The rehabilitation robotic system FRIEND, which has been developed at the Institute of Automation, University of Bremen, since 1997, belongs to the category ‘intelligent’ wheelchairs with mounted manipulator. The system consists of an electric wheelchair (SPRINT, Meyra, Germany) and a 6 DOF robot arm (MANUS, Exact Dynamics, Netherlands). The arm is connected to a multiprocessor PC, mounted on the backside of the wheelchair and connected via a CAN bus interface. As user interface an off the shelf speech recognition system is used.
An ‘intelligent’ tray is mounted at the front side of the wheelchair. Within this context ‘intelligent’ expresses its ability to measure the weights of objects placed upon the tray and calculate their placements relative to a fixed tray coordinate system. For object detection and autonomous arm control the system is equipped with a moveable stereo-camera system and a gripper mounted camera.
The software integration and administration of the robot arm, the user interface and the sensors is realized by an agent-oriented multilayer control architecture. On the lowest level, the control architecture consists of software servers that encapsulate the hardware of sensors (e.g. cameras) and actuators (e.g. robot arm). These entities offer their services via clients to the upper levels. In case that an autonomous operation has to be activated, e.g. a visually guided object grasping task, a sequencer which is placed in an medium level of the software creates dynamically closed loop control processes for sub-task execution by connecting the required clients. This functionality is a mandatory pre-requisite for autonomous task execution.