Semi-autonomous surface-tracking tasks using omnidirectional mobile manipulators

Despite the potential of mobile manipulators and applications where robots require a force-controlled physical interaction with the environment, the majority of robot automation nowadays is still based on fixed manipulators for free-motion tasks (e.g. welding, pick and place, or painting). In this work, we propose a control solution for omnidirectional mobile manipulators in force-tracking tasks, interacting with unknown surface geometries and with a human teleoperator in the control loop. Keeping a teleoperator in the loop makes the system widely applicable to unstructured environments. With little effort, a human can take care of the mobile base navigation, self-collisions, and collisions with the environment, as well as selecting the area of the asset surface to process. The teleoperator interfaces with the robot platform by commanding motion in the mobile base to increase the arm’s workspace and manoeuvrability. The operator can also command the movement of the end-effector, sliding on the surface geometry to process a specific area. Alternatively, he can let the controller execute a parametric trajectory (spiral or raster) for an autonomous area coverage and meanwhile telecommand the base in order to keep the arm in configurations with good dexterity. The autonomous controller, on the other hand, takes responsibility for following the unknown contour on the manipulated surface by only taking observations from a force/torque sensor attached to the arm’s wrist, exerting a prescribed force, and handling the motion control in the base and the arm so that both can follow their respective task requests. Overall, we have developed a user-friendly control scheme, where an operator with little training and using a joystick, can guide the robot system to perform a physically interactive task on the surface of an asset.

I. INTRODUCTION

Mobile manipulators have the capability to provide flexibility in the manufacturing process and task automation, yet they are not in widespread use, with most applications focusing on simplistic pick-and-place tasks [1]. Controlling the interaction forces between the robot arm and the environment opens new potential applications for mobile robot automation such as polishing, grinding, sanding, or Non-Destructive Evaluation (NDE). In applications such as sanding or polishing, by partially automating these tasks, the human operator would benefit from preventing health issues associated with holding vibrational tools regularly, inhaling dust particles generated in the process, or non-ergonomic postures.