System-level Calibration Research Articles

A System-Level Calibration Method for SINS Based on Observability Analysis

A System-Level Calibration Method for SINS Based on Observability Analysis

All-Parameter System-Level Calibration for SINS/CNS Based on Global Observability Analysis

Before using the strap-down inertial navigation system (SINS)/ celestial navigation system (CNS) integrated navigation system, the calibration of its error parameters is a necessary process to improve the system accuracy. In this paper, an all-parameter system-level calibration method has been proposed, which utilizes Kalman filtering for simultaneously estimating the bias, scale factor, misalignments of inertial measurement unit (IMU), and installation errors of the star sensor. The observation has been constructed using the inertial navigation output information and the starlight vector measured by the star sensor. The observability of the error parameters has been analyzed theoretically, and the optimal excitation conditions for each error parameter are obtained. The effects of the angle between the starlight vector and the optical axis of the star sensor, and the attitude of the IMU, on the estimation accuracy of the installation error of the star sensor are also given. Finally, a 10-order rotation scheme has been designed and all the error parameters can be optimally excited. The simulation and experimental results demonstrate that all the error parameters have better stability and repeatability, when compared with the traditional method, and the initial alignment error of 3.4" is better than 13.1" of the traditional method. Moreover, the installation error of the star sensor can be estimated with a high precision only when the angle between the starlight vector and the optical axis of the star sensor exceeds 1°. It is shown that the proposed method can effectively improve the navigation performance of the SINS/CNS integrated navigation system.

Research On High Precision Fiber Optic Platform System Temperature Compensation Technology

In a high-precision fiber optic platform system, temperature changes will have a significant impact on the start-up speed and actual application accuracy. In order to effectively improve the navigation accuracy of the system, the article analyzes the temperature characteristics of the system-level calibration error parameters and establishes a temperature error model. Finally, a temperature compensation test and a platform model calibration test are designed to verify the compensation effect. The test results show that the established temperature error compensation model is accurate and effective. The stability of error parameters has increased by an order of magnitude. The method improves the performance of the fiber optic platform at the start-up stage, and has a small amount of calculation, which has high engineering application value.

Optimal Path Planning Method for IMU System-Level Calibration Based on Improved Dijkstra’s Algorithm

The calibration path of system-level calibration directly affects the incentive effect of the error term and thus the calibration accuracy. Currently, the planning of system-level calibration paths is predominantly designed based on personal experience, resulting in insufficient incentive for error terms, low calibration accuracy, and long calibration times. Therefore, this study proposes a system-level calibration optimal path planning method based on an improved Dijkstra’s algorithm. First, the system-level calibration optimal path planning problem was modeled as a multi-fork regular root tree model, and the adaptability of Dijkstra’s algorithm was improved. Second, a 30-dimensional Kalman filter model was designed for system-level calibration. Then, simulation experiments were conducted, and the results demonstrated that the calibration accuracy of the error term reached 90% within 330 s. Finally, a Micro-Electro-Mechanical system (MEMS) inertial sensor, model PA-IMU488B, was used for experimental verification, and the results were compared with the discrete calibration results. The results indicate that the bias and scale factor errors of the MEMS inertial sensor reached the target accuracy within 5 min. The optimal path planning method for system-level calibration proposed in this study is not dependent on a high-precision turntable, is applicable to sensors of different accuracies, and decreases calibration time while ensuring calibration accuracy.

A Method for Improving the Precision of FOG Scaling Coefficient Calibration Based on the High Precision Turntable

Aiming at the problem that the calibration accuracy of FOG depends on the precision of turntable, the relationship between the rotation excitation mode calibration and system-level calibration of FOG and the precision of turntable is analyzed. Firstly, the error model of fog is given, and the optimal rotation path is designed based on the principle of rotation excitation mode calibration. The rotation excitation mode calibration and system-level calibration simulation are carried out respectively. The comparison results show that when the precision of the turntable is 1”, the scale coefficient error of the rotation excitation mode calibration is about 60% lower than that of the system calibration. Through further simulation, it is found that the scale coefficient error of the gyroscope calibrated with 10 turns of the turntable is about 50% lower than that of the gyroscope calibrated with 5 turns, and the scale coefficient error can be effectively reduced by increasing the number of turns of the turntable. Finally, the actual experiment is carried out, and it is proved that the calibration accuracy of the rotating excitation mode is higher than that of the system level when the precision of the turntable is higher, which has a certain practical significance for improving the precision of the inertial navigation beacon.

