Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Electrical Engineering

Major Professor

Donald W. Bouldin

Committee Members

Frank Speckhart

Abstract

A system for the detection and counting of small objects is presented. This system was designed, implemented, and tested successfully. The system can detect objects as small as 1 mm. Accuracy is maintained at flow rates of 110 objects/s although normal flow rates are generally less than 20 objects/s. Tests revealed an overall accuaracy of 99.867%. This system works in conjunction with a small object counting machine. The counting machine separates the objects so that they fall through a small tube in a somewhat single-file fashion. The machine is designed specifically for handling and counting pharmaceutical pills that range in size from 1 to 25 mm. The pills fall through a clear plastic square tube where they are detected and counted by this system. The majority of the circuitry was implemented in a complex programmable logic device (CPLD) chip. The chip interfaces with infrared light-emitting diode (IRLED) sensor circuits that produce voltage pulses as objects fall through the small tube. The chip uses a pattern recognition algorithm that interprets these pulses and produces a counter output that is read by the counting machine's microcontroller chip where count totals are tallied. The pattern recognition chip can detect two objects should they fall through simultaneously. The chip also eliminates double counts caused by objects that might fall in such a manner that two pulses are generated by one object. This thesis discusses three schemes for the arrangement of IRLEDs for detection of falling objects; steady beam arrays of IRLEDs, pulsed arrays of IRLEDs, and a single IRLED-lens combination with a single chip pixel array sensor.

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