Setting Up the Continuously Rotating Laser

The laser is either mounted on an instrument stand, on a surface or on the table of the machine. The system uses single-axis targets that have position-sensing detectors (PSDs) to pick up the center of energy of the laser beam, and digital readouts to display the readings.

To measure flatness a "buck-in" procedure (means to make parallel to) is followed. First, a horizontal continuously rotating laser plane is "bucked in" or adjusted so it is parallel to 3 reference points (see "Choosing A Reference Point") on a table, set of ways or surface. To accomplish this, the targets are all placed on one reference point and adjusted up or down such that they detect the laser plane. At that point, the targets are all zeroed and then repositioned so that one target sits on each reference point. The laser scan plane is then adjusted, using the built-in pitch and roll adjustments, until all three targets produce the same value or zero; thus making the laser parallel to the reference points. This could also be accomplished by using one target, zeroed on the closest reference point to the laser, and moving it back and forth from the reference points until it produces a reading of zero at all 3 points.

Measuring Flatness

Once the laser has been bucked in, the target is moved to user-specified points on the surface and the resulting reading is a measure of the deviation of the measurement point from the reference point, which produces a flatness profile. The measurement will produce either a "+" or "-" sign. A "+" reading means the target is higher than the reference points and a "-" reading means the target is lower than the reference points.

Measuring Levelness

To measure levelness of a surface, the laser leveled using the built-in level vials. Then a target is placed on one reference point and adjusted up or down so that it detects the laser plane. After zeroing the target on the reference point, it is moved to any other point on the surface and a measurement of levelness (flatness) is produced with the target displaying the deviation of the measurement point from the reference point.

Measuring Parallelism

To measure parallelism of 2 surfaces using our continuously rotating lasers, the laser plane has to be bucked in to 3 reference points on the first surface (see Measuring Flatness above). After that, a target is placed on the second surface on one reference point, adjusted so it detects the laser plane and zeroed. It can then be moved to other points on the surface and any deviation from the reference point is a measure of the parallelism of the first surface to the second. At least 3 points should be measured. However, the best way to determine parallelism is to measure both surfaces with the laser plane and enter the data into our Plane5 software. Plane5 will calculate the least-squares best-fit plane for both surfaces and then compare them, providing the best measure of parallelism. Another benefit of Plane5 is that the "buck-in" procedure is not needed because the software removes the slope error from the laser not being parallel to the surface.

Measuring Straightness

To measure (horizontal) straightness of a surface or machine axis, 2 reference points and one vertical laser plane are needed. First, a target is mounted horizontally at the closest reference point to the laser and adjusted so that it detects the laser. Nex,t is it zeroed and moved to the farthest reference point from the laser. Using the yaw adjustment built into the laser base, the laser plane is adjusted so that it produces the same reading on both reference points. The laser is now parallel or "bucked in" to the reference points. Finally, the target is placed at user-specified intervals along the surface or machine axis and any deviations from zero are a measure of straightness relative to the reference points.

If the target is mounted such that its top is to the left of the laser plane, then a "+" reading means the measured point is to the "left" of the reference points and a "-" reading means the point is to the right of the reference points.

Measuring Complete Machine Geometry Using Reference Points

To completely measure the geometry on most machining centers, 5 reference points are needed.

First, the horizontal scan plane is "bucked in" or adjusted so it is parallel to 3 reference points on the table or the X-axis ways. To accomplish this, the targets are all zeroed on one reference point and then 2 of the 3 are placed such that there is a target on each reference point. The laser scan plane is then adjusted until all three targets produce the same value or zero.

Next, one of the vertical scan planes is adjusted so it is parallel to 2 reference points along an axis, preferably the X axis, using horizontally mounted targets. The targets are mounted either on the side of the table when the laser is mounted on a stand or in the spindle head when the laser is mounted on the table. The laser is then adjusted so that it produces the same readings on both reference points.

After completing the 2-point "buck-in" of the vertical laser plane, it is likely that the horizontal laser plane will need some minor adjustment. Once the 5-point "buck-in" is completed, measurements can begin on any axis.

Flatness (vertical straightness) is measured with a vertically mounted target detecting the horizontal laser plane, and straightness (horizontal) is measured with a horizontally mounted target detecting a vertical laser plane. Measurements are taken by positioning the targets (that have been zeroed on the reference points) along an axis at user-specified intervals. The target will display the deviation of the point being measured from the reference points. Since the targets provide live alignment data, any errors found that are greater than allowed tolerances can be adjusted using the targets as digital indicators.

Measuring Squareness

After bucking in the laser to the 5 reference points and determining the flatness and straightness of the machine axes, measuring squareness is a simple process. First, to measure Y-to-Z squareness, the column/spindle is lowered to its lowest Z position and a target is positioned horizontally to pick up the vertical laser plane that is perpendicular to the X axis. Second, the target is zeroed. Finally the column is traversed (raised) along its axis. The data will produce a measurement of both the straightness of the Z axis and the squareness of Y axis to the Z axis.

To measure X-to-Y squareness, the same target setup for the Z-to-X measurement is used. However, instead of raising the column, the table or column (which ever is moveable) is then traversed (moved) along the Y axis and the result is a measure of both Y straightness and X-to-Y squareness.

The same process is followed for Z-to-X squareness except that the target is positioned and zeroed to detect the vertical laser plane that is parallel to the X axis. The column is traversed up again and the resulting data is a measure of the Z "flatness" and Z-to-X squareness.

A note on squareness

To truly measure squareness, one must compare the least-squares, best-fit line of the one axis to the other axis. If this is not done, bad reference points or severely worn ways might produce what looks like a squareness error, but in fact is not. To facilitate this type of analysis, one of Hamar Laser software programs may be used that automatically calculate the best-fit line.

Analyzing Machine Geometry Data

Our Machine Tool Geometry Software analyzes lines of motion for a machine tool, similar to the methodology used in ASME's B5.54 Standard. Our Plane 5 Software analyzes multiple planes and surface types (squares, rectangles, frames, ways, circles and rings) and presents the analysis in 3D graphics. Both sets of software automatically download alignment data, save data analyses and produce alignment reports.

A word of caution: if the machine is going to be aligned, rather than just measured, then it is important to put the laser on an instrument stand. If the laser is on the machine bed or table, adjusting it will most likely move the laser and thus affect the setup.