Vibration reduction for flexible spacecraft attitude control using PWPF modulator and smart structures

PurposeTo provide an approach to active vibration reduction of flexible spacecraft actuated by on‐off thrusters during attitude control for spacecraft designers, which can help them analysis and design the attitude control system.Design/methodology/approachThe new approach includes attitude controller acting on the rigid hub, designed by using pulse‐width pulse‐frequency modulation integrated with component command technique, and the piezoelectric material elements as sensors/actuators bonded on the surface of the beam appendages for active vibration suppression of flexible appendages, designed by optimal positive position feedback (OPPF) control technique. The OPPF compensator is devised by setting up a cost function to be minimized by feedback gains, which are subject to the stability criterion at the same time, and an extension to the conventional positive position feedback control design approach is investigated.FindingsNumerical simulations for the flexible spacecraft show that the precise attitude control and vibration suppression can be accomplished using the derived vibration attenuator and attitude control controller.Research limitations/implicationsStudies on how to control the on‐off actuated system under impulse disturbances are left for future work.Practical implicationsAn effective method is proposed for the spacecraft engineers planning to design attitude control system for actively suppressing the vibration and at the same time quickly and precisely responding to the attitude control command.Originality/valueThe advantage in this scheme is that the controllers are designed separately, allowing the two objectives to be satisfied independently of one another. It fulfils a useful source of theoretical analysis for the attitude control system design and offers practical help for the spacecraft designers.

For near-Earth spacecraft, many environmental forces are utilized to unload reaction wheels. However, effects like magnetic force or atmospheric friction hardly exist in deep-space environments where solar sails operate. Thus, this paper proposes an unloading method that uses reflectivity control devices to generate Solar Radiation Pressure (SRP) torque to conduct the unloading process of solar sails operating in deep space. Firstly, the basic principles of the Reflectivity Control Device (RCD), satellite kinetic model, and Pulse Width Pulse Frequency (PWPF) modulator are given. Secondly, based on the torque envelope obtained by traversing all switch combinations of RCD, a novel strategy using a PWPF modulator is specially designed to achieve efficient unloading. In the end, we carry out numerical simulations and analyze the influence of different parameters, through which the validity of the proposed torque resolution scheme is demonstrated.

ASTER, the first Brazilian mission to the deep space, targets the exploration of the triple asteroid system known as 2001 SN263. The mission requires an attitude controller robust and capable of coping with the non-linearities and the uncertainties present during the exploration phase. For such requirements, this paper studies the applicability of two controllers, designed based on the sliding mode control (SMC) technique, one of the controllers include an adaptive law used to compensate for the spacecraft’s inertia variation. One application is performed where gain scheduling is used for controlling two different phases: exit from tumbling and track a dynamic reference. The actuators of the attitude control loops are impulsive thrusters. They are activated by pulse width modulation (PWM) or pulse width pulse frequency modulation (PWPFM). Simulation studies, performed in realistic scenarios, show that the SMC can maintain stability and performance when these modulation techniques are used to approximate the continuous commands. It is also shown that PWM can provide better performance, but at a higher control cost. In this sense, PWPFM is more appropriate with respect to the fuel consumption and activation times.

The wing flutter is a dynamic instability of a flight vehicle associated with the interaction of aerodynamic, elastic, and inertial forces (aeroelastics phenomena). In this study, just the primary control is investigated. Also, in order to control the two-dimensional wing flutter, the force jet and pulse width pulse frequency (PWPF) are suggested. The PWPF modulator has the advantage of almost linear operation, low jet gas consumption, flexibility in addressing various needs, and good accuracy in presence of oscillations. This scheme makes use of quasi-steady dynamic premises and incompressible flow, as well as the thin airfoil theory. It should be noted that, to justify the application of the aerodynamic theory, we have speculated that the thruster jet ejected through a nozzle with a diameter smaller than several millimeters has a supersonic regime (with Mach number of the order of M≈3.5). Consequently, the interference of the thruster jet in the boundary layer, flow, and circulation around the airfoil which are characterized by low speed would be negligible. The operation of the jet as a thruster is handled by the PWPF modulator, and the process output is fed back to the system via a PD controller. In order to control the wing flutter oscillation, the location of installing the actuator on the airfoil is investigated.

