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106 Part II: Metrology
Part II.E.5
or redefining any or all of those keys to execute any of 20 different programs
containing up to 100 keystrokes each. The keypad includes a joystick capable of
X-, Y-, and Z-axis control.
Another feature of the comparator shown in Figure 11.5 is an electric screen
protractor that reads angles directly to either a minute or 0.01°. The angular setting
of the protractor is displayed on an LED readout at the bottom right of the screen.
The machine has built-in provisions for either diascopic projection (contour illumination)
or episcopic projection (surface illumination) via a high- intensity
tungsten- halogen light source. Lens changing is facilitated by the use of quickchange,
bayonet-type lens holders. Seven different lens magnifications are available,
ranging from 5× to 100×, all with an optical focusing range of 76 mm (3 in.).
This comparator includes the edge-sensing device, the computerized digital readout,
and one lens.
5. DIGITAL VISION SYSTEMS
Define and describe how digital cameras,
online surface inspection, and other digital
systems are used in quality inspection.
(Comprehension)
Body of Knowledge II.E.5
Typically, a machine vision system is PC-based, using a group of devices to receive,
analyze, and interpret the image of a real scene. The system makes judgments on
the image using predefined criteria set by the user. This information can be used
to automate go/no-go inspection decisions, assembly verification, part location
and machine guidance, gauging/dimensional measurements, feedback control
loops, and a host of other tasks (Fabel 1997).
It is a common misperception that machine vision systems provide generic
optical detection and processing capabilities. While every system includes essential
functions, most customers require some level of customization in development
and should be cautious of vendors claiming to have “one-size-fits-all”
solutions. Systems perform best in their own tightly controlled, highly specialized
environment.
Application requirements vary drastically by industry, but a number of components
are common to every machine vision system. Technology is evolving
rapidly in all these areas, creating new opportunities on the manufacturing floor.
The following are common components (Fabel 1997):
• Cameras. CCD cameras are becoming smaller, lighter, and less
expensive. Images are sharper and more accurate, and the new
dual-output cameras produce images twice as fast as previous models.
A new generation of CCD color cameras adds another dimension to