Variable Stiffness and Impedance Control of a Soft Pneumatic Actuator With Tunable Collision Dynamics and Trajectory Following

Abstract State-of-the-art soft manipulators are unable to vary stiffness continuously, are complex to manufacture, and have limited control bandwidth. In this work, we present a novel planar bidirectional pneumatically actuated soft manipulator that advances all three limitations—the stiffness is continuously tunable by a factor of 1.6, the actuator is manufactured from a single 3D print, and we are able to demonstrate free-space tracking of a time-varying signal. We are also able to modify the impedance of the actuator during a collision using a dynamic model-based feed-forward and feedback controller and demonstrate an increase in virtual stiffness by a factor of 4. The incorporation of feedback resulted in 0.7 mm tip position root-mean-square error (RMSE) (a reduction of 47% over the purely feed-forward controller) while tracking a 5 mm amplitude sinusoid up to 0.75 Hz across the entire stiffness range.