This paper presents performance comparison of a novel hybrid control algorithm and a Positive Position Feedback (PPF) control law for vibration suppression with low energy consumption. The proposed hybrid control method combines a bang-bang active controller with a PPF control law and results in a significant reduction of actuation energy requirement due to its ability to switch the actuation voltage source between external power supply and PPF feedback controller. Experimental results show that a single mode vibration control system using this proposed hybrid controller consumes 46% less power compared to the traditional PPF control system to give the same settling time. Experiments also reveal that substantial nonlinearity exists in the piezoelectric constant of the transducer, especially under high voltage actuation. The voltage dependent behavior of electromechanical coupling coefficient is identified empirically and represented by a curve fit expression. A real time adaptive control algorithm is developed to account for the voltage dependent behavior of the coupling coefficient and the simulation results are validated experimentally.

In this study, a Hardware-In-the-Loop (HIL) simulator using thrusters is developed to validate the spacecraft attitude system. To control the attitude of the simulator, eight cold gas thrusters are aligned with roll, pitch and yaw axis. Also linear actuators are applied to the HIL simulator for automatic mass balancing to compensate the center of mass offset from the center of rotation. The HIL simulator consists of an embedded computer (Onboard PC) for simulator system control, a wireless adapter for wireless network, a rate gyro sensor to measure 3-axis attitude of the simulator, an inclinometer to measure horizontal attitude, and a battery set to supply power for the simulator independently. For the performance test of the HIL simulator, a bang-bang controller and Pulse-Width Pulse-Frequency (PWPF) modulator are evaluated successfully. The maneuver of 68 deg. in yaw axis is tested for the comparison of the both controllers. The settling time of the bang -bang controller is faster than that of the PWPF modulator by six seconds in the experiment. The required fuel of the PWPF modulator is used as much as 51% of bang-bang controller in the experiment. Overall, the HIL simulator is appropriately developed to validate the control algorithms using thrusters.

: POSITIVE position feedback (PPF) control was introduced by Goh and Caughey in 1985 to control vibrations of large exible space structures. A PPF controller has several distinguished advantagesas compared to then widely used velocity feedbackcontrol laws. It is insensitive to spillover, where contributions from unmodeled modes affect the control of the modes of interest. As a second-order low-pass lter, a PPF controller rolls off quickly at high frequencies and is well suited to controlling the lower modes of a structure with well separated modes. Because of these advantages, PPF controller along with smart materials, in particular PZT (lead zirconatetitanate) type of piezoelectricmaterial, has been applied to many exible systems to achieve active damping. The design of a PPF controller requires the natural frequency of a structure. In practice, the structuralnatural frequencymay not be known exactlyor itmay varywith time.When the frequencyused in thePPF controller is different from that of the structure, the performance of the PPF control will adversely affected. Despite that PPF control is widely researched in literature, robustness study of PPF control when natural frequency is inexactly known is not reported. This motivates the authors to conduct experimental study of robustness of PPF control in active vibration suppression of a smart exible structure.

This paper presents a new method of active vibration control (AVC) of flexible composite cantilever beams. A recursive least mean squares (LMS) based filter is used to perform on-line system identification, updating a positive position feedback (PPF) controller in real-time. With conventional time-invariant PPF control the damping ratio and natural frequency are selected based on the structural response, with the feedback path taking the form of a second-order filter; therefore having performed an off-line system identification of the plant dynamics, this controller is relatively straightforward to implement. Some structures undergo parameter changes over time and actuation in the control sequence can contribute to this change in the system dynamics. PPF control is optimized when an accurate estimation of the natural frequency is available. It is demonstrated that the recursive LMS algorithm can be used to provide a continual on-line estimation of the plant dynamics, for robust control of a slender glass fiber beam. The result is an increase in vibration attenuation, which is robust to variations in the beam properties. It is shown that this controller delivers a high performance settling time when compared with the standard PPF controller for free vibration in the first mode. Robustness of the technique is further demonstrated by altering the fundamental frequency of the beam, via the addition of a lumped mass. The adaptive controller re-tunes itself to this parameter variation, ensuring a high level of vibration suppression is upheld.

Positive position feedback (PPF) control is widely used in active vibration control offlexible structures. To ensure quick vibration suppression, a large PPF scalar gain is oftenapplied. However, PPF control with a large scalar gain causes initial overshoot, which isundesirable in many situations. In this paper, a fuzzy gain tuner is proposed to tune thegain in the positive position feedback control to reduce the initial overshoot while stillmaintaining quick vibration suppression. The fuzzy system is trained by a batch leastsquares algorithm based on desired input–output data so that the trained fuzzysystem can behave like the training data. A 3.35 m long composite I-beam withpiezoceramic patch sensors and actuators is used to demonstrate the fuzzy PPFcontrol. For comparison purposes, three types of control methods are used in theexperiment: a standard PPF control, a standard PPF control with traditionalfuzzy gain tuning, and a PPF control with batch least squares fuzzy gain tuning.Experimental results clearly demonstrate that PPF control with batch least squares fuzzygain tuning behaves much better than the other two control methods in terms ofsuccessfully reducing the initial overshoot and quickly suppressing vibration.

