Prosthetic hands typically come in three varieties: purely cosmetic models; hooks and other low-cost mechanical appendages that provide a limited range of motion; and electronic versions that better mimic natural hand movements yet can cost tens of thousands of dollars. Mark Stark’s prosthetic incorporates the best elements of each. Although its minimalist plastic assembly is nearly as light and inexpensive as a common steel hook, it looks and moves like a high-end electronic hand.
Stark, who makes his living designing valves for dryers and other appliances, got into prosthetics in part to help his friend, Dave Vogt, who was born without a left hand. Stark’s creation is electronics-free, but its fingers each have three knuckles (two on the thumb) that bend separately to conform to anything the wearer grasps, including irregularly shaped objects that a hook can’t hold.
Hooks attach to a socket at the end of an amputee’s arm and are operated by a cable that runs up to a shoulder harness. When the wearer shrugs his shoulders, the cable pulls the hook open; when he relaxes, the cable slackens and the hook closes. The Stark Hand screws into the same socket-and-cable system but adds a lever on the palm that connects to five more cables, each running up the back of a finger. A shoulder movement triggers the lever to tug all five fingers open at once, and the individual cables let each finger rebound on its own. Springs in each joint contract until each finger comes to rest on an object, so some fingertips can curl around, say, a wineglass stem while others grasp the cup. The springs exert a level of pressure gentle enough to hold an egg but strong enough that you can lift a chair.
Vogt now wears the hand everywhere except to his job as a machinist, where he has to do heavy lifting for which a hook still works better. A more durable production version, which will use tougher plastics and sleeker parts, could be on the way as early as this winter. Edison Nation, a company that helps inventors develop their ideas, recently selected Stark’s hand for commercial development and is now in talks to license it to a major prosthetics manufacturer.
Name: The Stark Hand
Inventor: Mark Stark
Time: 7 years
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.