Detection of irregularities in a convex surface, such as a tire sidewall, using band-pass filtering

• US 6,539,789 B1
• Filed: 07/16/2001
• Issued: 04/01/2003
• Est. Priority Date: 10/28/1998
• Status: Expired due to Term

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Hanke, Randolf, Kostka, Guenther, Schmitt, Peter, Hassler, Ulf
• Primary Examiner(s): Noori, Max
• Assistant Examiner(s): Dickens, Charlene
• Application Number:
  US09/807,740
• Time in Patent Office: 624 Days
• Field of Search: 731/46, 731/462, 731/463, 731/465, 731/468, 340/442-448, 152/415, 152/419, 356/348, 356/347, 356/375, 356/376, 356/360, 356/3.01, 356/3.03, 250/559.29, 250/559.31, 250/559.4, 250/202, 318/577, 318/640
• US Class Current: 73/146
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50
• CPC Class Codes: G01M 17/027 using light, e.g. infrared, ultraviolet or holographic techniques
• CPC Class Codes: G06T 2207/30108 Industrial image inspection
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A device for the contactless detection of a potentially existing essentially edge-free irregularity in a convex surface, which has a structuring that is delimited by edges, comprises a unit for creating a three-dimensional representation of the surface, a unit for extracting the convexity from the three-dimensional representation of the surface and for smoothing the edges of the structuring so as to obtain a convex-free representation of the convex surface which exhibits the irregularity and the structuring, whose edges have now been smoothed, a unit for comparing the convex-free representation with a threshold value so as to identify areal regions of the convex-free representation which are determined by a predetermined relationship to the threshold value, and a unit for analyzing the areas of the identified regions, a region being detected as an irregularity if its area exceeds a predetermined area. When this device is used to carry out quality control of tires, bulges or constrictions can therefore be identified with certainty in real-time operation and can be distinguished from an inscription or marking which has been intentionally provided on the tire.

Claims

1. A device for the frictionless detection of a potentially existing essentially edge-free irregularity in a surface, the surface having a convexity, the surface having the irregularity, and the surface having a structuring, wherein the structuring is delimited by edges and does not constitute an irregularity, comprising:

a unit for creating a three-dimensional representation of the surface, the three-dimensional representation of the surface having the convexity, the irregularity and the structuring;

a unit for extracting, connected to the unit for creating, the unit for extracting being operative to extract the convexity from the three-dimensional representation of the surface created by the unit for creating and to smooth the edges of the structuring so as to obtain a representation of the surface, the representation of the surface not including the convexity of the surface, and including the irregularity and the structuring with smoothed edges;

a unit for comparing, connected to the unit for extracting, the unit for comparing being operative to compare the representation with a threshold so as to identify regions of the representation which are determined by a predetermined relationship to the threshold value to obtain identified regions; and

a unit for analyzing, connected to the unit for comparing, the unit for analyzing being operative to analyze area values of the identified regions,

wherein a region is detected as the irregularity if the area value of the region exceeds a predetermined area value.

2. A device according to claim 1, wherein the unit for extracting has a band-pass filter unit with an upper and a lower cut-off frequency, the lower cut-off frequency being so chosen that the convexity is suppressed and the upper out-off frequency is so chosen that the edges are smoothed but the irregularity is scarcely affected.

3. A device according to claim 1, wherein the unit for extracting comprises:

a first low-pass filter, whose cut-off frequency is so chosen that the edges are smoothed but the irregularity is not affected;

a second low-pass filter, whose cut-off frequency is so chosen that the convexity is suppressed; and

a subtraction unit for subtracting the output signal of the second low-pass filter from the output signal of the first low-pass filter.

4. A device according to claim 1, wherein the unit for extracting has a non-linear filter.

5. A device according to claim 1, which also comprises:

a unit for eliminating pixel artifacts from the three-dimensional representation of the surface, the unit for eliminating being connected to the unit for creating.

6. A device according to claim 1, wherein the unit for analyzing has a unit for eliminating singular artifacts.

7. A device according to claim 1, wherein the unit for analyzing has a two-dimensional median filter so as not to suppress those regions which are greater than the predetermined area value so that an image of the surface is created in which the irregularity alone is marked.

8. A device according to claim 1, wherein the unit for creating comprises:

a laser with precircuited cylinder optics to generate a fan beam for illuminating the convex surface; and

a matrix camera for detecting the diffuse fan beam reflected from the convex surface.

9. A device according to claim 8, wherein the surface is a tire, the essentially edge-free irregularity is a bulge or a constriction on a sidewall of the tire, and the structuring is a marking introduced on the sidewall, the laser and the matrix camera being so arranged that a radial height line of the tire is recorded and the unit for creating also comprises:

a control unit for controlling the image repetition rate of the matrix camera and the speed of rotation of the tire so as to obtain a desired spatial resolution in the tire circumference direction.

10. A device according to claim 9, wherein the matrix camera is arranged to record a height line of the torus-shaped sidewall in each photograph and the unit for creating comprises:

a matrix memory in which the height lines generated by the matrix camera are stored one after the other so as to obtain the three-dimensional representation of the tire sidewall.

11. A method for the frictionless detection of a potentially existing essentially edge-free irregularity in a surface, the surface having a convexity, the surface having the irregularity, and the surface having a structuring, wherein the structuring is delimited by edges and does not constitute an irregularity, comprising the following steps:

creating a three-dimensional representation of the surface, the three-dimensional representation of the surface having the convexity, the irregularity and the structuring;

extracting the convexity from the three-dimensional representation of the surface and smoothing the edges of the structuring so as to obtain a representation of the convex surface, the representation of the surface not including the convexity of the surface, and including the irregularity and the structuring with smoothed edges;

comparing the representation with a threshold so as to identify regions of the representation which are determined by a predetermined relationship to the threshold value to obtain identified regions; and

analyzing area values of the identified regions,

wherein a region is detected as the irregularity when the area value of the region exceeds a predetermined area value.

12. A method according to claim 11, which is used for the quality control of a tire, comprising the following steps:

detecting a bulge or constriction as the irregularity on a sidewall of the tire, the sidewall of the tire constituting the surface; and

rejecting the tire if it has the bulge or the constriction.