Tentative workshop schedule and presentation title (A full-day workshop for a plan of 8 hours; then each presentation is about 35 min)

(List below is not in the final sequence of presentation)

Notice for Workshop Registration

1) Conference registrants can sign up for workshops directly through the registration site at ECC 2013 Registration Site

8:30am - 6:00pm - ETH Zurich, 8092 Zurich, Switzerland

* Morning:

Workshop Descriptions

Introduction to Fault-tolerant Control and Cooperative Control: Motivation, Concept, History, Existing and Future Developments, and Applications to a Multiple Quadrotor UAVs Testbed (Dr. Zhang)

Unmanned systems including Unmanned Aerial Vehicles (UAVs) are gaining more and more attention during the last few years due to their important contribution and cost effective application in several tasks such as surveillance, search, rescue, military and security applications. A team of researchers at the Department of Mechanical and Industrial Engineering of Concordia University, with the support from three Canadian-based industrial partners (Quanser Inc., Opal-RT Technologies Inc., and Numerica Technologies Inc.), have been working on a Networked Fault-Tolerant Cooperative Autonomous Vehicles (NFTCAV) research project as well as for Flight Control Systems and Fault Diagnosis and Fault Tolerant Control Systems courses teaching using multiple quadrotor helicopter UAVs. The main objective of the project is to provide theoretical and experimental results on on-line and on-line UAV modeling, cooperative decision-making and tasks assignment, trajectory and path planning, formation flight, fault diagnosis and fault-tolerant control, and at the same time to transfer quickly the research outcomes to the undergraduate and graduate courses teaching. A set of unmanned vehicles testbeds with several quadrotor UAVs have been built at the Department of Mechanical and Industrial Engineering of Concordia University based on the financial support of NSERC (Natural Sciences and Engineering Research Council of Canada) since 2007, with the help of Quanser Inc. for the testbed development. In this presentation, brief introduction to the concept on fault-tolerant control and cooperative control will be given first. Historical development and new challenges in this active research area will be outlined. An overview of our past, current and future research activities and research outcomes on fault diagnosis, fault-tolerant control, path and trajectory planning/re-planning and cooperative control with applications to unmanned systems including the quadrotor helicopter UAV, NASA's GTM fixed-wing UAV and an Airbus A380 model UAV, will be presented.

Iterative Design Towards Improved Fault Tolerance: A Framework for Improved SUAS Airworthiness (Dr. Chen)

In order to guarantee the airworthiness of a SUAS, there are some redundancies that need to be implemented in the design of UAS. But too many redundancies place a hard condition on the payload of UAS. This presentation aims at providing recommendation on what kind of faults in actuators are forbidden that we should make a backup in the design of UAS and what kind of faults are allowed without affecting the performance of UAS. It is common that when design a feedback controller the physical property of system are often overlooked. In this presentation, we put the 'physics' of UAV back in the design of fault tolerant controller for a fixed-wing test-bed and we try to find what are the maximum faults that can be tolerated in this kind of UAS. The results presented are intended to support the ongoing discussion on airworthiness and SUAS integration into the National Airspace System. Simulation results with different faults are also presented to validate the effectiveness of the presented fault tolerant controllers and other related airworthiness techniques.

Sliding Mode Schemes for Fault Detection and Fault Tolerant Control (Dr. Edwards)

Sliding mode methods have been historically studied because of their strong robustness properties to a certain class of uncertainty. This is achieved by employing nonlinear control/injection signals to force the system trajectories to attain in finite time a motion along a surface in the state-space. The associated reduced order dynamics, whilst constrained to the surface is called the sliding motion, and possess strong robustness properties. This talk will consider how these ideas can be exploited for fault detection (specifically fault signal estimation) and subsequently fault tolerant control. The talk will also describe an application of these ideas to aerospace systems. It will describe flight simulator results associated with the EL-AL 1862 Bijlmermeer scenario studied as part of the GARTEUR AG16 action group on fault tolerant control. The controller design was carried out without any knowledge of the types of faults/failures occurring on the aircraft, and employs sliding mode methods. The results demonstrate the successful real-time implementation of the proposed fault tolerant control scheme on a motion flight simulator configured to represent the EL-AL aircraft.

