Vibration Disturbance Research Articles

Regulation of the frictional characteristics disc brake

The article presents the results of an experimental study of the influence of external vibration disturbances on the working elements of the friction unit, which simulate the power circuit of the disc brake: brake pad and brake disc. The studies were carried out on the original friction machine reproducing the interaction conditions of the disc brake elements on a scale of 1:100. Vibration impact on the working elements of the friction unit was carried out by means of a drive, which allowed to implement a sequence of power pulses in the frequency range 5–100 Hz. It is shown that due to the vibration disturbances of the working elements it is possible to influence the friction characteristics within 20–25%.

Contact force detection and control for robotic polishing based on joint torque sensors

In robotic polishing applications, the rotating polisher will generate strong vibration disturbance, which makes it more difficult to detect and control the contact force. This paper proposes a novel and practical method to detect and control the contact force using the built-in sensors (motor encoders and joint torque sensors) for actual robotic polishing in harsh conditions of strong vibration disturbance. An extended state observer based on the robot dynamic model is developed to estimate the contact force in real time, and a new and efficient adaptive filter combining insights of the notch filter with the tracking differentiator is designed to relieve the strong vibration disturbance of torque signals from the eccentrically rotating polisher. On the basis of efficient force detection, a hybrid position/force control method based on the inner joint torque controller is proposed to realize accurate force control in actual robotic polishing of curved surfaces. With the proposed contact force detection and control methodology, the robot is potential to achieve satisfied polishing applications in which some usual accessories, such as the six-axis force/torque sensor or Remote Center Compliance device are absent. Experimental results confirm the effectiveness and accuracy of the proposed contact force detection method in conditions of strong vibration disturbance from the rotating polisher. In addition, the curved surface polishing experiments indicate that the new hybrid position/force control framework performs well on rejecting the strong disturbances while maintaining high force control accuracy of polishing, and the quality of polished surface is greatly improved.

An Improved Real-Time Transfer Alignment Algorithm Based on Adaptive Noise Estimation for Distributed POS

Distributed position and orientation system (POS) plays an important role in the fields of aerial remote sensing, which serves the sensors by precise motion information. For distributed POS, the slave systems consist of low accuracy inertial sensors, which must depend on the high accuracy motion information of the master to proceed transfer alignment (TA) to improve accuracy. Generally, the TA filtering algorithms perform superior performance when the noise statistical characteristic is known and accurate, however like gust, engine vibration and other external disturbances both will cause the inertial sensors output with unknown, varying noises and performance decline. Aiming at this, a variational Bayesian central difference Kalman filtering algorithm for distributed POS real-time TA is developed to suppress the effect of external noise, incorporating the central difference Kalman filtering (CDKF) algorithm and variational Bayesian (VB) adaption theory. In detail, the algorithm is to apply the noise estimation by VB adaption to the CDKF algorithm to achieve real-time TA accuracy enhancement. Distributed POS flight test is devoted for the algorithm validation, by the comparison, evident progress in TA accuracy has been presented.

Finite Element Analysis for Indentation Formation Process of Angular Contact Ball Bearing for Space Equipment under Impulsive Vibration

Impulsive vibration during rocket launch has the risk of causing indentations inside the bearings of reaction wheel mounted on a satellite. The indentations induce the vibration disturbance during the bearing rotation, which is harmful to precision equipment. In order to investigate the mechanism of the indentation formation, we carried out the experiments and finite element simulation for simplified reaction wheel. Based on the results of simulation, we estimated the depth of plastic deformation and wear using Palmgren’s formula and PV value, respectively. The indentation depth of simulation shows good agreements with that of experiment. The results also show that the wear between balls and rings is dominant factor of indentation formation, as compared with the plastic deformation. The amount of wear is greatly affected by the location of ball. In the location where the contact direction between ring and ball is parallel to the vibration direction, contact pressure contributes the wear as compared with slip velocity. Inversely, in the location where the contact direction is perpendicular to the vibration direction, the slip velocity contributes the wear and induces the larger wear region.

