**6. Conclusions**

In order to simplify the complex process of determining the parent point that needs to traverse the random tree and reduce the number of redundant points in the random tree, a PPRO-RRT algorithm, combined the PPD strategy with the RO strategy, was proposed in this paper. The following conclusions were drawn through experiments and comparative analysis: (1) the PPD strategy significantly speeds up path planning, and the RO strategy reduces the number of redundant points; (2) the PPRO-RRT algorithm outperforms the other improved RRT algorithms for both simple and complex environments; (3) the experimental results by IRB1410 shows that the manipulator can safely avoid obstacles using the PPRO-RRT algorithm. However, compared with the RRT\* algorithm, the algorithm proposed in this paper may produce longer paths and would be modified in the future in terms of shorter path lengths. The improved algorithm in this paper is relatively unsuitable for the scene with narrow channels. In terms of practical applications, the improved algorithm in this paper can be applied to the path planning problems of intelligent vehicles, manipulators, UAVs, etc. to speed up their path planning.

**Author Contributions:** Conceptualization, Z.Z. and Y.T.; Methodology, L.T., C.Z., Z.Z. and Y.T.; Software, L.T.; Validation, L.T., Y.T. and Z.Z.; Formal analysis, L.T., Y.Z. and Z.W.; Investigation, L.T., Y.T. and Z.Z.; Resources, L.T. and Y.Z.; Data curation, L.T.; Writing—original draft preparation, L.T.; Writing—review and editing, L.T., Y.Z. and Z.W.; Visualization, L.T., Y.Q. and Z.Z.; Supervision, C.Z., Y.T., Y.Z. and Y.Q.; Project administration, C.Z., Y.Q. and Z.W.; Funding acquisition, C.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China (grant number 31971668) and the Beijing College Students' Innovation and Entrepreneurship Training Program (grant s20201002114).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

