Evangelos E. Milios

IROS Conference 2007 Conference Paper

Robust design for bilateral teleoperation system with Markov jumping parameters

• Weimin Shen
• Jason Jianjun Gu
• Evangelos E. Milios

This paper presents a robust design for the general bilateral teleoperation system with Markov jumping parameters. Although passivity-based approach and robust design-based approach can stabilize the bilateral teleoperation system, sufficient conditions are too conservative. In this paper, requirements for a general bilateral teleoperation system are given first. Next, time delays on the internet are modeled by a Markov process with nine states, three for the forward communication branch and three for the backward communication branch. Based on the requirements of the master and the slave controllers, the standard robust design are carried out. Then, with the model of internet time delays, the bilateral teleoperation system is reconstructed by a Markov jumping system. Based on the mode-dependent stability conditions for the stochastic time delay system, the closed-loop controller is designed to obtain the less conservative stable system and to therefore improve the performance of tracking and transparency. Simulation has been carried out and the results verify the feasibility and efficiency of the proposed approach.

IROS Conference 2005 Conference Paper

A visually guided swimming robot

• Gregory Dudek
• Michael Jenkin
• Chris Prahacs
• Andrew Hogue
• Junaed Sattar
• Philippe Giguère
• Andrew German
• Hui Liu

We describe recent results obtained with AQUA, a mobile robot capable of swimming, walking and amphibious operation. Designed to rely primarily on visual sensors, the AQUA robot uses vision to navigate underwater using servo-based guidance, and also to obtain high-resolution range scans of its local environment. This paper describes some of the pragmatic and logistic obstacles encountered, and provides an overview of some of the basic capabilities of the vehicle and its associated sensors. Moreover, this paper presents the first ever amphibious transition from walking to swimming.

IROS Conference 2005 Conference Paper

Vision data registration for robot self-localization in 3D

• Pifu Zhang
• Evangelos E. Milios
• Jason Jianjun Gu

We address the problem of globally consistent estimation of the trajectory of a robot arm moving in three dimensional space based on a sequence of binocular stereo images from a stereo camera mounted on the tip of the arm. Correspondence between 3D points from successive stereo camera positions is established through matching of 2D SIFT features in the images. We compare three different methods for solving this estimation problem, based on three distance measures between 3D points, Euclidean distance, Mahalanobis distance and a distance measure defined by a maximum likelihood formulation. Theoretical analysis and experimental results demonstrate that the maximum likelihood formulation is the most accurate. If the measurement error is guaranteed to be small, then Euclidean distance is the fastest, without significantly compromising accuracy, and therefore it is best for on-line robot navigation.

IROS Conference 2004 Conference Paper

AQUA: an aquatic walking robot

• Christina Georgiades
• Andrew German
• Andrew Hogue
• Hui Liu
• Chris Prahacs
• Arlene Ripsman
• Robert Sim
• Luz Abril Torres-Méndez

This paper describes an underwater walking robotic system being developed under the name AQUA, the goals of the AQUA project, the overall hardware and software design, the basic hardware and sensor packages that have been developed, and some initial experiments. The robot is based on the RHex hexapod robot and uses a suite of sensing technologies, primarily based on computer vision and INS, to allow it to navigate and map clear shallow-water environments. The sensor-based navigation and mapping algorithms are based on the use of both artificial floating visual and acoustic landmarks as well as on naturally occurring underwater landmarks and trinocular stereo.

IROS Conference 2003 Conference Paper

Experiments in free-space triangulation using cooperative localization

• Ioannis M. Rekleitis
• Gregory Dudek
• Evangelos E. Milios

This paper presents a first detailed case study of collaborative exploration of a substantial environment. We use a pair of cooperating robots to test multi-robot environment mapping algorithms based on triangulation of free space. The robots observe one another using a robot tracking sensor based on laser range sensing (LIDAR). The environment mapping itself is accomplished using sonar sensing. The results of this mapping are compared to those obtained using scanning laser range sensing and the scan matching algorithm. We show that with appropriate outlier rejection policies, the sonar-based map obtained using collaborative localization can be as good or, in fact, better than that obtained using what is typically considered to be a superior sensing technology.

ICRA Conference 2003 Conference Paper

Probabilistic cooperative localization and mapping in practice

• Ioannis M. Rekleitis
• Gregory Dudek
• Evangelos E. Milios

In this paper we present a probabilistic framework for the reduction in the uncertainty of a moving robot pose during exploration by using a second robot to assist. A Monte Carlo Simulation technique (specifically, a Particle Filter) is employed in order to model and reduce the accumulated odometric error. Furthermore, we study the requirements to obtain an accurate yet timely pose estimate. A team of two robots is employed to explore an indoor environment in this paper, although several aspects of the approach have been extended to larger groups. The concept behind our exploration strategy has been presented previously and is based on having one robot carry a sensor that acts as a "robot tracker" to estimate the position of the other robot. By suitable use of the tracker as an appropriate motion-control mechanism we can sweep areas of free space between the stationary and the moving robot and generate an accurate graph-based description of the environment. This graph is used to guide the exploration process. Complete exploration without any overlaps is guaranteed as a result of the guidance provided by the dual graph of the spatial decomposition (triangulation) of the environment. We present experimental results from indoor experiments in our laboratory and from more complex simulated experiments.

