The harmonious robot

To describe the design methodology and human‐centre functionality of the whole arm manipulator (WAM) developed originally at MIT and brought to commercial fruition by Barrett Technology.

The WAM arm is driven by cable‐and‐cylinder transmissions, which uniquely exhibits zero backlash with low friction and low inertia, endowing the WAM with good open‐loop “backdrivability”. Two key benefits of the high backdrivability are: motion control through joint torque control, which enables the intrinsic sensing of forces over the whole arm and makes it inherently safe to humans; operation directly in the Cartesian domain without the need for inverse kinematics calculations, providing very rapid responsiveness as demonstrated in the “baseball robot” of Tokyo University. Another benefit of the WAM is its kinematic redundancy through the 4‐dof (degrees‐of‐freedom) main axes (7‐dof with the wrist). Recent major advances in the WAM include the “puck”, the world's smallest fully‐featured servo‐controller that eliminates the need for an external controller cabinet, and a safety circuit that limits, by a set amount, the power flow from the WAM to a person or object while not inhibiting the reverse from human to arm. The WAM's intrinsic force control has allowed the development of software‐defined haptic walls, which are being exploited by partners such as the CMU (Carnegie Mellon University) Robotics Institute, in patient rehabilitation, and Mako Surgical, for use in joint surgery.

The Barrett WAM's good open‐loop backdrivability has initiated the development of novel human‐centred robot applications that will expand the use of robots outside the factory and into human‐inhabited areas.

Presents the design methodology, features and applications of the Barrett WAM human‐centred robot.