Experimental two-arm system (2006)
Humanoid two-arm system for the experimental investigation of two-handed manipulation
The development of humanoid robots has made significant progress in the passed years. Impressive walking robot systems were developed. However, the capabilities of these robots to manipulate objects or interact with the scene are in general quite limited.
The objective of the development was to build a manlike upper body with two arms and two hands. The system will be used to test programming and control concepts for two-handed manipulation.
Development from modular DLR light weight robots and hands
The system design uses prior work of the institute, namely the DLR light weight robot (LWR) and the DLR hand. The newly developed torso is based on LWR technology. Like humans, who enlarge their workspace by using coordinated arm and leg movements, the torso expands the grasp-space of the robot hands which results from arm movements.
The modular design of the LWR enables the configuration of a human-like left and right arm.
Modular control architecture
From a control point of view, two-handed manipulation can be dealt with in a number of ways. When grasping a big crate, for example, one arm can act as master while the other merely follows the movement. An intuitive approach implemented at the DLR describes the movement of the crate. The arms are connected to the crate using virtual springs.
To be able to test different approaches despite the high complexity of the complete system in a simple and yet flexible manner, a new software architecture, the aRD-concept ("agile Robot Development"), was developed at the institute. Using this concept, the classical, predominately monolithic control structure is dissolved into a fine-grained net of communicating modules. The individual modules can be run distributed on multiple processors. Even the execution across computer borders under strict real-time conditions is possible.
The implementation consists of a collection of libraries which was kept very small and some configuration tools. It allows to easily integrate a variety of standard tools such as Matlab / Simulink for controller design.
Structure of the complete system
The complete system is made up of two arms with 7 degrees of freedom (DOF) each, two hands with 12+1 DOF each, a PanTilt unit for the head with 2 DOF and a torso with 3 DOF as well as one passively coupled link. Thus the system has a total of 43 controllable degrees of freedom.
In addition to the torque sensors in each controllable link, 6 DOF torque sensors were integrated in the wrists and fingertips.
Perception with 3D-sensor technology
Apart from the tactile perception, the visual perception plays an important role in manipulation tasks. Ideally, it is possible to estimate the position of an arbitrary object or even to reconstruct its 3D geometry. For this purpose, the DLR multi-sensory 3D modeler (3DMo) is integrated into the system.