Abstract
The domain of underwater soft robotics has the potential to revolutionize how we interact with the ocean through robotic control. In order to perform a broad range of conformable object manipulation, developments in multi-modal sensing technologies are needed in the underwater realm of soft robotic end effector development. However, concurrent tactile technologies have certain limitations over directional force and shape sensing. In particular, they are expensive, difficult to fabricate, and mostly unsuitable for underwater use. In this work, we propose a simple and cost-effective solution for a novel shape sensing algorithm and multi-directional force sensing system based on widely available and inexpensive piezo-resistive flex sensors. Both sensing systems are intended to be utilized in a soft robotic gripper which is fabricated to be employed for underwater applications in our lab. The shape sensing algorithm estimates the curvature of the soft gripper quite accurately based upon two-part compound radius flex-sensor readings embedded in each finger. We also make use of four flex sensors within a silicone-made hemispherical shell structure for the synthesis of a flexible multi-directional force sensing system to get the force readings. Each sensor was place 90° apart and aligned with the curve of the hemispherical shape. If the force is applied on the top of the hemisphere all the flex sensors would bend uniformly and yield nearly identical readings. When force is applied from a different direction, a set of flex sensors would characterize distinctive output patterns to localize the point of contact as well as the direction and magnitude of the force. The deformation of the fabricated soft sensor due to applied force was simulated numerically and compared with the experimental results. The fabricated sensor was experimentally calibrated and tested for characterization including an underwater demonstration. The overall goal of this work is to demonstrate a viable conceptual design solution for waterproofed multi-modal sensing within the soft robotic design framework for a wide variety of underwater robotic applications.