Roger Ezekiel Beck

Bio: Roger Ezekiel Beck is an academic researcher. The author has contributed to research in topics: Linear programming & Linear system. The author has an hindex of 1, co-authored 1 publications receiving 36 citations.

Backstepping and control allocation with applications to flight control

Abstract: In this thesis we study a number of nonlinear control problems motivated by their appearance in flight control. The results are presented in a general framework and can also be applied to other areas. The two main topics are backstepping and control allocation.Backstepping is a nonlinear control design method that provides an alternative to feedback linearization. Here, backstepping is used to derive robust linear control laws for two nonlinear systems, related to angle of attack control and flight path angle control, respectively. The resulting control laws require less modeling information than corresponding designs based on feedback linearization, and achieve global stability in cases where feedback linearization can only be performed locally. Further, a method for backstepping control of a rigid body is developed, based on a vector description of the dynamics. We also discuss how to augment an existing nonlinear controller to suppress constant input disturbances. Two methods, based on adaptive backstepping and nonlinear observer design, are proposed.Control allocation deals with actuator utilization for overactuated systems. In this thesis we pose the control allocation problem as a constrained least squares problem to account for actuator position and rate constraints. Efficient solvers based on active set methods are developed with similar complexity to existing, approximate, pseudoinverse methods. A method for dynamic control allocation is also proposed which enables a frequency dependent control distribution among the actuators to be designed. Further, the relationship between control allocation and linear quadratic control is investigated. It is shown that under certain circumstances, the two techniques give the same freedom in distributing the control effort among the actuators. An advantage of control allocation, however, is that since the actuator constraints are considered, the control capabilities of the actuator suite can be fully exploited.

Spacecraft thruster control allocation problems

Abstract: We consider the control allocation problem in a spacecraft thruster configuration. It consists on the determination of the force command to be sent to each thruster in order to point the total torque and/or thrust vectors. Here, we state four possible practical problems and propose a control allocation algorithm based on a subgradient optimization, which is shown to be faster than existing allocators.

Fault-tolerant Control Allocation for Multirotor Helicopters Using Parametric Programming

Abstract: This paper addresses the issue of flight safety and reliability of unmanned multirotor helicopters. New applications involve the use of such flying platforms to perform inspection of industrial facilities, bridges, dam walls, etc. In this context, the multirotor helicopter is teleoperated by a distant human user. 1 The capability of fault-tolerance against rotor or motor is a major asset to guarantee the success of the mission and the safety of the surrounding environment. This paper contributes to fault-tolerant flight of multirotor helicopter with the following four points. First, given the configuration of the multirotor vehicle, this paper shows how to calculate the maximum torques that can be produced on each vehicle axis. Second, a method to investigate the static controllability of the vehicle in any arbitrary fault configuration is described. Third, a control allocator for multirotor systems is developed with performance going beyond performance obtained with classical methods, such as the pseudo-inverse method. The proposed control allocator is indeed capable of exploiting the whole attainable control set. Fourth, this control allocator is fault-tolerant, as it can efficiently cope with the loss of one or more actuators. The control allocation problem is formulated as a parametric program and solved for an explicit solution, which is stored in lookup tables. Therefore, the control allocator requires very low computational power and immediately provides an optimal solution to the torque commands issued by the flight controller. The performance of the control allocator is evaluated on a real six-rotor helicopter. Finally, based on the real experiments, the paper investigates 1) the impact of faults and 2) the influence of the reconfiguration delay on the flight stability. These experiments show that this control allocation strategy successfully increases flight performance and maintains stability of the vehicle in case of actuator(s) total failure.

Aircraft Load Alleviation During Maneuvers Using Optimal Control Surface Combinations

Abstract: Control laws in aeronautics are designed to ensure, above all, good handling qualities. However, during extreme maneuvers, which have to be taken into account for aircraft certification, a number of critical structural load limits cannot be guaranteed by this baseline controller. To avoid some modifications of the control law, a solution consists of judiciously exploiting the redundancy of the control surfaces. The aim of this paper is first to find an optimal strategy of the control surface use, which leaves the initial flight behavior unmodified but alleviates a structural load during a selected maneuver. Model predictive control theory solves this offline control allocation problem under actuator saturation constraints. In addition, an identification procedure is proposed to synthesize a new mixing unit that can reproduce this optimal strategy. This methodology is applied to a flexible transport aircraft to alleviate the bending moment at the external wing during a sudden and strong roll maneuver.