Dean Kamen’s project to design and build the most advanced arm prosthesis, now called the Luke Arm, has wrapped up its mandate, and DARPA, the sponsor of the project, will be deciding whether to continue funding the arm and apply for clinical trials.
In order to make a better arm, Kamen first had to figure out what was wrong with the old one. Part of the reason the technology was still in “the Flintstones” was a lack of agility: a human arm has 22 degrees of freedom, not three. The Luke Arm prosthetic is agile because of the fine motor control imparted by the enormous amount of circuitry inside the arm, which enables 18 degrees of freedom. The engineers fought for space inside the arm and created workarounds when they couldn’t have the space they needed, such as using rigid-to-flex circuit boards folded into origami-like shapes inside the tiny spaces, which are connected by a dense thicket of wiring.
The arm has motor control fine enough for test subjects to pluck chocolate-covered coffee beans one by one, pick up a power drill, unlock a door, and shake a hand. Six preconfigured grip settings make this possible, with names like chuck grip, key grip, and power grip. The different grips are shortcuts for the main operations humans perform daily.
The Luke arm also had to be modular, usable by anyone with any level of amputation. The arm works as though it had a very complicated set of vacuum cleaner attachments; the hand contains separate electronics, as does the forearm. The elbow is powered, and the electronics that power it are contained in the upper arm. The shoulder is also powered and can accomplish the never-before-seen feat of reaching up as if to pick an apple off a tree.
It must be less than what a native limb would have weighed, because in an amputee the human skeletal system can no longer be used as a method of attachment. Instead, for amputations above the elbow, a user is strapped into a kind of harness. Deka engineers modeled the arm based on the weight of a statistically average female arm (about 3.6 kg), including all the electronics and the lithium battery. Amazingly, titanium, the legendarily light material, is too heavy to keep the arm under its weight limit—it can’t be made thin enough without bending—so the arm is mostly aluminum.
More at IEEE Spectrum Online…
Flashbacks: Dean Kamen’s DARPA Arm in the Lab, Dean Kamen and His Arm, Dean Kamen’s Robotic Arm Part Deuce, Cyborg Arm: DARPA Recruits Dean Kaman, Dean Kamen Talks Medgadgets
(hat tip: Engadget)