ХАРАКТЕР ПРОЯВУ НЕЛІНІЙНОСТЕЙ ПРИ ВІБРАЦІЙНОМУ ЗБУДЖЕННІ РУХУ ЕЛІПСОЇДАЛЬНОГО РЕЗЕРВУАРА З РІДИНОЮ ІЗ ВІЛЬНОЮ ПОВЕРХНЕЮ

The problem with vibration disturbance of the reservoir of ellipsoidal shape, partially filled with a liquid, is under consideration. For the construction of the model, we use the before developed method, based on the use of non-Cartesian parametrization of the domain, occupied by a liquid. And the method of the auxiliary domain for satisfying boundary conditions on tank walls above the unperturbed free surface of a liquid, where the liquid can pass in its perturbed motion. The liquid is considered as ideal incompressible. The mathematical model of the system is constructed based on the variational formulation of the problem in the form of the Hamilton–Ostrogradskiy principle. The motion of a liquid free surface is given in the form of decomposition with respect to normal modes of oscillations. Amplitude parameters of oscillations of a liquid free surface together with parameters of the translational motion of the reservoir form a complete independent system of parameters, for which the resolving system of ordinary differential equations is constructed. The constructed model includes nonlinear properties of the system and corresponds to the model of the combined motion of the liquid with the reservoir. According to its structure, the model has considerable similarities with the case of the cylindrical reservoir. The practical implementation of the method is done for vibration disturbance of the system motion in the horizontal plane for the case of extended and compressed ellipsoidal reservoirs. The analysis of the character of manifestation of the dynamical behavior of the system in different ranges of frequencies of motion disturbance shows that mainly this system behaves as a system with the soft type of nonlinearities. The system output to the steady mode of oscillations is not observed. Modulation of oscillations of a liquid free surface is considerably manifested for most modes. Increased attention is paid to the study of regularities of variation of a period of the oscillation modulation. It was ascertained that due to compression of the spectrum of liquid oscillations with the increase of the wavenumber, the simultaneous considerable effect of several frequencies is manifested in the system reservoir–liquid, which leads to complex modulation envelope lines.

ВЕРИФІКАЦІЯ АЛГОРИТМУ КЕРУВАННЯ РЕЗЕРВУАРАМИ З РІДИНОЮ НА ОСНОВІ КОМПЕНСАЦІЇ СИЛОВОГО ВІДГУКУ В РІЗНИХ ДІАПАЗОНАХ ПРОЯВУ НЕЛІНІЙНОСТЕЙ

Problem about motion of a reservoir with liquid with a free surface is considered based on the compensation of a force response of the liquid on reservoir walls. Such an approach is selected since usual methods of control of mechanical system motion are mostly intended for linear systems of relatively small dimension. However, models of dynamics of the combined motion of reservoirs with liquid are described with relatively high-dimensional nonlinear systems ordinary differential equations. For obtaining the mathematical model of combined motion of a reservoir with liquid with a free surface we use the Hamilton–Ostrogradskiy variational principle, for which it is possible to determine analytically all internal forces of interaction of system component parts. Namely using this algorithm, we determine the main vector of forces of the liquid pressure on reservoir walls (force response of liquid). The algorithm of the motion control of the reservoir with liquid is based on the inclusion of the compensation of the liquid force response to controlling actions, this reduces the motion of the system reservoir–liquid, where the effect of forces from oscillating liquid on the reservoir motion is eliminated. This algorithm was tested for problems of impulse and vibration disturbance of the translational motion of the system in the horizontal plain. We consider the disturbance of the system motion by a force rectangular impulse applied to the reservoir wall, the duration of the impulse is lesser than a quarter of the period of a liquid free oscillations according to the first normal mode. Amplitudes of the impulse were selected with the purpose of analysis of the behavior of the controlled system in different ranges of manifestation of nonlinearities. We state the problem to verify the accuracy of this algorithm for three ranges of manifestation of nonlinear properties in the system, namely, for the linear range (amplitudes of waves on a free surface h do not exceed 0,1 of the radius of a free surface (  <0,1R); for the weakly nonlinear range (  <0,2R) and for the strongly nonlinear range with maximum amplitudes of waves about  =0,32R. Numerical modeling enables the determination of errors of developed algorithm, which does not exceed 0,5 %, although they insignificantly increase with the increase of amplitudes of oscillations on a free surface of liquid. At the same time perturbations on a free surface of liquid for the controlled motion are always greater than for the uncontrolled motion.

Passive vibration suppression of large space truss structures by viscous damping

Viscous damping methods are commonly employed to suppress the vibration due to their simple design, low cost, and stable damping performance. However, the harsh space environment makes the normal viscous dampers suspicious to various failures. This paper proposes a novel and robust design of viscous damper to provide high damping under low-frequency vibration disturbance in space. The characterisation of the damper at low-frequency and large displacement is first investigated by numerical analysis and then validated by experiments. Based on the results of the damper, this paper presents an optimal design strategy for the damping system of large space truss structures, which is critical for space mission because there is no sufficient damping in such space structures. The design is further optimised by weighted-sum that includes the damping characteristics of dampers and elastic flexibility of space truss structures. The effect of the damping system is demonstrated by the optimal design of a 60-bay truss structure. The results show that the damping ratios of the first three modes of the truss structure can be increased by over 10% with two viscous dampers. Comparisons between the structure with and without dampers demonstrate that significant vibration suppression at low-frequency bandwidth can be achieved satisfactorily.

