Variable stiffness soft pneumatic sensing chambers for tactile sensing and haptic devices

This paper discusses the development of a sensing system based on Soft Pneumatic Sensing Chambers (SPSCs) with discretely variable stiffness. The geometric and setup parameters affecting the sensibility and stiffness of the system are first identified through a simplified analytical formulation. Then, a deformation model is implemented to estimate and compare the static performance of four notable SPSC types. Furthermore, SPSCs manufactured through different methods are experimentally characterized in terms of performance and overall reliability. Notably, for SPSC units fabricated from TPU 60A, on average, stiffness increases by 60%, from 5.0 to 8.0 N/mm, when switching between low and high stiffness conditions, while the pressure sensitivity increases more than tenfold, from 0.5 to 6.1 kPa/mm. Furthermore, it is shown that static performance can be accurately predicted across different setup pressures using the geometric data estimated from tests at a single pressure. Finally, two applications are presented, namely, tactile sensing for robotic grasping, and haptic interaction. In these contexts, the advantages of the proposed sensing system over existing solutions are discussed, highlighting the trade-off between functionality and compactness.