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Industrial robot arms experience position inaccuracies due to the output cogging torques of the DC servomotors. Therefore, in an attempt to resolve these position problems, an electro-rheological (ER) robotic system is considered as an actuator to drive the robot arm rapidly in both directions. This ER robotic system consists of two ER clutches, an ER brake, a gear train, an encoder and a robot arm. The ER clutches produce clockwise and anti-clockwise rotations. The ER brake decelerates and halts the robot arm. The main aim of this paper is to validate a controller model of the ER robotic arm. Next, a trend study is used to determine the optimum working conditions of the ER actuated-robotic arm. The robotic displacements of both the ER rotary devices and the commercial DC servomotors are compared in terms of position accuracy and speed of response. Finally, the repeatability of the robotic end positions is examined in order to determine the importance of the ER brake.

Electro-rheological (ER) fluid devices are becoming more popular in the industrial applications. This is due to the fast speed of response and large output dynamics of the ER actuators. The usefulness of this ER dynamic response is considered in the material winding processes where fast output bi-directional responses are essential. Therefore in the present paper, an ER twin clutch mechanism is proposed. This clutch mechanism consists of two identical clutches that rotate in opposite directions. But the bi-directional output dynamics of the clutch mechanism is not well understood due to its non-validation in the past. The main aim of this paper is to model the reciprocating responses of the clutch mechanism and then perform model validation with the measured test results. The close agreements between the modeled and experimental data indicate that the ER output angular velocity and displacement responses’ models of the clutch mechanism are validated. These validated models can then be used to predict accurately the reciprocating output responses of the twin ER clutch mechanism for future research studies.

Aircraft landing gears are subjected to a wide range of excitation conditions, which result in conflicting damping requirements. A novel solution to this problem is to implement semi-active damping using magnetorheological (MR) fluids. This paper presents a design methodology that enables an MR landing gear to be optimized, both in terms of its damping and magnetic circuit performance, whilst adhering to stringent packaging constraints. Such constraints are vital in landing gear, if MR technology is to be considered as feasible in commercial applications. The design approach focuses on the impact or landing phase of an aircraft's flight, where large variations in sink speed, angle of attack and aircraft mass makes an MR device potentially very attractive. In this study, an equivalent MR model of an existing aircraft landing gear is developed. This includes a dynamic model of an MR shock strut, which accounts for the effects of fluid compressibility. This is important in impulsive loading applications such as landing gear, as fluid compression will reduce device controllability. Using the model, numerical impact simulations are performed to illustrate the performance of the optimized MR shock strut, and hence the effectiveness of the proposed design methodology. Part 2 of this contribution focuses on experimental validation.

Electro-rheological (ER) fluid devices are smart actuators that possess several advantages such as controllable output dynamics and fast speed of response. Due to these output capabilities, an ER clutch is studied for the possibility of actuating the robotic arm. This is achieved by laying a few objectives. The main focus of this paper is to perform model validations of an ER velocity response of this ER clutch. Next, it is aimed to determine a method for rapid energization and de-energization of the ER output velocity for delivering fast start-stop robotic motions. The third aim is to employ the trend study on the ER output velocity response in order to define suitable input parameters for optimum ER robotic performances. The final aim is to determine the reliability of the tested ER fluids shearing in the ER clutch for long-term robotic applications.

Robot arm positioning is an important factor in the robotic process. However, the robot manipulator experiences positioning inaccuracies. This positioning error is due to the dynamic inefficiencies of its actuator: DC servomotor. In a bid to resolve this actuator problem, an electro-rheological (ER) clutch-brake mechanism is employed. This clutch-brake mechanism can actuate and halt the motion of the robot arm. This rotary mechanism consists of two similar clutches that are driven to rotate in the opposite directions and an individual ER brake that provides braking torques to halt the manipulator at the required positions. The main aim of this paper is to establish a control strategy for the ER actuated robot arm by means of model validation with the experimental results. This study is conducted to understand the ER robotic positioning control for future applications.

Positioning accuracies of the robot arms are important at fast maneuvering speeds of the manipulators. In the past, many researchers had investigated the precisions of the robotic arms. They reported that these robotic positioning errors are caused by the dynamic inefficiencies of the robotic actuators; DC servomotors. Therefore, in order to resolve this actuator's issue, a twin electro-rheological (ER) clutch mechanism that consists of two counter-rotating ER clutches is employed. This is due to its output dynamics being unaffected by the output cogging torque of the driving motors. Also, this clutch mechanism can perform rapid reversal responses in bi-directional mode. In this present paper, two kinematics models that describe the output angular velocity and displacement behaviors of this clutch mechanism undergone validations. Next, the trend studies of these angular kinematics responses are conducted in order to determine the methodology to generate the fastest reversal motions of the clutch mechanism.

