82 research outputs found
Wheel-INS2: Multiple MEMS IMU-based Dead Reckoning System for Wheeled Robots with Evaluation of Different IMU Configurations
A reliable self-contained navigation system is essential for autonomous
vehicles. Based on our previous study on Wheel-INS \cite{niu2019}, a
wheel-mounted inertial measurement unit (Wheel-IMU)-based dead reckoning (DR)
system, in this paper, we propose a multiple IMUs-based DR solution for the
wheeled robots. The IMUs are mounted at different places of the wheeled
vehicles to acquire various dynamic information. In particular, at least one
IMU has to be mounted at the wheel to measure the wheel velocity and take
advantages of the rotation modulation. The system is implemented through a
distributed extended Kalman filter structure where each subsystem
(corresponding to each IMU) retains and updates its own states separately. The
relative position constraints between the multiple IMUs are exploited to
further limit the error drift and improve the system robustness. Particularly,
we present the DR systems using dual Wheel-IMUs, one Wheel-IMU plus one vehicle
body-mounted IMU (Body-IMU), and dual Wheel-IMUs plus one Body-IMU as examples
for analysis and comparison. Field tests illustrate that the proposed multi-IMU
DR system outperforms the single Wheel-INS in terms of both positioning and
heading accuracy. By comparing with the centralized filter, the proposed
distributed filter shows unimportant accuracy degradation while holds
significant computation efficiency. Moreover, among the three multi-IMU
configurations, the one Body-IMU plus one Wheel-IMU design obtains the minimum
drift rate. The position drift rates of the three configurations are 0.82\%
(dual Wheel-IMUs), 0.69\% (one Body-IMU plus one Wheel-IMU), and 0.73\% (dual
Wheel-IMUs plus one Body-IMU), respectively.Comment: Accepted to IEEE Transactions on Intelligent Transportation System
Excitation of atoms in an optical lattice driven by polychromatic amplitude modulation
We investigate the mutiphoton process between different Bloch states in an
amplitude modulated optical lattice. In the experiment, we perform the
modulation with more than one frequency components, which includes a high
degree of freedom and provides a flexible way to coherently control quantum
states. Based on the study of single frequency modulation, we investigate the
collaborative effect of different frequency components in two aspects. Through
double frequency modulations, the spectrums of excitation rates for different
lattice depths are measured. Moreover, interference between two separated
excitation paths is shown, emphasizing the influence of modulation phases when
two modulation frequencies are commensurate. Finally, we demonstrate the
application of the double frequency modulation to design a
large-momentum-transfer beam splitter. The beam splitter is easy in practice
and would not introduce phase shift between two arms.Comment: 11pages, 7 figure
Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion
The superradiant Rayleigh scattering using a pump laser incident along the
short axis of a Bose-Einstein condensate with a density distortion is studied,
where the distortion is formed by shocking the condensate utilizing the
residual magnetic force after the switching-off of the trapping potential. We
find that very small variation of the atomic density distribution would induce
remarkable asymmetrically populated scattering modes by the matter-wave
superradiance with long time pulse. The optical field in the diluter region of
the atomic cloud is more greatly amplified, which is not an ordinary mode
amplification with the previous cognition. Our numerical simulations with the
density envelop distortion are consistent with the experimental results. This
supplies a useful method to reflect the geometric symmetries of the atomic
density profile by the superradiance scattering.Comment: 7pages,4 figures, Optical Express 21,(2013)1437
Long-time nonlinear dynamical evolution for P-band ultracold atoms in an optical lattice
We report the long-time nonlinear dynamical evolution of ultracold atomic
gases in the P-band of an optical lattice. A Bose-Einstein condensate (BEC) is
fast and efficiently loaded into the Pband at zero quasi-momentum with a
non-adiabatic shortcut method. For the first one and half milliseconds, these
momentum states undergo oscillations due to coherent superposition of different
bands, which are followed by oscillations up to 60ms of a much longer period.
