differential amplification circuit
21
with the right and left signal components being out of phase in some cases, and with the amplitudes of the right and left signal components being shifted, in other cases. In the case in which the amplitudes are shifted from each other, the amplitude of the differential output is simply changed, since the right and left signal components are sine waves. On the other hand, when the right and left signal components are out of phase, the output signal is out of phase with the reference signal.
As another conventional example, Japanese Examined Patent Application Publication No.
6-13970
describes that a drive signal is applied to the detection sideface of a vibrator in such a manner that the phase difference angle between the vector of an output voltage, caused by the angular velocity when a vibrator is rotated, and the vector of the null voltage when the vibrator stops, becomes 90°. The angular velocity is detected based on a phase difference in the combined vector.
In this example, the amplitude of the output from the vibrator has a linearity. On the other hand, the relation between the phase difference and the sensitivity is not linear, and the non-linearity tends to change in accordance with the null phase. For this reason, it is desirable to digitize the amplitude of the Coriolis force.
For example, Japanese Unexamined Patent Application Publication No. 62-150116 describes that sample-and-hold is carried out at the time when the angular velocity, caused by oscillation-driving, becomes maximum and minimum.
Furthermore, in Japanese Unexamined Patent Application Publication No. 7-260493, it is described that a difference in current passing through a piezoelectric device is detected, and sample-hold is carried out at the timing when the displacement velocity of a vibrator detecting the difference becomes zero. However, it is not described how the sample-and-held signal is digitized.
Japanese Unexamined Patent Application Publication No. 8-146056 discloses a phase difference detection circuit for a gyroscope. Although the circuit outputs signals which can be directly processed by a microcomputer, the phase difference of the detected signal is adversely affected by the change of the temperature. That is, the phase difference detection circuit has a problem that it is difficult to detect an angular velocity precisely and stably.
SUMMARY OF THE INVENTION
Accordingly, it is a main object of the present invention to provide an angular velocity detection circuit for a vibrating gyroscope which can output a digital signal corresponding to a detected angular velocity. Another object of the present invention is to provide an angular velocity detection circuit for a vibrating gyroscope in which a null voltage can be detected and corrected.
The present invention also provides a vibrating gyroscope comprising such an angular velocity detection circuit and a method of detecting an angular velocity.
In accordance with a first aspect of the invention, a method of detecting angular velocity comprises generating a differential signal from a vibrator, the differential signal having a Coriolis force proportional to angular velocity if the vibrator is rotated; generating a timing signal based on the differential signal; and applying the differential signal to a voltage-time converter which, based on the timing signal, converts the differential signal to a pulse train having a duty cycle proportional to the angular veloci
Kwok Helen
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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