Disney transmission allows lighter, smoother-moving robot limbs

Combining hydraulic and pneumatic mechanisms, the transmission is claimed to be much less bulky than a fully-hydraulic system, and enables movements so precise that a robot equipped with such arms could pick up an egg without breaking it or even, Disney claims, thread a needle. Such robots would be suitable for applications where they would need to interact closely with people, Disney claims.

The system was built by John Whitney, an assistant professor of mechanical engineering at Northeastern University in Boston, Massachusetts, while he was a research associate at Disney, working with a fellow research associate, Tianyo Chen of The Catholic University of America, who built the arms. In a conventional hydraulic transmission, a robot joint would have two liquid-filled hydraulic cylinders paired against each other, to push and pull the joint elements. But the new design pairs a liquid-filled cylinder against a pneumatic – that is, air-filled – cylinder instead. This cylinder acts as a constant-force air spring, pre-loading the joint and allowing it to move smoothly in both directions with half the number of bulky hydraulic lines than would otherwise be needed.

Reducing the hydraulics means that the robot limbs can be both smaller and lighter, Whitney explained. Lighter limbs are necessary for robots that interact with humans, as they have less momentum when they move and therefore if there is any accidental contact with a person, the impact force is less than that of a heavier arm. "This technology enabled us to build robot arms that are light, fast, and dexterous," Whitney said. "They have an incredible life-like nature, offering a combination of small mass, high speed, and precise motion not seen before."

The transmission system is almost frictionless and also has very little ‘play’, meaning that the limbs have no freedom to move without the transmission being engaged. "For now, the robot is remotely controlled by a human operator, but we would expect the same level of mechanical performance once the motions are automated,” said Jessica Hodgins, vice president at Disney Research and a professor of robotics at Carnegie Mellon, who co-authored a paper on the system that will be presented at the IEEE Conference on Robotics and Automation, in Stockholm next week.

The researchers incorporated the transmission into the arms of an upper-torso robot, equipped with stereo cameras mounted in its head - built by John Mars of Disney Research - that relayed images to an operator hidden behind a screen who was operating the arms of an identical control figure. The transmission allowed the contact forces ‘felt’ by the robot’s hands to be transmitted faithfully back to the operator.