Disturbance observer based sliding mode control for unmanned helicopter hovering operations in presence of external disturbances

Numerous control techniques are developed for miniature unmanned helicopters to do hover operation with each method having its own advantages and limitations. During the hover operation helicopters suffer from unknown external disturbances such as wind and ground effect. For a stable operation, these disturbances must be compensated accurately. This paper presents a disturbance observer based sliding mode control technique for small-scale unmanned helicopters to do hover operation in presence of external disturbances. To counteract both matched and mismatched uncertainties a new sliding surface is designed based on the disturbances estimations. The controller design is based on the linearized state-space model of the helicopter which effectively describes helicopter dynamics during the hover operations. The model mismatch and external disturbances are estimated as lumped disturbances and are compensated in the controller design. The proposed controller reduces chattering and is capable of handling matched and mismatched uncertainties. The control performance is successfully tested in Simulink

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

A System of Autonomously Flying Helicopters for Load Transportation

Die Arbeit beschreibt Entwurf, Umsetzung und Validierung eines autonomen Lastentransportsystems, welches auf Basis mehrerer Modellhubschrauber realisiert wurde. Abhängig von den Anforderungen der zu transportierenden Last kann die Anzahl der verwendeten Hubschrauber individuell angepasst werden. Die präsentierten Modelle und Regler wurden durch Computersimulationen und reale Flugversuche verifiziert. Zwei nichtlineare Modelle werden präsentiert: Ein Model für Konfigurationen bestehend aus einem Helikopter und einer Last (single-lift) und eines für Konfigurationen bestehend aus zwei bzw. mehreren Helikoptern und einer Last (dual- und multi-lift). Neben diesen komplexen Modellen werden vereinfachte Modelle vorgestellt, die für den Reglerentwurf verwendet werden. Ein generischer Orientierungsregler wird entwickelt, der für die Regelung aller beschriebenen Transportkonfigurationen verwendet werden kann. Durch die Nutzung dieses Reglers vereinfacht sich der Entwurf der Translationsregler erheblich. Drei Translationsregler werden beschrieben: Ein Regler für single-lift Konfigurationen, der eine aktive Unterdrückung von Lastschwingungen erlaubt, und ein verteilter Regler für multi-lift Konfigurationen. Weiterhin wird ein dual-lift Regler präsentiert, der eine Kombination der anderen Regler darstellt. Die Regler für dual- und multi-lift Konfigurationen verwenden keine mechanischen Hilfskonstrukte wie Abstandshalter. Die Position der Last wird durch die Orientierung des Seils, gemessen nahe dem Helikopterrumpf, bestimmt. Externe Störungen wie Windstöße können eine Eigenschwingung des Seils anregen, welche die ermittelte Lastposition verfälscht. Die Eigenschwingung des Seils sowie der Einfluss der verwendeten Messeinrichtung werden analysiert. Auf Basis dieser Analyse wird ein Lastbeobachter entwickelt und in mehreren Experimenten verifiziert. Dieser Lastbeobachter ist von essentieller Wichtigkeit für den sicheren Betrieb des Lastentransportsystems, insbesondere bei schlechten Wetterbedingungen. Die entwickelten nichtlinearen Modelle des Systems wie auch die Regler der single- und multi-lift Konfigurationen wurden durch Flugversuche validiert. Dabei hat das System bewiesen, dass es auch bei sehr schlechten Wetterbedingungen einsetzbar iThis work covers the design, realization and validation of an autonomous load transportation system, utilizing several small size helicopters. The number of participating helicopters is configurable for the described system, depending on the requirements of the transported load. The presented models and controllers have been validated in computer simulation and flight experiments. Two non-linear models are presented: One model covers single-lift and one model covers dual- and multi-lift configurations. Simplified models are introduced beside the complex models, which are utilized for the translation controller design. A generic orientation controller is presented, which is applicable for the control of all presented slung load configurations. The utilization of this controller significantly simplifies the design of the translation controllers. The independence from the actual slung load configuration is achieved through measurement of the rope force vector in the rope attachment point, which is located on the helicopter fuselage. Three translation controllers are described: A controller for single-lift configurations, which allows the active compensation of load oscillations and a distributed controller for multi-lift configurations. A dual-lift translation controller is presented, which resembles a combination of single- and multi-lift translation controller. The presented controllers for dual- or multi-lift configurations do not utilize auxiliary constructs, like spreader-bars. The position of the load is estimated from the measured orientation of the rope, close to the helicopter fuselage. External disturbances, like wind gusts, are able to stimulate internal oscillations of the rope, which disturb the estimated load position. The internal motion of the rope as well as the influence of the used measurement device are analyzed and a flexible rope model is presented. Based on the results a load motion observer is developed and validated in several experiments. This load motion observer is essential for the safe operation of the slung load system, especially during bad weather conditions. The derived non-linear models of the system as well as the proposed controllers for single- and multi-lift configurations have been validated in flight experiments. The system has been proven to be operable even in presence of adverse weather conditions

Indoor navigation systems for unmanned aerial vehicles

Ph.DDOCTOR OF PHILOSOPH

Nonlinear robust H∞ control.

