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Low cost CVG for high-grade north finders and targeting systems
Abstract
Low-cost accurate orientation as required for targeting, pointing and personal navigation is generally obtained by using FOGs (Fibre Optical Gyros) and DTGs (Dynamically Tuned Gyros). When considering the alignment time and the complexity of the system, those gyros within strapdown systems have shown themselves to be particularly relevant and today numerous systems are operated this way. However, reliability and cost are still two key drivers and new applications are seeking alternatives which are more cost effective. In spite of the emergence of Vibratory Gyros Technology, as illustrated by the high grade Hemispherical Resonator Gyro (HRG), the cost for 1 mrad accuracy is still high which prevents the effective deployment across the civilian market of accurate True North-Finders (TNF) and pointing systems. INNALABS Ltd has risen to the challenge and has developed a low-cost CVG (Coriolis Vibratory Gyroscope) able to meet the market demand for low-cost accurate TNF and pointing systems. Although the INNALABS' CVG has been developed primarily for stabilisation control systems and tactical grade systems, some specific refinements of the control loop electronics are leading to few 0.01 °/hr bias stability and ARW better than 0.01 °/√hr as required for 1 mrad accuracy. Statistical data on key performance characteristics will be presented including the bias stability and the output noise. As an example of a practical implementation, the 2 position method for True North measurement will be described with a result consistent with 1 mrad heading accuracy. This underlines the capability of INNALABS' technology of branching into the TNF and the pointing market segments.
... The MEMS accelerometer is installed on the X axis, and the gyro on the Y axis of the m-frame. Considering the gyro's bias E b , the gyro's output is expressed as: W iemy = ω ie * sin α(sin L cos θ sin γ − cos L cos φ sin γ sin θ + cos L cos γ sin φ)+ ω ie * cos α(sin L sin θ + cos L cos θ cos φ) + E b (11) where W iemy represents the gyro's output. To simplify the above formula, A and B are used: ...
... From the above Equations (11) and (12), we can see that the modulated gyroscope output is relevant to the earth rotation rate. The amplitude of the modulated signal can be used as a good verification of true north finding. ...
... Then Equations (11) and (14) can be rewritten as follows: ...
Gyro north finders have been widely used in maneuvering weapon orientation, oil drilling and other areas. This paper proposes a novel Micro-Electro-Mechanical System (MEMS) gyroscope north finder based on the rotation modulation (RM) technique. Two rotation modulation modes (static and dynamic modulation) are applied. Compared to the traditional gyro north finders, only one single MEMS gyroscope and one MEMS accelerometer are needed, reducing the total cost since high-precision gyroscopes and accelerometers are the most expensive components in gyro north finders. To reduce the volume and enhance the reliability, wireless power and wireless data transmission technique are introduced into the rotation modulation system for the first time. To enhance the system robustness, the robust least square method (RLSM) and robust Kalman filter (RKF) are applied in the static and dynamic north finding methods, respectively. Experimental characterization resulted in a static accuracy of 0.66° and a dynamic repeatability accuracy of 1°, respectively, confirming the excellent potential of the novel north finding system. The proposed single gyro and single accelerometer north finding scheme is universal, and can be an important reference to both scientific research and industrial applications.
... In recent years, vibrating sensors have become ubiquitous [1][2][3]. This is because of their simple design (no moving parts), robustness, and continuous improvements in algorithms and electronics. ...
... Despite of not being deeply addressed in the modern literature, it is one of the main obstacles in the development of inertial sensors [10,11]. In fact, in the development of the ring laser gyroscope, it was the lock-in of frequencies of two counter-rotating laser [3] beams, which posed the biggest challenge to overcome, in order to achieve a fully functional optical sensor [10]. ...
In recent years, vibrating sensors have become ubiquitous. This is because of their
simple design (no moving parts), robustness, and continuous improvements in algorithms
and electronics. Nowadays, vibrating gyroscopes are replacing well-established optical
technologies like ring laser and fiber optics gyroscopes.
