Daniel J. Pack

Cooperative Control of UAVs for Localization of Intermittently Emitting Mobile Targets

Compared with a single platform, cooperative autonomous unmanned aerial vehicles (UAVs) offer efficiency and robustness in performing complex tasks. Focusing on ground mobile targets that intermittently emit radio frequency signals, this paper presents a decentralized control architecture for multiple UAVs, equipped only with rudimentary sensors, to search, detect, and locate targets over large areas. The proposed architecture has in its core a decision logic which governs the state of operation for each UAV based on sensor readings and communicated data. To support the findings, extensive simulation results are presented, focusing primarily on two success measures that the UAVs seek to minimize: overall time to search for a group of targets and the final target localization error achieved. The results of the simulations have provided support for hardware flight tests.

Fire-fighting mobile robotics and interdisciplinary design-comparative perspectives

The objective of this paper is to illustrate the benefits of an autonomous fire-fighting robot design competition as an effective tool for undergraduate education. It presents experiences at the United States Air Force Academy, USAF Academy, CO; Pennsylvania State University-Abington; and Trinity College, Hartford, CT, together with the results of the contest surveys conducted in collaboration with The Technion*Israel Institute of Technology, Haifa. The primary goal of the design project is to create an autonomous mobile robot that navigates through a maze searching for a fire (simulated by a burning candle), detects the candles flame, extinguishes the flame, and returns to a designated starting location in the maze. The fire-fighting design contest promotes interdisciplinary design and teamwork. To accomplish the stated goal, students must integrate knowledge gained from such classes as engineering design, circuits, controls, signals and systems, computer programming, mathematics, and engineering mechanics. Within the three institutions, the contest has been successfully utilized as a foundation for a wide range of educational goals. These activities include freshman design, robotics courses, K-12 outreach, senior design projects, and undergraduate research.

Developing a Control Architecture for Multiple Unmanned Aerial Vehicles to Search and Localize RF Time-Varying Mobile Targets: Part I

In this paper, we present a control architecture that allows multiple Unmanned Aerial Vehicles (UAVs) to cooperatively detect mobile RF (Radio Frequency) emitting ground targets. The architecture is developed under the premise that UAVs are controlled as a distributed system. The distributed system-based technique maximizes the search and detection capabilities of multiple UAVs. We use a hybrid approach that combines a set of intentional cooperative rules with emerging properties of a swarm to accomplish the objective. The UAVs are equipped only with low-precision RF direction finding sensors and we assume the targets may emit signals randomly with variable duration. Once a target is detected, each UAV optimizes a cost function to determine whether to participate in a cooperative localization task. The cost function balances between the completion of detecting all targets (global search) in the search space and increasing the precision of cooperatively locating already detected targets. A search function for each UAV determines the collective search patterns of collaborating UAVs. Two functions used by each UAV determine (1) the optimal number of UAVs involved in locating targets, (2) the search pattern to detect all targets, and (3) the UAV flight path for an individual UAV. We show the validity of our algorithm using simulation results. Hardware implementation of the strategies is planned for this coming year.

Toward finding an universal search algorithm for swarm robots

We present a novel cooperative search algorithm for distributed, independent swarm robots. The focus of this paper is three fold: (1) identify fundamental issues associated with searching an area by multiple robots; (2) design a metric to measure the cooperation among multiple robots to complete a search; and (3) propose an effective search algorithm for swarm robots.

Perception-based control for a quadruped walking robot

The progress made so far in the study of legged robots has dealt mostly with the issues of leg coordination, gait control, stability, incorporation of various types of sensors, etc. But what is missing in most of these robots is some perception-based high-level control that would permit a robot to operate intelligently. For the high-level control, a model-based method to recognize a staircase using a single 2D image of a 3D scene is studied. The staircase recognition is achieved by obtaining the pose of a camera coordinate frame which aligns model edges with image edges. The method contains the matching, the pose estimation, and the refinement procedures. A new matching scheme is proposed to reduce the complexity of correspondence search between model and image features. This is accomplished by grouping edges with certain geometric characteristics together. The refinement process uses all matched features to tightly fit the model edges with camera image edges. The resulting recognition is used to guide the robot to climb stairs.

