3,541 research outputs found
Comparing laser and polychromatic confocal optical displacement sensors for the 3D measurement of cylindrical artefacts containing microscopic grooved structures. [In special issue: Metrology and Properties of Engineering Surfaces]
No full textA scanning system has been developed for measuring the surface of early cylinder mechanical sound
recordings to high precision, both for surface preservation and for post-processing of the data to recover
the sound encoded in the grooves. Research has identified that high sensor axial resolution is required
to resolve the smallest amplitude groove modulations contained on typical cylinder artefacts resulting
in the selection of confocal laser and white light (polychromatic) confocal sensors as suitable sensing
technologies. This paper presents data acquired by the two confocal sensor technologies, comparing the
measured surface profiles with data obtained using a stylus profilometer. We investigate limitations of
the sensors, relating their characteristics to the ongoing development of the scanning system
A comparison of optical sensing methods for the high precision 3D surface profile measurement of grooved surfaces
No full textA non-contact method has been shown to be the preferred solution for the scanning of valuable early sound recordings, such as wax cylinders and flat discs for the purpose of cultural preservation [1]. This paper describes the operating principles and compares the performances of four different sensing techniques, including scanning white light interferometer (SWLI), con-focal laser (CL), con-focal white light sensor (WL), and atomic force microscope (AFM), in a range of measurement tasks. The con-focal systems described in this paper are used in a 3 dimensional (3D) cylinder scanning system for the measurement of wax cylinder recordings, where the 3D data is used to create a map of the measured surface. The generation of the map allows the sound recorded on the surface to be decoded without physical contact to the surface. The main advantage of the con-focal system is the scanning speed. Reference samples with sinusoidal and rectangular profiles are used to investigate the effects of surface inclination angle and the interaction between the sensor head and the measured surface. The effects of precision mode, grid spacing and spot size on surface height measurements are investigated
An Algorithmic Approach to the Optimal Extraction of Signals from Intelligent Sensors
No full textThis paper describes the development of an intelligent sensor architecture, where signal conditioning is performed onboard the sensor itself, in software. Our proposed architecture uses data-based models of the sensor for signal conditioning and fault detection, so that the sensor is robust to degradation and its processed output includes an estimate of uncertainty with each measurement value for higher level sensor management processes such as data fusion. We use a data-based kernel representation for the signal conditioning system, which avoids deriving physical models of the sensor from first principles. A sparse realisation of the kernel model provides fast predictions and opportunities for efficient updating of the sensor model to enable reconfiguration of the sensor model based on incoming data. We show that these techniques have the ability to detect degradation in a MEMS sensor, using elevated temperatures in laboratory conditions
Comparing laser and polychromatic confocal optical displacement sensors for the 3-D measurement of cylindrical artefacts containing microscopic grooved structures
No full textA scanning system has been developed for measuring the surface of early cylinder mechanical sound recordings to high precision, both for surface preservation and for post-processing of the data to recover the sound encoded in the grooves. Research has identified that high sensor axial resolution is required to resolve the smallest amplitude groove modulations contained on typical cylinder artefacts resulting in the selection of confocal laser and white light (polychromatic) confocal sensors as suitable sensing technologies. This paper presents data acquired by the two confocal sensor technologies, comparing the measured surface profiles with data obtained using a stylus profilometer. We investigate limitations of the sensors, relating their characteristics to the ongoing development of the scanning system
The relationship between surface incline and con-focal chromatic aberration sensor response
No full textThe limiting performance characteristics of con-focal chromatic aberration displacement sensors are angular tolerance and the gauge range over which an output is provided. The sensor selected in this study is used to measure groove profiles in early recorded surfaces. The sensor is used in a 3 dimensional cylinder scanning system for the measurement of wax cylinder recordings, where the 3 dimensional data is used to create a map of the measured surface for archival purposes. The generation of the map allows the sound recorded on the surface to be decoded without physical contact to the surface. It has been shown in a previous study that data resolution of 10-20nm are required for this application, and that the relationship between the data output and the surface incline is critical to system performance. To understand the relationship with surface slope the sensor is used here in a study of the measurement of calibration ball surfaces, and follows a previous study on machined grooves with known angular properties. In this study a range of calibration spherical surfaces are used to investigate the relationship between the sensor output and measurement parameters, including the distance between the sensor optical head and the surface. A linear least squares method is used to evaluate the 3D radius of the measured surfaces, and this is used as a parameter to evaluate the systematic errors. The results show that there is a low level of systematic form error typically below 1?m, but that this error has a significant impact on the evaluation of the radius. Recommendations are made on methods for optimisation of sensor performance
