Method of controlling a laser gyro by the amplitude of the winking signal
View Patent ↗A push-pull method of controlling a laser gyro. At least three mirrors form a closed-loop light path for two laser beams propagating in opposite directions, which is subjected to movement. At least two of the mirrors are associated with actuators connected to push-pull control members for controlling the positions of the mirrors to minimize the amplitude of the winking signal which occurs in a lased intensity signal of the laser beams. The method includes detecting the frequency of the winking signal of at least one laser beam, and of triggering the measurement of the amplitude of the winking signal when the frequency of the winking signal is less than a predetermined threshold corresponding to passing into a dead band of the gyro.
1. A push-pull method of controlling a laser gyro comprising:
providing at least three mirrors for implementing a closed loop light path for two laser beams propagating in opposite directions,
subjecting the gyro also to dither movement,
providing actuators which are associated with at least two mirrors, said actuators being connected to push-pull control members for controlling the positions of the mirrors so as to minimize the amplitude of a winking signal occurring in a lased intensity signal of the laser beams,
measuring a frequency of the winking signal of at least one laser beam,
triggering measurement of an amplitude of the winking signal when the measured frequency of the winking signal is less than a predetermined threshold corresponding to passing into a dead band of the gyro, and
controlling said actuators through said push-pull control members through the measurement of the amplitude of the winking signal.
2. A method according to claim 1 , further comprising:
providing the gyro with an interferometer receiving the laser beams and generating therefrom an interference signal comprising two fringe signals that are substantially in quadrature, and
filtering at least one fringe signal with high-pass filtering, and
comparing an amplitude of the filtered signal with the predetermined threshold corresponding to passing into the dead band, to trigger said measurement of the amplitude of the winking signal when the filtered signal is less than the predetermined threshold.
3. A method according to claim 2 , further comprising rectifying the filtered signal before the step of comparison with the predetermined threshold.
4. A method according to claim 3 , further comprising filtering the two fringe signals, rectifying the resulting signal, and adding the rectified signal to produce a sum signal prior to performing a comparison with the predetermined threshold.
5. A method according to claim 4 , further comprising smoothing the sum signal by low-pass filtering prior to being compared with the predetermined threshold.
6. A method according to claim 2 , further comprising modulating the predetermined threshold as a function of the amplitude of one of the fringe signals.
7. A method according to claim 2 , the step of measuring the amplitude of the winking signal includes sampling the winking signal extracted from a lased intensity of one of the laser beams.
8. A method according to claim 7 the step of measuring the amplitude of the winking signal includes taking measurements on a plurality of dead-bang crossings, calculating the amplitude of the winking signal based on the measurements of the dead-bang crossing, and providing an output to control the push-pull control members.
9. A method according to claim 1 wherein an entry speed of the gyro is less than or equal to 0.8 times a maximum speed for the dither movement.
10. A method according to claim 1 , further comprising controlling the push-pull control by applying to one mirror actuator a signal representative of the sum of a path length control and a winking adjustment control, and by applying to another mirror actuator a signal representative of a difference between the path length control and the winking adjustment control.