Simply structured controllers for vibration suppression in long rotors

Peer reviewedPublisher PD

Selected topics on the active control of helicopter aeromechanical and vibration problems

This paper describes in a concise manner three selected topics on the active control of helicopter aeromechanical and vibration problems. The three topics are as follows: (1) the active control of helicopter air-resonance using an LQG/LTR approach; (2) simulation of higher harmonic control (HHC) applied to a four bladed hingeless helicopter rotor in forward flight; and (3) vibration suppression in forward flight on a hingeless helicopter rotor using an actively controlled, partial span, trailing edge flap, which is mounted on the blade. Only a few selected illustrative results are presented. The results obtained clearly indicate that the partial span, actively controlled flap has considerable potential for vibration reduction in helicopter rotors

The NASA controls-structures interaction technology program

The interaction between a flexible spacecraft structure and its control system is commonly referred to as controls-structures interaction (CSI). The CSI technology program is developing the capability and confidence to integrate the structure and control system, so as to avoid interactions that cause problems and to exploit interactions to increase spacecraft capability. A NASA program has been initiated to advance CSI technology to a point where it can be used in spacecraft design for future missions. The CSI technology program is a multicenter program utilizing the resources of the NASA Langley Research Center (LaRC), the NASA Marshall Space Flight Center (MSFC), and the NASA Jet Propulsion Laboratory (JPL). The purpose is to describe the current activities, results to date, and future activities of the NASA CSI technology program

Active control of turbulence-induced helicopter vibration

Helicopter vibration signatures induced by severe atmospheric turbulence have been shown to differ considerably from nominal, still air vibration. The perturbations of the transmission frequency have significant implications for the design of passive and active vibration alleviation devices, which are generally tuned to the nominal vibration frequency. This thesis investigates the existence of the phenomena in several realistic atmospheric turbulence environments, generated using Computational Fluid Dynamic (CFD) engineering software and assimilated within a high-fidelity rotorcraft simulation, RASCAL. The RASCAL simulation is modified to calculate blade element sampling of the gust, enabling thorough, high frequency analyses of the rotor response. In a final modification, a numerical, integration-based inverse simulation algorithm, GENISA is incorporated and the augmented simulation is henceforth referred to as HISAT. Several implementation issues arise from the symbiosis, principally because of the modelling of variable rotorspeed and lead-lag motion. However, a novel technique for increasing the numerical stability margins is proposed and tested successfully. Two active vibration control schemes, higher harmonic control 'HHC' and individual blade control 'IBC', are then evaluated against a 'worst-case' sharp-edged gust field. The higher harmonic controller demonstrates a worrying lack of robustness, and actually begins to contribute to the vibration levels. Several intuitive modifications to the algorithm are proposed but only disturbance estimation is successful. A new simulation model of coupled blade motion is derived and implemented using MATLAB and is used to design a simple IBC compensator. Following bandwidth problems, a redesign is proposed using H theory which improves the controller performance. Disturbance prediction/estimation is attempted using artificial neural networks to limited success. Overall, the aims and objectives of the research are met

Robust vibration control of a flexible manipulator in presence of payload uncertainty

This paper presents the results of hybrid vibration controllers applied for vibration suppression of flexible manipulator. The model of the manipulator is assumed to be uncertain due to varying payload. To cater for the model uncertainty the proposed hybrid controller combines robust input shaping for command input with μ-controller applied for active vibration suppression using smart materials. Dependence of hybrid controller performance on design frequencies of input shaper is also studied. Results showed that the performance of hybrid controller is strongly dependent on the parameters used for designing input shaper, and the effectiveness of the hybrid controller can be substantially increased by judiciously selecting the design frequencies of input shaper. Effectiveness of the proposed controller is demonstrated by comparative studies with hybrid controllers formed by robust input shaping and PPF (positive position feedback) controller. Results are compared for suppressing vibrations resulting from slewing motion of manipulator, where the slewing motion is controlled by the PD controller. Results of comparisons showed that the μ-controller gave better performance in terms of settling time and energy consumption than those using PPF

Робастне управління інерціальними стабілізованими платформами для наземних рухомих об’єктів на підставі Н∞-синтезу

