Modeling and Control of Artificial Bladder Enabled by Ionic Polymer-Metal Composite

In our previous study, an artificial bladder enabled by Ionic Polymer-Metal Composite was developed for depth control of bio-inspired robots [1]. The device consists of a gas chamber whose the volume is controlled by a solenoid valve and an electrolysis gas generator, thus changing the device's buoyancy. In this paper, we present a continued study on modeling and control of the artificial bladder. A nonlinear dynamic model is developed for feedback control of the device. The model can be divided into two cascaded sub-models that capture net gas generation dynamics and motion dynamics, respectively. The stability analysis of motion dynamics has shown that the device with open-loop control is unstable. A dual-loop feedback control is designed to stabilize the unstable dynamics and improve the depth maneuvering accuracy. Simulation results shows that the feedback control enables the device to change its depth up to 0.2 m in one-step diving with about 50 seconds setting time. With multiple-step diving, the device can position itself at arbitrary depth underwater.