Vibration Compensation Research Articles

Development of two color laser diagnostics for the ITER poloidal polarimeter

Two color laser diagnostics using terahertz laser sources are under development for a high performance operation of the Large Helical Device and for future fusion devices such as ITER. So far, we have achieved high power laser oscillation lines simultaneously oscillating at 57.2 and 47.7 μm by using a twin optically pumped CH(3)OD laser, and confirmed the original function, compensation of mechanical vibration, of the two color laser interferometer. In this article, application of the two color laser diagnostics to the ITER poloidal polarimeter and recent hardware developments will be described.

Interferometer Systems on LHD

This paper describes the interferometer systems on the Large Helical Device (LHD). LHD is equipped with five interferometer systems, each of which has a different operational purpose and measurable electron density range. A single-channel millimeter-wave interferometer is mainly used for low-density plasmas along a horizontal line of sight on the equatorial plane. Wavelengths of 1 and 2 mm are used for vibration compensation based on two-color interferometry, which has been used since the first operation of LHD. A 13-channel CH3OH laser interferometer (wavelength of 119 μm) covers almost the whole poloidal cross sections of LHD plasmas with a chord separation of 90 mm. It routinely provides temporal behavior and profiles of the electron density. The laser has been developed as a collaboration between the National Institute for Fusion Science (NIFS) and Chubu University. An 80-channel CO2 laser interferometer (10.6 μm) is employed for high-density plasmas such as superdense core plasmas. It adopts an imaging technique with three slablike beams and array detectors to measure the density profile precisely. A phase contrast imaging interferometer, which measures density fluctuations, is combined with the CO2 laser interferometer. Since LHD has strong magnetic shear, a distribution of the density fluctuations is evaluated by using shear technique. A conventional millimeter-wave (4 mm) interferometer is also installed at a divertor region to measure dynamic density responses in a divertor leg. The phase counter used on these interferometers was originally developed at NIFS. The phase resolution of a typical phase counter is 1/100 fringe with a temporal response of 10 μs.

Scanning beam medium infra-red interferometry for plasma density measurements

In magnetically confined fusion experiments interferometry is commonly used to measure plasma electron density. This because interferometry is a very reliable technique, not affected by calibration problem. The main drawbacks of interferometers are the integral characteristic of the measurement and the fringe loosing problem. Scanning beam interferometry can always overcome the former problem and in some cases the second as well. The advantages of the scanning beam technique can better exploited in two colours vibration compensated medium infra-red (MIR) interferometers. Indeed the short wavelength of the probing beams provide small beam sizes allowing plasma density measurement along many non-overlapping paths, furthermore the vibration compensation system relaxes the requirement of massive interferometer structures embracing the fusion device, actually allowing to install back-reflecting mirror directly attached to the experimental machine.As an example of application of this technique the two-color medium-infra-red-compensated scanning beam interferometer installed on the Frascati Tokamak Upgrade (FTU) experiment is presented. We present also a preliminary design of a scanning interferometer for the new proposed Fusion Advanced Studies Torus (FAST) experiment. The interferometer uses retroreflectors installed inside the vessel to back reflect the scanning beams; this will allow realizing scanning beams measuring from the plasma edge. This feature in principle can solve the fundamental problem of interferometers: the fringe loosing problem.

In-vessel optic system Design of FIR interferometer/polarimeter system for KSTAR

An FIR interferometer/polarimeter system will be constructed in the Korea Superconducting Tokamak Advanced Research (KSTAR) device for electron density profile measurements. Due to the complex inner-wall geometry and long diagnostics ports, a specially designed in-vessel optic system is necessary to ensure a sufficient number of beam lines for inversion of the density profile. A single channel on the vertical center line and seven channels on the tangential plane will be placed using corner-cube reflectors mounted on the vacuum vessel. To avoid interferences with in-vessel structures such as neutral beam protection tiles and diagnostics systems, the positions of these beam lines are designed carefully using an in-vessel beam positioning module placed inside a narrow diagnostics port. Since these in-vessel optic components must be mounted on the vacuum vessel, a vibration compensation system needs to be integrated on the module. Designs of the corner-cube reflectors and the beam positioning modules have been performed for these purposes. A prototype corner-cube reflector will be installed on KSTAR before the 2010 campaign and vibration compensation performance and surface degradation due to plasma will be tested.

