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Chapter 11: E. Specialized Inspection Equipment 109
4. Most CMMs have automatic data recording, which minimizes operator
influence.
5. Part alignment and setup procedures are greatly simplified by using
software supplied with computer-assisted CMMs. This minimizes
the setup time for measurement.
6. Data can be automatically saved for further analysis.
Coordinate Measuring Machine Classification
Although coordinate measuring machines can be thought of as representations of
a simple rectilinear coordinate system for measuring the dimensions of differentshaped
workpieces, they naturally are constructed in many different configurations,
all of which offer different advantages. CMMs provide means for locating
and recording the coordinate location of points in their measuring volumes.
Traditional coordinate measuring machines are classified according to their configurations,
as follows:
1. Cantilever configuration, in which the probe is attached to a vertical
machine ram (z-axis) moving on a mutually perpendicular overhang
beam (y-axis) that moves along a mutually perpendicular rail
(x-axis). Cantilever configuration is limited to small and medium-sized
machines. It provides for easy operator access and the possibility of
measuring parts longer than the machine table.
2. Bridge-type configuration, in which a horizontal beam moves along
the x-axis, carrying the carriage that provides the y-motion. In other
configurations, the horizontal beam (bridge structure) is rigidly attached
to the machine base and the machine table moves along the x-axis. This
is called fixed bridge configuration. A bridge-type coordinate measuring
machine provides more rigid construction, which in turn provides
better accuracy. The presence of the bridge on the machine table makes
it a little more difficult to load large parts.
3. Column-type configuration, in which a moving table and saddle
arrangement provides the x and y motions and the machine ram
(z-axis) moves vertically relative to the machine table.
4. Horizontal arm configuration features a horizontal probe ram (z-axis)
moving horizontally relative to a column (y-axis), which moves in a
mutually perpendicular motion (x-axis) along the machine base. This
configuration provides the possibility for measuring large parts. Other
arrangements of the horizontal arm configuration feature a fixed
horizontal arm configuration in which the probe is attached and moving
vertically (y-axis) relative to a column that slides along the machine base
in the x direction. The machine table moves in a mutually perpendicular
motion (z-axis) relative to the column.
5. Gantry-type configuration comprises a vertical ram (z-axis) moving
vertically relative to a horizontal beam (x-axis), which in turn moves
Part II.E.6