Angular rate sensor

Details Angular rate sensor Angular rate sensor

2000-04-21

2002-02-12

Kwok, Helen (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Angular rate using gyroscopic or coriolis effect

C073S504160

Reexamination Certificate

active

06345533

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an angular rate sensor.
BACKGROUND OF THE INVENTION
FIG. 3
shows an example of angular rate sensors proposed in the past. In
FIG. 3
, a support pin
101
made of metal is press-fitted perpendicularly and secured in a weight plate (not shown in the figure), and one end of another support pin
102
also made of metal is press-fitted and secured in the support pin
101
in an orthogonal direction to it. A block
103
made of metal is fixed by soldering at the other end of the support pin
102
, which also serves as a common terminal. Vibration plates
104
and
105
are fixed at both ends of the metal block
103
. A piezoelectric element
106
is bonded on the vibration plate
104
to constitute a vibration exciter
150
, and another piezoelectric element
107
is bonded on the vibration plate
105
to constitute a means
160
for detecting a level of vibrations. A tip of the vibration plate
104
is extended in a manner to form a right angle with the piezoelectric element
106
to become a detecting plate
108
. A tip of the vibration plate
105
is also extended in the same manner to form a right angle with the piezoelectric element
107
to become another detecting plate
109
. Piezoelectric elements
110
and
111
are bonded respectively on the detecting plates
108
and
109
, to constitute detecting means
170
and
180
for detecting a Coriolis' force generated in proportion to an angular rate. All of the above complete an element unit
112
of a tuning-fork type angular rate sensor.
A structure of
FIG. 3
further comprises;
(a) a current amplifier circuit
120
for amplifying an output signal from the piezoelectric element
107
provided on the vibration plate
105
to detect a level of vibrations of the vibration plate
105
, which vibrates in a tuning-fork phenomenon in concert with vibrations of the vibration plate
104
;
(b) a full-wave rectifier circuit
122
for producing a D.C. voltage by rectifying an output signal (i.e. a signal at a point “A”, of which a signal voltage waveform is shown in
FIG. 4
) of a band-pass filter circuit (hereinafter referred to as “BPF circuit”)
121
, wherein an output signal of the current amplifier circuit
120
is input;
(c) an automatic gain control circuit (hereinafter referred to as “AGC”)
123
whose amplification factor for the output signal of the BPF circuit
121
varies according to a magnitude of an output signal of the full-wave rectifier circuit
122
;
(d) a driver circuit
124
(an output signal of this circuit, i.e. a signal at a point “B”, has a voltage waveform shown in
FIG. 4
) for driving the piezoelectric element
106
bonded on the vibration plate
104
according to a magnitude of an output signal of the AGC
123
;
(e) a charge amplifier circuit
125
for inputting and amplifying output signals of the piezoelectric elements
110
and
111
, which detect a Coriolis' force generated in proportion to an angular rate;
(f) a synchronous detection circuit
127
for detecting an output signal of a BPF circuit
126
, wherein an output signal of the charge amplifier circuit
125
is input; and
(g) a sensor output terminal
129
for outputting an output signal of a low-pass filter circuit (hereinafter referred to as “LPF circuit”)
128
, wherein an output signal of the synchronous detection circuit
127
is input.
In addition, a reference voltage generating means
132
comprises a power supply
130
and a buffer
131
. The reference voltage generating means
132
supplies a reference voltage to each of the above-cited circuits through a circuit resistance
133
(let a resistance value be “R1”).
A terminal
135
is also provided for connecting the reference voltage generating means
132
to the support pin
102
via the circuit resistance
133
and another circuit resistance
134
(let a resistance value be “R2”). The foregoing elements constitute a driving circuit
136
.
The element unit
112
of a tuning-fork type angular rate sensor and the driving circuit
136
complete the angular rate sensor.
In the prior art technique, an alternate current “i” flows from the driver circuit
124
toward the reference voltage generating means
132
via the terminal
135
by passing through the vibration exciter
150
at all the time, even in an ordinary vibrating condition of the tuning fork.
In addition, a demand for reduction in size of the angular rate sensors necessitates an integration of the driving circuit
136
into an IC tip form. This consequently reduces a width of wiring pattern, which in turn increases resistance values of the individual circuit resistances
133
and
134
.
Ripple voltage of a large magnitude defined by (R
1
+R
2
)·i is therefore generated between the circuit resistances
133
and
134
(this ripple voltage is observed at a point “C”, and a waveform of the signal voltage is shown in FIG.
4
).
The ripple voltage subsequently causes a substantial difference between the reference voltage input to individual circuits and the voltage at the terminal
135
. A displacement current flows as a result (this displacement current is observed at a point “D”, of which a signal current waveform is shown in
FIG. 4
) from the piezoelectric elements
110
and
111
. This displacement current is input in the charge amplifier circuit
125
, and an output signal voltage of it appears at a point “E” (a waveform of the signal voltage is shown in FIG.
4
). However, this signal voltage turns into an output signal of the synchronous detection circuit
127
and appears at a point “F” (a waveform of this signal voltage is shown in
FIG. 4
) without being cut off in a process of synchronous detection, since it is in a same phase as the waveform of the signal voltage at the point “A”, i.e. a timing signal, of the synchronous detection circuit
127
. This output signal eventually becomes an offset voltage (this offset voltage is observed at a point “G”, as shown in FIG.
4
), and it comes out at the output terminal
129
. This offset voltage denoted as &Dgr;V is given by a formula (1):
&Dgr;V=A·D·
(
R
1
+
R
2
)·i·(1
/C
0
)·(
Cs
1
+
Cs
2
)·sin &phgr;  (1),
where:
A is a gain of the low-pass filter and the band-pass filter;
D is a detection coefficient;
C
0
is a feedback capacity of the charge amplifier, in pF; and
Cs
1
and Cs
2
are electrostatic capacities of the piezoelectric elements
110
and
111
, in pF.
In addition, it is likely that a variation occurs with the reference voltage input to the individual circuits, since ripple voltage of a large magnitude defined by R
1
·i is generated in the circuit resistance
133
.
SUMMARY OF THE INVENTION
An angular rate sensor of the present invention comprises:
(a) a vibration exciter for providing a vibration body with vibrations;
(b) a means for detecting a level of vibrations of the vibration body;
(c) a detecting means for detecting a Coriolis' force produced in proportion to an angular rate;
(d) a current amplifier circuit for amplifying an output signal of the means of detecting a level of vibrations;
(e) a full-wave rectifier circuit for producing a D.C. voltage by rectifying an output signal of a band-pass filter circuit, wherein an output signal of the current amplifier circuit is input;
(f) an automatic gain control circuit whose amplification factor for the output signal of the band-pass filter circuit varies according to a magnitude of an output signal of the full-wave rectifier circuit;
(g) a driver circuit for driving the vibration exciter in accordance with a magnitude of an output signal of the automatic gain control circuit;
(h) a charge amplifier circuit for inputting and amplifying a signal detected by the detecting means for detecting a Coriolis' force;
(i) a synchronous detection circuit for detecting an output signal of a band-pass filter circuit, wherein an output signal of the charge amplifier circuit is input;
(j) a sensor output terminal for outputting an output signal of a low-pass filter circuit, wherein an output signal of the synchronous detection

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