Feb 18, 2016 | By Benedict

Zhe Xu and Emanuel Todorov, engineers from the University of Washington, Seattle, have built a highly complex 3D printed robotic hand. The pair obtained a 3D scan of a cadaver skeleton in order to design 3D printed bones for the biomimetic device.

To build the most realistic robotic hand, one should intentionally ignore 90% of the biological mechanisms of a human hand, replacing them with decidedly un-human mechanisms such as hinges and gimbals. It sounds paradoxical, doesn’t it? How can a robotic hand that willfully discards biological mechanisms in favor of inorganic machinery be more realistic than one that tries to replicate those biological mechanisms? It’s a reasonable question to ask, and one that must be answered with an examination of the concept of “realism”.

Most designers of robotic hands have one objective in mind: To achieve realistic hand movement. To do this, the simplest and most effective route usually involves mimicking muscle and tendon movements with mechanical substitutes. It’s cheaper and easier to produce a hand made of levers and linkages than it is to make artificial bones, muscles, and tendons, therefore biomechanical realism—otherwise known as “biomimesis”—gets forsaken in favor of kinetic realism. Robotic hands which adopt this model sure won’t look like a human hand on the inside, but the movements they produce can faithfully mimic those of a human hand… up to a point.

Zhe Xu, a post-doctoral associate at Yale, and Emanuel Todorov, a professor at the University of Washington, recently worked together on a research project in which they built a highly biomimetic, anthropomorphic, 3D printed hand—one which mimics human hand movement by replicating actual biomechanical processes. They have, in other words, taken the long way round in order to arrive at a superior design, eliminating the “undesirable discrepancies between…human and robotic hands” that appear when the “salient biomechanical features of the human hand are discarded”.

Xu and Todorov’s 3D printed robotic hand is not only more realistic—mechanically and kinetically—than most robotic hands, it also allows a user to control the device using completely natural hand movements of their own. By monitoring the exact movements of user's own hand, the incredibly complex device is able to replicate those intricate muscle and tendon movements on the artificial hand.

The secret to this near-perfect symmetry lies in the engineers’ attention to biological detail. Each artificial bone of the robotic hand was 3D printed according to a detailed 3D scan obtained from the skeleton of a cadaver; artificial joint ligaments were made from high strength Spectra strings, with laser-cut rubber replacing soft tissue; tendons were also recreated from Spectra; and artificial muscles were made from 10 Dynamixel servos. Don’t be fooled into thinking the pair took a shortcut on those muscles: the cable routing between the servos closely mimics the carpal tunnel of a human hand.

After reproducing the bones of the cadaver in 3D printed plastic, the engineers were able to reproduce the unfixed joint axes of real human hands, whilst the complex network of artificial muscles, tendons, and ligaments have resulted in incredibly realistic thumbs and finger movement. Just like a real human hand, the robotic device is able to grasp objects such as coins, balls, and a cell phone, with the user not required to learn any complex operational procedures beyond the natural flexing of their own hand.

The 3D printed robotic hand’s ease of use could make it an attractive proposition in telemanipulation—the human-controlled “handling” of items, often hazardous ones, with artificial hands. However, the researchers are most excited about the prospect of their device being used in limb regeneration research: “We are going to collaborate with researchers from biology and tissue engineering to further explore [the hand's] potential to serve as a bio-fabricated device/scaffold in the emerging fields of neuroprosthetics and limb regeneration,” they write.

Zhu and Todorov will present their research paper, “Design of a Highly Biomimetic Anthropomorphic Robotic Hand Towards Artificial Limb Regeneration,” at ICRA in Stockholm, Sweden, in May.



Posted in 3D Printing Application



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