Abstract
With the introduction of computer numeric control (CNC) to manufacturing machines such as lathes, mills or the more exotic wire-erosion machines we have seen a dramatic increase in our ability to produce increasingly large components with ever improving accuracy. Inspired by this technological advance engineers are designing more products to take advantage of this ability, increasing the demands on accuracy even further. Largely driven by this virtuous circle is the field of co-ordinate metrology. Here both manufacturing machines and the products they produce are being checked against the stringent dimensional tolerances of modern engineering.As the number and the accuracy of CNC machines improves so must the techniques used in metrology. In fact, the accuracy used by metrologists must always be a step ahead of manufacturing to be able to calibrate manufacturing machines. Lasers have revolutionised the area of co-ordinate metrology. Because laser can emit light with highly stable wavelength the offer unprecedented accuracy in measuring distance differences or changes through fixed frequency, differential interferometry. Instruments such as laser trackers which have rapidly become the dominant instruments in large scale, high accuracy metrology utilise this ability and combine it with angle measurements to determine three dimensional displacements. The angle measurements normally limit the accuracy of laser trackers. Laser tracers, originally developed by NPL and aimed at even higher accuracies, operate without angle measurement. They only measure the distance to the target but do so from several positions allowing the displacements to be computed from the distance measurements alone by process called sequential multilateration. Laser tracers are close to the top of the food chain of metrology instrument. They are ultra high accuracy instruments that can be used to calibrate other metrology instruments, as well as CNC machines. One of the major drawbacks of differential interferometry is the need for the laser beam to continuously illuminate the same target. If the beam is broken, for example because the new target position is reached on a path which is partially obscured or because the tracker can not follow the target fast enough, the measurement needs to be restarted, requiring valuable operator time.In this project we seek to introduce the ability to measure absolute distances with accuracies comparable to those obtained from differential interferometry into laser tracers. We will try to integrate a technology called Frequency Scanning Interferometry (FSI), in a form developed in the John Adams Institute for Accelerator Science (JAI) at Oxford University into a laser tracer allowing it to robotically switch between targets and be tolerant to beam brakes.As an additional benefit, FSI is capable of measuring the distance to several targets at the same time if a wide laser beam is used to illuminate many targets at the same time. Exploiting this ability could lead to instruments that can not only measure the position of a target but also its orientation in space.Among all of these technological developments we will also critically look at ways of reducing the cost of FSI to make it more attractive for a wide range of applications in co-ordinate metrology.FSI works because modern lasers can not only have a single very well defined wavelength but they can - thanks to developments in the telecommunications industry - also continuously change this wavelength with time. So lasers are again set to improve co-ordinate metrology in a fundamental way.
Planned Impact
We believe that the primary beneficiaries or this research will be: 1. Companies producing instruments for dimensional metrology 2. Industries using or producing CNC manufacturing machines 3. Industries using dimensional metrology instruments or services 4. Aero space industry 5. Researchers in dimensional metrology at other national institutions (PTB, NIST, BIPM) 6. Manufacturers of large scale optics 7. Researchers from astrophysics 8. Researchers from accelerator science 9. Researchers from space science 10. Researchers from particle physics We have described examples for applications of our research in the above areas (4. to 10.) in the section of academic beneficiaries. We will focus here on the industrial and societal benefits arising from these applications in industries that produce or use them. In the first instance UK industries producing metrology instrumentation can obtain licenses for our technologies to build metrology instruments or OEM components for such instruments. They could either sell these directly or use them to provide metrology services. The UKs most significant manufacturer of metrology instruments is Renishaw. Renishaw's product range incorporates distance measurement and probe and CMM devices which could benefit from our technology. We expect sales of instruments based on our technology to primarily go to manufacturers or large scale users of CNC manufacturing machines. Large numbers of the latter can be found in the aerospace and automotive industry as well as general purpose mechanical machining companies all of which are present in the UK. Clients for dimensional metrology services such as calibration services for CNC or CMM machines are likely to be smaller companies for whom it would be uneconomical to purchase metrology instruments and train staff to use them. The primary benefit of using an FSI enhanced laser tracer for the calibration of a CMM or CNC machine lies in the more rapid and more accurate measurement. The process is also more automated and less man power intensive, in particular of multidimensional information about the tool or probe head is required. These benefits lead ultimately to less machine down-time, lower calibration process costs and, via the improved accuracy, to better production quality. We seek to exploit our research through a UK spin-out company that could sell or license FSI based technology world wide. Here it is particularly important to mention that in ETALON AG, we already have a potential first customer who is directly involved in the project and who is the marked leader in laser tracer production. We estimate the time to market for an OEM FSI system integrated into a laser tracer to be less than a year after the end of this project. To ensure that our research has a rapid impact on and high relevance to future industrial users we are collaborating with ETALON AG as our industrial partner. ETALON is well placed to ensure that aspects most relevant to the marketability maintain a high profile in our research. This should ensure that the technology should be ready for licensing immediately after the project is completed. We will also publish our work in relevant peer reviewed journals and present it at international conferences and trade shows. We already have and will continue to establish direct contacts with UK industries that may be interested in our developments. We have already approached Renishaw and have invited them to visit our group at Oxford to discuss possible collaborations and use cases. NPL has extensive contact to many areas of UK industry already which we will use to publicise our developments. Last but not least the PDRA in this project will be trained on the job in many aspects of commercial applications of FSI and develop contacts with interested UK industries. This will make him or her a highly valuable for any UK company working in this area.
