Jingtai Liu

Kinematic Modeling and Analysis of Skid-Steered Mobile Robots With Applications to Low-Cost Inertial-Measurement-Unit-Based Motion Estimation

Skid-steered mobile robots are widely used because of their simple mechanism and high reliability. Understanding the kinematics and dynamics of such a robotic platform is, however, challenging due to the complex wheel/ground interactions and kinematic constraints. In this paper, we develop a kinematic modeling scheme to analyze the skid-steered mobile robot. Based on the analysis of the kinematics of the skid-steered mobile robot, we reveal the underlying geometric and kinematic relationships between the wheel slips and locations of the instantaneous rotation centers. As an application example, we also present how to utilize the modeling and analysis for robot positioning and wheel slip estimation using only low-cost strapdown inertial measurement units. The robot positioning and wheel slip-estimation scheme is based on an extended Kalman filter (EKF) design that incorporates the kinematic constraints for accuracy enhancement. The performance of the EKF-based positioning and wheel slip-estimation scheme are also presented. The estimation methodology is tested and validated experimentally on a robotic test bed.

Preparation of Li4Ti5O12 Nanorods as Anode Materials for Lithium-Ion Batteries

Li 4 Ti 5 O 12 nanorods are fabricated after calcination of the hydrated lithium titanate precursor, which is prepared from hydrothermal treatment of titanate nanorods in aqueous LiOH based on titanate nanorod reactivity. The morphology, composition, and phase transformation of the calcined samples at different temperatures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Titanate nanorods as starting materials exhibit higher chemical reactivity, regarded as a structure template for retaining the one-dimensional structure of final products after calcination. The formation of Li 4 Ti 5 O 12 nanorods is related to ion-exchange reaction and Ostwald ripening process due to high chemical reactivity of titanate nanorods. The galvanostatic charge/discharge tests were conducted to measure the electrochemical performance of the Li 4 Ti 5 O 12 nanorods. It is demonstrated that the Li 4 Ti 5 O 12 nanorods calcined at 800°C have excellent high rate discharge capability and good cycle stability during insertion and extraction processes, owing to the good crystallinity, unique structure, and the short diffusion distances originated from one-dimensional morphology.

A two-view based multilayer feature graph for robot navigation

To facilitate scene understanding and robot navigation in a modern urban area, we design a multilayer feature graph (MFG) based on two views from an on-board camera. The nodes of an MFG are features such as scale invariant feature transformation (SIFT) feature points, line segments, lines, and planes while edges of the MFG represent different geometric relationships such as adjacency, parallelism, collinearity, and coplanarity. MFG also connects the features in two views and the corresponding 3D coordinate system. Building on SIFT feature points and line segments, MFG is constructed using feature fusion which incrementally, iteratively, and extensively verifies the aforementioned geometric relationships using random sample consensus (RANSAC) framework. Physical experiments show that MFG can be successfully constructed in urban area and the construction method is demonstrated to be very robust in identifying feature correspondence.

Modeling and motion stability analysis of skid-steered mobile robots

Skid-steered mobile robots are widely used because of the simplicity of mechanism and high reliability. However, understanding of the kinematics and dynamics of such a robotic platform is challenging due to the complex wheel/ground interactions and kinematic constraints. In this paper, we attempt to develop a kinematic and dynamic modeling scheme to analyze the skid-steered mobile robot. We model wheel/ground interaction and analyze the robot motion stability. As an application example, we present how to utilize the kinematic and dynamic modeling and analysis for robot localization and slip estimation using only low-cost strapdown inertial measurement units (IMU). The extended Kalman filter (EKF)-based localization scheme incorporates the kinematic constraints. The performance of the EKF-based localization and slip estimation scheme are presented. The estimation methodology is tested and validated on a robotic testbed.

Competitive Multi-robot Teleoperation

This paper proposes a novel kind of multi-operator multi-robot(MOMR) teleoperation systems - the competitive teleoperation system. Compared with the conventional collaborated MOMR teleoperation system, features and properties of the competitive teleoperation system are presented. Futhermore, major concerns of research and development for this kind of systems are discussed subsequently. Finally, telegame, a kind of Internet-based competitive teleoperation systems, is built as the prototype to support the future research on this aspect and some experimental results are presented to support the discussion.

