Design and Dynamic Analysis of a Bio-Inspired Three-Finger Gripper for Mechanized Saffron Flowers Harvesting

Document Type : Original Article

Authors

1 PhD Student, Mechanical Engineering of Biosystem Department, Aburaihan Faculty, University of Tehran, Tehran, Iran.

2 Associate Professor, Mechanical Engineering of Biosystem Department, Aburaihan Faculty, University of Tehran, Tehran, Iran.

3 Associate Professor, Department of Mechatronics Engineering, School of Intelligent Systems Engineering, College of Interdisciplinary Science and Technology, University of Tehran, Tehran, Iran.

4 Associate Professor, Department of Agronomy and Plant Breeding Sciences, Aburaihan Faculty, University of Tehran, Tehran, Iran.

Abstract

Introduction: Saffron (Crocus sativus L.) is one of the most valuable agricultural products in Iran, contributing over 90% of the world’s total production. Despite its economic importance, the harvesting process remains fully manual, labor-intensive, and time-consuming, leading to high labor costs and potential contamination. The mechanization of saffron harvesting has been hindered by the flower’s fragility, irregular planting patterns, and short harvesting period. In recent years, robotic systems equipped with intelligent end-effectors have shown promise for delicate crop harvesting. However, no practical gripper specifically designed for saffron flowers has been successfully implemented. Therefore, this study aimed to design, model, and analyze the dynamic behavior of a three-finger robotic gripper inspired by the natural hand motion used in manual saffron picking in order to provide a feasible solution for the mechanized harvesting of saffron flowers.

Materials and Methods: In this study, a three-finger mechanical gripper inspired by the manual harvesting of saffron flowers was designed and modeled. The design, developed in SolidWorks, replicated the natural motion of human fingers to enable accurate flower picking without causing damage. Since manual harvesting involves holding the flower with three fingers to separate it from its sheath, the gripper was equipped with three fingers arranged 120° apart to mimic this action. The system is driven by a single electric motor connected to a cam–follower mechanism that converts rotary motion into linear movement. This motion is transmitted through prismatic joints to the fingers, causing them to open and close simultaneously. Two parallel springs between the slider and finger links ensure continuous contact between the cam and follower, allowing smooth and synchronized finger motion. The mechanism’s single degree of freedom enables all three fingers to move together, simplifying control while maintaining stability and precision. A complete 3D model of the gripper, including fingers, cam-follower, and springs, was created in SolidWorks and dynamically analyzed in MSC ADAMS. All parts were modeled as rigid bodies with appropriate joints and constraints. The cam motion was defined as a time-dependent displacement to simulate constant-speed rotation, instead of applying a real motor torque. The spring stiffness and contact parameters were defined based on the characteristics of the saffron flower.

Results and Discussion: The simulation results demonstrated that the designed three-finger gripper performed efficiently and consistently. The maximum displacement of each finger was approximately 8 cm, providing a suitable workspace corresponding to the typical dimensions of saffron flowers. This confirms that the gripper can easily encompass the flower during the harvesting process. The velocity analysis indicated that the finger speed upon contact with the flower stem was less than 10 mm/s, a level low enough that the resulting force is minimal and prevents mechanical impact or damage to the delicate flower structure. Furthermore, the contact forces generated by the fingers were very close to the target value (0.9 N to 1.2 N), remaining within the safe range for handling the flower without deformation or detachment. Minor variations between the forces applied by individual fingers (less than 5%) were attributed to small geometric asymmetries in the model or numerical effects from the dynamic simulation, both negligible in practice. Overall, the obtained results confirm that the designed gripper provides smooth and synchronized motion, appropriate workspace, and safe interaction forces. These findings validate the effectiveness of the proposed design for mechanical harvesting of saffron flowers, ensuring stable and gentle operation consistent with the natural hand motion observed in manual picking.

Conclusion: The results confirm that the bio-inspired three-finger gripper developed in this study can effectively replicate manual saffron harvesting, maintaining both structural stability and gentle contact with the flower. The dynamic analysis results demonstrate its potential for use in mechanized saffron harvesting systems, which could reduce labor requirements and improving operational efficiency. Future research will focus on prototyping and field testing to evaluate real-world performance, as well as further optimizing the actuation mechanism for integration with autonomous or semi-automatic harvesting systems.

Keywords

References

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