Stiffness estimation of delicate objects using a soft haptic whisker

Soft whiskers allow for haptic sensing without damaging or altering the object being tested, which is particularly advantageous in delicate environments. A novel method for stiffness estimation using a soft haptic whisker is proposed in this research. The whisker, fabricated from Thermoplastic Polyurethane (TPU), deforms upon contact with objects, allowing for non-invasive stiffness measurement. Utilizing force and moment readings at the whisker's base, the system calculates the object's stiffness based on shape deformations modeled using the Cosserat rod theory. Experimental validation was conducted on both flexible tree saplings in a lab and delicate plant structures, such as strawberry stalks and leaves, in a polytunnel. Results demonstrate that the soft whisker can measure stiffness without damaging the objects, offering up to 30 times lower contact forces compared to a rigid probe. This method provides a safe, efficient solution for interacting with sensitive environments, opening possibilities for its application in robotic manipulation of delicate items.