42239647
Velocity control of mobile manipulators
When a serial-chain manipulator is mounted on a mobile base, the end-effector motion must be decomposed into the motion of the base and the motion of the manipulator. The determination of actuator rates for a given end-effector motion is typically underconstrained. By associating with each joint, a compliance function, local as well as global solutions for the inverse kinematics of kinematically redundant systems can be obtained. The rate decomposition problem is formulated using screw theory. Analytical expressions are obtained for the local solution for perfectly general systems, including those with nonholonomic constraints. Global integral solutions are also obtained using this framework. Nonholonomic systems require that additional constraints be imposed to remove the nonholonomy in the system. The basic goal of allocating the end-effector motion between the manipulator and its mobile base according to user-prescribed preferences is demonstrated using computer simulations and experiments.<<ETX>>
18117520
Control and Coordination of Multiple Mobile Robots in Manipulation and Material Handling Tasks
We describe a framework and control algorithms for coordinating multiple mobile robots with manipulators focusing on tasks that require grasping, manipulation, and transporting large and possibly flexible objects without special purpose fixtures. Because each robot has an independent controller and is autonomous, the coordination and synergy are realized through sensing and communication. The robots can cooperatively transport objects and march in a tightly controlled formation, while also having the capability to navigate autonomously. We describe the key aspects of the overall hierarchy and the basic algorithms, with specific applications to our experimental testbed consisting of three robots.
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.
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.
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.
8409648
Secured Web access
We discuss various secured Web access schemes using dynamic and static approaches. In a static approach the access environment, that is, the set of authorized users, the mode of access, their access rights, etc., are predefined. This approach is suitable only for a static set up where the user requirements do not change frequently. In the dynamic approach, on the other hand, the authorized user set is defined when Web pages access requests appear. An interested user to the Web is authenticated by necessary information provided by the user. Once the information is verified, the user is either given conditional access, timed access, or full access only to the information relevant to the user.
26507710
Graph Partitioning for Dynamic, Adaptive, and Multi-phase Computations
Algorithms that find good partitionings of highly unstructured graphs are critical in developing efficient algorithms for problems in a variety of domains such as scientific simulations that require solution to large sparse linear systems, VLSI design, and data mining. Even though this problem is NP-hard, efficient multi-lev el algorithms have been developed that can find good partitionings of static irregular meshes. The problem of graph partitioning becomes a lot more challenging when the graph is dynamically evolving (e.g., in adaptive computations), or if computation in multiple phases needs to be balanced simultaneously. This talk will discuss these challenges, and then describe some of our recent research in addressing them.
15030712
Impact of mobility on transaction management
We examine the impact of mobility on three different options to managing mobile transactions. Using an analytic performance study we show that no one management approach is always the best and that the performance is impacted by the location management strategy used. The primary objective of this work is to illustrate that the underlying implementation strategies do indeed impact mobile transaction processing and should be considered when proposing mobile transaction processing techniques.
35078097
An adaptive location management algorithm for mobile computing
In mobile computing mobile hosts or mobile units move randomly from one place to another within a well-defined geographical area. This requires some mechanism for identifying the exact location of a mobile host. Such mechanisms are usually referred to as location management and is one of the essential components for supporting mobility. In the past a number of efficient location management schemes have been suggested but they lack adaptability. We believe that an adaptable location management scheme is more desirable because of frequent change in the location of mobile hosts. In this paper, we report a location management algorithm, which adapts to the constant changing scenario. Our algorithm makes use of some of the concepts of location management schemes proposed in the past.
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?”.