Configuration Control of a Mobile Dexterous Robot: Real-Time Implementation and Experimentation

This article describes the design and implementation of a real- time control system with multiple modes of operation for a mobile, dexterous manipulator. The manipulator under study is a kinematically redundant seven-degree-of-freedom arm from Robotics Research Corporation, mounted on a one-degree-of- freedom motorized platform. The manipulator-plus-platform system has two degrees-of-redundancy for the basic task of end-effector placement and orientation. The redundancy reso lution is achieved by accomplishing two additional tasks using the configuration-control technique. The system allows a choice of arm-angle control or collision avoidance for the seventh task, and elbow-angle control or platform placement for the eighth task. In addition, joint-limit avoidance tasks are auto matically invoked when any of the manipulator joints approach their limits. The system is robust to singularities, and the user is capable of assigning weighting factors to end-effector mo tion, joint-limit avoidance, and redundancy resolution tasks. The motion-control algorithms are executed at 1.1 ms on two MC68040 processors in a VME-bus environment running the VxWorks real-time operating system. The article describes the hardware and software components of the manipulator- control system. Experimental results on real-time control of the Robotics Research arm are also presented.