A highly stretchable hydrogel sensor for soft robot multi-modal perception

Soft robots attracted surging interests in recent years due to its enhanced safety, and it significantly contributes to its human-robot interaction application. However, the compliant system has infinite dimensions, which remained challenging for accurate state perception and control. Embedded soft sensors are the potential solutions to this problem as they can trigger electrical or optical signals even when stretched. Yet current conductive material’s upper strain limit are not large enough. Here we design a highly stretchable hydrogel resistive sensor for soft fingers’ multi-modal perception with a simple and low cost fabrication method. The hydrogel’s maximum tensile strain is up to 1200 %, which ensures to tolerate the pneumatic actuator’s large deformation, and its water loss can be as low as 0.0625 % within 30 days. We demonstrated the sensor’s multi-modal perception for the actuator’s state estimation, as it can effectively monitor the soft fingers’ bending, twisting, and external forces with high sensitivity, low hysteresis and high reliability. In addition, we also explore the impact of the hydrogel sensor on the pneumatic actuator’s dynamics, and it provides insights into how the sensor’s placement location influence the perception. This study could lead to improved soft robot system’s kinematics study and potentially more accurate close-loop control.