Patent GB-707518-A (GB)
Title: Improvements in or relating to gyro-compasses
IPC: G01C19/36
Filed: 1950-05-26
Abstract: 707,518. Gyroscopic apparatus. SPERRY CORPORATION. May 26., 1950 [May 28, 1949]. No. 23331/52. Divided out of 707,446. Class 97(3) In a gyro-compass having a gravity-responsive control element for rendering the directional element northseeking by the application of torques about a horizontal axis in dependence on tilt of the directional element and damping means controlled by the gravity-responsive element for applying torques about the vertical axis in dependence on tilt of the directional element to damp the oscillations of the compass about the meridian, the said damping means are rendered ineffective by displacement of the gravity responsive element by an amount materially more than the amount it is displaced during a normal tilt of the directional element during the action of acceleration forces on the gravity-responsive element of the order of those occurring during turns or changes of speed of the ship carrying the compass having a north-south component. Alternatively the damping means may be so arranged in conjunction with the gravity responsive element as to be unaffected by the action of acceleration forces acting on said element. The gravity responsive element may be controlled by a time-delay device, e.g. by a silicone damping fluid permitting movement of the device during longperiod accelerations e.g. due to gravity acting during a tilt of the directional element and eliminating movement of the gravity-responsive element during short period accelerations e.g. during turns or changes of speed having a north-south component. As shown a mass 13 supported in antipendulous fashion by leaf springs 14, 15 on a bracket 19 secured to the gyro-casing 6 applies a meridian-seeking torque about the E-W horizontal axis 7 of the compass and is movable along the direction of the gyro axis 8 under the influence of gravitational or other accelerations. To provide the compass with a dual period as described in Specification 707,446 an additional torque is provided by a pair of oppositely directed jets produced by e.g. rotation of the rotor wheel or by impeller 25<SP>1</SP> in an extension 25 of the casing 6 and issuing from slots 24, 24' to produce an unbalanced force or torque. The direction of the jets is inclined to the vertical so as to produce a component torque about the vertical axis 2 of the compass and so reduce the tilt. The vertical component of the jet blast provides the additional torque aforesaid. On shifting of the weight 13, due to tilt of the gyro axis baffle plates 21, 22, with apertures 23 therein, attached to the mass vary the normally balanced jets, but upon further, shift due, e.g. to turns or changes in speed, the slots 24, 24<SP>1</SP> are wholly covered by the baffle plates and rendered ineffective. Damping means, such as a paddle in a viscous liquid e.g. silicone fluid retards the shift of the mass 13 so that it is not responsive to accelerations due to pitch and roll. In an alternative construction the aforesaid additional torque may be produced by a second mass on the opposite side of the gyro casing and the air jets are then disposed in an east-west direction and associated with the first mass which is made so stiff by damping means that it responds only to slow earth-induced tilt of the gyro so that the compass damper formed by the jets is unchanged during short accelerations e.g. due to turns or changes of speed. In a further modification the first mass may be less damped so as to respond to the shorter accelerations and the second mass highly damped, the jets being associated with the first mass but being so changed in construction as to become ineffective when the first mass moves an increased amount to close both the jet ports as in Fig. 2. Specification 612,723 also is referred to.