An Improved System-Level Calibration Scheme for Rotational Inertial Navigation Systems.

The system-level calibration technology of rotational inertial navigation is one of the main methods to improve the accuracy of inertial navigation, and the design of the calibration scheme is the key to calibration technology. By the establishment of the error model of inertial navigation system, a 30-position calibration scheme is designed in this study. Based on the 30-dimensional Kalman filter, the constant errors, scale factor errors and installation error of gyroscope and accelerometer are identified. Comparing the traditional schemes and the 30-position scheme with the simulation experiment, the observability of the 30-position scheme is higher, the residual error of the estimated sensor is smaller and the navigation positioning accuracy after the estimated inertial sensor error parameter compensation is higher, which verifies the feasibility of the 30-position scheme. Finally, the measured experiment uses the 30-position scheme to estimate the error of a certain type of IMU sensor, and the calibration curve of the error parameter is well converged before the end of the calibration experiment, so it has certain practical value.

W-band Scalable 2×2 Phased-Array Transmitter and Receiver Chipsets in SiGe BiCMOS for High Data-Rate Communication

This article presents a pair of W-band phased-array transmitter (TX) and receiver (RX) chipsets in a 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> SiGe BiCMOS process for high data-rate wireless communication. Both the chips integrate four compact front-end channels in 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 distribution, and the distance between the adjacent RF pads is less than 1.8 mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.56\lambda $ </tex-math></inline-formula> at 90 GHz) to fit for the tight antenna array and enable array scaling by tiling multiple unit cells. A 6-bit active phase shifter based on the improved phase-inverting variable gain amplifiers is leveraged to achieve high phase-shift precision and bandwidth concurrently. A noise reduction technique using a parallel inductor to resonate with the parasitic capacitors of the cascode transistors is adopted in the low-noise amplifier design. A novel miniature power combiner, which occupies a much more compact area than the Wilkinson power combiner while delivering great RF performance, is proposed and elaborately analyzed. System-level calibration for local oscillator (LO) leakage and dc-offset suppression is enabled by introducing digitally controlled current sources into the up-conversion and down-conversion mixers. On-wafer measurements for the TX chip exhibit a single-channel IF-to-RF conversion gain (CG) of 26 dB, a competitively high output 1-dB compression point (OP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1\,dB}}$ </tex-math></inline-formula> ) of 11 dBm. The RX chip achieves an RF-to-IF CG of 19.5 dB with 9-/14-GHz IF/RF 3-dB bandwidth, a noise figure of 7.7 dB, and an input 1-dB compression point of −28 dBm. The phase-shift characteristics are verified by the TX/RX front-end measurements, achieving a 6-bit phase resolution with minimum rms phase/gain error smaller than 0.83°/0.45 dB and a large phase-shift bandwidth higher than 20 GHz. Preliminary wireless transmission test using a low-cost die-on-printed circuit board (PCB) prototype demonstrates wireless data rates of 1.6 and 0.8 gigabits per second (Gb/s) at distances of 0.4 and 1 m with 256-quadratic-amplitude modulation (QAM) and 16-QAM modulated signals, respectively.

An Improved System-Level Calibration Method of Strapdown Inertial Navigation System Based on Matrix Factorization

This paper develops an improved system-level calibration method for the strapdown inertial navigation system (SINS). It solves the problems of too many dimensions of state variables and installation error matrix coupling. To solve the two problems, the improved system-level calibration method derives the physical causes of the installation error matrix. The installation error matrix is decomposed into skew symmetric matrix and symmetric matrix. Then the appropriate system-level calibration scheme is designed based on the velocity error equations and attitude error equations. The designed system-level calibration scheme separates the coupled installation error matrix parameters by changing the value of strapdown matrix. Simulation results demonstrate that the proposed method is feasible. The relative errors of gyro calibration parameters are between 0.03% and 0.70%, and the relative errors of accelerometer calibration parameters are between 0.01% and 0.24%. For comparison, the navigation and positioning experiments are also performed to evaluate the proposed method. The results indicate that the improved system-level calibration scheme is better than the traditional system-level calibration scheme. The positioning error is reduced by more than 30%.

