A Method of Error Separation for Fiber Optical Gyroscope Based on Star Sensor Measurement

Fiber optic gyroscopes (FOGs) are vital components for manned, unmanned, and autonomous platforms, as well as applications requiring extremely accurate data for stabilization, pointing, orientation of payloads, and navigation and control. FOG-based inertial systems also provide highly accurate data for all types of navigation, positioning, and georeferencing systems. Substantial improvements in the performance of FOGs and FOG-based inertial systems at KVH are directly related to advancements in the design and manufacture of optical fiber, as well as in manufacturing operations and signal processing. Open-loop FOGs, such as those developed and manufactured by KVH Industries, offer tactical-grade performance in a robust, small package. The success of KVH FOGs and FOG-based inertial systems is due to a series of key innovations including the development of proprietary D-shaped fiber with an elliptical core, as well as KVH's ThinFiber. KVH continually improves its FOG manufacturing processes and its signal processing, with the goal of improving accuracies across its entire FOG product line. KVH acquired its FOG capabilities, including its patented E·Core® fiber, when the company purchased the assets of Andrew Corporation's Sensor Products Group in 1997. E·Core fiber is unique in that the light-guiding fiber core — critical to the FOG's performance — is elliptically-shaped. The elliptical core results in an optical path with low loss and high polarization-maintaining ability. In 2011, KVH developed its ThinFiber, a 170-micron diameter dual acrylate-coated fiber that retains the full performance characteristics of E·Core fiber. ThinFiber has enabled the development of compact, high-performance open-loop FOGs, which are also used in a line of FOG-based inertial measurement units (IMUs) and inertial navigation systems (INS).

The article presents a telemetry system for monitoring the bit trajectory during well drilling. Fiber-optic closed-loop gyroscopes are the main sensitive element in the telemetry system. The gyroscopes allow determining the azimuth and zenith angles of the well with a high accuracy exceeding most magnetometers. There is no need to use the expensive non-magnetic steels in the body of the telemetry system and non-magnetic drill pipes in the drill string. Fiber-optic closed-loop gyroscopes allow using the telemetry system when drilling near the casing of adjacent wells and magnetized rocks. An inertial navigation system is installed in the developed telemetry system as a measuring unit containing three angular velocity sensors and three accelerometers mounted rigidly. The sequence and results of simulation of a hydraulic link for data transmission from the bottom of the well to the top are described. Pilot tests of the telemetry system were carried out at well No. 450 of the Tatsuksinskoye field. The obtained values of the spatial intensity of the borehole curvature in depth are close in values to the directional survey data for the borehole. The trajectory obtained during the lift is close to the trajectory gathered from directional survey data.

The Star Sensor can be used to assist the inertial navigation system (INS) for navigation and positioning, restraining the accumulated error caused by the inertial components. During the integrated navigation process, the Star Sensor is installed above the INS, generated installation errors between the INS body coordinate system and the Star Sensor body coordinate system. In order to increase the system accuracy, a new gyro error model is established in this paper which taken full account of various error factors. The gyro drifts and the gyro errors coefficients are considered as the state variables. The attitude information of Star Sensor is used as the high-accurate information to construct the observation with the attitude information of INS. Taken the nonlinearity of the actual system into account, the nonlinear filter Cubature Kalman Filter (CKF) is used to estimate the gyro errors commendably. The experiment results showed that the positioning error reduced a lot by utilizing this novel method.

Navigation of Hypersonic vehicles in the radio frequency (RF) blackout area during atmospheric reentry is challenging as the vehicles can only use the inertial navigation system (INS) as autonomous navigation method in this area. In this paper, strapdown inertial navigation system (SINS) based on the Fiber Optic Gyroscope (FOG) is used for navigation in blackout area. However, without external navigation measurement, the errors of SINS caused by the FOG drift and accelerometer bias would cumulate with time and degrade navigation accuracy. To solve this problem, single axis rotation modulation along with the azimuth axis of the body frame is adopted. The Generic Hypersonic Vehicle (GHV) model designed by NASA Langley Research Center is used to build the reentry fight model which can generate navigation information for simulation. Through derivation the error equations of FOG SINS in the North-East-Down (NED) navigation frame, the principle of error compensation by rotation modulation can be well understood. The simulation results show that rotation modulation can effectively decrease the impact of inertial sensor drift and improve the navigation accuracy in blackout area.

