![]() The HRG is extremely reliable because of its very simple hardware (two or three pieces of machined fused quartz). Originally used in space applications (Attitude and Orbit Control Systems for spacecraft), HRG is now used in advanced inertial navigation systems, in attitude and heading reference systems, and HRG gyrocompasses. Therefore, the gyros can operate in either a "whole angle mode" that sense the standing waves' position or a "force rebalance mode" that holds the standing wave in a fixed orientation with respect to the gyro. The electronics which sense the standing waves are also able to drive them. The device is then able to sense rotation. Therefore, when subject to rotation around the shell symmetry axis, the standing wave does not rotate exactly with the shell, but the difference between both rotations is nevertheless perfectly proportional to the input rotation. This is the wave inertia effect, discovered in 1890 by British scientist George Hartley Bryan (1864–1928). It causes a slow precession of a standing wave around this axis, with an angular rate that differs from input one. ![]() In application to the HRG shell, Coriolis forces cause a precession of vibration patterns around the axis of rotation. ![]() When coated, tuned, and assembled within the housing, the Q factor remains over 10 million. Such resonators have to be fine-tuned by ion-beam micro-erosion of the glass or by laser ablation in order to be perfectly dynamically balanced. The Q factor is limited by the coating (extremely thin film of gold or platinum) and by fixture losses. This shell is driven to a flexural resonance by dedicated electrostatic forces generated by electrodes which are deposited directly onto separate fused quartz structures that surround the shell.įor a single-piece design (i.e., the hemispherical shell and stem form a monolithic part ) made from high-purity fused quartz, it is possible to reach a Q factor of over 30-50 million in vacuum, thus the corresponding random walks are extremely low. The HRG makes use of a small thin solid-state hemispherical shell, anchored by a thick stem. Although the HRG is a mechanical system, it has no moving parts, and can be very compact. ![]() The gyroscopic effect is obtained from the inertial property of the flexural standing waves. This shell is driven to a flexural resonance by electrostatic forces generated by electrodes which are deposited directly onto separate fused-quartz structures that surround the shell. An HRG is made using a thin solid-state hemispherical shell, anchored by a thick stem. The Hemispherical Resonator Gyroscope (HRG), also called wine-glass gyroscope or mushroom gyro, is a compact, low-noise, high-performance angular rate or rotation sensor. ![]()
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