Patent GB-972762-A (GB)
Title: Improvements in or relating to gyroscopes
IPC: G01C21/18
Filed: 1961-02-06
Abstract: 972,762. Gyroscopic apparatus. SVENSKA A.B. GASACCUMULATOR. Feb. 6, 1961 [Feb. 8, 1960], No. 4362/61. Heading G1C. In an inertial navigation system in which a gyroscopic rotor 16 is mounted in inner gimbal 18 and outer gimbal 20, a constant torque being applied e.g. by a spring 23, to one of the gimbals, such as the inner gimbal 18 so that the gyroscope precesses at a constant rate about the axis of the other gimbal, as shown it precesses on shaft 22 about bearings 21, secondary precession due to disturbing torques is compensated by a pick-up 25 which detects the angle between the two gimbals 18, 20 applies a signal to amplifier 36 and this controls a torquer 38. The rotor 16 may be driven by a constant frequency crystal-controlled oscillator 39 through amplifier 40, and shaft 22 may carry a ring 48 having at least one blackened sector 45 which co-operates with a light source 46 and photocell 47 on an outer, ring 44 rotatably mounted on shaft 22. The voltage from photo-cell 47 passes through amplifier 50 to phase detector 52 where it is compared with the frequency from oscillator 39 after being demultiplied in frequency divider 53. The output from detector 52 controls a servomotor 58 rotating ring 44 relative to ring 48 and is also available in line 57 as an output signal for comparing with the frequency generated by a pendulum responding to gravity as in Specification 962,669. In practice ring 48 has 360 blackened segments separated by light segments and a second ring may be provided having 36 black and white segments for co-operating with a second photo-cell. The system may be so adjusted that a given speed ratio between the two discs and a given pulse frequency in line 57 indicates that the gyroscope is free from external accelerations, and the effect of the rotation of the earth can be compensated by changing the rate of precession of the gyroscope by adjusting spring 23 so that the pulse frequency in line 57 is that in the absence of earth's rotation. To suppress periodic oscillations of the inner gimbal at the natural frequency of this part of the suspended system, the pick-up 25 also supplies voltage to an amplifier 62 controlling torquer 60 on inner gimbal shaft 19. The modulated frequency from amplifier 62 is compared in a phase detector 66 with a constant reference frequency from oscillator 39, demultiplied in frequency divider 64, the phase detector 66 being in a shunt circuit also containing a damping device, such as a variable reactance 68, so arranged as to damp out self-oscillation and keep the natural oscillation frequency of the gimbal system in step with the reference frequency from divider 64. Alternatively the voltage in the feedback loop may actuate an electromagnet whose armature varies the tension in spring 23, or a core of magnetostrictive material may be used. The rotor 16 may be mounted in a closed casing Fig. 4, not shown, forming the inner gimbal which is floated within fluid in a casing forming the outer gimbal, the suspension axis being formed by torsion bars which constitute the spring 23. Alternatively, Fig. 8, not shown, a pair of such inner gimbals may be mounted within one outer gimbal by torsion bars, the rotors rotating in opposite directions. In further arrangements the spring 23 may be replaced by, or augmented by, the centrifugal force of eccentrically disposed weights on the rotor.