Presence Of External Vibrations Research Articles

A wavefront division multiplexing holographic scheme and its application in looking through diffuser

We present a spatial light modulator (SLM) assisted compact holographic method and illustrate its application by imaging through a random scattering medium. The merit of the proposed method is wavefront division multiplexing, i.e. the dual wavefront modulations over a single SLM. Two different wavefront shapes: a reference-light shape and a phase object, are combined over the SLM. One advantage of this scheme is the flexible modulation of the reference light. The experimental implementation of this method is demonstrated by quantitatively reconstructing different phase objects from the randomly scattered light. This new scheme greatly simplifies the experimental configuration and presents a better stability even in presence of external vibrations, opening avenues for the holography-based scattering imaging application.

ASTATIC IDENTIFIER IN THE CONTROL SYSTEM OF THE GYROTHEODOLITE’S SENSITIVE ELEMENT

The basic features of working conditions of means of ground orientation are considered. It is shown that in the presence of external vibration the appearance of additional measurement error is possible. The main characteristics of external vibration are given. A new feedback controller structure has been proposed, which includes an astatic state identifier. The mathematical model of the device in the form of space of states taking into account external vibration is considered. It is proposed to control the position of the sensitive element by the method of modal control by an incomplete state vector. It is assumed that the measured parameter for identifying the state vector is the angle of deviation of the sensitive element of the gyrotheodolite in azimuth. The analysis of observability at the set structure of matrices of a condition and measurements is carried out. To reduce the estimation error that occurs due to the presence of uncontrolled vibration, the state identifier uses both proportional and integrated feedback channels. The coefficients of an observer with an astatic component in the equation of state are determined under the assumption that the evaluation process should be aperiodic. Simulation of the work of the astatic identifier on the basis of the developed software model is carried out. The coefficients of the software model are selected on the basis of constructive solutions used at the present stage of development of systems for determining azimuthal directions based on gyrotheodolites. The coefficients of the observer for the given parameters of the device are calculated. The simulation results showed that the application of the proposed method can significantly reduce the impact of the constant component of external vibration. The error of estimating the angular coordinates and velocities used in the control system of the position of the sensing element, the astatic status identifier goes to zero, while the static system has a constant component of the error. In further research it is planned to build a generalized system, which includes control of the motion of the sensing element both in the azimuth and in the non-gyrostabilized plane.

Dedicated Nonlinear Control of Robot Manipulators in the Presence of External Vibration and Uncertain Payload

Robot manipulators are often tasked with working in environments with vibrations and are subject to load uncertainty. Providing an accurate tracking control design with implementable torque input for these robots is a complex topic. This paper presents two approaches to solve this problem. The approaches consider joint space tracking control design in the presence of nonlinear uncertain torques caused by external vibration and payload variation. The properties of the uncertain torques are used in both approaches. The first approach is based on the boundedness property, while the second approach considers the differentiability and boundedness together. The controllers derived from each approach differ from the perspectives of accuracy, control effort, and disturbance properties. A Lyapunov-based analysis is utilized to guarantee the stability of the control design in each case. Simulation results validate the approaches and demonstrate the performance of the controllers. The derived controllers show stable results at the cost of the mentioned properties.

Defect detection in deep groove ball bearing in presence of external vibration using envelope analysis and Duffing oscillator

This paper deals with detection of local defects existing on races of deep groove ball bearing in the presence of external vibrations using envelope analysis and Duffing oscillator. Experiments have been carried out using a test rig for capturing the vibration signals of test bearing. The external vibration has been imparted to the housing of the test bearing through electromechanical shaker. In envelope analysis the centre frequency has been selected using the spectral kurtosis for the filters length of 32 and 64 for different bandwidths. Through this study, it has been revisited and confirmed that the defect detection in envelope analysis mainly depends on the selection of centre frequency and bandwidth. The spectra of selected centre frequency with several bandwidths have been studied and compared for identification of defective frequency. The system defined by the Duffing equation entered into the periodical state from the chaotic state at the critical value of disturbing periodic force in the presence of defective bearing signal. The state change has been identified using the phase plane trajectories and Lyapunov exponents of Duffing equation. It is worth to mention here that envelope spectrum reveals the information about the defect frequencies and their harmonics. However, the Duffing oscillator only confirms the presence of defect frequencies by indicating closed phase plane trajectories and negative Lyapunov exponents. Authors believe that for speedy assessment about the presence of defects on races of rolling element bearings, the use of Duffing oscillator may be preferred.

