# Path Planning for Laser Cladding Robot on Artificial Joint Surface Based on Topology Reconstruction
## 5 Experimental Validation  
### Automatic Path Generation Process  
In order to realize the path planning method proposed in this paper, the authors developed a processing software based on C# and.net framework 4.5. The laser cladding path was generated and simulated using the processing software on a PC platform (CPU: Intel Core i3-4160 3.60 GHz; RAM 4.0 GB; OS: Microsoft Windows 10). An acetabular cup of an artificial hip joint with an outer diameter of 46 mm was selected as an example to verify the automatic generated path. The parameters related to path planning are listed in Table 3.  
The complete path generation process is shown in Figure 13. The STL model of the acetabular cup surface was sliced by five parallel planes in direction Z. Figure 13b shows five transversal lines with cladding spacing of 6 mm obtained by using the slicing algorithm based on a topological relation. Each single transversal line was connected by numerous intersection points in a laser scanning sequence. Figure 13c shows all the intersection points directly obtained. Figure 13d shows that the full path of the laser cladding consisted of five transversal lines end to end, each of which could be treated as single-pass cladding. To ensure the continuity of the cladding processing, the connecting lines were added between different single-pass cladding. When passing through the connecting lines, the robot moved without laser and powder. Figure 13e shows the direct result of the robot interpolation points with a defocus distance of 15 mm. Figure 13f shows the simplified result with an allowable arch height error of 0.5 mm. Obviously, this not only guaranteed the shape precision of the surface machining, but also reduced the number of robot interpolations.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Model size & \(\Phi\) 46 mm \\ Slice direction & Z \\ Cladding spacing & 6 mm \\ Defocus distance & 15 mm \\ Allowable arch height error & 0.5 mm \\ \hline \hline \end{tabular}
\end{table}
Table 3: Parameters related to path generation.  
Some key results of automatic path generation are listed in Table 4. Through topology reconstruction, the amount of data extracted and saved from the STL model was greatly reduced. The number of interpolation points were simplified from 850 to 74. The compression ratio of the interpolation points was approximately 8.7%, which contributed to reducing the size of the final robot program. On the other hand, the elapsed time of automatic path generation that involved software operations and computer processing was less than 30 seconds. When the full path was generated, the coordinates and normal vectors of the interpolation points were used to calculate the position and pose of the robot, which were finally transformed to the robot program.  
Figure 13: Path generation process. (**a**) Acetabular cup STL model. (**b**) Transversal lines with cladding spacing at 6 mm. (**c**) All intersection points. (**d**) Full laser cladding path. (**e**) Direct result. (**f**) Simplified result with an allowable arch height error of 0.5 mm.  
In the same case, the manual teaching method needed more than two hours to edit the processing program. Therefore, compared with the traditional manual teaching method, the automatic path generation method proposed in this paper had great advantages in saving time, improving efficiency and ensuring safety.