Fiber optic gyro with self-diagnostic function

• US 5,108,181 A
• Filed: 06/17/1991
• Issued: 04/28/1992
• Est. Priority Date: 06/21/1990
• Status: Expired due to Term

• Current Assignee: Japan Aviation Electronics Industry Limited
• Original Assignee: Japan Aviation Electronics Industry Limited
• Inventors: Nakagami, Kouichi
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US07/716,280
• Time in Patent Office: 316 Days
• Field of Search: 356/350
• US Class Current: 356/464
• CPC Class Codes: G01C 19/721 Details
• CPC Class Codes: G01C 19/726 Phase nulling gyrometers, i.e. compensating the Sagnac phase shift in a closed loop system

Abstract

In a fiber optic gyro which is constituted by a negative feedback loop in which the phase difference between right-handed light and left-handed light propagating through an optical fiber coil is detected from their interference light and a ramp wave of a frequency corresponding to the detected phase difference is generated by a ramp generated and is applied to a feedback phase modulator to reduce the phase difference between the right-handed light and the left-handed light, a diagnostic signal generated by a diagnostic signal generator is applied via a combining circuit to the closed loop and the corresponding response signal is extracted therefrom. Based on the response signal, a diagnostic unit diagnoses a fault of the fiber optic gyro.

Claims

1. A fiber optic gyro with a fault diagnostic function, comprising:

a light source for emitting a light beam to an optical path;

an optical fiber coil which makes at least one loop;

optical splitter/coupler means which splits said light beam from said optical path for incidence to both ends of said optical fiber coil and couples together light beams emitted therefrom after having propagated therethrough as right-handed light and left-handed light and provides the resulting interference light onto said optical path;

feedback phase modulating means connected in series between one end of said optical fiber coil and said optical splitter/coupler means, for providing a phase difference between said right-handed light and said left-handed light;

photoelectric converting means supplied with said interference light from said optical path, for converting its intensity into an electric signal;

phase detecting means for detecting information on said phase difference between said right-handed light and said left-handed light contained in said electric signal from said photoelectric converting means;

ramp wave generating means for generating a ramp wave of a frequency corresponding to the level of the detected signal from said phase detecting means, said ramp wave from said ramp wave generating means being provided to said feedback phase modulating means so that said phase difference between said right-handed light and said left-handed light is reduced to zero to thereby form a closed loop which effect negative control;

diagnostic signal generating means for generating a predetermined diagnostic signal;

signal combining means for combining said diagnostic signal from said diagnostic signal generating means with said closed loop; and

diagnostic means which obtains a response signal responsive to said diagnostic signal from said closed loop and makes a fault diagnosis based on said response signal.

2. The fiber optic gyro of claim 1, wherein said signal combining means is connected between said phase detecting means and said ramp wave generating means, for superimposing said diagnostic signal on the output of said phase detecting means.

3. The fiber optic gyro of claim 1, wherein said signal combining means is connected between said ramp wave generating means and said feedback phase modulating means, for superimposing a ramp wave for diagnostic use, as said diagnostic signal, on the output of said ramp wave generating means.

4. The fiber optic gyro of claim 1, wherein said signal combining means is diagnostic phase modulating means connected in series between one end of said optical fiber coil and said optical splitter/coupler means and said diagnostic signal generating means superimposes a ramp wave for diagnostic use, as said diagnostic signal.

5. The fiber optic gyro of claim 1, which further includes bias phase modulating means connected in series between one end of said optical fiber coil and said optical splitter/coupler means and bias signal generating means for applying a bias phase modulating signal to said bias phase modulating means so that said right-handed and said left-handed light propagating through said optical fiber coil are given bias phase alternating every propagation time thereof, and wherein said signal combining means is provided between said bias signal generating means and said bias phase modulating means, for superimposing said diagnostic signal on said bias phase modulating signal.

6. The fiber optic gyro of claim 1, 2, 3, 4, or 5, wherein said response signal from said closed loop is the output of said phase detecting means.

7. The fiber optic gyro of claim 1, 2, 3, 4, or 5, wherein said response signal from said closed loop is the output of said fiber optic gyro corresponding to said ramp wave.