Lock-in Thermography for Process Integrated Non-Destructive Evaluation of Carbon Fibre Reinforced Aircraft Stuctures

Reliable process integrated quality assurance for the manufacturing of large-scale CFRP aircraft structures, such as fuselage shells, cargo doors or components of a central wing box, belongs to one of the most challenging objectives for nondestructive testing. Beside the well known key criteria like non-contact measurement and imaging options as well as the maximum failure detection resolution and defect selectivity even more aspects have to be considered: the penetration depth into the component’s material, the scanning and measurement speed, the coverage area as well as the accessibility of the structure (inspection condition with single side or two side accessibility). The probably most significant requirements for process integrated non-destructive inspection are the measurement time and data evaluation. Therefore the coverage area and the measurement speed are quite important. For example common ultrasound inspection screens the component’s surface line by line until the whole area is scanned. This requires quite a lot of time and as soon as the component’s shape includes curved or ribbed areas, it becomes difficult to receive proper signals of the material’s interior structure. In contrast, the main benefit of optical inspection methods is the coverage of relatively large areas within one exposure time but on the other hand only features which are located near the component’s surface can be detected. However, lock-in thermography seems to be a good compromise of all these boundary conditions as it is monitoring the time dependent change of thermal waves that are emitted by the structure component. Depending on the excitation frequency of the induced thermal waves, it is possible to collect information of the material’s microstructural features from different depths and to cover relatively large areas within one measurement cycle. A single side accessibility of the structure component is absolutely sufficient and measurement time as well as data acquisition and interpretation can be performed within the order of minutes. Detecting and localizing material defects or significant microstructural changes is relatively easy since changes in the material’s thermal diffusivity are clearly distinguishable in the visual data mapping of the component’s surface. As previous work has shown, even a proceeding resin front of an infiltration process can be detected and visually displayed. Focusing the benefits and potentials it is shown that lock-in thermography is a valuable non-destructive inspection tool that can be used as part of a process integrated quality assurance system for CFRP structure component manufacturing

Multi-scale metrology for automated non-destructive testing systems

This thesis was previously held under moratorium from 5/05/2020 to 5/05/2022The use of lightweight composite structures in the aerospace industry is now commonplace. Unlike conventional materials, these parts can be moulded into complex aerodynamic shapes, which are diffcult to inspect rapidly using conventional Non-Destructive Testing (NDT) techniques. Industrial robots provide a means of automating the inspection process due to their high dexterity and improved path planning methods. This thesis concerns using industrial robots as a method for assessing the quality of components with complex geometries. The focus of the investigations in this thesis is on improving the overall system performance through the use of concepts from the field of metrology, specifically calibration and traceability. The use of computer vision is investigated as a way to increase automation levels by identifying a component's type and approximate position through comparison with CAD models. The challenges identified through this research include developing novel calibration techniques for optimising sensor integration, verifying system performance using laser trackers, and improving automation levels through optical sensing. The developed calibration techniques are evaluated experimentally using standard reference samples. A 70% increase in absolute accuracy was achieved in comparison to manual calibration techniques. Inspections were improved as verified by a 30% improvement in ultrasonic signal response. A new approach to automatically identify and estimate the pose of a component was developed specifically for automated NDT applications. The method uses 2D and 3D camera measurements along with CAD models to extract and match shape information. It was found that optical large volume measurements could provide suffciently high accuracy measurements to allow ultrasonic alignment methods to work, establishing a multi-scale metrology approach to increasing automation levels. A classification framework based on shape outlines extracted from images was shown to provide over 88% accuracy on a limited number of samples.The use of lightweight composite structures in the aerospace industry is now commonplace. Unlike conventional materials, these parts can be moulded into complex aerodynamic shapes, which are diffcult to inspect rapidly using conventional Non-Destructive Testing (NDT) techniques. Industrial robots provide a means of automating the inspection process due to their high dexterity and improved path planning methods. This thesis concerns using industrial robots as a method for assessing the quality of components with complex geometries. The focus of the investigations in this thesis is on improving the overall system performance through the use of concepts from the field of metrology, specifically calibration and traceability. The use of computer vision is investigated as a way to increase automation levels by identifying a component's type and approximate position through comparison with CAD models. The challenges identified through this research include developing novel calibration techniques for optimising sensor integration, verifying system performance using laser trackers, and improving automation levels through optical sensing. The developed calibration techniques are evaluated experimentally using standard reference samples. A 70% increase in absolute accuracy was achieved in comparison to manual calibration techniques. Inspections were improved as verified by a 30% improvement in ultrasonic signal response. A new approach to automatically identify and estimate the pose of a component was developed specifically for automated NDT applications. The method uses 2D and 3D camera measurements along with CAD models to extract and match shape information. It was found that optical large volume measurements could provide suffciently high accuracy measurements to allow ultrasonic alignment methods to work, establishing a multi-scale metrology approach to increasing automation levels. A classification framework based on shape outlines extracted from images was shown to provide over 88% accuracy on a limited number of samples

