Strapdown Inertial System Research Articles

MEMS strapdown inertial attitude measurement system using rotational modulation technology.

Attitude determination involves the integration of methodologies and systems for estimating the time varying attitude of moving objects. Strapdown Inertial Attitude Measurement System (SIAMS) is among the most widely used navigation systems. The development of cost effective Micro Electro Mechanic System (MEMS) based inertial sensors has made attitude measurement system more affordable. However, MEMS sensors suffer from various errors that have to be calibrated and compensated to get acceptable attitude results. Given the auto-compensation of inertial sensor bias in rotation error modulation, the objective of this paper is to develop a MEMS-based rotary SIAMS, in which the significant sensor bias is automatically compensated by rotating the IMU, to offer comparable performance with respect to a tactical-grade Inertial Measurement Unit (IMU). With the analysis of the relationship between the MEMS error and misalignment, a MEMS calibration model is derived, and a combined calibration method of multi position rotation is applied to estimate the deterministic sensor errors such as bias, scale factor, and misalignment. Simulation and experiment results indicate that the proposed method can further modulate and compensate the MEMS errors, thereby improving the MEMS attitude accuracy.

Hinged Set of Guidance of a Controlled Fire-extinguishing Bomb

The guidance system of a fire-extinguishing bomb in the form of a hinged guidance kit is considered, which turns the bomb into a simple and fairly cheap fire-extinguishing device of the "throw and forget" type, optimized for mass production and use. In order to increase the accuracy of dropping a fire-extinguishing bomb, it is proposed to install a cheap high-precision and compact GPS navigation satellite system and a strapdown inertial system on an ordinary fire-extinguishing bomb. The algorithm of complex information processing of their systems, built on the basis of the improved method of the mutual compensation, in which for improve the quality of the error estimation procedure, the sluggishness of second-order Butterworth filters is compensated is proposed. The guidance system controls the trajectory of the fire-extinguishing bomb as a means of "first strike" and this increases the efficiency of further use of traditional flood systems by 50...70 times.

Error Compensation of Strapdown Inertial Navigation System for the Boom-Type Roadheader under Complex Vibration

The strapdown inertial navigation system can provide the navigation information for the boom-type roadheader in the unmanned roadway tunneling working face of the coal mine. However, the complex vibration caused by the cutting process of the boom-type roadheader may result in significant errors of its attitude and position measured by the strapdown inertial navigation system. Thus, an error compensation method based on the vibration characteristics of the roadheader is proposed in this paper. In order to further analyze the angular and linear vibration of the fuselage, as the main vibration sources of the roadheader, the dynamic model of the roadheader is formulated based on the cutting load. Following that, multiple sub-samples compensation algorithms for the coning and sculling errors are constructed. Simulation experiments were carried out under different subsample compensation algorithms, different coal and rock characteristics, and different types of roadheader. The experimental results show that the proposed error compensation algorithm can eliminate the effect of the angular and linear vibration on the measurement accuracy. The coning and sculling error of the strapdown inertial navigation system can reduce at least 52.21% and 42.89%, respectively. Finally, a strapdown inertial navigation error compensation accuracy experiment system is built, and the validity and superiority of the method proposed in this paper are verified through calculation and analysis of the data collected on the actual tunneling work face.

Methods and Algorithms for Correcting Kinematic Equations in the Problem of Determining the Orientation of an Object

Algorithms of a strapdown inertial orientation system with an inertial measurement module consisting of a three-component gyroscope, accelerometer, and magnetometer are considered. The aim of the work is to improve the algorithms for processing sensor information to ensure the asymptotic stability of the system, tuning for the Schuler period and the low-pass filter with a given bandwidth. The kinematic Poisson equations with positional and integral-positional correction based on the information of accelerometers and magnetometers are considered. The stability and frequency characteristics of the system in relation to the sensor output signals are analyzed. It is shown that the positional correction in each channel does not allow you to adjust the system for the Schuler period. The integral-positional correction allows this adjustment, but in relation to the gyroscope signals, the system is a bandpass filter and does not suppress noise in the bandwidth. The advantages of using positional correction with cross-links in the sense of tuning the frequency characteristics of the system to the Sharper frequency and the third-order low-pass filter are shown. The analysis of the influence of angular velocities confirmed the asymptotic stability of the system with their changes in a given range. The results of mathematical modeling confirmed the compensation of errors in the initial orientation system display, the reduction of noise power in the estimates of the orientation angles in relation to the noise in the sensor signals, and the ability to configure the system for the Schuler period.

