A Three-Axis Laser Gyro System for Borehole Wireline Surveying

The US Army has a requirement for a highly accurate inertial/TACAN hybrid navigation system. This paper describes the navigation system architecture developed to meet this requirement, the specific hardware selected and the development status. At the beginning of the Integrated Inertial Navigation System (IINS) development program it was anticipated that significant technological advances would take place in its life cycle. In addition, mission requirements were expected to change as the system evolved. Particular attention was therefore given to the IINS system architecture, specifically the partitioning of hardware and software functions as well as the means of data transmittal between the subsystem elements. The paper describes in detail the design trade-offs made as well as hardware selections. The system is configured using several different manufacturers' equipment making the data interface and its configuration control of great importance. The above considerations lead to the conclusion that the appropriate data bus interface standard would be MIL-STD-1553. This interface standard not only facilitates configuration control during system development, but will allow rapid integration with future aircraft systems that will use it as a primary means of data transmittal. The paper describes in detail the signal interface between the subsystem element, onboard mission equipment and flight instruments. The most significant change anticipated in the course of the IINS life cycle is the substitution of Global Positioning System User Equipment for the external update function currently provided by TACAN. Another area where technology insertion may be deemed appropriate is the substitution of a strapdown inertial navigation unit (INU) employing ring laser gyros (RLG) for the currently employed conventional gimballed INU. The INU employed in the IINS is built to a form, fit and function specification, which will allow substitution of a RLG INU when such a unit is qualified and in production. The system hardware and software is structured so that these changes can be accomplished with a minimum of effort. The paper also describes the federated processing structure which allows this flexibility with particular attention to the inertial/TACAN update algorithm and data bus control functions. The paper concludes with a brief summary of the development status of the IINS, currently in full scale engineering development.

Suppression of the G-sensitive drift of laser gyro in dual-axis rotational inertial navigation system

Now a days, Unmanned Aerial Vehicles (UAVs) have been exploited in numerous civil and military aspects such as disaster management and border monitoring. Although most of these UAVs are equipped with Global Navigation Satellite System (GNSS) / Inertial Navigation System (INS) reliable integrated system for localization proposes, they are susceptible to lose their GNSS signals under some environmental and artificial challenging circumstances such as, flying in urban areas, jamming, and spoofing. In such complicated scenarios, the navigation solution will degrade rapidly due to the accumulated INS drift errors. Although various aiding sensors such as cameras, and radar are employed to mitigate the INS drift errors, their estimated positioning accuracy is still affected by some factors. This paper presents a nested optimal filter approach (G-H filter, Extended Kalman Filter (EKF)) for UAVs in GNSS denied environment, to enhance the estimated positioning accuracy by integrating the Radar Odometry (RO)/INS/MAG to sustain a reliable navigation solution during GNSS outage. First, the UAV relative velocity is calculated based on image processing approach from the radar range doppler map, then the G-H filter is deployed to improve the accuracy of the vehicle estimated forward velocities based on the vehicle dynamic characteristics to reduce the effect of unrealistic velocity estimate from the radar. These improved velocities are then fused with the Inertial Measurement Unit (IMU), magnetometer, and barometer via EKF to mitigate the positioning RMS errors during the GNSS signals outages. The experimental results demonstrate the proposed system's ability to notably enhance the 3D positioning accuracy during the GNSS signal outage by more than 99% when compared to a stand-alone IMU dead reckoning solution.

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.

