In June 2002, Lockheed Martin Aeronautical Systems (LMAero) in Marietta, GA opened the initial stages of their new high-rate production line for the F/A-22 Raptor, the U.S. Air Force's new air superiority fighter jet. LM Aero has been in an EMD (Engineering & Manufacturing Development) program that sustained a relatively low production rate of aircraft that are used to test every aspect of the airframe, avionics, and engines. During the program, LM Aero produced one aircraft about every six months. Using the new production line, that rate will gradually increase to one plane every six days by late 2006.

The F-22 fuselage is manufactured in three pieces -- the forward section is built in Marietta, the midsection is made in Fort Worth, and the aft section is produced in Seattle.

Final assembly takes place in Marietta. The performance specifications of the F-22 have driven the manufacturing requirements to tolerances that are uncommonly tight, even for aviation. The ability to quickly and accurately align and mate the three large fuselage sections was a top priority for the tooling department.

"A major obstacle that the alignment system had to overcome was that we required a TIR of 0.004 in. from the designed center positions of 16 wing nodes spanning 18 ft on each side of the plane," reports James Keywood, department manager during the design and build phase of this system. "No two nodes have a common axis. Other design goals were quick setup, simple operation, robust design, rapid alignment and mate, and of course, accuracy. Delta Sigma used an 'airplane-in-the-loop' design that guarantees all of our critical points will be where they belong.

"Another critical element of the tool design was the ability for the entire assembly jig to move down the first 278 ft of the assembly line and then return to the start of the line under its own power. Our engineers designed a 'skate' concept and Delta Sigma Corp won the bid over the competition to automate the skates. They designed and built the mechanisms that provide drive power, the transition between the precision rail and wheels, and the steering controls," says Keywood. "Delta Sigma also designed and built the precision alignment system on top of the skates using an 8-camera machine vision system and a 16-axis servo system. They took an extremely complicated procedure and made it simple and fast."

Dr. Brett Haisty, vice president of Engineering at Delta Sigma, was responsible for the overall design of the system. "After the fuselage is assembled, the wings cross the mid-aft mate joint with roughly half the nodes on each side of the joint. The tolerances are very tight. Lockheed requested noncontact, three-dimensional measurements with sub-mil accuracy in eight locations -- six measuring wing nodes and two measuring tooling holes in the weapons bay. Setup could not take more than 10 minutes and the system had to be designed so new operators could typically be trained to setup and use the system with less than an hour of OJT."

"We selected DVT for our machine vision cameras even though we had never used them before. The feature set, hardware quality, and especially the free training and support provided by DVT made them a valuable ally on this program," continues Haisty.

"We designed a set of 'pins' and put the cameras in them so that they fit in a set of tooling holes that look into the wing lugs. This accurately simulates the wing joining the fuselage. Since the cameras are inside the pins that attach the wings, they measure the misalignment, report the errors back to the control computer, which, in turn, calculates the moves required of every axis to solve for 14 axes simultaneously."

"The key to making this work was that Brett figured out how to recalibrate the cameras every 60 milliseconds to achieve the accuracy specification, and he developed a very precise geometric model that allows the control software to analyze how any movement of a motor will affect all the measured positions before it moves," states Terry Clark, an electrical engineer at Delta Sigma. "The fuselage is extremely rigid so it is not possible to align just one point at a time. You must align all the points at the same time. I suppose that is why no one ever did it this way before."

While the "airplane-in-the-loop" concept leaves nothing to chance from a measurement standpoint, it makes the control system much more complex, due to the cross-axis coupling that is inherent when the motion input and measurement positions are located far apart. For example, it generally takes seven motors on one fuselage section to move one wing node into position. This is because it is not possible to move one node without moving all of them. So, all seven motors will have a new position to align one node without losing position on the other nodes. A traditional "seek zero" algorithm would simply cause the plane to go into an unrecoverable oscillation.

"This program has been an example of what teamwork is all about," states Lockheed's James Keywood. "From starting the automation design in September 2001, to mating our first fuselage in June 2002, our engineers, along with Delta Sigma's team, made every major milestone on time during that 9-month period. In fact, the new tooling was completed one aircraft ahead of the schedule. We completed the alignment and mating of our first jet in about 10 minutes. By every measure, this has been a remarkably successful program."

So successful, in fact, that LM Aero in Fort Worth, TX purchased a similar system to assemble the mid-fuselage section. Two of these assembly systems have been installed, and a third is planned for the third quarter of 2006.

"The fact that such high levels of automation can be economical on production programs such as the F/A-22, where only about 300 aircraft are going to be built, shows just how far we have come in getting the cost of automation down," says Haisty. "Companies like Lockheed -- one of the leading innovators on the planet -- are constantly looking for new and better ways of doing traditional tasks. They are not just looking for what will be good next year, but what will be good 10 years from now."