Photogrammetry for Precise, Rapid Module Alignment in the Mu2e Tracker

Abstract

We discuss a photogrammetry technique to measure the inter-module alignment in the Mu2e tracker. The tracker consists of 216 modules each with 96 straw tubes. The relative alignment of the straw tubes in a module was previously measured by an X-ray technique, which tied the straw tube measurements to three fiducials per module. The photogrammetry technique uses an array of 15 cameras to make precise position measurements of the module fiducials in a global tracker coordinate system. Measurements of the fiducial position and radius on the camera's CCD yield ~$25 μm$ resolution in the transverse directions and < $300 μm$ along the camera axis. In addition, we describe a procedure to combine the images with "local" mechanical measurements to yield $<100 μm$ precision along the camera axis. The technique offers a touch-less, rapid (~1 hour), and affordable metrology approach within the requirements of the tracker.