Hemispherical resonator gyroscope

Hemispherical Resonator Gyroscope (HRG)

The Hemispherical Resonator Gyroscope (HRG), also called wine-glass gyroscope or mushroom gyro, is made using a thin solid-state hemispherical shell, anchored by a thick stem. 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. Gyroscopic effect is obtained from the inertial property of the flexural standing waves. HRG has no moving parts, is extremely reliable and very accurate.

Operation

The HRG makes use of a small thin solid-state hemispherical shell, anchored by a thick stem. 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.

For 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 Q-factor over 30-50 million in vacuum, so, the corresponding random walks are extremely low. The Q is limited by coating (extremely thin film of gold or platinum) and by fixture losses.[1] Such resonators have to be fine-tuned by ion-beam micro-erosion of the glass or by laser ablation. When coated, tuned and assembled within the housing, the Q factor remains over 10 million.

In application to the HRG shell, Coriolis forces cause a precession of vibration patterns around the axis of rotation. It causes a slow precession of a standing wave around this axis, with an angular rate that differs from input one. This is the wave inertia effect, discovered in 1890 by British scientist George Hartley Bryan (1864–1928).[2]

Therefore, when subject to rotation around the shell symmetry axis, the standing wave does not totally rotate with the shell. The difference between both rotations is nevertheless perfectly proportional to the input rotation. The device is then able to sense rotation.

The electronics which sense the standing waves are also able to drive them. 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.

Advantages

The HRG is extremely reliable because of its extremely simple hardware. It has no moving parts; its core is made of a monolithic part which includes the hemispherical shell and its stem.[3] They demonstrated outstanding reliability since their initial use in 1996.[4]

The HRG is extremely accurate and is not sensitive to external environmental perturbations. The resonating shell weighs only a few grams and it is perfectly balanced which makes it insensitive to vibrations, accelerations and shocks.

Thanks to the extremely high Q factor of the resonating shell, the HRG has an extremely low angular random walk and extremely low power dissipation.

Disadvantages

HRG is a very high-tech device which requires sophisticated manufacturing tools. The control electronics required to sense and drive the standing waves, is somewhat sophisticated. This high level of sophistication strongly limits the dissemination of this technology.

HRG are relatively expensive due to the cost of the precision ground and polished hollow quartz hemispheres. Sagem overcame this issue thanks to an innovative design. Rather than depositing electrodes on an internal hemisphere that must perfectly match the shape of the outer resonating hemisphere, electrodes are deposited on a flat plate that matches the equatorial plan of the resonating hemisphere.

Applications

  1. HRG are used in space applications (satellites and spacecraft)[3]
  2. HRG are used marine maintenance-free gyrocompass[5][6] and Attitude et Heading Reference Systems[7]
  3. HRG are used in Target locators[8] and land navigation systems [6][9][10]
  4. HRG are poised to be used in Commercial Air Transport navigation systems [11][12]
  5. HRG are poised to be used in Space launchers [13]

See also

References

  1. ↑ Sarapuloff S.A., Rhee H.-N., and Park S.-J. Avoidance of Internal Resonances in Hemispherical Resonator Assembly from Fused Quartz Connected by Indium Solder //Proceedings of the 23rd KSNVE (Korean Society for Noise & Vibration Engineering) Annual Spring Conference. Yeosu-city, 24–26 April 2013. – P.835-841.
  2. ↑ Bryan G.H. On the Beats in the Vibrations of a Revolving Cylinder or Bell //Proc. of Cambridge Phil. Soc. 1890, Nov. 24. Vol.VII. Pt.III. - P.101-111.
  3. 1 2 The Hemispherical Resonator Gyro: From Wineglass to the Planets, David M. Rozelle
  4. ↑ Hemispherical Resonator Gyro
  5. ↑ http://www.raytheon-anschuetz.com/product-range/product-detail/69/Horizon-MF-Gyro-Compass
  6. 1 2 http://www.defenseworld.net/news/9978/Sagem_To_Highlight_Wide_Range_Of_Warfare_Products_At_Defexpo_2014
  7. ↑ http://www.navyrecognition.com/index.php?option=com_content&task=view&id=721
  8. ↑ www.vectronix.ch/html/en/news_press/current_news/vectronix_wins_innovation_award
  9. ↑ Sagem wins new order for SIGMA 20 navigators on MBDA surface-to-air weapon systems
  10. ↑ Sagem to Supply Seeker and Firing-Posts Optronics for MBDA’s New MMP Medium-Range Missile
  11. ↑ Sagem unveil SkyNaute inertial navigation system
  12. ↑ https://www.sagem.com/content/sagem-carries-out-first-flight-test-hrg-based-navigation-system-commercial-aircraft
  13. ↑ C. Negri, E. Labarre, C. Lignon, E. Brunstein, E. Salaün A NEW GENERATION OF IRS WITH INNOVATIVE ARCHITECTURE BASED ON HRG FOR SATELLITE LAUNCH VEHICLES - International Conference on Integrated Navigation Systems Saint Petersburg, Russia, May 2015

Bibliography

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