This paper describes progress on a new technique to detect pipeline features and leaks using signal processing of a pressure wave measurement. Previous work (by the present authors) has shown that the analysis of pressure wave reflections in fluid pipe networks can be used to identify specific pipeline features such as open ends, closed ends, valves, junctions, and certain types of bends. It was demonstrated that by using an extension of cross-correlation analysis, the identification of features can be achieved using fewer sensors than are traditionally employed. The key to the effectiveness of the technique lies in the artificial generation of pressure waves using a solenoid valve, rather than relying upon natural sources of fluid excitation. This paper uses an enhanced signal processing technique to improve the detection of leaks. It is shown experimentally that features and leaks can be detected around a sharp bend and up to seven reflections from features/leaks can be detected, by which time the wave has traveled over 95 m. The testing determined the position of a leak to within an accuracy of 5%, even when the location of the reflection from a leak is itself dispersed over a certain distance and, therefore, does not cause an exact reflection of the wave.

Magnetorheological (MR) and electrorheological (ER) dampers are known to exhibit nonlinear behaviour which can make it difficult to predict their performance, particularly when they are integrated into engineering structures. As a result it can be impossible to properly assess the feasibility of using such semi-active devices to solve practical engineering problems. In this paper, a new model format is proposed which represents an extension of earlier work by the authors. The proposed model is more general and yet maintains the physical significance of key parameters. A novel model updating (or system identification) technique is developed so that the model can account for the behaviour of various configurations of device without the need for prior knowledge of the fluid properties. The technique relies upon the iterative adjustment of the model's stiffness parameter so that the quasi-steady behaviour of the device can be estimated. Correlation between a bi-viscous model and the estimated quasi-steady behaviour is used as the criterion for choosing the most suitable value of stiffness. The modelling technique is completed by establishing empirical shape relationships between the pre-yield parameters, post-yield parameters, yield force and the applied excitation conditions. The modelling and identification procedures are applied to an MR damping device and the results are validated by comparing predicted and experimental responses under both non-sinusoidal and broadband excitation conditions.

In the squeeze-flow mode of operation, electrorheological (ER) fluid is placed between two electrodes, which are free to translate in a direction roughly parallel to the direction of the applied electric field. Consequently, the ER fluid is subjected to alternate tensile and compressive strokes and shearing of the fluid also occurs. Available displacements are small but large forces are available from compact devices and there are many potential applications, notably in vibration isolation. The present authors have spent several years developing mathematical models to account for the observed behaviour of ER fluids in squeeze-flow. Previous attempts at modelling squeeze-flow behaviour have been partially successful but there have always been discrepancies. These discrepancies have generally been attributed to the difficulty of estimating the yield stress developed within the ER fluid when an electric field is applied. In the present paper, the authors describe a new approach in which the yield stress is determined iteratively by minimizing the difference between observed and predicted values of the transmitted force. Using this technique, force/displacement and force/velocity plots are predicted and compared with values from an experimental facility. It is shown that agreement between model predictions and experimental observation is excellent and significantly better than those obtained using existing models.

In this paper the authors discuss the progress that has been made over the past decade in active constrained-layer damping (ACLD). ACLD treatments combine the best features of passive and active control of structural vibrations. By way of introduction the paper describes well-established techniques for passive control of structural vibrations and noise. A concise discussion of the development of so-called ‘smart’ (or ‘intelligent’) actuators and sensors and the emergence of suitable control algorithms show how passive techniques were extended to produce ACLD. A comprehensive literature review follows. It is shown how the passive and active components of ACLD complement each other to enable control of both high and low frequency modes of vibration. The active elements allow structures to adapt to suit a changing environment while the passive elements provide a fail-safe mechanism. Because of the available technology, these benefits are available without significant penalties in terms of cost, weight and complexity.

This paper is concerned with an experimental and theoretical determination of the rheological performance of an electrorheological (ER) fluid when subjected to time-dependent applied loads. The experimental facility was built as a squeeze cell in which the fluid is sandwiched between two electrodes, one fixed and the other moving, which permits the instantaneous measurement of the mechanical and electrical responses of the fluid. The transient rheological characteristics of the fluid were assessed for various mechanical force levels and for constant voltage excitation of the fluid. Input and output stress levels across the fluid were monitored enabling the dynamic response of the fluid to be determined using a combination of displacement, force, velocity and acceleration transducers. The experimental results were compared with the results from a modified theoretical analysis, which employs a bi-viscous shear stress/shear strain characteristic of the electrically stressed fluid together with a fluid yield stress, which has a strain-direction dependence on the electric field.

