An accelerometer based-feedback technique for improving dynamic performance of a machine tool

A novel concept for improving machine dynamic performance was developed and realised, a virtual metrology frame, for a small size CNC machine with flexible frame. Its implementation in a simplified linear motion system shows a reduction in the magnitude of the first resonance in the plant frequency response function by 12 dB. Realising the concept required developing a real -time accelerometer-based measurement technique. It shows a low sensor noise σ=30 nm with optimal phase delay of <70 μs

Fast figuring of large optics by reactive atom plasma

The next generation of ground-based astronomical observatories will require fabrication and maintenance of extremely large segmented mirrors tens of meters in diameter. At present, the large production of segments required by projects like E-ELT and TMT poses time frames and costs feasibility questions. This is principally due to a bottleneck stage in the optical fabrication chain: the final figuring step. State-of-the-art figure correction techniques, so far, have failed to meet the needs of the astronomical community for mass production of large, ultra-precise optical surfaces. In this context, Reactive Atom Plasma (RAP) is proposed as a candidate figuring process that combines nanometer level accuracy with high material removal rates. RAP is a form of plasma enhanced chemical etching at atmospheric pressure based on Inductively Coupled Plasma technology. The rapid figuring capability of the RAP process has already been proven on medium sized optical surfaces made of silicon based materials. In this paper, the figure correction of a 3 meters radius of curvature, 400 mm diameter spherical ULE mirror is presented. This work demonstrates the large scale figuring capability of the Reactive Atom Plasma process. The figuring is carried out by applying an in-house developed procedure that promotes rapid convergence. A 2.3 μm p-v initial figure error is removed within three iterations, for a total processing time of 2.5 hours. The same surface is then re-polished and the residual error corrected again down to& lambda;/20 nm rms. These results highlight the possibility of figuring a metre-class mirror in about ten hours

Optimized estimator for real-time dynamic displacement measurement using accelerometers

This paper presents a method for optimizing the performance of a real-time, long term, and accurate accelerometer based displacement measurement technique, with no physical reference point. The technique was applied in a system for measuring machine frame displacement. The optimizer has three objectives with the aim to minimize phase delay, gain error and sensor noise. A multi-objective genetic algorithm was used to find Pareto optimal estimator parameters. The estimator is a combination of a high pass filter and a double integrator. In order to reduce the gain and phase errors two approaches have been used: zero placement and pole-zero placement. These approaches were analysed based on noise measurement at 0g-motion and compared. Only the pole-zero placement approach met the requirements for phase delay, gain error, and sensor noise. Two validation experiments were carried out with a Pareto optimal estimator. First, long term measurements at 0g-motion with the experimental setup were carried out, which showed displacement error of 27.6 ± 2.3 nm. Second, comparisons between the estimated and laser interferometer displacement measurements of the vibrating frame were conducted. The results showed a discrepancy lower than 2 dB at the required bandwidth

CFD analysis of an enhanced nozzle designed for plasma figuring of large optical surfaces

For addressing the correction of Mid Spatial Frequency (MSF) errors on metre scale optical surfaces induced by sub aperture figuring process, a new generation of non-contact plasma based surface figuring tools has been created at Cranfield University. In this context, this paper presents an investigation that focuses on novel enhanced nozzles that were created for a Radio Frequency (RF) Inductively Coupled Plasma (ICP) torch. The characteristics of plasma jet delivered by prototype nozzle and a selected enhanced nozzle are compared using an in-house created CFD model. The enhanced nozzle design is based on the results previously obtained throughout a numerical analysis that enabled to identify the key design aspects of these nozzles. This enhanced nozzle is predicted to provide 12.5% smaller footprint and 15.5% higher temperature

Investigation of power dissipation in a collimated energy beam

To satisfy the worldwide demand for large ultra-precision optical surfaces, a fast process chain - grinding, polishing and plasma figuring- has been established by the Precision Engineering Institute at Cranfield University. The focus of Cranfield Plasma Figuring team is the creation of next generation of highly collimated energy beam for plasma figuring. Currently, plasma figuring has the capability to shorten processing duration for the correction of metre-scale optical surfaces. High form accuracy can be achieved (e.g. 2.5 hours and 31 nm RMS for 400mm diameter surface). However, it is known that Mid Spatial Frequency (MSF) surface errors are induced when the plasma figuring process is carried out. The work discussed in this paper deals with the characterisation of highly collimated plasma jets delivered by the Inductively Coupled Plasma (ICP) torches. Also a computational fluid dynamics (CFD) model is introduced. This model is used to assess the behaviour of the plasma jet within the best known processing condition. Finally temperature measurement experiments were performed to determine the energy dissipated values that characterise best the ICP torch coil and its De-Laval nozzle

