Unwanted Vibrations Research Articles

Optimal Hardware and Control Co-Design Applied to an Active Car Suspension Setup

For complex systems, it is not easy to obtain optimal designs for the hardware architecture and control configurations. Every design aspect influences the final performance, and often the interactions of the different components cannot be clearly determined in advance. In this work, a novel co-design optimization method was applied that allows the optimal placement and selection of actuators and sensors to be performed simultaneously with the determination of the control architecture and associated controller tuning parameters. This novel co-design method was applied to a state-space model of a downscaled active car suspension laboratory setup. This setup mimics a car driving over a specific road surface while active components in the suspension have to increase the driver’s comfort by counteracting unwanted vibrations. The result of this co-design optimization methodology is a Pareto front that graphically represents the trade-off between the maximum performance and the total implementation cost; the co-design results were validated with measurements of the physical active car suspension setup. The obtained controller tuning parameters are compared herein with existing controller tuning methods to demonstrate that the co-design method is able to determine optimal controller tuning parameters.

Active vibration control of slewing drives with gear backlash

Geared transmissions with high reduction ratios are widely utilized in drive technology. Common to these drives is the occurrence of considerable gear backlash. If operating scenarios with repeated reversals of the rotational direction or changing load directions occur, the backlash will be traversed. To overcome the gear play, rotation angles of several hundred degrees can be required at the motor. As a result, unwanted vibrations can occur and high dynamic loads may arise. It is shown that an active vibration control strategy based on full state feedback (LQG) allows to reduce both the dynamic overload and the time for reversing the drive. The model-based design approach relies on two angular measurements only. Multibody system simulations of an exemplary drivetrain are used to verify the possible improvements.

Simultaneous out-of-plane and in-plane vibration mitigations of offshore monopile wind turbines by tuned mass dampers

To effectively extract the vast wind resource, offshore wind turbines are designed with large rotor and slender tower, which makes them vulnerable to external vibration sources such as wind and wave loads. Substantial research efforts have been devoted to mitigate the unwanted vibrations of offshore wind turbines to ensure their serviceability and safety in the normal working condition. However, most previous studies investigated the vibration control of wind turbines in one direction only, i.e., either the out-of-plane or in-plane direction. In reality, wind turbines inevitably vibrate in both directions when they are subjected to the external excitations. The studies on both the in-plane and out-of-plane vibration control of wind turbines are, however, scarce. In the present study, the NREL 5 MW wind turbine is taken as an example, a detailed three-dimensional (3D) Finite Element (FE) model of the wind turbine is developed in ABAQUS. To simultaneously control the in-plane and out-of-plane vibrations induced by the combined wind and wave loads, another carefully designed (i.e., tuned) spring and dashpot are added to the perpendicular direction of each Tuned Mass Damper (TMD) system that is used to control the vibrations of the tower and blades in one particular direction. With this simple modification, a bi-directional TMD system is formed and the vibrations in both the out-of-plane and in-plane directions are simultaneously suppressed. To examine the control effectiveness, the responses of the wind turbine without control, with separate TMD system and the proposed bi-directional TMD system are calculated and compared. Numerical results show that the bi-directional TMD system can simultaneously control the out-of-plane and in-plane vibrations of the wind turbine without changing too much of the conventional design of the control system. The bi-directional control system therefore could be a cost-effective solution to mitigate the bi-directional vibrations of offshore wind turbines.

Vibration Analysis for Machine Monitoring and Diagnosis: A Systematic Review

Untimely machinery breakdown will incur significant losses, especially to the manufacturing company as it affects the production rates. During operation, machines generate vibrations and there are unwanted vibrations that will disrupt the machine system, which results in faults such as imbalance, wear, and misalignment. Thus, vibration analysis has become an effective method to monitor the health and performance of the machine. The vibration signatures of the machines contain important information regarding the machine condition such as the source of failure and its severity. Operators are also provided with an early warning for scheduled maintenance. Numerous approaches for analyzing the vibration data of machinery have been proposed over the years, and each approach has its characteristics, advantages, and disadvantages. This manuscript presents a systematic review of up‐to‐date vibration analysis for machine monitoring and diagnosis. It involves data acquisition (instrument applied such as analyzer and sensors), feature extraction, and fault recognition techniques using artificial intelligence (AI). Several research questions (RQs) are aimed to be answered in this manuscript. A combination of time domain statistical features and deep learning approaches is expected to be widely applied in the future, where fault features can be automatically extracted from the raw vibration signals. The presence of various sensors and communication devices in the emerging smart machines will present a new and huge challenge in vibration monitoring and diagnosing.