This paper describes an iterative closed-loop procedure for the performance optimization of an Inertial Navigation System (INS) based on Fiber Optic Gyro (FOG) technology for airborne applications. The proposed approach focuses on the tuning of the Indirect Kalman Filter (IKF) covariance matrices using inertial sensor errors budgets gathered by the analysis of Allan Variance in a reliable calibration environment. The proposed method identifies a base metrics for predicting the actual filter performance, selecting a suitable combinations of IKF tuning parameters in order to satisfy the system specifications for a particular application. The engineering optimization process spans from the sensor raw data acquisition up to the performance test on the real target HW platform, carrying out the various intermediate steps of algorithm design, simulation runs, code porting and deployment on the embedded INS, lab and on-field testing for performance verification and final comparison of the acquired data output with simulation results to feed the successive tuning iteration. The matching effectiveness between simulated and real data is presented to highlight the beneficial features of this approach.

The subject of the article is the fiber-optic fiber-optic gyro system used in inertial navigation, control and stabilization systems. The purpose of the article is to study the design of the schematic diagram of the transmitting device of the optical fiber system and to make the necessary calculations for the transmitting device of the optical fiber system. Problem to be solved is the justification of technical solutions, the implementation of which in the practice of measurement will allow to substantiate the process of designing the schematic diagram of the transmission device of the fiber-optic system of the fiber-optic gyroscope used in inertial navigation, control and stabilization systems. The article deals with: stages of designing the schematic diagram of the transmitting device of the fiber optical system; certain calculations have been made regarding the damping of the site in relation to the designed single-fiber communication system; diagram of the optical transmission device under development. Conclusions: It is advisable to use the proposed technical solutions both in the modernization of existing fiber-optic gyroscopes and in the creation of perspective samples intended for use in inertial navigation, control and stabilization systems

Initial alignment is of vital importance to inertial navigation systems (INS). The two main methods of self-alignment, the traditional gyro-compassing alignment method and the Kalman filter method, are discussed. We apply and compare the two methods via simulation and test in use of a strapdown inertial navigation system (SINS) based fiber optic gyroscope (FOG), respectively. The simulation and test show that Kalman filter method is better in convergent time and accuracy of attitude and azimuth, however, gyro-compassing alignment method is better in robustness. This provides a useful reference for designing alignment algorithm for FOG SINS.

As an important part of the inertial device in the ship strap-down inertial attitude measurement and navigation system, the high reliability of fiber optic gyroscopes (FOGs) is significant for the long-term precision of navigation systems and mission success for ships. Due to the combined impact of the external service environment and internal physical field, the performance of FOGs will gradually degrade. Although many studies are dedicated to the degradation analysis and reliability assessment of FOGs, few have considered the 3-axis dependent degradation processes of FOGs simultaneously. Confronted with this problem and taking the scale factor and zero bias as two main degradation characteristics of the FOGs, this paper develops the degradation path model for each marginal degradation process on each of x, y and z axis. The unknown model parameters are estimated by maximum likelihood estimation method based on accelerated degradation test data. Furthermore, considering the dependence between the two marginal degradation processes on each axis, the reliability of the FOGs is evaluated by adapting the Gaussian copula function. It can be illustrated that the proposed degradation model and reliability assessment method are effective for FOGs and other products with 3-axis dependent degradation processes.

