According to Chris Jones, Director for Research Advancement and Senior Principal Investigator at iRobot, the inflatable design offers several unique advantages including a decrease in weight (important for easy mobility), an increase in compactness (key to maneuverability), a higher strength-to-weight ratio, increased flexibility and suppleness, and cheaper materials.
The robot is inflated and deflated with an on-board pump, and is able to move its joints without embedded motors or an internal skeleton.
Essentially, there are air-tight plastic bags inside a skin made of a non-elastic constraining fabric. Air is pumped into the bags which gives the arm volume and shape. Then as the bags reach the fabric skin, they can’t expand any more, and that’s what gives the arm rigidity. Movement and manipulation are controlled by a series of actuators and cables that run through the inside and act as tendons. Servos at the arm’s joints take slack in and out of the cables, which create motion, or “tendon actuated articulation.”
By increasing the arm’s internal pressure, engineers can give it the strength to lift heavier objects.
The arm weighs a half-pound (regular PackBot arms are between 15 and 20 pounds), but can lift up to two or three pounds at present—as mentioned, that’s a much higher “strength-to-weight” ratio than you see with the average robot.
DARPA is awarding another $625,000 contract to iRobot to continue advancing the AIR for future military use. Other concepts include an arm that might not be tendon actuated, but that might move by inflating and deflating different compartments in the arm, sort of like opposing muscles in a human arm The AIR pictured is an early prototype, but as more advanced variations are developed over time, one can expect the issue of affordability to remain a focus.