Mold number reader with field optics photodetector

摘要

A mold number reader for detecting code marks at the heel of a transparent bottle or the like, such code marks desirable being in the form of dots or balls protruding from the bottle's heel. During rotation of the bottle, its heel portion is illuminated with a structured light source in the form of a narrow rectangle, which light is selectively reflected by code marks and collected by field-type optics. The use of a well defined light source of small area provides a high input signal level, while the field optics enjoys a high depth of field and hence decreased sensitivity to bottle placement during inspection. The light source may be a modulated laser diode and the signal processing electronics may include a demodulator to process the photodetector output signal. The use of heterodyned signal processing decreases the sensitivity to ambient light and other sources of noise in the output signal.