High-Density Robotic Painting: Latest Trend Lowers Costs
by Randy Schuetz, Tech. Leader, Painting & Dispensing
, and Mary Kay Morel, Staff Writer/Editor, Motoman
Motoman Robotics Posted 11/14/2008
Technology advances, including the use of wall-mounted or shelf-mounted paint robots with hollow wrists, collision-avoidance software, conveyor tracking, and computer simulation have made it possible for manufacturers to incorporate high-density robotic concepts into their painting operations. Robotic painting improves quality and consistency and significantly reduces costs and cycle times, while high-density booth layouts save considerable floorspace.
For example, typical automotive paint booth widths have been reduced by 25 percent (from approximately 20 ft to 15 ft), and the overall length of their paint booths has been reduced 50 percent by using high-density layouts with wall- or shelf-mounted robots.
For every square foot of reduced spray booth floor space, the exhaust and air make-up (supply air) requirements will be reduced significantly. For example, a spray booth measuring 20 ft. W x 40 ft. L operating at a typical 60 ft per minute of exhaust airflow velocity will require 48,000 cfm. However, a spray booth measuring 15 ft. W x 20 ft. L operating at 60 ft per minute will require only 18,000 cfm, which translates to a 62.5 percent reduction in supply air.
To provide proper ventilation, make-up air must be brought in to replace air that is exhausted from the spray paint booth. Temperature of this make-up air needs to be between about 60º-85 º Fahrenheit, depending on the paint process. Depending on the temperature of the outside air, this make-up air might have to be heated or cooled to maintain it at the proper temperature. Lowering the amount of make-up air required also means associated energy cost to heat or cool it, which result in a significant cost savings.
To reduce pollution, exhaust air containing Volatile Organic Compounds (VOCs) and other hazardous components often needs to be incinerated before it can be released into the environment. Less exhaust volume also means less incineration expense, and less energy required to run the incinerators, an additional benefit.
New wall- or shelf-mounted paint robots are able to access hard-to-reach areas of the part or vehicle body more effectively than traditional floor-mounted models, while also keeping the robots above most paint overspray, which reduces maintenance costs. In addition, large parts or assemblies can be painted with multiple robots that are wall- or shelf-mounted at different height levels, allowing one robot to paint the lower portion of a part while another paints the upper portion. With the help of anti-collision software, multiple robots can work in very close proximity to each other in the spray booth.
The new wall- or shelf-mounted painting robots also have slim hollow robot arms with internally routed air lines, paint hoses, and cables that allow the robot arm and spray gun to access difficult- to-reach areas. On many automotive, truck and other paint lines, the same model wall- or shelf-mounted robots can also open and close doors, hoods and trunk lids, as needed, due to increased payload.
Conveyor tracking features allow robots to track parts as they move down a conveyor or overhead carrier and adjust the robot path for variations in the conveyor speed. Advanced robot controllers also allow robot motion to be coordinated with that of servo positioners to provide smooth, seam-free paint application. Many types of part positioners, as well as wall- or ceiling-mounted robot tracks and robot transport beams can be used in paint environments. However, these part positioners and robot transporters might need to be modified due to explosion-proof requirements for application of flammable paint materials.
Factory Mutual-approved controllers with air purge systems to achieve Class 1, Division 1 explosion-proof ratings are the standard for electrical equipment, including most paint robots powered by electric servo motors. Typically, the paint robot controller is located outside of the actual paint booth to increase safety and reduce costs. Often, menu-driven paint gun spray control features, color change and other functions are available from the robot teach pendant, which can be used inside the spray booth, making programming much easier. Robots can easily follow complex spray paths, maintaining a constant spray gun orientation, gun travel speed, and ultimately a consistent paint film thickness.
Today, highly accurate PC-based robot simulation software allows creation and testing of high-density layouts, spray paths, cycle times, etc. The painting simulation can effectively model painting of a part or vehicle on the computer to determine the number of robots required, eliminate interference between robots, optimize the robot location, and reduce the spray booth size. When simulations are used, painting robots can be installed and operational in up to 30 percent less time, which reduces installation costs.
Simulation tools can also be used to develop robot painting programs off-line. These programs can be downloaded to the robot controller and run with little or no touch-up programming. Off-line programming increases productivity by allowing the actual robots remain in production while programs are developed or modified.
Robotic painting reduces repetitive motion injuries and keeps plant personnel away from potentially hazardous materials, including VOCs , isocyanates and various carcinogens. Paint robots are generally easy to cost-justify through material savings alone, which can be significant – as high as 35 percent versus manual painting. Robotic spray applications provide consistent film thickness control, correct color and gloss, and excellent overall appearance without runs or sags.
New wall- or shelf-mounted paint robots maximize valuable floor space and reduce operating and maintenance cost for the manufacturing facility. Robotic painting reduces exposure risk for human workers, and high-density robotic paint booths significantly improve productivity and cycle time, while reducing energy use and environmental pollutants.