Measurement and Study of Mechanical Characteristics of Hydroponic Lettuce for automatic harvesting

To design an automatic harvesting machine for hydroponic lettuce, the physical and mechanical properties of hydroponic lettuce were investigated and analyzed. Moisture content of stem, root and leaf, geometric characteristics, pulling force, and root cutting force were studied for harvesting hydroponic lettuce. The pulling force was examined by a tensile experiment, and the root cutting force was investigated by a shear experiment on the electronic universal testing machine. The moisture content of hydroponic lettuce was obtained by direct drying. The experiment data were processed using regression analysis and mathematical statistics method. A regression equation and the law of numerical distribution were obtained. The results showed that the geometrical characteristics of the hydroponic lettuce had little change, and the distribution of physical parameters was concentrated. Moisture content was found statistically similar in stem and root (around 91%), while the highest moisture content was found in the leaf of 95.73%. The root cutting force decrease with the increase of cutting speed and decrease with the cutting position move downward. The minimum average root cutting force in the experiment was 1.41 N. The average pulling force was 13 N. This study provides adequate theoretical support for the design of the automatic harvesting machine of hydroponic lettuce.