Showing papers by "Ivan Petrović published in 2009"

Experimental comparison of trajectory tracking algorithms for nonholonomic mobile robots

Abstract: 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.

Extending functionality of RF Ultrasound positioning system with dead-reckoning to accurately determine mobile robot's orientation

Abstract: In this paper we show how to accurately track position and orientation of a mobile robot using positioning only RF Ultrasound transceiver system and dead-reckoning. The solution is based on geometrical displacement of the positioning device from the axis of rotation of the robot which brings dependency in position of the device and robot's orientation and enables the correction of the absolute orientation of the robot. Estimation is done via Extended Kalman Filter with variable discretization time because of stochastic nature of measurement arrival times. We describe and analyze the main sources of noise in odometry and position device readings. We also suggest the method for measurement outlier elimination derived from empirical measurement analysis. Experimental verification of the proposed method is presented that yields position error aprox. 1±2.5 centimeters and 1±2 degrees.

Experimental Comparison of Sonar Based Occupancy Grid Mapping Methods

Abstract: For successful usage of mobile robots in human working areas several navigation problems have to be solved. One of the navigational problems is the creation and update of the model or map of a mobile robot working environment. This article describes most used types of the occupancy grid maps based sonar range readings. These maps are: (i) Bayesian map, (ii) Dempster-Shafer map, (iii) Fuzzy map, (iv) Borenstein map, (v) MURIEL map, and (vi) TBF map. Besides the maps description, a memory consumption and computation time comparison is done. Simulation validation is done using the AMORsim mobile robot simulator for Matlab and experimental validation is done using a Pioneer 3DX mobile robot. Obtained results are presented and compared regarding resulting map quality.

Stereo Image Registration Based on RANSAC with Selective Hypothesis Generation

Abstract: An approach for registration of sparse feature sets detected in stereo images taken from two different views is proposed. The approach is based on the RANSAC paradigm which ensures robustness to outliers. The strategy proposed in this work is to apply a multi-step procedure in the hypothesis generation stage of RANSAC using approximate information about the relative camera pose between the two views obtained e.g. by odometry. The data is taken from the input data set one by one and used to pose a geometric constraint for selection of the next data. This strategy reduces the number of false hypothesis in the RANSAC procedure. The presented technique is evaluated using both synthetic data and real data obtained by a stereo camera system mounted on a mobile robot.

Distance keeping for underwater vehicles - tuning Kalman filters using self-oscillations

Abstract: This paper describes the use of Kalman filtering in distance keeping for underwater vehicles. The vision-based distance keeping module has been mounted on a micro-ROV equipped with a camera. Distance from a plane-like obstacle is determined on the basis of the laser dot projections within the frame. Since these measurements are not reliable a Kalman filter is designed - unknown dynamic model parameters are determined using the self-oscillation experiments which prove to be simple and time preserving. Finally, an I-PD controller is designed based on the Kalman filter estimates. The main task of the controller is to keep the vehicle perpendicular to the surface at a desired distance.

RANSAC-Based Stereo Image Registration with Geometrically Constrained Hypothesis Generation

Abstract: An approach for registration of sparse feature sets detected in two stereo image pairs taken from two different views is proposed. Analogously to many existing image registration approaches, our method consists of initial matching of features using local descriptors followed by a RANSAC-based procedure. The proposed approach is especially suitable for cases where there is a high percentage of false initial matches. The strategy proposed in this paper is to modify the hypothesis generation step of the basic RANSAC approach by performing a multiple-step procedure which uses geometric constraints in order to reduce the probability of false correspondences in generated hypotheses. The algorithm needs approximate information about the relative camera pose between the two views. However, the uncertainty of this information is allowed to be rather high. The presented technique is evaluated using both synthetic data and real data obtained by a stereo camera system.

Integration of Focused D* and Witkowski's Algorithm for Path Planning and Replanning.

Abstract: The paper presents a new path planning and replanning algorithm based on two-dimensional occupancy gri d map of the environment, which integrates the focused D* (FD* ) algorithm and Witkowski’s algorithm. The FD* algorithm is used for fast replanning and Witkowski’s algorithm is used for generating all optimal paths in the grid map. Our algorithm finds the shortest path in the geometrical space based on the g rid map calculations. The path optimality is proved. Path planning is used together with Dynamic Window local obstacle avoidan ce algorithm to produce smooth robot motion. The algorithms were tested using Pioneer 3DX mobile robot equipped with a laser range finder.

The comparison of Matlab/Simulink and proprietary code generator efficiency

Abstract: The paper compares efficiency of program code automatically generated by Simulink and proprietary graphical integrated development environment. Three test applications were built and used to generate code: simple logical function, simple arithmetical function and a complex application program. Generated code is executed on target with Texas Instruments TMS320F2812 microcontroller. Execution time of the code is measured and number of lines of assembly code is recorded. It is shown that, in hands of skilled application engineer, proprietary environment produces code that executes faster and conforms better to the real-time paradigm.

