A robot trajectory sample algorithm for optimizing thermal spraying torch velocity on the complex surface

During the process of thermal spray applications, the spray torch is usually driven by the robot, and its movements are in turns controlled by robot trajectories. The increasing requirements of coating productivity lead to the objectivity of generating robot trajectories on the complex surface. However, when the spray torch moves in a constant given torch velocity, the large curvature change of the coating surface will cause the sudden transition of one or several robot axes and thus lead to the undulation of torch velocity. This study aims at introducing a new trajectory point sample algorithm for optimizing the robot trajectory, and thus leads to desired torch velocity. Thermal distribution analysis of the thermal spray process is carried out to check the reliability of the optimization algorithm and the optimized robot trajectory.

I. Introduction

During thermal spray process, coating materials (e.g. metals, alloys, and ceramics) are fed in spray torch and heated to a molten or semi-molten state and then accelerated towards the substrate to form a coat. Traditionally, two robot trajectory generation methods are applied to control the spray torch movements: on-line method is suitable for rapidly generating trajectories on the simple shaped coating surface (e.g. planar), but for complex free-form surface which requires hundred even thousand trajectory points, the on-line method seems to be time-consuming and hard to guarantee the trajectory accuracy. Off-line method refers to the possibility to transfer the well-designed robot trajectory through simulation software to the real robot cell. Such simulation software (e.g. RobotStudio™ in this case) is usually equipped with robot library and robot accessories which can be used to build up the simulation model same as the real robot cell components. It provides a virtual workstation for users to integrate the robot defined parameters (e.g. scanning step, spray distance, torch velocity) into robot trajectory and to realize the coating homogeneity.