It is becoming increasingly feasible for robots to share a workspace with humans. However, for them to do so safely while maintaining agile performance, they need the ability to smoothly handle the dynamics and uncertainty caused by human motions. Markov Decision Processes (MDPs) serve as a common framework to formulate robot planning problems. However, because of its single-agent formulation, such planner cannot account for human reaction when evaluating robot actions. The robot can thus suffer from unsafe motions and move in ways that are hard for nearby humans to understand. To resolve this, we instead model robot planning in human workspaces as a Stochastic Game, and contribute a robust planning algorithm, which enables the robot to account for its prediction errors in human responses to prevent collision, while not losing agility, opposed to traditional maximin optimization techniques, by applying maximin operation only at "critical states". We validate the approach under partial knowledge of pedestrian behaviors, and show that our approach encounters zero collision despite imperfect prediction, while improving path efficiency, compared to baselines.

To enable robots to smoothly interact with humans during their travels together as a group, robots need the ability to adapt their motions under environmental changes and ensure all group members’ routes are feasible. To achieve this ability, robots require knowledge of the final destination and the subgoals in between. In practice, such information is seldom shared explicitly among group members, and may be frequently updated. Under this uncertain setting, maintaining travel efficiency and behavior appropriateness becomes a challenge. Previous literature approached the problem by generating compliant coordinating motions inspired by human groups, with subgoal uncertainty remaining isolated from the plan evaluation process. We show that such coordination can lead the robot to "bad" transient states where inefficient planning and lost tracking may incur. We propose to resolve the problem by formulating the coordinating motion as a Bayesian stochastic game, to plan for the robot as a group member, in the meanwhile considering the long-term effect of uncertainty during path coordination. We show that the approach improves travel efficiency and partner tracking robustness, by preventing assertive decisions during the inference update process. Moreover, the approach presents "agency", in the sense that it can generate human-like motions, which can be applied and contribute to the pedestrian simulation literature; the approach also affords variants from the human-like motions to generate robot behaviors based on sensing capabilities, contributing to the methodology of robot behavior design.

Communication among team members is important for efficient teamwork, to coordinate behavior and ensure that all team members have the information they need to complete the task. To enable effective communication and thus efficient teamwork, we propose a multi-agent planning approach to revealing information based on its benefit to joint team performance. By explicitly modeling the partner's knowledge and behavior, our approach allows a robot in a team to reason about when information is useful, how the communication is effective, and to communicate through efficient actions. That is, the robot provides only the necessary information for task completion, provides the information at the time that it is needed, and through the action(s) that optimizes team performance. We validated this approach in a human study in which participants walk together with a robot to a destination that is known only to the robot. We compared to a legible motion generation approach, and showed that users perceived our approach as more natural, socially appropriate, and fluent to team with, while being both more predictable and intent-clear. The ratings of our approach are equal or higher than legible motion across all 18 survey items.

Intelligent mobile robots have recently become able to operate autonomously in large-scale indoor environments for extended periods of time. In this process, mobile robots need the capabilities of both task and motion planning. Task planning in such environments involves sequencing the robot’s high-level goals and subgoals, and typically requires reasoning about the locations of people, rooms, and objects in the environment, and their interactions to achieve a goal. One of the prerequisites for optimal task planning that is often overlooked is having an accurate estimate of the actual distance (or time) a robot needs to navigate from one location to another. State-of-the-art motion planning algorithms, though often computationally complex, are designed exactly for this purpose of finding routes through constrained spaces. In this article, we focus on integrating task and motion planning (TMP) to achieve task-level-optimal planning for robot navigation while maintaining manageable computational efficiency. To this end, we introduce TMP algorithm PETLON (Planning Efficiently for Task-Level-Optimal Navigation), including two configurations with different trade-offs over computational expenses between task and motion planning, for everyday service tasks using a mobile robot. Experiments have been conducted both in simulation and on a mobile robot using object delivery tasks in an indoor office environment. The key observation from the results is that PETLON is more efficient than a baseline approach that pre-computes motion costs of all possible navigation actions, while still producing plans that are optimal at the task level. We provide results with two different task planning paradigms in the implementation of PETLON, and offer TMP practitioners guidelines for the selection of task planners from an engineering perspective.

Mobile robots moving in crowded environments have to navigate among pedestrians safely. Ideally, the way the robot avoids the pedestrians should not only be physically safe but also perceived safe and comfortable. Despite the rich literature in collision-free crowd navigation, limited research has been conducted on how humans perceive robot behaviors in the navigation context. In this paper, we implement three local pedestrian avoidance strategies inspired by human avoidance behaviors on a self-balancing mobile robot and evaluate their perception in a human-robot crossing scenario through a large-scale user study with 98 participants. The study reveals that the avoidance strategies positively affect the participants' perception of the robot's safety, comfort, and awareness to different degrees. Furthermore, the participants perceive the robot as more intelligent, friendly and reliable in the last trial than in the first even with the same strategy.