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Magnetorheological (MR) fluids, which stiffen in the presence of magnetic fields, have been shown to be an effective means for controlling the inflation of soft actuators. However, past efforts have largely focused on binary control. Proportional control schemes have faltered due to the difficulty in producing sufficient magnetic fields without requiring large amounts of electrical power. Electropermanent magnets (EPMs) offer one solution to this issue, since they can produce magnetic fields which are similar in magnitude to permanent magnets, they can be controlled electrically, but they do not require any power to hold their state. In this letter, we use EPMs to control the material properties of an MR fluid, allowing us to modulate the pressure within soft actuators. We demonstrate and quantify this behavior for several classes of soft actuators via bending and blocked force testing. We then demonstrate the ability to independently control the actuation of multiple-DoFs systems operating in both a binary and fully-modulated manner, thus providing an important step towards the development of reprogrammable, autonomous soft robots.
McDonald et al. (Tue,) studied this question.