Robotics: Science and Systems XXII

Knowing When Not to Help: Active Estimation of Human Reachability for Just-Right Robot Assistance

Ziang Liu, Yunting Yan, Christy Sum Yu Cheung, Tailai Ying, Bodong Liu, Shiqin Tong, Alexander Orkwis, Katherine Dimitropoulou, Tapomayukh Bhattacharjee

Abstract:

Robots that physically interact with humans must decide not only how and when to help, but also when not to help. In physical caregiving and collaborative manipulation, robots can over-assist by misestimating user capability or defaulting to helping when users can act independently. Physical functionality is highly individual, only partially observable, difficult to specify a priori, and assistance policies are often not grounded in user-specific ability, making calibrated intervention challenging.
    We address this by actively inferring human joint-space reachability from sparse interaction. Our framework represents reachability using a compositional parametric model where a box constraint is deformed by local Gaussian primitives. We learn a latent space that decodes to these parameters and structure it using biomechanical anchors from musculoskeletal simulation and clinical anchors from retrieval-augmented reasoning over rehabilitation literature. The robot maintains a belief over this manifold and actively selects calibration queries to infer user-specific functionality.
    We evaluate through computational experiments and real-robot studies with participants wearing resistance bands. Our method achieves ≈0.50 IoU within 20 queries. In sandwich making, reachability-aware assistance significantly improves user perception of physical engagement (χ^2(3) = 18.29, p < .001) without increasing workload. In Action Research Arm Test-inspired manipulation, we demonstrate online adaptation capacity.

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Bibtex:

  
@INPROCEEDINGS{LiuZ-RSS-26, 
    AUTHOR    = {Ziang Liu AND Yunting Yan AND Christy Sum Yu Cheung AND Tailai Ying AND Bodong Liu AND Shiqin Tong AND Alexander Orkwis AND Katherine Dimitropoulou AND Tapomayukh Bhattacharjee}, 
    TITLE     = {{Knowing When Not to Help: Active Estimation of Human Reachability for Just-Right Robot Assistance}}, 
    BOOKTITLE = {Proceedings of Robotics: Science and Systems}, 
    YEAR      = {2026}, 
    ADDRESS   = {Sydney, Australia}, 
    MONTH     = {July}, 
    DOI       = {10.15607/RSS.2026.XXII.119} 
}