Compound Model of Twisted and Coiled Polymer Actuators Describing Relationship Between Output Force and Excitation Current

Recently discovered twisted and coiled polymer actuators (TCPAs) show huge potentials in the field of soft robots due to advantages of low cost, large deformation and force, high energy density, long life, compact size, and easy to drive. To realize practical applications of the TCPA in soft robots, the study on its dynamic modeling is necessary. However, the TCPA has an obvious hysteresis nonlinearity, bringing obstacles to its modeling. Although some hysteresis models for the TCPA have been established, the study on its rate-dependent hysteresis modeling is still insufficient. To address this issue, a compound model has been established, in which the thermomechanical model is developed by cascading the backlash-like model and a dynamic linear system to depict the relationship between the output force and temperature. In addition, a thermoelectric model has been developed based on the first law of thermodynamics, whose function is to depict the relationship between the temperature and excitation current. All fitness values in the model validation of the compound model are larger than 87.949%. Hence, the compound model has a good generalization performance.