PhD Thesis Defense

Title: Agile Load Transportation Systems Using Aerial Robots

By: Ms. Ivana Palunko

Advisor: Dr. Rafael Fierro

Date: Aug 21st 2012, 3:15 PM

Location: ECE, Room 118

In this doctoral dissertation, we address problems that occur during load transport using aerial robots, i.e., small scale quadrotors.

First, detailed models of such transportation system are derived. These models include nonlinear models of a quadrotor, a quadrotor carrying a fixed load and a quadrotor carrying a suspended load.

Second, the problem of quadrotor stabilization and trajectory tracking with changes of the center of gravity of the transportation system is addressed. This problem is solved using adaptive control based on output feedback linearization that compensates for dynamical changes in the center of gravity of the quadrotor. Effectiveness and robustness of the proposed adaptive control scheme are verified through simulation results. The second method used to solve this problem is a least square policy iteration algorithm. This is a model free adaptive algorithm based on reinforcement learning.

The third problem we address is a problem of a swing-free transport of suspended load using quadrotors. Flying with a suspended load can be a very challenging and sometimes hazardous task as the suspended load significantly alters the flight characteristics of the quadrotor. In order to deal with suspended load flight, we present a method based on dynamic programming which is a model-based offline method. The second investigated method we is based on the Nelder-Mead algorithm which ensures swing-free maneuvers of the suspended load. This method is model free and it can be used for offline or online generation of the swing-free trajectories.

Besides the swing-free maneuvers with suspended load, load trajectory tracking is another problem we solve in this dissertation. In order to solve this problem we use a Nelder-Mead based algorithm. In addition, we use an online least square policy iteration algorithm.

At the end, we propose a high level algorithm for navigation in cluttered environments considering a quadrotor with suspended load. Furthermore, distributed control of multiple quadrotors with suspended load is addressed.

The proposed hierarchical architecture presented in this doctoral dissertation is an important step towards developing the next generation of agile autonomous aerial vehicles. These control algorithms enable quadrotors to display agile maneuvers while reconfiguring in real time whenever a change in the center of gravity occurs. This enables a swing-free load transport or trajectory tracking of the load in urban environments in a decentralized fashion.