22 research outputs found
ReLoc-PDR: Visual Relocalization Enhanced Pedestrian Dead Reckoning via Graph Optimization
Accurately and reliably positioning pedestrians in satellite-denied
conditions remains a significant challenge. Pedestrian dead reckoning (PDR) is
commonly employed to estimate pedestrian location using low-cost inertial
sensor. However, PDR is susceptible to drift due to sensor noise, incorrect
step detection, and inaccurate stride length estimation. This work proposes
ReLoc-PDR, a fusion framework combining PDR and visual relocalization using
graph optimization. ReLoc-PDR leverages time-correlated visual observations and
learned descriptors to achieve robust positioning in visually-degraded
environments. A graph optimization-based fusion mechanism with the Tukey kernel
effectively corrects cumulative errors and mitigates the impact of abnormal
visual observations. Real-world experiments demonstrate that our ReLoc-PDR
surpasses representative methods in accuracy and robustness, achieving accurte
and robust pedestrian positioning results using only a smartphone in
challenging environments such as less-textured corridors and dark nighttime
scenarios.Comment: 11 pages, 14 figure
SelfOdom: Self-supervised Egomotion and Depth Learning via Bi-directional Coarse-to-Fine Scale Recovery
Accurately perceiving location and scene is crucial for autonomous driving
and mobile robots. Recent advances in deep learning have made it possible to
learn egomotion and depth from monocular images in a self-supervised manner,
without requiring highly precise labels to train the networks. However,
monocular vision methods suffer from a limitation known as scale-ambiguity,
which restricts their application when absolute-scale is necessary. To address
this, we propose SelfOdom, a self-supervised dual-network framework that can
robustly and consistently learn and generate pose and depth estimates in global
scale from monocular images. In particular, we introduce a novel coarse-to-fine
training strategy that enables the metric scale to be recovered in a two-stage
process. Furthermore, SelfOdom is flexible and can incorporate inertial data
with images, which improves its robustness in challenging scenarios, using an
attention-based fusion module. Our model excels in both normal and challenging
lighting conditions, including difficult night scenes. Extensive experiments on
public datasets have demonstrated that SelfOdom outperforms representative
traditional and learning-based VO and VIO models.Comment: 14 pages, 8 figures, in submissio
EMA-VIO: Deep Visual-Inertial Odometry with External Memory Attention
Accurate and robust localization is a fundamental need for mobile agents.
Visual-inertial odometry (VIO) algorithms exploit the information from camera
and inertial sensors to estimate position and translation. Recent deep learning
based VIO models attract attentions as they provide pose information in a
data-driven way, without the need of designing hand-crafted algorithms.
Existing learning based VIO models rely on recurrent models to fuse multimodal
data and process sensor signal, which are hard to train and not efficient
enough. We propose a novel learning based VIO framework with external memory
attention that effectively and efficiently combines visual and inertial
features for states estimation. Our proposed model is able to estimate pose
accurately and robustly, even in challenging scenarios, e.g., on overcast days
and water-filled ground , which are difficult for traditional VIO algorithms to
extract visual features. Experiments validate that it outperforms both
traditional and learning based VIO baselines in different scenes.Comment: Accepted by IEEE Sensors Journa
Most Lithium-rich Low-mass Evolved Stars Revealed as Red Clump stars by Asteroseismology and Spectroscopy
Lithium has confused scientists for decades at almost each scale of the
universe. Lithium-rich giants are peculiar stars with lithium abundances over
model prediction. A large fraction of lithium-rich low-mass evolved stars are
traditionally supposed to be red giant branch (RGB) stars. Recent studies,
however, report that red clump (RC) stars are more frequent than RGB. Here, we
present a uniquely large systematic study combining the direct asteroseismic
analysis with the spectroscopy on the lithium-rich stars. The majority of
lithium-rich stars are confirmed to be RCs, whereas RGBs are minor. We reveal
that the distribution of lithium-rich RGBs steeply decline with the increasing
lithium abundance, showing an upper limit around 2.6 dex, whereas the Li
abundances of RCs extend to much higher values. We also find that the
distributions of mass and nitrogen abundance are notably different between RC
and RGB stars. These findings indicate that there is still unknown process that
significantly affects surface chemical composition in low-mass stellar
evolution.Comment: 27 pages, 10 figures, 3 table
Ring Laser Gyro G-Sensitive Misalignment Calibration in Linear Vibration Environments
The ring laser gyro (RLG) dither axis will bend and exhibit errors due to the specific forces acting on the instrument, which are known as g-sensitive misalignments of the gyros. The g-sensitive misalignments of the RLG triad will cause severe attitude error in vibration or maneuver environments where large-amplitude specific forces and angular rates coexist. However, g-sensitive misalignments are usually ignored when calibrating the strapdown inertial navigation system (SINS). This paper proposes a novel method to calibrate the g-sensitive misalignments of an RLG triad in linear vibration environments. With the SINS is attached to a linear vibration bench through outer rubber dampers, rocking of the SINS can occur when the linear vibration is performed on the SINS. Therefore, linear vibration environments can be created to simulate the harsh environment during aircraft flight. By analyzing the mathematical model of g-sensitive misalignments, the relationship between attitude errors and specific forces as well as angular rates is established, whereby a calibration scheme with approximately optimal observations is designed. Vibration experiments are conducted to calibrate g-sensitive misalignments of the RLG triad. Vibration tests also show that SINS velocity error decreases significantly after g-sensitive misalignments compensation
Analysis and Performance Evaluation of a Novel Adjustable Speed Drive with a Homopolar-Type Rotor
The use of a magnetic adjustable speed drive is a popular choice in industrial settings due to its efficient operation, vibration isolation, low maintenance, and overload protection. Most conventional magnetic adjustable speed drives use various forms of the permanent magnets (PMs). Due to the PMs, this type of machine has continuous free-wheeling losses in the form of hysteresis and induced eddy currents. In recent years, the homopolar-type rotor has been widely used in high-speed machines, superconducting machines, and in the application of flywheel energy storage. This study proposes a new application of the homopolar-type rotor. A novel adjustable speed drive with a homopolar-type rotor (HTR-ASD), which has obvious advantages (no brush, no permanent magnet, and no mechanical flux regulation device), is designed and analyzed in this study. Its speed and torque can be adjusted only by adjusting the excitation current. Firstly, in this study, the structure, operation principles, and flux-modulated mechanism of the HTR-ASD are studied. The homopolar-type rotor has a special three-dimensional magnetic circuit structure with the same pole. The 3D-FEM is usually used to calculate its parameters, which is time consuming. In this study, an analytical method is developed to solve this issue. To analytically calculate the torque characteristics, the air gap magnetic flux density, and the winding inductance parameter, the equivalent circuit and the air gap permeance are researched to simplify the analysis. Then, the key parameters of the HTR-ASD are calculated. Finally, the performance of the HTR-ASD is comparatively studied using the analytical method and finite element method, and a comparison of the results is carried out. The comparison indicates that the analytical method is in good agreement with simulation results, and that it is very helpful for designing homopolar-type rotor machines. According to the analysis, the proposed adjustable speed drive displays a great performance in relation to the operating characteristics of a flexible mechanical speed drive