Video Inspection Software User’s Guide
Section 7: Reference Frames
Establishing a reference frame and datuming are accomplished using a variety of alignment operations. These operations may be used individually or in combination and will be based upon the capability of the measuring machine as well as the alignment requirements of the application. Datuming operations can be performed in the form of explicit datum feature measurements, by modifying the individual coefficient values of previously measured features or by constructing datums from existing features. In three axis systems, the M3 can perform a primary part alignment by evaluating the surface-level of the part, a secondary x-axis part skew alignment and finally establish a datum point which is the origin of the 2D or 3D coordinate system. When measuring a datum-dependent part, it is advisable to establish a level, skew and datum alignment first, and then measure the features associated with that datum. If multiple datums or reference frames are required, establish the initial datum and measure the associated features. Then proceed to the next datum and measure the features associated with it. Always try to follow the sequence of establishing a datum and then measuring the features associated with that datum. The skew, or secondary alignment, can be offset by the user when the skew line position is located where it cannot be measured directly by the system. This offset skew position is identified by values from other measured or constructed features. The skew alignment can also be rotated to specified angular values by the user to facilitate measurements based on angular secondary alignments. NOTES Establishing a complete primary, secondary and tertiary reference frame may not always be required, even in three axis systems. Some three axis systems and the associated applications will not require that a level be performed. In these cases, a skew alignment and datum zero point are typically adequate for successful part of alignment and measurements. Most well-maintained systems include stage surfaces that are level with only extremely minor variations. In video systems that have level variations across the surface of the stage that are smaller than the video camera depth of field, performing a video leveling operation is not beneficial.
Establishing a Reference Frame
The M3 measurement reference frame can consist of: • Part leveling (a primary datum plane) • Skew alignment (secondary alignment) •
Part Datum (measurement coordinate system origin)
Part Leveling When the surface plane of a part is not orthogonal to the measuring axes, small cosine errors can be generated during the measurement process. These errors can be eliminated by leveling the part. To measure a primary datum plane: 1 Select the desired probe from the probe menu. Measure toolbar > Probe menu > Desired probe 2 Press the Datum Plane button of the Datum menu. Measure toolbar > Datum menu > Datum plane button
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