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When Easton LaChappelle of Unlimited Tomorrow started working to build his first prosthetic hand, he was still in his teens. Six years later, he has gone from early prototypes to a refined product. LaChappelle’s goal now is to develop working robotic prosthetics that can be manufactured in such a way as to lower costs dramatically. Having the right motion components is, of course, key to his design.
Amputees and those born without a limb have lacked robotic prosthetic options that are reasonably priced and offer long-term dependable use. People missing limbs are often stigmatized for their differences, and children are confronted with the inability to do what other children can do, and they may be ridiculed by their peers — sometimes with devastating results.
Typical prosthetic devices for children and adults can run between $30,000 and $100,000, said Rhinebeck, N.Y.-based Unlimited Tomorrow. Because children are also growing, this pricing is totally out of reach for many families.
Unlimited Tomorrow address need for accessibility
In comparison, Unlimited Tomorrow plans to launch its advanced prosthetic hand later this year for about $10,000. The company’s goal is to make their technology affordable and accessible and it has introduced groundbreaking emerging technologies to do so.
For example, the company makes its robotic hands and arm prostheses with a 3D Printing process called MultiJet Fusion (MJF) that is able to match skin tone as well as include any personal variations in coloring that may exist, such as freckles or birthmarks.
The fingernails are magnetic and can be painted or decorated in a number of ways as well. This is especially important for children who are concerned about looking like and being able to live like their friends and siblings.
Scans of an opposing limb, along with other measurements, are taken to generate the socket and device unique to the person — providing a perfect fit for its user without extensive trial and error.
Not only does Unlimited Tomorrow focus on aesthetics; it also take suggestions from users to refine the function of prosthetics. For example, it might place motors in the palm rather than the arm to provide better wrist movement. This also helps with user acceptance.
Since each of the company’s devices is made from a high-resolution digital scan, it typically fits better than standard prosthetics. The best thing about these robotic prosthetics isn’t their color, their operation, or their long life, but the smiles on the children and young people using them.
Scaling for functionality
Functionality and usefulness are critical for a robotic prosthetic to meet the challenges of everyday living. LaChappelle started out with large-scale technologies to work out the kinks in his designs and to prove his theories years before coming up with what he’s producing now.
If you can imagine suddenly not having the ability to use one of your hands, you can also imagine what an amputee or someone born without a limb must go through day after day. And once the prosthetic is integrated into a person’s life, a breakdown can become an enormous irritation. This meant that long-life and dependability was essential.
The company struggled with durability with its early designs. The motors and gearboxes it chose worked well enough, but because of the stress of everyday use — especially considering the dynamic actions of children — the components would often break down after a few months’ operation.
“We needed to find a motor and gearhead that was not only accurate and repeatable, but much more reliable than what we were using at the time,” said LaChappelle,
Finding precision motion control
After researching the possibilities, Unlimited Tomorrow decided to incorporate two motors designed and manufactured by Taunton, Mass.-based maxon. “Not only did we get a higher quality motor; we also got considerable increases in speed and torque in the same size package,” LaChappelle said.
Because the maxon motors are small, they fit easily inside a child’s robotic hand, which was the test of footprint that mattered. “This also allowed us to use the same motors in the child’s prosthetic as we do in adult prosthetics, reducing the number of components we need to have on hand,” added LaChappelle.
These motors are housed in the palm of the robotic hand along with all the electronics. The motors, with their greater power density and higher speeds and torques, use special haptic sensors as feedback so that the robotic hand’s grip can be precisely controlled.
The maxon products used for the robotic hands are the company’s DCX 12S series of motors and the GPX 12HP series of gearheads. The brushed DC motors operate from battery power for multiple days — batteries recharge using a wireless charging device.
The motors can operate at speeds of over 9,000 rpm on voltages from 3V to 12V to provide a 1.6W output. Maximum continuous torque outputs are around 1.9 mNm.
The motors are designed using precious metals and ball bearings for smooth operation. The GPX 12HP is a planetary gearhead offering quiet operation in a wide variety of reduction ratios depending on the nature of the application.
Precise control of the motion system is done through unique muscle sensors that the company has developed. Muscle data is processed using AI algorithms to decode the user’s intent and then translate this data into hand motions. Haptic feedback is incorporated into the device to allow a sense of touch to be perceived, creating a human-like feedback loop.