In modern aerospace technology, strapdown inertial navigation systems (SINS) are widely used, using fiber-optic (FOG) or ring laser (CLG) gyroscopes. During the operation of such systems, the sensitivity axes are rotated relative to the basic coordinate system. The resulting angles between the axes of the base coordinate system and the axes of sensitivity of the navigation system (non-orthogonality) are one of the factors leading to an increase in the measurement errors of the device, which affects the measurement accuracy. During operation, the system is affected by vibrations of various nature, the impact of which can contribute to the appearance of non-orthogonality. The purpose of this work is to determine the maximum permissible vibration amplitudes affecting the SINS body according to the permissible values ​​of the deviation of the FOG sensitivity axes for two variants of the SINS layout. An approach to determining the permissible amplitudes of an external harmonic impact on the unit of a strapdown inertial navigation system based on fiber-optic or ring laser gyroscopes is considered. A design scheme, mathematical and finite element models for calculating natural frequencies and forced oscillations of a strapdown inertial navigation system unit have been developed. In various frequency ranges, numerical calculations have determined the boundary values ​​of the amplitudes of the external harmonic impact on the base of specific configurations of the SINS assembly. It has been established that dangerous states take place in the region of the 1st natural frequency of the system, as well as near higher frequencies. Comparison of the results for design options 1 and 2 allows us to conclude that in order to weaken the effect of vibrations on the accuracy of the SINS unit, it is advisable that the lowest natural vibration frequencies for the SINS assembly be as high as possible (more than 1000 Hz).
 Key words: vibration; fiber optic gyroscope; strapdown inertial navigation system; finite element method; natural frequencies and modes of vibration.

Life cycle cost containment of the strategic weapons system (SWS), without loss of ultra high performance, is a very important goal of the entire Navy Strategic Systems Program community. Boeing is responding by guiding large advances in the state-of-the art of fiber optic gyro technology and developing a new associated navigation system. All of the very stringent strategic weapons system (SWS) performance, reliability, and maintainability requirements continue to be exceeded by the electrostatically supported gyro navigator (ESGN). The electrostatically supported gyro (ESG), in production for over 25 years, is the most critical and costly component of the current inertial navigation system. ESGs, however, are extremely expensive to manufacture and repair. Furthermore, the system-level electronic components are difficult to replace because they are rapidly becoming obsolete. The current initiative is focused on containing total ownership costs, especially maintenance costs, without any relaxation of performance, reliability, or maintainability requirements. The key element of this initiative is new gyro technology based on rapidly improving precision IFOG performance, along with cost reduction of fiber and manufacturing processes. This paper discusses the challenges and the approach currently being taken to further the development of high precision interferometric fiber optic gyro (IFOG) technology and its associated inertial navigation system for application to the SSBN.

Maneuvering spacecraft, a state-of-art platform, is paid more and more attention on for the upcoming space exploring. The integration of CNS (Celestial Navigation System) and INS (Inertial Navigation System) is the promising autonomous navigation candidate for maneuvering spacecraft. However, the star image of CNS may be heavily degraded by the large attitude variation in the spacecraft maneuvering. The effect of the attitude variation on the star image is twofold: the enlarged areas and the reduced pixel gray value of the star image. Both of them will degrade the extracting accuracy of the star image center directly. Therefore, the feasibility of CNS for the maneuvering spacecraft mainly depends on the mitigation of the effect of the attitude variation on the star image. In this paper, the star image motion is modeled when the spacecraft attitude is maneuvering firstly. The pixel gray value of the star image is also formulated in the span of exposure according to the camera exposure model. Then, the motion compensation values for the star image are deduced with the INS angular velocity in the rolling, yaw, and pitch axes respectively. The compensated star image's center is extracted accurately in the following. Finally, the compensation method is validated by simulations. The simulation results prove that the star image center extraction is as accurate as 0.1 pixel with the aiding of a tactical INS even though the spacecraft angular velocity is as large as 30º/s.

