Design and fabrication of an underactuated end effector for plum picking by a single SMA spring

Abstract In the contemporary manufacturing sector, the integration of automation and intelligent technologies has emerged as a crucial driving force for enhancing productivity and product quality. This study proposes an underactuated picking manipulator end-effector design utilizing a shape memory alloy (SMA) spring to address challenges related to labor shortages and inefficiencies in the harvesting process of economic forest fruits, such as plums and peaches. Through comprehensive analysis involving theoretical frameworks, simulations, and experimental validations, it is demonstrated that the SMA spring-based underactuated picking end-effector developed in this research can achieve non-destructive harvesting of plums or other perishable fruits with diameters ranging from 20 mm to 70 mm. In contrast to conventional picking end-effectors, the proposed SMA spring underactuated design replaces motorized drive systems with SMA springs, thereby simplifying the mechanical structure. The control system of the end-effector incorporates feedback closed-loop control for gripping force management, which precisely regulates the contraction force of the SMA spring to ensure stability and reliability during the gripping process. This study offers a valuable technical reference for automated and intelligent harvesting within agroforestry contexts while also presenting innovative concepts for flexible gripping applications in intelligent manufacturing.