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Geometrical metrology at micro scale: new approach and application to microfluidic devices
Full text linkAbout 30 years ago, in the industry for the production of semiconductors, started the race for the reduction of the dimensions of several electronic components. The trend followed the well-known Moore’s law and the dimensions of the chips halved every 18 months. The effect of reduction of the dimensions of products and components involved other scientific and technological fields. Products with micrometric dimensions, i.e. with one fundamental dimension in the range of micrometres, are presents in different domains including mechanics, biology, physics and medicine. The micro engineering concerns with the design, the realization and the industrialization of these products with micrometric dimensions. A fundamental phase of micro engineering is product/process quality control and related measurements. The metrology at micro scale is part of the manufacturing chain of micro products during the design, with the definition of the specifications, during the manufacturing, for the control of the process and in the final phase for the verification of specifications. The measurement of the dimensions and geometries at micrometric level is nowadays in evolution: several aspects, including the development of instruments and measurement techniques, need more studies.
The thesis here presented wants to contribute increasing the knowledge in the field of micro metrology and to provide useful solutions to improve the dimensional and geometrical characterization of micro products.
Although, the research has been developed to be valid in general, it is included as an integral part of the European project “CellDiaSp”. The project, in collaboration with international partners, provides for the realization of a microfluidic platform for cells analysis.
The metrological activities, required by the project, are needed to characterize the dimensions and the geometry of prototypes, mould inserts, masters and finite products, in order to guarantee the respect of the specifications and the functionality of the final product.
The first phase of the research deals with the study of the state of the art of metrology and of the relevant measurement techniques that can be used at micro scale.
Successively the application of some of these techniques to the replication processes has been studied. These processes, such as micro injection moulding, are used to obtain mass production and a cost reduction. It has been considered the possibility to measure the components presents in the process of replication, that is the inserts and the replicated parts and to evaluate the quality of the replication process through the calculation of single parameters such as parameters used in the measurement of surfaces. It resulted that this is possible only in few specific cases and that it is preferable to perform a complete three dimensional characterization of the dimensions and geometries of the product of replication.
It has been decided to focus the attention on two typologies of instruments: the scanning probe microscopes and the optical profilometers. These instruments are adapted to the measurement of the parts to be investigated within the project and, moreover, they are the best candidates to be implemented as coordinate measuring instruments, even if they were originally developed as surface measurement instruments.
The problem of “drift”, an effect that reduces the accuracy of the measurements performed through atomic force microscopes, has been treated. The causes of the phenomenon have been identified and solutions to the reduction of this error have been provided.
In order to obtain coordinate measurements from the atomic force microscopes and from the optical profilometer, a new technique for the data analysis has been developed.
The new methodology is presented applied to a case study of a microfluidic channel measured through optical profilometry. The technique is inspired by the international standards in the field of geometrical product specification and verification, with particular reference to coordinate metrology. However, these standards can’t be directly applied to product with micrometric dimensions and they require new solutions for the analysis of the data. A dedicated software has been developed to treat the data, acquired through a confocal microscope, both as image and as point cloud, taking advantage of both approaches and related representation. Specific procedures of filtration and thresholding have been developed to perform the extraction of the points and the association of the geometrical features for the evaluation of dimensions and geometries of the sample. The developed software provides a semi-automatic and repeatable way for the coordinate measurement of micrometric components.
Finally, the developed technique has been validated using a case study: the measurements of microfluidic channels with cylindrical section used in the realization of peristaltic pumps
Dimensional metrology of microstructured channels using quantitative 3D optical microscopy
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Investigation on the accuracy of CT measurements for wear testing of prosthetic joint components
No full textWear testing of prosthetic joint components is fundamental for understanding wear mechanisms and improving the quality of manufactured orthopaedic prostheses. To this end, accurate measuring solutions are needed for quantifying wear volumes and characterizing the geometry of worn bearing surfaces. In this work, capability and accuracy of industrial computed tomography in wear assessment of prosthetic components are investigates. Advantages and limitations are determined in comparison with measurements by coordinate measuring machines
Performance verification of a confocal microscope for 3D metrology tasks
No full textDimensional and geometrical inspection of parts manufactured at micro and nanometric scales is currently difficult due to several limitations of possible inspection techniques. For example, SEM images provide only mostly qualitative information, while micro and nano precision CMMs require long measuring times and probe dimensions may limit the access to specific features. On the other hand, some optical microscopy techniques have the capability to acquire quantitative surface topography information as areal maps. Although they are primarily designed for surface topography measurements, they can be used to obtain geometric information as well. In particular, imaging confocal microscopy is a common technique for the 3D measurement of surface topography. Objectives used in confocal microscopy have a large numerical aperture that allows high lateral resolution (up to 0.2 μm) and high measurable local slope (up to 60°). Measurable local slope is a fundamental parameter when measuring parts such as MEMS, microfluidic channels, or optical devices. Beneath the capability of confocal microscopy to detect surfaces with high local slope, the measurement is affected by errors related to the slope angle of the surface with respect to the optical axis. This work proposes a method to easily quantify the magnitude of this error when measuring with a confocal microscope. The method is based on measurements of calibrated spheres and association of measurement errors to local surface slope
R1234yf flow boiling heat transfer in a rectangular channel heated from the bottom
No full textThis paper presents some preliminary experimental measurements collected during flow boiling heat transfer of low-GWP refrigerant R1234yf in an asymmetrically heated rectangular plain channel. The asymmetrical heating is the common boundary condition that occurs in many different applications, for instance, in almost all the electronic devices, which are now pushing the cooling demands to more and more greater requirements. From this standpoint, the analysis of the flow boiling heat transfer efficient and eco-friendly refrigerants can open new frontiers to the electronic thermal management. The experimental measurements were carried out at the department Department of Industrial Engineering of the University of Padova by imposing two different heat fluxes, 50 and 100 kW m-2, at a constant saturation temperature of 30 °C; the refrigerant mass velocity was varied between 50 and 200 kg m-2 s-1, while the vapour quality varied from 0.2 to 0.95. The developed measuring technique permits to estimate the flow boiling heat transfer coefficient and the critical value of vapour quality at the onset of the dryout
Validation of on-machine microfeatures volume measurement using micro EDM milling tool electrode as touch probe
No full textIn micro electrical discharge milling, process parameters have to be empirically calibrated in order to achieve high precision machining; to this end, on-machine measurement of the material removed is of paramount importance. The capability of electrical discharge machines in detecting electrical contacts between the electrodes can be exploited to perform dimensional measurements, using the tool electrode similarly to the touch probe in a coordinate measuring machine. In this work an investigation of the accuracy of the on-the-machine volume measurements in a micro electrical discharge milling setup is carried out and an evaluation of the error affecting on-machine measurements is provided
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