A Stäubli RX 60 robot working with two fully integrated vision systems has dramatically improved production for a crucial component of the U.S. Navy’s Aegis Weapons System
Stäubli Robotics Posted 03/14/2012
The component is a 12' x 12' aluminum base plate, which holds thousands of tiny ceramic windows forming a protective front for an array of phasers at the heart of the computer-controlled AN/SPY-1 radar system.
Designed and developed by Lockheed Martin Naval Electronic & Surveillance Systems-Surface Systems, Moorestown, NJ, the Aegis Weapon System has been described as the most capable surface-launched missile system the United States Navy has ever put to sea. Lockheed management, which has routinely upgraded the system since its inception over two decades ago, decided three years ago that the evolution of new technology presented an opportunity to vastly improve production performance.
The plate itself, in its completed state, is a 12' x 12' aluminum sheet containing over 4000 1" x 3" holes tightly fitted with ceramic “windows” plus another 2000 large and small recessed screw holes into which flush-fitting covers or “buttons” are set. While the completed plate appears to be simple enough, manufacturing it to the quality and accuracy demanded by the Navy and Lockheed Martin is far from simple.
Lockheed Martin turned for assistance to Advance Design, Inc., a small design/engineering firm in Bristol, PA. The most pressing concerns that Lockheed wanted to address were to improve working conditions for their operatives as well as improving productivity. The main working area was a bridge, under which the array moved. A section of the array was exposed through an opening in the bridge; through this opening, the ceramic window (or button) was inserted into the plate. Prior to that step, however, a cam-driven dispensing system-- on the floor of the shop-- was applying RTV, a one-part silicone adhesive, to the parts (windows and buttons), which were then placed in a carrier. To hold the part in the carrier, the dispenser “over-applied” the adhesive. The carrier was then put on a conveyor belt, which carried it to the top of the bridge. There, a robot picked up the carrier and aligned the part over the hole or pocket in the plate. Next, the robot flipped the carrier over so the part now faced the hole, but was held on the carrier by the excess adhesive that had been applied. To release the part from the adhesive holding it, two small pins pushed the part out and into the hole. This procedure, though workable, proved messy at best and potentially catastrophic at worst.
It was necessary to follow the robot and wipe up all of the excess adhesive as well as cleaning the carriers for the next batch. If glue got into the phaser, replacement could cost $200,000, which made the precision of glue laying a prime concern.
Even when things were working smoothly, the array production line was not a fun place to be. Ergonomically, these were very undesirable jobs nobody wanted them. Operatives needed to work on their hands and knees on a bridge with a hole in it. They had cushions up there (in an attempt to ease the discomfort). It was so stressful and uncomfortable that the eight workers required to run the system were rotated every 20 minutes.
As if that weren’t enough, the old robot could only handle the 4350 windows; the 1600 small and 500 large buttons had to be put in place manually.
Advent Design engineers knew they would need the flexibility and work envelope of a six axis robot fitted with a vision system and called in Stäubli Robots to advise on the most suitable model from their RX range. Stäubli recommended their RX60 six-axis model which had the speed, accuracy and repeatability to work to the demanding tolerances of this application.
Advent proposed employing two Cognex camera systems with Checkpoint II software, fitted to the Staubli RX-60 robot arm. Everything needed to complete the array (other than the main control panel) would be mounted on a single cart, which traveled along a 14-foot track on the bridge. That included the two cameras, the robot, the adhesive dispensing system, and two cassettes, one loaded with the ceramic windows and one with the large and small buttons. By incorporating everything in a single cart, there would be no hand-offs; no need to rely on a secondary operation— like the separate adhesive dispensing unit used in the old system. The cart would move along the track above the array, stop every couple of feet, complete work on a 2' x 2' section of the plate and then move on to the next sector.
The two Cognex cameras each performed multiple functions. The first camera directed the cart to its first “rough” position above the array. At this point, the RX60 robot would use suction grippers to pick up a ceramic window from the part cassette and submit it to the camera for inspection to check for any cracks or broken edges. The robot then submits the window to the adhesive dispenser, which deposits a thin bead of RTV adhesive around the window’s perimeter. The camera then looks at it again and checks the quality of the bead and to ensure no adhesive falls onto the costly phaser.
Once the bead is approved, the second camera— incorporated into the robot’s end effector-- takes over. The second camera performs a fine alignment: it locates the hole or pocket where the window is to go and, after the robot places it, inspects the placement to make sure it is correct. After the two-foot square section is completed, the robot moves to the next rough position and the entire procedure is repeated.
For a vision system to perform flawlessly in these circumstances, Advent engineers had to surmount several demanding obstacles. The clearance between the size of the hole and the size of the window was tight at only .005"; also, there were sharp edges on the hole and part. The task was to pick the parts and place them accurately without breaking the brittle ceramic windows. To accomplish this, Advent engineers had to program the Cognex and Staubli units— both of which are independent systems— to effect a flawless integration of vision and robotics.
There was at least one other justification for the robot/vision system. With the old system, every time a new array was brought in for window/button insertion the new array had to be lined up to the bridge. The radar face had to be level and aligned in skew to the robot on the track. This was a crucial operation since the array had to be leveled within .020". To accomplish this, a crew spent a half-day adjusting screws and cranking the corners up and down until the 12' x 12' plate was perfectly level.
With the new system, it was no longer necessary to make such a fine alignment, The robot finds the pockets, checks the skew and makes adjustments for it every time it places a window. You can literally lay the plate in crooked and the robot will find it.
Lockheed Martin was delighted with the new system. Quality, of course, had always been their first concern. They had been looking to maintain the production rate and product quality of the previous system. The new system went well beyond that, it significantly boosted the quality and overall throughput time of an array.
The time involved in inspection has been dramatically reduced. Previously, a maintenance person remained on the bridge; now he’s on call. An operator is always on hand, but the system basically runs unattended. Meantime, workers who used to spend their time on their hands and knees cleaning adhesive spills now spend their time working on other aspects of the next array while the current array is being populated.
Maintenance costs have been virtually eliminated. Not only has downtime disappeared, materials costs have also plummeted. What used to require a 5-gallon pail of adhesive, valued at $500, is now accomplished with a single $50 tube.
What about those back-breaking chores that workers had to perform to clean up the excess adhesive? History now, Lockheed Martin personnel can now do what they’re good at doing. With the same crew, there have been no repetitive motion injuries or similar injuries to hands, knees and wrists. And because the adhesive goes on the parts and not on the floor, the work environment— once a grungy white with adhesive covering everything and everyone— is now near spotless. It still looks new after 2 years!, a Lockheed Martin executive commented.