Design and experiment of vibration-collision coupling electronic fruit (VCCEF) device

Fruits are continuously subjected to the multiple mechanical loads, such as the vibration, collision, and impact during harvesting, sorting, and transportation. The coupling scenario can often lead to the fruit quality deterioration and post-harvest losses. However, the existing electronic fruit devices have been mostly designed for the single-load scenarios, such as the dropping, extrusion, and collision. The sensors and data acquisition cannot accurately capture the dynamically mechanical response of the single and clustered fruits under vibration-impact coupling scenarios. It is required to explore the evolution mechanism of the post-harvest mechanical damage to the fruits. In this study, a vibration-collision coupling electronic fruit (VCCEF) device was developed to simultaneously acquire the dynamic response of the fruit vibration acceleration and collision force. The fresh grapes were taken as the experimental object. The device was composed of a three-dimensional vibration, a three-dimensional collision measurement, and a vibration-impact data synchronous acquisition. A triaxial acceleration sensor was integrated inside a spherical shell with the piezoelectric ceramics. The synchronous and high-precision data acquisition was then achieved in the collision impact force, vibration acceleration, and coupled dynamic responses. Meanwhile, a double pedicel-fruit composite was constructed for the data acquirement. Synchronous acquisition, analysis, and verification were realized for the multi-fruit vibration-impact data. Finally, a series of tests were also carried out to explore the vibration-impact coupling evolution of the multi-fruit-pedicel systems. Three-dimensional vibration measurement was calibrated after exploration. Test results showed that the relative error of the triaxial acceleration was ranged from 4.24% to 7.27%, fully meeting the test requirements within an acceptable range. The coefficient of determination (R²) of the collision force-induction voltage fitting curve reached 0.9957, indicating an excellent fitting. The vibration-impact coupling tests were also conducted on the double fruit under different deflection angles (30°/45°/60°/75°). The vibration-impact patterns of the fruit particles were similar among the four groups of the deflection angles. At the moment when the vibration-impact occurred, the peaks were instantaneously obtained in the collision force of the piezoelectric ceramic shell and the acceleration of the internal triaxial acceleration sensor, with a time deviation of 71 ms between the two peak moments, indicating the excellent synchrony. The collision force peak of the double pedicel-fruit device increased from 1.19 to 2.59 N, with a total increase of 117.65%. Furthermore, there was a non-linear increase in the collision force peak, as the deflection angle increased. The output signal of the piezoelectric ceramic was positively correlated with the force rate, according to the direct "mechanical-electrical energy" conversion. Its response to sudden changes in the instantaneous force then reached the microsecond level. The response of the triaxial acceleration to the collision exhibited the significant directionality, indicating the differential variations in the deflection angle. Among them, the peak value (absolute value) of the Y-axis acceleration increased by 210% in total from 30° to 75°, which was always the largest component among the three axes. There was the strongest correlation with the collision force peak. The electronic fruit was used to accurately capture the variations in the collision force under different deflection angles, fully meeting the measurement requirements of the fruit micro-collisions; Subtle differences were identified from the acceleration under various deflection angles, in order to characterize the "instantaneous loading" feature of the collisions. In conclusion, the VCCEF can be expected to accurately monitor the vibration-impact dynamic information among fruits. The finding can provide the equipment and methodological support for the time-domain response and dynamic transmission of the fruit unsteady collisions, in order to optimize the mechanical parameters of the fruit harvesting and transportation.