In this paper I present an overview of the factors and problems that must be considered in designing low-vibration buildings. Subjects covered include vibration criteria for different occupancies; sources of vibration and response predictions; major design factors for vibration control.
Two case histories are presented that illustrate two aspects of the design problem. The first is entitled "The Role of Special Foundations in the Design of Low Vibration Buildings." The second is entitled "The Role of Sprung Floors in the Design of Low Vibration Environments."
It is desirable that the vibration environment in buildings used to house vibration sensitive equipment, be reliably predicted before the equipment is required to perform. Within an existing building, this qualification of a facility may be possible by direct measurement. However, in the case of internal re-structuring or a new design some means of prediction is required at the concept stage, to give a reasonable assurance before resources are committed, that the installation will perform satisfactorily over the life of the building.
Basic principles of vibration isolation are presented using a simple single-degree-of-freedom-model. This model is used to explain the design of linear spring and damper isolation systems. Governing equations for air spring isolators are reviewed. The relationship between system isolation efficiency and table or platform performance is shown. Some problems with current configurations of vibration isolation systems are analyzed.
The use of X-ray interferometry makes possible the calibration of microdisplacement transducers to precisions of around 10 pm on a relatively routine basis. Naturally, this is not achieved without careful mechanical design, especially with regard to vibration isolation and thermal stability. A facility has been constructed, and is described here, for the evaluation of this method. Its performance when operating with a single-crystal silicon monolithic interferometer is examined. In many respects the system design follows conventional patterns, for example in using a high mass base supported on active air-springs. However, as the most sensitive parts are required to have controlled motion while in operation, particular attention is paid to the active force-loops. A solenoid-based force transducer is shown to have ideal characteristics for this application.
The purpose of controlling the environment of the metrology laboratory is to subdue whatever disturbances seriously affect the intended work. The elements of the environment which require some degree of control and typical constraints are: Table 1. Metrology Laboratory Environmental Control Specifications Temperature level usually 20°, 23° or 25°C Temperature constancy from ±0.01° to ±2°C Temperature uniformity from 0.02° to 2°C Relative humidity 35% to 55% Pressure 5 to 10 mm W.C. gage Lighting 50 to 100 foot candles Cleanliness < 1 million particles over one micron size per cubic meter air Noise 35 on noise criteria curve from 20 to 9,600 Hz Electrical fields avoid RF interference and magnetic masses. Vibration <50 nM displacement below 200 Hz at instrument base. These limitations are included in standards which are still a matter of discussion. Of these - temperature excursion and vibration cause the greatest concern. Special notice is made of vibration - the constraint on which there appears to be least agreement. Selected design efforts are described to illustrate the wide range of solutions to these problems and the difficulty of arriving at a consensus on standards for environmental control.
This paper describes a practical calibration method considering the base strain of vibration pickups. Generally the base strain occurs at a connecting surface to be fastened each other and is an important factor influencing the sensitivity of the pickups. The authors have experimentally examined whether the sensitivity about one of the pickups to be calibrated is different or not between both measuring arrangements, that is, comparison calibration and actual vibration test. According to the experiment, the sensitivity in the arrangement of actual vibration test is higher by 4 % than that of comparison calibration even if it depends on base strain. A primary calibration by a laser interferometer system is also performed with high accuracy in this paper. The experimental results show some difference of the sensitivity between different arrangement methods of the pickups.
There is as yet no accepted standard for the vibration limits of scientific, medical and surgical microscopes. In order to service recent consultancy contracts, the Wolfson Unit for Noise and Vibration Control (WUNVC) has found it necessary to deliberately vibrate such instruments in a controlled manner over a range of frequencies and levels in order to obtain a subjective assessment of acceptability from the operator. Several examples of these ad hoc experiments are presented and compared to other research findings for vibrating displays as a tentative contribution to the development of acceptable standards.
This paper describes the mobility approach to vibration isolation calculations and gives some simple formulae for predicting the point mobilities of structural elements for use in isolation calculations. The power flow approach to machinery installation analysis is outlined, the objective being to use the method to facilitate good installation design. It is inevitable that some vibration is transmitted into supporting structures, particularly at high frequencies, and vibration power transmission may be studied in order to identify transmission mechanisms with the objective of vibration control. Recent developments in structural intensity measurement techniques are therefore also reviewed.
