DETERMINATION OF PROPER FREQUENCY BANDWIDTH FOR 3D TOPOGRAPHY MEASUREMENT USING SPECTRAL-ANALYSIS .1. ISOTROPIC SURFACES

Areal spectral analysis is applied to achieve proper frequency bandwid th for topography measurements from machined surfaces. The effect of a liasing on the spectrum of surface features due to a large sample spac ing is evaluated. The characteristics of low-frequency components of a surface are also investigated. The low-frequency limit of measurement for obtaining the genuine features of a surface can be decided from t he spectral analysis of low-frequency components of the surface. The g uidelines for topography measurement are proposed for selecting an app ropriate sampling bandwidth of surfaces with due consideration of limi ted computer memory. The guidelines developed are applied to study the general patterns of spectra from a range of isotropic engineering sur faces. An example is given to demonstrate the selection of a temporary sample spacing for a further measurement searching for the low-freque ncy cut-off of a surface, which may be in turn used to determine the h igh-frequency limit with an estimate of aliasing influence. In spectra l analysis, circular spectra and/or accumulation spectra have been sho wn to be suitable for the analysis of sample surfaces from isotropic m achining processes.