A rotary mount for positioning a stretched wire axis within a coordinate measurement machine

The European Organisationfor Nuclear Research(CERN)is studying future colliders for increasing the chances of new discoveries. Among themthere isthe Compact Linear Collider (CLIC). Thiselectron-positron collider with a sub-micrometric beam size wouldrequirea pre-alignment of its thousands of elements withintolerances at the micron level.For this, atestbench where thepre-alignmentis performed in one single series of measurements using a stretched wire as a referenceis being considered.This study is the focus of the PACMANproject, a study on Particle Accelerator Components’Metrology and Alignment to the Nanometre scale. This projectis a Marie-Skłodowska Curie Program supported by the European Commission (FP7 Program) [1].This series of measurements consists in the alignment ofa stretched wire at the theoretical position of the beamineach collider element, followed by its location with respect to references positioned outside the element.The challenge is to measure the form error of this wire with 0.1 μm accuracy and its position with 0.5 μm precision on aCoordinate Measuring Machine (CMM). For this purpose, a non-contact sensor is being mounted on a support so that it can rotate. This paper introduces the requirementsfor this support and the sensor: no magnetic fields created, high accuracy on the positioning, low error motion, open on the side; and it describes and discusses the technical solutions: from the material to use to the bearings, including the kind of sensor.