An optical rangefinder for autonomous robot cart navigation.

A simple, low cost, infra-red rangefinder has been developed for investigation of autonomous robot cart navigation in factories and similar environments. A 2mW 0.82micron LED source (not a laser) is 100% amplitude modulated at 5MHz and used to form a collimated 1" diameter transmit beam that is unconditionally eye-safe. Returning scattered radiation is focussed by a 4" diameter coaxial Fresnel lens onto a p-i-n silicon photodiode. Range is determined from the phase shift between the 5MHz modulation on the transmitted and received signals. Use of a rotating mirror provides 360degrees polar coordinate coverage of both distance and reflectance out to ~20 ft. around the vehicle. Both radial and angular resolution correspond to ~1 inch at a ranging distance of 5 ft., with an overall bandwidth of ~ 1KHz. The ranging resolution at 20 ft. is ~2.5 inches and approaches the theoretical limit possible for the radiated power, bandwidth, optics and receiver employed.