The problem of showing that Lagrangian Coherent Structures (LCS) are useful in determining near optimal trajectories for autonomous underwater vehicles (AUVs) known as gliders is investigated. This paper extends our preliminary results in couple ways. First, the ocean current flows are modeled by 3D B-spline functions in which the input variables are latitude, longitude and time, and the output variable is the ocean current velocity in 2D. The 3D (2D and time-varying) B-spline model of the ocean current is utilized in the Nonlinear Trajectory Generation (NTG) algorithm to find the optimal trajectory of the glider. The trajectories found using the 2D and time-varying B-spline ocean flows model are compared with the trajectories from 2D B-spline model in which the time is assumed to be constant in the ocean current model. In the second part of the paper, the dynamical glider model is established and controlled by gyroscopic forces rather than the simplified kinematic glider model as in the previous work. Finally, numerical solutions of several scenarios and animations of glider trajectories are presented. The results show that the 2D and time-varying B-spline ocean model not only can make the whole trajectory generating process much easier, but also the glider can reach the same destination in a comparable time and with much less energy than it does with the previous 2D ocean current model for both the kinematic and dynamic glider models. Both of the kinematic and dynamic glider optimal trajectories, successfully generated with 2D and time varying ocean current B-spline models, are shown to correspond to LCS.

This paper describes design and construction of an Autonomous Mobile Robotics Systems Testbed in detail. The testbed is an indoor experimental platform for developing and validating theoretical as well as practical research work in identification, coordinative and cooperative control, trajectory generation, computational intelligence, and sensing for multiple autonomous mobile robotics systems. It provides a designated space for multiple mobile robots while tracking their position and orientation in real-time using an overhead vision system. Several problems encountered in developing the testbed such as multi-camera color consistency, radial lens distortion, hat pattern design are clearly addressed. The testbed is analyzed for its performance and several experiments with ER1 mobile robots are presented.

Active vision systems with independent eye motion are required to update extrinsic parameters continuously to perform stereo reconstruction. The stereo parameters could be calculated through forward kinematics model plus head-eye parameters of each eye. The head-eye parameters could be calibrated through traditional head-eye calibration method separately. However, head-eye calibration method could not reduce the impact of the kinematics model errors, which may cause reconstruction result unacceptable. Instead, we propose an integrated two-pose calibration method to calculate head-eye parameters of both eyes simultaneously to reduce the impact of model error by deriving two new equations from two poses of the robotic bionic eye. The implemented algorithm has been validated on GAZEBO and our robotic bionic eye. The results demonstrate that the head-eye parameters obtained by our method are more accurate and more robust to kinematics model errors. We have also analyzed the reason why the proposed method is better.

This article presents a compensated positive position feedback strategy for active control of flexible structures with piezoelectric actuators. In the proposed compensated positive position feedback method, a negative feedback compensator is involved to remedy the deficiency of traditional positive position feedback and to introduce roll-off characteristic at low frequencies. Thus, compensated positive position feedback controllers can be developed with minimal influences on lower order modes and cause no steady-state error to the controlled system. For demonstration purpose, the design processes and the effectiveness of the compensated positive position feedback method are illustrated by active control of a cable net structure with integrated piezoelectric stacked actuators. The numerical simulations demonstrate that compared to the conventional positive position feedback method, the proposed compensated positive position feedback approach overcomes the fundamental defects of frequency shift and spillover into lower order modes and achieves the goal of step-tracking with zero steady-state error. These comparative results confirm the efficacy and superiority of the proposed compensated positive position feedback methodology in active control of flexible structures.

The quadrotor, as a kind of Unmanned Aerial Vehicles (UAVs), has become a hot research topic, due to its small size, easy configuration, good stealthy characteristics, etc. It is a typical nonlinear system with coupling multi-variables. Therefore, it is difficult to optimize trajectory in real-time and its trajectory optimization research is limited so far. In this paper, we firstly establish a quadrotor dynamic model by Newton-Euler equations and simplify it properly. Then a Gauss Pseudo-spectrum Method (GPM) with the hp-adaptive mesh refinement algorithm is proposed to solve the problem which is a nonlinear optimal control problem with path and boundary constraints. The results verify that the method can effectively generate satisfied optimal trajectories for the aircraft and it provides mathematical foundation for the further engineering applications.