THE BIRD-CAGE METHOD USED FOR MEASURING CYLINDRICITY. A PROBLEM OF OPTIMAL PROFILE MATCHING.
The bird-cage method used for measuring cylindricity is reported to be the most effective, as it pro- vides the most detailed information about an analyz ed ob- ject. The average values of profiles measured with the cross- section and the generatrix methods may differ sligh tly, yet this may result from some design imperfections of t he measurement instruments used. In this study, the pr oblem of optimal profile matching is formulated and solved. As a result, the differences between the values of the r egistered profiles at the points of intersection of the scann ing trajecto- ries can be minimized.
APPLYING THE NORMALIZED CROSS CORRELATION FUNCTION TO THE COMPARISON OF CYLINDRICITY PROFILES 1
In practice, differences between cylindricity profi les of machine parts have been evaluated either visually or by comparing the numerical values of se lected cylindricity parameters. Since visual assess ment of profile coincidence is approximate and qualitative in character, and the point-based comparison of numerical values of selected cylindricity parameter s is often insufficient, a new approach to the prob lem has become necessary. The main assumption of the method is that by using the normalized cross correlation function, it is possible to determine the coefficient of profile coincidence, to carry out quantitativ e assessment of this coincidence, and, finally, to re present the profiles in one graph. By applying the Legendre/Fourier type of approximation, we obtain a universal form of the normalized cross correlation function, which permits us to compare cylindricity profiles registered by means of different measuring strategies different measuring devices. Computer-aided measurement of geometrical quantities frequently involves comparing measured profiles so as to study their repeatabilit y at a given test stand or determine the accuracy o f a measuring device in relation to another. Traditionally, two methods have been used: - visual comparison of profile coincidence, - comparison of numerical values of selected cylindri city parameters. Unfortunately, both methods are reported to possess serious drawbacks. The visual method for profile comparison is of approximate character. It permits qualitative assessment of their coincidence only. A quantitative analysis is not po ssible. The comparison of numerical values of selected cylindricity parameters, on the other hand , is frequently insufficient, because the parameters are point-based and the assessment is no t unique and objective. Looking for better solutions has become vital. There has been a need t o develop such methods for comparison of cylindricity profiles that will permit a quantitati ve analysis of profile coincidence. The concept discussed in this paper is based on the results concerning the comparison of roundness profiles. The normalized cross correlatio n function is employed to determine the numerical coefficient of coincidence of two profile s, which allows graphical representation of these profiles in one diagram (1). 2. DEFINITION OF THE COEFFICIENT OF CYLINDRICITY PROFILE COINCIDENCE
Cylindricity — a well known problem and new solutions
Abstract The past twenty years have seen a continued increase in importance of computer aided measurement techniques as a means to control industrial production. At the same time the basic definitions governing design, production and quality control of workpieces have undergone first steps of international harmonization and standardization. Focal points of interest included the definitions of nominal, real and substitute geometrical features. The cylinder is a characteristic example of feature both on the side of design and production as well as on the side of measurement. The application of CAD, CAE and CAM also puts new demands on inspection and testing in computer integrated production processes. A sophisticated measurement technique, among other things, is considered a most crucial requirement for the production of industrial goods of a controlled and optimized quality. The evaluation of measuring data obtained can be done on CAD and CAE computer using different extensive algorithms. So results of various measuring devices can be compared and an optimization is possible. This is shown by the example of cylindrical workpiece features.