An experimental investigation of dynamic motions of a small-scale magnetoactive soft robot undergoing large nonlinear movements

Small-scale magnetoactive soft robots (MSRs) with multimodal locomotion and wireless actuation capabilities have emerged in recent years for various highly sensitive and precise biomedical tasks such as targeted drug delivery and minimally invasive therapies. MSRs comprise magnetoactive elastomers consisting of micron-sized hard magnetic particles, such as neodymium-iron-boron (NdFeB), suspended or arranged into an elastomeric matrix. These robots generally exhibit large deformation under an applied magnetics stimulus, which is considered favorable for the aforementioned applications. Only limited efforts, however, have been reported on characterization of such robots. This is likely due to their nonlinear dynamics, especially under large deformations and hysteretic stress-strain characteristics, which strongly depend on the magnitude and frequency of the external magnetic stimuli. This study experimentally investigated and analyzed the real-time nonlinear and hysteretic responses of a MSR fabricated in the form of a cantilever beam made of a magnetoactive elastomer. An experiment was designed to characterize dynamic responses of the MSR under different magnetic stimuli at relatively higher frequencies to evaluate the rate-dependent hysteresis effect. A hardware-in-the-loop technique in conjunction with a PID controller was implemented, which permitted the generation of a precise and uniform magnetic field. The MSR was subjected to uniform magnetic loading perpendicular to the robot’s length leading to large amplitudes and rates of harmonic movements of the MSR. The experiments were performed under different intensities, ranging from 2 to 30 mT, at frequencies up to 3 Hz. The measured data were analyzed to obtain response time-histories and frequency response characteristics of the MSR, apart from the motion snapshots.