US 4,862,594 A · Magnetic compass system for a vehicle

Abstract

A compass and method of operation are disclosed for finding the heading of a vehicle. The heading is found using a compass having a rotor with a compass magnet thereon and means on the rotor defining a reference line in known relation with the polar axis of the magnet. The angular displacement of the rotor is measured between alignment with the direction reference axis and alignment with the local magnetic field. A search coil is used to torque the rotor so that it reaches a reference position in which the reference line thereon is aligned with the direction reference axis. A reference position encoder generates a pulse when alignment is achieved. An angular displacement encoder produces a digital signal which changes with each predetermined increment of rotation of the rotor and which is indicative of the direction of rotation. A microcomputer processes the signals to provide a cumulative count of the increments of rotation. The microcomputer adds a stored magnetic variation value to the cumulative count to provide an indication of true heading. A direction display is adapted to exhibit one direction symbol of a set of symbols for different vehicle headings with each symbol corresponding to a different range of counts in the cumulative count. The microcomputer converts the cumulative count to a different direction value for each different range and the display is changed when there is a change of direction value. The microcomputer provides a logical hysteresis to prevent the display from flashing between different symbols when the cumulative count is at a marginal value of a given range. The microcomputer also provides a time damping of the display by imposing a time delay before changing the display from one symbol to another.

Claims29

Dependent claims

The method of finding the heading of a vehicle with a compass which includes a compass frame, a compass magnet on a rotor which is mounted for rotation on said frame so that it seeks to orient the polar axis of the magnet with the local magnetic field and which includes a reference line defined on the rotor having a predetermined offset angle, other than zero, relative to the polar axis of the magnet, said vehicle having a direction reference axis which has a known angular relation with the direction of the vehicle, said compass frame having an orientation axis extending perpendicular to the axis of rotation of said rotor, said method comprising the steps of:

fixedly mounting said compass frame on said vehicle with said orientation axis in a known angular direction relative to said direction reference axis,
turning the rotor between one angular position in which the reference line is in alignment with the orientation axis and another angular position in which the polar axis of the rotor is aligned with the local magnetic field,
measuring the angular value of the turning motion between said angular positions,
and obtaining a value for said heading by adding or subtracting said angular value of turning motion, depending upon the direction of the turning motion, to or from the offset angle to obtain the vehicle heading with reference to the magnetic north direction.

1 more element

The method of finding the heading of a vehicle with a compass which includes a compass frame, a compass magnet on a rotor which is mounted for rotation on said frame so that it seeks to orient the polar axis of the magnet with the local magnetic field and which includes a reference line defined on the rotor having a predetermined offset angle, other than zero relative to the polar axis of the magnet, said vehicle having a direction reference axis which has a known angular relation with the direction of the vehicle, said compass frame having an orientation axis extending perpendicular to the axis of rotation of said rotor, said method comprising the steps of:

fixedly mounting said compass frame on said vehicle with said orientation axis in a known angular direction relative to said direction reference axis,
allowing the rotor to assume any arbitrary angular position relative to said orientation axis,
turning the rotor through a sufficient angle so that said reference line reaches alignment with said orientation axis,
allowing the polar axis of the rotor to become aligned with the local magnetic field so that the reference line is in a predetermined angular relation with the magnetic north direction,
and measuring the value of the angular displacement between the direction of the reference line when it is aligned with the orientation axis and the direction of the reference line when the polar axis of the rotor is aligned with the magnetic north direction.

2 more elements

The method of measuring the value of magnetic variation for use in finding the heading of a vehicle with a compass which includes a compass frame, a compass magnet on a rotor which is mounted for rotation on said frame so that it seeks to orient the polar axis of the magnet with the local magnetic field and which includes a reference line defined on the rotor having a predetermined offset angle other than zero relative to the polar axis of the magnet, said vehicle having a direction reference axis which has a known angular relation with the direction of the vehicle, said compass frame having an orientation axis extending perpendicular to the axis of rotation of said rotor, said method comprising the steps of:

fixedly mounting said compass frame on said vehicle with said orientation axis in a known angular direction relative to said direction reference axis,
orienting said vehicle so that the direction reference axis is in alignment with the true north direction,
allowing the rotor to assume any arbitrary angular position relative to the direction reference axis,
turning the rotor through a sufficient angle so that said reference line reaches alignment with said orientation axis,
allowing the polar axis of the rotor to become aligned with the local magnetic field so that the reference line is in a predetermined angular relation with the magnetic north direction,
and measuring the value of the angular displacement between the direction of the reference line when it is aligned with the orientation axis and the direction of the reference line when the polar axis of the rotor is aligned with the magnetic north direction,
and obtaining a value for said magnetic variation by adding or subtracting said angular value of turning motion, depending upon the direction of the turning motion, to or from the offset angle to obtain the vehicle heading with reference to the magnetic north direction,
whereby said angular displacement corresponds to the value of the magnetic variation angle at the location of said vehicle.

5 more elements

The method of compensating a magnetic compass of a vehicle for magnetic deviation, said compass including a rotor mounted for rotation on a compass frame, said compass frame having an orientation axis in a known angular relation with the direction reference axis of the vehicle, a compass magnet on said rotor which seeks to orient the polar axis of the magnet with the local magnetic field, a reference line defined on the rotor having a predetermined angular position other than zero relative to the polar axis of the magnet, a compensation coil adjacent said rotor, said method comprising the steps of:

turning the rotor through a sufficient angle so that said reference line reaches alignment with said orientation axis,
allowing the polar axis of the rotor to become aligned with the local magnetic field,
measuring the value of the angular displacement between the direction of the reference line when it is aligned with the orientation axis and the direction of the reference line when the polar axis of the rotor is aligned with the local magnetic field,
displaying one direction symbol of a set of symbols for different vehicle headings on a display device in accordance with the measured value, there being a different symbol for each of a plurality of directions including said known deviation,
orienting said vehicle so that said direction reference axis is in alignment with a known direction with reference to magnetic north,
and adjusting the current through said compensation coil until said display device displays the direction symbol corresponding to the known direction.

3 more elements

Apparatus for finding the heading of a vehicle having a direction reference axis which has a known angular relation with the direction of the vehicle, said apparatus comprising:

a compass which includes a compass frame, a compass magnet on a rotor which is mounted for rotation on said frame so that it seeks to orient the polar axis of the magnet with the local magnetic field,
said frame having an orientation axis extending perpendicular to the axis of rotation of said rotor, said compass frame being fixedly mounted on said vehicle with said orientation axis in a known angular direction relative to said direction reference axis,
means on said rotor defining a reference line having a predetermined offset angle other than zero relative to the polar axis of the magnet,
means for turning the rotor to one angular position in which the reference line is in alignment with said orientation axis,
means for measuring the angular value of the turning motion between said one angular position and another angular position in which said polar axis is aligned with the local magnetic field,
and means for adding or subtracting said angular value, depending upon the direction of the turning motion, to or from the offset angle to obtain the vehicle heading with reference to the magnetic north direction.

3 more elements

Dependencies are inferred from the claim text.

Magnetic compass system for a vehicle

Life of this patent

Magnetic compass system for a vehicle

Life of this patent

Abstract

Claims29