Coordinated Control of Hydraulic Mobile Manipulators

In this paper, we propose a solution to the problem of path following for a hydraulic mobile manipulator. First, we provide a solution to the trajectory generation for each joint given desired path of the work tool. The solution is based on forward kinematics and stability theory of dynamics systems. Avoiding inverse kinematics reduces computational effort and complexity. We then introduce a feedback control strategy that makes the work tool follow the desired trajectory. The solution is so called time-coordinated path following (TC-PF). Firstly, the solution relies on path-following instead of trajectory tracking, thus avoiding performance limitations inherited by trajectory tracking. Secondly, a coordination algorithm is added to the feedback system that synchronizes all joints guaranteeing that the work tool stay in the neighborhood of the desired path even if a joint fails to follow its trajectory. In other words, if one of joints exhibits slow dynamics, all other joins will slow down in such a way to keep the work tool on the path. Similar idea can be extended to operation of multiple mobile manipulators in close vicinity.