Abstract
<title>Abstract</title> <p>Integrating high-fidelity sensing and active feedback within a single flexible substrate remains a fundamental challenge in haptic interfaces due to the catastrophic signal crosstalk between co-located channels. This paper presents FusionTouch, a glove-free spherical haptic interface based on a cross-domain transparent architecture centered on optical accessibility, enabling multimodal sensing and haptic feedback on a flexible spherical skin. Leveraging a bio-inspired textile fabrication process, the skin seamlessly integrates a pneumatic support layer, a protective layer and a bidirectional layer composed of ITO, conductive hydrogel, and near-infrared markers, allowing electrical stimulation, optical sensing, photothermal modulation, and pneumatic support to work synergistically within the same interface while reducing interlayer imaging interference. Its spherical form factor is ergonomically inspired by the resting posture and manipulation movements of the human hand, conforming to the naturally curved and compact configuration of a relaxed hand, thereby improving ergonomic suitability for glove-free interaction. Powered by graph neural network and two-stream network algorithms, FusionTouch supports high-fidelity hand pose estimation (mean absolute error: 0.36°), three-dimensional surface deformation reconstruction (median error: 1.28 mm), and contact force estimation (mean absolute error: 0.093 N), while simultaneously providing localized electrotactile, photothermal, pneumatic stiffness, and optional vibrotactile feedback. Demonstrations in robotic teleoperation, virtual reality, and robot-assisted massage validate FusionTouch as a glove-free platform for bidirectional physical human–machine interaction and as a generalizable strategy for designing shared-surface interfaces that unify multimodal perception and haptic feedback.</p>