Networked control is key to aerospace testing

A new jig for testing critical wing components has allowed an airliner wing builder to increase throughput by 75%.

A new jig for testing critical wing components has allowed an airliner wing builder to increase throughput by 75%.

Employing 186 servo drives with tightly co-ordinated motion control, the jig's operation relies on Mitsubishi control solutions and ultra-high-speed networking built on a backbone of Mitsubishi's SSCNET technology.

The design of an aircraft wing is a deceptively complex business involving large quantities of critical parts such as stringers - the lateral ribs inside the structure that determine the wing's shape and lift characteristics.

Manufactured from aluminium alloy to keep the wing as light as possible, each stringer is unique and has its own individual dimensional profile.

Comprehensive testing of the stringers is vital, with the test jig needing to operate to axis dimensions accurate to within 0.2mm.

But with demand for aircraft increasing daily, the testing station was becoming a production bottleneck with its slow testing speed and long setup times.

Further, its dated, open-loop design meant the jig needed constant recalibration to maintain accuracy.

Another serious drawback was that the jig was unable accommodate stringers for new aircraft.

Looking for a quality checking system that would dramatically improve throughput, specialist systems integrator CR Solutions was asked to assess technical options.

The test bed CR Solutions subsequently developed is 22m long, with 86 actuator stations employ employing a total of 186 lead-screw actuators.

These vary the jig's test angles to match the stringer's profile, with the required movement of the actuators monitored as a precise measure of the stringer's dimensions.

Each is driven by a Mitsubishi servomotor.

To control and co-ordinate all the sequential moves of the testing procedure, CR Solutions opted for Mitsubishi A173 motion controllers.

Eight controllers are linked together over a TCP/IP Ethernet network to a central Scada system.

The motion controllers provide the control data for the 186 servo amplifiers, each driving one of the servomotors mounted up to 20m away.

The central Scada PC provides a local operator interface to the test rig allowing full visualisation of the entire operation.

In addition, it also acts as a data hub between the test rig and plant's production network.

When a stringer is tested, its unique CAD profile data is sent from the production database to the test systems central Scada PC, over the factory's internal Ethernet network.

The PC then extracts the profile data from the CAD file and creates a set of real co-ordinates.

These are then sent via an OPC server interface across the network to the motion controllers.

The high precision A173 motion controllers use their integral interpolation commands to provide smooth synchronised axis movement, whilst calculating the movement distance needed to meet the stringer profile, and checking against the real co-ordinate data.

The high-speed, high-precision control bettered the brief's requirement for 0.2mm measurement accuracy, providing an accuracy of 50um.

At the same time, up to four stringers can be tested at a time on the jig, dramatically increasing throughput.

Key to the fast reaction of the system is the speed of the SSCNET network used to connect the servo amplifiers to the motion controllers, as Steve Bennett of CR Solutions explains: "The 186 servo drives had to be networked and co-ordinated together".

"The cost of conventional analogue control was far too high and had a lower reliability than intelligent control".

"When we evaluated potential suppliers, we found that there were only two truly deterministic networks that met the high data processing requirements, Sercos and SSCNET, the latter being Mitsubishi's proprietary motion controller network".

"Sercos was soon discarded as a viable option as it was a loop network, where the loss of a drive would mean the loss of the network, and the cost of building in redundancy was prohibitive".

"This meant Mitsubishi's SSCNET was the only viable networking solution".

As well as handling the control and sequencing of the test jig's operations, the A173 motion controllers also provide all alarm handling in conjunction with the Scada PC which stores all the alarms historically.

Should an alarm occur, an alarm page on the Scada PC appears.

CR Solutions designed the system to link the alarm indicators to a comprehensive 'service and maintenance' diagnostic tool, even interfacing the alarms to active PDF files stored on the Scada PC to help deal with any issues.

The PDF files are themselves linked to video/audio clips and CAD files, which show to the operator, in the easiest possible way, exactly what is wrong and how to proceed to rectify the fault.

Wing production throughput has increased by 75% with the new jig, giving a payback period of less than a year for the entire solution.

As well as providing increased throughput, the new system is also geared towards providing high system availability, not even requiring recalibrating after power downs.

The new test jig has also been built to be flexible.

It gives closed loop feedback and will accommodate new aircraft designs and even longer stringers if necessary.

Indeed, such was the success of the new test jig that three more have been ordered.

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