Purpose: Operation of inertially stabilized platforms mounted on the ground vehicles is accompanied by influence of significant parametrical and various coordinate  disturbances. To keep high operating characteristics of a system in such difficult conditions it is possible using approach to robust system design. Creation of robust inertial stabilized platforms requires further research and development in contrast to design of robust systems of motion control. Methods: One of the modern approaches to robust system design proposed by modern control theory is H¥-synthesis. Problems, which are important for practical applications, it is convenient to solve using method of the mixed sensitivity as it takes into consideration conflicting design goals including robust performance and stability. The method is combined with loop-shaping that allows achieving desired amplitude-frequency characteristics of the designed system. This is achieved by choice of the appropriate weighting transfer functions, which define bounds of the designed system amplitude-frequency characteristics. Results: Grounded recommendations to the choice of components of inertially stabilized platforms operated on the ground vehicles are represented. The mathematical model of the system with gearless drive is developed. The optimization criterion is derived and weighting transfer functions are chosen. The structure of the robust controller in the form of quadruple of state space matrices is represented. Results of synthesised stabilization system simulation show its resistance to significant parametrical and coordinate disturbances taking place during its operation on the ground vehicle. Conclusions: Efficiency of the proposed design approach is proved by results of simulation in conditions of significant parametrical and coordinate disturbances. Obtained results can be widespread on inertially stabilized platforms operating on the other type of vehicles, for example, special aviation aircrafts, carrying out cartographic surveys, monitoring and other similar functions. They can be also useful for design of unmanned aerial vehicles equipment.Цель: Эксплуатация инерциальных стабилизированных платформ, установленных на наземных подвижных объектах, сопровождается действием значительных параметрических возмущений. Для сохранения высоких эксплуатационных характеристик системы в таких сложных условиях возможно использовать подход, основанный на проектировании робастных систем. В отличие от проектирования робастных систем управления движением, создание робастных инерциальных стабилизированных платформ требует дальнейшего исследования и развития. Методы: Одним из современных подходов к проектированию робастных систем, предлагаемых современной теорией управления является H¥-синтез. Задачи, важные для практических применений, целесообразно решать с помощью метода, поскольку он учитывает противоречивые цели проектирования, в том числе достижение робастного качества и робастной устойчивости. Этот метод сочетается с формированием контуров управления с заданными характеристиками проектируемой системы, что обеспечивается выбором весовых передаточных функций, которые определяют границы амплитудно-частотных характеристик. Результаты: Представлены обоснованные рекомендации по выбору составляющих инерциальных стабилизированных платформ наземных подвижных объектов. Разработана математическая модель системы с безредукторным приводом. Получен критерий оптимизации и определены весовые передаточные функции. Определена структура робастного регулятора в виде четверки матриц пространства состояний. Результаты моделирования синтезированной системы стабилизации показывают ее устойчивость к значительным параметрическим и координатным возмущениям, которые имеют место в условиях эксплуатации на наземном подвижном объекте. Выводы: Эффективность предложенного подхода к проектированию подтверждается результатами моделирования  в условиях значительных параметрических и координатных возмущений. Полученные результаты могут быть распространены на инерциальные стабилизированные платформы, эксплуатируемые на других подвижных объектах, например, самолетах специальной авиации, которые выполняют функции картографических съемок, мониторинги и другие аналогичные функции. Они также могут быть полезными при проектировании оборудования беспилотных летательных аппаратов.Мета: Експлуатація інерціальних стабілізованих платформ, встановлених на наземних рухомих об’єктах супроводжується впливом значних параметричних збурень. Для збереження високих експлуатаційних характеристик системи у таких складних умовах можна використовувати підхід, заснований на проектуванні робастних систем. На відміну від проектування робастних систем управління рухом, створення робастних інерціальних стабілізованих платформ потребує подальшого дослідження та розвитку. Методи: Одним із сучасних підходів до проектування робастних систем, що пропонується сучасною теорією управління, є H¥-синтез. Завдання важливі для практичних застосувань зручно вирішувати за допомогою методу змішаної чутливості, оскільки він враховує суперечливі цілі проектування, у тому числі досягнення робастної якості та робастної стійкості. Цей метод поєднується з формуванням контурів управління із заданими характеристиками проектованої системи, що досягається вибором вагових передатних функцій, які визначають границі амплітудно-частотних характеристик. Результати: Представлено обґрунтовані рекомендації щодо вибору складових інерціальних стабілізованих платформ наземних рухомих об’єктів. Отримано критерій оптимізації та визначено вагові передатні функції. Розроблено математичну модель системи з безредукторним приводом. Визначено структуру робастного регулятора у вигляді четвірки матриць простору станів. Результати моделювання синтезованої системи стабілізації показують її стійкість до значних параметричних та координатних збурень, що мають місце в умовах експлуатації на наземному рухомому об’єкті. Висновки: Ефективність запропонованого підходу до проектування підтверджується результатами моделювання в умовах значних параметричних та координатних збурень. Отримані результати можуть бути поширені на інерціальні стабілізовані платформи, що експлуатуються на інших рухомих об’єктах, наприклад, літаках спеціальної авіації, що виконують функції картографічних зйомок, моніторингу та інших подібних функцій. Вони можуть також бути корисними під час проектування обладнання безпілотних літальних апаратів

