Honeycomb-Inspired Metamaterial for Tactile Sensors with Variable Stiffness

The material's stiffness plays a crucial role in tactile sensors and stiffness controllers of robot joints, facilitating safe and effective robot-environment interactions. Conventional controllers or sensors require a priori information about stiffness modulation to efficiently control environmental collisions and reduce their detrimental effects. Therefore, such inflexibility of real-time stiffness variation may cause instability if the dynamic mechanical system (a mass-spring-damper) changes during execution. In this paper, we tackle the problem using a honeycomb metamaterial with a tunable stiffness to design a tactile sensor capable of detecting physical contact with low and high-impact forces. We experimentally demonstrate that dynamic modification of the honeycomb structure reduces the maximum impact force by ≈ 30%, mitigating the rapid collision with the environment during contact detection. The results show that the honeycomb attachment allows for a more precise and controlled impact with varying degrees of energy and momentum transfer. The honeycomb attachment can be a valuable tool for grasping, explosive motion generation, and tactile sensing, requiring low-or-high-impact and controllable contact. Our study highlights the potential of using negative stiffness honeycomb structures to improve the functionality of tactile sensors.