Disconnect device for jam tolerant linear actuators

Final Report Summary - FASTDISC (Disconnect device for jam tolerant linear actuators)

Executive Summary:
The FASTDISC project is part of the CleanSky activity System for Green Operations (SGO). One demonstration objective in this research program is the development of a fully electric swash plate actuation.
For fully electrical helicopters the electrification of the primary flight control is considered to be the key technology. The primary flight control of helicopters is performed by positioning of a swash plate with three degrees of freedom. Since the loss of one of these degrees of freedom is classified as safety-critical, the control system requires a fail-safe and fault-tolerant design. The research focuses at the direct replacement of hydraulic actuators by electromechanical ones. A special feature of the electromechanical actuators is that the mechanical jam of the drive train is classified as a safety-critical failure. In the current approach redundant electromechanical actuators are implemented on system level, while a disconnect device (DD) is installed in the drive train of each actuator to prevent a potential mechanical jam failure. When a jammed electromechanical actuator is decoupled from the flight control system, the redundant actuators are still capable to take over the control function.
One main contribution to this technology is followed up in the HEMAS project which comprises an electromechanically actuated DD. The FASTDISC project aims at improvements on the design, further analysis on DDs and the realisation of two advanced designs covering the following principles:
reversible disconnect device (RDD), preferred electromechanical
irreversible disconnect device (IDD), preferred pyrotechnical
The project work was devided in three work packages:
Study and evaluation of disconnect device concepts
Disconnect devices detailed design
Disconnect devices manufacturing and validation testing
And carried out by 4 cooperation partners:
the Institute of Engineering Design and Industrial Design of the University of Stuttgart (USTUTT)
the Italian company Umbra (Umbra)
the German company PyroGlobe (PyroG)
the Swiss company phi Engineering (phi)
In concept studies six reversible and six irreversible mechanisms were developed and described in detail. An electro-magnetic principle for the RDD and a pyrotechnical principle for the IDD were selected for detailed prototype design.
The detailed design and the test specification were approved during the CDR. For both RDD and IDD prototypes were manufactured.
Most of the test addressed in the validation testing could be passed successfully. Especially the disconnect functionality and the endurance and the environmental capabilities could be validated. Only the RDD show an insufficient disconnect behavior if only one coil of the solenoid is activated and at low temperatures. Other shortcomings are insufficient static stiffness of the IDD and insufficient backlash of both RDD and IDD. Therefore, design modifications and recommendations were derived to achieve the requirements and for improvement of the prototype design.
As a result, the project work has carried out disconnect devices heigly reliable for primary flight control systems, in compact design for the swash plate actuation and of low weight for aerospace applications.

