Every apple destined for the fresh market is picked by the human hand. Despite extensive research over the past four decades, there are no mechanical apple harvesters for the fresh market commercially available, which is a significant concern because of increasing uncertainty about the availability of manual labor and rising production costs. The highly unstructured orchard environment has been a major challenge to the development of commercially viable robotic harvesting systems. This paper reports the design and field evaluation of a robotic apple harvester. The approach adopted was to use a low-cost system to assess required sensing, planning, and manipulation functionality in a modern orchard system with a planar canopy. The system was tested in a commercial apple orchard in Washington State. Workspace modifications and performance criteria are thoroughly defined and reported to help evaluate the approach and guide future enhancements. The machine vision system was accurate and had an average localization time of 1.5 s per fruit. The seven degree of freedom harvesting system successfully picked 127 of the 150 fruit attempted for an overall success rate of 84% with an average picking time of 6.0 s per fruit. Future work will include integration of additional sensing and obstacle detection for improved system robustness.

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Abstract. Fresh market apple harvesting is a difficult task that relies entirely on manual labor. Much research has been done on the development of mechanical harvesting techniques. Several selective harvesting robots have been developed for research studies, but there are no commercially available robotic systems. This article discusses the design and development of a novel pneumatic 3D-printed soft-robotic end-effector to facilitate apple separation. The end-effector was integrated into a robotic system with five degrees of freedom that was designed to simplify the picking sequence and reduce costs compared to previous versions. Apples were successfully harvested using the low-cost robotic system in a commercial orchard during the fall 2017 harvest. A detachment success rate on attempted apples of 67% was achieved, with an average time of 7.3 s per fruit from separation to storage bin. By conducting this study in an orchard where problematic apples were not removed to increase the detachment success rate, current pruning and thinning practices were assessed to help lay the foundation for future studies and develop strategies for successfully harvesting apples that are difficult to detach. Keywords: Apple catching, Apples, Automated harvesting, Field experimentation, Harvesting robot, Soft-robotic gripper.

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This paper investigates the deflected behavior of unimorph circular piezoelectric diaphragm actuators under electrical loading. Among many other factors that affect the actuators' performance, the effects of the boundary conditions, the thickness ratio of piezoelectric to substrate layers, and the radius of piezoelectric layer bonded to the metallic substrate on the resulting deflection of circular actuators are examined. Analytical models are presented with which to optimize the thickness ratio, and the radius ratio of piezoelectric to substrate for various boundary conditions. Experimental results for two circular actuators with different piezoelectric coverage are also demonstrated to validate the models. The measured deflections for the experimentally tested clamped diaphragms show close correlation with the analytical transverse deflections for elastically supported edge. The analytical solutions presented here can be used to optimize the transverse deflection of circular piezoelectric diaphragm actuators.

This paper presents an analysis of the energy generating performance in a pressure-loaded system using piezoelectric transducer technology. The energy harvesting device in this study is a partially covered, simply supported piezoelectric unimorph circular plate to convert energy from fluctuating pressure into electrical energy. The analysis includes comprehensive modeling and a parametric study to provide a design primer for a specific application in which the frequency of fluctuating pressure is well below the natural frequency of the harvester. An expression for the total power output from the device for a given applied pressure is shown, and then used to determine optimal design parameters. It is shown that the device's deflection and stress under load are the limiting factors in the design. The analytical results indicate that the PMN-PT harvesters can generate over one order of magnitude more power than the PZT harvesters for any substrate material. Some possible factors that can degrade energy harvesting performance are also discussed.

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