Abstract
Displacement laser interferometer systems are widely used for the calibration of machine tools and CMMs (Coordinate Measuring Machines). Additionally, they are often the workhorse in dimensional calibration laboratories, where they act as the basic metrological traceability link for many calibrations. This paper gives a review of the calibration of such systems, where several approaches, such as the calibrations of separate components or the system as a whole, are reviewed. The calibrations discussed are: the laser frequency, the counting system, software evaluation of the environmental conditions, environmental and material temperature sensor calibration and the calibration of optics that is part of the system. For these calibrations considerations are given about the ways these can be carried out and about establishing the re-calibration intervals.
Highlights
Displacement laser interferometer systems have entered the market since the early 1970s [1] and have become the de facto reference standard for dimensional measurements in which displacements are involved [2]
A comparison of the displacement interferometer laser light source to an iodine-stabilized He-Ne laser establishes a direct traceability to a primary standard and to the meter definition
To this frequency-stabilized light source, a laser interferometer displacement measuring system consists of a number of components that all may give deviations and contribute to the final uncertainty in various ways; it is generally considered that a frequency calibration of the light source on its own may be not sufficient to declare a system as ‘calibrated’ and/or ‘traceable’
Summary
Displacement laser interferometer systems have entered the market since the early 1970s [1] and have become the de facto reference standard for dimensional measurements in which displacements are involved [2]. Where L is the displacement, N is the number of interference fringe-counts, δ is the fractional where Li is the indicated length, is laser the material temperature and αmnthe materialindex expansion interpolation between counts, λv isTmthe wavelength in vacuum and the refractive of air a is linear coefficient of the measured object or calibrated scale. When object or a read-out scale wasand measured, this measurement was corrected to 20 ◦ C This led to the basic equation for the operation of a displacement laser interferometer system: The calibration may consist of calibrating all individual variables in Equation (1), i.e., the vacuum The common aspect is that displacements are measured by interferometry
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