In this paper, we describe the fabrication and testing of a stretchable fabric sleeve with embedded elastic strain sensors for state reconstruction of a soft robotic joint. The strain sensors are capacitive and composed of graphite-based conductive composite electrodes and a silicone elastomer dielectric. The sensors are screenprinted directly into the fabric sleeve, which contrasts the approach of pre-fabricating sensors and subsequently attaching them to a host. We demonstrate the capabilities of the sensor-embedded fabric sleeve by determining the joint angle and end effector position of a soft pneumatic joint with similar accuracy to a traditional IMU. Furthermore, we show that the sensory sleeve is capable of capturing more complex material states, such as fabric buckling and non-constant curvatures along linkages and joints.

Materials exhibiting variable stiffness properties have great potential for use in the growing field of soft robotics. Soft structural materials allow a robot to fit into enclosed spaces, resist shock and vibration, or even reconfigure its geometry and adapt to various environments. Rigid structural materials on the other hand allow environmental interactions through application of force and load-bearing capabilities. Materials that can be selectively switched between these two extremes could greatly expand the functionality of a robot that requires the properties of both. In this paper, we introduce a conductive epoxy composite that is self-softening through Joule heating via direct application of electrical current. The polymer can then become load-bearing and rigid again after being formed into a new shape. We demonstrate the capabilities of this material by attaching a pneumatic actuator and showing that the resulting variable stiffness device can be softened from its initial rigid state, reshape itself using the pneumatic actuator, then become rigid again and hold this new position without additional power being supplied to the actuator.

In this paper, we present a fluidically functionalized soft-bodied robot that integrates both sensing and actuation. Rather than combining these functions as an afterthought, we design sensors and actuators into the robot at the onset, both reducing fabrication complexity and optimizing component interactions. We utilize liquid metal strain sensors and pneumatic actuators embedded into a silicone robotic gripper. The robot's body is formed by curing the silicone in complex 3D printed molds. We show that the liquid metal strain gauges provide a repeatable resistance response during robotic actuation. We further show that, given sufficient control over other time-dependent variables, it is possible to determine when the robot begins gripping an object during actuation.