Exoskeletons show promise as an assistive device for those who face a temporary or permanent disability. Unfortunately, their utility is limited due to their bulkiness, which makes them cumbersome to wear. A team at Carnegie Mellon University may have a solution to this weighty problem — an exoskeleton that is lightweight, low power, and highly mobile.
The research into a cutting-edge exoskeleton was spearheaded by Steve Collins, associate professor of biomechanical engineering at Carnegie Mellon, and Stuart Diller from Carnegie Mellon’s department of mechanical engineering. The pair created a lightweight component called an electro-adhesive clutch mechanism that forms part of an exoskeleton and weighs only 26 grams.
As its name implies, the electro-adhesive clutch is comprised of several thin electrode sheets that are coated with a dielectric material and held together by electrostatic adhesion. Each flat layer has a spring that allows it to stretch in response to the movement of a joint. These clutches can be aligned to other clutches in a parallel arrangement to form a strip that functions almost like a tendon. By varying the number of springed clutches, researchers can fine-tune the stiffness of the mechanical joint.
Not only is the clutch material lightweight and adjustable, it is also energy efficient. The research team tested the mechanism on an ankle exoskeleton and found that the clutched springs only engaged when the foot touched the ground. This “engage-on-demand” method of operation produced additional torque density and consumed less power than similar electrically controlled clutches. And at three times the torque density and half the power, these differences were certainly significant.
The researchers believe this breakthrough will kick off the development of future lightweight exoskeleton materials. They hope to use their low-power clutches in tandem as they develop new actuator designs for exoskeletons. They also anticipate a customizable option that allows researchers and physicians to develop exoskeletons that can be adjusted remotely. This feature would enable the manipulation of the stiffness of a joint using controls built into the system and made accessible online.
