A Straight Twisted Polymeric Fiber Actuator (STPFA) has attracted attention as a new rotational actuator because it is soft, lightweight, silent, and inexpensive. It can rotate when heating, and be back when cooling. However, it is difficult to improve the response, especially in the cooling phase when using natural cooling. In order to improve the response in natural cooling, antagonistical actuation is one of the effective methods. However, the diactivated-side actuator generates a disturbance-like torque when the other-side actuator is activated due to its passive torsional spring-like characteristics. In order to realize the antagonistical actuating module using a pair of rotational-type STPFA, in this paper, the models are constructed that can estimate the torque generated at both ends of an antagonistically arranged rotational STPFA from the change in heater resistance. A sensorless output torque control method is proposed for the total torque obtained as the difference between the torques at the two ends using the proposed STPFA models. The effectiveness of the proposed method is demonstrated through fundamental experiments using a prototype module.
