Rate Gyroscope

a gyroscopic device used in finding the angular velocity of an object on which it is mounted. The most widely used type of rate gyroscope uses an astatic restrained gyroscope. In such a rate gyroscope (see Figure 1) the rotor of the gyroscope is mounted in the gimbal ring (frame). Rotation of the frame is limited by a spring, which creates a restoring moment. The natural oscillations of the gyroscope are extinguished by the damper.

Figure 1. Diagram of a rate gyroscope: Oξηζ are axes of the reference system; Oxyz are axes of the gimbal ring.

If the object is rotated around the axis Oζ (the input axis) with an angular velocity ω_ζ, the frame will rotate around the axis Oη (the output axis) to an angle β. The dependence of this angle on ω_ζ is given by the equation β = ω_ζH/c, where H is the moment of momentum of the gyroscope and c is a coefficient that depends on the stiffness of the spring and on the location of the point where the spring is attached. The values of β are read from the potentiometer; they define the magnitude of ω_ζ. The sensitivity threshold of a rate gyroscope, in terms of angular velocity of an object, is on the order of tenths of a degree per second. Some other types of rate gyroscopes, which use a floating suspension, are even more accurate.

Rate gyroscopes are used in aircraft as turn indicators and sensing elements in automatic stabilization systems and on ships in roll-and-pitch dampers and other systems. They may also be used in inertial navigation systems.

Devices that simultaneously determine both the angular velocity and the angular acceleration of an object also exist. Such devices are called rate gyroscope-accelerometers; they utilize an astatic gyroscope with three degrees of freedom. Devices of this type are used, for example, in aircraft autopilots.