Showing papers by "Zexiang Li published in 2017"

Development and experimental verification of a hybrid vertical take-off and landing (VTOL) unmanned aerial vehicle(UAV)

Abstract: In this paper, we present the design and verification of a hybrid vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAV) of the type named dualsystem or extra propulsion VTOL UAV. This paper features the comprehensive system development of such VTOL UAVs from all aspects, including the aircraft design and implementation, onboard devices integration, ground station support, and long distance communication. We proceed with aerodynamic analysis, mechanical design, and controller development. Finally, we verify by experiment that this hybrid VTOL UAV has the desired aerodynamic performance, flight stability, endurance and range. In addition, with the designed flight controller, the VTOL UAV can achieve full autonomous flight in a real outdoor environment. It serves a good platform for future research, such as vision-based precise landing, motion planing and quick 3D mapping, as well as service applications, such as medicine delivery.

Design and implementation of a quadrotor tail-sitter VTOL UAV

Abstract: We present the design and implementation of a quadrotor tail-sitter Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV). The VTOL UAV combines the advantage of a quadrotor, vertical take-off and landing and hovering at a stationary point, with that of a fixed-wing, efficient level flight. We describe our vehicle design with special considerations on fully autonomous operation in a real outdoor environment where the wind is present. The designed quadrotor tail-sitter UAV has insignificant vibration level and achieves stable hovering and landing performance when a cross wind is present. Wind tunnel test is conducted to characterize the full envelope aerodynamics of the aircraft, based on which a flight controller is designed, implemented and tested. MATLAB simulation is presented and shows that our vehicle can achieve a continuous transition from hover flight to level flight. Finally, both indoor and outdoor flight experiments are conducted to verify the performance of our vehicle and the designed controller.

A unified control method for quadrotor tail-sitter UAVs in all flight modes: Hover, transition, and level flight

Abstract: This paper presents a unified control framework for controlling a quadrotor tail-sitter UAV. The most salient feature of this framework is its capability of uniformly treating the hovering and forward flight, and enabling continuous transition between these two modes, depending on the commanded velocity. The key part of this framework is a nonlinear solver that solves for the proper attitude and thrust that produces the required acceleration set by the position controller in an online fashion. The planned attitude and thrust are then achieved by an inner attitude controller that is global asymptotically stable. To characterize the aircraft aerodynamics, a full envelope wind tunnel test is performed on the full-scale quadrotor tail-sitter UAV. In addition to planning the attitude and thrust required by the position controller, this framework can also be used to analyze the UAV's equilibrium state (trimmed condition), especially when wind gust is present. Finally, simulation results are presented to verify the controller's capacity, and experiments are conducted to show the attitude controller's performance.

Design, implementation and verification of a quadrotor tail-sitter VTOL UAV

Abstract: This paper presents the design and implementation of a cost-effective, lightweight, yet power efficient tail-sitter Vertical Take-off and Landing (VTOL) unmanned aerial vehicle (UAV). The UAV consists a pair of wings for efficient level flight and four rotors for attitude control. The aerodynamic and mechanical configurations of the UAV are designed and implemented from scratch to meet the required power efficiency, and subsequently optimized to enhance the stability and maneuverability. The developed VTOL UAV has a weight and cost comparable to a typical quadrotor, while consuming only half power, as shown by real flight tests. In addition, it can achieve all key VTOL maneuvers, including vertical take-off, landing, hovering, cruising and transition.

A hierarchical control approach for a quadrotor tail-sitter VTOL UAV and experimental verification

Abstract: We present a hierarchical control approach that can be used to fulfill autonomous flight, including vertical takeoff, landing, hovering, transition, and level flight, of a quadrotor tail-sitter vertical takeoff and landing unmanned aerial vehicle (VTOL UAV). A unified attitude controller, together with a moment allocation scheme between elevons and motor differential thrust, is developed for all flight modes. A comparison study via real flight tests is performed to verify the effectiveness of using elevons in addition to motor differential thrust. With the well-designed switch scheme proposed in this paper, the aircraft can transit between different flight modes with negligible altitude drop or gain. Intensive flight tests have been performed to verify the effectiveness of the proposed control approach in both manual and fully autonomous flight mode.

Time-optimal and energy-efficient trajectory generation for robot manipulator with kinematic constraints

Abstract: This paper designs an algorithm to generate time-optimal and energy-efficient trajectory for manipulators along a predefined geometric path. The path is first parameterized by cubic spline, then the trajectory generation problem is transformed into a nonlinear optimization problem with single state variable. After discretization, Sequence quadratic programming(SQP) method is applied for optimal solution. Finally, applications to a 6-DoF manipulator along different paths demonstrates the feasibility of the proposed method.

Tool path interpolation and redundancy optimization of manipulator

Abstract: In this paper, tool path interpolation and redundancy optimization algorithms are designed for the industrial manipulator to perform tasks exhibiting 1-DoF redundancy such as the welding, cutting etc. B-spline is applied for the tool path interpolation and then by minimizing the energy consumption while avoiding singularity and respecting joint limits at the same time, the optimal trajectory can be obtained. The problem is formulated and solved by nonlinear optimization method. POE(Product of exponential) model is used for robotic kinematic and dynamic analysis to simplify the problem. Experiments were conducted to illustrate the feasibility of our method.