Abstract
Fluidic soft robots bring a high degree of dexterity and adaptability to robotics problems requiring safe interaction with complex structures. While they can be low cost and easy to manufacture, they can also be difficult to control due to their typical reliance on external pressure sources that can become bulky as more degrees of freedom are introduced to the robot. Various techniques from microfluidics and fluid logic have been used to introduce valves into soft robots to increase their autonomy, although this has frequently introduced unwanted rigidity. This paper introduces a magnetorheological (MR) fluid valve that uses magnetic fields to control the pressure within a continuous flow fluidic actuator. A predictive model for the pressure drop in such a flow is presented and validated experimentally. Guidelines for the design of single and multi-actuator systems with a single inlet and outlet are presented. The introduction of actuation methods that simplify fluidic control via the application of magnetic fields could lead to robots capable of increased autonomy in a scalable and compliant format.
Supplementary Videos
This movie shows the three class of devices tested. For each, a continuous flow of MR fluid was provided using a peristaltic pump.
First, the 1 DoF loop actuator is shown. With the application of a magnetic field downstream of the actuator, the pressure increases, and the actuator bends.
Second, the gripper consisting of three coupled actuators is shown. With the application of a magnetic field downstream of the device, all three actuators bend simultaneously.
Finally, the device consisting of two independent actuators is shown. Using two magnets, every combination of the device's bending states can be achieved. The inset shows the location of the magnetic fields and the resulting bending states. Upon removal of the magnets, some undesired movement is observed in the actuators as the pressure in the device comes to equilibrium. Asynchronous deactivation of the fields such that the pressurized actuator could drain directly to the outlet before allowing flow into the unpressurized actuator could be used to compensate for this phenomenon.
This movie shows the gripper actuator consisting of three coupled PneuNet actuators being used to grip a plastic cup. With the application of a magnetic field downstream of the actuator, the three coupled actuators simultaneously inflate, allowing the gripper to grasp a 4 g cup. When the magnetic field is removed, the actuators deflate and the gripper drops the cup.
This movie shows selective actuation of a robot with five magnetically controlled DoFs: four independent legs and one gripper consisting of six coupled actuators. Each DoF has its own logic node which in combination can be used to achieve all the logical states of actuation. Since the actuators are connected in series, actuating one DoF also actuates the other DoFs upstream. This may be avoided by using the magnets to block the actuation of the upstream actuators. It may also be exploited to inflate sets of actuators as desired. The inset diagram shows the locations of the magnets in red and the inflated actuators in blue. The video includes several actuator combinations from both a top-down and front view. Other actuator combinations are possible, but are not shown.