Foreign body detection by reflected polarised infrared light - esp. for ejection from vegetables processed in food factory

摘要

Foreign bodies travelling along a conveyor together with loose vegetables are detected and ejected by a device using a multi-channel system. This depends upon the reflection of polarised infra-red light and is erected above the conveyor. Each channel consists of a modulated infra-red light source, synchronised with the light sources of the other channels, and an infra-red receiver which detects the reflected light. The signal obtd. is amplified and filtered and is fed to a delayed automatic amplifier control circuit. This attempts to hold the output signal at a definite level, and the output signal is fed to at least one double comparator. There the signal is compared continuously with two independent reference levels which can be adjusted for all channels in common. These comparators deliver an output signal when the output signal of the automatic amplifier control circuit is outside the interval between the two reference levels, and this output signal from the comparators is used to energise an ejector for seperating the foreign bodies from the good prods. The common reference levels determining the greater or lesser reflection limits are adjusted by thumb wheel switches via digital analog converters. The ejection instructions from the comparators are assembled in gps. for the control of a single ejector for each gp. The signals are fed to a shift register which moves the instruction through and puts on a signal when the object to be removed reaches the ejector. Each ejector is controlled for a period corresponding to the length of the object to be removed. Process reliably and automatically prevents the inclusion of dirt, small animals, etc. in the goods filled into containers for deep freezing or canning.