IROS Conference 2002 Conference Paper

Multi-robot cooperative localization: a study of trade-offs between efficiency and accuracy

• Ioannis M. Rekleitis
• Gregory Dudek
• Evangelos E. Milios

This paper examines the tradeoffs between different classes of sensing strategy and motion control strategy in the context of terrain mapping with multiple robots. We consider a larger group of robots that can mutually estimate one another's position (in 2D or 3D) and uncertainty using a sample-based (particle filter) model of uncertainty. Our prior work has dealt with a pair of robots that estimate one another's position using visual tracking and coordinated motion. Here we extend these results and consider a richer set of sensing and motion options. In particular, we focus on issues related to confidence estimation for groups of more than two robots.

IROS Conference 2001 Conference Paper

Collaborative exploration for the construction of visual maps

• Ioannis M. Rekleitis
• Robert Sim
• Gregory Dudek
• Evangelos E. Milios

We examine the problem of learning a visual map of the environment while maintaining an accurate pose estimate. Our approach is based on using two robots in a simple collaborative scheme. Without outside information, as a robot collects training images, its position estimate accumulates errors, thus corrupting its knowledge of the positions from which observations are taken. We address this problem by deploying a second robot to observe the first one as it explores, thereby establishing a virtual tether, and enabling an accurate estimate of the robot's position while it constructs the map. We refer to this process as cooperative localization. The images collected during this process are assembled into a representation that allows vision-based position estimation from a single image at a later date. In addition to developing a formalism and concept, we validate our results experimentally and present quantitative results demonstrating the performance of the method in over 90 trials.

ICRA Conference 2000 Conference Paper

Multi-Robot Collaboration for Robust Exploration

• Ioannis M. Rekleitis
• Gregory Dudek
• Evangelos E. Milios

This paper presents a new sensing modality and stratagem for multirobot exploration. The approach is based on using pairs of robots that observe each other's behavior, acting in concert to reduce odometry errors. We assume the robots can both directly sense nearby obstacles and see each other. This allows the robots to obtain a map of higher accuracy than would be possible with robots acting independently by reducing inaccuracies that occur over time from dead reckoning errors. Furthermore, by exploiting the ability of the robots to see each other, we can detect opaque obstacles in the environment independently of their surface reflectance properties. Two different algorithms, based on the size of the environment, are introduced with a complexity analysis, and experimental results in simulation and with real robots.

IJCAI Conference 1997 Conference Paper

Multi-Robot Exploration of an Unknown Environment, Efficiently Reducing the Odometry Error

• Ioannis M. Rekleitis
• Gregory Dudek
• Evangelos E. Milios

This paper deals with the intelligent exploration of an unknown environment by autonomous robots. In particular, we present an algorithm and associated analysis for collaborative exploration using two mobile robots. Our approach is based on robots with range sensors limited by distance. By appropriate behavioural strategies, we show that odometry (motion) errors that would normally present problems for mapping can be severely reduced. Our analysis includes polynomial complexity bounds and a discussion of possible heuristics.

IROS Conference 1995 Conference Paper

Experiments in sensing and communication for robot convoy navigation

• Gregory Dudek
• Michael Jenkin
• Evangelos E. Milios
• David Wilkes

This paper deals with coordinating behaviour in a multi-autonomous robot system. When two or more autonomous robots must interact in order to accomplish some common goal, communication between the robots is essential. Different inter-robot communications strategies give rise to different overall system performance and reliability. After a brief consideration of some theoretical approaches to multiple robot collections, we present concrete implementations of different strategies for convoy-like behaviour. The convoy system is based around two RWI B12 mobile robots and uses only passive visual sensing for inter-robot communication. The issues related to different communication strategies are considered.

ICRA Conference 1995 Conference Paper

Optimal Global Pose Estimation for Consistent Sensor Data Registration

• Feng Lu 0001
• Evangelos E. Milios

We consider the problem of consistent range data registration in modeling an unknown environment. The problem is expressed as the optimal estimation of pose variables under the maximum likelihood criterion. By treating all the history of robot poses as variables and solving them simultaneously, consistency is enforced. We formulate relative pose constraints from both matched scans and odometry measurements to construct a network of measurements. Then we derive closed-form pose estimates as well as their covariance matrices. Examples of global scan registration using both real and simulated data are presented.

