Prediction model-based learning adaptive control for underwater grasping of a soft manipulator

Soft robotic manipulators have promising features for performing non-destructive underwater tasks. Nevertheless, soft robotic systems are sensitive to the inherent nonlinearity of soft materials, the underwater flow current disturbance, payload, etc. In this paper, we propose a prediction model-based guided reinforcement learning adaptive controller (GRLMAC) for a soft manipulator to perform spatial underwater grasping tasks. In the GRLMAC, a feed-forward prediction model (FPM) is established for describing the length/pressure hysteresis of a chamber in the soft manipulator. Then, the online adjustment for FPM is achieved by reinforcement learning. Introducing the human experience into the reinforcement learning method, we can choose an appropriate adjustment action for the FPM from the action space without the offline training phase, allowing online adjusting the inflation pressure. To demonstrate the effectiveness of the controller, we tested the soft manipulator in the pumped flow current and different gripping loads. The results show that GRLMAC acquires promising accuracy, robustness, and adaptivity. We envision that the soft manipulator with online learning would endow future underwater robotic manipulation under natural turbulent conditions.