Optical fiber gyroscope for automotive navigation

The DoD goals for inertial sensors have included achieving high accuracy performance and small size at a low cost. This goal has always been a challenging endeavor, since small size and high accuracy have often been costly and technically difficult to achieve. In 1998, the Army patented a fiber sensor coil winding concept that would facilitate the opportunity to make the Fiber Optic Gyroscope (FOG) more competitive in cost with relation to the commonly-used Ring Laser Gyro (RLG). Recent advances in FOG sensor coil winding techniques appear to show great promise in the improved performance. The novel Crossover-Free (CF) winding technique eliminates fiber crossovers and allows the use of inexpensive single-mode fiber (SMF). Experiments were conducted with the use of an analog, open-loop testbed, which was characterized with a 1 km quadrupolar SM sensor coil. Various sensor coil configurations were spliced into the FOG testbed and bias drift tests were conducted. Different fiber lengths, coil diameters, and fiber wind configurations were evaluated. The Crossover-Free sensor coils were precision wound by a semi-automated Fiber Placement Machine (FPM) developed by Stanley Associates. The Crossover-Free sensor coils test results are compared to standard precision wound coils. The bias errors caused by the fiber crossovers in standard SM sensor coils are also discussed and compared to the near elimination of the crossovers in the CF design.

Gyroscopes and accelerometers are unique devices, the critical input sensors for inertial navigation and surveying systems. Among the many types of gyroscopes only a few have proved adequate for precise inertial applications. These are the ring laser gyroscope (RLG), electrostatic suspended gyroscopes (ESG), air-bearing floated-gimbal spinning mass gyroscopes, and dynamically tuned rotor gyroscopes (DTG). All have been developed to a high art among precision instruments, with supremely low noise and bias errors. Extensive acceptance of inertial navigation systems in commercial flight service, particularly using RLGs, has also required and stimulated development of practical and competitve reliability, cost, and lifetime.A few currently emerging gyroscope technologies might play a role in future inertial systems, but it is not yet clear whether they can advance to be competitive in performance and cost with current gyroscopes. Most notable is the fiber-optic gyroscope (FOG), another form of optical gyroscope, which in the last several years has advanced to a state suitable for engineering prototypes in aircraft attitude heading and reference systems. Another is the hemispherical resonator gyroscope (HRG), which uses the precession of vibrations on the rim of a “wine glass” shaped quartz resonator.

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.

Draper Laboratory's experience with Interferometer Fiber Optic Gyro (IFOG) technology started via an Internal Research and Development effort in 1978. This work led to developing fiber optic gyros in which significant advances in IFOG component technologies, assembly, integration, and test were achieved. In excess of 30 patents have been issued to Draper as a result of this pioneering effort. More recently, Draper collaborated with JPL to transition their fiber optic breadboard gyro to a space qualifiable instrument for interplanetary long duration missions. During the initial phase, brassboard gyros were designed and fabricated that demonstrated performance that bettered NASA's CRAF-Cassini spacecraft objectives. In the second phase, the Engineering Model gyro was developed to meet mission qualification tests. Concurrent with this later phase, analysis, tests and qualification activities were performed to validate that gyro components would realize the required 16 year life. Two major inventions (patent pending) were conceived; one provides for continuous adaptive scale factor stability and the other integrates the optical source and photodetector into a single component [Source Integrated Detector (SID)], thereby eliminating a coupler and several splices thus reducing loss by 6 db. Using the above technologies and the implementation of common mode rejection of laser noise, Draper has defined a low noise high performance gyro in which rate power spectral density (PSD) is projected to be < 7 X 10-7 (deg/hr)2/Hz. In those applications, where the PSD < 4 X 10-5 (deg/hr)2/Hz is sought, a small size three component (SID, integrated optics circuit and fiber coil) gyro is easily implemented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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).&#x0D; Key words: vibration; fiber optic gyroscope; strapdown inertial navigation system; finite element method; natural frequencies and modes of vibration.

The Sagnac phase shift between two counterpropagating beams is the basis for all optical gyroscopes [11, although it is detected in a variety of ways. In the ring laser gyro and various "closed loop" optical gyroscopes, the scale factor (e.g. counts per unit rotation rate) is fixed by the area of the optical medium whereas the phase reading fiber optic gyroscope (FOG) has a scale factor which increases with increasing length of optical fiber. Thus development of low-loss fibers holds the possibility of extremely sensitive gyroscope operation, and has made the FOG a competitive optical gyroscope. Although most of the first decade of FOG development has concentrated on improving sensitivity, attention is now turning to other aspects of performance.

