Estudi i desenvolupament d'un nou sistema d'inspecció de stents basat en tècniques de metrologia òptica
Stent quality control is a critical process. Coronary stents have to be inspected 100% so no defective stent is implanted into a human body. We have developed an optical non-contact measurement instrument that provides stent inspection in an automated and high-speed approach, delivering the user all...
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| Formato: | tesis doctoral |
| Fecha de publicación: | 2017 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | catalán |
| OAI Identifier: | oai:upcommons.upc.edu:2117/108237 |
| Acesso em linha: | https://hdl.handle.net/2117/108237 https://dx.doi.org/10.5821/dissertation-2117-108237 |
| Access Level: | acceso abierto |
| Palavra-chave: | Microscopia Metrologia òptica Visió per computador Inspecció de stents Inspecció visual Microscopy 0ptical metrology Machine vision Stent inspection Visual inspection Àrees temàtiques de la UPC::Ciències de la salut |
| Resumo: | Stent quality control is a critical process. Coronary stents have to be inspected 100% so no defective stent is implanted into a human body. We have developed an optical non-contact measurement instrument that provides stent inspection in an automated and high-speed approach, delivering the user all the necessary information to assess whether a stent is valid or needs to be rejected. As regards to the instrument design, we have developed and built an optical sensor head that obtains high resolution colour images of the stent surfaces at high speed. Acquired images contain not only contour information of the struts, but also depict the edges roundnesses caused by the surface treatment. This has been achieved by the integration of a triple illumination system in combination with a high precision rotational stage and an area seen camera, which also acquires in line-scan mode. As a result, a patent filed by Sensofar Medical, S.L. protects this invention, which is also being commercialized by the same company. Regarding to the rotational system, different driving configurations have been analysed, and the motion errors that they produce to the images have been studied. Taking this into account, manufacturing tolerances have been established accordingly to guarantee high quality image acquisition. As regards to image acquisition and analysis, we have studied and characterized the difference between the image obtained with a conventional, bright field microscope and the proposed system. Moreover, we have introduced a new method to measure sidewalls critical dimensions, consisting of taking the same, line-scanned images at a certain observation angle. Together with a correction model, 1-micron precision measurements are obtained. To be able to process the measurements in an automated approach, we have developed critical dimension measurement algorithms for the four stent surfaces: abluminals (inner and outer) and luminal (sidewalls). Additionally, we have studied, developed and implemented defect detection algorithms controlled by a sensitivity parameter adjusted by the user. Defects are also classified in a supervised classifier approach by means of a previous training with a defects database. The instrument has also been enabled with tridimensional measurement capabilities, based on coherence scanning interferometry to obtain the topography and roughness of any surface. This technique is also used to characterize defects in 30 in order to reduce the stent rejection rate and thus increasing the process efficiency, as the height of the candidates which maybe are not defects can be also assessed. Besides, this technique can also measure the transparent film thicknesses of drug eluting stents. In this case, due to the cylindrical shape of the samples, measured thicknesses are altered by the local slope at the measuring point, so we have proposed and evaluated two correction models that provide the thickness 30 map corrected automatically. All the capabilities described provide a number of advantages in the stent production and quality control stages. Specifically, objectivity and traceability of these processes are significantly increased, making stents every day more safe devices, reducing the restenosis rate, cardiac accidents or illnesses resulting from an implant malfunction. |
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