Active vibration control modules for damping, compensation, measurement and dynamic testing.

The active vibration control module was introduced previously as part of active vibration damping system for optical tables and other precision vibration isolated platforms. This paper describes steps to expand the application of those modules to other tasks, namely, compensation of forced vibration in local areas and dynamic testing of structures. Vibration damping of most significant structural modes had been achieved using a small number of properly placed active dampers. This did not affect forced tonal vibration. Current state of the art does not offer a practically feasible way to suppress all vibration, forced and normal, over the total table surface. However, by placing vibration control modules around a local area of the table supporting a vibration sensitive device, it is possible to abate forced tonal vibration in this area. Feedback control for vibration compensation will be discussed along with experiments demonstrating stable concerted work of several vibration control modules. In application to dynamic testing, the actuator is excited by white noise, and the sensor signal is processed to calculate the dynamic compliance. The test data show that the vibration control modules can be used to measure dynamic compliance with precision comparable to that of dedicated vibration measurement systems.

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.

2D34 Compensation for slippage and vibration of planetary rover with flexible structures

This paper proposes the synthesis procedure for the motion control system to simultaneously reduce slippage and vibration in a planetary rover. It is confirmed that the slippage generating in early phase of the rover motion is involved with acceleration and deceleration of the driving mechanism. The vibration due to flexibility of the rover is also induced by self-motion, that is acceleration and deceleration. Therefore, in this paper, we focus on the design of the acceleration target for the control system. The acceleration profile is then derived only by solving a regulator problem with an initial velocity and taking account of the maximum value in acceleration.

Suspension system having active compensation for vibration

A suspension system for a seat of a vehicle comprises a base, a linkage, and a seat attached to the base via the linkage. A pneumatic shock absorber provides a respective resistance level against movement of the seat with respect to the base based on a corresponding pressure level of air or gas within the pneumatic shock absorber. A set of cylindrical members are spaced apart beneath the seat. A tension member is arranged to engage the cylindrical members. The tension member is attached to the seat via a bracket. An electric motor is capable of driving one of the cylindrical members. A first sensor is arranged to detect first sensor data associated with an instantaneous position of the seat versus time. A controller generates a first control signal for the electric motor to change a height of the seat in opposition to a change in the instantaneous position of the seat and a second control signal to change the pressure level.

Elevator with vertical vibration compensation

The present invention provides an elevator comprising a car (1) arranged to travel along guide rails (6) within a hoistway (8) and a main drive (52,54,56,DMC) to propel the car (1). A sensor (30;40) is mounted on the car (1) to measure a vertical travel parameter (Vc;Ac) of the car (1), a comparator (32) compares the sensed car travel parameter (Vc;Ac) with a reference value (Vr;Ar) derived from the main drive (52,54,56,DMC), and an auxiliary motor (24) is mounted on the car (1) to exert a vertical force (F) on at least one of the guide rails (6) in response to an error signal (Ve;Ae) output from the comparator (32).

Conceptual Design of a Dispersion Interferometer Using a Ratio of Modulation Amplitudes

Since a dispersion interferometer is free from mechanical vibrations, it does not need a vibration compensation system even for a probe beam with a short wavelength. This paper describes a new signal processing of the dispersion interferometer using a ratio of modulation amplitudes with a photoelastic modulator. The proposed method is immune to changes in detected signal intensities, thus making the signal processing system simple. Designs of the optical system of the dispersion interferometer for proof of principle, especially specification of a nonlinear optical crystal, are also shown.

