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Image Cone Models Detect Roselle Calix (Hibiscus sabdariffa) Weight Remotely

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Applied Engineering in Agriculture. 32(6): 685-695. (doi: 10.13031/aea.32.11611) @2016
Authors:   Federico Hahn, Alejandro Barrientos, Tim Jenkins, Javier Hernández
Keywords:   Geometrical properties, Hibiscus sabdariffa, Image processing, iPhone, Non-contact weight measurement, Roselle.


Roselle () is cultivated for its human health benefits. Roselle calyxes are dried to extend their shelf life while trying to maintain their antioxidant properties. Small-scale Mexican producers require driers of 1 ton per day to avoid calyx pathogen contamination. Prior to this, a 1-calyx prototype had to be built in order to study energy consumption per flower, best calyx position during drying and the effect of airflow recirculation. Producers want to know when the calyx has reached the final relative humidity (RH) to stop the drying process; so a remote weighting system was developed. Three image processing algorithms were proposed based on the geometry of a truncated cone that resembles the roselle calyx. The images were acquired with an iPhone running with a timer application. High correlations between the surface model and calyx weight were found for both fresh and dried calyxes (R2 values of 0.98 and 0.99 respectively). Geometrical dimensions remained constant as the drying process took place, such that inter-calyx height was consistently 33% of calyx height and waist height was 73% of calyx height. Images taken from a 100 kg drier helped to foresee the problems that could be encountered to obtain the calyx parameters. The use of the geometric dimensions reduced the number of measurements required per calyx to two: inter-calyx waist distance and inter-calyx diameter. A high correlation of 0.97 was obtained between calyx weight and the predicted volume with the surface model using those two measurements.

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