ABOUT THE ACCURACY OF SOME “ADVANCED” ALGORITHMS FOR STRAPDOWN INERTIAL ORIENTATION SYSTEMS

Introduction. The main problem when developing algorithms for strapdown inertial orientation systems is to increase their accuracy. Most of the algorithms cited in the well-known literature (see, for example, [1] – [4]) rely on the simplified Borets formula, in which the term on the right-hand side does not take into account the term of the differential orientation equation with a double vector product. It is of interest to find out how the "expansion" of the orientation equation will affect the accuracy of the algorithm, taking into account the discarded term.Main part. The methodology for studying the accuracy of algorithms is reduced to determining the values of two unknown parameters that characterize the accuracy of the algorithm: the order of accuracy and the proportionality coefficient. This approach allows modeling only for some specific values of the amplitude and frequency of the base oscillations, and generalize the results to any amplitudes and frequencies. Evaluation of the effectiveness of the considered algorithms is carried out by means of a comparative study of the systematic error of the well-known two-step algorithms, based on measurements of increments of the quasi-coordinates of the base rotation at each step of the survey of meters. Conclusions. The use of an additional term in the orientation equation does not always lead to an increase in accuracy compared to algorithms using a simplified form of the orientation equation. Studies have shown that accuracy decreases in the region of small values of the frequency parameter. An algorithm obtained empirically was also studied, the use of which leads to a significant increase in accuracy (by two orders of magnitude in the region of small values of the frequency parameter). In general, it is possible to restore the full-term member in the regular order to the exact precision in simple procedures, as well as to the significant lower-order operation.

The Use of Gravity Reductions in the Indirect Strapdown Airborne Gravimetry Processing

Strapdown airborne gravimetry (SAG) is one of the most efficient techniques used in geodesy and geophysics for acquiring gravity data on relatively large regions in a faster and cost-effective way or to fill in the gravity data gaps on areas where it is neither practical nor possible to make terrestrial measurements. Recent studies have shown that accuracies of 1 mGal and precision of sub-mGal levels are possible with the strapdown inertial systems modified for gravimetry (e.g., temperature stabilization). Besides the advancements in the instrumentation, data processing and integration algorithms are evolving consistently. This study investigates the contribution of long- and short-wavelength gravity reductions following the remove–restore procedure in the indirect SAG processing, where the gravity disturbance at flight altitude is modeled stochastically as an additional system state in the Kalman filter sense. The proposed method is implemented to the airborne data collected in central Turkey in 2018 with a thermally stabilized strapdown inertial measurement unit of navigation-grade type. The inclusion of the long- and short-wavelength gravity reductions in the SAG processing limits the in-run bias variations of the Z-accelerometer and changes the parameters of the third-order Gauss–Markov gravity state model significantly. Utilization of the reduced gravity disturbance in the processing provides better long-wavelength stability in the solution by reducing the mean bias of about 2.60 to 0.65 mGal between the airborne gravity estimates and a high-resolution global gravity model. Moreover, a remarkable improvement in the internal precision is achieved when the gravity reductions are introduced into the SAG solution. Comparisons at the crossover points demonstrate that the application of gravity reductions yields considerably lower crossover residuals than the standard solution without reductions. The non-adjusted crossover differences of the long- and short-wavelength removed and restored SAG solution result in an RMSE value of 0.79 mGal, that is, 40% better precision than the standard solution.