The pipeline systems used to carry liquids and gases for the ventilation of buildings, water distributions networks, and the oil and chemical industries are usually monitored by a multiplicity of pressure, flow, and valve position sensors. By comparing the input signal to a valve with the pressure reading from the network using cross-correlation analysis, the technique described in this paper enables a single sensor to be used for monitoring. Specifically, the offset and gradient change of the cross-correlation function show the time delay between the input wave and the acquired output signal. These reflections arise from junctions, valves, and terminations, which can be located effectively using the cross-correlation technique. Investigations using a T-shaped pipe network have been conducted with a valve inserted in the pipeline to introduce artificial water hammer-type perturbations into the system. Both computational and experimental data are presented and the results are compared with the actual pipe network geometry. It is shown that it is possible to identify the location of various features of the network from the reflections and thus to perform either system characterisation or condition monitoring.

Surface damping treatments are often effective at suppressing higher frequency vibrations in thin-walled structures such as beams, plates and shells. However, the effective suppression of lower frequency modes usually requires the addition of an active vibration control scheme to augment the passive treatment. Advances in the technologies associated with the so-called smart materials are dramatically reducing the cost, weight and complexity of active structural control and make it feasible to consider active schemes in an increasing number of applications. In this paper, the authors present a numerical and experimental study of the application of active constrained layer damping to a clamped–clamped plate. Specifically, a passive constrained viscoelastic damping layer is augmented with an active scheme employing a PZT patch as the actuator. In the opening sections of the paper, emphasis is placed upon establishing a suitable model of the plate. Starting with an established finite element formulation it is shown how model updating and model reduction are required to produce a low order state-space model which can be used as the basis for active control. The effectiveness of the formulation is then demonstrated in a numerical study. Finally, in the description of the experimental study, it is shown how modes in the frequency range from 0 to 600 Hz are effectively suppressed: the two lowest modes (bending and torsional) through active control using only a single sensor and single actuator in the feedback loop, the higher modes (around 10 in number) by the constrained passive damping layer. The paper's original contribution lies in the experimental demonstration that given a sufficiently accurate model of the plate and passive constrained damping layer, together with a suitable active feedback control algorithm, spillover effects are not significant even when using a single sensor and single actuator. The experimental traces show, in some instances, minor effects due to spillover. However, it can be concluded that the presence of the passive layer introduces sufficient damping into the residual modes to avoid any major problems when using only the minimum amount of active control hardware.

Semi-active damping devices offer improved performance over passive devices, without the power requirements or instability problems of fully active devices. Smart fluids (electrorheological and magnetorheological) are well suited to use in semi-active dampers—their flow properties can be rapidly altered, with a low-power requirement. However, the force/velocity response is highly non-linear, and this is without doubt hindering the development of effective control strategies. In this paper, the authors develop a new model of an electrorheological damper. The key advantage of this model is that its algebraic form is suitable for use in control system design, whilst it is able to predict and explain observed behaviour. The model consists of a spring, mass, and damper connected in series. The spring stiffness term is based upon the fluid bulk modulus, and the mass is determined from the fluid density. The damping characteristic utilizes a modified non-dimensional Bingham Plastic function. The model predictions are compared with experimental results at a range of operating frequencies. Excellent agreement was achieved by updating the stiffness and viscosity parameters using experimental data.

It is now well known that smart fluids (electrorheological (ER) and magnetorheological) can form the basis of controllable vibration damping devices. With both types of fluid, however, the force/velocity characteristic of the resulting damper is significantly nonlinear, possessing the general form associated with a Bingham plastic. In a previous paper the authors suggested that by using a linear feedback control strategy it should be possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors describe a comprehensive investigation into the implementation of this linearization strategy on an industrial scale ER long-stroke vibration damper. Using mechanical excitation frequencies up to 5 Hz it is shown that linear behaviour can be obtained between well defined limits and that the slope of the linearized force/velocity characteristic can be specified through the choice of a controller gain term.

This paper is concerned with an experimental investigation of the performance of an ER fluid in oscillatory squeeze-flow and a comparison of the results with those predicted by a quasi-steady theoretical model in which the rheological behaviour of the fluid is assumed to follow a bi-viscous shears stress/shear rate characteristic. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. Of particular interest is the temporal variation in the force transmitted through the fluid in response to changes in the oscillation frequency and amplitude and the level of applied AC and DC voltages. The magnitude of the transmitted forces in the AC case is seen to be not only a function of the applied voltage but also of the shape of the input waveform and the electrical excitation frequency. In all cases these forces are found to be smaller than those seen in the corresponding DC case.

