Method and device for determining an angled structure in the surface of a precision machined cylindrical work piece
View Patent ↗A method for determining a helical groove structure, for example in the form of flutes, in the surface of a finely finished cylindrical workpiece, in particular the ground mating bearing surface of radial shaft sealing rings, which is characterized in that a camera is used to record at least one image of the illuminated surface of the workpiece, which image reproduces the helical groove structure in the surface of the workpiece. A device for carrying out a method includes a CCD camera with a macrolens, a radial bearing device for the workpiece, an illuminating device and an image reading and image processing device.
1. A method for operating a camera to determine a structure of machining marks on a surface of a cylindrically finely finished workpiece, the camera and the workpiece being mutually aligned, the method comprising the steps of:
recording an image of surface characteristics of the workpiece; and
in order to determine a helically running structure of the machining marks, performing the steps of:
performing a Radon transformation of the image, and
determining a helix angle of those of the machining marks that are helical;
rotating the workpiece;
recording a plurality of images if the surface characteristics of the workpiece at a constant twisting angle;
providing a plurality of Radon transforms by performing the Radon transformation for each one of the plurality of images;
extracting a Radon strip from each one of the plurality of Radon transforms;
juxtaposing the Radon strips of the Radon transforms of each one of the plurality of images in a Radon strip image; and
performing a correlation analysis of the juxtaposed Radon strips.
2. The method according to claim 1 , further comprising the step of:
providing a scale at a level of the surface of the workpiece.
3. The method according to claim 1 , further comprising:
illuminating the surface of the workpiece to generate a high contrast between flute peaks and troughs of the surface of the workpiece.
4. The method according to claim 1 , further comprising:
choosing an image section for recording.
5. The method according to claim 4 , wherein the image section includes a number of flutes, the number selected to be within a range between 5 and 50.
6. The method according to claim 1 , wherein the image is an enlarged grey-scale image.
7. The method according to claim 1 , wherein the image is recorded via a macrolens.
8. The method according to claim 1 , wherein the determining of the helix angle further comprises:
calculating a difference between a first angle and a second angle.
9. The method according to claim 8 , further comprising:
determining from the Radon transformation, an angular position of flutes of the surface of the workpiece, wherein the first angle is a defined angle of the camera relative to the workpiece, and the second angle is the angular position of the flutes.
10. The method according to claim 5 , wherein the plurality of images are recorded at fixed angular spacings.
11. The method according to claim 5 , wherein the plurality of images are non-overlapping images.
12. The method according to claim 5 , wherein the helix angle is a small helix angle.
13. A method for operating a camera to determine a structure of machining marks on a surface of a cylindrically finely finished workpiece, the camera and the workpiece being mutually aligned, the method comprising:
rotating the workpiece;
recording a plurality of images of surface characteristics of the workpiece at a constant twisting angle;
to determine a helically running structure of the machining marks, performing the following:
providing a plurality of Radon transforms by performing a Radon transformation for each one of the plurality of images;
extracting a Radon strip from each one of the plurality of Radon transforms;
juxtaposing the Radon strips of the Radon transforms of each one of the plurality of images in a Radon strip image;
performing a correlation analysis of the juxtaposed Radon strips; and
determining a helix angle of those of the machining marks that are helical;
independently of the Radon transformation, producing a Fourier transform of at least one of the plurality of images;
forming a periodogram from the Fourier transform;
filtering the periodogram in accordance with an operation of a comb filter;
determining a spacing parameter of the comb filter in conjunction with a maximization of a periodic power component;
calculating the periodic power component as a ratio of a proportion of the machining marks to the surface, wherein the spacing parameter of the comb filter corresponds to an estimated value of a periodic length of a helical groove structure; and
calculating a number of threads of the helical groove structure from the helix angle and the periodic length.
14. The method according to claim 13 , wherein the periodogram is formed by squaring the Fourier transform's absolute value.