Fiducial mark search using sub-models

• US 6,681,039 B1
• Filed: 06/03/2002
• Issued: 01/20/2004
• Est. Priority Date: 04/03/1998
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Roberts, Karen J., Sarachik, Karen B.
• Primary Examiner(s): Dastouri, Mehrdad
• Application Number:
  US10/160,858
• Time in Patent Office: 596 Days
• Field of Search: 382/141, 382/144, 382/145, 382/146, 382/147, 382/148, 382/149, 382/150, 382/151, 382/209, 382/217, 382/218, 382/220, 382/103, 382/203, 382/219, 345/420, 345/441
• US Class Current: 382/151
• 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
• CPC Class Codes: H05K 1/0269 for visual or optical inspection

Abstract

A method is disclosed for finding a pose of a geometric model of a fiducial mark within an image of a scene containing the fiducial mark. The method includes receiving input from a user including geometric model shape information and geometric model dimensions, selecting a pre-defined model having sub-models by using the model shape information, the pre-defined model being parameterized by the geometric model dimensions; and then using the pre-defined model to find an image of the fiducial mark in the image of the scene. The act of selecting a pre-defined model having sub-models, includes pre-defining a model such that the sub-models and the relationships among the sub-models are selected by exploiting knowledge of features and properties of the fiducial sought so as to provide more accurate location of the fiducial. The invention provides enhanced ease of use of a sub-model-based search method by requiring only the shape and dimensions of the fiducial sought. An appropriate model and it'"'"'s sub-models are automatically provided. The model and it'"'"'s sub-models are particularly appropriate to the application when they are based on knowledge of the variability of the fiducial, and other aspect of the behavior of the fiducial throughout a manufacturing process, for example.

Claims

1. A method for finding a pose of a geometric model of a fiducial mark within an image of a scene containing the fiducial mark, the method comprising:

providing a plurality of pre-defined geometric models, each pre-defined geometric model having geometric sub-models, each pre-defined geometric model including shape information and excluding gray-level information, and each pre-defined geometric model being parameterizable using dimensional information;

selecting a pre-defined geometric model from among the plurality of pre-defined geometric models by specifying shape information of a desired geometric model;

parameterizing the predefined geometric model by specifying dimensional information of the pre-defined geometric model; and

using the pre-defined geometric model to find the fiducial mark in the image of the scene to provide a pose of the geometric model.

2. The method of claim 1, wherein providing a plurality of pre-defined geometric models includes:

pre-defining a geometric model such that the geometric sub-models and the relationships among the geometric sub-models are selected by exploiting knowledge of features and properties of the fiducial mark.

3. The method of claim 1, further comprising:

using the pose of the geometric model to provide at least one fiducial dimension measurement; and

comparing the at least one fiducial dimension measurement to at least one tolerance range.

4. The method of claim 1, wherein providing a plurality of pre-defined geometric models comprises:

pre-defining a geometric model such that the geometric sub-models and the relationships among the geometric sub-models are selected such that unimportant and inconsistent features of the fiducial mark are not included.

5. The method of claim 1, wherein providing a plurality of pre-defined geometric models comprises:

pre-defining a geometric model such that the geometric sub-models and the relationships among the geometric sub-models are selected so as to include features of the fiducial mark that are known to be reliably located under different machining conditions.

6. The method of claim 1, wherein providing a plurality of pre-defined geometric models comprises:

pre-defining a geometric model such that the geometric sub-models and the relationships among the geometric sub-models are selected so as to exclude features of the fiducial mark that are known to be subject to degradation or widely varying.