Precise answer

For many years strict accuracy specifications have meant that the aerospace industry has been unable to successfully automate drilling and riveting tasks with the speed and precision required.

That could be about to change thanks to a robotic platform, developed by UK metrology company

and robotics specialist

, that allows robots to drill and rivet with ±0.1mm tolerance.

The platform, using a standard KUKA robot and a high-speed photogrammetry system from Metris, has halved the time taken to drill and rivet aircraft wings at Airbus' Filton plant.

The system is the result of an Airbus-initiated research project that called on KUKA and Metris to design a robot that could meet an accuracy of ±0.2 mm, which is required in many of Airbus' application areas.

'We did a number of tests for years with out-of-the-box robots to see if they were capable of moving to a position with a tolerance of ±0.2mm, and the conclusion was that they couldn't,' said Metris business director Roger Holden. 'There wasn't a robot on the market that could do that.'

Holden said his company decided to see how it could improve a robot's accuracy by installing a new kind of metrology system.

'A few people have tried to combine metrology systems with robots before, but one of the stumbling blocks has been the actual industrialisation,' he said. 'This is mainly because those systems were lab-based software and the users were exposed to too much source code so they couldn't actually maintain the equipment.'

So the researchers devised a more user-friendly gateway into controlling the system with Windows XP. But that didn't solve all the problems.

'Another reason people failed was issues with the deployment of the technology,' said Holden. 'Some measuring devices cannot track multiple frames at high speed.'

So Metris researchers worked on implementing high-speed photogrammetry to monitor the robot's position relative to the target spot for drilling or riveting on the wing part.

The system, called the K-Series Optical CMM, comprises three linear CDD cameras that use high-frequency infrared light-emitting diodes (LEDs) for measurements. Using triangulation, the system works out the exact location of each LED point in three axes, X, Y and Z. With clusters of three or more LEDs and a fast processing time of up to 1,000Hz on a single LED, the system can track objects in six degrees of freedom live.

One camera can measure 256 LEDs at once, and the system is configured to see a minimum of five LEDs, which allows it to compute an accurate, six-axis frame to guide the robot.

Feedback continuously flows back to the robot controllers, which means the robot is made aware if it has been deflected off target by factors such as temperature fluctuations or mechanical play. The robot is then able to co-ordinate that data and make necessary compensations. This adaptive control has been programmed into the controller as a background task.

Holden said that since the robots carry out tasks with great positional accuracy at a faster rate than a person, they could be used for a range of tasks, such as sealant application, component handling, fastening and machining. However, the initial use of drilling is a big enough job in itself. According to Airbus, the company needs 50 million holes drilled a year.

'Today, the biggest issue in aerospace is drilling holes, but it may change in the future with composites where people are looking for bonding rather than rivets and holes,' said Holden. 'However, today the majority of the market is drilling and we have a solution that fills it.'

After the company's success at Filton, it plans to implement the system with a Canadian aircraft manufacturer in January.

Holden said that although Metris is pleased with the system's accuracy, the company hopes to make it even faster.