Simultaneous tool posture and polishing force control of unknown curved surface using serial-parallel mechanism polishing machine

In automotive manufacturing, the repair polishing process of an automotive body is still manually performed by skilled polishing workers. This is because skilled workers can appropriately control the polishing motion and force according to the workpiece conditions based on their experience. However, the number of skilled workers has been decreasing. Additionally, the skill development of younger workers has not been satisfactorily conducted. To overcome such problems, in a previous research investigation, we developed a serial-parallel mechanism polishing machine that effectively reproduced the polishing motion and force of skilled workers. This replication system, however, had limited use because the acquired polishing techniques could not adapt to various workpiece conditions, such as shape and size. The present study aimed to expand the polishing method for application to curved surfaces, in other words, adapt the replication system to changes in the workpiece shape. In the past polishing methods for curved surfaces, the workpiece shape was acquired by using CAD data or external sensors that often led to an increase in process time and cost. However, the newly proposed method in this study requires neither CAD data nor external sensors, and was able to effectively achieve simultaneous posture and force control on unknown curved surface. The experimental results showed that the skilled polishing techniques were successfully replicated on an unknown curved surface and the surface roughness was greatly improved by integrating the newly proposed method into the skilled polishing replication system.