Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-07-10
2003-07-01
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C356S459000, C372S094000
Reexamination Certificate
active
06586725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ring laser, and more particularly to a gyro apparatus for detecting rotation utilizing a semiconductor laser, in particular a gyro apparatus capable of detecting the rotating direction, and a driving method and a signal processing method therefor.
2. Related Background Art
As the gyro apparatus for detecting the angular velocity of rotation, there are already known a mechanical gyro having a rotor or an oscillator, and an optical gyro. Particularly the optical gyro is causing a revolution in the field of gyro technology, since it can be activated instantly and has a wide dynamic range.
Within such-optical gyro, there are known a ring laser gyro, an optical fiber gyro, a passive ring resonator gyro etc. The ring laser gyro utilizing a gas laser is already commercially employed in the airplanes or the like.
Also as a compact ring laser gyro of high precision, there is proposed a gyro based on a semiconductor ring laser formed on a semiconductor substrate, as disclosed in the Japanese Patent Publication No. 62-39836, the Japanese Patent Application Laid-open No. 4-174317 and the Japanese Patent Publication No. 6-38529.
The gyro based on the semiconductor ring laser enables reduction in the device size, in the electric power consumption and in the start-up time in comparison with the mechanical gyro having an oscillator, and is therefore suitable for use as an antivibration control device for preventing the error in phototaking by hand vibration in a still camera and a video camera.
In such a gyro, the beat frequency contains the information of angular velocity. For detecting the beat frequency, there are a method of converting the beat frequency into a voltage signal by a frequency-voltage conversion circuit, and a method of directly detecting the beat frequency by a frequency counter.
SUMMARY OF THE INVENTION
However, the conventional ring laser gyro is incapable of detecting the rotating direction by its output signal. Therefore the rotating direction is detected by applying a small rotational vibration (dither) and utilizing the correlation between such dither and the signal.
Also the Japanese Patent Publication No. 62-39836 and the Japanese,Patent Application Laid-open No. 4-174317 do not suggest the specific method for detecting the rotating direction.
In consideration of the foregoing, an object of the present invention is to provide an optical gyro capable of detecting the angular velocity and the rotating direction with sufficient accuracy.
Another object of the present invention is to provide a driving method for the optical gyro, capable of suppressing the variation in the beat frequency at the standstill state.
(1) At first a case of employing two ring lasers will be explained.
The optical gyro of the present invention is provided with ring lasers and detection means for detecting the beat frequency of the ring lasers, wherein there are a first ring laser which increases the beat frequency when the angular velocity increases to a certain direction from the standstill state, and a second ring laser which increases the beat frequency when the angular velocity increases regardless of the rotating direction, and such first and second ring lasers are positioned so as to be optically independent of each other.
In a such configuration, the beat frequencies of the two ring lasers correspond to the frequencies of the variations in the impedances of the respective ring lasers, and such changes in the frequencies corresponding to the variations of the impedances have respectively different dependences on the angular velocity. It is therefore possible to obtain the angular velocity by signal processing of such changes. In the following, a more detailed description will be given on a configuration employing a semiconductor ring laser as the ring laser.
In the semiconductor ring laser, the relationship between the angular velocity and the signal frequency becomes non-linear or the signal cannot be obtain, in a certain angular velocity range, though such situation depends on the shape of the wave guide path to a certain extent.
By employing the two semiconductor ring lasers of mutually different angular velocity dependence, with different angular velocity ranges of such non-linearity, it is possible to obtain the signals from the two semiconductor ring lasers and to execute signal processing by employing either of the signals or combining the signals. Such process allows to obtain the angular velocity without being influenced by the non-linearity.
Also in the first semiconductor ring laser, the frequency change corresponding to the variation in the impedance is not symmetrical with respect to the rotating direction (sign of the angular velocity), and this fact can be utilized for detecting the rotating direction.
Also by executing addition or subtraction with suitable weighting on the frequency changes corresponding to the variations in the impedances in the two semiconductor ring lasers, the beat frequency in the first semiconductor ring laser in the standstill state can be obtained. Therefore, that it is possible to execute feedback control to suppress the variation in beat frequency in the stand still state. Also, it is possible to reflect the variation in the beat frequency in the standstill state on the single processing for obtaining the angular velocity.
Consequently, a gyro, in which precisely measures the angular velocity and the rotating direction, can be constructed from such two semiconductor ring lasers.
Also the signal processing method for the optical gyro of the present invention is featured in that the angular velocity is detected from the signal of the first ring laser when the absolute value of the angular velocity is smaller than a predetermined value, and the absolute value of the angular velocity is obtained from the signal of the second ring laser when the absolute value of the angular velocity is larger than the predetermined value.
Also the signal processing method for the optical gyro of the present invention is featured in that, in a prespecified first angular velocity range, the signal from the first ring laser and the signal from the second ring laser are processed to determine the beat frequency of the standstill state, and, in a second angular velocity range, the angular velocity is obtained from the aforementioned beat frequency of the standstill state,and the signal from the first semiconductor ring laser.
It is further featured in that the angular velocity ranges are determined from the result of processing of the signal from the first ring laser and the signal from the second ring laser, and the method of signal processing is switched according to such ranges.
Furthermore, the signal processing method for the optical gyro of the present invention is featured in that the signal from the first ring laser and the signal from the second ring laser are processed and the rotating direction is detected from the result of such processing.
Also the driving method for the optical gyro of the present invention is featured in that the signal from the first ring laser and the signal from the second ring laser are processed to determine a value corresponding to the beat frequency at the standstill state, and feedback control is executed so as to stabilize such a beat frequency.
Furthermore, the optical gyro of the present invention is featured in that a first ring laser having a tapered area asymmetrical to the optical wave guide and a second ring laser not having an asymmetrical tapered area are positioned so as to be optically independent.
(2) In the following a case of employing three ring lasers will be explained.
The optical gyro of the present invention is provided with mutually optically independent three or more semiconductor ring lasers, including at least a pair of the semiconductor ring lasers showing mutually opposite changes in the frequency of the variation in the impedance with respect to the rotation in a direction, and a ring laser in which the beat frequenc
Mizutani Natsuhiko
Numai Takahiro
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