1176742
Dynamic role assignment for cooperative robots
Proposes a methodology for coordinating multi-robot teams in the execution of cooperative tasks. It is based on a dynamic role-assignment mechanism in which the robots assume and exchange roles during cooperation. We model the role assignment under a hybrid systems framework, using a hybrid automaton to represent roles, transitions and controllers. Using a multi-robot simulator, the methodology is demonstrated in a cooperative transportation task, in which a group of robots must find and cooperatively transport several objects scattered in the environment.
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.
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.
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.
34436430
An Integrated Data Structure with Multiple Access Paths for Database Systems and its Performance
Abstract In the past a number of file organizations have been proposed for processing different types of queries efficiently. To our knowledge none of the existing file organizations is capable of supporting all types of accesses equally efficiently. In this paper we have taken a different approach for designing an integated data structure which offers multiple access paths for processing different types of queries efficiently. The data structure reported here can be implemented on disk based as well as main memory database systems, however, in this paper we report its behavior mainly in main memory database environment. Our approach is to fuse those data structures which offer an efficient access paths for a particular type. To show the feasibility of our scheme we fused the B+-tree, the grid file and extendible hashing structures, using a proper interface. We implemented and measured its performance through simulation modeling. Our results show that the data structure does improve concurrency and offers a higher throughput for a variety of transaction processing workloads. We argue that our scheme is different than creating secondary indexes for improving concurrency. In the absence of a data strucure which can provide all types of access equally efficiently, an integrated data structure is an acceptable solution which offers an efficient way for increasing the performance of database management systems.
39362526
Main memory database recovery algorithms and their performance
In main memory systems recovery becomes more complex mainly due to the volatility of main memory and the elimination of the separation of data storage (disk) and data processing locations (main memory). In a disk based database system, it is the disk copy that represents the stable database restored after a system failure; but in MDBSs, the main memory copy of the database must be recovered. The paper discusses the recovery issues in MDBSs and presents a somewhat detailed performance study of two recovery algorithms, one using a shadow approach and the other update-in-place.<<ETX>>
18344625
Concurrent operations on extendible hashing and its performance
Extendible hashing is a dynamic data structure which accommodates expansion and contraction of any stored data efficiently. In this article, an algorithm has been developed for managing concurrent operations on extendible hashing by achieving optimal memory utilization by supporting directly expansion and contraction, page split, and merge. The results of this study have been encouraging in the sense that it seems to provide a higher degree of concurrency compared to other algorithms on an extendible hash file.
27496319
An efficient CCM KRISHNA for high contention environment and its performance comparison with WDL
Abstract Commonly known concurrency control mechanisms (CCMs) based on two-phase locking are known to be unsuitable for high contention environment. One of the main reasons for their inefficiency is the high level of wasted work, which occurs because of redundant roll-backs, and inappropriate blocking in resolving conflicts. This happens mainly because these CCMs resolve conflicts using pre-defined policies; an approach which sets a limit on their efficiency. Recently a class of CCM, called Wait Depth Limited (WDL) has appeared in the literature, which claims to overcome some of these problems. We also recognize limitations and unsuitability of commonly known locking based CCMs for high contention environment, and present a class of CCMs called KRISHNA which offers a simple heuristic based and efficient solutions to these problems. We establish our claim with a detail simulation study and show that one of the CCMs of KRISHNA class outperforms WDL class in the majority of high contention environments. We argue that our CCMs are based on a simple approach, and are easy and cheaper to implement.
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.