PLATO Hand: Shaping Contact Behavior with Fingernails for Precise Manipulation

Dong Ho Kang1, Aaron Kim1, Mingyo Seo1, Kazuto Yokoyama2, Tetsuya Narita2, Luis Sentis1
1The University of Texas at Austin 2Sony Group Corporation
Email: dongho@utexas.edu
arXiv

Abstract

We introduces the PLATO Hand, a dexterous robotic hand with a hybrid fingertip that embeds a rigid fingernail within a compliant pulp. This design shapes contact behavior to enable diverse interaction modes across a range of object geometries. We develop a strain-energy-based bending–indentation model to guide the fingertip design and to explain how guided contact preserves local indentation while suppressing global bending. Experimental results show that the proposed robotic hand demonstrates improved pinching stability, enhanced force observability, and successful execution of edge-sensitive manipulation tasks, including paper singulation, card picking, and orange peeling. Together, these results show that coupling structured contact geometry with force-motion transparent mechanism provides a principled, physically-embodied approach to precise manipulation.

Manipulation Demo

Contact/Collision Compliance

Passive compliance through backdrivable quasi-direct drive actuators enables safe and adaptive responses to unexpected contact forces.

Flicking Object

High-acceleration strikes achieved through low gear ratios and minimal reflected inertia generate rapid motions to propel objects with controlled impulse.

Texture Sensing

High force sensitivity from fingernail sensors identifies surface properties during tactile exploration and probing interactions.

Catching Object

Fast actuation and low-latency communication enable precise timing and trajectory-based grasping to intercept moving objects.

Edge Insertion Manipulation

Sharp fingernails puncture and manipulate soft surfaces with controlled penetration forces for orange peeling tasks.

Contact-rich Manipulation

Precision tasks such as coin picking combine proprioceptive force control with fingernail sensing for simultaneous contact detection and force regulation.

Design Overview

The PLATO Hand combines a hybrid rigid-soft fingertip with quasi-direct drive (QDD) actuators and linkage mechanism. The fingernail not only increases flexural rigidity at the fingertip, stabilizing the soft pulp to enlarge contact area for adaptive and stable grasping, but also provides a rigid and concentrated contact point for transparent force transmission. Combined with high-bandwidth proprioceptive actuation, the PLATO Hand achieves precise dexterous manipulation across a variety of challenging tasks.

PLATO Hand Design

The PLATO Hand employs a biomimetic fingertip that combines a rigid fingernail with a compliant, deformable fingerpulp to structure local contact mechanics. This hybrid construction separates local contact compliance from global fingertip stiffness, allowing deformation during contact to be shaped independently of overall rigidity.

Fingertip With vs Without Fingernail

The fingernail improves pinching stability by stabilizing contact during pullout. Tests on flat, concave, and convex surfaces showed that fingertips with a rigid fingernail (top) consistently achieved higher pullout forces than fingertips without one (bottom). The fingernail prevents the fingertip from bending by redirecting strain energy into local indentation to its pulp, which helps maintain stable contact with the object. This effect is especially noticeable on curved surfaces and becomes even more important when the fingertip pulp is softer.

The PLATO Hand is able to achieve most tasks in the Grasp Taxonomy using three fingers; the inclusion of rigid fingernails extends its capabilities for precise manipulation tasks.

Manipulation Taxonomy

BibTeX

@misc{kang2026platohand,
  author    = {Kang, Dong Ho and Kim, Aaron and Seo, Mingyo and Yokoyama, Kazuto and Narita, Tetsuya and Sentis, Luis},
  title     = {PLATO Hand: Shaping Contact Behavior with Fingernails for Precise Manipulation},
  journal   = {arXiv preprint arXiv:2602.05156},
  year      = {2026},
}