Opto-mechanical modelling of an additive manufacturing laser scanning head including assembly defects

International audienceAdditive manufacturing (AM) machines used in SLM or SLA are composed of galvanometric scanning system in order to focus and steer a laser beam to melt raw materials. A major problematic in these AM processes is to master the laser spot position which essentially depends on the machine geometry and the galvanometers angular positions. In literature, most of existing models make strong assumptions concerning the geometry of the laser scanning system. Moreover, the position of the laser spot is often obtained by interpolating a table of correspondence, experimentally determined, between the angular positions of the galvanometers and the cartesian coordinates in the working plane. All these approximations induce deviations of the laser spot compared to the desired position and affect machine performance. This article presents two kinematic models of the galvanometric laser scanning system in an AM machine: a nominal model of the system and a model with assembly defects consideration. These kinematic models, often used for machine tools and robots, are here applied to create a virtual AM machine. Thereby, the laser spot position can be simulated knowing the geometry of the machine, the possible assembly defects, and the orientation of the galvanometers. The second kinematic model is then used to extract the influence of assembly defects on the laser spot position. The work described in this paper allows us to highlight and quantify the theoretical impact of an assembly defect on the precision of the laser spot position in an AM machine

Optical Coherence Tomography guided Laser-Cochleostomy

Despite the high precision of laser, it remains challenging to control the laser-bone ablation without injuring the underlying critical structures. Providing an axial resolution on micrometre scale, OCT is a promising candidate for imaging microstructures beneath the bone surface and monitoring the ablation process. In this work, a bridge connecting these two technologies is established. A closed-loop control of laser-bone ablation under the monitoring with OCT has been successfully realised

Development of an irradiation laser system for phototherapy mediated by nanoparticles

Cancer is a disease associated with high morbidity and mortality, which led to the devel-opment of clinical techniques to deal with this illness. Phototherapy is one of these methods. It is seen as a good solution to this problem due to its low invasiveness and prevention of DNA damage of healthy cells with the usage of non-ion-ising radiation. Advances in this technology have been made, and, in order to increase the safety of the procedure, it has been coupled with photosensitising agents, particles characterized by high absorbance at specific wavelengths. Since these agents possess high affinity towards tumour cells, it is possible to induce necrosis or apoptosis of unhealthy tissue with localised thermal energy. Nevertheless, increased safety and optimisation are pursued so it was considered that a beam delivering system capable of almost exclusively target tumour cells, protecting healthy ones, independently of the size of the cancer, should be the next step since few literature was found on the development of these systems. Two resolutions are proposed. A zoom lens based optical system able to dynamically vary its output beam diameter, focusing on the malignant tissue at once, and a galvanometric mirror system that allows the scanning of the area of the tumour, requiring a sweeping pattern due to the smaller output beam diameter employed. Despite both solutions producing promising results, to achieve clinical implementation is still needed the development of an apparatus that integrates the zoom lens based system and the testing in the laboratory of the galvanometric mirror system.O cancro é uma doença associada a elevada morbilidade e mortalidade, o que levou ao desenvolvimento de técnicas clínicas para lidar com esta enfermidade. A fototerapia é um desses métodos e é tomada como uma boa solução para esse problema, devido a ser pouco invasiva e prevenir danos ao ADN de células saudáveis, por usar radiação não ionizante. Para aumentar a segurança do procedimento, introduziu-se nesta terapia agentes fotos-sensibilizantes, partículas caracterizadas por alta absorbância em comprimentos de onda especí-ficos. Como estes agentes possuem alta afinidade com as células tumorais, é possível induzir necrose ou apoptose de tecido não saudável com energia térmica bem localizada. No entanto, aumentar a segurança e a otimização é necessário e, por isso, foi considerado que um sistema de entrega de feixe capaz de focar quase exclusivamente células tumorais, prote-gendo as saudáveis, independentemente do tamanho do cancro, deveria ser o próximo passo, uma vez que pouca literatura foi encontrada sobre o desenvolvimento desses sistemas. Duas resoluções são propostas. Um sistema ótico baseado em lentes de zoom capaz de variar dinamicamente o diâmetro do feixe de saída, atingindo o tecido maligno de uma só vez, e um sistema de espelhos galvanométricos que permite a cobertura da área do tumor, exigindo um padrão de varrimento, devido ao menor diâmetro do feixe de saída. Apesar de ambas as soluções produzirem resultados promissores, para alcançar uma im-plementação clínica ainda é necessário o desenvolvimento de um aparelho que integre o sistema baseado em lentes de zoom e o teste em laboratório do sistema de espelhos galvanométricos

