A two-dimensional vision system with optical ranging capability

Abstract

This paper describes an optical three-dimensional (3D) camera developed by combining a two-dimensional intensity image and non-contact time of flight (TOP) range image. The camera system consists of an amplitude modulated light source, an image dissector tube, a phase measuring circuit, and a host PC for system control. A semiconductor diode laser light source or a white light source and Kerr cell is used to generate continuously high frequency modulated light for bulk illumination of the scene to be viewed. A compact, 25 mm diameter image dissector camera (Hamamatsu N2730 or R4193) is used as a receiver to detect the modulated light and generate both a two-dimensional intensity image and a range image. The range is obtained by measuring the phase between the received signal and the transmitted signal. With the large detection area and the random access property of the image dissector camera, it is easy to scan systematically and electronically the illuminated area, within the frame, to identify the required object. Three different modulated frequencies (between 10 MHz and 45 MHz) have been used to obtain a range accuracy of 4 mm, over a distance of 10 m, within a time period of 10 ms per pixel. A demonstration of the three-dimensional vision system has been given, having an update time of 1 s during which a high resolution intensity image (300 × 300 pixels) is produced together with a limited number (100) of range measurements obtained for important features.