Achim Wagner

Image-guided surgery

Interventional video tomography (IVT), a new imaging modality, achieves virtual visualization of anatomic structures in three dimensions for intraoperative stereotactic navigation. Partial immersion into a virtual data space, which is orthotopically coregistered to the surgical field, enhances, by means of a see-through head-mounted display (HMD), the surgeons visual perception and technique by providing visual access to nonvisual data of anatomy, physiology, and function. The presented cases document the potential of augmented reality environments in maxillofacial surgery.

Dispersive ionic space charge relaxation in solid polymer electrolytes. - II. Model and simulation

Dynamic Monte-Carlo simulations of ionic space charge relaxations are carried out using a three-dimensional model for thermally activated ion hopping in a multiwell energy structure. In this model a solid polymer electrolyte is embedded between two ideal blocking electrodes. The polymer is subdivided into 100×100×100 lattice cells. Positive ions (typically 1000) are distributed on the cells. To provide charge neutrality a negative background charge, constant in space and time, is introduced. The positive ions are able to hop between neighboring cells, surmounting energy barriers of distributed heights. The barrier heights consist of an intrinsic part due to the polymer structure, a part due to the Coulomb interaction of the ions, and a part due to the externally applied field. To calculate the interaction between the ions and the electrodes a method of images is used. Periodical boundary conditions are used for those lattice surfaces which are not in contact with the electrodes. The ionic space charge pol...

Dispersive ionic space charge relaxation in solid polymer electrolytes. I. Experimental system polyethylene oxide

As a model system for solid polymer electrolytes thin polyethylene oxide (PEO) films (0.6–30 μm) are prepared as Al–PEO–Al and as Al–PEO–Si structures with blocking electrodes. Dielectric measurements (capacitance and loss angle) are carried out in a frequency range of 3 mHz⩽f⩽1 MHz in atmospheres of different relative humidities (0%–75%) and at different temperatures (293–313 K). The nominal permittivity varies from 4 at high frequencies to up to 150 000 at low frequencies. We find true volume polarization in the high frequency range and a thermally activated space charge relaxation process in the low frequency range. Its time constant exhibits a remarkable dependence on the sample thickness, the relative humidity, the ion concentration, and the temperature. Due to the absorbed dipolar water molecules the activation energy of this process is decreased, leading to higher mobility of the ions. An increase in ion concentration also leads to a lower activation energy. The ions are able to move through the sa...

Cascaded Kalman and particle filters for photogrammetry based gyroscope drift and robot attitude estimation

Based on a cascaded Kalman-Particle Filtering, gyroscope drift and robot attitude estimation method is proposed in this paper. Due to noisy and erroneous measurements of MEMS gyroscope, it is combined with Photogrammetry based vision navigation scenario. Quaternions kinematics and robot angular velocity dynamics with augmented drift dynamics of gyroscope are employed as system state space model. Nonlinear attitude kinematics, drift and robot angular movement dynamics each in 3 dimensions result in a nonlinear high dimensional system. To reduce the complexity, we propose a decomposition of system to cascaded subsystems and then design separate cascaded observers. This design leads to an easier tuning and more precise debugging from the perspective of programming and such a setting is well suited for a cooperative modular system with noticeably reduced computation time. Kalman Filtering (KF) is employed for the linear and Gaussian subsystem consisting of angular velocity and drift dynamics together with gyroscope measurement. The estimated angular velocity is utilized as input of the second Particle Filtering (PF) based observer in two scenarios of stochastic and deterministic inputs. Simulation results are provided to show the efficiency of the proposed method. Moreover, the experimental results based on data from a 3D MEMS IMU and a 3D camera system are used to demonstrate the efficiency of the method.

