Locating an image of an object having a concentric profile

• US 6,252,986 B1
• Filed: 12/18/1998
• Issued: 06/26/2001
• Est. Priority Date: 04/03/1998
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Chang, Yian Leng
• Primary Examiner(s): Johns, Andrew W.
• Assistant Examiner(s): Azarian, Seyed H.
• Application Number:
  US09/216,071
• Time in Patent Office: 921 Days
• Field of Search: 382/203, 382/204, 382/205, 382/206, 382/103, 382/108, 382/287, 382/288, 382/291, 382/303, 382/226, 219/121.65, 219/121.66, 219/121.84, 219/121.85
• US Class Current: 382/203
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06V 10/44 Local feature extraction by analysis of parts of the pattern, e.g. by detecting edges, contours, loops, corners, strokes or intersections; Connectivity analysis, e.g. of connected components

Abstract

A method is provided for finding an image of an object having a concentric profile, wherein the concentric profile has an inner profile and an outer profile, and wherein the inner profile is in concentric relationship with the outer profile. In another general aspect of the invention, a method is provided for finding an image of an object having a concentric profile, the concentric profile having a plurality of constituent profiles, where each profiles of the plurality of constituent profiles scales independently in a fine search phase. The methods of the invention can find circular profiles of a nozzle that scale non-uniformly as well as that scale uniformly, and therefore can be used to find one or more rings or profiles of the image of a nozzle. Further, the methods of the invention can provide superior accuracy regarding the position of the nozzle for many applications. Moreover, certain aspects of the relationship between the inner and outer profiles of the image of the nozzle, such as a bent nozzle condition, can be effectively inspected by the methods of the invention.

Claims

1. A method for finding an image of an object having a concentric profile, the concentric profile having an inner profile and an outer profile, the inner profile being in concentric relationship with the outer profile, the method including:

creating a single model of the object using the inner profile and the outer profile;

creating a compound model of the object having an inner sub-model based on the inner profile, and an outer sub-model based on the outer profile;

in a coarse search phase, searching for the object using the single model to provide coarse location information;

in a fine search phase, searching for the object using the coarse location information and the compound model to provide fine object location and object scale information.

2. The method of claim 1, wherein the fine object scale information includes:

an inner profile diameter and an outer profile diameter.

3. The method of claim 1, wherein each sub-model of the compound model is a closed two-vertex curvilinear shape that spans 180 degrees.

4. The method of claim 1, wherein each sub-model includes information representing polarity.

5. A method for finding an image of an object having a concentric profile, the concentric profile having a plurality of constituent profiles, the profiles being in concentric relationship with each other, the method including:

creating a single model of the object using the plurality of constituent profiles;

creating a compound model of the object having a sub-model for each profile of the plurality of constitutent profiles;

in a coarse search phase, searching for the object using the single model to provide coarse location information;

in a fine search phase, searching for the object using the coarse location information and the compound model to provide fine object location and object scale information.

6. The method of claim 5, wherein each of the profiles of the plurality of constituent profiles scales independently in the fine search phase.