On-the-fly laser machining: a case study for in situ balancing of rotative parts

On-the-fly laser machining is defined as a process that aims to generate pockets/patches on target components that are rotated or moved at a constant velocity. Since it is a nonintegrated process (i.e., linear/rotary stage system moving the part is independent of that of the laser), it can be deployed to/into large industrial installations to perform in situ machining, i.e., without the need of disassembly. This allows a high degree of flexibility in its applications (e.g., balancing) and can result in significant cost savings for the user (e.g., no dis(assembly) cost). This paper introduces the concept of on-the-fly laser machining encompassing models for generating user-defined ablated features as well as error budgeting to understand the sources of errors on this highly dynamic process. Additionally, the paper presents laser pulse placement strategies aimed at increasing the surface finish of the targeted component by reducing the area surface roughness that are possible for on-the-fly laser machining. The overall concept was validated by balancing a rotor system through ablation of different pocket shapes by the use of a Yb:YAG pulsed fiber laser. In this respect, first, two different laser pulse placement strategies (square and hexagonal) were introduced in this research and have been validated on Inconel 718 target material; thus, it was concluded that hexagonal pulse placement reduces surface roughness by up to 17% compared to the traditional square laser pulse placement. The concept of on-the-fly laser machining has been validated by ablating two different features (4 × 60 mm and 12 × 4 mm) on a rotative target part at constant speed (100 rpm and 86 rpm) with the scope of being balanced. The mass removal of the ablated features to enable online balancing has been achieved within < 4 mg of the predicted value. Additionally, the error modeling revealed that most of the uncertainties in the dimensions of the feature/pocket originate from the stability of the rotor speed, which led to the conclusion that for the same mass of material to be removed it is advisable to ablate features (pockets) with longer circumferential dimensions, i.e., stretched and shallower pockets rather than compact and deep

On-the-fly laser machining: a case study for in situ balancing of rotative parts

On-the-fly laser machining is defined as a process that aims to generate pockets/patches on target components that are rotated or moved at a constant velocity. Since it is a nonintegrated process (i.e., linear/rotary stage system moving the part is independent of that of the laser), it can be deployed to/into large industrial installations to perform in situ machining, i.e., without the need of disassembly. This allows a high degree of flexibility in its applications (e.g., balancing) and can result in significant cost savings for the user (e.g., no dis(assembly) cost). This paper introduces the concept of on-the-fly laser machining encompassing models for generating user-defined ablated features as well as error budgeting to understand the sources of errors on this highly dynamic process. Additionally, the paper presents laser pulse placement strategies aimed at increasing the surface finish of the targeted component by reducing the area surface roughness that are possible for on-the-fly laser machining. The overall concept was validated by balancing a rotor system through ablation of different pocket shapes by the use of a Yb:YAG pulsed fiber laser. In this respect, first, two different laser pulse placement strategies (square and hexagonal) were introduced in this research and have been validated on Inconel 718 target material; thus, it was concluded that hexagonal pulse placement reduces surface roughness by up to 17% compared to the traditional square laser pulse placement. The concept of on-the-fly laser machining has been validated by ablating two different features (4 × 60 mm and 12 × 4 mm) on a rotative target part at constant speed (100 rpm and 86 rpm) with the scope of being balanced. The mass removal of the ablated features to enable online balancing has been achieved within < 4 mg of the predicted value. Additionally, the error modeling revealed that most of the uncertainties in the dimensions of the feature/pocket originate from the stability of the rotor speed, which led to the conclusion that for the same mass of material to be removed it is advisable to ablate features (pockets) with longer circumferential dimensions, i.e., stretched and shallower pockets rather than compact and deep

Modélisation d'une chaine opto-mécanique de fabrication additive avec prise en compte des défauts d'assemblage

International audienceLes machines de fabrication additive utilisées dans les procédés SLM et SLA sont composées d'un système de balayage laser permettant de focaliser et diriger un faisceau laser pour fusionner la matière brute (poudre ou liquide). Une des problématiques majeures consiste à maitriser la position du spot laser dans le plan de travail. Celle-ci dépend essentiellement de la géométrie de la machine et de la position angulaire des galvanomètres. Dans la littérature, la plupart des modèles utilisent des hypothèses restrictives sur la géométrie du système de balayage. Ces hypothèses induisent des déviations sur la position réelle du spot laser comparée à la position désirée, ce qui affecte les performances de la machine. Cette communication présente deux modèles géométriques du système de balayage laser : un modèle nominal et un modèle avec prise en compte des défauts géométriques d'assemblage. Ces modèles géométriques, souvent utilisés en usinage et en robotique, sont ici mis en oeuvre pour créer une machine de fabrication additive virtuelle. En utilisant ces modèles, la position du spot laser peut être simulée en connaissant certains paramètres géométriques de la machine et l'orientation des galvanomètres. Le second modèle géométrique est utilisé pour extraire l'influence des défauts d'assemblage sur la position du spot laser. Il permet également d'accélérer le processus de construction des tables de correspondance tout en maîtrisant les erreurs d'interpolation effectuées. Le travail réalisé permet de mettre en évidence et quantifier l'impact de chaque défaut d'assemblage sur la précision de positionnement du spot laser

Robot Assisted Laser Osteotomy

In the scope of this thesis world\u27s first robot system was developed, which facilitates osteotomy using laser in arbitrary geometries with an overall accuracy below 0.5mm. Methods of computer and robot assisted surgery were reconsidered and composed to a workflow. Adequate calibration and registration methods are proposed. Further a methodology for transferring geometrically defined cutting trajectories into pulse sequences and optimized execution plans is developed