A DESIGN FOR A VISUAL-MOTION TRANSDUCER

Autonomous vehicles could benefit greatly from visual-motion sensors of sufficiently low cost that 10 or 20 of them could be distributed around the vehicle's periphery. Conventional arrangements with CCD cameras, framestores and computers are too expensive. A design is outlined here that builds on well-known schemes using gratings. The grating principle is illustrated by the fact that a man with a torch, walking at night behind a railing, seems to flash. The frequency of flashing is proportional to his velocity. A major drawback is that backward and forward motion are not distinguished. The key development here is the use of commutation as a means of modulating the grating output signal. This is equivalent, in the illustration above, to simulating stroboscopic motion of the railing. Thus, when the man is stationary, there is flashing at a resting frequency. When he moves one way the frequency increases, and for motion the opposite way, frequency decreases. Results from an analogue implementation of the visual motion transducer are presented. The current transducer measures translational motion across the grating. The design is also shown to be capable of extension to direct measurement of the divergence and curl of the flow field.