CMM

Coordinate measuring machines (CMMs) have three-dimensional measurement capabilities (X, Y, and Z directions), unlike hand tools such as micrometers, vernier calipers, or height/depth gauges, which are limited to measurement in only one direction at a time.

CMMs accurately track a probe tip in 3D space and create dimensional measurements through shape building via the points taken through contact with the measurement piece. An even greater number of points can be taken over a larger area on the part to map the surface and compare to CAD data for shape, form, and warpage inspection.

A powerful advantage of coordinate measuring machines (CMMs) is that they can measure items that are difficult to measure with other measuring machines to a high degree of accuracy.

Another feature that stems from the CNC nature of the measurement system is the ability to measure the three-dimensional coordinates of a specific point (a hole, etc.) from the virtual origin with a hand tool such as a caliper or micrometer. Also, measurement using virtual points and virtual lines and geometrical tolerances are difficult with other measuring machines but can be measured with a 3D CMM machine.

Coordinate measuring machines (CMMs) are automated inspection tools. Skilled programmers create a measurement routine or program by measuring any required 3D or GD&T dimensions on a part.

Once the program is registered and an origin point is established through a coordinate system, parts can then be fixtured in place and operators can have the coordinate measuring machine run an automated measurement procedure. While there is a good amount of time invested in the program creation, the actual part inspection can be left to run automatically.

See literature that reviews how to improve inspection efficiency and finish incoming inspection faster. Examples include Coordinate measuring machine (CMM) bottleneck prevention through quick part inspection, by anyone, anywhere in the facility.

More Details

CMMs generally have a device coordinate system that is set in the object.
The device coordinate system is defined by the device, for example, the direction of the axis that moves in the lateral direction is the X axis, and the direction perpendicular to the stage surface is the Z axis. Therefore, depending on the orientation of the object to be measured, it may differ from the reference plane or reference line of the object itself. Since it is difficult and inaccurate to physically place this on the machine coordinates, the work coordinate system is set according to the reference plane or reference line of the object.
This way, aligning the orientation of the workpiece with the orientation of the reference coordinates is called alignment.

There are three pieces of information required to set the work coordinate system.
The first is the plane that is the reference plane, and the direction perpendicular to this plane is the Z axis.
The second line is the reference line, which is generally the X-axis and the vertical direction is the Y-axis. The straight line may be measured directly from the object, or it may be a straight line connecting two different points (such as two holes) with a virtual line.
The third point is the origin. This origin is the 0 point of each coordinate value of X, Y and Z. It is also possible to specify a specific point (for example, the center point of a specific hole) as the origin, or a virtual point (intersection point) where two straight lines intersect.

Generally, a user would select a measurement target called "element" such as a plane via a software menu and begin measurement. In the case of a contact type coordinate measuring machine, the stylus tip is brought into contact with the object to be measured, and the measurement point is taken. The element is measured by measuring the minimum number of measurement points specified for each element. If the number of measurement points is further increased, it is often calculated by the least squares method.
In addition to planes, measurement elements include lines, points, circles, cylinders, cones, and spheres.
Dimensions and 3D shapes are measured by calculating the distances and angles between measured elements.

Some elements have three-dimensional shapes such as cylinders and cones, but some elements do not have three-dimensional shapes such as lines and circles. These elements are generally projected on a plane (moved perpendicular to the plane direction) so that they can be measured correctly. The plane that is projected is called the reference plane or projection plane.

Coordinate measuring machines can also measure using virtual lines and points.
Various examples of virtual elements are used, such as intersections between straight lines, tolerances between planes, intersections between planes, and circles between cones and planes.
It can be said that measurement using these virtual elements, which is difficult to measure with hand tools such as calipers, is unique to 3D measurement.

To set and measure correctly, specialised knowledge and skills are required.
It is required to maintain an appropriate temperature in the measurement room and stabilise the temperature of the object.

Since it is necessary to calibrate every time various settings and probe angles are changed, it is not easy to support frequent product changes.
Since a measurement room is required, it is difficult to perform frequent measurements while processing the object.

The installation requires a large space and the construction of an environmentally-controlled quality lab which is extremely expensive.
Maintenance costs for the measurement environment and measuring equipment can be a burden.
Significant time is required to program the CMM for a few reasons. The required time run the part to the quality lab, acquiring the appropriate temperature for the part, fixturing, calibration for each probe tip and the time needed to complete the measurement.

Coordinate measuring machines (CMMs) are intricate inspection tools with many moving parts, temperature and humidity sensitive components, and various fragile items. This makes the harsh production environments where there's a much higher potential for costly damage or nonoptimal measurement conditions places where conventional CMMs can struggle, leading to inaccuracies during the inspection. Quality labs are designed to be safe zones, environmentally regulated, and provides favorable conditions for proper inspection.

KEYENCE's XM Series handheld coordinate measuring machine is a portable, shop floor Coordinate measuring machine (CMM) designed to enable any user to easily and accurately measure 3D and GDT features, anywhere. Once the part is measured, the system automatically records the data and creates an inspection report. Our latest unit allows for CAD comparison and 3D CAD export. When compared to a traditional Coordinate measuring machine (CMM), companies see a significant reduction in inspection time and increased throughput through shop floor checks by anyone, helping to eliminate any Coordinate measuring machine (CMM) backlog.