Whole-Body MPC for a Dynamically Stable Mobile Manipulator

Autonomous mobile manipulation is the cutting edge of the modern robotic technology, which offers a dual advantage of mobility provided by a mobile platform and dexterity afforded by the manipulator. A common approach for controlling these systems is based on the task space control. In a nutshell, a task space controller defines a map from user-defined end-effector references to the actuation commands based on an optimization problem over the distance between the reference trajectories and the physically consistent motions. The optimization however ignores the effect of the current decision on the future error, which limits the applicability of the approach for dynamically stable platforms. On the contrary, the Model Predictive Control (MPC) approach offers the capability of foreseeing the future and making a trade-off in between the current and future tracking errors. Here, we transcribe the task at the end-effector space, which makes the task description more natural for the user. Furthermore, we show how the MPC-based controller skillfully incorporates the reference forces at the end-effector in the control problem. To this end, we showcase here the advantages of using this MPC approach for controlling a ball-balancing mobile manipulator, Rezero. We validate our controller on the hardware for tasks such as end-effector pose tracking and door opening.