A new theory is proposed for the full-information finite and infinite horizontime robust H∞ control that is equivalently effective for the regulation and/or tracking problems of the general class of time-varying nonlinear systems under the presence of exogenous disturbance inputs. The theory employs the sequence of linear-quadratic and time-varying approximations, that were recently introduced in the optimal control framework, to transform the nonlinear H∞ control problem into a sequence of linearquadratic robust H∞ control problems by using well-known results from the existing Riccati-based theory of the maturing classical linear robust control. The proposed method, as in the optimal control case, requires solving an approximating sequence of Riccati equations (ASRE), to find linear time-varying feedback controllers for such disturbed nonlinear systems while employing classical methods. Under very mild conditions of local Lipschitz continuity, these iterative sequences of solutions are known to converge to the unique viscosity solution of the Hamilton-lacobi-Bellman partial differential equation of the original nonlinear optimal control problem in the weak form (Cimen, 2003); and should hold for the robust control problems herein. The theory is analytically illustrated by directly applying it to some sophisticated nonlinear dynamical models of practical real-world applications. Under a r -iteration sense, such a theory gives the control engineer and designer more transparent control requirements to be incorporated a priori to fine-tune between robustness and optimality needs. It is believed, however, that the automatic state-regulation robust ASRE feedback control systems and techniques provided in this thesis yield very effective control actions in theory, in view of its computational simplicity and its validation by means of classical numerical techniques, and can straightforwardly be implemented in practice as the feedback controller is constrained to be linear with respect to its inputs

Modelling and control of a twin rotor MIMO system.

In this research, a laboratory platform which has 2 degrees of freedom (DOF), the Twin Rotor MIMO System (TRMS), is investigated. Although, the TRMS does not fly, it has a striking similarity with a helicopter, such as system nonlinearities and cross-coupled modes. Therefore, the TRMS can be perceived as an unconventional and complex "air vehicle" that poses formidable challenges in modelling, control design and analysis and implementation. These issues are the subject of this work. The linear models for 1 and 2 DOFs are obtained via system identification techniques. Such a black-box modelling approach yields input-output models with neither a priori defined model structure nor specific parameter settings reflecting any physical attributes. Further, a nonlinear model using Radial Basis Function networks is obtained. Such a high fidelity nonlinear model is often required for nonlinear system simulation studies and is commonly employed in the aerospace industry. Modelling exercises were conducted that included rigid as well as flexible modes of the system. The approach presented here is shown to be suitable for modelling complex new generation air vehicles. Modelling of the TRMS revealed the presence of resonant system modes which are responsible for inducing unwanted vibrations. In this research, open-loop, closed-loop and combined open and closed-loop control strategies are investigated to address this problem. Initially, open-loop control techniques based on "input shaping control" are employed. Digital filters are then developed to shape the command signals such that the resonance modes are not overly excited. The effectiveness of this concept is then demonstrated on the TRMS rig for both 1 and 2 DOF motion, with a significant reduction in vibration. The linear model for the 1 DOF (SISO) TRMS was found to have the non-minimum phase characteristics and have 4 states with only pitch angle output. This behaviour imposes certain limitations on the type of control topologies one can ado·pt. The LQG approach, which has an elegant structure with an embedded Kalman filter to estimate the unmeasured states, is adopted in this study. The identified linear model is employed in the design of a feedback LQG compensator for the TRMS with 1 DOF. This is shown to have good tracking capability but requires. high control effort and has inadequate authority over residual vibration of the system. These problems are resolved by further augmenting the system with a command path prefilter. The combined feedforward and feedback compensator satisfies the performance objectives and obeys the constraint on the actuator. Finally, 1 DOF controller is implemented on the laboratory platform

Eleventh Annual Conference on Manual Control

Human operator performance and servomechanism analyses for manual vehicle control tasks are studied

Twentieth Annual Conference on Manual Control, Volume 1

The 48 papers presented were devoted to humanopeator modeling, application of models to simulation and operational environments, aircraft handling qualities, teleopertors, fault diagnosis, and biodynamics

Twelfth Annual Conference on Manual Control

Main topics discussed cover multi-task decision making, attention allocation and workload measurement, displays and controls, nonvisual displays, tracking and other psychomotor tasks, automobile driving, handling qualities and pilot ratings, remote manipulation, system identification, control models, and motion and visual cues. Sixty-five papers are included with presentations on results of analytical studies to develop and evaluate human operator models for a range of control task, vehicle dynamics and display situations; results of tests of physiological control systems and applications to medical problems; and on results of simulator and flight tests to determine display, control and dynamics effects on operator performance and workload for aircraft, automobile, and remote control systems

Research and technology, 1992

Selected research and technology activities at Ames Research Center, including the Moffett Field site and the Dryden Flight Research Facility, are summarized. These activities exemplify the Center's varied and productive research efforts for 1992