Günter Hommel

Disseminating messages among highly mobile hosts based on inter-vehicle communication

We present an approach to distributing messages among highly mobile hosts in ad hoc networks. We focus on using direct radio communication between moving vehicles on the road that requires no additional infrastructure. Thus, the vehicles need to organize access to the radio channel in a decentralized manner. We derive the medium access control from the standard IEEE 802.11. Also, the vehicles use omnidirectional antennas implying that a sender can transit to multiple hosts simultaneously. As an example, we study a road accident that is reported to nearby vehicles. Simulations show that the quality of the proposed protocol by measuring how many vehicles inside a zone-of-relevance are informed under various conditions.

Role-based multicast in highly mobile but sparsely connected ad hoc networks

We present an approach to multicasting messages among highly mobile hosts in ad hoc networks. We suggest a new definition of a role-based multicast that suits the special needs of inter-vehicle communication: rather than by explicit identification, a multicast group is defined implicitly by location, speed, driving direction and time. As an example, we study a road accident that is reported to nearby vehicles. We focus on sparse deployment of the system which is likely to occur soon after the system is introduced to the market. In this state, the resulting ad hoc network tends to be disconnected. We tailor the proposed algorithm to overcome this problem of network fragmentation. Simulations show us the quality of the proposed protocol by measuring how many vehicles inside a multicast area are informed in time under various conditions.

A Human--Exoskeleton Interface Utilizing Electromyography

This paper presents a human--machine interface to control exoskeletons that utilizes electrical signals from the muscles of the operator as the main means of information transportation. These signals are recorded with electrodes attached to the skin on top of selected muscles and reflect the activation of the observed muscle. They are evaluated by a sophisticated but simplified biomechanical model of the human body to derive the desired action of the operator. A support action is computed in accordance to the desired action and is executed by the exoskeleton. The biomechanical model fuses results from different biomechanical and biomedical research groups and performs a sensible simplification considering the intended application. Some of the model parameters reflect properties of the individual human operator and his or her current body state. A calibration algorithm for these parameters is presented that relies exclusively on sensors mounted on the exoskeleton. An exoskeleton for knee joint support was designed and constructed to verify the model and to investigate the interaction between operator and machine in experiments with force support during everyday movements.

TimeNET: a toolkit for evaluating non-Markovian stochastic Petri nets

Stochastic Petri nets are well suited for the model-based performance and dependability evaluation of complex systems. Most commonly, the firing times of the transitions are exponentially distributed, leading to an underlying continuous-time Markov chain. In order to increase the modeling power, several classes of non-Markovian SPNs were defined, in which the transitions may fire after a nonexponentially distributed firing time. TimeNET (Timed Petri Net Evaluation Tool) is a software package for the modeling and evaluation of SPNs in which the firing times of the transitions may be exponentially distributed, deterministic, or more generally distributed. TimeNET has been developed at the Technical University of Berlin in several research projects.

Development and control of a hand exoskeleton for rehabilitation of hand injuries

Hand injuries are a frequent problem. The great amount of hand injuries is not only a problem for the affected people but economic consequences follow because rehabilitation takes a long time. Physical therapy after an operation is associated with high personnel expenses. To improve therapy results and reduce cost of rehabilitation a hand exoskeleton was developed. The hand exoskeleton was specifically designed to accomplish requirements of medical applications. For research on control algorithms and rehabilitation programs a prototype supporting all four degrees of freedom of one finger was build. The device can be easily attached and also be adjusted to deformed and scarred hands. In view of the fact that a lot of hand injuries affect only one finger, this prototype could already be functional in physical therapy. This paper presents the construction and the control system of the hand exoskeleton and possible applications in therapy of hand injuries. For the position control a PID controller was implemented and evaluated. The resulting control system allows following of recorded trajectories with sufficient accuracy.

Petri Net Modelling and Performability Evaluation with TimeNET 3.0

This paper presents TimeNET, a software tool for the modelling and performability evaluation using stochastic Petri nets. The tool has been designed especially for models with non-exponentially distributed firing delays. A general overview of the software package and its new features is given. The graphical user interface is completely rewritten. It integrates different model classes in a user-friendly and consistent way. One of the recent enhancements is an environment for the modelling and performance evaluation of manufacturing systems based on coloured stochastic Petri nets. A manufacturing system is modelled and analysed as an application example.

Predicting the intended motion with EMG signals for an exoskeleton orthosis controller

In this paper, we present a method to calculate the intended motion of joints in the human body by analysing EMG signals. Those signals are emitted by the muscles attached to the adjoining bones during their activation. With the resulting intended motion, a leg orthosis can be controlled in realtime to support disabled people while walking or climbing stairs and help patients suffering from the effects of a stroke in their rehabilitation efforts. To allow a variety of different motions, a human body model with physical properties is developed and synchronized with data recorded from the pose sensors. Computing the intended motion is performed by converting calibrated EMG signals to muscle forces which animate the model. The algorithm was evaluated with experiments showing the calculated intended motion while climbing one step of a stair. The algorithm and the experimental results are both shown.

Application of EMG signals for controlling exoskeleton robots.

Abstract Exoskeleton robots are mechanical constructions attached to human body parts, containing actuators for influencing human motion. One important application area for exoskeletons is human motion support, for example, for disabled people, including rehabilitation training, and for force enhancement in healthy subjects. This paper surveys two exoskeleton systems developed in our laboratory. The first system is a lower-extremity exoskeleton with one actuated degree of freedom in the knee joint. This system was designed for motion support in disabled people. The second system is an exoskeleton for a human hand with 16 actuated joints, four for each finger. This hand exoskeleton will be used in rehabilitation training after hand surgeries. The application of EMG signals for motion control is presented. An overview of the design and control methods, and first experimental results for the leg exoskeleton are reported.

Towards modeling and evaluation of ETCS real-time communication and operation

The future European Train Control System (ETCS) will be based on mobile communication and overcome fixed blocks. It is introduced in order to increase track utilization and interoperability throughout Europe while reducing trackside equipment cost. Data processing on board the train and in radio block centers as well as the radio communication link are crucial factors for the safe and efficient operation. Their real-time behavior under inevitable link failures needs to be modeled and evaluated. The paper presents a stochastic Petri net model of communication failure and recover behavior. A second model for the exchange of location and movement authority data packets between trains and radio block centers is presented and analyzed. Performance evaluation of the model shows the significant impact of packet delays and losses on the reliable operation of high-speed trains.

Mechanical design and motion control of a hand exoskeleton for rehabilitation

Hand injuries are a frequent problem. The great amount of hand injuries is not only a problem for the affected people but economic consequences follow because rehabilitation takes a long time. To improve therapy results and reduce cost of rehabilitation a hand exoskeleton was developed. For research on control algorithms and rehabilitation programs a prototype supporting all four degrees of freedom of one finger was built (s. Fig. 1). In view of the fact that a lot of hand injuries affect only one finger, this prototype could already be functional in physical therapy. A robust sliding mode controller was proposed for motion control of the hand exoskeleton. The performance of the controller was evaluated for step response. In a second experiment varied forces where applied during the sensor was set to hold a constant position. Finally the controller was set to follow a complete trajectory.