Soft Robots Mimic Biological Movements

At Harvard University, researchers have developed a model for designing soft robots. The special features of these robots include bending as a human index finger does and twisting like a thumb when a single pressure source powers the robots.

For long, scientists have followed a process of trial and error for designing a soft robot that moves organically—twisting as a human wrist does, or bending just like a finger. Now, at the Wyss Institute for Biologically inspired Engineering and the Harvard JA Paulson School of Engineering and Applied Sciences, researchers have developed a method for automatically designing soft actuators that are based on the desired movement. They have published their findings in the Proceedings of the National Academy of Sciences.

To perform the biologically inspired motions, the researchers turned to mathematics modeling for optimizing the design of the actuator. According to Katia Bertoldi, Associate Professor and coauthor of the paper, now they do not design the actuators empirically. The new method allows them to plug in a motion and the model gives them the design of the actuator that will achieve that motion.

Although the design of a robot that can bend as a finger or a knee does can seem simple, it is actually an incredibly complex process in practice. The complications of the design stems from the fact that one single actuator cannot produce the complex motions necessary. According to the first author of the paper, Fionnuala Connolly, who is also a graduate student at SEAS, the design requires sequencing the actuator segments. Each of them performs a different motion, with only a single input actuating them all.

The team uses fiber-reinforced, fluid-powered actuators. Their method uses mathematical modeling for optimizing the design of the actuators, which perform a certain motion. With their method, the team was able to design soft robots that bend and twist just as human fingers and thumbs do.

SEAS have developed an online, open-source resource that provides the new methodology in the form of a Soft Robotic Toolkit. This will assist educators, researchers, and budding innovators in designing, fabricating, modeling, characterizing, and controlling their own soft robots.

The robotics community has long been interested in embedding flexible materials such as cloth, paper, fiber, and other particles including soft fluidic actuators, which consist of elastomeric matrices. These are lightweight, affordable, and easily customizable to a given application.

These multi-material fluidic actuators are interesting as the robotics community can rapidly fabricate them in a multi-step molding process. Only a simple control input such as from a pressurized fluid achieves the combinations of extension, contraction, twisting, and bending. Compared to the existing designs, new design concepts are using fabrication approaches and soft materials for improving the performance of these actuators.

For instance, motivating applications are using soft robotics such as heart assist devices and soft robotic gloves for defining motion and forcing profile requirements. It is possible to embed mechanical intelligence within these soft actuators for achieving these performance requirements with simple control inputs. The challenge lies in the nonlinear nature of the large bending motions the hyper-elastic materials produce, which make it difficult to characterize and predict their behavior.