Improving defect detection of rolling element bearings in the presence of external vibrations using adaptive noise cancellation and multiscale morphology

Identifying the signals of defective rolling element bearings of industrial machines in the presence of external vibrations is a difficult task. Therefore, in this article, attempt has been done to improve the defect detection of rolling element bearings in the presence of external vibrations using adaptive noise cancellation (ANC), self-adaptive noise cancellation (SANC), and mathematical multiscale morphology (MMM). Circular defects (diameter = 400 µm), on either of the races of the test bearings, have been artificially created and external random vibrations have been imparted to the defective test bearings using an electromechanical shaker in the experimentation reported herein. The defective bearing signal-to-external noise (vibration) ratio has been significantly enhanced after the application of ANC, SANC, and MMM. This resulted in the clear identification of defect frequencies in the vibration spectrum. It is essential to mention here that in ANC technique the least mean square (LMS) algorithm with and without signum function has been used. However, in MMM technique, triangular structural elements are utilized during the closing operation and bottom-hat transform (BHat). In comparison to the LMS algorithm without signum function, the LMS algorithm with signum function has been proved more effective and efficient in minimizing the error. Authors noticed that the MMM filter is much effective for noise removal.

Preparation of self-compacting ultra-high toughness cementitious composite

A self-compacting ultra-high toughness cementitious composite (UHTCC) reinforced by discontinuous short polyvinyl alcohol (PVA) fibers, which exhibits self-compacting performance in the fresh state and strain-hardening and multiple cracking behavior in the hardened state, was developed through controlling flow properties of fresh mortar matrix at constant ingredients concentrations determined by micromechanical design and ensuring uniform fibers dispersion. The superplasticizer was utilized to adjust its flow properties in the fresh state. A series of flow tests, including deformability test, flow rate test, and self-placing test, were conducted to characterize and quantify the fluidity performance of fresh mortar matrix and self-compactability of fresh UHTCC. It is revealed that the utilization of superplasticizer is efficient in producing the fresh mortar matrix with desirable fluidity and the resulting self-compacting UHTCC. In addition, results of four point bending tests on the developed self-compacting UHTCC confirm the insensitivity of mechanical performance of self-compacting UHTCC to the presence of external vibrations as well as the flexural characteristics of deformation hardening and multiple cracking.

Asymptotic tracking control scheme for mechanical systems with external disturbances and friction

In this paper, a novel control scheme is proposed for the tracking problem of mechanical systems in the presence of external vibrations and friction. An acclerometer is installed on the load frame in the mechanical systems to detect the external vibrations. Then a neural network (NN) compensator with accelerometer signal as its input is adopted for feedforward compensation of external vibrations. Another NN is employed to compensate for the unknown system dynamics thereby compensate for friction. To eliminate the residual reconstruction error coming from NN approximation, the robust integral of the sign of the error (RISE) feedback term is integrated into the control scheme. A Lyapunov stability analysis is performed to show that the proposed control scheme can be used to yield a semi-global asymptotic tracking result rather than uniformly ultimately bounded (UUB) results derived by typical NN-based controllers. In particular, exact models of the plant, external disturbances and the accelerometer are not needed. A comparative study on system performance is conducted on a two-link robot manipulator between the proposed control scheme and the main conventional control methods for showing satisfactory tracking performance of the proposed control scheme.

System and method for weighing items such as mailpieces in the presence of external vibration

A system and method for weighing of items such as mailpieces in the presence of external vibration such as ground noise. The system includes a scale system having a platform connected to a load cell, which provides an output signal to an analog-to-digital converter. The resulting digital output signal is processed by a low pass filter and analyzed by a microprocessor to determine weights of items on the platform. The microprocessor also determines postage amounts as functions of the weights and outputs these postage amounts to a postage meter. The system also includes an accelerometer and a limit detector for generating a no go signal if external vibrations exceed a predetermined limit. The microprocessor accepts a weight as valid if the external vibrations do not exceed the limit at any time while the weight is being determined and otherwise initiates an alternative weight determining method.

System and method for weighing items such as mailpieces in the presence of external vibration

A system and method for weighing of items such as mailpieces in the presence of external vibration such as ground noise. The system includes a scale system having a platform connected to a load cell, which provides an output signal to an analog-to-digital converter. The resulting digital output signal is processed by a low pass filter and analyzed by a microprocessor to determine weights of items on the platform. The microprocessor also determines postage amounts as functions of the weights and outputs these postage amounts to a postage meter. The microprocessor determines the weights as the median of the peak to valley difference of the digital output signal when the digital output signal peak to valley difference is less than a predetermined value. The microprocessor identifies peaks and valleys of the digital output signal by determining when the derivative of the signal changes sign. The microprocessor estimates the weight as an average of a sum of medians for N preceding cycles if the digital output signal does not converge.