The present work aims at proposing a rigorous analysis of the mathematical and numerical modelling of ultrasonic piezoelectric sensors. This includes the well-posedness of the final model, the rigorous justification of the underlying approximation and the design and analysis of numerical methods. More precisely, we first justify mathematically the classical quasi-static approximation that reduces the electric unknowns to a scalar electric potential. We next justify the reduction of the computation of this electric potential to the piezoelectric domains only. Particular attention is devoted to the different boundary conditions used to model the emission and reception regimes of the sensor. Finally, an energy preserving finite element/finite difference numerical scheme is developed; its stability is analyzed and numerical results are presented.

In this paper, we develop a method for mobile robot control using ultrasonic sensors to determine displacement constraints between two parallel planes. Robot control has been simulated for this situation. Results obtained by simulation and experimentation are presented. A degraded mode which considers the use of one valid ultrasonic sensor is studied. In this case, a new model is developed and new results are analyzed.

This paper deals with the perception mode of smart wheelchairs. First we evoke the many mobility aid prototypes developed in rehabilitation robotics by considering the point of view of perception. Then we describe the localization mode of the VAHM**. We show how the odometric, ultrasound, and vision sensors are used in a complementary way in order to locate the wheelchair in its known environment. The mode of adjustment of the odometric position by the least-squared method using ultrasonic measurements is detailed. Then the use of vision to perceive the vertical segments of the environment so as to refine the orientation is presented. The results of the tests carried out on the wheelchair are given and commented.

This paper is part II of a paper published in the previous issue of Robotica. This part proceeds from the assumption that 3D features have been calssified into either a plane, a 2D corner type I or II, or a 3D corner using the Maximum Likelihood Estimator. The location of the 3D features from the results of the Maximum Likelihood Estimation are derived here. Experimental results characterising the ultrasonic sensor and its application to a robot localisation problem are presented in this paper.

Current mobile robot ultrasonic localisation techniques use sensor systems which rely on features in a horizontal plane. The implicit assumption is that the room boundary on the horizontal plane is not obstructed by objects such as furniture. This assumption is often not realistic and restricts the versatility and portability of these systems. The solution proposed in this paper is the provision of sensing flexibility to use other 3D room boundaries (e.g. ceiling-wall intersections) as 3D natural beacons. We propose a 3D ultrasonic sensor array that uses a Maximum Likelihood Estimator to match the echo arrival times to different object classes and to determine the location of the 3D target. This method does not require fast data acquisition or powerful computing. It has been implemented on a robot localisation application with the Extended Kalman Filter. This paper is the first of two parts, and presents theoretical results on target classification and minimum transducer requirements. The second part, in the next issue of Robotica, presents experimental results on the characterisation of the sensor and its application to robot localisation, and includes the references for the both papers.

This paper presents a novel approach for seam tracking using ultrasonics. An ultrasonic seam tracking system has been developed for robotic welding which tracks a seam that curves freely on a two-dimensional surface. The seam is detected by scanning the area ahead of the torch and monitoring the amplitude of the waves received after reflection from the workpiece surface. Scanning is accomplished by using two ultrasonic sensors (a transmitter and a receiver) mounted on a stepper motor such that the transmitter angle is the same as the receiver angle. The motor is mounted on the end-effector just ahead of the welding torch and covers a ninety degree arc in front of the torch. If there is no seam then the receiver receives most of the transmitted waves after reflection, but if there is a seam then most of the transmitted waves are dispersed in directions other than that of the receiver. The system has been tested and is very robust in the harsh environments generated by the arc welding process. The robustness of the system stems from using various schemes such as time windowing, a waveguide, air and metal shields, and an intelligent sensor manager. This ultrasonic system offers some distinct advantages over traditional systems using vision and other sensing techniques. It can be used to weld very shiny surfaces, and is a very economical method in terms of cost as well as computational intensity. The system can be used to detect seams less than 0.5 mm wide and 0.5 mm deep.