7496057
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.
5542960
Metrics for analysis and optimization of grasps and fixtures
We develop two quality measures for the analysis and optimization of grasps and fixtures. The first metric is a measure of stability and is obtained by analyzing the effect of small perturbations in the position of the grasped object or small disturbance forces on the grasped object The second metric is a measure of robustness to errors in the positions of the fixture elements. In addition, we explore the effect that the stiffness of the fixture elements has on these two quality measures and propose a design optimization approach to maximize stability and robustness to errors.
7023425
A Paradigm for Dynamic Coordination of Multiple Robots
In this paper, we present a paradigm for coordinating multiple robots in the execution of cooperative tasks. The basic idea in the paper is to assign to each robot in the team, a role that determines its actions during the cooperation. The robots dynamically assume and exchange roles in a synchronized manner in order to perform the task successfully, adapting to unexpected events in the environment. We model this mechanism using a hybrid systems framework and apply it in different cooperative tasks: cooperative manipulation and cooperative search and transportation. Simulations and real experiments demonstrating the effectiveness of the proposed paradigm are presented.
15738427
A potential field based approach to multi-robot manipulation
We describe a framework for controlling and coordinating a group of robots for cooperative manipulation tasks. The framework enables a decentralized approach to planning and control. It allows the robots to approach the object, organize themselves into a formation that will trap the object, and then transport the object to the desired destination. Our controllers and planners are derived from simple potential fields and the hierarchical composition of potential fields. We show how these potential field based controllers and planners benefit complex group interactions, specifically for manipulating and transporting objects in the plane. Theoretically, we show how we can derive results on formation stability with potential field based controllers in many cases. Simulation results demonstrate successful application to a wide range of examples without showing sensitivity to parameters. Because the framework is decentralized at both trajectory generation level and the estimation and control agent level, our framework can potentially scale to groups of tens and hundreds of robots.
6879835
Calibrating an air-ground control system from motion correspondences
In this paper we consider the problem of controlling the motion of a vehicle moving on a ground plane based on aerial imagery. In the course of this work we propose a novel analysis of the relationship between the velocity of the vehicle on the ground plane and the velocity of its projection in the image. We show that this relationship provides information about a subset of the parameters of the homography relating the ground plane to the aerial image plane and describe how we can recover this relationship from available measurements.
29516211
Control of Contact Interactions with Acatastatic Nonholonomic Constraints
A robot arm performs many tasks by interacting with objects or other robots in the environment. It is important for the robot arm to be able to exhibit controlled interactions with the objects and other robots. The contact motion between the robot arm and an object can be rolling, sliding, or separation. In this article, we address the problem of maintaining rolling contact between the robot arm and an external moving object. We assume that a nominal model of the motion of the moving object is available. The dynamic system that characterizes the motion of the robot arm and the moving object in this case is acatastatic and nonholonomic. We have designed a nonlinear feedback for the control of such a system that successfully maintains rolling contact. Simulation results are presented to demonstrate the effectiveness of the system.
33425730
A Superior Algorithm for Mutual Exclusion in Computer Networks - VISHNU
5480787
Parallel Formulations of Decision-Tree Classification Algorithms
Classification decision tree algorithms are used extensively for data mining in many domains such as retail target marketing, fraud detection, etc. Highly parallel algorithms for constructing classification decision trees are desirable for dealing with large data sets in reasonable amount of time. Algorithms for building classification decision trees have a natural concurrency, but are difficult to parallelize due to the inherent dynamic nature of the computation. In this paper, we present parallel formulations of classification decision tree learning algorithm based on induction. We describe two basic parallel formulations. One is based on Synchronous Tree Construction Approach and the other is based on Partitioned Tree Construction Approach. We discuss the advantages and disadvantages of using these methods and propose a hybrid method that employs the good features of these methods. We also provide the analysis of the cost of computation and communication of the proposed hybrid method. Moreover, experimental results on an IBM SP-2 demonstrate excellent speedups and scalability.
18650185
Minimization, Learning, and Conformance Testing of Boolean Programs
Boolean programs with recursion are convenient abstractions of sequential imperative programs, and can be represented as recursive state machines (RSMs) or pushdown automata. Motivated by the special structure of RSMs, we define a notion of modular visibly pushdown automata (modular VPA) and show that for the class of languages accepted by such automata, unique minimal modular VPA exist. This yields an efficient approximate minimization theorem that minimizes RSMs to within a factor of k of the minimal RSM, where k is the maximum number of parameters in any module. Using the congruence defined for minimization, we show an active learning algorithm (with a minimally adequate teacher) for context free languages in terms of modular VPAs. We also present an algorithm that constructs complete test suites for Boolean program specifications. Finally, we apply our results on learning and test generation to perform model checking of black-box Boolean programs.
37917309
Management of Concurrency in Interpolation Based Grid File Organization and its Performance
The mathematical structure of the interpolation based grid file organization provides a suitable platform for supporting a high degree of concurrency under a concurrency control mechanism. To demonstrate this capability, we first identified its useful properties for designing a concurrency control mechanism and then developed a deadlock-free two-phase locking based mechanism using dynamic attributes of transactions. To establish the usefulness of our system (concurrency control and the file organization), we measured its performance through simulation modeling. We show that our system handles a number of different types of workloads efficiently and the directory overhead does not strictly depend on the type of workload.
47057582
Covering Rectilinear Polygons with Axis-Parallel Rectangles
We give an $O(\sqrt{\log n})$ factor approximation algorithm for covering a rectilinear polygon with holes using axis-parallel rectangles. This is the first polynomial time approximation algorithm for this problem with an $o(\log n)$ approximation factor.