System-level calibration method for complex error coefficients of strapdown inertial navigation system

System-level calibration method for complex error coefficients of strapdown inertial navigation system

A system-level calibration method including temperature-related error coefficients for a strapdown inertial navigation system

The calibration of error coefficients for accelerometers and laser gyros is an effective way to improve the navigation precision of strapdown inertial navigation systems. The calibration parameters often change with temperature. This paper proposes a system-level calibration method including temperature-related error coefficients. The method includes an improved 18-step calibration scheme with temperature being changed by using a thermal chamber. A 42-dimensional Kalman filter is applied to estimate the error parameters including the bias, scale factor errors, installation errors and temperature-related error coefficients of accelerometers. This method has the great advantage of simplifying the calibration procedure and is widely applicable to all temperature-related error coefficients. Compared with the traditional calibration method at different temperature points, the calibration time of the proposed method is shortened by 24 h. The feasibility of this method is verified by simulations and navigation experiments. The results of navigation experiments show that the maximum positioning errors in pure inertial navigation decrease by approximately 30% after temperature compensation.

Two-stage calibration of a 6-axis force-torque sensor for robust operation in the Mars 2020 robot arm

ABSTRACT A main objective of the Mars 2020 rover mission (Perseverance) is to collect and preserve samples of rock and soil from the Martian surface. To accomplish this task, the Perseverance Rover carries a Sampling and Caching Subsystem outfitted with Coring Drill mounted on a 5 degree-of-freedom (DoF) robotic arm. Safe operation of the Robotic Arm and its tools relies on force feedback, provided by a custom Force-Torque Sensor (FTS) which is positioned to sense end-effector external loads. This work describes the methods and algorithms used in the calibration of the Robotic Arm FTS to achieve the required force-feedback accuracy over all expected Mars and Earth operating environments. Specifically, we use a two-stage, least-squares optimization process to generate an FTS calibration model that is fit to both sensor-level and system-level calibration data, while implicitly compensating for offset, scaling, and thermal errors observed during sensor integration into the robotic arm system. This technique is compatible with remote FTS re-calibration while the rover is operating on Mars. Data collection strategies, standalone versus system-integrated sensor findings, results of validation exercises in Earth-ambient and Mars-like environments, and initial FTS commissioning data on Mars are all included.

Reducing the Effect of the Accelerometer-Slope Bias Error on the Calibration Error of a High-Precision RLG INS System-Level Fitting Method

In recent years, navigation technology has rapidly developed. System-level calibration technology for inertial navigation system (INS) has been widely used because it does not rely on high-precision equipment. However, INS introduces a bad coupling error in high-precision ring laser gyroscope (RLG) scale-factor error estimation, accompanied by a large accelerometer-slope bias error. To solve this problem, an improved system-level fitting calibration method is proposed, which changes the 90° rotation increment to 450°, while maintaining the original calibration sequence. Compared with the traditional system-level calibration method, the calibration error of the gyroscope scale-factor error is reduced to 0.2 times, under simulation conditions, without affecting the calibration accuracy of the other parameters. The extreme difference of the gyroscope scale-factor calibration error on multiple experiments reduces from 4.75 to 1.40 ppm under experimental-verification conditions. The mean values of the gyroscope scale factor were closer to the real reference values (no more than 2 ppm). The integral calibration results meet the requirements of a high-precision RLG INS. The proposed method maintains the original calibration sequence and exhibits small changes with high practicability. The proposed method is suitable for applications with high requirements for gyroscope scale factor accuracy, such as highly dynamic aircraft.