Intelligent sensors—a generic software approach
No full textDesignating a sensor as intelligent is a long-standing term implying that it provides more functionality than merely providing an output measurement. Since there is some discrepancy governing what makes a given sensor intelligent, this paper defines the features required for improving confidence in sensor measurements, from the sensor management perspective. We describe a software framework used to implement tasks such as condition monitoring onboard the sensor itself, rather than at the traditional supervisory level. The algorithms include data-based models, which allows for modelling of non-linear effects and estimation uncertainty, which is a prerequisite for data fusion. Density estimation for novelty detection is demonstrated for an accelerometer that is purposely damaged in an environmental chamber
A comparison of precision optical displacement sensors for the 3-D measurement of complex surface profiles
No full textNon-contact optical sensors, combined with a raster scanning system, can be used in surface metrology applications such as MEMS processing to build high-precision topological surface maps representing the surface profile. We compare three optical displacement sensors for the measurement of complex surfaces, focussing on early sound recordings, and recommend sensor selection based on parameters including measurement area, time and resolution.<br/
Non-contact surface metrology for preservation and sound recovery from mechanical sound recordings
No full textDespite careful storage, early mechanical recordings on cylinders and flat disc formats have been identified as at risk from deterioration, caused mainly by material degradation and biological attack from mould growth. There is therefore an urgency to transfer the content of culturally-important artefacts to digital format to preserve the recordings’ content for archival posterity. However, some recordings are too precious to risk playback using conventional stylus methods because the very act of using a mechanical stylus playback system may in some circumstances contribute to further damage to the integrity of the sound contained in the recording’s groove, caused by wear. Other artefacts, such as 78s exhibiting delamination of the shellac from the metallic substrate, may be too damaged for a stylus to be a practical method for transfer. In recent years there has been a significant quantity of research aimed at developing optical measurement systems for mechanical recordings for non-contact sound recovery. 2-D imaging systems using high-resolution photography have been developed for flat disc recordings where the sound modulations are encoded as lateral undulations of the sound-carrying groove. However, in cylinder recordings and some 78s the modulations are in a vertical plane relative to the groove, in so-called ‘hill and dale’ modulations. To measure these features requires 3-D surface profiling using optical sensors that measure the surface topology by determining the displacement distance between the surface and the sensor. Systems have been independently developed by the Ukrainian Institute for Information Recording Problems, Syracuse University (US) and Hokkaido University group in Japan for 3D measurement of the sound carrying groove. However, these methods require a tracking system to guide the optical sensor in the nominally helical path around the cylinder to follow the groove. This tracking must be robust at time of measurement, a task which is made difficult by damage and deformation of the artefact’s surface.An alternative transfer strategy being developed through collaboration between the University of Southampton, the British Library Sound Archive, and TaiCaan Technologies Ltd, uses optical sensors to measure the recording’s surface in its entirety. A significant outcome from this approach is the full high precision digital record of the artefact’s surface form for preservation, which is available for future research. The post-measurement processing of the surface topology data makes use of image and signal processing to reconstruct the audio content of the recording. This aspect of the research is aimed at facilitating access to the audio content of culturally-important artefacts by current generations. In this paper we provide a detailed overview of the scanning process for cylinder recordings, the data processing techniques used to recover the audio from the data and describe the high sensor precision required for measuring the surface for successful audio extraction. We show examples of groove damage thought to originate from repeated stylus playback, and highlight the advantages offered by this scanning strategy for application to damaged or even broken recordings
Non-contact surface metrology for preservation and sound recovery from mechanical sound recordings
No full textOptical, non-contact audio recovery methods provide an alternative means for retrieving audio content rather
than risking traditional stylus transfer early sound recordings. The system differs from other optical systems
because the whole surface is scanned, providing a permanent record of the recording’s surface topology,
despite possible further degradation of the artefact. This paper describes the sensing and scanning
methodology, and their implications for the motion control system, and the signal processing techniques for
audio recovery from the surface measurement data. A comparison with stylus transfer is inc
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