Vibrating gyroscopes are based on the Coriolis Effect. For instance, when a standing
wave is excited in an axisymmetric structure (resonator) and an angular rate is applied; the
Coriolis acceleration that appears on the structure causes the vibrating pattern to rotate
around its symmetry axis, with a velocity proportional to the external angular rate.
Non-ideal vibrating sensors suffer from a well-known effect called lock-in. For external
angular velocities smaller than the lock-in rate, the standing wave does not rotate and the
sensor fails to operate. For instance, Coriolis Vibrating Gyroscopes (CVGs), working in
the Whole Angle Mode (WAM), have a lock-in threshold proportional to the difference
between the inverse of the maximum and the inverse of the minimum values of the
damping time constant. Recently, a Slow Variables (SV) method has been used to
demonstrate this effect as well as to calculate the lock-in angle.
In this work, using a Fast Variables (FV) method, we derive the lock-in condition without
making any assumptions and/or approximations. We solve the dynamics exactly and we
find equivalent conditions for the system's eigenvalues to those known for the Damped
Harmonic Oscillator (DHO), i.e., angular rate decreasing to zero – over-damped dynamic,
lock-in – critically damped dynamic, and free rotation – under-damped dynamic. Therefore,
we can explain the lock-in effect without resorting to a nonlinear theory (SV method) but by
the form of the roots of an eigenvalue problem of a linear system (FV method).
... Разработка и изготовление твердотельных волновых гироскопов (ТВГ) является наукоемким процессом, включающим в себя большое количество различных технологических процессов [1][2][3][4], требующих оптимизации и автоматизации. На сегодняшний день при изготовлении ТВГ большинство операций проводится и контролируется человеком, причем большое количество информации заносится и хранится на бумажных носителях. ...
Статья посвящена разработке информационно-сетевого комплекса (ИСК) для сопровождения производственных операций контроля, диагностики и настройки точностных характеристик твердотельных волновых гироскопов с целью повышения качества изделий и эффективности технологических процессов.Для этого сначала проведен анализ существующих информационных систем сопровождения автоматизации технологических процессов и их контроля. Обсуждается возможность использования таких систем в производстве твердотельных волновых гироскопов.В результате предложена структура ИСК, разделяющаяся на физическую и информационную подсистемы. В ней физическая подсистема представляет собой набор коммутирующих устройств в виде стендов с промышленными компьютерами, узлов связи, серверов и персональных компьютеров и других периферийных устройств. А информационная подсистема включает программное обеспечение для автоматизации технологических операций и анализа получаемых данных. Предполагается, что программное обеспечение анализа данных будет также производить запросы к базе данных и обрабатывать большие объемы информации с использованием алгоритмов машинного обучения.Для повышения эффективности всей системы организуется автоматический сбор физических и точностных параметров изделий на разных этапах их производства. Среди основных планируемых результатов работы ИСК выделены: оптимизация технологических процессов и выявление сложных многофакторных нелинейных зависимостей параметров качества от параметров технологических операций, а также автоматическое оперативное выявление неисправного оборудования с выработкой рекомендаций по его ремонту и автоматический оперативный контроль уровня квалификации операторов с регулировщиками.Отдельно обсуждаются способы интегрирования ИСК в производственный процесс изготовления твердотельного волнового гироскопа.
... Following in the footsteps of these pioneers and after the launch of its tactical grade Coriolis Vibratory Gyroscopes [7] [8], InnaLabs® recently introduced the AI-Q-2010, AI-Q-1410 and AI-Q-710 Quartz Pendulous Servo Accelerometers. These Accelerometers are the latest addition to InnaLabs® quality line of high performance "built in Europe" and ITAR-Free sensors targeted at navigation, tactical, control and measurement applications. ...
