Automatic offline path planning of robots grinding multi-curved surfaces on large ship propellers – A human-in-the-loop approach

Multi-curved components represent a particular challenge when machining with robots, as the machining is subject to a wide range of technical limits depending on the robot system used. An example of such a multi-curved component can be found in the ship propeller, which is one of the most important components of a ship and represents a relatively complex part in the production process. Manufacturing in the casting process is resource- and time-consuming and requires extensive finishing, which also includes grinding to final size. Technologically, this operation is still performed manually or mechanically assisted and requires employees with a high level of experience in the operation and handling of grinding technology. In order to prevent the increasing shortage of skilled workers and to make the finishing process independent from employee-specific knowledge, it is necessary to develop an automatic grinding process. In this context, offline path planning for multi-curved surfaces has emerged as a particular challenge, since existing approaches do not sufficiently consider the robot axis positions nor the pose limits of the end effectors. This work starts by presenting the current state of research and then introduces a human-in-the-loop approach that solves the problem of 3D trajectory planning using two-dimensional viewing planes. The trajectories thus found are projected onto the surface of the propeller and analyzed for potential collisions with the robot, grinding efficiency and reachability. Furthermore, it is possible to calculate an automatic removal characteristic by overlaying a simplified casting model and ideal model of a propeller.