Collision avoidance in a recursive nested behaviour control structure for Unmanned Aerial Vehicles

In this paper, the collision avoidance behaviour in a recursive nested behaviour control structure for Unmanned Aerial Vehicles will be discussed. The architecture is an extension of the behaviour-based recursive control structure, which has been applied successfully to mobile robot applications. The system structure, as an abstraction of multiple cascaded control loops with feedback mechanisms, is robust against disturbances and model uncertainties. The obstacle awareness and collision avoidance are considered to be the most important issues in the field of Unmanned Aerial Vehicles (UAV), thus more attention will be paid to this topic. The collision avoidance utilizes a potential field method tailored for UAV application domain. The formulation of a repulsion forces based on radar sensor measurement is presented. The implementation of the collision avoidance system is also described.

Easing Wheelchair Control by Gaze-based Estimation of Intended Motion

Abstract An assistive system easing wheelchair control for severely disabled users is presented. To compensate for the restricted information that can be provided using speciality controls, the persons gaze is used to estimate the intended motion direction. The novelty of the presented method is that motion-relevant portions of natural gaze behavior can be distinguished from non-relevant. Producing wheelchair movement only from relevant gaze information leads to an increased acceptance of powered wheelchairs in the user group and to improved safety.

Modified particle petri nets for hybrid dynamical systems monitoring under environmental uncertainties

A real-time system in its environment constitutes a complex dynamic system (in general hybrid), which requires the development of new methods of modeling and monitoring. This paper presents the Modified Particle Petri nets (MPPN) approach, which combines Petri nets and particle filtering in order to model and monitor Hybrid Dynamical Systems (HDS) and their interaction with the environment. The approach considers the uncertainty of the process on both discrete and continuous variables as well as the environmental uncertainties. It presents relevant concepts of Petri nets within a probabilistic framework and how uncertainty is introduced (i) in the hybrid marking of the Petri net in order to represent an uncertain knowledge about all next possible hybrid states (ii) as well as in the process noise, which is incorporated into the filter. A marking updating of the Petri nets according to noisy measurements made by the system and a decision making algorithm are then used in order to estimate the hybrid system state, to detect inconsistencies and to attribute these to different kinds of faults. An example of mobile robot application modeled using MPPN is presented to show the usability of the approach.

Individual Ability-Based System Design of Dependable Human-Technology Interaction

Abstract This paper highlights the importance of considering especially individual differences in intelligence when designing systems and interfaces due to their impact on operator performance in new and unfamiliar situations. For this purpose, an approach is introduced which allows assessing performance-relevant abilities of the operators on the basis of their performance on everyday life tasks. In order to increase the overall human-machine system dependability, guidelines are derived about appropriate reconfigurations of the technical system and/or its interface on the basis of the assessed performance-relevant abilities. The impact of this new approach to dependable system and interface design is discussed.

A comment on dielectric hole burning

The method of dielectric hole burning is used to distinguish a homogeneous broadened spectrum from a distribution of relaxation times in a dielectric material. After stimulation with a sinusoidal high electric field a time-dependent shift of the response function Φ(t) is observed. This shift is considered to be induced by a frequency selective absorption of energy and an increase of a local fictive temperature. A computer simulation, which is based upon the model of asymmetric double-well potentials for dipole orientations, also shows a time-dependent shift of the response function after applying and removing a sinusoidal high electric field. This behavior is explained considering the time-dependent polarization only. It is shown in this article that it is not necessary to assume an increase of a local fictive temperature caused by a frequency selective absorption of energy.

Generic system architecture for dependable interactive systems: A flying robot example

A generic system architecture for dependable interactive systems is proposed. The architecture is an extension of the behavior-based recursive control structure, which has already been applied successfully to robotic applications. The interaction between multiple robots or between a human user and robotic systems takes place on multiple behavioral levels providing fixed interfaces. A complex system is decomposed into levels according to the dynamics of behaviors and bandwidth of the interfaces. Signals from and to multimodal interface devices are processed according to the behavior-related information contents and fused within the behavior levels. The system structure, as an abstraction of multiple cascaded control loops with feedback mechanisms, is robust against disturbances and model uncertainties. The usage of the generic system architecture is demonstrated on the example of a semi-autonomous flying robot.