An instrument consisting of a rapidly spinning wheel so mounted as to use the tendency of such a wheel to maintain a fixed position in space, and to resist any force which tries to change it. The way it will move if a twisting force is applied depends on the extent and orientation of the force and the way the gyroscope is mounted. A free vertically spinning gyroscope (in gimbals, two semicircular mountings at right angles, such that the mounted object can turn in any direction) remains vertical as the carrying vehicle tilts, so providing an artificial horizon. A horizontal gyroscope will maintain a certain bearing, and therefore indicate a vessel's heading as it turns. Modern gyroscopes no longer have a spinning wheel. In an Interferometric Fibre-Optic Gyro (IFOG), a laser beam is split into two waves which pass in opposite directions round a fibre-optic coil. If the coil rotates, there will be a difference in intensity of the light when it returns to the detector. The difference is converted into the degree of rotation. In a ring laser gyro (RLG), laser light is reflected by mirrors in both directions through a closed optical channel. If the gyroscope rotates, the two beams will not arrive exactly in phase at the detector, resulting in an interference fringe pattern. Interpretation of this pattern determines the degree of rotation of the gyroscope.
A gyroscope is a device for measuring or maintaining orientation, based on the principle of conservation of angular momentum.
Description and diagram
Within mechanical combinations or devices constituting portions of machines, a conventional gyroscope is a mechanism comprising a rotor journaled to spin about one axis, the journals of the rotor being mounted in an inner gimbal or ring, the inner gimbal being journaled for oscillation in an outer gimbal which in turn is journaled for oscillation relative to a support. The inner gimbal is mounted in the outer gimbal so as to pivot about an axis in its own plane, which axis is always normal to the pivotal axis of the outer gimbal.
The axle of the spinning wheel defines the spin axis. The rotor is journaled to spin about an axis which is always normal to the axis of the inner gimbal. The wheel responds to a force applied about the input axis by a reaction force about the output axis.
A gyroscope flywheel will roll or resist about the output axis depending upon whether the output gimbals are of a free- or fixed- configuration. Examples of some free-output-gimbal devices would be the attitude reference gyroscopes used to sense or measure the pitch and roll and yaw attitude angles in a spacecraft or airplane. The rotor simultaneously spins about one axis and is capable of oscillating about the two other axes, and thus, except for its inherent resistance due to rotor spin, it is free to turn in any direction about the fixed point. Some gyroscopes have mechanical equivalents substituted for one or more of the elements, e.g., the spinning rotor may be suspended in a fluid, instead of being pivotally mounted in gimbals. A control moment gyroscope (CMG) is an example of a fixed-output-gimbal device that is used on spacecraft to hold or maintain a desired attitude angle or pointing direction using the gyroscopic resistance force. In other cases, the center of gravity of the rotor may be offset from the axis of oscillation, and thus the center of gravity of the rotor and the center of suspension of the rotor may not coincide.
History
The gyroscope effect was discovered in 1817 by Johann Bohnenberger and invented and named in 1852 by Léon Foucault for an experiment involving the rotation of the Earth. The American Elmer Sperry followed with his own design in 1910, and other nations soon realized the military importance of the invention—in an age in which naval might was the most significant measure of military power—and created their own gyroscope industries. The Sperry Gyroscope Company quickly expanded to provide aircraft and naval stabilizers as well, and other gyroscope developers followed suit.
In the first several decades of the 20th century, other inventors attempted (unsuccessfully) to use gyroscopes as the basis for early black box navigational systems by creating a stable platform from which accurate acceleration measurements could be performed (in order to bypass the need for star sightings to calculate position).
Properties
A gyroscope exhibits a number of behaviours including precession and nutation. Gyroscopes can be used to construct gyrocompasses which complement or replace magnetic compasses (in ships, aircraft and spacecraft, vehicles in general), to assist in stability (bicycle, Hubble Space Telescope, ships, vehicles in general) or be used as part of an Inertial guidance system.
The fundamental equation describing the behavior of the gyroscope is:
where the vectors and are, respectively, the torque on the gyroscope and its angular momentum, the scalar is its moment of inertia, the vector is its angular velocity, and the vector is its angular acceleration.
It follows from this that a torque applied perpendicular to the axis of rotation, and therefore perpendicular to , results in a motion perpendicular to both and . The angular velocity of precession is given by the cross product:
Precession can be demonstrated by placing a spinning gyroscope with its axis horizontal and supported loosely (frictionless toward precession) at one end. Instead of falling, as might be expected, the gyroscope appears to defy gravity by remaining with its axis horizontal, when the other end of the axis is left unsupported and the free end of the axis slowly describes a circle in a horizontal plane, the resulting precession turning. The torque on the gyroscope is supplied by a couple of forces: gravity acting downwards on the device's centre of mass, and an equal force acting upwards to support one end of the device. The motion resulting from this torque is not downwards, as might be intuitively expected, causing the device to fall, but perpendicular to both the gravitational torque (downwards) and the axis of rotation (outwards from the point of support), i.e.
As the second equation shows, under a constant torque due to gravity or not, the gyroscope's speed of precession is inversely proportional to its angular momentum. This means that, for instance, if friction causes the gyroscope's spin to slow down, the rate of precession increases.
Gyrostat
A gyrostat is a variant of the gyroscope.
U.S. Patents
In the USPTO classification scheme, the generic locus for gyroscope patents is Class 74, Machine element or mechanism, and Subclass 5R. The combinations of gyroscopes with other devices are placed in subclass 5.22. Reissued U.S. Patent RE024880, "Rate Gyroscope with torsional suspension"
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