Research On The Key Technologies Of Marg-Sensor-Based AHRS

Tri-axial anisotropic magneto-resistive (AMR) magnetometers, as well as tri-axialmicro electro-mechanical system (MEMS) accelerometers and gyros, have theoutstanding advantages of small size, low cost, low power consumption, etc. Thecombination of the above three types of sensors, which is called MARG sensor,provides an efficient and reliable solution for attitude determination and navigation. Theattitude and heading reference systems (AHRS) based on MARG sensors have highperformance and versatility. Therefore, the research on its theory and technology hasacademic and practical significance.The research presented in this dissertation is focused on several critical problemsin the development and application of the AHRS based on MARG sensor. The majorcontributions are listed below.Firstly, aiming at the calibration and compensation for the errors of tri-axialmagnetometers and accelerometers, the calibration methods for tri-axial vector fieldsensors, especially the calibration techniques without external equipments, are studiedand discussed in depth. The ellipsoid fitting method, which was commonly used in theexisting literature, is analyzed in detail. It is pointed out that the inherent defect of theellipsoid fitting method is that it cannot identify and compensate the mutualmisalignment, or inter-triad misalignment, between different sensors. The impact of thisdefect on the AHRS is also revealed. And then the dot product invariance method fortri-axial vector field sensors calibration is introduced, which brings in essentialenhancement for the calibration results. The dot product invariance method can also beused with the ellipsoid fitting method, in order to form a self-calibration scheme fortri-axial vector field sensors without the aim of external equipment.Secondly, the cross product calibration method is presented for the calibration oftri-axial MEMS gyros, especially the calibration without a rate table or other precisiondevices. The cross product calibration method uses the measurement of calibratedtri-axial vector field sensors as the reference, instead of external equipment, to carry outthe calibration of tri-axial MEMS gyros. And its precision is very close to that of thetradition method using a rate table. Moreover, the combination of the cross productcalibration method, the dot product invariance method, and the ellipsoid fitting methodcan accomplish the fully automatic in-use calibration for MARG sensor, and thus it hasgreat significance for the applications of MARG sensor. Thirdly, the attitude fusion and filtering problem of MARG-based AHRS isdiscussed. After the comparison of different filtering methods, the multiplicative attitudeerror vector is chosen as the basis of attitude fusion and filtering. Then themultiplicative extended Kalman filters (MEKF), the multiplicative unscented Kalmanfilters (MUKF), as well as the generalized complementary filters (GCF), are presentedand analyzed. The critical points in the design and implementations of the above threealgorithms are discussed. Furthermore, numerical simulations of the above threealgorithms are performed in different software and hardware environments, to evaluateand compare their performance. The GCF is proved to be an efficient, stable, andreliable solution for attitude fusion and filtering.Last but not least, for the attitude determination using the gravity and thegeomagnetic vectors, the CORDIC (coordinate rotation digital computer) algorithm isadopted. The dual-vector CORDIC (DV-CORDIC) algorithm is presented, which canimprove the computational efficiency. The error sources and the upper bound of errorsfor CORDIC and DV-CORDIC are analyzed in depth, and the expressions of the angleuncertainties are also given and verified by numerial simulations. Simulation resultsalso prove that the precision of32-bit DV-CORDIC algorithm can achieve the level ofsingle precision floating point arithmetic, but the former has an obvious advantage incomputation speed over the latter.