Olle Wijk

Triangulation-based fusion of sonar data with application in robot pose tracking

In this paper a sensor fusion scheme, called triangulation-based fusion (TBF) of sonar data, is presented. This algorithm delivers stable natural point landmarks, which appear in practically all indoor environments, i.e., vertical edges like door posts, table legs, and so forth. The landmark precision is in most cases within centimeters. The TBF algorithm is implemented as a voting scheme, which groups sonar measurements that are likely to have hit the same object in the environment. The algorithm has low complexity and is sufficiently fast for most mobile robot applications. As a case study, we apply the TBF algorithm to robot pose tracking. The pose tracker is implemented as a classic extended Kalman filter, which use odometry readings for the prediction step and TBF data for measurement updates. The TBF data is matched to pre-recorded reference maps of landmarks in order to measure the robot pose. In corridors, complementary TBF data measurements from the walls are used to improve the orientation and position estimate. Experiments demonstrate that the pose tracker is robust enough for handling kilometer distances in a large scale indoor environment containing a sufficiently dense landmark set.

Feature based CONDENSATION for mobile robot localization

Much attention has been given to CONDENSATION methods for mobile robot localization. This has resulted in somewhat of a breakthrough in representing uncertainty for mobile robots. In this paper we use CONDENSATION with planned sampling as a tool for doing feature based global localization in a large and semi-structured environment. This paper presents a comparison of four different feature types: sonar based triangulation points and point pairs, as well as lines and doors extracted using a laser scanner. We show experimental results that highlight the information content of the different features, and point to fruitful combinations. Accuracy, computation time and the ability to narrow down the search space are among the measures used to compare the features. From the comparison of the features, some general guidelines are drawn for determining good feature types.

Localization and navigation of a mobile robot using natural point landmarks extracted from sonar data

Abstract In this paper we present a new technique for on-line extraction of natural point landmarks in an indoor environment. The landmarks are filtered out from sonar data taken from a mobile platform. By storing point landmark positions in a reference map, we can achieve absolute robot localization by doing matching between recently collected landmarks and the reference map. The matching procedure also takes advantage of compass readings to increase computational speed and make the performance more robust. The technique is easily extended to also encompass local robot localization, which is used when the robot navigates autonomously. The position accuracy of the robot as well as its capability to navigate using natural landmarks is illustrated in a number of real world experiments.

Triangulation based fusion of ultrasonic sensor data

Ultrasonic sensors are still one of the most widely used sensors in mobile robotics. A notorious problem in the use of sonar data is the lack of good spatial resolution, which typically results in a high uncertainty in the resulting map of the environment. In the paper a triangulation technique is used for filtering of data so as to obtain an improved grid map of the environment. The basic technique is described and it is outlined how it can be used for identification of natural landmarks.

Investigation of the dehydration schemes of NdCl3-6H2O, TbQ3·6H2O and DyCl3·6H2O using a fluidized bed

Abstract The dehydration schemes of NdCl 3 ·6H 2 O, TbCl 3 ·6H 2 O and DyQ 3 ·6H 2 O were investigated by the fluidized bed technique. Hydrolytic reactions were avoided by using dry mixtures of argon and hydrogen chloride as fluidizing gas. Results were followed up by both chemical and thermal analyses. Non-isothermal as well as isothermal techniques were used. The isothermal technique disclosed the complete dehydration schemes: NdCl 3 ·6H 2 O and TbCl 3 ·6H 2 O were decomposing to their anhydrous compounds through the reaction steps 6→3→ 2 → 1 → 0; DyCl 3 ·6H 2 O was decomposing accordingly as 6 →3 → 1 → 0. The technique presented, of using a fluidized bed to disclose dehydration schemes, is new and shows promise for further successful investigations.