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Controller design based on disturbance observer for twisted and coiled polymer actuators

A novel artificial muscle actuator called as twisted and coiled polymer actuator can be easily fabricated by commercially available Nylon fibers. It can be thermally activated and has remarkable properties such as large deformation and flexibility. The actuator using conductive Nylon fibers can be activated by Joule heating and easily controlled; however, it is reported that dynamics exhibit nonlinear property due to a heat transfer and a thermomechanical property. In addition, it is reported that dynamic characteristics change from several conditions such as load, ambient temperature and the fabrication method. These finding suggested that the actuator may not able to achieve high accuracy control compared to electrical motors. Therefore, it is desirable to construct controllers that have good robustness and high tracking performance. PID controls with nonlinear compensator have been applied for the twisted and coiled polymer actuator. The PID controller should be adjusted for good robustness and high tracking performance depending on external disturbance, load weight fluctuation or reference signal. In this paper, a control system with the disturbance observer is applied to solve these problems. The actuator model is identified by using input-output data and a control system is designed to compensate the external disturbance based on the actuator model. The validity of the applied method is investigated through numerical simulations.