Experimental Investigations and Modeling of the Rubber- Asphalt Sliding Pair Dynamics

Abstract: A laboratory model for experimental investigations of the rubber-asphalt sliding pair has been designed to better understand the dynamic behavior of the friction force in the contact patch between the car tire and the road. Its design is described and some experimental results are given. These results confirm that in order to describe friction force in contact between the car tire and the road it is essential to use a dynamic friction model. Moreover, they indicate that the existing dynamic friction models might be physically incorrect in regards to the change of friction coefficient for an asperity bristle passing through the contact surface.

Geometrically Constrained RANSAC for Stereo Image Registration in Presence of High Ambiguity in Feature Correspondence

Abstract: An approach for registration of sparse feature sets detected in two stereo image pairs taken from two different views is proposed. Analogously to many existing image registration approaches, our method consists of initial matching of features using local descriptors followed by a RANSAC-based procedure. The proposed approach is especially suitable for cases where there is a high percentage of false initial matches. The strategy proposed in this paper is to modify the hypothesis generation step of the basic RANSAC approach by performing a multiplestep procedure which uses geometric constraints in order to reduce the probability of false correspondences in the hypothesis. The algorithm needs approximate information about the relative camera pose between the two views obtained e.g. by odometry. However, the uncertainty of this information is allowed to be rather high. The presented technique is evaluated using both synthetic data and real data obtained by a stereo camera system.

Internet Based Teleoperation for Cooperative Navigation and Manipulation

Abstract: The Internet is a very fast evolving new technology, allowing people to electronically connect to places that are thousands of miles apart. By combining network technologies with the capabilities of mobile robots and manipulators, Internet users can discover and physically interact with far-away places thereby, creating opportunities of resource sharing, remote experimentation and long-distance learning. This paper presents a general concept of Internet based teleoperation, which structures a teleoperation system into three layers. The concept was applied in developing a teleoperation system that enables two human operators to safely control two cooperative mobile robots in unknown and dynamic environments from any two PCs connected to the Internet by installing a developed client program on them and by using simple force feedback joysticks. On graphical user interfaces, the operators receive images forwarded by the cameras mounted on robots, and on the joysticks they can feel forces forwarded by developed obstacle prevention algorithm based on the dynamic window approach. To overcome the instability caused by the unknown and varying time delay an event-based teleoperation method is employed to synchronize actions of each robot with commands from its operator. Through experimental investigation it is confirmed that developed teleoperation system enables the operators to successfully accomplish cooperative navigation and manipulation tasks in complex environments.

Implementation of Fuzzy-Model Based Autotuning Power System Stabilizer

Abstract: Adaptive power system stabilizers presented in last decade mainly address the way of PSS parameters adaptation and are less interested in way of its implementation. Almost all of algorithms are developed in floating point arithmetic despite the facts that digital automatic voltage regulators, within PSSs typically have to be implemented, are mostly based on 16 or 32-bit fixed point processors. The paper presents implementation process of newly proposed fuzzy-model based autotuning power system stabilizer on fixed point platform. Accent is placed on implementing RLS algorithm used for plant model parameters estimation due to the fact that this is numerically the most intensive part of proposed PSS algorithm. Here presented implementation stages and directions are results of the PSS implementation, but can be translated to implementation of any other, numerically intensive, algorithm in fixed point arithmetic (i.e. intended for fixed point processor targets).

Internet Based Teleoperation for Cooperative Navigation and Manipulation

Abstract: The Internet is a very fast evolving new technology, allowing people to electronically connect to places that are thousands of miles apart. By combining network technologies with the capabilities of mobile robots and manipulators, Internet users can discover and physically interact with far-away places thereby, creating opportunities of resource sharing, remote experimentation and long-distance learning. This paper presents a general concept of Internet based teleoperation, which structures a teleoperation system into three layers. The concept was applied in developing a teleoperation system that enables two human operators to safely control two cooperative mobile robots in unknown and dynamic environments from any two PCs connected to the Internet by installing a developed client program on them and by using simple force feedback joysticks. On graphical user interfaces, the operators receive images forwarded by the cameras mounted on robots, and on the joysticks they can feel forces forwarded by developed obstacle prevention algorithm based on the dynamic window approach. To overcome the instability caused by the unknown and varying time delay an event-based teleoperation method is employed to synchronize actions of each robot with commands from its operator. Through experimental investigation it is confirmed that developed teleoperation system enables the operators to successfully accomplish cooperative navigation and manipulation tasks in complex environments.

Experimental Investigations and Modeling of the Rubber-Asphalt Sliding Pair Dynamics

Abstract: A laboratory model for experimental investigations of the rubber-asphalt sliding pair has been designed to better understand the dynamic behavior of the friction force in the contact patch between the car tire and the road. Its design is described and some experimental results are given. These results confirm that in order to describe friction force in contact between the car tire and the road it is essential to use a dynamic friction model . Moreover, they indicate that the existing dynamic friction models might be physically incorrect in regards to the change of friction coefficient for an asperity bristle passing through the contact surface.