Robotic Painting

In recent years, advances in robotic paintshop applications have provided significant performance improvements in terms of application efficiency, quality and operating costs. Users and potential users of painting robots are looking for reduced capital costs, smaller footprints, reduced installation time and cost, and the ability to process a wider range of vehicles.

To meet these goals, a new design approach has been successfully applied to robotic painting systems. This has spawned the latest phase in robotic paint systems, which can provide significant benefits to end-users in all areas described above.

Some History

How did we get to this point? When paintshop robots were in their infancy, much of the focus was on making the robot manipulators perform robustly. Early hydraulic robot applications suffered from lower than desired uptime, limited motion accuracy and repeatability and high maintenance requirements. Hydraulic robots were applied in many automotive manufacturing facilities for painting both vehicle interiors and exteriors.

This initial application phase was instrumental in further quantifying the capability and benefits of using robots for vehicle painting. It also provided a better understanding of the areas of improvement required for paint robots to make them more cost-effective for manufacturing.

The introduction of the first electric painting robot with a hollow wrist in 1985 provided significant improvements in the areas of limitation identified in previous robots. From the mid-80s through the mid-90s, paintshop robot system design was focused on making the robot manipulator operate at acceptable performance and uptime levels. In addition to a standard robot for painting vehicle exteriors, six- and seven-axis robots were used with various hood, decklid and door opening devices to paint exterior and interior cut-in areas, with the target of a 100% robotic paint application.

Through this phase, the focus was on increasing system uptime, improving the user interface, making programming easier and successfully applying robots to moving-line interior and exterior painting processes. Additional effort was devoted to effectively adapting generic paint fluid delivery equipment, color changers and spray applicators to the standard robot.

Introduction of the electric painting robot and other incremental improvements significantly advanced overall system uptime and paint quality. Some key improvements still needed were to reduce paint waste in color change and application and to improve the reliability of the paint application equipment adapted to the robot.

The first painting robot to have integrated paint process equipment was introduced in 1996. The FANUC P-200 was the first robot designed around the painting equipment. For example, to minimize paint waste, color changers were mounted on the arm of the robot as close as possible to the spray applicator. Also, the paint fluid supply lines were routed through the center of the robot base, enabling the robot to “rotate around” the paint lines as opposed to having them managed through external means. This new robot design approach and hose management technique improved paint line reliability.

In addition, the control software was designed so that the most critical painting processes (such as gun trigger control) were given high priority in the software code. This change allowed for more precise (< four millisecond) trigger control to reduce paint waste.

In summary, the enhancements of this phase provided significant improvements in application efficiency, system uptime and overall duty cycle of the equipment, along with reducing operating and capital equipment costs.

Robot Optimization

In the late 1990s and the first part of this decade, the focus was on the optimization of two application areas: 100% robot-applied electrostatic rotary atomizer (or “bell”) exterior painting, and robotically applied interior vehicle bell painting for door interiors, engine compartments, deck lids and so on. For exteriors, 100% bell application was enabled by improvements in bell design and paint materials. These advances combined to enable metallic paints to be applied by bells with acceptable color and appearance levels. Previously, to achieve acceptable appearance, vehicle exteriors were painted with air-atomized spray guns for at least one of the two coats of metallic basecoats. This bell-bell process significantly reduced paint usage (20–40%) over previous processes.

By the early 2000s, interior painting matured as early problems with the coordination and robustness of the opening devices were resolved. Also, in many installations, the more efficient bell applicators replaced spray guns for interior painting. A key enabler of using bells for interior painting was optimization of the “focused” or “vortex” spray pattern, which allowed bells to achieve uniform film thickness on areas with many edges and different surface orientations (such as the hinge area of a door jamb).

Today, 100% of the vehicle interior and exterior painting applications can use robotics, achieving excellent paint transfer efficiency. Also, from the mid-1990s to the early 2000s, the applicator mix between spray guns and bells on robots for automotive applications shifted from approximately 85% guns and 15% bells in 1995, to 85% bells and 15% guns.

Variations on a Theme

Throughout the first two decades of paint robot development, robot manufacturers promoted a “common” robot and paint application system for all applications. While some robot variations existed in terms of different arm lengths, the basic design consisted of a six-axis robot, sometimes adapted to a seventh axis linear rail to increase the work envelope along the direction of the conveyor. Basically, robot and application equipment was common between interior and exterior painting applications.