Tools for Teaching Autonomous Unmanned Vehicle Systems (Mr. Fulford)

Unmanned Vehicle Systems (UVS) are growing in popularity across a broad spectrum of applications such as search and rescue, military, mining, and environmental surveillance. Likewise, the UVS research community is growing and there is an increasing demand for novel hardware and software platforms on which to develop and test UVS algorithms and controllers.

To meet the growing demand for new technologies to teach and develop the next-generation unmanned systems, this workshop presents the latest technologies for UVS teaching and research. As part of this workshop, we will review how leading universities have integrated autonomous unmanned systems into their teaching and research programs using this state-of-the-art rapid controls prototyping framework and open-architecture data acquisition hardware designed for unmanned systems. This workshop will also demonstrate how innovative hardware-in-the-loop systems can be used to augment virtual 3D UVS missions in order to teach fundamental control concepts while motivating students with exciting, real-world UVS applications. More advanced concepts will be introduced with specific focus on tools for autonomous unmanned vehicle systems. Demonstrations will show autonomous unmanned vehicle missions planned out and executed in simulations with rendered 3D visualization. Topics and Target Audience: - Autonomous unmanned systems for teaching and research; - Rapid control development tools; - Real-time control; - Tools for simulation and operation; - Curriculum for unmanned vehicle systems.

Fault Diagnosis and Fault Tolerant Control for Civil Aircraft: Industrial State-of-Practice for Flight Control Systems (Dr. Goupil)

This presentation deals with industrial practices and strategies for Fault Tolerant Control (FTC) and Fault Detection and Diagnosis (FDD) in civil aircraft by focusing mainly on a typical Airbus Electrical Flight Control System (EFCS). This system is designed to meet very stringent requirements in terms of safety, availability and reliability that characterized the system dependability. Fault tolerance is designed into the system by the use of stringent processes and rules, which are summarized in the presentation. The strategy for monitoring (fault detection) of the system components, as a part of the design for fault tolerance, is also described in this paper. Real application examples and implementation methodology are outlined. Finally, future trends and challenges are presented. A focus is made on the global optimization of the future aircraft towards a more sustainable flight guidance and control. Indeed, highlighting the link between aircraft sustainability and FDD, it can be demonstrated for example that improving the fault diagnosis performance in flight control systems allows to optimize the aircraft structural design (resulting in weight saving), which in turn helps improve aircraft performance and to decrease its environmental footprint.

Observed-based Fault Diagnosis Incorporating Online Control Allocation for Spacecraft Attitude Stabilization under Actuator Failures (Dr. Hu)

This work proposes a novel observed-based fault diagnosis incorporating online control allocation scheme for an orbiting spacecraft in the present of actuator faults/failures, unexpected disturbances and even input saturation. The proposed scheme solves a difficult problem of spacecraft fault tolerant control design that compensates for severely total loss of actuator effectiveness failure and even time-varying fault so that the overall system is stable even further under external disturbances and input saturation as well. This is accomplished by developing an observer-based fault diagnosis mechanism to reconstruct or estimate the actuator faults/failures. Accordingly, an online control allocation scheme is then used to redistribute the control signals to the healthy actuators in the case of faults/failures without reconfiguring the controller, in which the control signal distribution is based on the reconstructed actuator effectiveness level. Simulation results using a rigid spacecraft model show good performance in fault, even certain total actuator failure scenarios and external disturbance as well as actuator input saturation, which validates the effectiveness and feasibility of the proposed scheme.

Recent Progress on Tolerant Flight Control for Damaged Aircraft (Dr. Liu)

Based on previous work on passive fault tolerant control to aircraft that suffers from vertical tail damage, it investigates recent progress both in theoretical development and in application front. Theoretical development includes the parameterization in fault detection and filter design; the extension of passive fault tolerant control to active FTC; as well as a recent work in time-variant domain. In application front, nonlinear aircraft model has been developed to test the applicability of the proposed design. Different application cases as well as flight simulation results are also introduced.

