Inertial-Magnetic Sensors for Assessing Spatial Cognition in Infants

This paper describes a novel approach to the assessment of spatial cognition in children. In particular we present a wireless instrumented toy embedding magneto-inertial sensors for orientation tracking, specifically developed to assess the ability to insert objects into holes. To be used in naturalistic environments (e.g. daycares), we also describe an in-field calibration procedure based on a sequence of manual rotations, not relying on accurate motions or sophisticated equipment. The final accuracy of the proposed system, after the mentioned calibration procedure, is derived by direct comparison with a gold-standard motion tracking device. In particular, both systems are subjected to a sequence of ten single-axis rotations (approximately 90 deg, back and forth), about three different axes. The root-mean-square of the angular error between the two measurements (gold-standard vs. proposed systems) was evaluated for each trial. In particular, the average rms error is under 2 deg. This study indicates that a technological approach to ecological assessment of spatial cognition in infants is indeed feasible. As a consequence, prevention through screening of large number of infants is at reach

Software calibration for AK8963 magnetometer based on optimal ellipsoidal fitting

With the rapid development of mechatronics, systems in package (SiP), in particular the MPU-9250 inertial measurement Unit 9DOF (MPU-6050 6DOF and AK8963 3DOF), are becoming ubiquitous in applications for autonomous navigation purposes. Nevertheless, they suffer from some accuracy problems related to axis misalignment, disturbances, and deviation over time that make them unable to work autonomously for a long time. This paper will present a simple and practical calibration method using a least-squares based ellipsoid fitting method to calibrate and compensate for the error interference of the AK8963 sensor. Towards the end of this paper, a comparison between before and after the calibration is presented to study the software compensation effect and the stability of the magnetic sensor under study

Robust Ellipsoid Fitting Using Axial Distance and Combination

In random sample consensus (RANSAC), the problem of ellipsoid fitting can be formulated as a problem of minimization of point-to-model distance, which is realized by maximizing model score. Hence, the performance of ellipsoid fitting is affected by distance metric. In this paper, we proposed a novel distance metric called the axial distance, which is converted from the algebraic distance by introducing a scaling factor to solve nongeometric problems of the algebraic distance. There is complementarity between the axial distance and Sampson distance because their combination is a stricter metric when calculating the model score of sample consensus and the weight of the weighted least squares (WLS) fitting. Subsequently, a novel sample-consensus-based ellipsoid fitting method is proposed by using the combination between the axial distance and Sampson distance (CAS). We compare the proposed method with several representative fitting methods through experiments on synthetic and real datasets. The results show that the proposed method has a higher robustness against outliers, consistently high accuracy, and a speed close to that of the method based on sample consensus.Comment: 13 page

Online Inertial Measurement Unit Sensor Bias And Attitude Estimation For The Calibration And Improved Performance Of Attitude And Heading Reference Systems

Dynamic instrumentation and estimation of vehicle attitude is critical to the accurate navigation of land, sea, and air vehicles in dynamic motion. The focus of this thesis is the development of algorithms for improved performance of attitude and heading reference systems (AHRSs) and robotic vehicle navigation. inertial measurement unit (IMU) sensor bias estimation methods for use in the calibration of AHRSs and an adaptive attitude estimator operating directly of SO(3) are reported. The reported algorithms provide online calibration and attitude estimation methods which enable more accurate navigation for robotic vehicles. This thesis differentiates AHRSs into two categories – AHRSs that estimate true-North heading and those that estimate magnetic north heading. Chapters 3-5 report several novel algorithms for micro-electro-mechanical systems (MEMS) IMU sensor bias estimation. Observability, stability, and parameter convergence are evaluated in numerical simulations, full-scale vehicle laboratory experiments, and full-scale field trials in the Chesapeake Bay, MD. Chapter 6 reports an adaptive sensor bias observer and attitude observer operating directly on SO(3) for true-North gyrocompass systems that utilize six-degrees of freedom (DOF) IMUs with three-axis accelerometers and three-axis angular rate gyroscopes (without magnetometers) to dynamically estimate the instrument’s time-varying true-North attitude (roll, pitch, and geodetic heading) in real-time while the instrument is subject to a priori unknown rotations. Stability proofs for the reported bias and attitude observers, preliminary simulations, and a full-scale vehicle trial are reported. The presented calibration methods are shown experimentally to improve calibration of AHRS attitude estimation over current state of the art sensor bias estimation methods, and this thesis presents a true-North gyrocompass system based on adaptive observers for use with strap-down IMUs. These results may prove to be useful in the development of navigation systems for small low-cost robotic vehicles

