Angular velocity detector and apparatus having angular...

Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system

Reexamination Certificate

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C250S231180, C356S459000, C372S094000

Reexamination Certificate

active

06465771

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a angular velocity detector, and more specifically an apparatus which detects a rotational angular velocity utilizing a ring laser type gyroscope.
2. Related Background Art
Conventionally known as gyroscopes for detecting angular velocities of moving bodies are mechanical gyroscopes having rotors and oscillators as well optical gyroscopes. The optical gyroscopes in particular which can be started momentarily and have broad dynamic ranges are renovating the art of gyroscope technology. The optical gyroscopes are classified into a ring laser type gyroscope, an optical fiber gyroscope, a passive type ring resonator gyroscope and so on. Out of these optical gyroscopes, the ring laser type gyroscope which uses a gas laser was developed earliest and has already been put to practical used in aircrafts and so on. As a ring laser type gyroscope which is compact and has a high accuracy, there has recently been available a semiconductor laser gyroscope which is integrated on a semiconductor substrate.
FIG. 12
is a plan view illustrating an optical gyroscope which is capable of detecting not only an angular velocity but also a rotational direction. Reference numeral
10
denotes a quartz tube, reference numeral
11
denotes an asymmetrical tapered portion of a light waveguide path, reference numeral
12
denotes a mirror, reference numeral
13
denotes an anode, reference numeral
14
denotes an electrode terminal, reference numeral
15
denotes a cathode, reference numeral
100
denotes a counterclockwise laser beam and reference numeral
110
denotes a clockwise laser beam.
In a configuration described above, the quartz tube
10
is formed by boring a quartz block. Then, the mirror
12
is attached to the quartz tube
10
. Furthermore, the anode
13
, the electrode terminal
14
and the cathode
15
are attached to the quartz tube
10
. Then, the quartz tube
10
is filled with helium gas and neon gas, and a voltage is applied across the anode and the cathode to start electric discharge and supply an electric current. The counterclockwise laser beam
100
and the clockwise laser beam
110
are oscillated in the quartz tube
10
.
When the quartz tube
10
stands still, the laser beam
100
and the laser beam
110
have substantially the same oscillation frequency of 4.73×10
15
Hz and an oscillation wavelength &lgr; of 632.8 nm. However, an oscillation threshold value for the laser beam
100
is smaller than that for the laser beam
110
since the tapered portion
11
of the light waveguide of the path has an asymmetrical shape. Accordingly, the laser beam
100
has an optical intensity which is higher than that of the laser beam
110
. As a result, an oscillation frequency f
1
of the laser beam
100
is 20 MHz higher than an oscillation frequency f
2
of the laser beam
110
. The laser beam
100
and the laser beam
110
interfere with each other in the quartz tube
10
. A signal having an amplitude of 100 mV and a frequency of 20 MHz is obtained by adjusting a power source current so as to be constant and monitoring a voltage across the electrode terminal
14
and the cathode
15
. In other words, a beat voltage can be detected even when the quartz tube
10
stands still.
When the quartz tube
10
is rotated clockwise at a velocity of 1 degree per second and a side of the resonator is 10 cm long, the oscillation frequency f
1
of the counterclockwise laser beam
100
is increased by 248.3 kHz. On the other hand, the oscillation frequency f
2
of the clockwise laser beam
110
is decreased by 248.3 kHz. Accordingly, the beat frequency is (f
1
−f
2
)=20 MHz+496.6 kHz. When the quartz tube
10
is rotated counterclockwise at a velocity of 1 degree per second, on the other hand, the beat frequency is (f
1
−f
2
)=20 MHz−496.6 MHz. Since absolute values of the increase and the decrease of the beat frequency are proportional to the rotational speeds and the rotational directions have one-to-one correspondence to the increase and decrease of the beat frequency, the optical gyroscope is capable of detecting not only rotational speeds but also rotational directions. Though the quartz tube
10
is driven with the constant current and changes of a terminal voltage are measured in this example, changes of a current supplied to a terminal may be detected when the quartz tube
10
is driven with a constant voltage. Furthermore, changes of impedance of electric discharge may be detected directly with an impedance meter. Though helium gas and neon gas are used in this example, any gas is usable so far as the gas can be excited by a laser beam. Furthermore, the light waveguide path may have any form which surrounds a rectangle, a hexagon, a triangle, a circle or the like.
The gyroscope indicates changes of a terminal voltage having a predetermined frequency due to interference between the laser beam
100
and
110
even in a standstill condition free from an angular velocity. Furthermore, this frequency is increased when a clockwise rotational angular velocity is applied to the gyroscope and decreased when a counterclockwise angular velocity is applied to the gyroscope.
FIG. 13A
exemplifies changes of angular velocity applied to the gyroscope taking a positive side and a negative side of an angular velocity &OHgr;=0 as clockwise and counterclockwise respectively. An example of angular velocity traced in a solid line
51
indicates that a clockwise angular velocity changes into a counterclockwise angular velocity with time lapse.
FIG. 13B
which shows changes of a terminal voltage Vg of the gyroscope corresponding to the changes of the angular velocity indicated by
51
indicates that a changing frequency a beat voltage changes lower as the angular velocity changes due to interference with a laser beam as indicated by a curve
52
.
FIG. 13C
is a voltage waveform diagram of a rectangular wave
53
which is obtained by comparing the terminal voltage indicated by
52
with a level of Vref shown in FIG.
13
B. Information of the angular velocity can be obtained by measuring, for example, time intervals of rising edges of a voltage of the rectangular wave
53
or a number of edges within a predetermined time.
FIG. 14
shows relationship between an angular velocity applied to the gyroscope and a beat voltage taking a beat frequency at an angular velocity
0
as fo. In
FIG. 14
, a maximum angular velocity within a necessary range for detection is denoted as &OHgr;mx, a beat frequency at this angular velocity is denoted as fmx, a minimum angular velocity within the necessary range for detection is denoted as &OHgr;mn and a beat frequency at this angular velocity is denoted as fmn. &OHgr;o denotes an angular velocity at which the beat frequency is 0. A straight line
54
indicates that the beat frequency is enhanced as an angular velocity is increased in a clockwise direction and lowered as angular velocity is increased in a counterclockwise direction. Appliances which utilize built-in gyroscopes (for example, cameras, binoculars and navigators) have necessary ranges for detection of angular velocities and necessary detecting resolutions demanded dependently on characteristics of the appliances respectively. In a case where an angular velocity is detected with a gyroscope built in a still camera to prevent image blur, for example, it is sufficient, as already known, to detect the angular velocity with a resolution on the order of 0.1 degree/second within a range on the order of −20 to +20 degrees/second. In an example of the above described camera, &OHgr;mx=+20 degrees/second and &OHgr;mn=−20 degrees/second. Furthermore, there are a frequency characteristic and so on which are required dependently on characteristics of the appliances utilizing the built-in gyroscopes and in case of an image blur preventive system of the above described still camera, it is necessary to prevent a phase delay from exceeding ±15° within a range of DC

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