Energy efficacy analysis of a mechanical shaker in sweet cherry harvesting

• Field tests for assessing the energy efficacy of mechanically harvesting cherry.
• Majority of applied fruit removing energy was kept on the excited branch.
• Higher excitation frequency achieved higher fruit removal efficiency.
• Energy efficacy decreased rapidly with increasing accumulative harvesting duration.

To obtain the baseline information for designing a high efficiency mechanical sweet cherry harvester, a series of dynamic and harvesting tests were conducted in orchards. In the dynamic test, a mechanical shaker was used to shake branches of target trees. Three trees were randomly selected for the study and each studied branch of the tested trees was divided into three response zones where one accelerometer was mounted on each zone to record the response to the input excitations. The kinetic energy induced by the input excitation in each response zone was tracked during the course of energy delivery. Results from these dynamic response tests showed that the kinetic energy delivered to an excited branch on average accounted for 60%, 77%, 92% and 95% of input excitation energy at shaking frequency of 6, 10, 14, and 18 Hz, respectively. Harvesting tests were also conducted using shaking frequencies of 14 and 18 Hz, and test trees were shaken using a sequence of four 5 s long intermittent excitations. On average, the shaker removed 67 ± 16% of the fruit during the first cycle of 18 Hz shaking, and 42 ± 16% with 14 Hz shaking. The shaker energy efficacy, defined as the percentage fruit removal per kilo-joule of input energy, was 6.9 ± 2.2% kJ−1 and 7.4 ± 1.3% kJ−1 during the first cycle of 14 and 18 Hz shaking, respectively. The results indicated that the 18 Hz shaking frequency reached higher fruit removal efficiency when compared to the 14 Hz shaking frequency with similar energy efficacy.