Speaker
Description
Large machines for fusion research and the fusion rectors have hostile environmental conditions characterised by high level of radiation, vacuum and temperature both in the vessel and in the port cell and the close area, commercial displacement sensors like linear and rotary encoders and their electronics are not suitable with this conditions. This problem has been approached and solved by developing an optical and optoelectronic concept for the reading section of rotary and linear encoders able to resist to the hard environmental conditions. In this concept the driving electronics of the system is placed far from the hostile environment and the connections to the sensor are realised by means of suitable optical fibers. Some of these devices was developed by us to instrument more complex systems, they have been also validated and tested in vacuum, temperature and radiation over long periods.
The paper describe a recent activity of design and simulation that has been performed in order to overcame the sole critical aspect of such methodology that is related to the very close reading distance between the static part and moving part of the encoder. The new design increases the reading distance of many times to relax the requisites of the associated mechanics thus making the system more reliable in case of large temperature gradients and levels. An upgraded concept of the optical and optoelectronics reading section has been conceived; being based on micro optics and micromechanics, before the implementation we have chosen to develop a custom 3D simulation tool both to validate the concept and to optimize the micro optical and micromechanical design. The tool is based on ray tracing algorithms developed using the 3D vector geometry. It was implemented using Mathematica and an optimization phase has been necessary to be able to perform simulations of hundreds of thousands of rays in useful time. Different choices in the design has been simulated in order to perform a trade-off analysis based on criteria of robustness, low cost, commercial availability of the components and depending on the environmental conditions. A brief description of the ray tracing algorithm is presented, followed by the numerical results obtained for the different choices of the configuration that have been evaluated in the trade-off analysis. The optimal design chosen for the implementation is discussed and presented in the paper and the expected characteristics are reported. An analysis of the possibility of increasing the resolution and the accuracy of the sensor by means of inter-mark interpolation is included. An outline of the driving electronics and its main characteristics is also presented showing that the new design optimizes also this part. The design is presented with the aim to show a suitable solution for displacement and rotary sensors, which can be adopted in diagnostics and/or in remote handling systems of large fusion machines or in other fields where similar hostile environmental conditions are present.
| Eligible for student paper award? | No |
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