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HRG by SAGEM
From Laboratory to Mass Production
Alain Jeanroy, Gilles Grosset, Jean-Claude Goudon, Fabrice Delhaye
Avionics Division, Sagem, Boulogne-Billancourt, France
fabrice.delhaye@sagem.com
Abstract—For more than two decades, Sagem has built up its
expertise through different developments and applications of
CVG (Coriolis Vibrating Gyros). One example is the well-known
HRG (Hemispherical Resonator Gyroscope). This paper shows
the large panel of applications covered with HRG, in a nominal
configuration system and in a redundant inertial skewed system.
We also evoke the ultimate performance application obtained
with specific system configuration, thanks to the remarkable
properties of the HRG. In the end, we describe the industrial
aspects deployed to address all these applications.
Keywords—Hemispherical Resonator Gyro, Inertial System,
Navigation
I. I
NTRODUCTION
When Sagem started development of the Coriolis Vibrating
Gyros in 1985, the technical choices were rapidly based on
three main principles:
• The first principle was to use an axisymmetric
resonator: this property leads to resonators exhibiting
naturally good characteristics in terms of frequency
isotropy, damping isotropy and balance.
• The second principle was to obtain the best tuned and
balanced resonator possible: a very good isolation of
the vibrating mode of the resonator is necessary if one
needs stable performances, independent from the
environment. Even with an axisymmetric resonator
some complementary tuning and balancing is required.
• The third principle was to use the whole angle mode of
control: this mode minimizes the amplitude of the
forces applied for the control of the vibration and
therefore minimizes the errors caused by the
electronics, the detectors and actuators defects. This
mode leads to a very good scale factor (based on the
Bryan factor) and allows high dynamics.
Using these principles as a basis, Sagem has built up its
expertise through different developments and applications of
CVG [1]. One example is the well-known HRG, which uses a
fused Quartz resonator. This material exhibits an extraordinary
high Q factor and is well adapted to high performance when
associated with electrostatic pick-off and actuators. A thin film
metallic deposit on the resonator enables the electrostatic
control of the vibration with moderate impact on the Q factor.
Moreover, a Sagem patent [2] introduces a flat electrodes
design which greatly improves the simplicity of the gyroscope
and the ease of manufacturing. As a result, this type of
resonator vibrates at 7 kHz and exhibits a time constant beyond
500 seconds. Therefore, when associated with the whole angle
mode of control, it meets the highest demanding applications
requirements.
II. C
ONVENTIONAL APPLICATIONS
A. Standalone products
A space radiation hardened rate gyro dedicated to AOCS
(Attitude & Orbital Control System) was the first standalone
product designed with HRG technology in 2007 (Fig. 1). To
date, 8 orbiting telecom satellites are using Sagem HRG and
more than 100 spatial grade gyros have already been delivered.
Fig. 1. Regys 20 high reliability HRG spatial rate gyro unit
Simultaneously, the very low size, weight, and power
consumption of the HRG made possible the design of a
portable north-finder operating with only one gyro, typically
able to reach a 2 mils accuracy within 180 seconds (Fig. 2).
Fig. 2. Sterna ultra lightweight northfinder
These developments led to the inception of the BlueNaute
Marine gyrocompass family in 2011 [3], aimed towards the
maintenance free concept thanks to the exceptional reliability
of the HRG technology. In the same packaging size (6 liters
and 4.5 kg, Fig. 3), the family ranges from a basic IMO
(International Maritime Organization) gyrocompass to a high
978-1-4673-6939-8/16/$31.00 ©2016 IEEE
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end Titanium model offering 0.1° rms seclat heading and a
1 Nm/h position accuracy. More recently, a naval version
named Sigma 20M was launched, complying with harsh
military environments without impact on performances. To
date, hundreds of systems equip vessels around the world,
including US Coast Guards ships.
Fig. 3. BlueNaute and Sigma 20M Naval HRG INS
Concurrently, Sagem developed a Tactical Land INS
(Inertial Navigation System) named Sigma 20 (Fig. 4). The
heading accuracy of the family ranges from 8 down to 1 mils
rms.
