Curvature and Contact Sensing with Optical Waveguides for Soft Silicone Pneumatic Actuator

Optical waveguide sensors exhibit fast response, radically low power consumption, and offer one of the most efficient means of detecting bends in soft actuators. They are, however, sensitive to non-uniform deformations at high curvature and external stimuli and much remains to be done to improve their robustness and resilience. In this study, we present a series of improvements to the design and fabrication of a soft multi-point waveguide sensor. The developed pressure-sensitive sensor measures bending longitudinally along a soft silicone pneumatic actuator (SSPA). SSPAs exhibit uniform bending behaviour as compared to fabric-based actuators, which makes for a more stable medium within which to embed our sensor. Additionally, the sensor can detect bending behaviour at multiple points in a soft actuator. In previous work, we demonstrated the multi-point sensor's ability to accurately measure curvature in a fabric finger. In this paper, we report on various enhancements to the waveguide sensor that optimise its performance in various bending scenarios. The design is optimised in terms of novel material use for the sensor housing, reduction in size and weight, plus, by integrating with an SSPA, we achieve bending beyond 90°. The newly optimised sensor's characteristics and increased sensitivity are investigated by performing reliability tests, ten-cycle cyclic-compression tests, and free bending. In addition, we subject the actuator to bending while grasping various shapes, including a sphere, a hollow cylinder, a cube, and a hexagon, while varying the pressure intake.