Estimating the Tree Canopy Acceleration Required for Optimal Mechanical Harvesting Performance

Mechanical harvesting of ripe fruit should significantly increase fruit picking productivity and reduce harvesting times and operating costs. This study presents the optimal average gravitational acceleration of grapefruit tree branches obtained with a self-propelled citrus canopy shaker that varied the number, vibrational speed, and canopy penetration depth of the beating arms. Accelerometer sensors measured vibration and acceleration, and the fast Fourier transform (FFT) algorithm analyzed the vibration data. The acceleration values reflected the behavior of the tree branches in response to harvester shaking and varied with different harvester configurations and accelerometer placements in the tree canopy. The magnitude of the gravitational acceleration (g) increased significantly by increasing the number of shaking beaters, the shaker’s penetration into the tree canopy, and increasing the harvester’s shaking speed. The initial 14 beaters only provided acceleration values of 8.00 g maximum, 1.93 g minimum, and 5.044 g averages. Using 26 beaters yielded a maximum of 14.09 g, a minimum of 6.27 g, and an average of 8.65 g. Increasing the shaking speed also increased the forces applied to the tree canopy. An average of 7.387 g, achieved at 45.3 in/s, increased to 8.004 g at 65.9 in/s. Higher (g) values resulted in increased grapefruit fruit dislodgement, with 100% fruit removal on some trees.