Set-Based Control for Autonomous Spray Painting

Abstract

In this paper, a method is presented for lowering the energy consumption and/or increasing the speed of a standard manipulator spray painting a surface. The approach is based on the observation that a small angle between the spray direction and the surface normal does not affect the quality of the paint job. Recent results in set-based kinematic control are utilized to develop a switched control system, where this angle is defined as a set-based task with a maximum allowed limit. Four different set-based methods are implemented and tested on a UR5 manipulator from Universal Robots. Experimental results verify the correctness of the method, and demonstrate that the set-based approaches can substantially lower the paint time and energy consumption compared to the current standard solution. Note to Practitioners —This paper is motivated by the observation that uniform paint coating can be achieved even when the spray direction is not normal to the spray surface. By allowing a small orientation error, the manipulator maintains a constant spray velocity along the surface while following a more energy efficient trajectory at the end-effector. By doing so, this velocity can also be increased as the proposed method requires less torque during the turns than the current industry standard. The method proposed in this paper is based on a kinematic control method and generates reference trajectories for the manipulator configuration and velocity every time step which are inputs to the manipulator dynamic controller. If tracked, the references will allow the paint gun to follow the trajectory, including both straight line segments and turns, with constant velocity and thus achieve uniform paint coating. We show how to calculate the reference state of the manipulator and present the explicit expressions for solving and implementing the algorithms. The approach can also be used for other applications where an offset in the end-effector orientation improves performance, such as welding and 3-D printing.