음파를 이용한 수박의 내부품질을 비파괴적으로 판정하는 시스템을 개발하였다. 개발된 수박품질판정기는 크기가 $200{ imes}200;mm$, 무게가 290 g로 휴대가 가능하여 수박 재배포장, 집하장, 슈퍼마켓 등 현장에서 쉽게 사용가능하도록 개발하였다. 수박의 음파수집한 후 음파데이터에서 영교차율, 피크(peak)점간 거리 표준편차, 시간파형에서 진폭 적분값, 주파수대역 에너지, 영점빈도수와 같은 특징인자를 추출하여 내부품질을 판정할 수 있는 주성분회귀 모델개발에 이용하였다. 개발된 수박의 주성분회귀 모델의 상관계수는 0.79, SEC는 0.28로 판정정확도는 87% 이었으며, 모델 검증한 결과 상관계수가 0.78, SEP가 0.785로 판정정확도가 83%이었다. 생산자 내부품질판정 정확도를 조사한 결과, 생산자 판정 정확도는 75% 이었다.
Watermelons (Citrulus vulgaris Schrad) are usually sorted manually by weight, appearance, and acoustic impulse, so grading of maturity and internal quality is subject to inaccuracies. It was necessary to develop a nondestructive evaluation technique of internal watermelon quality to reduce human error. Thus, acoustic characteristics related to internal quality factors were analyzed. Among these factors, three (ripeness, presence of an internal cavity, and blood-colored flesh) were selected for evaluation. The number of peaks and the sum of peak amplitudes for watermelons with blood-colored flesh were lower than for normal fruits. The portable evaluation system has an impact mechanism, a microphone sensor, a signal processing board, an LCD panel, and a battery. A performance test was conducted in the field. The internal quality evaluation model showed 87% prediction accuracy. Validation was conducted on 72 samples. The accuracy of quality evaluation was 83%. The quality of samples was evaluated by an inspector using conventional methods (hitting the watermelon and listening to the sounds), and then compared with prototype results. The quality evaluation accuracy of the prototype was better than that of the inspector. This nondestructive quality evaluation system could be useful in the field, warehouse, and supermarket