Istraživanje stabilnosti kod unutrašnje obrade struganjem pomoću vretena bušilice sa pasivnim prigušivanjem ograničavajućim slojem

The vibrations produced in a boring tool in internal turning deteriorate the machined surface quality and reduce the tool life, which results in a massive noise during the machining. Therefore, unwanted vibrations are necessary to be eliminated by improving the boring bar's dynamic stiffness and damping capacity. This paper investigates a passive constrained layer damping (CLD) boring bar with a hybrid damping layer to study the internal turning system's stability. Initially, the dynamic models of the conventional and CLD tools are thoroughly studied using Euler-Bernoulli beam theory (EBT) and validated them with finite element modelling (FEM). The frequency response functions (FRFs) obtained from the impact hammer tests are used to estimate the modal parameters. With modal parameters, the semi-analytical stability lobe diagrams (SLDs) are plotted for the boring system with the conventional and CLD boring bar. Tool-tip responses for various cutting conditions are simulated numerically to validate and to study stability. The cutting experiments with traditional and CLD boring bar are conducted for stability analysis and compared tool-tip responses with numerical results. It is observed that both the numerical and experimental results agree with the selected cutting conditions from SLDs. It is also observed that the CLD boring bar with a hybrid damping layer reduced the vibration displacements by five times compared to the conventional one.

Separation of the Structure Signal by the Maximal Overlap Discrete Wavelet Transform and Fast Fourier Transform

Power spectral density (PSD) is used for evaluating a structure’s vibration process. Moreover, PSD not only shows a discrete form of vibration but also presents various components in a vibration structure. The superposition of multiple vibration patterns on the same spectrum poses difficulty in analyzing the spectral information in the way needed to find the structure’s discrete vibration. This paper proposes a method for separating the synthetic vibration signal into a structure’s discrete vibration and other extraneous vibrations using the maximal overlap discrete wavelet transform (MODWT) method combined with the method of fast Fourier transform (FFT). With the combination of these two algorithms, MODWT and FFT, the signals of the synthesized vibration have been separated into component signals with different frequency ranges. This means that PSD will be formed, which is based on the combination of the single power spectra of the component signals. Thus, the single spectrum of each of these constructed components can be used to evaluate the types of discrete vibrations coexisting in a structure’s vibration process. The survey results in this paper show the sensitivity and suitability of select types of discrete vibrations to be separated out during the assessment of the structural change, so as to achieve the best possible plan for eliminating the unwanted and unexpected noise and vibration components.

Online Digital Image Stabilization for an Unmanned Aerial Vehicle (UAV)

The Unmanned Aerial Vehicle (UAV) video system uses a portable camera mounted on the robot to monitor scene activities. In general, UAVs have very little stabilization equipment, so getting good and stable images of UAVs in real-time is still a challenge. This paper presents a novel framework for digital image stabilization for online applications using a UAV. This idea aims to solve the problem of unwanted vibration and motion when recording video using a UAV. The proposed method is based on dense optical flow to select features representing the displacement of two consecutive frames. K-means clustering is used to find the cluster of the motion vector field that has the largest members. The centroid of the largest cluster was chosen to estimate the rigid transform motion that handles rotation and translation. Then, the trajectory is compensated using the Kalman filter. The experimental results show that the proposed method is suitable for online video stabilization and achieves an average computation time performance of 47.5 frames per second (fps).

Dynamic reaction of machine tools to transient cutting conditions

Transient machining conditions often occur during the milling process, especially when complex toolpath layouts are deployed. Although modern CAM-aided toolpath generation algorithms aim at keeping the cutter engagement conditions as constant as possible and avoid sudden changes, this can not always be ensured. These transients are accompanied by temporary peak excursions in cutting forces and changing dynamic content of the excitation forces. This may have the potential to excite unwanted vibrations in the machining process and even may initiate chatter. Using a virtual process simulation environment it is possible to predict resultant dynamic forces along a complete NC tool path with high time and angular resolution and gain insights into the dynamics of transient events during machining operations. This simulation environment has the capability to use an analytical cutting force model, which spares extensive testing and parameter identification beforehand. Besides, well known empirical cutting formulations can be used as well. The results of the dynamic force prediction is compared against experimental results for different toolpath layouts and the dynamic behavior of the machine tool under cutting conditions will be discussed.

