Testing aerospace subsystems only at the time when they are assembled in the finished aircraft is neither safe nor cost-effective – no one wants to either fly untested equipment or have to go back to the drawing board when it should be the end of the design process. And so the aerospace industry came up with the ‘Iron Bird’ philosophy. The Iron Bird provides simulation of an entire aircraft, allowing various subsystems to be plugged into it to undergo testing at a much earlier stage in the design and verification process.
It is a ‘hardware in the loop’ philosophy that has proved invaluable to aerospace companies, and has now found favour in the rail industry. Train manufacturer Bombardier is the company behind ‘Train Zero’ – the project that aims to cut costs and development times of its next generation rolling stock. It has particular relevance to the company’s contract to supply the new trains for Crossrail, but all future train developments will also make full use of the facility.
The consultancy that has designed the system for Bombardier is Frazer Nash, whose brief was to develop a facility that could ‘efficiently develop, integrate and validate train electrical and control systems.’
Colin Freeman, senior consultant with Frazer Nash commented: “The Iron Bird example is always cited where the aerospace industry builds an aeroplane before it flies, bringing all the systems together. And they see massive benefits in terms of their testing, their time to market, their ability to respond to customer change, need, requirements and so on. So there was a desire within Bombardier to take a step change and do something better and different, and that coincided with them looking at developing that next kind of generation of trains. They were looking at a platform-based approach where they could develop these core systems and then tailor things around customer needs.”
Model based engineering
Initially the brief had been to improve and shorten the test and validation process but Frazer Nash proposed a model based engineering approach. In this methodology system requirements are modelled early in the design phase and those requirements can be verified through hardware in the loop tests. Freeman added: “The ultimate aim is to shorten the time that it takes when you actually have that first train built and you come to do the signoff type tests that your customer needs, it effectively passes first time. All of the heartache that you might have suffered previously has been removed by the more targeted, smarter way in the Train Zero facility.”
Bombardier works with a lot of third-party suppliers for many of its subsystems. Traditionally those subsystems interface to the train control and monitoring systems found in the driver’s cab, but they are now also starting to interface with each other. Consequently there is starting to be a greater requirement to do such things as diagnostic and prognostic testing, and the requirements on those individual subsystems are getting more and more complex.
“Hardware in the loop testing fundamentally is intended to bring those bits of equipment together in the manner that means they think they’re on the real train,” explained Freeman. “So you can bring in a heating system, you can bring in the door system. You can bring in the propulsion system. You can connect them to the real, bona fide train control system which Bombardier has assembled for the Train Zero lab. The entire software-based train control and monitoring system which will exist on the Crossrail train is already built in the Train Zero lab. The third-party bits of hardware that are there - sometimes it’s an internally developed piece of hardware, sometimes it’s a third party company they work with - can now all come together, have simulation models written around them.”
Train Zero, which is housed at Bombardier’s main manufacturing site in Derby, is purely static, but still has the capability of testing and simulating all moving parts and the environments (e.g. getting too hot) that they might experience.
All these subsystems do of course have a wide variety of different interfaces and this presented Frazer Nash with one of its early challenges.“We had to look at the needs of each individual system and say, okay, what interfaces does that have with the train? What interfaces does it have with the outside world? What interface does it have with other systems? How much of that is going to be real, how much of that is going to be simulated?” said Freeman. Typically that involved breaking the system down into elements of the controller, the actuators that it drives, and the plant - the real world environment that goes on around that - and the sensors that monitor it. Freeman continued: “When we came to the point of how can we realise it, what’s the best software? What’s the best hardware? What’s the best approach to use? That’s where we brought National Instruments to the table.”
What complicates the picture is that there are nine fundamental designs of train carriage and each has many further variations, ranging from the drive systems right down to the lighting in the drivers cabin. Each configuration must be tested as a unique solution. Freeman said; “The National Instruments kit that we used gave us that distributed IO so we could take appropriate test resources and put them where they needed to be on the Train Zero. Every time something changes, it’s relatively simple to make sure that that’s had a negligible impact on the rest of the design.”
Test management
In terms of the software, it quickly became apparent that the NI VeriStand platform was ideal in that it created a single environment in which to combine, execute and manage all the tests. It meant that software and models the suppliers had already worked on could be bought together, irrespective of whether it was in C or C++, MatLab or LabView, it was no longer a bespoke Bombardier environment. “We could compile them altogether, put them all behind a nice neat front-end which looks to all intents and purposes like drive desktop train,” added Freeman, “and not have to throw away things - really great stuff that’s been done by both Bombardier and the suppliers for this new approach. Its allowed us to pick up what already existed, add to it, refine it, take it in a certain direction, but certainly not throw anything away.”
The actual hardware platform behind the Train Zero is PXI based, an advantage of that being in its easy deployment, as Freeman observed: “We’ve got a PXI based hardware platform and VeriStand gives us access to those resources straight out of the box. We can easily configure that hardware within the VeriStand environment to either communicate direct to a controller or we can take our models, compile them, place them within that VeriStand environment and quickly build up the entire train.”
Consequently, Train Zero has the potential of playing an important role in the design process. No longer will suppliers - internal or external – have to work to a initial specification and then hope it works in a final solution. Instead suppliers can use Train Zero as an ongoing part of their own iterative design process, therefore encouraging innovation.
Trains, effectively, can be designed by Bombardier and its partners in tandem, and the first product of Train Zero should be ready in 2017 in advance of the opening of Crossrail.
