TOLERANCE EVALUATION WITH REDUCED MEASURED POINTS

• US 20120209553A1
• Filed: 02/11/2011
• Published: 08/16/2012
• Est. Priority Date: 02/11/2011
• Status: Active Grant

• Current Assignee: Quality Vision International, Inc.
• Original Assignee: Quality Vision International, Inc.
• Inventors: Doytchinov, Kostadin, Prôkai, Tibor, Kirjakov, Dimitar
• Granted Patent: US 8,447,549 B2
• Time in Patent Office: Days
• US Class Current: 702/81
• CPC Class Codes: G01B 21/047 Accessories, e.g. for positioning, for tool-setting, for measuring probes
• CPC Class Codes: G06T 2207/10028 Range image; Depth image; 3D point clouds
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/0006 using a design-rule based approach

Abstract

A method of determining whether a part satisfies tolerance criteria includes making a multiplicity of measurements of the part, reducing the number of measured points to a number of boundary points that define a boundary within which all measured points are encompassed and comparing the boundary to a tolerance limit of a normal surface to determine whether the part conforms to the tolerance.

Claims

1. A method for determining whether a part satisfies a tolerance criterion comprising the steps of:

making a multiplicity of measurements of the part, each measurement defining a measured point on the part;

reducing the number of measured points to a number of boundary points that define a boundary within which all measured points are encompassed; and

comparing the boundary to a tolerance limit of a nominal surface to determine whether the part conforms to the tolerance.

2. The method of claim 1, wherein the reducing step comprises grouping the measured points into a plurality of sets of spatially contiguous measured point subsets and reducing the number of measured points in each measured point subset to a reduced subset.

3. The method of claim 2, further comprising, for each measured point subset, creating a top and a bottom boundary surface nominally parallel to the surface defining the tolerance limit, the top and bottom boundary surfaces enclosing all the measured points in the reduced subset.

4. The method of claim 3, further comprising for each reduced subset, creating side walls perpendicular to the surface defining the tolerance limit that enclose all the measurements in the set.

5. The method of claim 1 further comprising filtering the multiplicity of measurements.

6. The method of claim 5 wherein said filtering comprises noise filtering and outlier removal.

7. The method of claim 1 further comprising performing a best-fit analysis on using the reduced number of data points.

8. The method of claim 1, further comprising fitting at least one convex hull to the boundary points.

9. The method of claim 8, comprising fitting two convex hulls to the boundary points to define a space within which all measured points are contained.

10. The method of claim 2 wherein each reduced subset is represented by a three-dimensional shape that encompasses all points in the corresponding measured point subset.

11. The method of claim 10, wherein the three-dimensional shapes associated with the reduced subsets are stitched together to form a surface defining the part.

12. The method of claim 10, wherein each three-dimensional shape is a rectilinear box.

13. The method of claim 11 in which the comparing step comprises comparing the coordinates of the corners of the rectilinear boxes to the normal surface defining the tolerance limit.

14. The method of claim 1, further comprising displaying the results of the determination of whether the part conforms to the tolerance.

15. The method of claim 14, wherein the displaying step comprises displaying a representation of the manufactured part and a representation of the nominal surface of the part.

16. The method of claim 15, wherein the representation of the manufactured part comprises a display of one of at least one of the boundary points and a surface defined by the boundary points.