The hardware platform for our research is a WAM (Whole Arm Manipulation) robot shown in the figure. It has been developed by Barrett Technology. It is a light weight, high speed 7DOF manipulator about the size of a human arm. It is controlled by applying torques to the servo motors in the joints. One important aspect of the design is that all joints are backdrivable thus allowing the user to move the arm by contact with any part of the arm. The backdrivability of the WAM is generated by using special cable transmissions, reducers and differentials. Robots using wrist sensors can not sense any force applied anywhere at the arm beside the hand since non-backdrivable worm gears are used. Particularly during motion all joint torques and resulting forces at links and the hand have to be controlled and monitored tightly if a human is within reach of the manipulator. By not only applying but also measuring the torques in all joints the distinction between actuator and sensor is vanishing.


The WAM robot arm and the Barrett Hand (courtesy of Barrett Technology)

The hand is a dextrous 3-finger 4DOF gripper designed for usage with the WAM arm. The two outer fingers can be rotated around the palm of the hand, so different gripping configurations can be used for different shaped objects. Each finger has 2 joints with clutches applying a programmed gripping force to the object when closing the fingers. A large variety of objects can be grasped without the need for sophisticated grasping algorithms. The hand is almost as simple to program as a simple two finger gripper but provides the gripping performance of an articulated three finger hand.