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. An HRG 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. The gyroscopic effect is obtained from the inertial

property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depending on the nature of the property, an owner of property may have the right to consume, alter, share, r ...

of the flexural standing waves. Although the HRG is a mechanical system, it has no moving parts, and can be very compact.

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 dedicated electrostatic forces generated by electrodes which are deposited directly onto separate

fused quartz Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...

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

, it is possible to reach a

Q factor In physics and engineering, the quality factor or ''Q'' factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is defined as the ratio of the initial energy stored in the resonator to the energy ...

of over 30-50 million in vacuum, thus the corresponding

random walk In mathematics, a random walk is a random process that describes a path that consists of a succession of random steps on some mathematical space. An elementary example of a random walk is the random walk on the integer number line \mathbb Z ...

s are extremely low. The

is limited by the coating (extremely thin film of gold or platinum) and by fixture losses. 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. When coated, tuned, and assembled within the housing, the

remains over 10 million. In application to the HRG shell,

Coriolis force In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

s cause a

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In oth ...

of vibration patterns around the

axis of rotation Rotation around a fixed axis is a special case of rotational motion. The fixed- axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as wobbling or precession. According to Euler's r ...

. It causes a slow precession of a

standing wave In physics, a standing wave, also known as a stationary wave, is a wave that oscillates in time but whose peak amplitude profile does not move in space. The peak amplitude of the wave oscillations at any point in space is constant with respect ...

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). 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. 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. Originally used in space applications (Attitude and Orbit Control Systems for spacecraft), HRG is now used in advanced

inertial navigation system An inertial navigation system (INS) is a navigation device that uses motion sensors ( accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity ...

s, in

attitude and heading reference system An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for aircraft, including roll, pitch, and yaw. These are sometimes referred to as MARG (Magnetic, Angular Rate, and Gravity) sens ...

s, and HRG gyrocompasses.

Advantages

The HRG is extremely reliable because of its very simple hardware (two or three pieces of machined fused quartz). It has no moving parts; its core is made of a monolithic part which includes the hemispherical shell and its stem. They demonstrated outstanding reliability since their initial use in 1996 on the ''

NEAR Shoemaker ''Near Earth Asteroid Rendezvous – Shoemaker'' (''NEAR Shoemaker''), renamed after its 1996 launch in honor of planetary scientist Eugene Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Labora ...

'' spacecraft. The HRG is highly 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. The HRG exhibits superior SWAP (Size, Weight, and Power) characteristics compared to other gyroscope technologies. The HRG generates neither acoustic nor radiated noise because the resonating shell is perfectly balanced and operates under vacuum. The material of the resonator, the

, is naturally radiation hard in any space environment. This confers intrinsic immunity to deleterious space radiation effects to the HRG resonator. Thanks to the extremely high Q factor of the resonating shell, the HRG has an ultra-low angular

and extremely low power dissipation. The HRG, unlike optical gyros (

FOG Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...

and RLG), has inertial memory: if the power is lost for a short period of time (typically a few seconds), the sensitive element continues to integrate the input motion (angular rate) so that when the power returns, the HRG signals the angle turned while power was off.

Disadvantages

The HRG is a very high-tech device which requires sophisticated manufacturing tools and processes. The control electronics required to sense and drive the standing waves are sophisticated. This high level of sophistication limits the availability of this technology; few companies were able to produce it. Currently three companies manufacturing HRG:

Northrop Grumman Northrop Grumman Corporation is an American multinational aerospace and defense technology company. With 90,000 employees and an annual revenue in excess of $30 billion, it is one of the world's largest weapons manufacturers and military tech ...

, Safran and Raytheon Anschütz. Classical HRG is relatively expensive due to the cost of the precision ground and polished hollow quartz hemispheres. This manufacturing cost restricts its use to high-added-value applications such as satellites and spacecraft. Nevertheless manufacturing costs can be dramatically reduced by design changes and engineering controls. 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 plane of the resonating hemisphere. In such configuration, HRG becomes very cost effective and is well suitable for high grade but cost sensitive applications.

Applications

* Space – Inside the

Spacecraft Bus A satellite bus (or spacecraft bus) is the main body and structural component of a satellite or spacecraft, in which the payload and all scientific instruments are held. Bus-derived satellites are opposed to specially produced satellites. Bus ...

in the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope which conducts infrared astronomy. As the largest optical telescope in space, its high resolution and sensitivity allow it to view objects too old, distant, or faint for the Hubble Sp ...

and other satellites and spacecraft * Sea – Marine maintenance-free gyrocompasses as well as

s Naval navigation systems for both surface vessels and submarines * Land – Target locators, land navigation systems, and artillery pointing * Air – HRG are poised to be used in Commercial Air Transport navigation systems

References

{{Reflist

Bibliography

* Lynch D.D. HRG Development at Delco, Litton, and Northrop Grumman. Proceedings of Anniversary Workshop on Solid-State Gyroscopy (19–21 May 2008. Yalta, Ukraine). - Kyiv-Kharkiv. ATS of Ukraine. 2009. * L.Rosellini, JM Caron - REGYS 20: A promising HRG-based IMU for space application - 7th International ESA Conference on Guidance, Navigation & Control Systems. 2–5 June 2008, Tralee, County Kerry, Ireland * D. Roberfroid, Y. Folope, G. Remillieux (Sagem Défense Sécurité, Paris, FRANCE) - HRG and Inertial Navigation - Inertial Sensors and Systems – Symposium Gyro Technology 2012 * A Carre, L Rosellini, O Prat (Sagem Défense Sécurité, Paris,France) HRG and North Finding -17th Saint Petersburg International Conference on Integrated Navigation Systems 31 May – 2 June 2010, Russia * Alain Jeanroy; Gilles Grosset; Jean-Claude Goudon; Fabrice Delhaye - HRG by Sagem from laboratory to mass production - 2016 IEEE International Symposium on Inertial Sensors and Systems * Alexandre Lenoble, Thomas Rouilleault - SWAP-oriented IMUs for multiple applications- Inertial Sensors and Systems (ISS), 2016 DGON - Karlsruhe, Germany * Fabrice Delhaye - HRG by Safran - The game-changing technology - 2018 IEEE International Symposium on Inertial Sensors and Systems - Lake Como, Italy * Fabrice Delhaye; Jean-Philippe Girault - SpaceNaute®, HRG technological breakthrough for advanced space launcher inertial reference system - 25th Saint Petersburg International Conference on Integrated Navigation Systems 31–29 May 2018, Russia * B.Deleaux, Y.Lenoir - The world smallest, most accurate and reliable pure inertial navigator: ONYX™ - Inertial Sensors and Systems 2018, Braunschweig - 12 September 2018, Germany * Y. Foloppe, Y.Lenoir - HRG CrystalTM DUAL CORE: Rebooting the INS revolution - Inertial Sensors and Systems 2019, Braunschweig - 10 September 2019, Germany * F. Delhaye, Ch. De Leprevier - SkyNaute by Safran – How the HRG technological breakthrough benefits to a disruptive IRS (Inertial Reference System) for commercial aircraft - Inertial Sensors and Systems 2019, Braunschweig - 11 September 2019, Germany Aerospace engineering Aircraft instruments Avionics Missile guidance Navigational aids Navigational equipment Spacecraft components Technology systems

Operation

Advantages

Disadvantages

Applications

See also

References

Bibliography