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PublicationPerformance comparison between model-based and machine learning approaches for the automated active alignment of FAC-lenses( 2020)Due to their short focal lengths, FAC lenses significantly influence the performance of high-power diode laser systems. In addition to the shape, coating and surface quality, high demands are placed on the assembly accuracy for these microoptical components. In order to optimally align and position the lenses despite varying properties (e.g. focal length), active alignment strategies are used. The automation of the active alignment process for production offers enormous potential. Compared to manual processes, the reproducibility and accuracy of the alignment is increased. For the automation of the active alignment process, a deep understanding of the system behaviour is necessary. To control a diversity of variants cost-effectively and robust, new approaches must be taken into account. Concepts of AI or machine learning are great for this kind of generalization and adoption and they have many advantages for the active alignment of systems like DOEs or free-form-optics, with a complex system behaviour. In this publication, we want to compare the performance of a classically model-based algorithm and a machine learning approach for the automated active alignment of FAC-lenses. The model-based algorithm uses a physical model of the metrology system (including the FAC to be aligned) to estimate a misalignment in 4-DOF. The machine learning algorithm consist of a deep neuronal network which was trained with image data.
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PublicationAutomated sensor-guided packaging of diamond tools( 2020)Automated, ultra-precise packaging strategies reduce production time and costs while increasing yield, quantity, and precision, making them one of the main research and development questions in the field of production technology. Fraunhofer IPT develops sensor-guided assembly solutions for packaging and testing of optical and non-optical components to meet the demand. In this paper, we present a prototypical process for the automated, ultra-precise passive alignment using the assembly of a diamond engraving tool as an example. The challenge is to place a diamond measuring three millimetres in its largest dimension into a groove of similar size and to position the tip of the diamond within tolerances of a few micrometres and arcminutes. This six dimensional assembly problem is tackled by feeding live camera data to an image processing algorithm and by aligning the diamond using Fraunhofer IPT's ultra-precise micromanipulator, collectively forming an automated, closed-loop assembly process. Thus, a fully automated packaging process with very high accuracy and reliability is proven to be technically possible.
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PublicationOCT measurement of aspheric polymer lenses for adaptive assembly of micro optical imaging objectives( 2020)
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PublicationHigh precision automated tab assembly with micro optics for optimized high-power diode laser collimation( 2020)The industrial assembly processes for fast axis collimation (FAC) lenses with high power laser diodes are continuously being improved and automated. The system requirements allow for various solutions for the attachment process of the micro-optic component, the standard being active assembly relative to the light emitting laser-diode facet with joining by a UV-curable glue at attachment positions outside of the laser beam-path. To facilitate higher degrees of freedom and to optimize the results in the joining process with tighter tolerances in some critical functions, the FAC mounted on tab is one of the possible solutions and a viable process option. We report the results of high accuracy preassembly of FAC on tab with respect to the specific requirement of a target assembly back focal length within tight tolerance values.
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PublicationAutomated PM-fiber array assembly with high-precision four DOF alignment( 2020)Polarization maintaining fibers arrays are key enablers to process high bandwidth data, representing a powerful part within the photonic integrated chip technology. The different channels increase the information density and allow to multiple singles through one fiber bulk at the same time. Due to fiber's small dimensions (ø125 mm) they can be integrated in existing infrastructure easily and are very flexible at the same time. However, the compact design together with the flexible material properties demands for new precise tools and technologies to reach the necessary precision during packing. The Fraunhofer-Institute for Production Technology IPT develops, together with their partners Phix and Aixemtec, new handling and assembly tools, as well as processes as one of the leading companies in this field. In the self-developed assembly cell, the fiber handling tool-head operations automatically to pick up, manipulate and tack single fibers to a glass plate or fiber to chip. Each fiber is moved by a portal robot within the assembly cell with micrometer accuracy but also can be rotated with a repetition accuracy less than 0.01°. Advanced illumination units observation techniques allow to package fibers arrays much quicker and more robust than before. Therefore, additional camera systems and material characteristics are used to develop smart alignment routines. As a result, the observation of the orientation of the PM-fiber core as well as the fiber layout during the assembly process leads to high quality products within fast production cycles. Due to the flexible construction of the assembly call also PIC packaging and fiber-to-chip coupling is possible.
