End-Effector Technologies

The efficiency and effectiveness of end-effectors greatly influence the overall performance of the robotic systems as they come into direct contact with the objects being manipulated by the robot. Considering the extensive need of robotic technologies for various labor-intensive tasks in agriculture, end-effectors for agricultural robots are required to handle a great diversity of objects, such as fruit, leaves, flowers, stems, and even animal body parts. Example end-effectors that depict special challenges faced in agricultural robotics are the end-effectors for picking fresh market fruit such as tomato, apples and oranges. There have been wide research and development efforts around the world in developing efficient and robust fruit picking end-effectors. Therefore, this chapter provides a comprehensive review on the existing end-effectors for fresh-market fruit picking/harvesting. The end-effectors were categorized according to the principle of fruit picking: (i) fruit-holding mechanisms; (ii) stem-holding mechanisms; and (iii) direct separation. Specially for fruit-holding end-effectors, five different categories of methods for flexible fruit holding were introduced in detail: (i) elastic buffering; (ii) under-actuated fingers; (iii) flexible driving; (iv) clamping force feedback system; and (v) air suction. With reference to these methods, crucial parameters for designing an effective picking end-effector were discussed in depth including finger configuration, number of fingers, and physical property of fruit. Besides, major challenges on picking fresh market fruit with an automatic end-effector were discussed. Finally, some thoughts and insights on the future trends in technology advancement and potential solutions for overcoming the existing technical challenges were presented.