Patent GB-839024-A (GB)
Abstract: 839,024. Gyroscopic apparatus. SOC. D'APPLICATIONS GENERALES D'ELECTRICITE ET DE MECANIQUE S.A.G.E.M. Aug. 6, 1957 [Aug. 10, 1956], No. 24737/57. Class 97(3) In a gyroscopic apparatus, at least two gyroscopes mounted on a platform, each having two degrees of freedom only and their input axes being inclined, preferably at right-angles, to each other, the platform is mounted with two degrees of freedom; the gyroscopes can rotate the platform, in response to deflections of their output axes, about two axes both at an angle to a reference direction; and at least two indicators are mounted on the platform to detect deviations thereof from the reference direction about axes parallel to the input axes of the gyroscopes, each indicator generating a torque tending to deflect, about its output axis, the gyroscope, the input axis of which is not parallel to the axis of response of the detector so that the platform behaves as an oscillatory system having a stable position of equilibrium in the reference direction. Gyroscopic elements. As shown in Fig. 1, the gyroscope rotor 1 is mounted in a gimbal 3 and is spun about an axis X. The gimbal 3 is journalled for rotation about an output axis Y in the element frame. When the element is rotated about an input axis Z (at right-angles to axis X, Y), the gimbal 3 rotates about output axis Y, the angle of rotation being damped e.g. by hydraulic means, and indicated by a signal from an electric detector 5a, 5b. The angle through which the gimbal 3 turns thus depends on the integral of the torque applied about the input axis Z, starting from an initial position of the gimbal, in the absence of torque about the axis Y; but additional rotation may be imparted by a torque about axis Y, produced by a torque motor 6. Application to gyro-compass. As shown in Fig. 2, an outer gimbal 8 is journalled in mounting 7 fixed in a craft or vehicle, and is rotatable by an electric motor 10. An inner gimbal 13 is journalled in the outer gimbal 8 for rotation, by means of an electric motor 15 mounted on gimbal 8, about an axis preferably at right-angles to the axis of rotation of gimbal 8. A circular platform 18 is mounted on gimbal 13 for rotation by means of an electric motor 20, a scale of angles on the platform being read against a mark 19 on gimbal 13, at right-angles to the gimbal axis. Two gyroscopic elements 23, 24 with gyroscopes, as described above, are mounted on the platform wth their output axes Y1, Y2 parallel to the 0-180‹ direction of the scale on the platform edge, their spin axes X1, X2 at right-angles, and their input axes Z1, Z2 also at right-angles. The platform also carries tilt indicators 25, 26 for detecting tilt about the 90-270 degrees axis and the 0-180 degrees axis respectively. Indicator 25 controlls the torque motor m1 of gyroscope 23, detector d1 of which controlls an amplifier supplying current to motor 20. Indicator 26 is connected to one stator winding of an angle resolver 27, the angle between the rotor and stator of which is equal to the angle indicated by index 19 on the scale on platform 18. The detector d2 of gyroscope 24 is connected to the other stator winding, so that a signal is generated in the rotor winding which is dependent on the signals from indicator 26 and detector d2, and on the angle indicated on the angle scale. This signal controls, through amplifiers not shown, the motors 10, 15. The arrangement is such that the signals from indicator 26 cause movements of motors 10, 15 so that the platform 18 tilts about the 0.180 degrees axis while signals from detector 'd2 tilt the platform about the 90-270 degrees axis. When the platform is level and the zero on the angle scale points true North, the horizontal component of the earth's rotation is parallel to the output axes Y1, Y2 of the gyroscopes, which are therefore unaffected by this component. The vertical component of the earth's rotation has no effect on gyroscope 24, since it acts about its spin axis X2; but it produces about the input axis Z, of the gyroscope 23 a torque proportonal to latitude. The error produced may be disregarded, or it may be eliminated by applying a signal, variable with latitude, to torque motor m1, to provide a counterbalancing torque. Meridian-seeking action of system. If the platform 18, remaining horizontal, is deviated e.g. to the East, the horizontal component of the earth's rotation may be further resolved into a component parallel to the axes Y1, Y2 and a further component parallel to the spin axis X1 of gyroscope 23 and to the input axis Z2 of gyroscope 24. Gyroscope 23 is unaffected, but gyroscope 24 processes so that its detector d2, by controlling the action of motors 10, 15, causes the platform to tilt about the 90- 270 degrees axis so that the zero mark rises. Since the axis of this rotation is parallel to the input axis Z2, gyroscope 24 is precessed back byv an amount equal to its original displacement. 