Sep 5, 2016 | By Benedict

The Technology Office Innovation Laboratory (TOIL) at MIT’s Lincoln Laboratory is improving 3D printed hand technology by studying finger motion mechanics, adding non-electronic temperature and tactile feedback, and incorporating motors. The research will be used by e-NABLE and similar groups.

The e-NABLE Flexy 3D printed hand

International 3D printed hand community e-NABLE has grown rapidly over the last few years. The organization, created in 2011 by husband-and-wife team Ivan and Jen Owen, is now something of a global 3D printing phenomenon after scores of its volunteers successfully lent “a helping hand” to limb-different children around the world by printing cheap, functional robotic hands. To date, the entire project has mostly focused around a handful of core designs which can be printed and assembled for around $50, though many volunteers have adapted the design for specific recipients and purposes. Now, in a bid to increase the quality of affordable, mass-producible prostheses, a group of experts at TOIL, part of MIT’s Lincoln Laboratory, is looking to get behind the project by developing new technologies before passing on its findings to e-NABLE and other nonprofit groups.

Although the process of building a 3D printed hand is relatively simple—hence the huge number of volunteers carrying out such work for e-NABLE and similar organizations like the Wounded Warrior Project—the process of designing a functional 3D printed hand can be much more difficult. David Scott, manager of TOIL, is therefore leading a group of researchers (Naomi Hachen, Luke Johnson, Keri Mroszczyk, and Samuel VanNoy) on a mission to improve the popular free-to-download hand designs currently available on the internet.

TOIL researcher Naomi Hachen

To get acquainted with the 3D printed prostheses available through e-NABLE, the team downloaded, printed, and assembled a number of models. Most were 3D printed in PLA, as recommended, before being assembled. For most models, the assembly process involved connecting fingers to a tensioner block, which is positioned on the back of the wrist via strings woven through holes in the plastic and tied to individual pins. The tensioner block anchors the elastic strings, which a user can stretch by bending their wrist, a movement which creates tension and causes the fingers to “grip.”

The TOIL team found that current 3D printed hand designs have certain limitations. Obstructing one finger, for example, causes all fingers to become immobile, which limits grip. Lack of proper grip can, for many reasons, be problematic, so the researchers looked to come up with new designs in which each finger would act independently, contributing to improved grip and flexibility. Their solution? A “whippletree,” a clever structure consisting of a central joint connected to several linkages. When one link of the whippletree is obstructed, the central joint pivots to distribute force evenly through each linkage. One e-NABLE design actually implemented a whippletree, but without connecting the thumb. TOIL went a step further, creating a five-finger whippletree that enables each digit to move independently, letting users firmly grip objects of virtually any shape.

TOIL's whippletree

Scott and his team have also found other ways to improve common 3D printed hand designs. For example, they have been able to add passive temperature feedback to the design by adding a color-changing, heat-reactive filament to the plastic. The thermochromic material changes color immediately when heat is applied to its surface, letting users “feel” the heat of their surroundings more fully. “It's important for users to know whether or not a surface is hot,” said VanNoy. “If the users detect heat, they can potentially prevent personal injury and hand damage, such as melting.”

Although not yet dully developed, the TOIL team is also creating a tactile feedback component that could allow users to feel pressure. The clever component uses flexible tubing running from the fingertip to the forearm, with small sets of pockets at each end and resting on the user’s arm. The tubes will be filled with an as-yet-undecided fluid, which will be squeezed from the 3D printed fingertips to the skin of the user’s arm when pressure is applied. The degree of fluid pressure on the arm will let the user know how hard they are squeezing.

While Hachen, Mroszczyk, and VanNoy have spent most of their time looking to optimize e-NABLE 3D printed hands, Johnson has also spent some time creating more robust designs which use motorized parts. These prostheses, which can be scaled for those without a wrist to those without an entire arm, are being built especially for members of the Wounded Warrior Project, a nonprofit for war veterans. Using 3D printed gears, motors, and an Arduino, Johnson was able to create a 3D printed arm which can be controlled via attached muscle sensors.

Luke Johnson's motorized 3D printed arm with e-NABLE Flexy hand

On Johnson’s 3D printed arm, which costs around $350 to build and is compatible with an e-NABLE hand, each muscle sensor is connected to an individual input pin on the Arduino, which then signals the motor on the arm to act accordingly. “Different sensors can be programmed to different muscles,” Johnson said. “For example, if the user flexes her chest muscle, that movement could signal the motor to bend the elbow. If the user flexes her back, the hand could form a grip.” The motors used in the arm can lift 25 pounds, but the team is currently testing the weight-lifting capabilities of the 3D printed plastic parts.

The TOIL team will continue with its research over the next few months, after which it will send its finished designs to e-NABLE and the Wounded Warriors Project. “When I saw the existing e-NABLE hands, I knew that they could be better,” Johnson said. “Since starting this project, I have gained an array of knowledge from circuitry to engineering. But the most important part of this project is helping people. That knowledge is heartwarming.”

 

 

Posted in 3D Printing Application

 

 

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