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Obtaining the effective gripper dimensions for a kiwifruit harvesting robot using kinematic calibration procedures

Chi Kit Au (School of Engineering, University of Waikato, Hamilton, New Zealand)
Michael Redstall (School of Engineering, University of Waikato, Hamilton, New Zealand)
Mike Duke (School of Engineering, University of Waikato, Hamilton, New Zealand)
Ye Chow Kuang (School of Engineering, University of Waikato, Hamilton, New Zealand)
Shen Hin Lim (School of Engineering, University of Waikato, Hamilton, New Zealand)

Industrial Robot

ISSN: 0143-991x

Article publication date: 1 December 2021

Issue publication date: 30 June 2022

165

Abstract

Purpose

A harvesting robot is developed as part of kiwifruit industry automation in New Zealand. This kiwifruit harvester is currently not economically viable, as it drops and damages too many kiwifruit in the harvesting task due to the positional inaccuracy of the gripper. This is due to the difficulties in measuring the exact effective dimensions of the gripper from the manipulator. The purpose of this study is to obtain the effective gripper dimensions using kinematic calibration procedures.

Design/methodology/approach

A setup of a constraint plate with a dial gauge is proposed to acquire the calibration data. The constraint plate is positioned above the robot. The data is obtained by using a dial gauge and a permanent marker. The effective dimensions of the gripper are used as error parameters in the calibration process. Calibration is exercised by minimizing the difference between target positions and measured positions iteratively.

Findings

The robot with the obtained effective dimensions is tested in the field. It is found that the fruit drops due to positional inaccuracy of the gripper are greatly reduced after calibration.

Practical implications

The kiwifruit industry in New Zealand is growing rapidly and announced plans in 2017 to double global sales by 2025. This growth will put extra pressure on the labour supply for harvesting. Furthermore, the Covid pandemic and resulting border restrictions have dramatically reduced seasonal imported labour availability. A robotic system is a potential solution to address the labour shortages for harvesting kiwifruit.

Originality/value

For kiwifruit harvesting, the picking envelope is well above the robot; the experimental data points obtained by placing a constraint plate above the robot are at similar positions to the target positions of kiwifruit. Using this set of data points for calibration yields a good effect of obtaining the effective dimension of the gripper, which reduces the positional inaccuracy as shown in the field test results.

Keywords

Citation

Au, C.K., Redstall, M., Duke, M., Kuang, Y.C. and Lim, S.H. (2022), "Obtaining the effective gripper dimensions for a kiwifruit harvesting robot using kinematic calibration procedures", Industrial Robot, Vol. 49 No. 5, pp. 865-876. https://doi.org/10.1108/IR-09-2021-0198

Publisher

:

Emerald Publishing Limited

Copyright © 2021, Emerald Publishing Limited

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