System Identification of Force of a Silver Coated Twisted and Coiled Polymer Muscle

The demand of using artificial muscle similar to the human muscle is significantly increased during past decades. Recently, silver-plated Twisted and Coiled Polymer (TCP) muscle was employed in many research projects. A first order differential equations (1st ODE) was used to predict the force of this muscle, assuming that the TCP muscle acts similar to a mechanical spring that has variable stiffness depending on the electrical power supplied. Thus, extensive study should be performed on different types of TCP muscles to reach a conclusion. In this paper, a black box system identification method is used to examine the behavior of TCP muscles under different input conditions. Different order differential equations are compared with experimental results. Prediction error method (PEM) is used for estimation of the force of silver-plated TCP muscle with several linear time invariant (LTI) discrete time state space system. In addition, we suggest a fast method (rule of thumb) to model a TCP muscle. Moreover, two key parameters have been introduced to compare the quality of the TCP muscle from force perspective.