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4 results on '"Aschraf N. Danun"'

1. (Non-)linear stiffness customisation of metallic additive manufactured springs

Author

Aschraf N. Danun, Oliver Poole, Edouard Tarter, Patrick Beutler, and Mirko Meboldt

Subjects
laser powder bed fusion, 3d-printing, automation, compliant mechanisms, design synthesis, design freedom, Science, Manufactures, TS1-2301
Abstract

Additive manufacturing (AM) facilitates the fabrication of compliant mechanisms through its free-form and design customisation capabilities. Specifically, the properties of kinetic mechanisms such as springs can be extended with regards to their inherent (non-)linear stiffness functions. This allows for the customisation of AM springs according to user preferences. By combining the design synthesis approach of building blocks with the structural optimisation approach for AM, it is possible to define and customise spring stiffness functionalities. The optimisation process employs an automated computational framework based on a genetic algorithm scheme, which has been demonstrated through randomised and reference case studies. This framework enables the attainment of linear, progressive (stiffening), and degressive (softening) stiffness curves. The manufacturability of the springs has been validated through laser powder bed fusion using stainless-steel material 17–4 PH (H900). The springs have resulted in an accuracy error of maximum 6.48% and precision error of maximum 5% through compression testing.

Published
2023
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2. Additive manufactured continuum mechanisms based on shape-programmable and micro-sized building blocks

Author

Aschraf N. Danun, Remo Elmiger, Fabio Leuenberger, Luca Niederhauser, Jan Szlauzys, Lorin Fasel, and Mirko Meboldt

Subjects
miniaturisation, compliant mechanisms, customization, design automation, design synthesis, Science, Manufactures, TS1-2301
Abstract

Micro-additive manufacturing techniques have the potential to meet the demand for miniaturised functional components for minimally invasive surgical instruments. These techniques create monolithic, compliant mechanisms with micro-sized free-form structures that can be tailored to patient-specific surgical procedures. The automated design synthesis of the mechanisms using building blocks results in structures that are shape-programmable. This is achieved through an algorithmic-based computational workflow, which automatically converts user-specified 2D and 3D curves into discrete curve segments. The actuated motion of the mechanisms can be designed to move in a specific way, both forwardly and inversely. The mechanisms are manufactured using micro-laser powder bed fusion and hardenable stainless steel 17-4 PH. By carefully selecting the process parameters, it is possible to 3D-print micro-sized features such as a compliant beam thickness of 80 μm and an actuation hole of 100 μm. Both 2D planar curved mechanisms and 3D spatial curved mechanisms have been implemented and experimentally validated.

Published
2023
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3. Building Block Synthesis of Self-Supported Three-Dimensional Compliant Elements for Metallic Additive Manufacturing

Author

Philip Dalla Palma, Mirko Meboldt, Aschraf N. Danun, and Christoph Klahn

Subjects
0209 industrial biotechnology, Computer science, Building Block Approach, Design elements and principles, 02 engineering and technology, Spring (mathematics), 020901 industrial engineering & automation, Block (telecommunications), Powder bed fusion, 0202 electrical engineering, electronic engineering, information engineering, Design Principles, Design for Additive Manufacturing (DfAM), Compliant Mechanisms, Design Synthesis, business.industry, Mechanical Engineering, Compliant mechanism, 020207 software engineering, Structural engineering, Computer Graphics and Computer-Aided Design, Spring, Computer Science Applications, Design synthesis, Mechanics of Materials, business
Abstract

Compliant mechanisms gain motion through the elastic deformation of the monolithic flexible elements. The geometric design freedom of metallic additive manufacturing enables the fabrication of complex and three dimensional (3D) compliant elements within mechanisms previously too complicated to produce. However, the design of metallic additive manufactured mechanisms faces various challenges of manufacturing restrictions, such as avoiding critical overhanging geometries and minimizing the amount of support structure, which has been reported in a few cases. This paper presents a synthesis approach for translational compliant elements, involving building blocks based on leaf-type springs and covering building orientations between 0° and 90°. In particular, this range is approached by the synthesis of self-supported 3D building blocks with orientations of 0°, 45°, and 90°. The compliant elements are built based on linear and circular plane curves and compared numerically according to their mechanical performance to create preferable building blocks. The applicability of the presented procedure and the manufacturability of the compliant mechanisms are proven by printing individual 3D building blocks and their serial aggregation with laser based powder bed fusion. Consequently, several prototypes are demonstrated, including a bistable switch mechanism and a large displaceable rotational spring joint. In addition, a small-scale highly maneuverable segment of a surgical instrument with a grasping mechanism at the distal end is proposed., Journal of Mechanical Design, 143 (5), ISSN:1050-0472, ISSN:1528-9001

Published
2021
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4. A Magnetically Navigated Microcannula for Subretinal Injections

Author

Bradley J. Nelson, Alexandre Mesot, Quentin Boehler, Samuel Charreyron, Matthias D. Becker, and Aschraf N. Danun

Subjects
Retinal Disorder, Microscope, Computer science, Swine, Biomedical Engineering, Retina, law.invention, Injections, 03 medical and health sciences, 0302 clinical medicine, Optical coherence tomography, Retinal Diseases, law, Microscopy, medicine, Animals, 030304 developmental biology, 0303 health sciences, medicine.diagnostic_test, Macular degeneration, medicine.disease, Cannula, 3. Good health, medicine.anatomical_structure, 030221 ophthalmology & optometry, Tomography, Optical Coherence, Biomedical engineering
Abstract

Retinal disorders, including age-related macular degeneration, are leading causes of vision loss worldwide. New treatments, such as gene therapies and stem cell regeneration, require therapeutics to be introduced to the subretinal space due to poor diffusion to the active component of the retina. Subretinal injections are a difficult and risky surgical procedure and have been suggested as a candidate for robot-assisted surgery. We propose a different actuation paradigm to existing robotic approaches using remote magnetic navigation to control a flexible microcannula. A flexible cannula allows for high dexterity and considerable safety advantages over rigid tools, while maintaining the benefits of micrometer precision, hand tremor removal, and telemanipulation. The position of the cannula is tracked in real-time using near-infrared tip illumination, allowing for semi-automatic placement of the cannula and an intuitive user interface. Using this tool, we successfully performed several subretinal injections in ex-vivo porcine eyes under both microscope and optical coherence tomography visualization. ISSN:0018-9294 ISSN:1558-2531

Published
2020

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