The harmonious robot

Abstract

Purpose -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. Design/methodology/approach -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. Findings -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. Originality/value -Presents the design methodology, features and applications of the Barrett WAM human-centred robot.Keywords Robotics, Man machine interface Paper type Technical paperThe world's first industrial robot, the hydraulically powered Unimate developed in the late-1950s, was designed as a replacement for human workers operating in monotonous, hazardous or unpleasant environments. It was large, powerful and dangerous such that it had to be ring fenced to protect humans. While this was not a problem in the industrial factory it excluded its use in less structured, particularly humanpopulated environments. It meant that robots did not find their way into the office, the hotel, the home or the hospital. For that to happen, a completely new concept of robot was needed that would work safely and in harmony with humans.This was the scenario some 20 years ago when researchers at MIT examined the fundamentals of robot technology to produce a design methodology for robots that were intrinsically safe. The aim was a human-centred robot that would more safely interact with people and its environment. The outcome of this project was the whole arm manipulator (WAM), which has been further developed and brought to commercial fruition by Barrett Technology, based in Cambridge, Massachusetts and marketed unde...

A low-cost compliant 7-DOF robotic manipulator

“…The Barrett WAM [2], [3] is a cable-driven robot known for its high backdrivability and smooth, fast operation. It has high speed (3 m/s) operation and 2 mm repeatability.…”

Discrete-time redundancy resolution at the velocity level with acceleration/torque optimization properties

“…On the other hand, the latest generation of research-oriented manipulators allows a torque-controlled behavior [7][8][9]. In order to take full advantage of this possibility, a dynamic model of the robot is needed, possibly including also joint/transmission compliance [10].…”

Building safer robots: Safety driven control

“…Although a robot was not used to perform tasks in these environments, we did consider the dimensions and capabilities of the Care-O-bot 3 mobile robot [40]. This robot was chosen over others such as the WillowGarage PR2 [41], as it is narrower and its manipulator can be stowed away, allowing it to navigate more cluttered environments with less structuring required. An example robot was beneficial, as it helped us understand how a robot would operate within space limitations and in the presence of typical hazards.…”