This paper is concerned with an experimental investigation of a comparison of the rheological performance of an ER fluid, consisting of a carrier with a range of solid phase sizes, in oscillatory squeeze-flow under DC conditions. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. It is seen that the dynamic performance of the fluid, in terms of the capacity for the transmission of imposed forces across the fluid, is highly dependent on the size of the dispersed solid phase and has an optimum value which is dependent on the mean value of the interelectrode gap. In addition the paper includes some measurements of the current through the fluid which may help to shed some further light on the mechanism of the ER effect. Finally the implications of the results to vibration control are discussed. Copyright 1999 Academic Press.

This paper is concerned with an experimental investigation in which an electrorheological (ER) fluid is applied to control vibration. The fluid is sandwiched between two planar electrodes, the upper one fixed while the lower one is subjected to an oscillatory sinusoidal motion and is energized either by a constant voltage or by a constant field. In this dynamic squeeze flow it is seen that the force transmitted across the fluid is greater when the applied electrical field is maintained at a constant level, controlled with reference to the instantaneous gap between the electrodes. In addition, we compare the experimental results with those from an existing theoretical model in which the fluid is assumed to have a bi-viscous rheological characteristic.

This paper is concerned with an experimental comparative assessment of the mechanical performance of an ER fluid in oscillatory squeeze flow under various AC conditions. Interest in this topic arose from the desire to employ the fluid in this way in a shortstroke vibration damper. In this investigation the fluid is sandwiched between two parallel plane electrodes, the upper one being fixed and the lower one vibrating normal to its plane. The magnitude of the transmitted force across the fluid is seen to be highly dependent on the shape of the input waveform, on the mechanical vibration frequency as well as on the electrical excitation frequency and level of applied voltage.

In previous papers a technique for comparing the performance of a particular electrorheological (ER) fluid in different situations was derived from steady, laminar, shear and flow mode experimental data and static cell tests. By plotting non-dimensional Hedström Number (He) and Friction Coefficient (Cf) against Reynolds Number (Re) via use of the Bingham plastic constitutive equation, one continuous and overlapping relationship was shown for constant field excitation over a range of operating conditions and geometries. In the present work the same treatment is extended to a different fluid, of higher solid volume fraction and different constituents, which was tested on different instruments at a different uniform temperature, so as to attest the generality of the technique. In doing this the methodology of converting low shear rate Couette viscometer data to practical flow valve performance predictions is illustrated.

This paper is concerned with an experimental and theoretical study of the characteristics of two ER fluids and their application to vibration control when used in squeeze flow. It is seen that when the fluids are sandwiched between two electrodes, the lower one oscillating and the upper one fixed, displacement control of the lower electrode can be achieved by control of the applied field. Of particular interest is the dependence of the force transmitted across the fluids on oscillation frequency and applied field. A time-dependent theoretical model is seen to satisfactorily predict the device performance when allowance is made for a non-linear dependence of the post-yield shear stress on shear rate.

In this paper, the authors describe the development of a mathematical model of a controllable vibration damper intended for eventual application to ground-vehicle suspension systems. The damper under investigation employs electro-rheological (ER) fluid as the working medium which enables a continuously variable damping force to be provided in response to an electrical control signal. There are some difficulties inherent in characterizing the ER damper's behaviour which the present study attempts to overcome. The paper begins by describing a novel form of non-dimensionalization which drastically reduces the number of variables required to characterize the quasi-steady behaviour of the ER fluid. The construction of the ER damper is described and, on the basis of physical reasoning, it is shown how a dynamic model can be derived by taking account of ER fluid inertia and compressibility. A recently developed iterative scheme is introduced in order to solve the resulting non-linear equations of motion. The paper concludes with a case study involving the application of the ER damper to controlling the lateral vibrations of a rail vehicle.

Electro-rheological (ER) fluids are now regarded as one of the most versatile of the materials available for building smart structures and machines. In principle, ER fluids promise an elegant means of providing continuously variable forces for the control of mechanical vibrations. In practice, the development of industrial devices has been hampered by the unavailability of suitable ER fluids. Prompted by recent advances in ER fluid development this paper provides a comprehensive survey of ER devices for vibration control. The key modes of operation are identified and progress towards a unified approach to visualizing the macroscopic behaviour is summarized before presenting a comprehensive survey which includes contributions to the identification of ER fluid dynamics and the application of feedback control. The discussion of results includes some thoughts on future trends.

In this paper, the authors describe a systematic procedure for classifying the modes of operation of ER fluids. The classification is achieved by treating an ER device as a generalized modulator and examining the different variables which can be assigned to the input, output, and control ports. This leads to a matrix, each of whose blocks corresponds to a mode of operation. It is shown how examination of these blocks leads to classification of existing applications and a systematic means of broadening.

