Perforated paper feed apparatus with an optical system for detecting the presence and/or motion of the paper

摘要

A perforated paper feed mechanism such as a tractor has an optical system for detecting the presence of the form and particularly the motion of the form and utilizes a reflector which may be mounted on the lid of the tractor at one end of the tractor (where the paper enters or leaves the tractor). The optical system may be implemented by a prism which folds the path of light from a light source (an LED) to a photo detector (a photo-transistor) the path is aligned with the perforations in the paper. Since the perforations are spaced, the photo transistor provides a train of pulses as the paper is fed by the tractor. A pulse detector responds to the presence or absence of pulses within a given period of time comparable to the time when perforations are fed past the optical path. An output from the detector thus indicates whether the paper is in motion and is being fed by the tractor. Failure to receive pulses indicates either the absence of paper (paper out) or a jam in the feed.