A novel artificial muscle actuator referred to as a 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 uses conductive nylon fibers and can be activated by Joule heating and is easily controlled electrically. However, asymmetric response characteristics due to a speed difference in heating–cooling are a problem. In the case of actuation in air, the cooling speed depends on the external temperature, and is slower than the heating speed. To solve these problems, we apply an antagonistic structure. The validity of the applied method is investigated through numerical simulations and experiments. The response characteristics of the PID feedback control and the 2-DOF control of the displacement are investigated.
A twisted and coiled polymer actuator (TCPA) is a novel soft actuator. It is fabricated by twisting nylon thread or fishing line. It can be thermally activated and has remarkable properties such as high power/mass ratio and large deformation. By applying conductive nylon fibers to the actuator, it can be electrically driven by Joule heating. However, if a controller of the actuator is designed without considering an input saturation, the control performance may be descended by windup phenomena. In this paper, to solve this problem, a feedback control with an anti-windup compensator is applied. The validity of the applied method is investigated through numerical simulations and experiments.
New parameter-tuning methods, called data-driven tuning, have been proposed, which can derive the controller parameters without using plant models. These include iterative feedback tuning (IFT), virtual reference feedback tuning (VRFT), and fictious reference iterative tuning (FRIT). In this study, a simple data-driven tuning method is proposed. Through closed-loop experiments, one-shot input data and the initial controller parameters are obtained, based on which the control system is tuned. The tuned control system can realize a high tracking performance, and the desired response can be obtained. Furthermore, the validity of the proposed method is investigated through numerical simulation and experiments, which establish that the control performance is improved by the proposed parameter-tuning method. The proposed method can obtain appropriate controller parameters.
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