Our analysis shows the dephasing from the nonlinear interaction is very
conducive to the long-period oscillations induced by the variable force due to
the harmonic confinement.Comment: 8 pages, 7 figure
Wheel-SLAM: Simultaneous Localization and Terrain Mapping Using One Wheel-mounted IMU
A reliable pose estimator robust to environmental disturbances is desirable
for mobile robots. To this end, inertial measurement units (IMUs) play an
important role because they can perceive the full motion state of the vehicle
independently. However, it suffers from accumulative error due to inherent
noise and bias instability, especially for low-cost sensors. In our previous
studies on Wheel-INS \cite{niu2021, wu2021}, we proposed to limit the error
drift of the pure inertial navigation system (INS) by mounting an IMU to the
wheel of the robot to take advantage of rotation modulation. However, Wheel-INS
still drifted over a long period of time due to the lack of external correction
signals. In this letter, we propose to exploit the environmental perception
ability of Wheel-INS to achieve simultaneous localization and mapping (SLAM)
with only one IMU. To be specific, we use the road bank angles (mirrored by the
robot roll angles estimated by Wheel-INS) as terrain features to enable the
loop closure with a Rao-Blackwellized particle filter. The road bank angle is
sampled and stored according to the robot position in the grid maps maintained
by the particles. The weights of the particles are updated according to the
difference between the currently estimated roll sequence and the terrain map.
Field experiments suggest the feasibility of the idea to perform SLAM in
Wheel-INS using the robot roll angle estimates. In addition, the positioning
accuracy is improved significantly (more than 30\%) over Wheel-INS. The source
code of our implementation is publicly available
(https://github.com/i2Nav-WHU/Wheel-SLAM).Comment: Accepted to IEEE Robotics and Automation Letter
FF-LINS: A Consistent Frame-to-Frame Solid-State-LiDAR-Inertial State Estimator
Most of the existing LiDAR-inertial navigation systems are based on
frame-to-map registrations, leading to inconsistency in state estimation. The
newest solid-state LiDAR with a non-repetitive scanning pattern makes it
possible to achieve a consistent LiDAR-inertial estimator by employing a
frame-to-frame data association. In this letter, we propose a robust and
consistent frame-to-frame LiDAR-inertial navigation system (FF-LINS) for
solid-state LiDARs. With the INS-centric LiDAR frame processing, the keyframe
point-cloud map is built using the accumulated point clouds to construct the
frame-to-frame data association. The LiDAR frame-to-frame and the inertial
measurement unit (IMU) preintegration measurements are tightly integrated using
the factor graph optimization, with online calibration of the LiDAR-IMU
extrinsic and time-delay parameters. The experiments on the public and private
datasets demonstrate that the proposed FF-LINS achieves superior accuracy and
robustness than the state-of-the-art systems. Besides, the LiDAR-IMU extrinsic
and time-delay parameters are estimated effectively, and the online calibration
notably improves the pose accuracy. The proposed FF-LINS and the employed
datasets are open-sourced on GitHub (https://github.com/i2Nav-WHU/FF-LINS)
Algorithm Improvement of the Low-End GNSS/INS Systems for Land Vehicles Navigation
Recent advances in MEMS IMUs give the potential to develop affordable low-end GNSS/INS systems for land vehicles navigation (LVN). To improve the performance of low-end GNSS/INS systems, we made detailed quantitative analysis to the computation terms of the INS navigation equation in regard to accuracy impacts and computation loads and then proposed a simplified INS algorithm and adjusted the corresponding Kalman filter of GPS/INS integration. Comprehensive analysis was made to get the quantitative impacts of each simplified term. Results of road test have shown that the degradation of the navigation accuracy caused by the algorithm simplification was much less than that caused by the sensors errors of the MEMS IMU. Meanwhile, the computation load could be reduced by 70% with the simplified algorithm, and the reduction can go further to reach nearly 95% by downsampling IMU data rate simultaneously. Therefore, it is feasible to simplify the INS algorithm without losing accuracy and get benefits of reducing the computation load, which can further enhance the real-time performance of the navigation. The work has special significance for the applications that have limited processor resource and request strict real-time response, such as a deeply coupled GPS/INS receiver
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