Christof Röhrig

The Virtual Lab for controlling real experiments via Internet

The aim of the Virtual Lab project is to provide students access via the Internet to various experiments in control engineering, which are situated in control laboratories at several universities. Three German universities are currently developing the Virtual Lab as a network of remotely accessible laboratories in order to set up a prototype experimental environment. Students under consideration are usually located at geographically distributed location (e.g. at home) and have remote access to our experiments. The Virtual Lab is based on a distance education concept due to the fact that certain students (e.g. professionals) may be interested in studying even at places which are far away from campus eliminating the necessity to be there in person. In the Virtual Lab they are able to gain some practice in control theory at their convenience thereby saving travel time and cost. An approach based on a client/server architecture written in Java is proposed. This paper discusses the requirements of remote experimentation and presents the technical structure and first results of the project.

Indoor location tracking in non-line-of-sight environments using a IEEE 802.15.4a wireless network

Indoor location tracking of mobile robots or transport vehicles using wireless technology is attractive for many applications. IEEE 802.15.4a wireless networks offer an inexpensive facility for localizing mobile devices by time-based range measurements. The main problems of time-based range measurements in indoor environments are errors by multipath and non-line-of-sight (NLOS) signal propagation. This paper describes indoor tracking using range measurements and an Extended Kalman Filter with NLOS mitigation. The commercially available nanoLOC wireless network is utilized for range measurements. The paper presents experimental results of tracking a forklift truck in an industrial environment.

A multiuser virtual-reality environment for a tele-operated laboratory

In engineering studies, concepts taught through lectures are often complemented by laboratory experimentation. This contribution presents a collaborative virtual environment for a tele-operated laboratory. Students have access to the tele-operated laboratory via the Internet from anywhere at any time. They control the experiments exclusively with their standard Web browser; no additional software is needed. The collaborative environment allows the experimentation in a team. Group members are able to interact and discuss the results of their work. A real collaboration, such as in local experimentation, is possible. The tele-operated laboratory is based on a client/server architecture, which is implemented in the Java programming language.

Java-based Framework for Remote Access to Laboratory Experiments

Abstract This paper presents a platform independent approach to remote experimentation. It addresses a wide area of problems occurring in conjunction with remote laboratory experiments, starting with access management procedures via remote control to network- based analysis of measured data. It presents the architecture of the remote laboratory at the University of Hagen. Students have access to the experiments via Internet from anywhere at any time. They control the experiments exclusively with their standard Web browser, no additional software is needed. The remote laboratory is based on a client/server architecture, which is mainly implemented in the Java programming language. The methods and software modules developed for the lab are generic and frequently used in several remote experiments at some German universities. Furthermore the paper discusses the motivation of remote experimentation.

Estimation of position and orientation of mobile systems in a wireless LAN

In this paper, a method to estimate position and orientation of a mobile system in an indoor scenario is described. The proposed method for localizing the mobile system is based on the use of signal strength values of WLAN access points in range. A radio map based method and Euclidean distance in combination with Delaunay triangulation and interpolation is proposed. The radio map method is divided in two phases. In the initial calibration phase, the radio map is built by moving around and storing signal strength values of an omnidirectional antenna and a beam antenna at various predefined points of the indoor environment. In the localization phase the mobile system moves in the same environment and the localization engine estimates position and orientation of the system. The main disadvantage of radio map based methods is the high manual effort to build the map in the calibration phase. The use of Delaunay triangulation and interpolation allows a radio map with a low density of calibration points and reduces the time for manual generation of the map. The paper presents the experimental results of measurements in an office building.

Tracking of transport vehicles for warehouse management using a wireless sensor network

A warehouse management system is a key part of the supply chain and controls the movement of goods within a warehouse. Usually the state of a warehouse is managed in a central database, which must be updated for every storage and retrieval activity. The entire process is prone to errors, because it relies on manual activities performed by employees. This paper presents a technique to monitor the manual transportation processes of goods in a warehouse, in order to update the database automatically. In the proposed scenario, transport vehicles such as forklift trucks or pallet jacks are equipped with wireless sensor nodes and every storage and retrieval activity is reported to the warehouse management system. Tracking of transport vehicles is performed with nanoLOC sensor nodes, which offer range measurement capabilities. This radio positioning system determines the range between two devices by measuring the signal propagation delay. The paper describes the tracking of transport vehicles with range measurements and trilateration using the Extended Kalman Filter. It presents experimental results of tracking a forklift truck in a warehouse.

Localization of Sensor Nodes in a Wireless Sensor Network Using the nanoLOC TRX Transceiver

A wireless sensor network consist of spatially distributed autonomous sensor nodes for data acquisition. Accurate localization of sensor nodes is a strong requirement in a wide area of applications. This paper describes the localization of sensor nodes using range measurements and trilateration with the Extended Kalman Filter. The commercially available nanoLOC sensor network is utilized for range measurements. Experimental results show, that a localization accuracy better than 0.5 m can be achieved in most cases.

Identification and compensation of force ripple in linear permanent magnet motors

The main problem in improving the tracking performance of linear permanent magnet motors is the presence of force ripple caused by the irregular magnetic field of the permanent magnets and inaccuracy in electronic commutation by the servo amplifier. The paper presents a method to identify and compensate the effect of the force ripple in servo control. A physical model of the linear motor and the force ripple is derived first. The identification of the model parameters is done in a closed position control loop by measurement of the control signal for movements with different load forces. No additional sensors are necessary. A comparison of the tracking performance with and without ripple compensation is given.

The Virtual Lab for teleoperated control of real experiments

The Virtual Lab is an experimental setup for students in control systems engineering, which is accessible via Internet. The experimental system is an omnidirectional vehicle; several different tasks can be carried out with this vehicle ranging from kinematics and dynamics analysis to controller design and system identification. Teleoperation control options for these experiments have been chosen in addition to conventional practice because of the following two major reasons: to share this experimental setup with other universities, and to simplify experiments for home-learners and professionals in a distance teaching environment.

Mobile Robot Localization using WLAN Signal Strengths

Localization is a key problem in mobile robotics. This paper presents a method to estimate position and heading of a mobile robot in an indoor scenario. The proposed method for localizing the mobile robot is based on the use of received signal strengths values of WLAN access points in range. A radio map based method and Euclidean distance in combination with interpolation is proposed. Measured signal strength values of an omnidirectional antenna and a beam antenna are compared with the values of the radio map, in order to estimate position and heading of the mobile robot. The paper presents the experimental results of measurements in an office building.