Fiber optic gyroscopes (FOGs) are developed for industrial and consumer applications. The bias error, which is determined by electrical circuits rather than the optical system, varies between 0.01 and 36 deg/hr depending on the construction of the electrical system. The scale factor error at each input rate is less than 0.5% in the temperature range of -30 to 85 degree(s)C. These FOGs are compact, highly reliable, and need only a +12 V D.C. power source. They are ready for mass production.

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.

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 advantages and the characteristics of the fiber optic gyroscopes (FOGs) for the space application, compared with the traditional mechanical gyroscope and the laser gyroscope, have been mentioned. There are differences of the FOG designing between application in space and other conditions especially the radiation-resistant, low power cost and less weight of the FOG. The key techniques of the fiber optic gyros technology have been proposed and some test results have been discussed.

The global positioning system (GPS) trajectory data are extensively utilized in various fields, such as driving behavior analysis, vehicle navigation systems, and traffic management. GPS sensors installed in numerous driving recorders and smartphones facilitate data collection on a large-scale in a high-frequency manner. Therefore, map-matching algorithms are indispensable to identify the GPS trajectories on a road network. Although the local map-matching algorithm reduces computation time, it lacks sufficient accuracy. Conversely, the global map-matching algorithm enhances matching accuracy; however, the computations are time consuming in the case of large-scale data. Therefore, this study proposes a method to improve the accuracy of the local map-matching algorithm without affecting its efficiency. The proposed method first executes the incremental map-matching algorithm. It then identifies the mismatching links in the results based on the connectivity of the links. Finally, the shortest path algorithm and the longest common subsequence are used to correct these error links. An elderly driver’s driving recorder data were used to conduct the experiment to compare the proposed method with four state-of-the-art map-matching algorithms in terms of accuracy and efficiency. The experimental results indicate that the proposed method can significantly increase the accuracy and efficiency of the map-matching process when considering high-frequency and large-scale data. Particularly, compared with the two-benchmark global map-matching algorithms, the proposed method can reduce the error rate of map-matching by nearly half, only consuming 18% and 58% of the computation time of the two global algorithms, respectively.

Shupe error, a kind of bias error over temperature-varying environments, still exists even with strict quadrupolar winding pattern, and it affects the environment adaptability of fiber optical gyroscope (FOG) and limits its application. A novel configuration to realize optical compensation for Shupe error in FOG is promoted, employing the opposite polarity of Shupe error in two FOGs working with polarization-maintained (PM) fiber’s fast and slow axis, respectively, in a single PM fiber coil. Analysis is also made for polarization non-reciprocity (PNR) in both FOGs, based on which the optimum coupling angles between integrated optic chip and PM fiber coil are obtained to guarantee that Shupe error arising from both FOGs can be counteracted to zero, and PNR error is suppressed to be minimum at the same time.

Development of an automated fiber optic winding machine for gyroscope production

Fiber optical gyroscopes (FOGs) have been applied widely in navigation for mobile robots. The precision of outputs from FOGs is affected significantly by uncertain disturbances due to road conditions in practice. It is urgent to eliminate uncertain disturbances from outputs of sensors in harsh environments. This paper proposes an adaptive method of signal processing base on wavelet and fuzzy logic for outdoor mobile robots in different road condition. Property of disturbances in different outdoor road is taken into account to determine filtering thresholds in this research. Corresponding characteristics of real-time data were processed by a fuzzy logic inference system when mobile robots moved, and then they were de-noising by means of wavelet technique. It was proved that this proposed adaptive method can eliminate disturbances due to road irregularities and improve accuracy of surrogate data by experiments.

This paper proposes using TRIAD and Unscented Kalman Filter (UKF)algorithms in a sequential architecture as a part of the small satellite attitude estimation algorithm. This TRIAD+UKF approach can provide accurate attitude estimates for the satellite by calibrating the magnetometers in real-time. A complete calibration model for the magnetometers, considering bias, scale factor, soft iron and nonorthogonality errors, is assumed. In algorithm's first stage, the TRIAD uses the available vector measurements (e.g. from Sun sensor and magnetometers)to estimate a coarse attitude. In the second stage, these estimated values are used as quaternion measurements in the UKF algorithm, together with angular rate measurements provided by a triad of gyros. The state vector for the UKF is composed of the attitude, gyro biases and the magnetometer error terms. In result, we get fine attitude estimate for the satellite by calibrating the magnetometers against scaling, soft iron, nonorthogonality and bias errors in real-time. We evaluate the algorithm for a hypothetical nanosatellite by numerical simulations. The results show that the attitude of the satellite can be estimated with accuracy better than 1deg and the magnetometers can be fully calibrated.