Design and Locomotion Control of a Soft Robot Using Friction Manipulation and Motor-Tendon Actuation

Robots built from soft materials can alter their shape and size in a particular profile. This shape-changing ability could be extremely helpful for rescue robots and those operating in unknown terrains and environments. In changing shape, soft materials also store and release elastic energy, a feature that can be exploited for effective robot movement. However, design and control of these moving soft robots is non-trivial. The research presents design methodology for a 3D-printed, motortendon actuated soft robot capable of locomotion. The modular design of the robot facilitates rapid fabrication, deployment and repair. In addition to shape change, the robot uses friction manipulation mechanisms to effect locomotion. The motor-tendon actuators comprise of nylon tendons embedded inside the soft body structure along a given path with one end fixed on the body and the other attached to a motor. These actuators directly control the deformation of the soft body which influences the robot locomotion behavior. Static stress analysis is used as a tool for designing the shape of the paths of these tendons embedded inside the body. The research also presents a novel modelfree data-driven control approach for soft robots which interact with the environment at discrete contact points. This approach involves discretization of factors dominating robot-environment interactions as states, learning of the results as robot transitions between these robot states and then optimization of a cost function to find desired control sequence. The clever discretization allows the framework to exist in robot’s task space, hence, facilitating calculation of control sequences without modeling the actuator, body material or details of the friction mechanisms. The flexibility of the framework is experimentally explored by applying it to robots with different friction mechanisms and different shapes of tendon paths. Keywords—soft robotics, model-free control, motor-tendon, locomotion, highly deformable, additive manufacturing, friction manipulation mechanism