A Study On Helmholtz Resonant For Volume Measurement And Detection Of Watermelon Internal Hollow

China is a major watermelon producer as well as a major watermelon consumer, the detection and grade of watermelon quality has capacious market future. However, it has long been a challenge to obtain fast and ac-curate volumetric measurements.This study aims to investigate a new method-Helmholtz Resonant in predicting the volume of watermelon, and then get the density information to predict the hollow of watermelon. Main research content, results and conclusions are summarized as follows:(1) An experiment systym based on the Helmholtz Resonant theory was set up to realize the watermelon volume detection. The main part consisted of a signal generator, an amplifier, a loudspeaker, a resonator, a microphone (INV9206), data acquisition module (NI USB-4431) and data analysis software.(2) The suitable parameters of the Helmholtz resonant system was investigated to get precise volume detec-tion. By single-factor and orthogonal experiments, optimal parameters combination was220mm of dis-tance from microphone to port opening,120mm of height from loudspeaker to port opening and10s of testing time. A number of65watermelons were estimated using this system and the actual volumes of watermelons were measured by water-filling method. The result showed that the determination coeffi-cients R2for the calibration sets (47watermelons) and validation sets (18watermelons) were0.9655and0.9568, respectively. A percentage of72.2of the samples were found to have a relative volume error low-er than7%.(3) To improve the modeling result,176watermelons separated into calibration set (119) and validations set (57) were measured. The resonant frequency and actual volume were modeled in liner, quadratic, negative quadratic regression methods. The result was that the negative quadratic gave a better vulome prediction with a relative error of5.232%. When the density was below0.925g/cm3, there were some cracks in some watermelon. And below0.877g/cm3, the lower the density, the bigger the cracks showed. The Binary Lo-gistic and SVM (Support Vector Machine) methods were used to judge the watermelon with or without hollow and the Binary Logistic method based on negative quadratic model showed a better performance in predicting the hollow of watermelon with an overall correct of82.5%.(4) An online non-destructive system to detect the density of watermelon was established. The system in-cludes the measurement, delivery and controlling parts. The measurement part contains gravity and vol- ume detection units which could realize the density deduction. The delivery part contains speed chain, stoppers and electronic approach switches. By controlling the stoppers, electronic approach switches, motor the controlling part realize the online delivery and measurement.