More Robots Take Up Painting, Coating and Dispensing, Too

When you think about the millions of products that require a painted surface or perhaps a coating to protect a paint job or natural finish, it's not surprising there are thousands of robots performing these tasks as well as dispensing sealant to close gaps or join components.

Automating these jobs is on more and more 'to-do' lists because manufacturers want to minimize employee contact with the sometimes toxic paints and other compounds used in these operations. Potential ill effects on personnel and environmental hazards concern the federal Environmental Protection Agency and the Occupational Safety and Health Administration, as well as other state, regional and national groups.

Automation also improves application appearance, consistency and throughput and often means a savings in materials through greater application efficiency. Robots' greater precision 'results, today, in savings of 20% to 30%' in paint or other coatings,' states Carl Traynor, director of Marketing at Motoman, Inc., West Carrollton, OH.

Robots performing painting, coating and dispensing jobs are most likely to be found in the automotive industry, but there are many installations at companies making a host of other products, including motorcycles, bicycles, boats, jet skis, household and office appliances, telephones, furniture, washers, dryers and toys. One difference between these deployments and automotive work cells is that the robots may be smaller. In addition, nonautomotive companies generally have a shorter history of painting, coating and dispensing by robot.

Robot types
Painting robots, and often those for dispensing and coating, generally are equipped with six axes, three for the base motions and three for applicator orientation. Some units incorporate machine vision for guidance or to check application quality. Today, these top-of-the-line machines are, almost universally, electrically driven, rather than powered hydraulically or pneumatically. In addition, unless used solely for applications where flammable and/or explosive vapors are not present, 'most [painting, coating and dispensing] models are explosion-proof,' reports Einar Endregaard, director of sales and engineering for Behr Robotics, Inc., Auburn Hills, MI.

Unlike materials handling robots, robots for painting, coating and dispensing generally are equipped with long arms, not only to enable a considerable reach, but also to permit access into narrow spaces to treat difficult-to-touch targets. Robots for these operations are built for specific operations with joints that can reach complex curves, angles and planes on almost any product or part.

One painting robot now on the market has a work envelope (circumference of reach) measuring 18 feet wide by 9 feet in left to right action, reports Rick Dobreff, manager of the Robot Paint and Seal Systems at ABB Flexible Automation Inc., New Berlin, WI.

While it is a pedestal unit, other robot painters, coaters and dispensers are track- or gantry-mounted. Although gantry systems generally are not used in automotive painting, rail-tracking robots are found in all the newer paint shops at General Motors Corp., Detroit, MI; DaimlerChrysler Corp., Auburn Hills, MI; and Ford Motor Co., Dearborn, MI. Track and gantry mounting enable a robot to hover below or above the action and ride along with the parts carriers to perform complicated tasks without slowing the line speed.

A gantry-mounted unit is used by boat manufacturers to spray fiberglass chop (small lengths of fibers suspended in a matrix) to strengthen and stiffen panels. The gantry enables the robot to move the length of the boat, a range of travel that would require two pedestal units.

Industry leaders say that there is virtually no operation for which a robot and end-effector tools cannot be built. The only limitation is the cost of the attendant specialization and complexity and whether the application is of sufficient size to justify the expense. Even a 'standard' robot for the tasks noted above is likely to run at least $50,000. More sophisticated units will cost $200,000 to $300,000, and with the typical automotive installation employing 40 to 60 robots in sealer, primer and clearcoat operations, system price tags can climb into the millions.

End effectors
As with any robotic application, end effectors play an essential role in painting, coating and dispensing cells. Conventional spray guns use air to atomize the paint particles and control the pattern size. Electrostatics can be used to aid transfer efficiency.

More recent in development are liquid- and powder-handling 'bell' applicators, which fill a cup with a liquid or powder and rotates it at high speed to atomize the particles. Volume, rotation speed and air velocity control pattern size. Here, too, electrostatics may be used to aid transfer efficiency. Recent improvements in bell atomization technology have now made bells particularly well-suited for handling metallic paints. Bell applicators are replacing less efficient spray guns not only for exterior painting, but also for interior panels and under-the-hood tasks. In fact their greater flexibility often means interior and exterior painting can be performed by a common applicator.

For sealants, FANUC Robotics North America, Inc., Rochester Hills, MI, has integrated a servo-driven shot dispenser into a robot controller to supply an accurate amount of sealant to the airless or air-assisted gun applicator. It applies either an extruded seam or ribbon of material to the product part or junction of parts. Two-part mixing systems can be incorporated where needed.

Some painting devices also dispense coating materials ranging from overcoats that protect painted surfaces to finishes that cover fine surfaces of metal, plastic or wooden products. Others for more viscous applications act more like extruders. Opus Automation, Flamborough, ON, integrates robots from KUKA Robotics Corp., Sterling Heights, MI, that Opus President and Director of Engineering Peter Young believes are well suited to many extrusion-based applications because of their path-following capability and accuracy of performance. Opus also uses robots from CRS Robotics Corp., Burlington, ON, for small dispensing applications.

A new application, sprayable damper, applies sound-deadening material to parts to eliminate noise, vibrations and harshness related to the operation of products such as vehicles and appliances. Polyvinyl chloride, epoxy or water-based materials replace the die-cut pads previously used and can be patterned to apply the exact thickness of material needed at each point. 'The liquid damper material is less expensive than the die-cut pads and reduces vehicle weight three to five pounds,' says Martin Rola, director of Technical Engineering for Paint Shop Automation at FANUC.

'For the future, as more pumpable, sprayable materials are developed, we will see increased opportunities for automation,' predicts Ray Guzowski, senior staff engineer at FANUC. 'Combining multiple robot applications such as foam cavity fill, seam sealing and sprayable damper into a single system also helps improve the business case for sealing automation,' he adds.

What's next?
Industry experts agree the number of robotic painting, dispensing and coating installations is rapidly growing, not only in automotive, but also in other manufacturing operations.

Even broader adoption will depend on meeting customer demands for ease of operation. 'A major objective should be simplification of control systems,' declares David Hoffstetler, service manager at Stäubli Unimation Inc., Duncan, SC. Smart systems, now evolving, may be the way to provide simple push-button control.

There's also growing demand for greater integration between robot and related equipment such as pumps for paint or other fluids and servo-controlled orienters. For example, on automotive lines servo-controlled mechanical devices often are used to open doors, hoods and decks so the robot arm and effector can move underneath and/or inside structures for painting, coating or sealant placement. 

Manufacturers also are looking for more specifically focused products like FANUC's new P-200T robot with AccuChop software. Targeted especially for the marine and bathwares industries, the system consists of an inverted painting robot mounted on a gantry, an integrated closed loop fluid delivery system and process control package designed for gelcoat (resin and catalyst) and chopped fiberglass (resin, catalyst and glass) applications.

Finally, as limitations on volatile organic compound emissions become more stringent, tomorrow's units must be compatible with water-based paints, coatings and sealants. This generally can be accomplished by changing the end effector to one designed to accommodate the characteristics of the water-based fluids, which generally contain a higher solids content.