Stochastic Estimation of Orientation Parameters of an Antenna Complex based on Strapdown Inertial System Measurements

The problem of high-precision determination of the spatial orientation of the antennas of radio complexes located on high-rise masts of various designs is considered. It is established that the methods currently used, based on measurements of satellite navigation systems and autonomous measurements of strapdown inertial orientation systems, do not provide the required accuracy in solving the problem. It is shown that the low accuracy of existing methods is due to both weak noise immunity of information processing algorithms and the lack of the ability to take into account the dynamic properties of orientation parameters measured under conditions of high intensity interference, the properties of which, as a rule, are not taken into account. A dynamic algorithm is proposed for estimating the stochastic orientation parameters of the antenna of a radio complex, which is invariant to the nature of the movement of the mast base and provides stability and the required estimation accuracy under general assumptions about the nature of the interference of the sensitive elements of the strapdown inertial orientation system. The Rodrigue–Hamilton parameter vector was used as the observed state vector – the antenna orientation parameter vector – and the vector of measurements of the angular velocity sensors of the strapdown inertial system was used as the observation vector for it. The instrumentation of the strapdown inertial system includes three accelerometers and three angular velocity sensors located orthogonally at the center of mass of the antenna. Based on the obtained non-linear stochastic equations for the dynamics of the change in the parameter vector of the current orientation of the strapdown inertial orientation system on a moving base and the equations of their observation, a stochastic model of measurement signals for sensitive elements of the strapdown inertial orientation system, a non-linear (generalized) Kalman filter is constructed that provides the desired solution to the problem of estimating the parameters of the current antenna orientation on a perturbed base. We present the results of a numerical experiment and a conclusion about the possibility of using a fi lter to solve the problem of operational orientation of antennas of radio engineering complexes using medium- and high-precision strapdown inertial orientation systems and without correction over a long time.

Stochastic evaluation of orientation parameters for an antenna complex using strapdown inertial system measurements

When solving the problem of high-precision spatial orientation of antennas of radio engineering complexes placed on high-rise masts of various designs, one of the main tasks is to increase the accuracy of their angular orientation in the conditions of inevitable disturbances of the mast base (due to wind disturbances, operation of various units, etc.) and interference of measurement of antenna orientation parameters by various measuring systems. Currently used methods based on measurements of satellite navigation systems and autonomous measurements of attitude and heading reference system do not provide the required accuracy for solving the problem of antenna orientation, located on a highly dynamic mobile base. This circumstance is due both to the weak noise immunity of algorithms of information processing and the inability of accounting for the dynamic properties of orientation parameters measured also in the presence of noise of high intensity, whose properties also usually are not taken into account. In this regard, the article considers a dynamic algorithm for estimating the stochastic parameters of the antenna orientation of the radio engineering complexes, invariant to the nature of the movement of the mast base and providing stability and the required accuracy of the evaluation under the most general assumptions about the nature of interference of the sensing elements attitude and heading reference system. As the observed state vector – the vector of antenna orientation parameters, the vector of Rodriguez–Hamilton parameters is used, and as the vector of observation of it – the vector of measurements of angular velocity sensors of a strapdown inertial system, which consists of three accelerometers and three angular velocity sensors located orthogonally in the center of mass of the antenna. Based on the nonlinear stochastic equations of dynamics of change of the vector of parameters of the current orientation attitude and heading reference system on the moving base and stochastic models of the measuring signals sensing elements attitude and heading reference system, a non-linear (generalized) Kalman filter, providing the desired solution of the problem of estimation of the parameters of the current orientation of the antenna on the perturbed basis, was built. The results of the numerical experiment allow us to conclude that it can be used to solve the problem of operational orientation of radio engineering complexes antennas placed on masts, using medium-and high-precision attitude and heading reference system without correction for a long time.

