Surface Metrology Equipment

Surface metrology equipment is used to measure the surface finish and/or geometry of engineering components. Surface texture and topology characteristics include surface roughness, contour, form, waviness and defects. There are two main types of surface metrology equipment: form gages and surface profilometers. Form gages, form gaging systems, and contour measuring machines are used to inspect parameters such as roundness, angularity, squareness, straightness, flatness, runout, taper and concentricity. Surface profilometers measure roughness, waviness and other finish or surface texture parameters by either contact or non-contact methods. Contact or stylus-based instruments drag a sharp, pointed tool across the surface. Height variations of the tip are recorded and hen used to form a texture profile of the surface. Non-contact instruments measure surface texture by optically scanning the surface with a light or laser. Optical or light-based profilometers can also use triangulation or interferometry to measure or capture a surface profile. Most contact or stylus-based surface metrology equipment provides a two-dimensional (2D) or line profile; however, non-contact devices can provide three-dimensional (3D) or areal-topography measurements.  

Surface metrology equipment differs in terms of measurement capabilities. In addition to 2D or 3D measurements, form gages and surface profilometers can measure parameters such as coaxiality, cylindricity, defect, taper, flatness, eccentricity and concentricity, harmonic content, and hybrid parameters. Coaxiality is a measure of one axis to another axis. Cylindricity is a condition of a surface of revolution in which all points on the surface are equidistant from a common axis. Taper is a narrowing or differential variation in diameter along the axial or length dimension of a cylindrical part. Flatness places all of the points on a part’s surface within a single plane. Eccentricity is a ratio which describes the shape of a conic section. Concentricity is twice the eccentricity. Harmonic content or shape variations are repeated undulations which occur in a 360° rotation. Most surface metrology equipment describes harmonic frequencies in undulations per revolution (UPR).   

Measurement capabilities for surface metrology equipment may include: patterns (lay), parallelism, roundness, runout, roughness, squareness, angularity, spacing, step height, straightness, thickness, waviness, warp and bow. Lay is a surface texture with a predominant directional pattern due to machining, grinding, or other processing. Parallelism describes the equidistance between two planes or surfaces. Roundness is measured using the minimum radius separation (MRS), least-squares center (LSC), or minimum inscribed circle (MIC) methods. Runout is measured by determining the radial difference between two concentric reference circles drawn to just enclose the profile of the part or cylindrical surface under evaluation. Roughness profiles are the finer scale surface variations that remain after form and waviness variations have been filtered out of the raw profile. Squareness or perpendicularity is a measure of variation of the part's surface from a 90° angle to the reference surface. Spacing parameters measure the horizontal or lateral peak-and- valley variations of a profile along the surface. Surface metrology equipment that measures step height, straightness, thickness, waviness, warp and blow is also commonly available.

• Squareness Measurement
  Squareness or perpendicularity is a measure of variation of the part's surface from a 90° angle to the reference surface. Squareness can be measured by determining the deviation of the part's surface...
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• Tight Squeeze: Optical Imaging For Cramped Quarters
  A six-step strategy helps fit imaging systems onto semiconductor equipment where space is at a premium. Fundamental parameters of an imaging system include the depth of field, field of view,...
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• Optical Profiling Techniques for Characterizing Free-Form Optics
  Optics that deviate from the traditional spherical shape are increasingly popular in optical designs because of their superior image quality, reduced cost, and smaller space requirements. The...
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