Magnetorheological Fluid‐Based Flow Control for Soft Robots

Abstract

Soft robots are uniquely suited to solving many of the most complex, sensitive problems facing the robotics community. [1] With distributed degrees of freedom (DoF) and compliant structures, they can operate with motions and in locations that are unavailable to their traditional rigid counterparts. [2,3] Even a simple, low-cost soft robot can have a high degree of dexterity, adaptability, and redundancy, allowing for safe interaction with a variety of environments and biological structures. [4-6] While a variety of actuation methods have been explored, such as shape-memory alloys, [7,8] dielectric elastomers, [9] ionic polymers, [10,11] and hydrogel-based actuators, [12-14] among others, fluid-powered soft robots remain the most widespread due to their capacity to deliver large forces, large strokes, ease of fabrication, low cost, and safety. [4,15] In these systems, a fluid (liquid or gas) is used to pressurize a soft structure in a controllable way. Often, soft robot motion is achieved by embedding inflatable chambers within the elastomeric device and by exploiting the geometry or the mechanical properties of the materials comprising the structure such that controllable deformation can be obtained upon pressurization. [16] Previous work has demonstrated complex multi-DoF platforms achievable via progress in the manufacturing of soft structures. [17-22] However, as scientists and engineers continue to develop innovative systems that push the boundaries of dexterity and miniaturization, existing soft robots' limitations become apparent by way of several unsolved challenges related to controlling such complexities. Primarily, current fluidic-powered soft robots require one individually controlled fluidic line for each DoF, leading to various fundamental issues, including 1) how to individually control a large number of lines, 2) the limitations on the robot scale induced by the physical dimensions and quantity of external fluidic connections for a given number of DoFs, 3) the inability of the fixed fluidic network within the soft robot to adapt to the robot's changing needs, and 4) the need for tubing tethered to external flow control elements that together limit the independence and motility of the robot. While the limitations to mobility that a tether of tubes introduces to a soft robot are evident, the tubing itself also introduces a number of complications to the robot's dynamics and overall design. Large lengths of tubing between the robot and its pressure source may allow it to operate more remotely but introduce a control delay due to resistance proportional to the tube's length. Such delays reduce the speed of the robot, whereas the losses similarly reduce efficiency. While stiffer tubing can mitigate such effects, it limits the intrinsic advantages of soft robots and alters the delicate

Sensing in Soft Robotics

“…A magnetic field can also be used to actuate a soft robot, − and it has recently been intensively investigated (Figure f). The orientation of the magnetic domain is controlled or preprogrammed locally in the soft robot either by printing or microfabrication .…”

“…A fundamental criterion for a soft robot is to have a soft contact with the desired object; hence, the materials used for soft robotics are typically polymers that are stretchable, compressible, and flexible. Therefore, in the fabrication of a majority of the reported soft grippers, silicones, polyurethanes, gels, dielectric elastomer, Ecoflex, , urethane rubber, and epoxy-urethane composite are used. The mechanical properties of these commonly reported materials are listed in Table for reference.…”

A Data‐Driven Review of Soft Robotics

“…Some researchers were able to circumvent this issue by embedding small ferrous particles within a soft-bodied matrix as composites. [490,566,567] Exciting recent work examined the use of magnetorheological fluids in soft robots for magnetic control and operation, [568,569] while other researchers demonstrated the transportation of fluids and solids across a "soft magnetic carpet." [570] Optical media were only seen in 23 actuators and five sensors, a small quantity relative to the 342 soft robotic components recorded.…”

Harnessing Nonuniform Pressure Distributions in Soft Robotic Actuators

“…, respectively. "Classic" FEAs predominantly occupy quadrant (IV), [12,[17][18][19][20][21][22][23][24][25][26] where a spatially uniform pressure distribution is coupled with quasistatic transient behavior. Recent work on dynamic response and combustion-driven FEAs falls in quadrant (I), [14,[27][28][29][30][31] where a spatially uniform pressure distribution (as t à s =t à i ≫ 1) and solid inertia dominate.…”