portfolio: DARPA Revolutionizing Prosthetics 2009 - 15 dof hand power plant

project summary

client: New World Associates/John Hopkins Applied Physics Laboratory (DARPA's Revolutionizing Prosthetics Program)

faced with the task of duplicating the functionality of the human hand and wrist with an electro-mechanical powerplant, Kinea Design focused on ways to provide optimal power and energy efficiency, as well as minimize the weight and volume of the powerplant, all without compromising aggressive speed and torque requirements or reducing the sheer quantity of degrees of actuation. Kinea invented a novel cobotic powerplant to be located in the forearm region, weighing less than two pounds, which couples artificial tendons actuating 15 hand joints to a single electro-magnetic motor via infinitely-variable rolling-contact transmissions. The 15 infinitely-variable transmissions draw power as needed for their respective hand joint from a common shaft driven by a single motor. This architecture proved more lightweight and more power and energy efficient than using 15 motors paired to 15 fixed-ratio drivetrains.

in just the 6 weeks after settling on the use of infinitely-variable transmissions, Kinea designed, built and operated an experience-prototype powerplant that could actuate 3 hand joints, and serve as a testbed for evaluating sensing and actuation requirements. The critical infinitely-variable transmission components were near the target size, but all other design constraints where relaxed. Data from the experience-prototype proved valuable in guiding the remaining design process, and justifying the infinitely-variable transmission approach.

in the ensuing design process, Kinea addressed the weight and volume constraints of prosthetics by rewinding and repackaging motors, developing custom drivetrains, devising custom sensors and performing FEA on load bearing components. The level of component integration for prosthetics prohibits the use of off-the-shelf solutions for actuation, drivetrains and even sensing. If utilized, the housings of such components must be removed and replaced by other structures within the prosthetic mechanism, redundant sets of rolling-element bearings eliminated, and factor-of-safety more closely analyzed. The requirements that activities of daily living of the prosthesis placed on the duty-cycle of hundreds of bearings and gears was carefully analyzed and used in the design process to ensure reliability. The short-term duty cycle was also considered, and motors were selected knowing they would be operated intermittently well beyond their continuous rated thermal limits.

where no off-the-shelf solution existed, Kinea designed and manufactured bearings and gears for the drivetrain connecting each infinitely-variable transmission to an artificial tendon actuating the hand joint. Repeating this success, Kinea developed another drivetrain allowing a 0.2 Watt motor to shift the ratio of each of the infinitely-variable transmissions. In both cases, the gear reducers where a non-conventional type that obtains large reductions in a single step at the expense of careful mechanical design and introduction of custom bearings to handle large stresses in the limited space. The small scale of these components required tolerances on the order of +/-5 microns (+/- 0.0002 inch).

kinea Design integrated sensing into the design, developing sensors for the control of the electro-mechanical powerplant that fit in the space dictated by the drivetrain geometry. Off-the-shelf ICs were packaged on custom circuit-boards to form the sensor element, and custom target scales were integrated into the moving components.

throughout the project, Kinea collaborated with several partners of the Revolutionizing Prosthetics 2009 team, supporting the development of interface requirements to assure a smooth integration process, and iterating on design of the interfaces. The electro-mechanical powerplant and forearm structure that Kinea delivered was successfully interfaced with a hand and wrist, elbow, and control electronics all developed at separate institutions. Kinea staff supported this integration after delivery, and developed the control algorithms and software for the electro-mechanical powerplant.

gallery

press:

• for press clippings about this project, click here.

videos:

• for a video demo of the Proto2 hand, click here.
• for a video of an initial prototype of the cobotic transmission, click here.
• Popular Mechanics 2007 Award.

pictures:

kinea Design is proud to participate with other international technology leaders, including Otto Bock Healthcare Products, New World Associates, and the Biomechatronics Development Laboratory of the Rehabilitation Institute of Chicago, and Van Doren Designs, on the ground-breaking Revolutionizing Prosthetics Program 2009 under the direction of The Johns Hopkins University Applied Physics Laboratory (JHU/APL).

The Revolutionizing Prosthetics 2009 is funded by the Defense Advanced Research Projects Agency (DARPA).