In recent years, precious observations by autonomous underwater vehicle (AUV) have been performed. Tracking and navigation of AUV are important for precious observations. In Japan agency for Marine-earth Science and Technology (JAMSTEC) the observations with AUV ldquoURASHIMArdquo have been implemented in deep ocean area. AUV URASHIMA is navigated by an inertial navigation system (INS) mainly. The absolute position of AUV is tracked on the support vessel with super short base-line (SSBL) method of acoustic positioning. And sometime the own position in AUV is updated by the SSBL estimation result to correct the drift error of INS. However the SSBL is not so accurate. So the position correction includes the SSBL error and the position correction is performed drastically. In this paper, a method for accurate tracking of AUV and rapid correction of the INS status is proposed. The tracking is mainly achieved by SSBL on the support vessel. Additionally the INS data is transmitted from AUV including the acoustic positioning signal. The INS output of relative position to past own position is very accurate within short time. The INS data is used for tracking. Furthermore the position result estimated on the vessel is transmitted to AUV with next interrogation signal. And the own position in AUV is rapidly updated with accurate estimation. Some digital data including INS data is modulated with phase shift keying (PSK) method and direct sequence spread spectrum (DSSS) technique for transmission with acoustic positioning signal. The proposed method was considered by simulation. And good results were obtained.

The medium accuracy standard ring laser gyro (RLG) inertial navigation unit (INU) exemplified by Litton's LN-93 system has benefited from continual improvements during the production process such that the present navigational accuracy and reliability are better by a factor of two or more over the original requirements as defined by SNU 84-1. Performance enhancements are now available which further improve navigation performance to the high-accuracy category while maintaining the reliability of the production system. Two enhancement mechanizations are described-one that requires software-only changes to improve inertial performance, and one that employs a self-contained (embedded) GPS to augment the inertial performance. These enhancements may be applied in combination to provide uniquely effective immunity to GPS spoofing countermeasures. These enhancements retain the present standard RLG INU form factor, mounting, and electrical interface, and are therefore particularly advantageous for retrofit application. Potential retrofit applications with various aircraft avionics architectures are discussed. >

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.

A particular alignment mechanization for a nonmaneuvering vehicle is described which uses a monitor gyro to estimate the slave inertial navigation system (INS) equivalent east gyro drift rate and thus improves azimuth alignment. A state-space model of the dynamic system with measurements is developed. Results of covariance simulations employing Kalman filter estimation are presented for two master INS position update scenarios, one involving frequent and very accurate updates and the other including infrequent and coarse updates. The ef fects of position updates and the monitor gyro on the quality of transfer alignment are demonstrated and analyzed.

Precise navigation is a vital need for many modern vehicular applications. The global positioning system (GPS) cannot provide continuous navigation information in urban areas. The widely used inertial navigation system (INS) can provide full vehicle state at high rates. However, the accuracy diverges quickly in low cost microelectromechanical systems (MEMS) based INS due to bias, drift, noise, and other errors. These errors can be corrected in a stationary state. But detecting stationary state is a challenging task. A novel stationary state detection technique from the variation of acceleration, heading, and pitch and roll of an attitude heading reference system (AHRS) built from the inertial measurement unit (IMU) sensors is proposed. Besides, the map matching (MM) algorithm detects the intersections where the vehicle is likely to stop. Combining these two results, the stationary state is detected with a smaller timing window of 3 s. A longer timing window of 5 s is used when the stationary state is detected only from the AHRS. The experimental results show that the stationary state is correctly identified and the position error is reduced to 90% and outperforms previously reported work. The proposed algorithm would help to reduce INS errors and enhance the performance of the navigation system.

Generally, an autonomous under vehicle (AUV) is equipped with some navigation devices to know its own position and motion. One of them is an inertial navigation system (INS). The INS calculates its own absolute position and attitude using just internal sensors in real time. And the position accuracy depends strongly on precision of inertial sensors. In particular, the precision of optical gyroscopes strongly influences the position and attitude accuracy. And moreover, the precision depends on the size of them. In fact, it is necessary that the size of INS becomes large in order to improve the position accuracy. Based on that, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) developed a compact and high-performance INS which can be installed easily into a small AUV and output accurate position and attitude. It was developed with homegrown technology which is caused by JAMSTEC's knowledge and the technical capabilities of a domestic manufactures. In this paper, its schema, specifications and functions are described.

