Soft Robotics for Chemists
by Lauren Hartle
The paper introduces the concept of soft robotics to an audience of chemists, discussing promising applications of this technology as well as describing a particular set of prototypes of "soft robots" fabricated by the Whitesides group.
According to Whitesides, et al:
"The robotics community defines "soft robots" as: 1) machines made of soft—often elastomeric—materials, or 2) machines composed of multiple hard-robotic actuators that operate in concert, and demonstrate soft-robot-like properties..."
The researchers used a series of air channels and chambers that acquire curvature when filled with air. Three methods of producing curvature using air pressure were demonstrated, and "starfish" grippers were fabricated and used to pick up various objects, including an egg and an anesthetized mouse. Applications of the "grippers" include manipulation of delicate) (where the highly compliant gripper surface is appropriate) and irregularly-shaped objects (where the ability of the grippers to bend to accommodate different shapes is crucial)
Main Results and Figures
The devices (Figure 1) consist of a series of connected air chambers that can be inflated by an inserted tube. Curvature in these "strips" is achieved when one side of a chamber buckles and stretches more than the opposing side. In the top device, this is accomplished with chambers with thin (and hence less stiff) and thick walls opposite each other. In the lower device, this is accomplished with a composite device, made with highly compliant Ecoflex and (stiffer) PDMS.
In Figure 2, the choice of "strain-limiting layer", i.e., which part of the device (and which material) experienced the least volume expansion (and hence constrained the expansion of other parts). In the first image, a convex shape was formed when the thick lower wall formed the strain-limiting layer. In the second and third image, PDMS or polyester fabric on the thin upper wall served as the strain-limiting layer, resulting in a concave shape.
Figure 3 shows the design and fabrication of a try-layer gripper; a layer of PDMS between two patterned layers of Ecoflex. The gripper can be actuated in either direction, concave or convex, by manipulating air flow in the channels in the Ecoflex layers.
Figure 4 shows the successful use of a 14 cm and 9 cm-diameter gripper device to pick up an anesthetized mouse and an uncooked egg, respectively. The device adapts well to irregularly shaped objects and delicate tasks. The grippers could hold objects up to 10 cm in diameter and 300g in weight.
Additional patterning can be used to enhance the gripping ability of the device.
The paper presents an inexpensive, low power, versatile gripping device, as a proof-of-concept for a broader class of pneumatically-actuated devices (PneuNets). Provided that the load is not too high, these simple devices can replace the more expensive, feedback-loop based hard robotic grippers. Further optimization could improve the device's performance, and ample parameter space remains in terms of surface functionalization/structure, material properties, and gripper geometry.