Position Control of a Biomimetic IPMC Underwater Propulsor: Fid-Bau Portal

Position Control of a Biomimetic IPMC Underwater Propulsor

Gupta, Ankur / Mukherjee, Sujoy

In this study, a dynamic model is used for the position control of an ionic polymer-metal composite (IPMC) actuated underwater propulsor. A time trace of actuation parameters versus voltage input is observed. The transfer function between the applied voltage and tip displacement is almost linear and flat before the cut-off frequency because of the mechanical damping. Also, a transfer function between the applied voltage and tip velocity is taken and this particular transfer function shows a sudden rise while approaching resonant frequency. This observation is clear to suggest that at this stage, highest vibration velocity is achieved by the fin tip. It can be seen from bode plots that the optimal range of actuation frequency can be identified and it will be helpful in getting maximum thrust production. Since Reynolds number depends on the length and width of IPMC, consideration of the length of IPMC propulsor is an important factor. The length of the IPMC propulsor is considered to be small as one of the objectives of the present study is to design miniaturized propulsor. Power consumption by the propulsor is an important factor, and it has also been considered in this study. Further, swimming speed is calculated for various input sinusoidal voltages. Power spent during actuation is calculated for various conditions. A parametric study is done by taking different fluid viscosities, IPMC strip lengths, widths of IPMC strip, and different voltage inputs to compare the results for different conditions. It can be seen that the average thrust and Reynolds number values depend on the length and width of IPMC strip as well as on input voltage. In order to give controlled input and obtain controlled system response, a proportional integral derivative (PID) control is implemented on the transfer functions. In this study, the displacement of 2 mm is considered as the desired value of deflection for the particular input and it is achieved via controlled input voltage. It was found that the system can be controlled for displacement by controlling the input voltage using a PID closed-loop position control. Also, a comparison is done with a fuzzy controller with improved controlled parameters like overshoot, settling time, and steady-state error.