Making a commercial atomic force microscope more accurate and faster using positive position feedback control

This paper presents experimental implementation of a positive position feedback (PPF) control scheme for vibration and cross-coupling compensation of a piezoelectric tube scanner in a commercial atomic force microscope (AFM). The AFM is a device capable of generating images with extremely high resolutions down to the atomic level. It is also being used in applications that involve manipulation of matter at a nanoscale. Early AFMs were operated in open loop. Consequently, they were susceptible to piezoelectric creep, thermal drift, hysteresis nonlinearity, and scan-induced vibration. These effects tend to distort the generated image and slow down the scanning speed of the device. Recently, a new generation of AFMs has emerged that utilizes position sensors to measure displacements of the scanner in three dimensions. These AFMs are equipped with feedback control loops that work to minimize the adverse effects of hysteresis, piezoelectric creep, and thermal drift on the obtained image using proportional-plus-integral (PI) controllers. These feedback controllers are often not designed to deal with the highly resonant nature of an AFM's scanner nor with the cross coupling between various axes. In this paper we illustrate the improvement in accuracy and imaging speed that can be achieved by using a properly designed feedback controller such as a PPF controller. Such controllers can be incorporated into most modern AFMs with minimal effort since they can be implemented in software with the existing hardware. Experimental results show that by implementing the PPF control scheme, relatively good images in comparison with a well-tuned PI controller can still be obtained up to line scan of 60 Hz.

Diamagnetic measurements in the STOR-M tokamak by a flux loop system exterior to the vacuum vessel

Diamagnetic measurements of poloidal beta have been performed in the STOR-M tokamak by a flux loop placed exterior to the vacuum chamber with compensation for the vacuum toroidal field using a nonenclosing coplanar coil, and vibrational compensation from auxiliary coils. It was found that in STOR-M conditions (20% toroidal magnetic field decay over discharge) there is significant influence on the diamagnetic flux measurements from strong residual signals, presumably from image currents being induced by the toroidal field coils, requiring further compensation. A blank (nonplasma) shot is used specifically to eliminate the residual component which is not proportional to the toroidal magnetic field. Data from normal Ohmic discharge operation is presented and calculations of poloidal beta from coil data (beta(theta) approximately 0.5) is found to be in reasonable agreement with the values of poloidal beta obtained from measurements of electron density and Spitzer temperature with neoclassical corrections for trapped electrons. Contributions present in the blank shot (residual) signal and the limitations of this method are discussed.

Limiting performance of active vibration compensation in free multi‐degree‐of‐freedom mechanical systems.

Examples of free (not supported) mechanical system requiring active vibration control range from space structures to vibration‐isolated platforms for sensitive equipment. While active damping systems reducing resonance vibrations of the structure received significant attention and reached practical implementation, active vibration compensation, or cancellation of forced vibration, is still problematic in complex systems. In this work, active vibration compensation is considered in frame of limiting performance approach that aims at estimating the best results attainable in the whole class of linear multi‐degree‐of‐freedom systems. Several design goals are considered, including absolute and relative displacements of various points of the system. The resulting estimates are valid for all possible sets of internal active forces. The limiting performance is estimated in terms of frequency domain and work performed by active forces on system displacements, which is considered a measure of the control effort. These estimates are expressed as exact inequalities in explicit analytical form. Active force distributions emerging from limiting performance analyses can assist in finding rational system configurations and optimal controls. Minimum active work, expressed in terms of passive subsystem parameters, provide a criterion for optimization of a structure as a potential host for an active vibration control system.

Piezoelectric drive systems in ultraprecision machines: a review of the state-of-the-art

The production of ultraprecision and micromachined components has been enabled by the development of a range of drive system technologies with commensurate resolution. In particular, systems based on piezoelectric actuators have provided an alternative to mechanical drive systems. These actuators have been incorporated in drive systems for high resolution positioning of atomic force microscopes, high frequency vibration compensation and high speed valves for diesel injection. The performance of systems based on piezo actuators is characterised by high electromechanical advantage, submillisecond response times and nanometric resolution. In many cases the inherent limited range of travel has been compensated by the design of flexure systems. When combined, these provide precision control free of friction and backlash, otherwise unattainable with conventional mechanical drives. The objective of this paper is to give an overview of the current state-of-the-art. It will highlight the novel application of these alternative technologies. The advantages of piezoelectric technology and their limitations will be discussed.

