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The underlying physical principle is that a vibrating object tends to continue vibrating in the same plane even if its support rotates. The Coriolis effect causes the object to exert a force on its support, and by measuring this force the rate of rotation can be determined. Vibrating structure gyroscopes are simpler and cheaper than conventional rotating gyroscopes of similar accuracy. Inexpensive vibrating structure gyroscopes manufactured with MEMS technology are widely used in smartphones, gaming devices, cameras and many other applications. This section may contain improper references to self-published sources. This type of gyroscope was developed by GEC Marconi and Ferranti in the 1980s using metal alloys with attached piezoelectric elements and a single-piece piezoceramic design.
Subsequently, in the 90s, CRGs with magneto-electric excitation and readout were produced by American-based Inertial Engineering, Inc. California, and piezo-ceramic variants by Watson Industries. The resonator is operated in its second-order resonant mode. Standing waves are elliptically-shaped oscillations with four antinodes and four nodes located circumferentially along the rim. One of the elliptical resonant modes is excited to a prescribed amplitude.
Coriolis forces acting on the resonator’s vibrating mass elements excite the second resonant mode. The angle between major axes of the two modes is also 45 degrees. A closed loop drives the second resonant mode to zero, and the force required to null this mode is proportional to the input rotation rate. This control loop is designated the force-rebalanced mode. Piezo-electric elements on the resonator produce forces and sense induced motions. This electromechanical system provides the low output noise and large dynamic range that demanding applications require, but suffers from intense acoustic noises and high overloads. A piezoelectric material can be induced to vibrate, and lateral motion due to Coriolis force can be measured to produce a signal related to the rate of rotation.
This type of gyroscope uses a pair of test masses driven to resonance. Their displacement from the plane of oscillation is measured to produce a signal related to the system’s rate of rotation. Meredith registered a patent for such a device in 1942 while working at the Royal Aircraft Establishment. Further development was carried out at the RAE in 1958 by G. Also called a hemispherical resonator gyroscope or HRG, a wine-glass resonator makes using a thin solid-state hemisphere, anchored by a thick stem, and driven to a flexural resonance of this shell, the nodal points of which are measured to detect rotation. Q-factor greater than 30-50 million in vacuum, so the corresponding random walks are extremely low.
The Q is limited by the coating, an extremely thin film of gold or platinum, and by fixture losses. Safran and Northrop Grumman are the major manufacturers of HRG. A wheel is driven to rotate a fraction of a full turn about its axis. The tilt of the wheel is measured to produce a signal related to the rate of rotation. These are packaged similarly to other integrated circuits and may provide either analog or digital outputs. In many cases, a single part includes gyroscopic sensors for multiple axes.