Dr. Pratt recalled an incident when the researchers first realized that series elastic actuation was the key to freeing robots from their cages. While working on an early humanoid robot named COG, in a project led by Rodney Brooks, the founder of Rethink Robotics who was then director of the M.I.T. artificial intelligence lab, they were demonstrating how the robot could do tasks like writing with a pencil and paper. However, there was a bug in the software, causing the robot’s arm to repeatedly bang the table.
Dr. Brooks decided it was an opportunity to demonstrate the safety of the technology. He placed himself between the table and the arm, which began spanking him.
Roboticists describe this original approach as “passive compliance.” Today there are other approaches — “active compliance” — that use software and sensors to blend speed and precision of more rigid robots with operations that are safe around humans.