Machine vision techniques for inspection of dry-fibre composite preforms in the aerospace industry

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents the results of a three year investigation into machine vision techniques for in-process automated inspection of dry-fibre composite preforms. Efficient texture analysis based techniques have been developed, tested, and implemented in a prototype robotic assembly cell. Industrial constraints have been considered in the development of all the algorithms described. A single channel texture analysis model is described which can successfully segment images containing only a few textures. The model is based on convolution of the image with small kernels optimised for the task, and is elegant in the sense that it is computationally simple and easily realisable in low cost hardware. A new convolution kernel optimisation algorithm is described. It is demonstrated that convolution kernels can also be optimised to perform as edge operators in simple textured images. A novel boundary refinement algorithm is described which reduces the inspection errors inherent in texture based boundary estimates. The algorithm takes the form of a local search, using the texture estimate as a guiding template, and selects edge points by maximising a merit function. Optimum parameters for the merit function are obtained using multiple training images in conjunction with simple function optimisation algorithms.This study is funded by the Engineering and Physical Sciences Research Council (EPSRC) and Dowty Aerospace Propellers Ltd

Calibration and 3D Mapping for Multi-sensor Inspection Tasks with Industrial Robots

Le ispezioni di qualità sono una parte essenziale per garantire che il processo di produzione si svolga senza intoppi e che il prodotto finale soddisfi standard elevati. I robot industriali sono diventati uno strumento fondamentale per condurre le ispezioni di qualità, consentendo precisione e coerenza nel processo di ispezione. Utilizzando tecnologie di ispezione avanzate, i robot industriali possono rilevare difetti e anomalie nei prodotti a una velocità superiore a quella degli ispettori umani, migliorando l'efficienza della produzione. Grazie alla capacità di automatizzare le attività di ispezione ripetitive e noiose, i robot industriali possono anche ridurre il rischio di errore umano e aumentare la qualità dei prodotti. Con il continuo progresso tecnologico, l'uso dei robot industriali per le ispezioni di qualità si sta diffondendo in tutti i settori industriali, da quello automobilistico e manifatturiero a quello aerospaziale. Lo svantaggio di una tale varietà di compiti di ispezione è che di solito le ispezioni industriali richiedono configurazioni robotiche specifiche e sensori appropriati, rendendo ogni ispezione molto specifica e personalizzata. Per questo motivo, la presente tesi fornisce una panoramica di un framework di ispezione generale che risolve il problema della creazione di celle di lavoro di ispezione personalizzate, proponendo moduli software generali che possono essere facilmente configurati per affrontare ogni specifico scenario di ispezione. In particolare, questa tesi si concentra sui problemi della calibrazione occhio-mano, ovvero il problema di calcolare con precisione la posizione del sensore nella cella di lavoro rispetto all'inquadratura del robot, e del Data Mapping, utilizzato per mappare i dati del sensore nella rappresentazione del modello 3D dell'oggetto ispezionato. Per la calibrazione occhio-mano proponiamo due tecniche che risolvono con precisione la posizione del sensore in più configurazioni robotiche. Entrambe considerano la configurazione robot-sensore eye-on-base e eye-in-hand, vale a dire il modo in cui discriminiamo se il sensore è montato in un punto fisso della cella di lavoro o nel braccio terminale del manipolatore