Fig. 4. Sigma 20 HRG Tactical Land INS
In 2015 the SkyNaute family was launched (Fig. 5). The
SkyNaute family of INS is dedicated to Commercial Aircraft
(Fig. 6 shows a compliancy with 2 Nm/h standards). At only 3
liters and 3 kg, the HRG proves once again its ability to
compete with legacy RLG systems, while saving payload and
maintenance costs for the airlines thanks to its outstanding
reliability.
Fig. 5. SkyNaute HRG INS for Commercial Aircrafts
Fig. 6. Inertial navigation error over a real 12 hour flight
B. Integrated modules
Beside its integrated units, Sagem proposes a complete
IMU (Inertial Measurement Unit) family named Primus
(Fig. 7), which is built around its HRG and dedicated to OEM
applications. Gyro bias stability is the key differentiating driver
between members of the family, ranging from 0.1°/h (Primus
100) up to 0.01°/h (Primus 400).
Fig. 7. Primus HRG IMU family
The AASM Hammer (Air Ground Modular Weapon),
capable of operating in GPS denied environment, benefits from
the HRG accuracy. By introducing the modular approach of the
same guidance kit, Sagem developed a wide range of guidance
kits adapted to different payloads (Fig. 8). The outstanding
accuracy of the weapon mainly relies on its inertial sensors,
contributing to both guidance and control. To date, more than
4,000 units have been produced to serve the AASM Hammer
program.
Fig. 8. The AASM Hammer family, using HRG
Based on the Primus family, Sagem is subsequently
developing a north-finder & north keeper. This technology
requires 3 HRG, designed to be integrated in portable systems
(Fig. 9), in the scope of the JETS program for the PAVAM
(Precision Azimuth & Vertical Angle Module). The SWaP
(Size, Weight & Power) features of HRG are particularly suited
to man portable applications, with a power consumption
requirement below 4 W.
Fig. 9. Long range multi-function infrared binoculars
In parallel and capitalizing on the fusion of in house
optronics and inertia technologies, Sagem integrates a
geolocation function in GPS denied environment within its
Paseo sight dedicated to artillery target locator (Fig. 10).
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Fig. 10. Paseo modular advanced stabilized sight
The Primus concept demonstrates once again the industrial
interest of the modular approach.
III. A
DVANCED APPLICATIONS
A. Inertial Redundant Skewed system
Thanks to the ultra-compactness of its HRG shown in
Figure 11, Sagem designs Redundant Inertial Skewed Systems
with an unparalleled volume and mass, aiming to comply with
fail operational and fail safe requirements needed for aircraft or
satellite launchers (ability to detect a sensor failure, isolate it
and reconfigure the inertial system).
Whereas the Ariane 5 navigation system is composed of
two IRS (Inertial Reference System) and includes a
“supervisor” function in charge of switching from the first IRS
to the second one, the Sagem solution [4] would consist in a
single redundant IRS (6 skewed axis) which offers not only a
higher level of accuracy than the present configuration but a
much higher safety level (fail operational / fail safe system)
than the present navigation system (only fail safe).
Even if the total number of sensors remains identical to
current system (6 gyros and 6 accelerometers), Sagem
multisensory architecture provides a real improvement to the
safety: in case of failure, multiple reconfiguration solutions are
available. Thus this architecture is robust to two sensors
failures (for example 2 gyros, or 2 accelerometers, or even 2
gyros & 2 accelerometers) whereas in classical system one non
detected failure can contribute to the loss of the launcher.
The IRS (Fig. 11) is basically composed of:
• a strap-down inertial platform: six gyros and six
accelerometers are integrated on a single inertial
assembly,
• redundant electronic boards,
• a mechanical hermetic housing,
• dampers to protect the inertial assembly from high
shocks.
Fig. 11. Views of sensors, assembly and mechanical housing
The HRG technology allows a full redundant IRS (6 axis,
fail op/fail safe) with a better SWaP than a classical non
redundant IRS.
B. Ultimate performance application
Some applications require extremely specific performance
characteristics. As far as gyro inertial performance is
concerned, the most demanding application is submarine
navigation, which requires bias stability over days, weeks, or
even months.
The ultimate technology for this application has been the
Electro Static Gyroscope (ESG) that Sagem developed in the
80's and 90's. In fact, an ESG is a really poor gyroscope, with
very low dynamic range and many other limitations. Its real
performance comes not only from its mechanical & electrical
perfection, but also from the way it is operated by the ESG
navigator, in order to compensate short-medium-long term
errors.
