Mišel Brezak

Real-time Approximation of Clothoids With Bounded Error for Path Planning Applications

We present a method for real-time computation of clothoid coordinates that guarantees bounded approximation error over a wide range of clothoid parameters provided that the clothoids orientation change and length areReal-time approximation bounded. It is shown that coordinates of clothoid with any parameters can be computed from those of a single clothoid (with fixed parameters), using appropriate geometrical transformations. A comprehensive analysis is given on how to determine a required set of clothoids and, based on this, how to sample a clothoid in a lookup table in order to achieve required approximation precision. The algorithm is computationally very efficient and therefore suitable for real-time path planning, as well as for other applications that benefit from fast clothoid computation.

Time-optimal trajectory planning along predefined path for mobile robots with velocity and acceleration constraints

This paper is concerned with the problem of finding an optimal velocity profile along the predefined path in order to traverse the path in shortest time. A dynamic model of the mobile robot that accounts for robot actuator constraints is derived. It is shown how to use this dynamic model to express acceleration limits and velocity limit curve required by the optimal time-scaling algorithm. The developed trajectory planning algorithm is demonstrated on the Pioneer 3DX mobile robot. A method is very flexible and can be extended to account for other constraints, such as limited grip between the robot wheels and the ground.

Path Smoothing Using Clothoids for Differential Drive Mobile Robots

Abstract This paper presents a new online path-smoothing algorithm for smoothing a path that consists of straight line segments and is primarily intended for differential drive mobile robots. Algorithm allows non-zero initial path curvature, which is important for replanning. Further, algorithm uses clothoid curves as primitives for path smoothing, which have inherent property that their curvature changes proportionally with distance traveled along the curve.

Experimental comparison of trajectory tracking algorithms for nonholonomic mobile robots

This paper presents an experimental overview of common trajectory tracking methods for nonholonomic mobile robots: linear control, nonlinear control and model predictive control. All methods are compared experimentally on a two-wheel mobile robot with differential drive. The goal was to determine which control method is the best with respect to robustness and low trajectory tracking error. Thereby, a special emphasis is given on a fast real-time trajectory tracking and behavior in conditions near robot velocity and acceleration limits.

Global Vision Based Tracking of Multiple Mobile Robots

This paper presents a new global vision system for tracking of multiple mobile robots, with special emphasis on following requirements: (i) high measurement precision and accuracy, (ii) robustness to light intensity changes, (iii) ability to track unlimited number of robots, and (iv) high speed and real time operation. In order to fulfill these requirements we use an IEEE 1394 camera with 80 fps, which delivers images in so called Bayer format. We also design a specific robot mark that enables measurement of robot locations directly in Bayer format image with subpixel precision. The developed vision system fulfils all of given requirements, which was verified by carefully performed experiments.

Parquet Sorting and Grading Based on Color and Texture Analyses

In this paper a computer vision algorithm for automatic parquet slab sorting is described, as a part of a real time automatic parquet slab sorting system. Various computer vision algorithms and methods for automatic visual inspection and automatic classification have been analyzed. Developed algorithm consists of three main stages: color analysis, texture analysis and defects detection. The color analysis is based on the percentile values obtained from the cumulative histogram of the image and texture analysis is based on the second order statistical features obtained from gray level co-occurrence matrix. Detection of defects is implemented as the segmentation method, based on the adaptive binary threshold algorithm, which is based on a local square regions and connected component analysis methods. This way we have achieved a very accurate classifying process with about 90 percent of accuracy, which greatly outstands results of human inspector, that are about 60-70 percent.

Global Vision Based Tracking of Multiple Mobile Robots in Subpixel Precision

This paper presents a new global vision system for tracking of multiple mobile robots, with special emphasis on following requirements: (i) high measurement precision and accuracy, (ii) robustness to light intensity changes, (iii) ability to track unlimited number of robots, and (iv) high speed and real time operation. In order to fulfill these requirements we use an IEEE 1394 camera with 80 fps, which delivers images in so called Bayer format. We also design a specific robot mark that enables measurement of robot locations directly in Bayer format image with subpixel precision. The developed vision system fulfils all of given requirements, which was verified by carefully performed experiments.