robotico, rispettivamente. Inoltre, uno dei principali contributi di questa tesi è un approccio generale alla calibrazione occhio-mano che è anche in grado di gestire, grazie a una formulazione unificata di ottimizzazione del grafo di posa, configurazioni di ispezione in cui sono coinvolti più sensori (ad esempio, reti multi-camera). In definitiva, questa tesi propone un metodo generale che sfrutta un risultato preciso e accurato della calibrazione occhio-mano per affrontare il problema del Data Mapping per i robot di ispezione multiuso. Questo approccio è stato applicato in diverse configurazioni di ispezione, dall'industria automobilistica a quella aerospaziale e manifatturiera. La maggior parte dei contributi presentati in questa tesi sono disponibili come pacchetti software open-source. Riteniamo che ciò favorisca la collaborazione, consenta una precisa ripetibilità dei nostri esperimenti e faciliti la ricerca futura sulla calibrazione di complesse configurazioni robotiche industriali.Quality inspections are an essential part of ensuring the manufacturing process runs smoothly and that the final product meets high standards. Industrial robots have emerged as a key tool in conducting quality inspections, allowing for precision and consistency in the inspection process. By utilizing advanced inspection technologies, industrial robots can detect defects and anomalies in products at a faster pace than human inspectors, improving production efficiency. With the ability to automate repetitive and tedious inspection tasks, industrial robots can also reduce the risk of human error and increase product quality. As technology continues to advance, the use of industrial robots for quality inspections is becoming more widespread across industrial sectors, ranging from automotive and manufactury to aerospace industries. The drawback of such a large variety of inspection tasks is that usually industrial inspections require specific robotic setups and appropriate sensors, making every inspection very specific and custom buildt. For this reason, this thesis gives an overview of a general inspection framework that solves the problem of creating customized inspection workcells by proposing general software modules that can be easily configured to address each specific inspection scenario. In particular, this thesis is focusing on the problems of Hand-eye Calibration, that is the problem of accurately computing the position of the sensor in the workcell with respect to the robot frame, and Data Mapping that is used to map sensor data to the 3D model representation of the inspected object. For the Hand-eye Calibration we propose two techniques that accurately solve the position of the sensor in multiple robotic setups. They both consider eye-on-base and eye-in-hand robot-sensor configuration, namely, this is the way in which we discriminate if the sensor is mounted in a fixed place in the workcell or in the end-effector of the robot manipulator, respectively. Moreover, one of the main contributions of this thesis is a general hand-eye calibration approach that is also capable of handling, thanks to a unified pose-graph optimization formulation, inspection setups where multiple sensors are involved (e.g., multi-camera networks). In the end, this thesis is proposing a general method that takes advantage of a precise and accurate hand-eye calibration result to address the problem of Data Mapping for multi-purpose inspection robots. This approach has been applied in multiple inspection setups, ranging from automotive to aerospace and manufactury industry. Most of the contributions presented in this thesis are available as open-source software packages. We believe that this will foster collaboration, enable precise repeatability of our experiments, and facilitate future research on the calibration of complex industrial robotic setups