Hinf Detection, Isolation and Tolerant Control: A Tutorial on Aerospace Applications (Dr. Marcos)

The fields of fault detection and isolation (FDI) and fault tolerant control (FTC) have attracted much attention from control engineers, especially in the (aeronautical and space) flight control community during the last thirty years. The most common approach to provide a system with FDI/FTC functionality is to use hardware redundancy and voting schemes. The main drawbacks with this approach are the added complexity and the costs resulting from the additional weight and volume of the redundant elements, which especially critical in aerospace systems. Model-based FDI approaches address those drawbacks using a mathematical model of the monitored system to detect, identify and compensate or correct abnormal behaviour. Since no mathematical model is exact, robustness to modeling uncertainty becomes a critical issue. Among the model-based methods, those based on Hinf optimization are increasingly of interest due to the explicit treatment of uncertainty in its formulation. In this tutorial a practical look is presented to the design of open-loop Hinf FDI filters and integrated inf FTC controllers for aerospace applications.

Model-based Fault Diagnostic and Fault-tolerant Control of an Over-actuated UAV (Dr. Noura)

Several studies have dealt with fault-tolerant control to make UAVs achieve their mission with more reliability and safety. So far, very few methods were demonstrated through real applications. The FTC problem is based on two main steps: monitoring the health of the UAV and modifying the control law according to the malfunction detected and isolated. The objective is to present an overview of the major faults (sensors, actuators, controllers, components) in aircrafts in general and mainly in UAVs. The problem of FTC for UAVs and its importance will be stated and the latest techniques developed will be presented. Control surface failures will be mainly considered. Signal-based and model-based FDD techniques will be presented. Cases of non-measured actuator positions and redundant actuators will be also addressed. Control surface failures may reduce the flight envelope and the UAV may become unstable. Moreover to compensate for the faults, the healthy actuators may operate close to their saturation position. FTC design is led taking into account these various aspects.

Fault Diagnosis and Tolerant Control of Aerospace Systems using LPV Techniques (Dr. Puig)

The problem of robust fault detection is addressed using an adaptive threshold generation for non-linear systems described by means of LPV models. Adaptive thresholds are generated using an interval LPV observer that generates a band of predicted outputs taking into account the parameter uncertainties bounded using zonotopes. The interval LPV observer is designed via pole placement using Linear Matrix Inequalities (LMI). LPV fault sensitivity analysis is used to characterize the minimum detectable fault as well as to determine the limitations of proposed FDI strategy. The isolation task uses the fault estimation to isolate the faults. Fault estimation relies on the knowledge about the faulty system behavior using the fault sensitivity concept.

On the other hand, the FTC problem is addressed using three approaches. The first one is a LPV FTC design based on Admissible Model Matching (AMM), where a set of admissible models is used, which provide stability/performance guarantees. The main contribution of this approach is to accommodate the controller guarantying that the system closed-loop behavior is in the set of admissible behaviors. This accommodation involves the on-line controller reconfiguration in presence of parametric faults and the fault estimation. This estimation is considered as a scheduling variable that allows the reconfiguration of the controller. The second approach consists in adapting the faulty plant to the nominal controller instead of adapting the controller. That is, the faulty plant together with the reconfiguration block allows to the controller to see the same plant as before the fault. When a sensor fault is considered, an observer is used to calculate a replacement value. This approach is known as virtual sensor. By duality, the results can also be applied to derive a virtual actuator when the actuator fault is considered.

Finally, an integrated FTC design procedure for LPV systems that considers the fault estimation using an unknown input observer and a virtual actuator is proposed. The FTC controller is implemented as a state feedback controller. This controller is designed such that it can stabilize the faulty plant using LPV techniques and LMIs.

The effectiveness and performances of the FDI/FTC methods will be illustrated with several examples with special emphasis in a two-degree of freedom helicopter.

