publications

2024

1. IROS 2024

   Learning Coordinated Maneuver in Adversarial Environments

   Zechen Hu, Manshi Limbu, Daigo Shishika, and 2 more authors

   In 2024 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2024

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   This paper aims to solve the coordination of a team of robots traversing a route in the presence of adversaries with random positions. Our goal is to minimize the overall cost of the team, which is determined by (i) the accumulated risk when robots stay in adversary-impacted zones and (ii) the mission completion time. During traversal, robots can reduce their speed and act as a ‘guard’ (the slower, the better), which will decrease the risks certain adversary incurs. This leads to a trade-off between the robots’ guarding behaviors and their travel speeds. The formulated problem is highly non-convex and cannot be efficiently solved by existing algorithms. Our approach includes a theoretical analysis of the robots’ behaviors for the single-adversary case. As the scale of the problem expands, solving the optimal solution using optimization approaches is challenging, therefore, we employ reinforcement learning techniques by developing new encoding and policygenerating methods. Simulations demonstrate that our learning methods can efficiently produce team coordination behaviors. We discuss the reasoning behind these behaviors and explain why they reduce the overall team cost.

2. ICRA 2024

   Scaling Team Coordination on Graphs with Reinforcement Learning

   Manshi Limbu, Zechen Hu, Xuan Wang, and 2 more authors

   In 2024 IEEE International Conference on Robotics and Automation (ICRA), 2024

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   This paper studies Reinforcement Learning (RL) techniques to enable team coordination behaviors in graph environments with support actions among teammates to reduce the costs of traversing certain risky edges in a centralized manner. While classical approaches can solve this non-standard multi-agent path planning problem by converting the original Environment Graph (EG) into a Joint State Graph (JSG) to implicitly incorporate the support actions, those methods do not scale well to large graphs and teams. To address this curse of dimensionality, we propose to use RL to enable agents to learn such graph traversal and teammate supporting behaviors in a data-driven manner. Specifically, through a new formulation of the team coordination on graphs with risky edges problem into Markov Decision Processes (MDPs) with a novel state and action space, we investigate how RL can solve it in two paradigms: First, we use RL for a team of agents to learn how to coordinate and reach the goal with minimal cost on a single EG. We show that RL efficiently solves problems with up to 20/4 or 25/3 nodes/agents, using a fraction of the time needed for JSG to solve such complex problems; Second, we learn a general RL policy for any N-node EGs to produce efficient supporting behaviors. We present extensive experiments and compare our RL approaches against their classical counterparts

2023

1. IROS 2023

   Team coordination on graphs with state-dependent edge costs

   Manshi Limbu, Zechen Hu, Sara Oughourli, and 3 more authors

   In 20230 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2023

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   This paper studies a team coordination problem in a graph environment. Specifically, we incorporate “support” action which an agent can take to reduce the cost for its teammate to traverse some high cost edges. Due to this added feature, the graph traversal is no longer a standard multi-agent path planning problem. To solve this new problem, we propose a novel formulation that poses it as a planning problem in a joint state space: the joint state graph (JSG). Since the edges of JSG implicitly incorporate the support actions taken by the agents, we are able to now optimize the joint actions by solving a standard single-agent path planning problem in JSG. One main drawback of this approach is the curse of dimensionality in both the number of agents and the size of the graph. To improve scalability in graph size, we further propose a hierarchical decomposition method to perform path planning in two levels. We provide both theoretical and empirical complexity analyses to demonstrate the efficiency of our two algorithms.

   @inproceedings{limbu2023team,
     title = {Team coordination on graphs with state-dependent edge costs},
     author = {Limbu, Manshi and Hu, Zechen and Oughourli, Sara and Wang, Xuan and Xiao, Xuesu and Shishika, Daigo},
     booktitle = {20230 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)},
     year = {2023},
     organization = {IEEE},
   }

2. ICRA 2023

   Human-robot teaming on graphs with state-dependent edge cost.

   Manshi Limbu, Zechen Hu, Sara Oughourli, and 3 more authors

   In 3rd RT-DUNE IEEE/RAS International Conference on Robotics and Automation (ICRA) Workshop, 2023

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   We are interested in designing coordinated group motion, where the safety or cost for one agent to move from one location to another may depend on the support provided by its teammate. For example, consider a scenario where a team of human and robot must traverse an environment with some “risk” edges as shown in Fig. 1. Those risks might represent actions such as going up a ladder, crossing a "shaky" bridge, or walking through a dark tunnel. In these situations, a human (or robot) teammate can support the other by holding the ladder, stabilizing the bridge, or lighting up the tunnel. We capture the feasibility of these "supporting" actions in the green dashed arrows in Fig. 1, extending from the nodes from which the support can be provided. The core questions we seek to answer are: (i) when such support/coordination is beneficial, and (ii) how to best coordinate the actions as a team to minimize the overall cost. We formulate a problem that incorporates support actions to a minimum-cost graph traversal problem. We then propose a solution approach based on the notion of joint state graph (JSG) formulation, converting the problem into single-agent path planning. To address the curse of dimensionality, a hierarchical decomposition method based on Critical Joint State Graph (CJSG) is introduced for two-level planning. Complexity and statistical analyses demonstrate the efficacy of our algorithm.

   @inproceedings{limbu2023tean,
     title = {Human-robot teaming on graphs with state-dependent edge cost.},
     author = {Limbu, Manshi and Hu, Zechen and Oughourli, Sara and Wang, Xuan and Xiao, Xuesu and Shishika, Daigo},
     booktitle = {3rd RT-DUNE IEEE/RAS International Conference on Robotics and Automation (ICRA) Workshop},
     year = {2023},
     organization = {IEEE},
   }