Automation of Process Planning for Automated Fiber Placement

Process planning represents an essential stage of the Automated Fiber Placement (AFP) workflow. It develops useful and efficient machine processes based upon the working material, composite design, and manufacturing resources. The current state of process planning requires a high degree of interaction from the process planner and could greatly benefit from increased automation. Therefore, a list of key steps and functions are created to identify the more difficult and time-consuming phases of process planning. Additionally, a set of metrics must exist by which to evaluate the effectiveness of the manufactured laminate from the machine code created during the Process Planning stage. This work begins with a ranking process which was performed through a survey of the Advanced Composites Consortium (ACC) Collaborative Research Team (CRT). Members were interviewed who possessed practical process planning experience in the composites industry. The Process Planning survey collected general input on the overall importance and time requirements for each function and which functions would benefit most greatly from semi-automation or full automation. Layup strategies, in addition to dog ears, stagger shifts, steering constraints, and starting points, represented the group of functions labeled as process optimization and ranked the highest in terms of priority for automation. The laminates resulting from the selected parameters are evaluated through the occurrences of principal defect metrics such as fiber gaps, overlaps, angle deviation and steering violations. This document presents an automated software solution to the layup strategy and starting point selection phase of Process Planning. A series of ply scenarios are generated with variations of these ply parameters and evaluated according to a set of metrics entered by the Process Planner. These metrics are generated through use of the Analytical Hierarchy Process (AHP), where relative importance between each of the fiber features are defined. The ply scenarios are selected which reduce the overall fiber feature scores based on the defects the Process Planner wishes to minimize

Aquatic escape for micro-aerial vehicles

As our world is experiencing climate changes, we are in need of better monitoring technologies. Most of our planet is covered with water and robots will need to move in aquatic environments. A mobile robotic platform that possesses efficient locomotion and is capable of operating in diverse scenarios would give us an advantage in data collection that can validate climate models, emergency relief and experimental biological research. This field of application is the driving vector of this robotics research which aims to understand, produce and demonstrate solutions of aerial-aquatic autonomous vehicles. However, small robots face major challenges in operating both in water and in air, as well as transition between those fluids, mainly due to the difference of density of the media. This thesis presents the developments of new aquatic locomotion strategies at small scales that further enlarge the operational domain of conventional platforms. This comprises flight, shallow water locomotion and the transition in-between. Their operating principles, manufacturing methods and control methods are discussed and evaluated in detail. I present multiple unique aerial-aquatic robots with various water escape mechanisms, spanning over different scales. The five robotic platforms showcased share similarities that are compared. The take-off methods are analysed carefully and the underlying physics principles put into light. While all presented research fulfils a similar locomotion objective - i.e aerial and aquatic motion - their relevance depends on the environmental conditions and supposed mission. As such, the performance of each vehicle is discussed and characterised in real, relevant conditions. A novel water-reactive fuel thruster is developed for impulsive take-off, allowing consecutive and multiple jump-gliding from the water surface in rough conditions. At a smaller scale, the escape of a milligram robotic bee is achieved. In addition, a new robot class is demonstrated, that employs the same wings for flying as for passive surface sailing. This unique capability allows the flexibility of flight to be combined with long-duration surface missions, enabling autonomous prolonged aquatic monitoring.Open Acces

A continuum robotic platform for endoscopic non-contact laser surgery: design, control, and preclinical evaluation

