DCC Motion Edge Targeting

DCC Targeting on points allows high accuracy point-of-contact when capturing data points while controlling one axis against a nominal value. This feature ensures that the CMM can capture a point on feature such as a knife edge, see figure 3.

Targeting rules can be attached to 1D, 2D and 3D Point features. To assign, highlight the feature in the inspection report and activate the sub menu by right clicking, see figure 1. Choose [Apply Targeting Parameters] from the menu.

figure 1, Activating

This command will activate a dialog where you can set targeting parameters, see figure 2.

figure 2, Target Parameters

There are four steps used in setting the targeting characteristics. Every step must be completed and the "Use Target Data" must be checked for the operation to be completed.

Step 1 - Choose Target Axis

Targeting is designed to allow exact control on one axis at the point of capturing a data point. As shown in figure 3, we can target a surface such as a knife edge by controlling the Z axis.

figure 3, Z Axis target on a Knife Edge

Step 2 - Enter PCS Target Value

Using the example is figure 3, we first start be ensuring the Part Coordinate System has been established on the top surface. Our Z axis target would then be 0.00 which ensures the probe contacts the edge at the equator of the stylus.

Step 3 - Enter Max +/- Limit

All systems that have drive capabilities, whether it is a CMM or a CNC Mill, will attempt to move along a target vector starting at a given XYZ point 1 to a XYZ point 2. If it was possible to chart the deviation while in motion, you will see a small deviation from the actual position to the target vector. This is referred to as a dog leg effect or tunneling.

The value you enter in step 3 should reflect a small enough value to allow the DCC controller to follow the motion vector, yet large enough not to produce poor results by capturing the data point to far from the stylus equator. In most examples, a value of 0.00015" works well.

Step 4 - Enter Max. Retries

During the inspection process, Geomet will drive to the designated measurement point. Should it identify that point to be outside the limits on the controlled axis, Geomet will return to the stand off point before the measurement point. When it returns the the SO, the speed will be reduced 50% and Geomet will attempt to capture the data point again.

This cycle is continued until either the max tries values has been reach, or the target position on the controlled axis falls within the max limit established in step 3. You will notice the Geomet displays the missed value on a small dialog while in the re-measure cycle.