Dynamic modeling of thermo-sensitive hydrogel describing its complex energy conversion mechanism with hysteresis nonlinearity

Thermo-sensitive hydrogel (TSH) demonstrates a lot of promise for soft robots. However, the TSH presents challenges for modeling due to its complex energy conversion mechanism and hysteresis nonlinearity. To address this issue, a dynamic model consisting of an electro-thermal model and a thermo-deformation model is developed in this paper. In which, the electro-thermal model is established for describing the relationship between the driving voltage and the temperature of the TSH. The thermo-deformation model consisting of a Prandtl-Ishlinskii model, a polynomial model and a transfer function model is established between the temperature and the deformation of the TSH. In addition, the thermo-deformation model describes the asymmetric and rate-dependent hysteresis nonlinearity of the TSH. Moreover, due to the analytic inverse of the thermo-deformation model, it is convenient to design a model-based controller to achieve the high-precision deformation control of the TSH. Next, unknown parameters in the above models are determined based on the nonlinear least squares algorithm by using the data from the experiment. Finally, model validations are performed, and the fit values are all greater than 89.40 %. Thus, the established dynamic model can accurately describe the complex energy conversion mechanism with hysteresis nonlinearity of the TSH and has great generalization ability.