Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2001-01-17
2003-01-21
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C310S316020
Reexamination Certificate
active
06508123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular velocity sensor, and more specifically, it relates to an angular velocity sensor using a vibration-type angular velocity detecting element.
2. Description of the Related Art
Recently, angular velocity sensors have been used in cameras, car navigation systems, overturn detection of a car, posture control sensors and the like. In order to prevent blurring due to hand shaking when taking a picture with a camera, in order to indicate the car route in the car navigation system, and in order to improve safety when traveling by car, an angular velocity signal of the angular velocity sensor is used.
FIG. 6
shows a circuit block diagram of a conventional angular velocity sensor. Numeral
1
is an angular velocity detecting element which is provided with a vibrator
11
, a driving electrode part
12
, a driving electrode part
13
, a detecting electrode part
14
and a detecting electrode part
15
. The vibrator
11
has a ground electric potential and the driving electrode part
12
and the driving electrode part
13
vibrate the vibrator
11
electrostatically. Also, the detecting electrode part
14
and the detecting electrode part
15
detect a displacement of the vibrator
11
electrostatically. Numeral
2
and numeral
3
are capacitance-voltage converting circuits and the capacitance-voltage converting circuit
2
is provided with a junction field effect transistor (hereafter, called a JFET)
21
and the capacitance-voltage converting circuit
2
is provided with a JFET
31
. A gate
21
a
of the JFET
21
is connected to the detecting electrode part
14
of the angular velocity detecting element
1
and is connected to a source
21
c
of the JFET
21
via a gate resistor
21
d.
Also, a gate
31
a
of the JFET
31
is connected to the detecting electrode part
15
and is connected to a source
31
c
of the JFET
31
via a gate resistor
31
d.
A drain
21
b
of the JFET
21
and a drain
31
b
of the JFET
31
are each connected to a direct current source Vcc, and the source
21
c
is connected to a ground via a source resistor
21
e
and the source
31
c
is connected the ground via a source resistor
31
e.
Also, the source
21
c
is an output terminal of the capacitance-voltage converting circuit
2
and the source
31
c
is an output terminal of the capacitance-voltage converting circuit
3
and the voltage across the source resistor
21
e
is an output signal and the voltage across the source resistor
31
e
is an output signal.
Numeral
4
is an alternating-current amplifying circuit, and is provided with two amplifiers
41
and
42
and direct-current-blocking-capacitors
43
and
44
. Outputs of the capacitance-voltage converting circuits
2
and
3
are respectively connected to inputs of the amplifiers
41
and
42
via the direct-current-blocking-capacitors
43
and
44
, and the output signals are amplified. Numeral
5
is a driving control circuit which is provided with a non-inverting amplifier circuit
51
, a driving signal forming circuit
52
and an inverting amplifier circuit
53
. Outputs of the amplifiers
41
and
42
are connected to inputs of the non-inverting amplifier circuit
51
and the output of the non-inverting amplifier circuit
51
is connected to the input of the driving signal forming circuit
52
. The output of the driving signal forming circuit
52
is connected to the driving electrode part
13
of the angular velocity detecting element
1
and is connected to the driving electrode part
12
via the inverting amplifier circuit
53
. N numeral
6
is an output circuit which is provided with a differential amplifier
61
, a synchronous detecting circuit
62
, an offset adjusting circuit
63
and a sensitivity adjusting amplifier
64
. The inputs of the differential amplifier
61
are connected to outputs of the amplifiers
41
and
42
and the output of the differential amplifier
61
is connected to the input of the sensitivity adjusting amplifier
64
via the synchronous detecting circuit
62
. The output of the offset adjusting circuit
63
is connected to the input of the sensitivity adjusting amplifier
64
.
The operation of the above-described circuit block will be explained. When a driving signal having a constant frequency and a constant amplitude is applied to the driving electrode parts
12
and
13
of the angular detecting element
1
from the driving control circuit
5
, the vibrator
11
is driven and vibrates at a specific mechanical vibration frequency in a predetermined direction. The driving control circuit
5
usually applies a driving signal of a frequency approximately the same as the mechanical resonance frequency of the vibrator
11
, for example, 10 kHz, to the driving electrode parts
12
and
13
. When an angular velocity is applied to the vibrator
11
of the angular velocity detecting element
1
, the vibrator
11
is displaced in a direction orthogonal to the vibrating direction of the vibrator
11
, that is, in a direction in which a Coriolis force occurs, and variations in the electrostatic capacitance appear at the detecting electrode parts
14
and
15
. The vibrator
11
vibrates with a vibration vector obtained by adding the Coriolis force and the driving force.
Two signals with phases differing from each other by 180 degrees are output from the detecting electrode parts
14
and
15
of the angular velocity detecting element
1
and are supplied to the capacitance-voltage converting circuits
2
and
3
. The frequency of the output signal is the vibration frequency of the vibrator
11
, and the phase of the output signal is delayed by 90 degrees with respect to the phase of the driving signal. The capacitance-voltage converting circuits
2
and
3
respectively convert capacitance variations at the detecting electrode parts
14
and
15
of the angular velocity detecting element
1
into voltages. The direct current component of the output signals from the capacitance-voltage converting circuits
2
and
3
are blocked by the direct-current-blocking capacitors
43
and
44
and the output signals are amplified by the amplifiers
41
and
42
. Two outputs from the amplifiers
41
and
42
are input into the non-inverting amplifier circuit
51
and the differential amplifier
61
. The non-inverting amplifier circuit
51
adds the outputs of the two amplifiers
41
and
42
and extracts a vibration amplitude signal component for the driving signal driving the angular velocity detecting element. Also, the differential amplifier
61
obtains the difference between the two output signals of the amplifiers
41
and
42
and extracts an angular velocity signal component due to the Coriolis force.
The driving signal forming circuit
52
, which is provided with a chopping-wave forming circuit and an amplitude adjusting circuit, receives as input a signal having a vibration amplitude signal component from the non-inverting amplifier circuit
51
to form a chopping-wave signal and outputs a driving signal maintaining the vibration of the angular velocity detecting element
1
. The driving signal is supplied to the driving electrode part
13
of the angular velocity detecting element
1
and is supplied to the driving electrode part
12
via the inverting-amplifier circuit
53
after phase-inversion by 180 degrees. With this operation, the vibrator
11
of the angular velocity detecting element
1
is energized by the driving signals, the phases of which differ by 180 degrees from each other, and vibrates at a constant amplitude. The vibration amplitude signal component is fed back from the non-inverting circuit
51
to the driving signal forming circuit
52
, and thereby a self-excitation oscillating system for driving the angular velocity detecting element
1
is formed.
The angular velocity signal component obtained from the differential amplifier
61
is supplied to the synchronous detecting circuit
62
. The synchronous detecting circuit
62
executes synchronous detection for the output signal of the differential ampl
Hasegawa Tomoyasu
Yaji Kaneo
Keating & Bennett LLP
Kwok Helen
Murata Manufacturing Co. Ltd.
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