KaRMA: A Kinematic Metric for Fine Manipulation Ability in Robotic Hands
For robotic hand designers and manipulation researchers, KaRMA provides a more direct measure of fine manipulation dexterity than static proxies, though it is limited to spherical objects and rolling contacts.
The paper introduces KaRMA, a kinematic metric that quantifies a robotic hand's ability to perform in-hand manipulation of a spherical object via rolling. Evaluated on 16 hands, KaRMA distinguishes hands that rank identically under static metrics and reveals tradeoffs invisible to existing baselines.
Traditional robotic hand metrics focus on static properties such as workspace, manipulability, and grasp stability. However, these metrics do not directly measure dexterity under the standard definition in robotic manipulation: the ability to continuously change an object's pose within the hand while maintaining contact from an initial grasp. We introduce Kinematic Rolling Manipulation Ability (KaRMA), a kinematic-only metric for fine manipulation that quantifies reachable in-hand translation and reorientation of a spherical test object within a two-finger precision pinch through feasible rolling motions. KaRMA enforces joint limits, collision constraints, rolling contact, and antipodal force feasibility, then investigates reachable in-hand object poses via breadth-first search over translation and rotation primitives. KaRMA reports three scores: translational coverage (KaRMA-T), rotational coverage (KaRMA-R), and sensitivity to the initial grasp (KaRMA-S). We evaluate KaRMA on 16 widely used robotic hands and compare against static baselines, showing that KaRMA separates hands that rank identically under static proxies, reveals translation-rotation tradeoffs invisible to existing baselines, and is qualitatively consistent with selected published task benchmarks where Jacobian-based metrics can be misleading.