Применение лазерного гироскопа в бесплатформенных инерциальных системах

Применение лазерного гироскопа в бесплатформенных инерциальных системах

Strapdown inertial navigation curve measurement system of full-section roadheader in coal mine

Strapdown inertial navigation curve measurement system of full-section roadheader in coal mine

Shockproof Precision Strapdown Inertial Navigation System Development for Terrestrial Applications

The paper discusses the structure, algorithms and testing results for a hybrid precision strapdown inertial navigation system (SINS) which is resistant to fast extreme impacts. Impact resistance of the precision SINS is provided by incorporating an auxiliary strapdown inertial attitude control system (SIACS) based on rough sensors that can endure fast extreme shocks without losing the attitude accuracy; and by post-processing of inertial sensors data performed in the onboard computer simultaneously with the main navigation task. The post-processing procedure is designed to identify the moment of shock occurrence and to repeat the attitude problem solving in the onboard computer based on the auxiliary SIACS data within the time interval of exposure to the extreme shock. In the absence of shocks, the auxiliary SIACS is calibrated in accordance with the data of the main precision SINS. The main precision SINS is based on precision fiber-optic gyros (FOG) and the auxiliary SIACS—on micromechanical gyros (MMG). Thus, a hybrid-type precision SINS has been constructed, which has demonstrated required accuracy level during on-ground vehicle tests, including shock tests.

Refinining the Drift Model of a Strapdown ESG for Orbital Spacecraft

Refinement of the electrostatic gyroscope (ESG) drift model aboard an orbital maneuverable satellite for remote sensing of the Earth’s surface is considered. Some changes of the drift model also hold for the ESG ground-based applications. The paper also analyzes the quasi-continuous correction mode of the ESG-based strapdown inertial attitude reference system (SIARS) using raw (unsmoothed) data from the star tracker and the extended Kalman filter (EKF) algorithm. A special feature of solving the problem of SIARS output data correction and the calibration problem in this mode is rejection of incorrect measurements. The algorithm for this problem solution is described. The ESG drift model is given both for the SIARS calibration mode in order to ensure an adequate prediction of ESG drifts over a long time interval and for the quasi-continuous correction mode under spacecraft maneuvering conditions. The results of data processing of the flight tests of the SIARS and the star tracker aboard one of the spacecraft are discussed.

Strapdown Inertial Attitude System Based on Ring Laser Gyro Algorithm

Background. The paper is dedicated to improving the accuracy of strapdown inertial systems by improving the algorithmic software. Objective. The aim of the paper is the development and analysis of the accuracy of a strapdown inertial orientation system algorithms. Methods. Construction of a strapdown attitude reference system algorithms based on kinematic equation of Poisson and quaternions. The input data for the orientation algorithms are signals from the real laser gyroscopes installed in the system. Orientation equation integration is performed using the Runge–Kutta methods. Results. The attitude system errors, depending of the different vehicle motions are determined. Conclusions. Research of selected orientation algorithms and numerical integration showed their high accuracy. They may be used in the design of precision strapdown inertial systems.

Analysis of accuracy requirements for an inertial navigation system in synthetic aperture radars

This paper describes the effect of trajectory signal phase distortion on the image received by a millimeter-wave automobile synthetic aperture radar (SAR). Calculations of the requirements for the errors of the sensors included in a strapdown inertial system that provide the resultant image with acceptable quality are given. Parameters of different grade inertial sensors are analyzed; recommendations for choosing inertial sensors depending on SAR operating conditions and required resolution are analyzed.

Development and research of complex algorithm of inertial system for human motion parameters estimation

