Design and Experiment of Underactuated End-effector for Citrus Picking

WEI Bo, HE Jinyin, SHI Yang, JIANG Guangli, ZHANG Xianyu, MA Ying

Abstract

Aiming to achieve the development of mechanized and intelligent citrus picking, an underactuated end-effector for citrus picking robot was proposed. Through the fusion control strategy of grip and deflection, the end-effector was able to achieve the stable picking of citrus with different sizes and ovality. According to the needs of picking citrus of different sizes and the analysis of human hands movement patterns, a double-link parallel finger was designed. The double-link parallel finger included two sets of four-link mechanism, which were designed for underactuated finger to enable the end-effector to adapt to different citrus sizes. On the basis of statics analysis, the motors were determined. Besides, a rotatory joint was added to the finger root to fit closely with the citrus. This design can not only protect the orange skin from being scratched by finger edges, but also can increase the contact area and thus increase the friction. In order to ensure the finger rotating correctly, the motor drive control system model was established according to the selected motor characteristics. Laying the establishment of this system model, the servo control strategy based on current feedback was proposed. Finally, the finger movement simulation and the citrus picking experiment using the end-effector were performed. Simulation results showed that the structure can satisfy the design requirements of realizing citrus picking of different sizes and ovality in terms of kinematics. A prototype of the picking end-effector was made and citrus picking experiments were carried out in the experimental environment. The experimental results showed that when the end-effector pinked citrus with diameter ranging from 30mm to 100mm, the average success rate was 98.3% and the average time was 5.3s. It had the advantages of strong adaptability, stable grip, and no damage of the fruit.


Keywords: picking robots, citrus, end-effector, underactuated, compliance control

 

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