Specification

It is well known that the definitions of parameters should be unambiguous to avoid being open to different interpretations by both users and metrology software developers. What is not so well known is that parameters should also have stable or robust definitions in order that they reflect genuine properties of a surface. Here a parameter definition is considered mathematically stable if a 'small' change in the profile implies a 'small' change in the parameter value. Unfortunately the parameter definitions given in ISO 4287 – 1997[4] (and ISO 4288 - 1996)[5] are not always unambiguous or stable. Since these specification standards were first drafted, much knowledge has been gained into unambiguous and stable definitions of surface texture parameters. This new knowledge has been used in the present project to re-evaluate the parameter definitions and produce unambiguous stable definitions that are consistent (where possible) with those in the international standards.

The basic framework of the SoftGauges developed within the project is shown in figure 1 below.

Softgauge Basic Framework
ISO 4287-1997[4]
(ISO 4288-1996)[5]

SOFTGAUGE POINTS

Assume:

Ls Filtered; Equally spaced; No Form

FILTRATION Gaussian Filter (ISO 11562)[6]
R	W	P
Lc High Pass	Lc Low Pass	No Filter

	FIELD PARAMETERS		FEATURE PARAMETERS
	Amplitude	Other	Peak/Valley	Spacing
	Ra, Rq, Rsk, Rku, Rp, Rv, Rz	Rt	Rc	RSm
Feature Type [1]	Points	Points	Local Peak/Valley	Crossovers
Segmentation[2]	Cut-off	Evaluation	Based on feature	Based on feature
Combination[3]	None	None	Remove insignificant features	Remove insignificant features
Attributes	Cut-off	Evaluation	Significant features	Significant features
Statistics	Mean/Max	Value	Mean/Max	Mean/Max

Figure 1 Softgauge basic framework

Notes:
1. Feature type is the basic element from which subsequent calculations are determined.
2. Segmentation is used to determine the initial portions of the profile.
3. Combination removes "insignificant" segments to leave significant segments. This removes artificially small segments due to noise, etc. making the measurand stable.

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Specification of Parameters