Data processing: generic control systems or specific application – Generic control system – apparatus or process – Digital positioning
Reexamination Certificate
2000-12-15
2004-04-27
Patel, Ramesh (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Digital positioning
C700S047000, C700S056000, C700S058000, C700S061000, C700S066000, C700S118000, C700S163000, C700S186000, C700S187000, C382S154000, C382S153000, C382S159000, C382S181000
Reexamination Certificate
active
06728582
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to machine vision systems and more particularly to uses for advanced machine vision search tools that register patterns transformed by at least two translational and at least one non-translational degree of freedom.
2. Background Information
The use of advanced machine vision systems and their underlying software is increasingly employed in a variety of manufacturing and quality control processes. Machine vision enables quicker, more accurate and repeatable results to be obtained in the production of both mass-produced and custom products. Basic machine vision systems include one or more cameras (typically having solid-state charge couple device (CCD) imaging elements) directed at an area of interest, frame grabber/image processing elements that capture and transmit CCD images, a computer and display for running the machine vision software application and manipulating the captured images, and appropriate illumination on the area of interest.
Many applications of machine vision involve the inspection of components and surfaces for defects that affect quality. Where sufficiently serious defects are noted, a part of the surface is marked as unacceptable/defective. Machine vision has also been employed in varying degrees to assist in manipulating manufacturing engines in the performance of specific tasks. One task using machine vision is visual servoing of robots in which a robot end effector is guided to a target using a machine vision feedback. Other applications also employ machine vision to locate a stationary and/or moving pattern.
The advent of increasingly faster and higher-performance computers, has enabled the development of machine vision systems that employ powerful search tools. Such search tools enable a previously trained/stored image pattern to be acquired and registered/identified regardless of its viewed position. In particular, existing commercially available search tools can register such patterns transformed by at least three degrees of freedom, including two translational degrees (x and y-axis image plane) and a non-translational degree (rotation and/or scale, for example). One particular implementation of an advanced search tool is the rotation/scale-invariant search (RSIS) tool. This tool registers an image transformed by at least four degrees of freedom including the two translational degrees (x and y-axis image plane) and at least two non-translational degrees (z-axis(scale) and rotation within the x-y plane about an axis perpendicular to the plane). Some tools also register more complex transformations such as aspect ratio (rotation out of the plane whereby size on one axis decreases while size in the transverse axis thereto remains the same). These search tools, therefore, enable a specific pattern within the field of view to be located within a camera field of view to be positively identified and located accurately within the vision system's internal reference system (an x, y, z, rotation coordinate system, for example). The RSIS and other advanced search tools particularly allow for the identification and acquisition of patterns having somewhat arbitrary rotation, scaling (e.g. distancing) and translation with respect to the reference system. In other words, the tool is sufficiently robust to recognize a desired pattern even if it is rotated and larger/smaller/skewed relative to a “model” or trained pattern within the vision system. In addition advanced search tools are capable of tolerating a reasonable degree of occlusion and contrast/illumination changes in the viewed pattern while still properly registering the pattern.
In general, advanced machine vision tools acquire an image of an object via a camera and analyze the outline or a particular part of the object, such as a predetermined fiducial mark or other pattern. The processing speed of the underlying computer in which the tool resides is sufficient to enable a very large number of real time calculations to be completed in a short time frame. This particularly enables the search tool to determine the coordinates within an image reference system for each analyzed point in the viewed area, and correlate these through repetition with a desired pattern. The search tool may map the locations of various points in the captured image to stored points in the model image. A pattern is registered if the mapping falls within accepted tolerances and parameters. Using various decision algorithms, the tool decides whether the viewed pattern, in a particular rotation and distance (scale) corresponds to the desired search pattern. If so, the tool confirms that the viewed pattern is, in fact, the pattern for which the tool is searching and fixes its position and orientation.
Machine vision systems having a three-degree-of-freedom, or greater, capability (such as RSIS) are available from a number of commercial vendors including Hexavision® from Adept Technology, Inc. of San Jose, Calif. , and the popular Patmax® system from Cognex Corporation of Natick, Mass. Advanced machine vision search tools such as Patmax® also have the ability to take advantage of the previous known position of a search subject or target. This narrows the search area to positions relatively near the last known location. Therefore, searching is relatively faster on the next cycle since a smaller area is searched. In addition, these search tools can tolerate partial occlusion of a pattern and changes in its illumination, adding further to their robustness with respect to less advanced machine vision approaches.
One goal of machine vision is to provide a more accurate technique for estimating the position of an object in three dimensions. The z-axis(scale) registration function within an advanced search tool, while increasingly effective at defining the distance of an object along the camera axis, is typically less accurate than the corresponding registration functions within the translational degrees of freedom (x and y image plane). For example, the image position in the translational axes (x, y) is typically accurate to 1/40 of a pel. Conversely scale information derived by the search tool is typically accurate to no more than approximately 0.1% of total distance. This can be a large error where the optical range of the setup is large (i.e. for every one meter of camera standoff from the subject, error is greater than one millimeter). This error can be particularly significant in high-precision operations.
A variety of techniques are used for measuring the distance or range of a remote pattern or object. Triangulation is one accepted technique.
Accordingly, it is an object of this invention to provide a system and method for determining the three-dimensional position of an object accurately, effectively and rapidly using a machine vision system based upon principles of triangulation.
SUMMARY OF THE INVENTION
This invention overcomes the disadvantages of the prior art by providing a system and method for determining the three-dimensional position of an object using a machine vision system that correlates two separate camera images of the object, and derives a three-dimensional location thereof based upon triangulation upon the separate images. Each camera transmits captured image data to the machine vision system which includes an advanced machine vision search tool capable of registering each image transformed by at least two translational degrees of freedom (x and y-axis image plane) and at least one non-translational degree of freedom (z-axis(scale)) perpendicular to the image plane). By using at least two search tool results, derived from each of the respective cameras, and the transformation relating to the search tool results, three-dimensional position information on the viewed object is derived. The position information enables the system and method of this invention to thereby provide more-accurate three-dimensional position information on the underlying object.
In a preferred embodiment both cameras are spatially separated, typically on opposite side
Cognex Corporation
Loginov William
Patel Ramesh
Pham Thomas
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