Error aware multiple vertical planes based visual localization for mobile robots in urban environments

A novel error-aware visual localization method is proposed that utilizes vertical planes, such as vertical building facades in urban areas as landmarks. Vertical planes, reconstructed from coplanar vertical lines, are robust high-level features if compared with point features or line features. Firstly, the error models of vertical lines and vertical planes are built, where maximum likelihood estimation (MLE) is employed to estimate all vertical planes from coplanar vertical lines. Then, the closed-form representation of camera location error variance is derived. Finally, the minimum variance camera pose estimation is formulated into a convex optimization problem, and the weight for each vertical plane is obtained by solving this well-studied problem. Experiments are carried out and the results show that the proposed localization method has an accuracy of about 2 meters, at par with commercial GPS operating in open environments.

A novel sliding mode control for series elastic actuator torque tracking with an extended disturbance observer

To realize ideal force/torque source in applications such as monopod hopping robots and assistive robots, force/torque controlled series elastic actuators(SEA) are widely used components. Most of existing SEA force/torque control approaches are based on the simple SEA whose force/torque output is proportional to the position of the motor with respect to the payload, however the structure of SEAs is becoming more and more complex, which leads to a nonlinear trend in SEA models. To overcome the problem, we propose a general control method, which is not restricted by the SEA mechanical structure, to control SEA output torque based on nonlinear disturbance observer(NDOB). Specifically, the presented strategy yields the first control solution, with guaranteed theoretical analysis, to successfully address the nonlinear SEA torque control problem, with simultaneous payload angular velocity identification as an additional benefit. The tracking performance of the designed control system is theoretically ensured by Lyapunov analysis. Furthermore, taking a nonlinear SEA for instance, simulation and experimental results suggest the effectiveness and superior performance of the proposed method by comparing it with existing method.

Gesture-based telemanipulation of a humanoid robot for home service tasks

Humanoid robots can be of great assistance to accomplish dexterous manipulation tasks for the impaired and elderly people, but diversity of the environments and complexity of autonomous algorithms still keep as challenging obstacles. In this paper, we proposed a gesture-based telemanipulation scheme to control the NAO humanoid robot. Taking advantage of the Leap Motion Controller, an intuitive and straightforward way for human-robot interaction has been realized. The NAO robot is telemanipulated to accomplish locomotion, dexterous manipulation and composite tasks, and validated by various experiments. This provides a promising technique for service robotics to deliver assistance for activities of daily living at home or in caring agencies, which could be of greatly help for the impaired and elderly people in an aging society.

Fusion of Haptic and Gesture Sensors for Rehabilitation of Bimanual Coordination and Dexterous Manipulation.

Disabilities after neural injury, such as stroke, bring tremendous burden to patients, families and society. Besides the conventional constrained-induced training with a paretic arm, bilateral rehabilitation training involves both the ipsilateral and contralateral sides of the neural injury, fitting well with the fact that both arms are needed in common activities of daily living (ADLs), and can promote good functional recovery. In this work, the fusion of a gesture sensor and a haptic sensor with force feedback capabilities has enabled a bilateral rehabilitation training therapy. The Leap Motion gesture sensor detects the motion of the healthy hand, and the omega.7 device can detect and assist the paretic hand, according to the designed cooperative task paradigm, as much as needed, with active force feedback to accomplish the manipulation task. A virtual scenario has been built up, and the motion and force data facilitate instantaneous visual and audio feedback, as well as further analysis of the functional capabilities of the patient. This task-oriented bimanual training paradigm recruits the sensory, motor and cognitive aspects of the patient into one loop, encourages the active involvement of the patients into rehabilitation training, strengthens the cooperation of both the healthy and impaired hands, challenges the dexterous manipulation capability of the paretic hand, suits easy of use at home or centralized institutions and, thus, promises effective potentials for rehabilitation training.

Structure and electrochemical properties of Zr(V0.2Mn0.2Ni0.6 − xCox)2.4 hydrogen storage alloys

Abstract The structure and hydrogen absorbed properties of a series of the multicomponent Zr(V 0.2 Mn 0.2 Ni 0.6 − x Co x ) 2.4 alloys have been investigated as a negative electrode in the metal hydride batteries. The crystal structure turned out to change as a function of substituted cobalt from a cubic C15 type structure to a hexagonal C14 type structure. There were anomalies in the relation among the hydrogen plateau pressure from PCT, electronic factor of the alloy and A 2 B 2 tetrahedral interstice for hydrogen occupation. The Zr(V 0.2 Mn 0.2 Ni 0.5 Co 0.1 ) 2.4 electrode was used to evaluate the electrochemical characteristics including activation, cycle life, electrocatalytic activity and hydrogen adsorption. It was found that both the hydrogen adsorption process and hydrogen diffusion process took place in the electrochemical impedance spectra of the electrode used here.