Compensation of torsional vibrations in rods by piezoelectric actuation

In this paper, the piezoelectric compensation of torsional vibrations in rods caused by external excitations is studied. As an illustrative example, a laminated rod containing piezoelectric shear actuators is assumed to be fixed at the one end, and the other end is subjected to a torsional couple; additionally, a distributed torsional couple per unit length is acting. In such a system, cross-sectional warping is known to be present. The consideration of piezoelectric eigenstrains requires an extension of Saint Venant’s theory of torsion, which is achieved by introducing an additional warping function. Using D’Alembert’s principle, the boundary value problems for Saint Venant’s warping function, the additional warping function and the torsional angle are obtained. From the latter boundary value problems, the distribution of piezoelectric actuation is derived in order to completely compensate the external excitations, i.e. an analytical solution of the corresponding shape control problem is obtained. Finally, the results are verified by means of three-dimensional finite element computations.

Calibration of a high spatial resolution laser two-color heterodyne interferometer for density profile measurements in the TJ-II stellarator

A high spatial resolution two-color (CO(2), lambda=10.6 microm, He-Ne, lambda=633 nm) interferometer for density profile measurements in the TJ-II stellarator is under development and installation, based in the currently operational single channel two-color heterodyne interferometer. To achieve the objectives of 32 channels, with 4-5 mm lateral separation between plasma chords, careful design and calibration of the interferometric waveforms for both the measurement and vibration compensation wavelengths are undertaken. The first step has been to set up in our laboratories an expanded-beam heterodyne/homodyne interferometer to evaluate the quality of both interferometric wavefronts, a reported source of poor vibration compensation and thus low resolution in the density profile measurements. This novel interferometric setup has allowed us to calibrate the spatial resolution in the profile measurements resulting in approximately 2 mm lateral resolution in the reconstruction of the interferometric wavefront.

Development of terahertz laser diagnostics for electron density measurements

A two color laser interferometer using terahertz laser sources is under development for high performance operation on the large helical device and for future burning plasma experiments such as ITER. Through investigation of terahertz laser sources, we have achieved high power simultaneous oscillations at 57.2 and 47.6 microm of a CH(3)OD laser pumped by a cw 9R(8) CO(2) laser line. The laser wavelength around 50 microm is the optimum value for future fusion devices from the consideration of the beam refraction effect and signal-to-noise ratio for an expected phase shift due to plasma. In this article, recent progress of the terahertz laser diagnostics, especially in mechanical vibration compensation by using a two color laser operation and terahertz laser beam transmission through a dielectric waveguide, will be presented.

Book Review: Manfred Nader, Compensation of Vibrations in Smart Structures: Shape Control, Experimental Realization and Feedback Control.

ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und MechanikVolume 88, Issue 10 p. 816-816 Book Review Book Review: Manfred Nader, Compensation of Vibrations in Smart Structures: Shape Control, Experimental Realization and Feedback Control . T. Nestorović, T. Nestorović MagdeburgSearch for more papers by this author T. Nestorović, T. Nestorović MagdeburgSearch for more papers by this author First published: 25 September 2008 https://doi.org/10.1002/zamm.200890018AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume88, Issue10October 2008Pages 816-816 RelatedInformation

Limits to the sensitivity of a low noise compact atomic gravimeter

A detailed analysis of the most relevant sources of phase noise in an atomic interferometer is carried out, both theoretically and experimentally. Even a short interrogation time of 100 ms allows our cold atom gravimeter to reach an excellent short term sensitivity to acceleration of 1.4×10-8g at 1 s. This result relies on the combination of a low phase noise laser system, efficient detection scheme and good shielding from vibrations. In particular, we describe a simple and robust technique of vibration compensation, which is based on correcting the interferometer signal by using the ac acceleration signal measured by a low noise seismometer.

Anti-Jerk & amp; Idle Speed Control with Integrated Sub-Harmonic Vibration Compensation for Vehicles with Dual Mass Flywheels

Anti-Jerk & amp; Idle Speed Control with Integrated Sub-Harmonic Vibration Compensation for Vehicles with Dual Mass Flywheels