| 摘要 |
1,116,416. Lasers. HONEYWELL Inc. 22 March, 1966 [2 April, 1965], No. 12668/66. Heading H1C. To prevent locking in to a common frequency of the two light beams passed in opposite directions around a ring laser angular rate sensor when low rotational rates are sensed, the two beams are biased by electrical or mechanical oscillations which cause periodic variations of their respective frequencies. As shown in Fig. 1, light beams 18, 26 emitted by a laser active' medium 10 pass along a closed path formed by reflectors 12, 14, 16, an output being obtained through reflector 12 which is partially lighttransmitting. The two light beams are combined by a reflector 20 and partially-transmitting reflector 22, and together produce a moving fringe pattern at a detector array 24 when the ring laser is rotated. The direction and rate of movement of the fringe pattern detected are determined respectively by the direction of movement of the ring laser and its rotational rate about an axis 28. The passage of the fringe bars is recorded by a counter 45 which is connected through a comparator 52 to an output counter 54, the rate of count being determined by rate monitors 60, 66. Monitor 66 improves the linearity of the system by controlling the power supplied to the active medium from a power source 68 and potentiometer 70. Monitor 60 closes a switch 62 when the rotational rate is low and so connects a power source 64 to an A.C. bias source 37, the A.C. bias being applied to a coil 43 which establishes a magnetic field in a Faraday medium 35. The medium, in association with quarter-wave plates 31, 33, produces an effective path length difference for the two oppositely-directed beams when energized and a resultant frequency difference which is sufficient to avoid locking in. To prevent an accumulated error on the counter 45, the bias source is reversed periodically so that the error signal is cancelled. Because of the modulation introduced by the sine wave bias which gives an additional count, a compensatory count in a counter 50 driven by the bias source is applied to the comparator 52. A mechanical bias is used in Fig. 2, in which the ring laser system is mounted for mechanical oscillation on a base 102 by leaf springs 90, 92, 94, reciprocation being produced by an electromagnet 122 which is driven by an oscillator 120. The two output beams passed by a partially-transmitting reflector 110 are combined by a prism 112 fixed to the base, this prism by changing the path length of the beam 106 as the ring laser reciprocates providing automatic compensation for the error due to frequency shift, Fig. 3 (not shown). |