Passive vibration suppression of large space truss structures by viscous damping

Viscous damping methods are commonly employed to suppress the vibration due to their simple design, low cost, and stable damping performance. However, the harsh space environment makes the normal viscous dampers suspicious to various failures. This paper proposes a novel and robust design of viscous damper to provide high damping under low-frequency vibration disturbance in space. The characterisation of the damper at low-frequency and large displacement is first investigated by numerical analysis and then validated by experiments. Based on the results of the damper, this paper presents an optimal design strategy for the damping system of large space truss structures, which is critical for space mission because there is no sufficient damping in such space structures. The design is further optimised by weighted-sum that includes the damping characteristics of dampers and elastic flexibility of space truss structures. The effect of the damping system is demonstrated by the optimal design of a 60-bay truss structure. The results show that the damping ratios of the first three modes of the truss structure can be increased by over 10% with two viscous dampers. Comparisons between the structure with and without dampers demonstrate that significant vibration suppression at low-frequency bandwidth can be achieved satisfactorily.

Eksperimen Gangguan Getaran Pada Fenomena Cloaking Cahaya Tampak Sistem Empat Lensa

Creating optical illusions or invisible objects by using cloaking devices is still being a concern for many researchers in the world. The cloaking devices are working in visible spectrum regime, large dimention, and replicable. Addition with the full-field of light, no new materials, simple infrastructure, and scale easily may be considered an ‘ideal’ cloaking device. Based on four lenses cloaking system by Choi’s work shows an idea for solution of blindspot large vehicle’s problem. The set up for this optical system is regular covex lenses non-aberation based on educational laboratory framework. The experimental confirmation that cloaking area with 4f convex lenses is limited to certain areas only, not 100 % of the object to be observed can disappear from the view. Vibration disturbance generated by rotor module (wheels disturbance analogy on vehicles) applied on the system demonstrate that below on 2000 rotation per minutes (rpm) equal 33.34 hertz, optical illusion is still consistent. The results support the information to create optical cloaking prototype for optimizing large vehicle driver’s visibility as alternative solution blindspot’s problem.

Rapid attitude maneuver of the space tether net capture system using active disturbance rejection control

Abstract. The space tether net capture system is a spacecraft system with a mounting tether net for capturing targets. It has the advantages of reusability and the adaptability to capture varying targets with different geometries or flying-motion statuses. However, due to its flexible tether net, the system shows strong nonlinearity, which makes it difficult to achieve the desired control performance for rapid and accurate maneuvering; moreover, this limits the ability of the tether net system to capture fast-moving targets. This paper focused on the maneuver controller design of the space capture system with a large flexible tether net. Firstly, based on the absolute node coordinate method, the dynamic model of the space tether net system is established, which can accurately describe the geometric and material nonlinearities of the space tether net. Then, a two-loop active disturbance rejection control is proposed for the rapid and high-precision maneuvering of the flexible system; meanwhile the second-order extended state observer is designed to estimate and compensate for the tether net vibration disturbance. The simulation validated the proposed control, which could complete the rapid and accurate maneuvering and also compensate for the disturbance caused by the vibration of the flexible tether net.

Coupled CFD and particle resuspension models under combined effect of mechanical and aerodynamic disturbances

Particle resuspension in indoor spaces constitutes a concern to human health as it re-introduces deposited particles on surfaces into the bulk air. Resuspension can occur due to indoor human activities causing aerodynamic and mechanical vibration disturbances. The objective of the work is to develop a simplified model that can predict resuspension triggered by the simultaneous action of aerodynamics and vibration forces from hard floor material. The mathematical model was coupled with computational fluid dynamics (CFD) model to predict, through a probabilistic approach, the rates of particle resuspension from indoor surfaces due to indoor activities. The developed model accounted for the reduction of adhesive forces due to vibrations and for the lift and drag forces and moments due to the fluid flow while setting the resuspension condition to predict the resuspension rates. The resuspension model was validated by published literature data on particle resuspension due aerodynamic and mechanical disturbances and good agreement was found. Resultsshowed that particle resuspension exhibited a rapid burst during the first 25 s of the disturbance before decreasing to negligible values. Resuspension rates also increased when vibrations were accounted for with aerodynamic disturbances. For different indoor surfaces, it was found that resuspension fractions were the smallest for glass surfaces, followed by marble and linoleum. Moreover, resuspension fractions increased by 48.4%, 60.5% and 63% for glass, marble and linoleum when aerodynamic disturbances were accompanied with vibrations. A decrease in surface roughness can increase adhesive forces, and stiffness values reducing the effect of vibrations on enhancing resuspension.

