Self-Sensing for Twisted String Actuators Using Conductive Supercoiled Polymers

The twisted string actuator (TSA), as a recently discovered artificial muscle, has attracted a lot of attention as a compliant and powerful actuation mechanism. A TSA consists of two strings attached to a motor on one end and a load on the other end. The motor’s rotation twists the strings and generates linear actuation. A common challenge is to obtain TSAs’ strains using compact approaches. Previous studies exclusively utilized external position sensors that not only increased system cost, size and complexity, but also lowered actuator compliance. In this paper, self-sensing strategies are presented to estimate TSAs’ strains without external sensors. By incorporating conductive and stretchable nylon strings, called super-coiled polymer (SCP) strings, into TSAs, their strains can be estimated from the resistance values of SCP strings. Two self-sensing configurations are realized: (1) TSA with one regular string and one SCP string, and (2) TSA with two SCP strings. Experiments are conducted to show the correlation between the length and resistance of TSA under different conditions. Polynomial and Preisach hysteresis models were successfully employed to capture the Length – Resistance correlation and to estimate TSA’s length using the resistance.

Hysteresis Identification of Bidirectional Magneto-Rheological Actuators Employing Preisach Model

As known, the aim of this paper is to present the field hysteresis behavior of a BMR actuator via identifying the hysteresis model. In order to realize this purpose, firstly, a BMR actuator is manufactured. The feature of this actuator has two disks which are rotated in opposite direction at the same speed and two coils are placed directly on each side of the housing. The two input signals consisting of velocity and current are applied to the BMR actuator to investigate the characteristic of this actuator. Secondly, a proper Preisach hysteresis model is built with two inputs and one output to estimate the torque of the actuator. Finally, the accuracy and the effectiveness of the model are demonstrated by the errors comparison between the constructed hysteretic curves and the experimental ones