This paper presents a prioritizable Inertial Measurement Unit (IMU) array, referred to as the Prio-IMU, which is a systematic approach to mitigate the problem of insufficient sensor's Full-Scale Range (FSR) and bandwidth, in the case of foot-mounted Inertial Navigation Systems (INS). The Prio-IMU integrates multiple IMUs with different sensor characteristics, aligns all the sensor measurements to a universal coordinate frame, and prioritizes the usage of each integrated sensor based on different scenarios. We developed a Prio-IMU prototype integrating two IMUs (ICM-20948 and ICM-20649) and a 3-axis accelerometer (ADXL375) and conducted a series of pedestrian navigation experiments involving walking and running. We observed that during the heel-strike phases of running activity, accelerometer and gyroscope measurements as large as 70 [gravity (g)] and 2600 [degree per second (dps)] could be picked up by the developed Prio-IMU prototype. The experimental results showed that the navigation accuracy of the Zero-velocity-UPdaTe (ZUPT)-aided INS using the proposed Prio-IMU was improved by 79% and 82% along the horizontal and vertical directions, as compared to the case of using a single IMU.

In this paper, we present the requirements specification to develop the small ring laser gyroscope(RLG) which is applicable to the medium-grade inertial navigation system(INS) widely used as a main navigation system. To this end, first we analyse the performance specifications of RLG which is needed to configure the medium-grade INS and then we present the design results of RLG to meet the performance specifications, based on the overseas technology survey and the theoretical analysis. It is also shown in this paper what technology is required to develop a small RLC.

The circular probable error is a little larger in the ground dynamic navigation test of the laser gyroscope Strap down inertial navigation system, so a better vibration damping system needs to be designed for SINS with laser gyro. Through analysis for the model of the vibration and the old vibration damping system, a new system of the double free degree be bring forwarded to reduce the response of random vibration on inertial navigation system. During the design, considering the installing plate is part of the vibration damping system and reckoning the inner space of the tactical missile carefully , using the finite element dynamic optimization method, a satisfactory installing plate and a damper with better dynamic characteristics is designed, then through ground vibration experiment and the designed of repetition parameter optimization, now the new vibration damping system can work effectively and the effect of vibration absorbing has achieved the requirement, it can be applied to the aircraft.

Rotation modulation technology could effectively improve the accuracy of the inertial navigation system (INS) by compensating for the biases of the inertial sensors automatically. However, the carrier angular motion and rotation control error could reduce the rotation modulation effect and then decrease the navigation accuracy. To address this problem, for the single-axis rotation INS, a novel rotation control scheme is presented. The control scheme employs the fiber optic gyros to control the inertial measurement unit (IMU) rotation angular velocity so that the INS with both rotation modulation and azimuth motion insulation functions. Furthermore, in order to reduce the control error, this study adopts two ways: optimizing the control strategy and shortening the delay time. The former way is to control the IMU rotating about the z-axis of the platform frame with respect to the navigation frame, rather than the up-axis of the navigation frame. The latter way is to apply interrupt mode rather than inquiry mode to complete the data transfer between the navigation and the control processors. The simulation and experimental results demonstrate that: the proposed method would not only realize the rotation modulation of the biases of the inertial sensors, but also achieve the insulation of the azimuth motion. The steady-state control error of the control system is less than 10" and the overshoot control error is less than 50". Compared to the traditional SRINS, the navigation position error in the single-axis rotation/azimuth-motion insulation INS could reduce 50% in some navigation application.

Gravity-aided inertial navigation system (GAINS) is one of the essential research fields in underwater navigation technology, and one of the key problems to be solved is the selection of suitable matching areas. Distinctive from previous studies, the concept of Matching Capability of Areas (MCA) is defined from the perspective of the whole system, not just the 2-D image characteristics. The key factors affecting the MCA are analyzed, including heading, matching length, inertial navigation system (INS) initial position error, gravimeter error, map error, and INS drift. Taking these experimental conditions as a prior information, the method based on conditional probability to calculate the MCA is proposed, which can estimate the probability of matching within the required error limits in the given digital gravity map (DGM). After implementing a long-distance marine experiment, the validity of the MCA is verified and it is more comprehensive and effective than traditional characteristic parameters.