Multi-robot planning with conflicts and synergies


Multi-robot planning (mrp) aims at computing plans, each in the form of a sequence of actions, for a team of robots to achieve their individual goals, while minimizing overall cost. Solving mrp problems requires modeling limited domain resources (e.g., corridors that allow at most one robot at a time), and the possibility of action synergy (e.g., multiple robots going through a door after a single door-opening action). Optimally solving mrp problems is hard as it is a generalization of the single agent planning domain which is known to be NP-hard, and frequently requires considering the states of all the robots, resulting in an exponentially growing joint state and action space. In many mrp domains, robots encounter situations where they have conflicting needs for constrained resources, or where they can take advantage of what each other is doing to form synergies. In this article, we formulate the problem of multi-robot planning with conflicts and synergies (mrpcs), and develop a multi-robot planning framework, called iterative inter-dependent planning (iidp), for representing and solving mrpcs problems. Within the iidp framework, we develop the algorithms of increasing dependency and best alternative which exhibit different trade-offs between plan quality and computational efficiency. Extensive experiments covering the suggested algorithms have been performed using both an abstract-domain simulator, where we can automatically generate a variety of domain configurations, and a practical mrpcs instantiation that focuses on multi-robot navigation. In the navigation domain, we model plan costs with temporal uncertainty, and present a novel shifted-Poisson distribution for accumulating temporal uncertainty over actions. In comparison to baseline approaches, our algorithms produce significant reductions in overall plan cost, while avoiding search in the joint state space. In addition, we present a complete demonstration of the implementation of the model on a team of real robots.

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  1. 1.

    This article is based upon a previous conference publication (Zhang et al. 2017). It extends the conference paper in formalizing a framework for multi-robot planning, proposing a novel algorithm, and testing the algorithms on larger scale problems of up to 50 agents as opposed to 3. None of the material (including the conference paper) has appeared in any other journal submission.

  2. 2.

    Ties can be broken in favor of the agent with the longest action sequence or by any other metric.

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    Note that in this example best alternative performs the same as increasing dependency and so we only refer to increasing dependency.

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    For example, such delays can be caused by forcing the robot to stop and say “excuse me” as is done by CoBots Veloso et al. (2015).

  5. 5.

    In implementation, the integrals are replaced by summation operations, because action completions only happen at specific time instances (e.g., Fig. 7).

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    The code for our simulated environment is publicly available at

  7. 7.

    If two robots try to pass each other, there is a significant risk that they will bump into each other and become entangled. In contrast, at least in our environment, we find that most people give way to the robots by standing close to the wall.


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This work has taken place in the Learning Agents Research Group (LARG) at the Artificial Intelligence Laboratory, The University of Texas at Austin. LARG research is supported in part by grants from the National Science Foundation (IIS-1637736, IIS-1651089, IIS-1724157), the Office of Naval Research (N00014-18-2243), Future of Life Institute (RFP2-000), DARPA, Intel, Raytheon, and Lockheed Martin. Peter Stone serves on the Board of Directors of Cogitai, Inc. The terms of this arrangement have been reviewed and approved by the University of Texas at Austin in accordance with its policy on objectivity in research.

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Correspondence to Harel Yedidsion.

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Jiang, Y., Yedidsion, H., Zhang, S. et al. Multi-robot planning with conflicts and synergies. Auton Robot 43, 2011–2032 (2019).

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  • Multi-robot planning
  • Planning under temporal uncertainty
  • Intelligent mobile robotics