This paper is concerned with the theoretical analysis of the compressive squeeze performance of an electrorheological (ER) fluid sandwiched between two parallel circular electrodes, the upper one fixed and the lower one oscillating sinusoidally normal to its own plane. It is shown how the force transmitted through the fluid on the upper electrode varies with amplitude and frequency of oscillation together with applied potential difference and also how the fluid, modelled by a bi-viscous characteristic, responds when electrically stressed compared with its unstressed, Newtonian counterpart. Finally, the relevance of the theoretical results to the determination of the mechanical properties of an ER fluid in squeeze is discussed.

This paper describes the application of sequential frequency domain techniques to the estimation of mass, stiffness, and damping parameters using measured frequency response functions from a portal frame rig. The theory of the method has been described in the authors’ previous publications. A portal frame is representative of many engineering structures. It is lightly damped and may be thought of as an element of several larger structures such as bridges, transmission towers, and the steel foundations of modern power generating plant. The results offered in this paper are thus of interest to a broad range of engineering problems where it is required to obtain mathematical models in terms of physical parameters.

Aircraft landing gears are subjected to a wide range of excitation conditions with conflicting damping requirements. A novel solution to this problem is to implement semi-active damping using magnetorheological (MR) fluids. In part 1 of this contribution, a methodology was developed that enables the geometry of a flow mode MR valve to be optimized within the constraints of an existing passive landing gear. The device was designed to be optimal in terms of its impact performance, which was demonstrated using numerical simulations of the complete landing gear system. To perform the simulations, assumptions were made regarding some of the parameters used in the MR shock strut model. In particular, the MR fluid's yield stress, viscosity, and bulk modulus properties were not known accurately. Therefore, the present contribution aims to validate these parameters experimentally, via the manufacture and testing of an MR shock strut. The gas exponent, which is used to model the shock strut's nonlinear stiffness, is also investigated. In general, it is shown that MR fluid property data at high shear rates are required in order to accurately predict performance prior to device manufacture. Furthermore, the study illustrates how fluid compressibility can have a significant influence on the device time constant, and hence on potential control strategies.

Flexibility and speed of response are two key requirements in the design of machinery for high-speed manufacturing operations. These two requirements are often conflicting and their resolution requires considerable ingenuity on the part of the designer. A novel actuator based upon the use of twin electro-rheological (ER) clutches is described together with its modification to control the motion (angular displacement, angular velocity) of a robot manipulator arm. The development of a new experimental facility involving the robot manipulator arm is described. In the basic twin ER clutch facility, the motion of a toothed belt is controlled by manipulating the electric field applied to each ER clutch. The belt, in turn, controls the angular position and velocity of the robot arm. The use of twin clutches allows motion to be imparted in opposite directions without the need for return springs or similar mechanisms. To improve the positional performance an ER brake is added to the robot arm mechanism. The extension to the dynamic model for the ER clutch mechanism to incorporate the robot arm and ER brake is outlined and is validated experimentally. The displacement response of the robot arm is then examined as a trend study using different motor driving speeds. The positional accuracy of the robot arm and its repeatability is then demonstrated.

Magnetorheological (MR) fluids provide a novel solution to adapt damping levels in aircraft landing gear, so that optimal performance can be achieved over a wide range of conditions. The present study helps to demonstrate the feasibility of this solution by sizing an MR valve within the constraints of an existing commercial (passive) oleopneumatic shock strut. Previous work on MR landing gear has tended to focus on potential control strategies rather than design and sizing issues. However these latter aspects are of great importance in aircraft systems, where space and weight are vital design constraints. To aid the sizing analysis performed in this study, accurate quasi-steady and dynamic impact models of passive and MR oleopneumatic landing gears are developed. The model is validated against experimental data incorporating the passive device, which is then used as a benchmark for the MR designs and to assess fail safety. The dynamic model is particularly important as it incorporates fluid compressibility, which may be a significant contributor to the overall response of the device in an impact scenario. The present study also aims to give further insight into high velocity MR valve flow, which will be inevitable during impulsive loading. This area remains largely unexplored and particular importance is given to valve Reynolds number since turbulent values are known to reduce device performance. The feasibility of an MR landing gear will be largely dependant on these factors.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Recent research into the use of thermal barrier coatings has shown that they can provide sufficient additional damping, reducing vibration levels and significantly extending the life of the coated component. Various deposition techniques may be employed to apply ceramic coatings with Air Plasma Spraying (APS) and Electron Beam - Physical Vapour Deposition (EB-PVD) being the most widely used. However, one has to take into account that even when the starting ceramic material is the same, the microstructures of the resultant coatings depend strongly on the deposition technique. The objective of this paper is to study of the differences in the damping behaviour and stiffness of an yttria-stabilised zirconia (YSZ with 8%wt yttria) coating deposited by APS and by EB-PVD. Both damping and stiffness of these two YSZ coatings were estimated from tests performed at room and high temperatures. Moreover, this paper presents the microstructural characterisation of these two YSZ coatings using scanning electron microscopy, and attempts a correlation of the differences in their properties to their microstructure.