Project Context and Objectives:
Objective of the project was the development, manufacture and validation testing of disconnect devices (DDs) for integration in the drive train of an electromechanical actuator to prevent a potential mechanical jam failure. The investigations covered two different priciples, one fully testable reversible system (RDD) and one irreversible or “Single Shot” system (IDD) that may be not pre-flight testable.
The project work was devided in three work packages:
The 1st work package focused on the identification of requirements and concept studies for DDs. Objective was the selection of concepts for further development each for the RDD and for the IDD.
The 2nd work package focused on the development of the selected concepts. Objective was the detailed design of the prototypes and the definition of the preliminary test plan for the validation testing.
The 3rd work package focused on the implemantation and the validation testing of the test specimen. Objective was the verification of the required functionality of the DDs together with the generation of improvements on the design w.r.t. the evaluation of the test results. Furthermore, the project documentation was part of this work package.
Therefore, the project work was carried out by 4 cooperation partners:
The Institute of Engineering Design and Industrial Design of the University of Stuttgart (USTUTT) has research experience in and expert knowledge on the development of fast operating connect/disconnect devices.
The Italian company Umbra (Umbra) is a highly competent manufacturer and supplier of components for the aerospace industry like ballscrews, actuators and EMA drives.
The German company PyroGlobe (PyroG) is a highly competent manufacturer and supplier of pyrotechnical components and will participate on the irreversible system.
The Swiss company phi Engineering (phi) has experience in methodical product development and the development and testing of electromechanical actuators.
In the following sections the scope of work and the results of the several work packages are discriped in detail.
2.1 Work Package 1 Study and evaluation of disconnect device concepts
2.1.1 Work Package 1.1 Identification of requirements
The main function of the mechanisms is to compensate mechanical jams of the actuator drive trains. Therefore, in this work package the general description of highly available actuator arrangements and the definitions/classifications of the most relevant characters relating to the DD were outlined. Focusing on the decoupling function, a literature study summarizes and evaluates the most relevant patents and publications with respect to this topic. The deliverable of WP 1.1 is the approved list of requirements.
2.1.2 Work Package 1.2 Concept studies for disconnect devices
Based on the list of requirements, this work package addressed the concept studies for RDDs and IDDs by using methodical product development tools. The first development step involves the abstracted task formulation to recognize the essential challenges. The following step contains the generation of the different function structures for reversible and irreversible designs. The derived active principles are combined to active structures. Six reversible and six irreversible mechanisms are selected and described in detail. In the last step the selected concepts are evaluated with respect to the appointed criteria (see Call for Proposal) and additional criteria from the list of requirements. The results of these investigations were presented in the concept design review. In this connection an electro-magnetic principle for the RDD and a pyrotechnical principle for the IDD was selected for detailed prototype design.
2.2 Work Package 2 Disconnect devices detailed design
2.2.1 Work Package 2.1 Development of the selected concepts
At first the preliminary design of the RDD and the IDD comprising the dimensioning, investigations on the functionality, definition of interfaces and integration of the devices into the EMA was carried out. The preliminary design was approved during the Preliminary Design Review and is shown in Appendix A.
2.2.2 Work Package 2.2 Prototype design of the disconnect devices
Based on the results of the Preliminary Design Review the detailed design of the RDD and the IDD comprising functional and stress analysis for subassemblies and components, design and shop drawings for electromechanical and mechanical parts, definition, selection and sourcing of purchase parts and consumables was performed. The detailed design of the prototypes was approved during the Critical Design Review.
2.2.3 Work Package 2.3 Development of test scenarios and settings
Based on the results of the Preliminary Design Review the preliminary validation test plan including test facilities, test methods, list of test cases and success criteria w.r.t. the required functionality was defined and approved during the Critical Design Review.
2.3 Work Package 3 Disconnect devices manufacturing and validation testing
2.3.1 Work Package 3.1 Manufacture of parts and components for the first prototypes and the test facilities
Based on the detailed design of the DDs and the preliminary validation test specification necessary documents for the manufacturing of the prototypes and preparation of the test rigs were prepared. Major task was the manufacture of the prototypes containing two specimens for the RDD und one specimen for the IDD. Furthermore, the preparation of the test facilities was performed. For basic static tests a test rig of Airbus and for extended static and dynamic tests test rigs of Umbra were foreseen. Appendix B shows the manufactured prototypes.
2.3.2 Work Package 3.2 Detailed specification for the validation testing
Based on the priliminary test specification the final definition of the validation testing of the prototypes was worked out. This includes basic static tests focussing the disconnect function, extended static tests focusing stiffness, environment and dynamic tests focussing endurance and extended functional limits like unintended disconnection. To give an overview, the validation test matrix described in the deliverable of WP 3.2 is presented in Appendix C.
2.3.3 Work Package 3.3 Execution of validation testing according to test specification
Objective of this work package was the performance of the validation testing of the prototypes.
Basic static tests for the RDD were performed at USTUTT. The tests show some unexpected results as the required disconnect function could not be provided for the basic RDD design w.r.t. insufficient activating force.
Therefore, for the extended static and dynamic tests the material of the solenoid was modified. All tests could be passed successfully with the exception of:
Partly compliant disconnection capability. The modified solenoid material causes a more stable disconnection behavior but is still insufficient in case only one of the two redundant solenoids is activated.
Insufficient backlash.
Partly compliant environmental capability. All tests in the temperature range of -20 up to 180 °C were passed successfully, but the tests at low temperatures of -40 °C and -54 °C show an insufficient disconnection behavior.
Basic static tests for the IDD were performed at PyroGlobe and extended static and dynamic tests were performed at Umbra. All tests could be passed successfully with the exception of:
Insufficient static stiffness.
Insufficient backlash.
In Appendix D some important test results are shown.
2.3.4 Work Package 3.4 Evaluation of the validation testing and continuative improvements on the disconnect devices
Objective of this work package was the evaluation of the validation testing and the derivation of design modifications and recommendations.
For the non compliant requirements of both the RDD and the IDD root cause anlyses were performed. Design modifications and recommendations were derived to achieve the requirements and for improvement of the prototype design. The results were presented and discussed at the final project meeting and accepted by the topic manager. Therefore, it is evident that this has to be addressed in subsequent investigations.
The specification compliance matrix is outlined in Appendix E for both concepts.
2.3.5 Work Package 3.5 Project documentation
The objective of this work package is the preparation of the technical documentation. The report lists all technical documents related to the project.
2.3.6 Work Package 3.6 Project conclusion
The objective of this work package is the preparation of the final report. The present report will be the publishable summary part of the final report.

Project Results:
The project work has carried out two principles of disconnect devices for the disconnection of electromechanical actuators applied in primary flight control system especially the swash plate actuation:
fully testable electromechanical design meeting partly the disconnect functional requirements,
not fully testable pyrotechnical design meeting all disconnect functional requirements.
The main advantages of the developed disconnect devices are:
heigly reliable design applicable for primary flight control systems,
compact design convenient for the implementation in the swash plate actuation,
low weight of the RDD and extrem low weight of the IDD meeting the leight weight construction requirements for aerospace applications.
Some items of the requirement specification could not be achieved. Therefore, design modifications and recommendations were derived and should be addressed in subsequent investigations.

Potential Impact:
The developed disconnect devices demonstrate the possibilities on one hand for the application of electromechanical actuators in primary flight control systems and on the other hand for the replacement of hydraulic actuators by electromechanical ones.
The first item enables to look for prospective applications in primary flight control suitable for electromechanical actuation.
The second one offers a broader view on linear actuators especially for industrial applications and safety critical applications.

List of Websites:
http://www.iktd.uni-stuttgart.de/forschung/antriebstechnik/FASTDISC/index.php?lang=en

Final Report Summary - FASTDISC (Disconnect device for jam tolerant linear actuators)

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