A multiple-beam optical sensing system for an article vendor having a delivery station to which an article to be vended is delivered during the vend which system includes first and second optoelectronic emitters, first and second optoelectronic detectors, a circuit for energizing the emitters, and a...http://www.google.com.au/patents/US4252250?utm_source=gb-gplus-sharePatent US4252250 - Multiple-beam optical sensing system for an article vendor