Design of Fault-tolerant Control Methods Based on Reliability (Dr. Theilliol & Dr. Zhang)

Faults or failures such as defects in components, instruments, controllers and/or control loop can cause undesired reactions and consequences such as damages to technical parts of the plant, to human life or to the environment. Traditionally, the objective of Fault Tolerant Control System (FTCS) is to maintain its current performance close to the desired one and preserve its stability conditions despite of component and/or instrument faults; in some circumstances a reduced performances may have to be accepted as a trade-off leading to a sub-optimal outcome. Design of control systems to achieve fault-tolerance for closed-loop control of safety-critical systems has been an active area of investigation for many years. It becomes more and more clear that there are certain trades-offs between achievable normal performance and fault-tolerance capability. However, despite of the many efforts in control community, most of the contributions did not consider or take into account the reliability of components, algorithms or soft computing structures to guarantee such performance and to reduce the gap between nominal and faulty case. This contribution aims at presenting new and innovative research results on how to design Fault Tolerant Control Systems with particular attention to consider and combine reliability analysis in the design procedure and/or real-time control synthesis. Current and future research is presented in order to solve the above challenging research problems devoted to safety-critical systems such as flying vehicles, unmanned aerial vehicles (UAVs), missiles, airships etc.

Multiple UAS Operations: Toward Verifiable Autonomy (Dr. Tsourdos)

There are many applications using autonomous systems such as unmanned aerial vehicles: surveillance/attacking, traffic monitoring, search and rescue, and so on. Nowadays the applications and missions become so various and complex that the systems become more complicated. Those missions are related not only with civil purpose but also with military one so usually safety-critical. Diverse sensors are equipped in the systems for safety and redundancy, furthermore, a group of autonomous systems has been recently considered for more effective mission performance. As the systems are complicated, reliability of systems must be verified at the design level. There are some methods to verify the reliability of systems at the design level such as a simulation in a virtual environment, a test with a mock-up, and formal methods. Firstly, test with a mock-up costs a lot of money and time to perform and does not always guarantee the safety during it processes. Simulation costs less money and time than for the test, but it is not always easy to consider all the possible scenarios and situations. In contrast formal methods are based on solid mathematical techniques and offer quantifiable answers to questions related with reliability of systems, and thus they are widely used to verify the safety-critical or high-autonomy systems. Model-checking is an automatic technique based on formal methods for verifying finite state system. It checks whether the system satisfy the properties or not automatically. There are three parts of process in model-checking: modeling, specification, and verification. This contribution aims at presenting new and innovative research results on how to model multiple UAS systems as multi-agent systems using formal methods to captures their specifications that would enable to validate their performance and finally how to verify their performance in the presence of faults.

Workshop materials:

To be delivered to participants during and before workshop with the presentation slides, notes and other necessary supporting documents.

Workshop References (Author with bold face is one of the speakers at this workshop):

- Halim Alwi, Christopher Edwards, and Chee Pin Tan, Fault Detection and Fault Tolerant Control using Sliding Modes, Springer, 2011.

- Antonios Tsourdos, Brian White, and Madhavan Shanmugavel, Cooperative Path Planning of Unmanned Aerial Vehicles, Wiley, 2011.

- Christopher Edwards, Thomas Lombaerts, and Hafid Smaili (Eds.) Fault Tolerant Flight Control: A Benchmark Challenge, Springer, 2010.

- Camille-Alain Rabbath and Nicolas Lechevin, Safety and Reliability in Cooperating Unmanned Aerial Systems, World Scientific Publishing, 2010.

- Hassan Noura , Didier Theilliol, Jean-Christophe Ponsart, and Abbas Chamseddine, Fault-tolerant Control Systems: Design and Practical Applications, Springer, 2009.

- Mufeed Mahmoud, Jin Jiang, and - Youmin Zhang-, Active Fault Tolerant Control Systems: Stochastic Analysis and Synthesis, Springer, 2003.

- Youmin Zhang and Jin Jiang, Bibliographical Review on Reconfigurable Fault-tolerant Control Systems, Annual Reviews in Control, vol. 32, no. 2, Dec. 2008, pp. 229-252 (Ranked No. 1 in the "Top 10 Cited" and No. 6 in "Most Downloaded" articles published in the last five years at the journal).

- Other references will be provided during the workshop to participants.