Safety-guaranteed Virtual Decomposition-based Control of Robot Manipulators using Visual Feedback

This paper peruses the problem of controlling robotic manipulators by utilizing visual feedback signals while meeting safety requirements and ensuring closed-loop stability. Accordingly, the paper employs a hybrid observer to estimate an end-effector pose (position and orientation) that combines tip-frame acceleration and angular velocity measurements obtained from an inertial measurement unit with bearing measurements of known landmarks obtained from a stereo camera. The estimated pose is then utilized as a Cartesian feedback to close the control loop. A virtual decomposition control (VDC) method is introduced to control the manipulator, as it is well-suited for controlling complex robots like exoskeletons and humanoid robots. For the first time, by utilizing a quadratic program, control barrier functions are incorporated with VDC as a safety filter, enabling the robot manipulator to avoid potential collisions involving both humans and external obstacles and to handle joint limits. By means of the Lyapunov stability theorem, the combined observer-controller scheme is guaranteed to be asymptotically stable. To demonstrate the effectiveness of the proposed vision-based control structure, a simulation study is performed on a 6-degrees-of-freedom (DoF) long-reach manipulator.