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 0.82μ 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 360° 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 ∿lKHz. The ranging resolution at 20 ft. is ∿2.5 inches, which is close to the theoretical limit possible for the radiated power, bandwidth, optics and receiver employed. The system is capable of reading wall bar codes “on the fly” and is in addition capable of simultaneously ranging and acting as a wideband optical communication receiver. Total parts cost for the optical transmitter, Fresnel lens, receiver and all the electronics is <$200. The remaining major parts, consisting of the rotating mirror, ring mounting, motor and incremental encoder, cost <$500.
KeywordsAutomatic Gain Control Automate Guide Vehicle Optical Ranger Fresnel Lens Automate Guide Vehicle System
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