The orifice plate flow meter is the most common form of differential pressure flow meter used in industry. The standard discharge coefficient, which is defined by both British Standard and ISO 5167, is only valid if the flow approaching the meter is perfectly settled and fully developed. However, in practical applications the flow approaching the orifice meter is often disturbed by pipe-fittings and consequently the measurements become inaccurate. Basically, the design of the orifice plate meters that are independent of the upstream disturbances is a main goal for orifice plate metering. This task can be achieved either by using a long straight settling length upstream and downstream of the orifice plate or using a flow conditioner upstream of an orifice plate. In addition, the standard orifice plate is vulnerable when metering dirty flow due to the accumulation of dirt in front of the orifice plate which can alter the accuracy of metering as well. In this paper the effect of the swirler flow conditioner for both standard and non-standard flow conditions has been investigated in an experimental rig and validation of the results has been justified with the appropriate CFD domains. In these investigations the effect of different designs of swirler flow conditioners have been examined in asymmetric and swirling flow profiles. The results so far show the cone swirler flow conditioner has a desirable effect for both asymmetric and swirling flow disturbances. They also show the error of metering for non-standard velocity profiles with the swirler flow conditioner is typically 1.5% compared to around 4% for a standard orifice plate. Moreover using a swirler conditioner tends to keep particles in suspension and thus prevents the accumulation of dirt particles in front of orifice plate. All experimental and numerical results here are presented for different velocity profiles both swirling and asymmetric profiles, mass flow rates and for β = 0.5.Copyright © 2005 by ASME

This paper describes a novel damping treatment, namely hard ceramic coatings. These materials can be applied on almost any surface (internal or external) of a component. Their effect is the significant reduction of vibration levels and hence the extension of life expectancy of the component. The damping features of air-plasma-sprayed ceramic coatings (for example amplitude dependence, influence of initial amplitude) are discussed and the experimental procedure employed for testing and characterising such materials is also described. This test procedure is based around a custom-developed rig that allows one to measure the damping (internal friction) of specimens at controlled frequencies, strain amplitudes and, if required, various temperatures. A commonly used Thermal Barrier Coating, Yttria Stabilised Zirconia (8%), is used to demonstrate the above mentioned features. The damping effectiveness of this coating is then compared against two established damping treatments: polymer Free Layer Damping (FLD) and Constrained Layer Damping (CLD). The paper discusses the major issues in characterising ceramic damping coatings and their damping effectiveness when compared against the "traditional" approaches. Finally, the paper concludes with suggestions for further research.

There is much current interest in the development of smart fluid clutches for use in the design of high-speed machinery. This interest stems from the flexibility, controllability and fast response of such fluids. In this paper the authors outline the modifications to an Electro-rheological clutch mechanism for a robotics application. The clutch mechanism consists of twin ER clutches that are driven in opposite directions. By controlling the electric field applied to each clutch it is possible to cause a toothed belt to move in a desired manner in each direction. This belt motion can then be used to control the motion of a robot arm via a gear train. To improve the positional performance an ER brake is added to the robot arm mechanism. The extension to the dynamic model for the ER clutch mechanism to incorporate the robot arm and ER brake is outlined and is validated experimentally. The displacement response of the robot arm is then examined as a trend study using different motor driving speeds and load inertias. The positional accuracy of the robot arm and its repeatability is then demonstrated over a significant number of reciprocating tests.

This paper is concerned with an experimental investigation of the performance of an ER fluid in oscillatory squeeze-flow and the development of a quasi-steady theoretical model in which the rheological behaviour of the fluid is assumed to follow a bi-viscous shear stress/shear rate characteristic. The fluid is sandwiched between two parallel plane electrodes, the upper one fixed and the lower one oscillating normal to its plane. Of particular interest is the temporal variation in the force transmitted through the fluid in response to changes in the oscillation frequency and the applied DC voltage. In addition the paper includes an account of an experimental assessment of the response of the fluid to a step change in applied voltage. Finally the relevance of the work in the application to vibration control in a short-stroke damper is discussed.