Since the advent of the laser, optical metrology has found a much wider use in engineering and is now providing engineers with previously unobtainiable data. The measurement of modal behaviour has traditionally been achieved through the use of accelerometers requiring some form of contact with the structure to be measured. There are however, cases where contact is neither possible or desirable. Laser techniques can provide both point and full-field vibration data remotely and at Gaydon Technology several forms of Doppler and holographic interferometer are utilised. This paper reports on the application of Electronic. Speckle Pattern Interferome try (ESPI), sometimes referred to as T.V. holography, to the analysis of engineering structures.ESPI allows dynamic and static analysis of structures to be undertaken remotely, full-field and in real-time by monitoring changes in the speckle field of a coherently illuminated object. The paper details why GTL has chosen an ESPI system, the basic principles and features of the GTL system and concludes by reviewing a number of applications.
The structural engineer's interest in vibration can generally be summarised as a desire to know the modes of vibration which an engineering structure can assume, the resonant frequencies, the sharpness of the resonances (related to the damping forces in and on the structure) and their amplitudes under given driving forces. Most of all he is interested in the non-resonant vibration of the structure under the influence of a random driving force, and he would like to determine the direction (in three dimensional space), as well as amplitude, of the motions involved. In industries in which exceptionally high levels of structural integrity are required through long periods of continuous or near continuous operation, such os the aeronautical or nuclear industries, accurate vibration analysis is an essential first step towards an assessment of the fatigue life of the structure. In this case the most important factor is the dynamic stress in the structural material. Measurement tools available to the engineer, in order to obtain the information he needs, are numerous, varied in character, and generally unable to meet all the needs outlined above. They may be contacting (e.g. accelerometers or straingauges) or non contacting (for example holographic interferometry, ESPI or SPATE). They may provide data continuous in space (holographic interferometry) , with limited spatial resolution (ESPI), or discrete point measurements (accelerometers, laser vibrometers). Whilst accelerometers provide data continuous in time, and ESPI has limited time resolution, holographic interferometry is in general severely limited in its usefulness because it can only provide data for a given moment in time, and successive holograms are either limited in number or difficult to relate in time. On the other hand it is now possible to derive the full direction of motion from holographic records, whereas a single accelerometer is usually only able to measure acceleration in one direction. The final choice of measurement technique is a compromise based on an evaluation of the cost, the reliability, the sensitivity, the accessibility of the structure to contact techniques, and the importance of obtaining a full and accurate analysis. Because of the great importance attached, in the nuclear industry, to obtaining the fullest possible analysis of structural vibrations, all available methods of vibration analysis are constantly being assessed, and, where appropriate, utilised. This paper describes the use of pulsed lasers to analyse vibrations of parts of operating nuclear reactors. The techniques used to allow these sophisticated systems to operate remotely under difficult site conditions are described and the results obtained presented together with an analysis of their value and limitations. In order to fully derive the motion vector it is desirable to take more than one hologram simultaneously, and this is best achieved using optical fibres. Some results of experiments with optical fibres are presented. A more general use of holographic interferometry for vibration analysis will only occur when well engineered robust equipment is available which can be operated by non-specialist staff, and when the techniques are developed for analysing results obtained under non-resonant conditions. There is some discussion of these points.
Holography and allied techliques such as electronic speckle pattern interferometry (ESPI) have the potential to provide the engineer with a powerful measuring technique. Why, therefore, is it not a technique readily available and widely used? Several arguments can be put forward; complexity, skill level, ease of use, in-situ capability, and ability to interpret results.
One of the basic problems when designing a new production facility or planning an expansion of a current facility, is the lack of a serious attempt to consider the detrimental effects of natural and/or induced ground vibrations. These unnoticed disturbances, which are always present, usually become apparent when the facility is completed and in active use. Control of these harmful or distracting vibrations in factories, buildings, hi-tech assembly areas, and laboratories, is most cost-effective when planned in the advanced or architectural stages. Afterthoughts or quick fixes have proven to be most expensive while being marginally effective at best.