El cuerpo musulmán en el imaginario jesuita barroco

Jesuits of the seventeenth and eighteenth centuries— even those living relatively closely to Muslim lands— often had no personal knowledge of Muslims, and yet the figure of the Muslim loomed large in the baroque Jesuit imagination. Because Jesuit formation involves the visualization of events and persons never seen, Jesuits of this period were in a special position to construct an imaginary Muslim, which they derived from translations of the Qur’an, from artworks, including book illustrations, and from the patterns and symbolism of Jesuit emblematics. This essay explores how baroque Jesuit visualization of the Muslim body was shaped by these factors, and also by other Europe-wide phenomena such as turcica literature.Los jesuitas de los siglos XVII y XVIII, incluso los que vivían relativamente cerca a tierras islámicas, no tenían a menudo un conocimiento personal de los musulmanes. Sin embargo, la figura del musulmán fue cobrando mucha importancia en el imaginario jesuita del Barroco. Puesto que la formación jesuita consistía en la visualización de los eventos y las personas, aunque sin haber sido vistas, los jesuitas de este período se encontraban en una situación muy especial para la construcción de un Musulmán imaginario, tomado de las traducciones del Corán, de obras de arte, incluyendo ilustraciones de libros, y de los patrones y símbolos de los emblemas jesuitas. Este ensayo explora cómo la visualización del cuerpo del musulmán en el barroco jesuita fue influida por estos factores, y también por otros fenómenos surgidos del ámbito europeo, como la literatura turca

Contacto, Confrontación, Acomodo: Jesuitas e Islam, 1540-1770

The encounter between Jesuits and Muslims in the seventeenth and eighteenth centuries had as a point of connection the shared engagement with the spoken and written word. But Jesuit efforts both to convert and to understand this “people of the Book” were hampered by the Jesuits’ lack of deep theological understanding of Muslim sacred texts, and by the fact that this faith was not at a sufficient distance from the European Catholic heartland to receive the “longer view” that Jesuits could apply to the religious traditions of India and the Far East. The overstretched commitments of the Jesuits, and the European Society’s emphasis on polemical strategies, which did not prove workable in predominantly Muslim cultures, significantly limited the successes of Jesuits seeking to convert Muslims. The modest gains Jesuits made in the Ottoman and Mughal Empires and in other Muslim societies nevertheless provided narratives of achievement, heroism, and sacrifice that added elements to Jesuit self-presentation and to the narrative of the Society’s progress. Jesuit contacts with Islam continued during and after the Suppression and are still an aspect of the Society’s program today.El encuentro entre jesuitas y musulmanes en los siglos XVII y XVIII tuvo como punto de conexión el compromiso compartido con la palabra hablada y escrita. Pero, los esfuerzos de los jesuitas por convertir y entender a este grupo de la “gente del Libro” se vieron obstaculizados por su falta de conocimiento teológico profundo de los textos sagrados musulmanes. Igualmente, fue un obstáculo el hecho de que la fe musulmana no estaba a suficiente distancia del centro del catolicismo europeo como para recibir una “visión lejana” que se aplicaba a las tradiciones religiosas de la India y el Extremo Oriente. Los compromisos de los jesuitas, así como el énfasis que la Compañía ponía en Europa a las estrategias polémicas, que ya se había probado como poco efectivo en zonas de cultura islámica, limitaron mucho los éxitos de los jesuitas para convertir musulmanes. Sin embargo, los modestos avances conseguidos en los imperios Otomano y Mugal –y en otros lugares-, produjeron algunas narrativas de logros, heroísmo y sacrificio que añadieron elementos a la autorepresentación jesuita y a las narrativas de los progresos de la Compañía. Los contactos jesuitas con el Islam continuaron durante y después de la supresión y siguen siendo una parte del programa de la Compañía en la actualidad

The Years of Jesuit Suppression, 1773–1814: Survival, Setbacks, and Transformation

The years leading up to the suppression of the Jesuits and the forty-one years, beginning in 1773, of the actual suppression, are analysed here, with special attention to individuals not usually covered in works dealing with this topic. Readership: All interested in Jesuit history, in the cultural and religious history of the late eighteenth and early nineteenth centuries

Analysis of De-Laval nozzle designs employed for plasma figuring of surfaces

Plasma figuring is a dwell time fabrication process that uses a locally delivered chemical reaction through means of an inductively coupled plasma (ICP) torch to correct surface figure errors. This paper presents two investigations for a high temperature jet (5000 K) that is used in the context of the plasma figuring process. Firstly, an investigation focuses on the aerodynamic properties of this jet that streamed through the plasma torch De-Laval nozzle and impinged optical surfaces. Secondly, the work highlights quantitatively the effects of changing the distance between the processed surface and nozzle outlet. In both investigations, results of numerical models and experiments were correlated. The authors’ modelling approach is based on computational fluid dynamics (CFD). The model is specifically created for this harsh environment. Designated areas of interests in the model domain are the nozzle convergent-divergent and the impinged substrate regions. Strong correlations are highlighted between the gas flow velocity near the surface and material removal footprint profiles. In conclusion, the CFD model supports the optimization of an ICP torch design to fulfil the demand for the correction of ultra-precision surfaces