Exploration of a Mobile Robot Based on Sonar Probability Mapping

1996 ◽  
Vol 118 (1) ◽  
pp. 150-157
Author(s):  
Byung-Kwon Min ◽  
Dong Woo Cho ◽  
Sang-Jo Lee ◽  
Young-Pil Park
Keyword(s):  
Probability Theory ◽  
Mobile Robot ◽  
Dimensional Space ◽  
Bayesian Probability ◽  
Autonomous Mobile Robot ◽  
Two Dimensional ◽  
Probability Map ◽  
Work Area

This paper suggests a new exploration strategy of an autonomous mobile robot in an unknown environment. Determination of a temporary goal based on a representation of work area named exploration quadtree is proposed. The exploration quadtree provides the information on quality of the regions concerned in a robot’s workspace. Using this quadtree the robot easily finds the next temporary goal that makes exploration more efficient. The quadtree is made up from a sonar probability map that is constructed by sonar range sensing and Bayesian probability theory. We then propose a method that plans a path between the determined temporary goals based on a probability map. The developed methods were implemented on a real mobile robot, AMROYS-II, which was built in our laboratory, and shown to be useful enough in a real environment that can be projected onto a two-dimensional space.

Experimental investigation of mapping and navigation based on certainty grids using sonar sensors

Robotica ◽  
1993 ◽  
Vol 11 (1) ◽  
pp. 7-17 ◽  
Author(s):  
Jong Hwan Lim ◽  
Dong Woo Cho
Keyword(s):  
Mobile Robot ◽  
Bayesian Model ◽  
Range Data ◽  
Autonomous Mobile Robot ◽  
Two Dimensional ◽  
On Certainty ◽  
Probability Map ◽  
Sonar Sensors ◽  
Sonar Sensor ◽  
Sensor Information

SUMMARYA mapping and navigation system based on certainty grids for an autonomous mobile robot operating in unknown environment is described. The system uses sonar range data to build a map of the robot's surroundings. The range data from sonar sensor are integrated into a probability map that is composed of two dimensional grids which contain the probabilities of being occupied by the objects in the environment. A Bayesian model is used to estimate the uncertainty of the sensor information and to update the existing probability map with new range data. The resulting two dimensional map is used for path planning and navigation. In this paper, the Bayesian updating model which was successfully simulated in our earlier work is implemented on a mobile robot and is shown to be valid in the real world by experiment.

scholarly journals Limitations of LEED-Structure Determination of Reconstructed Crystal Surfaces

1982 ◽  
Vol 37 (10) ◽  
pp. 1103-1118 ◽  
Author(s):  
H. Jagodzinski
Keyword(s):  
Structure Determination ◽  
Crystal Surface ◽  
Dimensional Space ◽  
Point Group ◽  
Two Dimensional ◽  
Crystal Surfaces ◽  
Difficult Situation ◽  
3 Dimensional ◽  
Lattice Constants

Although a strictly ordered reconstructed crystal surface may have the two-dimensional symmetry prescribed by the bulk (two-dimensional subsymmetry of the 3-dimensional space group), it belongs more frequently to a subgroup. In the LEED-pattern a lower symmetry of the translation group can easily be detected on account of the superstructure reflections observed. In this case anti-phase domains can hardly be avoided. An even more difficult situation arises if the symmetry of the point group is violated, although the symmetry of the diffraction pattern is not altered at the end of the reconstruction. Twin domains without changes of lattice constants have to be taken into account.Dynamical scattering of anti-phase domains is calculated by applying the "Cluster embedded chain"-method for various distributions of domains. It is shown that the incoherent superposition of scattering amplitudes, normally applied in LEED-calculations may lead to serious errors in structure determination. This effect is even more pronounced for twin domains. As an example we discuss the reconstruction of the (001)-surface of Si and Ge, and show that the wellknown (2 X 1)-structure is an averaged structure only, consisting of anti-phase domains with the (4 x 2)-structure. It may be concluded therefrom that none of the present model structures of this reconstruction agrees with this experimental observation.

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