Doctor of Philosophy

dissertationMotion capture has applications in many fields. A need has arisen for motion capture systems that are low-cost, mobile, and intuitive. An attitude heading reference system (AHRS) calculates the global orientation of a rigid body by synthesizing the output from an array of sensors. A complete motion capture system utilizing gyroscopes, accelerometers, and magnetometers attached to the main body segments of a human is proposed. This is accomplished by providind a low-cost calibration procedure for micro electro-mechanical system (MEMS) gyroscopes, accelerometers, and magnetometers in order to create a custom AHRS unit. The accuracy of reproducing global orientations using these AHRS units is analyzed for individual modules as well as redundant groups of AHRS nodes for increased accuracy. In order to make the system intuitive, a localization procedure for finding the locations of all AHRS units attached to the body is proposed. Sensors were successfully calibrated to an accuracy sufficient for AHRS development. The accuracy of the AHRS units was verified and led to a functioning motion capture system. The localization procedure was verified with volunteer subjects and successfully finds the location of all attached AHRS units

A novel multi-target modular probe for multiple Large-Volume Metrology systems

Recent studies show that the combined use of Large-Volume Metrology (LVM) systems (e.g., laser trackers, rotary-laser automatic theodolites (R-LATs), photogrammetric cameras, etc.) can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. Unfortunately, the sensors of a specific LVM system are usually able to localize only specific targets (i.e., active/passive elements positioned in the measurement volume) and not necessarily those related to other systems (e.g., the reflective markers for photogrammetric cameras cannot be used for R-LATs or laser trackers); this represents an obstacle when using combinations of different LVM systems. This paper describes the design of a new modular probe, with different typologies of targets and integrated sensors, which allows to simplify the measurement process. The probe is versatile as the number of targets, their typology and spatial position can be customized depending on the combination of LVM systems in use. A detailed analysis of the technical and functional characteristics of the probe is followed by the presentation of a mathematical/statistical model for the real-time probe localization. Description is supported by realistic application examples

The US/UK World Magnetic Model for 2020-2025

This report contains a complete description of the World Magnetic Model (WMM) 2020. Section 1 contains information that users of WMM2020 require in order to implement the model and software in navigation and heading systems, and to understand magnetic charts, poles and geomagnetic coordinate systems. Section 2 contains a detailed summary of the data used and the modeling techniques employed. Section 3 contains an assessment of the model uncertainties and a description of the error model provided with the WMM2020. Section 4 contains charts of all the magnetic elements at 2020.0 and their expected annual rates of change between 2020.0 and 2025.0. These predicted changes are based upon the best knowledge of the geomagnetic main field evolution at the time the WMM was released. Sponsored by the U.S. National Geospatial-Intelligence Agency (NGA) and the U.K. Defence Geographic Centre (DGC), the World Magnetic Model (WMM) is produced by the U.S. National Oceanic and Atmospheric Administration’s National Centers for Environmental Information (NOAA/NCEI) and the British Geological Survey (BGS). It is the standard model used by the U.S. Department of Defense (DoD), the U.K. Ministry of Defence, the North Atlantic Treaty Organization (NATO) and the International Hydrographic Organization (IHO), for navigation, attitude and heading referencing systems using the geomagnetic field. It is also used widely in civilian navigation and heading systems