The WAM Arm
The hardware platform for our research is a WAM (Whole Arm Manipulation)
robot shown in the figure. It has been developed by
It is a light weight, high speed 7DOF manipulator about the size of a
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
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
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.
Feedback & Queries: Jochen Heinzmann
Date Last Modified: Thursday, 24th Oct 1997