Any form of vibration which interferes with the operation of a sophisticated astronomical telescope is undesirable. Ideally, the problems which could give rise to vibrations should be anticipated and corrected prior to, or during, the construction stages. However, in spite of all precautions, vibration problems have been experienced on certain telescopes after completion. Usually, at this stage, it is difficult to solve such problems and often the solutions are complex and expensive. This presentation assesses the levels of vibration found in telescope installations at the La Palma Observatory in the Spanish Canary Islands, and attempts to qualify acceptable magnitudes for these and other installations. At one of these telescope installations on the ROQUE DE LOS MUCHACHOS, certain conditions of operation arose in which vibration proved to be a problem of great concern. Initially, a number of in-house attempts were made to find the cause of the problem but it was soon realised that professional consultants with advanced equipment were needed to analyse the situation. This resulted in a team of V.C.I. consultants being invited to assist with the project further. The problem was re-examined by the consultants of V.C.I. and a new approach, which is related in this appraisal, was employed. This paper, therefore, reviews a series of special trouble-shooting vibration tests which are designed to specifically highlight problem areas so that corrective solutions and remedies can be accurately deduced. Although certain of these vibration tests have been established for other purposes, it is believed that many of the techniques discussed in this paper are novel in relation to their application to observatories.
In many sensitive instruments and production machines, the achievable resolution is limited by the ever-present building vibrations. A new dynamic isolation system is described that effectively removes these vibrations and has clear advantages over the traditional soft passive isolation system.
EVIS is the first commercial active vibration control system suitable for general purpose application. It's design closely follows the guidelines and principles described by Sandercock in the previous paper. We First present quantitative operating data For the system, and then discuss some of the unique qualitative aspects of that performance. Some examples of specific applications which are particularly well suited for active control technology are discussed. We have found that the usual models for understanding the operation of conventional passive vibration control systems are not adequate when considering the corresponding active systems. Therefore we discuss a simplified model which has proved useful for estimating the operational benefits of active systems in actual applications.
Development of ultraprecision machines requires motion mechanisms with dynamic characteristics being sufficiently resistive to environmental disturbances as well as vibration control devices isolating from them. In the paper active application of frictional forces to the machines are proposed in viewpoint of this point. Further, new strategies for various problems resulting from application of frictional forces are also proposed for linear feed mechanism and the test results are shown. They are load compensation unit, composite bearing guideway and force operation feed mechanism.
In order to enable measurement by dynamic holography, it is necessary to reduce as much as possible the amplitude of the bending displacement of the large surface plate where the testing machine is placed. We produced a large surface plate supported by an air mount. Then we forecast the natural frequency and amplitude of the surface plate, and compared them with the results of our experiment. In addition, after the dynamic dampers which had been developed to reduce the amplitude were attached to the surface plate, we re-forecast the amplitude and compared it with the results of our experiment. As a result, we recognized that the dynamic dampers were effective in reducing the resonance amplitude of the surface plate. In the experiment, the amplitude was reduced to 1/6.
Vibrations in a photocopier reduce the resolution of the image on the copy. Typically the image is transmitted via a system of four or six mirrors and a transmission lens to the photoreceptor. In a scanning copier two or three of these mirrors scan the document at a speed which synchronises the motion of the image with that of the photoreceptor. Vibrations of the mirrors, lens or photoreceptor cause the image of a point to move with respect to the photoreceptor during the exposure time, generating a two dimensional spread function. These vibrations can be controlled by both active and passive means. This paper outlines methods of image analysis used to identify the sources of the image disturbance, and means used to minimise their effects.
The quality of optical surfaces produced by diamond machining depends on a very high level of isolation of both inherent and transmitted vibrational disturbances at submicron scales. The surface texture of a diamond turned surface consists of a periodic structure whose geometric shape depends on tool geometry and machine feed parameters. The finite compliance of the machine structures and the workpiece will result in the generation of small-scale vibrations. Resonances may thereby arise and spurious additional periodic perturbations will be produced on the diamond machined surface. Form errors will also arise as a result of workpiece vibration. Understanding the natural modes of vibration has been addressed using interferometric and piezoelectric measurement techniques. These will be discussed in this paper with reference to the production of high quality diamond turned surfaces.
Honeycomb tables are fast becoming the standard for use in optical laboratories to eliminate vibration. Honeycomb structures typically have resonances above 100Hz which can cause detrimental effects to the optical experiment in progress. Since the higher frequency resonant modes of the table can cause motion of the table, a top method of eliminating these disturbances by damping must be incorporated into the table construction.