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Machine Vision - Applications

light computer wafer systems

The semiconductor industry has become the largest user of automated vision systems. A silicon wafer that will become hundreds of microchips starts as a finely machined disc about 7.9 in (200 mm) in diameter. Before the disc is split into individual chips, the wafer undergoes dozens of steps—some of which are indiscernible by the human eye. To ensure the wafer maintains that sequence, sorting systems using optical character recognition (OCR) identify each wafer, sort it in a clean room environment and report the results to a central network.

For manufacturing, one can classify machine vision applications into four categories: gauging, inspection, identification, and alignment. Gauging refers to measuring critical distances on manufactured parts. Vision software can quickly and consistently measure certain features on a component and determine whether the part meets tolerance specifications. Inspection means looking to see if a mechanical part has been assembled properly. For example, inspecting the pins in an electronic connector to check for missing pins or bent pins. Alignment often involves using pattern-matching software to locate a reference object and then physically moving the object within some tolerance. Identification refers to classifying manufactured items. In an automotive assembly plant, parts often need to be identified or sorted using vision, such as tires by the tread pattern or inner and outer diameter.

Another application for machine vision that is becoming more popular as the technology improves is biometrics, or the identification of a person through his or her readily accessible and reliably unique physical characteristic. These features are compared via sensors against a computer system's stored values for that characteristic. Some commonly used identifiers include hand proportions, facial image, retinal image, finger prints, and voice print. The advantages of biometrics are that they cannot be lent like a physical key or forgotten like a password. A leading concern in the development of such applications, however, is how to avoid rejecting valid users or approving impostors. Such devices would be applicable for security systems at banks, offices, and Internet network applications.

Resources

Periodicals

Braggins, Don. "3-D Inspection and Measurement: Solid Choices for Industrial Vision." Advanced Imaging (October 1994): 36-39.

Hanks, John. "Hanks on Machine Vision: Understand Your Application." National Instruments VerticalNet Online Publications. (March 22, 2000).

Hardin, Winn. "Vision Systems Guide Wafers Through Manufacturing Process." VerticalNet Publications. (March 1, 2000).

Harding, Kevin G. "Current State-of-the-Art of Contouring Techniques in Manufacturing." Journal of Laser Applications (Summer/Fall 1990): 41-47.

Institute of Electrical and Electronics Engineers, Inc. Computer 33, no. 2 (February 2000).

Lake, Don. "Lighting and Imaging, Part 2: Making It All Work Right." Advanced Imaging (June 1994): 66-69.

Weiss, Stephanie A. "Photonics Drives Auto Manufacturing." Photonics Spectra (April 1994): 76-85.

Scott Christian Cahall

KEY TERMS

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Diffuse reflector

—When the light hitting a rough surface is reflected in all directions. Such a surface can be thought of as consisting of many small-scale flat facets.

Optical character recognition

—The process of applying pattern-matching methods to character shapes that have been read into a computer to determine the character that the shapes represent.

Optical sensor

—One that measures light characteristics. These sensors either measure intensity change in one or more light beams or look at phase changes in the light beams by causing them to interact or interfere with one another.

Processor

—The computer "brain," or the main component that makes a computer work. These are typically a microprocessor on a single silicon chip.

Specular reflector

—The reflection from a smooth surface or when the angle of reflection equals angle of incidence.

Surface reflectivity

—The amount of light or visible radiation that is reflected or scattered in varying degree by the outside shell of all objects.

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