Optimal Sensing in Soft Pneumatic Actuators via Stretchable Optical Waveguides

Stretchable optical waveguides have been explored as a route to enhancing the sensing capabilities of soft actuators. Certain properties and qualities they possess recommend them for this task – their biological plausibility, compliance, low power consumption, and heightened responsiveness to external stimuli. Though well regarded for their efficiency, their practical application warrants a more detailed examination as regards their sensitivity, robustness, and resilience when integrated with various manipulators. There is a dearth of comprehensive, wide-ranging studies that investigate the relationship between soft sensors and actuators, both in terms of integration and sensor performance – the present study endeavours to fill this void. Here we present a series of findings as to the interdependent relationship at the nexus of soft actuator sensorisation, sensitivity and responsiveness. Building on our previous work and prior waveguide designs, we examine the influence of sensor location and placement along the deformation axis on responsiveness, repeatability, and longevity. Location is key as, during bending, one side experiences tension, while the other compression. Placement is identified as ’straight’ or ’loose’. Three PneuNet-based actuators were used in three design configurations: one without any additional modifications, one with a few rigid exoskeleton reinforcements, and one covered fully with rigid exoskeleton reinforcements. The purpose of applying the exoskeletons is to hold the waveguide-based sensors and to suppress any bubble formation. Each design enables the straightforward integration of sensors, so that the relationship between soft actuator design and sensor performance is easy to assess when applying various pressure intakes (from 0 to 7.1 psi) to actuate the bending motion.