The advantages of mechanical gyros, such as high precision, endurance and reliability, make them widely used as the core parts of inertial navigation systems (INS) utilized in the fields of aeronautics, astronautics and underground exploration. In a high-g environment, the accuracy of gyros is degraded. Therefore, the calibration and compensation of the gyro G-sensitivity coefficients is essential when the INS operates in a high-g environment. A precision centrifuge with a counter-rotating platform is the typical equipment for calibrating the gyro, as it can generate large centripetal acceleration and keep the angular rate close to zero; however, its performance is seriously restricted by the angular perturbation in the high-speed rotating process. To reduce the dependence on the precision of the centrifuge and counter-rotating platform, an effective calibration method for the gyro g-sensitivity coefficients under fiber-optic gyroscope (FOG) monitoring is proposed herein. The FOG can efficiently compensate spindle error and improve the anti-interference ability. Harmonic analysis is performed for data processing. Simulations show that the gyro G-sensitivity coefficients can be efficiently estimated to up to 99% of the true value and compensated using a lookup table or fitting method. Repeated tests indicate that the G-sensitivity coefficients can be correctly calibrated when the angular rate accuracy of the precision centrifuge is as low as 0.01%. Verification tests are performed to demonstrate that the attitude errors can be decreased from 0.36° to 0.08° in 200 s. The proposed measuring technology is generally applicable in engineering, as it can reduce the accuracy requirements for the centrifuge and the environment.

Currently, Fiber-Optic Gyroscopes (FOGs) stand as a significant leap in inertial navigation sensor technology within the field of automation, control and navigation. There has been a recent global emphasis on exploring and enhancing high-precision Inertial Navigation Systems (INS), focusing on the pivotal role of fiber optic gyros as a fundamental sensor. FOGs are leading in many aspects over the mechanical gyros which were used before in earlier decades as they are lighter in weight, require no moving parts in operation, with higher sensitivity, and quicker in both start-up and warm-up procedures. In our present work we will investigate the performance of FOG under a distinct operational condition—namely, Near-Zero Rotation Rate for both basic and phase modulation configurations. We will use OptiSystem software package to simulate both configurations and show the initial challenges encountered during the simulation and detailed how subsequent phases effectively addressed these issues and pointing out the significant conclusion.

Direct optical path measurement in fibre-optic gyroscopes: A potential method for compensating slow-drifting errors

Inertial navigation provides a unique ability to know where one has been, where one is currently, and where one is going, given only a starting position. The laws of physics permit the sensing of dynamic motion without external information, making inertial systems impervious to jamming, masking, or spoofing. Measurements of six degrees of freedom are required - three linear accelerations, and three angular rates - to fully propagate the velocity, position, and orientation of the system. The first inertial sensors are traced to the early 19th century and specialized inertial guidance systems appeared in the 1940s, yet inertial navigation systems did not become commonplace until the 1960s. This is largely due to the fact that requirements for navigation accuracy inertial sensors - accelerometers and gyroscopes - are very challenging. In the past fifty years, significant evolutionary and revolutionary changes have taken place in the designs of inertial sensors and systems. These include the progression from fluid-filled to dry instruments and the transition from mechanically complex stabilized inertial platforms to computationally intensive strapdown systems. Gyroscopes have evolved from large mechanical devices to highly refined precision mechanical sensors. Optical rotation sensors such as the ring laser gyro and the fiber optic gyro have enabled new system designs and capabilities. Coriolis vibratory gyroscopes such as the hemispherical resonator gyro are capable of extreme accuracy and reliability; new opportunities for miniaturizing these types of sensors will lead to new classes of accuracy for inertial navigation systems. Advanced gyroscope technologies such as the nuclear magnetic resonance gyroscope which uses atomic spin to detect rotation have already been demonstrated to achieve navigation accuracy requirements. Cold atom technologies may also provide the opportunity for very high accuracy accelerometers and gyroscopes in the future. Inertial navigation technologies and applications of the past, present, and future are discussed.