Development of enhanced absolute distance interferometry for in industrial and accelerator applications..

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics


With the introduction of computer numeric control (CNC) to manufacturing machines we have seen a dramatic increase in the ability to produce increasingly large components with ever improving accuracy. Inspired by this technological advance engineers are designing products to take advantage of this ability, increasing the demands on accuracy further. The field of co-ordinate metrology is driven by this virtuous circle. Here both manufacturing machines and the products they produce are checked against the stringent dimensional tolerances of modern engineering. This demand for improved accuracy requires improved techniques. Instruments such as laser trackers, now the dominant instruments in large scale, high accuracy metrology, combine classical differential interferometry with angle measurements to determine three dimensional displacements. The angle measurements often limit their accuracy. Laser tracers, originally developed by NPL, aim at even higher accuracies measure only the distance changes of the target, doing so from several positions, allowing the 3D displacements to be computed by sequential multilateration. These ultra high accuracy instruments are used to calibrate other metrology instruments, as well as CNC machines. One of the major drawbacks of this use of differential interferometry is the need for the laser beam to continuously illuminate one target while it is being moved between positions. This process is time consuming. If the beam is broken the measurement needs to be restarted, requiring further valuable operator time. AMULET is a knowledge transfer project with collaborators from the JAI, NPL and ETALON AG. Its basic mission is to introduce the ability to measure absolute distances with accuracies comparable to those obtained from differential interferometry, into laser tracers, using technology developed at the JAI for accelerator applications. As a knowledge transfer project, AMULET focuses on aspects that can safely be brought to market within the project's 3 year timescale, giving the highest priority to the basic mission. The collaboration also plans to extend the capabilities of the technology increasing its market reach. This is the area where contributions from a graduate student will be most valuable. The student will focus on the higher risk, more complex scientific issues. The areas to be addressed are: 1 Multi target capability enabling multi dimensional measurements from a single interferometer, leading to a increased potential for new metrology products b reduced systematic errors due to target orientation 2 Combined function interferometry, using multiple lasers and multiple reference interferometers in the same measurement will allow us the get a sub nm accuracy for displacement measurements b improved practicability/reliability of reference systems c potential for cost reduction 3 Simulation and prototype evaluation of multilateration networks, for monitoring and stabilisation of the CLIC final focus quadrupoles, a providing a challenging application, focusing this aspect of research b providing a critical contribution to a leading edge fundamental science project (CLIC). c The techniques will also be applied to model CNC machines with embedded mulitlateration networks (EMLN). The benefits from the above program are: - Higher market impact for new products; - A link between the CLIC community and interested industrial partners; Connections to CLIC as a technology driver, and the CLIC collaboration with its unique pool of expertise, much of it UK based, will prepare the grounds for the next round of knowledge transfer from accelerator science. - Contributions to fundamental science; the contributions to CLIC are in areas critical to its feasibility. Even if some of the students work on higher risk technologies, does not generate significant commercial interest during the studentship, it is of scientific importance, leading to a world class thesis.


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