Localizing RF Targets with Cooperative Unmanned Aerial Vehicles

Unmanned aerial vehicles (UAVs) play an important and expanding role in both civilian and military missions, such as search and rescue, intelligence collection, surveillance, or reconnaissance. Currently, UAVs require human operators to control and direct their flights and sensors. To expand their effectiveness and exploit their inherent capabilities, we seek to develop robust techniques for multiple UAVs to cooperatively operate without direct human control. Our current research interest is to develop algorithms and simulate techniques to enable UAVs to search for, detect, and locate mobile ground targets emitting radio frequency signals. This paper investigates the task of combining sensor data from multiple UAVs to obtain accurate and reliable target locations. The sensors collect only coarse angle-of-arrival information and we apply Kalman filtering techniques to estimate the angle to the target. The estimated angles from multiple UAVs are sufficient to develop control laws for the UAVs to converge on an orbit about the target and collect additional measurements to further improve the estimation of the targets position. We explore a sensor fusion process embedded in a simple control law that allows multiple UAVs to cooperate in the target localization task and coordinate their motion using a leader-follower approach. We demonstrate the cooperative sensing techniques using simulation results.

An omnidirectional gait control using a graph search method for a quadruped walking robot

Two major approaches exist for devising gait control for a legged machine: 1) finding a sequence of leg and body movements of a robot on the basis of kinematic and possibly dynamic considerations assuming all foot placements are valid; and 2) selecting leg and body movements first on the basis of feasibility of foot placements and then accepting those that also satisfy kinematic and possibly dynamic constraints. Consider now the problem of a legged robot pursuing a quarry. With the first approach, the robot will be limited to operating over a relatively flat terrain. If the terrain is uneven, however, the robot will have no choice but to take recourse to the second approach even though it is computationally more demanding. The work done so far in the second approach is limited by either the constraint that the overall direction of ambulation of the robot is known in advance, or by the constraint that the foot placements are limited to the points of a grid superimposed on the topographic map of the terrain. In this paper, the authors discuss how a free gait can be generated for following a quarry without invoking such constraints.

A simplified forward gait control for a quadruped walking robot

Presents a simplified forward gait for a quadruped walking robot. The proposed gait is a straight line, periodic, monotonically forward (SLPMF) gait and can easily be used for adaptive gait control, requiring only simple modifications. The authors show that given a support pattern, meaning a polygon generated by connecting the feet positions that are in contact with the ground, only certain sequences of leg movements will generate the SLPMF gait. The authors also introduce a useful method to determine how to preserve stability of a quadruped robot during the motions called for by an SLPMF gait. The authors also discuss the leg design from a hardware standpoint; the design permits independent joint control.<<ETX>>

Localization of ground targets using a flying sensor network

In this paper we propose a novel cooperation control method for multiple unmanned aerial vehicles (UAVs) to search, detect, and locate ground targets. We assume that our UAVs are only equipped with rudimentary angle of arrival sensors and the ground targets are mobile radio frequency (RF) emitters. In addition to the mobility, we assume our targets emit signals with random duration and frequency. Our cooperative UAVs function as a reconfigurable sensor network whose goal is to minimize target localization time and the target location error. The proposed control method extends our previous work on distributed control architecture for multiple UAVs by introducing localized hierarchical control structures. Such structures are dynamically established by local leaders that autonomously emerge in response to individual sensor readings, allowing efficient coordination of activities among nearby UAVs. The sensor network uses Kalman filtering techniques to minimize the target location error and the target localization time by combining current and past captured sensor values from multiple UAVs. We validate our proposed control method with simulation results that illustrate its performance under varying levels of cooperation among the members of the sensor network

Microcontrollers Fundamentals for Engineers And Scientists

This book provides practicing scientists and engineers a tutorial on the fundamental concepts and use of microcontrollers. Today, microcontrollers, or single integrated circuit (chip) computers, play critical roles in almost all instrumentation and control systems. Most existing books arewritten for undergraduate and graduate students taking an electrical and/or computer engineering course. Furthermore, these texts have beenwritten with a particular model of microcontroller as the target discussion. These textbooks also require a requisite knowledge of digital design fundamentals. This textbook presents the fundamental concepts common to all microcontrollers. Our goals are to present the overarching theory of microcontroller operation and to provide a detailed discussion on constituent subsystems available in most microcontrollers. With such goals, we envision that the theory discussed in this book can be readily applied to a wide variety of microcontroller technologies, allowing practicing scientists and engineers to become acquainted with basic concepts prior to beginning a design involving a specific microcontroller. We have found that the fundamental principles of a given microcontroller are easily transferred to other controllers. Although this is a relatively small book, it is packed with useful information for quickly coming up to speed on microcontroller concepts.