The aerospace industry has talked about using robots for many years. However, until recently, most efforts were hindered by accuracy issues.
The aerospace industry has talked about using robots for many years. However, most efforts were hindered by accuracy issues. Aerospace drilling and fastening applications require tight tolerances to produce high-strength airframes and avoid the risk of cracking.
“In the mid-1990s, Boeing tried using a six-axis robot to join the body of its 777 jetliner,” says Dick Slansky, a former Boeing engineer who now serves as senior analyst at ARC Advisory Group (Dedham, MA). However, the automated body assembly tool failed because of accuracy problems. “Today, composites have completely changed the game, and adaptive controls have improved accuracy,” Slansky points out.
“People in aerospace have wanted to use robots for the last 20 years,” adds John Hartmann, vice president of Electroimpact Inc. (Mukilteo, WA). “Over the years, there have been many false starts and lots of empty promises. The three biggest problems were payload, stiffness and accuracy.
“Most robot manufacturers have addressed the payload issue,” explains Hartmann. “Stiffness is still a problem, because of the high force and pressure that is applied to aerospace parts with clamps.” In aerospace drilling applications, clamp loads can range from 50 to 400 pounds. At full clamp load, skating or unintentional movement can be more than 0.05 inch, which throws the position of end effectors out of tolerance.
“The biggest challenge with robots today is still accuracy, but it’s being worked on,” notes Hartmann. “We’re currently exploring several different options and I’m confident that we’ll get there within the next year.”
“The challenge with robotic systems has historically been dimensional accuracy over the entire work envelope,” says Martin Wimmer, R&D manager at Vought Aircraft Industries Inc. (Irving, TX). That’s why many off-the-shelf robots used in the aerospace industry often rely on some sort of adaptive feedback mechanism to meet the required tolerances.
“Until recently, there have been limitations on the processes which industrial robots have been capable of performing,” explains Rush LaSelle, general manager of western operations at FANUC Robotics America Inc. (Rochester Hills, MI). “Many high-accuracy applications, such as drilling and fastening, have exceeded the performance capabilities of robots unless cumbersome ancillary systems [are] employed to increase local accuracies. However, these solutions had previously not been sufficient for many of the large assemblies and components.”
According to LaSelle, robots have been considered repeatable for quite some time in the aerospace industry, but accuracy had not been considered sufficient. Now, with the increasing level of offline programming and cad-to-path processing, accuracy has been moving to the forefront.
“[We have] refined the use of secondary feedback to improve the robots’ overall accuracy to a point where it is now an effective platform from which to drill and fasten airframe components and assemblies,” adds LaSelle. He says the use of secondary feedback, in addition to primary servo systems, eliminates much of the localized accuracy hardware and processes that previously deterred manufacturers.
“Current articulated arm robots are not yet capable of obtaining some of the tolerances needed for aerospace processes, like drilling and fastening, without some form of external sensor guidance technology, which adds cost and complexity to an automation system,” explains Mike Beaupre, technology manager at KUKA Robotics Corp. (Clinton Township, MI).
“Robots are repeatable, but not necessarily accurate,” adds Joseph O’Brien, aircraft group program specialist at Comau Inc. (Southfield, MI). “There has been considerable effort by robot manufacturers and integrators to increase accuracy, including multiple encoders, software enhancements, various methods of guidance and localized correction. This is an ongoing process.”
Many observers believe a major research project funded by the Air Force Research Laboratory (AFRL, Dayton, OH) for military aircraft manufacturing will eventually trickle down to other sectors of the aerospace industry and spur widespread use of robotics. Phase one of the affordable accurate robot guidance (AARG) project has just kicked off.
The purpose of the two-year project is to develop a robotic guidance system that can be applied to drilling and fastening applications. The prototype cell will be used by engineers at Northrop Grumman’s Palmdale, CA, plant to assemble center fuselages for the F-35 Joint Strike Fighter. Fuselages are shipped to Lockheed Martin’s plant in Fort Worth, TX, for final assembly.
Dr. Don Kinard, technical operations deputy for F-35 global production operations at Lockheed Martin says several challenges still need to be addressed before more robots are used in aircraft manufacturing. “Lower cost, higher tolerance robots capable of high positional and machining accuracy are required to reduce capital costs and increase manufacturing flexibility, such as reticulating arm robots vs. gantry systems,” he explains. “Current systems are space- and capital-intensive.”
According to Kinard, there also needs to be improvement in robot location technology, including laser and vision positioning. In addition, he believes the aerospace industry must develop better integration of robotic technologies and RFID locator devices, leading to more automated material handling and material positioning implementations.
Accuracy Is No. 1 Challenge
May 4, 2009