Innovative and affordable wearable solution for suppression of hand tremors

Hand tremor influences a huge number of individuals around the world. Tremor is characterised as unintended, cadenced muscle development. Albeit most tremors neither reason serious medical issues nor threaten life, most patients experience many troubles in performing everyday exercises. It is humiliating to numerous individuals, particularly more seasoned people. Tremor negatively affects personal satisfaction and decreases the ability to perform everyday life undertakings such as eating, drinking, writing, and changing clothing. Some patients with mild tremor do not visit doctors if tremor does not hinder their daily life activities. Their situations often worsen over time. There is currently very few to almost no external solution existing to cope with this medical condition. We have developed a glove that is able to dynamically conceive the motion of a user's hand and ascertain the difference between intentional movement and unintentional movement. Further, we have quantified, verified and attempted to provide a haptic response to the users' fingers with the help of coin motors to help counteract the unwanted vibration.

Modulationof The Recirculation Region Within Two Inline Square Rib Due toMagnetohydrodynamic FlowUsingComputational Fluid Dynamics

This study presents the turbulent flow around two square ribs. The numerical computations performed using k–ε model at Reynolds number (Re) = 60000 to quantify the turbulent transport measures. The magnetic field has been applied by Hartmann number (Ha) to generate the magnetohydrodynamic (MHD) flow. The reduction of recirculation region was observed due to the application of magnetic field in the flow. The weak recirculation has an effect on small vorticity generation, which leads to small turbulent kinetic energy (TKE) and TKE dissipation rate generation in the wake region behind the rib. The induced magnetic field is capable of controlling the vortex structures around the square ribs. Results in decreasing magnitude of turbulence level around and between the spaces of the square ribs. It may be hypothesized that by introducing magnetic field, the unwanted vibrations (due to vortex shedding behind the rib) of fully submerged structures can be controlled.

Data-Driven Iterative Trajectory Shaping for Precision Control of Flexible Feed Drives

With recent advances on material processing technologies, design requirements on modern manufacturing equipment are shifting toward achieving higher speed and accuracy rather than stiffness and load capacity. Motion systems used in additive or ultraprecision manufacturing equipment need to be designed to achieve greater dynamic positioning accuracy. As a result, feedforward (FF) control becomes an effective tool. This article presents a novel and practical FF controller design methodology to widen tracking bandwidth of precision motion systems suffering from structural dynamics and friction-induced disturbances. The proposed feedforward controller is designed to, first, compensate for the closed-loop servo dynamics to widen the command tracking bandwidth, second, mitigate unwanted vibrations, and third, compensate friction disturbance-induced positioning errors. The FF controller is structured in a trajectory prefilter form where the FF compensation signal is injected into the reference trajectory rather than torque command. This facilitates the FF controller to be applied conveniently without intervention with the servo controller. FF controller parameters are identified (tuned) automatically through machine in-the-loop-iterations. Parameter identification is posed as a convex optimization problem to realize safe and reliable auto-tuning. The proposed FF controller and its parameter tuning methodology are tested experimentally on an industrial scale multiaxis machine tool and its performance is validated.

Scientific Visualization of the Results of a Numerical Experiment of the Nonlinear Dynamics of a Nanoscale Beam Structure

The paper presents the results of scientific visualization of the nonlinear dynamics of contact interaction of a nanoscale beam structure under the action of an external harmonic load. The beam structure consists of two beams obeying the kinematic hypotheses of Euler-Bernoulli and S.P. Timoshenko. The constructed mathematical model takes into account geometric and constructive nonlinearities. The size-dependent behavior of the structure is implemented on the basis of the modified moment theory of elasticity. The resulting system of partial differential equations is reduced to a system of ordinary differential equations by the second order finite difference method. The Cauchy problem is solved by the fourth order Runge-Kutta method. In this work, using the methods of scientific visualization of the results of applying the methods of nonlinear dynamics, the influence of the size-dependent parameter and external load on the vibrations of the beam structure is investigated. As methods for studying nonlinear dynamics, the work uses wavelet spectra based on the mother Morlet, Fourier power spectra, signals. The use of scientific visualization methods makes it possible to develop specific recommendations for the operating conditions of the beam structure. This, in turn, makes it possible to avoid unwanted vibration modes of beam nanostructures, which are widely used as sensitive elements of sensors of micro and nano electromechanical systems.