Vibration Suppression and Isolation for Rapeseed Grain Cleaning Loss Sensor

Rapeseed cleaning loss is an important factor to weigh rapeseed combine harvester performance. With the development of sensor technology, establishing a rapeseed cleaning loss monitoring system can be interesting and necessary. However, the rapeseed combine harvester made in China is always with larger vibration, which is not beneficial for sensor monitoring accuracy. Experiment results indicate that inertia force from vibrating sieve unbalanced motion has the greatest influence on the monitoring accuracy of the sensor in its installation position. To reduce the effect of vibration on monitoring accuracy of the sensor, the vibration absorption and isolation structure for cleaning loss sensor has been designed. Moreover, the vibration isolation design was performed on the basis of vibration suppression. The vibration isolation rubber was designed to isolate the vibration at the joint of the sensor with the frame. The experimental results shown that the above design can reduce the vibration disturbance and highlight the grain collision signal greatly, which is beneficial for improving the sensor discrimination ability.

Identification of the vibration error of the navigation accelerometer during its static tests

This article describes the vibration error of the navigation accelerometer caused by the nonlinearity of its metrological model.Vibration error is the regular steady-state error in the time-average output of accelerometer during vibratory disturbances. It is defined that error varies with the amplitude and frequency of the vibrations and consists of additive and multiplicative components. The additive components are only dependent on the vibration value and determined by even nonlinear coefficients. The multiplicative components are also dependent on measured acceleration and determined by the asymmetric of sensitivity, odd nonlinear coefficients, and cross-sensitivity. To express these dependencies, an appropriate mathematical model was developed.The method of experimental estimation of the vibration error based on the developed model was proposed. The main idea of the method is to evaluate parameters of the developed model during static tests in the terrestrial gravitational field and to calculate error according to the specific vibration characteristics – the amplitude in the case of harmonic vibration profile or the frequency band and the power spectral density in the case of random vibration.The effectiveness of the proposed method has been tested by using three types of navigation accelerometers in comparison with the results of classical dynamic testing in various vibration conditions (harmonic, white noise, etc.). The mismatch between the calculated values of the vibration error and the reference results did not exceed 35%, which confirms the correctness of reasoning regarding the type of proposed functional dependence.

On vibration characteristics of thermal field emission electron gun filament

Thermal field emission electron gun is used as electron source in scanning electron microscope. Its filament made by tungsten wire is bended like a hairpin and is prone to vibration disturbance, therefore deteriorating outcome images. To model filament’s mechanical performance under vibrating conditions, finite element modal analysis was carried out, and frequency response was calculated. It was shown that the filament was more sensitive to lateral excitation, and due to its unique structure, vibration characteristics were different in two lateral directions. Stiffness of the two lateral directions was compared through static calculation to verify the calculated mode order. Besides, characteristics between room temperature and working temperature were compared. If allowed, electron gun should be mounted in the way that its sensitive direction be kept away from the most intensive excitation’s direction.

Youla parameterized adaptive vibration control against deterministic and band-limited random signals

Abstract Multiple narrow band deterministic and band-limited random disturbance signals will occur during machining process, which will cause vibration and have negative effect on the cutting accuracy. For instance, in a lathe system, spindle rotation can produce narrow band deterministic vibration disturbance and turning process can lead to band-limited random vibration disturbance. In this paper, a H∞ controller with augmented Youla (Q) parameterized adaptive regulation approach is proposed to reject both random and deterministic disturbances. The parameter Q is converged to the desired value by online tune of a recursive least squares (RLS) algorithm. An experimental evaluation on a lathe system has been carried out to indicate the effectiveness of this approach. The result illustrates that the proposed adaptive control method can effectively attenuate the lathe vibrations against the unknown deterministic and band-limited random disturbances.

