Generally, painting robots for automotive assembly plants are full-blown seven-axis robots. Or it may be that the painting is not being done (at least not primarily) by a painting robot, but with a bell machine system, instead.
On the one hand, this could mean more flexibility than is necessary, especially when it comes to painting exteriors (i.e., the seven-axis robot). On the other hand, this could mean more limitation than is desired (i.e., the bell system and its general inability to readily access such things as tailgates and rocker panels).
While Fanuc Robotics (Rochester Hills, MI) certainly has one of the industry-leading seven-axis painting robots with its P-200E, and while it is a supplier of both robots and applicators to suppliers of bell systems, according to Martin D. Rola, director, Engineering, Product and Application, Paintshop Automation, “We looked at previous installations, we looked at what is out there, and we decided to develop a machine that would provide flexibility, efficiency, and reduced operating costs.”
That is, they would do that by engineering a robot that would do one thing and one thing well: Exteriors. Just exteriors. Which, right off the bat, meant that the machine would be simpler than its seven-axis brethren (the P-200E, which can handle both inside and out). Yet, at the same time, because it is a robot, it would have far greater flexibility than the typical bell system. “Exteriors. We optimized the design around that,” Rola says.
The robot that they developed, the P-500, is actually the 10th generation painting robot the company has introduced. (This machine is quite fresh: July 2003 marks its initial customer application). And while the robot was the primary focus of attention during the development program, the Fanuc engineers took into account the fact that a robot wouldn’t be working by itself painting automotive exteriors, that it would be part of a system of multiple robots, working in a booth. All of that was taken into account, so, arguably, the P-500 is more than just “a robot.”
Among the drivers behind the P-500 development were:
- Robustness, as in three-shift operation
- Simplicity—in setup, in use, in maintenance
- Low operating cost, from low color-change waste and high transfer efficiency to energy savings in the booth
- Reduced capital expenditure, taking into account not just the robot, but also the entire booth.
The payoff takes the form of a five-axis arm (no waist; no wrist) that is mounted on a rail along the top of the spray booth. In point of fact, there are generally two or three robots per rail, two rails (opposite) per booth.
There are several things that this location does. For one thing, it provides greater visibility than is the norm when either floor-mounted robots or bell systems are in a booth. By also reducing the amount of equipment outside of the booth, by having a low-profile controller, and by doing things like putting the pneumatic panel on board the robot, if a booth is constructed with glass walls (or at least with glass panels strategically located) an operator can have visibility to the entire operation. For another thing, because the robot arms are elevated, and because the paint tends to fall down, the arms (a nonconductive nylon is used to construct the arms) stay cleaner than might otherwise be the case.
As previously noted, the robot doesn’t have a waist. This contributes to the robots being in a booth that is smaller than would be the case if they did, because the robots can travel to either end of the spray booth without requiring a safety zone. Robots with a waist require the safety zone on either end of the booth because it is possible that the robot could rotate on its waist, thereby going out of the confines of the booth with its end effector. Which consequently requires the extra feet for safety. “We can go as small as a 16-ft. booth,” Rola says. Smaller booths mean that there are reduced costs for energy (e.g., for the air downdrafts, under-floor water).
Speaking of a booth with bells (usually something like three bells per side of the booth that can go up and down, pivot, and some in and out capacity; an overhead beam with three or four bells that go up and down and have some rotation), Rola says that when it comes to application efficiency, the P-500 has the edge. That is, he says the bell system is “almost like a carwash. A vehicle goes by, and you either spray it or your don’t.” In other words, say that it is the lower half of the vehicle, where there are wheel wells, versus above the belt line where there is solid metal below the windows. In the case of the lower portion, there is time when the spray is off lest empty space get sprayed. “With a robot, you’re chasing the vehicle,” he says. “You’re not waiting for the vehicle. You maximize the spray time.”
One of the statements they make about the robotic system: “If you’re not color-changing, you’re painting.” (Color changes, incidentally, can be performed on the P-500 in less than 10 seconds. Because there may be four or six robots versus nine to 11 bells, the amount of waste associated with color change is reduced.)
One of the reasons why they are able to track the vehicle and paint where needed is because the ServoBell applicator can provide both large- and small-vortex spray patterns. Rola says that one of the tests for transfer efficiency of an atomizer is to have it spray a flat panel and to then determine how much paint goes on the panel. Vehicles, of course, have curved surfaces and comparatively thin pillars. Applying paint to those surfaces is trickier and undoubtedly a better test of transfer efficiency.
A key benefit of the P-500 system—a benefit that some vehicle manufacturers would have undoubtedly like to have been able to realize—is that it can accommodate various vehicles in a single booth: “Even with a small booth we can paint a small car and a large truck,” Rola claims. While there are certainly other considerations, such as skid size or the oven, the paint booth would not be the restrictor when, say, a taller vehicle based on the platform of a shorter vehicle suddenly became popular.