Inertial motion capture is one most perspective technology for estimation of human motion parameters. Such systems use a network of inertial measurement units (IMUs) which are mounted on human body segments. To estimate kinematic motion parameters inertial motion capture systems (IMCS) is used data about body segments orientation. Algorithms which are used in IMCS are characterized by static and dynamic accuracy. Static accuracy of such systems is 0,2-0,5 degrees. But their dynamic accuracy during accelerating motions degrades to 2 degrees (RMS error). This study is intended for research and development of complex algorithm for work of one IMU of IMCS. Complex algorithm uses algorithm of strapdown inertial navigational system in geographical frame corrected by information of velocity and position data. These data are gotten using biomechanical skeleton model. The error level of such correction signals was estimated. A complex algorithm uses biomechanical velocities and positions to estimate velocity and position errors of data which are gotten from algorithm of strapdown system. These errors are used to form special correction signals in Poisson equation, equations for velocity and position calculation. It is shown effectiveness of proposed algorithm for kinematic human motion parameters estimation during accelerating segment motion. Maximal pitch and roll errors don’t exceed 0,8 degree. Positional RMS error is 0,04 m, velocity – 0,38 m/s. Such results show effectiveness of algorithm for estimation of segment orientation and position. Segment’s velocity signal has less error when it is gotten uses biomechanical skeleton model.

Study on a Ship with 6 Degrees of Freedom Inertial Measurement System and Related Technologies

We research ship 6 DOF inertial measurement method and displacement reconstruction form acceleration signal to establish the strap-down inertial navigation measurement system through sensors configuration technology. The inertial measurement system consists of three groups of vertically mounted angular rate and acceleration sensors. Through designing an FIR integration filter and studying the ship displacement signal reconstruction from the acceleration, the filter parameters design method and implementation way were determined. By means of the beam vibration to analog ship heave motion reconstructs linear displacement form acceleration signals. The root mean square error of the reconstructed line displacement is 0.004 mm, and the mean value of the displacement peak value is 5.92%, which is close to the design precision of the filter. The test shows that the measurement system and the FIR filter to achieve the predetermined precision with noise suppression.

NON-HAMILTONIAN UNNORMALIZED QUATERNIONS OF HALF-ROTATION IN ALGORITHMS OF STRAPDOWN INERTIAL SYSTEMS

The application of non-Hamiltonian unnormalized quaternions of half-rotation in algorithmsof strapdown inertial systems is considered in the article. Non-Hamiltonian unnormalized quaternionscan be zero in contrast to the classical Hamiltonian normalized quaternion with the parameters of theEuler (Rodrigues–Hamilton), their rates are not constant and depend on the Euler angles of final rotation

Strapdown inertial navigation system of pendulum type

We consider two implementations of an isotropic oscillator to be used in the construction of a strapdown inertial system of new type [1]. The first implementation is a contact-free suspension of an electrically conductive ball used in electrostatic gyros, and the second implementation is a 3D combination of elastic constraints holding a mass point.

An In-Flight Emergency Alignment Scheme for Aircraft MINS with Assistant of Airborne SAR

The alignment of a strapdown inertial navagation system (SDINS) is the process whereby the orientation of body frame is determined with respect to the navigation frame [. In a broad sense, alignment of SDINS can be classified as initial alignment and in-flight alignment (IFA). The IFA is performed with IMU and external sensors during the vehicle flight [2,, in which the primary assistant sources are satellite system, radar, or other airborne equipment, offering reference signals like position, velocity, or attitude to assist the alignment process [4,. However, these sources have disadvantages in redundancy, independence, and stability, which will be incipient faults in emergency take-off or warfare. So it is necessary for us to analyse the subsidiary airborne equipments and design new in-flight alignment scheme.

An Intuitive Approach to Inertial Sensor Bias Estimation

A simple approach to gyro and accelerometer bias estimation is proposed. It does not involve Kalman filtering or similar formal techniques. Instead, it is based on physical intuition and exploits a duality between gimbaled and strapdown inertial systems. The estimation problem is decoupled into two separate stages. At the first stage, inertial system attitude errors are corrected by means of a feedback from an external aid. In the presence of uncompensated biases, the steady-state feedback rebalances those biases and can be used to estimate them. At the second stage, the desired bias estimates are expressed in a closed form in terms of the feedback signal. The estimator has only three tunable parameters and is easy to implement and use. The tests proved the feasibility of the proposed approach for the estimation of low-cost MEMS inertial sensor biases on a moving land vehicle.