Stretchable Shape-Sensing Sheets

Abstract

Soft robot deformations are typically estimated using strain sensors to infer change from a nominal shape while taking a robot-specific mechanical model into account. This approach performs poorly during buckling and when material properties change with time, and is untenable for shape-changing robots that don't have a well-defined resting (unactuated) shape. Herein, these limitations are overcome using stretchable shape sensing (S3) sheets that fuse orientation measurements to estimate 3D surface contours without making assumptions about the underlying robot geometry or material properties. The S3 sheets can estimate the shape of target objects to an accuracy of ≈3 mm for an 80 mm long sheet. The authors show the S3 sheets estimating their shape while being deformed in 3D space and also attached to the surface of a silicone three-chamber pneumatic bladder, highlighting the potential for shape-sensing sheets to be applied, removed, and reapplied to soft robots for shape estimation. Finally, the S3 sheets detecting their own stretch up to 30% strain is demonstrated. The approach introduced herein provides a generalized method for measuring the shape of objects without making strong assumptions about the objects, thus achieving a modular, mechanics model-free approach to proprioception for wearable electronics and soft robotics.