It is now widely accepted that smart fluids in the so-called squeeze-flow mode have many potential applications in vibration damping and isolation. In squeeze-flow the fluid is subjected to forces imposed by oscillating electrodes (or poles) which alternatively subject the fluid to tensile and compressive loading. Consequently displacement levels are limited to a few millimeters but large force levels are available. Modeling of smart fluid squeeze-flow devices is a complex process, primarily since the fluid is liable to be subjected to simultaneous changes in the inter-electrode gap and the strength of the applied electric (or magnetic) field. Consequently the authors have developed a comprehensive test facility dedicated to the study of smart fluids in dynamic squeeze-flow operation. In the present paper, the authors will describe a new approach to modeling smart fluids in squeeze-flow. The analysis relates specifically to an electrorheological fluid modeled using a bi- viscous shear stress/shear strain characteristics. By assuming that the electrically stressed fluid has a yield stress which is dependent on the strain direction, it will be shown how the model is able to account for observed experimental behavior.

Smart fluid devices are now seen as an attractive solution to vibration damping problems. They offer superior performance compared to passive devices, without involving the cost, weight and complexity of fully active damping strategies. However, the inherent non-linearity of smart fluid dampers makes it difficult to fully exploit their capabilities, due the problems in applying an effective control strategy. In the past much of the research focused on complex controllers involving techniques such as neural networks and fuzzy logic. In recent years, however, an alternative approach has been adopted, whereby classical control techniques are used to linearise the damper's response. As a result some applications for smart fluid damping now use combinations of proportional, integral, or derivative control methods. However, it appears that these controllers can become unstable in much the same way as for a truly linear system. In order to investigate this instability it is suggested that a sufficiently accurate model of the damper's response is required, so that the onset of instability can be reproduced numerically. In this contribution, a model updating technique is described whereby an existing ER damper model is updated in line with experimental data. The paper begins with an overview of the experimental test facility and the modeling approach. The updating algorithm is then described, and it is shown how the updated model improves significantly on the accuracy of the model predictions.

The feasibility of using a well-known twin ER clutch linear reversing mechanism as a robotic actuator is demonstrated. High speed of response, displacement and positional accuracy can be obtained bi-directionally. A validated mathematical model of the apparatus provides a basis for the control strategy. Positional accuracy is enhanced by an ER brake which works in sequence with the clutch excitation switches. The robot arm, in rotational displacement is tested over a large number of cycles, speeds, displacements and inertial loads and the quality of control compared to that of competitive conventional servo motors.

There is much current interest in the development of smart fluid clutches for use in the design of high speed machinery. In this paper, the authors employ an ER clutch mechanism in a robotic application. This clutch mechanism consists of twin ER clutches which are driven in opposite directions by two electric motors. By controlling the electric field applied to each clutch, it is possible to control the angular displacement of a robot arm. Before considering control, an established mathematical model is validated. The purpose of this model validation is to help design a control strategy for accurate positioning of the robot arm. Through the use of a Simulink program and a digital controller, both the simulated and experimental angular displacements are compared and shown to be in close agreement. Finally, the displacement response of the ER- driven and DC servo-actuatored robot arm are compared and conclusions are drawn as to the suitability of the ER clutch mechanism as a robotic actuator.

Ongoing research at the University of Sheffield is currently concerned with the design and construction of magneto- rheological (MR) squeeze-flow vibration damper. Previous work has demonstrated the feasibility of employing such a device as the key component in a controllable vibration isolator. The work also demonstrated the inadequacies of existing mathematical models which do not account for the observed behavior of MR fluids in squeeze flow. In parallel with investigations into the behavior of MR dampers, a collaborative programme between the Universities of Liverpool and Sheffield is also in progress. Here attention is focussed on ER fluids in squeeze-flow and a new test facility has been constructed for use in the development and validation of mathematical models. It is anticipated that this collaborative programme will assist in the development of both ER and MR squeeze-flow models. In this paper, the authors present a summary of progress to date.

This section presents a case study and theoretical example to illustrate how control may be applied to achieve a specific vibration isolation performance. with a linearised, viscous type, overall damper characteristic as an alternative to that of the steadily excited Bingham plastic fluid. The study is followed through from the point of view of an ER fluid, but for an MR fluid the consideration is ahnost exactly the saine.

It is now becoming well-established that there is enormous potential for the application of smart fluids to a variety of problems in vibration control. In the development of materials and devices emphasis has been placed upon electro-rheological (ER) fluids which consist of a suspension of micron-sized, semiconducting particles in a dielectric base liquid. The application of an electric field of sufficient intensity causes a rapid (and reversible) increase in the ER fluid’s resistance to flow. A 1996 survey paper [1] explained the fundamental operating principles of ER fluids and described the possible modes of operation. However the main purpose of the paper was to review applications of ER fluids to vibration control.

