Jarosław Majchrzak

Distance Estimation With a Long-Range Ultrasonic Sensor System

This paper presents the results of tests conducted with an ultrasonic proximity measurement system (composed of Polaroid 600 sensors and a Sonar Ranging Module SN28827), which is used in sensory subsystems in many mobile robots. The tests took into account distances ranging from 0.4 to 11 m. The analysis of the obtained measuring results created the basis for selecting a distance estimator that would guarantee the smallest measuring errors in the whole measuring range of the system. The research described was carried out in a closed room at constant environmental conditions so as to eliminate the influence of external factors on the measurement result. Each measuring series was composed of 100 measurements. For the best estimator chosen in such environment, the value of absolute measuring error never exceeded plusmn 0.03 m. Histograms that present the scatter of measurement results are also included. The minimal number of measurements necessary to achieve a reliable measurement with the selected distance estimator was determined. It is shown that in order to achieve a relative measuring error smaller than 1% with 0.99 probability there is a need to perform at least seven measurements. A proposition of the distance measuring procedure with the chosen estimator is presented. The analysis described in this paper helps to evaluate the reliability of measurements performed with ultrasonic sensors.

A backstepping approach to control a nonholonomic mobile robot

A trajectory tracking control problem for a nonholonomic mobile robot by making use of a kinematic oscillator has been solved. Firstly, a time varying oscillator is examined to control the nonholonomic mobile robot based only its kinematics. Secondly, a backstepping procedure is proposed to include robot dynamics and the servo loop. It is shown that overall multilevel controller is asymptotically globally stable to a small error different from zero. A wide range of simulation results are presented which illustrate the behaviour of the controller with respect to tuning its parameters. Some preliminary experiments are reported too.

Basic characteristics of IEC flickermeter processing

Flickermeter is a common name for a systemthatmeasures the obnoxiousness of flicker caused by voltage fluctuations. The output of flickermeter is a value of short-term flicker severity indicator, Pst. This paper presents the results of the numerical simulations that reconstruct the processing of flickermeter in frequency domain. With the use of standard test signals, the characteristics of flickermeter were determined for the case of amplitude modulation of input signal, frequency modulation of input signal, and for input signal with interharmonic component. For the needs of simulative research, elements of standard IEC flickermeter signal chain as well as test signal source and tools for acquisition, archiving, and presentation of the obtained results were modeled. The results were presented with a set of charts, and the specific fragments of the charts were pointed out and commented on. Some examples of the influence of input signals bandwidth limitation on the flickermeter measurement result were presented for the case of AM and FM modulation. In addition, the diagrams that enable the evaluation of flickermeters linearity were also presented.

Posture Stabilization of a Unicycle Mobile Robot — Two Control Approaches

State feedback control issues for nonholonomic systems are still very challenging for control researchers. Among the group of nonholonomic systems one can number wheeled mobile vehicles, manipulators with nonholonomic gears, free-floating robots, underwater vessels, nonholonomic manipulator’s grippers, dynamically balanced hopping robots and others [4, 10, 15]. Difficulties in designing effective stabilizers arise from nonintegrable kinematic constraints imposed on system evolution. These constraints impose restriction on admissible velocities of controlled dynamic systems, preserving however their controllability. Moreover, lower dimensionality of the control space U ⊂ ℝm in comparison to the configuration space Q ⊂ ℝn (n > m) causes difficulties in control design, especially for stabilization task problems [5]. Despite the problems mentioned, many different feedback control strategies for nonholonomic kinematics in automatics and robotics literature have been proposed - see for example [7], [18] or [8]. Still, some important problems, like robustness to control signals limitations existance, intuitive contoller parameter tunning and good control quality during transient stage seem to remain open issues and involve further research. In this paper two different stabilization approaches to the mentioned problems, with alternative solution in comparison to existing strategies, are described. The presented approaches are applied to derive two stabilizers to solve the stabilization task for a unicycle mobile robot, taking into account control limitations.

Control System for Designed Mobile Robot - Project, Implementation, and Tests

Thanks to highly sophisticated control techniques, modern mobile robots are capable of accomplishing advanced tasks. Briefly, mobile robots can be dived into two main branches: research devices and consumer devices. The firs class usually consists of prototypes used for testing and verification of various control algorithms. The latter is represented by efficient, dependable and fulfilling industrial safety requirements robotic vehicles, often distributed as closed systems. During the design and test phase, the imperfections of a completely custom design may not allow to perform advanced tests, thus lengthening the construction phase. In order to eliminate this problem, the authors have designed the robot so that its crucial parts were previously known, tested and proved to be reliable. The control system consists of distributed pieces of software and hardware, each of which accomplishes precisely defined tasks. A fast serial communication bus is used to exchange information, what makes possible the use of module elements of control system. The modularity of the control system in range of hardware and software allows easy modification of components of the control system (the exchange), the diagnostics of drives as well as the introduction of an alternative controller or a measuring sensor in case of breakdown.Moreover the presence of a communication bus makes it possible to integrate the control system with measuring devices and drives. The utilization of independent arrangements of control drives makes it possible to use synchronous drives with position or speed control, independently from the main driver, which enlarges control precision [3]. The robot served as a testbench for various control algorithms thanks to which it was possible to determine the effectiveness of the design.

Design and Control of a Heating-Pipe Duct Inspection Mobile Robot

During operation of the heating net, there may appear leakages and failures in places which are hard to access. Repair of underground heating-pipe ducts requires using heavy equipment as well as temporarily removing neighboring infrastructure elements which are obstacles. This implies high costs of penetrating the failure place, so it is advisable to minimize the risk of erroneous choice of the intervention place. Localization of the failure place is difficult due to its inaccessibility or lack of information or proper tools. So, very expensive is the wrong choice of the exploration place, when failure localization is uncertain. There exist acoustic monitoring devices for rough detection of leakage, from the ground level over the damage, sensitive to the noise of outgoing steam or warm water. Nevertheless, essential is the possibility of estimation of the leakage with one’s eyes. Therefore, construction of a tool which could reach places inaccessible even for a well equipped operator is very important. This situation is due to atmospheric conditions and dimension of places which should be reached.

On selected features of mobile robot control system

In this paper the results of research of mobile robot control system are presented, namely the quality of regulation with and without on-board velocity controllers taken into account. To verify the behaviour of the control system an time-varying controller was chosen which has nontrivial computing requirements. The algorithms parameters used to control real object were set during simulations performed with described controller. The control system consists of kinematic oscillator algorithm implemented in real time operating system (RTAI Linux) and PI on-board controllers. Experimental results were obtained on a new mobile robot platform, Mini-Tacker 3.0.

Real time controller for a nonholonomic mobile robot

In this paper the usage of controller implemented in real time operating system (RTAI Linux) for nonholonomic robot control is presented. The multilayer controller enables user interaction for on-line performance visualization and setting of parameters for reference trajectory and control algorithm. To verify and present capabilities of the controller, a kinematic oscillator algorithm was chosen, which has nontrivial computing requirements. The algorithms parameters used to control real object were set during simulations performed with described controller. The paper presents results of simulations and real robot behavior experiments as well.