Video-speed Triangulation Range Imaging

When a light plane is projected on a scene, the resulting profile line can be recorded by a camera system looking from aside. This technique for range imaging with a 1-D or 2-D video camera is well known. It takes the recording of an image line (say 256 pixels) to establish the position of one profile point. If a 1-D video camera (line camera) is replaced by a Position Sensitive photo Detector (PSD) the position is found from only two current values, simultaneously measured. A speed gain of 256 is thus achieved. However, like the line camera the PSD is a 1-D detector that needs a scanning device to measure the different parts of the profile lineWe want the speed gain without the scanning. Therefore, we propose to replace the 2-D videocamera by a novel type of line profile detector: an array of PSDs that allows recording of a profile in a video line time (64us)To realize a video-speed range camera a PSD-array chip has been constructed. On the 10 × 10 mm2 large chip a row of 96 single PSDs have been implemented to be read out externally. In the experimental configuration a fan beam strikes the surface of a test object (cross section 100 × 30 mm2). With a 50 mm camera-lens the illuminated profile of the surface is imaged on the array sensor. The arrangement used is of the triangulation type: the height z at a lateral position xi at the object is sharply imaged at position z’ on the corresponding single PSD numbered “i”. The position z’ and thus the height z follow directly from both currents of the PSDUsing a 2MHz clock and a multiplexing system all 96 PSDs can be read out in less than a video line time. By moving the object relative to the fan beam (either by a conveyor belt or by a scanning mirror) a real time video image of 256 range profiles is formedIn this paper preliminary results are given, based on the read-out of a subset of eight PSDs of the array sensor