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Design of an End-effector with Application to Avocado Harvesting

Jingzong Zhou, Xiaoao Song, Konstantinos Karydis

TL;DR

This work tackles avocado harvesting by designing a rigid, five-finger end-effector mounted to a robotic arm that first grasps the fruit and then applies a rotational moment to detach it from the peduncle. A force-based analysis guides finger geometry and motor requirements, and preliminary experiments validate concept feasibility. In-lab tests with Hass avocados show a 100% success rate across sizes and viewing poses, with CV grasping requiring less arm rotation than FV. Comparisons with vacuum suction demonstrate limitations of suction on avocados, underscoring the practical value of a rigid, two-stage end-effector for reliable field harvesting and motivating future perception, autonomy, and field deployment work.

Abstract

Robot-assisted fruit harvesting has been a critical research direction supporting sustainable crop production. One important determinant of system behavior and efficiency is the end-effector that comes in direct contact with the crop during harvesting and directly affects harvesting success. Harvesting avocados poses unique challenges not addressed by existing end-effectors (namely, they have uneven surfaces and irregular shapes grow on thick peduncles, and have a sturdy calyx attached). The work reported in this paper contributes a new end-effector design suitable for avocado picking. A rigid system design with a two-stage rotational motion is developed, to first grasp the avocado and then detach it from its peduncle. A force analysis is conducted to determine key design parameters. Preliminary experiments demonstrate the efficiency of the developed end-effector to pick and apply a moment to an avocado from a specific viewpoint (as compared to pulling it directly), and in-lab experiments show that the end-effector can grasp and retrieve avocados with a 100% success rate.

Design of an End-effector with Application to Avocado Harvesting

TL;DR

This work tackles avocado harvesting by designing a rigid, five-finger end-effector mounted to a robotic arm that first grasps the fruit and then applies a rotational moment to detach it from the peduncle. A force-based analysis guides finger geometry and motor requirements, and preliminary experiments validate concept feasibility. In-lab tests with Hass avocados show a 100% success rate across sizes and viewing poses, with CV grasping requiring less arm rotation than FV. Comparisons with vacuum suction demonstrate limitations of suction on avocados, underscoring the practical value of a rigid, two-stage end-effector for reliable field harvesting and motivating future perception, autonomy, and field deployment work.

Abstract

Robot-assisted fruit harvesting has been a critical research direction supporting sustainable crop production. One important determinant of system behavior and efficiency is the end-effector that comes in direct contact with the crop during harvesting and directly affects harvesting success. Harvesting avocados poses unique challenges not addressed by existing end-effectors (namely, they have uneven surfaces and irregular shapes grow on thick peduncles, and have a sturdy calyx attached). The work reported in this paper contributes a new end-effector design suitable for avocado picking. A rigid system design with a two-stage rotational motion is developed, to first grasp the avocado and then detach it from its peduncle. A force analysis is conducted to determine key design parameters. Preliminary experiments demonstrate the efficiency of the developed end-effector to pick and apply a moment to an avocado from a specific viewpoint (as compared to pulling it directly), and in-lab experiments show that the end-effector can grasp and retrieve avocados with a 100% success rate.
Paper Structure (12 sections, 10 figures, 3 tables)

This paper contains 12 sections, 10 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Preliminary Experimentation for Harvesting
  3. End-effector Design
  4. Working Assumption
  5. Design Overview
  6. Force Analysis
  7. Experimental Testing and Results
  8. Experimental Setup
  9. Harvesting Work Flow
  10. System Validation, Comparative Assessment of Different Grasping Poses, and Discussion of Key Findings
  11. Comparison with Vacuum Gripper
  12. Conclusions and Future Research Directions

Figures (10)

  • Figure 1: We developed a custom-built end-effector attached to an off-the-shelf 6-DOF robotic arm for avocado harvesting.
  • Figure 2: Fruit coordinate system and viewpoints for the avocado.
  • Figure 3: Instances of force measurement tests from three grasping directions.
  • Figure 4: Our working assumption is to model an avocado as a cylinder.
  • Figure 5: Mechanical diagram of the developed end-effector.
  • ...and 5 more figures