Control allocation for mobile manipulators with on-board cameras

This paper presents a new set of approaches for teleoperation of mobile manipulators with on-board cameras. Mobile manipulators consist of a robotic arm which provides for interaction and manipulation, and a mobile base which extends the workspace of the arm. While the position of the onboard camera is determined by the base motion, the principal control objective is the motion of the manipulator arm. This calls for intelligent control allocation between the base and the manipulator arm in order to obtain intuitive control of both the camera and the arm. We implement virtual mass-spring-damper forces between the end-effector and the camera so that the camera follows the end-effector with an overdamped characteristics. The operator therefore only needs to control the end-effector motion, while the vehicle with the camera will follow naturally. The operator is thus able to control the more than six degrees of freedom of the vehicle and manipulator through a standard haptic device. The control allocation problem, i.e., whether the vehicle or manipulator arm actuation is applied, is then performed automatically so that the operator can concentrate on the manipulator motion.