Also, the “robot paint equipment” was considered to be the robot manipulator, the fluid delivery equipment and the spray applicator. During system assembly, each robot or set of “robot paint equipment” was connected to other equipment such as the pneumatic controls, seventh-axis linear rail, air preparation panels, operator panel and cell control PLC through various means.

In a typical installation, the equipment was assembled on the robot manufacturer’s floor, debugged, loaded with preliminary programs and cycled through a test run (typically 20 hrs) for system performance verification.

The system was then disassembled, packaged, shipped to the customer and re-assembled. After installation, it was debugged and installation-specific items—for example, setting the pneumatic delay required for valve actuation based on the location of the solenoid, or calibrating a closed-loop air flow meter system—were addressed.

In general, deliverables consisted of the paint robot equipment and the system elements such as controls, pneumatics and so on. Robot suppliers integrated the two parts and provided the integrated system to the end-user.

Systems provided in the early 2000s were highly effective and efficient painting systems with high uptime. Paint robot application technology had matured to the point where all major automotive manufacturers almost unilaterally considered it the application method of choice. Given this, there was not an obvious “next step” defining what could be done to make an incremental improvement for paint robot applications. However, from a high-level perspective, several questions were raised regarding potential limitations of the existing approach. These included:

• Is having a common robot for both interior and exterior applications the best approach?
• If not, are there unique advantages if the application focus was more refined?
• Are there elements in the robot design that can change to make the overall system more effective or easier to
  implement?
• What is the right definition of the “product”? Is it a painting robot, a painting robot with application equipment,
  a painting system?

• For deliverables to the end-user, which components should be considered “product” and which should be
  considered “system”?

App-Specific Robots

Finding the best answers to these questions and developing the appropriate solution resulted in the next phase in paint robot systems: application-specific paint robots. An example of a product that represents this phase of robot development is the P-500 painting system developed by our company in 2003.

This system provides increased spray performance compared with traditional robot applications, reduces end-user capital and operating costs, and can be installed and commissioned very rapidly. It differed from previous robot generations in that it included elements that were not traditionally associated with robotic paint systems.

Previously, the product scope was limited to robot manipulators and fluid delivery/spray application equipment, and did not limit the scope of the target application. This new definition refined the process by limiting applications to exterior vehicle painting and broadened it by adding the element of rapid, low-cost installation, commissioning and operation. This new definition clearly described what the end-user was purchasing and provided additional focus for product design rationalization.

Other capabilities that differentiated this robot from previous generations were its small footprint and its application flexibility. It was designed to paint in smaller spray booths, reducing both capital and operating costs, while still maintaining flexibility to accommodate a range of vehicle sizes without compromise.

Also, this robot could handle waterborne paint formulations as simply and efficiently as solvent-borne materials. Up to this point, most application equipment used for waterborne paint suffered from either decreased performance (in the form of increased material usage and maintenance of external-charge bells) or was relatively complex, such as the many different versions of direct-charge systems with canister exchange or docking stations.

The design of this robot cleaned up the floor space outside the booth by eliminating equipment not required immediately outside the spray booth in the aisle way. It also addressed the issue of blocked the visibility of the painting process from the operators of the equipment.

This product has exceeded expected performance targets, and has changed the automotive industry’s approach to exterior vehicle painting by popularizing the use of rail-mounted robots elevated from floor level. Since July 2003, hundreds of FANUC P-500iA paint robots have been installed in many customer sites around the world. The design spawned innovative thinking which generated multiple patents and patent applications in areas relating to robot design, process equipment design, product maintenance, programming methods, and installation.

System Benefits

The P-500 system provides best-in-class uniformity and spray process efficiency. Patented process approaches and optimized application equipment design minimize the amount of overspray produced during painting.

Direct capital cost to customers was significantly reduced in two areas: (1) the price of the robot system has been reduced; and (2) the robot system design fits in a much smaller footprint. In some cases, the space required was reduced by over 40%. This significantly reduces spray booth construction costs.

High efficiency combined with reduced booth operating costs and reduced maintenance has provided over a 20% operating cost reduction compared to previous robot systems in many cases. Systems have been installed and commissioned in less than one week to support limited downtime at end-user facilities.

For waterborne electrostatic bell painting, the system provides a highly efficient direct-charge application without external docking or canister exchange systems. This new method significantly increases application efficiency for waterborne systems, reduces material usage and significantly cuts associated complexity and maintenance costs.

Revised and simplified controls architecture reduces the number of control panels required, freeing up aisle space outside the booth. Also, the robots are typically elevated to approximately seven feet in the air, providing a clear process viewing window for the operators and also allowing placement of access doors directly beneath the robots.