40202530
Decentralized control of cooperating mobile manipulators
This paper addresses the design and control of autonomous mobile platforms manipulating and transporting a grasped object. Each platform is equipped with a manipulator arm. In order to hold an object in a stable grasp, the arms have to apply and maintain appropriate contact forces to ensure force closure. We describe an architecture and a real time control system that allow the coordinated control of multiple, heterogeneous, mobile manipulators. In this architecture, a lead robot plans, based on available sensory information, and follows a suitable trajectory. The other robots follow a desired formation with respect to the leader while maintaining a stable grasp. There are three main contributions in this paper. We present the real time control system and our approach to rapidly prototype the control code. We describe a novel, forklift-like arm and a control scheme that allows us to easily control the Cartesian stiffness or impedance. Finally, we describe the details of an experimental testbed and results that demonstrate the robustness of the control scheme.
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.
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.
45908534
KRISHNA - Concurrency Control Algorithms based on Dynamic Attributes
Three new concurrency control mechanisms that utilizes the dynamic attribute of concurrent transactions for resolving conflicts are presented. Our study shows that their performance is superior to all well-known two-phase concurrency control mechanisms. There are a large number of such algorithms but we report our findings since our approach has some unique features worth exploring.
4677633
A Strategic Modeling Technique for Change Management in Organizations Undergoing BPR
Modern day organizations seek to rationalize, innovate, and adapt to changing environments, and circumstances as part of Business Process Reengineering (BPR) efforts. Irrespective of the process reengineering program selected, and the technique used to model, BPR brings with it the issues of organizational, and process changes, which involves managing organizational changes (also called “change management”). Change management is non-trivial, as organizational changes are difficult to accomplish. Though some attempt has been made to model change management in enterprise information systems using conventional conceptual modeling techniques, they have just addressed “what” a change process is like, and they don’t address “why” the process is the way it is. Our approach is novel in the sense that it presents an actor-dependency-based 5-phased technique for analyzing, and modeling early-phase requirements of change management that provides the motivations, intents, and rationales behind activities.
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.
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?”.
5622554
Equilibria in topology control games for ad hoc networks
We study topology control problems in ad hoc networks, where network nodes get to choose their power levels in order to ensure desired connectivity properties. Unlike most other work on this topic, we assume that the network nodes are owned by different entities, whose only goal is to maximize their own utility that they get out of the network without considering the overall performance of the network. Game theory is the appropriate tool to study such selfish nodes: we define several topology control games in which the nodes need to choose power levels in order to connect to other nodes in the network to reach their communication partners while at the same time minimizing their costs. We study Nash equilibria and show that -- among the games we define -- these can only be guaranteed to exist if all network nodes are required to be connected to all other nodes (we call this the Strong Connectivity Game). We give asymptotically tight bounds for the worst case quality of a Nash equilibrium in the Strong Connectivity Game and we improve these bounds for randomly distributed nodes. We then study the computational complexity of finding Nash equilibria and show that a polynomial-time algorithm finds Nash equilibria whose costs are at most a factor 2 off the minimum cost possible; for a variation called Connectivity Game, where each node is only required to be connected (possibly via intermediate nodes) to a given set of nodes, we show that answering the question, if a Nash equilibrium exists, is NP-hard, if the network graph satisfies the triangle inequality. For a second game called Reachability Game, where each node tries to reach as many other nodes as possible, while minimizing its radius, we show that 1+o(1)-approximate Nash equilibria exist for randomly distributed nodes. Our work is a first step towards game-theoretic analyses of ad hoc networks.