With the development of the HRG in the 2000's - 2010's,
Sagem has learned how system operation can dramatically
boost the gyro performance by a ratio in the thousands. The
experience gained with ESG, although somewhat different, was
nevertheless extremely useful.
Very long term navigation is now accessible through HRG
technology, either in strap-down or in gimbaled architectures.
Sea tests have already proven that the Sagem HRG meets the
requirements for submerged navigation over the course of days
or months.
IV. A
WORLD
-
CLASS INDUSTRIAL FACILITY
In 2012, Safran expanded its Montluçon site in central
France to accommodate a new plant dedicated to the
production of inertial navigation systems. It covers 19,000
square meters of floors, including 6,000 square meters of clean
rooms where the ring laser gyros, hemispherical gyros and
navigation systems are manufactured and assembled. First in
Europe in terms of industrial capacity, the Coriolis facility
(Fig. 12) has become the world’s leading production unit in the
field of hemispherical resonator gyros. This scalable, modular
industrial facility will be in a position to adapt to changing
requirements with the ramp-up in new HRG technology.
Fig. 12. Coriolis plant
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Designed to offer large-scale production capacities, to
improve the efficiency of production processes, and to reduce
industrial cycles, the construction of Coriolis followed three
guiding concepts:
• The quality of physical flows through the optimization
of staff and equipment traffic, automated stores, and
ergonomic working positions;
• The high technical level of the infrastructures for total
control of the manufacturing processes, particularly
through permanent control of the temperature,
humidity and cleanliness of the facility;
• The modularity and scalability, giving the facility the
scope to adapt to growing industrial requirements with
the capacity to extend production areas.
Though initially developed for very specific applications,
Sagem dramatically simplified the HRG design, reducing it to
only 6 parts, allowing an optimized process flow to reduce unit
cost. The sensor technologies make use of a mature process
adapted from the microelectronics industry.
Fig. 13. Resonators test
A SPC (Statistical Process Control) is operational, which
provides data validation of the manufacturing repeatability of
key parameters: intrinsic characteristics (e.g.: resonator Quality
Factor, Fig. 13), and sensors performances (e.g.: bias).
Robustness of the definition has been demonstrated by
HASS (Highly Accelerated Stress Screening) with
overstresses, combined random six-degree-of-freedom
vibration and rapid thermal change rate. These tests effectively
force product weak links to emerge by accelerating fatigue.
Long term ageing campaigns, without gyro or electronic
failure, demonstrated long term reliability.
V. C
ONCLUSION
If the scientific community always regarded the HRG as a
premier gyro with outstanding accuracy and reliability
characteristics, few anticipated that HRG would be capable to
address the mass market. Thanks to innovative design and
massive industrial investment, Sagem was capable to achieve
it.
Fig. 14. HRG by Sagem
With its robust 20mm diameter resonator (Fig. 14), Sagem
is able to address an unmatched range of applications through
scalable electronics and advanced system architecture. From
very cost effective marine compass to ESG grade strategic
navigation, from tripod mounted north finder to space launcher
navigation, the Sagem HRG is able to fulfill needs for accuracy
in harsh environmental conditions while doing so in a very cost
effective way.
HRG is more than an innovative gyro technology; it is a
disruptive technological breakthrough. In the same way, optical
gyros (RLG and FOG) replaced the mechanical gyros, HRG is
redefining the landscape of inertial navigation (Fig. 15).
Fig. 15. Future gyro technology applications
R
EFERENCES
[1] G. Remillieux, F. Delhaye, Sagem Coriolis Vibrating Gyros: a vision
realized, in Proceedings of Karlsruhe Conference on Inertial Sensors and
Systems, 2014
[2] A. Jeanroy, P. Leger, HRG flat electrodes, Patent US 6474161
[3] A. Jeanroy, A. Bouvet, G. Remillieux, HRG and Marine applications in
Proceedings of 20th Saint Petersburg International Conference on
Integrated Navigation Systems, 2013
[4] 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 applications in Proceedings of 22th Saint
Petersburg International Conference on Integrated Navigation Systems,
2015
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