The application of laser technologies in surgical interventions has been accepted in the clinical domain due to their atraumatic properties. In addition to manual application of fibre-guided lasers with tissue contact, non-contact transoral laser microsurgery (TLM) of laryngeal tumours has been prevailed in ENT surgery. However, TLM requires many years of surgical training for tumour resection in order to preserve the function of adjacent organs and thus preserve the patient’s quality of life. The positioning of the microscopic laser applicator outside the patient can also impede a direct line-of-sight to the target area due to anatomical variability and limit the working space. Further clinical challenges include positioning the laser focus on the tissue surface, imaging, planning and performing laser ablation, and motion of the target area during surgery. This dissertation aims to address the limitations of TLM through robotic approaches and intraoperative assistance. Although a trend towards minimally invasive surgery is apparent, no highly integrated platform for endoscopic delivery of focused laser radiation is available to date. Likewise, there are no known devices that incorporate scene information from endoscopic imaging into ablation planning and execution. For focusing of the laser beam close to the target tissue, this work first presents miniaturised focusing optics that can be integrated into endoscopic systems. Experimental trials characterise the optical properties and the ablation performance. A robotic platform is realised for manipulation of the focusing optics. This is based on a variable-length continuum manipulator. The latter enables movements of the endoscopic end effector in five degrees of freedom with a mechatronic actuation unit. The kinematic modelling and control of the robot are integrated into a modular framework that is evaluated experimentally. The manipulation of focused laser radiation also requires precise adjustment of the focal position on the tissue. For this purpose, visual, haptic and visual-haptic assistance functions are presented. These support the operator during teleoperation to set an optimal working distance. Advantages of visual-haptic assistance are demonstrated in a user study. The system performance and usability of the overall robotic system are assessed in an additional user study. Analogous to a clinical scenario, the subjects follow predefined target patterns with a laser spot. The mean positioning accuracy of the spot is 0.5 mm. Finally, methods of image-guided robot control are introduced to automate laser ablation. Experiments confirm a positive effect of proposed automation concepts on non-contact laser surgery.Die Anwendung von Lasertechnologien in chirurgischen Interventionen hat sich aufgrund der atraumatischen Eigenschaften in der Klinik etabliert. Neben manueller Applikation von fasergeführten Lasern mit Gewebekontakt hat sich die kontaktfreie transorale Lasermikrochirurgie (TLM) von Tumoren des Larynx in der HNO-Chirurgie durchgesetzt. Die TLM erfordert zur Tumorresektion jedoch ein langjähriges chirurgisches Training, um die Funktion der angrenzenden Organe zu sichern und damit die Lebensqualität der Patienten zu erhalten. Die Positionierung des mikroskopis chen Laserapplikators außerhalb des Patienten kann zudem die direkte Sicht auf das Zielgebiet durch anatomische Variabilität erschweren und den Arbeitsraum einschränken. Weitere klinische Herausforderungen betreffen die Positionierung des Laserfokus auf der Gewebeoberfläche, die Bildgebung, die Planung und Ausführung der Laserablation sowie intraoperative Bewegungen des Zielgebietes. Die vorliegende Dissertation zielt darauf ab, die Limitierungen der TLM durch robotische Ansätze und intraoperative Assistenz zu adressieren. Obwohl ein Trend zur minimal invasiven Chirurgie besteht, sind bislang keine hochintegrierten Plattformen für die endoskopische Applikation fokussierter Laserstrahlung verfügbar. Ebenfalls sind keine Systeme bekannt, die Szeneninformationen aus der endoskopischen Bildgebung in die Ablationsplanung und -ausführung einbeziehen. Für eine situsnahe Fokussierung des Laserstrahls wird in dieser Arbeit zunächst eine miniaturisierte Fokussieroptik zur Integration in endoskopische Systeme vorgestellt. Experimentelle Versuche charakterisieren die optischen Eigenschaften und das Ablationsverhalten. Zur Manipulation der Fokussieroptik wird eine robotische Plattform realisiert. Diese basiert auf einem längenveränderlichen Kontinuumsmanipulator. Letzterer ermöglicht in Kombination mit einer mechatronischen Aktuierungseinheit Bewegungen des Endoskopkopfes in fünf Freiheitsgraden. Die kinematische Modellierung und Regelung des Systems werden in ein modulares Framework eingebunden und evaluiert. Die Manipulation fokussierter Laserstrahlung erfordert zudem eine präzise Anpassung der Fokuslage auf das Gewebe. Dafür werden visuelle, haptische und visuell haptische Assistenzfunktionen eingeführt. Diese unterstützen den Anwender bei Teleoperation zur Einstellung eines optimalen Arbeitsabstandes. In einer Anwenderstudie werden Vorteile der visuell-haptischen Assistenz nachgewiesen. Die Systemperformanz und Gebrauchstauglichkeit des robotischen Gesamtsystems werden in einer weiteren Anwenderstudie untersucht. Analog zu einem klinischen Einsatz verfolgen die Probanden mit einem Laserspot vorgegebene Sollpfade. Die mittlere Positioniergenauigkeit des Spots beträgt dabei 0,5 mm. Zur Automatisierung der Ablation werden abschließend Methoden der bildgestützten Regelung vorgestellt. Experimente bestätigen einen positiven Effekt der Automationskonzepte für die kontaktfreie Laserchirurgie