Ultrasonic Local Positioning System with Large Covered Area

Abstract

This work describes the design of a ultrasonic local positioning system (ULPS) with large covered area. The beacons have been designed with a cylindrical PVDF transducer (piezofilm transducer) to which a conical reflector has been connected to enlarge the covered area and to guarantee 3D indoor positioning. The proposed ULPS for mobile robots (MR) uses simultaneous emissions from ultrasonic beacons. In order to solve the problem of simultaneous emissions from ultrasonic beacons, the well-known technique, direct sequence code multiple division access (DS-CDMA), is used. This technique encodes the ultrasonic signal with a 255-bit Kasami code for every beacon. It implies the emitted signal by every beacon to have a wide bandwidth. PVDF-based transducers suitably guarantee this requirement. Their cylindrical or semi-cylindrical shape makes the emission pattern not suitable when using them as ultrasonic beacons, often located in the ceiling of an indoor room. To adapt the emission pattern and to increase the covered area in the ground, the design process of a conical reflector is described.