Abstract
A Reconfigurable Modular Robotic System (RMRS) consists of multiple interconnected robots and can achieve various functionalities by rearranging its modular robots, such as transporting loads of various shapes. The path planning for an RMRS involves the system motion and also its formation arrangements. Sampling-based path planning for the RMRS might be inefficient due to the formation variety. Recently, convex subsets of the obstacle-free workspace, referred to as polygon nodes, are instead sampled to formulate constrained optimization problems. The success rate of sampling is however unsatisfactory due to connectivity requirements. This paper proposes an obstacle-aware mixture density network to guide the generation of polygon nodes, where the connectivity of polygon nodes is guaranteed by non-zero Minkowski differences between the formation geometry and the intersection of nodes. Subsequently, Convex-Polygon Trees* (CPTs*) are proposed to connect these polygon nodes in an RRT* manner, outputting candidates of convex optimization problems. The optimality degeneration due to distance approximation is proven bounded and the computational complexity is shown linear to the Lebesgue measure of the entire workspace space. Numerical simulations have shown that in most tested large and cluttered environments the CPT* is more than 8 times faster than an existing constrained optimization method. The results have also shown CPT*’ improved scalability to large environments and enhanced efficiency in dealing with narrow passages.
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Abbreviations
- \(\mu _i\), \(\sigma _i\), \(\pi _i\) :
-
Parameters of the ith Gaussian
- \(\omega \) :
-
Subset of workspace covered by a sliding window
- \(\omega _{free}\) :
-
Subset of obstacle-free workspace covered by a sliding window
- \(\phi \) :
-
Formation path
- \(\Phi ^*\) :
-
Optimal polygon path
- \(\phi ^*\) :
-
Optimal (sub-optimal) formation path
- \(\delta \) :
-
Minimum distance from the formations along this path to the obstacles
- e :
-
Encoding of obstacles in \(\omega \)
- O :
-
Point clouds of the obstacles within \(\omega \)
- q :
-
RMRS configuration
- \({\textbf {q}}_0\) :
-
Initial RMRS configuration
- s :
-
Aggregated RMRS state
- u :
-
Expansion direction
- x :
-
Sampled position
- \({\textbf {x}}_{new}\),\(\mathcal {P}_{new}\) :
-
Newly sampled position, newly sampled polygon node
- Z \((\mathcal {P})\) :
-
Vectorized representation of \(\mathcal {P}\)
- \(\mathcal {A}_i\) :
-
Geometry of the ith formation
- \(\mathcal {A}_i({\textbf {q}}), \mathcal {A}(s)\) :
-
Occupancy of RMRS in the workspace under Formation i at configuration q (i.e., at state s)
- \(\mathcal {B}_i\) :
-
The ith obstacle
- \(\mathcal {C}\) :
-
Configuration space
- \(\mathcal {G}\) :
-
Set of goal formation states
- \(\mathcal {I}_\Phi \) :
-
Index set of the polygon nodes in \(\Phi \)
- \(\mathcal {I}_\textit{A}\), \(\mathcal {I}_\textit{B}\) :
-
Index set of formation arrangments, obstacle index set
- \(\mathcal {P}\),\(\mathcal {P}_\textit{i}\) :
-
Sampled polygon (polygon node), the i sampled polygon
- \(\mathcal {P}_0\),\(\mathcal {I}_\textit{G}\) :
-
Polygon node containing initial formation state, Polygon node containing goal formation state
- \(\mathcal {P}_\textit{i}\),\(\textit{i}+1\) :
-
Intersection of \(\mathcal {P}_\textit{i}\) and \(\mathcal {P}_\textit{i}+1\)
- \(\mathcal {S}\) :
-
Aggregated RMRS state space
- \(\mathcal {W}\) :
-
Workspace
- \(\mathcal {W}_{free}\) :
-
Obstacle-free workspace
- \(\pi \) :
-
Homotopic transform
- I :
-
Formation variable
- \({\varvec{I}}_0\), \({\varvec{I}}_g\) :
-
Initial formation arrangement, goal formation arrangement
- \(\textit{J}_\Phi \) :
-
Cost associated with the polygon path \(\Phi \)
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Acknowledgements
This work is supported by the National Natural Science Foundation of China #62003110 and the Shenzhen Science and Technology Innovation Foundation #JCYJ20210324132607018, #JSGG20210420091804012, and #GXWD20220811163649003
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Lu, W., Xiong, H., Zhang, Z. et al. Scalable Optimal Formation Path Planning for Multiple Interconnected Robots via Convex Polygon Trees. J Intell Robot Syst 109, 63 (2023). https://doi.org/10.1007/s10846-023-01994-0
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DOI: https://doi.org/10.1007/s10846-023-01994-0