Thomas Röfer

Vision-based fast and reactive Monte-Carlo localization

This paper presents a fast approach for vision-based self-localization in RoboCup. The vision system extracts the features required for localization without processing the whole image and is a fist step towards independence of lighting conditions. In the field of self-localization, some new ideas are added to the well-known Monte Carlo localization approach that increase both stability and reactivity, while keeping the processing time low.This paper presents a fast approach for vision-based self-localization in RoboCup. The vision system extracts the features required for localization without processing the whole image and is a fist step towards independence of lighting conditions. In the field of self-localization, some new ideas are added to the well-known Monte Carlo localization approach that increase both stability and reactivity, while keeping the processing time low.

SimRobot – a general physical robot simulator and its application in robocup

This paper describes SimRobot, a robot simulator which is able to simulate arbitrary user-defined robots in three-dimensional space. It includes a physical model which is based on rigid body dynamics. To allow an extensive flexibility in building accurate models, a variety of different generic bodies, sensors and actuators has been implemented. Furthermore, the simulator follows an user-oriented approach by including several mechanisms for visualization, direct actuator manipulation, and interaction with the simulated world. To demonstrate the general approach, this paper presents multiple examples of different robots which have been simulated so far.

A versatile and safe mobility assistant

The Bremen autonomous wheelchair implements obstacle avoidance plus driving and routing assistance in a shared-control system. This article shows how the tasks of reliably detecting obstacles in the environment and safely avoiding these obstructions are solved.

Architecture and applications of the Bremen Autonomous Wheelchair

Abstract This article presents the Bremen Autonomous Wheelchair as a platform for the realization of rehabilitation applications. In the field of assistive technologies, the necessities for safety on the one hand and adaptability to various impairments of potential users on the other hand dominate design decisions. A safe system architecture for the Bremen Autonomous Wheelchair is proposed and a hierarchy of low level application modules is presented. Furthermore, a route navigation approach that provides a high level of support is described in detail.

Navigating a smart wheelchair with a brain-computer interface interpreting steady-state visual evoked potentials

In order to allow severely disabled people who cannot move their arms and legs to steer an automated wheelchair, this work proposes the combination of a non-invasive EEG-based human-robot interface and an autonomous navigation system that safely executes the issued commands. The robust classification of steady-state visual evoked potentials in brain activity allows for the seamless projection of qualitative directional navigation commands onto a frequently updated route graph representation of the environment. The deduced metrical target locations are navigated to by the application of an extended version of the well-established nearness diagram navigation method. The applicability of the system proposed is demonstrated by a real-world pilot study in which eight out of nine untrained subjects successfully navigated an automated wheelchair, requiring only some ten minutes of preparation.

Evolutionary gait-optimization using a fitness function based on proprioception

This paper presents a new approach to optimize gait parameter sets using evolutionary algorithms. It separates the crossover-step of the evolutionary algorithm into an interpolating step and an extrapolating step, which allows for solving optimization problems with a small population, which is an essential for robotics applications. In contrast to other approaches, odometry is used to assess the quality of a gait. Thereby, omni-directional gaits can be evolved. Some experiments with the Sony Aibo models ERS-210 and ERS-7 prove the performance of the approach including the fastest gait found so far for the Aibo ERS-210.

Fast and Robust Edge-Based Localization in the Sony Four-Legged Robot League

This paper presents a fast approach for edge-based self-localization in RoboCup. The vision system extracts edges between the field and field lines, borders, and goals following a grid-based approach without processing whole images. These edges are employed for the self-localization of the robot. Both image processing and self-localization work in real-time on a Sony Aibo, i. e. at the frame rate of the camera. The localization method was evaluated using a laser range sensor at the field border as a reference system.

A Taxonomy of Spatial Knowledge for Navigation and its Application to the Bremen Autonomous Wheelchair

A new taxonomy is proposed that relates different navigational behaviors in a hierarchical and compositional way. Elementary navigation tactics are combined to tactical navigation in routes; landmarks in space are contrasted to routemarks in networks of passages. Survey knowledge comes in at the level of strategic navigation. The Bremen Autonomous Wheelchair is then presented as a vehicle for experimentation in robotics, both to model biologically plausible navigational behaviors and to develop efficient navigational mechanisms for a technical application. The implementation on the autonomous system is based on the use of basic behaviors and the identification of routemarks. The actual recognition of artificial routemarks is described and early results of the current work on the identification of natural 3-D marks are presented.

Controlling an automated wheelchair via joystick/head-joystick supported by smart driving assistance

With this work, we encourage the application of smart driving assistance algorithms to support the operator of an automated wheelchair in complex navigational situations. On the basis of an empirical study in which eight untrained subjects performed a given course using a conventional joystick and a proportional head-joystick respectively, we are able to prove benefits resulting from the application of a newly developed driving assistance module. Altering the translational and rotational velocities in situations where an obstacle blocks the user-commanded way, the driving assistance module significantly improves driver-performance by preventing all collisions along the way.

A behavior architecture for autonomous mobile robots based on potential fields

This paper describes a behavior-based architecture which integrates existing potential field approaches concerning motion planning as well as the evaluation and selection of actions into a single architecture. This combination allows, together with the concept of competing behaviors, the specification of more complex behaviors than the usual approach which is focusing on behavior superposition and is mostly dependent on additional external mechanisms. The architecture and all methods presented in this paper have been implemented and applied to different robots.