Wyniki wyszukiwania - BazTech

1

Fuzzy adaptive-predictive decentralized control of discrete time interconnected systems

Tzafestas S., Kyriannakis E., Apostolikas G.

Systems Science

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2002

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Vol. 28, nr 1

5-24

EN

Proposes an approach for the design of discrete-time decentralized control systems with m-step delay sharing information pattern, employing model-based predictive control (MBPC) combined with fuzzy prediction for the interconnections among the subsystems. A state space model is used at each control station to predict the corresponding subsystem output over a long-range time period. The interaction trajectories are considered to be non-linear functions of the states of the subsystems. For all cases the interconnections and the necessary predictions for them are estimated by an appropriate adaptive fuzzy identifier based on the generation of linguistic IF-THEN rules and the on-line construction of a common fuzzy rule base. Representative computer simulation results are provided and compared for nontrivial example systems.

2

Visibility and occlusion culling algorithms in architectural walkthroughs

Pantazopulos I., Tzafestas S.

Image Processing & Communications

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2002

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Vol. 8, no 2

33-46

EN

In this paper we review occlusion culling techniques appeared in the last decade. These techniques are used for achieving real/interactive time rendering. The characteristics of these techniques are outlined and a synopsis table is given at the end.

3

Integration of topological and metric maps for indoor mobile robot path planning and navigation

Zavlangas P., Tzafestas S.

Image Processing & Communications

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2002

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Vol. 8, no 1

55-64

EN

Autonomous mobile robots need to use spatial information about the environment in order to effectively plan and execute navigation tasks. The information can be represented at different levels of abstraction, ranging from detailed geometric maps to coarse topological maps. Each level is adequate for some sub-task, but not for others. In this paper, we consider the representation of spatial knowledge at two different levels of abstraction, which are commonly considered in the robotics literature : the geometric level, and the topological level. We propose to represent the environment by local metric maps connected into a topological network. This technique allows us to use maps that are not metrically consistent on the global scale, although they are metrically consistent locally. The structure allows also the combination of abstract global reasoning and precise local geometric computations. Moreover, this structure reflects the typical organization of indoor environments, where rooms and hallways define independent but connected local working spaces. To navigate in the environment, the robot uses the topological information to plan a sequence of sectors to traverse, and uses the metric information in each sector to locally move within the sector and to the next one. The functioning of the proposed system with respect to omnidirectional mobile robots and results of simulated experiments are presented.

4

A differential motion planning algorithm for controlling multi-robot systems handling a common object

Tzafestas C., Prokopiou P., Tzafestas S.

Control and Cybernetics

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2000

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Vol. 29, no 2

567-584

EN

Multi-robot systems have substantially increased capabilities over single-robot systems and can handle very large or peculiar objects. This paper presents a differential (incremental) motion planning algorithm for an m-robot system (m >or=2) to cooperatively transfer an object from an initial to a desired final position / orientation by rigidly holding it at given respective points Q[sub 1], Q[sub 2],..., Q[sub m]. One of the robots plays the role of a "master" while other robots operate in the "slave" mode maintaining invariant their relative positions and orientations during the system motion. The method employs the differential displacements of the end-effector of each robot arm. Then, the differential displacements of the joints of the m robots are computed for the application of incremental motion control. The algorithm was tested on many examples. A representative of them is shown here, concerning the case of three STAUBLI RX-90L robots similar to 6-dof PUMA robots. The results obtained show the practicality and effectiveness of the method, which, however, needs particular care for completely eliminating the cumulative errors that may occur.

5

Fuzzy image processing : a review and comparison of methods

Tzafestas S., Raptis S.

Image Processing & Communications

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1999

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Vol. 5, no 1

3--24

EN

This paper presents a comprehensive review of fuzzy image processing methods. Specifically the following image processing problems are considered: (i) Image comprehension. (ii) image segmentation, (iii) image classification, (iv) image analysis, (v) image filtering, (vi) image understanding. In practice, an image cannot always be interpreted always exactly and perfectly. This is due to the existence of noise or the way the image is obtained, or, finally, to incorrect understanding of the image information content. These difficulties can be faced successfully through fuzzy logic and fuzzy reasoning. The field of image processing via fuzzy logic was initialed after Zadeh's 1965 seminar paper and is still expanding with new important results and applications. This paper is devoted to the treatment of still images, but some of the methods can be extended to the case of moving (video) images. The methods considered are critically discussed. Finally, a comparison of the effectiveness of (i) c-means, (ii) classical c-means, and (iii) adaptive clustering algorithms is made.

6

Non-standard State-space Models for 2D Systems

Gałkowski K., Theodorou N., Tzafestas S.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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1999

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Vol. 47, nr 1

91-101

EN

In this paper, non-standard 2D state space models of the Roesser type and their equivalence under similarity and elementary operations are discussed. Non-standard models cover a wider repertory of systems than traditional ones of both theoretical and practical importance.

7

Model-based predictive control of large-scale systems using a neural estimator

Tzafestas S., Kyriannakis E., Anthopoulos Y.

Applied Mathematics and Computer Science

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1998

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Vol. 8, no 3

585-598

EN

An approach to the design of discrete-time decentralized controI systems based on model-based predictive controI (MBPC) and neural estimation is proposed. The class of interconnected large-scale systems (LSS) is considered, and a model is used at each controI station to predict the corresponding subsystem output over a long time period. In the case of subsystems with m-step delay information patterns the non-locally available interaction trajectories are estimated by a multi-layer neural network trained on-line with a modified backpropagationtype algortithm. Representative computer simulation results are provided and compared for a set of illustrative examples. The proposed controI scheme shows better performance than the other schemes, and also covers the important case where the subsystems' interactions are nonlinear.