HapMorph: a pneumatic framework for multi-dimensional haptic property rendering

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Abstract Haptic interfaces that can simultaneously modulate multiple physical properties remain a fundamental challenge in human-robot interaction. Existing systems typically allow the rendering of either geometric features or mechanical properties, but rarely both, within wearable form factors. Here, we introduce HapMorph, a pneumatic framework that enables continuous, simultaneous modulation of object size and stiffness through antagonistic fabric-based pneumatic actuators (AFPAs). We implemented a HapMorph prototype designed for hand interaction, achieving size variation from 50 to 104 mm, stiffness modulation up to 4.7 N/mm, and a wearable mass of just 21 g. Through systematic characterization, we demonstrate independently controllable size and stiffness properties via dual-chamber pressure regulation. Human perception studies with 10 participants reveal that users can distinguish nine discrete states across three size categories and three stiffness levels with 89.4% accuracy and 6.7 s average user response time. We further demonstrate extended architectures that combine AFPAs with complementary pneumatic structures to enable shape or geometry morphing with concurrent stiffness control. Our results establish the antagonistic pneumatic principle as a pathway toward next-generation haptic interfaces, capable of multi-dimensional property rendering within practical wearable constraints.