Gyrocompass

In a gyrocompass including a first gimbal, a gyro motor mounted in the first gimbal and including a gyro rotor mounted to rotate about a horizontally alignable spin axis, a body in which the first gimbal is mounted to be rotatable about a vertically alignable axis of rotation, a housing in which the body is rotatably suspended, a verticality device associated with the body for allowing the body to assume an orientation in the housing in which the axis of rotation is vertical, a follow-up device including a pickup mounted for sensing the angular position, about the axis of rotation, of the gimbal relative to the body, and a drive connected for rotating the body relative to the housing about the axis of rotation in dependence on the position sensed by the pickup, the improvement wherein:

• said drive comprises a stepping motor for rotating the body with highly uniform steps in defined positions;
• said follow-up device further comprises a restraining circuit and a torquer connected between said pickup and said first gimbal for restraining said first gimbal at a defined angular position, about the axis of rotation, relative to said body, said restraining circuit providing a signal representative of the angular velocity of said first gimbal about the axis of rotation;
• and said gyrocompass further comprises means for determining the direction to true north from signals representative of said angular velocity.

Method for operating a gyrocompass which is composed of a first gimbal, a gyro motor mounted in the first gimbal and including a gyro rotor mounted to rotate about a horizontally alignable spin axis, a body in which the first gimbal is mounted to be rotatable about a vertically alignable axis of rotation, a housing in which the body is rotatably suspended, a verticality device associated with the body for allowing the body to assume an orientation in the housing in which the axis of rotation is vertical, a follow-up device including a pickup mounted for sensing the angular position, about the axis of rotation, of the first gimbal relative to the body, and a drive connected for rotating the body relative to the housing about the axis of rotation in dependence on the position sensed by the pickup, and in which said drive comprises a stepping motor for rotating said body with highly uniform steps in defined positions, said follow-up device further includes a restraining circuit and a torquer connected between said pickup and said first gimbal for restraining said first gimbal at a defined angular position, about the axis of rotation, relative to said body, said restraining circuit providing a signal representative of the angular velocity of said first gimbal about the axis of rotation, and said gyrocompass further includes means for determining the direction to true north from signals representative of said angular velocity, said method comprising:

• rotating said body, by means of said stepping motor, about the axis of rotation, to at least two successive, mutually spaced, arbitrary angular positions;
• effecting first measurements of the angular velocity of said first gimbal about the axis of rotation at each of the angular positions;
• deriving from the angular velocity measurements a first estimated value for the azimuth angle between the spin axis and north for one of the arbitrary angular positions;
• and thereafter rotating said gyro motor by means of said stepping motor about the axis of rotation through an angle dependent of the estimated azimuth angle value in such a manner as to achieve a rough alignment of the spin axis with the north direction.