Dynamic analysis and stabilizing control of three-axis spherical gimbal

Nowadays, stabilized gimbals have been popular products on the present market for unmanned aerial vehicle. Rejecting multi-periodic vibration disturbance is a key point for accuracy motion of the gimbal under the flight operation of unmanned aerial vehicle. In this study, a stable control scheme of a three-axis spherical gimbal is proposed, where a new method for synthesizing multi-iterative learning control algorithm is exported. To design the controller, the mathematic modeling of the three-axis control system is earned and determined by spectrum analysis of the proposed gimbal. Performance and stability of the control system are analyzed and are evaluated in an experimental disturbance rejecting control system. Both computer simulation and experimental results are presented to illustrate the effectiveness of the proposed iterative learning controller design.

High-Precision Attitude Tracking Control of Space Manipulator System Under Multiple Disturbances

Precise attitude control of space manipulators plays an important role in advanced on-orbit assembly tasks. The vibration of flexible appendage and inertial uncertainties encountered in the operating process, however, may cause attitude error or even safety threats to the space manipulator system. In this article, a high-precision attitude control scheme of a space manipulator system is designed via a combination of disturbance observer (DO), prescribed performance-based H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control, and iterative learning control (ILC) techniques. The proposed control scheme consists of three portions: 1) a DO that estimates the vibration disturbance caused by flexible appendage of base satellite; 2) a robust H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller with prescribed performance to attenuate the inertial uncertainties resulting from capture of an unknown object; and 3) an ILC for improving the transient and steady-state process in the presence of a repetitive on-orbit assembly task. This novel control scheme can not only handle the flexible vibration and inertial uncertainty of the space manipulator but also achieve satisfactory tracking performance. Both simulation and experimental results confirm the superiority of the proposed control strategy.

The Simulation of Vortex Structures Induced by Different Local Vibrations at the Wall in a Flat-Plate Laminar Boundary Layer

The compact finite difference scheme on non-uniform meshes and the Fourier spectral hybrid method are used to directly simulate the evolution of vortex structures in a laminar boundary layer over a flat plate. To this end, two initial local vibration disturbances, namely, the positive–negative and the negative–positive models, at the wall were adopted. The numerical results show that the maximum amplitudes of vortex structures experience a process of linear growth and nonlinear rapid growth. The vertical disturbance velocity and mean flow shear and the derivative term of the stream-wise disturbance velocity and the span-wise disturbance velocity, are important factors for vortex structure development; the high- and low-speed stripe and the stream-wise vortex are consistent with structures seen in full turbulence. The maximum amplitude of the negative–positive model grows more quickly than that of the negative–positive model, and the detailed vortex structures are different for the two models. The mean flow profiles both become plump, which leads to the instability of the laminar boundary layer. The way in which the disturbance is generated with different local vibrations influences the dynamics of vortex structures in a laminar boundary layer.

Optimal control and state estimation for unmanned aerial vehicle under random vibration and uncertainty

In the past decade, many approaches that attempted to solve the problem of optimal control and parameter estimation of an unmanned aerial vehicle with a priori uncertain parameters simply implied two ways to solve such problem. First, by the formation of optimal control based on a refined mathematical model of the unmanned aerial vehicle, and second, by using the estimation and identification methods of the model parameter of the unmanned aerial vehicle based on measured data from flight tests. However, the identification of the dynamic parameters of the unmanned aerial vehicle is a complicated task because of a number of factors such as random vibration noise, disturbance, and uncertainty of the sensor measurements. Due to the influence of random vibration noise, the problem of correlated vibration noises and uncertainty has encountered inevitably, and the accuracy of the state estimation for unmanned aerial vehicle is degraded. This study concentrates on the optimal control and state estimation for the unmanned aerial vehicle under the combination of both random vibration noise and uncertainty collected by the sensors. The effects of random vibrations at various stages of a large-scale flight that are a priori uncertain require the inclusion of identification algorithms in the optimal control loop. The results showed that the method used in the analysis had been able to provide accurate estimations.

Anti-disturbance iterative learning tracking control for space manipulators with repetitive reference trajectory

Purpose This paper is concerned with the repetitive trajectory tracking control for space manipulators under model uncertainties and vibration disturbances. Design/methodology/approach The model uncertainties and link vibration of manipulators will degrade the tracking performance of space manipulators; in this paper, a new hybrid control scheme that consists of a composite hierarchical anti-disturbance controller and an iterative learning controller is developed to solve this problem. Findings The composite hierarchical controller can effectively attenuate model uncertainties and reject vibration disturbances, whereas the iterative learning controller is able to improve the tracking accuracy for repetitive reference trajectory. Originality/value The proposed scheme compensates for the shortcomings of iterative learning control which can only deal with repetitive disturbances, ensuring the accuracy and repeatability of space manipulators under model uncertainties and random disturbances.