# Performance and Effectiveness of the Passive-Compliant Citrus-Picking Manipulator
## 5 Discussion and Conclusions  
This study designed a passive-compliant citrus harvesting robotic hand, utilizing a spring-assisted gripping structure that allows it to adapt to citrus fruits of different sizes \begin{table}
\begin{tabular}{c c c c c} \hline
**Fruit Diameter Range/mm** & **65–75** & **75–85** & **85–95** & **Mean Value** \\ \hline \multirow{3}{*}{Number of rotations} & (0,1) & 52 & 21 & 25 & 32.7 \\  & (1,2) & 60 & 63 & 35 & 53.7 \\  & (2,3) & 20 & 40 & 55 & 38.3 \\  & (3,4) & 8 & 16 & 25 & 16.3 \\ \hline \multirow{3}{*}{Picking quantity Damage rate/\%} & 140 & 140 & 140 & 140 \\  & 4 & 2 & 5 & 3 \\ \cline{1-1}  & 2.9 & 1.4 & 3.6 & 2.6 \\ \hline \end{tabular}
\end{table} 
Table 2: Capture test results. Figure 11: Orchard citrus-picking experiment. Figure 12: Citrus harvesting experiment results. without the need for pressure sensors. Additionally, the floating connection structure of the nut seat enables each gripping component to move independently under the drive of a single motor, allowing the gripping components to automatically conform to the citrus surface. This improves the adaptability to the fruit shape without requiring complex feedback control, thereby simplifying the system structure. Based on static analysis, the relationship between the gripping force of the harvesting hand and the spring force was derived, providing a theoretical basis for determining spring parameters for the harvesting of different spherical fruits. A physical prototype of the harvesting hand was constructed, and citrus harvesting tests were conducted both in the laboratory and orchards. The experimental results show that the harvesting hand has good adaptability to citrus fruits of varying sizes and ellipsoid shapes. Each gripping component automatically conforms to the citrus surface, and after rotating four turns without applying pulling force, the fruit detaches completely with a damage rate of 2.6%. Currently, rigid robotic hands [35] typically rely on multiple motors to drive independent joints, combined with force sensors for precise control to ensure stable fruit grasping. However, this approach increases system cost and heavily depends on sensors. Underactuated robotic hands [29], on the other hand, achieve multi-degree-of-freedom motion with fewer driving units, often using flexible joints or adaptive structures to improve grasping capability. Nevertheless, most underactuated robotic hands still require external sensors or precise mechanical modeling to adjust the gripping force and avoid fruit damage or slipping. The passive-compliant robotic hand in this study outperforms rigid robotic hands in terms of harvesting adaptability, structural simplification, and gripping stability. Additionally, it achieves an adaptive grasping ability similar to that of underactuated robotic hands without requiring complex sensor control. Experimental results show that this robotic hand is suitable for orchard environments and effectively reduces the risk of fruit damage. However, future research will need to optimize the rotation harvesting angle to reduce fruit damage caused by branch interference and extend testing to different fruit varieties to enhance its generalizability. Conceptualization, D.Z. and H.Y. ; methodology, D.Z. ; software, H.Y. and W.Z. ; validation, H.Y. ; investigation, H.Y. ; data curation, H.Y. ; writing--original draft preparation, D.Z. and H.Y. ; writing--review and editing, Z.Y. and H.Y. ; funding acquisition, D.Z. All authors have read and agreed to the published version of the manuscript.