James P. Ostrowski

Modeling and control of formations of nonholonomic mobile robots

This paper addresses the control of a team of nonholonomic mobile robots navigating in a terrain with obstacles while maintaining a desired formation and changing formations when required, using graph theory. We model the team as a triple, (g, r, H), consisting of a group element g that describes the gross position of the lead robot, a set of shape variables r that describe the relative positions of robots, and a control graph H that describes the behaviors of the robots in the formation. Our framework enables the representation and enumeration of possible control graphs and the coordination of transitions between any two formations.

A vision-based formation control framework

The invention relates to a rack for electronic plug-in units, comprising a backplane. The backplane comprises at least one connector to which a connector provided in the electronic plug-in unit connects when the plug-in unit is pushed into the rack. The backplane is attached to the rack with a fastener made of a resilient material. A moment arm is formed between a point which attaches the fastener to the rack and the backplane. When the plug-in unit is pushed into the rack, there is a tolerance for alignment of the connectors enabling connection of the connectors. Furthermore, when the plug-in unit is in the rack, the mobility of the backplane prevents the connectors and/or the backplane from breaking as the rack moves.

Controlling formations of multiple mobile robots

We investigate feedback laws used to control multiple robots moving together in a formation. We propose a method for controlling formations that uses only local sensor-based information, in a leader-follower motion. We use methods of feedback linearization to exponentially stabilize the relative distance and orientation of the follower, and show that the zero dynamics of the system are also (asymptotically) stable. We demonstrate in simulation the use of these algorithms to control six robots moving around an obstacle. These types of control laws can be used to control arbitrarily large numbers of robots moving in very general types of formations.

Control of a quadrotor helicopter using visual feedback

We present control methods for an autonomous four-rotor helicopter, called a quadrotor, using visual feedback as the primary sensor. The vision system uses aground camera to estimate the pose (position and orientation) of the helicopter. Two methods of control are studied - one using a series of mode-based, feedback linearizing controllers, and the other using a backstepping-like control law. Various simulations of the model demonstrate the implementation of feedback linearization and the backstepping controllers. Finally,. we present initial flight experiments. where the helicopter is restricted to vertical and yaw motions.

Hybrid control of formations of robots

We describe a framework for controlling a group of nonholonomic mobile robots equipped with range sensors. The vehicles are required to follow a prescribed trajectory while maintaining a desired formation. By using the leader-following approach, we formulate the formation control problem as a hybrid (mode switching) control system. We then develop a decision module that allows the robots to automatically switch between continuous-state control laws to achieve a desired formation shape. The stability properties of the closed-loop hybrid system are studied using the Lyapunov theory. We do not use explicit communication between robots; instead we integrate optimal estimation techniques with nonlinear controllers. Simulation and experimental results verify the validity of our approach.

Dynamic modelling and configuration stabilization for an X4-flyer

Abstract A model for the dynamics of a four rotor vertical take-off and landing (VTOL) vehicle known as an X4-flyer is proposed. The model incorporates the airframe and motor dynamics as well as aerodynamic and gyroscopic effects due to the rotors for quasi-stationary flight conditions. A novel control strategy is proposed for configuration stabilization of quasi-stationary flight conditions. The approach taken involves separating the rigid body (airframe) dynamics from the motor dynamics, developing separate control Lyapunov functions for the coupled systems and then bounding the perturbation error due to the interaction to obtain strong practical stability of the complete system.

Motion planning for anguilliform locomotion

We investigate issues of control and motion planning for a biomimetic robotic system. Previous work has shown that a successful approach to solving the motion planning problem is to decouple it into the two subproblems of trajectory generation (feedforward controls) and feedback regulation. In this paper, we investigate basic issues of momentum generation for a class of dynamic mobile robots, focusing on eel-like swimming robots. We develop theoretical justification for a forward gait that has been observed in nature, and for a turning gait, used in our control laws, that has not been extensively studied in the biological literature. We also explore theoretical predictions for novel gaits for turning and sideways swimming. Finally, we present results from experiments in motion planning for a biomimetic robotic system. We show good agreement with theory for both open and closed-loop control of our modular, five-link, underwater swimming robot using image-based position sensing in an aquatic environment.

Visual servoing with dynamics: control of an unmanned blimp

Image-based control of free-flying mechanical systems is addressed, with application to an indoor vision-guided blimp. A methodology is developed for incorporating the physical parameters of a mechanical system into the image plane for performing visual servoing. It is noted that under suitable conditions, namely the existence of a diffeomorphism between image features and robot pose, many tools from mechanical system control theory can be used directly when applied in the image plane. It is shown that when a suitable Jacobian map exists between pose and features, dynamics for vision-based control of aerial and underwater vehicles can easily be formulated. Experimental results show initial success at spatial tracking of simple objects.

Nonholonomic mechanics and locomotion: the snakeboard example

Analysis and simulations are performed for a simplified model of a commercially available variant of the skateboard, known as the Snakeboard. Although the model exhibits basic gait patterns seen in a large number of locomotion problems, the analysis tools currently available do not apply to this problem. The difficulty lies primarily in the way in which the nonholonomic constraints enter into the system. As a first step towards understanding systems represented by their model the authors present the equations of motion and perform some controllability analysis for the snakeboard. The authors also perform numerical simulations of possible gait patterns which are characteristic of snakeboard locomotion.<<ETX>>

Quadrotor control using dual camera visual feedback

In this paper, a vision-based stabilization and output tracking control method for a four-rotor helicopter has been proposed. A novel 2 camera method has been described for estimating the full 6 DOF pose of the helicopter. This two camera system is consisting of a pan-tilt ground camera and an onboard camera. The pose estimation algorithm is compared in simulation to other methods (such as four point method, and a stereo method) and is shown to be less sensitive to feature detection errors on the image plane. The proposed pose estimation algorithm and non-linear control techniques have been implemented on a remote controlled quadrotor helicopter.