Autonomous unmanned air vehicle flight control systems require robust path generation to account for terrain obstructions, weather, and moving threats such as radar, jammers, and unfriendly aircraft. In this paper, we outline a feasible, hierarchal approach for real-time motion planning of small autonomous fixed-wing UAVs. The approach divides the trajectory generation into four tasks: waypoint path planning, dynamic trajectory smoothing, trajectory tracking, and low-level autopilot compensation. The waypoint path planner determines the vehicle 's route without regard for the dynamic constraints of the vehicle. This results in a significant reduction in the path search space, enabling the generation of complicated paths that account for pop-up and dynamically moving threats. Kinematic constraints are satisfied using a trajectory smoother which has the same kinematic structure as the physical vehicle. The third step of the approach uses a novel tracking algorithm to generate a feasible state trajectory that can be followed by a standard autopilot. Monte-Carlo simulations were done to analyze the performance and feasibility of the approach and determine real-time computation requirements. A planar version of the algorithm has also been implemented and tested in a low-cost micro-controller. The paper describes a custom UAV built to test the algorithms.

The subject of this paper is the motion control problem of wheeled mobile robots (WMRs) in environments without obstacles. With reference to the popular unicycle kinematics, it is shown that dynamic feedback linearization is an efficient design tool leading to a solution simultaneously valid for both trajectory tracking and setpoint regulation problems. The implementation of this approach on the laboratory prototype SuperMARIO, a two-wheel differentially driven mobile robot, is described in detail. To assess the quality of the proposed controller, we compare its performance with that of several existing control techniques in a number of experiments. The obtained results provide useful guidelines for WMR control designers.

Abstract — This paper presents preliminary development of autonomous sensor-guided behaviors for a six-legged dynamical robot (RHex). These behaviors represent the first exteroceptive closed-loop locomotion strategies for this system. Simple motion models for RHex are described and used to deploy controllers for inertial straight line locomotion and visual line following. Results are experimentally validated on the robot. I.

This paper considers the trajectory tracking problem for unmanned air vehicles (UAVs). We assume that the UAV is equipped with an autopilot which reduces the twelve degree-of-freedom (DOF) model to a six DOF model with altitude, heading, and velocity command inputs. In this paper we restrict our attention to planar motion. One of the novel features of our approach is that we explicitly account for heading and velocity input constraints. For a fixed wing UAV, the velocity is constrained to lie between two positive constants, and therefore presents particular challenges for the control design. We propose a control Lyapunov function (CLF) approach. We first introduce a CLF for the input constrained case, and then construct the set of all constrained inputs that render the CLF negative. The control input is then selected from this "feasible" set. The proposed approach is then applied to a simulation scenario, where a UAV is assigned to transition through several targets in the presence of multiple dynamic threats.

This paper considers the problem of constrained nonlinear tracking control for small fixed-wing unmanned air vehicles equipped with longitudinal and lateral autopilots. Four different controllers based on SDRE, Sontag's formula, geometric parameterization, and saturation are proposed and compared to show their strength and weakness under different application scenarios. Issues of measurement noise and input uncertainties are also addressed under the input-to-state stability framework. The effectiveness of the approaches are demonstrated through detailed simulation studies.

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Abstract — Control concepts for mobile service robots are a key issue in robotic research. With the use of mobile robots in the domestic area, further challenges entails new designs facilitating efficient control concepts for fast motion with reduced computational capacity. This paper presents motion control designed for an autonomously acting two-wheel driven robot, which fits in a cuboid with 75x75x150mm. Due to the outstanding design of mechanical and electrical components, the robot is capable to perform high precision movements up to a speed of 2.5m/s, featuring a vision unit that allows a fast environment recognition interpreting current position based on an application dependent world model. Based on predictive control algorithms, trajectory tracking and point stabilization are facilitated. The use of realtime communication for all units allows fast interaction of all components exchanging information, which is indispensable for fast motion control. I.

Abstract — We develop a tracking controller for the dynamic model of unicycle mobile robot by integrating a kinematic controller and a torque controller based on Fuzzy Logic Theory. Computer simulations are presented confirming the performance of the tracking controller and its application to different navigation problems.

Abstract — The problem of formation tracking can be stated as multiple vehicles are required to follow spatial trajectories while keeping a desired inter-vehicle formation pattern in time. This paper considers vehicles with nonlinear dynamics and nonholonomic constraints and very general trajectories that can be generated by some reference vehicles. We specify formations using the vectors of relative positions of neighboring vehicles and use consensus-based controllers in the context of decentralized formation tracking control. The key idea is to combine consensus-based controllers with the cascaded approach to tracking control, resulting in a group of linearly coupled dynamical systems. We examine the stability properties of the closed loop system using cascaded systems theory and nonlinear synchronization theory. Simulation results are presented to illustrate the proposed method. I.

Trajectory tracking is an important behaviour for mobile robots. This paper addresses the nonlinear trajectory tracking control problem for a nonholonomic car-like mobile robot with a constrained state. Compared with the existing works on the nonholonomic car-like mobile robots, the state constraint is emphasized in this work. The controllability of the system under the state constraint is checked firstly from the sense of nonlinear geometric control. A nonlinear tracking controller is then achieved by taking advantage of the dynamic feedback linearization technique. Moreover, the obtained controller can be exploited to simultaneously solve both the tracking and regulation problems of the car-like mobile robot with the constrained state. The effectiveness of the proposed control law to trajectory tracking control is demonstrated by simulation results.