Technology Reflecting Real-World Experience
Concurrent with the development of coating robots, a joint development team comprising members of EG development and Suzuka's skilled coating-line operators began a new task. Their objective was to transplant operator techniques to the robots in time for the start of operations on the third line. On the actual line, tracking of the coating process was begun along with the preparation of the overall system.
The angle at which material is sprayed from the gun head is critical to the coating process, as is the gun head speed of movement. Moreover, a distance must be constantly maintained between the gun head and body surface. Through years of experience, the operators learn to control the gun head using their bodies and senses. For example, in the actual coating process they stop the gun just before the coating material being sprayed onto the surface would start to run. The coating film they create is even in all areas, with precision ensured down to a level of microns.
Before this kind of expertise could be passed on to the robot, each separate technique would have to be analyzed in detail. Of course, the skilled operators were also human beings; they simply could not give their very best performance time after time. Therefore, the team recorded its coating operation on video in order to pinpoint the optimal actions. Next, the most effective gun actions were chosen according to three criteria: the spray angle of coating material at the gun head, distance from the body, and the gun's speed of movement. Teaching sheets were then created in order to transplant the coating techniques to the robot.
"Operators acquire their skills through years of experience," said Hiroshi Arai, who was involved in the development as engineer in charge of coatings at EG's Third Engineering Block. "These techniques are therefore very logical, and they truly reflect human wisdom. In today's computer age, the promotion of automation depends on how to incorporate these techniques and make use of that human wisdom."
The task of teaching the robot began in November of that year. A cone-shaped jig was attached to the head of the robot's gun as a means of simulating the spray angle of the coating material. Using a hand-held console, the operators input their skills to the computer. In the beginning, it was quite a struggle. Although the robots were taught the actions exactly as performed by the operators, it did not mean the machines could immediately begin by producing the greatest degree of coating quality.
Since the body surfaces had many curves, the team often found it necessary to fine-tune the data it had entered in order to align the movement of the robot with the actual contours of the body. Another problem was that the teaching sheet specified only the total time of a coating operation. The specific spray pattern used to complete the operation within the specified time depended on the expertise of individual operators. To enable the robot to operate at the same level of effectiveness, trials using a dummy vehicle were repeated in order to determine the optimal spray pattern.
The outer-panel-top multi-coat robots provided a significant increase in the following capabilities of the spray gun.
The trajectory of spray from the spray gun indicates that paint is always applied to the body surface at a right angle.
A relatively higher degree of difficulty was encountered in teaching the robot to emulate coating actions along the body's inner panels and there was more limited workspace available. For example, to paint a corner area of the door, the operators would take several steps to complete the coating of the edge at the corner of the door, because doing so allowed them to maintain constant gun speed and ensure even coating. The team attempted teaching the robot to perform a one-shot coating along the edge of the door corner, but the resulting coating film was still uneven. This revealed that the method used by the operators was more practical.
The development team analyzed each individual operator action for assimilation by the robots. Moreover, they repeated that process for each Honda model so that the robots could handle the line being produced by the factory.