The challenge:
Develop three alternator test benches for a military aircraft model. The banks must test three types of alternators (AC, DC and APU), coupled to a shaft that rotates at the speed of the turbine, with different load conditions. The mechanical system that simulates the airplane turbine (drive) must be able to provide a shaft that rotates at the same speed as the airplane turbine (25.000rpm). This is the key part of the project since the high mechanical torque and speeds of up to 25.000 rpm require a highly reliable real-time refrigerant flow and temperature monitoring system so as not to destroy the system. The hardware/software architecture for the control of the automated test of the three benches must provide high reliability against errors and extreme robustness
The solution:
A portable test bench for APU alternators and a fixed mechanical test bench for AC and DC alternators. Both banks are controlled with a cRIO-9082 with a real-time operating system with great determinism and robustness that controls different NI 9144 slaves that allow low-level distributed control and immediate response to failures with high determinism and maximum reliability of the three banks thanks to to their programmable FPGAs.
Introduction
EADS is a world leader in the aeronautics and space, defense and related services sectors. EADS encompasses Airbus, the world's leading manufacturer of the most innovative commercial and military aircraft.
6TL Engineering has more than 25 years of experience as a manufacturer of alternator drive solutions and has been chosen on several occasions as a provider of alternator test laboratories for different aircraft models. In 2012, the European manufacturer EADS needs to equip a new laboratory for testing new alternators and 6TL is once again the selected supplier.
The benches will be used to carry out tests on said alternators in the entire range of revolution regimes by means of speed ramp profiles and working the alternators against different resistive and inductive loads. Those in charge of providing the movement are the drives, based on high-power alternating motors controlled via CANOpen. The sophisticated mechanics in the final stage of the drive guarantee a speed in its output shaft of up to 25.000rpms for the AC and DC banks and 15.000rpm for the APU bank.
Riding at these high speeds implies a lubrication and cooling system that guarantees the health of all mechanical parts. This is achieved by injecting synthetic oil with special benefits in the most critical parts of the system, such as the output bearings, due to their extreme mechanical stresses. Strict monitoring of the temperature of the mechanical parts that get hotter is vital within the bank control system.
This is the reason why they are highly instrumented with temperature probes, flow probes (to detect a correct injection of the oil flow) and pressure probes (to detect a potential obstruction of the refrigeration circuit or any oil leak in the same) The management of the refrigeration, greasing and temperature control of the oil and mechanical components, is carried out by the SLAVES (1 per bank). The SLAVES have been implemented with the NI 9144 devices, but not in their normal distributed periphery operation (which also), but rather they have been endowed with intelligence (through the personalized programming of their FPGA) so that, once received The MASTER orders can work autonomously, controlling variables, alarms and error conditions with maximum speed and without depending on an operating system. This, together with the electrical design of the maneuver, provides great security for the bench in the event of a failure, as it ensures that the system continues to be cooled until the safe stop (for example, in the event of a failure in communications with the MASTER, or by reaching a critical temperature in any bearing). The person in charge of the high-level maneuver is the MASTER, which, implemented in a cRIO-9082 RT, communicates with the SLAVES through Ethercat to achieve the maximum possible determinism and security. Its basic function is to give orders to the SLAVES about what they should do (orders that are executed autonomously in the SLAVE) and it receives the status, and all the bank variables, from them. The MASTER also communicates with the engines via CAN Open to program the desired acceleration and speed. Likewise, the control of the load banks is implemented within the MASTER. In this way the MASTER takes the simultaneous and independent control of the three banks to a higher level than that of the slaves.
The architecture is completed with the user program (HOST) where all the bank's control and visualization options are centralized. The HOST communicates with the MASTER via Ethernet. For this, the LabVIEW "Network Streams" tool has been used bidirectionally (to send orders and to receive the complete status of the MASTER and SLAVES).
On the one hand it is possible to see the alarms present in the system. Also configure the bank (sensor scaling, security limits, etc.). Finally, the main screen contains all the information of the three banks in an accessible way. The developed software architecture allows the benches to be managed independently (each one carrying out a different test) and simultaneously (although it does not necessarily have to be that way).
The HOST SW is developed to be intuitive and error-proof. Unauthorized maneuvers are not allowed depending on the state in which the bank is located. Information is also displayed clearly, using color codes to highlight emergency conditions, the use of indicator lights, etc. If there is a fault in a bank, the bank is stopped safely, but even if the fault has disappeared (for example the temperature has returned to its normal level), the error continues to appear on the alarm screen until it is reset, helping the user to detect the problem that caused the stoppage. At the level of internal operation, all the maneuver orders, both from the user and from the MASTER, are recognized by their receivers, thus ensuring their reception or a pop-up notifying the user that an order has not been recognized. The set provides a very reliable system.
Conclusion:
The NI hardware/software combination used has allowed the development of a complete system meeting the requirements of robustness, determinism, maximum security, and independent control. The development of an intuitive and functional user interface has been achieved. The control of the banks, the management of the maneuver and the user program, hang from a single centralized LabVIEW project, which is the backbone of the development of the project. Through the use of a single tool with its extensions (Real-Time and FPGA), the entire architecture has been deployed from the high level of user to the low level of maneuvering, without having to resort to other systems or programming languages, which has simplified development.
Finally, the result obtained with the test benches built has met the high requirements that were set out, with which the level reached in the execution of the project has been fully satisfactory.
