PHANTOM Hand

Teng Yan; Jiongxu Chen; Qixiang Hua; Yue Yu; Zihang Wang; Yaohua Liu; Bingzhuo Zhong

cs.ROMar 24, 2026

PHANTOM Hand

Authors: Teng Yan, Jiongxu Chen, Qixiang Hua, Yue Yu, Zihang Wang, Yaohua Liu, Bingzhuo Zhong

Organizations: The Hong Kong University of Science and Technology (Guangzhou)

Abstract

Tendon-driven underactuated hands excel in adaptive grasping but often suffer from kinematic unpredictability and highly non-linear force transmission. This ambiguity limits their ability to perform precise free-motion shaping and deliver reliable payloads for complex manipulation tasks. To address this, we introduce the PHANTOM Hand (Hybrid Precision-Augmented Compliance): a modular, 1:1 human-scale system featuring 6 actuators and 15 degrees of freedom (DoFs). We propose a unified framework that bridges the gap between precise analytic shaping and robust compliant grasping. By deriving a sparse mapping from physical geometry and integrating a mechanics-based compensation model, we effectively suppress kinematic drift caused by spring counter-tension and tendon elasticity. This approach achieves sub-degree kinematic reproducibility for free-motion planning while retaining the inherent mechanical compliance required for stable physical interaction. Experimental validation confirms the system's capabilities through (1) kinematic analysis verifying sub-degree global accuracy across the workspace; (2) static expressibility tests demonstrating complex hand gestures; (3) diverse grasping experiments covering power, precision, and tool-use categories; and (4) quantitative fingertip force characterization. The results demonstrate that the PHANTOM hand successfully combines analytic kinematic precision with continuous, predictable force output, significantly expanding the payload and dexterity of underactuated hands. To drive the development of the underactuated manipulation ecosystem, all hardware designs and control scripts are fully open-sourced for community engagement.

Figures & tables

Fig. 1: Overview and DOF mapping of PHANTOM Hand. (a) Human hand annotated with anatomical DOFs (MCP/PIP/DIP, thumb MP/IP, and CMC). (b) The PHANTOM hand with 15 joint DOFs $q_{1}\!-\!q_{15}$ : four long digits each with MCP/PIP/DIP flexion–extension, and the thumb with IP/MP flexion–extension and CMC abduction–adduction.

Fig. 2: Tendon routing and analytic modeling for four fingers. Four-finger figure-eight routing from full extension to an intermediate flexion: straight segments $L_{k}$ , joint pulleys of radius $R_{i}$ , cables connected to the servo hubs (purple), the passive ”cable-spring” return path (green), parameters related to the closed-form geometric expression of the MCP joint ( $\alpha$ , $d_{1}$ , $d_{2}$ ), and joint angles $q_{\text{MCP}}$ , $q_{\text{PIP}}$ , $q_{\text{DIP}}$ . $q_{i,\text{ref}}$ (where $i=\{\text{DIP},\text{PIP},\text{MCP}\}$ ) denotes the structural geometric limits of the independent finger module for analytical derivation, while the actual operational range limits are constrained by the palm housing to prevent excessive flexion.

Fig. 4: PHANTOM hand expressibility benchmark: hand gestures and grasping patterns. Left: Hand gestures, including precise thumb-to-finger opposition (thumb opposing the index, middle, and ring fingers respectively), representative multi-finger combinations and digit gestures 0-8. Right: An extended set 16 representative grasps under the same controller, covering diverse contact topologies (enveloping, lateral, and tip pinches) and tool morphologies (rod-like, ring-like, and press-type), for cross-task consistency assessment. All results from the same control stack (analytic mapping + mechanics-based compensation), no additional sensing.

Finger Joint	Joint Label	Admissible Workspace $[q_{\min},q_{\max}]$ (rad)
Thumb IP	$q_{1}$	$[0.00,0.99]$
Thumb MP	$q_{2}$	$[0.00,1.25]$
Index DIP	$q_{3}$	$[0.00,1.31]$
Index PIP	$q_{4}$	$[0.00,1.61]$
Index MCP	$q_{5}$	$[0.00,1.27]$
Middle DIP	$q_{6}$	$[0.00,1.28]$

TABLE I: Admissible workspace of each finger joint of PHANTOM hand. All values are in radians, corresponding to the joint indices

q_{1}\sim q_{15}

Fig. 5: Comparative analysis of joint angle residuals under uncompensated and compensated control. This figure illustrates the relationship between the angle residuals and the servo control angles for target joints across the five fingers. The red circles represent the original uncompensated residuals (Residual_ideal), while the green squares denote the residuals after mechanics-based compensation (Residual_comp). All subplots are standardized with a Y-axis range from

-2.0

+2.0

degrees to facilitate a direct comparison of performance.

