Developing a Specialized Test Bench for Aircraft Alternators
"We combined NI CompactRIO hardware with NI LabVIEW software to create a complete system that meets the requirements of power, determination, maximum security, and independent control."
- David Batet,
Developing three test benches for AC, DC, and auxiliary power unit (APU) alternators on a military aircraft model.
Using NI CompactRIO and NI LabVIEW to create a portable test bench for APU alternators and a test bench with fixed mechanics for AC and DC alternators.
Our company, NI Silver Alliance Partner 6TL Engineering, has more than 25 years of experience as a solutions provider for alternator control, and has been chosen several times as an alternator test bench provider for different aircraft models. In 2012, the European manufacturer EADS chose our company to create a test laboratory for new alternators. EADS is a worldwide leader in the aeronautics, space, defense, and services sectors. Airbus, a company in the EADS group, is one of the main manufacturers of the most innovative military and commercial aircraft.
EADS needed to test the aforementioned alternators across the entire range of engine speeds by observing speed ramp profiles and alternators working against different resistive and inductive loads.
The drive provides movement based on high-power AC motors controlled via CANopen. The sophisticated mechanics in the final stage of the drive ensure speed in its output shaft of up 25,000 rpm for AC and DC benches and 15,000 rpm for the APU bench. Rotation at these high speeds implies a lubrication and cooling system that ensures the safety of all mechanical parts. This is achieved by injecting synthetic oil for special uses in the most critical parts of the system, such as the output bearings, given the extreme mechanical stress they are under.
Strict monitoring of the temperature of the mechanical parts that reach the highest temperatures is vital in the control system of benches. The system is equipped with temperature sensors, flow sensors to detect correct oil flow injection, and pressure sensors to detect a potential blockage of the cooling circuit or any leakage of oil into the system.
The cooling, lubrication, and oil temperature control and mechanical components handling management are carried out by “slaves” (one per bench). We implemented slaves with the NI 9144 EtherCAT C Series chassis, but not in their normal operation of distributed periphery. The slaves are intelligent through customized FPGA programming so that, upon receipt of the orders from the master, they can work autonomously to control variables, alarms, and error conditions with maximum speed and without relying on an OS. This, coupled with the electrical design of the maneuver, provides great security for the bench in case of failure, because it ensures the system remains safely cooled until safe stop (for example, in the case of a drop in communications with the master, or if any bearing reaches a critical temperature).
The master is in charge of the high-level maneuver, which is implemented in an NI cRIO-9082 RT controller and communicates with the slaves via EtherCAT for the maximum detection and security possible. The controller’s basic function is to give orders to the slaves on what to do, which the slaves carry out autonomously, and to receive status and all variables from the benches.
The master also communicates with the engines via CANopen to program the desired acceleration and speed. Furthermore, the load bench control is implemented in the master. Thus, the master carries out the simultaneous and independent control of the three benches at a higher level than the slaves.
The architecture is completed by the user software, called ”host,” that we created using NI LabVIEW. The software is the central location for bench control and monitoring. The host communicates with the master via Ethernet. For that purpose, we used the network streams tool bidirectionally to send commands and receive the full status from the master and slaves.
The user can see the alarms in the system and configure the bench with scaled sensors and safety limits. The main screen contains all of the information of the three benches. With the software architecture we developed, the user can independently and simultaneously manage the benches, with each performing a separate test.
We developed the host software to be intuitive and fail-safe. Depending on the status of the bench, unauthorized maneuvers are not allowed. The information is clearly shown using color coding to highlight emergency conditions.
If there is a failure in a bench, the bench safely stops, but even if the failure disappears (for example, the temperature returns to normal), the error still appears in the alarms display until reset to help the user find the problem that caused the shutdown. At the level of internal operation, all operation commands both from the user and master are recognized by their receptors, thereby ensuring the receipt of the same, or a pop-up alerting the user that a command is not recognized.
NI Products Meet High Standards
We created an intuitive, functional user interface, along with bench control, maneuver management, and the user program, in a single LabVIEW program that coordinates the development of the whole project. By using a single tool with its extensions (LabVIEW Real-Time Module and LabVIEW FPGA Module), the whole architecture was deployed from the high user level to the low maneuver level without resorting to using other systems and programming languages, which simplified development. The results obtained with the test benches we built meet the high standards required.
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