Proprioception and Control of a Soft Pneumatic Actuator Made of a Self-Healable Hydrogel

The current evolutionary trends in soft robotics try to exploit the capacities of smart materials to achieve compact robotics designs with embodied intelligence. In this way, the number of elements that compose the soft robot can be reduced, as the smart material can cover different aspects (e.g., structure and sensorization) all in one. This work follows this tendency and presents a custom-designed hydrogel that exhibits two smart features, self-healing and ionic conductivity, used to build a pneumatic actuator. The self-healing capability provides the actuator's structure with the ability to self-repair from damages (e.g., punctures or cuts), an important quality to prolong the life cycle of the actuator. The ionic conductivity enables the actuator's proprioception: the structure itself serves as a curvature sensor. The behavior of this proprioceptive curvature sensor is analyzed in this work, studying its linearity, stability, and performance after a self-healing process. This sensor is also proposed as feedback in a closed-loop scheme to automatically control the actuator's curvature. A proportional-integral-derivative controller is designed based on an empirical model of the actuator's dynamics, and then validated in experimental tests, proving the proprioceptive sensor as proper feedback. These control tests are performed over undamaged and self-healed actuators, thus demonstrating all the capabilities of our soft material.