Dynamic balancing of RECOVER robotic system

This paper presents a novel robotic system for the lower limb rehabilitation of post-stroke survivors. The model presented in this paper aims to demonstrate an innovative solution that helps in the mobilization of the hip and knee flexion/extension and the ankle plantar flexion/extension and eversion/inversion motions. The paper focuses on achieving the dynamic balancing of the hip-knee module, which due to high accelerations peak values and large size is prone to a certain degree of instability, leading to shaking forces and unwanted vibration that might reduce the safety feelings of the patient. A dynamically balanced mechanism will reduce noise, wear and fatigue and allow higher payload capacity.

Utilizing Macro Fiber Composite to Control Rotating Blade Vibrations

This work applies an active control algorithm, using a macro fiber composite (MFC) to mitigate the unwanted vibrations of a rotating blade. The algorithm is a second-order oscillator, having the positive displacement signal of the blade for input and the suitable control force to actuate the blade for output. This oscillator is linearly coupled with the blade, having in mind that their natural frequencies must be in the vicinity of each other. The rotating blade is modeled by representing two vibrational directions that are linearly coupled. An asymptotic analysis is considered to understand the resulting nonlinear phenomena. Several responses are included to portray the dynamical behavior of the system under control. From the results, we observe the asymmetry between the blade’s vibrational directions. Moreover, a verification is included for comparing the analytical and numerical results.

Exploitation of composite materials as vibration isolator and damper in machine tools and other mechanical systems: A review

Abstract Vibration isolators are devices that separate materials from sources of vibration. This review article focused on damping control through passive approaches. Damping principle and measurement of damping properties of composites were discussed. It further examined the vibration isolation and damping behaviour of selected composites and composite coating materials. Since vibration is detrimental to any mechanical system; therefore, habitable spaces and techniques are usually developed to avoid the transfer of vibration to a system. Similarly, shock absorbers or dampers are developed to limit the occurrence of stresses that could take place in a mechanical system and providing better reliability for the system. Damping is the energy dissipation in a material and is of significance in dynamic systems like the steering and suspension in turbo-machinery mounting and automotive, and tracking systems in aircraft which require damping from shock vibrations. One crucial mechanical characteristic of composites is their damping-ability. They are can protect engineering materials from failure which occurs typically from accrued damages. In recent years composite materials are developed on tools and other mechanical equipment to isolate them from vibration and to act as an absorber of shock, which improves material performance and reduces the probability of failure. Single and multi-layered coatings have been designed for several mechanical devices such as cutting tools. Damping composite coatings have been applied on materials usually to suppress the unwanted noise and vibration levels in different production industries. These coatings were also found to improve materials hardness and reduce the coefficient of variation of failure, especially in cutting tool materials.

An experimental study on granular dissipation for the vibration attenuation of skis

Due to the continuous deformations and irregularities of the surface of snow, alpine skis exhibit dynamic excitation, leading to drastic vibrations and decreased manoeuvrability. Therefore, attenuating these unwanted vibrations, while ensuring that the ski experience is not compromised, is an important challenge. The possibility of using granular material in a damping device is studied in this paper. A container that was partially filled with loose granules was fixed at the tip of an alpine ski to suppress vibrations by dissipating energy through collisions. The performance was verified experimentally by studying the transient response of a ski mounted in a horizontal cantilever orientation. Moreover, on-snow tests were performed. Different numbers of plastic granules were used as a dissipating material. To identify the nonlinear damping characteristics of the system, a Hilbert transform was used. In the laboratory test, the displacement amplitude decay was up to 16 percentage points higher when a granular dissipator was attached to the ski than without the damper. During field testing, acceleration amplitudes were 9% lower compared to the ski without the dissipator. This solution could possibly be adapted to other boardsports on a wide variety of terrain, including ground, water and snow.