'The tilt of the platform about the 90-270 degrees axis affects the indicator 25. which applies a signal to torque motor m1 of gyroscope 23, which is thus precessed, causing its detector d1 to apply a signal to motor 20 to rotate platform 18 in a sense to move the zero of the angle scale towards true North. Since the axis of this rotation is parallel to the input axis Z1 of gyroscope 23, the gyroscope is precessed back to its former position. Since the platform 18 is still tilted, however, the torque applied by indicator 25 and torque motor m1 is maintained, and platform 18 rotates so that the zero mark overshoots the North position and moves to the West. The action of the earth's rotation on the gyroscope 24 is now the opposite of its previous action, so that the platform tilts so that the zero mark falls, and then moves back towards true North. The movement of the system continues, so that the zero mark traces out an elliptical path about its true North position. By suitable design of the system, in particular by choice of the moment of inertia of gyroscope 23 and the value of the torque exerted by torque motor m1, the period of the motion can be made equal to 84.4 minutes to provide ballistic correction. In order that the system should settle with the zero at North, the movement must be damped, e.g. by providing a winding on the torque motor m2 which is so controlled by indicator 25, that, when the table is tilted the gyroscope 24 is precessed in a direction to reduce the tilt through action of detector d2 and motors 10, 15. The damping may be varied by suitable design, particularly by choice of the moment of inertia of gyroscope 24 and the torque exerted by torque motor m2, and may be discontinued when required by breaking the connection between indicator 25 and torgue motor m2. To minimize rolling and pitching errors, the damping time constants of the indicators 25, 26 are made respectively large and small compared with the mean pitching period of the craft. The speed and course error is corrected by a torque supplied by a signal applied to torque motor m2 from a device such as a potentiometer 28. The motors 20, 10, 15 may be combined with angle transmitters to enable the ship's heading, pitch and roll to be indicated at a remote point. Directional gyroscope. The system shown in Fig. 2 can be modified to act as a directional gyroscope by disconnecting indicator 25 from torque motor m1 and the device 28 from the torque motor m2. The action of the earth's rotation on the gyroscope 23 is compensated as described above. Any rotation of the platform imparts a torque about the input axis Z1 of the gyroscope 23, which energizes motor 20 to restore the platform to its original position. A re-setting torque may be applied by applying a signal to torque motor m1. Artificial horizon. As shown in Fig. 5, a circular platform 118 is mounted similarly to platform 18 in gimbals 108, 113 supported by a base 107, the gimbals being rotatable by motors 110, 115. The platform 118 is kept with its mark 119 pointing true North by a motor 120 controlled by e.g. a compass through an amplifier (not shown). The gyroscope assemblies 123, 124 have their spin axes X3, X4 perpendicular to platform 118; their output axes Y3, Y4 pointing North and East respectively; and their input axes Z3, Z4 pointing West and North respectively. Indicators 125, 126, responsive to tilt about the East-West and North-South axes respectively, are mounted on platform 118 and connected respectively to torque motor m4 of gyroscope 124 and to torque motor m3 of gyroscope 123. The detectors d3, d4 are each connected to one winding of an angle resolver 127, the rotor of which is oriented with the heading of the craft. The angle resolver gives two outputs so connected to motors 110, 115 that signals from detector d3 cause the motors to operate in such a way that the platform 118 turns about its East-West axis, while the detector d4 causes rotation about the North-South axis. The input axis Z3 of gyroscope 123 is perpendicular to the earth's axis, but the horizontal component of the earth's rotation sets up a torque about the input axis Z4 of gyroscope 124. A counteracting torque is set up by means 129, consisting e.g. of a potentiometer adjustable with latitude providing a voltage applied to an auxialiary winding of torque motor m4. Now, if there is a tilt about the North-South axis so that the East side of platform 118 is lower than the West side, the indicator 126 produces a torque in motor m3 of gyroscope 123, urging the upper end of its axis to the East. Detector d3 then energizes motors 110, 115 so that platform 118 turns about its East- West axis, so that the North side is lowered. This movement about an axis parallel to the input axis Z3 of the gyroscope 123 causes a precession of its spin axis X3 back to the vertical. The indicator 125 now energizes torque motor m4, so that the upper end of the spin