Stretchable Laser-Induced Graphene Sensors for Soft Grippers Proprioception

In the domain of soft robotics, systems are designed and realized with highly deformable materials and structures, which can be exploited in soft grippers to feature an extended range of motion. This has the potential to replicate and outperform the high dexterity of manipulation of the human hand.¹ Although the intrinsic properties of soft materials already guarantee high safety and adaptability, soft grippers require closed-loop control and continuous feedback during the interaction with the target for precise monitoring and real-time position adjustment. It is therefore crucial to incorporate in these structures sensors that are soft, flexible, and lightweight, to also minimize the physical impact on the host system.<br/>Within this context, we propose the sensorization of a finger-based soft gripper made of silicone actuators. The fingers are equipped with piezoresistive Laser-Induced Graphene (LIG) tracks to exploit their exceptional sensitivity to mechanical deformation for proprioceptive feedback. LIG is a three-dimensional conductive nanomaterial fabricated with single-step local pyrolysis of different polymeric precursors by scribing with commercial Infrared (IR) laser engravers. LIG applications span different fields, including soft and wearable electronics, robotics, and energy storage devices.^2–4<br/>LIG tracks were scribed on polyimide with a CO₂ IR laser and transferred to silicone to prevent stiffness mismatch during integration. Two piezoresistive strain sensor designs have been investigated, with extensive static, dynamic, and fatigue tensile tests. After the selection of the best design, a finite element method (FEM) study was conducted as a preliminary evaluation to assess the position of the neutral bending plane of the fingers and therefore determine the best sensor integration position. The sensor was then embedded in the robot’s fingers to receive feedback on the fingers’ bending angle. The theoretical study has been validated in real working scenarios with experimental static, dynamic, and fatigue results on fingers under relaxed and various bending conditions, and a highlight of the best integration solution is provided.<br/>Our study introduces a novel method for measuring of bending angle in a finger-based pneumatic soft gripper and lays the foundation for future studies on this promising LIG sensor solution for soft robots. Moreover, this sensor, combining lightness and flexibility with a cost-effective, simple, and rapid fabrication process, could be adapted for pressure/contact, temperature, and humidity sensors, leading to fully proprioceptive and exteroceptive soft robots.<br/><br/>(1) Pagliarani, N.; Cianchetti, M. et al. In <i>2023 IEEE International Conference on Soft Robotics (RoboSoft) </i><b>2023</b>, 1-7.<br/>(2) Lin, J. et al. <i>Nat. Commun.</i> <b>2014</b>, <i>5</i>, 5714.<br/>(3) Ye, R.; James, D. K.; Tour, J. M. <i>Adv. </i><i>Mater.</i> <b>2019</b>, <i>31</i>, 1803621.<br/>(4) Dallinger, A. et al. <i>ACS Appl. Mater. Interfaces</i> <b>2020</b>, <i>12</i>, 19855