Real-time RMS active damping augmentation: Heavy and very light payload evaluations

Controls-Structures Integration Technology has been applied to the Space Shuttle Remote Manipulator System (RMS) to improve on-orbit performance. The objective was to actively damp undesired oscillatory motions of the RMS following routine payload maneuvering and Shuttle attitude control thruster firings. Simulation of active damping was conducted in the real-time, man-in-the-loop Systems Engineering Simulator at NASA's Johnson Space Center. The simulator was used to obtain qualitative and quantitative data on active damping performance from astronaut operators. Using a simulated three-axis accelerometer mounted on the RMS, 'sensed' vibration motions were used to generate joint motor commands that reduced the unwanted oscillations. Active damping of the RMS with heavy and light attached payloads was demonstrated in this study. Five astronaut operators examined the performance of active damping following operator commanded RMS maneuvers and Shuttle thruster firings. Noticeable improvements in the damping response of the RMS with the heavy, Hubble Space Telescope payload and the very light, astronaut in Manipulator Foot Restraint payload were observed. The potential of active damping to aid in precisely maneuvering payloads was deemed significant

Benefits assessment of active control technology and related cockpit technology for rotorcraft

Two main-rotor active control concepts, one incorporating multicyclic actuators located just below the swashplate, and the other providing for the actuators and power supplies to be located in the rotating frame are considered. Each design concept is integrated with cockpit controllers and displays appropriate to the actuation concept in each case. The benefits of applying the defined ACT/RCT concepts to rotorcraft are quantified by comparison to the baseline model 412 helicopter. These benefits include, in the case of one active control concept; (1) up to 91% reduction in 4/rev hub shears; (2) a flight safety failure rate of 1.96 x 10 to the 8th power failures per flight-hour; (3) rotating controls/rotor hub drag reduction of 40%; (4) a 9% reduction in control system weight; and (5) vibratory deicing. The related cockpit concept reduces pilot workload for critical mission segments as much as 178% visual and 25% manual

Robust Control of Nonlinear Multibody Flexible Space Structures

A generic nonlinear math model of a multibody flexible system is developed. Asymptotic stability of such systems using dissipative compensators is established. It is proved that, under certain conditions, this class of systems exhibit global asymptotic stability under dissipative compensation. The dissipative compensators considered are static as well as dynamic dissipative compensators. The stability proofs are based on passivity approaches, Lyapunov methods, as well as a key property of such systems, i.e., skew-symmetricity of certain matrix. The importance of the stability results obtained is that the stability is robust to parametric uncertainties and modeling errors. For static dissipative compensators, it is shown that stability is not only robust to parametric uncertainties and modeling errors but also to certain actuator and sensor nonlinearities. Actuator nonlinearities considered are (0, ∞) sector monotonically non-decreasing type, which include realistic nonlinearities such as the saturation nonlinearity. In the presence of dead-zone and hysteresis type nonlinearities, system trajectories do not approach equilibrium point asymptotically, however, it is shown that there is a compact region of ultimate boundedness and system trajectories do not go unbounded. The sensor nonlinearities considered are (0,$\infty$) sector nonlinearities. A more versatile class of dissipative compensators, called dynamic dissipative compensators, is next considered. A control designer has more design freedom with dynamic dissipative compensators than with the static dissipative type. The increased design degrees of freedom can be used to enhance the performance of the control system. The synthesis techniques for static as well as dynamic dissipative compensators for multibody, nonlinear, flexible systems are currently unknown and it is a topic of future research. The asymptotic stability property of a static dissipative controller for multibody, nonlinear, flexible space structures is demonstrated through a simulation example. The example system used consists of a flexible 10-bay truss structure with a flexible, 2-link manipulator arm attached at one end of the truss. This example system is representative of the class of spacecraft envisioned for the future missions. For dynamic dissipative compensators an application example is shown for a multibody planar system with an articulated member. The controller design is based on locally linearized models in the configuration space of the articulated member. This example also demonstrates the use of dissipative compensators in the integrated design framework

Micro guidance and control synthesis: New components, architectures, and capabilities

New GN&C (guidance, navigation and control) system capabilities are shown to arise from component innovations that involve the synergistic use of microminiature sensors and actuators, microelectronics, and fiber optics. Micro-GN&C system and component concepts are defined that include micro-actuated adaptive optics, micromachined inertial sensors, fiber-optic data nets and light-power transmission, and VLSI microcomputers. The thesis is advanced that these micro-miniaturization products are capable of having a revolutionary impact on space missions and systems, and that GN&C is the pathfinder micro-technology application that can bring that about