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PublicationOffline development of active alignment based on empirical virtual environments( 2020)Active or sensor guided alignment presents a promising production approach for high-quality optical products and helps to overcome challenges in the tolerance chain. Application fields such as fast-axis collimation increasingly deploy automated productions solutions in order to improve and ensure stable quality even with relatively low production volume. The advantages are offset by the high demand towards the engineering as upfront cost, common to all automated production solutions with integrated evaluation of the system function. In this paper, we present our approach to overcome this problem. We propose the use of virtual environments, which are derived from empirical data generated with minimized effort in early phases of the product development. We will present options for building the necessary dataset and how our solution can derive an empirical simulation due to the application of artificial intelligence. Our solution is independent from ray tracing simulations and reflects defects, deviations and tolerances as observed in the actual product samples. This allows developing alignment algorithms offline, without the need for costly machine time and the risk of damage due to manual errors. We will present validation results, which demonstrates the capability to transfer active alignment algorithms from the virtual environment to actual automation equipment. Next to FAC alignment and the high-power laser industry our virtual environment solution is of special interest to application in the field of diffractive optical elements (DOE) and free-form optics, where low volume or changing designs demand adaptable automation solutions.
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PublicationInvestigation of the negative influence of cooling lubricants on the deformation of the machine tool structure( 2019)Cooling lubricants have a significant influence on the thermal state of a machine tool. The fluid absorbs the thermal energy of the cutting process and dissipates it to prevent wear of the tool and distortion of the work piece. However, the unpredictable flow of the cooling lubricant also transfers the energy to the machine tool structure and can thus have a negative impact on the produced work piece quality. While the thermal behaviour of machine tools under the influence of thermal environmental conditions is already the subject of ongoing research projects, the influence of cooling lubricants on the thermal state of the machine tool and thus the achievable manufacturing accuracy is still largely unexplored. This paper investigates the thermally induced deformations of the machine tool structure, as well as the impact on the Tool Centre Point (TCP).
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PublicationAutomated sprue removal from injection moulded micro-optics with ultrasonic cutting( 2019)Injection moulding is key to fast mass production for smart devices, mobility and medical products, like micro-optics, covers and lab-on-a-discs respectively. For optics, several million if not billions of small lenses are merged into objectives. One characteristic type of objective holder is the lens barrel. The successful assembly of lenses with diameters of just a couple of millimetres into a lens barrel is an error-prone task antagonized with mass production and an optical inspection at the end of the assembly. Before the assembly and after the manufacture of the individual optics, the sprue separation takes place. This is a critical moment because even optics whose dimensions are within the target tolerance after manufacturing can be damaged by improper action. Common methods here are the separation by means of a blade, hot wire, laser or saw blade. Each of these methods has its advantages and disadvantages, but all have in common the introduction of stress and/or heat into the component. The Fraunhofer IPT investigates a much more elegant way removing the sprue from injection-moulded optics in an automated environment. Based on the ultrasound technology developed by IPT back in the 1980s, we use a high frequency generator to get an AC voltage and piezo crystal for the inverse piezoelectric effect. The crystal oscillates with a high frequency and low amplitude. Next, the l/2 to l/4 sonotrode amplifies the amplitude. The sonotrode is designed with a CAD model, simulated in ANSYS and the complete experimental verified on real lenses afterwards.
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PublicationLaser-based measurement of thermo-elastic structural deviation of machine tools( 2019)Thermo-elastic deformations are one of the most significant sources of machine tool inaccuracies. The structure components of the machine tools can elongate and also bend due to inhomogeneous distribution of temperature in the machine structures. There are numerous methods to measure and monitor structural deformations. However, the measurement of the structural bending is still very challenging procedure. In this paper, a simple laser-based sensor is introduced for the measurement of the structural bending of machine tool components. The sensor is made of a laser unit, a precision optics based on charge-coupled device (CCD) and electronics for image processing. These measuring hardware are mounted in a metal tube: the laser at one end of the tube and the CCD at the other end of the tube. With the change of the laser beam position on the CCD, the bending of the tube can be measured perpendicular to the laser line of sight in two dimensions. To measure the accurate laser position, an image processing algorithm is applied and embedded in the integrated electronics. For the validation of the sensor capability, the sensor is mounted on two different machine tools. The measurement of the sensor is applied under thermal loads of axis movements after ISO 230-3. The sensor potential is analyzed with the correlation between the sensor measurement and different independent validation measurements.
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PublicationPolygon scanner based ultra-short pulse laser processing for continuous manufacturing( 2019)Enabling of continuous photomasking using a pulsed laser source and polygon scanners to achieve high repetition rates and pulse energy, precise beam guiding and stable handling of the moving web with the applied photomask resist.
