Gyroscopic Devices

electromechanical devices containing gyroscopes and designed for the determination of parameters characterizing the motion (or position) of the object in which they are installed, as well as for the stabilization of the object. Gyroscopic devices are used for solving navigational problems, for the control of moving objects, and so on.

The most important criteria characterizing the various gyroscopic devices used in technology are the type of gyroscope, the physical principle of construction of the sensing element, the type of suspension, and the purpose of the device.

Types of gyroscope. There are two basic types of gyroscopes: those with three and two degrees of freedom. Gyroscopes with three degrees of freedom are divided into balanced (or astatic) and unbalanced (or positional) types.

In astatic gyroscopes, the center of gravity coincides with the point of intersection of the axes of the gimbal suspension (that is, with the point of suspension). The force of gravity does not affect the motion of the axis of such a gyroscope, and deflections caused by external disturbances may only be generated by force moments in the suspension axes (frictional force moments and others). In the absence of external force moments, the gyroscope is called free. Although astatic gyroscopes do not exhibit selectivity with respect to a given direction—that is, a “directing force” tending to bring the axis of the gyroscope into a certain position—they are utilized in a number of gyroscopic devices, such as directional gyroscopes and vertical gyroscopes; precision gyroscopes may be used without correction devices.

Positional gyroscopes are gyroscopes that are selective with respect to some direction; deviation of its axis from this direction generates a directing force that tends to return the gyroscope’s axis to the given position. Two methods are used for generating positional properties in gyroscopic devices. The first method consists in displacing the center of gravity of the gyroscope relative to the suspension point. This method is used in gyrocompasses, in which the directing force arises during the deviation of the gyroscope axis from the plane of the meridian, and in gyropendulums, in which the directing force arises because of the deviation of the gyroscope’s axis from the local vertical. Another method consists in using an astatic gyroscope in conjunction with a suitable correction system—for example, the pendulum type.

Gyroscopes with two degrees of freedom are most often used in gyroscopic devices as differentiating and integrating gyroscopes, which differentiate (integrate) the incoming signal—that is, they measure the derivative (or integral) of the quantity to which the gyroscopic device reacts. For example, in a rate gyroscope the differentiating gyroscope, reacting to the rotation of the object, measures its angular velocity, whereas the integrating flotation gyroscope, reacting to the angular velocity of the object, measures the angle of its rotation.

Physical principles of construction of the sensing elements of gyroscopes. A distinction is made among gyroscopes with mechanical and fluid rotors, as well as vibrational, laser, and nuclear gyroscopes. The most widespread gyroscopes contain mechanical rotors, in which the angular-momentum carrier is a rapidly rotating massive solid body—the rotor. (The carrier may also be a fluid medium.) The sensing elements of vibrational gyroscopes are vibrating masses (for example, a rotor with an elastic suspension, or elastic plates); this type of gyroscope is used for determining the angular velocity of objects. A laser gyroscope is a device in which an optical quantum generator of directional radiation is used and which contains a closed planar circuit (formed by three or more mirrors) in which two light fluxes (rays) circulate in opposite directions; it is also used to determine the angular velocity of the object. The nuclear gyroscope is based on the property that the atomic nucleus contains protons that have spin and orbital moments of momentum, as well as the associated magnetic moments. In this case, the existence of a nuclear mechanical moment of rotation imparts gyroscopic properties to the nucleus, and the presence of a magnetic moment makes it possible to orient the axis of this gyroscope in space and to determine its position. Nuclear gyroscopes may be used as directional stabilizers and as rate gyroscopes.

Types of gyroscope suspensions. Gyroscopes with mechanical rotors may have mechanical, flotation, gas, magnetic, or electrostatic suspensions. Gyroscopes with mechanical suspensions in the form of a gimbal suspension are used in the majority of gyroscopic devices.

Fluid, or flotation, suspensions are used in various free and restrained gyroscopes to reduce the load on the mechanical supports (for example, in a flotation integrating gyroscope); as a result, gyroscopes of these types are little affected by the action of vibrational, impact, and other disturbing actions and are highly accurate.

A significant increase in the accuracy of gyroscopic devices is achieved by using gyroscopes with gaseous suspensions. The rotor of these gyroscopes is usually spherical and is supported by a very thin layer of gas that forms between the rotor and the special support. Such a sphere is virtually a free gyroscope. Gaseous supports may also be used in the suspension axes of the rotor and gimbal rings.

Gyroscopes with a magnetic suspension, in which the rotor is a ferrite sphere that is suspended by a magnetic field, are used in some gyroscopic devices. The required characteristics of the field are automatically controlled by a special monitoring system. Another variety of the magnetic suspension is the so-called cryogenic rotor suspension, in which the interaction of the magnetic fields created by currents in superconductors is used. The supporting forces of the magnetic field arise upon changes of the rotor’s position with respect to the suspension elements. The material of the rotor, the coils of the electromagnets, and the special grids are rendered superconducting by copious cooling.

In gyroscopes with an electrostatic suspension, the rotor consists of a hollow sphere whose outer surface has high conductivity. The rotor is placed between electrodes to which high voltage regulated by a special control system is fed. Under the influence of electrostatic forces, the rotor becomes centered in the space between the electrodes.

Main gyroscopic devices. Gyroscopic devices are divided into the following groups according to their purpose: (1) Devices for determining angular deviations of objects. This group includes the various astatic and positional gyroscopes—directional gyroscopes, which determine the azimuthal deviations of the object (the angles of yaw of a ship or aircraft), and vertical gyroscopes or gyropendulums, which determine the deviation of an object with respect to the plane of the horizon (pitch and roll angles of a ship, as well as the angles of pitch and bank of an aircraft). (2) Gyroscopic devices for determining angular velocities and angular accelerations of the objects, which make use of differential gyroscopes. These include rate and vibratory gyroscopes, which determine the angular velocities of an object’s rotation, and gyroscopic rate accelerometers, which determine the angular velocities and accelerations of an object’s rotation. (3) Gyroscopic devices for determining the integrals of input quantities, in which integrating gyroscopes are utilized. This group includes gyroscopic integrators of angular velocities, which determine the angles of deflection of an object; integrating-differential gyroscopes, which determine the angles and angular velocities of the rotation of an object; and also gyroscopic integrators of linear accelerations, which are used for determining the linear velocity of an object. (4) Gyroscopic devices for the stabilization of an object or individual instruments and devices, as well as for determining the angular deflections of an object, called gyrostabilizers. (5) Gyroscopic devices for solving problems of navigation. This group includes gyrocompasses, which determine the course of an object and the azimuth (bearing) of the direction of orientation; gyromagnetic compasses, which determine the magnetic course of the object; gyroscopic devices for determining the latitude of a location; gyrolatitude compasses, for determining the course and latitude of an object’s location; gyrohorizon compasses, for determining the course of the object and of its angles of deflection with respect to the plane of the horizon; inertial navigational systems, which are designed for determining a number of parameters required for the navigation of objects; orbital gyroscopes, which are used to determine the angles of yaw of artificial earth satellites; and gyropilots, which automatically control a ship’s course.

Gyroscopic devices are used in the navy, in aeronautics, in rocketry and space technology, and in the national economy for solving a variety of navigational problems and guidance tasks involving moving objects, as well as in performing certain special activities (surveying, geodetic, topographical, and other tasks).