Apple Impact Bruising Mechanism And Targeted Shake-and-Catch Harvesting For Fresh Market Apples In Trellis Trained Trees

Developing mechanical harvesting is an effective approach to improve productivity and reduce intensity. Mass shake-and-catch harvesting offers an alternative solution to potentially obtain high harvest efficiency. However, it needs to address a crucial challenge of reducing harvest induced fruit damages before being popularized. This paper aimed at exploring the apple impact bruising rules on varying surface zones qualitatively and quantitatively by studying apple impact bruising mechanisms from theoretical modelling and experimental methods innovation. In addition, the feasibility of the targeted shake-and-catch harvesting was verified by field trials for the new trellis trained apple trees. The major works were summarized as follows:(1) Based on Hertz contact theory and elastoplastic mechanics, the equations of contact force and relative proximity as well as contact force and bruising area were deduced for the collision between two fruits considering the softening characteristics when plastic deformation occurring.Then, the theoretical method was verified by examples and finite element simulation. It was further applied to the case of fruit impacting catching surface. Finally, the effect of different factors on apple impact bruising damage was discussed based on the theoretical equations.(2) Studied apple bruising mechanism by simulating the free collision between two fruits on varying surface zones via a developed pendulum-type impact device. The relationship between contact force and fruit bruised area was verified. And the quality assessment models for each fruit surface zone were obtained with seven different levels of normal impact force. The results indicate that the bruising resistant ability of apple surface zone gradually decreases along the direction from stem to calyx in the view of bruising probability; the impact force should be controlled around 15 N for bruising free collision between two apples.(3) Studied apple bruising mechanism for varying surface zones impacted by cushioning materials using the pendulum device under seven varying levels of impact force. The relationship for the contact force and fruit bruised area was also verified through this experiment. The quality assessment models were obtained for each fruit zone impacted by each of the three types of cushioning materials. The results indicate that the bruising-resistance of tested apples was noticeably improved with the use of cushioning materials, namely Polyurethane foams with different pressure ratings of 2.1-11 kPa; the improvement with foam pressure ratings of 2.1?4.8 kPa was more obvious while the difference was only slight with foam pressure ratings of 4.8?11 kPa; among the three surface zones of an apple from stem to calyx, the fruit bruising resistance near to stem is the weakest while the difference of that for the other two zones is slight; when"jazz" apple is cushioned, the foam with 5.0 kPa pressure is suggested to select and bruising-free impact force should be controlled under 160 N, since the bruising resistant ability tends to be saturated when the pressure reaches a certain value.(4) Studied apple bruising mechanisms for other cultivars when impacted by cushioning materials under seven varying levels of impact force. And the quality assessment models for fruit surface zone which is more sensitive to bruise were obtained with seven equivalent drop heights.Results indicate that the foams with the pressure of 2.1?11 kPa could obviously improve the ability of each variety to resist bruising damage, and the greater the pressure, the greater the increment; the ability varied greatly for different varieties of apples; the bruising free equivalent heights for the "jazz","Granny Smith" and "Envy"" apples when cushioned by these foams were 54,38 and 34 cm, respectively.(5) Studied shake-and-catch harvesting for fresh market apple in trellis trained trees, such as vertical fruiting wall and V architectures, and developed an electromotor driven vibration device and fruit capturing platform. The deceleration and separation mechanism for the capturing platform was determined by indoor drop test using an electronic fruit impact instrument. This mechanism was also verified by field experiment carried out in an orchard in which trees were trained in vertical fruiting wall architecture. Results show that when the excitation frequency was 15, 20 and 25 Hz, the fruit removal efficiencies were 84%, 86% and 92% respectively, and the percentages of apples that satisfied fresh market grades were 90%, 94% and 80% respectively.Results indicate that the proposed targeted shake-and-catch harvesting can obtain higher fruit removal efficiency and quality,and has a promising potential.The results of this study can provide the baseline information and theoretical support for the optimization of fruit capturing device during shake-and-catch harvesting,and also provide an effective new approach for mechanical harvesting fresh market apples.