Aug 28 2007
Multimillion dollar budgets and massive equipment make the recent commissioning of 42 eight-axis motion controllers with more than 200 motors and amplifiers from Motion Solutions Australia perhaps the country's biggest motion control project. But what makes this such an interesting case study is the uncompromising operating environment of Australia's new $350 million OPAL nuclear reactor.
Opened by Prime Minister John Howard in April 2007, the OPAL reactor produces most of the radiopharmaceuticals used in Australia. OPAL is also home to the $35 million Neutron Beam Instrument Project (NBIP) undertaken within ANSTO’s Bragg Institute. The OPAL neutron beam instruments utilise a non-invasive technique known as neutron scattering, which allows scientists to investigate the atomic structure of new materials, chemical reaction kinetics and biological processes. 'Big things' are expected from the Bragg Institute. Its new technology is attracting the best and the brightest scientists from all around the world – so much so, bookings for time with the Bragg Institute’s instruments are expected to be oversubscribed by a factor of two.
Each of the Bragg Institute’s eight instruments will run 24 hours a day, 340 days per year and has an accounting charge out rate of between $5,000 and $10,000 per day. The success of the facility hinges on its reputation for flawless accuracy and instrument reliability. Motion control with the utmost precision is essential, explains Bragg Institute electrical project engineer for the Australian Nuclear Science and Technology Organisation (ANSTO), Dr Frank Darmann.
"The Bragg Institute’s new instruments will be so popular, ANSTO can cherry pick the best scientists when it's taking bookings and hopes breakthroughs that lead to quality publications in highly respected journals and potentially, a Nobel Prize, will be made here," he says, "but users won't come if the machines break down or the accuracy is low. To do great science, you not only need inspired and talented scientists but you also need equally talented, motivated and dedicated technicians, draftsmen, and engineers. Without them, no instrument will be of the right quality to attract international scientific talent."
With that in mind, Dr Darmann took no chances when selecting and integrating the overall motion control solution for the neutron scattering instruments, testing the alternatives for six months at a cost of $380,000, representing 12 per cent of the $3 million budget for the electrical engineering and motion control installation.
"I bought a controller, drives and motors for one of the instruments from three different suppliers," he says, "They didn't know the scale of what we were planning here. Support was, and is, very important to us. If people don't reply to emails you can be sure they won't be responsive in an emergency. Only one of them, Motion Solutions Australia, showed they were interested by answering our questions quickly, knowledgeably and conscientiously."
Also among the criteria for selection was simplicity of integration. Since the programming was to be completed by ANSTO staff members, Dr Darmann was determined to standardise on one relatively easy to use system.
"The project is complex enough already without making it needlessly more complicated," he says. "I worked on each of the systems initially to establish a benchmark. I also had a student work on each of the motion control systems to see if he could work them out in an afternoon. Some of them we never managed to fully integrate with the motor drivers and encoders – they were just too tricky, had no or minimal local support, required special encoder interface electronics or the overseas support was woeful. So we abandoned them."
"In contrast, the components supplied by Motion Solutions Australia, which included Galil motion controllers, Parker stepper drives and Empire Magnetics radiation hardened motors weren't difficult to use. For example, we have feedback via a 1 MHz synchro-serial interface, a standard motion encoder data format. The Galil controller accepts this signal format as standard so all that is required is to do the configuration in the controller’s program and it works. We have completed this on 168 axes so far with zero problems.”
The NBIP is technically challenging and called for sophisticated precision motion control. Each instrument has between 24 and 32 axes and each axis of motion is encoded with precision absolute encoders.
"Using contract and expert ANSTO staff, we constructed the motion control centres for all instruments in–house," Dr Darmann said.
"This meant we could control the quality of the installation of the Galil controllers and the way they were integrated, thereby fully leveraging all the benefits of the Galil controller. It would be no use having the best value controllers in the world if the whole package surrounding them was not managed very closely. We needed a system that was reliable, maintainable, and upgradeable. The specifications on neutron scattering instruments rarely stay constant – scientists always push the boundaries of what’s possible. The Galil controller and the integrated system allow that to occur relatively easily.
"We also had to decide whether to use absolute encoders or incremental encoders across the 200 axes. Incremental encoders lose their position when the system is turned off or fails. That means upon initialisation or recovery, each axis must be tared off or homed to some fixed point and then moved back to where it was. This is time consuming and can be inaccurate.
"Absolute encoders can remember their last location. The decision to go with absolute encoding was made after careful consideration and visits to seven similar European institutions. By employing an absolute encoding technique, we have eliminated one more risk of instrument downtime during operations – an important one, given there are over 200 encoders in the project. That decision cost the project $270,000 but, when one considers that these instruments have a daily charge out rate of between $5,000 and $10,000, it was a small price to pay."
The cost of the project reflects the scale and uniqueness of the tasks at hand, says Dr Darmann.
"The NBIP is a big project in lots of ways. Plenty of movement demands a lot of motors, the instruments typically cover 42 square metres or more and you're moving at least 700kg around on precision polished granite floors. And then, this is anything but a typical application because we also need a high level of accuracy, reproducibility and resolution with such large masses. Some of the motors are radiation-hardened and cost multiples of standard motors, for example. We needed an amplifier and controller system that could control specialised and relatively small yet expensive motors."
"Apart from cost, the unusual requirements add to the importance of good support from the supplier and we've been very grateful to Motion Solutions Australia for that. Galil, for example, uses 25-bit feedback as standard but we needed 32-bit feedback. They wrote new firmware for us and we had it in place within eight weeks. We wouldn't have got that elsewhere."
The Motion Solution Australia lead engineer who worked closely with Dr Darmann, Matthew Dorhauer, says “working with Dr Darmann and ANSTO engineers has been a rewarding and challenging experience”. In fact, says Motion Solutions Australia manager Clem Berenger, the NBIP motion control installation, which he believes is the largest of its kind in the country, has developed a new Austral