The gyro is a new silicon micromechanical gyro, which has no a driving structure but only a sensing structure. The non-driven gyro is installed on a rotating carrier and utilizes the spinning of the carrier to obtain an angular momentum. When the carrier produces a transverse rotation, the sensing mass of the gyro is acted by Coriolis force to sense the input angular velocity. In applications, we found that the shock causes the Si pendulum to go out of steady state, and to fail to work. So, the stability is a key problem. In this paper, we put forward a feasible way to overcome this problem. The method uses modeling in state space to construct a state feedback controller. We firstly introduce the working mechanism of the gyro and obtain the dynamic equation. Then we use Riccati equation to design a steady controller that has a 'sandwich' structure. For the stabilizing controller, we calculate the anti-torsion stillness coefficient and analyze the damping. Finally, some shock tests had been done. The theoretical simulation and experimental test shown that the designed stabilizing controller makes the gyro reach an asymptotic steady state in a short time.
The Hemispherical Resonator Gyro (HRG) has proven itself to be an ultra-reliable technology for space application with over 20 million operation hours and 100% mission success. Northrop Grumman Navigation Systems Division is developing a terrestrial inertial navigation system, INS, based on the proven space technology that can be used for precision pointing applications. The Precision Pointing System (PPS) design yields a small size and lightweight system and will require only a few watts of power to operate. To achieve this small sized INS, the PPS utilizes a new golf-ball sized milli-HRG (mHRG) that is based on the current HRG 130P production gyro design used in extremely accurate space pointing systems. The power reduction is derived from a new electronics design based around low power elements.
We report high-Q and wide dynamic range MEMS gyroscopes and accelerometers for development of a very compact IMU capable of North finding and tracking over dynamic environment. The vacuum packaged SOI rate sensors utilize symmetric Quadruple Mass Gyroscope (QMG) architecture with measured quality factors of 1.2 million and proven sub-°/hr Allan deviation of bias. The true North detection was accomplished in conventional amplitude modulated (AM) rate measuring mode and showed 0.003 radian measurement uncertainty. The North (azimuth) tracking over dynamic environment necessitates a wide dynamic range, for which the same QMG transducer is switched to a frequency modulated (FM) modality. The test results for FM operation experimentally demonstrated a wide linear input rate range of 18,000 °/s and inherent self-calibration against temperature changes. Vertical alignment of the IMU and acceleration sensing is enabled using resonant accelerometers with 5 μg performance. The accelerometer is self-calibrated against temperature variations, enabled by differential frequency measurements. We believe the developed low dissipation inertial MEMS with interchangeable AM/FM modalities may enable wide dynamic range IMUs for North-finding and inertial guidance applications previously limited to systems based on optical and quartz inertial sensors.
Sagem improvements made in the design, the process and the control of the HRG help to reach high performance while keeping the intrinsic simplicity of the Coriolis Vibrating Gyros family. Therefore it allows the HRG to challenge the laser gyros for strapdown inertial navigation. The simplicity derives from many patented innovations which lead to a very compact gyro with a very low number of components. The manufacturing takes advantage of this simplified design and of a new automatic tuning and balancing process which reduces sensitivities to mechanical environment. While using a Whole Angle mode of control which leads to very good scale factors, a new full digital electronics provides gain and phase accuracy at the level needed by the 0.01°/h class of bias performance. The paper explains these choices and presents the results obtained by the Sagem HRG during tests. Thanks to these characteristics, new applications are developed, especially when compactness, low consumption, reliability and maintenance free long term performance are needed as it is the case with Marine Gyrocompass or Marine Attitude and Heading Reference Systems. The architecture of the Sagem marine AHRS BlueNaute™ is presented and many test results are given, including those obtained on marine vessel.
We report progress toward a MEMS gyroscope suitable for northfinding in pointing and targeting applications. In-run bias stability of 0.03 deg/hr and ARW of 0.002 deg/rt(hr) have been achieved. Gyro performance was measured on tuning-fork type MEMS gyroscopes using DSP-based breadboard electronics. These bias stability and ARW results are within about 6X and 2X, respectively, of meeting the typical gyrocompass requirements for pointing and targeting applications (1 milliradian azimuth precision at 65 degrees latitude with 5 minute integration time). A MEMS gyrocompass meeting these requirements would substantially reduce the size, weight and power of pointing and targeting instruments. The test methodology will be presented, as well as test data on carouseling the sensor to reduce the effects of long-term bias drift.
High-grade CVG for Stabilisation Control Systems and Tactical Grade Systems
- J Beitia