Predicting thrust of aircraft using artificial neural networks

PurposeThe purpose of this study is to make artificial neural network (ANN)-based prediction about thrust using the flight control parameters of aircrafts.Design/methodology/approachIn today’s transportation, airplanes have an important place because of their safety, quality and speed. One of the most important parameters affecting the secure flying of aircrafts is the thrust value of aircraft engines. Determining the optimum thrust value should be investigated. If thrust value is less than optimum level, the flight safety runs a risk. Otherwise, fuel consumption goes high and some unwanted vibrations occur that cause uncomfortable flight. In this study, multi-layer perceptron ANNs, which are one of the intelligent optimization methods and frequently used in the literature, are preferred to predict the optimum thrust value during take-off, cruise and landing. The actual flight data, which is taken from the black box of an Airbus A319 aircraft, is used to train ANN models using back propagation algorithms. Velocity, altitude and ambient temperature values of the aircraft are selected as inputs and the thrust value is selected as output. During the training process of ANN, eight different training algorithms with different structures are used to figure out optimum ANN model with minimum error.FindingsDifferent ANN models were trained using eight different training algorithms. The ANN model with minimum error has multi-layer perceptron structure, which is trained using Levenberg–Marquardt (LM) algorithm.Research limitations/implicationsTo obtain the ANN structure with minimum error training, process takes more than a day depending on the capacity of a computer for LM training algorithm. But after training process, the trained ANN model produces sufficient output in a few milliseconds.Practical implicationsTotally 15,670 input-output data sets are obtained from an Airbus A319 aircraft. 12,889 of them are used as training data and the rest of the data sets, selected randomly are used as test data. Test data sets are never used in training phase, and the obtained results show that the ANN model successfully predicts thrust value using unseen input data.Social implicationsThe ANN could be used as an alternative method to predict other flight control parameters of aircrafts.Originality/valueTo the best of authors’ knowledge, this study is the first example in literature to predict the thrust value of the aircraft using ANN.

Tunable vibration control in a microelectromechanical resonator array by means of parametric coupling between mechanical and electrical modes

Vibration control in flexible structures at both the micro and macro scale has been a subject of considerable research interest over the last few decades. Various active, semi-active and passive vibration control schemes have been proposed for applications ranging from attenuating unwanted vibrations in structural components to controlling the ring down time in high-Q mechanical oscillators. Here, we present a simple, yet highly effective method to passively attenuate large amplitude resonant vibrations in an array of membrane-based microelectromechanical (MEM) resonators. By capacitively coupling the MEM array to a resonant electrical circuit tuned to half the mechanical resonance frequency, the vibrational energy in the array can be converted to electrical energy via parametric mode coupling between the mechanical and electrical resonator. Simulation and experimental studies indicate that both the rate of vibration attenuation and the degree of suppression can be effectively controlled by tuning electrical parameters such as the resistance and the initial voltage in the circuit. The extension of the control scheme to multi-mode vibrations by making use of multiple shunted electrical resonators will also be briefly discussed.

Wave Attenuation of a Pre-Tensioned Wire with Periodic Spring Supports Subjected to a Moving Force

The pantograph-catenary system is essential to the operation of modern railways. The overhead catenary system serves to deliver steady electric power to the trains running on the railways. The propagation of waves in the catenary system can be significantly affected by its interaction with the pantograph. To investigate the wave transmission via the contact wires of a catenary system, a simplified model composed of a pre-tensioned wire suspended by periodic spring supports is adopted. For a periodic structure with wider band gaps (or stop bands), a larger cluster of frequencies of the transmitting waves can be filtered out. This is beneficial to the maintenance of the catenary system as unwanted vibrations have been reduced. To widen the band gaps, a resonator can be equipped on each of the spring supports for attenuation of a wider range of transmitting waves in the pre-tensioned wire. In this study, a unit cell conceived as the spring–resonator–wire unit is adopted to formulate the dispersion equation in closed form, from which the critical condition for widening the band gaps is derived. In addition, the moving pantograph is modeled as a moving force. From the exemplar study, it was shown that the installation of proper resonators on a catenary system can increase the gap bandwidth, such that the pantograph-induced wave transmission in the contact wires will be attenuated or filtered out.

Robust control for vibration control systems with dead-zone band and time delay under severe disturbance using adaptive fuzzy neural network

This study proposes a novel adaptive control method to deal with the dead-zone and time delay issues in actuators of vibration control systems. The controller is formulated based on a type-2 fuzzy neural network integrating with a new modification of Riccati-like equation. The developed new type Riccati-like equation is significant as it reduces energy consumption of control inputs to minimum. Two approaches are suggested to improve performance of the system using the basic elements of Riccati equation. In addition, a fuzzy neural network is applied to approximate the unmodeled dynamics and a sliding mode controller is developed to enhance the robustness of the system against uncertainties and disturbances. After proving the stability of the proposed controller via Lyapunov criterion, the effectiveness of the proposed approach is validated based on computer simulation for vibration control of a vehicle seat suspension. It is demonstrated that the unwanted vibrations due to external excitations are well controlled despite of the presence of dead-zone and time delay in actuators. Furthermore, when comparing with other two state-of-the-art robust controllers [23,33], the proposed controller provides better vibration suppression capacity and requires less energy consumption.