Fig. 6: Mean Absolute Error (MAE) comparison of joint angles for five fingers of PHANTOM Hand under uncompensated and compensated conditions. The red bars represent the MAE between real joint angles and ideal joint angles (without compensation), while the green bars denote the MAE between real joint angles and compensation joint angles (with compensation). The fingers include the thumb (with MP and IP joints) and four fingers (each with MCP, PIP and DIP joints). The MAE is calculated in the unit of degrees ( ∘ ).

Fig. 7: Characterization of fingertip force and variable load manipulation of the PHANTOM hand. (a) Quantitative measurement of fingertip output: the index finger exhibits a stable maximum force of 3.06 N. (b) Flexible wire clamping: the thumb and index finger cooperatively exert a minimal contact force to securely hold a thin wire.

Finger	Thumb	Index	Middle	Ring	Pinky
Force (N)	3.35	2.87	2.51	2.73	2.33

TABLE II: Measured average fingertip forces of the PHANTOM hand. The data represent the mean output force of each finger calculated from five independent experimental trials using the digital force gauge shown in Fig. 7 .

Explore similar work

Design and stability analysis of an underactuated hand with passively rotating fingers
Jul 21, 2026Léonie Plancoulaine, Sylvain Guégan, Franck Plestan +1Robotic Hand Design Robotic Grasping
LS2N, LS2N - équipe RoMas · Nantes Université, École Centrale Nantes, CNRS, LS2N, UMR 6004, 44300 Nantes, France · LGCGM +2
A Quasi-Direct-Drive Underactuated Asymmetric Hand for Dexterous and Efficient Grasping and Manipulation
Sep 23, 2026Benjamin Davis, Chase Kidder, Hannah S. StuartRobotic Hand Design Robotic Grasping
Embodied Dexterity Group, Dept. of Mechanical Engineering, University of California Berkeley, Berkeley, CA, USA · General Motors, Warren, MI, USA
H-PAC Hand: Control-Oriented Modeling and Tendon-Elasticity Compensation for an Underactuated Robotic Hand
Aug 17, 2026Teng Yan, Jiongxu Chen, Teng Wang +5Robotic Hand Design Tendon-Driven Actuation
The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, China · Southeast University, Nanjing, China

Jul 21, 2026J/K move · Enter open · S save

Design and stability analysis of an underactuated hand with passively rotating fingers

Léonie Plancoulaine, Sylvain Guégan, Franck Plestan, Damien Chablat

LS2N, LS2N - équipe RoMas · Nantes Université, École Centrale Nantes, CNRS, LS2N, UMR 6004, 44300 Nantes, France · LGCGM+2

Robotic Hand Design Robotic Grasping

Open paper AskPDF arXiv

This paper presents an innovative design and stability analysis of an underactuated robotic finger with spatial mobility, designed to enhance gripping dexterity in robotic hands. The finger architecture incorporates a revolute joint at its base, enabling passive spatial rotation that facilitates both cylindrical and spherical grasping. With only two phalanges per finger, the design simplifies kinematic complexity while supporting precision and enveloping grasps. Stability criteria, based on the moment at the finger base joint induced by contact forces, are introduced to ensure reliable object gripping and prevent ejection during manipulation. The study also examines a differential mechanism that distributes a single actuation torque across multiple fingers, allowing adaptive and coordinated motion. This mechanism enhances the hand's ability to grasp diverse object shapes with minimal pre-grasp adjustments, leveraging passivity for autonomous adaptation. Theoretical findings are experimentally validated using a fully mechanical prototype, demonstrating versatility in performing cylindrical, spherical, parallel, and enveloping grasps. The integration of underactuation-both within individual fingers and among multiple fingers-reduces mechanical complexity, cost, and control demands while preserving functional adaptability. This work advances the development of compliant robotic hands suitable for applications requiring dexterity and robustness, such as agricultural robotics, logistics, assistive technologies, and waste sorting. Future research will focus on automating actuation and refining control strategies to further improve grasp stability and precision, paving the way for autonomous manipulation in unstructured environments.

Abstract

Explore similar work

Design and stability analysis of an underactuated hand with passively rotating fingers

A Quasi-Direct-Drive Underactuated Asymmetric Hand for Dexterous and Efficient Grasping and Manipulation

H-PAC Hand: Control-Oriented Modeling and Tendon-Elasticity Compensation for an Underactuated Robotic Hand