5968452
Visual and haptic collaborative tele-presence
Abstract The core of a successful sense of presence is a visually, aurally, and haptically compelling experience. In this paper, we introduce the integration of vision and haptics for the purposes of remote collaboration. A remote station acquires a 3D-model of an object of interest which is transmitted to a local station. A user in the local station manipulates a virtual and the remote object as if he/she is haptically and visually at the remote station. This tele-presence feeling is achieved by visually registering the head-mounted display of the local user to the remote world and by dynamically registering the local object both visually and haptically with respect to the remote world. This can be achieved by adequate modeling and feedforward compensation including gravity compensation for the robotic manipulator with which the operator interacts. We present multiple scenarios where such a capability will be useful. One is remote design where a user tests a remotely designed docking station by inserting a virtual laptop into a model of the 3D docking station transmitted from a remote site. Medical robotics provides another possible scenario in which a resident is given surgical training to perform a virtual laparoscopy on a 3D exterior model of a patient, including tomographic registration of anatomical structures. We present results from numerous experiments from both the visual and haptic aspects as well as in integrated form.
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.
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.
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.
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.
7638167
Congruences for Visibly Pushdown Languages
We study congruences on words in order to characterize the class of visibly pushdown languages (Vpl), a subclass of context-free languages. For any language L, we define a natural congruence on words that resembles the syntactic congruence for regular languages, such that this congruence is of finite index if, and only if, L is a Vpl. We then study the problem of finding canonical minimal deterministic automata for Vpls. Though Vpls in general do not have unique minimal automata, we consider a subclass of VPAs called k-module single-entry VPAs that correspond to programs with recursive procedures without input parameters, and show that the class of well-matched Vpls do indeed have unique minimal k-module single-entry automata. We also give a polynomial time algorithm that minimizes such k-module single-entry VPAs.
5147118
Location dependent query processing
The advances in wireless and mobile computing allow a mobile user to perform a wide range of aplications once limited to non-mobile hard wired computing environments. As the geographical position of a mobile user is becoming more trackable, users need to pull data which are related to their location, perhaps seeking information about unfamiliar places or local lifestyle data. In these requests, a location attribute has to be identified in order to provide more efficient access to location dependent data, whose value is determined by the location to which it is related. Local yellow pages, local events, and weather information are some of the examples of these data.
In this paper, we give a formalization of location relatedness in queries. We differentiate location dependence and location awareness and provide thorough examples to support our approach.
8261257
TCOT-A Timeout-Based Mobile Transaction Commitment Protocol
We present a transaction commit protocol, "Transaction Commit On Timeout (TCOT)," based on a "timeout" approach for Mobile Database Systems (MDS), which can be universally used to reach a final transaction termination decision (e.g., commit, abort, etc.) in any message-oriented system. Particularly suited for a wireless environment, a timeout mechanism is the only way to minimize the impact of the slow and unreliable wireless link. We compare TCOT to a modified version of 2PC to show its superiority based on commit time.
10751860
Multilevel Diffusion Schemes for Repartitioning of Adaptive Meshes
For a large class of irregular mesh applications, the structure of the mesh changes from one phase of the computation to the next. Eventually, as the mesh evolves, the adapted mesh has to be repartitioned to ensure good load balance. If this new graph is partitioned from scratch, it may lead to an excessive migration of data among processors. In this paper, we present schemes for computing repartitionings of adaptively refined meshes that perform diffusion of vertices in a multilevel framework. These schemes try to minimize vertex movement without significantly compromising the edge-cut. We present heuristics to control the tradeoff between edge-cut and vertex migration costs. We also show that multilevel diffusion produces results with improved edge-cuts over single-level diffusion, and is better able to make use of heuristics to control the tradeoff between edge-cut and vertex migration costs than single-level diffusion.
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.