Measurement Anchoring

When parts that a sensor is scanning move on a transport mechanism such as a conveyor, their position typically changes from part to part in one or both of the following ways:

  • along the X, Y, and Z axes (basically, horizontally and vertically)
  • around the Z axis (orientation angle)

When the position and angle variation between parts is minor—for example, when scanning electronic parts in trays—you can anchor one tool to one or more measurements from another tool to compensate for these minor shifts. As a result, Gocator can correctly place the anchored tool's measurement regions on each part. This increases the repeatability and accuracy of measurements.

For cases where movement from part to part is more drastic, you can use part matching to compensate. However, in order for part matching to work properly, the entire part typically must be visible in the field of view.

For example, the following image shows a surface scan of a PCB. A Surface Dimension height measurement returns the height of a surface-mount capacitor relative to a nearby surface (the F1 region).

In the following scan, the part has shifted, but the measurement regions remain where they were originally configured, in relation to the sensor or system coordinate system, so the measurement returned is incorrect:

When you set a tool's anchor source, an offset is calculated between the anchored tool and the anchor source. This offset is used for each frame of scanned data: the anchored tool's measurement region is placed in relation to the anchor source, at the calculated offset.

In the following image, after the Surface Dimension tool is anchored to the X and Y measurements from a Surface Hole tool (placed over the hole to the lower left), Gocator compensates for the shift—mostly along the Y axis in this case—and returns a correct measurement, despite the shift.

You can combine the positional anchors (X, Y, or Z measurements) with an angle anchor (a Z Angle measurement) for optimum measurement placement. For example, in the following scan, the part has not only shifted on the XY plane but also rotated around the Z axis. Anchoring the Surface Dimension tool to the Z Angle measurement of a Surface Edge tool (placed on the lower edge in this case) compensates for the rotation, and the anchored tool returns a correct measurement.

If Z Angle anchoring is used with both X and Y anchoring, the X and Y anchors should come from the same tool.

If Z Angle anchoring is used without X or Y anchoring, the tool's measurement region rotates around its center. If only one of X or Y is used ,the region is rotated around its center and then shifted by the X or Y offset.

Several anchors can be created to run in parallel. For example, you could anchor the measurements of one tool relative to the left edge of a target, and anchor the measurements of another tool relative to the right edge of a target.

You can combine positional anchors (X, Y, or Z) with angle anchors (Z Angle) for optimum measurement placement.

To anchor a profile or surface tool to a measurement:

1. Place a representative target object in the field of view.

In Profile mode

  • Use the Start or Snapshot button to view live profile data to help position the target.

In Surface mode

  • Select a Surface Generation type (Surface Generation) and adjust Part Detection settings (see Part Detection) if applicable.
  • Start the sensor, scan the target, and then stop the sensor.
2. On the Measure page, add a suitable tool to act as an anchor.

A suitable tool is one that returns an X, Y, or Z position or Z Angle as a measurement value.
3. Adjust the anchoring tool's settings and measurement region, and choose a feature type (if applicable).

You can adjust the measurement region graphically in the data viewer or manually by expanding the Regions area.

The position and size of the anchoring tool’s measurement regions define the zone within which movement will be tracked.

If you intend to use angle anchoring and the part in the initial scan is rotated too much, you may need to rotate the anchoring tool's region to accomodate this rotation. For more information on region rotation, see Regions.

See Feature Points for more information on feature types.
4. Add the tool that you want to anchor.

Any tool can be anchored.
5. Adjust the tool and measurement settings, as well as the measurement regions, on a scan of the representative target.
6. Click on the tool's Anchoring tab.
7. Choose an anchor from one of the drop-down boxes.

If the sensor is running, the anchored tool’s measurement regions are shown in white to indicate the regions are locked to the anchor. The measurement regions of anchored tools cannot be adjusted.

The anchored tool’s measurement regions are now tracked and will move with the target’s position and angle under the sensor, as long as the anchoring measurement produces a valid measurement value. If the anchoring measurement is invalid, for example, if part moves outside its measurement region, the anchored tool will not show the measurement regions at all and an “Invalid-Anchor” message will be displayed in the tool panel.
8. Verify that the anchored tool works correctly on other scans of targets in which the part has moved slightly.

To remove an anchor from a tool:

1. Click on the anchored tool's Anchoring tab.

Select Disabled in the X, Y, or Z drop-down.