Abstract
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 paper, 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 highly reprogrammable, autonomous soft robots.
Promotional Video
Researchers from Boston University’s Morphable Biorobotics Lab have developed a way to control soft robots using magnetorheological fluids.
Magnetorheological (MR) fluids are made of a suspension of iron particles in a carrier fluid, like water.
In the presence of a magnetic field, MR fluids solidify.
MR fluids have been used to control the inflation of soft fluidic actuators, but previous efforts have been binary in nature.
Now, fully modulated control is possible using electropermanent magnets.
An electropermanent magnet (EPM) can be electronically controlled like an electromagnet, but, like a permanent magnet, produces a steady magnetic field without consuming power.
By controlling a brief pulse of current, an EPM can have its field modulated to any value between zero and a maximum dictated by its materials.
The researchers used this effect to control the solidification of a flowing MR fluid and the pressure in an attached soft actuator.
In this way, devices with multiple degrees of freedom could be proportionally controlled in an electronic manner with as few external pressure lines as possible.
This was demonstrated using a two degree of freedom platform that could change its elevation and angle to any point in its workspace using only electrical stimulus to the EPMs.
The researchers hope this work could lead to more advanced onboard control methods for fluidically actuated soft robots, improving their autonomy and allowing them to more easily interact with the world around them.
Video By: Kevin J. McDonald
Boston University College of Engineering
Department of Mechanical Engineering
Morphable Biorobotics Lab