It is now well established that magnetorheological (MR) fluids can provide the basis for constructing controllable vibration damping devices. Moreover, the characteristics of MR fluids are generally compatible with industrial requirements and there is enormous scope for commercial exploitation. In this paper the authors describe the design and construction of a vibration isolator which incorporates an MR damper. The damper is unusual in that it operates in the squeeze-flow mode. A quasi-steady model of the MR damper is summarized and then extended to include the vibration isolator dynamics. Model predictions are compared with experimental results. It is shown that by employing the MR damper a wide range of control can be exercised over the transmissibility of the vibration isolator. Numerical experiments are used to show that a feedback control strategy can provide even more control over transmissibility.

It is now well established that magneto-rheological (MR) fluids can provide the basis for constructing controllable vibration damping devices. Moreover, the characteristics of MR fluids are generally compatible with industrial requirements and there is enormous scope for commercial exploitation. In this paper the authors describe the design and construction of a vibration isolator which incorporates an MR damper. The damper is unusual in that it operates in the squeeze-flow mode. A quasi-steady model of the MR damper is summarised and then extended to include the vibration isolator dynamics. Model predictions are compared with experimental results. It is shown that by employing the MR damper a wide range of control can be exercised over the transmissibility of the vibration isolator. Also the quasi-steady model is able to account for observed behaviour.

Magneto-rheological (MR) fluids are rapidly rising in prominence as a means of producing controllable damping devices for vibration control. MR fluids can be used in various modes of operation in order to provide damping forces. One of the least exploited of these modes is commonly known as squeeze-flow, where large, controllable forces can be generated over relatively small displacement ranges. In this paper the authors describe a recently constructed test facility in which an MR squeeze-flow device is incorporated as the damping element in a vibration isolator.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

It is widely acknowledged that the inherent non-linearity of smart fluid dampers is inhibiting the development of effective control regimes, and mass-production devices. In an earlier publication, an innovative solution to this problem was presented -- using a simple feedback control strategy to linearize the response. The study used a quasi-steady model of a long-stroke Electrorheological damper, and showed how proportional feedback control could linearize the simulated response. However, this initial research did not consider the dynamics of the damper's behavior, and so the development of a more advanced model has been necessary. In this article, the authors present an extension to this earlier study, using a model of the damper's response that is capable of accurately predicting the dynamic response of the damper. To introduce the topic, the electrorheological long-stroke damper test rig is described, and an overview of the earlier study is given. The advanced model is then derived, and its predictions are compared to experimental data from the test rig. This model is then incorporated into the feedback control simulations, and it is shown how the control strategy is still able to linearize the response in simulations.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electrically-structured (ES) fluids offer a potentially elegant means of introducing greater flexibility into a range of industrial machines and structures, and are especially suited to controllable vibration damping. The authors have developed a technique for characterizing ES fluids, leading to a mathematical model and practical device design procedure, the principles of which are verified by testing with an industrial scale, long-stroke electro- rheological damper, suited to the needs of a rail vehicle lateral suspension. In this paper, the model is applied to predict the effect on the test damper steady state performance, and performance envelope, of the principle variables of operating temperature, mechanical displacement amplitude and frequency, and control field excitation, which influence the controllability and control requirements of the damper, and to show that the test damper should achieve the desired range of control.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper is concerned with an experimental investigation of a comparison of the rheological performance of an ER fluid in oscillatory squeeze-flow under DC and AC conditions. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. The magnitude of the transmitted force across the fluid in the AC case is seen to be highly dependent on the shape of the input waveform and on the electrical excitation frequency. In all cases this force is found to be smaller than that seen in the corresponding DC case. It is seen that the performance of the ER fluid depends dramatically on the size of the dispersed solid phase and has an optimum value which is dependent on the inter-electrode gap. Finally the implications of the results to vibration control and the trend of future work into squeeze flow behaviour are discussed.

The development of controllable suspension dampers for ground vehicles is the subject of much current research. In this paper the authors describe aspects of a design methodology for controllable dampers which use electro-rheological (ER) fluid as the working medium. This methodology is based upon a non- dimensional characterization of ER fluid data which allows measurements obtained from small-scale tests to be used to predict the behavior of industrial-scale vibration dampers. The ER damper is represented via a Bingham plastic constitutive relationship, augmented by terms to account for fluid inertia and compressibility. An industrial-scale test facility is described and the first available set of experimental results are presented. A comparison is made between model predictions and observed behavior.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.