11162423
Optimal Gait Selection for Nonholonomic Locomotion Systems
This paper addresses the optimal control and selection of gaits in a class of nonholonomic locomotion systems that exhibit group symmetries. We study optimal gaits for the snakeboard, a representative example of this class of systems. We employ Lagrangian reduction techniques to simplify the optimal control problem and describe a general framework and an algorithm to obtain numerical solutions to this problem. This work employs optimal control techniques to study the optimality of gaits and issues involving gait transitions. The general framework provided in this paper can easily be applied to other examples of biological and robotic locomotion.
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.
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.
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.
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.
11171759
A Study of Priority Cognizance in Conflict Resolution for Firm Real-Time Database Systems
Real-Time Database Systems (RTDBSs)must meet time constraints in addition to the integrity constraints present in most other database systems. From the late 1980s a significant amount of research work has been performed on the design and performance evaluation of Concurrency Control Mechanisms (CCMs) for RTDBSs [5, 4,7, 8, 11]. Given the spate of papers on (firm) real-time CCMs of the late 80s and early 90s, there appears to have been a reduction in the number of papers in recent years. More recent works (e.g., [6]) study non-traditional real-time scenarios. We have not been able to discover papers reporting significant performance gains from CC strategies designed for traditional firm RTDBS in the past few years. One plausible explanation is that performance gains are harder to achieve. One way in which higher performances can potentially be reached is by utilizing priority information in conflict-resolution. Indeed, the authors of [5] ask the question “How can the priorities be used to improve the performance of the optimistic algorithm?”.
40462435
A concurrency control mechanism based on extendible hashing for main memory database systems
A non-preemptive deadlock-free concurrency control mechanism based on extendible hashing has been presented for main memory database system. The algorithm makes use of the verification process of the optimistic concurrency control algorithm and two-phase locking policy to manage concurrent operations on sharable data. We also present a comparison of our algorithm with other two-phase locking mechanisms and show that our algorithm is more robust, easier to implement and provides a higher degree of concurrency than other algorithms on extendible hash file.
1752850
High Performance Data Mining
Recent times have seen an explosive growth in the availability of various kinds of data. It has resulted in an unprecedented opportunity to develop automated data-driven techniques of extracting useful knowledge. Data mining, an important step in this process of knowledge discovery, consists of methods that discover interesting, non-trivial, and useful patterns hidden in the data [SAD+93, CHY96]. The field of data mining builds upon the ideas from diverse fields such as machine learning, pattern recognition, statistics, database systems, and data visualization. But, techniques developed in these traditional disciplines are often unsuitable due to some unique characteristics of today's data-sets, such as their enormous sizes, high-dimensionality, and heterogeneity. There is a necessity to develop effective parallel algorithms for various data mining techniques. However, designing such algorithms is challenging, and the main focus of the paper is a description of the parallel formulations of two important data mining algorithms: discovery of association rules, and induction of decision trees for classification. We also briefly discuss an application of data mining to the analysis of large data sets collected by Earth observing satellites that need to be processed to better understand global scale changes in biosphere processes and patterns.
206849499
Recovery in Main Memory Database Systems
In this paper we present a recovery mechanism for main memory database, which does not treat volatile RAM as a buffer and uses a limited size non-volatile RAM for efficient logging and archiving. It allows database recovery in parallel to the execution of normal transactions, it combines Undo and Redo into a single operation in many situations and eliminates the need for checkpointing. Under partial recovery our algorithm manages to identify and recovers only dirty data for bringing the entire database into a consistent state.
14504228
Location dependent data and its management in mobile databases
In traditional ways of managing data, the relationship between the data and the geographical location of the organization it represents, is usually ignored. In wireless computing this property of "location transparency" is in fact often replaced by a "location dependency" property. Furthermore, the mode of issuing queries (the geographical location where the queries originate, the way they are issued, etc.) on such data determines the outcome. Location dependent data is data whose value depends on its location. The objective of the paper is to introduce this topic and spawn further related research.