Dynamic Modeling and Feedforward Control of Jaw Movements Driven by Viscoelastic Artificial Muscles

Artificial muscles based on dielectric elastomer actuators (DEAs) have been used to mimic the motion of the human jaw. However, DEAs show strong nonlinear behavior coupled with rate dependent viscoelastic phenomena. Under cyclic actuation, the viscoelastic creep coupled with hysteresis further makes control of these viscoelastic membranes difficult. In this paper, we develop a nonlinear dynamic model based on the principles of nonequilibrium thermodynamics to account for viscoelasticity. Furthermore, the damping and inertial effects of the jaw and membrane are taken into account, relating the deformation of the membrane to the voltage applied. Experimental results are found to be consistent with theoretical predictions. The feedforward controller is then developed based on a viscoelastic nonlinear dynamic model. The controller can be used to track the sinusoidal, triangular, and staircase trajectories accurately. Finally, a video demonstrating the jaw movement in the speech, “I Have a Dream,” by Dr. Martin Luther King Jr. has been shown to illustrate the effectiveness of the controller. This is one of the first efforts to control of soft robots driven by viscoelastic DEAs.