Building and Controlling Fluidically Actuated Soft Robots: From Open-loop to Model-based Control

My thesis describes the creation and control of soft robots made of deformable elastomer materials and powered by fluidics. We embed soft fluidic actuators into self-contained soft robotic systems, such as fish for underwater exploration or soft arms for dynamic manipulation. We present models describing the physical characteristics of these continuously deformable and fully soft robots, and then leverage these models for motion planning and closed-loop feedback control in order to realize quasi-static manipulation, dynamic arm motions, and dynamic interactions with an environment.

The design and fabrication techniques for our soft robots include the development of soft actuator morphologies, soft casting techniques, and closed-circuit pneumatic and hydraulic powering methods. With a modular design approach, we combine these soft actuator morphologies into robotic systems. We create a robotic fish for underwater locomotion, as well as multi-finger hands and multi-segment arms for use in object manipulation and interaction with an environment.
The robotic fish uses a soft hydraulic actuator as its deformable tail to perform open-loop controlled swimming motions through cyclic undulation. The swimming movement is achieved by a custom-made displacement pump and a custom-made buoyancy control unit, all embedded within the soft robotic fish. The fish robot receives high-level control commands via acoustic signals to move in marine environments.

The control of the multi-segment arms is enabled by models describing the geometry, kinematics, impedance, and dynamics. We use the models for quasi-static closed-loop control and dynamic closed-loop control. The quasi-static controllers work in combination with the kinematic models and geometric motion planners to enable the soft arms to move in confined spaces, and to autonomously perform object grasping. Leveraging the models for impedance and dynamics, we also demonstrate dynamic arm motions and end-effector interactions of the arm with an environment. Our dynamic model allows the application of control techniques developed for rigid robots to the dynamic control of soft robots. The resulting model-based closed-loop controllers enable dynamic curvature tracking as well as surface tracing in Cartesian space.

R. Katzschmann. “Building and Controlling Fluidically Actuated Soft Robots: From Open Loop to Model-based Control.” Massachusetts Institute of Technology, USA, May 2018. [PDF]