Bistable Valves for MR Fluid-Based Soft Robotic Actuation Systems

Magnetorheological (MR) fluids have unique characteristics that make them well-suited for soft robotic actuation systems. Two particularly interesting applications are bistable valves and force-amplified grippers, which only require power to switch states. These design topologies can not only make MR fluid actuation systems more efficient, but can also allow them to be constructed from entirely compliant materials. In this work, we describe new bistable valve mechanism concepts; the first design is constructed using traditional rigid components while the second design is composed of entirely compliant materials. This includes liquid metal coils, compliant magnetic composites, and silicone flexures. The MR valve concept is modeled using magnetic field theory and scaling laws are determined from MR fluid holding pressure experiments. Then, experimental results are used to show that rough tubing surfaces can withhold an average of 5× more pressure than smooth tubing surfaces. Both rigid and compliant valve topologies are then constructed and tested, showing the ability to hold up to 88 kPa and 37 kPa of pressure, respectively. These valves are then implemented for controlling a soft multi-fingered PneuNet gripper and a new force-amplified MR fluid gripper, which has the ability to provide up to 324$\%$ higher load capacity than purely pressure-driven mechanisms (with the addition of a 25 mm diameter and 12.7 mm thick Nd-Fe-B magnet). Finally, we show how these bistable valves and grippers can be used for grasping and manipulation applications.