Influencing factors analysis of supercontinuum laser monochromator in calibration of polarization remote sensors

Relative spectral responsivity and the in-band spectral response non-consistency of polarization remote sensors are the basic parameters for laboratory calibration. In this paper, a spectrally-resolved calibration facility was assembled for the calibration of relative spectral responsivity by using novel supercontinuum laser and monochromator. Taking three polarization channels of 490 nm, 670 nm and 910 nm as examples, the relative spectral responsivity of the channel polarization remote sensors was obtained under the two states of the monochromator output light directly and the monochromatic light steered into an integrating sphere respectively, and the polarization state of the calibrated light source was measured under the two states. The experimental results show that there are obvious changes in degree of linear polarization (DOLP) and polarization orientation angle in the mode of direct output light of monochromator, and the non-consistency of in-band spectral response of the three polarization channels were 0.91%, 4.25% and 1.06%, respectively. When the monochromatic light steered into the integrating sphere, the DOLP of the light source decreases significantly, and the non-consistency of in-band spectral response were 0.15%, 0.47% and 0.57%, respectively, which indicates that depolarized light source can be effectively applied to the spectral responsivity calibration of polarization remote sensors. And the system-level calibration facility based on supercontinuum laser and monochromator has wide application prospects in the calibration of polarization remote sensors.

A Fast Calibration Method for Dynamic Lever-Arm Parameters for IMUs Based on the Backtracking Scheme

Calibration is vital to improving the accuracy of the strapdown inertial navigation system (SINS). Calibration is one of the crucial phases before the operation of SINS and requires high accuracy and speed. Traditional system-level calibration methods have the disadvantages of long calibration times and complicated path design. A fast calibration method for the lever arm and other error parameters is proposed in this article. To shorten the calibration time and improve the calibration accuracy, a backtracking calibration method in inertial frames based on the reduced-order Kalman filter is proposed. Simulations and experiments are given to illustrate the effectiveness of the novel calibration method. The calibration process can be completed in 10 min, which is greatly shortened compared with traditional methods. The calibration time is shortened, and the calibration accuracy is improved. Furthermore, navigation experiments show that the velocity and position accuracies of the SINS are improved significantly after compensation with the calibration results, fully illustrating the significance of the proposed calibration method in improving the navigation performance.

超连续激光单色仪系统级光谱响应度定标比对验证

超连续激光单色仪系统级光谱响应度定标比对验证

In-Field Calibration Method for DTG IMU Including g-Sensitivity Biases

Navigation performance can be significantly enhanced by the inertial measurement unit (IMU) calibration. Aiming at the dynamically tuned gyro IMU, a novel in-field calibration method is proposed in this paper. Taking gravity and earth’s rotation rate as a reference, all accelerometer errors, the constant biases, and the g-sensitivity biases of gyro can be calibrated using the unscented Kalman filter based on the norm-observed method. The scale factor errors and installation errors of gyro can be estimated though the Kalman filter with velocity errors as observation. In order to guarantee that all error parameters are observable, a 26-position and its optimized 12-position rotation schemes are designed. The proposed method can achieve correct calibration without a high-precision turntable. Besides, it can improve the ability of analysis and the deviation of interference sources when some error parameters are calibrated unreasonable. The simulations and in-field calibration experiments are conducted to verify the effectiveness of the proposed method. The simulations demonstrate that the calibration accuracy of two schemes is almost equivalent. Compared with the system-level calibration, the calibration results of two schemes are within a reasonable range. The semi-physical simulations indicate that finding out and separating interference sources can be achieved easily with the proposed method. Thus, the proposed method has great application values in in-field calibration.

A Full-Parameter Self-Calibration Method Based on Inertial Frame Filtering for Triaxis RINS Under Swaying Base

The navigation performance of the rotational inertial navigation system (RINS) could be greatly improved by self-calibration of error parameters. The traditional instrument-level calibration depends on high-precision turntable. System-level calibration takes zero velocity as a reference to estimate error parameters. However, zero velocity is invalid in the situation of swaying base and the calibration accuracy will be decreased with the traditional method. Aiming at the swaying base environment, the filtering method for tri-axis RINS in an inertial frame is proposed in this paper. Taking the velocity errors in the inertial frame as the reference, full-parameter calibration on swaying base can be achieved. Simulation verifies the feasibility of the proposed method. Experimental results demonstrate the stability of the proposed method is better than the traditional calibration method, and it satisfies the application requirements. Thus, the proposed method has great application values under swaying base.

