Planning Alignment

Sensors are aligned to compensate for mounting rotations and offsets of sensors: unaligned sensors, when scanning, produce inaccurate scan data and measurement results. However, depending on your measurement and accuracy requirements, you may not need to perform the built-in alignment procedure. In addition to the time and effort required to prepare alignment targets and perform the procedure, the transformations applied to scan data (the corrections) that result from the alignment procedure can reduce the maximum available frame rate, which in turn determines how fast you can scan and measure parts, or the maximum available precision in measurements.

In general, if the inaccuracies are below your required tolerances, or inaccuracies are on an axis that doesn't affect your measurements, you can simply manually set a Z reference within the sensor's scan area (for example, to set the Z = 0 origin to be at the level of the conveyor).

The following sections refer to rotations and offsets on the X, Y, and Z axes. If you are not familiar with the coordinate systems used by Gocator sensors, see Coordinate Systems. Furthermore, when viewing the diagrams below, consult the coordinate system information of your sensor provided in Sensors to get the correct orientation of the X, Y, and Z axes relative to an unaligned sensor. Note that as a rule of thumb, Y increases moving from the camera to the laser emitter.

The following sections describe the three main effects of not aligning certain degrees of freedom of a sensor; use this information to decide which alignment method to use. Remember that after mounting a sensor, it's unlikely that there will only be a mounting inaccuracy on or around a single axis. To clarify the impact of the rotations and offsets we describe below, we touch on them independently.

Y Angle

An unaligned sensor scanning with a Y angle rotation produces data rotated on the XZ plane. It does not distort geometry, unlike Z angle rotation (see below). So for example, with a flat object, data from one side would appear higher than data from the other side:

An exaggerated Y angle of roughly 6 degrees, producing a profile rotated around Y

Although transformations to compensate for a Y angle mounting inaccuracy don't affect frame rates, if the resulting Z offset is acceptable in your application, you may be able to save the time and effort of performing the alignment procedure.

Y Offset

Y offset occurs in dual- or multi-sensor systems when sensors are shifted differently along the Y axis, the parts of a combined profile coming from different sensors to be offset along Y. In some situations, sensors are intentionally shifted along the Y axis, for example, with high resolution sensors, whose FOV is too small to get complete coverage when placed side by side.

Z Angle

An unaligned sensor scanning with a Z angle rotation produces data skewed on the XY plane: it creates a Y offset dependent on X position (the Z angle introduces a cosine error). So for example, a rectangular object would appear skewed along the direction of travel, and wider than it actually is.

An exaggerated Z angle of roughly 8 degrees, producing a skewed scan.
Scan data is slightly wider along X because the laser line produces a longer profile.

However, if your application only involves measuring the height of a feature on the scanned target (so position along the Z axis), although the scan data will be inaccurate, the distortion that Z angle introduces may have no effect on your measurement results.

You can use the sensor itself to determine the mounting angle and the impact on resulting scan data. For example, you can scan a rectangular or square target whose corners are exactly 90 degrees, and then use two Surface Edge tools (for details, see Edge) on adjacent sides to fit an edge line to those edges, and then use the Feature Intersect tool to determine the angle between those lines (for details, see Intersect).

Note that although a Z angle mounting inaccuracy also reduces the effective FOV of a sensor, with Z angles less than 5 degrees, the impact on the FOV is minimal. (To calculate this impact, multiply the FOV by the cosine of the Z angle.)