The performance of a magnetorheological rotary actuator featuring a wavy boundary shape

Magnetorheological (MR) fluids are smart materials whose rheological properties can be reverse modified by applying a magnetic field, making them highly suitable for utilization in adaptive actuators. In this work we investigate the performance of adaptive circular-cylindrical rotary actuators featuring an MR fluid in the working gap between rotor and stator, where the impact of different stator boundary geometries is considered: a waveform shaped contour (referred to as star contour) and a reference actuator featuring a constant gap width (referred to as drum contour). The associated comparative measurements, conducted using the same average magnetic field strengths, aimed at an empirical characterization, where particularly the formation of chains under operating conditions was observed. The findings indicate that the star contour demonstrates a number of advantages in comparison to the drum geometry. The enhanced performance is attributed not only to the effect of shear mode but also to the contribution of magnetophoretic force, which promote the formation of denser chain structures and facilitate increased torque transmission. The actuator with the star contour exhibits some characteristics which are desirable for emulating conventional mechanical rotary knobs using these actuators.