Despite large forces sustained in short bursts animals are able to dynamically run, jump, and land. Traditional robots with geared motors have difficulty sustaining these large, instantaneous forces over short periods of time. And, although researchers have tried to create bio-inspired robots with pneumatic or wire-driven actuators, few possess a biologically correct musculoskeletal structure. In order to study the natural capabilities of invertebrate animals, researchers at Tokyo University’s ISI Lab (Ryuma Niiyama, Satoshi Nishikawa, and Yasuo Kuniyoshi) attempted to build a more accurate model with the Athlete Robot. They recently presented their work at the 2010 International Conference on Humanoid Robots in Nashville.
Unlike conventional systems that use on/off valves, this one uses proportional valves that can transform an electrical signal into a corresponding air flow. The McKibben artificial muscles have an extremely high power-to-weight ratio and are configured to match the human anatomy, including range of motion. For example, it is capable of jumping 50cm (20″) into the air, which is remarkable for a robot of its size. Even when standing still it is more wobbly than its rigid cousins, but the sway is similar to that observed in humans. And, thanks to its elastic properties (power and compressed air is supplied externally), the robot can land softly from a 1 meter (3’3″) drop – a big problem for conventional geared robots. The researchers found that they could also control the falling direction after ground impact by changing the stiffness of the joints. All told the robot weighs only about 10kg (22 lbs) for all its 125cm (4’1″).
Earlier versions of the robot included pneumatic actuators for the lower leg, but they have opted for prosthetic blades similar to those worn by double amputees in the latest version. It has PID controllers at each joint, touch sensors in its feet, and an IMU on its torso for detecting the robot’s orientation. Currently it can only run for 3 to 5 steps (at 1.2 meters per second) before falling down, but the researchers are hopeful about improving its capabilities.
Could Athlete Robot become Japan’s version of Boston Dynamics’ PETMAN? Only time will tell, but this line of research looks very promising.
Images from “Design Principle Based on Maximum Output Force Profile for a Musculoskeletal Robot” (Ryuma Niiyama, Yasuo Kuniyoshi)