Telemetry system based on fiber-optic gyroscopes

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).

A Star Sensor based Fiber Optical Gyroscope Error Separation method (SSFES) was proposed, which can be applied in the Fiber Optical Gyroscope (FOG) performance evaluation and fault diagnosis for the space-borne Inertial Navigation System (INS) & Celestial Navigation System (CNS) combined navigation system. The method takes the satellite rotational angular rate and the attitude quaternion to separate the long-term drift component from the FOG output and provides the useful information for FOG error compensation and model construction. The output quaternion of the star sensor was utilized to reconstruct the satellite rotational angular rate information, which was then used to separate the error component from the FOG output. Simulations have been carried out to verify the method and have shown that the error component of FOG output can be extracted efficiently by SSFES and the algorithm is easy to be performed by the onboard computers.

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.

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.

For its obvious high accuracy in a long term, rotary inertial navigation system becomes popular. However, as errors increasing with time are changed into periodic errors with zero mean, the accuracy of its azimuth angle decreases in view of short term and can’t fully satisfy the need of users such as flight control system. The precision of azimuth angle is studied by analyzing its influence factor and establishing the scale factor error model and drift models of fiber optic gyro and the measurement error model of photoelectric encoder. Correction for fiber optic gyro and photoelectric encoder based on their mutual assistance is designed to improve the short-term accuracy of rotary inertial navigation system’s azimuth angle. Experimental results in a fiber optic gyro based rotary inertial navigation system verify the proposed method.

With the development of laser and optical fiber, the north finding system (NFS) with fiber optic gyroscopes (FOGs) has become an active trend in inertial technology research. This paper demonstrates the error analysis of dynamic north-finding with a fiber optic gyroscope and a new way for the FOGs noise measurement in the dynamic implementation. Moreover, in order to suppress the north-finding error caused by FOG bias drift, especially for the small azimuth angle, we propose a modified dynamic north-finding scheme by taking advantage of the dynamic method. The experiments verify the validity of the proposed error analysis for the dynamic implementation. Experimental results show that for a FOG with bias instability of 0.005°/hr, the average (Avg) north-finding bias error is less than 0.03° (0.5 mrad) around 2° azimuth angle by the proposed modified scheme. And compared with the conventional dynamic north-finding, this scheme reduces the estimated error (1σ) of azimuth angle and the bias error (Avg) by 22% and 23.8%, respectively, at the small azimuth angle. For a poorer-performance FOG with 0.0262°/hr bias instability, the proposed method is more effective and reduces 32.4% estimated error (1σ) of azimuth angle.

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.

Theoretical and experimental results of studies on a stability of slow-speed motion generated by different type rotatingplatforms designed for an investigation of angular velocity meters are presented. An application of fibre optic gyroscopewith sensitivity 0.2 deg/h and drift range of Earth rotation give possibility for measurement real rotation generated byplatforms in their all work range. Especially, a possibility of a measurement in the lowest range is a new possibility. Themethod presented in paper has given also a possibility to investigate error sources of generated rotation velocity.Keywords: fibre optic gyroscope, slow-speed velocity investigation, mechanical construction examination, simulation 1. INTRODUCTION The modem aircraft angular velocity sensors need slow-speed measuring stands of special kinds for their testing. Thosestands need appropriate standard sensors, as well as reliable research methods. So the problem emerges: how and whatexamine them? This problem is especially important, because modem inertial navigation system uses angular velocitysensors with sensitivity ofrange ofO.O1 deg/h.1The quality research of TOTEM (used by 1-22 aircraft), LTN-l 0 1 (An-28 aircraft) or LCR-92 (made by AFTI) systems, alsoneed suitable class of slow-speed stands, used as standard source of angular velocity. However, from observation of anaction of the stands existing in Poland, one can conclude the generated by them angular velocity has disturbances increasingwith a decrease of an average velocity generated by the stand.2 Till now the only method of measurements of thoseoscillations has been an observation of a shift of light spot used as an indicator of the uniformity of rotary movement.Another solution of this problem is an application of the optoelectronic sensor to measure real oscillations of those stands.Thus, the suitable adopted fibre optic gyroscope has been used for measurements.

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.

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 high-precision inertial navigation systems, suppressing the random errors of a fiber-optic gyroscope is of great importance. However, the traditional rule-based autoregressive moving average modeling method, when applied in Kalman filtering considering colored noise, presents inherent disadvantages in principle, including inaccurate state equations and difficulties in state dimension expansion. To this end, the noise characteristics in the fiber-optic gyroscope signal are first deeply analyzed, a random error model form is clarified, and a new model-order determination criterion is proposed to achieve the high-precision modeling of random errors. Then, based on the effective suppression of the angle random walk error of the fiber-optic gyroscope, and combined with the linear system equation of its colored noise, an adaptive Kalman filter based on noise-spectrum information decoupling is designed. This breaks through the principled limitations of traditional methods in suppressing colored noise and provides a scheme for modeling and suppressing fiber-optic gyroscope random errors under static conditions. Experimental results show that, compared with existing methods, the initial alignment accuracy of the proposed method based on 5 min data of fiber-strapdown inertial navigation is improved by an average of 48%.

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.

Fiber optic gyroscope (FOG) is a new type of angular velocity sensor in the field of inertia technology. Its non-moving parts and all-solid-state characteristics leads to many advantages compared with traditional electromechanical gyro and ring laser gyro. Scale factor is a key parameter of FOG, which affects the angle measurement accuracy. Closed-loop feedback phase modulation is an important method to enhance the scale factor stability in FOG. The multifunctional integrated optical circuit (MIOC) is the actuator of closed-loop feedback, and the mean wavelength stability of transmission spectrum at full temperature affects the scale factor stability of FOG. With the improvement of FOG's accuracy, the effect of the mean wavelength shift on FOG's performance are becoming more and more important, which has been an important factor limiting the scale factor stability enhancement. Based on the optical waveguide theory, we found out alignment deviation (axial gap, transverse dislocation and axial angle deviation) is the main factor of the mean wavelength stability, and verified by coupling experiments. Moreover, the mean wavelength is the most sensitive to the transverse dislocation. Take z=10 μm for example, the mean wavelength increases by 134 ppm relative to the wavelength of 1.31 μm when x increased from 0 to 2 μm. Secondly the axial gap, the mean wavelength increase by 19 ppm when z increased from 0 to 20 μm. Thirdly the angle deviation plays a minor role, and the mean wavelength decreases by 5 ppm when θ increased from 0° to 2°. This study is of great significance to optimize MIOC, and to provide device guarantee for the enhancement of scaling factor stability of FOG.