ICRA Conference 1995 Conference Paper

Position Estimaton Using Equidistance Lines

• Erwin Prassler
• Evangelos E. Milios

An approach to perception-based position estimation is presented. The approach employs a representation of positional information which is based on a global, curvilinear coordinate system which is grounded in the real world. This coordinate system is spanned by the contours of visible objects and by so-called equidistance lines which are constructed from the object contours. Equidistance lines can be computed from arbitrarily curved contours and do not require an analytical representation of these contours. The main advantage of a spatial representation based on equidistance lines is that it does not depend on the existence of salient spatial features in the environment. Furthermore, the global curvilinear coordinate system allows a straightforward transition between the local frames of reference associated with local perceptions. To estimate the position of a robot vehicle over a sequence of local sensor images requires only a minimal number of object contours to be visible or partially visible in these images and a qualitative correspondence of these object contours to be maintained.

IROS Conference 1994 Conference Paper

ARK: autonomous mobile robot for an industrial environment

• Michael Jenkin
• N. Bains
• J. Bruce
• T. Campbell
• Brian Down
• Piotr Jasiobedzki
• Allan D. Jepson
• B. Majarais

This paper describes research on the ARK (Autonomous Mobile Robot in a Known Environment) project. The technical objective of the project is to build a robot that can navigate and carry out survey/inspection tasks in a complex but known industrial environment. Rather than altering the robots environment by adding easily identifiable beacons the robot relies on naturally occurring objects to use as visual landmarks for navigation. The robot is equipped with various sensors that are used to detect unmapped obstacles, landmarks and objects. This paper describes the robot's industrial environment, it's control architecture, and some results in processing the robot's range and vision sensor data for navigation. >

IROS Conference 1994 Conference Paper

Motion planning amongst arbitrarily moving unknown objects

• Erwin Prassler
• Evangelos E. Milios

An approach to motion planning amongst arbitrarily moving unknown objects is presented. As opposed to other approaches to motion planning we avoid the assumption that the motion parameters and the shape of moving objects are known a priori or can be predicted over longer time intervals. By giving up this assumption, traditional methods such as space-time representation and search in space-time no longer apply. Our approach is based on a massively parallel network of simple processing elements. A relaxation process, which is driven by the simultaneous execution of a simple formula in these processing elements, creates a two-dimensional distribution of real numbers, denoted as potentials, which encodes information about collision-free trajectories. Our approach is different from classical algorithmic motion planning in that we do not employ an analytical planning or search algorithm. Instead, desired behaviors, such as the avoidance of moving objects, are achieved through adroit manipulation of the two-dimensional potential distribution. >

IROS Conference 1993 Conference Paper

A taxonomy for swarm robots

• Gregory Dudek
• Michael Jenkin
• Evangelos E. Milios
• David Wilkes

In many cases several mobile robots (autonomous agents) can be used together to accomplish tasks that would be either more difficult or impossible for a robot acting alone. Many different models have been suggested for the makeup of such collections of robots. In this paper the authors present a taxonomy of the different ways in which such a collection of autonomous robotic agents can be structured. It is shown that certain swarms provide little or no advantage over having a single robot, while other swarms can obtain better than linear speedup over a single robot. There exist both trivial and non-trivial problems for which a swarm of robots can succeed where a single robot will fail. Swarms are more than just networks of independent processors - they are potentially reconfigurable networks of communicating agents capable of coordinated sensing and interaction with the environment.

IROS Conference 1993 Conference Paper

Global navigation for ARK

• Michael Jenkin
• Evangelos E. Milios
• Piotr Jasiobedzki
• N. Bains
• K. Tran

ARK (Autonomous Robot for a Known environment), is a visually-guided mobile robot which is being constructed as part of the Precarn project in mobile robotics. ARK operates in a previously mapped environment and navigates with respect to visual landmarks that have been previously located. While the robot moves, it utilizes an active vision sensor to register the robot with respect to these landmarks. As the landmarks may be scarce in certain regions of its environment, ARK plans paths which minimize both path length and path uncertainty. The global path planner assumes that the robot will use a Kalman filter to integrate landmark information with odometry data to correct path deviations as the robot moves, and then uses this information to choose a path which reduces the expected path deviation.

IROS Conference 1993 Conference Paper

Landmark selection for path execution

• Xiaotie Deng
• Evangelos E. Milios
• Andranik Mirzaian

A commonly used approach to self-location is for the robot to use point features or landmarks. Landmarks are typically difficult to detect and track with video or range sensors, and hence it is sensible to try to minimize the number of times the robot abandons the tracking of an already detected landmark to detect and pursue another. The problem addressed is how to select the landmarks that the robot is to detect and track over different parts of a given path. Several algorithms with different amounts of flexibility, generality and complexity are proposed. The authors address the uniform cost case (all landmarks have equal cost of detection and tracking), and the weighted cost case (each landmark has its own cost). The case of different sets of landmarks having different utility measures is also treated. The algorithm complexity is low-order polynomial in the number of landmarks k, the number of straight line segments of the path, and the number of shadows cast on the path by each landmark, except when taking into account the usefulness of landmarks in groups, which is exponential in k.

IROS Conference 1992 Conference Paper

A Combined Extended Circular Image And Spatial Occupancy Approach To 2-D Contour Matching

• Evangelos E. Milios
• Timothy J. Horton