Robust control with disturbance observer for twisted and coiled polymer actuator

A twisted and coiled polymer actuator can be easily fabricated by commercially available fishing line. It can be actuated by heating and generate large and flexible deformation. The actuator using conductive nylon fibers can be activated by Joule heating and easily controlled; however, actuator dynamics exhibit nonlinear property. Also, dynamic is varied by several conditions such as an external load, a wind speed and the fabrication method. Therefore, controllers should realize good robustness and high tracking performance. In this research, a control system using the disturbance observer was applied to solve these problems. The nominal model was identified by using input-output data and a disturbance observer was designed to compensate the external disturbance based on the nominal model. The validity of the applied method was investigated through numerical simulations and experiments. Numerical simulations and experiments confirmed that the tracking performance and robustness is improved by the feedback system with the disturbance observer.