An Improve Hybrid Calibration Scheme for Strapdown Inertial Navigation System

This paper develops an improved hybrid calibration scheme for the strapdown inertial navigation system (SINS) that combines the advantages of an optimal rotational norm calibration method and an improved system-level calibration method. To accurately determine the scale factors and misalignment error of gyros triad, the optimal rotation norm calibration method is applied. Similarly, the improved system-level calibration method based on the 24-dimensional error state Kalman filter (ESKF) plays an important role in accelerometer calibration and gyro biases calibration. The clockwise and counterclockwise multi-cycles rotation scheme is designed to eliminate the effects of the Earth's rate and gyros biases, and then provide accurate rotational norm to completely determine the gyros triad scale factors and misalignment. In addition, the improved ESKF system-level calibration method is employed to estimate accelerometer parameters and gyros biases. Simulation test verify the validity of the proposed method, and the calibration experiences and the verification tests of the two high-precision optical gyros inertial measurement units (IMU) are carried out. For comparison, the traditional 30-dimensional system-level calibration is also performed. The attitude error of high maneuvering swing test indicate that the gyros calibration accuracy of hybrid calibration scheme is better than that of traditional system-level calibration scheme. Furthermore, the positioning error of pure inertial navigation solution in static and dynamic condition for two calibration methods indicate that the hybrid calibration scheme significantly improves the positioning accuracy, especially in the dynamic experiment, that is, the proposed scheme provides a more accurate calibration of the IMU.

An iterative optimization method for estimating accelerometer bias based on gravitational apparent motion with excitation of swinging motion.

Field calibration is an important method to guarantee the accuracy of a strapdown inertial navigation system. Zero velocity update based on the zero-velocity constraint when the carrier is without translational motion is a typical system-level calibration method. In zero velocity update, there is a coupling between biases and horizontal misalignment angles. The accuracy of horizontal misalignment angles is determined by the equivalent accelerometer biases in horizontal directions, which means that improving the accuracy of horizontal angles needs accurate calibration of accelerometer biases. Meanwhile, alignment with gravitational apparent motion is widely used taking advantages of its alignment ability in a swinging condition. But it is an analytical method and cannot calibrate sensor biases and is always dealt as a coarse alignment method. In order to calibrate accelerometer biases and utilize advantages of the alignment method with gravitational motion, a method to estimate accelerometer biases based on an iterative optimization method and gravitational apparent motion is presented in this paper. First, accelerometer biases are introduced to calculate apparent acceleration and an objective function is constructed. Then, Newton's iteration is applied to iteratively optimize the parameters describing gravitational apparent motion and accelerometer biases. As revealed by the theoretical analysis and experimental results, different patterns of gravity and accelerometer biases will be generated when the carrier exhibits a swinging motion; thus, the convergence of the proposed algorithm will be ensured. After accelerometer biases are removed, initial alignment performed with the gravitational apparent motion reconstructed by the estimated parameters gives nearly zero horizontal misalignment angles.

A Three-Stage Accelerometer Self-Calibration Technique for Space-Stable Inertial Navigation Systems.

As a specific force sensor, the tri-axis accelerometer is one of the core instruments in an inertial navigation system (INS). During navigation, its measurement error directly induces constant or alternating navigation errors of the same order of magnitude. Moreover, it also affects the estimation accuracy of gyro drift coefficients during the initial alignment and calibration, which will indirectly result in navigation errors accumulating over time. Calibration can effectively improve measurement accuracy of the accelerometer. Device-level calibration can identify all of the parameters in the error model, and the system-level calibration can accurately estimate part of these parameters. Combining the advantages of both the methods and making full use of the precise angulation of the space-stabilized platform, this paper proposes a three-stage accelerometer self-calibration technique that can be implemented directly in the space-stable INS. The device-level calibration is divided into two steps considering the large amount of parameters. The first step is coarse calibration, which identifies parameters except for the nonlinear terms, and the second step is fine calibration, which not only identifies the nonlinear parameters, but also improves the accuracy of the parameters identified in the first step. The follow-on system-level calibration is carried out on part of the parameters using specific force error and attitude error to further improve the calibration accuracy. Simulation result shows that by using the proposed three-stage calibration technique in the space-stable INS, the estimation accuracy of accelerometer error can reach order of magnitude. Experiment results show that after the three-stage calibration, the accuracy of latitude, longitude, and attitude angles has increased by over 45% and the accuracy of velocity has increased by over 22% during navigation.