Design and Testing of an End-Effector for Tomato Picking

Abstract

Based on the structural shortage of an agricultural labor force and the continuous increase in tomato planting scale in China, as well as the limitation of a greenhouse working environment on the development of tomato picking productivity, a motor-driven end-effector for a tomato picking robot based on a hybrid force/position control strategy was designed. First, a hybrid force/position control strategy was applied to control the picking process. Consistent with this strategy, the mechanical structure design of the end-effector was determined. The maximum torque of the finger joint motor was verified by applying a load to the end-effector fingertip under a parabolic linear angular velocity. Second, the D-H method was used to establish the end-effector single-finger and whole-hand coordinate systems and to perform forward and inverse kinematic analysis. The Monte Carlo method was used to analyze the workspace of the end-effector, and an isochronous interpolation algorithm was used to analyze the angular displacement of the motor. A basic algorithm for starting, stopping and accelerating the finger joints was designed to achieve the smooth movement of the end-effector. The control system for the end-effector was designed based on STM32F103ZET6, and the end-effector remote wireless debugging system was designed based on Tiny6410. Finally, a test prototype of the tomato picking end-effector was manufactured and picking tests were conducted, which showed that our tomato picking end-effector moved smoothly. The proposed control algorithm reduced the impact force and recorded the contact force between the end-effector and the tomato in real time, and the end-effector essentially achieved nondestructive picking. Therefore, our tomato picking end-effector demonstrated good utility in practice.

Adaptive End-Effector Buffeting Sliding Mode Control for Heavy-Duty Robots with Long Arms

“…The hybrid force/position control strategy [14] is the idea of simultaneously using a position controller and force controller for control, as shown in Figure 1. For robots facing multiple degrees of freedom, the selection matrix S and (I − S) can be introduced to determine the control mode of each joint.…”

Design and experimentation of multi-fruit envelope-cutting kiwifruit picking robot

“…Fruit and vegetable-picking robots are generally composed of robotic arm, end-effector, mobile mechanism, and control system. In recent years, scholars have conducted a series of studies on fruit and vegetable picking robots such as kiwifruit ( Fang et al., 2023 ; Gao et al., 2023 ), apple ( Miao and Zheng, 2019 ; Kuznetsova et al., 2020 ), citrus ( Mehta and Burks, 2014 ; Sun et al., 2023 ), tomato ( Ling et al., 2019 ; Wang T. et al., 2023 ) and so on. For example, Williams et al.…”

“…Fruit and vegetable-picking robots are generally composed of robotic arm, end-effector, mobile mechanism, and control system. In recent years, scholars have conducted a series of studies on fruit and vegetable picking robots such as kiwifruit (Fang et al, 2023;Gao et al, 2023), apple (Miao and Zheng, 2019;Kuznetsova et al, 2020), citrus (Mehta and Burks, 2014;Sun et al, 2023), tomato (Ling et al, 2019;Wang T. et al, 2023) and so on. For example, Williams et al (2020) designed a four-armed parallel kiwifruitpicking robot, which separated the fruit from the stalk by rotation after the end-effector gripped the kiwifruit with two fingers, the fruit was automatically collected into a fruit box after each picking action the average time required for harvesting each fruit was 5.5 seconds, with a fruit recognition rate of 76.3% and a successful harvesting rate of 51%.…”