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Vol: 55(69) No: 4 / December 2010 

Retrofitting a Length Measuring Machine for Linear Scale Calibration
Gyula Hermann
Department of Intelligent Engineering Systems, Óbuda University, Faculty of Informatics, Bécsi út 93B, 1034 Budapest, Hungary, phone: (+36-1) 666-5535, e-mail: hermann.gyula@nik.uni-obuda.hu
Kálmán Tomanyiczka
Metrology Division, Hungarian Trade Licensing Offics, Németvölgyi út 37-39, 112 Budapest, Hungary, phone: (+36-1) 458-5854, e-mail: tomanyiczka@mkeh.hu


Keywords: linear scale calibration, length measuring machine, nanometer resolution, ultrasonic piezomotor

Abstract
The paper describes a project with the aim of retrofitting a length measuring machine for the calibration of linear scales, with scale division in the micrometer range. It consists of an optical system, including a CCD camera with a built-in computer, for capturing the line width and the scale division, through the lens and backlight illumination. The motion system carrying the scale scale is driven by a pair of symmetrically located ultrasonic piezomotors providing nanometer resolution. To control the carriege motion Cerebella Model Articulated Controller (CMAC) was used. The paper starts with presenting the various definitions of the scale division. From these definitions simple algorithms, to determine the pitch, are derived. The main point is to minimize the effect of non-linearity and diffraction, by using high resolution optics and through the lens illumination, hereby improving measurement accuracy. The displacement is measured by an HP heterodyne laser interferometer. The scale division is determined by correcting the measured displacement with distance between the optical axis and the line position determined by the camera. For higher resolution the CCD camera system can be replaced by a near field microscope.

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