# Grasping Claws of Bionic Climbing Robot for Rough Wall Surface: Modeling and Analysis
## 4 Analysis of the Grasping Claws Module Based on ANSYS Workbench  
### Secondary Claws  
An analysis of the claw structure of reptiles revealed that the claws need to meet the following requirements: (1) loading forces applied on hook tips are reasonably distributed to prevent failure of elastic joints caused by stress concentration; and, (2) multiple hooks are independent. That is, while slipping on a rough wall surface, if a hook grasps a protuberance on the wall and forms mechanical interlocking, other hooks can still search regions that can be grasped along the slipping direction.  
In order to analyze whether the design of the elastic claws meets the above requirements and verify the operating safety of the hooks, Solidworks was adopted for modeling, and the model was simplified according to the actual demand (Figure 7). After being imported in the ANSYS Workbench for mesh generation (Figure 8), \(11,306\) nodes and \(5229\) elements were attained. The properties of the materials that were used for producing the claws are listed in Table 1.  
Figure 6: Relationship of maximum bending stress of hook with hook shaft diameter.  
Figure 7: Simplified geometric model of the spiny foot.  
The connecting plate was fabricated with 65 Mn steel with large yield strength, while the hooks were manufactured with #45 steel. When the two pairs of tiny hooks were mechanically interlocked with the wall surface, the hooks and the elastic steel sheets were deformed and the resulting grasping force pointed to the interior of the wall surface. Suppose that the mass of the grasping module of the claws was 0.5 kg, then 5 N pointing to the interior of the wall and vertical to the tips hooks was applied to the claws in each simulation.  
The simulation results are shown in Figure 9.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Item** & **Density [kg/m\({}^{3}\)]** & **Young’s Modulus [MPa]** & **Poisson’s Ratio** & **Yield Strength [MPa]** & **Tensile Strength [MPa]** \\ \hline
45\# & 7890 & \(2\times 10^{5}\) & 0.3 & 355 & 610 \\
65 Mn & 7810 & \(1.98\times 10^{5}\) & 0.26 & 784 & 980 \\ A1 & 2770 & \(7.1\times 10^{4}\) & 0.33 & 250 & 250 \\ \hline \end{tabular}
\end{table}
Table 1: Properties of materials used for the grasping claws module.  
Figure 8: Mesh model of the spiny foot.  
Figure 9: Displacement of the spiny feet. (**a**) Cloud picture for the displacement of a single hook under 5 N; (**b**) Cloud picture for the displacement of a pair of hooks each bearing 2.5 N; (**c**) Cloud picture for the displacement of a pair of hooks each bearing 1.25 N; (**d**) Cloud picture for the displacement of a pair of hooks bearing 3.75 and 1.25 N respectively.  
Figure 9a illustrates the displacement when a hook detaches from the wall surface, while the other hooks the wall. The largest displacement (0.82302 mm) was found at the tip hook. Figure 9b demonstrates the displacement when each of the pair of hooks bears 2.5 N. Under this condition, the largest displacement was found to be 0.82527 mm at the tip of the hooks. It can be seen from Figure 9a,b that the displacement of the other pair of tiny hooks was 0. It indicates that even though a pair of hooks grasp the wall, the other pair of hooks can still search positions that can be grasped along the slipping direction.  
Figure 9c shows the displacement when the four hooks of two pairs of claws grip the wall. The displacement of the hooks was 0.41203 mm. The displacement under the condition that one pair of the hooks bear 3.75 N, while the other pair is subjected to 1.25 N, as illustrated in Figure 9d. The largest displacement (0.61803 mm) was observed at the tip hook that bore 3.75 N. The above two conditions reveal that, when the two pairs of tiny hooks simultaneously hook the wall, they are independent and not affected by each other.