Abstract
Twisted string actuators (TSAs) have exhibited high performance in numerous mechatronic applications. Most existing studies on control of TSAs assume that the external force applied to the TSA is measurable or predictable. Furthermore, existing studies also assume that all the TSA parameters such as the motor properties and string stiffnesses are accurately known. However, the system parameters could be difficult to measure, could change over time due to general wear and tear, and creep. The external forces applied to the TSA could be difficult to predict or measure. In this study, parameter estimation and control strategies were developed for TSAs, assuming little or no knowledge about the system parameters. Firstly, a parameter estimation strategy which utilized the least squares algorithm and gradient algorithm is presented. Secondly, an adaptive control strategy based on model reference control with feedback linearization is proposed. The developed estimation and control strategies were tested to be effective through simulation. The performance of the proposed control strategy was compared with a proportional controller (PC) and a proportional controller with a feedforward term (PCFF). The average TSA length tracking error for the proposed controller, PC, and PCFF were 2.6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> m, 1.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> m, and 7.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> m, respectively.
Published Version
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