In this study, the Genetic Algorithm (GA) was used to search the 4 modes filter frequencies to be applied to the multiple Positive Position Feedback (PPF) controller. The PPF technique, which makes use of generalized displacement measurements to maximize damping in a specific mode effectively and accomplish vibration suppression was employed as control scheme. However it is necessary to tune the filter frequency of the controller to the structural resonance prior to compensator design. Another disadvantage in the multi mode PPF control is that the lower mode natural frequency is shifted to the low-ward as the effect of the higher mode control by PPF controller. To minimize the effect of frequency shift and search the optimal filter frequencies for the multiple modes PPF controller, the GA was applied. The generally used fitness function of the GA in low modes PPF control, the square sum of sensor voltage output hardly distinguishes the definite difference in higher modes. Instead of it, in this study, the GA with the fitness function as the power spectrum information was performed. As a result of GA algorithm with this fitness function, the optimal filter frequencies of higher modes were found successfully.

This paper presents experimental results of vibration suppression of a flexible structure using a miniaturized digital controller, called modular control patch (MCP). The MCP employs a TI-C30 digital signal processor and was developed by TRW for the United States Air Force for future space vibration control. In this research, the MCP is used to implement different control algorithms for vibration suppression of a cantilevered aluminum beam with piezoceramic sensors and actuators. Positive position feedback (PPF) control, strain rate feedback (SRF) control, and their combinations were implemented. Experiments found that PPF control is most effective for single-mode vibration suppression, and two PPF filters in parallel are most effective for multi-mode vibration suppression. Further experiments demonstrated the robustness of PPF control. PPF can achieve effective vibration suppression when there is a 20% error in modal frequency.

This paper is concerned with the implementation of the active vibration suppression controller using analog circuit and microprocessor. The target active vibration controller is the positive position feedback(PPF) controller since it provides a simple algorithm suitable for both analog circuit and digital controllers. In this study, the analog PPF controller is realized using an operational amplifier and the digital PPF controller is realized using a low-cost micro-controller. The circuit diagrams are explained in detail. We then discuss the advantages and disadvantages of both methods from the view of practical implementation. Experimental results show that both implementation methods can be effectively used for the active vibration control but need to be chosen based on the mission objective.

A Positive Position Feedback controller for vibration control of wind turbines

In this article, active vibration control of a micro-actuator for hard disk drives using self-sensing actuation is presented. The micro-actuators used in this article are a slider type and a suspension type. The self-sensing performance of the installing position is compared and evaluated. An assembly including these micro-actuators may not be able to sense some vibration of suspension modes. Feedback control results of direct velocity feedback and positive position feedback are presented. The feasibility of these self-sensing approaches as a vibration suppression control on the micro-actuator was verified. Using the slider type micro-actuator, the sway mode spike signal in power spectrum density was suppressed by 76% using the direct velocity feedback control, and by 60% using the positive position feedback control. Using the suspension type micro-actuator, the suspension second bending mode spike signal in power spectrum density was reduced by 74% using the direct velocity feedback control, and by 96% using the positive position feedback control. The control scheme using self-sensing signals can partially dampen the suspension modes.

This paper studies the attitude control problem of spacecrafts with flexible appendages. It is well known that the unwanted vibration modes, model uncertainty and space environmental disturbances may cause degradation of the performance of attitude control systems for a flexible spacecraft. In this paper, the vibration from flexible appendages is modeled as a derivative-bounded disturbance to the attitude control system of the rigid hub. A disturbance-observer-based control (DOBC) is formulated for feedforward compensation of the elastic vibration. The model uncertainty and space environmental disturbances as well as other noises are merged into an “equivalent” disturbance. We design a composite controller with a hierarchical architecture by combining DOBC and PD control, where DOBC is used to reject the vibration effect from the flexible appendages. Numerical simulations are performed to demonstrate that by using the composite hierarchical control law, disturbances can be effectively attenuated and the robust dynamic performances be enhanced.