Kiwifruit harvesting impedance control and optimisation

Abstract

This study proposes a flexible kiwifruit grasping strategy using impedance control to extend storage time, reduce picking costs, and minimise mechanical damage during harvesting. The main contribution of this strategy is integrating a fuzzy PID controller into the impedance-based kiwifruit picking system, which significantly reduces mechanical damage during the picking process. Compression tests were performed on kiwifruit to obtain viscoelastic parameters, and the Burgers model was used to describe the rheological behaviour to understand the deformation characteristics of kiwifruit under force. Subsequently, a force-based impedance control system was established using the relationship between contact force and gripper displacement to achieve precise control of the fruit-grasping process. Additionally, to enhance the performance of the impedance control system, an optimised solution was applied at the controller output. Simulation analysis shows that the optimised fuzzy PID control strategy reduced the system's settling time from 1.91 s to 1.08 s compared to traditional impedance control systems. Experimental results further validate that the new control strategy effectively reduces fruit damage, achieving flexible and high-quality kiwifruit picking. This approach also provides valuable technical references for the post-harvest automation of other soft fruits and vegetables.