Humanoid compliant whole arm dexterous manipulation: Control design and experiments

Whole arm manipulation (WAM) allows robotic manipulators to grasp or even manipulate bulky and heavy objects. The idea is that a robot basically wraps around a bulky object to grasp it. This furthermore allows to grasp relative heavy objects, since the center of gravity of the object is located more closely to the first joints of the robot. Whole arm manipulation significantly increases the manipulation skills of a robot and makes it more useful in human environment and was already applied to carry bulky and heavy objects [9], [10], or a human dummy [11]. In the past only few controllers dedicated for WAM were presented. In this paper we propose a new impedance controller on object level that considers the grasp of a bulky object with contacts on the (passive) robot chest and on each forearm of a two-armed robot system. This included to locate the object frame along with the passive contact frame, so that only object rotations need to be commanded. The controller was successfully implemented on DLR Justin. A gymnastic ball with a diameter of 0.45 m was securely grasped and the object was rotated in three dimensions.